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Photovoltaic grid-connected detection

2020-06-30 15:32:04

76% of our country is full of light, and the distribution of light energy resources is relatively uniform. Compared with hydropower, wind power, nuclear power, etc., solar power generation does not have any emissions and noise, so I will allow the editor and you to talk about the problem of photovoltaic power grid connection in detail. 

I. definition of grid connection of photovoltaic power generation. 

Photovoltaic power generation system can be divided into off-grid photovoltaic power generation system and grid-connected photovoltaic power generation system. The investment of grid-connected photovoltaic power generation system is 25% less than that of off-grid photovoltaic power generation system. 

Photovoltaic grid-connected power generation system is the solar photovoltaic power generation system connected with the conventional power grid, sharing the task of power supply. When there is sunshine, the alternating current generated by the photovoltaic system is supplied directly to the AC load, and then the remaining power is input into the grid, or all the generated electricity is directly incorporated into the grid. When there is no sun, the load is powered entirely by the power grid. 

Second, the structure and principle of photovoltaic grid-connected system. 

The structure diagram of the photovoltaic grid-connected system is shown in the following figure, which mainly includes photovoltaic cell array, bus box, DC cabinet, photovoltaic system controller, inverter, battery pack device, distribution boost system and so on. The photovoltaic cell array is composed of a number of photovoltaic cell modules in series and parallel, which converts solar energy into electric energy through a photoelectric conversion device, and the convergent box collects and raises the output voltage of the photovoltaic cell array to be transmitted to the inverter through the DC cabinet. the inverter inverts the DC current into sinusoidal alternating current, and the resulting alternating current can be supplied directly to the AC load, and then the voltage is raised to the requirement of grid connection through a boost transformer, and finally connected to the power grid. At the same time, the power grid has the function of remote monitoring and data collection.

Third, the impact of distributed photovoltaic generation connected to the grid on power quality? 

Photovoltaic power generation has the characteristics of volatility, discontinuity and dispersion, and the power quality is extremely unstable. Therefore, the power quality monitoring device is mainly installed in front of the grid to achieve real-time monitoring of power quality in all aspects. 

1.Voltage flicker and fluctuation. 

The start-up of large-scale distributed photovoltaic system and the influence of voltage control equipment of photovoltaic system and feedback link often lead to flicker and fluctuation of the line. 

2. Harmonics, interharmonics, high-order harmonics and harmonic subsets. 

Pulse modulation technology is usually used in photovoltaic power stations to convert direct current into alternating current, and a large number of harmonics will be generated in this process. Because of the characteristics of the switching elements of the inverter, there are serious high-frequency harmonics near the integer times of the switching frequency. The existence of such harmonics will cause current distortion. 

3. Voltage transient events occur frequently. 

Large-scale distributed photovoltaic power generation system will cause voltage rise, sag and many other transient events during start-up. 

4. The power fluctuates greatly. 

Because the power factor of the controller integrated by the inverter is generally about 0.99, it is necessary to compensate the reactive power to the power grid. 

The output active power and reactive power need to be monitored in real time.

4. So the question is, who is the escort for photovoltaic power generation to be connected to the grid? 

1.Fully functional and accurately locate power quality problems. 

Guangzhou Xuantong Electric PM610 power quality on-line monitoring device has passed the certification of electromagnetic compatibility in Cape Laboratory, electromagnetic compatibility certification of National Power Network Electric Science Academy, certification of Experimental Research Center of State Power Network Electric Power Science Institute and Guangxi Institute of Electrical Sciences, and the measurement accuracy is completely in line with IEC61000-4-30A standards and national standards. The device not only has basic voltage, current and frequency measurement and recording, but also supports 1-50 harmonic analysis, long flicker and short flicker monitoring, voltage fluctuation and fault recording, component measurement and voltage unbalance analysis, power system frequency fluctuation monitoring and recording and power quality exceeding the standard.

2. PQS power quality monitoring system realizes unified management in the background. 

In order to monitor the power quality in the photovoltaic grid-connected mode in real time, it is necessary to carry out on-line power quality monitoring to realize the unified management of background monitoring. 

The main functions of Guangzhou Zhiyuan electronic power quality online monitoring system are as follows: 

Real-time data viewing, you can monitor terminal equipment data in real time through tables, trend charts, vector diagrams and other ways. 

Historical data query, users can view the power data of a specified period of time, and carry out statistical analysis. 

Event alarm notification. Users can view specified time periods and specified types of transient and steady-state event alarms. 

Report statistics function, statistics report by hour, day, month, custom time period, provide report preview, and export report to Excel, RTF format documents, convenient to help users summarize power quality problems.

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