# IGBT firing circuit, building my own 90hp AC drive.



## etischer (Jun 16, 2008)

Im in the process of trying to upgrade a 2 hp AC drive to 90 hp. Im doing this by using bigger external IGBTs. 

I'm making progress. The IGBT's I have won't be easy to integrate, but I have been learning. 

Here is what the firing signal looks like. This is a PWM version of the top half of a sine wave being fed into the drives IGBT Pack










Zoomed in it looks like a square wave with varying width pulses. This is with no IGBT connected, the voltage increased from 14v to 18v because the load was removed.










Here I have my external "big" IGBT connected, and the firing circuit falls on its face, only 5v pk-to-pk. 










I think I have sourced some IGBT's with less trigger current requirements, and hope to have my motor turning soon! Checking to see if anyone has and free advice they'd like to share =)


Here is the IGBT I took out.


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## Nate (Jul 10, 2008)

*Your big IGBT module has way to much gate capacitance for the factory 2HP drivers to handle. You may need to hook a much bigger driver to the IGBT module then fire this driver with the 2HP driver output.*


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## etischer (Jun 16, 2008)

Wow, there are some smart people in this forum, I wasn't expecting to get an answer. 

It makes sense that the capacitance is too large, instead of an instantaneous rise, it is slowly ramping up as the cap charges. This also explains why my IGBT was acting like a latch. 

I didn't see a capacitance spec on the data sheet for this device. I think the "smart power module" I'm planning to buy will work better than an IGBT. The power module has the 7 igbts and some extra circuitry to fire the igbts. We'll see next week if it works!

thanks for a quick reply. 
Eric.


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## TheSGC (Nov 15, 2007)

I want that Fluke meter you have..... I have built a DC controller that uses an IGBT and it seems to work on all my bench tests. 

Definately check out the specs on the driver. I ended up with a homemade driver using transistors to drive up the voltage. It's crude, but it works.


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## etischer (Jun 16, 2008)

I bought the fluke scopemeter on ebay for $425 after shipping. Looks like it was never used. I even used it for a couple hours using the battery. They are on there all the time, the Fluke 123 scopemeter was what I really wanted, but got such a good deal on this, I don't mind the bigger size. 



TheSGC said:


> I want that Fluke meter you have..... I have built a DC controller that uses an IGBT and it seems to work on all my bench tests.
> 
> Definately check out the specs on the driver. I ended up with a homemade driver using transistors to drive up the voltage. It's crude, but it works.


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## Nate (Jul 10, 2008)

*Yes there are some very smart people here! I don't consider myself to be one of them though. I just know those big modules have some large gate capacitance but then they are very high amperage. The gate capacitance is actually filtering your output signal and trying to make a smoother DC out of it.*

*I like your meter also! I will have to check with eBay, $425 for a Fluke Scopemeter is a very good price.*


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## aeroscott (Jan 5, 2008)

Nate said:


> *Yes there are some very smart people here! I don't consider myself to be one of them though. I just know those big modules have some large gate capacitance but then they are very high amperage. The gate capacitance is actually filtering your output signal and trying to make a smoother DC out of it.*
> 
> *I like your meter also! I will have to check with eBay, $425 for a Fluke Scopemeter is a very good price.*


a little peace of very smart is great , then we just keep adding to that, great work in helping me understand ,thanks


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## lazzer408 (May 18, 2008)

Try sticking a TC4422 or 4452 in line with your gate signal.


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## etischer (Jun 16, 2008)

Awesome, I'll try that first.

...actually, not sure this will work because I need an floating output. The trigger voltage for the IGBT is applied between the collector & emitter. For 3 IGBT's the emitter is ref. to ground. The other 3 IGBT's have the emitter tied to the motor leads (300V). 

Would probably work great for a DC motor, but 3 phase introduces more complexity. Guess thats why most AC drives use a "smart power module" instead of 7 IGBT's.


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## lazzer408 (May 18, 2008)

Ah yeh. The high side igbts need X volts (say ~15+) above their B+ rail aka. emitters. -doh!-

Does the 2hp unit provide that supply? If so maybe the 4422s will work but their grounsd needs to be tied to each emitter instead of B- ?

What are those 7pin ICs (I assume) shown in your first post. Gate drivers? Could they be replaced with a better driver? Wp Vp and Up inputs I would guess are the pwm input signal to the IC?


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## Nate (Jul 10, 2008)

etischer said:


> Would probably work great for a DC motor, but 3 phase introduces more complexity. Guess thats why most AC drives use a "smart power module" instead of 7 IGBT's.


*What would the 7th IGBT do or go? Am I missing something here?*


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## etischer (Jun 16, 2008)

The 7 pin drivers are internal to the "smart power module". 

The 2hp drive might actually have the isolated power supplies. The "smart power module" looks like it requires 4 isolated power supplies. I'll have to look into this. There are 6 IC's which interface with the "SPM" trigger inputs. That, and a few capacitors is all there is connected to the "SPM".

Here is a big picture of the circuit board. 
http://etischer.com/awdev/drive/605_vfd/DSCF2397.JPG

http://etischer.com/awdev/drive/605_vfd/DSCF2398.JPG

Thanks again for all the help, you guys do a good job keeping me motivated!



lazzer408 said:


> Ah yeh. The high side igbts need X volts (say ~15+) above their B+ rail aka. emitters. -doh!-
> 
> Does the 2hp unit provide that supply? If so maybe the 4422s will work but their grounsd needs to be tied to each emitter instead of B- ?
> 
> What are those 7pin ICs (I assume) shown in your first post. Gate drivers? Could they be replaced with a better driver? Wp Vp and Up inputs I would guess are the pwm input signal to the IC?


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## lazzer408 (May 18, 2008)

So I'm thinking your trying to drive the larger igbts with the pulse signal intended to trigger the original module's internal drivers? No wonder it's not working.  I was originally thinking the controller had descrete igbts. Maybe it would be better to find a controller that does rather then make that one work.


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## etischer (Jun 16, 2008)

LOL! Well, I didn't know what was inside until after I already bought the discrete IGBTS. Yea, the VFD uses the smart power module. The Eurotherm VFD's don't start using discrete igbt's until 100hp, at which point I might as well just use the drive the way it comes from the factory, cost is about $15k. 

I think the 300 amp smart power module will work =) I'm hoping.

I want to stick with the Eurotherm drives because I know I can run them purely off 300vdc, alot of other VFD's have control transformers and junk that require AC. I'm also very familiar with the drives, and have a good relationship with engineers at the factory. 

If this all works, Im set!






lazzer408 said:


> So I'm thinking your trying to drive the larger igbts with the pulse signal intended to trigger the original module's internal drivers? No wonder it's not working.  I was originally thinking the controller had descrete igbts. Maybe it would be better to find a controller that does rather then make that one work.


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## etischer (Jun 16, 2008)

Nate said:


> *What would the 7th IGBT do or go? Am I missing something here?*


The 7th IGBT is used for a brake resistor. When regen braking, the motor acts like a generator increasing the DC bus voltage. The 7th IGBT enegages a resistor across the DC bus to keep the voltage at a safe level. Since an EV has a huge battery pack, the voltage won't typically increase beyond a safe level and the 7th IGBT and brake resistor are probably not needed.


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## lazzer408 (May 18, 2008)

etischer said:


> LOL! Well, I didn't know what was inside until after I already bought the discrete IGBTS. Yea, the VFD uses the smart power module. The Eurotherm VFD's don't start using discrete igbt's until 100hp, at which point I might as well just use the drive the way it comes from the factory, cost is about $15k.
> 
> I think the 300 amp smart power module will work =) I'm hoping.
> 
> ...


