Method and system for operating an electrical grid

A controller for operating an electrical grid, said grid having coupled thereto:

• at least one fluctuating source of AC power generated from renewable energy,
• consumers creating a fluctuating AC power demand,
• at least one grid forming controllable inverter coupled to an electric battery, said controller being configured to:
• operate said at least one fluctuating source of AC power as a slave to said grid,
• control a grid frequency with said controllable inverter as a master controller to obtain a desired grid frequency,
• measure the grid frequency,
• supply power from said electric battery through said at least one grid forming controllable inverter to said grid when the measured grid frequency is below the desired grid frequency by more than a first lower margin, and
• withdraw power through said at least one grid forming controllable inverter from said grid to said electric battery when the measured grid frequency is above the desired grid frequency by more than a first upper margin;
• and wherein
• a controllable resistive load-bank is coupled to said grid, said resistive load-bank having a capacity to withdraw a variable amount of power from said grid, and said resistive load-bank having a capacity to change the amount of energy withdrawn from said grid faster than said battery can change the amount of power withdrawn from said grid, and wherein the controller is further configured to cause the resistive load bank to reduce power withdrawn from said grid when the measured grid frequency is below the desired grid frequency by more than a second lower margin, said second lower margin being smaller than said first lower margin, and increase power withdrawn from said grid by the resistive load-bank when the measured grid frequency is above the desired grid frequency by more than a second upper margin.

An energy supply system for operating a grid coupled to at least one fluctuating source of AC power generated from renewable energy and to consumers creating a fluctuating AC power demand,

• said system comprising a controllable inverter coupled to an electric battery configured to be coupled to said grid and a controller configured to:
• operate said at least one fluctuating source of AC power as a slave to the grid, measure a grid frequency,
• control the grid frequency with said controllable inverter as master controller to obtain a desired grid frequency,
• supply power from said electric battery through said controllable inverter to the grid when the measured grid frequency is below the desired grid frequency by more than a first lower margin, and
• withdraw power through said controllable inverter from the grid to said electric battery when the measured grid frequency is above the desired grid frequency by more than a second upper margin;
• and
• the system further comprises a controllable resistive load-bank is coupled to said grid, said resistive load-bank having a capacity to withdraw a variable amount of power from said grid, and said resistive load-bank having a capacity to change the amount of energy withdrawn from said grid faster than said battery can change the amount of power withdrawn from said grid, and wherein the controller is configured to:
• reduce power withdrawn from said grid by the resistive load-bank when the measured grid frequency is below the desired grid frequency by more than a second lower margin, said second lower margin being smaller than said first lower margin, and increase power withdrawn from said grid by the resistive load-bank when the measured grid frequency is above the desired grid frequency by more than a second upper margin.