A Centralized CB-MPC to Suppress Low-Frequency ZSCC in Modular Parallel Converters

The parallel operation of three-phase converters has become an effective way to achieve modularity. However, zero-sequence circulating current (ZSCC) will appear when the multiparalleled converter modules share a common dc link. In the event that the converters have different output powers and inevitable circuit parameter mismatch, low-frequency (LF) ZSCC can be produced. To address the LF-ZSCC issues, in this article, we propose a centralized carrier-based model predictive control (CB-MPC) scheme for modular parallel converters. This control scheme can be implemented either in master converters or in a dedicate central controller. The CB-MPC can achieve both power control and LF-ZSCC elimination. In addition, with carriers adopted, interleaving and fixed device switching frequency can be easily realized. As such, the benefits of model predictive control and interleaving can be combined. Based on the ZSCC model derived in this article, the elimination of LF-ZSCC can be achieved for more than two paralleled converters when they have different output powers and/or with parameter mismatch. The effectiveness of the proposed CB-MPC has been verified by the simulation and experimental results.

I. Introduction

Employing modularity has been the trend of power electronics system designs. Modular parallel converters have been widely applied in electrical motor drives [1], [2], wind turbine generators [3], [4], uninterruptible power supplies [5], [6], active power filters [7], microgrids with distributed generators [8], [9], etc. For grid-tied applications, such as interlinking system in the hybrid ac/dc microgrid and active front end of low voltage drives [10]–[12], modular system with multiple parallel converters is becoming popular. The modular parallel converters feature several advantages, e.g., fault-tolerant capability, flexible operation, scalability, lower maintenance and repair workload, and overall efficiency can be improved at lower system cost [1]–[12].