Abstract: A system and apparatus for autonomous charge balancing of an energy storage device of the microgrid. In one embodiment the apparatus comprises a power conditioner, coupled to the energy storage device, comprising a droop control module for operating the power conditioner, during an autonomous mode of operation, such that the state of charge of the energy storage device is autonomously driven toward the state of charge of at least one other energy storage device of the microgrid.

Abstract: A method and apparatus for power converter current control. In one embodiment, the method comprises controlling an instantaneous current generated by a power converter that is part of an AC battery such that the power converter appears, from the perspective of an AC line coupled to the power converter, as a virtual AC voltage source in series with a virtual impedance, wherein real and reactive phasor currents for the power converter are indirectly controlled by modifying amplitude and phase of a virtual AC voltage waveform that defines the virtual AC voltage source.

Abstract: A method and apparatus for autonomously operating a microgrid power generator. In one embodiment, the method comprises obtaining a first measurement of at least one grid parameter of a microgrid transmission line coupled to a power generator in a microgrid; comparing the first measurement to a turn-on threshold; initiating, when the first measurement is less than the turn-on threshold, power generation by the power generator; obtaining, after initiation of the energy generation, a second measurement of the at least one grid parameter of the microgrid transmission line; comparing the second measurement to a shut-down threshold that is greater than the turn-on threshold; and stopping, when the second measurement exceeds the shut-down threshold, the power generation by the power generator.

Abstract: A system and apparatus for autonomous charge balancing of an energy storage device of the microgrid. In one embodiment the apparatus comprises the energy storage device; and a power conditioner, coupled to the energy storage device, comprising a droop control module for operating the power conditioner, during an autonomous mode of operation, such that the state of charge of the energy storage device is autonomously driven toward the state of charge of at least one other energy storage device of the microgrid.

Abstract: A method and apparatus for power converter current control. In one embodiment, the method comprises controlling an instantaneous current generated by a power converter that is part of an AC battery such that (i) the power converter appears, from the perspective of an AC line coupled to the power converter, as a virtual AC voltage source in series with a virtual impedance, wherein real and reactive phasor currents for the power converter are indirectly controlled by modifying amplitude and phase of a virtual AC voltage waveform that defines the virtual AC voltage source, and (ii) active power flow is prioritized while the AC battery is operating in a charge mode.

Abstract: Method and apparatus for controlling power conditioners in a distributed resource island. In one embodiment, the method comprises comparing, at a power conditioner operating in a de-energized state, an input of the power conditioner to an input threshold, wherein the power conditioner is coupled to an islanded grid; operating the power conditioner, when the input exceeds the input threshold, in a soft-grid mode to generate a touch-safe AC voltage that is coupled to the islanded grid; comparing, by the power conditioner, an impedance of the islanded grid to a grid impedance range; comparing, by the power conditioner, load demand of the power conditioner to an activate threshold; and activating the power conditioner, when the impedance is within the grid impedance range and the load demand exceeds the activate threshold, to operate proximate its nominal output voltage.

Abstract: A method and apparatus for providing multi-phase power. In one embodiment, the apparatus comprises a cycloconverter controller for determining a charge ratio based on a reference waveform; and a cycloconverter, coupled to the cycloconverter controller and to a multi-phase AC line, for selectively coupling an alternating current to each line of the multi-phase AC line based on the charge ratio.

Abstract: Methods and apparatus for controlling power conditioners in a distributed resource island are provided herein. In one embodiment, an input of a power conditioner that is operating in a de-energized state and coupled to an islanded grid is compared to an input threshold. When the input exceeds the input threshold, the power conditioner is operated in a soft-grid mode to generate a touch-safe AC voltage that is coupled to the islanded grid. The power conditioner compares an impedance of the islanded grid to a grid impedance range and compares load demand of the power conditioner to an activate threshold; when the impedance is within the grid impedance range and the load demand exceeds the activate threshold, the power conditioner is activated to operate proximate its nominal output voltage.

Abstract: A method and apparatus for power converter current control. In one embodiment, the method comprises controlling an instantaneous current generated by a power converter such that that power converter appears, from the perspective of an AC line coupled to the power converter, as a virtual AC voltage source in series with a virtual impedance.

Abstract: System and apparatus for power conversion. In one embodiment, the apparatus comprising a DC stage, comprising a resonant circuit, for generating a high-frequency resonant current; and an AC stage for converting a high-frequency current, generated from the high-frequency resonant current, to an AC output current, wherein the AC stage comprises: a pair of serially-connected switches for (i) passing, during a first half of a cycle of an AC line, a positive portion of the high-frequency current, and (ii) passing, during a second half of the cycle of the AC line, a negative portion of the high-frequency current; and an unfurling bridge for unfurling a current waveform, formed from the positive and the negative portions, to generate the AC output current, wherein the unfurling bridge is operated at a frequency on the order of three orders of magnitude lower than an operating frequency of the serially-connected switches.

