Adjustable speed AC drive system control for operation in pulse

Details Adjustable speed AC drive system control for operation in pulse Adjustable speed AC drive system control for operation in pulse

1989-10-18

1990-05-15

Ro, Bentsu

Electricity: motive power systems

Positional servo systems

Pulse-width modulated power input to motor

318778, 318799, 318811, H02P 534

Patent

active

049261045

ABSTRACT:
A polyphase AC motor drive system comprises an electric power inverter and control means which enables operation in, and allows smooth transition between, a current controlled PWM mode and a quasi-square wave mode of operation. At low motor speeds, the system operates in PWM mode. At higher speeds, above the corner point speed of the motor, the system operates in a quasi-square wave mode. Smooth transitions between modes of operation are controlled by a microcomputer which counts the number of current chops made by a switching device in a preselected phase leg of the inverter over a time interval that varies with the desired fundamental period of the motor current. As speed increases and approaches the corner point, the number of chops decreases below a first predetermined number, and the system transitions from PWM to quasi-square wave mode. As speed decreases, the number of chops increases above a second predetermined number (larger than the first), and the system transitions back to PWM mode. A motor speed command is limited by an adjustable clamp circuit, depending upon the DC link voltage, resulting in a robust drive that is not affected by utility brownouts or line transients.

REFERENCES:
patent: 4327240 (1982-04-01), Gdula et al.
patent: 4777578 (1988-10-01), Jahns

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