A medium voltage grid-connected photovoltaic inverter system and a photovoltaic power generation system including the same are provided. The medium voltage grid-connected photovoltaic inverter system includes a photovoltaic inverter, a medium voltage transformer, a switchgear, and an inverter grid-connected controller. A low voltage side of the medium voltage transformer is connected to an alternating current output terminal of the photovoltaic inverter. An input terminal of the switchgear is connected to a high voltage side of the medium voltage transformer, and each phase of the switchgear includes two output terminals each for being connected to another switchgear. The inverter grid-connected controller is connected to a controlled terminal of the switchgear, and is configured to control the switchgear to switch off/on, so that the medium voltage grid-connected photovoltaic inverter system is disconnected from or connected to a grid.

An inverter converts power outputted from a distributed power supply into AC power, and outputs to an AC system. An inverter control circuit generates an AC voltage target value at a time of controlling the inverter, and generates a command value for control of the inverter as a voltage source. When the inverter is introduced into the AC system, the inverter control circuit sets a frequency of the AC voltage target value to a frequency of an AC voltage detected by an AC frequency detection circuit, and controls a phase of the AC voltage target value to be at least a leading phase with respect to the AC voltage of the AC system when a target value of the AC power is in a running direction.

An inverter converts power outputted from a distributed power supply into AC power, and outputs to an AC system. An inverter control circuit generates an AC voltage target value at a time of controlling the inverter, and generates a command value for control of the inverter as a voltage source. When the inverter is introduced into the AC system, the inverter control circuit sets a frequency of the AC voltage target value to a frequency of an AC voltage detected by an AC frequency detection circuit, and controls a phase of the AC voltage target value to be at least a leading phase with respect to the AC voltage of the AC system when a target value of the AC power is in a running direction.

A power conversion device including a power conversion circuit, an AC filter circuit, and a calculation unit. The power conversion circuit converts DC input power from a DC power supply to output a first AC output current and a first AC output voltage. The AC filter circuit filters the first AC output current and the first AC output voltage to generate a second AC output current and a second AC output voltage. The calculation unit calculates an estimated value of an upper impedance based on a difference value between a first voltage value and a second voltage value, the first voltage value being a value of the second AC output voltage at a time of stop of the power conversion circuit or at a time of zero output from the power conversion circuit or at a time of a certain amount of output from the power conversion circuit.

A method for controlling a wind power installation or a wind farm is provided. The method includes establishing that there is a grid fault within an electrical power supply grid operated by a grid operator and to which the wind power installation or the wind farm is electrically connected via a point of common coupling; switching electrical switches of the wind power installation or the wind farm using a control unit of the wind power installation or the wind farm which is operated by a low-voltage power supply, so that the wind power installation or the wind farm is voltage-free; testing an electrical store for ensuring the low-voltage power supply once the grid fault has been established; and switching further electrical switches of the wind power installation or the wind farm to a predefined switching state in which start-up of the wind power installation or the wind farm is possible.

A method for controlling a wind power installation or a wind farm is provided. The method includes establishing that there is a grid fault within an electrical power supply grid operated by a grid operator and to which the wind power installation or the wind farm is electrically connected via a point of common coupling; switching electrical switches of the wind power installation or the wind farm using a control unit of the wind power installation or the wind farm which is operated by a low-voltage power supply, so that the wind power installation or the wind farm is voltage-free; testing an electrical store for ensuring the low-voltage power supply once the grid fault has been established; and switching further electrical switches of the wind power installation or the wind farm to a predefined switching state in which start-up of the wind power installation or the wind farm is possible.

A grid forming vector current control system can be used for controlling a grid intertie. A first terminal is connected to a first power grid and a second terminal is connected to a second power grid. The terminals each include current control unit, a virtual admittance unit, and a phase locked loop (PLL) unit. The virtual admittance unit and the PLL unit are configured to emulate an inertia of a virtual synchronous machine (VSM) and a virtual current source is connected in parallel to the VSM. A controller is configured to use transient power consumed by the first VSM to generate a power-equivalent current reference to control the second virtual current source and to use transient power consumed by the second VSM to generate a power-equivalent current reference to control the first virtual current source.

A grid forming vector current control system can be used for controlling a grid intertie. A first terminal is connected to a first power grid and a second terminal is connected to a second power grid. The terminals each include current control unit, a virtual admittance unit, and a phase locked loop (PLL) unit. The virtual admittance unit and the PLL unit are configured to emulate an inertia of a virtual synchronous machine (VSM) and a virtual current source is connected in parallel to the VSM. A controller is configured to use transient power consumed by the first VSM to generate a power-equivalent current reference to control the second virtual current source and to use transient power consumed by the second VSM to generate a power-equivalent current reference to control the first virtual current source.

Electrical apparatus (20) includes an inverter (24) having input terminals for receiving DC input power and output terminals for coupling to an AC power grid. A pulse-width modulation (PWM) generator and drivers (26) drive the switches so as to control respective amplitudes, frequencies, and phases of the output current waveforms of the inverter. Control circuitry (28) receives measurements of respective time-varying voltages and currents on the input and output terminals, computes a model (40) that includes three virtual currents flowing in a synchronous machine that is emulated by the apparatus, wherein the three virtual currents are associated respectively with the three output current waveforms, and controls the PWM generator and drivers responsively to the three virtual currents so as to synchronize the amplitudes, frequencies, and phases of the three output current waveforms of the inverter with the three phases of the AC power grid.

The present invention relates to an inverter device. Regard to the problem in the traditional convert device that the user is difficult to obtain the information shown on the display panel in time; the state of the inverter can not be switched remotely after the user leaves; discharging or early switching-off caused by missing battery information; and the draught fan can only be at the state of ‘full-speed-start’ or switch-off, the invention provides an inverter device, it is configured with an extensible flexible wire to fix the display panel of the inverter to the place the user wants to for getting the information of the inverter in time; by virtue of wireless transmission, user can control the state of the inverter remotely; by adding a test module to the inverter device, it avoids the waste of electricity which is caused by the discharging of the battery-to-convert and switching off.