What did a 300a 'smart module' cost you?


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## etischer (Jun 16, 2008)

lazzer408 said:


> What did a 300a 'smart module' cost you?


dunno yet, I'll find out today hopefully


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## CNCRouterman (May 5, 2008)

Greetings all,
Since this is a fresh thread regarding AC control, I would like to ask WHY they need to have stuff like vector control, rotor position sensors etc.? Are you implementing such controls in your project etischer?
I have a lot of 3phase motors working around me right now, and not one of them has a clue what it's rotor position is at any given moment (disregarding the servos, of course), and even if they did, the power company sure doesn't!
I understand that industrial motor (frequency controllers) drives vary the frequency, and have a programmable voltage to frequency ramp.
I don't understand why there is so much talk about vector orientation control when I try to research AC motor drives.

Thank you in advance.


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## etischer (Jun 16, 2008)

Sensorless vector mode give better torque at low speed. Typically a dumb drive running in Volts/Hz mode needs a DC boost to get more torque. Sensorless vector provides the proper amount of boost. An AC motor needs some magentising current in addition to current to make the motor turn. 

Closed loop mode with encoder feedback gives even better torque response and finer speed regulation. 



CNCRouterman said:


> Greetings all,
> Since this is a fresh thread regarding AC control, I would like to ask WHY they need to have stuff like vector control, rotor position sensors etc.? Are you implementing such controls in your project etischer?
> I have a lot of 3phase motors working around me right now, and not one of them has a clue what it's rotor position is at any given moment (disregarding the servos, of course), and even if they did, the power company sure doesn't!
> I understand that industrial motor (frequency controllers) drives vary the frequency, and have a programmable voltage to frequency ramp.
> ...


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## etischer (Jun 16, 2008)

Powerex sells this interface board to work with their "Smart power modules"

http://www.pwrx.com/pwrx/docs/BP7B Application note.pdf

no time to look at it at the moment, but thought I'd pass it along


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## major (Apr 4, 2008)

CNCRouterman said:


> I understand that industrial motor (frequency controllers) drives vary the frequency, and have a programmable voltage to frequency ramp.
> I don't understand why there is so much talk about vector orientation control when I try to research AC motor drives.
> 
> Thank you in advance.


Hi CN,

With induction motor vector control it is not rotor position needed, but direction and velocity. And only with variable frequency control, not when powered from the fixed frequency mains. The rotor velocity is needed to accurately know the slip and be able to control the motor torque. This is done by breaking down the line current into 2 components mathematically so that the magnetizing current and torque producing current can be controlled independently. Two vectors. Simply controlling the frequency and voltage is suitable for many applications and rotor speed feedback is not required. But vehicle propulsion needs the torque control and therefore the closed loop vector control.

I have tried it without the closed loop and it is a breakneck ride!

Regards,

major


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## lazzer408 (May 18, 2008)

I don't have much experience in AC drives but I believe the vector controlled induction motors don't slip.


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## major (Apr 4, 2008)

lazzer408 said:


> I don't have much experience in AC drives but I believe the vector controlled induction motors don't slip.


Hi lazzer,

The induction motor must slip to do any useful work. Slip is the difference between the rotor frequency and the applied frequency. It is this difference that is responsible for inducing rotor current. No slip, no rotor current, no work. Vector control can allow the desired rotor frequency (or RPM) to be set and maintain that precisely which might give one the impression that there is zero slip. But I guarantee you; the applied frequency will be higher than the rotor frequency for motor action.

Regards,

major


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## lazzer408 (May 18, 2008)

major said:


> Hi lazzer,
> 
> The induction motor must slip to do any useful work. Slip is the difference between the rotor frequency and the applied frequency. It is this difference that is responsible for inducing rotor current. No slip, no rotor current, no work. Vector control can allow the desired rotor frequency (or RPM) to be set and maintain that precisely which might give one the impression that there is zero slip. But I guarantee you; the applied frequency will be higher than the rotor frequency for motor action.
> 
> ...


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## CNCRouterman (May 5, 2008)

OK, so that would mean that a "dumb" freq drive would be, as the name implies, controlling the frequency, hence the motors commanded rpm, and torque would be determined by the slip, more slip means more torque (up to either the torque limit for the motor, or the current limit of the controller/batt pack). It would be about as responsive in terms of speed as a farm tractor, almost instant response, but no conventional "power" feedback from your foot/seat sensors . Do I have it about right?

I can definitely relate to a closed loop servo control, the first CNC I ever worked on I had to build, and the second I had to learn how to "tune" the servos. Boy, I am glad I was working for somebody at that time, and he was understanding of the inordinate amount of head scratching required.

Back to the feedback loop part of the equation. If you have an encoder on the motor/servo, you can have speed, and probably position too if you want it. It was mentioned that there are two currents to control. That throws me a bit, I know that there are 6 to 9 wires going into the motor, but my experience has been limited to changing the connections for changing from 240 to 480V or the other way 'round. Do you mean that one would use these wire sets differently than in a conventional industrial setting?


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## Rod Fitzsimmons Frey (Jun 12, 2008)

lazzer408 said:


>


I don't understand the eye-roll, Lazzer... major is right, no slip == no torque. That's the way induction motors are: different control methods (like space-vector control) can't change that.


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## lazzer408 (May 18, 2008)

Rod Fitzsimmons Frey said:


> I don't understand the eye-roll, Lazzer... major is right, no slip == no torque. That's the way induction motors are: different control methods (like space-vector control) can't change that.


It's more like a 'thats what I meant' eye roll. I was 1-up'd by someone who knows more and could put it correctly.  Don't mine me.

CNCRouterman was asking about torque. I'd also like to know how a dumb invertor compairs to a vector invertor in terms of torque. Lets say both were drawing 100a from a 144v pack and both were at say ~200hz. Without a load I'd assume both motors would be running at roughly the same rpm but with a load on the shaft, say ~20ft lbs, which motor would hold a higher rpm? In other words, is the output power on an AC system proportionate to input power? Is it safe to say that a load _causes_ slip rather then saying slip is a requirement of torque? If an AC motor could be designed that there was 0 slip then the rotor would follow the field around as if it were mechanically coupled. Slip seems like a by-product of efficiency loss rather then a design goal or requirement.


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## Rod Fitzsimmons Frey (Jun 12, 2008)

lazzer408 said:


> Is it safe to say that a load _causes_ slip rather then saying slip is a requirement of torque? If an AC motor could be designed that there was 0 slip then the rotor would follow the field around as if it were mechanically coupled. Slip seems like a by-product of efficiency loss rather then a design goal or requirement.


There's the misunderstanding. Unlike a DC motor, an AC induction motor does not have any user-supplied current through the rotor. The current in the rotor is generated by the rotation of the stator's magnetic field. 

You know that if you move a wire through a magnetic flux, a current will be generated. Well, when the rotor is stationary (but the stator is energized) the bars in the rotor (the 'cage' in the squirrel cage) are being cut by the rotating magnetic field in the same way as that wire. A current is generated in the cage. That current generates it's OWN magnetic field, that opposes the stator's field. It's the interaction between the stator's magnetic field and the generated magnetic field that gives you some torque.

Imagine the rotor were rotating at exactly the same speed as the stator's magnetic field. Now the bars aren't being cut by flux lines. No current is generated; thus no back EMF, no torque.

