Device and method for determining step-out of synchronous motor

摘要

The expected power to be output from a synchronous motor is obtained based on a torque command value and revolution speed of the motor. Meanwhile electric power consumption is detected based on voltage and current actually applied to the motor. If a parameter derived from a deviation or a ratio of the two exceeds a predetermined threshold value, it is determined that step-out has occurred. When using the deviation of the expected power from the electric power consumption as the parameter, the threshold value is determined in relation to the torque command value and the revolution speed. When using the ratio of the expected power and the electric power consumption as the parameter, the threshold value is set in relation to the revolution speed. This enables step-out to be accurately determined with an extremely light computational load.