BLDC Motor Controller, Design, Waveforms, Thermal Tests

[Glenn0010]

So here are my Thermal Results

I ran the tests at Multiple switching frequencies 30kHz, 20kHz, 10kHz and a load current of 20A for all tests. The temperatures were allowed to reach steady state. Interestingly the it took quite a long time for steady state, around 15- 20 minutes which was more than I predicted.

This is my control an ambient temperature of toughly 23 degrees



30kHz:


Low side FETs

20kHz:


Low side FETs


High Side FETs

10kHz:


Low Side Fets


High Side Fets



Load Motor (Alternator) got very hot as can be seen ended up putting a desk fan on it and that dropped the temperature by a few degrees (to around 100)

I think the results are quite interesting, there is a major difference between the 30 and 20kHz frequency but roughly no difference between 20 and 10kHz. Also due to the low and high side FETs being directly on top of each other their temperature was practically identical. The phase wires also got warm, I guess they added as a heat sink as well.

The DC link capacitor got warm but nothing major.

Any thoughts?
 

[Glenn0010]

Right so the data did not really sit well with me, I did not like that the 10kHz and 20kHz were at the exact same temperature. So I ran all the tests again and allowed ample time for the FETs to reach steady state. Ant the results were better and made more sense



While at 10kHz the FETs ran the coolest, significant Motor "Whine" was introduced which is VERY annoying and unacceptable in my eyes. At 20kHz no audible noise could be heard. My original switching frequency was 30kHz so I have now moved to 20kHz which saves on a lot of losses and around 8 degrees of temperature.

I have also tested my P3 prototype with the integrated mosfet module and it worked fine. I will attach a 2mm aluminium plate as a heat sink and re run these tests.

[Glenn0010]

So Guys I finished my third design it is working well at full load but upon testing the Vds Voltage I spotted a problem!!!  I need your expert advice



As you can see the spike on turn off is relatively low, but the spike on turn on is massive and it just does not make sense for me. I was probing on the high side fet as seen below. I was probing from VCC to phase using a ground spring.

I am thinking it might be an issue in the measurement setup. Could it be that because I am probing over the GND pin with the ground spring there could be some interference emitted into my measurement due to the high currents?





It just does not make sense to me.

[MUR90]

Nice reporting of your project. I also seems to have spikes on battery voltage when high current is flowing through the motor. Already using RC snubbers and TVS diodes to clamp them.