So the answer is: no slip, no torque. Of course, increased load leads to higher torque requirements to reach equilibrium, so the rotor slows down (i.e. slip increases) which leads to the rotor cage being cut by the stator field faster, which leads to higher back EMF, which leads to more torque to balance the load. But the higher slip is a requirement of producing the necessary torque.

Its magnificence floored me once it clicked in my head. The induction motor is one of mankind's finest engineering achievements.


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## lazzer408 (May 18, 2008)

Rod Fitzsimmons Frey said:


> There's the misunderstanding. Unlike a DC motor, an AC induction motor does not have any user-supplied current through the rotor. The current in the rotor is generated by the rotation of the stator's magnetic field.
> 
> You know that if you move a wire through a magnetic flux, a current will be generated. Well, when the rotor is stationary (but the stator is energized) the bars in the rotor (the 'cage' in the squirrel cage) are being cut by the rotating magnetic field in the same way as that wire. A current is generated in the cage. That current generates it's OWN magnetic field, that opposes the stator's field. It's the interaction between the stator's magnetic field and the generated magnetic field that gives you some torque.
> 
> ...


Seems like a magnetic field is just pulling the rotor along like the fans in a torque convertor. Physically speaking there's induced currents created in the rotor creating an opposing field yadda yadda. Maybe I'm just confusing the typical 3-phase motor with synchronous motors or steppers where slip is a bad thing.


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## etischer (Jun 16, 2008)

So I bought one of these today to the tune of $360.












lazzer408 said:


> So I'm thinking your trying to drive the larger igbts with the pulse signal intended to trigger the original module's internal drivers? No wonder it's not working.  I was originally thinking the controller had descrete igbts. Maybe it would be better to find a controller that does rather then make that one work.


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## lazzer408 (May 18, 2008)

etischer said:


> So I bought one of these today to the tune of $360.


Looks alot like the original one. Where does the logic side of things get it's power from?


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## etischer (Jun 16, 2008)

I know I can setup a pot to be a torque setpoint with Sensorless Vector and Closed loop modes. I think a Volts/hz drive can only have a speed setpoint.


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## etischer (Jun 16, 2008)

lazzer408 said:


> Looks alot like the original one. Where does the logic side of things get it's power from?


The circuit board in the VFD has isolated dc supplies on board. Powerex also sells an interface board that has optoisolators and isolated power supplies, it just requires 24vdc input. I don't think I'll need that since the VFD was designed to talk directly to smart power modules. Getting excited, I really think this is going to work. The smart power module also eliminates alot of interconnect wiring. Battery connects to one side, motor connects to the other, much cleaner. I also only have one device to mount to a heat sink now.


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## Madmac (Mar 14, 2008)

From what I have read on motor control to date both Sensorless Vector and Closed loop modes require the motor phase currents to be measured. Looking at the PCB photo cannot see any means of doing this.

The single block driver is very interesting way forward. Not too bad a price when you add up all the separate parts.

Madmac


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## etischer (Jun 16, 2008)

There are two current transducers in series with two of the motor leads. They are not part of the Smart Power Modue. They measure L1 and L2 on the motor and simple subtraction calculates L3 from the user inputed Motor Current. I tried replacing the current feedback with two pots and could watch the current balance shift between different phases. 

The CTs in the drive are rated 25 amps which outputs 10volts. So I need to either find a CT which outputs 10volts at 300amps, or I need to have a parallel branch of motor lead that flows 25 amps though the CT when the motor is at 300 amps. The CT uses a hall effect sensor, it is more than just a current transformer, it requires 15vdc to work. 





Madmac said:


> From what I have read on motor control to date both Sensorless Vector and Closed loop modes require the motor phase currents to be measured. Looking at the PCB photo cannot see any means of doing this.
> 
> The single block driver is very interesting way forward. Not too bad a price when you add up all the separate parts.
> 
> Madmac


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## major (Apr 4, 2008)

CNCRouterman said:


> . It was mentioned that there are two currents to control. That throws me a bit, I know that there are 6 to 9 wires going into the motor, but my experience has been limited to changing the connections for changing from 240 to 480V or the other way 'round. Do you mean that one would use these wire sets differently than in a conventional industrial setting?


Hey CN,

No, there are just 3 wires from the motor to the inverter. It all is pretty complicated and I cannot explain it sitting at this keyboard. But in a nutshell, the phase currents from the inverter are the vector sum of the 2. Often called direct and quadrature. Or magnetizing and torque producing. They are out of phase with one another, but add up to a single AC current.

Here is an analogy I like to use. Imagine a DC shunt motor where the field is internally connected to the armature so it has only 2 terminals. Now, how could you design a controller to connect to the 2 terminals and control the armature and field currents separately? Hard to imagine. But that is what the vector control does for the AC induction motor.

Hope that helps,

major


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## Madmac (Mar 14, 2008)

> So I need to either find a CT which outputs 10volts at 300amps



Have a look at LEM for a very wide range of Hall current sensors
http://www.lem.com/hq/en/content/view/13/86/

Not the easiest site to navigate.


Madmac


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## lazzer408 (May 18, 2008)

Why not just put a resistor divider on the ct? Divide it by 10 and you should have 250a.


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## Madmac (Mar 14, 2008)

> Why not just put a resistor divider on the ct? Divide it by 10 and you should have 250a.


The semiconductor Hall device would need a power rail 10 times higher to get that to work. As standard it is 15 volts which limits max current / voltage swing. (ignoring any magnetic saturation issues)

Madmac


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## etischer (Jun 16, 2008)

I talked to LEM. The guy I talked to said he had some samples he can send me. The scaling is a bit strange, I won't beable to just drop in a replacement, but its a start

I can't just do a voltage divider, the original transducer would melt if I put 300 amps though it. 




Madmac said:


> The semiconductor Hall device would need a power rail 10 times higher to get that to work. As standard it is 15 volts which limits max current / voltage swing. (ignoring any magnetic saturation issues)
> 
> Madmac


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## lazzer408 (May 18, 2008)

What is the output of the current transducer? Can you use a current transformer instead?


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## etischer (Jun 16, 2008)

Output voltage = 2.5 volts if current =0
Output voltage =3.5 volts if current =25amps. New Current transducer will output 3.5volts if current =300 amps

I think I have found a unit that will work, it just needs 5 volt supply, the original one needed 15 



lazzer408 said:


> What is the output of the current transducer? Can you use a current transformer instead?


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## lazzer408 (May 18, 2008)

etischer said:


> Output voltage = 2.5 volts if current =0
> Output voltage =3.5 volts if current =25amps. New Current transducer will output 3.5volts if current =300 amps
> 
> I think I have found a unit that will work, it just needs 5 volt supply, the original one needed 15


I can't wait to see how it all works.


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## Wirecutter (Jul 26, 2007)

etischer said:


> Powerex sells this interface board to work with their "Smart power modules"
> 
> http://www.pwrx.com/pwrx/docs/BP7B Application note.pdf
> 
> no time to look at it at the moment, but thought I'd pass it along


That's one thing I liked about Powerex. As far as I've seen, they sell interface/driver boards for all their big IGBTs. If you start fishing through the selector guides, for any given big IGBT, they normally have a "recommended driver board" which has a separate DC-DC converter and a driver module for the particular family of IGBT. Seems like that would make life a lot easier for those of us who aren't already AC-motor-controller nerds. 

