Inertia Power Research Articles

Primary Frequency Control with an Air Handling Unit

The green energy transition threatens stability of the power grid due to associated reduction in grid synchronous inertia. Primary frequency control (PFC) can compensate for the challenge; however, sufficient procurement of primary frequency capacity could depend on more extensive employment of demand-side loads for PFC. Ventilation fans in particular present a promising class of such loads because of ubiquity of variable-frequency drives and relatively slow thermal and ventilation dynamics of indoor spaces. This research proposes a novel method for PFC by an air handling unit: the open loop control is shown to have favorable dynamic characteristics, and its impact on indoor climate is shown to be tolerable. This study suggests that the largely unused primary frequency capacity of ventilation fans could be exploited to provide primary frequency response for low inertia power grids.

A grid-forming approach utilizing DC bus dynamics for low inertia power systems with HVDC applications

While power electronic converters, such as voltage source converters (VSCs), are crucial for the operation of converter-dominated renewables and their integration with the electricity grid, their reliance on VSCs can pose a challenge. The limited inertia of these sources can lead to a deterioration of the rate of change of frequency, potentially causing power system stability issues. A grid-forming approach utilizing dc-link dynamics is one of the attractive alternatives to achieve grid synchronization and support grid frequency. Existing grid-forming control schemes, which assume a constant or virtually constant dc source, rely on a fixed physical dc-link capacitor. Nonetheless, the inertia support from such a capacitor is brief, owing to its limited energy storage capability. Consequently, enhancing inertia becomes imperative; otherwise, it may result in an increased rate of change of voltage on the dc side, potentially leading to issues with protection, undesirable interactions, and system instability. This paper proposes a new grid-forming control strategy that considers a virtual capacitor to achieve grid synchronization while simultaneously providing the network with inertia response services during power imbalances. Moreover, including a virtual resistor in the controller effectively attenuates power and dc voltage oscillations. Simulations using Simulink and small signal stability analysis are conducted to validate the efficacy of the proposed controller.

Inertia Energy-Based Required Capacity Calculation of BESS for Achieving Carbon Neutrality in Korean 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.

Low Inertia Power System Planning Considering Frequency Quality Under High Penetration of Renewable Energy

Low Inertia Power System Planning Considering Frequency Quality Under High Penetration of Renewable Energy

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

Second-Order Filter-Based Inertia Emulation (SOFIE) for Low Inertia Power Systems

The massive integration of power electronic converters into the power grid has led to a decrease in the mechanical inertia of power systems, causing an increase in the rate of change of frequency (RoCoF) that may lead to stability problems. The scientific community has focused on developing grid-forming control techniques, although their implementation implies a significant change in the firmware of the converter. Grid-supporting approaches, on the other hand, are an interesting alternative to add frequency support to the grid while preserving the original control structure of the converter. This paper proposes three new grid-supporting control techniques based on the dynamic behaviour of a synchronous machine (SM) and its equivalence with a second-order low-pass filter. They endow the converter with the capability of providing synthetic inertia, damping, droop-based <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p/f</i> primary response and virtual reactance. The dynamics of the proposed implementations are compared with a reduced-order synchronous machine by means of time-domain simulations and in-depth state-space-based small signal analyses. Besides, their operation is validated in a nine-bus low-inertia power system. Hardware-in-the-loop (HIL) laboratory results are used to validate experimentally the proposed techniques.

An Online Approach for Dimensioning Fast Frequency Response Reserve in a Low Inertia Power System

An Online Approach for Dimensioning Fast Frequency Response Reserve in a Low Inertia Power System

Resilient Operation of Grid-Forming Inverters under Large-scale Disturbances in Low Inertia Power System

Resilient Operation of Grid-Forming Inverters under Large-scale Disturbances in Low Inertia Power System

Investigating the Impact of Electrical Load Types on the Frequency Response of Low Inertia Power Systems

Investigating the Impact of Electrical Load Types on the Frequency Response of Low Inertia Power Systems

Enhancing Frequency Response Characteristics of Low Inertia Power Systems Using Battery Energy Storage

Enhancing Frequency Response Characteristics of Low Inertia Power Systems Using Battery Energy Storage

A New Fractional-Order Virtual Inertia Support Based on Battery Energy Storage for Enhancing Microgrid Frequency Stability

