可实现低频输电系统不对称故障穿越的M3C电容电压均衡控制策略

Asymmetric fault ride-through control strategy for low-frequency transmission systems realizing the capacitor voltage balance of modular multilevel matrix converters

低频输电作为一种新型输电技术,在海上风电送出、新能源场站送出等多个场景具有良好的应用前景。但在不对称故障下,故障侧功率不对称将严重影响模块化多电平矩阵变换器(modularmultilevelmatrixconverter,M3C)的电容电压均衡,对低频输电系统安全稳定运行产生不利影响。为此,提出了一种可实现低频输电系统不对称故障穿越的M3C电容电压均衡控制策略。首先,介绍M3C的系统结构及双αβ0数学模型,并分析不对称故障下电容电压不均衡的原因。然后,基于双αβ0数学模型针对输电线路不对称故障情况计算桥臂功率不均衡分量的表达式,通过M3C功率平衡关系引入电流补偿分量,消除桥臂功率的不均衡,并得到适用于不对称故障的环流控制目标,进而通过环流控制实现故障下M3C电容电压的均衡。最后,搭建基于M3C的低频输电系统仿真模型验证所提控制方案的可行性和有效性。

As a new transmission technology,low frequency transmission has good application prospects in several scenarios such as offshore wind power transmission and new energy field station transmission.However,with asymmetric faults,the power asymmetry on the fault side will affect the capacitor voltage balance of the M3C and affect the stable operation of the low frequency transmission system.Therefore,an M3C capacitor voltage balance control strategy that can realize asymmetric fault ride-through in low frequency transmission systems is proposed.First,the system structure and dualαβ0 mathematical model of an M3C are introduced,and the causes of capacitor voltage imbalance under asymmetric faults are analyzed.Second,based on the dualab0 mathematical model for the transmission line asymmetric fault case,the expression for the bridge arm power imbalance component is calculated.Then the M3C power balance relationship introduces the current compensation to eliminate the power imbalance.It also obtains the circulating currents control objective applicable to asymmetric faults.Then through the loop current control it achieves the M3C capacitor voltage balance under faults.Finally,a simulation model of the M3C-based low frequency transmission system is built to verify the feasibility and effectiveness of the proposed control scheme.