Integration of renewable energy resources (RERs) and complexities associated with varying load patterns urge the demand for energy storage systems (ESS) to ensure real power balancing of distribution system. Among various ESS, battery energy storage system (BESS) guarantees the reliable operation of microgrids in terms of economic and technical functionalities. The scheduling of microgrids becomes essential for the economic and optimal performance of both generating sources and loads. In this work, the load-shifting capability of BESS is utilized for the optimal scheduling of grid-connected microgrids. BESS has a significant role in the effective utilization of power from RERs during grid balancing. This paper discusses the scheduling of grid-connected microgrid with two scheduling strategies, which differ in the charging behaviour of BESS. Scheduling decisions are based on the value of locational marginal price (LMP) of distribution system. In scheduling strategy-I, BESS charges at off-peak hours, either from the PV system or from the grid. Meanwhile, in scheduling strategy- II, BESS charges from the PV system at peak or off-peak hours. These two scheduling methods are also compared with the scheduling of the distribution system without integrating the microgrid. The cost of power generation, power from the main grid, and active power losses of the distribution system are calculated by performing optimal power flow (OPF). The effectiveness of the proposed scheduling strategies are validated on the IEEE-69 bus system for 24 h time duration by using MATPOWER simulation tool. The results obtained after OPF establishes the requirement of effective utilization of BESS in PV integrated distribution system.

The presence of inverter-based renewable energy resources (IBRs) in the distribution system leads to various protection issues. These issues arise due to altered network configurations, restricted contribution of fault current and bidirectional power flows. The restricted contribution of fault current from IBRs is due to the thermal limitations of power electronic switches and the fault ride through requirements. Traditional over-current relaying methods in the distribution network fails to operate because of the modulated voltage and current output of IBRs. Also, the dynamic output of IBRs limits the operation of conventional over-current relays. The most commonly used IBR in the distribution system is solar PV, which is used for the protection studies of this paper. In this work, PSCAD/ EMTDC is chosen as the simulation platform. The solar PV plant model complies with IEEE 1547 standard. A new method is suggested to mitigate the protection issues caused by the solar PV integration. The new adaptive method is a modified version of the voltage-restrained over-current relay with an adaptive component. The proposed system is validated with the modified IEEE 33-bus test system and real time simulator in various scenarios and found to be operating satisfactorily.

Exponentially growing inverter-based resources (IBRs) are required to address the expanding global demand for electrical energy. To meet the criteria of the utility grid codes (GCs), several control techniques are utilized in IBR. For the protection of high-voltage transmission lines, distance protection is commonly used. The various control schemes employed in grid-connected renewable resources severely impact conventional distance protection. System non-homogeneity is caused by the phase angle modulation of the fault current, which malfunctions the distance relay. This paper proposes an adaptive distance protection approach for the transmission line connecting inverter-based resources. The proposed approach estimates the dynamic positive sequence impedance of the IBR to compute the phase angle of the faulted loop current to obtain the line impedance up to the fault location from the relaying point. The functionality of the adaptive scheme has been verified with the Mho relay on the transmission line connecting the solar power plant to the remote grid modelled in PSCAD/EMTDC.

Renewable integration with Inverter Based Resources (IBR) poses challenges to grid stability due to reduction in inertia and short circuit capacity. Considering the evolving grid code requirements due to massive renewable penetration, improved control strategies for from IBR is essential for providing ancillary services. Following an imbalance event, Rate of Change of Frequency (ROCOF) and nadir needs to be above Under Frequency Load Schedding (UFLS) settings to ensure reliability of grid. Wind generators can support the grid by extracting active power from the stored kinetic energy available in the rotor. Ancillary services from IBR, adaptive to varying system conditions is essential for ensuring grid stability and optimum resource utilisation. A modified Kundur two-area system is simulated in the EMTP platform to investigate inertia control strategies of DFIG. The inertial capability of DFIG system to a load disturbance is evaluated for fixed droop, linear droop and Fast Frequency Response (FFR) based strategies. Active power response to various auxiliary control signals, reference currents and voltages in rotor side control, mechanical and electrical powers, rotor speed of DFIG are analysed to validate the inertia extraction strategies.

