Impartial Sequential Model Predictive Control of Parallel T-Type Rectifiers for Power Sharing and Circulating Current Elimination

A parallel T-type rectifier connection is often required to improve the system capacity and stability in high-power applications. However, the parallel rectifier faces the challenges of zero-sequence circulating current (ZSCC) elimination, neutral-point (NP) voltage balance, dc voltage stability, and power sharing. First, to solve the multiobjective optimization problem of two parallel three-level T-type rectifiers with LCL filters (LCL-3LT(2) Rs), a double closed-loop control scheme is adopted. In this scheme, an impartial sequential model predictive control (ISMPC) is proposed as the inner loop controller for ZSCC elimination and NP voltage balance, and an adaptive droop control with voltage feedforward is designed as the outer loop controller to achieve dc voltage stability and power sharing for each rectifier based on its capacity. Second, the main influencing factors of ZSCC in LCL-3LT(2)Rs are analyzed, and ZSCC elimination is considered as one control objective in ISMPC. Finally, ISMPC is proposed to solve the problem that sequential model predictive control (SMPC) could not select the optimal solution due to the fixed priority and the excessive process of only controlling a single objective. The proposed method is tested on a prototype hardware platform of 10- and 5-kW parallel rectifiers. Experiment results demonstrate the superiority of this method over existing methods under several typical scenarios.