Abstract: Large and medium-sized photovoltaic power plants also have corresponding power supply characteristics and frequency anomaly response characteristics. They can participate in the voltage and frequency regulation of the power grid to a certain extent, and have the ability to withstand voltage abnormalities, so as to avoid detachment when the power grid voltage is abnormal and cause the power grid. Power loss. I. Technical requirements for photovoltaic power stations to access the power grid There are three types of grid-connected photovoltaic power stations in accordance with the voltage class: small photovoltaic power stations (with an access voltage rating of 0.4kV), medium-sized photovoltaic power stations (with an access voltage rating of 35kV), and large-scale photovoltaic power stations (with an access voltage rating of 66kV or more). . According to whether it is allowed to send power to the public power grid through public connection points, it can be divided into reversible and irreversible access methods. The requirements for the power quality of grid-connected photovoltaic power plants follow the following standards: GB/T1459-1993 "Power Quality Public Power Harmonics"; GB/T12325-2008 "Power Quality Public Power Harmonics" GB/T12326-2008 "Power Quality Public Power Harmonics" GB/T15543-2008 "Power Quality Public Power Harmonics" When the photovoltaic power station is connected to the grid, the direct current component fed to the grid does not exceed 0.5% of its AC rated value. Large and medium-sized photovoltaic power plants also have corresponding power supply characteristics and frequency anomaly response characteristics. They can participate in the voltage and frequency regulation of the power grid to a certain extent, have the ability to withstand voltage abnormalities, and avoid disconnection when the power grid voltage is abnormal, causing power supply power losses. . Second, photovoltaic power stations must meet the following conditions to access the power grid 1. PV power stations must set up grid-connected circuit breakers that are easy to operate, can be locked, and have obvious disconnection points at the inverter output summary points to ensure the personal safety of the maintenance personnel of power equipment. 2. The lightning protection and grounding of photovoltaic power stations and grid-connected devices shall comply with the requirements of the State Grid Corporation of China. The grounding resistance of the photovoltaic power station grounding grid shall be qualified and the grounding resistance shall be tested according to the specified period. 3. In case of abnormality or failure of the photovoltaic power station or power grid, the protection of equipment and personal safety shall be provided with appropriate relay protection functions to protect the safe operation of the power grid and photovoltaic equipment and ensure the personal safety of maintenance personnel and the public. The protection of photovoltaic power plants should meet the requirements of reliability, selectivity, flexibility, and quickness. 4. The over-current and short-circuit protection, anti-islanding capability, protection of inverter, and grid connection of photovoltaic power plants shall meet the requirements of the national grid. 5. The design and configuration of the secondary DC system of the photovoltaic power station and the discharge capacity of the battery shall comply with the technical requirements of the relevant regulations. 6. The power quality of the photovoltaic power plant meets the requirements of the regulations, voltage harmonics and waveform distortion, voltage deviation, voltage fluctuation and flicker, voltage unbalance, and DC component within the specified range. 7. The safety automatic device of photovoltaic power station should be fully configured as required. 8. The photovoltaic power plant to power grid dispatching agency has a reliable route for independent routing. 9. Photovoltaic power plants shall hire a test unit with appropriate qualification within 6 months of grid-connected operation to carry out the operational characteristics test of the photovoltaic power plant and provide the power grid enterprise with a test report of the operating characteristics. The test content shall meet the requirements of the State Grid. 10. The photovoltaic power station shall have the following materials and submit to the dispatching institution as required: Technical specifications and technical parameters of the main equipment of the photovoltaic inverter system and the output system; drawings, manuals, and debugging of relay protection and safety automatic devices related to the network. Report; Dispatch automation equipment technical specifications, technical parameters and equipment acceptance reports; motion information (including current transformers, voltage transformer ratio and telemetering full-scale value) related technical data; electrical system diagram, on-site operating procedures. III. Characteristics of grid-connected PV power generation 1. Photovoltaic power generation is characterized by randomness, intermittency, and obvious periodicity. It cannot be accurately predicted at present, and it cannot participate in the power balance to enter power generation planning arrangements. Photovoltaic power consumption can only be acquired in accordance with the requirements of the “Renewable Energy Lawâ€, and after grid-connected acquisition by the power grid company; 2. Photovoltaic power generation only generates electricity during the day, with no radiation at night and zero output. After the sunrise, the solar radiation gradually increased, and reached its peak at noon. The photovoltaic power station also increased its radiation intensity and increased its output. At noon, the output was maximum. 3. When a photovoltaic power plant has a contribution, other power sources in the power grid need to adjust their output and allow the load to be supplied by photovoltaic power generation. Affected by the weather, when the output of photovoltaic power generation is rapidly declining, other conventional energy sources must provide compensation and adjustment for their active power, in order to ensure continuous, reliable and safe power supply to the power load; 4. The volatility of PV power varies randomly according to the weather conditions, and is much faster than the normal load change of the power grid. When there are clouds drifting, the output of the photovoltaic power plant can be quickly reduced by up to 70%; 5. The adjustable capacity prepared for photovoltaic power generation cannot be completed by temporary shutdown, but is in a rotating standby state. The greater the installed capacity of photovoltaic power generation, the greater the rotational reserve prepared for this purpose; China's solar power shows the development trend of “large-scale centralized development, medium- and high-voltage access†and “decentralized development and low-voltage on-site accessâ€. The “large-scale development and high-pressure transmission†model has been adopted to develop large-scale photovoltaic power stations. In northwest and north China, the resources of sunshine are rich in desert and semi-desert regions, and these regions generally have a wide geographical area, and the local electricity load is small. Therefore, the power of the photovoltaic power plant to be constructed needs long distance transmission. Fourth, the impact of grid-connected PV power generation on the power grid 1. The randomness, intermittentity, and periodicity of lighting resources will make PV power generation generate a greater impact on the power grid; 2. Photovoltaic power generation is connected to the grid via power electronic inverters, which can easily generate harmonics and unbalanced three-phase currents. The randomness of output power can easily cause grid voltage fluctuations and flicker. 3. When the proportion of photovoltaic power generation in the power supply increases, it will affect the peak-shaving ability of the power grid; 4. With the continuous increase in the number and scale of photovoltaic power plants, lighting fluctuations and cyclical changes cause voltage rises in transmission lines, and voltage stability problems in long-distance transmission; 5. Photovoltaic power generation is connected to the distribution network, so that the distribution network system will change from a radial structure to a multi-power structure, and the size, direction and distribution characteristics of the current and short-circuit current will change; 6. The failure of the photovoltaic power generation system on the line affects the relay protection and reclosing action.
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