单相短路故障条件下级联模块中压光伏发电系统的有功功率回流抑制

Active Power Backflow Suppression of Cascaded Module Medium-Voltage PV Power Generation System During Single-Phase Short-Circuit Fault

有功功率回流是级联H桥型光伏并网逆变器在电网不对称跌落故障条件下固有的问题,可能导致系统没有平衡运行点,H桥直流母线电压持续增大,逆变器因过电压保护而停机脱网。为此,该文以电网故障发生率最高的单相短路故障为研究目标,回顾现有控制方法,并定量地分析其局限性——在电网电压跌落较深且光伏阵列输出功率较低的工作场景下无法避免有功回流。在此基础上,提出一种适用于级联模块化中压光伏发电系统在单相短路故障条件下的有功功率回流抑制策略,根据光伏阵列实际输出的有功功率将系统的运行划分为两个区域,通过合理地设计系统的调制度,并在不同的运行区域内采用不同的控制方法,能够提高级联H桥光伏并网逆变器对不同的输出功率以及不同电网跌落深度的适应性,以改善系统的故障穿越能力。最后,通过实验验证了所提控制策略的有效性和可行性。

Active power backflow is an inherent problem of cascaded H-bridge(CHB)PV gridtied inverters under the asymmetric grid voltage fault conditions,which may result in the system not having a balanced operation point,the continuous increase of H-bridge DC-bus voltage,and shutdown and disconnection due to overvoltage protection.Aiming at this issue,this paper took the single-phase short-circuit fault with the highest incidence of power grid fault as the research goal,reviewed the existing control methods,and quantitatively analyzed their limitations,that is,it is impossible to avoid active power backflow in the scenario of deep power grid voltage drop and low output power of PV array.On this basis,an active power backflow suppression strategy suitable for cascaded modular medium-voltage PV power generation system under single-phase short-circuit fault was proposed.According to the actual output active power of PV array,the operation of the system is divided into two areas.By reasonably designing the system regulation and adopting different control methods in different operation areas,the adaptability of the CHBPV grid-tied inverter to different output powers and different grid drop depths is improved,and the fault ride through ability of the system is also improved.Finally,the effectiveness and feasibility of the proposed control strategy were verified by the experimental results.