The "dual-high" characteristics of the new power system refer to the high proportion of renewable energy integration and the high proportion of power electronic equipment application. The integration of a high proportion of new energy leads to a decline in the short-circuit capacity and rotational inertia of the power system, making issues of frequency and voltage stability prominent and posing risks to the safe and stable operation of the power grid. In addition, the power grid cannot provide sufficient electricity to remote areas such as islands and mountainous regions, where there is a demand for microgrid construction. Compared with grid-following energy storage, grid-forming energy storage technology can compensate for the inertia damping missing in the system, provide reliable voltage and frequency support for the system, and especially offer effective support for microgrids.
From 1997 to 2009, many scholars, including A-A Edris from the IEEE Task Force, Professor Beck from the University of Rostock in Germany, and Professor Zhong Qingchang from the University of Sheffield in the UK, successively proposed concepts such as "Static Synchronous Generator", "Virtual Synchronous Generator", and "Synchronverter". By simulating the mathematical model of synchronous generators, these concepts virtualize the electromagnetic characteristics, rotor characteristics, frequency modulation, and voltage regulation characteristics of synchronous generators.
In 2021, the Solar Energy Technologies Office of the U.S. Department of Energy initiated the establishment of the Universal Interoperability for Grid-Forming Inverters (UNIFI) Consortium to achieve the seamless integration of inverter-based resources such as solar energy, wind energy, batteries, and electric vehicles.
On July 27, 2022, Tesla upgraded the 150MW/193.5MWh electrochemical energy storage system at the Hornsdale Power Reserve in Australia from grid-following to grid-forming.
In December 2022, the Australian Renewable Energy Agency allocated 175 million Australian dollars for the construction and transformation of 2GW/4.2GWh grid-forming energy storage projects. In the same month, China's first grid-forming energy storage power station - the first phase of the 12.6MW/26.8MWh grid-forming energy storage project at Xinguang Port in Jingmen, Hubei - was connected to the grid.
In 2023, the on-site test of the grid-connected performance of the grid-forming photovoltaic-storage system, jointly carried out by the Qinghai Electric Power Research Institute of the State Grid and the China Electric Power Research Institute, was implemented at the Gonghe Huarun Poverty Alleviation Photovoltaic Power Station in Qinghai. In the same year, Kehua Data applied grid-forming energy storage technology in a 100MW-level shared energy storage project in Ningxia.
From 2023 to September 2024, the cumulative total bidding volume of domestic grid-forming energy storage projects was approximately 3.63GW/8.37GWh.
Grid-forming energy storage and grid-following energy storage are two different energy storage technologies, with significant differences in their applications and functions in the power system.
Grid-following energy storage: The operating state of the energy storage system depends on the voltage and frequency of the power grid. In grid-following mode, the energy storage converter accurately captures the phase information of the power grid, measures the phase of the Point of Common Coupling (PCC) through a Phase-Locked Loop (PLL), and achieves synchronization with the power grid. This control mode means that the energy storage system itself cannot provide voltage and frequency support; it must rely on the stable voltage and frequency provided by the power grid to operate normally. In islanded and off-grid modes, the grid-following energy storage system cannot operate properly. Grid-following energy storage systems are more suitable for areas with good power grid stability.
Grid-forming energy storage: It simulates the characteristics of conventional synchronous generators, can independently set voltage parameters, output stable voltage and frequency, improve the voltage and frequency support capabilities of the converter, and enhance the stability of the power system. In terms of frequency and inertia support, the grid-forming energy storage system controls the release of energy stored on the DC side, which is equivalent to the mechanical energy of the synchronous machine's inertia or damping energy, thereby providing inertia response and oscillation suppression.
There are mainly two control technologies for inverters: grid-following control technology and grid-forming control technology. Currently, grid-connected energy storage inverters usually adopt grid-following control technology.
