TMS320F28377D: EPWM synchronization problem with Software forced synchronization scheme giving wrong frequency.

Part Number: TMS320F28377D

Tool/software: Code Composer Studio

Hi, 

I am working on full bridge converter and eventually used three of them to make a three port converter. Each full bridge has two switching legs.

I would like to generate six PWM signals (for six phase legs) with a variable phase shifts between them on six PWM channels EPWM1,EPWM2,EPWM3,EPWM4,EPWM5,EPWM6 which are connected with hardware. 

Now I know that one module should set as Master module and rest of those would be slave and sync in signal will flow module 1 to 6. So I set PWM1 module as master and other as slave. 

My phase logic are as below:

alpha, beta and gama are in the range +180 to -180 and phi12 and phi13 are in the range of -10 to +10. 

tbphs1 = -alpha/2;  // phase register 1 value    
tbphs2 = alpha/2; // phase register 2 value
tbphs3 = phi12 + (beta/2);  //phase register 3 value
tbphs4 = phi12 - (beta/2);  //phase register 4 value
tbphs5 = phi13 + (gama/2);   //phase register 5 value
tbphs6 = phi13 - (gama/2);   phase register 6 value

Now using EPWM1 as a master module, I have to set TBPHS =0 and PHSEN=DISABLE but by doing that I am not getting the required phase shift as the value for EPWM1 module is. tbphs1 = -alpha/2;  

As a result, I used EPWM7 module as master and all other six are as slave. But in this case, the frequency of other signals become incorrect. 

So what might be the issues with setting up the EPWM modules? Can EPWM7 be master while  EPWM1,EPWM2,EPWM3,EPWM4,EPWM5,EPWM6 are working as slave? Can the phase register values be negative? 

Can anyone advise me what would the best way to get the variable phase shifted signals ?

Kind regards,

Haque

Okay to answer your questions at the end,

No the phase values cannot be negative. You have to do your calculation so that you do not need negative numbers.

As far as what ePWM can be the master for the rest of the PWMs, you need to look at the PWM SYNC Chain.

ePWM7 cannot be the master for all of those PWMs.

Okay now for your application specific questions, can you send me a block diagram that describes what the PWM signals need to be?

Hi Nima,

Thank you for your reply.

I have uploaded a block diagram specific to my application.

I am basically using up-down counter to generate the 20 kHz switching signals. I used six PWM signals for six phase legs of the 3 converter. I need to maintain a phase shift between phase legs of each converters and also between the converter to converter. 

Now I have used PWM1 to PWM6 modules for the six phase legs. 

If I use PWM 1 as master module that means I need to disable PHSEN register and PWM1 will no longer respond to any phase shift but I need phase changes.

So I thought that I can use PWM7 module as master and then set PWM1~PWM6 as slave. 

Can you please look at the block diagram and advise me which should be best configuration of ePWM modules to get the required phase shift?

Also can I use an equal offset value to avoid any negative values in the phase register? Please let me know if you want to see the code or any further block diagram.

Regards

Haque 

Hi Nima,

Could you please look at my queries and get back to me?

Regards

Haque

Hi all,

In my practical application, I must need six EPWM channels (EPWM1, EPWM2, EPWM3, EPWM4, EPWM5 and EPWM6) for DC-DC converters. I also have the requirements for phase variation between the modules from -180 to 180 degree.

For the synchronisation, If I set EPWM1 as master module (by disabling the PHSEN and SYNCOSEL as TB_CTR_ZERO), I get the correct PWM frequency from all module. Since I must have to change the phase shift of the EPWM1 module for the correct functioning, I have to enable the PHSEN and when I do that this generates the wrong frequency.

There might be a couple of options I am thinking if the microcontroller allow

(i) Is there any setting option where EPWM1 can allow phase shift still being a Master module. If possible how can I do that? Can Master module allow phase shift or it should always sit to zero? I was thinking to use software forced synchronisation for EPWM1 and using TB_SYNC_IN to synchronize other five modules. My code setting is given below but this also gives me wrong frequency. Could you please look at it?



