The present application discloses a multi-channel grid-connected power generation system and a control method therefor, which lowers the system cost while reducing no-load losses of all step-up transformers. Multi-channel energy conversion devices in the system are each connected in parallel, by means of a step-up transformer, to the same collector line, one end of the collector line is connected to the grid by means of a switch device, and the on-off switching of the switch device is controlled by a control unit. The control unit sends a switch-off command to the switch device when same has determined that all of the energy conversion devices have entered a non-operating state. In the off state of the switch device, at least one energy conversion device, when meeting a start-up condition, starts to operate as a voltage source, and establishes an alternating-current voltage, so that the phase difference and amplitude difference of voltages at two ends of the switch device are both stable within an allowable error range. Then, the control unit sends a switch-on command to the switch device, and the other energy conversion devices start to operate as a current source to transfer energy to the grid.

A phasor measurement unit (PMU) of the present disclosure measures phasor, i.e., magnitude and phase angle of voltage and current, and related data from a specific location on the electrical gird synchronized to a common time source. The time-synchronized phasor is called a synchrophasor. In a system of the present disclosure, a plurality of PMUs transmit the synchrophasors and related data to a phasor data concentrator (PDC), which aggregates and time-aligns the data for real time and post analysis. The PMU of the present disclosure further functions as a power quality meter determining at least one of symmetrical components' phasor, frequency, rate of change of frequency, high-speed digital inputs, analog fundamental power and/or displacement power factor.

A phasor measurement unit (PMU) of the present disclosure measures phasor, i.e., magnitude and phase angle of voltage and current, and related data from a specific location on the electrical gird synchronized to a common time source. The time-synchronized phasor is called a synchrophasor. In a system of the present disclosure, a plurality of PMUs transmit the synchrophasors and related data to a phasor data concentrator (PDC), which aggregates and time-aligns the data for real time and post analysis. The PMU of the present disclosure further functions as a power quality meter determining at least one of symmetrical components' phasor, frequency, rate of change of frequency, high-speed digital inputs, analog fundamental power and/or displacement power factor.

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 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 physical address determining method, apparatus, and device, and a storage medium, and belongs to the field of solar power generation, includes: controlling at least two slave nodes to sequentially start up, and detecting a change status of an input voltage of the master node; dividing a photovoltaic power generation system into a plurality of photovoltaic strings; and for each candidate photovoltaic string, controlling any slave node located in the candidate photovoltaic string to start up and other slave nodes to shut down, and using the physical address as a physical address of the candidate photovoltaic string. This disclosure provides a manner of automatically determining a physical address of a photovoltaic string, thereby implementing photovoltaic-string locating and expanding a system function range. When an anomaly occurs, the anomaly can be eliminated in a timely manner, thereby improving system stability.

A physical address determining method, apparatus, and device, and a storage medium, and belongs to the field of solar power generation, includes: controlling at least two slave nodes to sequentially start up, and detecting a change status of an input voltage of the master node; dividing a photovoltaic power generation system into a plurality of photovoltaic strings; and for each candidate photovoltaic string, controlling any slave node located in the candidate photovoltaic string to start up and other slave nodes to shut down, and using the physical address as a physical address of the candidate photovoltaic string. This disclosure provides a manner of automatically determining a physical address of a photovoltaic string, thereby implementing photovoltaic-string locating and expanding a system function range. When an anomaly occurs, the anomaly can be eliminated in a timely manner, thereby improving system stability.

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.

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.

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.