VSC-HVDC向三相不对称无源网络供电的控制策略研究

Research on the Control Strategy of VSC-HVDC for Three-phase Asymmetric Passive Network Power Supply

VSC-HVDC具有良好的动静态性能,若采用合理控制策略则可调控有功与无功的输出,进而改善电能质量。然而现有控制策略在由VSC-HVDC向三相不对称无源网络供电时可能导致输出电压不对称,进而造成控制效果不理想。建立了VSC的内环d/q解耦控制器,整流侧定直流电压控制器和逆变侧定交流电压控制器。对于整流侧控制器,在电压外环,对PI参数增加模糊自整定;在电流内环,将PI控制改为两相静止坐标系下的PR控制,减少了超调和谐波输出量。对于逆变侧控制器,由于输出的三相电压产生畸变;利用PR控制可以无静差跟踪正弦信号,将逆变侧控制改造为“外环定电压PR控制—内环电流d/q解耦控制”,解决了三相交流电压的不平衡问题。仿真结果表明,该控制策略可提高整流侧超调时间和反应时间,并有效解决了逆变侧输出电压不对称的问题。

VSC-HVDC displays good dynamic and static performance.With reasonable control strategy,it can improve the power quality.However,the effect of the existing control strategy is unsatisfactory due to the fact that it may lead to asymmetric output voltage when VSC-HVDC provides power supply for the three-phase asymmetric passive network.This paper established an inner loop d/q decoupling controller,a constant DC voltage controller of the rectifier side and a constant AC voltage controller of the inverter side.The controller of the rectifier side increases PI parameters with fuzzy online auto-tuning at the outer voltage loop and replaces the PI control with PR control at the inner current loop,thus reducing the overshoot and harmonics.For the control of the inverter side,the three-phase voltage is imbalanced.To solve the problem,the control strategy of inverter is changed into“outer loop constant voltage and PR control-inner loop current d/q decoupling control”by using the PR control to track a sinusoidal signal without steady-state error.The simulation results showed that the refined control strategy improves the overshoot time and response time of the rectifier side,and solves the asymmetric output voltage of the inverter side effectively.