Suboptimal Pulse-Width Modulation Algorithm For Multilevel Converters And Parallel Operation Control Of Inverters

Multilevel inverter has been widely investigated for high-power applications in recent years. Various topologies and modulation strategies have been presented for utility and drive applications in the literature. Parallel inverters are often used to meet system power requirements beyond the capacity of the largest single structure, so they have been attracting increasing interest in the past few years as power converters of choice in high voltage and high power application. This paper is supported by A Foundation for the Author of National Excellent Doctoral Dissertation of P.R. China (200250). On the basis of researches, the thesis mainly focuses on some key modulation strategies of multilevel converters and parallel operation system, including following three aspects:1. To overcome the low voltage modulation index and low fundamental component, a novel suboptimal PWM technique (MSUBPWM) applicable to multilevel voltage inverter is presented. The simulation results show that the technique can improve output maximum voltage modulation index and fundamental component of output waveform mostly. The methods for establishing switching angles and optimizing modulation waveform are also derived. The results indicate that the method is validity.2. On the basis of Subharmonic PWM (SHPWM) technique and Phase-shifted PWM (PSPWM), a novel phase-shifted suboptimal pulse-width modulation technique is proposed. The new technique has following advantages: higher voltage modulation index and fundamental component, lower switching loss, better output waveform, higher equivalent switching frequency and lower total harmonic distortion.3. The difference of amplitude and phase between each module's output voltage can cause large loop-current among modules in parallel inverter system. The voltage regulator can restrain loop-current. The analysis of circuit and simulation indicate that the method is validity. The performance of parallel scheme is superior to that of single...