MMC Circulating Current Suppression Strategy based on PCHD-SMC Control

In view of the two-octave circulation problem in the operation of modular multilevel converter (MMC), the traditional control method can no longer meet the stability and dynamic response of the system. Combined with the nonlinearity and passivity of MMC, this paper proposes a passive sliding mode (Port-Controlled Hamiltonian with Dissipation-Sliding-Mode Control) (PCHD-SMC) control strategy under three working conditions: steady-state operation, active power abrupt change and grid-side voltage abrupt change. Firstly, the Euler-Lagrange (EL) model of the modular multilevel converter was constructed, and the generation mechanism of the internal circulation was analyzed. Secondly, the passivity of MMC is analyzed, and the passive controller based on the EL model is applied to the current inner loop control. Then, sliding mode control is introduced to solve the problem that passive control is too dependent on parameters, which increases the robustness of the system and realizes the suppression of the two-fold circulation component. Finally, a 23-level MMC inverter simulation model was built in MATLAB/Simulink to verify the effectiveness and reliability of the proposed strategy.