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I Use TMS320F280021 for LLC charging process, ePWM3 and ePwm4 are used to drive H-bridge LLC, with PWM operating frequency ranging from 80K to 150K, which is the upper and lower limits set by the software, and resonant operating frequency of 90KHZ. When the frequency of LLC is adjusted from 85K to close to 80K during the working process, there is an occasional possibility of the MOS transistor driving at the same height on the half bridge, which is not 100%. The MOS transistor is directly short circuited and the tube is burned out. May I ask if there are any issues with the configuration? Thank you!
The waveform is as follows:
Drive waveform and frequency at the moment before short circuit:
PWM setting code:
PWM LOAD Code:
Hi Qin,
Could you show me when the PWM CMP registers get updated and loaded by toggling a GPIO during your ADC ISR? According to your configurations is the following diagram representative of what is occurring before the short with AU = CMPAU, and BU = CMPBU, BD = CMPBD events? Is the highlighted red No. 32 row where the short occurs?
EPwm3Regs.AQCTLA.bit.CAU = AQ_SET;
EPwm3Regs.AQCTLA.bit.CBU = AQ_CLEAR;
EPwm3Regs.AQCTLA.bit.ZRO = AQ_CLEAR;
EPwm3Regs.AQCTLB.bit.CBD = AQ_SET;
EPwm3Regs.AQCTLB.bit.CAD = AQ_CLEAR;
EPwm3Regs.AQCTLB.bit.ZRO = AQ_CLEAR;
The data log you are capturing appears to have CMP values still even after the highlighted red portion, how come the PWM signals stop after the short? Can you verify that the TBCTR is continuously running after the short circuit occurs? When the short occurs, are you shutting off the PWM?
I believe there is something happening with the loading scheme of your setup, with an AQ event being missed because either CMPBU is greater than TBPRD or there is nothing in the shadow registers at the time the global load scheme occurs. Is there anything special about this last PWM period that is happening in the code?
Best,
Ryan Ma
Hi Ryan:
The following are normal charging process ePWM3 and GPIO toggling waveform.yellow and blue are ePWM,Green is GPIO.When the Green signal rise is begin to load PWM CMP registers. You can see the detail code as bellow.
void PWM_load() is use in the ISR.
The diagram what I show is save in a buffer every ISR,when the short circuit occurs,the hardware will occurs a TZ module protect and stop the PWM, and then write the buffer data to the use flash area.After a short circuit occurred, I read Flash data and CountNum variables,Through the count number I know when the error happen.The CountNum may not be the counting at that time,but it must be one of the previous times.
Yes,I suspect that scertain register is not set correctly or miss some seting.But I don't know.
On the other hand，I found a iInteresting things,when the ePwm frequency is change from high drop to low over 2K,it maybe occurs short circuit.The following table shows the data when errors is occur.The red line is the final CountNum record.
So,I write a program to simulate a frequency jumps.It run on a demo board.It can reproduce the phenomenon of short circuits.
The program is as follows:
The short-circuit waveform is as follows:yellow is low drive,green is high drive,blue is GPIO signal(ePMW load signal).
Do you have any good suggestions?
Thanks!
Hi Ryan:
"I believe it is a loading scheme issue with the counter compare registers. Can you try loading on CTR == PERIOD or ZRO for ePWM3?"
We had set the global Register GLDCFG and GLDCTL.The CTR == PERIOD or ZRO for ePWM3,is it right? So short circuits still occur.
EPwm3Regs.GLDCFG.all = 0x07FF;
EPwm3Regs.GLDCTL.bit.GLDMODE = 6;
"If you're using ePWM1 to sync the other ePWM modules, why are you changing ePWM3's and ePWM4's TBPRD."
Yes.We want using ePWM1 to sync the other ePWM modules.The ePWM1's,ePWM2's,ePWM3's,ePWM4's TBPRD are change as the same time.I removed the TBPRD loading for ePWM1 and ePWM2 in the code I showed you.All ePMW's TBPRD are load as the same time in the ISR.If it cause the ePWM's to become out of sync to each other?
"Could you synchronize ePWM3 and ePWM4's modules together since their TBPRD will be aligned with each other?"
How should I set it up?Could you show me the setting code？
On the other hand,We found some clues to this issue today. I test the frequency jumps code,and turn out all pwm.When the frequency change,the ePWM3A's period change first,but the ePWM1 is not change.Next cycle ePWM3B and ePWM1B are change,this time may causing a missed AQ.It caused a short circuit.
Do you have any idea?
As follow waveform:Yellow is ePWM3B,Green is ePWM3A,Blue is ePWM1A,Purple is ePWM1B.
ePWM3 period change:
ePWM1 period change:
Thanks!
