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The increasing interactivity between energy carrier networks such as electrical, natural gas (NG), and heating can be appropriately used for improving the operation optimality along with overcoming some challenges of those systems. With such a view, this paper studies the practical issue of power transmission lines congestion management in integrated multicarrier energy systems (MCESs) and makes a comparison with the only electrical operation mode. The MCES consisting of electrical and NG network infrastructures with exchanged energy between them is modelled by considering the several local energy hubs and their electrical and heat loads. Rescheduling of energy sources (power plants and gas wells) and demand side management in both electrical and NG networks have been utilized as the two important tools in the developed congestion alleviation framework. The proposed method confirms that the provided flexibility in the integrated operation of the MCESs can lead to a remarkable reduction in the congestion management cost index. Implementing the proposed congestion management framework on an assumed test MCES with a combined 39‐bus New England power system and 20‐node Belgium NG system demonstrates its effectiveness and applicability for the system operators. The issue of power transmission lines congestion management in integrated multi‐carrier energy systems (MCESs) has been studied. The proposed method confirms that the provided flexibility in the integrated operation of the MCESs can lead to reduction in the congestion management cost. [ABSTRACT FROM AUTHOR]

Microgrid inverters in the presence of faults, unavoidable modelling uncertainties, disturbance and harmonic current resulting from nonlinear loads should have small steady state tracking error, small THD and high robustness hence this subject has turned one of the motivations of this investigation. To achieve the stated goals, fractional adaptive sliding mode controller (FASMC) is proposed in this paper. The proposed controller increases the robustness, flexibility and degree of freedom. As far as in practice it is not easy to define the bounds of disturbances and guarantee the system stability, hence in next step, to overcome this challenge the adaptation laws are suggested. Then for the problem of determining the controller parameters, Particle Swarm Optimization (PSO) algorithm is used. The performance of the proposed technique is investigated for an islanded microgrid under different disturbances, also to verify the advantages of the proposed controller, the results are compared with other controllers. Finally, the proposed controller and PID controller are implemented experimentally on Arduino mega 2560 microcontroller. [ABSTRACT FROM AUTHOR]

A wide range of remedial action schemes (RAS) have been developed and deployed in field to take automated control actions to maintain system reliability and stability during adverse system conditions. According to the regulatory standards from North American Electricity Reliability Corporation (NERC), RAS applications deployed in field and their functionalities are required to be tested periodically. To do testing for the RAS, regular process that requires taking critical components offline is usually labor‐intensive and time‐consuming, especially for complex applications utilizing multiple measurement units and controllers from different substations. To overcome these challenges, this paper presents a remote testing architecture for remedial action schemes. Our proposed remote testing architecture is capable of accessing test signal generators, phasor measurement units (PMUs), RAS control units from multiple substations, managing tests for both centralized and distributed implementations of RAS. To address the effectiveness of the remote testing architecture, this paper presents the minimal wind curtailment applications with detailed alternative formulations of optimization models for RAS and highlights performance of the proposed remote testing of RAS. Simulation results for an IEEE standard test system and representative industry test cases demonstrate effective performance of the developed RAS testing mechanism. [ABSTRACT FROM AUTHOR]

Recently, microgrids (MGs) present a vital role in the transformation of the existing power networks to the smart grids. Connecting MGs to construct the multi-microgrid (MMG) system enhances the robustness of the system against disturbances and upgrades overall network performance. In this paper, the MMG, as a source of self-healing support to the distribution networks, is analysed extensively. In fact, the MMG strengthens the self-healing of the network by participating in the restoration of disturbed loads. In this study, an operational framework is proposed for the self-healing problem in radial interconnected MGs based on two-stage cyber communication network architecture. In the first stage, the local control system (LCS) within each MG, schedules the accessible resources according to the local power consumption target. In the second stage, a number of LCSs are communicated globally to perform self-healing action. The communication of LCSs is accomplished using a consensus algorithm. Nevertheless, when a fault takes place in MG and a line is eliminated, the healthy MGs, due to demand and supply information in the first stage, supply the on-outage loads as far as possible. To validate the effectiveness of the proposed framework, two benchmark distribution networks (the 33-bus and the 119-bus) are employed. [ABSTRACT FROM AUTHOR]

This paper deals with the modeling of discrete automatic gain control (AGC) controllers for an interconnected power system. The AGC supplementary controllers continuously try to reduce the ACE signal to zero by sending control commands/signals to the speed governor set points. Typically, control signals are sentin the form of discrete control pulses to adjust the generating unit outputs in discrete steps. However, in the preceding AGC studies, ZOH circuit has been misplaced in discrete supplementary controller models. Therefore, control signals feed to the speed governor set points no longer remains in discrete mode or in other words, controller action no longer remains in discrete steps. Therefore, the results and inferences drawn in these studies are erroneous and unrealistic. This paper presents the realistic model of discrete AGC controllers and removes the anomaly in existing works. Furthermore, it is also discovered that inappropriate selection of sampling period of ACE signal degrades the system dynamic performance or even cause system instability. Surprisingly, no proper guidelines/method has been provided yet to select the appropriate sampling period of ACE signals for discrete AGC operation. Here, a maiden attempt has been made to obtain the suitable values of ACE signal&s sampling periods using Shannon&s sampling theorem. [ABSTRACT FROM AUTHOR]

This paper proposes a WECS based on a back to back diode‐clamped multilevel inverter systems (DCMLI) fired comparatively by sinusoidal pulse width modulation (SPWM) and third harmonic injection pulse width modulation (THIPWM) techniques. DFIG performance is compared using these technologies for different wind speed under normal operation condition. The proposed approach shows that the DCMLI systems generate a nearly sinusoidal voltage with reduced total harmonic distortion (THD) thus upgrading the power quality of that produced by DFIG. As SPWM and THIPWM MLI are most common usage techniques in research, we applied them in the system to discuss a comparison of using those techniques to determine the number of levels that achieve the IEEE 519 criteria of THD which is less than 5% for both techniques (5th level for SPWM and 4th level for THIPWM) in all operation wind speed. Compared with simple PWM, and THIPWM have many advantages as lower THD, minimal number of switching to decrease switching losses and the output fundamental voltage is increased. Lastly, the paper investigates the variation of the frequency of induced rotor voltage and the active power flow due to the wind speed change when the rotor speed changes from super‐synchronous to sub‐synchronous speeds. [ABSTRACT FROM AUTHOR]

