Haghighat, M.,
Tafti, H.D.,
Gholipour shahraki, M.,
Niroomand, M.,
Townsend, C.D.,
Barajas, N.V.,
Liang, G.,
Konstantinou, G.,
Pou, J. IEEE Access (21693536)12pp. 168568-168580
Grid-connected photovoltaic (PV) systems enhance grid stability during frequency fluctuations by adopting power reserve control (PRC) and contributing to frequency regulation. The cascaded H-bridge (CHB) converter is a suitable choice for large-scale photovoltaic systems. This paper introduces a distributed PRC strategy designed for CHB-based PV systems, necessitating minimal inter-module communication and thus simplifying implementation. Each submodule (SM) within the CHB converter periodically engages in maximum power point tracking to assess the system’s total accessible PV power. Through coordinated control, the strategy evenly allocates the necessary power across sub-modules based on their PV power availability, offering a balanced power distribution while acknowledging operational constraints on power disparity among SMs. Simulation and experimental results confirm the efficiency of the proposed approach under various conditions, showcasing accurate PV power estimation, seamless transition between operating modes, fast dynamic response, and regulation of the dc-link voltages. © 2013 IEEE.
IET Renewable Power Generation (17521416)(14)
This research proposes the application of fractional-order sliding mode control (FOSMC) at the primary controller level to improve the stability of an islanded microgrid by adjusting its voltage and frequency. The control strategies used in the microgrid are performed in two levels (primary and secondary) in the islanded mode. Practically, most previous studies have worked to improve the primary controller. Droop control is one of the most commonly used methods at the primary level and is adopted in this study as well. The sliding mode control (SMC) strategy is normally used to control linear equations. Thus, the non-linear microgrid equations were transformed into some linear ones using the input-output feedback linearization technique. Further, a fractional sliding surface was acquainted. The sliding surface and FOSMC were designed to reject system uncertainties and organize the voltage and frequency. Design parameters were chosen using the Lyapunov stability theorem. The validation of the proposed method using Simulink-MATLAB confirms its effectiveness in enhancing level power sharing, regulating frequency, and maintaining voltage stability across the system. © 2024 The Author(s). IET Renewable Power Generation published by John Wiley & Sons Ltd on behalf of The Institution of Engineering and Technology.
IET Generation, Transmission and Distribution (17518687)18(19)pp. 3097-3107
The increasing penetration of the distributed energy resources (DER) in the power grid, which, while having significant advantages, also pose significant challenges. The behaviors of DERs differ from those of synchronous generators, particularly in abnormal conditions. For this reason, the power grid enforces grid codes to ensure that DERs perform properly in different conditions. For instance, short circuit faults and unbalanced grid voltage are severe transient events that inverters need to be able to pass through without disconnecting from the grid. Furthermore, the inverters are required to support the grid voltage by regulating the active and reactive power injections. This article proposes a voltage support control scheme to support grid voltage during asymmetrical voltage drop by utilizing an optimization problem. In this optimization problem, the active and reactive powers injected into the grid will be obtained optimally by considering constraints such as instantaneous active and reactive power oscillation magnitudes and peak current limitation. To aid in this purpose, the corresponding mathematical formulations such as instantaneous active and reactive power oscillation magnitudes will be obtained by using the currents and voltages in stationary reference frame. The proposed scheme will be verified by simulating it in MATLAB/Simulink under three different scenarios and tested on a real-time experimental Opal-RT platform. © 2024 The Author(s). IET Generation, Transmission & Distribution published by John Wiley & Sons Ltd on behalf of The Institution of Engineering and Technology.
