CONTROL SYSTEM FOR AN ALTERNATING CURRENT MOTOR

• US 3,700,989 A
• Filed: 03/31/1971
• Issued: 10/24/1972
• Est. Priority Date: 03/16/1968
• Status: Expired due to Term

• Current Assignee: Arne Jensen
• Original Assignee: Arne Jensen
• Inventors: Jensen, Arne
• Primary Examiner(s): Rubinson, Gene Z.
• Application Number:
  US05/129,966
• Time in Patent Office: 573 Days
• Field of Search: 318/227,230,231
• US Class Current: 318/798
• CPC Class Codes: H02P 27/047 V/F converter, wherein the voltage is controlled proportionally with the frequency
• CPC Class Codes: H02P 27/08 with pulse width modulation

Abstract

The invention relates to a control system for an alternating current motor such as a polyphase induction motor. The control system includes a DC to AC inverter in combination with voltage and frequency regulators with the voltage and frequency being dependent upon each other. Control means are provided which sense the inverter current and translate the data sensed into two voltages which are separately subtracted from the output of the voltage regulator to provide two corrected voltages for regulating the voltage regulator and the frequency regulator.

Claims

1. A control system for an alternating current motor such as a polyphase induction motor, the system comprising a voltage regulator for supplying a variable output voltage, an inverter for deriving from said output voltage an output alternating current for supply to said motor, a frequency regulator for controlling the frequency of operation of said inverter, first means to derive a first Voltage value in dependence upon the current supplied by said inverter to said motor, means for subtracting said first voltage value from the output voltage of said voltage regulator to obtain a first corrected voltage value which is used for regulating the output voltage of the voltage regulator, means to derive a second voltage value in dependence upon the current supplied by said inverter to said motor, and means for subtracting said second voltage value from the output voltage of the voltage regulator to obtain a second corrected voltage value which is used for regulating at the frequency of operation of said inverter.

2. A control system according to claim 1 further comprising an inductor connected in series with said motor so that in operation the current supplied by said inverter to said motor flows also in said inductor, rectifier means connected to said inductor, and a resistor connected to said rectifier means whereby the voltage developed across said resistor is dependent on the current flowing in said inductor, said first and second voltage values being derived from respective tappings on said resistor.

3. A control system according to claim 1 wherein said rectifier means is a bridge rectifier having two pairs of opposite terminals, one terminal being connected to said resistor, the opposite terminal being connected to said inductor, and the other two opposite terminals being connected by way of respective inductors to respective input terminals across which in operation is supplied an alternating current of constant amplitude, said respective inductors being coupled to said first-mentioned inductor.