Improve Frequency Stability Research Articles

Overload mitigation for grid-forming inverters in islanded microgrids with synchronous generators

The prevalence of inverter based resources (IBRs) in microgrid applications continues to increase. However, energy storage remains costly and so parallel operation of IBRs and synchronous generators (SGs) is expected for microgrids requiring sustained, independent operation. Grid-forming (GFM) control for inverters can improve frequency stability in these low inertia environments, but only if poor transient load sharing does not cause the GFM IBRs to exceed current or power limits as demonstrated in recent literature. In this paper, an overload mitigation strategy for GFM IBRs to address the poor transient load sharing problem is proposed. The approach includes several key aspects. First, closed loop control of inverter currents without integrating a phase locked loop is used. Second, the logic of the mitigation strategy is designed to be non-intrusive so that proportional load sharing through GFM operation resumes following the event. Last, the overload mitigation strategy is validated in several simulations with both switching device and average value models of inverters using RTDS. The simulation results demonstrate successful mitigation of overloads and seamless integration of the strategy in-spite of the high level of penetration of IBRs in the study system.

Smart Integration of Renewable Energy Sources Employing Setpoint Frequency Control—An Analysis on the Grid Cost of Balancing

The increasing installation of Renewable Energy Sources (RES) presents significant challenges to the stability and reliability of power systems. This paper introduces an advanced control method to mitigate the adverse effects of intermittent generation from RES on the power system frequency stability. The proposed approach emphasizes the critical role of Battery Energy Storage Systems (BESS) and RES in enhancing the resilience of modern power networks. The Generation Export Management Schemes (GEMS) are employed to curtail the excessive export of RES, thereby contributing to improved frequency stability. This research involves a comprehensive analysis of the dynamic behavior of the network under various operational scenarios, particularly focusing on power exchanges between RES, BESS, and synchronous generation units. Furthermore, this paper focuses on the economic implications of integrating RES into the grid, with a detailed cost of balancing (COB) modelling and analysis conducted to assess the financial viability of the proposed frequency management solutions. The analysis encompasses both short-term and long-term perspectives, providing insights into the development of economically sustainable smart power networks that effectively integrate renewable energy and storage technologies while maintaining system stability.

Effectiveness of BESS in Improving Frequency Stability of an Island Grid

Effectiveness of BESS in Improving Frequency Stability of an Island Grid

Carrier Phase Common-View Single-Differenced Time Transfer via BDS Penta-Frequency Signals

The BeiDou Navigation Satellite System (BDS-3) has officially provided services worldwide since July 2020. BDS-3 has added new signals for B1C, B2a and B2b based on old BDS-2 B1I and B3I signals, which brings opportunities for achieving high-precision time transfer. In this research, the BDS-3/BDS-2 combined penta-frequency common-view (CV) single-differenced (SD) precise time transfer model is established with B1I, B3I, B2I, B1C, B2a and B2b signals, including dual-, triple-, quad- and penta-frequency (abbreviated as DF, TF, QF and PF) ionosphere-free (IF) combination CV SD models. Taking four long baseline time links (from 637.6 km to 1331.6 km) as examples, the accuracy and frequency stability of the BDS-3/BDS-2 combined DF, TF, QF and PF SD time transfer models were evaluated. The experimental results show that the frequency stability of the TF, QF and PF SD models were improved by 2.5%, 5.3% and 8.5%, on average, over the DF SD model. Compared with the traditional DF (B1I/B3I IF combination) SD model, the standard deviation (STD) of the multi-frequency SD model was reduced by 5.9%, on average, and the frequency stability was improved by 4.0% on average, which had the most apparent effect on the improvement of short-term frequency stability. Specifically, the DF1 (B1C and B2a DF IF combination), TF1 (B1C, B2a and B2b TF IF combination), QF1 (B1C, B1I, B2a and B2b QF IF combination) and PF4 (B1C, B1I, B2a, B2b and B3I PF IF combination) SD models had better performance in timing, and the PF4 SD model had the best performance. Considering that the PF4 (one PF signal IF combination) SD model does not require an estimated inter-frequency bias and that its noise factor is minor compared with the PF1 (four DF signal IF combination), PF2 (three TF signal IF combination) and PF3 (two QF signal IF combination) SD models, we recommend the PF4 SD model for multi-frequency time transfer and the use of the PF2, PF2 or PF3 SD model to supplement the PF4 SD model in cases of penta-frequency observation loss.