Computers and Electrical Engineering (00457906)
A variation in load on a microgrid (MG) system has a significant impact on the MG's frequency. In addition, wind and photovoltaic power sources are significantly affected by weather fluctuations; thus, the system experiences frequent oscillations. This paper proposes an integral sliding mode control system that incorporates a disturbance observer (ISMCDO) for establishing a power balance and frequency regulation in a MG system. MATLAB/ Simulink is used to compare the results of this method and those of integral sliding mode controller (ISMC) and disturbance observer-based controller (DOBC). In addition, their performance indices are compared as well, where the results can verify the superiority of ISMCDO method in comparison with other techniques. Consequently, Utilizing the ISMCDO controller, the secondary controller performances in the MG system may be improved, which will ensure stability, flexibility, quick response, and maintenance of the load balance when sudden changes in loads and weather conditions occur. © 2022
IEEE Transactions on Industry Applications (00939994)(2)
Load frequency control (LFC) is a crucial application in modern power systems as it ensures the system frequency remains within an acceptable range through demand control and active power generation. However, as information and communication technology (ICT) becomes more prevalent in power system, there are both opportunities for improved reliability and efficiency as well as potential security threats. This article proposes an LFC approach that takes into account the simultaneous occurrence of false data injection (FDI) attacks on the sensor-controller side, disturbances in the states of the system and time delays in the controller-actuator side. To tackle these challenges, a slide mode observer is utilized to estimate system states and detect cyber-attack signals as an extra virtual state. Subsequently, a cyber-attack-resilient predictor slide mode controller is designed to establish a robust control law capable of overcoming system challenges, when all system states are not within reach. Therefore, the robust control law is designed based on the estimated states, cyber signal and measured system output. By integrating these techniques, the proposed methodology offers a promising solution to enhance the resilience and performance of power system faced with cybersecurity threats. It improves the response speed of the system and minimizes the maximum overshoot compared to some published resilience control laws, thereby ensuring secure and reliable load frequency control. Additionally, reducing the number of sensors in the system helps to reduce overall costs. Finally, the performance of the controller is also verified in real-time using the OPAL-RT simulator testbed. © 2023 Institute of Electrical and Electronics Engineers Inc.. All rights reserved.
IET Generation, Transmission and Distribution (17518687)(16)
The basis of traveling wave-based fault location methods is to extract the arrival times of transient signals in the power network. In this paper, a new method for extracting the traveling wave arrival times is presented. For this purpose, the aerial modes of three-phase voltage signals are extracted and two sequential sliding windows of unequal length move along with this signal. By fitting a line to the samples inside each of the two windows and calculating the angle between them, the traveling wave arrival times can be determined with high accuracy. Because this takes place in the time domain, there is no need to switch between time and frequency domains similar to those in Fourier transforms. On the other hand, fitting curves reduce the negative effects of noise and sampling frequency changes. EMTP-ATP is applied to perform the transient simulations and the results are then analysed in MATLAB to conduct the sensitivity analysis against the measurement noises, the sampling frequency, and the fault parameters. The proposed technique is compared to the common techniques such as discrete wavelet transforms and Hilbert Huang transforms. The results demonstrate that the proposed technique has acceptable performance and covers the drawbacks of common methods. © 2022 The Authors. IET Generation, Transmission & Distribution published by John Wiley & Sons Ltd on behalf of The Institution of Engineering and Technology.
