Current Zero-Crossing Shift During Compensation of Dead-Time Distortion in PWM VSI and Its Corrective Action in Current Sensor-Less Compensation

Accurate detection of current polarity is an important issue to achieve proper compensation of dead-time distortion in PWM VSI. This paper analyses the shift of zero-crossing instants of the inverter output current with respect to the modulating waveform of the inverter, after implementing the compensation process. In case, the current zero-crossings are detected by noting the notch positions of the uncompensated output voltage waveform, and compensation is continued on that basis, such a 'shift' ensures that the zero-crossing detection, post compensation is erroneous. This causes an error in current polarity detection, resulting in the problem for continuing the compensation process successfully. Detailed analysis of this phenomenon of current zero-crossing shift has been given in this paper, which depends on different operating parameters such as load series impedance angle, amplitude modulation index etc. Digital simulation and experimental verification have been performed to validate the proposed concept. This paper also proposes the application of this concept to achieve successful compensation, especially in the current-sensor-less compensation methods.