-Mark


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## lazzer408 (May 18, 2008)

Wirecutter said:


> That's one thing I liked about Powerex. As far as I've seen, they sell interface/driver boards for all their big IGBTs. If you start fishing through the selector guides, for any given big IGBT, they normally have a "recommended driver board" which has a separate DC-DC converter and a driver module for the particular family of IGBT. Seems like that would make life a lot easier for those of us who aren't already AC-motor-controller nerds.
> 
> -Mark


Don't forget about us power whores either. I'm up for a 50kw 3-phase drive.


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## skullbearer (Jul 9, 2008)

I'm not even sure I can feel confident in selecting an AC motor now, after reading this thread my head is throbbing... and now I'm off to try and find someplace that will break it all down for me. The only thing I understand is DC apparently.


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## Dennis (Feb 25, 2008)

> There's the misunderstanding. Unlike a DC motor, an AC induction motor does not have any user-supplied current through the rotor. The current in the rotor is generated by the rotation of the stator's magnetic field.
> 
> You know that if you move a wire through a magnetic flux, a current will be generated. Well, when the rotor is stationary (but the stator is energized) the bars in the rotor (the 'cage' in the squirrel cage) are being cut by the rotating magnetic field in the same way as that wire. A current is generated in the cage. That current generates it's OWN magnetic field, that opposes the stator's field. It's the interaction between the stator's magnetic field and the generated magnetic field that gives you some torque.
> 
> ...


You explained the concept in a simple yet informative way that if I had to do it would confuse people. Good Job. Are you a teacher? I have a degree in *Electronics Engineering Technology* (One step below an EE, sort of what you call the "nurse" and the engineer the "doctor") so it is hard for me to explain in simple terms..


To those who want to know a very beautiful detailed explanation on vector control then read this article: http://focus.ti.com/lit/an/bpra073/bpra073.pdf


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## skullbearer (Jul 9, 2008)

Your idea of a very beautiful explanation is my idea of a massive artery bursting inside my cerebral cortex. That aside, I learned about how Vector Control works, and that it seems to be the best application for AC EVs.

Not to mention Vector Controlled Motors are fairly available online with good warranties! For about $3k/7.5kW... then again, maybe they aren't the best for the current converter?


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## etischer (Jun 16, 2008)

http://etischer.com/awdev/drive/video/igbt_turns_motor.wmv











Click the link below to see a video!

http://etischer.com/awdev/

I got my motor to turn!!! Then two seconds later.. Kaboom!

Talking with Tech support the problem is too much inductance between my dc bus and the IGBT. They reccommend using flat plates of copper bus bar instead of wire. So on to round two.


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## etischer (Jun 16, 2008)

http://etischer.com/awdev/drive/bus.jpg

I got my bus bars and capacitor bank put together. I need to get some braided jumpers to connect the outer bars together. Does this look ok? I couldn't figure out a good way to make a laminated bus bar. I have teflon sheet to cover the bars and make them semi finger safe. I can't imagine having a laminated bar would make any difference with 6 caps only an inch away, but I dunno??? Hopefully this is fine... 

I'm using 6 400v 3,900uF caps. The bar is 3/16" thick, probably thicker than I needed, but it's nice to have rigid place to bolt up wires.


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## Madmac (Mar 14, 2008)

I would add three film caps, one across each cap pair. Mount with eyelets and keep leads as short as possible on main bus bar pair. 5mfd or 10mfd from a good quality source. They will help control the very fast edges.

Without building and testing knowing the correct value is next to impossible. Putting more than needed is best. (down side is they are not cheap).


Once built and tested you may find you can get away with three electrolytics.

Madmac


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## major (Apr 4, 2008)

etischer said:


> I'm using 6 400v 3,900uF caps. The bar is 3/16" thick, probably thicker than I needed, but it's nice to have rigid place to bolt up wires.


Hi etischer,

I'd put a bleed down resistor on the cap bank. Something so it discharges to below 50 volts in a minute or two after you shut down. Also, you'll need a hefty precharge circuit. And, as Madmac said, put on some snubbers.

Good luck with the next test.

major


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## etischer (Jun 16, 2008)

snubbers are just film caps? Are these designed specifically for IGBT snubbing, or do I just need to buy 10mF film caps? Thats 10 mili, or 10 micro? Where would be considered a reliable place to buy from?

I'll definitely put a bleed down resistor, I was also going to hard wire in a voltage tester, so it will light up and give indication of what voltage is present. 

Should I put in some MOV's, or will the caps just over power them?

thanks!
-eric

something like this?
http://cgi.ebay.com/5-Aerovox-RBPS-IGBT-Snubber-Capacitors-2-0UF-1000VDC_W0QQitemZ260271806765QQihZ016QQcategoryZ97184QQssPageNameZWDVWQQrdZ1QQcmdZViewItem


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## major (Apr 4, 2008)

etischer said:


> something like this?
> http://cgi.ebay.com/5-Aerovox-RBPS-...ryZ97184QQssPageNameZWDVWQQrdZ1QQcmdZViewItem


Eric,

Yeah, that's the ticket. You might not need 1000 volt rated, but wouldn't hurt. IGBT snubbers are low inductance film caps made to mount directly to single and dual modules. Not for that 6 pack. You can mount to your bus bar. Before specialized snubbers, they used film caps with very short leads. They clamp high frequency spikes.

Regards,

major


----------



## Madmac (Mar 14, 2008)

The capacitors on the DC rail are to try and control the circuit under high speed switching, to prevent any inductance ringing. The MOV is there to clamp any spikes either from the caps not doing there job well enough (possibly due to layout) or from other sources. 

The DC rail contactor opening and closing can cause the inductance of the battery cable to ring and generate high voltage spikes.

As Major says fit some bleed resistors on the capacitor bank....they store quite a bit of energy.

Fit three of the 2.2mfd's if you win them, will be a good starting point.

Madmac


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## etischer (Jun 16, 2008)

I have a precharge circuit, so the main contactor closing shouldn't introduce any distrubance or ringing. 

I won my auction, I might as well put all 5 snubbers on =)


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## OHM (Jun 30, 2008)

Eric, is it possible to give some of us a rough estimate of building such an AC controller to drive the same kind of Siemens motor?


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## etischer (Jun 16, 2008)

OHM said:


> Eric, is it possible to give some of us a rough estimate of building such an AC controller to drive the same kind of Siemens motor?


I would like to start selling a cheap controller once I get a working prototype. I'd guess in the $4-5k range? Hard to say until I actually have all the bugs worked out, and I'm actually running in sensorless vector mode. If you were looking to DIY, I'd guess about 2k in parts if you buy everything new.


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## OHM (Jun 30, 2008)

etischer said:


> I would like to start selling a cheap controller once I get a working prototype. I'd guess in the $4-5k range? Hard to say until I actually have all the bugs worked out, and I'm actually running in sensorless vector mode. If you were looking to DIY, I'd guess about 2k in parts if you buy everything new.


I would say it could be a good business if you can get the parts direct from the manufacturer. As 4-5k AC controllers are available. Im not saying its not worth it just a little harder to compete with established well priced controllers like Azure. If you could price it around the 3-3.5k mark you will have a winner. Maybe getting them made in India is an option once you reverse engineer them.


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## etischer (Jun 16, 2008)

Hmm, if I knew I could just buy something for $4000, I would have just done that. Do you have a link?





OHM said:


> I would say it could be a good business if you can get the parts direct from the manufacturer. As 4-5k AC controllers are available. Im not saying its not worth it just a little harder to compete with established well priced controllers like Azure. If you could price it around the 3-3.5k mark you will have a winner. Maybe getting them made in India is an option once you reverse engineer them.


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## OHM (Jun 30, 2008)

etischer said:


> Hmm, if I knew I could just buy something for $4000, I would have just done that. Do you have a link?


