用于E-STATCOM应用的Delta模块化多电平变换器分析

In this paper, the analysis of a Delta Modular Multilevel Converter operated as a STATCOM with energy storage is presented. The roles of the degrees of freedom (DOFs) of the converter are analyzed. The DOFs constitute the minimum set of parameters, in this case the arm level applied voltages, needed to completely define all the electrical variables of the circuit. The identification of the DOFs represent an important step in the understanding of the converter behaviour and allows the developing of control strategies. Firstly, the dynamic differential equations of the converter are derived. A diagonalization of the system of equations is performed, resulting in three decoupled circuits, each one having one DOF. Two of these equivalent circuits are related to the power transfer to the AC system, while the third one is related to the internal power balancing of the converter. Finally, the analysis is validated through simulations results which compare the mathematical expressions with an open loop switching model of the converter for different scenarios.