Enhancing long-term frequency stability of an actively mode-locked optoelectronic oscillator via a phase-locked loop.

A method to improve the frequency stability of microwave frequency comb (MFC) signals generated by an actively mode-locked optoelectronic oscillator (AML-OEO) is proposed and experimentally demonstrated. In the experiment, fundamental mode locking in the constructed AML-OEO is achieved, producing MFC signals with a center frequency of 2.165 GHz and a repetition rate of 396.629 kHz. By locking the MFC comb tooth to a stable reference source using a phase-locked loop (PLL), the stability of MFC's center comb tooth reaches 2.4 × 10-13@1000s and the frequency stability improves by more than two orders of magnitude on a second-level time scale compared to the free-running AML-OEO. The improved frequency stability of MFC signals makes AML-OEO suitable as high-performance microwave sources for various critical applications.

Optimal Placement and Sizing of Battery Energy Storage Systems for Improvement of System Frequency Stability

Optimal Placement and Sizing of Battery Energy Storage Systems for Improvement of System Frequency Stability

Improving primary frequency response in photovoltaic systems using hybrid inertia and intelligent control techniques

Abstract Low inertia poses a significant challenge to the widespread integration of photovoltaic (PV) systems into the grid, particularly affecting frequency stability. This paper addresses this challenge by proposing an advanced hybrid inertia (AHI) approach, characterized by the integration of real and virtual inertia, combined with the application of intelligent control techniques, to enhance the primary frequency response of a PV system. Internal inertia is provided by a synchronous generator (SG) acting as a compensator, while virtual inertia is generated through a real-time deloading strategy in the PV plant. The AHI is implemented on an isolated grid, utilizing various intelligent control techniques to improve frequency stability. The intelligent techniques employed include genetic algorithms (GA) and fuzzy logic controllers (FLC), which do not require mathematical modeling. This allows them to overcome the nonlinear dynamics of the PV plant and the uncertainties associated with climatic changes. These techniques are applied to the nonlinear components on the generator side, including the governor loop, DC-DC converter loop, and power reserve injection management loop. A frequency fluctuation scenario, induced by generating power perturbations in the proposed system, demonstrates and validates the improvement in frequency stability achieved by the HI and intelligent techniques. All tests are conducted using MATLAB Simulink. Various simulation results show a significant improvement in frequency stability through the incorporation of HI and intelligent control techniques.

A fuzzy-PID controller for load frequency control of a two-area power system using a hybrid algorithm

This paper presents the use of a new hybrid optimization approach known as particle swarm optimization and grey wolf optimizer (PSO-GWO) for improving frequency stability load frequency control (LFC) in tow-area power systems. The approach consists in optimizing the fuzzy proportional-integral-derivative (fuzzy-PID) controller parameters with meta-heuristic hybrid algorithm: PSO-GWO. This technique allows to have dynamic responses with the least possible frequency deviation in very short response times. The approach proposes to controls the tie-line power and the frequency deviation in the considered two-area power systems under variable perturbation in load and changing of system parameters in order to evaluate its effectiveness. The suggested hybrid algorithm-based fuzzy-PID controller is compared with various widely used control methods in the literature such as PID controller and algorithms such as PSO and GWO in order to evaluate its effectiveness and its robustness. Through the simulations carried out on MATLAB/Simulink, the proposed PSO-GWO fuzzy-PID and the objective function exhibit improved performance, achieving minimal objective values. The proposed technique proved to be quite powerful tool in the resolution of problems related to electrical power systems, particularly in load frequency control.

