模块化多电平换流器电容用量的标幺化分析与设计方法

子模块电容用量是影响模块化多电平换流器(modular multilevel converter,MMC)体积和成本的关键因素。提出了以单位容量额定储能值作为MMC电容用量的统一的衡量与直接设计指标,建立了直接描述MMC所需额定储能值与电容电压波动率之间关系的标幺化计算模型,使不同额定参数MMC的电容用量的衡量、计算和分析可以得到统一和简化。与以子模块电容值作为分析和设计指标的传统方法相比,MMC额定储能值标幺化计算模型去除了多种参数对计算过程的影响,揭示了基准调制比和输出功率范围是影响MMC额定储能值的关键因素。基于所提出的额定储能值标幺化计算模型,对MMC额定储能设计值随基准调制比和功率输出范围的变化规律进行了详细分析,为MMC电容用量的设计和优化提供了明确的依据。数字仿真和物理试验结果验证了所提方法的正确性。

Design and Analysis for Energy Storage Requirements of Modular Multilevel Converter Applying Per-unit Model

The submodule capacitance is a key factor affecting the volume and cost of modular multilevel converter (MMC). The normalized value of the energy stored in an MMC with respect to the rated capacity is taken as the unified index for evaluating the capacitance usage of an MMC. A per-unit model that describes the relationship between energy storage requirement (ESR) value and the fluctuation rate of capacitor voltage is established. Thereby, the evaluation, calculation and analysis of the ESR values of MMCs with different rated parameters can be unified and simplified. Compared with the conventional methods of taking the capacitance value as the design and analysis index, the per-unit model for calculating the ESR value eliminates the influence of various parameters on the calculation results. It is revealed that the ESR value is mainly affected by the base modulation index and the per-unit active and reactive power output. Based on the proposed model, the variation of the ESR value with the modulation index and the power output range is analyzed in detail, which provides a clear and accurate basis for the design and optimization of MMC capacitance usage. The results of digital simulation and experimental results verify the proposed methods.