If its able to power your Siemens I dont know but in Oz dollars mind you with a mark up but at US dollars id bet less than 4k!!!

http://www.bev.com.au/Docs/Azure%20-%20BEV%20Australian%20Price%20List.pdf

http://www.bev.com.au/Azure.htm

DMOC445 motor controller air-cooled $3,718AU$ liquid cooled $4,463AU$
peak - 78kW @ 312 V nominal - 38kW @ 312 V 96-98% efficiency.


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## lazzer408 (May 18, 2008)

uf = microfarad

10uf = 10 microfarad

...for clarification.


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## etischer (Jun 16, 2008)

Wow, that is a nice setup. Too bad I didn't see this when I was just starting out. For the hp I'm after I think I'd have to go with the $7700 drive though =) Lots of good stuff and reasonable prices



OHM said:


> If its able to power your Siemens I dont know but in Oz dollars mind you with a mark up but at US dollars id bet less than 4k!!!
> 
> http://www.bev.com.au/Docs/Azure%20-%20BEV%20Australian%20Price%20List.pdf
> 
> ...


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## OHM (Jun 30, 2008)

etischer said:


> Wow, that is a nice setup. Too bad I didn't see this when I was just starting out. For the hp I'm after I think I'd have to go with the $7700 drive though =) Lots of good stuff and reasonable prices


Ummm isnt 78kw peak enough for you!!??  it is for me!

Can I ask a dumb question?  Could I use this the Azure controller for a cheap 4 pole or 6 pole industrial ac induction motor?


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## etischer (Jun 16, 2008)

The next cheaper drive from Azure, the AC55. It is rated 25kw continuous, but my motor is rated 33 continuous. I want to be able to do atleast 80 mph on flat ground, and I have some long hills to conquer on my daily commute. 

The AC90 ($7k) is rated 50kw continuous which is ok. The drive I'm making should do 90kw continuous. I've made some progress.... here are some pics of my prototype so far. It is running a little 3hp motor, I'm waiting for my snubbers and want to scope things out before hooking up the ford/siemens traction motor. 





































OHM said:


> Ummm isnt 78kw peak enough for you!!??  it is for me!
> 
> Can I ask a dumb question?  Could I use this the Azure controller for a cheap 4 pole or 6 pole industrial ac induction motor?


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## aeroscott (Jan 5, 2008)

etischer said:


> The next cheaper drive from Azure, the AC55. It is rated 25kw continuous, but my motor is rated 33 continuous. I want to be able to do atleast 80 mph on flat ground, and I have some long hills to conquer on my daily commute.
> 
> The AC90 ($7k) is rated 50kw continuous which is ok. The drive I'm making should do 90kw continuous. I've made some progress.... here are some pics of my prototype so far. It is running a little 3hp motor, I'm waiting for my snubbers and want to scope things out before hooking up the ford/siemens traction motor.


nice to see some hardware , like the heat exchanger . never give up or move to fast . these things can weld , power a shop , induction melt stainless steel , plasma cut , power a mainframe computer or a really big house . just change the software . all this power in your car .


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## etischer (Jun 16, 2008)

aeroscott said:


> nice to see some hardware , like the heat exchanger . never give up or move to fast . these things can weld , power a shop , induction melt stainless steel , plasma cut , power a mainframe computer or a really big house . just change the software . all this power in your car .


Yep, with a firmware change, and a cut of a jumper, I can pump power back into the grid.


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## aeroscott (Jan 5, 2008)

etischer said:


> Yep, with a firmware change, and a cut of a jumper, I can pump power back into the grid.


 at this point I see controllers as the most important part of ev's .


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## OHM (Jun 30, 2008)

The Azure controller is 38kw nominal 78kw peak. 

The ACXX numbers you use are for the AC motors the ac90 is the truck motor.

the controller are only 2 one DMOC445 the other DMOC645.
http://www.electroauto.com/catalog/accontrol.shtml

Anyway we look forward to your creation!


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## etischer (Jun 16, 2008)

OHM said:


> The Azure controller is 38kw nominal 78kw peak.
> 
> The ACXX numbers you use are for the AC motors the ac90 is the truck motor.
> 
> ...


Ahh, so the spec sheet I was looking at was for their motor+drive combo. I guess since the price list lists the two items separately, you should be able to buy just the drive. Looks like a good plan B just incase I can't get my creation working the way I want.


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## lazzer408 (May 18, 2008)

Make your dc runs in a twisted pair. You have a bunch of antennas sticking up in the air.


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## joseph3354 (Apr 2, 2008)

etischer said:


> Yep, with a firmware change, and a cut of a jumper, I can pump power back into the grid.


what kind of power do you feed this thing?  are you just using the mains from your house? or are you using a dc source? this thread has truly peaked my interest because of the availability of low cost ac motors(used).can you use any type of three phase ac motor in this fashion?


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## etischer (Jun 16, 2008)

joseph3354 said:


> what kind of power do you feed this thing?  are you just using the mains from your house? or are you using a dc source? this thread has truly peaked my interest because of the availability of low cost ac motors(used).can you use any type of three phase ac motor in this fashion?


 
LOL, well I don't have a battery pack yet, so yea I'm running it off a pair of outlets in the wall (to get 208v). I'm converting the AC to DC using a bridge circuit. The controller I'm using can run any AC induction motor as far as I know. Speed range is 0-480hz, most motors run 1750 rpm at 60hz. There is an autotune feature which I hope still works after my external IGBT pack is installed. 

Lazzer: I'll take your advice and run twisted pair battery cable!


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## etischer (Jun 16, 2008)

Here's a video of the motor turning =)
http://etischer.com/awdev/drive/traction_motor_turns.wmv

I got my Ford Traction motor turning at 175 RPM today! It was a little jerky, but I'm hoping it's just because it was turning so slow. 11k rpm is max speed, so I was running around 1.5% speed. I'm not quite brave enough to run faster yet. Scope on the DC bus showed no voltage spikes over 5 volts. 



























This is what the firing signal looks like going into the IGBT, not as pretty as it was with the small IGBT pack, but hopefully just good enough to make it work.


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## coulombKid (Jan 10, 2009)

etischer said:


> Im in the process of trying to upgrade a 2 hp AC drive to 90 hp. Im doing this by using bigger external IGBTs.
> 
> I'm making progress. The IGBT's I have won't be easy to integrate, but I have been learning.
> 
> ...


It looks like a problem I had driving LEDs directly from microprocessor outputs. The total current requirements of the display were greater than the supply capability of the microprocessor. I built a display driver by using op-amps in a unity gain configuration. The output voltage was identical but the current delivering capacity of the op amps was far greater. With quad pack op-amps you would need two chips to drive six-pack IGBTs. I was able to feed the op-amps 15 VDC single ended but in your application you may need op-amps hooked to + and - 15 VDC to charge and discharge your big IGBTs quickly. This type of solution allows you to match impedences between your signal source and your load. Im not sure if you will need opto-isolation with the IGBTs you are using or not.


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## etischer (Jun 16, 2008)

The problem with that is three of the op-amps needs an isolated supply because they are common with the motor leads. 










