# [EVDL] AC power



## EVDL List (Jul 27, 2007)

I think it takes 2-3 HP to run the AC compressor. I wouldn't bother with
PWM, either direct connect the shafts, or use a belt drive to get the
right speed. Either way I'd just use the signal that normally turns on
the AC clutch to engage a relay that would turn on the motor.

If you have a traction motor with a tailshaft, you could even try driving
the AC off the tailshaft. Of course that means no AC when you're parked
unless you idle the motor.


>
> It is getting hot and I sure would like to keep the AC after conversion.
> I understand it is more weight
> I understand it is more current draw.
> However, it is no worse than a heater for those of you in the North.
> I am thinking about using a DC motor to run the compressor and possibly
> power steering pump. I hope the power is 1 or 1.5 HP.
> The question is how much power will the AC compressor actually require.
> It cools at 750 RPM idle in the IC configuration and is cold at 2000 RPM
> when driving. I am thinking simple PWM and a few speeds like the fan has.
> I have no idea where to start looking to find the power requirements or
> torque requirements. Any input would be appreciated.
> David, Pompano Beach FL
>
>
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## EVDL List (Jul 27, 2007)

> David Kerzel wrote:
> > It is getting hot and I sure would like to keep the AC after conversion.
> >
> I'm with you, David. I'm in Orlando, and I don't have A/C in my ICE.
> ...


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## EVDL List (Jul 27, 2007)

Roland has the slickest AC set up using factory parts that I have seen, I
will let him explain it. It is the smartest set up I have heard of.

On Sat, May 31, 2008 at 8:08 PM, Jude Anthony <[email protected]>


> wrote:
> 
> > David Kerzel
> 
> ...


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## EVDL List (Jul 27, 2007)

A Solectria Force aircon uses about 1kW. With motor efficiency figured in, 
that's roughly one horsepower. A larger or less efficient aircon would use 
more.

Whether PWMing the motor to adjust amount of cooling is really any more 
efficient than cycling it on and off (what most ICEV aircon does) is unclear 
to me. However, the Toyota Prius uses PWM, and that car (though it's an 
ICEV) is pretty seriously focused on efficiency. 

David Roden - Akron, Ohio, USA
EVDL Administrator

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## EVDL List (Jul 27, 2007)

On Sat, 31 May 2008 21:08:30 -0400, Jude Anthony <[email protected]>


> wrote:
> 
> 
> >> I have no idea where to start looking to find the power requirements or
> ...


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## EVDL List (Jul 27, 2007)

John,
Thanks for that great method for determining the power. I was hoping for a
number but knew it was not that easy.
The car is a Mitsubishi Eclipse and compared to my Volvo 240 it has ice cold
AC.
The same motor will run the power steering pump, possibly the vacuum pump,
and the AC compressor. That is why I am thinking variable speed since the
two pumps works well even at low speeds and pick up speed when the AC clutch
engages.
I have a second problem I am planning an AC motor so I will have a 330 volt
battery pack. I will actually be using a small industrial 3 phase inverter
for the motor control.
David Kerzel
Pompano Beach, Florida


Message: 25
Date: Sun, 01 Jun 2008 01:18:47 -0400
From: Neon John <[email protected]>
Subject: Re: [EVDL] AC power
To: Electric Vehicle Discussion List <[email protected]>
Message-ID: <[email protected]>
Content-Type: text/plain; charset=us-ascii

On Sat, 31 May 2008 21:08:30 -0400, Jude Anthony <[email protected]>


> wrote:
> 
> 
> >> I have no idea where to start looking to find the power requirements or
> ...


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## EVDL List (Jul 27, 2007)

> "David Kerzel" <[email protected]> wrote:
> 
> >John,
> >Thanks for that great method for determining the power. I was hoping for a
> ...


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## EVDL List (Jul 27, 2007)

I'd be interested in talking about one of the solectra motors. Hit me 
off list if you want.

