The invention relates to an island detection method of a photovoltaic grid-connected system. In views of the problems that independently-adopted passive detection mode is effective only when effective when mismatching degrees of source and load are large and a large non-detection zone (NDZ) can be accordingly provided; and when an active detection mode is independently-adopted, the system is disturbed, and therefore the disturbance results in instability of the system, and accordingly over-voltage / under-voltage is provided. An over-frequency / under-frequency detection method is combined with an improved impedance detection method to conduct island detection to the system, and therefore the NDZ is reduced to a minimum, quality of electric energy is improved and total harmonic distortion (THD) is reduced.

Island detection method of photovoltaic grid-connected system

In one aspect, a method for controlling the operation of a power generation system configured to supply power to an electrical grid may generally include detecting an occurrence of an islanding event associated with the power generation system and adjusting a regulator gain applied within a regulator of the power generation system to an islanding gain value in response to the detection of the islanding event, wherein the islanding gain value exceeds a maximum gain value defined for the regulator in the event of an occurrence of any ride-through transient event In addition, the method may include controlling a power converter of the power generation system based on a control signal generated by the regulator as the power generation system is being isolated from the electrical grid and shutting down the power generation system upon isolation of the power generation system from the electrical grid

System and method for controlling a power generation system based on a detected islanding event

Active island detection method of multi-distributed power supply tied-grid

The invention discloses a detection method, equipment and system of a one-phase island of a three-phase grid-connected inverter. Reactive currents are injected into output currents of the inverter, the phase difference between every two phases of voltages in a three-phase voltage is calculated before the reactive currents are injected, then the phase difference between every two phases of voltages in the three-phase voltage is calculated after the reactive currents are injected, and when the sum of phase difference values are greater than a set phase threshold value, the fact that the island happens is judged. By means of the method, the fact that whether the island happens or not can be judged accurately and effectively through the phase difference values, furthermore, due to the fact that the reactive currents are injected into the output currents of the inverter, the harmonic content of output wave forms is little, and only tiny reactive power change can be achieved in the grid-connecting process of the inverter. Compared with a disturbance method based on frequency or active power in the prior art, the injected reactive currents can not influence generating capacity.

Detection method, equipment and system of one-phase island of three-phase grid-connected inverter

The invention discloses an inverter parallel system and a control method thereof; the inverter parallel system comprises an integrated controller and a plurality of inverters having different DC ends, wherein AC ends of the inverters are connected in parallel so as to serve a system output end; the integrated controller is connected with a control module of each inverter; the inverter parallel system uses an indirect integrated control mode; the integrated controller generates a synchronic signal; the control modules of each inverters use a communication quantity and current sharing controller to realize current sharing control based on pqr coordinate change. Compared with an existing indirect integrated control mode, the system and method omit a phase-locking loop so as to prevent current sharing errors caused by differences of phase-locking loops of each inverter; the control strategy of the application can provide very good current sharing effects brought by three-phase four-line parallel system with unbalanced load.

Inverter parallel system and control method thereof

The invention discloses an island detection method of a high-power photovoltaic grid-connected converter. The method comprises the following steps of: determining whether a system operates at a grid-connected power generation state, and starting up an island detection algorithm instantly if the system is at the grid-connected power generation state; detecting whether the frequency of the voltage of a port power grid is within the normal range in real time, if the frequency is not within the normal range, considering that the system is at the island state, and carrying out automatic safety stop on the system; adding reactive current Iqdisturb with the duration of td periodically within the normal range; and superposing the reactive current Iqdisturb and reactive control Icqset of the converter, thus an axis q component reference Icqref of grid-connected current of the converter is formed finally. The contradiction between two aspects of reliability of detection and the quality after grid-connected electric energy reduction for the traditional island detection algorithm is effectively solved by the method provided by the invention, and the implementation method is simple and effective.

Island detection method of high-power photovoltaic grid-connected converter

The invention discloses a three-phase inverter parallel-connection control method without an output isolation transformer. The method comprises the following steps: an output end of each three-phase inverter is connected with an LCL filter, and a filtering capacitor of each LCL filter is connected with a dumping resistor in series, so that the stability is improved, the harmonic wave of a harmonic point is limited, and stability range of control parameters is increased. By means of pre-synchronization before parallel connection and carrier synchronization in the process of parallel connection operation, the phases among the three-phase inverters and parallel-connected communication buses are synchronized, carriers among the three-phase inverters connected in parallel are synchronized, and stability of parallel connection is guaranteed. By means of the algorithms combining pole assignment capacitor voltage control and virtual resistance matching control, the response speed of the inverters is improved, the control performance is improved, and the influence on parallel-connection current sharing by circuit resistance is lowered. By means of seamless mode switching and alternative current over-current and short-circuit failure protection base on three-ring control, under the condition of absence of the output isolation transformer, the three-phase inverter parallel-connection control method is used for independently resolving short-circuit failures of a parallel-connection micro power grid.

Three-phase inverter parallel-connection control method without output isolation transformer

Method for controlling three-phase current transformer in photovoltaic grid-connected power generating system

The invention discloses a three-phase grid-connected inverter unit which comprises a unit controller and three 2-unit IGBT (Insulated Gate Bipolar Translator) modules, wherein the IGBT modules are connected with the main controller through a drive and gate circuit and are connected with the DC side through a composite busbar In the invention, a three-phase bridge arm is formed by using the three identical IGBT modules, and a standard photovoltaic three-phase grid-connected inverter unit is formed by matching unit controllers and other auxiliary devices In photovoltaic power station applications with high-power electric energy transformation need, a high-power photovoltaic grid-connected inverter device can be formed by independently connecting a plurality of three-phase grid-connected inverter units in parallel on the grid side By using the three-phase grid-connected inverter unit, the maintenance time of the inverter device is reduced, the cost of large-scale industrial production is reduced, the power output capacity of a photovoltaic array is improved to the maximum extent, and the control is relatively simple and direct

Three-phase grid-connected inverter unit

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Papers

Island detection method of high-power photovoltaic grid-connected converter

Three-phase inverter parallel-connection control method without output isolation transformer

Method for controlling three-phase current transformer in photovoltaic grid-connected power generating system

Three-phase grid-connected inverter unit