在MW 級大功率直驅風電系統中，發電機出口電壓等級經常采用較低的690V，由于很大的定子電流，對于全功率變流器設計是不利的。常規的解決方案是采用傳統的兩電平變流器并聯來分攤容量，但是這是一種效率不高的解決方案。相比之下，多電平變流器具有較高的效率以及優越的諧波性能，只是在低壓應用中半導體成本很高，而且還存在電容電壓平衡控制的問題。本文提出一種基于直驅多相永磁同步發電機的三電平混合式變流器的拓撲方案，用以替代傳統的兩電平變流器并聯方案。通過
三電平變流器的串并聯組合，這種新方案不僅能夠克服三電平變流器電容中點電壓平和三次諧波電壓脈動，而且其成本也與常規兩電平并聯方案相當，最重要的是這種方案表現出極高的效率。本文詳細討論了這種技術方案的拓撲結構、參數設計以及電容平衡控制等關鍵性問題，最后其效率和成本與兩電平變流器方案進行了比較。
Abstract：The voltage of generator is often 690V in large direct-drive wind turbine. The high current amplitude is bad for the full-size
converter. The conventional solution is to connect several two-level converters in parallel in order to apportion power. But it’s not an
efficient solution. In contrast to it, the multi-level converters have the higher efficiency and predominant harmonic performance. But it is
a little expensive for the multilevel converters to be used in low voltage system due to high cost of semiconductor devices. And the
balance control of capacitor voltage is also a problem. This paper discusses a solution of combinational three-level converter topology
based on multi-phase permanent magnet synchronous generator. It’s a good substitute for the conventional solution of two-level converter.
By series and parallel combination of three-level converter, the solution can overcome the capacitor voltage unbalance and suppress the
capacitor voltage fluctuation caused by third-order harmonic current, and its cost is comparative with the conventional solution. What’s
more, this solution has very high efficiency. This paper discusses the circuit topology of the solution, parameter design, and another key problem, e.g. capacitor voltage balance control. Finally, the efficiency and cost of the different solutions are compared.