基于永磁直驱同步风电机组的分频海上风电系统控制策略

海上风电经分频输电线路传输的研究近年来引起国内外的关注。由去除机端换流器的多台基于永磁直驱同步发电机(PMSG)的风电机组、海底电缆和交交变频器组成的分频海上风电系统,可通过线路末端的交交变频器控制PMSG的转速捕获风能,可节省初始投资和运行维护费用。考虑变压器和输电线路的影响后,推导出分频海上风电系统的准稳态模型,基于转子平均磁链定向给出多机矢量控制器的设计原理;从曲线拟合的角度,给出多机组运行频率的求解方法;以4台PMSG为例,搭建了分频海上风电系统仿真模型。结果表明采用多机矢量控制方法,在不同风速条件下,风电机组的转速均能够跟随指令值,并实现风能的最优捕获。

Control Strategy for PMSG Based Wind Turbines in Fractional Frequency Offshore Wind Power System

Offshore wind power integration via fractional frequency transmission system (FFTS) has drawn increasing attention worldwide in recent years. The fractional frequency offshore wind power system(FFTS offshore) consists of paralleled-connected multi-pole permanent magnet direct-drive synchronous generators(PMSGs), subsea cable, and an onshore cycloconverter. In this system, the cycloconverter is used to control the rotating speed of the wind turbines to harvest maximum wind power, and the generator-side converters of PMSGs are no longer necessary in order to reduce the investment and operation and maintenance cost. A quasi-steady-model of FFTS offshore considering the influence of transformers and transmission lines is presented. In addition, a control scheme based on mean rotor flux orientation is demonstrated. The multi-machine optimal speed can be obtained via curve-fitting. Furthermore a simulation model of FFTS offshore with four PMSG wind turbines is built. Simulation results show that the rotating speed of PMSG wind turbines could follow reference very well under various wind conditions, and the proposed system structure can harvest the optimal wind energy. Thanks to its high efficiency and low cost, FFTS offshore offers another competitive method for offshore wind power integration.