Other Parts Discussed in Thread: SYSCONFIG
Hello,
I am using the SysConfig GUI in CCS to setup 6 phase shifted PWM waveforms, with complementary PWM, so 12 PWM waveforms total. The first 3 PWM waveforms are the primary set and the second 3 PWM waveforms are the secondary set. In each set, the waveforms are set to be shifted 120 degrees from each other and that is fixed. The phase that I want to vary is the phase between the primary set and secondary set so I have the secondary PWM A waveform sync’d to the primary PWM A waveform so that I can adjust the phase between these sets from 0 – 120 degrees; PWMs B and C in the secondary set are sync’d to the secondary PWM A waveform so that when the phase between the primary and secondary sets is adjusted, all of the waveforms remain 120 degrees shifted from each other. Other functions I am using on these waveforms are adjusting the duty cycle, dead-time, and switching frequency. I am are using the microcontroller in an open loop setup for now to operate in debug mode and just update the variables while running the power converter.
The parameters I am using are:
- Switching Frequency: 250kHz (Needs to be adjustable for testing purposes but for now we would mostly adjust from 240kHz to 260kHz)
- Dead-Time: 50ns (Needs to be adjustable as well, no specific range)
- Duty Cycle: 50% (Will most likely stay 50% at all times, will probably adjust to fine tune for testing purposes)
While setting all of this up, I am observing an issue I have yet to find an answer for. The issue I’m having and observing is:
- The phase shift between all waveforms is off by 1.5-2.5 degrees. Instead of 120 degrees between A & B and 240 degrees between A & C, I’m measuring 121.5 and 241.5 degrees respectively.
- I am unable to set the phase shift between primary PWM A and secondary PWM A to zero degrees. This issue most likely is the same as issue 1 but when I set the phase shift between these sets to zero, the o-scope measures 2.2 – 2.5 degrees. Even when I set the phase shift to 120 degrees, I am measuring 122.2 degrees.
I have looked at various examples and followed the training but I am unable to understand why the phase shift is off. Is there any way to eliminate this offset in phase shift?
