Dynamically change the dead time in 6PWM mode

[SnifMyBack]

Hi!

I'm currently working on a "custom" V/Hz controller with an ESP32 in 6PWM mode. I'm facing a problem where I need to be able to change the deadtime value even after the driver has been initialized. It is critical because I will be driving different IGBT module where the timming is not always the same.

I though of deleting the instance of the driver and starting again but it doesn't seems to possible (with the little knowledge in programming that I have at least).

Is there an alternative or do I need to wait for a possible update that will implement this kind of feature?

Thanks!

[runger1101001]

Hey, you're the first person to ask for this, I think. I agree, we should make both frequency and dead-time dynamically settable. At the moment it is not possible using SimpleFOC functions.

But, I think you can use the following code to set the dead time directly, bypassing the library (in this snippet dead_zone is the desired dead-time in terms of the total duty cycle, so dead_zone = 0.02 means 2% dead-time):

HardwareTimer *HT = ((STM32DriverParams*)driver.params)->timers[0];
  uint32_t dead_time_ns = (float)(1e9f/PWM_freq)*dead_zone;
  uint32_t dead_time = __LL_TIM_CALC_DEADTIME(SystemCoreClock, LL_TIM_GetClockDivision(HT->getHandle()->Instance), dead_time_ns);
  if (dead_time>255) dead_time = 255;
  if (dead_time==0 && dead_zone>0) {
    dead_time = 255; // LL_TIM_CALC_DEADTIME returns 0 if dead_time_ns is too large
    SIMPLEFOC_DEBUG("STM32-DRV: WARN: dead time too large, setting to max");
  }
  LL_TIM_OC_SetDeadTime(HT->getHandle()->Instance, dead_time); // deadtime is non linear!

[runger1101001]

Another assumption made here is that you are using all PWMs from the same timer. If you're using more than one timer, then you need to set the dead-time for each timer in this way.

[SnifMyBack]

Thanks for the really fast answer! I'm not in front of my computer at the moment but I will try to implement the said patch for the ESP32 platform. As for the timer selection, I use the default behavior of the library as I didn't specify any.

Another feature that would be awesome is the ability to change dynamically the active on low or high.

I can look to implement this myself but I'm not an expert in programming. What I can do, though, is sharing the code behind the V/Hz controller I'm developing. It's not pretty but it works as tested today on a big 3 phases motor!

Thanks again!

[runger1101001]

Ah - the code I sent is for STM32 - for ESP32 it would look a bit different, please let me check into it and send you a new snippet!

Another feature that would be awesome is the ability to change dynamically the active on low or high.

May I ask why you would want to do this?
Usually this is pre-determined by your choice of hardware, and to use the wrong mode often leads to the destruction of the driver, because the software thinks its switching the FETs off when its actually switching them on, and you get shoot-through and a dead driver as a result. I'd expect the same thing to happen if you switched to the wrong mode on the fly.

[runger1101001]

What I can do, though, is sharing the code behind the V/Hz controller I'm developing. It's not pretty but it works as tested today on a big 3 phases motor!

That would be awesome... our forum or discord would be the right place to tell people about it... I think there would be interest, also from me!

[runger1101001]

So, for ESP32, the following snippet should work (I haven't compiled this snippet, so there may be some small errors to solve):

Again, dead_zone is the dead time as a proportion of the PWM period, so 0.02 = 2% of the period is dead-time.

In a fortunate coincidence, this code also shows you how you might change the active-high behavior on ESP32 on the fly - it is configured via the same structure as the dead-time :-)

You'll have to #include the right headers in the cpp file where you add this code. Try with:

#include "drivers/hardware_specific/esp32/esp32_driver_mcpwm.h"

  int no_operators = 3;
  ESP32DriverParams* params = (ESP32DriverParams*)driver.params;
  uint32_t dead_time = (int)params->mcpwm_period * dead_zone;
  mcpwm_dead_time_config_t dt_config_high;
  dt_config_high.posedge_delay_ticks = dead_time;
  dt_config_high.negedge_delay_ticks = 0;
  dt_config_high.flags.invert_output = !SIMPLEFOC_PWM_HIGHSIDE_ACTIVE_HIGH;
  mcpwm_dead_time_config_t dt_config_low;
  dt_config_low.posedge_delay_ticks = 0;
  dt_config_low.negedge_delay_ticks = dead_time;
  dt_config_low.flags.invert_output = SIMPLEFOC_PWM_LOWSIDE_ACTIVE_HIGH; 
  for (int i = 0; i < no_operators; i++) {
      CHECK_ERR(mcpwm_generator_set_dead_time(params->generator[2*i], params->generator[2*i], &dt_config_high),"Could not set dead time for generator: " + String(i));
      CHECK_ERR(mcpwm_generator_set_dead_time(params->generator[2*i+1], params->generator[2*i+1], &dt_config_low),"Could not set dead time for generator: " + String(i+1));
  }

[SnifMyBack]

I’m truly thankful for your support! I will try the snippets you've sent ASAP.

May I ask why you would want to do this? Usually this is pre-determined by your choice of hardware, and to use the wrong mode often leads to the destruction of the driver, because the software thinks its switching the FETs off when its actually switching them on, and you get shoot-through and a dead driver as a result. I'd expect the same thing to happen if you switched to the wrong mode on the fly.

We are repairing industrial and railway equipment. My team are specialized in the high power stuff and are dealing with A LOT of inverter. Sometimes, equipment doesn't come with the controller that generate the required signals to make the 3 phases motor turn. So we use our in-house solution that are functionnal but always adequate to drive big motors (our 100hp is one of them).

Here comes your awesome librairy that help us generate those signals. SPWM, adjustable dead-time and selectable "active on H/L level" are the most usefull features for this kind of test. Making it dynamically adjustable helps us testing every unit with every combination of settings required for it.

Thanks again!