双闭环定交流电压控制下MMC换流站阻抗建模及稳定性分析

风电系统接入基于模块化多电平换流器(MMC)的高压直流(HVDC)输电系统是极具前景的输电方案,同时也面临较为突出的系统稳定性问题。小信号阻抗分析法是研究互联系统稳定的有效办法。然而,MMC的内动态特性使得精确建立其阻抗模型具有较大难度。文中采用多谐波线性化方法建立了采用双闭环定交流电压控制的MMC送端换流站小信号阻抗模型,可实现电流环对MMC阻抗影响的准确分析。针对直驱风机通过MMC-HVDC系统并网的系统,利用阻抗分析法分别分析了MMC电流环不同控制带宽下互联系统振荡的问题,为电流环参数优化设计提供了依据。最后,基于MATLAB/Simulink的仿真结果证明了阻抗模型和稳定性分析理论的正确性。

Impedance Modeling and System Stability Analysis of MMC with Double Closed-loop AC Voltage Control

The wind power integration via the modular multilevel converter (MMC) based high voltage DC (HVDC) transmission system is a promising scheme for power transmission, which also faces prominent stability problems. The small-signal impedance analysis method is an effective way to study the stability of interconnected systems. However, it is difficult to accurately build the impedance model of MMC due to its internal dynamic characteristics. By using the multi-harmonic linearization method, this paper develops a small-signal impedance model of the sending-terminal MMC with double closed-loop AC voltage control. Then the influence of current control loop on impedance characteristics is analyzed accurately. For the system in which the wind farms consisting of direct-driven wind generators are connected with MMC-HVDC system, the impedance analysis method is applied to analyze the oscillation of the interconnected system with different bandwidths of current control loop of MMC, which provides a basis for optimal parameter design of current control loop. The simulation results based on MATLAB/Simulink validate the correctness of the impedance model and stability analysis.