I traded six individual IGBT packs for a "smart power module" which has the six IGBTs and some signal processing in one brick. That problem has been solved. 




coulombKid said:


> It looks like a problem I had driving LEDs directly from microprocessor outputs. The total current requirements of the display were greater than the supply capability of the microprocessor. I built a display driver by using op-amps in a unity gain configuration. The output voltage was identical but the current delivering capacity of the op amps was far greater. With quad pack op-amps you would need two chips to drive six-pack IGBTs. I was able to feed the op-amps 15 VDC single ended but in your application you may need op-amps hooked to + and - 15 VDC to charge and discharge your big IGBTs quickly. This type of solution allows you to match impedences between your signal source and your load. Im not sure if you will need opto-isolation with the IGBTs you are using or not.


----------



## coulombKid (Jan 10, 2009)

major said:


> Hey CN,
> 
> No, there are just 3 wires from the motor to the inverter. It all is pretty complicated and I cannot explain it sitting at this keyboard. But in a nutshell, the phase currents from the inverter are the vector sum of the 2. Often called direct and quadrature. Or magnetizing and torque producing. They are out of phase with one another, but add up to a single AC current.
> 
> ...


My dumb question for the day: From what I understand the two current sensors allow calculation of all 3 phase currents via Kurkovs current law. The vector components of phase currents have to be resolved by the phase angle meter component of the processor, i.e. With high slip angles the current lags the voltage in electrical degrees and the imaginary component (magnetizing part) and the real part (torque producing) of the current can be resolved with the cosine rule. All the transforms and PID loops are implemented in software. Did I dumb it down correctly? My age may be showing by terminology, I had linear systems over 20 years ago.


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## major (Apr 4, 2008)

coulombKid said:


> The vector components of phase currents have to be resolved by the phase angle meter component of the processor,


Hi Kid,

Yeah, this is done in software using a model of the motor. Is why vector controllers have to be tuned to the particular motor.



> All the transforms and PID loops are implemented in software. Did I dumb it down correctly?


Yeah, you make it sound easy. It is quite complex from my viewpoint. I don't have a link, but there are web sites or books that explain this.

Regards,

major


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## coulombKid (Jan 10, 2009)

major said:


> Hi Kid,
> 
> Yeah, this is done in software using a model of the motor. Is why vector controllers have to be tuned to the particular motor.
> 
> ...


The college kids in Canada got-er-done as a senior design project using Matlab and Labview. I used Matlab 18 years ago in college but haven't had access to Labview. Its a tough nut. That is also why the Tesla management got rid of soo many engineers. At last count they still had 50 on the job. Their web site says they have 100s of hours of dyno time tuneing their system. Their 85 pound motor can reportedly go up to 13,000 RPM. They built their own 2-speed transmission because the torque they make would rip out a standard automotive transmission. One of our members related the story of taking a white knuckle ride with a standard open loop VFD. Was that you? I built a 3-phase phase angle meter back in 2000. I used a 8 channel A/D card and did the software in C++. I was like having a six channel color scope display on the post process print-out. I would sample, post process, then print out in Excel. Much much easier than acomplishing a LOT more than that in real time.


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## major (Apr 4, 2008)

coulombKid said:


> One of our members related the story of taking a white knuckle ride with a standard open loop VFD. Was that you?


I don't recall posting it, but I have driven open loop. They called it "sensorless vector control". I call it senseless vector control. More of a break-neck ride than white knuckle. Lots of problems. Throttle peddle was like an on-off switch. And no blend with friction brakes on regen. Makes a shaft encoder seem like money well spent.

You need real torque control.

major


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## coulombKid (Jan 10, 2009)

*Parrallax Propeller multi-micro-processor*

Has anyone looked into the Parrallax Propeller chip for driving IGBTs? It has a supervisory hub and 8 coordinated sub-micro-processors on a single chip. I wonder if one could hand each of six micro-processors its desired half sine wave period (time) and an engineering scalar proportional to the desired current flow. Each triggered in sequence could then do 1/6 of the processing independendently to generate a three phase control signal. Looks like they have a compiler called Spin and for us old grey-beards you can still program it in ASM.


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## ga2500ev (Apr 20, 2008)

*Re: Parrallax Propeller multi-micro-processor*

In addition the Propeller has at least one implemented Forth system that's completely embedded on chip. Hook it up to a serial port and have a complete high level embedded programming environment that runs at full speed.

ga2500ev


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## etischer (Jun 16, 2008)

Sensorless vector is supposed to be nearly as good as closed loop vector (encoder feedback). My first go around will be volts/hertz which is completely open loop, this will probably be the bucking bronco ride you guys are talking about. I hope to have sensorless vector running, I have all the components, just need to put them together and cross my fingers!



major said:


> I don't recall posting it, but I have driven open loop. They called it "sensorless vector control". I call it senseless vector control. More of a break-neck ride than white knuckle. Lots of problems. Throttle peddle was like an on-off switch. And no blend with friction brakes on regen. Makes a shaft encoder seem like money well spent.
> 
> You need real torque control.
> 
> major


----------



## ulnpiper (Sep 24, 2008)

*Re: Parrallax Propeller multi-micro-processor*



coulombKid said:


> Has anyone looked into the Parrallax Propeller chip for driving IGBTs? It has a supervisory hub and 8 coordinated sub-micro-processors on a single chip. I wonder if one could hand each of six micro-processors its desired half sine wave period (time) and an engineering scalar proportional to the desired current flow. Each triggered in sequence could then do 1/6 of the processing independendently to generate a three phase control signal. Looks like they have a compiler called Spin and for us old grey-beards you can still program it in ASM.


I've been reading up on it and plan to use it for a home built controller. It looks like a pretty interesting design for a microcontroller chip. Originally had planned to use a dsPIC until I discovered the Parrallax.

Just bought a 3 phase 1/2 horse motor to use on the test bench, and will begin collecting the other parts over the next couple of months.

My conceptual design is to use 3 of the processors to generate the PWM waves for the three phases, and then another for fault monitoring. #5 would be for the ADC on the throttle and possibly feedback loop calculations. Might need to put some of those calcs in the other processors.

It also has a built in sine lookup table that can be used for the PWM generation.

There is DC PWM code written for it, but nothing for AC that I could find.

-g


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## coulombKid (Jan 10, 2009)

*Re: Parrallax Propeller multi-micro-processor*



ulnpiper said:


> I've been reading up on it and plan to use it for a home built controller. It looks like a pretty interesting design for a microcontroller chip. Originally had planned to use a dsPIC until I discovered the Parrallax.
> 
> Just bought a 3 phase 1/2 horse motor to use on the test bench, and will begin collecting the other parts over the next couple of months.
> 
> ...


Consider the following:
For arguments between 0 and 90 degrees the sine table returns a result between 0 and 1.
2) To control my resultant wave-form at steady-state 100% I will need to multiply my sine wave times FLA. This will be my time dependent reference curve to compare system response to the model. The logic loop would be something like the following:

Loop2:
call ref(t)
A) turn A+ phase IGBT on.
Loop0:
B) Is current > ref + delta?.
C) If yes turn A+ phase IGBT off, else loop0
call ref(t)
Loop1
D) Is current < ref - delta?
E) If yes turn IGBT back on, else Loop1
Loop2 

There is, of course, a lot more to it but basically It could give you a saw-tooth wave superimposed on the back of your sine wave current form. 
The amplitude of the saw-tooth component would be about 2 delta. If your driver can switch the IGBT above 20 Khz you won't even hear it but you will want a thermistor on your IGBT heat sink. Thats why we love haveing a sine wave look-up table.


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## thingstodo (Jul 16, 2010)

etischer said:


> ...
> There is an autotune feature which I hope still works after my external IGBT pack is installed.
> ...


