Battery energy storage system with short circuit protection, and method

1. An energy storage system comprising:

a control unit;

a battery stack including a plurality of battery units, the battery units electrically connected in series, and each battery unit having at least one semiconductor switch and at least one battery module including a plurality of battery cells;

wherein each battery module is connected in series with a respective semiconductor switch, and the control unit is operatively connected to the at least one semiconductor switch and adapted to control the at least one semiconductor switch of every battery unit;

wherein the control unit includes a current monitor for monitoring the current through each battery module of at least one battery unit, and disconnects the battery module if the monitored current is above a short circuit threshold;

wherein the control unit disconnects the battery cell by activating the semiconductor switch; and

wherein the control unit disconnects all battery modules of every battery unit of the battery stack simultaneously.

2. The energy storage system as claimed in claim 1 ,

wherein each battery unit comprises a plurality of battery modules, each including a plurality of battery cell and being connected in series with a respective semiconductor switch, and

wherein each battery module and semiconductor switch connected in parallel with the other serial circuits of battery modules and semiconductor switches of the battery unit.

3. The energy storage system as claimed in claim 1 , wherein each battery unit includes a battery control unit for controlling the semiconductor switches.

4. The energy storage system as claimed in claim 1 , wherein each battery unit of the stack comprises a battery control unit operatively connected to the semiconductor switches of the battery modules of the battery unit.

5. The energy storage system as claimed in claim 1 , wherein the stack includes a stack control unit being operatively connected to the battery units of a battery stack.

6. The energy storage system as claimed in claim 5 , wherein the stack control unit is adapted to synchronise the control of the semiconductor switches of the battery units of the battery stack.

7. The energy storage system of claim 1 ,

wherein a plurality of stacks are arranged in series in a string of serially interconnected stacks of battery units,

wherein the string is arranged to provide a DC voltage input to a voltage source converter.

8. The energy storage system of claim 7 , comprising a plurality of strings.

9. The energy storage system as claimed in claim 1 , wherein the at least one semiconductor switch comprises a MOSFET.

10. The energy storage system as claimed in claim 1 , wherein the at least one semiconductor switch comprises an IGBT connected in parallel with a diode.

11. The energy storage system in claim 9 , wherein the MOSFET is arranged to conduct current only during discharge of energy from the battery module.

12. The energy storage system in claim 10 , wherein the IGBT is arranged to conduct current only during discharge of energy from the battery module, whereas the diode is arranged to conduct only during charging of the battery module.

13. A method for controlling an energy storage system comprising a control unit, a battery stack including a plurality of battery units, the battery units being arranged in series, and each battery unit having at least one semiconductor switch and at least one battery module including a plurality of battery cells, wherein each battery module is electrically connected in series with a respective semiconductor switch, and the control unit is operatively connected to the at least one semiconductor switch and adapted to control the at least one semiconductor switch of every battery unit, wherein the control unit includes a current monitor for monitoring the current through each battery module of at least one battery unit, and disconnects the battery module if the monitored current is above a short circuit threshold, and wherein the control unit disconnects the battery cell by activating the semiconductor switch, wherein the control unit disconnects all battery modules of every battery unit of the battery stack simultaneously, characterized by the steps of:

monitoring a current through each battery module,

instructing the semiconductor of all switches of every battery unit to simultaneously turn off, in the event that the current exceeds a first threshold.