According to data from the GGII (High-Tech Industry Research Institute Energy Storage Research Institute), the penetration rates of grid-forming energy storage in Australia, Europe, the United States, and China in 2023 were 23%, 8.6%, 2.6%, and 1.3% respectively. In terms of installed capacity of grid-forming energy storage, the cumulative installed capacity in Australia was approximately 0.53GW in 2023, 0.46GW in China, 0.34GW in Europe, and 0.21GW in the United States. GGII predicts that China's cumulative installed capacity of grid-forming energy storage will reach 2GW in 2024 and 7GW in 2025. In terms of total bidding volume, from 2023 to September 2024, the cumulative total bidding volume of China's grid-forming energy storage projects was approximately 3.63GW/8.37GWh.
GGII expects that the global penetration rate of grid-forming energy storage will reach 20% in the next 5 years. The "2024 White Paper on the Development of China's New Energy Storage Industry" predicts that China's cumulative installed capacity of new energy storage will reach 170GW by 2030. Assuming that grid-forming energy storage accounts for 15%-20% of new energy storage, it is estimated that China's cumulative installed capacity of grid-forming energy storage will reach 25.5GW-34GW by 2030.
1.300MW/1200MWh Grid-Forming Independent Energy Storage Project in Kizilsu Kirghiz Autonomous Prefecture, Xinjiang
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2."Photovoltaic-Storage-Direct Current-Flexible" New Power Distribution System Project in Zhuangshang Village, Ruicheng County, Yuncheng City
3.50MW/100MWh Energy Storage Power Station at Xinguang Port, Jingmen, Hubei
VI. Development of Grid-Forming Energy Storage and Virtual Power Plants
A Virtual Power Plant (VPP) integrates a large number of geographically dispersed distributed power sources, energy storage, adjustable loads, and other resources through advanced communication, control, and management technologies, forming a unified entity externally. It participates in the operation of the power system and power market transactions like a traditional power plant. Whether a virtual power plant can provide inertia support for the power grid like a traditional synchronous power plant is crucial to the safe and stable operation of the future power grid with high penetration of renewable energy. Virtual Synchronous Generator (VSG) control is an effective way for grid-forming inverters to provide inertia support. By simulating the rotor motion equation of a synchronous generator, VSG introduces an inertia link while retaining the frequency/power static error characteristics. The use of grid-forming inverters to build a synchronous virtual power plant can realize the dynamic optimal control of the inertia level of the virtual power plant.
VII. Future Development Trends of Grid-Forming Energy Storage
With the continuous increase in the penetration rate of new energy, the transformation from "grid-following" to "grid-forming" has become an industry consensus and one of the future development trends of energy storage technology.
The future development of grid-forming energy storage technology will show the following trends:
Trend 1: The development of grid-forming photovoltaic-storage integration technology will enable photovoltaic systems to have strong inertia support, instantaneous voltage stabilization, and fault ride-through capabilities, alleviating the frequency and voltage fluctuations of photovoltaic power generation and improving the economy of photovoltaic matching with energy storage.
Trend 2: Compared with synchronous machines, power electronic equipment has poor overcurrent capacity, and its power is easily limited when providing short-circuit capacity and inertia support. Manufacturers are committed to improving the overcurrent capacity of grid-forming devices.
Trend 3: For application scenarios such as distributed systems and microgrids, the switching between grid-connected and off-grid modes is crucial. The switching between grid-connected and off-grid modes may cause parameter oscillations in the system, which needs to be made smoother, mainly through algorithm optimization. The improvement of grid-forming control strategies is conducive to realizing the free switching between grid-connected and off-grid modes.
Trend 4: The increase in the proportion of grid-forming equipment leads to greater control difficulty. From the perspective of the power system, it is necessary to consider the reasonable configuration of grid-forming equipment and grid-following equipment.
Trend 5: The state has not yet issued unified standards for grid-forming equipment, and unified technical standards may be formed in the future.
Source: Zhang Jiaxun, Investment Department IV
Review: Xue Yao
Release: You Yi
