1. Introduction
Replacing synchronous generators with inverter-based renewable energy sources is leading to a reduction in the overall inertia of the system. Therefore, the increased integration of advanced power electronics-based generation in the system leads to a reduction in system inertia, making the system frequency more susceptible to interference and potential frequency instability.To regulate frequency deviations, this highlights the need to develop advanced auxiliary energy balancing services [1,2,3].
Several researchers have studied the impact of low inertia on power system stability and operation, mainly due to the significant penetration of renewable energy sources.The research was conducted in [1] The relationship between system inertia and operational difficulties arising from reduced system inertia was studied. This study shows that harnessing the inertia of energy storage systems (ESS) or converters to connect generated electricity can be a viable solution for low-inertia systems.
As an important focus area for the provision of ancillary services, the integration of battery energy storage systems (BESS) into the grid is receiving increasing attention.according to [4], frequency response services are included in the control structure of the BESS, enabling the system to provide the maximum rated active power within one second after the occurrence of a frequency disturbance.In their study, the authors [5] Examine the application of battery systems in secondary frequency control and area control error (ACE) mitigation for complete elimination.Previous studies have demonstrated the use of BESS to suppress power system oscillations [6,7].The intermittency of renewable energy sources such as wind and solar, coupled with the inherent inaccuracy of their predictions, requires the implementation of battery systems as a viable solution to these challenges, as shown in Ref. [8].
refer to [9] The use of BESS to provide inertial response (IR) and primary frequency response (PFR) is described. When only a few synchronous generators are online, a BESS with sufficient capacity can provide sufficient frequency reserve for the power system.refer to [10] The effects of using BESS to provide primary frequency management support in power systems with increasing amounts of renewable energy sources (RES), especially wind power, are studied in detail. To examine the overall improvement in frequency response brought about by using BESS, various forms of events were applied, including transient line outages, single line ground faults, and increased load demand at different wind penetration levels. The authors found that BESS effectively alleviates frequency oscillations by balancing energy deficits and absorbing excess energy, in which the use of BESS increased wind energy penetration by 3.58% to 5.21%. However, no strategy regarding BESS size and location has been proposed to improve frequency response and ROCOF.
The BESS scale plan proposed in [11] Completely based on the optimization of microgrid operating costs and minimization of BESS charging and discharging capacity. The study examines the effectiveness of the proposed technology in three different scenarios, depending on the microgrid’s connection status, by connecting to and selling power to the grid. However, system performance is not evaluated in terms of allowable frequency deviation or system rate of change of frequency (ROCOF) limits.
author [12] A two-level optimization model is proposed, which is converted into a mixed integer linear program to achieve maximum profit. The optimal energy storage capacity determined by the algorithm depends on the system fault conditions, the duration of load shedding under different fault scenarios, and the improvement in unit revenue profitability of the distribution system. However, neither the system operating conditions (including frequency and ROCOF) nor the system under different renewable energy penetration levels were studied.
Accurately determining the appropriate size and location of BESS is critical to significantly improve grid stability and economic efficiency by mitigating issues such as over- or under-sizing and selecting inappropriate BESS locations. [13]. However, most previous studies on energy storage layout have mainly focused on economic or steady-state factors, as well as considering the distribution system.There is relatively limited research on placing ESS in transmission systems to enhance stability. [7].The research was conducted in [14] A probabilistic assessment method is introduced to determine the appropriate size of BESS to improve grid security. This is achieved by examining different combinations of BESS rated power and energy capacity.
exist [15], provides a method to use historical frequency data to minimize the capacity of the BESS when providing main frequency reserve services for power system frequency regulation. However, this study did not address the issue of BESS placement because it only focused on predetermined locations.After the position is fixed, the controller parameters are optimized through Tabu-Search [16]. However, the optimal BESS placement for enhanced system frequency oscillation damping has not been thoroughly investigated.
BESS sizing method in [9] Primary frequency control and inertial response are performed using a 12-bus power system model and theoretical estimates of the inertia and power/frequency characteristics of the target system. However, the information provided does not disclose how or where the BESS is installed. In addition, Ref. [17] The impact of BESS on primary frequency control is studied in a simple low-order system frequency response model; however, BESS allocation and sizing issues are not included.
This research is in [18] A method to enhance transient voltage stability by determining the best location to connect the BESS is proposed. The authors propose a method to enhance voltage stability, formulate it as a voltage stability index, and then apply it using cross-entropy optimization (CEO). The results show that the potential stability is enhanced. Although the authors made progress in improving voltage stability, they ignored system frequency and ROCOF issues when determining where to place the BESS.