Kelly Hales

Sent from my iPhone



> Neon John <[email protected]> wrote:
> 
> > On Thu, 5 Jun 2008 18:26:28 -0400, "David Kerzel"
> > <[email protected]> wrote:
> ...


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## EVDL List (Jul 27, 2007)

I'd also like to hear if you decide to list some parts. You mentioned taking
the motors out of buses, what do you think is a good fit for the motor? Do
you think they'd work in a full sized pickup truck?

Dave Cover



> Kelly Hales <[email protected]> wrote:
> 
> > I'd be interested in talking about one of the solectra motors. Hit me
> > off list if you want.
> ...


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## EVDL List (Jul 27, 2007)

> "dave cover" <[email protected]> wrote:
> 
> >I'd also like to hear if you decide to list some parts. You mentioned taking
> >the motors out of buses, what do you think is a good fit for the motor? Do
> ...


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## EVDL List (Jul 27, 2007)

I could be wrong, and I certainly don't want to be a downer, but...

Didn't I read once that Solectira (Now Azure) won't sell the inverter
without the motor?
If that's true, and you don't have the inverters...

I hope I'm wrong, but probably worth checking.

> On Mon, 9 Jun 2008 19:22:56 -0400, "dave cover" <[email protected]>


> > wrote:
> >
> >>I'd also like to hear if you decide to list some parts. You mentioned
> >> taking
> ...


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## EVDL List (Jul 27, 2007)

I think you're right; I think you'd have to use a homebrew, Tri-Zilla,
or industrial VFD to run one of these.

-Morgan LaMoore



> Peter VanDerWal <[email protected]> wrote:
> > I could be wrong, and I certainly don't want to be a downer, but...
> >
> > Didn't I read once that Solectira (Now Azure) won't sell the inverter
> ...


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## EVDL List (Jul 27, 2007)

Hi John and All,

Have you thought about an electronic
commutator? Basically a sensor/powerstage version of a
regular commutator, mechanically timed. With that many
motors it might be worth doing. I'm trying something similar
with a single or dual disc style BLDC motor.

Jerry Dycus

----- Original Message Follows -----
From: Neon John <[email protected]>
To: Electric Vehicle Discussion List <[email protected]>
Subject: Re: [EVDL] AC power
Date: Mon, 09 Jun 2008 21:29:06 -0400

>On Mon, 9 Jun 2008 19:22:56 -0400, "dave cover"


> ><[email protected]> wrote:
> >
> >>I'd also like to hear if you decide to list some parts.
> >>You mentioned taking the motors out of buses, what do you
> ...


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## EVDL List (Jul 27, 2007)

> Have you thought about an electronic
> commutator? Basically a sensor/powerstage version of a
> regular commutator, mechanically timed. With that many
> motors it might be worth doing. I'm trying something similar
> with a single or dual disc style BLDC motor.

That works fine - its a common way to drive a brushless motor, but I think 
that these are AC induction motors, and I've never heard of that for 
induction motors. My first thought is that its unlikely to work, since 
induction motors need to be fed an AC signal that is oscillating faster than 
the rotor is spinning. This is the whole concept of "slip".

For BLDC motors its called trapezoidal commutation. This is simple since it 
can be done with only logic, but the drawback is that it is quite a bit less 
efficient, and quite a bit less smooth (torque ripple). Sorry I don't have 
numbers to go with it, but since efficiency is pretty important in an EV, 
trapazoidal commutation is not really suitable.
Jon 

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## EVDL List (Jul 27, 2007)

For an induction motor, there should be a difference between the
mechanical and electrical frequency, and this difference determines
the torque. A basic mechanical commutator would give you practically
zero torque. You could put gears between the motor and sensors, but
that would give you almost no control over the torque. You could put a
mechanical CVT between the motor and commutator, but this is extremely
complicated and expensive compared to the benefit you get.

