Hello,
I am designing a small IPM motor and I need to select a controller for the motor. I am thinking of using VESC® 6 MKIII.
I have a few questions and just want to make sure if VESC is right for me and if it supports everything I need.
I tried to find the answers myself, but not sure if those answers are correct.
Anyhow, I would be grateful if someone can answer to following questions (or to confirm my assumptions):
1) Does the VESC support sensorless FOC with MTPA (maximum torque per ampere) control?
-I saw on https://github.com/vedderb/bldc/pull/91 that the MTPA FOC is introduced last year, but I am not sure if the sensorless control is supported together with that.
2) What is the maximum stable PWM switching frequency that VESC can work with?
-I know that the default PWM frequency is 20 kHz, and I think that I read somewhere that 40 kHz is the upper stable limit. I am assuming that the max output sine frequency is approx. 10-20 lower to PWM frequency in FOC.
3) What are the safety features that VESC support if the motor trips at the maximum speed? Does VESC support short-circuiting of the motor terminals in that case?
- I think someone suggested short-circuiting motor terminal for high-speed trips but I am not sure if that is implemented within available VESC tool(s).
Many thanks!
I am yet to mess with MTPA but I see no reason why it would not work sensorless as VESC attempts to switch to sensorless anyhow as soon as you get reliable BEMF signals. The switching RPM threashold is specified in MC config.
Max reliable frequency is 30Khz with V7 or 60Khz without. I think I saw a few people attempted to go higher but it wasn't stable above 30Khz.
Safety features. Overcurrent, overvoltage, over temperature on controller and/or motor and power rollback, overspin (eRPM limit up 100K, maybe 150K).
Short circuiting phases for high speeds? Shorting phases would definitely not give you high speeds but cause abrupt braking.
Maybe you are referring to braking or "handbrake" in VESC terminology. That is implemented in the code and can be controlled over UART, ADC, etc.
NextGen FOC High voltage 144v/34s, 30kw (https://vesc-project.com/node/1477)
Thank you for your answer.
Not sure if that is handbrake.
What I meant in 3) is following:
Let's assume very high speed in the flux weakening region. The converter is supplying a lot of negative Id current to keep the voltage on the motor at a low level compared to BEMF. If in that case motor trips for some reason, MOSFETs will be opened and high BMF voltage from the motor will be connected to those opened MOSFETs . That voltage can be high enough to burn MOSFETs.
To make sure that will not happen, we can simply short circuit the motor with the MOSFETs. To do that all upper or all lower MOSFETs should be closed. In that case, the short current will flow and the motor will brake. Short circuit current may not even be that high and converter should withstand that current. The point is not to burn MOSFETs with the motor in the no-load condition at high speeds when the BEMF is very high.
So my question no. 3) was if that safety function is supported.
The question is: Can you detect that reliably and react fast enough?
I think there is nothing to detect.
Simply when the fault occurs (or when motor trips) instead of opening all the MOSFETs, it is required to short-circuit motor terminals with MOSFETs.
The cause of the fault is not important in this case.
So if a fault occurs when you are riding a skateboard for instance, it will just brake the motor and you fall off... The safest thing to do in most scenarios is to just let the motor freewheel until it stops. Unexpectedly stopping things suddenly can be bad. Unless this would only be the case for when the BEMF is above the bus voltage
Well, it depends on the application. Obviously, for the skateboard that would not be such a good idea...
However, for electric bikes, motorcycles or small cars I would rather deal with breaking compared to the burned power stage.
But to get back on question 3), can someone confirm if the explained short-circuiting of the motor during faults supported with the VECS tool?
I don't believe shorting phases to protect against overvoltage is a good strategy. Overvoltage should not happen in the first place with good design such as DC Link filtering and proper PCB layout. Also, the power stage components are better be rated well above any voltage that a motor can produced. A high speed overvoltage protection circuit would make sense for cases when things really go wrong even though they shouldn't.
Shorting phases at high RPM will create a dangerous stall of the motor.
NextGen FOC High voltage 144v/34s, 30kw (https://vesc-project.com/node/1477)
Shorting against overvoltage is a common practice in the automotive industry. Short circuit current is often below the maximum current of the converter in those applications, and since the short circuit current is mostly in negative d axis the torque is not that big. The braking torque, in that case, is certainly lower compared to the braking torque when you press the full break pedal. That all is valid for well designed IPM motors.
However, if you do the same with some SPM motors, you can expect fireworks and massive braking torques, stalling of the rotor etc. :)
It would interesting to read about this practice, maybe something we can adopt in VESC. Please provide some references, links where shorting was used as an overvoltage protection technique.
NextGen FOC High voltage 144v/34s, 30kw (https://vesc-project.com/node/1477)
Here are some patents, if I find more materials, I will post it here
https://patents.google.com/patent/DE102012002023A1/en
https://patents.google.com/patent/US7554276B2/en
Anyway, I would like to thank all of you for the answers.