风电场VSC-HVDC并网不平衡运行改善控制策略

风电场柔性高压直流输电(VSC-HVDC)系统交流不平衡运行时,并网输出功率存在二倍电网频率波动,并网电压、电流波形畸变,恶化风电场并网的电能质量。为改善风电柔性高压直流输电系统在交流不平衡状况下的并网性能,针对双馈风电场侧交流不平衡运行状况提出了一种改善控制策略。该改善控制策略在计及相关平波电抗器、变压器等值阻抗影响的基础上,建立了风电场VSC-HVDC系统不平衡运行数学模型,并提出基于正负序双dq解耦轴系下的正负序控制给定电流策略。最后,通过Matlab/Simulink仿真平台对比仿真引入改善控制策略前后的系统运行性能,对比结果表明所提改善控制策略可以有效抑制风电场并网功率波动,改善系统并网电压、电流波形。

An improved control strategy for wind farm with VSC-HVDC under unbalanced voltage

When there is unbalanced AC voltage in Wind farm with voltage source converter-high voltage direct current (VSC-HVDC) integration system, the output power to the grid will fluctuate with twice of the grid frequency, and the grid voltage and current waveforms, even more, will be distorted, hence the power quality of the wind farm provided will deteriorate badly. To improve the performances of wind farm VSC-HVDC system under unbalanced AC voltage, a doubly-fed wind farm VSC-HVDC system with unbalanced AC condition is discussed in this paper. Based on the positive and negative sequence double dq decoupling shafting, and taking into account the influence of equivalent impedance of the relevant reactor and transformer, the unbalanced mathematical model of the wind farm VSC-HVDC system is established. Moreover, an improved control strategy is realized with the construction of the positive and negative sequence current setting. Finally, a DFIG wind farm VSC-HVDC system is implemented on the Matlab/Simulink, comparisons of the simulation results with and without the proposed control strategy show that the proposed improved control strategy can effectively suppress the fluctuation of output power and improve the waveform of grid voltage and current.