Critical inertia can be defined as the minimum kinetic energy stored in generators that should be kept for maintaining the frequency stability of the power system. As the frequency control performance of the power system is maintained according to its control criterion, during the inertia response time frame, the expected energy imbalance can be calculated by accumulating the imbalanced power caused by the credible contingency and calculating the available inertia response by considering the allowable operating limit of the frequency. Since the frequency control criterion can be met when the available inertia response becomes larger than the expected energy imbalance, the critical inertia can be calculated by the kinetic energy of the generators, of which the available inertia response is equal to the expected energy imbalance due to the contingency. With this in mind, this paper derives the energy balance condition for the frequency stability in the inertia response time frame based on the frequency control criterion and calculates the minimum inertia, which should be kept in the generators from the energy balance condition for meeting the criterion. In addition, the effectiveness of the proposed method is verified through various case studies employing Korean power systems.

For power grids with a high penetration level of wind power generation, stochastic wind speed variation adversely affects the frequency stability. A variable-speed wind turbine generator would deloads its output by shifting the power operating point to provide frequency response. Because the wind speed variation directly affects the calculation of the operating point, difficulties arise in securing a reliable amount of the frequency response. This paper proposes a control scheme of a doubly fed induction generator (DFIG)-based wind generation providing the primary frequency reserve (PFR), which can improve its reliability and flexibility even with a continuously varying wind speeds. To achieve these objectives, the proposed scheme employs a de-loaded operation control loop associated with the rotational inertia characteristics of the DFIG. In addition, a static gain-based droop control loop was employed to release the required amount of active power from the system operator. In the proposed scheme, the optimal operating point for de-loaded operation varies more smoothly than it does in a conventional scheme by using the rotor inertia characteristics. The performance of the proposed control scheme is demonstrated using an EMTP-RV simulator under various wind speeds. The simulation results indicate that the proposed scheme significantly improves the frequency support capability of the DFIG in both the process of securing and providing the PFR.

Critical inertia can be defined as the minimum kinetic energy stored in generators that should be kept for maintaining the frequency stability of the power system. As the frequency control performance of the power system is maintained according to its control criterion, during the inertia response time frame, the expected energy imbalance can be calculated by accumulating the imbalanced power caused by the credible contingency and calculating the available inertia response by considering the allowable operating limit of the frequency. Since the frequency control criterion can be met when the available inertia response becomes larger than the expected energy imbalance, the critical inertia can be calculated by the kinetic energy of the generators, of which the available inertia response is equal to the expected energy imbalance due to the contingency. With this in mind, this paper derives the energy balance condition for the frequency stability in the inertia response time frame based on the frequency control criterion and calculates the minimum inertia, which should be kept in the generators from the energy balance condition for meeting the criterion. In addition, the effectiveness of the proposed method is verified through various case studies employing Korean power systems.

For power grids with a high penetration level of wind power generation, stochastic wind speed variation adversely affects the frequency stability. A variable-speed wind turbine generator would deloads its output by shifting the power operating point to provide frequency response. Because the wind speed variation directly affects the calculation of the operating point, difficulties arise in securing a reliable amount of the frequency response. This paper proposes a control scheme of a doubly fed induction generator (DFIG)-based wind generation providing the primary frequency reserve (PFR), which can improve its reliability and flexibility even with a continuously varying wind speeds. To achieve these objectives, the proposed scheme employs a de-loaded operation control loop associated with the rotational inertia characteristics of the DFIG. In addition, a static gain-based droop control loop was employed to release the required amount of active power from the system operator. In the proposed scheme, the optimal operating point for de-loaded operation varies more smoothly than it does in a conventional scheme by using the rotor inertia characteristics. The performance of the proposed control scheme is demonstrated using an EMTP-RV simulator under various wind speeds. The simulation results indicate that the proposed scheme significantly improves the frequency support capability of the DFIG in both the process of securing and providing the PFR.

While aiming to increase the dispatch of variable energy resources (VER) during the operation of a power system, the stability of the power system should be maintained, which can be realized by evaluating the penetration limit of the VER. This paper proposes a method for evaluating the penetration limit of VER. When a disturbance such as a generator trip occurs, the frequency stability depends on the inertia energy secured by generators, the characteristics of the primary frequency response, and the load response, which would change owing to an increase in the VER of the power system. In the proposed evaluation method, the frequency response performance of the power system is analyzed based on the historical operation data, and the penetration limit of VER is evaluated by applying the frequency criterion to maintain the frequency stability of the power system. Therefore, the potential penetration limit of VER can be estimated depending on the operating conditions. In addition, the effectiveness of the proposed evaluation method is verified by comparing the simulation results based on the Korean power system model-based simulation, and the online application is evaluated by applying it based on the real system operation data.

