Abstract
Under the goals of “carbon peaking and carbon neutrality,” the installed capacity of renewable energy generation in the power system continues to rise sharply. To address the frequency stability issues caused by the integration of large-scale renewable energy, energy storage system can be introduced to assist in grid frequency regulation. Leveraging their rapid response and high control accuracy, energy storage system can significantly improve the effectiveness of grid frequency regulation. This paper reviews the research status of energy storage system-assisted secondary frequency regulation of the power grid, including necessity and feasibility analysis, the establishment of a general model for energy storage system-integrated power grids, control strategies, and optimal capacity allocation. It also identifies current research shortcomings and outlines key future research directions and the application potential of this field.
1. Introduction
With the accelerating industrialization and urbanization processes, the environmental pollution and energy shortage issues caused by traditional fossil fuel consumption have become increasingly severe. The development and utilization of clean energy and the optimization of the energy structure to promote sustainable economic and social development have gained widespread recognition. To ensure sustainable development for human society, clean energy sources, represented by wind and solar power, have entered the field of power generation. Prioritizing the development of renewable energy such as wind and solar power is a crucial measure to achieve the “dual carbon” targets. However, the output power of renewable energy generation units, such as wind and photovoltaic power, exhibits instantaneous and complex characteristics due to the high proportion of power electronic devices, leading to dynamic imbalances between active power output and active power consumption, thereby causing frequency stability issues in the power system. Therefore, maintaining the stability of power system frequency to ensure safe and stable power operation has become a research focus under the background of high-proportion renewable energy integration. Effectively balancing the active power of power system sources and loads by increasing or decreasing the active power output of generators is a vital means to maintain system frequency stability. Currently, traditional frequency regulation sources in China mainly include thermal power units and hydropower units. However, these traditional frequency regulation units have disadvantages such as long response times and slow ramp-up rates, rendering traditional frequency regulation methods insufficient to meet current demands. Battery energy storage systems (BESSs), characterized by high automation levels and flexible control, can rapidly respond to load fluctuations and short-term changes, ensuring active power balance in the power system and thus playing a role in frequency regulation. Therefore, applying electrochemical energy storage to assist in grid frequency regulation holds significant theoretical research significance and engineering practical value.
2. Necessity and Feasibility Analysis of Electrochemical Energy Storage Participating in Grid Frequency Regulation
2.1 Necessity Analysis
Currently, China’s frequency regulation sources are still dominated by hydropower units and thermal power units, but both types of frequency regulation units have certain limitations due to their inherent characteristics, which can be summarized as follows:
- Hydropower Units: They possess excellent frequency regulation performance and can effectively meet system frequency regulation demands. However, they are limited by time and spatial factors, leading to significant limitations in frequency regulation applications.
- Thermal Power Units: Due to the influence of mechanical motion physics, they exhibit low ramp-up rates and long response lags. With the integration of renewable energy, frequency regulation instructions issued by the system change frequently. Thermal power units cannot promptly and accurately respond to these instructions, potentially leading to over-regulation, under-regulation, or even reverse regulation issues. Moreover, frequent changes in frequency regulation instructions can increase wear and tear on unit equipment, reducing service life and increasing generation costs.
2.2 Feasibility Analysis
In recent years, with the rapid development of large-scale electrochemical energy storage technology, its advantages in assisting traditional units in participating in grid frequency regulation have become increasingly prominent, which can be summarized as follows:
2.2.1 Technical Aspects
- Rapid Response: The response speed of electrochemical energy storage systems is fast, reaching millisecond levels, and can change the regulation direction according to demand scenarios, effectively reducing wear on frequency regulation units and extending their service life.
- Environmentally Friendly: Compared to thermal power units, electrochemical energy storage reduces pollution to the atmospheric environment during the frequency regulation process, making battery energy storage systems more environmentally friendly.
- Flexibility: Large-scale electrochemical energy storage systems can flexibly configure capacities according to different application scenarios to meet the requirements of primary frequency regulation (second-level time scale), secondary frequency regulation (minute-level time scale), and tertiary frequency regulation (hour-level time scale).
2.2.2 Economic Aspects
Energy storage system participation in secondary frequency regulation of the grid constitutes an auxiliary service, which is a paid service, and corresponding subsidies are provided based on the contribution rate. The National Energy Administration has formulated and issued two documents, the Interim Measures for the Management of Ancillary Services of Grid-connected Power Plants (Dian Jian Shi Chang [2006] No. 43) and the Working Plan for Improving the Compensation (Market) Mechanism for Ancillary Services in the Electricity Industry, to promote the development of ancillary services in the national electricity market.
2.2.3 Policy Aspects
On December 24, 2021, the National Energy Administration officially issued the Measures for the Management of Ancillary Services in the Electric Power Industry, which expands the scope of ancillary service providers, formally incorporates various types of energy storage power sources into grid-connected entity management, and encourages such energy storage to participate in ancillary services such as frequency regulation and peak shaving, marking an important measure to improve the construction of the electricity market.