The VFDs that I deal with (at work) have hall effect sensors on each phase and use the current sensed and the phase of the current to figure out the inductance and resistance of the motor when they are 'auto-tuning'. At least, that's about as good a guess as I can come up with, since Allen-Bradley, Mitsubishi, Siemens, Toshiba, and Cutler-hammer all treat that info as proprietary. I know that I have to remove the load reactor and wire straight to the motor for the auto-tune to work properly.

Since your Hall effect sensors would be scaled for 2 HP, how are you:
1 - scaling the current sensors
2 - doing that so fast that you can preserve the phase information

I'm looking at using a larger VFD purchased surplus (300 HP at 600 VAC) and using a 0.5 HP 208V sensorless vector VFD to 'run' it - generate the trigger signals for the larger IGBTs, get a scaled-down signal from the hall effect sensors, etc.


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## coulombKid (Jan 10, 2009)

Since I made that 2009 post Propbasic has come out for the Propeller allowing one to generate assembler code in Propbasic. This is many times faster than Spin interpreter. I took a break from my project and designed a digital dashboard with the Propeller. I'm trying to get the article ready for the August issue of NutsVolts magazine. My basic software phase error corrections would have to be found out using various size pure resistors, capacitors, coils, and combinations on the bench. since the Prop can do 20 mips per cog I doubt that the calculation time lag will significantly cause errors in the time domain as long as the firmware is mostly assembler. The hall effect sensors I have for the early low power experiments have opto-isolators built in so that will simplify the I/O.
Some systems watch the voltage rise and use that data. By watching current instead and switching to keep it close to a pure sine wave harmonic distortion issues should largely fall off the table. A watch dog cog would have to insure a consistent 120 degrees between sign waves too. Both acceleration torque and braking torque are roughly proportional to RMS current. Going with a current control calculation requires a lot of scratch bench work but should eliminate a lot of the really complicated vector drive methods required to carry it all off with a micro-controller that uses interrupts. If the Propeller II is released before I get back to the vector drive then then that will be the platform I use. As long as the motor can handle the full voltage generated during breaking, and the highest attainable pack voltage, then as far as the processor is concerned voltage becomes a major "don't care" except for fault detection.
There have been some contributors here that are very knowledgeable about the proprietary algorithms of which you speak. Thing is, they seem to be oblivious to the design workarounds in their own systems due to the limitations of an interrupt type controller and the older (slow) sampling devices entrenched in "proprietary" designs. A lot of the experiments I need to do weren't even possible just a few years ago. Why reinvent the wheel? There is a list of valid reasons a page long. Today's cutting edge is tomorrows propriety.


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## coulombKid (Jan 10, 2009)

thingstodo said:


> The VFDs that I deal with (at work) have hall effect sensors on each phase and use the current sensed and the phase of the current to figure out the inductance and resistance of the motor when they are 'auto-tuning'. At least, that's about as good a guess as I can come up with, since Allen-Bradley, Mitsubishi, Siemens, Toshiba, and Cutler-hammer all treat that info as proprietary. I know that I have to remove the load reactor and wire straight to the motor for the auto-tune to work properly.
> 
> Since your Hall effect sensors would be scaled for 2 HP, how are you:
> 1 - scaling the current sensors
> ...


 Remember, if your pack voltage is less than the rated operating voltage of your larger salvage VFD the the usable horse power may be proportionally less. To do this, read all the old posts from etscher you can find. He also solved the torque control problem by massaging the constants one can change in the supervisory vfd. Very bright lad.


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## coulombKid (Jan 10, 2009)

thingstodo said:


> The VFDs that I deal with (at work) have hall effect sensors on each phase and use the current sensed and the phase of the current to figure out the inductance and resistance of the motor when they are 'auto-tuning'. At least, that's about as good a guess as I can come up with, since Allen-Bradley, Mitsubishi, Siemens, Toshiba, and Cutler-hammer all treat that info as proprietary. I know that I have to remove the load reactor and wire straight to the motor for the auto-tune to work properly.
> 
> Since your Hall effect sensors would be scaled for 2 HP, how are you:
> 1 - scaling the current sensors
> ...


current sensors would need to be purchased with the correct current sensing range for the application. The spec sheet for them has bandwidth specifications that can show if they are fast enough to preserve phase angle accuracy. Likewise any A/D chips used with them also have bandwidth specifications for the same reason. The next Propeller II I referenced above is expected to have a clock of 160 Mhz with most instructions on a single clock cycle. With 8 cores that is a maximum of 1.28 Billion instructions per second. With that speed capability the hall effect sensor and any A/D converter chip become the limiting factor. By using parallel flash converters one can attain the speed. With 84 general purpose I/O pins the Prop II will be able to keep up with parallel communication flash converters if it has to.


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## etischer (Jun 16, 2008)

Wow, way to resurrect a two year old thread =)

I've got 15k miles on the inverter now, here is the updated thread:

http://www.diyelectriccar.com/forums/showthread.php/home-built-ac-drive-ford-siemens-27893p19.html


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## thingstodo (Jul 16, 2010)

etischer said:


> Wow, way to resurrect a two year old thread =)
> 
> I've got 15k miles on the inverter now, here is the updated thread:
> 
> http://www.diyelectriccar.com/forums/showthread.php/home-built-ac-drive-ford-siemens-27893p19.html


I went through the updated thread ... pretty impressive stuff!!

I also went through your web site. You're very thorough, you measure a LOT of stuff.

I don't see a lot of electrical build details ... pre-charge resistor, DC fusing, contactors.

You seem to have intimate knowledge of the VFD you've modified. Did you modify the VFD directly (for all I know, you might be into hacking firmware?) , are you using a separate micro?

You had talked about a kit, selling via ebay, etc - any news to share on that front?

Should I stay on this thread, or move to the updated thread?

I ask a lot of questions - one of my more annoying traits.


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## etischer (Jun 16, 2008)

My VFD is a pretty sophisticated controller already, so no need for a micro controller. 

A few things are holding me back from selling inverter kits:
- Liablity
- Endless hours providing tech support
- Lack of time 

You can ask questions in either thread, I'll let you choose =)





thingstodo said:


> I went through the updated thread ... pretty impressive stuff!!
> 
> I also went through your web site. You're very thorough, you measure a LOT of stuff.
> 
> ...


----------



## thingstodo (Jul 16, 2010)

coulombKid said:


> ...phase error corrections would have to be found out using various size pure resistors, capacitors, coils, and combinations on the bench. since the Prop can do 20 mips per cog ...


It's been a while (25 years) since I went through laPlace transforms, etc. I remember the big, important thing being consistency. If you have a sample rate higher than around 10X your max output frequency ... say about 4000 Hz, and your sampling rate is 250 microseconds +/- 0.1% (0.25 microseconds), your phase should be OK.




coulombKid said:


> ...I doubt that the calculation time lag will significantly cause errors in the time domain as long as the firmware is mostly assembler.


Agreed, but the assembler would be to maintain consistency (if you are counting cycles) or to handle the interrupts properly (if you are relying on a timer interrupt).



coulombKid said:


> ...By watching current instead and switching to keep it close to a pure sine wave harmonic distortion issues should largely fall off the table.


I have seen this on a demo for the 'old style' current-mode VFDs. There is no DC bus, there is a large reactor that stores the energy instead of capacitors. The voltage and current waveforms are very nice. The efficiency is not good below full load. The thyristors (not IGBTs) turn on at a lower frequency, but stay on for longer so they don't melt. The pulse width almost appears to be a variable width, instead of a variable number of pulses.



coulombKid said:


> ...Going with a current control calculation requires a lot of scratch bench work but should eliminate a lot of the really complicated vector drive methods required to carry it all off with a micro-controller that uses interrupts...


