A grid connection power conversion device is provided in which an amplitude of an output voltage from an inverter is increased stepwise from 0, after start-up of the power conversion device, to adjust the amplitude of the output voltage from the inverter to match an amplitude of a commercial system voltage as detected, and thereafter the inverter is connected to the commercial power system to start grid-connected operation. This makes it possible to prevent the voltage applied to a capacitor provided between the inverter and the commercial power system from abruptly increasing from 0V to the commercial system voltage at the start-up of the power conversion device, thereby making it possible to reduce an inrush current to the capacitor at the start-up without using an inrush current prevention circuitry.

In a method for black start of a power station including a plurality of inventers connectable to a local AC electrical grid, a first AC voltage is built up in the AC electrical grid by a first inverter, said first AC voltage being reduced in comparison with a rated voltage of the AC electrical grid by at least a quarter, and at least one second inverter is connected to the AC electrical grid after synchronization with the first AC voltage. After connection of the second converter, a second AC voltage, which is higher than the first AC voltage, is built up in the AC electrical grid.

In a method for black start of a power station including a plurality of inventers connectable to a local AC electrical grid, a first AC voltage is built up in the AC electrical grid by a first inverter, said first AC voltage being reduced in comparison with a rated voltage of the AC electrical grid by at least a quarter, and at least one second inverter is connected to the AC electrical grid after synchronization with the first AC voltage. After connection of the second converter, a second AC voltage, which is higher than the first AC voltage, is built up in the AC electrical grid.

A method can be used to control a voltage source converter of a power supporting arrangement to act as a virtual synchronous machine. The method includes obtaining a measured power level of the converter, processing the measured power level using a differential equation of an angular velocity of the virtual synchronous machine in order to obtain a control contribution, providing a phase angle of a physical quantity used to control the converter based on the control contribution, monitoring the ability of the converter to act as a virtual synchronous machine, determining that the ability of the converter to act as a virtual synchronous machine is deemed insufficient, and adjusting the control contribution by increasing the damping term and/or decreasing the moment of inertia term in response to determining that the ability of the converter to act as a virtual synchronous machine is deemed insufficient.

A method can be used to control a voltage source converter of a power supporting arrangement to act as a virtual synchronous machine. The method includes obtaining a measured power level of the converter, processing the measured power level using a differential equation of an angular velocity of the virtual synchronous machine in order to obtain a control contribution, providing a phase angle of a physical quantity used to control the converter based on the control contribution, monitoring the ability of the converter to act as a virtual synchronous machine, determining that the ability of the converter to act as a virtual synchronous machine is deemed insufficient, and adjusting the control contribution by increasing the damping term and/or decreasing the moment of inertia term in response to determining that the ability of the converter to act as a virtual synchronous machine is deemed insufficient.

A control system includes memory storing instructions and a processor configured to execute the instructions. The processor is configured to receive a first indication of a power grid voltage, receive a second indication of a power grid phase angle, receive a third indication of a generator voltage of power provided by a generator, and receive a fourth indication of a generator phase angle of power provided by the generator. The processor is configured to determine a voltage gap between the generator voltage and the power grid voltage and a time difference between the generator phase angle and the power grid phase angle. The processor is configured to generate a signal to cause the generator voltage and the generator phase angle to synchronize with the power grid voltage and the power grid phase angle, respectively.

A control system includes memory storing instructions and a processor configured to execute the instructions. The processor is configured to receive a first indication of a power grid voltage, receive a second indication of a power grid phase angle, receive a third indication of a generator voltage of power provided by a generator, and receive a fourth indication of a generator phase angle of power provided by the generator. The processor is configured to determine a voltage gap between the generator voltage and the power grid voltage and a time difference between the generator phase angle and the power grid phase angle. The processor is configured to generate a signal to cause the generator voltage and the generator phase angle to synchronize with the power grid voltage and the power grid phase angle, respectively.

A wind turbine is provided. The wind turbine includes a transformer having a low-voltage side and a high-voltage side. The transformer is configured to step up a voltage of the low-voltage side of the transformer to a voltage of an external grid. The wind turbine further includes an electrical power generating unit which is connected to the low-voltage side of the transformer and configured to feed an ac-power to the low-voltage side of the transformer. A charging device of the wind turbine is connected to the low-voltage side of the transformer and configured to charge the low-voltage side of the transformer when the generator does not feed ac-power to the low-voltage side of the transformer.

A wind turbine is provided. The wind turbine includes a transformer having a low-voltage side and a high-voltage side. The transformer is configured to step up a voltage of the low-voltage side of the transformer to a voltage of an external grid. The wind turbine further includes an electrical power generating unit which is connected to the low-voltage side of the transformer and configured to feed an ac-power to the low-voltage side of the transformer. A charging device of the wind turbine is connected to the low-voltage side of the transformer and configured to charge the low-voltage side of the transformer when the generator does not feed ac-power to the low-voltage side of the transformer.

A system and method for paralleling generators. A timing signal indicative of a waveform reference point of at least a first generator of the generators is received at a second generator. The receiving generator determines a closing time for a second generator breaker associated with the second generator in response the timing signal from the first generator. The first generator breaker and the second generator breaker, or an aggregated generator breaker is closed to a bus at the closing time.