Capacity-optimized grid-forming control

1 . A capacity-optimized AC grid-forming controller for power electronics converters, comprising:

a power-synchronization model configured to:

receive positive-sequence symmetrical components and negative-sequence symmetrical components of an output voltage and an output current;

generate a plurality of current references comprising a positive-sequence current reference and a negative-sequence current reference; and

generate an internal voltage phase reference and voltage magnitude reference; and a capacity constrainer configured to:

determine, based on the plurality of current references and a plurality of capacity limit terms, that a device coupled with the capacity-optimized AC grid-forming controller is capacity constrained;

determine optimum complex gains to scale the plurality of current references based on the plurality of capacity limit terms; and

responsive to the determination of capacity constraint, output scaled current reference to cause a power stage for the capacity-optimized AC grid-forming controller to adjust the output voltage or the output current, the scaled current reference scaled according to the optimum complex gains.

2 . The capacity-optimized AC grid-forming controller of claim 1 , wherein the power-synchronization model comprises a virtual synchronous machine model configured to:

generate a voltage phase reference and the voltage magnitude reference; and

generate the plurality of current references using the voltage phase reference and the voltage magnitude reference.

3 . The capacity-optimized AC grid-forming controller of claim 1 , wherein the power-synchronization model is configured to:

generate a voltage phase reference by drooping frequency with a first component of a positive sequence output component; and

generate the voltage magnitude reference by drooping with a second component.

4 . The capacity-optimized AC grid-forming controller of claim 3 , wherein:

the first component comprises:

a positive-sequence output real power; or

a positive-sequence output current component along a positive-sequence output voltage vector; and

the second component comprises:

a positive-sequence reactive power; or

a positive-sequence output current normal to the positive sequence output voltage vector.

5 . The capacity-optimized AC grid-forming controller of claim 1 , wherein the power-synchronization model comprises:

a first controller to generate the negative-sequence current reference, the first controller comprising at least one of:

a first virtual admittance; or

a first voltage controller; and

a second controller to generate the positive-sequence current reference, the second controller comprising at least one of:

a second virtual admittance; or

a second voltage controller.

6 . The capacity-optimized AC grid-forming controller of claim 1 , wherein the plurality of capacity limit terms comprise:

a minimum active power;

a maximum active power;

a minimum reactive power;

a maximum reactive power; and

a maximum current.

7 . The capacity-optimized AC grid-forming controller of claim 1 , wherein, to determine the optimum complex gains, the capacity constrainer is configured to predict a deviation between commanded values and the output voltage and the output current along a plurality of components thereof, the plurality of components comprising:

active power;

reactive power; and

current magnitude.

8 . The capacity-optimized AC grid-forming controller of claim 7 , wherein the prediction of the deviation is fed to a model adapter, the model adapter configured to provide, to the power-synchronization model, adaptation signals based on the plurality of components determined by the capacity constrainer.

9 . The capacity-optimized AC grid-forming controller of claim 8 , wherein the adaptation signals comprise:

a first adaptation term for frequency determined, by the model adapter, based on active power information; and

a second adaptation term for voltage based on reactive power information; or

a scaling factor for active power reference; and

a scaling factor for equivalent inertia and damping.

10 . The capacity-optimized AC grid-forming controller of claim 9 , configured to:

receive, from a user interface, the plurality of capacity limit terms, the plurality of capacity limit terms corresponding to:

a power output of a DC source;

a power output of an inverter; or

a reactive-active power mix limit of the inverter; and

store, by the capacity-optimized AC grid-forming controller, the plurality of capacity limit terms.

11 . A method for controlling grid-forming inverters in an electrical grid, comprising:

decomposing, by one or more processors, a measured or estimated output voltage vector and a measured or estimated output current vector into positive-sequence symmetrical components and negative-sequence symmetrical components of the measured or estimated output voltage vector and output current vector;

generating, by the one or more processors based on the decomposed positive-sequence symmetrical components and negative-sequence symmetrical components, symmetrical current references; and

responsive to determining, by the one or more processors, the symmetrical current references violate at least one of a plurality of capacity limit terms, adjusting, by the one or more processors, a combined current reference for a power stage of the grid-forming inverters.

12 . The method of claim 11 , wherein adjusting the combined current reference comprises:

predicting, by the one or more processors, a first deviation between commanded and expected values;

generating, by the one or more processors, first adaptation signals based on the first deviation;

predicting, by the one or more processors, a second deviation between the commanded and expected values; and

generating, by the one or more processors, second adaptation signals based on the second deviation.

13 . The method of claim 12 , wherein generating the first adaptation signals and the second adaptation signals comprises:

generating, by the one or more processors, a first adaptation term for frequency based on active power information; and

generating, by the one or more processors, a second adaptation term for voltage based on reactive power information; or

generating, by the one or more processors, a scaling factor for active power reference; and

generating, by the one or more processors, a scaling factor for equivalent inertia and damping.

14 . The method of claim 11 , wherein adjusting the combined current reference comprises:

predicting, by the one or more processors, a deviation between commanded and expected values according to a deterministic model; and

providing, by the one or more processors, an updated combined current reference to a current controller for the power stage of the grid-forming inverters.

15 . The method of claim 14 , wherein the deviation comprises a difference between commanded and expected:

active power;

reactive power; and

current magnitude.

16 . A grid-forming controller configured to:

decompose a measured or estimated output voltage vector and a measured or estimated output current vector into positive-sequence symmetrical components and negative-sequence symmetrical components of the measured or estimated output voltage vector and output current vector;

generate, based on the decomposed positive-sequence symmetrical components and negative-sequence symmetrical components, symmetrical current references;

determine the symmetrical current references violate at least one of a plurality of capacity limit terms; and

responsive to the determination, adjust a combined current reference for a power stage of grid-forming inverters.

17 . The grid-forming controller of claim 16 , wherein the grid-forming controller is configured to:

predict a first deviation between commanded and expected values;

generate first adaptation signals based on the first deviation;

predict a second deviation between the commanded and expected values; and

generate second adaptation signals based on the second deviation, the second adaptation signals configured to modulate a positive-sequence symmetrical current reference and a negative-sequence symmetrical current reference, to cause the adjustment to the combined current reference.

18 . The grid-forming controller of claim 17 , wherein the first adaptation signals and the second adaptation signals comprise:

a first adaptation term for frequency determined, by a model adapter, based on active power information;

a second adaptation term for voltage based on reactive power information;

a scaling factor for active power reference; and

a scaling factor for equivalent inertia and damping.

19 . The grid-forming controller of claim 16 , wherein the adjustment to the combined current reference is based on a provision, by the grid-forming controller, of an updated combined current reference to a current controller for the power stage, the updated combined current reference based on a prediction, of the grid-forming controller, of a deviation between commanded and expected values according to a deterministic model.

20 . The grid-forming controller of claim 19 , wherein the deviation includes a difference between the commanded and expected values for:

active power; reactive power; and current magnitude.