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Thursday February 9th 2023
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Current Waveform Investigation

I measure all three phase currents today to see if there might be visible phasing issues.  I only have a two channel scope so Phase 3 was not measured at the same time as Phase 2. The Phase 3 current is also being measured with a different current sensor.  With the scope settings it has a slightly different gain.

The waveforms are noisy and a little ratty looking, but the 120 degree phasing and amplitude balance look reasonable but I not an expert on this.

If anyone sees issues with these waveforms please elaborate.

Phase 1 to Phase 2 current

Phase 1 to Phase 3 current

Took some more measurements tonight.  Connected the inverter bridge supply input to 12 volt battery supply.  Connected a 100 ohm load from Phase 1 output to battery ground.  Compared the Microchip low side output drive signal (yellow) to the pulsed output across the 100 ohm resistor (green).

Looks like 12 microseconds turn-on delay and about half that on the turn off.  Looking at the time to turn off the top IGBT, one would speculate this is a programmed dead band to insure turn off the bottom IBGT before turning on the top again.  You can see the spike where the bottom IGBT is turned on.  Actually looks just a bit early. You can also see the small negative step where the bottom IGBT is commanded to go off about 6 microseconds before the top IGBT is commanded on.  I think all of this seems reasonable for this generation of high voltage IGBTs.

Also used a 10K and 1uF low pass filter on Phase 1 output to see if the filtered PWM signal had any significant discontinuities over the throttle range.  Every thing looked good.

Epanded view of open loop lower end frequency. Sinewave looks good.

Below shows the center aligned MicroChip PWM 1H (yellow) and PWM 2H (green) outputs and their difference (red) at plus and minus phase points.