Inertial and droop control are common methods for improving grid frequency control. Using the first‐order derivative of the frequency in the inertial control loop only investigates the rate of frequency variation, while other useful information is not taken into consideration. Accordingly, in this study, the application of a fractional‐order derivative (between 1 and 2) in the inertial control loop is proposed to have more useful frequency‐based information. To achieve this goal, firstly continued fraction approximations and secondly, the discretization is adopted by using the Tustin Method with Prewarping. Inertia loop and droop loop gain have a significant impact on the operation of the wind turbines and the power system frequency control. Therefore, in this paper, a novel method for the adaptive adjusting of droop and inertia control loops gains in DFIG is proposed. To utilize more frequency error information, fractional‐order adaptive law is proposed to update the loop gains and the inertia control loop. In order to have a robust system, which is permanently stable for every fractional order (FO), is used parameter space method. Simulation results demonstrate the proper performance of the FO‐based adaptive approach to increase the frequency nadir (FN) and decrease the frequency variations. [ABSTRACT FROM AUTHOR]

A cluster with multiple AC or DC microgrids (MGs) based on flexible DC interlinking and distributed energy storage systems is studied in this paper, which has been identified to have the following issues in terms of its primary control scheme: coordinated power control among slack terminals in the MG cluster, seamless operation mode transition for the interlinking converters and the common DC bus voltage control. A novel flexible control scheme that unifies the control of all the MGs only using local measured signals without further communications is proposed in this paper, which aims to improve control stability, and operation reliability and flexibility. Theoretical introduction and analysis are presented to explain the proposed control. The detailed average value model and small‐signal model of an MG cluster with two AC MGs and two DC MGs are simulated, respectively, with the proposed control in power systems computer‐aided design/electro‐magnetic transient design and control to verify the effectiveness in control stability and flexibility enhancement, and the impact of control parameters on the small‐signal stability of the considered cluster is analysed through root locus. [ABSTRACT FROM AUTHOR]

The ability of riding through the grid disturbances can increase the integration of microgrids into the distribution system. Consequently, a grid‐connected microgrid should provide ancillary services such as low voltage ride‐through (LVRT) capability and reactive power support to sustain the power system operations during abnormal grid conditions. The objective of this paper is to propose an LVRT scheme that improves the power quality of the entire microgrid. The developed method is implemented as the controller of the interface voltage‐sourced converter (VSC) of a distributed energy resource and consists of primary and secondary control levels. The former includes the cascaded voltage and current control loops and the droop controller, while the latter controls the reactive power injection during the balanced/unbalanced voltage sags/swells. The proposed scheme is developed based on the independent control of each phase and does not require calculation of symmetrical components. Moreover, it can be employed in the VSC control systems with various reference frames and is effective for droop‐based grid‐connected microgrids with both single‐phase and three‐phase four‐wire configurations. The proposed strategy is implemented using the hierarchical control system and preserves the plug and play capability. Several case studies are presented to verify the effectiveness of the proposed strategy. [ABSTRACT FROM AUTHOR]

Energy poverty limits the economy and social development throughout the world. Wind turbine reduces the energy costs and facilitates the development of renewable energy industry, which provides an effective solution to energy crisis and environment pollution and develops rapidly in recently years. In this paper, a radial basis function neural network (RBFNN) optimisation model predictive control (MPC) was proposed for large wind turbines. In accordance with the complexity and uncertainty of wind turbine operation, a linear model based on the blade element momentum theory was established and the influencing factors of the proposed model were evaluated. The MPC taking into full account three degrees of freedom control multivariate was enforced by RBFNN prediction model, which meets the requirements of specified operation region. Additionally, the RBFNN prediction model with the memory of complicated rules and changed trend was trained by a great deal of historical data. The RBFNN in combination with MPC solves global optimisation problems and improves the dynamic performance of system. Simulation results for three‐bladed 5 MW onshore wind turbine verified the effectiveness of the proposed method and confirmed the fact that the fatigue loads were significantly reduced in the turbine tower. [ABSTRACT FROM AUTHOR]

Uncertainities and variations of power generation through photovoltaic (PV) sources are major challenges for their integration with the distribution grid. Voltage rise and voltage drop issues limit the increase in PV penetration and loading levels, respectively. Moreover, it is important to maintain voltage levels as per grid code while ensuring that the PV power generation is not curtailed. In this paper, a voltage control method using smart transformer (ST) via dynamic optimal setpoints and limit tolerance is proposed in a residential distribution network. Performance indicators are developed to understand the impact of the proposed method on the system voltage profile. A method to determine the optimal inputs for voltage control methods depending on the day-ahead predictions of load demand and PV power profiles is developed. Further, a voltage control method of switching among three setpoints based on the voltage that determines the load side ac reference voltages for ST is proposed. The proposed method is compared with the method of switching between two setpoints based on current. The proposed method provides an improved voltage profile in the distribution network, which is tested on a CIGRE low voltage residential distribution network using PSCAD [ABSTRACT FROM AUTHOR]

Grid-connected converters are expected to provide ancillary service utilising their spare capacities during operation. This study proposes a novel control strategy for clustered micro-grids to compensate voltage-unbalance of the power grid at the point of common coupling. Every micro-grid are interfaced to the power grid through a micro-grid inverter (MGI). All MGIs are designed independently with positive-sequence (PS) and negative-sequence (NS) control loops. Every micro-grid autonomously performs grid synchronisation and mode switching. After grid-connecting, a dynamic capacity allocation method is proposed for the MGIs to optimise its PS and NS capacity according to the grid voltage unbalance factor. Furthermore, a V–I droop control of the NS control loops is developed, with which each MGI can regulate its NS current according to the NS voltage in a droop manner. With the proposed method, all micro-grids participate in grid voltage unbalance compensation according to their own potential capacities without communications. Finally, a micro-grid cluster model with three micro-grids is built on Matlab/Simulink to validate the proposed control strategy. [ABSTRACT FROM AUTHOR]

