New modulation strategy for a matrix converter with a very small mains filter

Abstract

While known modulation strategies for matrix converters are based on PWM or vector-modulation, this paper presents a novel time-discrete modulation method by which the switching state of the matrix converter is changed only at equidistant points in time. The decision about which switching state is to be set for the following sampling period, is made by use of a quality function. Using this approach, the switching state is selected in such a way as unity displacement factor is seen at the supply side whilst the load currents follow their reference values with good accuracy. The quality function mentioned above is determined via a mathematical model of the matrix converter and the controlled system. The one switching state that induces the optimum value of the quality function is selected for the next sampling interval. Measurements taken on a model plant, consisting of a matrix converter and a standard induction machine with a rated output power of 11 kW show that the matrix converter, equipped with the control method presented here, offers some advantages over systems with conventional frequency converters.