Method for controlling an uninterruptable power supply

1. A method for controlling an uninterruptable power supply arranged between a grid and a variable load,

the uninterruptable power supply comprising a DC link interconnecting a rectifier connected to the grid via a grid switch, an energy storage and an inverter connected to the load, and a switchable bypass connected between the grid switch and the load and in parallel with a path formed by the rectifier, the DC link, and the inverter such that switching of the grid switch opens or closes connection of the switchable bypass and the rectifier with the grid,

the method comprising:

monitoring a power supply of the grid;

comparing the power supply to a load requirement of the load; and

if the power supply meets the load requirement,

closing the grid switch such that the grid switch closes the connection of the switchable bypass and the rectifier with the grid; and

switching on the bypass, to supply the load with AC current from the grid.

2. The method of claim 1 , wherein the method further comprises:

monitoring a power demand of the load and a charge level of the energy storage; and

if there is a power surplus, where the power supply is higher than the power demand, and if the charge level is below a predetermined level,

activating the rectifier in a rectifying mode to rectify surplus AC current from the grid to DC current supplied to the DC link; and

charging the energy storage with the DC current.

3. The method of claim 1 , wherein the method further comprises:

monitoring a power demand of the load; and

if there is a power shortfall, where the power supply is lower than the power demand,

the method further comprises:

signaling the power shortfall to the load.

4. The method of claim 3 , wherein the method further comprises:

synchronizing the inverter to the grid in an inverting mode to invert DC current from the DC link to AC current to supply the power shortfall; and

discharging the energy storage.

5. The method of claim 4 , wherein

if the power shortfall is bigger than an inverting capacity of the inverter, the method further comprises:

synchronizing the rectifier to the grid in an inverting mode; and

inverting DC current from the DC link to AC current supplied to the load via the bypass.

6. The method of claim 1 , wherein

if the power supply is below the load requirement but meets a rectifier requirement,

closing the grid switch;

switching off the bypass;

activating the rectifier in a rectifying mode to rectify AC current from the grid to DC current supplied to the DC link; and

activating the inverter in an inverting mode to invert DC current from the DC link to AC current supplied to the load.

7. The method of claim 6 , wherein

if there is a power shortfall,

the method further comprises:

discharging the energy storage.

8. The method of claim 6 , wherein

if a charge level of the energy storage is below a predetermined level and if there is a power surplus,

the method further comprises:

charging the energy storage.

9. The method of claim 1 , wherein

if the power supply is below a rectifier requirement,

the method further comprises:

opening the grid switch;

activating the inverter in an inverting mode to invert DC current from the DC link to AC current supplied to the load; and

discharging the energy storage.

10. The method of claim 9 , wherein

if a power demand is bigger than an inverting capacity of the inverter,

the method further comprises:

switching on the bypass; and

assisting the inverter by operating the rectifier in an inverting mode to invert DC current from the DC link to AC current supplied to the load via the bypass.

11. The method of claim 5 , further comprising:

balancing the inverter and the rectifier.

12. A control device for an uninterruptable power supply, configured to execute the method of claim 1 .

13. An uninterruptable power supply with a control device of claim 12 .

14. A computer program, which when being executed by a processor, is adapted for performing the method of claim 1 .

15. A computer-readable medium, wherein a computer program according to claim 14 is stored.

16. The method of claim 10 , further comprising:

balancing the inverter and the rectifier.