I'm not familiar with the math, but I'll take your word for it.



coulombKid said:


> ...As long as the motor can handle the full voltage generated during breaking, and the highest attainable pack voltage, then as far as the processor is concerned voltage becomes a major "don't care" except for fault detection.


Interesting way to look at things. The motors that I deal with are rewound by our motor rewinder to 1700V insulation for 600 VAC motors, with an extra layer of insulating paper between the first two coils (as seen from the motor leads) and the iron of the stator. That seems to be where the motor insulation fails.

If your motor leads are more than 100 feet or so, there is a reflection of the pulses from the VFD that can set up as high as 2X applied voltage. Load reactors help to 'round out' the pulse and lessen the reflection. Dv/Dt filters are better, a pure sine wave filter is best.

I've had failures on motors that are not rated for Inverter duty (that I didn't realize were still on site) with 200+ foot lead lengths fail in a couple of weeks of continuous duty. For say 50 feet in an EV, that could mean months, or even years, of driving.



coulombKid said:


> ...There have been some contributors here that are very knowledgeable about the proprietary algorithms of which you speak. Thing is, they seem to be oblivious to the design workarounds in their own systems due to the limitations of an interrupt type controller and the older (slow) sampling devices entrenched in "proprietary" designs. A lot of the experiments I need to do weren't even possible just a few years ago. Why reinvent the wheel? There is a list of valid reasons a page long. Today's cutting edge is tomorrows propriety.


All designs require compromises - they worked around 'slower' sample rates. Good luck on your quest ... and keep us posted!


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## thingstodo (Jul 16, 2010)

coulombKid said:


> Remember, if your pack voltage is less than the rated operating voltage of your larger salvage VFD the the usable horse power may be proportionally less...


Yes, I expect that I can only get the rated 404A out of the IGBTs. At 600VAC, that's around 400 HP. At 200 VAC, perhaps 135 HP.

Since that's industrial rating for 24/7, I could maybe push it a bit.

Since the drive is over 10 years old .... maybe not.


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## thingstodo (Jul 16, 2010)

coulombKid said:


> current sensors would need to be purchased with the correct current sensing range for the application. The spec sheet for them has bandwidth specifications that can show if they are fast enough to preserve phase angle accuracy...


I guess as long as the current sensors are at least as good as the ones on the vector 'controlling' drive, and scaled to the same range (full scale at 5V, for example)

I guess it'll take some research, but I'm not that far into the project yet.


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## thingstodo (Jul 16, 2010)

OK - I'll choose this thread since it's a bit closer to the topic that I'm asking about.



etischer said:


> A few things are holding me back from selling inverter kits:
> - Liablity


Yes, there's always someone to sue you for a typo ... but advice - unless you are an engineer giving professional advice, you can't get sued for that, right?

I want to WORK on my vehicle, something that I haven't been able to do with an ICE newer than ... about 1970. I understand a gearbox, bearings, shocks ... not nearly enough about carburetors, differentials, rack & pinion, brakes, et al. So even what I could work on way back when, I was not good at.

I'm an electrical engineer - I should be able to work on an electric truck.

My first choice would be to purchase a modern controller so it's reliable and trouble-free. There are too many 0's in that price tag right now.

My next choice is to learn enough to do it myself, and carry spare parts for everything since we all make mistakes, especially me



etischer said:


> - Endless hours providing tech support


Tech support is painful at the best of times, yes. And no additional cash for that support.



etischer said:


> - Lack of time


One never has the time to do everything they want to do.


I wanted to reimburse you for (at least SOME of) the time you invested - that's why I asked about the kit. You made incredible progress, but it was a LOT of work for you.

After I sent the last message, I found a schematic in the Reliability tab of the web site. I notice that there is a 5A fuse on the 330V battery circuit, 10A for the DC/DC and the heater. What rating do the fuses have? I'm having trouble locating DC fuses above 125 VDC. The only guys I can find to talk about more than 125VDC discuss the required gap for fusing on DC much larger than AC, so they suggest derating AC fuses by 50% to 90%. 330 VDC * 10 gives you 3300V. A 5KV AC fuse is pretty expensive. The interrupt rating for your battery pack would be pretty large - maybe 5000 or 10000 amps?

What about the DC contactors you use? Are they AC rated or DC rated? If AC, what did you use for a derating? Again, the wind generator guys talk about using AC contactors rated 2X to 3X the rated DC current, 2X to 5X the rated voltage. That gives enough contact surface to survive opening DC instead of AC.

Why I'm paranoid about this - I have seen the arc chutes (where the arc is broken when the contacts open) on a 600VAC, 1200A Westinghouse breaker after it broke a DC fault - I don't remember the details on how DC managed to get onto this AC feeder, but I remember the pitting on the contacts. The silver plating burned off and the brass vaporized. The breaker was rated to break 16X rated current without damage on an instantaneous fault - 25,600 amps. The breaker itself was rated for ... 55 KA or 60 KA (with damage). The insulators that make up the arc chute had bits of silver and brass embedded in them. It held the blast, but it was a mess. So, with electricity at least, paranoia is healthy. A contactor and fuses on the DC, fuses between the battery packs rated for full DC voltage, high resistance grounding to the chassis to help track frame faults, fuses on the AC output .... because EVERYONE makes mistakes.

You said that the VFD you use was pretty advanced. I have a small VFD, but it's just V/Hz. I don't have the donor 'small' drive that will do the controls yet - what would you suggest? Does it have a minimum size (amps) to make the controls scale? The larger drive (rated 404A, 600VAC) is an older, non-vector model. It requires a 900 VDC bus - that's quantity 75 of 12V lead-acid batteries at 40 - 60 lbs each, depending on the brand. (I'm trying to source 'used' batteries from a fork truck dealer locally). 

So I'll get things working at 208V (minimum DC bus for the electronics on a sample 208VAC drive is 210 VDC) That only takes 17 batteries but it takes most of my available weight. 1150 lbs is all the weight the truck can hold, including me. 900 lbs for batteries, VFD, controls and charger.


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## etischer (Jun 16, 2008)

Fusing:
A50P300 is my main fuse. 300A @ 450VDC "semiconductor fuse". It is full of sand to take the place of the fuse element when it burns, to quench the arc. 

The aux fuses are KTK5 and FNQ-R 10 (going off memory). They probably aren't rated for high voltage DC, but I have blown them (due to DC-DC inrush) and haven't had an issue. You might check the fuse that comes installed in the Fluke meters, they might be "rated" for high voltage DC since the meter is designed for measuring high voltage DC


Contactors:
Heater and main contactor are the Kilovac ev200 contactors. My precharge contactor is a 3 phase ~2hp contactor with the 3 contacts wired in series. It noted a higher current rating if you series the 3 contacts. I am only using the contactor for "making" the circuit, it will not be breaking DC current so arcing shouldn't be an issue. The "make" current is limited by the precharge resistor. 

check out page 13, the "DC-1" ratings are listed. 
http://www.sprecherschuh.com/download/ssna9000/download/A/A11_CA8_v610.pdf

Interesting that a contactor rated to start an 11 amp motor is rated 0.1 amps @ 440vdc. 


If you're going to build a drive, I would go 312 vdc minimum. Not sure if you found my updated schematic:

http://etischer.com/awdev/drive/schematics/Drawing4a.pdf




thingstodo said:


> OK - I'll choose this thread since it's a bit closer to the topic that I'm asking about.
> 
> 
> 
> ...


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