(ii) If this is not possible, can I use EPWM7 as master module for all the above six modules. In this case, how can I establish a sync in between EPWM7 and EPWM1 as I can see from the diagram there is no physical connection between them.

(iii) If the above two solutions are not possible, how I can set any other EPWM module as Master? Because in my hardware implementation, I already configured EPWM1, EPWM2, EPWM3, EPWM4, EPWM5 and EPWM6 for the three converters.

(iv) I know the TBPHS value must be positive. Is that correct? If yes then how I can incorporate a positive number for negative phase shift into the TBPHS content?





void configure_pwm1()

{

EPwm1Regs.TBCTL.bit.CTRMODE = TB_COUNT_UPDOWN; // Count up

EPwm1Regs.TBCTL.bit.PHSEN = TB_ENABLE; // Disable phase loading - Master

EPwm1Regs.TBCTL.bit.HSPCLKDIV = TB_DIV1; // Clock ratio to SYSCLKOUT

EPwm1Regs.TBCTL.bit.CLKDIV = TB_DIV2;

EPwm1Regs.TBCTL.bit.PHSDIR = TB_DOWN; // Count DOWN on sync (=120 deg)

EPwm1Regs.TBCTL.bit.PRDLD = TB_SHADOW;

EPwm1Regs.TBCTL.bit. SWFSYNC = 0x1; // forced software synchronisation pulse for PWM module 1

EPwm1Regs.TBCTL.bit.SYNCOSEL = TB_SYNC_IN; // sync flow-through

}



void configure_pwm2()

{

EPwm2Regs.TBCTL.bit.CTRMODE = TB_COUNT_UPDOWN; // Count up

EPwm2Regs.TBCTL.bit.PHSEN = TB_ENABLE; // // Slave module -Enable phase loading

EPwm2Regs.TBCTL.bit.HSPCLKDIV = TB_DIV1; // Clock ratio to SYSCLKOUT

EPwm2Regs.TBCTL.bit.CLKDIV = TB_DIV2;

EPwm2Regs.TBCTL.bit.PHSDIR = TB_DOWN; // Count DOWN on sync (=120 deg)

EPwm2Regs.TBCTL.bit.PRDLD = TB_SHADOW;

EPwm2Regs.TBCTL.bit.SYNCOSEL = TB_SYNC_IN; // sync flow-through

}



void configure_pwm3()

{

EPwm3Regs.TBCTL.bit.CTRMODE = TB_COUNT_UPDOWN; // Count up

EPwm3Regs.TBCTL.bit.PHSEN = TB_ENABLE; // Enable phase loading

EPwm3Regs.TBCTL.bit.HSPCLKDIV = TB_DIV1; // Clock ratio to SYSCLKOUT

EPwm3Regs.TBCTL.bit.CLKDIV = TB_DIV2;

EPwm3Regs.TBCTL.bit.PHSDIR = TB_DOWN; // Count UP on sync (=240 deg)

EPwm3Regs.TBCTL.bit.PRDLD = TB_SHADOW;

EPwm3Regs.TBCTL.bit.SYNCOSEL = TB_SYNC_IN; // sync flow-through



}



void configure_pwm4()

{

EPwm4Regs.TBCTL.bit.CTRMODE = TB_COUNT_UPDOWN; // Count up

EPwm4Regs.TBCTL.bit.PHSEN = TB_ENABLE; // Enable phase loading

EPwm4Regs.TBCTL.bit.HSPCLKDIV = TB_DIV1; // Clock ratio to SYSCLKOUT

EPwm4Regs.TBCTL.bit.CLKDIV = TB_DIV2;

EPwm4Regs.TBCTL.bit.PHSDIR = TB_DOWN; // Count UP on sync (=240 deg)

EPwm4Regs.TBCTL.bit.PRDLD = TB_SHADOW;

SyncSocRegs.SYNCSELECT.bit.EPWM4SYNCIN=0x00; // Select Sync input source for EPWM4 000 selects EPWM1 sync out for mux



