Hardware Additions

Are there any features that you would like to add to the VESC?
Posts: 3
Joined: 05 Jun 2018, 09:16

Hardware Additions

Postby RuBisCO » 05 Jun 2018, 09:49

First off, I would like to say the VESC is an amazing piece and well designed hardware and firmware.
However, I noticed a few modifications to the hardware that could make it even better:

Filters on each of the phase voltage sense resistor dividers
After attempting successfully to design my own BLDC controller firmware using STMicroelectronic's nucleo ecosystem, I noticed that BEMF sampling and detection is much easier and much more stable if a capacitor is placed in parallel with the bottom resistor in the phase voltage sense resistor divider.
With a top resistor value of 39k, something like 3.3 or 4.7nF would probably work. (I used 10k and 10 nF)
Without the capacitors, I noticed that my control algorithm would only work effectively if I exclusively sampled on either the low side or high side of PWM, (and low side would only work properly if the output driver's resistance sufficiently level shifted the BEMF signal above ground :x ). If it sampled on both, the motor would sputter.
With the capacitors, I was able to sample whenever I wanted (arbitrarily during a PWM cycle, or several times during a PWM cycle) and my STM32F446 would detect zero crossings no problem.
I ask this because after experimenting with both a store bought and hand assembled VESC, both seemed to struggle to lock onto small BLDC motors.(unless I'm doing something wrong during detection, or since it's at a low voltage, 10V, there's too much hysteresis in the firmware? If hysteresis is the issue, which it might be since now that I think about it, the VESC essentially has four times the hysteresis that my controller used, then could we modify it in VESC tool?)

RC snubbers and other transient suppression on each phase
After watching my friend's VESC's DRV8302 blow up on the second test changing from BLDC to FOC (the phase A switch node and floating driver blew up which I am assuming cause the gate drive charge pump to blow up), I am really anxious about stepping up the switching frequency. (I need a high switching frequency because I want to drive an eBike with one of these, higher switching frequency, less sine wave distortion). I have also encountered application notes from Texas Instruments recommending RC snubbers on their 60V MOSFETs and gate drivers when attempting to push 12S li-ion (or a system voltage of 50.4V).

The VESC is a remarkable piece of engineering, and I believe that these minor additions to the hardware will help prevent some of the problems both my friends and I have experienced from occurring in the future.
Thank you.

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