Against the backdrop of the “dual carbon” goals and driven by various government policies and documents, relevant functional units across the country have successively issued relevant policies for electrochemical energy storage participating in grid ancillary services. The relevant policies issued by some provinces and cities are shown in Table 1. It can be seen that with the improvement of corresponding laws and regulations, the development prospects for the energy storage frequency regulation market are very promising.
Table 1: Relevant Policies on Energy Storage Frequency Regulation in Some Provinces and Cities
| Issuance Date | Issuing Unit | Document Name |
|---|---|---|
| April 2019 | National Energy Administration North China Regulatory Bureau | Implementation Rules for Frequency Regulation Ancillary Service Transactions in the Mengxi Electric Power Market |
| December 2019 | National Energy Administration Jiangsu Regulatory Office | Trading Rules for Ancillary Services (Frequency Regulation) in Jiangsu Electric Power |
| March 2020 | Xinjiang Uyghur Autonomous Region Development and Reform Commission | Management Measures for Power Generation-side Energy Storage in the Xinjiang Power Grid |
3. Research Status of Electrochemical Energy Storage Participating in Grid Frequency Regulation
3.1 Typical Demonstration Projects of Energy Storage Participating in Frequency Regulation
In recent years, more than 160 electrochemical energy storage projects have been commissioned or newly built in the field of auxiliary frequency regulation worldwide. Foreign research on the application of energy storage in frequency regulation started earlier and has entered the commercial operation stage. Some foreign energy storage frequency regulation demonstration projects are shown in Table 2.
Table 2: Foreign Energy Storage Frequency Regulation Demonstration Projects
| Project Name | Project Scale | Energy Storage Type |
|---|---|---|
| Laurel Mountain Energy Storage | 64MW/8MWh | Lithium-ion Battery |
| Presidio Battery Energy Storage | 4MW/32MWh | Sodium-sulfur Battery |
| Johnson City Energy Storage | 20MW/5MWh | Lithium-ion Battery |
The application of large-scale electrochemical energy storage in the field of auxiliary frequency regulation in China started relatively late. In recent years, with strong government support and the continuous maturity of electrochemical energy storage technology, related demonstration projects have developed rapidly. Some typical domestic demonstration projects are shown in Table 3.
Table 3: Domestic Energy Storage Frequency Regulation Demonstration Projects
| Project Name | Project Scale | Energy Storage Type |
|---|---|---|
| National Wind-Solar-Storage Demonstration Base | 14MW/63MWh | Lithium Iron Phosphate Battery |
| Southern Power Grid Baoqing Battery Energy Storage Station | 4MW×4h | Lithium-ion Battery |
| Beijing Shijingshan Thermal Power Plant Energy Storage System | 2MW | Lithium-ion Battery |
3.2 Research Status on Control Strategies and Optimal Capacity Allocation for Energy Storage Participating in Grid Frequency Regulation
Many domestic experts and scholars have conducted in-depth research on the control strategies and methods for energy storage participating in grid frequency regulation. Research on control strategies for energy storage in this context primarily focuses on the power allocation problem between energy storage units and traditional frequency regulation power sources.
In essence, the challenge lies in establishing reasonable control strategies to allocate power between traditional frequency regulation power sources and energy storage units, thereby fully leveraging their respective advantages and enabling the system’s active power to quickly reach a balanced state. This has become a research hotspot for many experts and scholars both domestically and internationally.
Various approaches have been proposed to address this issue. For instance, one study sets a threshold for the Area Control Error (ACE) to determine when to switch the energy storage battery into operation. Additionally, it integrates a State of Charge (SOC) self-recovery strategy to propose a control strategy for electrochemical energy storage to participate in secondary frequency regulation of the power grid. Another study divides the ACE signal into different intervals and considers two scenarios—energy storage participation in frequency regulation and SOC self-recovery of the energy storage battery—in different zones. It determines the charging and discharging power of the energy storage battery under different working conditions to maintain the stability of the power system frequency.
Moreover, research on the optimal capacity allocation of energy storage for grid frequency regulation is also crucial. Optimal capacity allocation aims to balance the need for sufficient energy storage capacity to respond to frequency fluctuations with economic considerations. Various factors, such as the response speed of energy storage devices, their control accuracy, and the economic benefits of participating in frequency regulation, need to be comprehensively considered to determine the optimal capacity of energy storage.
In summary, research on control strategies and optimal capacity allocation for energy storage participating in grid frequency regulation is continuously advancing. With the increasing integration of renewable energy sources and the growing demand for stable power system operation, the importance of energy storage in grid frequency regulation will further increase. Future research should focus on developing more efficient and economical control strategies and capacity allocation methods to fully realize the potential of energy storage in improving power system frequency stability.