This research presents a robust model predictive controller of two microgrids (MGs) interconnected via tie‐line (TL) power. Power system operations continue to face new challenges due to the large integration of renewable energy generation with an active load demand uncertainty and the management and control of bidirectional power flow between MGs and others uncertainties and system nonlinearities due to the power system operating condition. To handle these uncertainties and system nonlinearities a robust model using predictive control scheme is presented in this paper to achieve the control of the active power between two MGs when considering three disturbances scenario models. In the design process, uncertainties and nonlinearities of the system were taken into account and contributed to the robustness of the closed‐loop system. Robust control scheme development considering power system nonlinearities and uncertainties were used to improve the online close‐loop robustness. The model helped to achieve a desired active power regulation by coordinating the MGs and active power over‐shoot and under‐shoot time were reduced outstandingly. A Comparison was made between open‐loop and close‐loop simulation results, which indicate that the model can handle robustness while settling power deviation of the interconnected system. MATLAB environment was used to solve the optimisation problem. [ABSTRACT FROM AUTHOR]

The variable step size modified least mean square (VSSMLMS) learning algorithm based multifunctional double‐stage grid interactive photovoltaic (PV) system is implemented in this paper which feeds power to the grid and the load, ensures unity power factor operation and compensates reactive power. Along with this, it mitigates high grid neutral current during unbalanced loading condition. This algorithm uses variable step sizes to have a smooth dynamic and steady state performances. The boost converter (booster) is used in the first stage to extract peak power from a PV array using perturb and observe peak power point tracking technique. Next to this, a four leg voltage source converter (VSC) is placed to interlink the solar PV system to the grid and the loads. VSSMLMS‐based control technique is used to filter the fundamental component of load current and hence gate pulses are generated for the four‐leg VSC. This system is simulated in SIMULINK/MATLAB software under several working conditions and the obtained simulation results are validated on a developed laboratory prototype. The performance of the VSSMLMS‐based control technique is compared with that of the traditional LMS‐based technique. All results validate the IEEE‐519 standard. [ABSTRACT FROM AUTHOR]

In this study, an advanced control strategy is proposed for hybrid energy storage systems (HESS) to smooth wind power generation fluctuations. Compared with the limited performance of solo energy storage system, the HESS, composing of lithium‐ion battery (LiB) and a flywheel energy storage system (FESS), can comparatively show improved flexibility and adaptivity. A novel sequence control scheme for the HESS is proposed in this study to improve the overall economic and smoothing performances. Specifically, based on variable‐interval reference outputs, the control horizon of the HESS is statistically determined. Afterwards, a sequence control scheme for the HESS is presented to improve the internal collaboration of HESS media. Especially when the LiB and FESS are synchronously charging/discharging to smooth wind power, the charge/discharge power are optimally distributed between the LiB and FESS via an optimiser to minimise the equivalent cost during each control cycle. Case studies are conducted to demonstrate the performance of the proposed method. [ABSTRACT FROM AUTHOR]

One of the main subjects of Microgrid (MG) islanded operation is its stability. Using the Energy Storage Systems (ESSs) in MGs, the stability can be improved. To ensure the proper operation of the ESSs, their State of Charge (SoC) should be monitored and controlled. In this paper, a new decentralized control method based on the conventional droop method is proposed which considers different types of ESSs used in islanded MG, i.e. ESSs with high power density and high energy density. In the proposed method, the ESS units are divided into two main categories. The master ESS is the main primary frequency control unit and the other ESSs respond to active and reactive power variations of the load and participate in the secondary control of frequency. For each of these categories, a new control method is proposed. The proposed method, including the primary and secondary control, is decentralized, and based on local measurements. Moreover, in the proposed method, a SoC equalization of ESSs is considered. To assess the stability of the MG, a small signal stability model is developed. Three scenarios are simulated to verify the effectiveness of the proposed method in MG frequency control and ESSs SoC balancing. [ABSTRACT FROM AUTHOR]

This paper deals with the design and analysis of a virtual synchronous generator (VSG) control strategy applied to a renewable‐based system devoted to energy production in a stand‐alone microgrid context. The studied hybrid energy production system consists of renewable‐based energy production systems, a diesel power plant (DPP), and an energy storage system (ESS). The first part of the study will deal with the design of a single renewable energy source controlled using the VSG control strategy. In the second part, multiple renewable energy sources, similar to the one presented in the first part, will be connected in parallel to form a renewable farm. Finally, in a third part, the studied renewable farm will be integrated in a full hybrid system. In each part of the proposed study, the system power output will be evaluated and the voltage and frequency variations will be carefully analysed. [ABSTRACT FROM AUTHOR]

This paper presents a multi‐time hierarchical stochastic predictive control (MHSPC) scheme for an island microgrid, in which electric vehicles (EVs) can be used as mobile energy storages to improve power balance and realise load‐frequency control (LFC) with micro‐turbines (MTs). At the upper layer, a stochastic model predictive control is proposed to handle the EVs uncertainties on a long time scale, while optimising controllable power adjustment of MTs, the charge/discharge energy of the battery electric storage (BES) unit and guaranteeing EVs to be fully charged at the expected plug‐out time. At the lower layer, the coordination between EVs and MTs for LFC is achieved by a standard MPC framework on a short time scale. In this way, the power balance is met, and the frequency fluctuation is inhibited. Finally, simulation results are presented to illustrate the satisfactory operation of the island microgrid. [ABSTRACT FROM AUTHOR]

