Frequency Stability Of Power System Research Articles

Improved load frequency control considering dynamic demand regulated power system integrating renewable sources and hybrid energy storage system

Demand response (DR) has emerged as a key component of the future electric power system's reliability and frequency stability. This study explores the effect of DR regulation and hybrid energy storage (HES) on an identical two-area test power system that comprises of solar photovoltaic, wind turbine, biogas unit, and a thermal power plant for improved frequency regulation services. By including intrinsic communication latency in the DR loop, a generalised load frequency control (LFC) model of a hybrid hierarchical DR mechanism is developed. The stability of the analysed system before and after DR is compared in terms of stability margin. A Quasi- oppositional Harris Hawks Optimization (QOHHO) is suggested to optimize the coefficients of the proposed cascade fractional order two-degree-of-freedom CC[FO(TDOF)] controller. The supremacy of the proposed algorithm is affirmed by comparing its figure of demerit with different existing algorithms. The investigations also manifest the efficacy of proposed controller over proportional integral derivative with filter (PID) and two degree of freedom (tilt integral derivative with filter) [TDOF (TID)] controllers. QOHHO optimized designed controller performance is also evaluated for the studied system under random load disturbances. Furthermore, the suggested technique's practical feasibility is verified through experimental validation using OPAL-RT based real-time analysis.

Power system frequency stability using optimal sizing and placement of Battery Energy Storage System under uncertainty

In the literature, a variety of system uncertainty is not included in the frequency stability research. This research demonstrated that employing the probabilistic frequency stability analysis approach which accounts for the uncertainty of system parameters such as loads and generation uncertainty, resulted in a more accurate frequency stability assessment when compared to the deterministic technique. Additionally, this study proposes a framework for determining the optimal size and placement of Battery Energy Storage System (BESS) in power systems while taking into account the uncertainty associated with system generation and demand, as well as intermittent generation sources and contingency locations which have been rarely considered in the literature. The novelty of these methods is that they determine the optimal BESS size and placement based on the amount and location of the critical system loads. The methodologies have been validated using IEEE 39-bus and simplified SE-Australian power systems where the simulations were implemented using DIgSILENT/PowerFactory software with Python interface. The simulation results revealed that the optimal BESS size should not be equal to more than 4.5% from the system loads amount while the optimal BESS placement was acquired when the BESS are placed closer to around 30% of the system loads. Furthermore, by investigating the impact of the contingency and wind farm locations on the optimal BESS size, the contingency location had the greatest impact on the BESS properties, while the wind farm locations provided a negligible impact.

An Eagle Strategy Arithmetic Optimization Algorithm for Frequency Stability Enhancement Considering High Renewable Power Penetration and Time-Varying Load

This study proposes a new optimization technique, known as the eagle strategy arithmetic optimization algorithm (ESAOA), to address the limitations of the original algorithm called arithmetic optimization algorithm (AOA). ESAOA is suggested to enhance the implementation of the original AOA. It includes an eagle strategy to avoid premature convergence and increase the populations’ efficacy to reach the optimum solution. The improved algorithm is utilized to fine-tune the parameters of the fractional-order proportional-integral-derivative (FOPID) and the PID controllers for supporting the frequency stability of a hybrid two-area multi-sources power system. Here, each area composites a combination of conventional power plants (i.e., thermal-hydro-gas) and renewable energy sources (i.e., wind farm and solar farm). Furthermore, the superiority of the proposed algorithm has been validated based on 23 benchmark functions. Then, the superiority of the proposed FOPID-based ESAOA algorithm is verified through a comparison of its performance with other controller performances (i.e., PID-based AOA, PID-based ESAOA, and PID-based teaching learning-based optimization TLBO) under different operating conditions. Furthermore, the system nonlinearities, system uncertainties, high renewable power penetration, and control time delay has been considered to ensure the effectiveness of the proposed FOPID based on the ES-AOA algorithm. All simulation results elucidate that the domination in favor of the proposed FOPID-based ES-AOA algorithm in enhancing the frequency stability effectually will guarantee a reliable performance.

