电网电压骤降故障时双馈风机虚拟阻抗改进控制技术

针对电网电压骤降故障所导致的风电机组过电流问题,已有的基于虚拟电阻的过电流抑制技术无法兼顾过电流抑制效果和基频控制性能,同时未考虑系统的高频稳态性能,导致故障穿越期间的谐波抑制性能较差。为了兼顾故障穿越性能及故障穿越期间的谐波抑制性能,通过分析电网电压骤降时的双馈风机(DFIG)数学模型,研究了过电流及暂态磁链抑制机理,进一步基于虚拟阻抗技术,提出了电网电压骤降故障时DFIG改进控制技术。通过在机侧变流器转子电流控制环路中引入附加控制环,实现对暂态磁链振荡的抑制,从而提升DFIG低电压穿越性能。进一步地,对所提出的虚拟阻抗环节进行了参数设计分析,保证了该控制方法可以兼顾过电流抑制性能、高频性能及基频控制性能。最后,通过仿真结果验证了所提改进控制策略的有效性和可行性。

Improved Control Strategy of DFIG Based on Virtual Impedance Under Grid Voltage Dip Fault

In view of the over current problem of wind turbines caused by voltage dips, the existing over current suppression techniques based on virtual resistors cannot take into account both the over current suppression effect and the fundamental frequency control performance. At the same time, the existing techniques do not consider the high frequency steady state performance of the system, leading to the poor harmonic suppression performance during the fault ride through. In order to give consideration to both the performance of fault ride through and the harmonic suppression during fault ride through, the mechanism of over current and transient flux suppression is studied by analyzing the mathematical model of doubly fed induction generator (DFIG) in the case of voltage dips, and based on the virtual impedance technique, an improved control technique for DFIG under voltage dips is proposed. In the improved control technique, an additional control loop is added to the rotor current control loop of the machine side converter to suppress the transient flux oscillation and improve the performance of the DFIG. Furthermore, the parameters of the proposed virtual impedance link are designed and analyzed to ensure that the proposed control method can take into account over current suppression performance, high frequency performance and fundamental frequency control performance. Finally, simulation results verify the effectiveness and feasibility of the proposed improved control strategy.