Research On Six-phase Inductive Motor Direct Torque Control System

The research of theoretical analysis, design and simulation are carried out from the three aspects of 6-phase inductive motor's dynamic mathematical model, voltage space vector pulse width modulation (SVPWM) algorithm, direct torque control (DTC) system in this paper.According to the principle of electromechanical energy conversion, the dynamic mathematical model of 6-phase inductive motor in natural base is established on foundation of winding structure. It is transform to in harmonic base using 6-phase coordinate transformation matrix. The important conclusion is obtained through analysis in three kinds of subspace: 6-phase inductive motor is equivalent to two axis primitive machine in d-q subspace from the perspectives of electromechanical energy conversion, the DTC control strategy based on two axis primitive machine is also applicable for 6-phase inductive motor. The simulation model in Matlab/Simulink is made and the simulation results show the advantage of 6-phase inductive motor: fast transient response, correct steady response, high reliability.A new 6-phase SVPWM algorithm based on 12 medium voltage space vectors is designed on foundation of some common 6-phase SVPWM algorithm. The 12 maximal synthetic voltage space vectors are selected with the principle of minimizing stator harmonic current and switching loss, then the 12 medium voltage space vectors are gained by optimum synthesis. The action number, action time and action sequence of synthetic vectors are designed combined with mature 3-phase SVPWM algorithm.A new 6-phase inductive motor DTC system based on 12 medium voltage space voltage space vectors is designed on foundation of dynamic mathematical model, SVPWM algorithm and basic DTC system. The designed of system include three parts: (1) flux linkage and torque observer; (2) flux linkage and torque regulator; (3) inverter switching table. The designed of 6-phase inverter switching table nclude three parts: (1) medium voltage space vectors output table; (2) synthetic voltage space vectors output table; (3) inverter switching driving signal output table.The every partial and general simulation model in Matlab/Simulink are made and the simulation results show the advantage of the system: well stability ,fast transient response, correct steady response, small stator harmonic current.The simulation results show correctness and effectiveness of the new control strategy.