Study On The Combination Of Matrix Converters And Direct Torque Control Of Induction Machines

The applications of MC (Matrix Power Converter) in DTC (Direct Torque Control) of induction machines are presented. With its good performances, the DTC technique attracts a lot of researchers to study on it, and get great improvements in recent years. Now, the AC motor control system with DTC technique is widely used in more and more fields. But most of the power converters of AC motor control system with DTC technique are AC-DC-AC converters, in which the rectifiers are composed of diodes. The wide use of this kind of converters will seriously pollute the power network. MC have some good performances, first of all, it has unity power factor and less harmonic pollution. We call the AC motor control system with DTC technique in which MC displaced AC-DC-AC converter as MC-DTC system. This kind of system is possible to combine the advantages of MC with DTC schemes. This paper is to verify the effectiveness of the applications of MC in DTC of induction machines theoretically and by simulations.The principle of DTC and the realization of it are introduced. The concept of voltage space vector is presented. Based on the detailed analysis of the voltage space vectors of MC, the modulation method of MC is proposed to realize the DTC of induction machines; based on the detailed analysis of the current space vectors of MC, the modulation method of MC which can control the power factor is proposed to control MC-DTC system.The bi-directional switches discussed in this paper are made up with IGBTs paralleling with diodes. The four-step commutation is introduced to achieve security commutation of bi-directional switches. To speed up the simulation, the simulation model of the MC is improved.The simulation model of main circuit and control circuit of MC-DTC system is constructed with MATLAB, and lots of simulations are carried out. The results of simulations indicate that the proposed modulation method is effective and the performances of MC-DTC system, with excellent input characteristics, are superior to the DTC system in which the AC-DC-AC converter is used.