Low Inertia Power Systems Research Articles

Adaptive disturbance compensation based finite time sliding mode frequency control considering AVR loop for low-inertia power system

Adaptive disturbance compensation based finite time sliding mode frequency control considering AVR loop for low-inertia power system

Pricing balancing ancillary services for low-inertia power systems under uncertainty and nonconvexity

In renewable-rich power systems, declining rotational inertia and unpredictable power fluctuations make the system vulnerable to contingencies. Recently, this issue has garnered significant attention in practice and academia, aiming to enhance power system reliability through market mechanisms. This paper proposes a day-ahead joint market that integrates energy, reserve, inertia, and frequency response services. A frequency-constrained unit commitment (UC) model is developed employing a distributionally robust chance-constrained (DRCC) approach to account for the uncertainties in wind farm outputs. Additionally, a convex hull pricing (CHP) model is introduced to minimize uplift payments associated with the nonconvex nature of commitment variables. Case studies conducted on a 5-bus and a 118-bus power system demonstrate the efficacy of the proposed market design in reducing operational costs and promoting renewable energy utilization. Furthermore, the results highlight the effectiveness of the CHP model in minimizing the uplifts and enhancing market transparency.

Incentive-compatible primary frequency response ancillary service market mechanism for incorporating diverse frequency support resources

Frequency vulnerability will be prominent in future low-inertia power systems with high renewable penetration, which calls for primary frequency response (PFR) services from a wide range of entities. The challenge, however, is to design effective and fair market mechanisms to incentivize diverse PFR resources. To this end, this paper proposes a PFR ancillary service market mechanism to ensure the security of frequency nadir and quasi-steady-state (QSS) frequency while providing equitable settlements to multiple PFR providers. First, bidding rules are designed for accurate depictions of dynamic performances from diverse PFR resources. Then, a PFR market-clearing model, incorporating frequency security constraints that explicitly express PFR providers' contributions, is developed to deploy sufficient PFR resources while maximizing social welfare. Finally, two unified marginal PFR prices are derived to reflect the scarcity of frequency support capabilities for maintaining frequency nadir and QSS frequency security, enabling fair settlements to successful bidders based on their contributions. Moreover, the pricing and settlement mechanism is theoretically proven incentive-compatible, ensuring the PFR market stability. Case studies verify the proposed PFR market's effectiveness in ensuring frequency security, providing fair incentives to diverse PFR providers, maintaining market stability, and supporting scalable implementations.

Field Measurement and Analysis of Frequency and RoCoF for Low-Inertia Power Systems

Field Measurement and Analysis of Frequency and RoCoF for Low-Inertia Power Systems

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.

Minimum Energy Demands of Energy Storages for Fast Frequency Response: Formulation, Solution, and Implementation

Energy storage (ES) is a kind of promising but costly fast-frequency-response (FFR) resource in low-inertia power systems. This paper addresses the minimum demand of a power system for energy capacities of ES to providing sufficient frequency support, including the formulation, the optimal solution, and its practical implementation. First, the minimum energy control problem of ESs for providing FFR with transient frequency constraints is formulated and then converted into an optimal frequency trajectory planning counterpart. This transformation makes the transient frequency constraint tractable and allows to identify the optimal frequency trajectory that minimizes energy demand for ESs, which leads to an analytical expression of the system minimum demand for ESs energy capacities to ensure frequency security. Moreover, by unfolding the optimal frequency trajectory, the optimal control strategy of ESs is derived explicitly for the first time. The theoretical result directs to a practical controller implementation, which is referred to as the decentralized optimal energy frequency control (DOEFC). Finally, simulations on the modified IEEE 39- bus system verify our results and demonstrate the superiority of the DOEFC in reducing the energy capacity demand of ESs, defending successive disturbances, and hedging against parameter errors.

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

Frequency Control and Optimal Operation of Low-Inertia Power Systems With HVDC and Renewable Energy: A Review

With the integration of large-scale renewable energy sources (RES) and high voltage direct current (HVDC) based inter-regional transmission, modern power systems are facing low-inertia issues and poor frequency regulation capabilities. This paper conducts a comprehensive review on frequency control and optimal operation methods in this context. First, the frequency characteristic of a low-inertia power system is analyzed covering the whole frequency response process. Secondly, the impacts of RES and HVDC integration on system inertia and frequency performance are studied, and the system frequency characteristics considering RES and HVDC are analyzed. Then, the frequency response modes of various frequency regulation resources are compared from the perspective of “source-grid-load-storage”, including their basic control principles and frequency control strategies. Further, from the operation dispatch perspective, the frequency security-constrained power system optimal operation methods are reviewed. Finally, future research trends in this area are discussed.

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

Inertia Security Evaluation and Application in Low-Inertia Power Systems

Inertia Security Evaluation and Application in Low-Inertia Power Systems

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

System Restoration for Low-inertia Power Systems Incorporating Fast Frequency Response via Distributionally Robust Optimization

System Restoration for Low-inertia Power Systems Incorporating Fast Frequency Response via Distributionally Robust Optimization

RoCoF Constrained Unit Commitment Considering Spatial Difference in Frequency Dynamics

The post-disturbance rate of change of frequency (RoCoF) is a critical index for low-inertia power system frequency stability. This paper proposes a RoCoF constrained unit commitment model so as to enhance the frequency stability in operation time-scale, where the spatial difference in frequency dynamics is considered and the RoCoF constraint is enforced for each node. The maximum of node RoCoF is approximated by two terms, i.e., the initial post-disturbance node RoCoF and the maximum of the center of inertia (COI) RoCoF. Analytical expressions of the node initial RoCoF under typical disturbances are derived. Then, a tractable relationship between the node initial RoCoF and the working status of generators is obtained by the piecewise linearization approach. Simulation results carried out on the IEEE 39-bus system demonstrate the proposed model can limit the node RoCoF in an economic and accurate manner. The adaptability to renewable power generation and online application are also discussed.

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.

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