I would expect that a DC motor would outperform an AC induction motor
with a mechanical commutator in almost any respect.

-Morgan LaMoore



> jerryd <[email protected]> wrote:
> >
> > Hi John and All,
> >
> ...


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## EVDL List (Jul 27, 2007)

> "jerryd" <[email protected]> wrote:
> 
> >
> > Hi John and All,
> ...


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## EVDL List (Jul 27, 2007)

> For BLDC motors its called trapezoidal commutation. This is simple
> since it can be done with only logic, but the drawback is that it is
> quite a bit less efficient, and quite a bit less smooth (torque
> ripple). Sorry I don't have numbers to go with it, but since
> efficiency is pretty important in an EV, trapazoidal commutation is
> not really suitable.
> Jon 

This may be an over simplification. If a motor is wound for sinusoidial
then running it with trapizoidial will be less efficient and less
smooth, noticed mainly at lower rpms. If however the motor is wound for
trapizoidial drive then this effect is minimized. Trapizoidial drive can
have significantly less switching losses. One idea is to run sinusoidial
drive at lower frequencies to keep things smooth and within the DSP's
capabilities, then switch to trapozoidial drive at higher frequencies to
reduce switching losses and allow cheaper electronics to keep up.

The key is to hook up a scope and spin the motor and plot the BEMF profile.

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## EVDL List (Jul 27, 2007)

>> Have you thought about an electronic commutator?



> Neon John wrote:
> > That's basically what happens in a BLDC, as you know...
> > I have some doubts about it working very well in an induction motor. The
> > square wave contains so much harmonic energy that I'd expect a serious
> ...


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## EVDL List (Jul 27, 2007)

I think we've wandered from the original topic - which was using shaft 
sensors and trapezoidal scheme to drive an ac induciton motor (ACIM). My 
original point is that this can't work for an ACIM. But the efficiency 
discussion is an interesting one for BLDC motors, so I wanted to make some 
comments:

> trapizoidial drive then this effect is minimized. Trapizoidial drive can
> have significantly less switching losses.

I don't understand this at all? This comment would only apply if we're not 
discussing a PWM type drive - in other words a drive where the "voltage" 
applied to the motor leads is not variable. AFAIK, in a PWM drive, the 
switching losses are all going to come from the PWM transitions (at 5+KHz) 
not from the sinusoidal OR trapezoidal variations happening much slower 
<500Hz. Am I wrong about this? Do you know something I don't?

If you're comparing a pure trap drive with no pwm to a sine drive with PWM, 
that's a silly comparison and not worth talking about in terms of 
efficiency. The efficiency discussion does not drive the decision to use 
one or the other in that case. That discussion should be about whether you 
want to control torque output or not...

I hope everyone will agree that a sinusoidal scheme will be more efficient 
than a trapezoidal drive scheme. That's the reason for doing it.

>One idea is to run sinusoidial
> drive at lower frequencies to keep things smooth and within the DSP's
> capabilities, then switch to trapozoidial drive at higher frequencies to
> reduce switching losses and allow cheaper electronics to keep up.

I think this is a solution looking for a (non-existant) problem. If you've 
got a DSP that can do sinusoidal drive - then there is no reason not to do 
that at high speeds. Things don't get more computationally intense at 
faster speeds - that's the whole point of FOC. I think you might be 
misunderstanding switching losses, but if you know something I don't, I 
definately would love to hear more about it!

> The key is to hook up a scope and spin the motor and plot the BEMF 
> profile.

YES! that's a great point - by looking at the AC waveform you could tell a 
lot about what the motor wants to see driving it.

Jon 

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## EVDL List (Jul 27, 2007)

> Lee Hart <[email protected]> wrote:
> 
> >>> Have you thought about an electronic commutator?
> >
> ...


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## EVDL List (Jul 27, 2007)

> Jon Wagner wrote:
> > I think we've wandered from the original topic - which was using
> > shaft sensors and trapezoidal scheme to drive an ac induction motor
> > (ACIM).
> ...


