A load balancing apparatus balances the current supplied on each phase of a multiple phase supply, wherein each supply phase feeds an AC load, as well as an AC-DC converter. The apparatus measures the current supplied from each phase of the supply as well as the power consumed by each of the AC loads. The power consumed by each of the AC-DC converters is adjusted so that the sum of the current drawn by any one of the AC loads, plus the current drawn by the AC-DC converter on the same supply phase, is substantially balanced between the supply phases. Typically, the AC-DC converters supply a common DC bus, such as a battery. In some examples, each AC load includes a DC-AC converter configured to supply power from the common DC battery to one or more of the AC loads.

A method and apparatus for balancing loads on a split-phase islanded system. In one embodiment, the apparatus comprises a device, coupled between a DG and a plurality of loads, comprising: an autotransformer coupled to first and second phase lines and a neutral line of the split-phase islanded system; a plurality of switches to switch between coupling a corresponding load to the first phase line and coupling the corresponding load to the second phase line; and a controller for determining, when a load imbalance is identified, at least one load to be switched from one of the first or second phase lines to the other of the first or second phase lines to reduce the load imbalance, and controlling at least one switch to switch the at least one load from the one of the first or second phase lines to the other of the first or second phase lines.

A method for three-phase infeed of electrical power from a DC source into a three-phase AC grid by means of an inverter includes measuring phase-specific grid voltages of the three-phase AC grid, and determining a grid frequency from the measured phase-specific grid voltages. The method also includes generating phase-specific voltage reference values from the phase-specifically measured grid voltages and the determined grid frequency, and generating phase-specific target current values using phase-specific predetermined target current amplitude values, the phase-specific voltage reference values and respective grid voltage amplitudes.

A method and apparatus for balancing loads on a split-phase islanded system. In one embodiment, the apparatus comprises a device, coupled between a DG and a plurality of loads, comprising: an autotransformer coupled to first and second phase lines and a neutral line of the split-phase islanded system; a plurality of switches to switch between coupling a corresponding load to the first phase line and coupling the corresponding load to the second phase line; and a controller for determining, when a load imbalance is identified, at least one load to be switched from one of the first or second phase lines to the other of the first or second phase lines to reduce the load imbalance, and controlling at least one switch to switch the at least one load from the one of the first or second phase lines to the other of the first or second phase lines.

A converter for electrical connection to a three-phase electrical grid and a single-phase electrical grid is provided. The converter includes three DAB modules, each for converting a respective alternating current of a three-phase electrical grid. When connected to a single-phase electrical grid, the third DAB module is bi-directional such that it is operable to filter the power output of the first and second DAB modules. The converter further includes a filter capacitor in electrical communication with the third DAB module through a relay, wherein the relay is responsive to a controller to couple the third DAB module to the filter capacitor when the single-phase electrical grid is detected and to couple the third DAB module to a grid rectifier when the three-phase electrical grid is detected.

Disclosed are three-phase system and distributed control method. The three-phase system comprises three-phase circuits, of which each phase circuit including at least one power conversion cell; and at least three phase controllers for controlling each phase circuit, respectively, each phase controller including a communication interface through which the at least three phase controllers are in communications connection with each other; wherein the phase controllers of each phase circuit is configured for regulating bridge arm voltages of the at least one power conversion cell in the phase circuit by receiving signals sent from the phase controllers of other two phase circuits through the communication interface. The three-phase system and the distributed control method of the invention solve problems of balance of three-phase current and stabilization of three-phase DC voltages by coordination among the three phases. Thanks to the invention, the three phases can be independently controlled to improve control flexibility.

The disclosure discloses a system and method for suppressing unbalanced voltage at the Point of Common Coupling (PCC) of dispersed wind farm. According to the disclosure, the wind farm comprising a STATCOM and plurality of wind turbines, dispersed wind farm controller, STATCOM controller, wind turbine controller. The dispersed wind farm controller decides that whether the STATCOM or the wind turbines inject negative-sequence current or not. Adaptive virtual negative-sequence output admittance controller is incorporated into the STATCOM controller and wind turbine controller, which can provide the negative-sequence current reference according to their participation factor. The compensation efforts of STATCOM and wind turbines can be flexibly controlled by changing their participation factor, which is related to the voltage unbalance voltage reference and the remaining capacity. The disclosure has significant advantages in cost and effectiveness to suppress the unbalanced voltage of PCC and improve the wind farm Low voltage fault recovery capability.

Systems and methods for controlling power flow to and from an energy storage system are provided. One energy storage system includes an energy storage device and a bidirectional inverter configured to control a flow of power into or out of the energy storage device via a plurality of phases. The energy storage system further includes a controller configured to control the bidirectional inverter based on a load condition on one or more phases. The controller is configured to control the bidirectional inverter to store power generated by a generator set in the energy storage device and transmit power from the energy storage device to a load driven by the generator set in response to detecting a load imbalance between the phases.

Aspects of the subject disclosure may include, for example, embodiments detecting and correcting load imbalance on power supply phases within a managed scope using a software controlled power switch matrix that is resident in each power distribution unit supplying power in the managed scope. Managed scope could include a plurality of power distribution units supplying a plurality of circuit or equipment loads in a plurality of premises. On each PDU, the software controlled switch matrix maintains and changes physical coupling of power supply phases to circuit and equipment loads. Further embodiments include correcting power supply phase load imbalances through software commands to adjust the coupling of power supply phases to circuit or equipment loads. Embodiments are intended to help power administrators maintain power supply phase load balance effectively in a managed scope. Other embodiments are disclosed.

A power conversion device includes a power conversion circuit and a power conversion control circuit. The power conversion control circuit is configured to calculate a positive-phase sequence current command signal based on a positive-phase sequence voltage of the three-phase AC output voltage and a positive-phase sequence current of the three-phase AC output current, calculate a negative-phase sequence current command signal based on the first axis negative-phase sequence current command value, the second axis negative-phase sequence current command value, the first axis negative-phase sequence current value, and the second axis negative-phase sequence current value, and generate the switching control signal based on the positive-phase sequence current command signal and the negative-phase sequence current command signal.