The microgrid concept has gained enormous popularity in the power industry due to recent advances in the power electronic converter (PEC) technology and environmental concerns over green‐house gas emissions from power generation. Among microgrids, the hybrid AC/DC microgrid concept has been promoted as a viable concept to reduce energy conversion losses. However, hybrid AC/DC microgrids are susceptible to stability issues during high penetration of dynamic loads (e.g. induction machines). The non‐linear dynamics of induction machines result in sustained voltage/frequency oscillations following disturbances in the microgrid, which is a major challenge for stable operation of the hybrid AC/DC microgrid. The PEC‐based energy storage systems (ESSs) are used as an effective solution for power balancing in the microgrid; hence with the fast response of the PEC, microgrid voltage/frequency could be stabilised rapidly. Thus, a supplementary power oscillation damping (POD) controller is proposed in this paper for the ESS to damp low‐frequency oscillations (LFOs) in the hybrid AC/DC microgrid. The effectiveness of the proposed damping controller is verified using non‐linear simulations considering different penetration levels of dynamic loads and disturbances in a hybrid AC/DC microgrid. Results indicate that the proposed supplementary POD controller can significantly damp the LFOs in the hybrid AC/DC microgrid. [ABSTRACT FROM AUTHOR]

In this paper, real‐time parameter estimation based intelligent controller has been proposed for the optimum automatic generation control (AGC) operation of multi‐area interconnected power system. In earlier AGC studies, supplementary controllers were designed for presumed power system dynamic conditions, such as constant system loadings, fixed values of power system dynamic model parameters. However in practical AGC system, these power system model parameters, namely frequency bias parameter B, steam chest and reheater time constants TSC & TRH, power system time and gain constants Tp & Kp, load sensitivity factor D, etc., continuously varies depending upon the consumer's load demand and number of power generating units participating in AGC. The controller's operation no longer remains optimum as these system parameters changes from their initial values. In view of the above, parameter estimation based real‐time intelligent controller has been designed which automatically adjusts its controller gain settings to its optimum conditions in real‐time after sensing changes in power system model parameters. At first, different methodologies are presented to estimate dominant power system model parameters. Then, presented methodologies are utilised in the design of intelligent controller for AGC system. The proposed controller is successfully tested upon IEEE 39 bus system with various case studies. [ABSTRACT FROM AUTHOR]

The conventional hierarchical control in an islanded microgrid (MG) does not consider the long time‐span dynamics of distributed storages (DSs). The main challenge in control of battery energy storage systems (BESSs) is different levels of stored energy in terms of state of charge (SoC). In power droop control, the energy of the BESSs with lower initial SoC is drained earlier, and their capacities become unachievable. Moreover, using droop control to balance the SoC of BESSs, deviates the steady state frequency and voltage from the nominal values. However, restoration of the MG frequency employing the conventional distributed secondary controllers disturbs SoC‐balancing, since SoC of BESSs are ignored. In this paper, a new distributed storage secondary controller (DSSC) scheme is designed for restoration of the voltage and frequency of a stand‐alone MG, and to provide power‐sharing and SoC‐balancing, using a distributed cooperative architecture. The cooperative DSs are controllable and exchange the information with neighbor DSs through a communication network. The unknown output power of the uncooperative renewable distributed generation (DG) is considered as external disturbance to the DSSC. The designed DSSC is robust against the variation of the communication configuration, and eliminates the necessity to communicate with uncontrollable DGs and loads. [ABSTRACT FROM AUTHOR]

Modern power system involves growing use of open channel communication in secondary frequency regulation which introduces time delay in the automatic generation control loop which may lead to system instability. This study proposes a novel power system frequency stabiliser (PSFS) which is a modified secondary controller in order to improve the system stability in the presence of large communication delays. An auxiliary signal is added to the secondary controller to provide additional damping. The gain of the controller is obtained by meta‐heuristic methods. The proposed controller is first developed on a single area hydropower system and the same is then applied on the Western System Coordinating Council 3‐machine, 9‐bus power system. Furthermore, to show the effectiveness of the proposed PSFS in a large practical multi‐area system; it is also applied to the IEEE 39‐bus system. Results show that the proposed controller significantly improves the stability of a power system operating with large communication delay which is first considered as constant and then the stability improvement with the proposed PSFS in the presence of random communication delays is also shown. The PSFS performance is tested by the results obtained with MATLAB/Simulink simulations and further verified on a real‐time simulator. [ABSTRACT FROM AUTHOR]

Till this moment, the model of interconnected power systems in the automatic generation control (AGC) loops relies only on the synchronous generating units. In today's world, a high level of penetration of renewable energy sources (RES) is integrated to the power grids. This paper presents a novel power system model, which includes both conventional generating units and RES for studying the AGC problem of such systems. The control strategy in the AGC loops is based on the proportional–integral–derivative (PID) controller, which is optimally designed by the whale optimization algorithm (WOA). It represents a great challenge to this controller to deal with the RES uncertainties. The effectiveness of the WOA‐based PID controller is compared with other computation evolutionary algorithms‐based PID controller. The system performance is evaluated under different operating conditions. For achieving a realistic study, 1) real wind speed data that extracted from Zafarana location in Egypt are used, 2) solar irradiation and temperature data that extracted from a field test are implemented, and 3) an irregular wave energy condition is applied. The validity of the control strategy is verified using the simulation results, which are carried out using MATLAB environment. [ABSTRACT FROM AUTHOR]

The optimal power flow (OPF) problem for active distribution networks with distributed generation (DG) and a variety of discretely adjustable devices (e.g. on‐load tap‐changers, OLTCs) is essentially a non‐convex, non‐linear, mixed‐integer optimisation problem. In this study, the quadratic model of three‐phase OLTCs is proposed by adding branch currents as unknown variables, which guarantee a constant Hessian matrix throughout iterations. This study proposes a three‐phase OPF model for active distribution networks, considering a three‐phase DG model. The OPF model is solved by an interior point method incorporating a quadratic penalty function as opposed to a Gaussian penalty function. Furthermore, a voltage regulator is also incorporated into the OPF model to form an integrated regulation strategy. The methodology is tested and validated on the IEEE 13‐bus three‐phase unbalanced test system. [ABSTRACT FROM AUTHOR]

