Sequence-Based Control of an Isolated DC/AC Matrix Converter

Abstract

This paper describes the control of an isolated multiphase high-frequency-link (HFL) matrix inverter by controlling the time evolution of its switching states (or, switching sequences). It is referred to as the optimal-switching-sequence-based control (OSBC). Unlike several conventional control schemes, where, typically the control is based on averaged model of the inverter and the modulation scheme sets a predetermined switching sequence, OSBC synthesizes the fundamental switching sequence depending on the control needs on the fly. For instance, OSBC can seamlessly play with the inverter switching sequences if the input voltage of the inverter changes as evident in solar or wind-based energy systems. This necessitates that OSBC use a switching-sequence-based discontinuous (instead of averaged) modeling approach. Further, the stability of the closed-loop inverter is determined in OSBC using an advanced composite Lyapunov-function based approach, which also enables one to predetermine the reachability of the inverter dynamics for a given switching sequence. Thus, optimal control in OSBC is ensured under stability bound of the switching sequence. This provides a fundamental difference between OSBC and model predictive control for inverters. This also implies that in a multiobjective OSBC, one can shift the weights of the individual cost functions to yield better inverter performance without compromising the stability.