Frequency control enhancement for hybrid microgrid using multi-terminal multi-function inverter

Renewable energy sources (RESs) are considered a crucial energy transformation to reduce carbon emissions, so more RESs are being integrated into contemporary power systems. Power electronic converters are extensively utilized to connect power grids with renewable generators to manage the fluctuations and unpredictability of these renewable energy sources. This paper introduces a multi-terminal multi-function inverter (MT-MF) designed for a battery energy storage system (BESS) to maintain the frequency stability of a hybrid microgrid (MG). The MG comprises a photovoltaic generation system, a diesel generator, BESS, and two loads: one constant load and the other variable, fed through a medium-voltage radial feeding system. An introduced approach involves utilizing a model predictive control controlled virtual synchronous generator (MPC-VSG) for BESS. This method offers inertia support during transient states and improves the dynamic characteristics of system frequency. In addition, it enables the connection of multiple batteries, provides individualized control for each, and supports the injection of reactive power into the MG. The required power from the BESS is shared between the two batteries using the low pass filter technique. The simulation outcomes affirm the proposed control strategy’s effectiveness and underscore the MT-MF inverter approach’s potential in integrating extensive RESs. This paper also explores how the proposed technique outperforms other methods in improving frequency stability.

Integrated control strategy for 5G base station frequency regulation considering spatio-temporal variations in communication load

The decreasing system inertia and active power reserves caused by the penetration of renewable energy sources and the displacement of conventional generating units present new challenges to the frequency stability of modern power systems. Vast quantities of 5G base stations, featuring largely dormant battery storage systems and advanced communication technology, represent a high-quality fast frequency regulation resource for the power system. This paper proposes a double-layer clustering method for 5G base stations and an integrated centralized-decentralized control strategy for their participation in frequency regulation, considering the variability of available frequency regulation capacity due to spatial and temporal variations in base station communication loads. The proposed capacity model and control methods are evaluated using a case study of a two-machine test system with 10,000 real 5G base stations, demonstrating the effectiveness of the clustering method and the integrated control strategy in improving frequency stability.

Synergistic control for enhancing frequency stability in grid-integrated network with decentralized renewable energy resources, energy storage, and electric vehicles

The integration of Decentralized Energy Resources (DERs), Energy Storage Systems (ESS), and Electric Vehicles (EVs) into grid-connected networks presents a transformative paradigm in modern power systems. This article introduces a synergistic control framework tailored for optimizing frequency stability within grid-integrated distributed networks. The proposed approach leverages advanced control algorithms to orchestrate the dynamic interaction between DERs, ESS, and EVs, ensuring seamless operation and enhanced grid resilience. The effectiveness of the proposed control strategy is demonstrated in mitigating frequency deviations, thereby contributing to a more stable and reliable grid infrastructure. This article introduces a novel approach utilizing the Selfish Herd Optimization (SHO) algorithm to address this critical issue. Inspired by the self-preservation behavior observed in animal herding, the SHO algorithm is adapted to coordinate the operation of DERs with loads within a distributed network. By dynamically adjusting their output based on local frequency measurements, DERs collectively exhibit a self-organizing behavior, resulting in improved frequency stability. The SHO based PID controller is also proven to be far more effective at controlling frequency than the traditional PI controller. The findings underscore the potential of bio-inspired algorithms in enhancing the resilience of grid-integrated DER systems, offering a promising avenue for future grid control methodologies.

Effects of Battery Energy Storage Systems on the Frequency Stability of Weak Grids with a High-Share of Grid-Connected Converters

To achieve an energy sector independent from fossil fuels, a significant increase in the penetration of variable renewable energy sources, such as solar and wind power, is imperative. However, these sources lack the inertia provided by conventional thermo-electric power stations, which is essential for maintaining grid frequency stability. In this study, a grid resembling Madeira Island’s power generation mix was modeled using the Matlab/Simulink platform. The model included solar, wind, hydro, and thermo-electric generation to accurately represent the energy landscape of Madeira Island. Three scenarios were examined: one reflecting the current power generation on Madeira Island, a future scenario with a substantial rise in the percentage of photovoltaic (PV) generation, and the same future scenario but incorporating a battery energy storage system (BESS). Various analyses were conducted to assess the impact on frequency stability during a ground fault and rapid load/generation changes. In the future scenario without a BESS, the thermoelectric power plant generator desynchronized, leading to system collapse in several simulations. However, with the addition of a BESS, a significant improvement in frequency stability was observed. The thermoelectric power plant generator could return to a steady state after each disturbance. Furthermore, both the maximum frequency deviation and the absolute value of the Rate of Change of Frequency (ROCOF) were reduced, indicating enhanced system performance and stability.

