Switch EV is go! (part 3)

The Greenstage Team has been helping Switch EV with final tuning and testing on their Electric Holden Ute.  We decided to capture some of the action and we have put together a little montage, with a hint to what's coming next as well.



If you're after more information, check out earlier Switch EV blog posts part 1 and part 2.

Enjoy!

KiwiAC driving Switch EV Induction motor … Part 2: Motor Control

Following on from our bench testing earlier in June, Switch EV have installed their motor into their test vehicle and undergone some driveway testing. Sorry no video or photos this time, just output logs turned into pretty graphs (go LibreOffice!)
At the most basic level we are controlling motor current. Our serial output is not fast enough to report every current measurement (two performed every 12kHz), but we can see if the current is behaving within the region we expect. First we can compare the requested current output magnitude, vs raw, directly sampled phase currents. The vertical axis is a signed internal scale, where 32700 is approximately 1000 Amps.

Here you can see that every reported current is within the magnitude requested. Because of stroboscopic effects, (sampling windows and AC sinusoidal waveforms etc) it is expected that we would see values less than requested current.

Delving into the Motor Model at the heart of Field Oriented Control, we can check that the two current vectors, (magnetic flux producing Id and torque producing Iq) are controlling:  

Here, the error between requested Id and Iq are plotted as DId and Diq. The error is around 1%, which equates to a output Torque error of about 0.01% (output Torque is proportional to motor flux times torque current).
At the moment, we are controlling Flux and Torque to equal throttle position (thick grey line). Flux (the green line) should always be positive however, (as two negative numbers would multiply to a positive torque). We have set the throttle zero position to produce regen torque, to approximate engine braking, but only while moving. You can see at 175 seconds when the vehicle was stopped that the torque and flux trending to zero, no longer following the throttle position. A small acceleration occurs from 184-193 seconds, and a much greater one at 205 seconds.

This final graph shows power in the controllers DC bus, versus the calculated mechanical motor power (estimated torque times motor speed) and an estimation of the inverter and motor AC conduction losses. At the time the car was traversing undulating terrain, so change in speed does not correspond that well to delivered power.
Finally, a big thanks to Lachlan for putting together the data extraction scripts that made these graphs possible and to Switch EV for building such a great EV!
Stay tuned, driving videos coming soon...

KiwiAC driving Switch EV Induction motor

We have recently been helping to commission a new induction motor made be Switch EV (a NZ manufacturer).  We are pretty happy with the results so far and hope to be showing vehicle based dyno (dynamometer) results in the near future. For now though, here are some videos and images to whet your appetite.

The motor shown is being driven via a Gen 1 SKAI with a Greenstage KiwiAC control board and a 330V Lithium Iron Phosphate battery pack providing the energy.

As you can see the brake rotor on the dyno gets quite hot (hence the smoke!), it is absorbing the energy from the motor when we load it up to measure the torque.

Zero RPM torque tests showed we were achieving in excess of 600 Nm, which is "heaps" of torque and matching nicely with design goals.  Unfortunately the dyno didn't quite measure up and soon after we snapped the shear pin on the shaft.

Never mind, the dyno did its job and the Switch EV motor is ready for the next stage!  Stay tuned for more information...

Dyno Progress

For a while now we had the plan to build a dynamometer out of two Siemens made Ford Ranger AC motors. While no calibrated results could be made (through measuring the torque directly) the contraption would be very useful for comparative analysis of motor control regimes and settings.

The first steps (October last year) involved working out how to couple the two together. The motor shaft is hollow to allow a further shaft to run directly through the motor. The output end of the shaft has a helical gear directly machined into it, for a now unavailable planetary gear set. Others have suggested directly welding to the shaft, some have success using taper-lock devices directly on the gear.

In our situation, because of its non-critical nature (a failure is not likely to put anyone in a compromised situation), we decided to go with another untested route – developing a bush that works somewhat like an inside out double ended collet holder. Made of brass it may not be as strong as the rest of the equipment, but simple to make on the lathe, and not likely to damage the motors for future applications.

As previously mentioned Stephen designed and organised an adaptor plate for bolting the motors together. The motors are now coupled, and spinning just about as freely as individually so must be fairly close to aligned.

Due to the weight of the combined motors (over 130kg) we wanted to be able to wheel them around. We started to think about building a trolley but instead opted for far cheaper and easier option - a 200kg rated handcart.
Next came the job of hooking up the motor encoder and temperature sensors. Reportedly there isn't a plug available for the encoder connector on the motor, so a new arrangement is required. 

We made a stainless piece that reduces the hole to suit the M23 servo-motor style encoder connector used on standard Siemens motors.

 I don't think that the plastic connectors that the motors are delivered with were originally part of the plan. The tapped hole for the closest cover bolt breaks through into the hole for the connector. Worse still, an o-ring seal sits beyond where the bolt hole breaks through, which means the o-ring is damaged every time the fitting is removed or put back in. Not a clever design, but we will run with it for the mean time.