BACKGROUND

Distributed energy generation is key to a resilient energy supply, but distributed resources like solar power do not have any intrinsic surge capability like that provided by the angular momentum of a generator. Without some form of dispatchable energy storage, power surges, e.g., those produced when charging capacitors or starting or stopping a large motor, cause voltage fluctuations that can disrupt or damage other connected equipment. Moreover, most solar inverters can only supply power to a stable, well-regulated grid. As soon as the grid goes down, a solar array and conventional inverter turn off. This radically limits the effectiveness of solar power as an emergency or fail-safe power source.

Battery storage systems can provide surge capacity. If a grid node such as a residence is electrically disconnected from the power grid, e.g., via a master service disconnect switch or breaker, a battery storage system can regulate a voltage waveform that allows a conventional grid-tied solar inverter to feed power into the isolated node. At present, the cost of a battery storage system and its attendant power electronics may be excessive because electronics and magnetics may need to be sized for peak power, which may occur only for a second or two periodically through the day.

SUMMARY

Some embodiments described herein include novel microgrid system controllers that provide alternative approaches to providing and absorbing surge power and generating a high-quality, stable voltage waveform, while obviating excessive battery storage and power-electronics costs. Some embodiments comprise one or more of a generator, a flywheel, a motor, a motor-controller, a power source, a load switch, a source switch, and an auxiliary load. Some embodiments may further comprise a switch to connect and disconnect from the grid or apparatus to report the connection state to the grid.

In accordance with an embodiment, a microgrid system controller includes a regulated bus; a battery and charge controller switchably coupled to the regulated bus; a variable-frequency drive (VFD) inverter coupled to the battery and charge controller; a generator physically coupled to a rotatable flywheel and switchably coupled to the VFD inverter; a resistive load switchably coupled to the regulated bus; and a plurality of actuatable switches. The plurality of actuatable switches include a first actuatable switch configured to selectively couple a photovoltaic (PV) inverter to the regulated bus or to an external electrical panel; a second actuatable switch configured to selectively couple the regulated bus to the external electrical panel; a third actuatable switch configured to selectively couple the regulated bus to the battery and charge controller; a fourth actuatable switch configured to selectively couple the VFD inverter to the regulated bus or to the generator; a fifth actuatable switch configured to selectively couple the generator to the external electrical panel; and a sixth actuatable switch configured to selectively couple the resistive load to the regulated bus.

In an embodiment, wherein the plurality of actuatable switches comprise a seventh actuatable switch configured to selectively couple a user-configurable load to the regulated bus.

In another embodiment, where during a first state power from the PV inverter is supplied to the external electrical panel, the plurality of actuatable switches are configured such that: the first actuatable switch couples the PV inverter to the external electrical panel; the fourth actuatable switch couples the VFD inverter to the regulated bus; and the sixth actuatable switch is open so that the resistive load is not coupled to the regulated bus.

In another embodiment, where during a second state power from the PV inverter is supplied to the external electrical panel and to the regulated bus, the plurality of actuatable switches are configured such that: the first actuatable switch couples the PV inverter to the external electrical panel; the second actuatable switch couples the regulated bus to the PV inverter; a third actuatable switch couples the regulated bus to the battery and charge controller to charge a battery; the fourth actuatable switch couples the VFD inverter to the regulated bus; and the sixth actuatable switch is open so that the resistive load is not coupled to the regulated bus.

In another embodiment, where during a third state the VFD inverter provides an in-specification grid voltage waveform to the PV inverter, the plurality of actuatable switches are configured such that: the first actuatable switch couples the PV inverter to the regulated bus; the second actuatable switch is open so that the regulated bus is not coupled to the external electrical panel; the fourth actuatable switch couples the VFD inverter to the regulated bus; and the sixth actuatable switch is open so that the resistive load is not coupled to the regulated bus. A battery coupled to the battery and charge controller may be configured to power the VFD inverter, and the VFD inverter may be configured to provide the in-specification grid voltage waveform to the PV inverter.

In another embodiment, where during a fourth state power from the PV inverter is supplied to the generator to charge up mechanical energy of the rotatable flywheel, the plurality of actuatable switches are configured such that: the first actuatable switch couples the PV inverter to the regulated bus; the second actuatable switch is open so that the regulated bus is not coupled to the external electrical panel; the third actuatable switch couples the regulated bus to the battery and charge controller, and the battery and charge controller power the VFD inverter; the fourth actuatable switch couples the VFD inverter to a primary winding of the generator; the fifth actuatable switch is open so that the generator is not coupled to the external electrical panel; and the sixth actuatable switch is controlled to maintain the regulated bus within a grid voltage specification waveform by providing residual power from the PV inverter to the resistive load. The VFD inverter may be configured to provide a variable frequency and voltage waveform to the generator to charge up the mechanical energy of the rotatable flywheel. During a fifth state the fourth actuatable switch may couples the VFD inverter to a secondary or auxiliary winding of the generator.

