Islanding a plurality of grid tied power converters

A power system comprising:

• a plurality of power converters coupled together at a point of common coupling (PCC), wherein the power converters are configured to be coupled to a load at the PCC and the power converters are configured to provide a combined power converter output to the load;
• a switch coupled to the PCC, wherein the switch is configured to be coupled in series between the PCC and an external grid such that when the switch is closed the power system is in a grid-tied configuration and such that when the switch is open the power system is in an microgrid configuration;
• a control system comprising one or more controllers coupled to the plurality of power converters, the control system being configured to:
• enable the switch to open and close in response to a signal received from one or more sensors for monitoring the external grid;
• enable the power converters to operate in a current control mode when the switch is closed and when the power system is in the grid-tied configuration;
• transition the plurality of power converters from grid-tied mode to microgrid mode and synchronize the power converters such that the power converters share the load,
• wherein:
• the control system comprises a plurality of slave controllers each controlling one of the plurality of power converters and a master controller coordinating the plurality of slave controllers, and
• the control system being configured to transition the plurality of power converters from grid-tied mode to microgrid mode and synchronize the power converters such that the power converters share the load includes:
• the master controller being configured to:
• operate in voltage control mode by controlling the microgrid voltage amplitude and frequency;
• and
• generate active and reactive current commands for the slave controllers to follow;
• and
• the one or more slave controller being configured to
• receive the active and reactive current commands from the master controller;
• and
• enable their power converters to operate in current control mode during which the output current of a power converter coupled to a slave controller of the one or more slave controllers is controlled using the active and reactive current commands from the master controller.

A method of transitioning a plurality of power converters that are coupled together at a point of common coupling (PCC) from a grid-tied mode to a microgrid mode using a master controller and one or more slave controllers coupled to the power converters, the method comprising:

• opening an islanding switch coupled in series between the PCC and the external grid;
• setting, by the master controller, the microgrid voltage and frequency commands to the last known grid voltage and grid frequency;
• ramping, by the master controller, the microgrid voltage and frequency commands from the last known grid voltage and grid frequency to a nominal voltage and a nominal frequency;
• generating, by the master controller, active and reactive current commands for the one or more slave controllers to follow;
• operating the one or more slave controllers in current control mode during which the output current of a power converter coupled to a slave controller of the one or more slave controllers is controlled using the active and reactive current commands from the master controller.