Renewable integration is gaining momentum due to declining fossil fuel resources and environmental concerns all over the world. Widespread integration of renewable catering to global needs poses challenges to system operators for ensuring grid stability. Declining inertia due to inverter-based generation is a concern for stable system operation. Efficient control strategies are essential for the smooth operation of renewable integrated systems. Power generation from wind using a Doubly fed Induction Generator (DFIG) is widespread and is on an increasing trend. Following an imbalance event, frequency declines from the nominal value. The initial rate of deviation and nadir needs to be kept within limits to prevent under-frequency load shedding (UFLS) and blackouts. Power electronic interfaces present in Inverter based resources (IBR) hide the inherent inertia of the rotor from the grid. Inertia in the rotor of DFIG can be tapped using effective control strategies for improving nadir and Rate of Change of Frequency (RoCoF), so as to provide timely deployment of kinetic energy through primary response. Strategies mimicking conventional droop characteristics of governors are being used to provide frequency regulation. Nowadays, robust and adaptive strategies are essential to stabilise inverter-rich grids and to ensure the efficient operation of IBRs. Adaptive droop control and fast frequency response (FFR) strategies for providing frequency support are the theme of discussion in this work. The frequency deviations, rotor speed, control inputs, active current command, and active power output of DFIG with various control strategies are examined on the IEEE 9 bus system to validate the control strategies.

Technical advancements in the renewable sector lead to an increased penetration, primarily of wind generation, into the grid. Conventional generators, the main contributors to system inertia, are being replaced by wind generation to facilitate sustainable power production. Owing to minimal inertial support with converter-based generators, overall system inertia is reduced, which in turn causes severe issues in the power system network, mainly related to frequency stability. Emulating inertial response from wind turbines is a possible solution. Wind energy systems can be equipped with supplementary controllers to enhance system inertia by extracting energy stored in turbine rotors, blades, and other rotating parts. The advanced wind turbines, provided with inertial control, perform better than the conventional wind-penetrated system. However, adverse effects such as secondary frequency dip may be observed after the inertial response period. Static Synchronous Series Compensator (SSSC), a class of FACTS devices, is employed to improve the power transfer capability of tie lines, that connect remotely located wind farms to the grid. In addition to improving power quality, SSSC aids in the frequency stability of the grid by damping out low-frequency oscillations in lines and enhancing inter-area power exchange. In this paper, inertial support from wind turbine generators (WTG) is presented as a solution to enhance the primary frequency response capability of the wind-penetrated system. The system response is further enhanced with the integration of SSSC. The variation of net inertia and droop in the system with penetration is accommodated for analysis. The controller parameters are optimized with the latest Honey Badger Algorithm (HBA), which performs better than other meta-heuristic optimization methods. The efficiency of the HBA is also compared with other prominent algorithms.

The integration of solar photovoltaic (SPV) system to conventional grid causes various protection challenges in the distribution systems. These challenges arise due to modified network topologies, limited fault current contribution, and bidirectional power flows. The low fault current contribution of inverter-based resources is due to the thermal constraints of converter switches. The reduction in current contribution from inverter-based sources causes the maloperation of conventional over-current relaying schemes in the distribution system. Also, the varying load levels limit the operation of conventional voltage-restrained relays. In this paper, a new methodology is developed to mitigate the issues of existing over-current relays (OCRs). This approach uses local positive sequence current and voltage to modify the pickup current of the relay and makes it adaptive to different loading conditions. In this work, the SPV plant model is operated in voltage control mode where the SPV plant complies with grid codes, i.e., the fault ride-through (FRT) condition. The methodology developed is validated on an IEEE 9-bus system in PSCAD platform. Hardware-in-the-loop testing using Speedgoat real-time simulator as power system and Texas Instruments launchpad as relay validates the performance of the proposed method in real-time.

The world is drifting towards a renewable dominated power scenario. Among the renewable energy sources, wind power projects are gaining the prominence. In the new energy mix, many conventional paradigms are being redefined. For years, steam turbine time constants which were assumed as constant proved to be no longer constants as the generation schedule varies. With the increased penetration of renewable, conventional power plants are facing threat of shut down. Meanwhile, majority of synchronous machines in these conventional power plants such as thermal and nuclear stations are operated at partial generation schedule between 70 % and 90 %, due to various economic and environmental factors. The shut down of conventional power plants results in abatement of numerous synchronous machines. This work proposes the use of abandoned thermal generating units as synchronous condenser to aid dynamic frequency regulation in a high renewable penetrated power system with varying generation schedule. The synchronous condenser provides momentary active power support following a load change. Simulation studies were carried out under various scenarios of generation schedule and incorporation of synchronous condenser. Obtained results bridges the concepts of varying generation schedule and synchronous condenser and their effect on dynamic frequency regulation of power system has been analysed.

