System and method for starting a variable frequency drive with reduced arc flash risk

Patent metadata

Field	Value
Publication number	US-9680388-B2
Application number	US-201514870269-A
Country	US
Kind code	B2
Filing date	Sep 30, 2015
Priority date	Sep 30, 2015
Publication date	Jun 13, 2017
Grant date	Jun 13, 2017

Abstract

In one embodiment, a variable frequency drive system includes a main contactor, a variable frequency drive, a charging module structured to generate a magnetizing AC voltage, wherein the charging module is structured to selectively provide the magnetizing AC voltage to a transformer of the variable frequency drive, and a sensing and control circuit having a number of sensors operably associated with the variable frequency drive. The sensing and control circuit is structured to detect a short circuit condition in the variable frequency drive when the magnetizing AC voltage is provided to the transformer based on an output of at least one of the number of sensors, and responsive thereto prevent the main contactor from being closed and thereby prevent the main AC voltage from being provided to the transformer.

First claim

What is claimed is:

1. A variable frequency drive system, comprising:
a main contactor;
a variable frequency drive including:
a transformer selectively connectable to an AC source that provides a main AC voltage through the main contactor, the transformer having a number of sets of primary windings and a number of sets of secondary windings;
a converter coupled to the number of sets of secondary windings;
a DC link coupled to an output of the converter; and
an inverter coupled to the DC link;

a charging module structured to generate a magnetizing AC voltage, wherein the charging module is structured to selectively provide the magnetizing AC voltage to the transformer, wherein the charging module is structured to be selectively coupled to the AC source and generate the magnetizing AC voltage in response to receiving the main AC voltage; and
a sensing and control circuit having a number of sensors operably associated with at least one of the transformer, the converter, and the DC link, the sensing and control circuit being structured to detect a short circuit condition in the variable frequency drive when the magnetizing AC voltage is provided to the transformer based on an output of at least one of the number of sensors, and responsive thereto prevent the main contactor from being closed and thereby prevent the main AC voltage from being provided to the transformer.

2. The variable frequency drive according to claim 1 , wherein the magnetizing AC voltage is such that responsive to the magnetizing AC voltage being provided to the transformer, one or more of the number of sets of primary windings will be magnetized in a manner wherein a flux of the one or more of the number of primary windings is in phase with the main AC voltage provided from the AC source.

3. The variable frequency drive according to claim 1 , wherein each of the number of sensors is a voltage sensor.

4. A variable frequency drive system, comprising:
a main contactor;
a variable frequency drive including;
a transformer selectively connectable to an AC source that provides a main AC voltage through the main contactor, the transformer having a number of sets of primary windings and a number of sets of secondary windings;
a converter coupled to the number of sets of secondary windings:
a DC link coupled to an output of the converter; and
an inverter coupled to the DC link:

a charging module structured to generate a magnetizing AC voltage, wherein the charging module is structured to selectively provide the magnetizing AC voltage to the transformer; and
a sensing and control circuit having a number of sensors operably associated with at least one of the transformer, the converter, and the DC link, the sensing and control circuit being structured to detect a short circuit condition in the variable frequency drive when the magnetizing AC voltage is provided to the transformer based on an output of at least one of the number of sensors, and responsive thereto prevent the main contactor from being closed and thereby prevent the main AC voltage from being provided to the transformer, wherein each of the number of sensors is a voltage sensor, and wherein the number of sensors includes a number of first voltage sensors coupled to a terminal of one or more capacitors of the DC link.

5. The variable frequency drive according to claim 3 , wherein the number of sensors includes a number of first voltage sensors coupled to the number of sets of primary windings, a number of second voltage sensors coupled to an input of one or more rectifier bridges of the converter, and a number of third voltage sensors coupled to a terminal of one or more capacitors of the DC link.

6. The variable frequency drive system according to claim 4 , wherein the charging module is structured to be selectively coupled to the AC source and generate the magnetizing AC voltage in response to receiving the main AC voltage.

7. The variable frequency drive system according to claim 1 , wherein the charging module comprises an auxiliary transformer having a number of sets of auxiliary primary windings and a number of sets of auxiliary secondary windings, wherein one of the number of sets of auxiliary secondary windings is structured to be selectively coupled to the transformer.

8. The variable frequency drive system according to claim 7 , wherein the one of the number of sets of auxiliary secondary windings is structured to be selectively coupled to one of the transformer through an auxiliary contactor.

9. The variable frequency drive system according to claim 8 , wherein the variable frequency drive system includes a main power stage path including the main contactor, the transformer, the converter, and the DC link, the main power stage path having a first impedance, and wherein the variable frequency drive system includes an auxiliary stage path including a fuse, the auxiliary transformer, and the auxiliary contactor, the auxiliary stage path having a second impedance, wherein responsive to the short circuit condition the second impedance is greater than the first impedance.

10. A method of starting a variable frequency drive, the variable frequency drive including a transformer structured to be selectively coupled to an AC source that provides a main AC voltage, the transformer having a number of sets of primary windings, the method comprising:
generating a magnetizing AC voltage when the transformer is not coupled to the AC source;
providing the magnetizing AC voltage to the transformer when the transformer is not coupled to the AC source to magnetize one or more of the number of sets of primary windings;
determining whether a short circuit condition exists in the variable frequency drive when the magnetizing AC voltage is being provided to the transformer and the main AC voltage is not being provided to the transformer;
responsive to determining that a short circuit condition does exist in the variable frequency drive, preventing the main AC voltage from being provided to the transformer; and
responsive to determining that a short circuit condition does not exist in the variable frequency drive, providing the main AC voltage to the transformer and terminating the providing of the magnetizing AC voltage to the transformer, wherein the generating the magnetizing AC voltage comprises providing the main voltage to a set of primary windings of an auxiliary transformer, and wherein the providing the magnetizing AC voltage comprises coupling a set of secondary windings of the auxiliary transformer to the transformer when the transformer is not coupled to the AC source.

11. The method according to claim 10 , wherein the providing the magnetizing AC voltage to the transformer when the transformer is not coupled to the AC source to magnetize one or more of the number of sets of primary windings is in a manner wherein a flux of the one or more of the number of primary windings is in phase with the main AC voltage.

12. The method according to claim 10 , wherein the terminating the providing of the magnetizing AC voltage is performed before or after the providing of the main AC voltage to the transformer.

13. A method of starting a variable frequency drive, the variable frequency drive including a transformer structured to be selectively coupled to an AC source that provides a main AC voltage, the transformer having a number of sets of primary windings, the method comprising:
generating a magnetizing AC voltage when the transformer is not coupled to the AC source,
providing the magnetizing AC voltage to the transformer when the transformer is not coupled to the AC source to magnetize one or more of the number of sets of primary w

Assignees

• Eaton Corp

Inventors

• Simms Stan Rex
• Gibbs Irving Albert

Classifications

• H02M5/42 Primary

  by static converters · CPC title

• H02M1/32 Primary

  Means for protecting converters other than automatic disconnection · CPC title

• H02M5/45

  using semiconductor devices only · CPC title

• H02H11/005

  in case of too low isolation resistance, too high load, short-circuit; earth fault · CPC title