Frequency Control in Power Systems with Large Share of Wind Energy

Fast frequency response from wind turbines and plants has been playing an increasingly important role in our modern power system, which has a large share of wind energy integration. Frequency control from grid-following wind turbines and plants has been extensively investigated in the literature, whereas grid-forming frequency control methods have aroused people’s attention in recent years, with relatively little comparison available. This paper provides such a comparison, illustrating the differences between the two methods of providing frequency support in a power system. The comparison shows the superiority of grid-forming frequency control methods over grid-following ones, and gives a glance into power system frequency stability in the transition from grid-following to grid-forming frequency support supplied by wind power. The results are elaborated in a benchmark WSCC 9-bus system, which features detailed electromagnetic transient modeling of the components from a single converter, a wind turbine, and a wind plant to the whole power system.

Performance Comparison of Typical Frequency Response Strategies for Power Systems With High Penetration of Renewable Energy Sources

Droop control, inertia control, and PD control are three typical frequency response (FR) strategies of grid-tied inverters interfaced renewable energy sources (RES) to restrain the power system frequency indicators, i.e., frequency deviation ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Delta \omega $ </tex-math></inline-formula> ) and the rate of change of frequency (RoCoF). Due to the highly limited inverter capacity, the FR performance in power systems with high RES penetration should be optimized. To this end, this paper first analyzes the impact of high-penetration renewable energy injection on power system frequency stability, and derives the system frequency expressions in the absence of an FR scheme, and in the presence of droop/inertia/PD controls that are representative for various virtual synchronous generator-based FR schemes. Under the same constraint of available FR capacity, control parameter ranges of these FR schemes are obtained, and their optimal conditions for restraining the maxima of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Delta \omega $ </tex-math></inline-formula> and RoCoF are identified and compared analytically. Comparison conclusions are finally proved by the provided experiment and simulation results.

Automatic Generation Control of a Future Multisource Power System Considering High Renewables Penetration and Electric Vehicles: Egyptian Power System in 2035

Egypt aims to diversify electricity generation sources and targets 42% of its power capacity through different renewable energy sources (RESs) by 2035. Such an increased share of RESs will make grid operation and control more tedious and may have a negative impact on power system frequency stability. Therefore, this paper is the first study that studies the automatic generation control of future multi-source power systems (e.g., Egyptian Power System (EPS) in a future 2035 scenario) considering high RESs penetrations and electric vehicles (EVs). The RESs in this future scenario include photovoltaic plants, wind generation plants, concentrated solar power plants, and hydropower plants. The EPS also contains other traditional power plants based on fossil fuels (i.e., coal, oil, and natural gas) and nuclear power plants. Moreover, this study investigates the effect of participation of EVs in enhancing the frequency stability of the future-scenario EPS. Furthermore, this study proposes a fractional-order proportional integral derivative (FOPID) controller for load frequency control (LFC), and its parameters are tuned using RUNge Kutta optimizer (RUN), which is a new optimization algorithm. To assess the FOPID controller performance, it was compared with a proportional-integral-derivative controller, proportional-integral controller, and integral controller. The results showed the positive effect of EVs’ participation in frequency regulation of the future-scenario EPS, the effectiveness of RUN optimizer in LFC application, and the superior performance of the FOPID controller over its peers of controllers used in the literature in improving frequency stability through reducing frequency deviations caused by different disturbances and under various power system conditions.