Integration of Renewable Energy Sources (RESs) to distribution grid lead to formation of microgrids, which is a strategic approach to balance the generation and load in distribution system. This paper presents a scheduling algorithm for distribution system with minimizing the cost. Main objective of this paper is to minimize electricity cost by integration of RESs, in addition to that power imported from main grid, local marginal price of renewable resource connected bus and total distribution losses are calculated. The proposed algorithm is demonstrated by hourly varying load on an IEEE-69 bus system and results are compared with and without addition of RESs.

The development of distributed control algorithms with increased flexibility and faster convergence to deviation in MW-frequency has gained much research attention recently on load following of deregulated power system. The application of Rao algorithm for exemplary tuning of PID controller gains of two area thermal-thermal system has been explored in deregulated scenario. Rao algorithm is the robust and newly proposed method developed in 2020, which is of computationally simple with added advantage of independent of algorithm-specific parameters. The performance evaluation of controllers with Rao algorithm has been examined by considering the different scenarios of deregulated environment in AGC. Simulation studies carried out for performance comparison of Rao algorithm with other popular heuristic algorithms such as Grey Wolf optimization (GWO), Genetic Algorithm (GA) and Particle Swarm optimization (PSO) ensures the robustness and faster convergence of the proposed Rao algorithm.

The employing of Redox Flow Battery (RFB) for enhancing primary frequency capability of a power system with wind integration is presented in this paper. Differential evolution algorithm is manipulated for tuning the parameters of PID controller. The frequency and tie-line power variations of a multiarea, diverse source network is analyzed for better understanding. The system is examined to operate under three different wind penetration levels with and without inertial support from a wind turbine. The influence of RFB in enhancing the virtual inertial support with the wind turbine is also investigated.

Continuous growth of wind energy systems and increased wind penetration levels pose challenges in power system stability. Popular Wind Turbine Generators (WTGs) such as Doubly Fed Induction Generators (DFIGs) desired to have inertial response close to conventional synchronous generators to improve system inertia. Several strategies have been proposed to release the kinetic energy stored in the rotor of WTGs and provide an inertial response to the grid. However, after the inertial response, there is a possibility of secondary frequency dip and frequency oscillations. The extent of such undesirable events depend on the penetration level of the wind energy systems in the grid and the DFIG reserve which provided for inertial support. This paper proposes a control strategy to enable inertial response from DFIGs in coordination with Super-conducting Magnetic Energy Storage Systems (SMES) with minimized secondary effects. The simulation results show that the system succeeded in reducing the secondary dip and preventing the frequency oscillations during power system disturbances.

Developing an optimization algorithm with independent algorithm-specific parameters is crucial in tuning the controller parameters of Automatic Generation Control (AGC). In 2020, Rao developed a robust and newly proposed algorithm independent of algorithm-specific parameters with faster convergence and less computational complexities. This paper presents the AGC of a sample two-area interconnected multi-source power systems with fractional-order PID controllers optimized using the Rao algorithm. The objective function selected for tuning the optimal gain of the controller using the Rao algorithm is based on Integral Squared Error (ISE). The robustness of the Rao algorithm for parameter variations and load changes is compared with other metaheuristic algorithms such as Genetic Algorithm (GA), Grey Wolf Optimization (GWO), and Particle Swarm Optimization (PSO). The efficacy of the proposed tuning method for AGC application is validated using the dSPACE 1103 hardware-in-loop simulation.

Frequency stability is critical for resiliency and balanced operation of power systems. The growth of renewable based sources of generation pose challenges in maintaining frequency regulation of the system on account of reduced inertia. Coordinated control strategies need to be developed for renewable integrated power systems. A multi-source system consisting of thermal, gas and hydro sources integrated with wind generation is considered for analysis. Inertia available in the rotor of the Doubly Fed Induction Generator (DFIG) based wind turbine can be utilized for improving primary frequency support. The use of a Plug-in Electric Vehicle (PEV) for aiding the primary frequency control of a wind plant integrated two-area power system is also presented in this paper. Control parameters of the areas are optimized using the Differential Evolution algorithm. The system is examined to operate under 20% and 40% wind penetration levels, with and without support from the PEV. The frequency deviations, tie-line power variations, rotor speed variation of DFIG, and contribution of PEV for primary frequency control are investigated to validate the performance of the proposed system.

