A method for determining when a connection of a power system to a grid has been disconnected. The method includes the power system supplying a first amount of reactive power to the grid to which the power system is connected, and the power system determining if there is a frequency change within the grid. This includes if the frequency change does not exceed a predetermined threshold, the power system supplying a second amount of reactive power to the grid, and if the frequency exceeds a predetermined threshold, the power system supplying a first amount of reactive power to the grid.

Systems and apparatuses include a non-transitory computer readable media having computer-executable instructions embodied therein that, when executed by a circuit of a power system, causes the power system to perform functions to activate and deactivate routes. The functions include determining a plurality of source objects, each including source functions and being assigned a position on a one-line topology; determining one or more switch objects, each including switch functions and being assigned a position on the one-line topology; determining one or more bus objects, each including bus functions and being assigned a position on the one-line topology; determining one or more load objects, each including load functions and being assigned a position on the one-line topology; and allocating each object to one of a plurality of controllers, each of the controllers structured to cooperatively perform the source functions, the switch functions, the bus functions, and the load functions to provide operation of the system.

A control unit repeats the series of processing of comparing a first phase representing a phase of the first reference sine wave and being a phase included in the first synchronization signal, with a second phase that is the phase of the second reference sine wave when the first synchronization signal is received when the communication unit receives the first synchronization signal from the other inverter generator, changing a phase change amount per unit time of the second reference sine wave in accordance with the comparison result, continuing to update the phase of the second reference sine wave so that the phase of the second reference sine wave changes with a phase change amount per unit time after the change with reference to the first phase until the next first synchronizing signal is received from the other inverter generator. The control unit compares a third phase that is a phase included in the first synchronization signal received prior to the polarity reversal timing of the second reference sine wave by the communication unit and that is one of the first phases, with a fourth phase that is a phase of the second reference sine wave when the first synchronizing signal is received, changing the phase change amount per unit time of the second reference sine wave in accordance with the comparison result, and predicts the polarity inversion timing of the first reference sine wave by continuing updating the phase of the second reference sine wave so that the phase of the second reference sine wave changes with a phase change amount per unit time after the change.

A grid interconnection system for a power grid includes: a storage battery; a power conversion device that converts power from the storage battery into AC; and an interconnection control device that supplies power from a commercial power supply to a load and supplies power from the power conversion device to the load when the commercial power supply fails. When the commercial power supply is restored, the interconnection control device starts supply of power from the commercial power supply to the load, and stops supply of power from the power conversion device to the load after the supply of power from the commercial power supply to the load is started.

An apparatus according to an embodiment includes a control circuit to control operations of an inverter and a switch. The control circuit judges whether or not a power system has a power failure, based on values of the system voltage and a frequency of the power system; and calculates a phase difference between a phase of the output voltage of the inverter and a phase of the system voltage and generate, by means of the phase difference, an output frequency pattern for changing a frequency of the output voltage of the inverter. The control circuit, when it is judged that the power system has recovered from the power failure, controls the inverter to change the frequency of the output voltage of the inverter in line with the output frequency pattern, and closes the switch after the phase difference becomes smaller than or equal to a threshold.

A method and system are provided for transferring a load between a primary power source and a secondary power source. In accordance with the disclosure, a controller senses, via a sensor, an electrical signal providing power from the primary power source to the load. The controller also detects a non-conforming power event by determining that a parameter of the electrical signal is either more or less than a first threshold value. Responsive to the detection of the non-conforming power event, the controller determines a quantity of non-conforming power events that occur during a first time interval. The controller further can compares the determined quantity of non-conforming power events to a second threshold value. Responsive to the determined quantity of non-conforming power events being either greater or lesser than the second threshold value, the controller initiates a control signal, such as a control signal to initiate a load transfer.

A method and system are provided for transferring a load between a primary power source and a secondary power source. In accordance with the disclosure, a controller senses, via a sensor, an electrical signal providing power from the primary power source to the load. The controller also detects a non-conforming power event by determining that a parameter of the electrical signal is either more or less than a first threshold value. Responsive to the detection of the non-conforming power event, the controller determines a quantity of non-conforming power events that occur during a first time interval. The controller further can compares the determined quantity of non-conforming power events to a second threshold value. Responsive to the determined quantity of non-conforming power events being either greater or lesser than the second threshold value, the controller initiates a control signal, such as a control signal to initiate a load transfer.

A method for connecting a power transformer, located between an inverter of a wind turbine and an electrical grid to the electrical grid; the method comprises the steps gradually increasing a voltage at a primary side, of the transformer from a low starting voltage to a target voltage equal or close to a nominal voltage of the transformer, by means of the inverter of the wind turbine or by means of an auxiliary inverter, thereby increasing the voltage at a secondary side of the transformer wherein the gradually increasing of the voltage uses energy of an internal energy storage device, connecting the secondary side of the transformer to the electrical grid after predefined target conditions have been reached.

A method for controlling an inverter, and in particular a double stage inverter, for implementing a model of a synchronous generator is provided including implementing a rotor inertia using an intermediate dc-link capacitor without duplicating the emulated inertia in the controller, simulating the rotor speed based on a measured voltage of the dc-link capacitor, while allowing the voltage to change in a defined range, and mapping the changing voltage of the dc-link capacitor into the inverter as an internal frequency. A system for connecting a power generator to a power grid is also provided including a control device for an inverter, the control device implementing a model of a synchronous generator. The control device including a computer processor in electrical communication with a storage device with instructions stored thereon, that when executed on the computer processor, perform the method for controlling an inverter for implementing a model of a synchronous generator.

A method for controlling an inverter, and in particular a double stage inverter, for implementing a model of a synchronous generator is provided including implementing a rotor inertia using an intermediate dc-link capacitor without duplicating the emulated inertia in the controller, simulating the rotor speed based on a measured voltage of the dc-link capacitor, while allowing the voltage to change in a defined range, and mapping the changing voltage of the dc-link capacitor into the inverter as an internal frequency. A system for connecting a power generator to a power grid is also provided including a control device for an inverter, the control device implementing a model of a synchronous generator. The control device including a computer processor in electrical communication with a storage device with instructions stored thereon, that when executed on the computer processor, perform the method for controlling an inverter for implementing a model of a synchronous generator.