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

Claim 3:
4. A power conversion device comprising:
an inverter for converting DC voltage into AC voltage and supplying the AC voltage to a motor;
a motor speed calculation unit for calculating a speed of the motor from output pulses obtained from an encoder connected to the motor based on a motor speed instruction; and
a control unit for outputting the motor speed instruction to the motor speed calculation unit receiving the motor speed from the motor speed calculation unit and controlling the inverter,
wherein the motor speed calculation unit:
measures a duty ratio of a time of a half cycle from a rising edge to a falling edge of the output pulses to a time of a full cycle between rising edges of the output pulses;
outputs a duty measurement-in-progress signal to the control unit while the duty ratio is being measured;
calculates the speed using the half cycles of the output pulses if the duty ratio is within a prescribed range from 50%;
calculates the speed using the full cycles of the output pulses if the duty ratio is outside of the prescribed range from 50%; and
wherein the control unit fixes the motor speed instruction to a most recently determined value while the duty measurement-in-progress signal is being outputted.