三相模块级联型固态变压器均压/均功率控制策略研究

Research on Voltage and Power Balance Control for Threephase Cascaded Modular Solid-State Transformer

三相固态变压器是适用于智能电网的一种新型的智能电力电子设备,一般包括整流输入级、双有源桥DAB(dual active bridge)直流级和逆变输出级。为解决固态变压器在大功率传输和高输入交流电压工作条件下的高频功率开关管电压电流应力问题,一般采用多模块级联的拓扑结构,但这种拓扑给固态变压器带来了模块间的电压和功率不平衡问题和导致开关管过压过流及电网电流谐波增加等问题。为解决三相模块级联型固态变压器电压、功率的不平衡问题,提出一种新颖的控制策略。输入整流级采用一种基于共同占空比的三相dq0控制策略以保证输入交流电流三相对称,DAB级采用一种基于电压跟随的移相控制方法以实现模块间电压平衡,两级控制策略相配合以实现各模块间电压、功率平衡。仿真和实验均验证了所提控制策略的可行性和有效性。

Three stages solid state transformer （SST） is an emerging power electronic device applied in the micro- grid system. Limited by the voltage and power ratings of existing semiconductor switches, a multilevel topology is often adopted in the SST system. However, the multilevel topology has some disadvantages. A significant defect is voltage and power unbalance of each different H-bridge module, which often cause overvoltage or overcurrent problem. In order to eradicate such risks, an effective voltage and power balance control method is proposed in this paper. A common-duty- ratio based three-phase dq0 control strategy is proposed for the rectifier stage to balance power transferred by each phase and rectifier module, and a voltage-track based control method is presented for the Dual active bridge （DAB） stage to ensure the input voltages of DAB modules identical and regulate the output voltage of each DAB module. Both the simulation and experimental results have verified the effective of the proposed control method.