Dead-time Compensation Strategy For Voltage-source PWM Inverter

Voltage-source PWM inverters have gained increasing popularity in industrial applications. In their application areas, the ac machine drive is one of the most important parts. In the PWM inverter controlled process, dead-time is vital to avoid the shoot-through phenomenon of inverter legs. Although the dead-time is very short comparing with the modulation period, it causes waveform distortion of the output voltage when the turn-on/off frequency is very high or the output voltage is low. The distorted voltage may give rise to serious problems such as the current waveform distortion, increased torque ripples, and unstable operation. So it is necessary to compensate the inverter dead time effect. In this paper, an improved dead-time compensation strategy is presented for the continual space vector pulse width modulation (CSVPWM) taking zero-current clamp and parasitic capacitance effects into account. The dead-time compensation strategy of adjusting the space vector response time is proposed for the discontinual space vector pulse width modulation (DSVPWM). Theory analysis and simulation research for these two methods is carried on.Firstly, the influence of dead-time on output voltage and current is analyzed in detail, as well as parasitic capacity of switching devices on output voltage. Secondly, the dead-time compensation which takes zero-current clamp and parasitic capacitance effects into account has the demerit of variable reference value which is used to correct failure in polarity reversal of the dead-time compensation voltage, because the reference value is the amplitude of d-axis dead time compensation voltage which is varying with current. In view of this question, an improved dead-time compensation strategy is presented for voltage-source inverter. The improvement compensation strategy correct failure in polarity reversal of the current caused by the zero-current clamp phenomenon instead of correcting failure in polarity reversal of the dead-time compensation voltage. The reference value is the amplitude of s_γwhich is the function of the three-phase current signal function. It is a constant. Thirdly, using the MATLAB and Pspice simulation tools, the paper establish two simulation models of permanent-magnet synchronous motor (PMSM) vector control system which includes the improved dead-time compensation. Comparing and analyzing two kinds of simulation results, it is proved that the improved dead-time compensation is effective and the Pspice model is better in simulating the undesirable properties of voltage-source inverters.At last, the paper analyzes the difference between CSVPWM waveform and DSVPWM waveform, as well as the different characteristics of the dead-time influence on two waveforms. The dead-time compensation strategy of adjusting the space vector response time is proposed for the DSVPWM generated by the hardware of DSP TMS320LF2407A. The compensation strategy is used the adjustment of space vector response time to change the driving signal pulse width for realizing the dead-time compensation target. The simulation model of PMSM vector control system which includes dead-time compensation is established using the MATLAB simulation tools. Simulation results demonstrate the effectiveness of the proposed dead-time compensation strategy.