The application of FGI DCDC Converter in grid-connected Wind Turbine units
1.Background
Most of the areas rich in new energy in our country are close to the end of the power grid, and the short-circuit ratio at the transmission and connection points of new energy stations is generally low. When the short-circuit ratio drops to a certain extent, the grid connection of new energy stations may have stability issues such as sub-synchronous oscillation, which in turn may lead to situations such as wind curtailment that are not conducive to the consumption of new energy.
Grid-connected wind turbine units have stronger active and reactive power regulation capabilities, can sense grid disturbances, respond and support actively, overcome the voltage and frequency stability problems of the power system brought about by the large-scale grid integration of new energy, and improve the adaptability of short-circuit ratio. On the one hand, it addresses the issues of wind and solar power curtailment caused by safety margins, and helps increase the proportion of new energy consumption. On the other hand, it meets the application scenarios with special requirements for frequency stability, unit inertia, and active power output. The reason why the "grid-forming" function can be achieved in grid-forming wind turbine units is that an indispensable link lies in the DC/DC converter in the system. As a link between the energy storage component and the wind turbine converter, its main function is to automatically complete the bidirectional flow of energy between the energy storage component and the DC bus of the wind turbine converter according to the various working conditions of the wind turbine unit. So as to ensure that the wind power converter realizes various control functions.
2.Introduction to products
The grid-forming DC/DC converter developed by our company features two independent high-voltage DC bus interfaces, which can be compatible with the wind power converter system based on double-winding generators with a voltage level of 1140V. The entire machine adopts a modular design of power units, with each battery cluster corresponding to one set of DC/DC module, that is, one cluster is managed by one module, which can avoid circulating current between battery clusters.
Main features and technologies
Both the high and low voltage sides are equipped with buffer components, which can support the black start of the fan.
● Unit modular design, making it extremely easy to expand the overall capacity.
● The unit controls are independent of each other. In case of a failure, they can redundantly shut down and the entire machine operates under reduced capacity, significantly enhancing the reliability of the entire machine.
Two-level carrier phase-shifting technology reduces current ripple and extends battery lifespan.
● It supports multiple control modes such as constant current, constant voltage, and constant power, as well as inter-cluster SOC balancing function, meeting various application scenarios.
Application Case
A project of Hebei Jiantou is the first batch commercial project of grid-connected wind turbine generators in China. The grid-connected wind turbines adopted in this project represent the first exploration by domestic wind turbine manufacturing enterprises of the deep grid-connected function. It is a crucial step for grid-connected wind turbines to move from technological development to large-scale commercial application.
The switching time from full-power discharge to full-power charging of the DC/DC converter is 9ms, and the switching time from full-power charging to full-power discharge is 5.6ms. Both are less than 10ms, fully meeting the control requirements of the wind power converter.
A total of 5 grid-connected units were installed in this project. Each unit is equipped with our company's grid-connected DC/DC energy storage system. After on-site testing, all performance indicators met the requirements of the grid-connected units.
