Multiple UPS system having multi-way power tie system and intelligent power sharing control

1. A method of power sharing control in a multiple uninterruptible power supply (UPS) system having a plurality of multi-module UPS subsystems coupled to a power tie cabinet, each multi-module UPS subsystem having a plurality of UPS modules, each UPS module having a controller having a droop power sharing control loop and an average power sharing control loop, the power tie cabinet including power tie cabinet controls (PTC) controls, the method comprising:

periodically determining with the PTC controls a power error message for each multi-module UPS subsystem and passing it to a controller of that multi-module UPS subsystem; and

having the controller of each multi-module UPS subsystem use the power error message received from the PTC controls to determine power error data that it provides to the average power sharing control loop of the controller of each UPS module in that multi-module UPS subsystem and having the average power sharing control loop for each UPS module use the power error data for average power control.

2. The method of claim 1 wherein the multiple UPS system has N multi-module UPS subsystems and having the PTC controls determine the power error message (Perr_i) for an i th multi-module UPS subsystem in the multiple UPS system in accordance with the following equation:

Perr_i

=

Pi

*

(

∑

k

=

1

,

k

≠

i

N

⁢

Num

k

)

-

(

∑

k

=

1

,

k

≠

i

N

⁢

P

k

)

*

Num

i

∑

k

=

1

N

⁢

Num

k

where 1≦i≦N, k is k th multi-module subsystem of the N multi-module UPS subsystem, 1≦k≦N, Pi is power meter data that the PTC controls collect at a power meter of the i th multi-module UPS subsystem; Num i is the number of UPS modules online in the i th multi-module UPS subsystem, and N is the total number of multi-module UPS subsystems in the multiple UPS system.

3. The method of claim 2 wherein passing the power error message for each multi-module UPS system to the controller of that multi-module UPS system includes passing it every two seconds.

4. The method of claim 1 wherein the multiple UPS system has two multi-module UPS subsystems A and B, and having the PTC controls determine the power error message (Perr_A) for multi-module UPS subsystem A and the power error message (Perr_B) for multi-module UPS subsystem B in accordance with the following equations:

Perr_A

=

P

⁢

⁢

a

*

NumB

-

Pb

*

NumA

NumA

+

NumB

Perr_B

=

Pb

*

NumA

-

P

⁢

⁢

a

*

NumB

NumA

+

NumB

where Pa and Pb are power meter data that the PTC controls collect from a power meter of multi-module UPS subsystem A and a power meter of multi-module UPS subsystem B, respectively; and NumA and NumB are the total number of UPS modules online in multi-module UPS subsystem A and multi-module UPS subsystem B, respectively.

5. The method of claim 4 wherein passing the power error message for each multi-module UPS system to the controller of that multi-module UPS system includes passing it every two seconds.

6. A multiple uninterruptible power supply (UPS) system, comprising:

a plurality of multi-module UPS subsystems coupled to a power tie cabinet, each multi-module UPS subsystem having a plurality of UPS modules;

each UPS module having a controller having a droop power sharing control loop and an average power sharing control loop;

the power tie cabinet including power tie cabinet (PTC) controls, the PTC controls periodically determining a power error message for each multi-module UPS subsystem and passing it to a controller of that multi-module UPS subsystem; and

the controller of each multi-module UPS subsystem using the power error message received from the PTC controls to determine power error data that it provides to the average power sharing control loop of the controller of each UPS module in that multi-module UPS subsystem which is used by the average power sharing control loop for each UPS module for average power control.

7. The multiple UPS system of claim 6 wherein the multiple UPS system has N multi-module UPS subsystems, the PTC controls determine the power error message (Perr_i) for an i th multi-module UPS subsystem in the multiple UPS system in accordance with the following equation:

Perr_i

=

Pi

*

(

∑

k

=

1

,

k

≠

i

N

⁢

Num

k

)

-

(

∑

k

=

1

,

k

≠

i

N

⁢

P

k

)

*

Num

i

∑

k

=

1

N

⁢

Num

k

where 1≦i≦N, k is k th multi-module subsystem of the N multi-module UPS subsystem, 1≦k≦N, Pi is power meter data that the PTC controls collect at a power meter of the i th multi-module UPS subsystem; Num i is the number of UPS modules online in the i th multi-module UPS subsystem, and N is the total number of multi-module UPS subsystems in the multiple UPS system.

8. The multiple UPS system of claim 7 wherein the power error message for each multi-module UPS system is passed to the controller of that multi-module UPS system every two seconds.

9. The multiple UPS system of claim 6 wherein the multiple UPS system has two multi-module UPS subsystems A and B, the PTC controls determine the power error message (Perr_A) for multi-module UPS subsystem A and the power error message (Perr_B) for multi-module UPS subsystem B in accordance with the following equations:

Perr_A

=

P

⁢

⁢

a

*

NumB

-

Pb

*

NumA

NumA

+

NumB

Perr_B

=

Pb

*

NumA

-

P

⁢

⁢

a

*

NumB

NumA

+

NumB

where Pa and Pb are power meter data that the PTC controls collect from a power meter of multi-module UPS subsystem A and a power meter of multi-module UPS subsystem B, respectively; and NumA and NumB are the total number of UPS modules online in multi-module UPS subsystem A and multi-module UPS subsystem B, respectively.

10. The multiple UPS system of claim 9 wherein the power error message for each multi-module UPS system is passed to the controller of that multi-module UPS system every two seconds.