Design and modelling of an AI governed type-2 Fuzzy tilt control strategy for AGC of a multi-source power grid in constraint to optimal dispatch

The robust design and application of a novel type-2 fuzzy tilt controller (Type2-FTC) has been well demonstrated in this manuscript. This controller is anticipated to build automatic generation control (AGC) of a multi-area hybrid power system in concern to the optimal power generation scheduling. The combined action of AGC and optimal scheduling of a power system is referred as economic AGC or commonly ELD-AGC. At the initial stage of the analysis, the concept of only AGC has been discussed through various robust approaches. Then the extensive study on ELD-AGC of the proposed power system has been progressed under various controller actions. Further, the proposed Type2-FTC controller is designed ideally with employing an innovative quassi-opposition path finder algorithm (QO-PFA) in various operating conditions. The effectiveness and the viability of the proposed Type2-FTC controller has been verified over type-I fuzzy PID and conventional PID controllers for AGC as well as ELD-AGC of the multi area power system. In controller comparison study, it has been revealed that proposed Type2-FTC is a potential candidate to improve frequency stability of the system. Further, the analysis over technique study justifies supremacy of the suggested QO-FPA algorithm over standard PFA and PSO algorithms for optimal designing all implemented controllers.

Improving frequency regulation for future low inertia power grids: a review

The modern power system is witnessing an unprecedented increase in the penetration of renewable variable generation (VG) sources. Increased uptake of converter interfaced VG like solar PV and wind power while replacing conventional synchronous generators (SGs) introduces new challenges to grid operators in terms of dynamically handling frequency stability and regulation. Reducing the number of SGs while increasing non-synchronous, inertia-less converter interfaced VG reduces grid natural inertia, which is critical for maintaining frequency stability. To cure inertia deficiency, researchers, broadly, have proposed implementing supplemental control strategies to VG sources or energy storage systems to emulate natural inertia (virtual inertia (VI)). Alternatively, VG sources can be operated below their maximum power point (deloaded mode), making available a reserve margin which can rapidly be deployed in case of a contingency with the help of power electronic devices, to provide fast frequency response. This paper reviews recent solutions proposed in literature to address the low inertia problem to improve frequency stability. Additionally, it highlights the formulation of an optimization problem for VI sizing and placement as well as techniques applied in solving the optimization problem. Finally, gaps in literature that require further research were identified

Optimizing the Location of Frequency Regulation Energy Storage Systems for Improved Frequency Stability

The installation of battery energy storage systems (BESSs) with various shapes and capacities is increasing due to the continuously rising demand for renewable energy. To prepare for potential accidents, a study was conducted to select the optimal location for installing an input BESS in terms of frequency stability when the index assumes the backup input of the BESS. This study builds on the premise that installing a BESS on a bus in an area where active power absorption and transmission are the most active can significantly contribute to increasing the frequency recovery of the power system. Based on this premise, the magnitude of the active power flow and the proportional characteristics of the phase difference between buses were mathematically confirmed. This study also calculated the effective power sensitivity index of a bus with 13 FR-ESSs installed in a domestic system and reviewed the frequency output by establishing a table for each failure scenario. The results indicated that the effect of frequency rise can be estimated at the level of tidal current calculation. Thus, the study suggested a direction for subsequent studies to improve the sensitivity index.

