An uninterruptible power supply (UPS) system with stranded power recovery has a plurality of UPS modules with one or more of the UPS modules usable to provide stranded power to a recovered power bus. When a UPS module is used to provide stranded power to the recovered power bus, the AC/AC converter associated with that UPS module provides AC power that is synchronized with AC power being provided to the recovered power bus by each of the other AC/AC converters that are providing AC power. In this manner all of the AC/AC converters that are providing AC power to the recovered power bus have the same voltage, the same frequency, and are in phase.

The present disclosure provides a system-level protection system and method for sub/super-synchronous resonance/oscillation. The system includes a centralized protection coordinator arranged in a control center and a plurality of distributed protection relays arranged in a plurality of transformer substations or wind farms. Each distributed protection relay is configured to acquire a sub/super-synchronous impedance of the wind farm. The centralized protection coordinator is configured to acquire the sub/super-synchronous impedances measured by the plurality of distributed protection relays, to obtain a sub/super-synchronous aggregate impedance of the system according to a preset circuit topology and the sub/super-synchronous impedances, and to generate a system-level protection signal when the sub/super-synchronous aggregate impedance does not meet a stable condition. Each distributed protection relay is further configured to initiate a system-level protection according to the system-level protection signal.

The present disclosure provides a system-level protection system and method for sub/super-synchronous resonance/oscillation. The system includes a centralized protection coordinator arranged in a control center and a plurality of distributed protection relays arranged in a plurality of transformer substations or wind farms. Each distributed protection relay is configured to acquire a sub/super-synchronous impedance of the wind farm. The centralized protection coordinator is configured to acquire the sub/super-synchronous impedances measured by the plurality of distributed protection relays, to obtain a sub/super-synchronous aggregate impedance of the system according to a preset circuit topology and the sub/super-synchronous impedances, and to generate a system-level protection signal when the sub/super-synchronous aggregate impedance does not meet a stable condition. Each distributed protection relay is further configured to initiate a system-level protection according to the system-level protection signal.

A power supporting arrangement for a power grid includes a first and a second voltage source converter with an AC side and a DC side. A DC link interconnects the DC sides of the voltage source converters. A first switching arrangement includes a number of settable positions. The AC side of the second voltage source converter is connected to the power grid and the first switching arrangement is connected between a first synchronous machine. The AC side of the first voltage source converter and the power grid and operable to selectively connect the first synchronous machine to the power grid or to the AC side of the first voltage source converter.

A power supporting arrangement for a power grid includes a first and a second voltage source converter with an AC side and a DC side. A DC link interconnects the DC sides of the voltage source converters. A first switching arrangement includes a number of settable positions. The AC side of the second voltage source converter is connected to the power grid and the first switching arrangement is connected between a first synchronous machine. The AC side of the first voltage source converter and the power grid and operable to selectively connect the first synchronous machine to the power grid or to the AC side of the first voltage source converter.

A medium-voltage grid-connected photovoltaic inverter system includes: a photovoltaic inverter, a medium-voltage transformer, a medium-voltage switch, and an inverter grid-connected controller. A direct current input terminal of the photovoltaic inverter is connected to a direct current bus. 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 medium-voltage switch is connected to a high-voltage side of the medium-voltage transformer, and an output terminal of the medium-voltage switch is connected to a medium-voltage grid. A voltage sensor is integrated in the medium-voltage switch to detect a line voltage at the high-voltage side of the medium-voltage transformer and a line voltage at a side of the medium-voltage grid and generate a grid-connected voltage detection signal. The inverter grid-connected controller is connected to a controlled terminal of the medium-voltage switch and an output terminal of the voltage sensor.

A medium-voltage grid-connected photovoltaic inverter system includes: a photovoltaic inverter, a medium-voltage transformer, a medium-voltage switch, and an inverter grid-connected controller. A direct current input terminal of the photovoltaic inverter is connected to a direct current bus. 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 medium-voltage switch is connected to a high-voltage side of the medium-voltage transformer, and an output terminal of the medium-voltage switch is connected to a medium-voltage grid. A voltage sensor is integrated in the medium-voltage switch to detect a line voltage at the high-voltage side of the medium-voltage transformer and a line voltage at a side of the medium-voltage grid and generate a grid-connected voltage detection signal. The inverter grid-connected controller is connected to a controlled terminal of the medium-voltage switch and an output terminal of the voltage sensor.

Method and apparatus for generating green electrical power. A modified grid-tie configuration is provided in which electrical power is supplied to a load from a utility grid source and a photovoltaic (PV) source (e.g. solar panels). A grid-tie inverter generates alternating current (AC) power from the PV source that is phase aligned with AC power from the grid. In the event of a grid outage, a specially configured transfer switch disconnects the grid from the PV source and connects the PV source to a backup source. The grid-tie inverter again matches the AC power from the PV source with AC power from the backup source to enable continued operation of the PV source during the grid outage. The backup source may utilize an electrolyzer that generates stored hydrogen and a hydrogen fuel cell that converts the stored hydrogen to electricity.

Method and apparatus for generating green electrical power. A modified grid-tie configuration is provided in which electrical power is supplied to a load from a utility grid source and a photovoltaic (PV) source (e.g. solar panels). A grid-tie inverter generates alternating current (AC) power from the PV source that is phase aligned with AC power from the grid. In the event of a grid outage, a specially configured transfer switch disconnects the grid from the PV source and connects the PV source to a backup source. The grid-tie inverter again matches the AC power from the PV source with AC power from the backup source to enable continued operation of the PV source during the grid outage. The backup source may utilize an electrolyzer that generates stored hydrogen and a hydrogen fuel cell that converts the stored hydrogen to electricity.

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.