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Three-phase electronic inverter for variable speed motor

  • US 5,489,833 A
  • Filed: 05/31/1994
  • Issued: 02/06/1996
  • Est. Priority Date: 05/31/1993
  • Status: Expired due to Fees
First Claim
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1. A three-phase electronic inverter for driving a three-phase electric motor, comprising:

  • a direct current source connected to an alternating current network and having a positive and a negative terminal, a first rectifier bridge provided with said positive and negative terminals, a first TRIAC in circuit with said network and said first rectifier bridge, and a first optical coupler connected to a gate of said first TRIAC for controlling a voltage across said positive and negative terminal;

    a power transistor bridge provided with three arms, each of said arms having a pair of MOSFET or IGBT power transistors with series connected source-drain paths bridged between said positive terminal and said negative terminal of said direct current source;

    respective diodes connected across said source-drain paths;

    an output terminal tapped between the source-drain paths of each arm and connected to a respective winding terminal of a three-phase electric motor;

    means including a second rectifier bridge for deriving a low direct voltage from said network;

    control means receiving said low direct voltage and including a respective second TRIAC connected to a gate of one respective power transistor of each arm, and a respective second optical coupler connected to a gate of each second TRIAC for generating control pulses and applying said control pulses to gates of said power transistors in a cadence to produce across said windings square wave signals of alternating polarity and substantially 120°

    offset in phase from winding to winding; and

    means operable independently of the generation of said pulses, for triggering said first optical coupler and controlling a voltage level outputted by said source to increase said voltage level substantially linearly with increase in the frequency of said cadence and a speed of said motor determined by frequency of said square wave signals.

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