Control of a stabilizing energy storage in a microgrid

1. A method performed by control units, each for controlling a respective energy storage, configured for stabilizing a microgrid, the method comprising each of the control units:

obtaining a local deviation signal related to a voltage and/or frequency deviation from a local reference, as measured at a local point of the microgrid where the energy storage is connected and able to inject real and/or reactive power into the microgrid for stabilizing said microgrid;

obtaining a common deviation signal related to a voltage and/or frequency deviation from a common reference, as measured at a common point of the microgrid which is different from the local point, wherein the common deviation signal is identical for all the control units;

controlling the injection of real and/or reactive power by the energy storage into the microgrid based on the common deviation signal as long as the local deviation signal satisfies a first criterion;

switching from controlling the energy storage based on the common deviation signal to controlling the energy storage based on the local deviation signal in response to the local deviation signal satisfying a second criterion; and

returning from controlling the energy storage based on the local deviation signal to controlling the energy storage based on the common deviation signal in response to the local deviation signal satisfying a third criterion.

2. The method of claim 1 , wherein:

the obtaining a local deviation signal comprises receiving voltage and/or frequency measurements from the local point and comparing them to the local reference which is predefined and held in a storage unit of the control unit to calculate the local deviation signal; and

the obtaining a common deviation signal comprises receiving voltage and/or frequency measurements from the common point and comparing them to the common reference which is predefined and held in a storage unit of the control unit to calculate the common deviation signal.

3. The method of claim 2 , wherein the first criterion is that the deviation from the local reference is below a predefined magnitude threshold or that a change rate of the deviation from the local reference is below a predefined rate of change threshold.

4. The method of claim 2 , wherein the third criterion is that the deviation from the local reference is below a predefined magnitude return threshold or that a change rate of the deviation from the local reference is below a predefined rate of change return threshold.

5. The method of claim 1 , wherein the first criterion is that the deviation from the local reference is below a predefined magnitude threshold or that a change rate of the deviation from the local reference is below a predefined rate of change threshold.

6. The method of claim 5 , wherein the second criterion is that the deviation from the local reference is above the predefined magnitude threshold or that the change rate of the deviation from the local reference is above the predefined rate of change threshold.

7. The method of claim 6 , wherein the third criterion is that the deviation from the local reference is below a predefined magnitude return threshold or that a change rate of the deviation from the local reference is below a predefined rate of change return threshold.

8. The method of claim 5 , wherein the third criterion is that the deviation from the local reference is below a predefined magnitude return threshold or that a change rate of the deviation from the local reference is below a predefined rate of change return threshold.

9. The method of claim 1 , wherein the third criterion is that the deviation from the local reference is below a predefined magnitude return threshold or that a change rate of the deviation from the local reference is below a predefined rate of change return threshold.

10. A microgrid comprising a plurality of distributed generators, a plurality of energy storages, a plurality of control units and a plurality of loads, wherein the plurality of energy storages are connected in the microgrid for stabilizing said microgrid by being able to inject real and/or reactive power into the microgrid, each of said energy storages being connected to a respective control unit of the plurality of control units, each control unit comprising:

processor circuitry; and

a storage unit storing instructions that, when executed by the processor circuitry, cause the control unit to:

obtain a local deviation signal related to a voltage and/or frequency deviation from a local reference, as measured at a local point of the microgrid where the energy storage of the control unit is connected;

obtain a common deviation signal related to a voltage and/or frequency deviation from a common reference, as measured at a common point of the microgrid which is different from the local point, wherein the common deviation signal is identical for all the control units;

control the injection of real and/or reactive power by the energy storage into the microgrid based on the common deviation signal as long as the local deviation signal satisfies a first criterion;

switch from controlling the energy storage based on the common deviation signal to controlling the energy storage based on the local deviation signal in response to the local deviation signal satisfying a second criterion; and

return from controlling the energy storage based on the local deviation signal to controlling the energy storage based on the common deviation signal in response to the local deviation signal satisfying a third criterion.