Digital control method for operating UPS systems in parallel

• US 9,373,979 B2
• Filed: 10/07/2013
• Issued: 06/21/2016
• Est. Priority Date: 05/14/2010
• Status: Active Grant

• Current Assignee: Schneider Electric IT Corporation (Schneider Electric SE)
• Original Assignee: Schneider Electric IT Corporation (Schneider Electric SE)
• Inventors: Ghosh, Rajesh, Agrawal, Mahima, Tolakanahalli, Pradeep, Klikic, Damir
• Primary Examiner(s): Amaya, Carlos
• Application Number:
  US14/047,109
• Publication Number:
  US 20140103725A1
• Time in Patent Office: 988 Days
• Field of Search: 307/64, 307/65, 307/66
• US Class Current: 1/1
• CPC Class Codes: H02J 9/061 for DC powered loads
• CPC Class Codes: H02J 9/062 for AC powered loads
• CPC Class Codes: H02M 7/493 the static converters being arranged for operation in parallel

Abstract

Systems and methods of operating uninterruptible power supplies in parallel in a power distribution system to provide power to a load are provided. At least one uninterruptible power supply inverter provides power to the load. A communication interface provides a measured value of at least one of inverter output current of a first uninterruptible power supply and a measured value of the load current to a second uninterruptible power supply, and receives a measured value of at least one of inverter output current of the second uninterruptible power supply and the load current. A controller controls the uninterruptible power supplies to operate in one of a master state and a slave state. In the master state the uninterruptible power supply is configured to control the voltage to the load, and in the slave state the uninterruptible power supply is configured to determine a reference output current value based at least in part on at least one of the measured value of inverter output current of the second uninterruptible power supply and the measured value of the load current. The uninterruptible power supply in the slave state drives its inverter output current toward the reference output current value to provide its share of the load current.

Claims

1. An uninterruptible power supply configured to operate in parallel with a second uninterruptible power supply in a power distribution system, the uninterruptible power supply comprising:

a first inverter configured to provide power to a load;

a communication interface configured to be coupled to the second uninterruptible power supply via a communication channel, wherein the communication interface is further configured to receive at least one first status signal from the second uninterruptible power supply via the communication channel, the at least one first status signal indicating whether the second uninterruptible power supply is configured to operate in one of a master state or a slave state, the communication interface being configured to provide isolation between the uninterruptible power supply and the second uninterruptible power supply; and

a controller coupled to the first inverter and the communication interface and configured to control the uninterruptible power supply to operate in one of the master state and the slave state based on the at least one first status signal,

wherein in the master state, the uninterruptible power supply is configured to control voltage to the load, and in the slave state, the uninterruptible power supply is configured to control an output current value of the first inverter.

2. The uninterruptible power supply of claim 1, wherein the communication interface includes an isolation circuit configured to isolate the uninterruptible power supply from the second uninterruptible power supply.

3. The uninterruptible power supply of claim 2, wherein the isolation circuit includes at least one of an opto-isolator and an opto-coupler.

4. The uninterruptible power supply of claim 1, wherein the at least one first status signal received by the communication interface further indicates whether the second uninterruptible power supply is configured to operate in a bypass mode or an inverter mode, and wherein the controller is further configured to control the uninterruptible power supply to operate in one of the bypass mode or the inverter mode based on the at least one first status signal.

5. The uninterruptible power supply of claim 1, wherein the communication interface is further configured to provide at least one second status signal to the second uninterruptible power supply via the communication channel, the at least one second status signal indicating whether the uninterruptible power supply is configured to operate in the master state or the slave state.

6. The uninterruptible power supply of claim 5, wherein the at least one second status signal further indicates whether the uninterruptible power supply is configured to operate in the bypass mode or the inverter mode.

7. The uninterruptible power supply of claim 1, further comprising a first current sensor coupled to the first inverter and configured to measure the output current value of the first inverter.

8. The uninterruptible power supply of claim 7, wherein the communication interface is further configured to provide the measured output current value of the first inverter from the first current sensor to the second uninterruptible power supply via the communication channel.

9. The uninterruptible power supply of claim 8, wherein the communication interface is further configured to receive a measured output current value of a second inverter from a second current sensor within the second uninterruptible power supply via the communication channel.

10. The uninterruptible power supply of claim 9, wherein in the slave state the uninterruptible power supply is configured to determine a reference output current value based on the measured output current value of the second inverter received from the second uninterruptible power supply and to drive the output current value of the first inverter toward the reference output current value.

11. The uninterruptible power supply of claim 9, wherein the first current sensor is a current transformer configured to measure the output current value of the first inverter, provide the measured output current value of the first inverter to the communication interface, and provide electrical isolation between the uninterruptible power supply and the second uninterruptible power supply.

12. A method of distributing power using an uninterruptible power supply configured to operate in parallel with a second uninterruptible power supply to provide power to a load, comprising:

receiving, via a communication interface of the uninterruptible power supply, at least one first status signal from the second uninterruptible power supply, the at least one first status signal indicating whether the second uninterruptible power supply is configured to operate in a master state or a slave state of operation;

isolating, with the communication interface, the uninterruptible power supply from the second uninterruptible power supply;

controlling the uninterruptible power supply to operate in one of the master state and the slave state based on the at least one first status signal;

operating, in the master state, the uninterruptible power supply to control voltage to the load; and

operating, in the slave state, the uninterruptible power supply to control an inverter output current value of the uninterruptible power supply.

13. The method of claim 12, wherein the at least one first status signal received by the communication interface further indicates whether the second uninterruptible power supply is configured to operate in a bypass mode or an inverter mode, and wherein the method further comprises controlling the uninterruptible power supply to operate in one of the bypass mode or the inverter mode based on the at least one first status signal.

14. The method of claim 12, further comprising transmitting, via the communication interface, at least one second status signal to the second uninterruptible power supply, the at least one second status signal indicating whether the uninterruptible power supply is configured to operate in the master state or the slave state of operation.

15. The method of claim 14, wherein the at least one second status signal further indicates whether the uninterruptible power supply is configured to operate in the bypass mode or the inverter mode.

16. The method of claim 12, further comprising measuring an inverter output current value of the uninterruptible power supply.

17. The method of claim 16, further comprising providing the measured inverter output current value of the uninterruptible power supply to the second uninterruptible power supply via the communication interface.

18. The method of claim 12, further comprising receiving a measured inverter output current value of the second uninterruptible power supply via the communication interface.

19. The method of claim 18, further comprising:

determining a reference current value of the uninterruptible power supply based on the measured inverter output current value of the second uninterruptible power supply; and

controlling a duty cycle of a pulse width modulation control signal to drive an inverter output current of the uninterruptible power supply toward the reference current value.

20. An uninterruptible power supply configured to operate in parallel with a second uninterruptible power supply to provide power to a load, the uninterruptible power supply comprising:

an input configured to receive input power;

an inverter configured to provide output power to a load; and

means for electrically isolating the uninterruptible power supply from the second uninterruptible power supply and for operating the uninterruptible power supply in one of a master state and a slave state;

wherein in the master state, the uninterruptible power supply is configured to control voltage to the load, and in the slave state, the uninterruptible power supply is configured to control an output current value of the inverter.