International Journal of Electrical Power and Energy Systems (01420615)139
Penetration of inverter-based distributed energy (DG) resources into power grid has notably risen in recent years. Hence, new grid code standards require DGs to remain connected to the main grid even during faults and inject a certain amount of reactive power. However, in weak grids and during severe voltage faults, converters may fail to maintain their synchronization with the main grid. A main cause for this synchronization instability is the improper operation of synchronization unit which is phase locked loop (PLL). In literature, imitating the transient stability analysis of synchronous generators, swing equation and Equal Area Criterion (EAC) are applied to study the synchronization of grid-connected converters. In this paper, a new method based on EAC and swing equation is proposed to keep the damping coefficient in the swing equation positive, and consequently increase the maximum buffer area in EAC. Hence, the synchronization stability of voltage source converters (VSCs) connected to weak grids is enhanced. When the fault is detected, the proposed technique simply adds a certain gain of frequency deviation to the PLL and does not need any additional information of grid changes. The simulation results in MATLAB verify the viability of the proposed controller. © 2022 Elsevier Ltd
IET Generation, Transmission and Distribution (17518687)(6)
This paper proposes a high-speed and accurate method for extracting the arrival times (ATs) of traveling waves (TWs) in the power system that can be used for fault location applications and transmission line protection. The proposed method is based on the expression of the traveling wave as the exponentially damped component superimposed on the sinusoidal wave in a small time window. Also the sine component is removed by using approximation and consecutive differences of the input signal samples (the modal components of three-phase voltages or currents) from the resulting wave. Due to the fact that the estimation of traveling wave arrival times (TWATs) is done applying basic mathematical operations in the time domain, the proposed method, in addition to the simplicity of implementation, has the appropriate accuracy and speed for applications such as online fault location and protection purposes. In order to evaluate the performance of the proposed approach in fault locating, a 230 kV transmission line is modelled in EMTP/ATP. Then, the fault location under various conditions of faults such as changes in location and type of fault, fault conditions as well as variations in the measurement noise level and sampling frequency are studied using MATLAB. © 2021 The Authors. IET Generation, Transmission & Distribution published by John Wiley & Sons Ltd on behalf of The Institution of Engineering and Technology
Electric Power Systems Research (03787796)
This paper proposes a single-ended traveling-wave-based fault location scheme for transmission systems consisting of an overhead line combined with an underground cable. In the first step, the proposed algorithm uses the three-phase voltages measured through optical sensors at the fault locator installation bus to extract the traveling wave arrival times using two consecutive sliding windows and curve fitting. Then, using the arrival times of three consecutive collisions and changes of their polarity, the faulty section is identified. Finally, the exact location of the fault is determined. To evaluate the performance of the proposed algorithm, transient state simulations were performed in EMTP-ATP for various conditions of fault and system parameters. The transient signals are processed and the results prove the high accuracy of the proposed method. © 2022
Sustainable Cities and Society (22106715)78
Extreme dust storms (EDSs) are rare natural disasters, occurring with a higher rate of incidence and severity in recent years in coastal areas with humid climate. EDSs can hamper the operation of power distribution systems (PDSs) and other related urban infrastructures, and damage PDS insulation equipment. In this paper, a bi-level stochastic mixed-integer linear programming model is proposed for PDS resilience enhancement against EDSs. In the proposed model, the investment cost and total expected operating costs under the EDS conditions are minimized while considering uncertainties and PDS financial and operational constraints. The proposed actions for PDS resilience enhancement include pre-and post-EDS actions. Pre-EDS actions include simultaneous hardening of lines and substations, optimal placement of sectionalizing switches, and installation of emergency generators (EGs) in critical points. Post-EDS actions include damaged lines and substations repair, optimal network reconfiguration, power dispatch of EGs and optimal load shedding. The planning results at different budget levels show that coordinating pre-and post-event actions can reduce investment costs besides reducing operational costs. Implementation of the proposed model on the IEEE 33-bus test system and a large-scale PDS in Khuzestan province, a coastal province in southwestern Iran, confirms the efficiency of the proposed method for PDS resilience enhancement planning. © 2021
