中文摘要：

风电系统对中压大功率变流器的需求日益增加，大功率变流器已引起人们极大的兴趣。直接驱动型变速恒频风力发电是一种新型的发电技术，它具有无齿轮箱、机械磨损小、整机效率高，运行维护成本低等优点，在风力发电领域中有着很好的应用前景。为掌握变流器的设计制造技术，推动我国风电事业的发展，首先对直驱型变速恒频风力发电系统基本拓扑结构进行了对比分析，着重介绍了直接驱动型风力发电系统几种大功率变流器拓扑结构，比较了各种拓扑结构的优缺点、技术难点，以及实际应用中存在的问题，并对大功率变流器在风力发电系统应用中的可行性进行了相关分析与探讨，为直驱风力发电系统拓扑结构的选型提供了参考基础。采用的二极管箝位五电平级联H桥拓扑，结合了二极管箝位型多电平和级联H桥多电平的优势，需要较少的箝位二极管和独立直流电源，即可进一步提高输出电压等级。使用移相变压器和12脉波整流器作为输入电路，可以方便地应用在使用多相永磁同步发电机的直驱风电系统中。仿真和实验结果证实了所采用的拓扑及其控制方法的有效性。

英文摘要：

Direct-drive variable speed constant frequency wind power generation is a new type of power generation technology, and the direct-drive system needs a full power converter. We first introduced several basic topologies of direct-drive-type VSCF wind power systems, and compared advantages and disadvantages of each topology and problems in practical application. Topology of diode-clamped 5-level cascade H-bridge, which combines the advantages of diode-clamped multilevel and cascade H-bridge multilevel converter, can further improve the output voltage rating, and require few clamping diodes and separated DC-source. With phase-shifting transformer and 12-pulse rectifier,the topology may be easily applied in direct-drive wind power system using polyphased permanent magnet synchronous generator（PMSG）. The modulation strategy ,which integrates sub-harmonic SPWM and carrier phase-shifted SP- WM,can control the diode-clamped 5-level cascade H-bridge converter expediently, enhance the equivalent carrier frequency,and lower switching losses and filter volume. The validity of the topology and the adopted control Principle are verified by simulation and experiment results.