Determination of Control Requirements to Impose on CIG for Ensuring Frequency Stability of Low Inertia Power Systems

Power systems around the globe are undergoing a transformation characterized by a massive deployment of converter-interfaced generation (CIG) to effectively combat climate change. However, achieving a seamless transition from current power systems dominated by synchronous generators (SGs) to future ones with high levels of CIG requires overcoming several technical challenges. From a frequency stability perspective, reduced system inertia increases the frequency nadir after a loss of generation thereby endangering frequency stability. In this context, this paper proposes a novel methodology for determining control requirements to impose on CIG as their penetration in the network increases. Results of a case study based on the Chilean grid projected for the year 2046 show that, if only grid-following converters without frequency control capability are deployed, a maximum CIG penetration level of 75% can be achieved without threatening frequency stability. The Chilean system can reach a 99% CIG penetration, provided that the remaining CIGs are deployed in grid-following with frequency support capability. Finally, we show that if the last SG is replaced with a grid-forming converter, the system can still sustain frequency stability and exhibits a good dynamic performance. These results demonstrate that, at least from a frequency stability viewpoint, achieving a 100% based CIG system is technically possible. The proposed methodology can be used by energy regulators to define the control requirements necessary to impose on CIG for achieving renewable energy targets in a secure way. Although the obtained results are particular for the Chilean system, the proposed methodology can be applied to any power system.

A robust auto-synchronizer for synchronverter

The increasing deployment of inertia-less power electronic converters poses serious concerns on power system frequency stability. Synchronverter has certain features like virtual inertia, damping and voltage regulation embedded in its controller. Therefore, it can support system frequency and voltage in power grids. Like synchronous generator, it has ability to remain synchronized with the grid. However, it requires a synchronizer to track grid phase and frequency as reference before grid connection. This paper proposes a robust PLL-less Auto-synchronizer for synchronverter that allows it to synchronize with grid without interrupting its output power. The proposed synchronizer ensures fast synchronization independent of adverse grid conditions. Moreover, it has less computational burden on controller. The robustness of proposed synchronizer is validated by simulations. Results have shown that the proposed synchronizer is a fast and promising solution of synchronization of synchronverter with grid independent of certain grid conditions.

Research on super-capacitor fast power control system

In the context of carbon peak and carbon neutrality targets, high-proportion new energy power systems exhibit low inertia and weak damping characteristics. The frequency stability of the new power system has become a major problem for the safe and stable operation of the power grid. The traditional primary frequency modulation technology based on thermal power units or hydropower units has the defects of slow response speed and long frequency detection delay time. Therefore, we propose a multi-functional multiplexing super capacitor fast power control system, which has the functions of frequency stability control and voltage sag management. In the meantime, we proposed a fast frequency detection algorithm for cascaded signal delay, and the frequency detection delay is less than 10 ms. The system uses a high-speed communication ring network, and the communication delay is less than two milliseconds. Finally, we built a super capacitor energy storage system with a capacity of 50kW to verify that the super-capacitor has the ability to quickly and actively support the power system under frequency disturbances.

Center of Inertia Frequency Estimation Using Deep Learning Algorithm

Abstract Increasing the number of generation units connected to the grid via power electronic devices potentially implies negative impacts on the power system frequency stability and, depending on the power system inertia value, implies the necessary contribution of wind power plants to inertial response of the system. An alternative approach to the active power control of wind power plants, without the impact of local frequency deviation on the output power, is the application of a control strategies based on the center of inertia frequency. Since control schemes based on the input variable of the center of inertia frequency require a satisfactory level of signal transmission capacity in real time and the advanced telecommunication infrastructure of the power system, the paper considers an alternative approach to estimate the input signal value. According to the developed long short-term memory recurrent neural network, paper presents the idea of center of inertia frequency estimation by monitoring the speed of several generators in the system and passing the sequence of input data for a certain time interval, after the occurrence of imbalance, to the artificial intelligence module.