In another embodiment, the plurality of actuatable switches also include a seventh actuatable switch configured to selectively couple the regulated bus to a substantial short circuit.

In another embodiment, where during a sixth state power from the generator and rotatable flywheel is supplied to the external electrical panel, the plurality of actuatable switches are configured such that: the first actuatable switch couples the PV inverter to the regulated bus; the second actuatable switch, the third actuatable switch, and the sixth actuatable switch are controlled to maintain the regulated bus within a grid voltage specification waveform; the fourth actuatable switch is controlled to adjust generator efficiency, power factor, and frequency; and the fifth actuatable switch is closed to couple the generator to the external electrical panel.

In another embodiment, the external electrical panel is coupled to an energized grid, and a waveform of the VFD inverter phase locks with a waveform of the energized grid.

In another embodiment, the external electrical panel is coupled to a battery/inverter system, and a waveform of the VFD inverter phase locks with a waveform of the battery/inverter system.

In yet another embodiment, the PV inverter is coupled to a battery/inverter and a battery storage system, and a waveform of the VFD inverter phase locks with a waveform of an islanding inverter.

In accordance with another embodiment, a microgrid system controller includes a regulated bus; a battery and charge controller switchably coupled to the regulated bus; a multiple-phase VFD inverter coupled to the battery and charge controller; a generator physically coupled to a rotatable flywheel and electrically coupled to the multiple-phase VFD inverter; a resistive load switchably coupled to the regulated bus; and a plurality of actuatable switches. An output of the multiple-phase VFD inverter drives at least one of (i) a primary stator winding of the generator, or (i) a secondary stator winding of the generator. The plurality of actuatable switches include a first actuatable switch configured to selectively couple a PV inverter to the regulated bus or to an external electrical panel; a second actuatable switch configured to selectively couple the regulated bus to the external electrical panel; a third actuatable switch configured to selectively couple the regulated bus to the battery and charge controller; a fourth actuatable switch configured to selectively couple the generator to the external electrical panel; and a fifth actuatable switch configured to selectively couple the resistive load to the regulated bus.

In accordance with another embodiment, a microgrid system controller includes a regulated bus; a balancer comprising battery storage, the balancer coupled to an output of a PV system and coupled to the regulated bus; a battery and charge controller switchably coupled to the regulated bus; a VFD inverter coupled to the battery and charge controller and switchably coupled to the regulated bus; a generator physically coupled to a rotatable flywheel and a motor electrically coupled to the VFD inverter, the generator switchably coupled to an external electrical panel; a resistive load switchably coupled to the regulated bus; and a plurality of actuatable switches. The plurality of actuatable switches include a first actuatable switch configured to selectively couple the regulated bus to the VFD inverter; a second actuatable switch configured to selectively couple the regulated bus to the battery and charge controller; a third actuatable switch configured to selectively couple the generator to an external electrical panel; and a fourth actuatable switch configured to selectively couple the resistive load to the regulated bus.

In an embodiment, the balancer comprises direct current (DC) side battery storage.

In another embodiment, the VFD inverter is a multi-phase VFD, the motor is a multi-phase motor, and the generator is a single-phase generator.

In yet another embodiment, the microgrid system controller also includes a converter switchably coupled to the regulated bus, wherein the converter is configured to produce a storable energy source from direct current (DC) power; and a motor coupled to the converter and to the generator, the motor configured to drive the generator and rotatable flywheel.

In accordance with another embodiment, a microgrid system controller includes a regulated bus coupled to an output of a PV system; a battery and charge controller switchably coupled to the regulated bus; a multi-phase VFD inverter coupled to the battery and charge controller and switchably coupled to the regulated bus; a multi-phase generator physically coupled to a rotatable flywheel and coupled to the multi-phase VFD inverter, the multi-phase generator switchably coupled to an external electrical panel; a resistive load switchably coupled to the regulated bus; and a plurality of actuatable switches. The plurality of actuatable switches include a first actuatable switch configured to selectively couple the regulated bus to the three-phase VFD inverter; a second actuatable switch configured to selectively couple the regulated bus to the battery and charge controller; a third actuatable switch configured to selectively couple the three-phase generator to the external electrical panel; and a fourth actuatable switch configured to selectively couple the resistive load to the regulated bus.

In an embodiment, the multi-phase VFD inverter is a three-phase VFD inverter and the multi-phase generator is a three-phase generator.

In accordance with yet another embodiment, a microgrid system controller includes a battery storage device coupled an output of a PV system; a regulated bus coupled to the battery storage device coupled; a VFD inverter switchably coupled to the regulated bus; a generator physically coupled to a rotatable flywheel and coupled to the VFD inverter, the generator switchably coupled to an external electrical panel; a resistive load switchably coupled to the regulated bus; and a plurality of actuatable switches. The plurality of actuatable switches include a first actuatable switch configured to selectively couple the regulated bus to the VFD inverter; a second actuatable switch configured to selectively couple the generator to the external electrical panel; and a third actuatable switch configured to selectively couple the resistive load to the regulated bus.

