Hybrid generator system

A method of operating a hybrid generator system including an inverter connected to a facility alternating-current (AC) bus, a battery connected to a direct-current (DC) port of the inverter, a generator selectively connectable to the AC bus, an on-site renewable power source connected to the inverter, a controllable load bank, an isolation switch between the AC bus and a power grid, and a controller in communication with each component, the method comprising:

• in a first mode of use, during normal grid operation, maintaining the battery at a partial state of charge while the inverter operates in synchronism with the power grid to supply facility loads and to augment grid power during transient load surges without starting the generator;
• in a second mode of use, during a grid under-frequency event, exporting power from at least the battery through the inverter to the grid and, when the event persists beyond the battery's capacity, starting the generator and continuing export of power to the grid while supplying facility loads;
• in a third mode of use, during a grid outage, opening the isolation switch to isolate a facility and initially supplying facility loads from the battery through the inverter, then starting the generator to provide longer-duration support and optionally to recharge the battery;
• in a fourth mode of use, during a grid over-frequency condition or other excess-generation event, importing power from the grid to charge the battery through the inverter and, when battery capacity to absorb power is exceeded, connecting the controllable load bank to the inverter to consume surplus power;
• in a fifth mode of use, during a grid outage that requires surge power beyond generator capacity, synchronizing the inverter with the generator and connecting the generator directly to the facility AC bus while the inverter draws power from the battery in parallel with the generator for a duration limited by the battery's capacity;
• and
• controlling transitions among the modes according to sensed grid and facility conditions and commands received from a grid authority.

A method of operating a hybrid generator system;

• comprising;
• synchronizing an inverter with a power grid;
• maintaining a battery associated with the inverter at partial state of charge;
• detecting a grid under-frequency event;
• exporting power to the grid from the battery via the inverter;
• starting an engine-driven generator and continuing power export to the grid;
• and
• upon a grid outage, opening an isolation switch and supplying facility loads from the battery via the inverter until a generator assumes a longer-duration operation.