SLLA567 August   2021 MCF8316A , MCT8316A

 

  1.   Trademarks
  2. 1Introduction
  3. 2Concept
    1. 2.1 Optimizing acoustics with sensorless field-oriented control motor driver (MCF8316A)
      1. 2.1.1 PWM Modulation Schemes
      2. 2.1.2 Dead time compensation
      3. 2.1.3 Comparing audible noise before and after optimizing acoustics with MCF8316A
    2. 2.2 Optimizing acoustics with sensorless trapezoidal control motor driver (MCT8316A)
      1. 2.2.1 120° Trapezoidal commutation Scheme
      2. 2.2.2 Variable commutation Scheme
      3. 2.2.3 Comparing audible noise between 120° commutation and Variable commutation with MCT8316A
    3. 2.3 Comparing acoustic performance between Sensorless FOC motor driver (MCF8316A) and 180° sinusoidal motor driver (DRV10987)
  4. 3Summary
  5. 4References

2.1.1 PWM Modulation Schemes

The MCF8316 device supports continuous and discontinuous space vector PWM modulation schemes. In continuous PWM modulation, all the three phases are pulse width modulated at the same time as per the defined switching frequency. In discontinuous PWM modulation, one of the phases is clamped to ground for 120° electrical period, and the other two phases are pulse width modulated. Figure 2-1 shows the modulated average phase voltages for different modulation schemes.

Figure 2-1 Continuous and Discontinuous PWM Modulation Phase Voltages.

In continuous space vector modulation, phase current waveform shaping will be sinusoidal with no distortions. In discontinuous space vector modulation, we can expect phase current distortion for low inductance motors because only two phases are pulse width modulated. Figure 2-2 shows phase current waveform in discontinuous PWM modulation mode and the Fast Fourier Transform (FFT) of phase current. Figure 2-3 shows phase current waveform in continuous PWM modulation mode and the FFT of phase current. Phase current waveform in continuous modulation mode is cleaner and more sinusoidal compared to phase current waveform in discontinuous modulation mode.

Figure 2-2 Phase current waveform and FFT - Discontinuous PWM modulation
Figure 2-3 Phase current waveform and FFT - Continuous PWM modulation