|
Dimension |
Grid-Forming Energy Storage |
Grid-Following Energy Storage |
|
Control Logic |
Independently sets the grid voltage and frequency, acting as the "leader" of the power grid |
Relies on the grid voltage and frequency as reference benchmarks, acting as a "follower" of the power grid |
|
Independence |
Can operate independently (such as in islanded microgrids, black start) |
Must rely on a stable power grid for operation and cannot form a grid independently |
|
Core Function |
Actively constructs the power grid framework, providing voltage/frequency support, inertial response, damping oscillation, etc |
Passively responds to grid demands, adjusting active/reactive power (such as peak shaving and valley filling, smoothing fluctuations) |
|
Key Technologies |
Virtual Synchronous Generator (VSG), autonomous voltage and frequency control (V/f), multi-machine parallel coordination algorithms |
Phase-Locked Loop (PLL), PQ control mode, traditional inverters |
|
Response Speed |
Millisecond-level dynamic response (such as frequency regulation) |
Second-level to minute-level response (relies on external commands) |
|
Applicable Scenarios |
Power grids with a high proportion of new energy, weak grids/off-grid systems, black start, power grid fault recovery |
Grid-connected applications under stable and strong power grids (such as wind-solar-storage matching, user-side energy storage) |
|
Hardware Requirements |
High-dynamic power electronic converters, complex control algorithms |
Conventional inverters, relatively simple control |
|
Cost and Complexity |
High initial investment, high control complexity |
Lower cost, easy for large-scale deployment |
Source: https://zhuanlan.zhihu.com/p/29905526972
This article focuses on the comparison between grid - forming and grid - following energy storage. It elaborates on their technical principles, control methods, operational characteristics, application scenarios, and development trend. The aim is to provide a comprehensive understanding of these two types of energy storage for relevant professionals and offer references for the selection and application of energy storage technologies in different power system scenarios.
1.Technical principle
Grid-forming energy storage: By simulating the operational characteristics of traditional synchronous generators, it actively provides voltage and frequency support for the power grid. It can independently provide stable power to the load when the power grid does not exist or is unstable. The grid-type energy storage system is essentially a voltage source that can internally set voltage parameters and output stable voltage and frequency1.
Grid-following energy storage: It operates relying on the voltage and frequency of the power grid and is synchronized with the grid through phase-locked loop (PLL) technology. Grid-following energy storage systems are essentially current sources and cannot provide voltage and frequency support by themselves. They must rely on the voltage and frequency of the power grid1.
2.Control strategy
Grid-forming energy storage: It adopts a power synchronization strategy similar to that of a synchronous generator, regulating the active and reactive power output by adjusting the phase Angle and amplitude of the output voltage. The grid-structured converter can operate in parallel or off-grid mode. When supplemented with energy storage components or reserved backup capacity, the grid-structured converter can also provide virtual inertia and damping for the system2.
Grid-following energy storage: Its control strategy is to obtain the phase of the power grid through a phase-locked loop to control the amplitude and phase Angle of the current injected into the power grid. Grid-following converters rely on the power grid and must operate in parallel. They cannot provide voltage and frequency support by themselves2.
3.Operational characteristics
3.1Grid-forming energy storage
Overload capacity: The grid-type energy storage system has the ability to operate continuously for a long time at an alternating current of 110% of the rated current. At 120% of the rated current, the continuous operation time should be no less than 2 minutes. At 150% of the rated current, the continuous operation time shall be no less than 1 minute, and at 300% of the rated current, the continuous operation time shall be no less than 10 seconds3.
Active voltage support: Participate in the dynamic voltage regulation of the power system and provide short-term reactive power support during the system's transient period. Grid-type energy storage systems possess active power regulation characteristics similar to those of synchronous generators, and also have the ability to regulate internal power potential and reactive power voltage3.
Short-circuit current support: Grid-type energy storage should provide a certain short-circuit current, and its overload capacity should be no less than three times the rated current. The overload continuous operation time should be no less than 10 seconds. The short-circuit support capacity of grid-structured energy storage can be achieved through various means such as enhancing the capacity of converters and paralleling multiple units. When multiple machines are operating in parallel, the circulating current of the common machine is less than 5%3.
3.2Grid-following energy storage
Dependent on grid signals: Its control depends on the frequency and voltage signals of the power grid for regulation. This means that in grid-following energy storage, the power grid is the "main control" party, and the energy storage system merely serves as a supplementary regulator for the power grid4.
Power regulation: Mainly used for frequency regulation, load balancing, frequency adjustment, peak shaving, etc. in the power grid, helping the power grid maintain stability when demand fluctuates or the generation of renewable energy is unstable4.
