Uninterruptible power supply with a dual gain voltage regulator controlling an inverter output voltage based on active and reactive components of current

• US 8,791,597 B2
• Filed: 03/02/2011
• Issued: 07/29/2014
• Est. Priority Date: 03/12/2010
• Status: Active Grant

• Current Assignee: Vertiv Corporation (Vertiv Holdings Co.)
• Original Assignee: Liebert Corporation (Vertiv Holdings Co.)
• Inventors: Chen, Xian
• Primary Examiner(s): Barnie, Rexford
• Assistant Examiner(s): Mourad, Rasem
• Application Number:
  US13/038,438
• Publication Number:
  US 20120057377A1
• Time in Patent Office: 1,245 Days
• Field of Search: 307/64, 307/65, 307/66, 363/37, 363/95
• US Class Current: 307/64
• CPC Class Codes: H02J 9/062 for AC powered loads

Abstract

An uninterruptible power supply (UPS) system has an inverter having an output coupled to a primary side of an output transformer. The UPS system has a controller having a dual gain voltage regulator for controlling the output voltage of the inverter of a UPS system that uses active and reactive current components of a load current flowing out an output of the UPS system.

Claims

1. A method of controlling an output voltage of an inverter of an uninterruptible power supply (UPS) system, the UPS system including an output transformer having a primary side coupled to an output of the inverter and a secondary side coupled to an output of the UPS system, a controller that monitors a primary side voltage and load current flowing through the output of the UPS system, the method comprising:

a. decomposing with the controller the load current into active and reactive components and using them as approximations for I<sub>T—

active</sub> and I<sub>T—

reactive</sub>;

b. determining with the controller a voltage drop across the output transformer for a steady state mode of the UPS system (V_reg2) and also for a continuous mode of the UPS system (V_reg1), wherein V_reg1 and V_reg2 are determined by

V_reg1=G_active*I<sub>T—

active</sub>+G_{reactive(low)}*I<sub>T—

reactive</sub>

V_reg2=G_active*I<sub>T—

active</sub>+G_{reactive(high)}*I<sub>T—

reactive</sub>

where V_reg1 is the voltage drop across the output transformer for a continuous mode of the UPS system, V_reg2 is the voltage drop across the output transformer for a steady state mode of the UPS system, G_{reactive(low)} is a gain less than 300, G_{reactive(high)} is a pain greater than 1,000, I<sub>T—

active</sub> is the active component of the load current, and I<sub>T—

reactive</sub> is the reactive component of the load current, and

c. in each of the two modes, determining with the controller a voltage drop across the output transformer (V_TVR) to use in determining a desired inverter output voltage of the inverter by

V_TVR=V_reg1+Δ

V_T

where V_TVR is the voltage drop across the output transformer to use in determining a desired inverter output voltage, Δ

V_T is zero when the UPS system is not in the steady state mode and Δ

V_T=V_reg2−

V_reg1 when the UPS system is in the steady state mode; and

d. determining with the controller a desired inverter output voltage based on a nominal output voltage of the UPS system and V_TVR and controlling an actual inverter output voltage based on the desired inverter output voltage and the monitored primary side voltage.

2. The method of claim 1, including using a value in the range of 50 to 300 for G_{reactive(low)} and a value in the range of 1,000 to 2,000 for G_active in determining V_reg1 and using a value in the range of 4,000 to 6,000 for G_{reactive(high)} and a value in the range of 100 to 300 for G_active in determining V_reg2.

3. The method of claim 2 including determining V_reg1 a plurality of times each line cycle of an AC output voltage of the UPS system and determining V_reg2 no more than once per second.

4. The method of claim 3 including determining V_reg1 four times each line cycle of the AC output voltage of the UPS system.

5. An uninterruptible power supply (UPS) system, comprising:

a. an inverter having an output coupled to a primary side of an output transformer, the output transformer having a secondary side coupled to an output of the UPS system;

b. a controller configured to monitor a primary side voltage and load current flowing through the output of the UPS system, decompose the load current into an active and reactive components and uses them as approximations for I<sub>T—

active</sub> and I<sub>T—

reactive</sub>;

c. the controller configured to determine a voltage drop across the output transformer for a steady state mode of the UPS system (V_reg2) and also for a continuous mode of the UPS system (V_reg1), wherein V_reg1 and V_reg2 are determined by

V_reg1=G_active*I<sub>T—

active</sub>+G_{reactive(low)}*I<sub>T—

reactive</sub>

V_reg2=G_active*I<sub>T—

active</sub>+G_{reactive(high)}*I<sub>T—

reactive</sub>

where V_reg1 is the voltage drop across the output transformer for a continuous mode of the UPS system, V_reg2 is the voltage drop across the output transformer for a steady state mode of the UPS system, G_{reactive(low)} is a gain less than 300, G_{reactive(high)} is a gain greater than 1,000, I<sub>T—

active</sub> is the active component of the load current, and I<sub>T—

reactive</sub> is the reactive component of the load current; and

d. in each of the two modes, the controller configured to determine a voltage drop across the output transformer (V_TVR) to use in determining a desired inverter output voltage of the inverter by

V_TVR=V_reg1+Δ

V_T

where V_TVR is the voltage drop across the output transformer to use in determining a desired inverter output voltage, Δ

V_T is zero when the UPS system is not in the steady state mode and Δ

V_T=V_reg2−

V_reg1 when the UPS system is in the steady state mode; and

e. the controller configured to determine the desired inverter output voltage based on a nominal output voltage of the UPS system and V_TVR and controlling the inverter output voltage based on the determined desired inverter output voltage and the monitored primary side voltage.

6. The UPS system of claim 5 wherein G_{reactive(low)} is in the range of 50 to 300 and the value used for G_active in determining V_reg1 is in the range of 1,000 to 2,000 and G_{reactive(high)} is in the range of 4,000 to 6,000 and a value used for G_active in determining V_reg2 is in the range of 100 to 300.

7. The UPS system of claim 6 wherein the controller is configured to determine V_reg1 a plurality of times each line cycle of an AC output voltage of the UPS system and determines V_reg2 no more than once per second.

8. The UPS system of claim 7 wherein the controller is configured to determine V_reg1 four times each line cycle of the AC output voltage of the UPS system.