Regenerative ac to dc converter

• US 5,449,993 A
• Filed: 06/07/1994
• Issued: 09/12/1995
• Est. Priority Date: 06/07/1994
• Status: Expired due to Term

• Current Assignee: Nidec S R Drives Ltd (Nidec Corporation)
• Original Assignee: Switched Reluctance Drives Limited (Nidec Corporation)
• Inventors: Davis, Rex M.
• Primary Examiner(s): Ro, Bentsu
• Application Number:
  US08/255,698
• Time in Patent Office: 462 Days
• Field of Search: 318/701, 318/254, 318/138, 318/439, 318/696, 318/376, 363/34, 363/39
• US Class Current: 318/701
• CPC Class Codes: H02M 3/158 including plural semiconductor devices as final control devices for a single load
• CPC Class Codes: H02M 5/45 using semiconductor devices only
• CPC Class Codes: H02P 3/065 for stopping or slowing a reluctance motor

Abstract

A regenerative ac to dc convertor includes a thyristor bridge invertor and a rectifier having a dc link capacitor. A second capacitor is connected across the invertor. In a regenerative braking mode of the motor the invertor is arranged to return energy from the second capacitor to the ac supply. Circulating currents are inhibited by diodes connecting the dc link and second capacitor. A first diode is arrange to conduct from the positive terminal of the second capacitor to the positive terminal of the dc link capacitor. A second diode is arranged so that it conducts from the negative terminal of the dc link capacitor to the negative terminal of the second capacitor.

Claims

1. A regenerative ac to dc convertor for a switched reluctance motor, the convertor comprising:

a rectifier having an ac input and a dc output arranged to derive a uni-directional voltage from the ac input;

a first capacitor, having a positive terminal and a negative terminal, which capacitor is connected across the dc output of the rectifier to smooth the direct voltage output;

an invertor, having ac terminals connected with the ac input of the rectifier and dc terminals;

a second capacitor also having a positive terminal and a negative terminal, which second capacitor is connected across the dc terminals of the invertor; and

diode means by which both of the positive terminals and both of the negative terminals of the first and second capacitors are respectively connected together, such that a voltage across the second capacitor can only exceed a voltage across the first capacitor by an amount sufficient to cause the diode means to conduct.

2. A convertor as claimed in claim 1 in which the diode means comprise a first diode, connected to conduct from the positive terminal of the second capacitor to the positive terminal of the first capacitor, and a second diode, connected to conduct from the negative terminal of the first capacitor to the negative terminal of the second capacitor.

3. A convertor as claimed in claim 1, including inductance means by which the dc terminals of the invertor are connected across the second capacitor.

4. A convertor as claimed in claim 3 in which the inductance means comprise first and second inductors each of which is respectively connected between the positive and negative terminals of the second capacitor and each of the dc terminals of the invertor.

5. A convertor as claimed in claim 3 in which the invertor is a three-phase thyristor bridge, having two thyristors per phase serially connected with the inductance means across the second capacitor.

6. A convertor as claimed in claim 1 in which the invertor consists of a thyristor bridge.

7. A convertor as claimed in claim 1 in which the rectifier is a bridge rectifier.

8. A convertor as claimed in claim 7 in which the rectifier is a three-phase bridge, having two serially connected diodes per phase.

9. A control system for a switched reluctance motor having one or more motor windings and being operable in a motoring or regenerative braking mode, the control system including a regenerative ac to dc convertor for a switched reluctance motor, the convertor comprising:

a rectifier having an ac input for the or each phase of the ac supply and a dc output arranged to derive a uni-directional voltage from the ac input;

a first capacitor, having a positive terminal and a negative terminal, which capacitor is connected across the dc output of the rectifier to smooth the direct voltage output;

an invertor, having ac terminals connected with the ac input of the rectifier and dc terminals;

a second capacitor also having a positive terminal and a negative terminal, which second capacitor is connected across the dc terminals of the invertor;

diode means by which both of the positive terminals and both of the negative terminals of the first and second capacitors are respectively connected together, such that a voltage across the second capacitor can only exceed a voltage across the first capacitor by an amount sufficient to cause the diode means to conduct; and

switch means operable to control the current in the or each motor winding, the invertor being operable in the regenerative braking mode to inhibit circulating currents by drawing current from the second capacitor and partially discharging it until the diode means become non-conducting and being further operable to maintain the voltage across the second capacitor at a level at which the diode means remain non-conducting in the regenerative braking mode.