适用于海上风电分频输电的模块化多电平矩阵变换器故障穿越控制策略

Fault Ride-through Control Strategy of Modular Multilevel Matrix Converter for Fractional Frequency Transmission System

作为海上风电分频输电(fractional frequency transmission system,FFTS)的重要装置,模块化多电平矩阵变换器(modular multilevel matrix converter,M3C)的故障穿越是海上风电并网安全稳定运行的重要问题之一。为研究M3C故障穿越控制,首先基于M3C双dq坐标系下的数学模型和稳态控制策略,在MATLAB/Simulink中搭建仿真模拟电网发生三相对称故障的情况,分析M3C的暂态特性,并提出故障穿越策略。通过改变M3C低频侧交流电压指令,迫使风电场根据自身低电压穿越策略减少输出功率,从而降低M3C传输的有功功率;M3C工频侧采取有功平衡优先、剩余最大无功输出的控制策略以支撑网侧跌落电压;且根据系统对有功无功功率的需求分为有功无功兼顾、有功优先、无功优先3种场景的控制方案。仿真结果表明,所提策略可以根据不同的控制需求提升M3C故障穿越的能力,保证M3C各子模块电容平均电压不超过阈值,无需额外卸荷电路和通信即可实现电网故障期间的安全穿越,同时有利于维持风机持续并网运行和电网电压的恢复。

The fault ride-through of modular multilevel matrix converters(M3C),as an important device of fractional frequency transmission system(FFTS)technology for offshore wind power,is one of important issues on the safe and stable operation for offshore wind power integration.In order to study fault ride-through control of M3C,the paper first described the mathematical model and steady-state control strategy of M3C based on double dq axis.From the simulations of a three-phase symmetrical fault on the grid in MATLAB/Simulink,the paper analyzed the transient characteristics of M3C,and then proposed a fault ride-through strategy.The low frequency AC voltage references were regulated to force the wind farm to reduce their output power which were transferred through the M3C,and on the line frequency side,the maximized remaining reactive power capacity of the converter was utilized to support the grid voltage.According to the system demands for active and reactive power,there were three scenarios,active-reactive power trade-off,active power priority and reactive power priority.Simulation results show that the proposed strategy can improve fault ride-through capability of M3C according to different control requirements,ensure the average capacitor voltage of M3C below the threshold value,and realize safe fault ride-through without additional chopper circuit and communication.And it is beneficial to maintain continuous wind power integration and grid fault recovery.