考虑内部动态特性的模块化多电平换流器小信号模型

Small-Signal Model of the Modular Multilevel Converter Considering the Internal Dynamics

小信号模型是系统稳定性分析和进行参数设计的重要方法。目前对于模块化多电平换流器(modular multilevel converter,MMC)的小信号建模,通常忽略子模块电容电压波动、内部环流、环流抑制控制器等内部动态行为,从而简化状态空间模型的建立,但却对系统特征根和稳定性分析造成一定误差。文中考虑换流器的内部动态特性,建立了详细的MMC阀的小信号模型,所建立的小信号模型提供与外部控制器和交、直流系统方便的接口,具有较强的通用性。通过与电磁暂态仿真模型的动态响应对比,验证了所提出模型的准确性。同时,建立了简化的端模型的状态空间方程,并将简化模型和MMC详细模型的小信号分析结果进行对比,结果表明,应用简化的端模型评估系统动态特性存在一定误差,且对部分系统不稳定现象无法预估判断,从而验证了建立MMC详细小信号模型的必要性。

Small signal model is a general and important method to implement stability analysis and control parameters design. At present, on the small signal modeling of the modular multilevel converter（MMC）, the internal dynamics including the sub-module capacitor voltage fluctuations, the inner loop current, the loop current controller are often neglected, thus simplifying the state-space model, but bringing in some errors for the eigenvalues and stability analysis. A detailed small-signal model of the MMC with consideration of the internal dynamics of the converter was developed. The developed model provides convenient interface with the outer controller and the AC and DC system. The dynamics evaluation with this model was compared with a detailed electromagnetic transient simulation model, and the correctness of the model was validated. Besides, the small signal model of a simplified terminal model was also established and compared with the detailed MMC model. It is demonstrated the simplified model can not evaluate some instability phenomena accurately and the establishment of a detailed MMC model is necessary.