Looking for some help understanding the E-motors

[gwatpe]

(Insulated Gate Bipolar Transistor) A power transistor that has characteristics of both MOSFET and bipolar junction transistors (BJTs). Introduced in the 1980s. They are normally used in industrial type power switching circuits.

 

[anko]

Anko
Thanks for confirmation.
I go back to what I said.
If you look at your list of parameters, 34 thro to 41 are in pairs, and I think they may be the values of the controlled phases U & W and maybe feedback currents, so may not be what you are looking for to measure torque.
I an not sure of this but that is why I asked for your ideas of what cct we had, and where you thought the measuring point was.

I was not so much trying to establish torque, as I have that already. See below. I was trying to establish E-power consumption.

When I comes to torque, remember max torque per E-motor? Looks like I was able to determine which was front and which was rear . Values captured via OBDII were spot on (TRQ Nm row):

Furthermore, this picture tells us: IGBT voltages are same as battery voltages.
Diff values (whatever they are are) pretty steady at approx. 100 (%?).
Power output by battery was "only" 11.8 kW. All transformed to heat, as motor output was 0 (0 rpm).
Apparently, 11.8 kW of battery power can produce max torque even when motor efficiency is at it's lowest. So, I still don't understand why it will sometimes start the engine during heavy towing at very low speed.

 

[gwatpe]

Your test seems to concur with my experience, that it is torque and not power that is limiting under high loads like a very steep grade. At very low speeds, the EV motors, combined with electronic limits in the controls, protect the drive train from uneven front/back loadings. I found no benefit when the ICE was operating. Keeping all wheels in traction, so getting all the torque to all the wheels at a particular power level of about 20kW, was enough to climb the hill. The PHEV possibly has algorithms that attempt to predict future power needs, and starting the ICE under certain loadings is maybe one of the outcomes we might just have to live with.

PS the current probably needs to be divided by 10. What is the unit for Power + ?

 

[anko]

Indeed. At low speed you do not need 'any' power. Only torque matters.

A sI said the engine did engage when pulling my caravan out of a ditch. Even wit ha full battery. But it did not when I created this picture yesterday. And I needed to apply full brakes to do so, as the handbrake wasn't enough :mrgreen:

Current+ = C1 + C2
Current- = C1 - C2
Both should be Amps.

Dividing by 10 doesn't bring neither close to the 37 Amps that re leaving the battery.

I still think it could have to do with PWM: It is consuming 976 amps, but only part of the time and it averages out at 37. Could that be something?

 

[gwatpe]

In your test, the total power was shown as 25.4 , ? kW ? The battery voltage was shown as 318. The battery current would be I=P/V, = 79.8A . This is very close to the both motor Current -, shown as 80. The first Charge number of 37 is possibly Generator current ? The battery current may then be 80-37=43A only..

Generator power by calc would be 37 x 318 = 11.8kW. The second Charge value shown would be battery power.

The Current + may be motor phase winding current. This would be dependent on the PWM signals, and the resultant current boost ratio, determined from the ON/OFF proportion of the PWM signals, as a buck converter, in the way the IGBT, motor coils, diode and condenser work together. Torque is produced by current through the winding coils in a precise relationship to the rotor position.

I see some very useful data here now. Gaps in the PHEV data screens can possibly be filled.

 

[anko]

Battery voltage was 318 Volt
Battery current was 37 Amp

These values came straight from the OBDII responses.

Battery power was calculated my my web page as V (318) * A (37) / 1000 = kW (11.8)

There is no data from the generator in the picture. Which is fine, as the engine was not running ;-)

 

[gwatpe]

In your test, the total power was shown as 25.4 , ? kW ? The battery voltage was shown as 318. The battery current would be I=P/V, = 79.8A . This is very close to the both motor Current -, shown as 80. ..

I suppose my question is what is the 25.4 "Power -" related to then? You calculate 11.8kW by comparison. Both can't be true !! We have to identify any data precisely prior to any calcs.

I think that any display of data has to include all variables that may be relevant to any comparisons. If the generator power is part of an energy flow, then it should be there, as would be battery current. The petrol consumption as well as speed.

I think that a single number based on $/km could be derived and displayed. This could be equivalent to a real time economy gauge.

 

[anko]

Power+ and Power- numbers are the sae as the Current+ (current 1 + current 2) and Current- (current 1 - current 2) numbers, but then multiplied by battery voltage / 1000 by my web page. I've done that to see if I would get near the battery power number.

I also did a version where I multiplied with Condenser Voltages, but that didn't make a difference, as voltages were all the same.

 

[ian4x4]

I'm sorry but I do still do not understand some of your assumptions.

If you do not know where or what you are measuring then you cannot know the formula to convert amps to power.

If, as you say, you are measuring pulses, and not mean battery current output, then the voltage is changing at the motor coils so power is proportional to the square of the mean current.

Taking measurements when stationary cannot be representative of normal operation. That is of course unless all the rules of synchronous motors have changed. Please be patient with me as although I have a lifetime of electronics, you may have to explain the advances that have occurred over the last 15 years, which makes my version of theories obsolete.

 

[anko]

Hi Ian,

Believe me, I know virtually nothing of E-motors and I knew absolutely nothing about the before I started thinking about the PHEV. Well, almost ;-) But to me,

If, as you say, you are measuring pulses, and not mean battery current output, then the voltage is changing at the motor coils so power is proportional to the square of the mean current.

could be latin as well :lol:

In essence, I am trying to do a couple of different things:

- Verify / make visible that in parallel mode, the rear E-motor indeed produces some torque (as Mitsu claims) where the front E-motor only consumes a little bit of power to prevent E-drag.
- Make visible that when coasting in B0, some power will still go to the E-motors. As a matter of fact, some battery power will even go to the generator to prevent drag when you are in parallel mode (only in B0?) and lift the throttle / briefly hit the breaks. Even though the power meter shows 0. Similar, while towing with a slight head wind, the energy flow diagram might show the orange error from engine to wheels but no blue arrow. One would expect that this situation was neutral to the SOC. But it is not. SOC is dropping at that time, because battery power is used to prevent drag in both the E-moters and the generator.
- Make visible what happens when you switch from normal to 4WD lock mode, in (serial) EV and in parallel mode.
- Understand what happens when the car decides to start then engine at very low speeds, even when SOC seems sufficient.
- Etc.

Why? Just because we can. That is, if we indeed can. And I think I am on the right track.

So, I am doing different experiments with different objectives, not necessarily related. And I show 'results' of them in this one thread. But I do realise measurements at 0 RPM say nothing about efficiency at higher speeds

Indeed I do not know what I am measuring. But neither did I have any clue when I first saw the hex strings coming out of my OBDII dongle. I managed to crack them by looking at lots of samples and comparing them with readings from 'official' devices. And that brought quite a lot of successes. The same way, I was hoping to test different formulas for calculating E-power consumption and compare the results to battery output, to see if one of these formulas would give me a solid match. Should I find a match (over different tests and speeds) it would allow me to compare E-power in to mech power out and determine efficiency at different RPM's. Again, why? Because we can?

 

[anko]

BTW: I just read the construction of the rear motor is equal to that of the E-motor of the i-Miev.

 

[ian4x4]

Thanks Anko.

I think I need to change my reading to something like this.

Hybrid Electric Power Train Engineering and Technology: Modeling, Control ...
edited by Szumanowski, Antoni

Unfortunately I cant find a free online copy, but its summary says it goes into the problems/advantages of controlling the SOC in PHEVs, and HEVs, and talks of the control modelling to get the best efficiency, reliability, etc.

Please keep posting your results, I have learnt a lot about PHEVs.