Circulating Current Control for the Modular Multilevel Matrix Converter Based on Model Predictive Control

In this work, a continuous-control-set model predictive control (CCS-MPC) strategy, with a saturation scheme for protection, is presented for regulating the circulating currents of a modular multilevel matrix converter (M3C). The proposed approach is based on a state-space model of the M3C and allows protection and better utilization of the devices through a saturation scheme, which directly limits the arm currents and cluster output voltages by integrating the corresponding bounds as constraints of the CCS-MPC formulation. In order to solve the inherent optimization problem associated with the CCS-MPC, an active-set algorithm is implemented. Experimental and simulation results from a 27-cell M3C prototype validate the proposed strategy and illustrate the good performance achieved with the methodology presented in this work.

I. Introduction

The modular multilevel matrix converter (M3C) is an important power electronic topology that belongs to the modular multilevel converter (MMCs) family [1]–[5]. The M3C topology is composed of several full-bridge power cells (shown at the right-hand side of Fig. 1), which are grouped into nine power clusters. The series connection of a cluster with an inductance is referred to as an arm (shown at the left-hand side of Fig. 1). The M3C has been proposed as a prominent topology for low-speed high-torque drives since lower amplitude circulating currents are required compared to those utilized by other MMCs, particularly when an electrical machine is operating at low speed [6]–[8]. It has also been proposed for wind energy conversion systems (WECSs) based on permanent magnet synchronous machines [9], for improved fault ride-through control of doubly fed induction generators [10], and for low-frequency transmission systems [11]. As discussed in [12], in the future, it is highly possible that the M3C will replace the thyristor-based cycloconverters. An overview of M3C applications is presented in [13]. Fig. 1.

M3C.