With rapid growth of renewable energy sources (RESs) in modern power systems, the microgrids (µGs) have become more susceptible to the disturbances (e.g. large frequency/voltage fluctuations) than ...the conventional power systems due to decreasing their inertia constant. This low system inertia issue could affect the µGs stability and resiliency in the situation of uncertainties, thus threaten their dynamic security. Hence, preserving µG dynamic security is one of the important challenges, which is addressed in this study. Therefore, this study proposes a novel concept of frequency control incorporating a virtual inertia control-based optimal proportional–integral controller to emulate virtual inertia into the µG control loop, thus stabilising µG frequency during high penetration of RESs. Moreover, the proposed virtual inertia control system is coordinated with digital over/under frequency protection for enhancement of the frequency stability and preservation of the µG dynamic security because of the high integration level of the RESs. The simulation results of the studied µG are carried out using MATLAB/Simulink® software to validate the effectiveness of the proposed coordination scheme. Results approved that the proposed coordination scheme can effectively regulate the µG frequency and guarantee robust performance to preserve the dynamic security of µG with high penetration of RESs for different contingencies.
•This paper proposes a new frequency control strategy based on Virtual Synchronous Generator (VSG), which emulates the characteristics of a real synchronous generator and are as follows; the inertia ...and damping properties through the concept of virtual rotor as well as frequency control loops (i.e., primary and secondary frequency control) through the virtual primary and secondary control to compensate the reduction in system inertia that results from adding more RESs (e.g., non-inertia sources), thus stabilizing the system frequency during high penetration of RESs.•The proposed virtual inertia control system based on VSG is coordinated with digital over/under frequency protection for improvement the frequency stability and preservation the dynamic security of renewable power systems because of the high integration level of the RESs.•The virtual primary controller (i.e., proportional controller) and virtual secondary controller (i.e., integral controller) is combined to obtain on a PI controller, which is optimally designed by using Particle Swarm Optimization (PSO) for finding the optimal tuning of the virtual controller parameters, thus enhancing the power system stability and resilience.•The uncertainties of RESs and load are taken into consideration in the virtual controller design procedure. Thus, the proposed coordination scheme will ensure an evasion of system instability and collapsed.•The effectiveness of the proposed coordination scheme is tested and verified through small and large scales of power systems, Microgrid and real hybrid power system in Egypt, respectively. The simulations results proved that renewable power systems with the proposed coordinated scheme will provide better stability and performance for today’s power system, and for those of the future, which are expected to integrate more and more renewable energy; thus, the proposed coordination scheme will ensure an avoidance of power system instability and system collapse.
The renewable power systems have become more susceptible to the system insecure than traditional power systems due to reducing of the total inertia and damping properties that result from replacing the conventional generators with Renewable Energy Sources (RESs) as well as decoupling of the RESs from the AC grid using power converters. Therefore, maintaining the dynamic security of renewable power systems is the key challenge for integrating more RESs. This paper addresses a new strategy of frequency control including virtual inertia control based on Virtual Synchronous Generator (VSG), which emulates the behavior of conventional synchronous generators in large power systems, thus adding some inertia to the system control loop virtually and accordingly stabilizing the system frequency during high penetration of RESs. Moreover, the proposed virtual inertia control system-based VSG is coordinated with digital frequency protection for improvement the frequency stability and preservation the power system dynamic security because of the high integration level of the RESs. The effectiveness of the proposed coordination scheme is tested and verified through small and large scales of power systems, Microgrid (µG) and real hybrid power system in Egypt, respectively. System modelling and simulation results are carried out using Matlab/Simulink® software. The simulation results validated that the proposed coordination scheme can effectively regulate the system frequency and ensure robust performance to maintain the dynamic system security with high share of RESs for different contingencies.