Panah, P.G.,
Hoshmand, R.,
Gholipour shahraki, M.,
Macana, C.A.,
Guerrero, J.M.,
Vasquez, J.C. Sustainable Energy Technologies and Assessments (22131388)48
Islanded microgrids with high shares of RES are more exposed to frequency disturbances. The largest generator is typically in charge of frequency regulation. This study tries to upgrade this monopoly to a competitive market. A novel framework is proposed to invite prosumers of any kind/size to participate in a local ancillary service market. A multi-criteria decision-maker is developed to select the proper service from the pool of bids. Flexibility Flags and Prosumer Deviation Index are introduced to quantify the behaviors of individuals and the stability of autonomous microgrids. Furthermore, an innovative reward/punishment framework is suggested for the billing of subscribers. In this method, the extra cost of the activated reserved power is solely compensated by disturbance makers rather than the conventional way of blindly charging all subscribers for frequency regulation. An urban microgrid including electric vehicles, micro combined heat/power generator, thermostatic loads, and kinetic energy storage is considered for the performance assessment. The results indicate that electric vehicles and flexible loads are privileged. Also, the bill of the planned loads for the regulation service falls from 46–48% down to 3–6% under the proposed framework while the cost of frequency regulation drops by 59% when the unnecessary reserved power is modified. © 2021 Elsevier Ltd
International Transactions on Electrical Energy Systems (20507038)31(7)
This paper proposes a hybrid adaptive strategy to control virtual inertia of virtual synchronous generators (VSGs). The proposed technique can provide low frequency oscillation (LFO) damping and simultaneously improve primary frequency control (PFC) performance metrics. To this end, a control variable is defined to control extremum values of the VSG inertia during PFC process. The control variable uses an estimation of the grid frequency gradient to identify the PFC process stages following a power deficit event. The extremum of the VSG inertia to provide LFO damping is governed based on the control variable. In particular, the minimum value of the VSG inertia is restricted to its base value during the frequency arresting process in order to moderate the frequency rate of change. In contrast, the maximum value of the VSG inertia is limited to its base value in frequency recovery period to achieve a faster frequency recovery. The efficiency of the suggested method is validated through a power system with VSG penetration level as 50% of the system generation rating. The achieved results verify the superiority of the proposed scheme in the PFC improving and the LFO damping in comparison to the conventional strategy. Moreover, the suggested approach can efficiently decrease the required size of the VSG energy storage by about 50%. © 2021 John Wiley & Sons Ltd.
IET Generation, Transmission and Distribution (17518687)15(18)pp. 2618-2631
The present paper devises a second-order system frequency response (SFR) model for power systems integrating virtual synchronous variable speed wind turbines (VSWTs). The inertial response model of full converter VSWTs, in which grid-side converters are controlled using a virtual synchronous generator concept, is developed. The derived model is incorporated into the traditional SFR model deployed to estimate the frequency behaviour of the synchronous generators following infeed loss contingencies. The proposed SFR model formulates interaction between the VSWTs rotor speed reduction and the system frequency drop. The system loads inertia is also included in the SFR model. Additionally, an analytical approach to derive the suggested SFR model for the large power system including VSWTs with different capacities and operating points is presented. Solving the proposed model gives the analytical functions for estimating deviations in the system frequency as well as VSWTs rotor speed variations. Finally, the accuracy of the devised SFR model is verified through the time-domain simulations of a modified IEEE 39-bus system. Particularly, impact of the VSWTs virtual inertia on the efficiency of the proposed SFR model is studied. © 2021 The Authors. IET Generation, Transmission & Distribution published by John Wiley & Sons Ltd on behalf of The Institution of Engineering and Technology
IET Generation, Transmission and Distribution (17518687)15(7)pp. 1136-1143
