光伏直流升压汇集系统断线故障特性分析

Analysis on Characteristics of DC Line Breakage Fault in DC Step-up Collection System for PV Generation

光伏电站采用直流汇集方式能够解决采用交流汇集方式时的宽频域振荡问题和线路损耗大的问题,但是现有文献对直流升压汇集系统的故障特性特别是断线故障特性研究很少。针对基于IPOS结构的直流升压变换器单元的光伏直流升压汇集系统,提出了系统断线故障发展过程中,非故障线路上存在故障电流的特性。首先,分析了非故障线路上故障电流产生的机理;其次,按照故障点位置的不同,对故障电流引起的系统电压电流变化特性进行了分析,并推导了故障电流的计算表达式;再次,从继电保护的角度分析了故障电流对直流升压汇集系统的影响;最后,基于PSCAD/EMTDC搭建了直流升压汇集系统进行了仿真,验证故障特性分析的正确性。

The photovoltaic power plant adopts the DC stepup collection method to solve the problems of wide frequency domain oscillation and large line loss when using the AC collection mode.However,the research results related to the DC line breakage fault characteristics in the DC step-up collection system are seldom reported.Aiming at the photovoltaic DC stepup collection system based on IPOS structure,the characteristics of fault current in the non-fault DC bus are proposed.Firstly,the mechanism of fault current is analyzed.Secondly,according to the position of fault point,the variation characteristics of voltage and current caused by fault current are analyzed,and the calculation expression of fault current is derived.Thirdly,the influence of fault current on DC step-up collection system is analyzed from the perspective of relay protection.Finally,based on PSCAD/EMTDC,a DC step-up collection system is constructed,and simulation results show that the conclusion of above-mentioned fault analysis is correct.