Abstract: The traditional PI control and passive control have fixed internal control structure parameters, so when the system encounters disturbances, the same group of parameters cannot ensure the response speed and control results under multiple disturbances at the same time. First, the paper introduces the sliding mode control on the basis of MMC's Euler-Lagrange model to solve the problem of fixed internal parameters of passive control to improve the anti-disturbance operation ability of the system. Then, the original approaching law is optimized to reduce the vibration of the sliding mode control itself to keep the system having better dynamic characteristics. After building a MMC simulation model in the MATLAB/Simulink platform, the inner current loop applied with PI control, passive-sliding mode control and improved passive-sliding mode control respectively are compared. It verifies that the improved passive-sliding mode control has stronger anti-disturbance and faster response speed under the same simulation conditions. Moreover, as the approaching law is improved based on the sliding control, the vibration problem of sliding mode control itself is effectively reduced.

    Key words: modular multilevel converter; three-phase unbalance; passive-sliding mode control; approaching law