Voltage reading on B-G431B-ESC1 board floating around way up there at 11 volts. sine wave, just elevated

Anthony_Douglas · May 19, 2024, 4:40pm

Hey guys, I wanted to pluck this out of the sensorless drive thread because it gets too complicated in one thread sometimes.

I need reliable voltage readings for the voltages actually at the terminals of the motor. I use

  Va = driver.dc_a * driver.voltage_power_supply;
  Vb = driver.dc_b * driver.voltage_power_supply;

but the voltages are floating around up there, a nice sine wave but not centered around zero like they should be:

The offset appears to change, and I’d prefer to do things properly rather than just subtracting the apparent borkedness. Perhaps it’s possible that the voltages at the terminal are actually elevated like this, and that may help explain the excessive heating the board seems to exhibit even when it’s not even driving anything? IDK. They are hard to measure with an oscope because of course it’s not the actual voltage, it’s one step away from that. The actual voltage jumps around like crazy as the PWM of the inverter does it’s thing, but it gets translated by the inductance of the motor so the de facto voltage is as the pwm signal duty cycle multiplied by supply voltage indicates, correct?

Candas1 · May 19, 2024, 5:35pm

github.com

simplefoc/Arduino-FOC/blob/6eed7b00c9bc1e9f7ea7984aa02a9f7ea98db19b/src/drivers/BLDCDriver6PWM.cpp#L87


      
          
          
          // Set voltage to the pwm pin
          void BLDCDriver6PWM::setPwm(float Ua, float Ub, float Uc) {
            // limit the voltage in driver
            Ua = _constrain(Ua, 0, voltage_limit);
            Ub = _constrain(Ub, 0, voltage_limit);
            Uc = _constrain(Uc, 0, voltage_limit);
            // calculate duty cycle
            // limited in [0,1]
            dc_a = _constrain(Ua / voltage_power_supply, 0.0f , 1.0f );
            dc_b = _constrain(Ub / voltage_power_supply, 0.0f , 1.0f );
            dc_c = _constrain(Uc / voltage_power_supply, 0.0f , 1.0f );
            // hardware specific writing
            // hardware specific function - depending on driver and mcu
            _writeDutyCycle6PWM(dc_a, dc_b, dc_c, phase_state, params);
          }
          
          
          // Set the phase state
          // actually changing the state is only done on the next call to setPwm, and depends

Dc_x variables have values from 0 to 1, so not centered around 0.

Anthony_Douglas · May 24, 2024, 3:10pm

Ok, thanks, yes looks like if I just subtract half the power supply voltage I should get the actual terminal voltages…