Single AC loop control method based on circulating current compensation for MMC

For the modular multilevel converter (MMC) drive system, it is generally necessary to construct a control structure with two control degrees of freedom, namely the DC control loop and the AC control loop. The modulation module cannot be directly associated with the AC control loop controlled by the motor. To address this issue, a single-degree-of-freedom control method for AC control circuits is proposed, enabling the output of the motor control circuit to be directly used as the modulation reference signal, while the control of the DC control circuit serves as a compensation structure. The AC control circuit of the proposed method adopts a vector control structure, and the DC control circuit part uses a PIR controller to suppress the second harmonic component of the circulating current. Finally, the simulation results verified the effectiveness of the proposed method.