Commutation circuits for thyristor inverters

• US 4,405,977 A
• Filed: 08/26/1981
• Issued: 09/20/1983
• Est. Priority Date: 09/25/1980
• Status: Expired due to Fees

• Current Assignee: Concordia University
• Original Assignee: Canadian Patents and Development Limited
• Inventors: Bhagwat, Pradeep M., Stefanovic, Victor R.
• Primary Examiner(s): Shoop, William M.
• Assistant Examiner(s): Wong, Peter S.
• Application Number:
  US06/296,296
• Time in Patent Office: 755 Days
• Field of Search: 363/57-58, 363/96, 363/124, 363/135-139, 307/252 C, 307/252 M
• US Class Current: 363/124
• CPC Class Codes: H02M 7/5236 in a series push-pull arrangement

Abstract

The commutation circuit for commutating a conducting thyristor includes an inductance, a capacitance and a commutation thyristor all connected in series with the conducting thyristor and the dc source, the commutation thyristor initiates the commutation when triggered. The circuit further includes a first diode connected in reverse polarity across the commutation thyristor and a second diode connected in reverse polarity across the commutation thyristor-capacitance series circuit. The voltage across the capacitance is zero when each commutation cycle is initiated, and also when each commutation cycle ends.

Claims

1. In a thyristor circuit for applying a dc voltage through a thyristor to a load, a commutation circuit for the thyristor comprising:

inductance means, normally discharged capacitance means and a commutation thyristor connected in series with said thyristor;

a first diode connected in reverse polarity across the commutation thyristor; and

a second diode connected in reverse polarity across the series connected capacitance means and commutation thyristor.

2. A commutation circuit as claimed in claim 1 which includes a third diode connected in reverse polarity across said thyristor.

3. In an inverter circuit having at least a pair of first and second thyristors connected in series across a dc source with a first juncture between the first and second thyristors for connection to a load, a thyristor commutation circuit comprising:

a pair of series connected first and second commutation thyristors connected in parallel with the first and second thyristors;

a diode connected in reverse polarity across each of the first and second thyristors and the first and second commutation thyristors;

normally discharged first capacitance means connected to a second juncture between the first and second commutation thyristors and the first juncture; and

first inductance means series connected between the dc source and the pairs of thyristors.

4. A commutation circuit as claimed in claim 3 which further includes an ac switch and resistance means connected across the capacitance means for discharging the capacitance means.

5. A commutation circuit as claimed in claim 3 which further includes filter capacitance means connected across the dc source.

6. A commutation circuit as claimed in claim 5 which further includes:

a second inductance means connected between the dc source and the first inductance means;

a diode connected in reverse polarity across the second inductance means; and

second capacitance means connected in series with the second inductance means across the dc source.

7. A commutation circuit as claimed in claim 4, 5, or 6 wherein the first inductance means is a single inductor connected between the dc source and the pairs of thyristors.

8. A commutation circuit as claimed in claim 4, 5, or 6 wherein the first inductance means includes a first inductor connected between the dc source and the pairs of thyristors, and a second inductor connected in series with the capacitance means between the first and second junctures.

9. A commutation circuit as claimed in claim 4, 5, or 6 wherein the first inductance means consists of an inductor connected directly to each of the thyristors.

10. In an inverter circuit having at least a pair of inverter thyristors connected in series across a variable dc source with a first juncture between the inverter thyristors for connection to a load, a thyristor commutation circuit comprising:

a series circuit having a first blocking diode, a fixed dc source and a second blocking diode connected across the series connected inverter thyristors;

a pair of series connected commutation thyristors and a pair of series connected auxiliary thyristors connected in parallel across the fixed dc source, the juncture between the auxiliary thyristors being connected to the first juncture;

a diode connected in reverse polarity across each of the pair of inverter thyristors and the pair of commutation thyristors;

first capacitance means connected to a juncture between the commutation thyristors and the first juncture; and

first inductance means series connected between the fixed dc source and the pairs of commutation and auxiliary thyristors.

11. A commutation circuit as claimed in claim 10 which further includes an ac switch and resistance means connected across the capacitance means for discharging the capacitance means.