STM8 MCKIT1.0 BLDC sensorless control acquisition implementation analysis

In addition to collecting and comparing electric potential, it is also necessary to collect, calculate and process analog signals such as bus voltage, bus current, heat sink temperature, potentiometer, etc.

This priority processing is very important. However, ST wrote the program very well, at least I think so. It puts different tasks into accurate time periods for collection and processing.
First post its core AD collection and processing and then analyze it.

#ifdef SENSORLESS 
 @near @interrupt @svlreg void ADC2_IRQHandler (void)
 {
  if (ADC_State == ADC_SYNC)
  {
   // Syncronous sampling
   
   u16 data;
   u8 delay;
   u16 bemf_threshold;

   // Reset bit
   bComHanderEnable = 0;
    
   //clear interrupt flag
   ADC2->CSR &= (u8)(~BIT7);
     
   //left align - read DRH first
   data = ADC2->DRH;
   data <<= 2;
   data | = (ADC2->DRL & 0x03);   
   
   switch( ADC_Sync_State )
   {
    case ADC_BEMF_INIT:
     ADC2->CSR = (u8)((Current_BEMF_Channel|BIT5));
     BEMF_Sample_Debounce = 0;
     Zero_Sample_Count = 0;
     ADC_Sync_State = ADC_BEMF_SAMPLE;
     SetSamplingPoint_BEMF();
    break;

    case ADC_BEMF_SAMPLE:
     //detect zero crossing
     if( Current_BEMF == BEMF_FALLING )
     {
      if( Z_Detection_Type == Z_DETECT_PWM_OFF )
      {
       bemf_threshold = BEMF_FALLING_THRESHOLD;
      }
      else
      {
       bemf_threshold = hNeutralPoint;
      }

      if (Ramp_Step > FORCED_STATUP_STEPS)
      {
       if( data <   bemf_threshold   )
       {
        Zero_Sample_Count++;
        BEMF_Sample_Debounce++;
        if( BEMF_Sample_Debounce >= BEMF_SAMPLE_COUNT )
        {
         hTim3Th -= hTim3Cnt;
         GetStepTime();
 
         SpeedMeasurement();

         bComHanderEnable = 1;

         BEMF_Sample_Debounce = 0;
        }
       }
       else
       {
        BEMF_Sample_Debounce = 0;
       }
      }
     }
     else
     {
      if( Z_Detection_Type == Z_DETECT_PWM_OFF )
      {
       bemf_threshold = BEMF_RISING_THRESHOLD;
      }
      else
      {
       bemf_threshold = hNeutralPoint;
      }
  
      if (Ramp_Step > FORCED_STATUP_STEPS)
      {
       (data>bemf_threshold)
       {
        Zero_Sample_Count++;
        BEMF_Sample_Debounce++;
        if( BEMF_Sample_Debounce >= BEMF_SAMPLE_COUNT )
        {
         hTim3Th -= hTim3Cnt;
         GetStepTime();
  
         SpeedMeasurement();

         bComHanderEnable = 1;

         BEMF_Sample_Debounce = 0;
        }
       }
       else
       {
        BEMF_Sample_Debounce = 0;
       }
      }
     }
    break;

    case ADC_CURRENT_INIT:
     ADC2->CSR = (ADC_CURRENT_CHANNEL|BIT5);
     ADC_Sync_State = ADC_CURRENT_SAMPLE;
     SetSamplingPoint_Current();
    break;

    default:
    case ADC_AVCURRENT_INIT:
     ADC2->CSR = (ADC_AVCURRENT_CHANNEL|BIT5);
     ADC_Sync_State = ADC_AVCURRENT_CHANNEL;// ADC_USER_SYNC_SAMPLE;
     SetSamplingPoint_AVCURRENT();
    break;

  
    case ADC_CURRENT_SAMPLE:
     ADC_Buffer[ ADC_CURRENT_INDEX ] = data;
     break;

    case ADC_AVCURRENT_SAMPLE:
     ADC_Buffer[ ADC_AVCURRENT_INDEX] = data;
     break;
   }

   // Store the current channel selected
   bCSR_Tmp = ADC2->CSR;