BESS location issue also resolved [19] The aim is to enhance the voltage and frequency stability of weak power grids by utilizing binary gray wolf optimization technology.exist [20], the BESS distribution problem was examined for power grids with photovoltaic systems. The study utilizes Henry Gas Solubility Optimization (HGSO) and simulated annealing (SA) algorithms to minimize power losses and enhance the voltage distribution of the grid.refer to [21] A BESS allocation method involving wind power is proposed. The scheme utilizes linear programming and bi-variable piecewise linearization to minimize system operating costs and voltage variations.
Researchers are at [22] It has been shown that connecting utility-scale BESSs can improve the frequency response of transmission networks. By adjusting the size, positioning and controller parameters of the BESS, this study adopts the fitness-scaled chaotic artificial bee colony (FSCABC) method to reduce the ROCOF and frequency minimum.Likewise, researchers refer to [23] An optimization problem is proposed that exploits the idea of virtual inertia to determine the best location to increase inertia while minimizing cost.
Important insights can be drawn from the previously mentioned studies, allowing the identification of potential research opportunities regarding optimal utilization of BESS. Recent research has focused on utilizing optimization algorithms in power grids and other research areas. These interesting studies focus on enhancing voltage distribution, reducing generation costs and power losses, and minimizing investment costs and operation and maintenance expenses associated with storage systems. Despite the increasing research on the integration of BESS into the grid, there are still limitations in correctly addressing frequency deviations and ROCOF, especially for large emergencies (e.g., loss of generating units), which may strongly affect the best candidate bus BESS distribute. Furthermore, the high penetration level of RES must be considered when determining the optimal location of BESS. This is because renewable energy plants are showing huge growth in modern power grids. This work addresses the research gaps that will be highlighted in the next section.
Considering the above challenges, this paper proposes a strategy to determine the size, location and operation of BESS within the power grid to achieve frequency response control. First, the frequency deviation and ROCOF are evaluated after each simulated perturbation of the network. Therefore, large power contingencies at high wind power penetration levels are considered when calculating the required scale of BESS. Then, the position of the BESS is evaluated using the Prony method to (1) reconstruct the frequency response signal, (2) evaluate the eigenvalues and damping ratio of the frequency signal, and (3) determine the optimal position of the BESS to suppress the frequency oscillation of the system while Frequency deviation and ROCOF remain within acceptable limits.
The structure of this paper is as follows: Section 2 analyzes the frequency response characteristics of the power grid and introduces the ESS size determination method. Section 2.3 presents the background of the Prony method, which is used to analyze the system frequency signal and evaluate the location of the BESS. Then, Section 2.4 introduces the proposed strategy for BESS location, size and frequency regulation operation. To verify the effectiveness of the proposed BESS strategy, Section 3 presents simulations and analysis. Section 4 discusses the results. Finally, Section 5 provides conclusions.
4. Discussion
By applying the proposed BESS size, location and operation strategy to a test system under high power losses and different renewable energy penetration levels, the study case illustrates the effectiveness of this application method in enhancing frequency stability.
The simulation results in Table 1 show the effectiveness of the BESS selection method. The case study in Section 3 shows significant improvements in steady-state frequency deviation, frequency nadir, and ROCOF after implementing BESS. Frequency oscillations after significant power loss can be suppressed using BESS, as shown in Table 2. All the above improvements indicate that the BESS sizing method proposed in this paper can help system planners design and maintain system reliability through the use of BESS. It also helps prevent the BESS from being oversized or undersized.
The most important frequency-related safety constraint is UFLS.According to NERC, the most common first stage of UFLS operation typically occurs around 59.5 Hz to 59.3 Hz [33]. Therefore, one of the main benefits of integrating BESS into the grid is to avoid UFLS through the correct choice of size, location and operation strategy of the BESS in the grid.
By analyzing the frequency signal and identifying the busbar with the highest minimum damping ratio, the proposed BESS positioning method based on the Prony method can determine which busbar is most suitable for installing and operating a BESS for frequency regulation. The position of the BESS on bus 2 results in an increase in the frequency nadir, which enhances the frequency response of the system after sizable bursts. The eigenvalue analysis shows that the system is more stable after the implementation of BESS on bus No. 2, and the system stability is improved.