Frequency dynamics of power systems with temporally distributed disturbances

The frequency dynamics and stability of power systems is essentially affected by nature and characteristics of the disturbances occurring in the system. Conventionally, frequency transients are examined assuming a single disturbance applied at a given time. However, actual incidents in the power systems can be generally composed of a temporal sequence of events, and thus characterized by multiple power imbalances of different magnitudes and time offsets. The consideration of the effects of the temporal distribution of power imbalances is important for two main reasons: the impact on the frequency dynamics of the system in terms of frequency metrics such as minimum instantaneous frequency and maximum absolute rate of change of frequency, and the correct representation of the dynamic behaviour of the system also for complex events such system separation. The work provides an analytical approach for the theoretical study of the frequency dynamics with temporally distributed power imbalances. The analytical approach is then used to examine the impact of multiple disturbances having different magnitudes and time offsets on the typical frequency metrics used to characterize the transient performances of the system. The concepts derived in the work are finally applied to the case of an actual event occurred in the Continental Europe power system, showing the fundamental role of considering temporally distributed power imbalances for a correct and accurate assessment of the dynamics of the system.

A survey on development and prospect of wind turbines virtual synchronous control technology

The ongoing energy revolution has led to the gradual replacement of traditional synchronous generators by renewable enecorresponding authorrgy. This transformation of power generation mode reshapes power system dynamics and poses many challenges to reliable and efficient grid operation. With the continuous improvement of the penetration level of renewable energy represented by wind power in the power system, the synchronous mode of wind turbine will gradually become one of the main modes of system synchronization. In the case of coexistence of multiple synchronization modes, the synchronization mechanism of the whole power system will be fundamentally changed; at the same time, due to the response characteristics of wind turbine to the frequency and voltage dynamics of power grid and the traditional power supply, the synchronous mode of wind turbine will gradually become one of the main modes of system synchronization The frequency and voltage stability of power system also faces new challenges. The virtual synchronous generation technology can make the grid connected inverter simulate the operation mechanism of step generator and provide an effective method to solve the above problems. In this paper, the main technical routes to realize virtual synchronous control of wind turbines are summarized. From the aspects of stability analysis, control system optimization, performance analysis and evaluation, the research and engineering status of virtual synchronization technology in wind turbines are introduced, and the problems to be solved and technical requirements are prospected.

Enhancement of frequency stability of power systems integrated with wind energy using marine predator algorithm based PIDA controlled STATCOM

This paper proposes a novel optimized Proportional-Integral-Derivative-Acceleration (PIDA) controlled static synchronous compensator (STATCOM) to improve the frequency response of power systems through reactive power modulation. The proposed controller can maintain the system frequency within permissible limits upon load change or generation loss. The gains of the PIDA controller are fine-tuned using the Marine Predator Algorithm (MPA), which is a newly metaheuristic optimization technique. Moreover, the performance of the MPA-PIDA controlled STATCOM is tested in the two-area four-machine system (Kundur system) and the New England IEEE 39-bus system. The results show that the MPA-PIDA controller can provide better frequency response compared with the multi-band controller presented in the previous literature. In addition, the robustness of the proposed controller is verified when case studies are integrated with wind generation. The results show that the primary frequency response is greatly improved by using the MPA-PIDA controlled STATCOM in all studied cases. Moreover, the results are given in the form of time domain simulations using MATLAB/SIMULINK.

Impact of continuous stochastic and spatially distributed perturbations on power system frequency stability

With the increase in variable inverter-based renewable energy sources, power systems become increasingly subjected to stochastic sources. Considering the decline in rotational inertia, the consequence of the continuous spatially distributed perturbations is stochastic frequency dynamics. In this paper, the stochastic dynamics of the power system dynamics, subjected to spatially distributed disturbances, are investigated using a stochastic differential equation and the Fokker-Planck equation. This research shows that the reactance distance between perturbation sources, like wind farms, and the location of system inertia (synchronous generators/condensers), reduces the variance of the system’s rate of change of frequency probability density function. Thus, for a power system under continuous and spatially distributed stochastic feed-in, greater reactance distances decrease the probability of significant frequency dynamics.

