New modulation method for matrix converters

摘要

This thesis introduces a novel matrix converter modulation method based on space vector control referred to as the integrative method. The new scheme employs an original duty cycle determination method and is particularly suited to applications with high input frequencies. The new method can cope with unbalanced input conditions and/or failure of one of the input phases. The operation of the matrix converter in the non-linear overmodulation region is analysed. Matrix converter overmodulation is an important topic in matrix converter research because it increases the output/input voltage ratio, limited to a maximum of √3/2 in the high frequency synthesis methods. Unlike conventional modulation schemes, the new integrative method can operate in the overmodulation region without any change in the control algorithm. Unity output/input voltage ratio, that is close to the theoretical maximum of 1.05, is achieved by the integrative method. The cost for increasing the output/input ratio is the degradation of the output waveform quality. The problems associated with current commutation in matrix converters are studied and different commutation techniques are analysed. An original switch commutation method designed to minimise semiconductor switching losses is introduced. The method is based on the selection of the order in which matrix converter states are applied. The practical implementation of the integrative method using a TMS320C240 Digital Signal Processor is also presented. A low voltage matrix converter and a variable frequency three-phase voltage generator were used in the investigation. Simulation and experimental results of the new modulation method operating under several condition are presented.