面向分频海上风电送出的模块化多电平矩阵变换器改进V/f解耦控制策略

Improved V/f Decoupling Control Strategy for Modular Multilevel Matrix Converter for Fractional Offshore Wind Power Transmission

基于全桥功率模组的模块化多电平矩阵变换器(modular multilevel matrix converter,M3C)是海上风电送出中具有良好应用前景的新方案,但是M3C也存在工、低频电气分量在桥臂内的直接功率耦合现象。为此,提出适用于分频海上风电送出的新型M3C构网电压/频率(V/f)解耦控制策略。根据对子变流器瞬时功率的分析,提出桥臂电容电压的层次化控制方法,M3C各子变流器在工频侧独立控制,通过输入正序有功及负序电流实现桥臂电容电压的稳定。而M3C各子变流器在低频侧统一控制,通过电流双序闭环控制实现低频交流电压的稳定。根据工、低频解耦控制得到的电流参考值,在静止坐标系统下统一实现9个桥臂瞬时电流的完全独立控制。所提方法可有效降低M3C控制复杂度,提高所构建低频交流系统的稳定性。搭建仿真模型通过稳态、动态及工、低频典型故障实验全面验证所提策略的有效性。

The Modular Multilevel Matrix Converter(M3C)based on the full bridge power module is a new scheme for the offshore fractional frequency transmission which has good application prospect.However,the M3C also has the direct power coupling of the fundamental and the low frequency electrical quantities between the bridge arms.Therefore,this paper proposes a new voltage/frequency(V/f)decoupling control strategy of M3C for offshore fractional frequency transmission.With the analysis of the instantaneous power of the sub-converters,a hierarchical control method of the bridge arm capacitor voltage is introduced.Each sub-converter of the M3C is independently controlled at the fundamental frequency side to stabilize the bridge arm capacitance voltage through the positive and the negative sequence input currents.While they are uniformly controlled at the low frequency side to stabilize voltage and frequency of the AC system through the double sequence closed-loop current control.According to the current references obtained by the fundamental frequency and the low frequency decoupling control,the instantaneous currents of the nine bridge arms of the M3C is completely and independently controlled under the static coordinate system.The proposed strategy effectively reduces the control complexity of the M3C and enhances the stability of the established low frequency AC system.Simulation model is built up to comprehensively verify the effectiveness of the proposed strategy through the steady,the dynamic and the typical fundamental frequency and the low frequency faults experiments.