Sub-envelope modulation method to reduce total harmonic distortion of AC/AC matrix converters

AC/AC matrix converter is an array of power semiconductor switches that connects directly a three-phase AC source to another three-phase load. It can convert an AC power source with certain voltage and frequency to another AC load with variable voltage and variable frequency directly without DC link and bulk energy storage component. Classical modulation methods such as Venturini method and space vector modulation (SVM) method using AC-network maximum-envelop modulation, implement matrix conversion successfully. However, in the mean time they cause very high total harmonic distortion (THD). Since matrix converters directly link loads to sources, high THD heavily pollutes power system, and damages other equipment's work. It restricts to apply matrix converters in industrial applications. This paper presents a novel approach: Sub-Envelope Modulation (SEM) method to reduce THD of matrix converters effectively. The approach is extended to an improved version of matrix converters and the THD can be reduced further. The algorithm of the SEM method is described in detail here. The method regarding current commutation is also proposed. Simulation and experiment results are also presented to verify the feasibility of the SEM approach. The results will be very helpful for industry applications.