Research on a kind of diode-clamped cascade topology in direct-driven wind power system

With fast increasing of single wind turbine capacity, multi-level converter has been paid much attention. Topology of diode-clamped 5-level cascade H-bridge combines the advantages of diode-clamped multi-level converter and cascade H-bridge multi-level converter, which can further improve the output voltage rating and require fewer clamping diodes and separated DC-sources; With phase-shifting transformer and 12-pulse rectifier, the topology may be applied in direct-driven wind power system using polyphased permanent magnet synchronous generator (PMSG).The modulation strategy integrating sub- harmonic SPWM and carrier phase-shifted SPWM is adopted based on the topology, which can control the diode-clamped 5- level cascade H-bridge converter expediently and increase the equivalent carrier frequency and lower switching losses and filter volume. The validity of the proposed topology and its control principle adopted is verified by simulation and experimental results, which may provide possibility for the wind power system to be directly connected with medium voltage power grid without boost transformer.