CPS-SPWM flying capacitor three-level back-to-back converter applicative direct-drive wind power generator system

Abstract

Direct-drive wind power system was increasing attention due to its inherent high efficiency. By eliminating the need of a gearbox between the wind turbine and generator, direct-drive wind power systems are less expensive and also require less maintenance. With numerous advantages, the direct drive, grid-connected permanent magnet synchronous generator (PMSG) generation system represents one important trend of development for wind power applications nowadays. However, the system needs full-scale power converter and high quality power devices which have high voltage endurance level and can be modulated by PWM method. In order to solve the problem, a novel converter topology with back-to-back three level flying capacitor converter has been proposed for the application of PMSG to the VSCF power conversion. In recent devices power level, multilevel converter becomes the best choice without doubt, meanwhile Carrier phase-shifted SPWM technique (CPS-SPWM) also becomes preferred project because of SPWM realization of this technique in high power occasion. Three-level flying capacitor converter working conditions and Carrier phase-shifted SPWM technique (CPS-SPWM) application are analyzed and discussed in this paper. Good performance is attained even if the switching frequency is only 1k Hz as shown in the experimental results, which means that high equivalent switch frequency and current waveform under low switch frequency condition are realized. This feature enhances the reliability of the power conversion scheme and reduces the weight and volume of the system. The correlation between the theoretical and experimental results of some key issues showed the feasibility of the proposed VSCF power conversion scheme. This is very important for full-scale power converter in the wind power system.