Commutation circuit for load-commutated inverter induction motor drives

• US 4,847,747 A
• Filed: 09/26/1988
• Issued: 07/11/1989
• Est. Priority Date: 09/26/1988
• Status: Expired due to Fees

• Current Assignee: Westinghouse Electric Corporation (Paramount Global (f/k/a ViacomCBS Inc.))
• Original Assignee: Westinghouse Electric Corporation (Paramount Global (f/k/a ViacomCBS Inc.))
• Inventors: Abbondanti, Alberto
• Primary Examiner(s): Wong, Peter S.
• Application Number:
  US07/249,527
• Time in Patent Office: 288 Days
• Field of Search: 363/35, 363/37, 363/40, 363/96, 363/135, 363/136, 363/137, 363/138, 318/800, 318/801, 318/802, 318/803, 318/806-812, 318/510, 318/512
• US Class Current: 363/138
• CPC Class Codes: H02M 7/5152 with separate extinguishing means
• CPC Class Codes: Y10S 174/16 in a motive power system, e.g. electric motor control system

Abstract

In a load commutated inverter induction motor drive a parallel capacitor bank is used in part to force-commutate the thyristors of the inverter as triggered by auxiliary thyristors and turned off by the other part of the capacitor bank.

Claims

1. In a load commutated inverter induction motor (LCI/IM) drive including an AC power supply, a converter for rectifying said power supply and outputting between two DC terminals, a thyristor bridge inverter for applying an AC voltage on input lines to the motor, a DC-link between said converter and said inverter, with the inverter bridge being mounted across said DC terminals, and a capacitor bank in parallel with the induction motor for providing a leading power factor;

the combination of;

forced-commutation means interposed between said DC terminals and the input lines of the motor;

said forced-commutation means being actuated at low speed in relation to the oncoming and the offgoing thyristor of said bridge related to one DC terminal polarity;

said forced-commutation means being turned off by said parallel capacitor bank; and

said forced-commutation means including auxiliary capacitor means operative for forced-commutation at low speed and operative with said parallel capacitor bank above low speed in providing said leading power factor.

2. The LCI/IM drive of claim 1 with said forced-commutation means including inductor means cooperating with said auxiliary capacitor means in forcing said offgoing thyristor to recover.

3. The LCI/IM drive of claim 2 with said forced-commutation means including switching means for discharging said auxiliary capacitor means through said inductor means and through said offgoing thyristor.

4. The LCI/IM drive of claim 3 with said induction motor being a three-phase motor, said auxiliary capacitors being wye-connected across said motor input lines with a node point therebetween, said switching means including two auxiliary switches operatively connected between said node point and a corresponding one of said DC terminals.

5. The LCI/IM drive of claim 4 with said capacitor bank being delta-connected.

6. The LCI/IM drive of claim 4 with said capacitor bank being wye-connected.

7. The LCI/IM drive of claim 4 with said inductor means being inductors inserted on said input lines for thyristor protection.

8. The LCI/IM drive of claim 4 with said auxiliary switches being alternately gated upon the occurrence of a thyristor which is next in the bridge firing sequence.