4.Strengths and Weaknesses
4.1Grid-forming energy storage
Advantages: It has the ability to adjust its output in real time by mobilizing its own operation without external power supply. By adjusting the power output, it maintains the voltage output, forms a voltage source grid connection, and keeps the system stable. Additionally, in a weak power grid without a rigid voltage source, it can form an independent power grid5.
Disadvantage: The overcurrent capacity of the grid-forming PCS increases from 1.5 times to 3.0 times, so the cost is significantly higher than that of the grid-following type5.
4.2Grid-following energy storage
Advantages: The control structure is simple, and the phase-locked loop technology is relatively mature at present. Therefore, the system can be controlled under the condition that the current and the maximum power point of the system are determined5.
Disadvantages: Although the phase-locked loop technology relied upon for control is relatively mature, it still passively acquires stable frequency and voltage reference values provided by the power grid to operate normally. Moreover, the stability of its own control loop is weaker than that of grid-forming energy storage loops, and it cannot play an active role in supporting the system5.
5.Application scenarios
5.1Grid-forming energy storage
Weak power grids or areas at the end of power grids: The regional power grid structure is relatively weak, with limited transient regulation capacity. New energy is abundant but the load demand is low, making stability issues prone to occur. Grid-forming energy storage can effectively enhance the strength of these weak power grids, improve the grid-friendliness and carrying capacity of new energy6.
Source: http://xz.people.com.cn/n2/2024/1111/c138901-41037675.html
Island microgrid operation: For islands far from the mainland, remote mining areas, border guard posts, and certain industrial parks that require island operation, grid-type energy storage can be used as the main power source to independently form a stable microgrid and operate in coordination with other power sources such as photovoltaic and diesel generators to ensure reliable power supply6.
Source: http://www.cnnes.cc/hangye/20240604/8166.html
High proportion of new energy base transmission: In large-scale integrated wind, solar, thermal and energy storage bases or shared energy storage power stations, the configuration of grid-type energy storage can solve the stability problem of new energy DC transmission and improve the efficiency and reliability of transmission channels such as ultra-high voltage6.
Source: https://www.hoenergypower.cn/news_1/12.html
Provide grid auxiliary services: In the future power market, grid-forming energy storage can participate in auxiliary services such as primary frequency regulation, inertia response, and reactive power support by virtue of its rapid regulation capability and multiple support functions, and obtain profits6.
5.2 Grid-following energy storage
Grid frequency regulation and peak shaving: It can quickly respond to changes in grid frequency and load, and adjust the release of stored electrical energy4.
Power grid frequency regulation: By operating in synchronization with the power grid, it provides immediate support for fluctuations in power grid frequency4.
Load balancing: Providing power support during peak electricity demand periods to reduce the burden on the power grid4.
Overall, grid-following energy storage is suitable for application scenarios where the grid stability is relatively good and no additional voltage and frequency support is required. For instance, in large urban power grids, due to the well-developed grid structure and high stability, grid-following energy storage systems can effectively supplement the grid load and enhance the reliability of power supply1.
6.Development Trends
With the continuous increase in the penetration rate of new energy, the transformation from "following the grid" to "constructing the grid" has become a consensus in the industry and is also one of the future development trends of energy storage technology7.
As an emerging technology, grid-structured energy storage is still in the exploratory stage in the industry, facing challenges such as high technical barriers, high costs, and the lack of unified standards7.
Grid-forming energy storage technology is an essential need to support the construction of a new power system. To address the challenges brought by the "dual-high" power grid (high proportion of clean energy and high proportion of power electronic devices), such as randomness, volatility, low inertia, and discretization in power generation, grid-forming technology is required to provide support for frequency stability, voltage stability, and power Angle stability7.
In the future, with the advancement of technology and the reduction of costs, grid-structured energy storage systems are expected to be applied in more regions and become one of the key technologies for the power system's transition to a higher proportion of renewable energy7.
1.CSDN, "Triangulation difference between energy storage and with net energy storage" https://blog.csdn.net/sean9169/article/details/146165002
2. Zhihu, "Type structure network control technology" https://zhuanlan.zhihu.com/p/684706863
3. China Energy Storage Network, "What are the principles and technical indicators of grid-structured energy storage?" https://www.escn.com.cn/news/show-2121742.html
4. International energy storage network, "With net type energy storage type and structure network storage" https://www.chu21.com/html/chunengy-42328.shtml
5. The power network, "Contrast is aralyzed and with net energy storage technology" https://www.dianyuan.com/bbs/2738370.html
6. Storage network industry, "Net type energy storage: stable foundation stone of the future power grid" https://www.chujiewang.net/cxw/col133/9327
7. Power Grid, "Comprehensive Interpretation of Grid-Following and Grid-Forming Energy Storage: Technology Comparison and Future Trends" http://www.chinapower.com.cn/chuneng/dongtai1/20240627/251593.html
