A control device for drive-controlling a rotary machine needs the value of an electric constant (resistance or inductance) of the rotary machine.
In conventional measurement of an inductance constant of a rotary machine, AC power is applied with a rotor of the rotary machine fixed by a restraining tool, to measure the inductance constant. However, in a rotary machine connected to some machine, there is such a problem that the connected machine is damaged when the rotary machine rotates upon electric constant measurement. Therefore, a control device for rotary machine and an electric constant measurement method that are capable of measuring an electric constant with no rotation, are required.
As constant measurement device and method for rotary machine with no rotation, the following method is proposed. That is, respective voltage instructions when two levels of large and small DC currents are flown to a current control section are stored, a voltage value based on the larger one of the two levels of DC currents is sharply changed to a voltage value based on the smaller one, a time taken until the current change at this time reaches a predetermined value of the current step width between two levels is measured, and the measured time is divided by a measured value of a winding resistance, thereby calculating a d-axis inductance (for example, see Patent Document 1).
In addition, the following control method and device are proposed. That is, a q-axis current instruction and a d-axis current instruction are set at a first q-axis current instruction value and a first d-axis current instruction value, a d-axis current step instruction having a predetermined height is given to the control device, voltage corresponding to voltage drop due to a primary resistance of an electric motor is subtracted from a d-axis voltage instruction value generated in response to a deviation of a d-axis current detection value with respect to the step instruction, the voltage value obtained by the subtraction is integrated over a predetermined first integral time to generate a d-axis integral value, a d-axis change amount of a d-axis current detection value at the integral end point with respect to the d-axis current detection value at the integral start point is generated, similar calculation is performed for q-axis to generate a q-axis integral value and a q-axis change amount, an inductance ratio K is defined as K=(q-axis integral value/d-axis integral value)×(d-axis change amount/q-axis change amount), and a q-axis inductance is calculated by expression Lq=K×Ld (for example, see Patent Document 2).
In addition, the following control device and method are proposed. That is, voltage for causing DC excitation is applied to an induction electric motor, the induction electric motor is maintained in a stopped state, a signal for slightly changing secondary magnetic flux due to the DC excitation by using a sine wave, a triangle wave, or a saw-tooth wave having a low frequency is superimposed onto a voltage instruction or a current instruction, and a mutual inductance is calculated based on a current detection value and a voltage instruction or a voltage detection value (for example, see Patent Document 3).