With the increasing penetration of inverter based distributed generation, recent grid codes do not permit the disconnection of converters as soon as fault happens. Considering the fact that electrical grids are not purely inductive, the grid connected converters face instability issues by fault occurrence. Converters applying Phase Lock Loop (PLL) are not able to synchronize with the weak grid during deep low voltage faults. This paper proposes a novel control strategy based on virtual impedance to maintain the synchronization of grid connected converters during heavy decrease of the grid voltage. Utilizing a virtual impedance and the measured current at the point of common coupling, the inverter can be virtually synchronized to a point which has a stronger connection. The virtual impedance can be a rough estimation of the line impedance or resistance from point of common coupling to the fault point. Furthermore, to avoid the need for impedance estimation, a simple technique is also proposed. Simulation results with MATLAB confirms the competence of the proposed method in improving the synchronization stability of the grid connected converters. © 2020 The Authors. IET Generation, Transmission & Distribution published by John Wiley & Sons Ltd on behalf of The Institution of Engineering and Technology
IET Renewable Power Generation (17521416)15(1)pp. 58-72
Today, with growing expansion of renewable energy resources, electricity production is accompanied by uncertainties. The usage and optimal management of energy storage is one of the effective ways to compensate for these uncertainties. Compressed air energy storage (CAES) is one of the two bulk electricity storage methods for power systems, burning natural gas (NG) to extract the stored energy. Therefore, the NG price uncertainty and gas availability along with carbon emission resulting from burning NG can affect optimal bidding result of this unit. Hence, this study addresses the optimal bidding problem of CAES and wind units, considering the aforementioned issues, while taking into account uncertainties of day-ahead (DA) and balancing market prices, wind speeds, and NG prices and availability. Furthermore, the dynamics of natural gas flow in the pipeline is modelled. The stochastic programming (SP) method is proposed for solving this problem while taking risk into consideration. The scheduling has been presented for participation of generating company in DA and carbon emission markets. Simulation results indicate the capability of the proposed method in optimal bidding of CAES units while taking gas-burning related constraints into consideration. © 2020 The Authors. IET Renewable Power Generation published by John Wiley & Sons Ltd on behalf of The Institution of Engineering and Technology
Electric Power Systems Research (03787796)
This paper proposes a new unsynchronized parameter-free fault location scheme for transmission lines (an overhead line (OHL) combined with an underground cable (UGC)). Utilizing unsynchronized measurements at both ends, the proposed method accurately locates faults without requiring OHL and UGC parameters. Therefore, the variation of OHL and UGC parameters values do not affect its accuracy. In this method, first using distributed line model for UGC and OHL, the fault location problem is converted into a system of nonlinear equations problem according to both pre-fault and fault measurements. Then, using a novel algorithm, the system of nonlinear equations is solved. This algorithm consists of two stages which in the first one, the system of nonlinear equations is converted into an optimization problem and in the next stage, using the first stage results, the problem is solved by a modified Newton method. Simulation results performed by MATLAB, verify the high accuracy of the proposed method in determining the fault location (whether in UGC or in OHL). In these simulations, it is shown that the proposed method is independent of the fault resistance, synchronization angle, and fault type and consequently, is superior to the existing methods. Moreover, the simulation results confirm the ability and efficiency of the proposed model in estimating OHL and UGC parameters. © 2020 Elsevier B.V.
Sustainable Cities and Society (22106715)59
Power markets are undergoing structural alterations in accordance with emerging technologies. Traditional market rules and participants' behaviour are currently dominated by conventional power plants and synchronous generators. Renewable energy sources have gradually found their market share in the generation party specifically in developed countries. Apart from new energy resources, Demand Response Programs (DRP) have garnered attention due to substantial capabilities and potentials. This paper particularly sheds light on two flexible loads of Plugin Electric Vehicles (PEV) and cooling/heating responsive loads. PEV parking lots can be modelled as stochastic battery storages partially available for power exchange over short intervals. Besides, cooling/heating systems are naturally shiftable loads in short time horizons without deteriorating the resident's convenience. This study provides a comparative view of short-term power regulating markets in terms of bidding constraints and payment mechanisms. Consequently, a typical park & ride is considered as a reconfigurable urban microgrid to participate in short term regulating markets under different constraints. The results confirm that the internal coordination between the sub-units of microgrid brings more flexibility to enhance the total profitability. In addition, it is shown that the bidding constraints, as well as time slots, can be influential particularly in intermittent situations. © 2020 Elsevier Ltd
