Apparatus for controlling three-phase AC motor on two-phase modulation technique

摘要

An apparatus is provided to control a three-phase AC motor and comprises an inverter and a controller. The inverter powers the motor in response to a three-phase PWM command. The control circuit controls the inverter based on two modulation techniques selectively switched from one the other depending on information indicative of an operation state of the motor. One modulation technique gives the PWM command a first two-phase modulation allowing each phase voltage to be fixed at a predetermined voltage level in turn at intervals of an electrical angle of 2π/3. The other modulation technique gives the PWM command a second two-phase modulation allowing each phase voltage to be fixed at a predetermined voltage in turn at intervals of an electrical angle of π/3. The switchover can be made between the two-phase and three-phase modulations or can be made with consideration of temperature at switching elements.