DC PRE-CHARGE CIRCUIT

• US 20130121051A1
• Filed: 07/13/2012
• Published: 05/16/2013
• Est. Priority Date: 11/14/2011
• Status: Active Grant

• Current Assignee: Rockwell Automation Technologies Incorporated (Allen-Bradley Co., Inc.)
• Original Assignee: Rockwell Automation Technologies Incorporated (Allen-Bradley Co., Inc.)
• Inventors: Weiss, Bruce W., Busse, Doyle F., Keegan, Jeremy J., Wei, Lixiang, Loth, Michael W., Tallam, Rangarajan M., Patel, Yogesh
• Granted Patent: US 9,042,146 B2
• Time in Patent Office: Days
• US Class Current: 363/131
• CPC Class Codes: H02H 7/09 against over-voltage; against reduction of voltage; against phase interruption
• CPC Class Codes: H02M 7/48 using discharge tubes with control electrode or semiconductor devices with control electrode
• CPC Class Codes: H02M 7/537 using semiconductor devices only, e.g. single switched pulse inverters
• CPC Class Codes: H02P 6/20 Arrangements for starting H02P6/08 takes precedence
• CPC Class Codes: H02P 6/28 Arrangements for controlling current H02P6/10 takes precedence

Abstract

Systems and methods are provided for pre-charging the DC bus on a motor drive. Pre-charging techniques involve pre-charge circuitry including a manual switch, an automatic switch, and pre-charge control circuitry to switch the automatic switch between pre-charge and pre-charge bypass modes in response to an initialized pre-charge operation, input voltage sags, and so forth. In some embodiments, the pre-charge operation may be initialized by switching the manual switch closed. In some embodiments, the pre-charge operation may also be initialized by a detected voltage sag on the DC bus. The pre-charge circuitry may also be configured to disconnect to isolate a motor drive from the common DC bus under certain fault conditions.

Claims

1. A power system, comprising:

at least one inverter module, wherein the at least one inverter module comprises;

an inverter circuit configured to connect to a direct current (DC) bus;

a capacitive circuit configured to couple across the DC bus; and

a pre-charge circuit configured to charge the capacitive circuit, wherein the pre-charge circuit comprises;

at least one pre-charge resistor;

at least one manual switch configured to connect the at least one pre-charge resistor to the DC bus when closed and disconnect the at least one pre-charge resistor from the DC bus when open;

at least one automatic switch on the DC bus; and

pre-charge control circuitry configured to detect a state of the at least one manual switch and configured to open and close the at least one automatic switch.

2. The power system of claim 1, wherein the pre-charge control circuitry is configured to apply a pre-charge current through the at least one pre-charge resistor when a voltage of the DC bus is below a threshold.

3. The power system of claim 1, wherein the pre-charge control circuitry is configured to open the at least one automatic switch when a voltage of the DC bus is below a threshold.

4. The power system of claim 3, wherein the pre-charge control circuitry is configured to provide an indication to open the at least one manual switch when the voltage is below the threshold.

5. The power system of claim 4, wherein the at least one opened automatic switch and the at least one opened manual switch isolates the at least one inverter module from the power system.

6. The power system of claim 1, wherein the pre-charge circuit comprises at least one contactor configured to connect in series between the at least one manual switch and the at least one pre-charge resistor.

7. The power system of claim 6, wherein the pre-charge control circuitry is configured to open the at least one contactor when a voltage of the DC bus is below a threshold.

8. The power system of claim 1, wherein the pre-charge control circuitry is configured to control a flow of current through the at least one pre-charge resistor for a period of time to sufficiently charge the capacitive circuit to a threshold.

9. The power system of claim 1, wherein the at least one automatic switch comprises at least one motorized molded case switch.

10. The power system of claim 1, wherein the pre-charge circuit comprises at least one under-voltage delay element connected to the at least one automatic switch, wherein the at least one under-voltage delay element is configured to hold a threshold operating voltage on the DC bus for a period of time after a voltage in the DC bus is below the threshold operating voltage.

11. The power system of claim 1, wherein the pre-charge circuit comprises at least one contactor configured to connect to the at least one automatic switch, wherein the at least one contactor is configured to open based on a control signal from the pre-charge control circuitry when a voltage in the DC bus is below a threshold.

12. The power system of claim 1, comprising at least one fuse connected on the DC bus, wherein the at least one fuse is configured to interrupt current flow over the DC bus to the at least one automatic switch during a short circuit condition of the at least one inverter module.

13. A method, comprising:

receiving a first signal indicating that a manual switch is closed, wherein the closed manual switch is configured to couple a DC source in series with a resistor and an internal DC bus, wherein the DC source is coupled to a plurality of inverter modules, each inverter module comprises an inverter circuit, the internal DC bus coupled to the inverter circuit, and a capacitive circuit coupled across the internal DC bus;

automatically closing an automatic switch coupled between the DC source and the internal DC bus when the capacitive circuit has a voltage above a threshold.

14. The method of claim 13, comprising automatically opening the automatic switch when a fault condition is present on at least one of the plurality of inverter modules.

15. The method of claim 13, wherein the first signal indicates that a plurality of switches is closed, wherein each of the plurality of switches is coupled to a respective internal DC bus in each of the plurality of inverter modules.

16. The method of claim 13, wherein the first signal indicates that one manual switch coupled to each respective inverter module in the plurality of inverter modules is closed.

17. The method of claim 13, comprising operating the inverter circuit after the automatic switch is closed.

18. The method of claim 13, comprising disabling the inverter circuit when a fault condition is present on at least one of the plurality of inverter modules.

19. The method of claim 18, wherein the fault condition comprises one or more of a significant voltage drop in the internal DC bus, an opening of the manual switch while the inverter circuit is in operation, or any combination thereof.

20. The method of claim 13, comprising automatically opening a contactor coupled in series with the resistor when a fault condition is present on at least one of the plurality of inverter modules.

21. The method of claim 13, comprising automatically opening a contactor coupled in series with the first switch when a fault condition is present on at least one of the plurality of inverter modules.

22. The method of claim 13, comprising receiving a second signal that the manual switch has been opened after a fault condition present on at least one of the plurality of inverter modules has been removed to reset faults of a respective inverter module in which the fault condition is detected.

23. An inverter module comprising:

a power converter coupled to a first direct current (DC) bus and configured to convert DC power from the first DC bus to AC output power;

a first switch coupled between the first DC bus and a common DC bus;

a capacitive circuit coupled across the first DC bus;

a second switch configured to couple a resistor in series with the common DC bus and the first DC bus when closed; and

control circuitry configured to automatically close the first switch when a voltage of the capacitive circuit is above a first threshold.

24. The inverter module of claim 23, wherein the control circuitry is configured to automatically open the first switch when a voltage of the first DC bus is below a second threshold.

25. The inverter module of claim 24, wherein the control circuitry is configured to automatically close the first switch when the first DC bus is above the second threshold.

26. The inverter module of claim 23, comprising power converter drive circuitry configured to substantially control the power converter, wherein the power converter drive circuitry is configured to disable the power converter upon the detection of a fault condition.