Operation control apparatus for AC motors

• US 4,319,177 A
• Filed: 08/08/1980
• Issued: 03/09/1982
• Est. Priority Date: 08/15/1979
• Status: Expired due to Term

• Current Assignee: Fujitsu Limited
• Original Assignee: Fujitsu Limited
• Inventors: Ishida, Hiroshi, Kawada, Shigeki
• Primary Examiner(s): Smith, Jr., David
• Application Number:
  US06/176,337
• Time in Patent Office: 578 Days
• Field of Search: 318/798, 318/762, 318/806, 318/803, 318/808-811, 318/376, 363/56, 363/57
• US Class Current: 318/798
• CPC Class Codes: H02P 23/06 Controlling the motor in four quadrants
• CPC Class Codes: H02P 3/18 for stopping or slowing an ac motor

Abstract

An apparatus for controlling the operation of an AC motor wherein braking energy at the time of a reduction in motor speed is disposed of by regenerative braking. The apparatus includes a rectifier which is connected to the AC power source, a DC link which includes smoothing capacitors and a regenerative transistor bridge circuit, a variable voltage-variable frequency inverter. Further provided are a diode which is connected between the rectifier and the transistor bridge circuit and which is biased in the reverse direction at the time of regenerative braking, and a firing control circuit for detecting the reverse bias voltage of the diode to control the firing of each transistor in the transistor bridge circuit, the braking energy being fed back to the AC power source when the AC motor undergoes a reduction in speed. The apparatus, which provides stable regenerative operation, can be constructed simply and inexpensively, and reduced in size.

Claims

1. An apparatus for controlling the operation of an AC motor, which apparatus comprises:

a rectifier connected to an AC power source for converting alternating current into direct current;

a variable voltage-variable frequency inverter for applying drive signals to the AC motor upon receiving the direct current output of said rectifier, the supply voltage and frequency of said drive signals being varied in accordance with an externally applied command;

a transistor bridge circuit for regenerative action connected between said inverter and said rectifier, and comprising a plurality of transistors connected in the form of a bridge;

a smoothing capacitor connected between said transistor bridge circuit and said inverter;

a diode provided between said rectifier and said transistor bridge circuit and connected to a reverse biasing polarity when the AC motor operates in the regenerative braking region; and

a firing control circuit for detecting the reverse bias voltage of said diode thereby to control the firing of each transistor in said transistor bridge circuit;

braking energy being fed back to the AC power source side.

2. An apparatus for controlling the operation of an AC motor as claimed in claim 1, in which said firing control circuit controls the firing of said transistors of the regenerative transistor bridge circuit in accordance with the regenerative current in said regenerative transistor bridge circuit.

3. An apparatus for controlling the operation of an AC motor as claimed in claim 1, in which said firing control circuit includes a circuit for generating a plurality of firing control signals for controlling respective transistors of said regenerative transistor bridge circuit, and a circuit for supplying said firing control signals to respective transistors of said regenerative transistor bridge circuit in accordance with the reverse bias voltage of said diode.

4. An apparatus for controlling the operation of an AC motor as claimed in claim 3, wherein said circuit for generating said firing control signals is adapted to generate a firing control signal for simultaneously firing a pair of transistors of said regenerative transistor bridge circuit, said pair of transistors being connected to two phases of the maximum interphase voltage from said AC power source.

5. An apparatus for controlling the operation of an AC motor as claimed in claim 3, wherein said firing control circuit includes a circuit for comparing said reverse bias voltage of said diode with a reference voltage, and wherein said circuit for supplying said firing control signals is adapted to supply said firing control signal upon receipt of the output from said circuit for generating said firing control signal and the output from the comparator circuit.

6. An apparatus for controlling the operation of an AC motor as claimed in claim 3, wherein said firing control circuit further includes a comparator circuit adapted to compare said regenerative current in said regenerative transistor bridge circuit with a reference current, the output from said comparator circuit constituting the control input for said circuit for supplying the firing control signal.

7. An apparatus for controlling the operation of an AC motor as claimed in claim 3, wherein said firing control signal forms a six-phase firing control signal upon receipt of three-phase AC power from said AC power source.

8. An apparatus for controlling the operation of an AC motor as claimed in claim 6, wherein said circuit for supplying said firing control signals includes a gate circuit for producing the product of the output from said circuit for generating said firing control signals and the output from said comparator circuit, and flip-flop circuit adapted to hold the output of said gate circuit, said flip-flop circuit being adapted to be reset by the output from the current comparator circuit.

9. An apparatus for controlling the operation of an AC motor as claimed in claim 8, wherein said gate circuit and said flip-flop circuit are arranged in plural, the number of which corresponding to the number of said firing control signals.