Microgrids have a low inertia constant due to the high penetration of renewable energy sources and the limited penetration of conventional generation with rotating mass. This makes microgrids more susceptible to frequency stability challenges. Virtual inertia control (VIC) is one of the most effective approaches to improving microgrid frequency stability. Therefore, this study proposes a new model to precisely mimic inertia power based on an energy storage system (ESS) that supports low-inertia power systems. The developed VIC model considers the effect of both the DC-DC converter and the DC-AC inverter on the power of the ESS used. This allows for more precise and accurate modeling of the VIC compared to conventional models. Moreover, this study proposes a fractional-order derivative control for the proposed VIC model to provide greater flexibility in dealing with different perturbations that occur in the system. Furthermore, the effectiveness of the proposed fractional-order VIC (FOVIC) is verified through an islanded microgrid that includes heterogeneous sources: a small thermal power plant, wind and solar power plants, and ESSs. The simulation results performed using MATLAB software indicate that the proposed VIC scheme provides fast stabilization times and slight deviations in system frequency compared to the conventional VIC schemes. The proposed VIC outperforms the conventional load frequency control by about 80% and the conventional VIC model by about 45% in tackling load/RESs fluctuations and system uncertainty. Additionally, the studied microgrid with the proposed FOVIC scheme is noticeably more stable and responds faster than that designed with integer-order derivative control. Thus, the proposed FOVIC scheme gives better performance for frequency stability of low-inertia power systems compared to conventional VIC schemes used in the literature.

Optimal Allocation Strategy of Virtual Inertia and Damping for Improving the Small-signal Stability

The application of the virtual synchronous generator (VSG) control technology to engage the inertia response of renewable energy generation systems is an effective means of coping with the problem of weak inertia in power systems. To deal with the problem of small-signal stability in the weak inertia power system, this paper studies how the strength of virtual inertia and damping affect the small-signal stability, and proposes an optimal allocation strategy of virtual inertia and damping for improving the small-signal stability. The optimal allocation model of virtual inertia is constructed to minimize the energy imbalance of the system under small-signal by selecting the virtual inertia and damping as optimization variables. Regarding the aforementioned model, the evolutionary algorithm is used to obtain the optimal allocation of virtual inertia and damping. Simulations on a virtual synchronized microgrid system show the effectiveness of the proposed strategy in improving small-signal stability.

An instant inertia estimated and operation burden considered frequency regulation method for low inertia power systems

The application of virtual inertia (VI) has become a novel solution and new orientation for the frequency regulation of the high variable renewable energy (VRE) penetrated low inertia systems. How to provide a frequency regulation strategy for the system with VI is a key problem. Firstly, the power system is a multi inputs multi outputs (MIMO) system, in which the coupling characteristics of VI control and the primary and secondary frequency controls can’t be ignored. Secondly, the system inertia constant is time-varying and the estimation of it is crucial for gaining a satisfying regulation performance. This paper intends to provide a frequency regulation strategy for this problem. In this work, an Elman neural network (ENN) based inertia estimation with a deadband method is proposed for the identification of the system’s instant inertia. And the Laguerre function-based rate of change of frequency (ROCOF) constrained MIMO-MPC is constructed to provide the collaboration strategy. Then, the control parameters are tuned by the gravitational search algorithm (GSA) considering both the system performance indexes and the operation burden indexes. The proposed strategy is testified based on a three-area power system. The results prove not only the robustness of the controller but also the effectiveness of the ROCOF constraint, the operation burden index, and the instant inertia estimation method.

Frequency support by wave farms in low inertia power systems

New ancillary services and additional requirements for the grid integration of variable renewable energy (VRE) are being defined worldwide, in response to the technical challenges caused by increasing levels of VRE utilization in electric power grids. Currently, the use of wave energy is still limited to a few applications or demonstrations, where the level of penetration of wave power into the grid is not significant. To anticipate the future requirements for wave power integration, and the possibilities for provision of services, this paper considers the lessons being learned through the challenges caused by high penetration levels of other VRE sources into the grid, particularly wind power. On this basis, this paper presents an overview of grid support services that wave power plants can be expected to provide in power systems dominated by converter-interfaced generation, i.e. low inertia systems. Specifically, the focus is on services that support the active power balance in the power system. Then, the current capabilities and future perspectives for the provision of frequency support by wave farms are discussed.

