Research on Reduced Order Model of MMC Grid-Connected System

With the development and promotion of new energy power generation technology, power electronic equipment has become an important interface for new energy to access the distribution network, and the number of power electronic equipment in the distribution network has soared. However, this also leads to the higher and higher order of the mathematical model of the distribution network, which brings difficulties to the stability analysis of the system. To solve this problem, a nonlinear model reduction method of MMC grid-connected inverter based on singular perturbation theory is proposed in this paper, taking modular multilevel converter grid-connected inverter as an example. Firstly, the nonlinear model of MMC grid-connected inverter including voltage and current sampling delay, phase-locked loop, power outer loop and current inner loop is established by considering the coupling characteristics between the phase-locked loop and other control loops. Then the state variables of the system are divided into fast variables and slow variables according to the time scale through the participation factor analysis of the dominant modes, and then the fast variables are reduced based on the singular perturbation theory, so as to establish the reduced order model of the original system. This method can greatly reduce the computation and analysis complexity while ensuring the accuracy. Finally, the validity of the original model and the reduced order model is verified by MATLAB/Simulink time domain simulation.