Patent ID: 8264181

Claim:
A controller for a motor drive control system provided with an inverter, an alternating current motor that has an applied voltage controlled by the inverter, and a current detector that detects a motor current flowing between the inverter and the alternating current motor, the controller comprising: a rectangular-wave control unit that is configured to generate a control command of the inverter according to a rectangular-wave control that controls a voltage phase of a rectangular-wave voltage applied to the alternating current motor, so as to cause the alternating current motor to operate according to an operation command; a pulse width modulation control unit that is configured to generate a control command of the inverter by a pulse width modulation control based on comparison of a carrier wave with an alternating voltage command for causing the alternating current motor to operate according to the operation command; a control mode selection unit that is configured to select either control mode from among the rectangular-wave control and the pulse width modulation control in accordance with an operation state of the alternating current motor; and a current storage unit that is configured to store the final current state immediately before switching in the rectangular-wave control when the control mode is switched from the rectangular-wave control to the pulse width modulation control by the control mode selection unit, wherein the pulse width modulation control unit includes: a current command generation unit that is configured to generate a first current command according to the operation command in the pulse width modulation control; a command correction unit that is configured to take the final current state stored in the current storage unit as an initial value during switching of the control mode from the rectangular-wave control to the pulse width modulation control, and generate a second current command by correcting the first current command so as to smooth variations in a time axis direction; and a feedback control unit that is configured to generate the control command by the pulse width modulation control conducted according to a feedback control of the motor current based on the second current command.