Operational planning steps in smart electric power delivery system

This paper presents a comprehensive review of advanced technologies with various control approaches in terms of their respective merits and outcomes for power grids. Distributed energy storage control is classified into automatic voltage regulator and load frequency control according to corresponding functionalities. These control strategies maintain a power balance between generation and demand. Besides, three basic electric vehicle charging technologies can be distinguished, i.e. stationary, quasi-dynamic and dynamic control. For realizing charge-sustaining operation at minimum cost quasi-dynamic and dynamic strategies are adopted for in-route charging, while stationary control can only be utilized when the electric vehicle is in stationary mode. Moreover, power system frequency stability and stabilization techniques in non-synchronous generator systems are reviewed in the paper. Specifically, a synchronverter can damp power system oscillations and ensure stability by providing virtual inertia. Furthermore, it is crucial to manage the massive information and ensure its security in the smart grid. Therefore, several attack detection and mitigation schemes against cyber-attacks are further presented to achieve reliable, resilient, and stable operation of the cyber-physical power system. Thus, bidirectional electrical power flows with two-way digital control and communication capabilities have poised the energy producers and utilities to restructure the conventional power system into a robust smart distribution grid. These new functionalities and applications provide a pathway for clean energy technology. Finally, future research trends on smart grids such as IoT-based communication infrastructure, distributed demand-response with artificial intelligence and machine learning solutions, and synchrophasor-based wide-area monitoring protection and control (WAMPC) are examined in the present study.

Evaluating power system network inertia using spectral clustering to define local area stability

The transitioning from synchronous machine generation to large-scale integration of inverter-based renewable generation introduces new challenges in power system frequency stability. This paper proposes a new approach for evaluating power system frequency stability based on network clusters. First, the most common metrics for power system frequency stability are presented, with their advantages and disadvantages. Then, we establish the link between frequency response and network topology. Based on the pros and cons of current frequency stability metrics and the influence of network topology, a proposal is made for a new approach to evaluate frequency stability using Spectral Graph Theory to partition a power system network into clusters for analysis. Consider the displacement of synchronous generator inertia, together with the spatial–temporal fluctuations/noise fed in from spatially distributed variable renewable energy sources. Then the proposed clustering approach has two main advantages over traditional methods for evaluating power system frequency robustness. The first is a spatial awareness of a power system network in terms of frequency-stable areas. The second advantage is the ease of interpretation of the metric result for robust network planning.

Coordinated Sending-End Power System Frequency Regulation via UHVDC

The continuous improvement of new energy penetration reduces the inertia of the system, which leads to the frequency deviation and the rate of change of frequency (RoCoF) being easily exceeded. To improve the frequency stability of sending-end power systems with large-scale renewable energy access via ultra-high voltage direct current (UHVDC), the coordinated frequency control for UHVDC participating in system frequency regulation (FR) including primary FR and system inertial response is presented. Based on the simplified system model, the mechanism of UHVDC participation in system frequency support and its influence on receiving-end system frequency response characteristics are analyzed. Compared with the inertia response and primary FR of traditional synchronous generators, the parameter calculating method of UHVDC coordinated frequency response control is proposed. Based on the system root trajectory analysis, the influence of the frequency response control parameters on the sending-end system’s stability is analyzed, and the constraints of UHVDC participating in the system frequency response control are analyzed. Then, based on the RTDS verification platform containing the Lingshao ±800 kV UHVDC control and protection system, the system frequency response characteristics under different control strategies, operating conditions and control parameters are verified and analyzed. The experimental results show that the UHVDC frequency coordinated control can effectively increase the equivalent inertia of the sending-end system, restrain the RoCoF and the frequency deviation, and increase the FR capability of the UHVDC system.

