Manfred Bruckmann

Design of Pulse Patterns for Matrix Converters

Abstract For the matrix converter (Fig. 1) two basic methods are known to calculate the switching states and turn-on times necessary to generate the average output voltage and input current desired. One modulation technique is the direct method of Venturini and Alesina which controls each output phase separately and the other one is the space vector modulation or indirect method proposed by Huber, Borojevic and Burany which treats the complete converter as a whole. The paper presents a new pattern optimisation principle for the space vector modulation which reduces the switching losses of the matrix converter significantly. Already published optimisation techniques try to minimise the number of commutations within a switching period by different choice of the switching states for the zero voltage and by different arrangements of the switching states. These principles lead to pulse patterns which are quite similar to the Flat-Top Modulation or to the symmetrical use of zero switching states known from voltage source converters. The new optimisation method also takes into account the commutation voltage which is different for each individual switching operation and which has a strong influence on the switching losses. To minimize the commutation voltage it is necessary to follow a certain phase sequence, i.e. the input voltages must be connected to each output phase in a certain order. This order depends on the actual values of the input voltages. For the direct modulation technique this loss optimised sequence can be realized quite easily but for the space vector modulation no arrangement of switching states follows the loss optimised sequence. The paper proposes a technique to obtain the Loss Optimised Pulse Pattern out of the result of the space vector modulation by a subsequent phase oriented rearrangement of the switching states. The influence on switching losses and on harmonic distortion both on the input and on the output side will be discussed.