Method and arrangement for controlling an induction motor
First Claim
1. A method of controlling a three-phase induction motor driven by an inverter supplied with full-wave rectified mains alternating voltage to provide the respective phases (R, S, T) of the motor with drive voltages consisting of mainly square-shaped, in relation to a virtual zero reference level, positive and negative half periods which alternate at a fixed or adjustable drive frequency corresponding to the required speed, said method comprising the steps of:
- providing a signal (UM) which represents the variations in amplitude in the full-wave rectified mains alternating voltage, andmodulating said drive frequency with said signal (UM), said drive frequency increasing as said full wave rectified voltage increases, said drive frequency decreasing as said full wave rectified voltage decreases, the slippage losses in the motor thereby being minimized.
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Abstract
A device for controlling a three-phase induction motor that is driven by an inverter connection. The inverter is furnished to be fed with full-wave rectified grid alternating voltage (U) and supply the motor'"'"'s various phases (R, S, T) with the drive voltages phase-displaced in the normal way and which consist of mainly square, in relation to a virtual zero reference level, positive and negative half-periods which alternate at a fixed or adjustable drive frequency corresponding to the required speed. The full-wave rectified grid alternating voltage (U) supplied to the inverter is arranged to be supplied to respective motor phase (R, S, T) via an electronic switch connection (TR1H, TR1L ; TR2H, TR2L ; TR3H, TR3L) whose respective on and off periods are determined by the drive frequency which is generated by an oscillator device (15; 25). The last mentioned is arranged to be supplied with a voltage (Um) which directly or indirectly represents the rectified grid alternating voltage (U) for the purpose of modulating the drive frequency with a signal that represents the variations in amplitude of the rectified grid alternating voltage. The invention also comprises a method of controlling an induction motor of the type specified.
21 Citations
12 Claims
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1. A method of controlling a three-phase induction motor driven by an inverter supplied with full-wave rectified mains alternating voltage to provide the respective phases (R, S, T) of the motor with drive voltages consisting of mainly square-shaped, in relation to a virtual zero reference level, positive and negative half periods which alternate at a fixed or adjustable drive frequency corresponding to the required speed, said method comprising the steps of:
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providing a signal (UM) which represents the variations in amplitude in the full-wave rectified mains alternating voltage, and modulating said drive frequency with said signal (UM), said drive frequency increasing as said full wave rectified voltage increases, said drive frequency decreasing as said full wave rectified voltage decreases, the slippage losses in the motor thereby being minimized. - View Dependent Claims (2, 3)
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4. A device for controlling a three-phase induction motor, comprising an inverter, rectifying means connected to a mains AC network and supplying a full-wave rectified unsmoothed alternating voltage (U) to the inverter, said inverter providing to the respective phases (R, S, T) of the motor drive voltages which are mutually phase displaced 120°
- and consist of mainly square-shaped, in relation to a virtual zero reference level, positive and negative half periods which alternate at a fixed or variable drive frequency corresponding to the required speed, wherein the full-wave rectified mains alternating voltage (U) supplied to the inverter is also supplied to the respective motor phase (R, S, T) via an electronic switch coupling (TR1H, TR1L ;
TR2H, TR2L ;
TR3H, TR3L) the on and off periods of which, respectively, being determined by the drive frequency which is generated by an oscillator device (15;
25), said oscillator device having an input on which is applied a voltage (UM) which represents the rectified mains alternating voltage (U), said voltage (UM) applied to the oscillator device operating as a modulating signal superimposing on the drive frequency a signal representing said variations in amplitude of the rectified mains alternating voltage, said drive frequency increasing as said full wave rectified voltage increases, said drive frequency decreasing as said full wave rectified voltage decreases, the slippage losses in the motor thereby being minimized. - View Dependent Claims (5, 6, 7, 8, 9, 10, 11, 12)
- and consist of mainly square-shaped, in relation to a virtual zero reference level, positive and negative half periods which alternate at a fixed or variable drive frequency corresponding to the required speed, wherein the full-wave rectified mains alternating voltage (U) supplied to the inverter is also supplied to the respective motor phase (R, S, T) via an electronic switch coupling (TR1H, TR1L ;
Specification