NPC型直挂储能变流器桥臂断路故障下低电压穿越的容错控制

Fault-Tolerant Control of Low Voltage Ride-Through Under Bridge Arm Open-Circuit Fault of NPC Direct-Mounted Energy Storage Converter

NPC型直挂储能变流器长期运行可能发生桥臂断路故障造成设备停运以及影响低电压故障穿越,基于故障相与直流母线中点直连构成虚拟桥臂重构容错故障拓扑,提出了基于模型预测控制的桥臂容错低电压穿越控制策略。考虑重构后的容错拓扑结构降低了直流侧电压的利用率,研究分析了该容错结构进行低压穿越的最大输出电流整定方法。由于低电压穿越过程中电压跌落后的容错拓扑输出特性发生改变,对储能直挂容错结构的输出电流、电压进行模型预测矢量分析,推导出电压跌落与最大输出电流的关系式。在重构的空间电压矢量内选择能够支撑低电压穿越的矢量状态,控制储能变流器按照低电压穿越技术规范进行有功无功功率分配,支撑电网电压。仿真结果验证了所提出的控制策略保证容错拓扑结构可以在桥臂故障期间运行的有效性以及低电压穿越过程中提供无功功率支撑的可靠性。

Long-term operation of neutral-point-clamped(NPC)direct-mounted energy storage converter may cause the bridge arm open-circuit fault,which causes the shutdown of equipment and affects the low-voltage fault ride-through.In this paper,a virtual bridge arm is formed by directly connecting the faulty phase and the midpoint of the DC bus.The fault-tolerant topology is reconstructed,and a fault-tolerant low voltage ride-through(LVRT)control strategy based on model predictive control is proposed.Considering that the reconstructed fault-tolerant topology structure reduces the utilization rate of the DC side voltage,the maximum output current setting method of the fault-tolerant structure is studied and analyzed.Due to the change of the output characteristics of the fault-tolerant topology during the LVRT process,the model prediction vector analysis is carried out on the current and output volt⁃age of the direct-mounted fault-tolerant structure of the energy storage converter,and the relationship between the voltage drop and the maximum output current is deduced.In the reconstructed space voltage vector,a vector state that can support LVRT is selected,and the energy storage converter is controlled to allocate active and reactive power according to the LVRT technical specifications to support the power grid voltage.The simulation results verify that the proposed control strategy ensures that the fault-tolerant topology structure can operate during bridge arm faults and the reliability of reactive power support during low voltage ride-through.