A Closed-Loop Frequency Domain Analysis Method for Modular Multilevel Converters

The steady-state analysis is of great significance for the performance evaluation of modular multilevel converter (MMC), circuit parameter design, and semiconductor device selection. The bridge arm current and submodule capacitor voltage in MMC contain many harmonic components, and the traditional time domain method is relatively complex to analyze the steady-state. Therefore, this paper mainly uses the harmonic state-space (HSS) method to solve the frequency domain values of internal electrical variables in MMC. The main advantage of this paper in solving the steady-state value is that it only needs to write the harmonic state space equation of the main circuit equation, provide the reference value of the outer loop of the control circuit and an initial value close to the normal operation, and then calculate the steady-state value of the system. This article performs theoretical calculations and simulation verification, provides a reference for solving the steady-state values in other operating conditions.