In the evolving landscape of power system operations, maintaining stability becomes increasingly crucial for system operators. In this context, the rapid response capabilities of Battery Energy Storage Systems (BESS) are recognized as a resource that can effectively contribute to the stability of the power system. However, to evaluate the performance of BESS, an effective method is essential. This paper proposes an approach to assess the frequency response performance of BESS by quantitatively comparing it with the governor of conventional generators. Through this quantification, it becomes possible to reflect the contribution of BESS to securing reserve power and maintaining the stability of the power system.

Frequency response performance in power systems is becoming vulnerable due to the transition toward the higher penetration of renewable energy such as achieving carbon neutrality. In particular, reducing power system inertia energy as the asynchronous generation increases could result in violating the frequency stability constraint when a disturbance occurs in the power systems. In order to control the rapidly fluctuating frequency of the power system with low inertia, it is necessary to introduce fast frequency response resources such as a Battery Energy Storage System (BESS). This paper proposes a method to calculate the required capacity of BESS for compensating the frequency control performance of the power system using inertia energy. For calculating the required capacity of BESS, the inertia energy in the critical power system, where frequency control performance marginally satisfies frequency stability constraint, should be calculated. Also, the inertia energy in the evaluated power system having deficit inertia energy should be calculated. By comparing power systems that respond with different dynamics when the same disturbance occurs, the proposed calculation corresponds to the ratio of inertia energy deficiency based on critical power system inertia energy within the power imbalance. Through various case studies employing Korean power systems, the effectiveness of the inertia energy-based calculation method for the required BESS is verified by the fact that the BESS integrated power system marginally satisfies the frequency stability constraint. In these study cases, it is found that the instant response of BESS is very effective for compensating the frequency control performance of the low inertia power system. By applying the proposed method, it is also found that about 840 MW of BESS can achieve carbon neutrality in the Korean power system.

Increasing the penetration of variable energy resources (VER) can reduce the inertia and frequency response performance of power systems supported by replacement synchronous power generation. Therefore, it is necessary to manage the VER penetration limit in power systems for stable operation and to increase the operability to the desired level. This study proposes a method to evaluate and quantify the effect of increasing the penetration limit of VER by controlling a battery energy storage system (BESS). The BESS can provide a fast response, but frequency response performance varies depending on the operating conditions. In the proposed quantification method, various control methods of a BESS, operating conditions of the power system, and penetration conditions of additional VER were analyzed, and the effect of the BESS on increasing the penetration limit of VER was evaluated. This evaluation and analysis enabled the selection of the BESS operating conditions to achieve the target VER capacity in the power system. The proposed quantification method was analyzed through simulations based on the Korean power system model. Therefore, it can contribute to estimating the required performance of the BESS for each system operating condition required to achieve the VER target.

This paper proposes a control strategy of Battery Energy Storage System(BESS) for increasing the hosting capacity of the Variable Energy Resources (VER) in the distribution system by resolving any violation in bus voltages and line loading caused by the connection of VER. The effectiveness of the proposed algorithm was verified by study cases employing the real distribution system based test system in terms not only of the long term time-series simulation but also of the real-time simulation.

The high Penetration of RES could have a negative effect on the power system stability by reducing its system inertia. As one of its measures, the requirements for frequency response performance of RES has been strengthened by revising the grid code for RES in the Korean power system. In this paper, it is confirmed that the frequency response of the RES can contribute even in the system inertia, and a method for quantifying its contribution on the system inertia based on its frequency response is proposed. The effectiveness of the proposed method is verified by comparing the system inertia derived with the calculated inertia constant of RES with the system inertia derived from the simulated frequency response of the RES integrated power system. The Power Simulation Simulator for Engineering (PSS/E) which is a large-scale power system analysis program was used to model Korean power system integrated with RES for the case studies.

The number of plug-in electric vehicles (PEVs) has rapidly increased owing to the government’s active promotion policy worldwide. Consequently, in the near future, their charging demand is expected to grow enough for consideration in the planning process of the transmission system. This study proposes a stochastic method for modeling the PEV charging demand, of which the time and amount are uncertain. In the proposed method, the distribution of PEVs is estimated by the substations based on the number of electricity customers, PEV expansion target, and statistics of existing vehicles. An individual PEV charging profile is modeled using the statistics of internal combustion engine (ICE) vehicles driving and by aggregating the PEV charging profiles per 154 kV substation, the charging demand of PEVs is determined for consideration as part of the total electricity demand in the planning process of transmission systems. The effectiveness of the proposed method is verified through case studies in the Korean power system. It was found that the PEV charging demand has considerable potential as the additional peak demand in the transmission system planning because the charging time could be concentrated in the evening peak time.