微网电压暂降串并联协调补偿策略

Coordinated control strategy of series and shunt compensation of voltage sag in microgrid

微网一般处于配电网的末端容易受到由断路故障引起的电压暂降问题的危害。根据引起电压暂降的断路故障发生的位置,可以将电压暂降大致分为两类,程度较严重的外部电压暂降和较轻微的内部电压暂降;外部电压暂降是由发生在配电网中的断路故障引起的,内部电压暂降则是由发生在微网内部的断路故障引起的。因此对电压暂降的补偿应该根据其分类选择相应的补偿策略和补偿装置。基于对微网中电压暂降特性的分析提出了一种协调补偿控制策略。对于程度较严重的外部电压暂降,可以利用微网中的电动汽车充电站作为并联补偿装置协助容量不大的串联补偿装置动态电压补偿器补偿电压暂降。对于程度较轻的内部电压暂降,补偿装置只需要相对较小的容量,可以仅使用动态电压补偿器抑制电压暂降。进一步分析了补偿过程中的功率控制策略。微网是高电阻性的低压网络,网络中电压幅值的改善主要依赖于补偿装置的有功功率输出。基于这个特点在并联补偿装置的功率控制中采用P-U下垂特性。仿真试验结果证明了提出补偿策略的正确性与有效性。

Since Microgrid located downstream in distribution network,voltage sags caused by short circuit have become common power quality events that users of Microgrid have to face.According to where the short circuits occurred,voltage sags can be divided into two categories,the exterior voltage sag with lower voltage profile in whole Microgrid and longer duration and the interior voltage sag with limited effecting area and shorter duration.Exterior voltage sag caused by short circuit taking place in distribution network,and interior one caused by short circuit taking place in Microgrid itself.Therefore the compensation of voltage sag is also adjusted according to the category of sag,as well as choosing control strategy and capacity of compensator.In this paper the characteristics of two kinds of voltage sags are analyzed,according to the analysis results coordinated control strategy of voltage sags compensation have been proposed.Mitigating the exterior voltage sags needs relatively big capacity of compensator,so that power converters in electrical vehicle charging stations work as shunt compensator to assist series connected dynamic voltage restorer.Interior voltage sags need only small power capacity on mitigation;therefore only dynamic voltage restorer compensate voltage sag.In this paper the power control strategy is further studied.Microgrid is natural resistant network,which means the magnitude of voltage mainly depending on active power output of compensator.According to these features,the power control strategies of P-V droop is applied on voltage sag mitigation.The strategy proposed in this paper is approved to be effective by simulation test result.