Patent ID: 11870384
Assignee: HITACHI INDUSTRIAL EQUIPMENT SYSTEMS CO., LTD.
Field: Electrical machinery, apparatus, energy (Electrical engineering)
Classification: CPC G  H | IPC H

Claim 13:
14. A power conversion device comprising:
an inverter for converting DC voltage into AC voltage and supplying the same AC voltage to a motor;
a speed calculation unit for calculating the speed of the motor from output pulses obtained from an encoder connected to the motor; and
a control unit for receiving the speed from the speed calculation unit and controlling the inverter,
wherein the speed calculation unit:
measures the duty cycle during constant speed of the output pulses;
measures a first half cycle of the output pulse to calculate the motor speed by first calculation using the duty cycle during constant speed with respect to the first half cycle; and
measures a second half cycle of the output pulse to calculate the motor speed by second calculation using the duty cycle during constant speed with respect to the second half cycle;
wherein the first half cycle T1 that is the half cycle from first transition to second transition of the output pulse is measured,
wherein the second half cycle T2 that is the half cycle from the second transition to the first transition of the output pulse is measured, and
wherein the first calculation or the second calculation is applied to the half cycle whose measurement is ended most recently, and the most recent motor speed is calculated,
wherein the first calculation is N=60/((T1×100/D)×p)[rpm], and the second calculation is N=60/((T2×100/(100−D))×p)[rpm], where N is the rotation number (rpm) of the motor, D is the duty cycle during constant speed (%), the T1 is the length of the first half cycle (sec), the T2 is the length of the second half cycle (sec), and p is the number of pulses [ppr] generated by the encoder per revolution of the motor.