Research On Novel Carrier Phase-Shifted Spwm For Cascade Multilevel Converter

Multilevel converters as large capacity power converters are widely used in AC and DC power delivery, large capacity power quality control, large scale renewable energy power generation and middle/high voltage AC motor drive. Cascade multilevel converters are favored due to the less device they use, balancing work load and easily modularized design and assembly. For the cascade multilevel converter, the common switch modulation technology widely used is carrier phase-shifted SPWM. Huge obstacle happens during the large scale digital realization of carrier phase-shifted SPWM, because it spends a lot of PWM generators. However, it will be contribute to digitization and large scale realization of cascade multilevel converters to find a novel modulation technology which can save PWM generators.On the basis of reading a large number of related foreign and national literature, a novel carrier phase-shifted SPWM is put forwards by introducing unipolar SPWM into cascade multilevel converters in this article. The basic principles of two kinds of modulation methods with novel carrier phase-shifted SPWM is given, and frequency mathematical characteristics of two kinds of modulation method are analyzed through the double Fast Fourier Transform. Compared with the traditional carrier phase-shifted SPWM, the novel carrier phase-shifted SPWM can save a half of the PWM pulse generator.On the basis of the theoretical analysis, a series of simulating researches to cascade circuit are accomplished for the different number and phase (single phase and three-phase) by using the novel carrier phase-shifted SPWM, and the output harmonic characteristics are analyzed and compared. At the same time, the realized principle of single phase closed loop is given and accomplish the corresponding simulation.For the problem of two kinds of modulation method under the novel carrier phase-shifted SPWM, almost non-resource solutions are respectively given to solve the issue of thermal stability.A three-phase prototype of two series cascade converter is designed under digital control, and power is 1kW. The corresponding experimental researches are accomplished with the novel carrier phase-shifted SPWM. The experimental results demonstrate that the novel carrier phase-shifted SPWM are correct and feasible.