Undifferenced precise time transfer with information‐constraints

AbstractSatellite navigation systems enable long‐distance and high‐precision time transfers. The authors proposed an undifferenced precise time transfer method with information constraints in this study. A more accurate receiver clock offset can be obtained by constraining the station coordinate parameters and receiver clock offset parameters to achieve a precise time transfer. In this example, the research object is the time transfer link established by the Global Positioning System observation station using a caesium clock, rubidium clock, and hydrogen clock. The clock difference sequence of the time‐transfer link was calculated by combining the observation data and precise products. Following analysis of the examples, the following conclusions were reached. The undifferenced precise time transfer method based on information constraints can effectively be used to smooth the clock difference sequence of the receiver and the clock difference sequence of the time transfer link. To some extent, this method can also be used to reflect the performance of atomic clocks at Global Positioning System stations and is better suited for the precise time transfer of the equal‐clock long‐baseline time transfer link. Simultaneously, the frequency stability of this method is improved significantly in the short term compared to the traditional scheme without any constraints. The improvement of frequency stability is helpful to improve the accuracy of time transfer.

Improvement in Frequency Stability of Power Grids With High Penetration of Renewable Energy Sources: Market-Clearing and Pricing of Required Ancillary Services

In this article, a market-clearing (MC) and pricing method is proposed for ancillary services (ASs) that are needed for improvement in the frequency stability of power grids with high penetration of renewable energy sources (RESs). These ASs include primary frequency response (PFR) services for maintaining the rate-of-change-of-frequency and frequency nadir within the permissible ranges. Historically, the RESs did not provide the PFR services since there have been neither requirements nor incentives to do so. However, in this article, a pricing method is suggested to address the RESs’ incentives providing the PFR services. As a result, higher penetration levels of RESs are facilitated from both technical and economical viewpoints. From the technical point of view, the RESs’ participation in the PFR is necessary since the total inertial and governor responses of conventional generating units might not be sufficient for the frequency stability. In addition, from the economical point of view, with greater need for the PFR services and increase in their prices in long term, the ASs incomes might become a sizeable fraction of the RESs’ total incomes. In the case study, the effectiveness of the proposed MC and pricing method is verified using the IEEE 30-bus test system by comparing the results with existing methods.

도서지역 전력계통의 주파수 안정도 개선을 위한 가상동기기 기술 현장 적용

도서지역 전력계통의 주파수 안정도 개선을 위한 가상동기기 기술 현장 적용

A novel method to estimate maximum wind energy penetration level considering potential frequency support of wind power plants

Wind turbines’ installed capacity is expected to increase significantly in future power grids due to environmental concerns. Reductions in the power system inertia and frequency response due to increasing penetration levels of wind energy lead to a decrement in the frequency stability margin. This paper focuses on the frequency stability issue in power grids with high penetration level of wind turbines. The maximum allowable wind generation penetration level is first formulated as a function of primary frequency response and system inertia with/without considering operating reserve limits. Following that, the possibility of participation of wind turbines in the frequency stability improvement is investigated and the minimum required wind turbine participation is estimated as a function of wind energy penetration level. In this trend, a time-independent formulation for power system frequency response is utilized to increase the accuracy and reduce the computational complexity. A comprehensive analysis is performed on IEEE 39-bus test system to investigate the proposed methodologies. As results confirm, participation of wind turbines in the frequency control task leads to more secure operation of the power system.

A combined magnetic field stabilization system for improving the stability of 40Ca+ optical clock

Future applications of portable 40Ca+ optical clocks require reliable magnetic field stabilization to improve frequency stability, which can be achieved by implementing an active and passive magnetic field noise suppression system. On the one hand, we have optimized the magnetic shielding performance of the portable optical clock by reducing its apertures and optimizing its geometry; on the other hand, we have introduced an active magnetic field noise suppression system to further suppress the magnetic field noise experienced by the ions. These efforts reduced the ambient magnetic field noise by about 10000 times, significantly reduced the linewidth of the clock transition spectrum, improved the stability of the portable 40Ca+ optical clock, and created the conditions for using portable optical clocks in non-laboratory magnetic field environments. This active magnetic field suppression scheme has the advantages of simple installation and wide applicability.