Abstract: A method and apparatus for power converter current control. In one embodiment, the method comprises controlling an instantaneous current generated by a power converter such that that power converter appears, from the perspective of an AC line coupled to the power converter, as a virtual AC voltage source in series with a virtual impedance, wherein real and reactive phasor currents for the power converter are indirectly controlled by modifying amplitude and phase of a virtual AC voltage waveform that defines the virtual AC voltage source.

Abstract: A method and apparatus for controlling power conversion. In one embodiment, the method comprises computing a voltage ratio based on a voltage conversion in a resonant converter; comparing the voltage ratio to a threshold; and controlling, independent of switching frequency of the resonant converter, power output from the resonant converter based on whether the voltage ratio satisfies the threshold.

Abstract: A method and apparatus for power converter current control. In one embodiment, the method comprises controlling an instantaneous current generated by a power converter that is part of an AC battery such that (i) the power converter appears, from the perspective of an AC line coupled to the power converter, as a virtual AC voltage source in series with a virtual impedance, wherein real and reactive phasor currents for the power converter are indirectly controlled by modifying amplitude and phase of a virtual AC voltage waveform that defines the virtual AC voltage source, and (ii) active power flow is prioritized while the AC battery is operating in a charge mode.

Abstract: A method and apparatus for autonomously operating a microgrid power generator. In one embodiment, the method comprises obtaining a first measurement of at least one grid parameter of a microgrid transmission line coupled to a power generator in a microgrid; comparing the first measurement to a turn-on threshold; initiating, when the first measurement is less than the turn-on threshold, power generation by the power generator; obtaining, after initiation of the energy generation, a second measurement of the at least one grid parameter of the microgrid transmission line; comparing the second measurement to a shut-down threshold that is greater than the turn-on threshold; and stopping, when the second measurement exceeds the shut-down threshold, the power generation by the power generator.

Abstract: A system and apparatus for autonomous charge balancing of an energy storage device of the microgrid. In one embodiment the apparatus comprises the energy storage device; and a power conditioner, coupled to the energy storage device, comprising a droop control module for operating the power conditioner, during an autonomous mode of operation, such that the state of charge of the energy storage device is autonomously driven toward the state of charge of at least one other energy storage device of the microgrid.

Abstract: A method and apparatus for minimizing circulating currents on a power distribution line. In one embodiment, the method comprises dynamically adjusting a turns ratio of a tap changing transformer, the tap changing transformer coupled to a power grid distribution line that is also coupled to a plurality of microgrid branches wherein at least one microgrid branch of the plurality of microgrid branches comprises a distributed energy resource (DER), based on a reactive power measured locally to the tap changing transformer, to minimize current circulating on the power grid distribution line.

Abstract: System and apparatus for electrically coupling a microgrid to and from a power distribution grid. In one embodiment, the apparatus comprises an interconnect device, coupled to the microgrid and the power distribution grid, comprising (i) an overcurrent protection component (OPC) for interrupting a circuit during an overcurrent condition; and (2) a contactor component, coupled in series with the OPC and independently operable from the OPC, comprising (a) a set of contacts movable between a first position and a second position; (b) a first coil energizable to move the set of contacts from the first position into the second position; and (c) a second coil energizable, independently of the first coil, to maintain the contacts in the second position after the first coil is de-energized until a level of current flowing through the set of contacts is less than a lower current level.

Abstract: A method and apparatus for setting a virtual impedance ratio of a power conditioning unit (PCU). In one embodiment, the method comprises applying a disturbance to a virtual AC voltage of a power conditioning unit (PCU) operating in a virtual impedance droop control mode in which the PCU appears, from the perspective of a power grid coupled to the PCU, as a virtual AC voltage source in series with a virtual impedance; measuring the phase of the applied disturbance on the power grid; comparing the measured phase of the applied disturbance on the power grid to the phase of the disturbance; and adjusting, when the measured phase of the applied disturbance on the power grid differs from the phase of the disturbance by more than a threshold amount, a ratio of a resistive impedance of the virtual impedance to an inductive impedance of the virtual impedance.

Abstract: A method and apparatus for providing multi-phase power. In one embodiment, the apparatus comprises a cycloconverter controller for determining a charge ratio based on a reference waveform; and a cycloconverter, coupled to the cycloconverter controller and to a multi-phase AC line, for selectively coupling an alternating current to each line of the multi-phase AC line based on the charge ratio.

Abstract: A method and apparatus for line-cycle storage of a single-phase cycloconverter. The method includes receiving input power from an input port of the singe-phase cycloconverter and monitoring an AC output port of the single-phase cycloconverter. The method measures energy stored in a line-cycle energy storage circuit coupled to one line of the AC output port of the single-phase cycloconverter, and determines a phase difference between a monitored AC voltage of the AC output port and the measured voltage of the line-cycle energy storage circuit. The method controls switches in the single-phase cycloconverter to selectively store energy in the line-cycle energy storage circuit based on the phase difference.