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## EVDL List (Jul 27, 2007)

> Neon John wrote:
> > The modern "modified sine" pseudo square wave inverter uses some zero
> > off time to help the square wave look a little more like a sine wave
> > to inductive devices. That is, one polarity switches off, it stays
> ...


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## EVDL List (Jul 27, 2007)

> Lee Hart <[email protected]> wrote:
> > You can wind a motor to optimize it for many different coil waveforms. A
> > sinewave is common, because that's what you get from an AC outlet.
> > Sinewaves are the most efficient for the motor; but least efficient for
> ...


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## EVDL List (Jul 27, 2007)

> Morgan LaMoore wrote:
> > Why is a sine wave less efficient than a square wave to generate?
> 
> A square wave inverter will always have some off-time when both upper
> ...


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## EVDL List (Jul 27, 2007)

Some good stuff here - thanks Lee. My comments below:

>> I think we've wandered from the original topic - which was using
>> shaft sensors and trapezoidal scheme to drive an ac induction motor
>> (ACIM).
>
> There are circuits that drive an ordinary induction motor with a solid
..
> one. They were successful enough to use in commercial products.

I didn't know that - neat!

> A trapezoidal waveform is intermediate -- between the two. It is
> relatively easy to build an inverter that has a smooth linear ramp up
> (produced by PWM), then a flat top (upper transistor switched fully on),
> then another ramp down (PWM), and a flat bottom (lower transistor fully
> on). This has less loss than a sinewave inverter, but more than a square
> wave inverter. Likewise, the motor is designed to accept these softer
> edges. Its efficience is midway between the sine and square wave cases.

I was using a different terminology for "Trapezoidal". I have always heard 
this used to describe a standard hall effect commutated BLDC motor drive 
method (no ramp up at all - just look at the halls and turn on the correct 
phase at a constant PWM). I was completely unaware of an actual inverter 
that uses a ramp up, flat top, and ramp down. Why is this relatively easier 
to build than a sin wave inverter? I can't think of a design that would 
make it easy to make a trapezoid PWM waveform but not a sin waveform, so I'm 
interested to hear more about this! I am especially interested to hear how 
the inverter would know when to start the ramp-down in a BLDC application 
with only hall effect sensors on the shaft!

>>> One idea is to run sinusoidial drive at lower frequencies to keep
>>> things smooth and within the DSP's capabilities, then switch to
>>> trapozoidial drive at higher frequencies to reduce switching losses
>>> and allow cheaper electronics to keep up.
>
>> I think this is a solution looking for a (non-existant) problem. If
>> you've got a DSP that can do sinusoidal drive - then there is no
>> reason not to do that at high speeds.
..
> It's a real problem. The Toyota Prius, for example, does this. It's
> fairly common because you can't switch the inverter arbitrarily fast. At
> low base frequencies, the switching frequency is high enough to make a
> pretty good sinewave. At high motor speeds, you have so few points that
> the sinewave approximation gets bad -- you're better off giving up on it
> and going to a simpler waveform.

OK - I don't know the details of a prius motor, but lets look at an 
arbitrary motor example:
how about an 6 pole BLDC motor (3 pole pairs = 3 electrical rotations per 
mechanical rotation).

Lets say we want to sinusoidally commutate the motor. At a given 
mechanical RPM, the AC waveform would have to be a sin wave at a given 
frequency:

1000rpm -> 50Hz
2000rpm -> 100Hz
..
5000rpm -> 250Hz
10,000rpm -> 500Hz

Now lets say we want to PWM the motor at 10KHz (don't know the actual freq. 
but from the sound of a prius, I think this is in the ballpark). So at 
10,000 RPM (faster than the prius motor spins I would think) we get about 20 
PWM cycles per sine waveform. This is 10 PWM cycles for a half-wave, which 
ought to drive the motor pretty nicely IMO. So it would really depend on 
the number of poles, top speed of the motor, and the switching frequency.

