电网不对称故障下VSC-HVDC系统的直接功率控制

针对在电网传输线路发生不对称故障时,采用稳态的电压源换流器高压直流输电(VSC-HVDC)系统控制算法将引起直流电压波动,交流电流畸变等问题,提出采用改进的直接功率控制(DPC)算法对VSC-HVDC系统的稳态和暂态过程进行控制。该方法以瞬时无功功率理论和dq变换为基础,通过实时控制电压源换流器(VSC)系统输入输出功率平衡,从而完成系统的交直流功率传输。对于不对称故障时直流电压出现的波动问题,通过对输入的瞬时功率进行分解,采用正序功率和相位作为控制信号对电压波动进行抑制。最后,通过PSCAD软件对所提出的控制算法进行系统仿真,从仿真的结果看出当系统故障时,改进的算法能够有效的抑制直流电压的波动,降低电流的谐波含量。同时也验证了该算法不仅能够很好的完成系统的稳态和暂态的过程控制而且能够有效隔离电网故障增强电网的稳定性。

Direct Power Control of VSC-HVDC System Under Unsymmetrical Fault of Grid

To suppress DC voltage fluctuation and reduce the THD of AC current when the unsymmetrical fault happened in grid,we adopted an improved direct power control(DPC) algorithm to control the voltage source converter HVDC(VSC-HVDC) system’s steady state and transient state process.Based on instantaneous reactive power theory and dq transform,this algorithm was realized in power transmission control by using power balance management in real-time input and output of VSC system.The positive sequence power that got from the decoupled instantaneous input power of VSC system and positive phase was used as control signal to suppress the DC voltage fluctuation when the unsymmetrical fault happened.Finally,the whole VSC-HVDC system was simulated by the PSCAD software.The results show that the improved DPC algorithm can effectively suppress DC voltage fluctuation and lower the THD of AC current.Meanwhile,it has been proved that the VSC-HVDC system can isolate grid faults effectively and enhance stability of grid.