Hybrid Model Predictive Control of ANPC Converters With Decoupled Low-Frequency and High-Frequency Cells

Abstract

Active-neutral-point-clamped (ANPC) converters can be decomposed into a low-frequency cell (LFC) and a high-frequency cell (HFC), and fundamental-frequency operation of the LFC is becoming popular. However, balancing the dc-link voltage and three flying capacitor voltages while maintaining very fast control of the output current is always a challenging task, especially when the flying capacitor is small. This article proposes a hybrid model predictive control (MPC) to guarantee the fundamental-frequency operation of the LFC and achieve the fixed-switching frequency operation of the HFC. In the hybrid MPC, the classical MPC regulates the LFC, whereas the duty-cycle-optimized MPC regulates the HFC. The capacitor voltage balance is achieved by adjusting the duty cycles to avoid the weighting factor tuning process. The proposed MPC features a fixed switching frequency and improves the steady-state performance while guaranteeing the fundamental-frequency operation of the LFC. Simulation and experimental results on a five-level ANPC are presented to validate the advantages of the proposed hybrid MPC method over the classical MPC.