Converting the surplus power into rotor kinetic energy by changing the control functions of machine side converter (MSC) and grid side converter (GSC) is considered to be an efficient way for permanent magnet synchronous generator (PMSG)‐based wind turbine generator system (WTGS) to accomplish low‐voltage ride through (LVRT) without additional hardware components. However, because of the time delay of grid fault detection and the control system inertia, the dc‐link capacitor may still be subjected to overvoltage in the early tens of milliseconds after a grid fault happens. This study proposes a compositive control method of LVRT for PMSG‐based WTGS, in which the surplus power during LVRT is converted into rotor kinetic energy by controlling the electrical power of the PMSG according to the grid‐connected power of the GSC, and a crowbar circuit is reserved to consume the surplus power before MSC reacts to the grid fault. The proposed method does not change the control functions of MSC and GSC, and the related control parameters resetting can be avoid. Besides, it can also provide reactive power support to assist the grid voltage recovery. Simulations and experiments proved the proposed method to be feasible and effective. [ABSTRACT FROM AUTHOR]

This paper describes an intelligent sensor fault detection and compensation (FDC) scheme for a hybrid grid involving renewable energy (RE) sources with power electronic interfaces. To evaluate the sensor FDC scheme, a wound rotor induction generator (WRIG)‐based wind energy system connected to the hybrid grid is examined. The system employs a WRIG with excitation from DC RE grid via a single, rotor side converter. To analyse the dynamic performance, a decoupled voltage vector control is employed. The sensors involved in the control algorithm may not be ideal and if fault occurs might lead to system collapse. To overcome electrical sensor failure, a robust, intelligent sensor fault control scheme is proposed with ANFIS. A hardware‐free solution with PLL block is proposed for mechanical sensor fault. The ANFIS‐based FDC scheme involves a bank of observers that computes residuals, detects and isolates faults. When fault occurs, the observer output is utilised for the execution of control algorithm thereby avoiding system collapse. The focused system is simulated in MATLAB and experimentally tested with a dSPACE controller for various fault scenarios. The results show the effectiveness of the FDC scheme. [ABSTRACT FROM AUTHOR]

In this paper, a decentralized control strategy for inverter‐based distributed generation (DG) is proposed to enhance the accuracy of power sharing under unbalanced load conditions in low‐voltage microgrids. The proposed method includes two important saliences: (1) accurate unbalanced current injection from DGs, and (2) reduction of circulating real and reactive powers in an islanded microgrid. The features are complied with the proposed droop strategy utilized in the control system of each phase of DG converters. Based on the proposed triple‐droop control strategy, the real power sharing in an AC low‐voltage microgrid is significantly improved via P–V control strategy and the reactive power sharing accuracy is enhanced via Q–f control strategy. By this method, the amplitude of the output voltage of each phase of the converters is determined based on the amount of load connected to that phase. In addition, the efficiency of the microgrid is increased due to the circulating current reduction between DGs. A virtual impedance concept is also utilized to improve the accuracy of the proposed power sharing method. The feasibility and effectiveness of the proposed strategy are validated using MATLAB/SIMULINK software for International Council for Large Electric Systems (CIGRE) low‐voltage distribution network benchmark. [ABSTRACT FROM AUTHOR]

Two important and upcoming technologies, wind resources and microgrids, are increasingly being combined. Various control strategies can be implemented, and droop control provides a simple option without requiring communication between microgrid components. However, traditional droop control does not allow the microgrid to maximise the power available from the wind. This study proposes a novel droop control strategy, which implements a droop surface in higher dimension than the traditional strategy. Simulation results show that power from the wind can be maximised, while maintaining the system's bus voltage around a nominal value using a distributed multidimensional droop approach. Selection of the optimal droop relationship is discussed and simulation results are presented. [ABSTRACT FROM AUTHOR]

This study presents a method for integrating power sharing and participation in primary frequency response of power system for distributed energy resources in microgrids. This controller is based on power‐angle droop and results in thorough power sharing in islanded mode and constant power in grid connected state. It can be employed in microgrids along with the feature of plug and play for any kind of distributed generation resources involving synchronous generators. Also, this paper analyses the stability of the proposed controller and the conventional power‐angle droops in a microgrid with modelling in state‐space form and linearising around an operating point. It has been shown that the proposed controller results in more stability and accuracy than the conventional controllers. Also, eigenvalues are evaluated to find the best controller parameters for the microgrid stability. Finally, the controller response in different operating conditions of a test microgrid is assessed. [ABSTRACT FROM AUTHOR]

In the medium voltage direct current (MVDC) shipboard grid, the inherent inertial support from the DC capacitors is too small to resist step changes or fluctuations from the high power pulse load and propulsion load, which results in lower DC voltage quality. This study proposes a decentralised control algorithm for the MVDC shipboard hybrid energy storage system (HESS) to enhance the onboard survivability. This algorithm adjusts the droop control coefficient based on the bus voltage change rate adaptively, meanwhile the voltage differential signal processing and filtering are implemented by the trace differentiator. In addition, the proposed algorithm also has state-of-charge (SOC) balancing and SOC recovery abilities between multiple groups of energy storage devices. The parameter selection principle are analysed, and a variety of working conditions are simulated and verified in PSCAD. Theoretical analysis and simulation show that, HESS can achieve good power distribution and SOC management performance without communication compared to fixed droop coefficient control strategies, and the dynamic characteristics of bus voltage have been significantly improved. [ABSTRACT FROM AUTHOR]

With the real-time changes of wind speed and operating conditions, it is a challenge to fully tap the active power regulation ability and improve the control performance of automatic generation control (AGC) in a wind farm (WF). The essence of tapping the active power regulation ability is to realise the coordination and complementarity of each wind turbine's (WT's) dynamic adjustment performance (DAP). To address this, a novel data mining method is developed to derive the internal relations between WTs' output power and pitch angle, impeller speed and pitch angle during the power adjustment process, and a unified mechanism model is established to describe DAP of WTs. Based on the discovered relationship between WTs' DAP and its operating states, an active power distribution algorithm and a dynamic interval control method are proposed. Then, an active power dynamic interval control strategy that has been implemented using Java script in MyEclipse for WFs is further developed. The control strategy has been tested and applied in a 50 MW WF in northwest China. The preliminary results showed that the control strategy has improved the rapidity and accuracy of AGC in the WF. [ABSTRACT FROM AUTHOR]