International Journal of Electrical Power and Energy Systems (01420615)116
This paper proposes a two-layer hierarchical control structure to realize compensation of voltage unbalances optimally in different buses of islanded microgrids. The primary layer controls the microgrid voltage and frequency. The secondary layer is used to realize the unbalance compensation of the sensitive load bus (SLB). Improvement of the voltage unbalance factor (VUF) at the SLB may lead to an increase in VUF at local buses and/or DG terminals. A complementary part is designed and added to the secondary control in order to tune the compensation portion of each DG source while limitations of VUF at DG terminals and local buses are considered too. This method realizes multi-power-quality-level control through a simple yet effective solution. Simulation results are given to demonstrate the advantages of the proposed control scheme. © 2019 Elsevier Ltd
IET Renewable Power Generation (17521416)(4)
This study presents a new control scheme to provide both voltage regulation and power sharing within a DC microgrid. It includes both primary and secondary levels as well as the proposed auxiliary feedback. The secondary control distributes and uses the consensus algorithm to share power. First, the auxiliary feedback is formulated. Then the features of the feedback are analytically extracted to provide both voltage regulation and power sharing. Next, the particle swarm optimisation algorithm determines the parameters of the controller optimally. Following that, a series of simulations is carried out to show the performance of the proposed scheme in comparison with the conventional methods. Hence, to validate the advantages of the proposed scheme, a four distributed energy resource (DER) DC microgrid is considered, and the proposed approach is applied. Afterwards, the eigenvalue and sensitivity analysis show the effect of the parameters variation on microgrid stability. The results show that the applied method can regulate the voltage well and shares the power in the presence of the load demand as a disturbance besides the long-time delay associated with the secondary control as an uncertainty. © The Institution of Engineering and Technology 2019.
Journal of Energy Storage (2352152X)29
Today in developed megacities, municipal waste incinerators are a practical solution although they require a relatively high initial investment. On the other hand, E-Transport is growing in metropolitans along with the Renewable Energy Sources (RES). This study proposes an Urban Micro Grid (UMG) consisting of a Waste-to-Energy Combined Heat and Power generation unit (WtE-CHP) and series of Plugin Electric Vehicles (PEV). The main purpose is to provide ancillary services through the incorporation of PEVs as fast-responsive storages. The parking lots may aggregate to form PEV clusters and make bilateral contracts with WtE-CHP to be able to participate in the regulating power markets. A Crow Search Algorithm (CSA) is developed for the UMG operation. In addition, a data analysis section is provided focusing on the behavior of urban drives to extract the realistic probabilities for PEVs available during the daytime. Moreover, the power market of Denmark east (DK2) is considered for the case study of Copenhagen. The results confirm that in case the UMG succeeds in selling the products in the regulating up market, the economic value per MW is remarkably enhanced and the total profit is escalated. © 2020 Elsevier Ltd
Energy (18736785)171pp. 535-546
One effective way to compensate for uncertainties is the use and management of energy storage. Therefore, a new method based on stochastic programming (SP) is proposed here, for optimal bidding of a generating company (GenCo) owning a compressed air energy storage (CAES) along with wind and thermal units to maximize profits. This scheduling has been presented for the GenCo's participation in day-ahead energy and spinning reserve (SR) markets and CVaR is also considered as a risk-controlling index. Firstly, the obtained results are validated by comparing with those of two previous studies. Then, the complete results of the proposed method are presented on a real power system, which indicate the capability of SP in scheduling CAES units. Furthermore, it is observed that CAES units can gain greater profits in joint energy and reserve markets due to their high ramp rates. In addition, the value of stochastic solution (VSS) is used to quantify the advantage of the stochastic method over a deterministic one, which illustrates the advantage of SP-based optimal bidding method especially for CAES and wind units and also for risk-averse GenCos. Overall, it is concluded that the stochastic method is efficient for optimal-bidding of GenCos owning CAES and wind units. © 2019 Elsevier Ltd
