MMC柔性直流换流站无功级联控制策略

模块化多电平换流器(MMC)可独立解耦调节有功、无功功率,使得柔性直流换流站具有在交流系统电压跌落工况下提供无功支撑的潜能。提出了MMC柔性直流换流站无功级联的控制策略,即将定交流电压控制和定无功控制级联,其中定交流电压控制包括桥臂电流辅助控制环节,并在故障清除后瞬间进行积分环节清零重置控制。以中国张北±500 kV四端柔性直流电网工程为例进行了仿真验证,结果表明相对于传统的定无功或定交流电压控制方式,柔性直流换流站无功级联控制方式可以兼顾电网稳态无功调节和暂态无功支撑等需求,快速平稳地输出无功功率,能在保证MMC设备安全的前提下提供暂态无功支撑,并缓解故障清除瞬间可能发生的暂态交流过电压。

Reactive Cascaded Control Strategy of MMC Flexible DC Converter Station

Modular multilevel converter (MMC) has the characteristics of independently decoupling and regulating active power and reactive power, which makes the MMC flexible DC converter station has the potential to provide reactive power support when AC system voltage sags. This paper proposes a cascaded control strategy of reactive power for MMC flexible DC converter stations, which cascades constant alternating voltage control and constant reactive control. The constant alternating voltage control is added with an arm current auxiliary control, and instantaneous reset control of integration after clearing the fault is also introduced. The Zhangbei ±500 kV four-terminal flexible DC power grid project of China is taken as a simulation example. The results show that compared with the traditional constant alternating voltage control and constant reactive control, the reactive cascaded control mode for flexible DC converter stations can accommodate the steady-state reactive power regulation and transient reactive power support, and output reactive power quickly and smoothly. Furthermore, the designed strategy can ensure the safety of MMC when supporting transient reactive power, and can relieve constant AC overvoltage that may occur at the moment of fault clearing.