A battery energy storage system (BESS) is an effective solution to mitigate real-time power imbalance by participating in power system frequency control. However, battery aging resulted from intensive charge–discharge cycles will inevitably lead to lifetime degradation, which eventually incurs high-operating costs. This study proposes a deep reinforcement learning-based data-driven approach for optimal control of BESS for frequency support considering the battery lifetime degradation. A cost model considering battery cycle aging cost, unscheduled interchange price, and generation cost is proposed to estimate the total operational cost of BESS for power system frequency support, and an actor–critic model is designed for optimising the BESS controller performance. The effectiveness of the proposed optimal BESS control method is verified in a three-area power system. [ABSTRACT FROM AUTHOR]

This study focuses on analyzing the robust stability regions and robustness margin of a time‐delayed load frequency control (LFC) system with Electric Vehicles (EVs) using the Kharitonov Theorem. Communication time delays in LFC systems can jeopardize stability and reliability, leading to suboptimal controller performance. Integrating EVs into LFC systems enhances dynamical stability but introduces additional complexity. Therefore, it is crucial to employ robust analysis and controller design techniques to ensure system stability. In this study, we utilize the Kharitonov Theorem to determine the robust stability regions and stability boundaries in the parameter plane of the Proportional‐Integral (PI) controller. By considering communication time delays and parametric uncertainties in the LFC system with EVs (LFC‐EVs), the robust PI controller gains using these methods are efficiently computed. To evaluate the performance of the theoretically computed robust controller parameters, time‐domain simulations are conducted. [ABSTRACT FROM AUTHOR]

Low-inertia power systems suffer from a high rate of change of frequency (ROCOF) during a sudden imbalance in supply and demand. Inertia emulation techniques using storage systems, such as flywheel energy storage systems (FESSs), can help to reduce the ROCOF by rapidly providing the needed power to balance the grid. In this work, a new adaptive controller for inertia emulation using high-speed FESS is proposed. The controller inertia and damping coefficients vary using a combination of bang–bang control approaches and self-adaptive ones, to simultaneously improve both the ROCOF and the frequency nadir. The performance of the proposed adaptive controller has been initially validated and compared with several existing adaptive controllers by means of offline simulations, and then validated with experimental results. The proposed controller has been implemented on a real 60 kW high-speed FESS, and its performance has been evaluated by means of power hardware-in-the-loop (PHIL) testing of the FESS in realistic grid conditions. Both simulations and PHIL testing results confirm that the proposed inertia emulation control for the FESS outperforms several previously reported controllers, in terms of reducing the maximum ROCOF and improving the frequency nadir during large disturbances. [ABSTRACT FROM AUTHOR]

Distributed energy resources such as solar photovoltaic, wind and energy storage systems are increasingly being utilised within isolated and grid-connected microgrids. Their integration has prompted the move towards more advanced coordinated control for flexible, efficient and secure operation of microgrid-based power systems. This study presents a new power control method based on a canonical inverse model and implied synthetic inertia (SI), which is implemented on a voltage source converter-based power generator (VSC-PG) for frequency response support. The control method augments a traditional power controller whilst the SI technique is blended with a new switching mechanism which enhances the performance of the VSC-PG when it is utilised with SI provision capability. The switching mechanism acts only when necessary, without contradicting the main frequency regulating sources. For assessment, the above method and SI technique have been designed and modelled for a 630 kVA VSC-PG with DC-link battery bank. The VSC-PG was connected within an isolated/remote microgrid formed by an 11 kV feeder, 1 MVA diesel generator and variable load. The performances of the proposed power controller and SI provider have been tested and analysed using detailed Matlab/Simulink simulations and found to compare favourably with methods published in the literature. [ABSTRACT FROM AUTHOR]

Natural disasters, faults, or the sudden outage of major energy resources can create resilience issues in power systems. Modern distribution systems can reconfigure due to the use of automated protection and control techniques and the proliferation of distributed generators (DGs). If there are several DGs located nearby, distribution systems can be clustered into microgrids in an emergency condition. Clustering of distribution systems offers many benefits to achieve high system resilience. Moreover, demand response (DR) is an efficient way of increasing the operation quality and improving the resilience of the power system. This study discusses the impact of DR on the resilience of dynamically-clustered distribution systems. Accounting for the DR while clustering the distribution system can be beneficial for distribution system customers from the resilience and power quality points-of-view. To this end, the distribution clustering is performed using two different objective functions to improve its resilience and voltage profile. DR is formulated as new constraints applied to the distribution system clustering optimisation problem. This study proposes a multi-objective optimisation function that is solved by using an exchange market algorithm, Pareto efficiency method, and fuzzy satisfying approach. The simulations are performed on IEEE 33-bus test system. [ABSTRACT FROM AUTHOR]

Low-voltage ride-through (LVRT) compliance of wind energy conversion systems is one of the significant concerns for both the wind industry and the system operator. In this study, power electronic-assisted on load tap changer (OLTC) is proposed as a pragmatic solution to enhance LVRT performance of wind turbine generator (WTG). Furthermore, a coordinated control strategy between OLTC and WTG controller is proposed to mitigate post-fault over-voltage issues that are encountered due to the relatively slow dynamics of hybrid OLTC. The results suggest that employing hybrid OLTC does not only improve LVRT compliance of WTG but also significantly improve voltage dip-induced delayed active power recovery of WTG. [ABSTRACT FROM AUTHOR]

This work assesses the financial viability of a wind farm where turbines are equipped to provide frequency services. Two control strategies are compared: the former enables the frequency response provision by operating the turbines part loaded, the latter employs the kinetic energy stored in the turbines' rotating masses. The analysis accounts for typical factors affecting the wind farm operation, the wake effect and the forecast errors on wind availability. A two-stage optimisation model determines the day-ahead and (close to) real-time operation of the turbines, which profit from selling energy at the wholesale market (including subsidies), receiving availability payments for frequency services, while facing imbalance costs due to mismatches between forecasted and available wind. The two control strategies are applied to the Teesside Offshore Farm and the economic and financial performance are evaluated against a base case where the turbines do not provide frequency response service. Under current settings, the added value from frequency response capability is marginal. Changes to the market value of frequency services would favour the strategy based on part-load operation of the turbines. The scheme based on the deployment of kinetic energy becomes profitable when the duration of time window for frequency response reduces. [ABSTRACT FROM AUTHOR]