This study proposes a coordination of load frequency control (LFC) and superconducting magnetic energy storage (SMES) technology (i.e. auxiliary LFC) using a new optimal PID controller-based moth ...swarm algorithm (MSA) in Egyptian Power System (EPS) considering high wind power penetration (HWPP) (as a future planning of the EPS). This strategy is proposed for compensating the EPS frequency deviation, preventing the conventional generators from exceeding their power ratings during load disturbances, and mitigating the power fluctuations from wind power plants. To prove the effectiveness of the proposed coordinated control strategy, the EPS considering HWPP was tested by the MATLAB/SIMULINK simulation. The convention generation system of the EPS is decomposed into three dynamics subsystems; hydro, reheat and non-reheat power plants. Moreover, the physical constraints of the governors and turbines such as generation rate constraints of power plants and speed governor dead band (i.e. backlash) are taking into consideration. The results reveal the superior robustness of the proposed coordination against all scenarios of different load profiles, and system uncertainties in the EPS considering HWPP. Moreover, the results have been confirmed by comparing it with both; the optimal LFC with/without the effect of conventional SMES, which without modifying the input control signal.
Renewable energy sources (RESs) are growing rapidly and highly penetrated in microgrids (MGs). As a result of the replacement of the synchronous generators with a large amount of RESs, the overall ...system inertia might be dramatically reduced which negatively affected the MG dynamics and performance in face of uncertainties, leading to weakening of the MG stability, which considers being a serious challenge in such grids. Therefore, in order to cope with this challenge and benefit from a maximum capacity of the RESs, robust control strategy must be applied. Hence, in this paper, a new application of robust virtual inertia control-based coefficient diagram method (CDM) controller is proposed in an islanded MG considering high-level RESs penetration for enhancement the system's validity and robustness in face of disturbances and parametric uncertainties. The proposed controller's proficiency has been checked and compared with H-infinite controller using MATLAB/Simulink which approved that the CDM controller achieved superior dynamic responses in terms of accurate reference frequency tracking and disturbance reduction over H-infinite in all test scenarios. Thus, the proposed controller alleviates the difficulties of H-infinite controller such as the experience and necessary abilities to design the form of the weighting functions for the system. Consequently, the frequency stability is improved and approved that the proposed CDM-based virtual inertia controller can significantly support a low-inertia islanded microgrid against RESs and load fluctuations.
This paper presents a coordination strategy of Load Frequency Control (LFC) and digital frequency protection for an islanded microgrid (MG) considering high penetration of Renewable Energy Sources ...(RESs). In such MGs, the reduction in system inertia due to integration of large amount of RESs causes undesirable influence on MG frequency stability, leading to weakening of the MG. Furthermore, sudden load events, and short circuits caused large frequency fluctuations, which threaten the system security and could lead to complete blackouts as well as damages to the system equipment. Therefore, maintaining the dynamic security in MGs is one of the important challenges, which considered in this paper using a specific design and various data conversion stages of a digital over/under frequency relay (OUFR). The proposed relay will cover both under and over frequency conditions in coordination with LFC operation to protect the MG against high frequency variations. To prove the response of the proposed coordination strategy, a small MG was investigated for the simulation. The proposed coordination method has been tested considering load change, high integration of RESs. Moreover, the sensitivity analysis of the presented technique was examined by varying the penetration level of RESs and reducing the system inertia. The results reveal the effectiveness of the proposed coordination to maintain the power system frequency stability and security. In addition, the superiority of the OUFR has been approved in terms of accuracy and speed response during high disturbances.
► Conventional PSS is used in power system to damp the low frequency oscillations. ► The study system is fourth order linearized model of one machine power system. ► The paper is concerned with the ...discretization of a conventional PSS. ► The PIM digital design method is used to discretize the conventional PSS. ► For comparison, discrete PSS is compared with conventional PSS and Tustin’s PSS.