Supplementary Frequency Control for Low Inertia Power Systems

Supplementary Frequency Control for Low Inertia Power Systems

Nomadic Models of Postmodern Aesthetics: Soteriological Choice of the Teacher

Aim. The aim of the article is to define the concept of aesthetic competence of the nomad teacher of postmodern era based on a comparative analysis of two aesthetic models (metis paraesthetics and soteriological aesthetics). Methods. The subject of study is anthropotemporal methodology of acquiring aesthetic competence as an act of spiritual transformation (approaches, paradigm, priorities, criteria of effectiveness). The analysis of the stages of nomad’s dianoic choice in the process of understanding beauty as a boon was carried out using the method of epistemological design, according to which emotions function cognitively in aesthetic experience. The technology of spiritual self-coaching was chosen to activate all the structural components of aesthetic competence – the intention to correct aesthetic apperception and the competencies of emotional-reflective, value-semantic, aesthetic and worldview revaluation. Results. The implementation of the chosen technology opened up the possibility of reorientation for the nomad teacher: from the drive of the performer-trickster to a humble and grateful anticipation of the beauty as transcendent – to overcoming the power of inertia of previous dependence, responses to the calls of a pure (still “adventurous”) mind. A cluster analysis of the results of the completed tasks was carried out for the regression description of the efficiency of the technology. Conclusion. The soteriological concept of the aesthetic competence of the nomad teacher focuses attention on the essential coexistence of the teacher with students throughout the entire process of his self-determination. The practical experience of its implementation can make a positive contribution to reforming postmodern aesthetic education.

A Power-Angle-Based Adaptive Overcurrent Protection Scheme for Grid-Forming Inverter Under Large Grid Disturbances

As the capacity of renewable energy generation increases, grid-forming (GFM) inverters are deemed as promising solutions for low inertia power grids. However, power-electronic-based inverters have limited overcurrent capability, so additional overcurrent protection schemes are necessary. More importantly, the stability should not be jeopardized by using additional overcurrent protection schemes. However, GFM inverters with the conventional current reference limiting method tend to be unstable under large grid disturbances such as grid frequency drop. To address this problem, this paper proposes a virtual power angle limiting method. The main idea of this method is to limit the output power by limiting the power angle instead of directly limiting the current reference. Thus, the power synchronization control law is still satisfied when the overcurrent protection is triggered, so that the stability can be maintained. Besides, after redesigning the power angle limiting value, the proposed method is also suitable for grid voltage sag cases. A significant advantage of the proposed method is that the output current can be limited automatically during grid voltage sag or frequency drop events without the need of fault detection or tuning control structures and parameters. Simulation and experimental results have verified the effectiveness of the proposed method.

Fast frequency response services in low inertia power systems—A review

To fight global warming, the share of electricity generation from renewable sources is increasing in the energy mix. The replacement of conventional generation plants with inverter-based generation sources has led to a reduction in the system inertia and also change the nature of the frequency control in power systems. Thus, many system operators have introduced new techniques to enhance the system frequency stability such as the Fast Frequency Response (FFR) services. This paper reviews the state-of-the-art of most common tools proposed in the literature for participation in the FFR services as well as the challenges that are still facing each FFR tool. Furthermore, some of the control strategies proposed in the literature for each FFR tool have also been discussed and compared. Finally, some recommendations related to the adoption of FFR services in future power systems have been provided.

A frequency control scheme of a doubly-fed induction generator considering random wind speeds

The low inertia characteristic of the power system is increasingly prominent with the increase of wind power penetration. Therefore, the threat of random wind speeds and sudden frequency events to the frequency stability of a low inertia power system is further enhanced. It is necessary for wind power generators to provide frequency auxiliary service for the power system through appropriate control schemes. To address these issues, a frequency control scheme is proposed for a doubly-fed induction generator (DFIG) to support the frequency stability of the system in this paper, which can play a role in additional-loop-based frequency smooth control (FSC) and dynamic inertial control (DIC) by a smooth switcher. The objective of FSC is to smooth the frequency fluctuation caused by random wind speeds, load fluctuation, etc., while DIC aims at improving the frequency nadir (FN) and simultaneously preventing rotor speed over-deceleration during a large disturbance. In addition, a smooth switcher is proposed to coordinate the advantages of FSC and DIC. Note that the proposed approach can be automatically switched from FSC to DIC, while frequency deviation exceeds the given threshold due to a large disturbance. Finally, simulation results on the IEEE 14-bus system show the advantages of the proposed method in improving frequency stability under real complex situations while ensuring the stable operation of wind turbine generators.

Overview of Measures for Low Inertia Power System Due to Large-scale Introduction of Renewable Energies

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