The dynamics of the power electronic transformers (PETs) have brought great challenges to stability analysis of the AC/DC hybrid distribution network with PETs. In this study, a large disturbance stability analysis method is proposed for the AC/DC hybrid distribution network with PETs, based on the mixed potential function (MPF) theory. Firstly, the simple average models of the converters based on the controlled sources with the control links are presented to describe the dynamic characteristics of the AC/DC system, which are suitable for the MPF theory. Subsequently, the method of constructing the MPF for the non-linear links in PET is proposed to derive a stability criterion for the AC/DC hybrid distribution network. The effects of the AC and DC dynamic characteristics and the non-linear control links are both included in the criterion. Multiple scenarios of the faults or the large disturbances are used to investigate the effect of the stability criterion, and the results show that the stability state of the multi-PET distribution network could be reflected by the stability criterion under various large disturbances. Finally, the parameter-influence analysis method is proposed to improve the stability of the system. [ABSTRACT FROM AUTHOR]

Due to high wind power penetration into power system, synchronous generators may no longer be the dominant generation, which implicitly requires participation of wind power plants (WPPs) in the load-frequency control (LFC). Frequency, a common variable throughout the entire power system, is the key variable for LFC, which causes equal contribution of all distant and nearby WPPs in LFC. Power transfer from distant WPPs to the event location may overload the middle transmission lines leading to cascading failures. This study proposes an online dispatch rescheduling algorithm for WPPs participating in the LFC task to prevent over loading of transmission lines and hence cascading failures following severe frequency contingencies. The WPP dispatch limits are calculated based on line ampacity for each generation unit participating in the LFC task. Numerical simulations carried out in DigSilent PowerFactory on 39 bus IEEE standard test system, demonstrates the efficiency of suggested online dispatch rescheduling technique for keeping the loading rate of transmission lines, bus voltages and system frequency in range. [ABSTRACT FROM AUTHOR]

As the penetration of renewable energy sources increases, demand side resources like air conditioners (ACs), whose electricity consumptions account for a large share, present remarkable potentials as frequency reserves to maintain the electricity supply-demand balance. This study proposes a hybrid control framework based on a central controller and local controllers, under which air conditioning loads managed by the load aggregator are constructed as a virtual generator for frequency regulation. A well-founded setting and updating method of frequency deviation trigger values in consideration of lock on and off constraints is designed. In the level of the central controller, on the basis of priority lists, the actual droop curve composed of ACs is constructed and the initial frequency deviation trigger values are determined. In the level of the local controllers, on/off states of ACs are switched autonomously according to their trigger values. In order to prevent response power deviations caused by lock on and off constraints, a trigger value local update strategy is developed to adjust the frequency deviation trigger values in the local controllers, which would not increase communication burden between the central controller and local controllers. Simulation studies suggest the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

This study presents an analysis method of harmonic interaction characteristics between direct‐drive wind turbines (DDWTs) based on αβ coordinates and the relative gain array (RGA). First, considering the digital delay of inverters, the capacitive current feedback active damping is applied to suppress the resonance of LCL filter, and the output current of DDWT is regulated by quasi‐proportional resonant controller in the αβ coordinates and then combined with the topology of the direct‐drive wind farm (DDWF), the transfer function matrix of the DDWF is established. Second, based on the RGA principle, the relationship between parameters and harmonic interaction characteristics is quantitatively analysed. The results show that with the proportional coefficient increasing, the degree of negative interaction between DDWTs is strengthened, which increases the harmonic content in the negative interaction frequency band. However, the increase of resonance coefficient and number of DDWTs will weaken the degree of negative interaction. In addition, with the increase of capacitive current feedback coefficient and grid inductance, the interaction frequency gradually decreases. Finally, the DDWF model is built both on Matlab/Simulink and StarSim + PXI hardware‐in‐the‐loop platform to verify the analytical results. The harmonic interaction characteristics can be used to guide the parameter design of DDWTs, so as to optimise power quality of the wind farm. [ABSTRACT FROM AUTHOR]

An extra transient block (ETB) for virtual synchronous machine (VSM) that is able to provide extra transient damping and adjust transient inertial to better stabilise the frequency of the VSM in a shorter time during transient period without altering the steady‐state performance is proposed in this study. The ETB uses extra parallel series lead‐lag blocks to get the transient frequency output to make the stability of the VSM less intensive to the parameter design of the virtual inertial and damping coefficient so that an easier parameter design method can be used. In other words, this method helps to solve the contradiction between dynamic response and stable performance, especially when the damping coefficient cannot be freely modified to increase damping for a large inertial value because of the mutual dependence between damping coefficient and droop coefficient caused by the use of inner reference frequency. Moreover, a simplified method for the parameter design of the ETB is proposed and the small‐signal model of the ETB‐based VSM is also derived. After that, the power coupling situation is analysed and comparisons with other control strategies are presented. Furthermore, time‐domain simulation results are demonstrated to verify the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

Microgrids experience significantly different fault currents in different operating scenarios, which make microgrid protection challenging. Existing intelligent protection schemes rely on the extraction of appropriate fault features using statistical parameters. The selection of these features is difficult in a microgrid because of its various operating scenarios. This study develops a convolutional neural network‐based intelligent fault protection strategy (CNNBIPS) for microgrids that inherently integrates the feature extraction and classification process. The proposed strategy is directly applicable to three‐phase (TP) current signals; thus, it does not require any separate feature extractor. In the proposed CNNBIPS, TP current signals sampled by the protective relays are used as an input to three different CNNs. The CNNs apply convolution and pooling operations to extract the features from the input signals. Then, fully connected layers of the CNNs employ the features to develop fault‐type, phase, and location information. To analyse the efficacy of the proposed design, we execute exhaustive simulations on a standard microgrid test system. The results confirm the effectiveness of the proposed strategy in terms of detection accuracy, security, and dependability. Moreover, comparisons with previous methods show that the proposed approach outperforms the existing microgrid protection schemes. [ABSTRACT FROM AUTHOR]