}



void configure_pwm5()

{

EPwm5Regs.TBCTL.bit.CTRMODE = TB_COUNT_UPDOWN; // Count up

EPwm5Regs.TBCTL.bit.PHSEN = TB_ENABLE; // Enable phase loading

EPwm5Regs.TBCTL.bit.HSPCLKDIV = TB_DIV1; // Clock ratio to SYSCLKOUT

EPwm5Regs.TBCTL.bit.CLKDIV = TB_DIV2;

EPwm5Regs.TBCTL.bit.PHSDIR = TB_DOWN; // Count UP on sync (=240 deg)

EPwm5Regs.TBCTL.bit.PRDLD = TB_SHADOW;

EPwm5Regs.TBCTL.bit.SYNCOSEL = TB_SYNC_IN; // sync flow-through

}



void configure_pwm6()

{

EPwm6Regs.TBCTL.bit.CTRMODE = TB_COUNT_UPDOWN; // Count up

EPwm6Regs.TBCTL.bit.PHSEN = TB_ENABLE; // Enable phase loading

EPwm6Regs.TBCTL.bit.HSPCLKDIV = TB_DIV1; // Clock ratio to SYSCLKOUT

EPwm6Regs.TBCTL.bit.CLKDIV = TB_DIV2;

EPwm6Regs.TBCTL.bit.PHSDIR = TB_DOWN; // Count UP on sync (=240 deg)

EPwm6Regs.TBCTL.bit.PRDLD = TB_SHADOW;

EPwm6Regs.TBCTL.bit.SYNCOSEL = TB_SYNC_IN; // sync flow-through

EPwm6Regs.CMPCTL.bit.SHDWAMODE = CC_SHADOW; // Load registers every ZERO

}



Kind regards

Haque

Hello,

I had a similar issue recently. If you see a different frequency when changing the duty cycle of EPwm1 then it could be the same as me.

My issue was that by default the external synchronization signal EXTSYNCIN1 is brought directly to ePWM1 through the INPUT5 signal of the input x-bar. The default selection of INPUT5 is GPIO0, i.e EPWM1A so EPWM1 is actually resynchronizing on itself.

My workaround was to select an unused GPIO for INPUT5. In my case I chose GPIO95 because I have a 176-pin package where it is unbonded.

Something like this:

Hello Pierre,
Thanks for your advice. I am keeping duty cycle fixed for all EPWM modules. Your comments really helpful. I wanted to use EPWM7 as Master module due to my hardware limitation for EPWM1 to EPWM6 module. So I am thinking to use EXTSYNCIN1 for EPWM1 coming form EPWM7 though Crossbar. If you read my requirements that I posted previously you will understand more. 

Any additional comments and suggestions are highly appreciated. 

Hi Nima,
Could you please get back to me with your answer/suggestions? I am really waiting to hear from you to proceed in the next stage of coding. You can also have a look at my code and then suggest me the best.

I also merged the 2 E2E thread so now we have all the info in one place. I think my answer above should do the trick for your scenario.

Hi Nima,

Thank you very much for your reply with details suggestion. Sorry for the late reply.

I was able to make EPWM7 as master while EPWM1-6 as slave using the EXTSYNCIN for EPWM1 that comes from EPWM7. It seems work but I need to make sure I am getting the correct phase shift.

Also since I am using the up-down counter still the equation for negative phase shift will remain same as below

a negative phase shift is the same as TBPHS = TBPRD - (absoluteValue[TBPHS value you actually wanted which is negative])

Could you please explain bit more about the last three lines of answers that you have provided? Is it applicable for up-down counter?

Regards,
Haque

the last three lines of my explanation is for when you use EPWM1 as master. Since you are using EPWM7 and ext sync, you can ignore those lines.

If you need to change the phase of PWM1 you should sync. the time base externally, there is an X-bar input 5 /6 that will sync your main time base.
maybe this resolves your problem. Then only you can enable the phase shift of PWM 1.
Ashutosh