The Network Topology Metrics Contributing to Local-Area Frequency Stability in Power System Networks

The power system network topology influences the system frequency response to power imbalance disturbances. Here, the objective is to find the network metric(s) contributing to frequency transient stability. The graph Laplacians of six 4-node network topologies are analysed using Spectral Graph Theory. For homogeneous network connections, we show that the node degree measure indicates node robustness. Based on these analytical results, the investigation expands to a 10-node network topology consisting of two clusters, which provide further insight into the spectral results. The research then involves a simulation of a power imbalance disturbance on three 20-node networks with different topologies based on node degree, where we link the node degree measure to imbalance disturbance propagation through Wave Theory. The results provide an intuitive understanding of the impact of network topology on power system frequency stability. The analytical and simulation results indicate that a node’s sensitivity to disturbances is partially due to its node degree, reactance from disturbance location, and the link it has to other higher degree nodes (hierarchical position in network topology). Testing of the analytical and simulation results takes place on the nonhomogeneous IEEE-14 bus and IEEE-39 bus networks. These results provide insights into optimal inertia placement to improve the frequency robustness of low-inertia power systems. The network topology, considering node degrees, influences the speed at which the disturbance impact propagates from the disturbance location and how fast-standing waves form. The topology thus contributes to how fast the energy in a disturbance dissipates to zero.

Robust decentralized model predictive load-frequency control design for time-delay renewable power systems

Abstract A robust decentralized model predictive control (DMPC) design is proposed for frequency stability of hybrid renewable power systems considering high renewables energy penetration and nonlinearity effects. The Egyptian power system (EPS) considered as a test system comprises both traditional power stations (i.e., steam, gas, combined cycle, and hydraulic power plants) and renewable energy sources (RESs). Where the considered RESs contain both the wind power generated from Zafarana and Gabel El-Zeit wind farms and the solar power generated from Benban solar park, which is considered one of the world’s largest photovoltaic (PV) plants. To obtain an accurate insight into a real modern power system, this research takes into account the effects of the important nonlinearity such as generation rate constraints (GRCs), governor deadband (GDB), and communication time delay (CTD). The designed control is set based on the DMPC for each subsystem independently to ensure the frequency stability of the whole system as each subsystem has different characteristics and operating constraints than the others. Moreover, the decentralized control scheme has become imperative for large power systems due to the high cost of transmitting data over long distances and the probability of error occurrence with the centralized control scheme. To verify the effectiveness and robustness of the proposed DMPC for the EPS, it is compared with the centralized MPC (CMPC) scheme in different operating conditions. The simulation results, which are conducted using MATLAB/SIMULINK® software, emphasized that the proposed DMPC scheme can effectively handle several load disturbances, high uncertainty in the system parameters, and random communication delays. Hence, it can regulate the grid frequency and ensure the robust performance of the studied renewable power system with high RESs penetration and maximum communication delays in the system.

Performance enhancement of pumped storage units for system frequency support based on a novel small signal model

The fast and stable regulation of pumped storage is a basic guarantee for supporting various scenarios of renewable energy system. The operator pursues sensitive tracking performance, while underestimates the dynamic characteristics of hydraulic system and damping characteristics of pumped storage unit (PSU). These may aggravate the wear-tear of PSU operation, and decrease the frequency stability of power system. Therefore, a systematical study of improving overall regulation performance is conducted by applying PSU modeling, co-optimization and operation evaluation. First, the novel small signal model is proposed and the high-order hydraulic damping model is further derived. Apart from the ultra-low frequency oscillation mode, a new frequency oscillation mode caused by surge tanks is captured. Second, the co-optimization strategy is presented to coordinate the stability-tracking conflict. And then a comprehensive evaluation model, integrating 14 indicators is conducted to quantify the PSU performance and its contribution to power system, driving the favorable decision making of operators. Compared with the original scheme, the overall performance of PSU is improved by 20.76%, at the cost of 10.88% tracking capacity. The comparison of three measures including 12 scenarios verifies the competitive advantage of co-optimization strategy in multi-machine system. This paper supplies a novel tool for performance enhancement of PSU. It may have potential value in the stability of renewable energy systems with multiple hydropower units.