With the proliferation of intermittent renewable energy sources, power systems need to withstand an increasing number of disturbances that may affect system frequency. In this paper, we focus on the effects of high penetration level of wind turbine‐generators (WTG) on the power system operational planning from the frequency point of view. Specifically, an exact formulation for the minimum frequency calculation is presented to increase accuracy and speed of analyses. Then, the effect of WTG's frequency response on the power system frequency stability is investigated to compute the maximum acceptable generation outage as a function of penetration level. Finally, as an application to power system operational planning, the obtained frequency dynamics of the power system and the wind turbine frequency response are integrated into the unit commitment problem. Simulations are performed on the IEEE 39‐bus test system to study the effects of the WTGs on the frequency stability of the system. Results illustrate a more secure and reliable operation of the power system when the wind turbines participate in the frequency regulation task. Moreover, including the frequency response of the wind turbines in the unit commitment problem can reduce the ancillary cost, meanwhile increase the frequency stability of the system. [ABSTRACT FROM AUTHOR]

An optimal power routing (OPR) scheme between and within interlinking converters (ICs) in unbalanced hybrid AC–DC microgrids to minimise the power imbalance factor at the point of common coupling, active power losses, and voltage deviation indices for microgrids in grid‐connected operating mode is proposed in this study. These goals are achieved through a multi‐objective optimisation model by optimal distributing of mobile loads between available charging stations and at the same time, OPR within three phases of three‐phase four‐lag AC/DC converters. Numerical results obtained from implementing the proposed method on the modified IEEE 13‐bus system, as an unbalanced hybrid microgrid, and IEEE 34‐bus test system, as an unbalanced distribution system, demonstrate that proposed OPR algorithm is successful to satisfy the optimisation goals. For this purpose, four case studies are defined and studied to demonstrate the unique features of the proposed OPR comparing with other power routing schemes. In addition to simulation results, the OPR scheme between ICs is realistically implemented at Florida International University smart grid testbed to show the effect of the power routing on energy losses reduction. [ABSTRACT FROM AUTHOR]

Pumped‐storage unit (PSU) often acts as the peak and frequency modulation sources in modern power systems. The frequent operation condition conversions and tight hydraulic couplings with conduit system make its governing control a tough work in practise. To overcome the difficulty in the proportional–integral–derivative (PID) parameter tuning during transient processes, a hierarchical model predictive control (MPC) scheme, in which constrained generalised predictive control (CGPC) cooperates with classic PID is proposed. In the upper hierarchy of the MPC controller, CGPC acts as an auxiliary optimiser for the optimal PID parameters through online optimisation, whereas in the lower hierarchy, PID directly steers the movements of servomotor to control the guide vane opening; thus, to match the existing governing equipment in engineering practise. Also, typical constraints on the input/output signals and value ranges of PID parameters are discussed. Simulation experiments are conducted on a non‐linear distributed‐parameter simulation platform. It can precisely reflect hydraulic and mechanical dynamic behaviours of PSU and its conduit system. The results indicate that the proposed hierarchical MPC scheme not only outperforms in speed tracking and oscillation damping, but also attenuate instability phenomena caused by the negative 'S' character in pump turbine. [ABSTRACT FROM AUTHOR]

The use of inertia emulation in a microgrid has been growing as a promising control approach to maintain the bus voltage and frequency. An inertia emulation‐based control technique is proposed for a DC microgrid supplying AC loads in this study. The proposed work includes: (i) the DC bus voltage regulation using virtual inertia control and economic power management by a current sharing algorithm in cascade with a restoration control; (ii) AC load bus voltage and frequency regulation using virtual excitation emulation and inertia emulated control that utilises the emulated inertia and DC bus voltage. Further, it also provides inertia support to the grid. The coordinated current sharing algorithm manages the current (power) sharing between the grid and battery pack of electric vehicles based on electricity price and state of charge of the battery. The cascaded restoration control eliminates the steady‐state error in the DC bus voltage. Finally, the DC microgrid is simulated under various operating conditions to verify the performance of the proposed control approach. The simulation results reveal that the objectives are achieved successfully. [ABSTRACT FROM AUTHOR]

A distributed secondary layer control scheme for multi‐terminal high voltage direct current (MTDC) transmission systems is proposed. The proposed control scheme is achieved via solving a multi‐objective optimization problem. The objectives are defined such that: (i) the power losses of the system are minimized and (ii) the resiliency of the system in facing large disturbances and faults is enhanced. The second objective prevents the constant power converters to change their intended operating mode to avoid over‐voltages. Hence, the proposed scheme enhances the power commitment of such buses despite the occurrence of faults and large disturbances in the system. The proposed secondary controller is implemented in a distributed architecture using optimality condition decomposition. By employing the distributed scheme, the computational burden of the secondary level control is decreased and the autonomy of each zone in the MTDC grid is increased. The CIGRE B4 MTDC test system is employed to demonstrate the effectiveness of the proposed method. PSCAD and MATLAB are used to perform the simulations for the case studies. The simulation results verify that the proposed method enhances the resiliency of the MTDC systems by avoiding undesirable change of operations mode of constant power converters while decreasing losses of the system. [ABSTRACT FROM AUTHOR]

Here, a methodical research on the stability and response of a converter‐based generation model is conducted, focusing on the accompanying effects of a system split scenario in the (European) electricity transmission network. The purpose of this research is to analyse the behaviour of a generic but detailed model in case of extreme contingencies. In particular the focus is set on reduced short‐circuit power, high rates of change of frequency, and sudden voltage phase jumps at the point of common coupling (PCC). These effects are analysed by means of electromagnetic transient (EMT) simulations. In addition, the stability of the converter control is evaluated qualitatively. For the investigations carried out here, a single reduced wind turbine model with full‐size converter is used focusing on the interactions with the accompanying phenomena of a system split. The results show that reduced short‐circuit power as well as a large and sudden voltage phase jumps can be potential reasons for the converter system to disconnect from the grid. [ABSTRACT FROM AUTHOR]