Research On Dead-Time Compensation Strategy For Selective Harmonic Elimination Inverter

With the application of pulse width modulation(PWM) inverter in more and more fields, its performance is paid more and more attention. Harmonic pollution is one of problems can not be ignored. For this, in recent years many scholars have done research on harmonic suppression technology. Based on the comparative analysis of existing research, this paper studied the selective harmonic elimination PWM(SHEPWM) technique; and analyzed the influence of the dead time on the harmonic in the actual application, and proposed a new dead time compensation strategy.By setting the appropriate number of gap and switch angle, SHEPWM technique can eliminate certain low harmonic, which has the advantages of high quality of the output voltage waveform, and small current ripple. Taking the unipolar modulation as an example, a mathematical model of switching angle specific harmonic elimination was established. Through the analysis of nonlinear equation solution existing, this paper chose the homotopy algorithm to solve the harmonic elimination model, which was less dependent on the initial values, and have wide convergence domain. The establishment and solution of the homotopy equation were introduced in detail, and the homotopy equation of the newton homotopy structure was given. MATLAB was used to solve the problem in the offline state. The results show that the homotopy algorithm avoids the problem of initial value selection difficulties, realize the solution of the harmonic cancellation model quickly and accurately.In practical application, the dead time is often needed to avoid the straight through. The dead-time set in the traditional way leads to the distortion of the inverter output waveforms. In order to improve the waveform, the dead-time effect needs to be compensated. Taking the advance-off mode as example, the dead time effect was analyzed in this paper, while the inverter was controlled by SHEPWM. The curves of amplitude and total harmonic distortion(THD) at different dead time were given. The characteristics of the traditional dead time setting mode were compared and analyzed, based on which the novel dead time compensation strategy for SHEPWM inverter was put forward. The current of the switch tube and the corresponding continuous current diode during the dead-time compensation phase was analyzed in detail. Taking power MOSFET as example, the switch process was analyzed in this paper, and gave the empirical formula of the dead time.Finally, the SHEPWM control method and the dead time compensation strategy was verified by simulation and experimental analysis using simulation model and hardware platform. The results show that SHEPWM technology can effectively eliminate the harmonic to be eliminated; the dead time effect leads to waveform distortion, which increases the content of harmonic; the SHEPWM voltage waveform and the load current waveform are effectively improved after the dead time compensation strategy, and the waveform distortion caused by the dead time can be compensated effectively.