This paper is concerned with the plant modeling for the digital redesign of a continuous-time power system stabilizer PSS for a single machine power system using Plant-Input-Mapping PIM method. The traditional approach has been to use the bilinear transform (Tustin’s method), but this needs small sampling intervals which gives some difficulties with modern control. The presented technique guarantees the stability for any sampling rate as well as it takes closed-loop characteristics into consideration. The proposed technique is successfully applied to the discretization of the conventional continuous time PSS for single-machine power system. For comparison studies the proposed technique is compared with conventional continuous-time PSS and Tustin’s PSS. The simulation results show that the states of the proposed digital redesign technique closely match those of the conventional continuous-time PSS. The proposed digital redesign technique guarantees stability even with relatively slow sampling rates while Tustin’s method falls when sampling interval becomes larger.
With rapidly growing of Renewable Energy Sources (RESs) in renewable power systems, several disturbances influence on the power systems such as; lack of system inertia that results from replacing the ...synchronous generators with RESs and frequency/voltage fluctuations that resulting from the intermittent nature of the RESs. Hence, the modern power systems become more susceptible to the system instability than conventional power systems. Therefore, in this study, a new application of Superconducting Magnetic Energy Storage (SMES) (i.e., auxiliary Load Frequency Control (LFC)) has been integrated with the secondary frequency control (i.e., LFC) for frequency stability enhancement of the Egyptian Power System (EPS) due to high RESs penetration. Where, the coordinated control strategy is based on the PI controller that is optimally designed by the Particle Swarm Optimization (PSO) algorithm to minimize the frequency deviations of the EPS. The EPS includes both conventional generation units (i.e., non-reheat, reheat and hydraulic power plants) with inherent nonlinearities, and RESs (i.e., wind and solar energy). System modelling and simulation results are carried out using Matlab/Simulink® software. The simulation results reveal the robustness of the proposed coordinated control strategy to preserve the system stability of the EPS with high penetration of RESs for different contingencies.
In modern power systems, the penetration level of Renewable Energy Sources (RESs) is strikingly increasing. Where, many synchronous generators are being replaced by the RESs-based the power ...electronic devices, this will reduce the overall system inertia. Moreover, the intermittent nature of the RESs causes several control problems such as frequency/voltage instability problem. Hence, these disturbances threaten preservation the power system stability and can lead to system collapse. In addition, the secondary frequency control action (i.e., Load Frequency Control (LFC)) will not be sufficient to maintain the system frequency close to its scheduled value. Therefore, this paper proposes an application of Superconducting Magnetic Energy Storage (SMES) system based on an optimal PID controller, which is optimally designed by the Particle Swarm Optimization (PSO) to enhance the frequency stability of modern power systems due to high RESs penetration. From the perspective of the LFC, the proposed controlled SMES can be used as a feedback controller with the aim of supporting the frequency control loops for frequency stability enhancement of the power systems. Moreover, the effectiveness of the proposed control strategy is tested and verified through a real hybrid power system in Egypt (i.e., Egyptian Power System (EPS)) that includes thermal, gas, hydraulic power plants, wind, and solar energy. The obtained simulation results by Matlab/Simulink software reveal that the proposed control strategy achieved superior dynamic responses satisfying the LFC requirements in all test scenarios. Consequently, the frequency stability is improved regarding peak undershoot, peak overshoot, and settling time.
This paper presents a digital model of decentralized Load Frequency Control (LFC) using an optimal PID controller-based Particle Swarm Optimization (PSO) in Egyptian Power System (EPS) considering ...communication delays. The EPS includes both conventional generation units (i.e., non-reheat, reheat, and hydraulic power plants) with inherent non-linearities and wind power, which extracted from Zafarana wind farm, location in Egypt. Thus, the optimal digital controller-based Tustin’s technique is designed for every subsystem of the EPS separately to guarantee the stability of the overall closed-loop system. The performance of the proposed digital model is tested and compared with the analog model under variation in loading patterns, loading conditions, system parameters, wind farm penetration, and communication delays. Results approved that, the proposed digital model can effectively regulate the system frequency and guarantee robust performance under different conditions. Also, it gives a reliable performance at large sampling times, which means a reduction of implementation cost.
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