Ejina Banner is located at the westernmost end of Inner Mongolia Autonomous Region, with a vast territory and remote location. The power grid in Ejina region is only connected to the main grid through one circuit of 220kV line. The power grid was weak and the reliability of power supply was low, greatly affecting industrial and residential power consumption in the region. The "source grid load storage" new power system pilot project in Ejina region has built a 25MW/25MWh energy storage system and 7.2MW diesel generator on the basis of existing power grids, wind power, and photovoltaic power generation. By optimizing and integrating local source, grid, and load resources, and increasing regulatory and supportable resources, it has achieved that the regional power grid can operate in grid connection and off grid modes, strengthening the local power grid, by completely solving the problem of power supply reliability in Ejina Banner.
NR provided a complete set of grid-forming type energy storage system equipment and a "source-grid-load-storage" control and management system for the project. In addition to providing all the functions of conventional energy storage such as peak to valley shift, smooth new energy, black start, and power backup, the NR grid-forming type energy storage system also achieves power self-synchronization control by controlling the internal potential amplitude and phase angle, presenting a voltage source characteristic. The energy storage system configured for the project has a short time high overload capacity of 2.25 times, achieving local fast primary frequency modulation, rotational inertia, and other multi-time scale control functions, effectively improving system inertia and short circuit capacity, improving grid damping characteristics, and providing fast dynamic reactive compensation, enhancing voltage support for the grid. It is the cornerstone of stable operation of power grids in weak regions. In 2022, NR grid-forming energy storage systems were successively put into operation for five projects, reflecting the strong demand for grid-forming energy storage technology in the construction of new power systems.
RTDS Simulation Test of "Source-Grid-Load-Storage" in Ejina Region
The "source-gird-load-storage" control and management system is the core control system of the regional power grid. In addition to the scheduling functions of collecting, monitoring, and managing the regional power grid, it is more important to have the decision-making ability to ensure the stable operation of the power grid under various operating modes. For this purpose, NR has established a RTDS simulation test platform for the Ejina regional power grid, which has completed all the test contents, including unplanned and planned grid to off-grid transition, planned off-grid to grid transition, system steady-state and transient simulation under grid and off grid modes, system black start, and protection setting adaptability analysis, to evaluate the flexible switching ability and safety stability of the system in multiple operation modes. The correctness of the voltage source support function of grid-forming type energy storage and the coordinated control strategy of source network load and storage is verified, providing model and data support for on-site testing and future operation, and ensuring the smooth implementation of the project.
New power systems, especially regional systems, face several core issues of system security and stability - power and energy balance, short circuit current, voltage stability, and frequency stability. Conventional energy storage can only meet the needs of energy balance. The application of grid-forming type energy storage in the Ejina project has solved the problem of system stability during the promotion of "source-grid--load-storage" in recent years, supporting the frequency, voltage, and short circuit current of the system, improving the reliability of the system, and ensuring stable operation of the system.
The new power system pilot project in Ejina region is based on exploring the development path of building a highly integrated new power system with "source-grid--load-storage", providing a solid foundation and guarantee for establishing an advance power system stability awareness system, promoting the high-quality development of remote weak power grids, promoting the efficient use of clean energy.