Optimal Pulse Patterns of Six-Phase Voltage Source PWM Inverter for Double Three-Phase Wound AC Motors

In this work, we successfully applied a six-phase voltage source PWM inverter to a double threephase wound AC motor to attain both an increase in the capacity of the PWM inverter and a reduction in higher harmonics of the phase voltages of the motor. The system uses a coupling reactor, which has the same configuration as that of a three-phase transformer, inserted between the inverter and the motor by means of special windings. This eliminates the need for control to balance output currents from a pair of three-phase inverters. If six-phase voltages are controlled so that there exists no even-number harmonics in the same wave pattern, the coupling reactor concerned absorbs odd-number harmonic voltages other than the orders of 12p±1 (p=1, 2, 3, …). Hence the elimination of these harmonics from the phase voltages of the motor is achieved. It was possible to eliminate the higher harmonics of the phase voltages of the motor most effectively by applying the optimal pulse patterns obtained through the modern theory of control using Lagrange multipliers, resulting in the motor phase voltage patterns being substantially improved.