The influence and solution of grid-connected photovoltaic power generation on power quality

2) After the island effect occurs in the photovoltaic power generation system, if the original power supply mode is single-phase power supply mode, it may cause the problem of three-phase load asymmetry in the distribution network, and then reduce the overall quality of electricity consumption of other users.

3) In the process of power supply recovery, inrush current will be generated due to the asynchronism between voltage phases, which may cause the grid waveform to drop instantaneously.

4) In the location where the island effect occurs, its voltage and frequency fluctuate greatly, which reduces the power quality, and the voltage and frequency in the island are not controlled by the power grid, which may cause damage to the system electrical equipment and reclosing failures, and may also cause personal safety hazards to the power grid maintenance personnel. Ankerui manufacturer Wang Jinjing 13-77+443+09-92

For the impact of island effect, there are mainly the following solutions:

Optimize the island detection method of grid-connected photovoltaic power generation system, analyze the influence of photovoltaic power generation on the size, direction and distribution of fault current in distribution network, and improve the selection technology of load cutting speed and island division under fault conditions.

2) Improve the reliability of island detection technology, configure fast and effective anti-island protection function, accurately judge the island status under abnormal circumstances and quickly and effectively interrupt the grid connection.

Aiming at the power quality problem after photovoltaic access, the effective methods of suppressing harmonics are put forward: 1) Starting from the source of harmonic generation, the harmonic source is reformed to reduce harmonic injection. Wang Jinjing 13-77+443+09-92, 2) Device active or passive filter to absorb some specific number of harmonic current. 3) Install additional harmonic compensation devices.

3.2 Voltage fluctuation and flicker

In the traditional distribution network, the change of active power and reactive power with time will cause the system voltage fluctuation. For photovoltaic power generation, the change of active power of photovoltaic power generation system is the main factor that causes voltage fluctuation and flicker of access point. Wang Jinjing 13-77+443+09-92, the high power point of photovoltaic panels, the core components of photovoltaic power generation system, is closely related to radiation intensity, weather, season, temperature and other factors, and the random changes of these natural factors cause the output power to change greatly, resulting in frequent changes in the load power within a certain range. It causes the load terminal voltage fluctuation and flicker of grid-connected users.

At present, the solutions to the photovoltaic voltage fluctuation and flicker problems are as follows: 1) Optimize the control strategy of photovoltaic grid-connected inverters to improve the voltage stability; 2) Increase the short circuit capacity of the substation bus; 3) When the capacity of the photovoltaic power station is determined, its power factor is increased to increase the total active power, thereby reducing the amount of reactive power change and meeting the limit requirements of voltage fluctuations.

3.3 Harmonic Effects

Photovoltaic power generation is to convert solar energy into direct current through photovoltaic modules, and then through the grid-connected inverter to convert direct current into alternating current to achieve grid-connected. In the photovoltaic power generation system, the inverter is the main equipment to produce harmonics. The large number of applications of power electronic components in grid-connected inverters has improved the information and intelligent processing of the system, but it also increases a large number of nonlinear loads, causing waveform distortion and bringing a large number of harmonics to the system. The delay of the switching speed of the inverter will also affect the output of the overall dynamic performance within the power system, resulting in a small range of harmonics. If the weather (irradiance, temperature) changes greatly, the fluctuation range of harmonics will also become larger. Although the output current harmonics of a single grid-connected inverter are small, the output current harmonics of multiple grid-connected inverters will be superimposed after they are connected in parallel, resulting in the phenomenon of output current harmonics exceeding the standard. In addition, the parallel connection of inverters is easy to produce parallel resonance, which leads to the coupling resonance phenomenon, resulting in the expansion of specific harmonic current and the problem of excessive harmonic content of grid-connected current.

4 Ankerui Solutions

4.1 Online monitoring of power quality

The APView500 power quality online monitoring device adopts a high-performance multi-core platform and embedded operating system, and measures the power quality indicators according to the measurement methods specified in IEC61000-4-30 "Test and Measurement Technology - Power Quality Measurement Methods". It integrates harmonic analysis, waveform sampling, voltage dip/rise/interrupt, flicker monitoring, voltage unbalance monitoring, event recording, measurement control and other functions. Wang Jinjing 13-77+443+09-92, the device has reached IEC61000-4-30 Class A standard in all aspects of power quality index parameter measurement method standardization and index parameter measurement accuracy, clock synchronization, event marking function, etc. It can meet the requirements of power quality monitoring of 110kV and below power supply systems.