用于大功率直驱风电系统的三电平混合式高效率变流器

在MW 级大功率直驱风电系统中，发电机出口电压等级经常采用较低的690V，由于很大的定子电流，对于全功率变流器设计是不利的。常规的解决方案是采用传统的两电平变流器并联来分摊容量，但是这是一种效率不高的解决方案。相比之下，多电平变流器具有较高的效率以及优越的谐波性能，只是在低压应用中半导体成本很高，而且还存在电容电压平衡控制的问题。本文提出一种基于直驱多相永磁同步发电机的三电平混合式变流器的拓扑方案，用以替代传统的两电平变流器并联方案。通过
三电平变流器的串并联组合，这种新方案不仅能够克服三电平变流器电容中点电压平和三次谐波电压脉动，而且其成本也与常规两电平并联方案相当，最重要的是这种方案表现出极高的效率。本文详细讨论了这种技术方案的拓扑结构、参数设计以及电容平衡控制等关键性问题，最后其效率和成本与两电平变流器方案进行了比较。
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.