   // Set the Async sampling channel
   switch (ADC_Async_State)
   {
    default:
    case ADC_BUS_INIT:
     ADC2->CSR = (ADC_BUS_CHANNEL|BIT5);
     ADC_Async_State = ADC_BUS_SAMPLE;
    break;
    
    case ADC_TEMP_INIT:
     ADC2->CSR = (ADC_TEMP_CHANNEL|BIT5);
     ADC_Async_State = ADC_TEMP_SAMPLE;
    break;
   
    case ADC_USER_ASYNC_INIT:
     ADC2->CSR = (ADC_USER_ASYNC_CHANNEL|BIT5);
     ADC_Async_State = ADC_USER_ASYNC_SAMPLE;
    break;
   }

    // Disable ext. trigger
    ADC2->CR2 &= (u8)(~BIT6);
    //Start ADC sample
    ADC2->CR1 |= BIT0;

   ADC_State = ADC_ASYNC;
   
   if (bComHanderEnable == 1)
   {
    ComHandler();
   }
  }
  else
  {
   // Syncronous sampling
   u16 data;
   
   data = ADC2->DRH;
   data <<= 2;
   data |= (ADC2->DRL & 0x03 );

   //clear interrupt flag
   ADC2->CSR &= (u8)(~BIT7);

   // Restore the sync ADC channel
   ADC2->CSR = bCSR_Tmp;
 

    // Enable ext. trigger
    ADC2->CR2 |= BIT6;

   // Manage async sampling
   switch (ADC_Async_State)
   {
    default:
    case ADC_BUS_SAMPLE:
     ADC_Buffer[ ADC_BUS_INDEX ] = data;
     ADC_Async_State = ADC_TEMP_INIT;
    break;

    case ADC_TEMP_SAMPLE:
     ADC_Buffer[ ADC_TEMP_INDEX ] = data;
     ADC_Async_State = ADC_USER_ASYNC_INIT;
    break;

    case ADC_USER_ASYNC_SAMPLE:
     ADC_Buffer[ ADC_USER_ASYNC_INDEX ] = data;
     ADC_Async_State = ADC_BUS_INIT;
    break;
   }
   
   ADC_State = ADC_SYNC;    
  }
 }
#endif

I changed the above code a little bit, that is, to collect one more average current.

There are two types of AD acquisition, one is synchronous and the other is asynchronous. There are three acquisition channels in synchronous and three acquisition channels in asynchronous. The channels in synchronous are back EMF channel, instantaneous current, and average current. The channels in asynchronous acquisition are bus voltage, temperature value, and potentiometer.

Asynchronous acquisition is performed after synchronization is completed. Synchronous acquisition is triggered by channel 4 of TIM1.

Therefore, two analog signals are collected in each PWM cycle. The asynchronous collection channel has nothing to do with the ON and OFF states of PWM, so it is arranged in asynchronous collection. The back electromotive force in synchronous collection needs to be collected at a fixed time of PWM, either ON or OFF, depending on the zero-crossing comparison scheme of BEMF. The instantaneous current is generally collected at the TON moment. Because ST originally had a user channel for special PWM moments, I added the average current to this channel. In fact, the average current collection can also be put into asynchronous. It doesn't matter, the function is implemented without any problem.

In addition, the back-EMF channel in asynchronous acquisition is always set as the floating phase channel. Moreover, the back-EMF acquisition is between D and Z, that is, the asynchronous acquisition between the end of demagnetization and the zero crossing point is all back-EMF, while the instantaneous current acquisition is between Z and C, that is, the asynchronous acquisition between zero crossing and phase change is all instantaneous current. Therefore, the user's channel (average current) is between phase change and demagnetization.

 The sensorless solution of ST seems to be only applicable to industrial motors, such as motors with 4K speed under 4 pole pairs, so the starting parameters do not need to be changed. But if it is changed to a model aircraft motor, no matter how much the starting PWM is changed, it will never start successfully. Maybe I have found a trick, or maybe I have not set the right parameters. For high-speed motors, this kind of sensorless start may be reliable only by the frequency-boosting method. In the routines I wrote earlier, no matter what motor, the frequency-boosting method was used. No matter what motor, it can start normally, but the current in the starting process (about 1S) goes from large to small, at least it runs normally to the minimum current value.