The global electric-vehicle market is amped up and still on the rise. Significant reduction in dependence on fossil fuels and reduction in hazardous emissions are contributing to the higher penetration of electric vehicles. The fast active power controllability make Plug-in Electric Vehicles (PEV) an ideal contributor in the frequency regulation of power system. Power system loads are varying in nature and will force partial loading of conventional generating units. The turbine time constant of conventional generating units will change as per its generation schedule and it affects the power contribution of these generating units during frequency events. An aggregate Plug-in Electric Vehicle model is implemented in the considered two-area hydrothermal power system so as to respond to the power variations at different generation schedules of hydrothermal system. Hydrothermal system parameters are optimized using grey wolf optimization which is one of the recent heuristic algorithms employing integral squared error (ISE) based fitness function.

Wind power generation is gaining popularity due to technological advancements and issues related to fossil fuel depletion. High wind penetration poses challenges in grid operation in terms of power balancing due to the intermittent nature of wind speed. Flywheel energy storage system (FESS) with high cycle efficiency and power density is a suitable option for smoothing wind turbine power output. FESS consists of a spinning disc connected to a rotating electric machine which stores energy in the form of rotational kinetic energy thereby ensures controllable power dispatch between Wind Energy Conversion System (WECS) and grid. This paper proposes an integral sliding mode controller for DC machine based FESS model to ensure smooth power output. A non-linear controller is used to track non-linear power output, which assures asymptotic stability of the closed-loop system. The proposed robust control method is compared with Lyapunov based control implemented in an existing literature. Better performance in tracking and disturbance rejection is obtained and certain limitations in the existing work are clarified with proper justifications.

At present, increase in renewable penetration has paved the way for the shutdown of existing thermal power plants. This forced system operator, to operate remaining thermal power plants mostly around 70 % to 90 % of its generation schedule. In this paper, effect of varying steam turbine time constant on a re-heater based two-area thermal power system under deregulated environment is analysed. The analysis has been carried out for different scheduled power output of the plant, such as 100 %, 90 %, 70 % and 50 %. The steam turbine time constants for each generation schedule is determined and simulations were carried out for three scenarios, such as unilateral, bilateral and a case of contract violation. In each case, four generation schedule mentioned earlier is taken into account. A comprehensive study was done by analysing all the aspects of a deregulated two area reheater based thermal power system, considering various generation schedules.

Coordinated operation of superconducting magnetic energy storage (SMES) and thyristor controlled series compensator (TCSC) for dynamic frequency regulation on a multisource power system is presented in this paper. The optimal integral gains of the control areas are obtained by tuning a quadratic performance index consisting of frequency deviations and tie-line power error using integral squared error technique. The effects of generation rate constraint and governor dead band nonlinearities are also considered. Time domain simulations carried out in MATLAB on a sample two area multi-unit power system comprising hydro, thermal and gas power plants reveal that the SMES-TCSC combination can effectively damp out deviations in area frequencies and tie-line power flow following a sudden load perturbation with better transient performance and reduced settling time.

This paper discusses the impact of wind penetration on frequency control of a thermal dominated system considering Generation Rate Constraints (GRC) and dead band non-linearities. The hidden inertia emulation and coordinated operation of conventional power generation systems with wind energy can effectively alleviate the frequency excursions during sudden load disturbances. Conventional energy storage device like Flywheel Energy Storage (FES) system can be used in conjunction with wind integrated power system to overcome the intermittent nature of power generation. Thyristor Controlled Series Compensator (TCSC) is found to be effective in damping low frequency oscillations in weak tie-lines and supplement the frequency regulation. A stochastic population based evolutionary computation technique - Particle Swarm Optimization (PSO) is used to tune the controller gains. A strategy comprising inertia control, coordinated operation of conventional generation units with wind energy and TCSC-FES has been proposed to enhance the frequency regulation which is effective in controlling low frequency oscillations as established by the simulation results.

Thyristor controlled series capacitor (TCSC) is a series type flexible AC transmission system (FACTS) device which can effectively change the impedance of a transmission line. This paper is concerned with developing a linear incremental model for a TCSC and its application to improve the performance of automatic generation control (AGC) of two-area interconnected hydrothermal power system. The optimised integral gain values of AGC are obtained using integral squared error (ISE) technique. A quadratic performance index considering a step load perturbation in either of the areas is considered for minimisation. Simulation results suggest that, incorporating a TCSC is very effective in damping the low frequency oscillations in area frequencies as well as the tie-power after a sudden load perturbation in any of area compared to AGC without TCSC.