1.1 project overview
Huaneng Shanxi Dongmafang wind farm phase III project is connected to 110kV busbar through 35kV/110kV main transformer for grid connection, and the fan inverter is connected to 35kV bus through box-type transformer. Due to the instability of wind power generation, relevant national regulations require that the grid connection point voltage at the high voltage side of the station should be controllable, and the station should be equipped with dynamic reactive power compensation equipment to control the system voltage. The actual SVG device of the project is shown in Figure 1.1, and the project was put into operation in 2016.
Figure 1.1 photos of SVG equipment of Huaneng Dongmafang project
1.2 Technical scheme
This project adopts the centralized management mode of system voltage, and is equipped with SVG equipment under 35kV busbar. SVG equipment can dynamically control the system voltage in real time according to the voltage command set, and the voltage command is sent to SVG controller remotely by AVC control system.
The SVG equipment detects the busbar voltage of 110kV side in real time, and the received AVC command is taken as the voltage control target for closed-loop control.
1.2.1 SVG equipment information
SVG rated voltage: 36.75 kV (designed according to actual busbar rated voltage)
SVG rated capacity: ± 16 Mvar (according to 20% - 40% of the wind farm installed capacity)
SVG connection mode: wye-connection
1.2.2 SVG main circuit topology
The topology of the main circuit is shown in Figure 1.2. After cascading, the SVG modules are directly connected to the 35kV busbar through the connecting reactor.
1.3 Application effect
Figure 1.2 shows the set value of voltage command (the command is given by AVC system), the actual voltage of the system and the reactive power output by SVG.
Figure 1.2 system voltage control curve
According to CCTV, at 13:21 on December 25, 2018, with the successful grid connection of No. 57 wind turbine, 72 sets of wind turbine of State Power Investment Corporation Dafeng H3 offshore wind power project was successfully put into full capacity operation and grid connection.It marks that the farthest offshore wind farm in China has been put into operation, that the project has successfully realized full capacity grid connection, and that it has set three records among similar scale offshore wind power projects,which are commencement,completion and profit in the same year It also accumulates valuable experience for China to develop large capacity and large-scale offshore wind power in the deep-sea field.
At present, large-scale wind farms are composed of hundreds or even thousands of wind turbines with various types (doubly fed wind turbines, squirrel cage wind turbines, direct drive wind turbines, etc.), different control parameters and different operation modes. Most wind farms are located in remote areas, far away from the load center, and the short circuit ratio (SCR) of the grid connection point decreases with the increase of the number of wind turbines connected to the grid, forming a weak AC system. At the same time, large-scale wind farms often use high voltage direct current (HVDC) technology or series compensation technology to realize long-distance transmission. Relevant research shows that subsynchronous oscillation may occur when wind farm is integrated into weak AC system, series compensation system and HVDC system.