Comprehensive Control Strategy of Energy Storage Systems for Power Grid Frequency Regulation

Significance 

With the increasing global awareness of the need to drastically reduce the consumption of fossil fuels and replace them with low-carbon energy sources, the global demand for renewable energy sources like photovoltaic cells has soared. Although renewable energy is promising, its uncertainty and high volatility characteristics could negatively affect the stability of power systems. Additionally, replacing conventional generators with high renewable energy proportion reduces the inertia and primary frequency regulation (PFR) capacity of the system. These are some of the most important problems that must be addressed to realize the effective and efficient use of renewable energy.

Although energy storage systems (ESSs) have drawn attention in power system auxiliary services due to their flexibility and rapid control, they have a small capacity compared to the system capacity. Moreover, effective management of the limited capacity in PFR requires more effective control strategies. Recently, there have been attempts to develop effective ESS control methods based on virtual droop control and virtual inertia control for application in PFR. This approach has been used to simulate output responses of conventional generators and the combination has proved effective in reducing frequency deviation and frequency change rates in PFR. However, these attempts mostly concentrated on frequency regulation performance and ignored the state of charge (SOC). This could lead to overcharging or over-discharging, which could degrade the service life of ESSs.

Recently proposed adaptive droop control strategy taking into account the SOC feedback has several advantages, including preventing overcharging and over-discharging. Unfortunately, most of these strategies fail to consider SOC recovery, which limits PFR performance. To address these problems, Dr. Zhenshan Zhu, Mr. Chengtao Ye and Ms. Shiyu Wu from Fuzhou University in China proposed a comprehensive control method for ESS participating in PFR with adaptive SOC recovery. The integrated control strategy consisted of the PFR stage and SOC recovery stage. The work is currently published in the journal, International Transactions on Electrical Energy Systems.

The authors used a combination of the virtual inertia control and virtual droop control in the frequency deterioration phase in the PFR stage to minimize frequency deviation. On the other hand, the virtual droop control coupled with the virtual negative inertia control was used to increase the frequency recovery in the frequency recovery phase. An adaptive control method was introduced in the SOC recovery stage to enhance ESS’s capability to effectively participate in the PFR process by restoring SOC within the desired target range. Finally, the applicability of the proposed method was validated through simulation experiments conducted in a MATLAB Simulink environment.

The research team findings showed that the proposed control method could meet the needs for effective PFR performance by automatically restoring the SOC recovery to the desired limits, enhancing ESS capability to participate in the subsequent PFR processes effectively. Unlike the fixed target SOC method, it exhibited several advantages, including a reduced number of SOC recovery starts and a prolonged ESS life cycle without overcharging and over-discharging. The combination of the virtual inertia control, virtual negative inertia control and virtual droop control had two main benefits: reducing maximum frequency deviation and accelerating frequency recovery.

In summary, an adaptive SOC recovery-based control strategy consisting of the PFR stage and SOC recovery stage was proposed to ensure effective ESS participation in PFR. Compared with the conventional droop control, the frequency regulation performance of the present method was way much superior. In a statement to Advances in Engineering, Dr. Zhenshan Zhu, first and corresponding author stated that the integrated control strategy presented here would contribute to the advanced application of energy storage systems and renewable energy smoothing.

Comprehensive Control Strategy of Energy Storage Systems for Power Grid Frequency Regulation - Advances in Engineering
Figure 1. The flow chart of the proposed integrated control strategy
Comprehensive Control Strategy of Energy Storage Systems for Power Grid Frequency Regulation - Advances in Engineering
Figure 2. SOC curves under continuous load disturbance
Comprehensive Control Strategy of Energy Storage Systems for Power Grid Frequency Regulation - Advances in Engineering
Figure 3. SOC curves under different target SOC ranges

Reference

Zhu, Z., Ye, C., & Wu, S. (2021). Comprehensive control method of energy storage system to participate in primary frequency regulation with adaptive state of charge recoveryInternational Transactions on Electrical Energy Systems, 31(12), e13220.

Go To International Transactions on Electrical Energy Systems

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