AC/DC unity power-factor DC power supply for operating an electric motor

• US 5,471,125 A
• Filed: 09/09/1994
• Issued: 11/28/1995
• Est. Priority Date: 09/09/1994
• Status: Expired due to Term

• Current Assignee: Danfoss Drives A/S (Danfoss A/S)
• Original Assignee: Danfoss A/S
• Inventors: Wu, Jian M.
• Primary Examiner(s): Martin, David S.
• Application Number:
  US08/303,373
• Time in Patent Office: 445 Days
• Field of Search: 318/757-762, 318/798-803, 318/806-811, 318/729
• US Class Current: 318/803
• CPC Class Codes: H02M 1/4233 using a bridge converter comprising active switches
• CPC Class Codes: H02P 23/06 Controlling the motor in four quadrants
• CPC Class Codes: Y02B 70/10 Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes

Abstract

A unity power factor power supply for an electric motor. A switch-mode circuit is employed which, in a first mode, transfers power from AC main to a constant voltage DC bus. In a second mode, power generated on the DC bus is fed back to the main power supply. The circuit of the invention automatically maintains the DC bus voltage constant and sets an adequate operation mode by processing the DC bus voltage signal. In both operation modes, the unity power factor and sinusoidal waveform of the AC main side are maintained.

Claims

1. A unit power-factor direct current power supply for the supply of an inverter which operates a three phase motor load, said power supply having a pwm-controlled power converter supplied from a three phase alternating current source and comprising self-commutated semiconductor switch devices for delivering an output DC voltage for the supply of the load connected thereto, said converter having a control circuit comprising a voltage regulator having an input supplied with a signal representing a voltage deviation between a DC reference voltage and the output DC voltage and an output fed to a first input of three modulators as a current reference value, each of said modulators having a second input being connected to a sinusoidal phase voltage signal derived from the three phase alternating current source, said modulators having outputs comprising current reference signals, said current reference signals being applied to a gate signal circuit which includes means to produce firing pulses for operating switch devices of the converter, and including a sequence circuit connected to said gate signal circuit, said sequence circuit including means to allow the converter to operate in a first mode and a second mode depending on control deviation of said voltage regulator, the sequence circuit in the first mode generating a first switch pattern for controlling the switch devices to operate in a motor mode, the sequence circuit in the second mode generating a second switch pattern for controlling the switches in a generating mode, whereby in both modes currents of the three phase alternating current source are substantially sinusoidal, but in the second mode in a phase opposite to that of the voltages of the alternating current source, said second switch pattern being generated when the output DC voltage tends to rise above the DC reference voltage.

2. A power supply according to claim 1 in which the output from said voltage regulator is connected to said sequence circuit.

3. A power supply according to claim 1 including interval generator means providing an input to said sequence circuit, said interval generator means dividing each phase of said alternating current source into six equal intervals.

4. A power supply according to claim 1 including a pulse amplifier for amplifying said firing pulses.

5. A power supply according to claim 1 including an output filter capacitor, said DC voltage being delivered to said capacitor from said converter.