# 3-phase vector control questions.



## subcooledheatpump (Mar 5, 2012)

Yes a vector controller can adjust voltage and frequency independently. 

More importantly, it monitors the two currents at work in the induction motor, the magnetizing current, and the torque producing current. It also monitors the position of the rotor. 

With this information, and the software programmed into the microcontroller, the drive can keep the currents in the correct phase with each other, and therefore the correct angle in the motor which means peak torque. 

If the currents aren't in the correct phase, peak torque won't be produced. Normal VFDs do nothing to monitor the phase between the two currents, so they technically can't make an induction motor make peak torque at low speeds (below 5 Hz)

Some others explain it pretty well:

http://www.eng-tips.com/faqs.cfm?fid=1062


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## SandRailEV (May 11, 2012)

subcooledheatpump said:


> Yes a vector controller can adjust voltage and frequency independently.
> 
> More importantly, it monitors the two currents at work in the induction motor, the magnetizing current, and the torque producing current. It also monitors the position of the rotor.
> 
> ...


 
So, is this consistent with what you're saying?; 

At low RPM (and low frequency), say I were to "open the throttle wide" and call for max torque, a non-vector will quickly ramp up quickly to say 60hz and max volts, but the actual motor speed of course will lag behind syncronous speed while accelerating the car. During that accelerating time, the controller is putting out 60 hz continuously with the motor speed is catching up slowly (to syncronous speed) while reducing slip up until it reaches syncronous speed.

In the vector motor, when the throttle is jammed open, the controller increases voltage to max but increases frequency slowly ahead of motor speed? Do I have this correct?

If so, are you saying the vector motor will produce more torque during acceleration by limiting frequency response? Also if this is so, what difference if any will I see in efficiency during both said scenarios?

Thanks again for any info...

Tom


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## SandRailEV (May 11, 2012)

By the way Sub, I take it from your name you are in the HVAC field... Same here for 40 years now. I typically do light commercial & industrial along with commercial refrigeration. Self employed...


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## subcooledheatpump (Mar 5, 2012)

Basically yes, a vector drive will adjust all the outputs in accordance with whatever makes peak torque in the motor, be it frequency, voltage, or current angle (between the magnetizing current and the torque current)

It gets the information from current sensors, a model of the motor programmed into the software, and the speed sensor (shaft encoder) 

And yes a regular VFD just has a standard Volts to Hertz ramp, with torque boost. That means it doesn't actually know what the motor is doing, it just puts out whatever frequency you command it to. That can be a big problem because it can lead to an overcurrent which will trip the drive and/or damage the motor, and it won't make peak stall torque. The regular VFD eventually can make the motor produce peak torque, but it won't be at a low frequency and it won't be smooth because it's really not paying attention to the motor. Eventually it will get lucky though. 

So really, a vector (a sensored vector to be more precise) is needed for using an induction motor in an EV. I use a sensorless vector drive in my van, it works well enough, though eventually I will upgrade. Basically, drivers have to be trained to use the van because of the wacky way sensorless vector works. I want it to be better though

Yes I work in the HVAC field. The van I converted, I actually intend to use as a service/installation vehicle.


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## SandRailEV (May 11, 2012)

Ok, now I understand, mostly I think. So, to get that brute force low end torque, I really need the vector sensor... Do you know what brands & models of industrial drives have the inputs for vector & current? I am not sure quite yet how I will adapt a controller, whether I will get a big one right off or find a smaller one and change out the driver & IGBTs. I am leaning on the latter but that's a long ways off.. I am still working on rebuilding the running gear, and painting, and getting a windsheild, and, and, yeah etc...

Thanks for the info... As soon as I get the chassis done enough for wheels & tires, I'll post some pics and a project overview in the build section....


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## bjfreeman (Dec 7, 2011)

though I started with the 56F803 when Motorola was producing it, this is the same app-notehttp://www.diyelectriccar.com/forums/cache.freescale.com/files/product/doc/AN1930.pdf_3_-_Phase_ AC _Induction_ Motor _Vector_ Control Using a 56F80x


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## major (Apr 4, 2008)

SandRailEV said:


> My questions concern vector drive vs non-vector drive. What exactly is the advantage of vector drive?


Hi Sand,

Vector drive is a motor control method which enables a command input to determine the amount of motor torque. The only reliable true torque control schemes use motor speed sensing and are often referred to as closed loop vector control. There are open loop vector controls and sensorless vector controls, but these fall short of being able to accurately control torque over the entire range, especially at zero and low speed. And then there is non-vector control which is simply output in the proper voltage and frequency proportion with current limits, called V per f or V/f control. This is good only for speed control where the command input (throttle) would set speed (frequency) point and the controller would ramp the output to that value over a predefined time period. 

For a vehicle propulsion system you need to have the throttle pedal control the motor torque to approximate the feeling of the internal combustion drives we are used to driving. Having the throttle control motor speed is a breakneck exercise. Ask me how I know 

Regards,

major


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## SandRailEV (May 11, 2012)

Thanks Freeman and Major. After reviewing the literature, I can understand now why the vector sensor and control is desired. To put it in simple terms, it seems that vector control is a way to control slip and in doing so, the controller is in control of the load, not just the motor, so to speak.

Thanks again,

Tom


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