In light of what you just mentioned regarded the prius gate drive scheme, 
I'm curious to know the actual values for the prius (#poles, top rpm, and 
switching freq).

Jon



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## EVDL List (Jul 27, 2007)

> The other way to do it is to have a single PWM controller that steps the
> battery voltage down to whatever voltage you need. Then have a 3-phase
> bridge where the transistors are simply switched HHHHLLLLHHHHLLLL all
> the time. The output inductor of the PWM controller prevents
> shoot-through current. This is called a current-fed 6-step inverter.

So you're proposing two completely separate power stages with an inductor in 
between them???
Is this really simpler and cheaper any more?

I've never seen this for a motor drive. The motor drives I have seen all 
have only one 3-phase bridge and use the motor as the inductance. This of 
course requires high power AND fast switching in the 3-phase bridge.

Since the words "high-power, fast-switching, and efficiency" can only 
describe the more modern 3-phase bridges, and I've only seen fairly modern 
motor controllers - that would explain why I'd never seen what you describe 
above.

Jon 

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## EVDL List (Jul 27, 2007)

> Jon Wagner <[email protected]> wrote:
> 
> > > The other way to do it is to have a single PWM controller that steps the
> > > battery voltage down to whatever voltage you need. Then have a 3-phase
> ...


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## EVDL List (Jul 27, 2007)

Why is a sine wave less efficient than a square wave to generate?


To generate a sine wave, it shouldn't be less efficient, but to
generate three sine waves, maybe. At best you can have one of the
three legs hard-switched to a bus rail with two legs doing
PWM (switching losses).

A trapezoidal motor usually has one leg hard-switched to a bus
rail and one other leg is doing PWM, with the third leg left
idle.

My Solectria BLDC drives do this, and they were some of the most
efficient motor-drive combinations for a long time - maybe still?

-Dale

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## EVDL List (Jul 27, 2007)

> Jon Wagner wrote:
> >> The other way to do it is to have a single PWM controller that
> >> steps the battery voltage down to whatever voltage you need. Then
> >> have a 3-phase bridge where the transistors are simply switched
> ...


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## EVDL List (Jul 27, 2007)

> Jon Wagner wrote:
> > "Trapezoidal". I have always heard this used to describe a standard
> > hall effect commutated BLDC motor drive method (no ramp up at all -
> > just look at the halls and turn on the correct phase at a constant
> ...


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## EVDL List (Jul 27, 2007)

I think the 2 stage inverters also make regen easier to handle. You can
control the voltage separately from the commutation
It certainly makes normal control easier. The loss in efficiency of
having yet another transistor in series is sometimes offset by the
reduction in switching losses in the commuting transistors. Of Course,
These generalizations are dangerous, every design is unique and what is
better at one operating point may not automatically be better at another.

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## EVDL List (Jul 27, 2007)

> Jeff Shanab wrote:
> > I think the 2 stage inverters also make regen easier to handle. You can
> > control the voltage separately from the commutation
> > It certainly makes normal control easier. The loss in efficiency of
> ...


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## EVDL List (Jul 27, 2007)

This is from a diff group I read but seams to apply here


If you look over the golf car A/C system you can see that the heart of
the unit is a 12V hermetically sealed compressor. This are the same
kind that can be found in those mini fridges. From doing some
searching it looks like Danfoss is a leader when it comes to these
compressors http://compressors.
danfoss.com/<http://compressors.danfoss.com/>They produce 3 version of
these 12-24v compressors in there BD series, and 2 of those are listed
for solar applications in 10-45v.

One of these compressors coupled with a mini Vintage Air unit should
solve the A/C and heater concerns for most.

Joe in PA



> Lee Hart <[email protected]> wrote:
> 
> > Jeff Shanab wrote:
> > > I think the 2 stage inverters also make regen easier to handle. You can
> ...


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