High Penetration Of Renewable Energy Sources Research Articles

Two-Area Automatic Generation Control for Power Systems with Highly Penetrating Renewable Energy Sources

Currently, renewable energy sources (RESs) are gradually replacing traditional power sources that use fossil fuels. In some countries, such as Vietnam, RESs are developed on a massive scale and are concentrated in some key areas. This causes negative impacts on a power system when its transmission system is not deployed synchronously to release their capacity from these new renewable energy plants. An important challenge today is to ensure frequency stability in power systems with high uncertainty in RES output power. Additionally, the system requires solutions to prevent transmission line overloads during periods when RESs make a substantial contribution to the electricity generation capacity. Therefore, this paper builds an automatic generation control (AGC) system for a two-area power system with high penetration of RESs. This AGC system model aims to maintain system frequency stability amid unpredictable changes in RESs while also ensuring that tie-lines transmit the predetermined power levels to mitigate frequent congestion. By continuously monitoring and adjusting the system’s frequency, the challenges posed by the inherent variability of RESs can be effectively mitigated. The AGC model is simulated on DIgSILENT PowerFactory software and tested with a 106-bus system. The simulation results of this study show that the AGC system operates effectively, ensuring that the frequency returns to the rated value and maintaining the exchange capacity on the tie-lines after occurrences of RES power decrease events.

Load frequency control in power systems with high renewable energy penetration: A strategy employing P[formula omitted](1+PDF) controller, hybrid energy storage, and IPFC-FACTS

The high penetration of Renewable Energy Sources (RESs) in the modern power system poses a challenge to power system stability. This stability is affected by the stochastic, fluctuating output of RESs, which is influenced by weather conditions, and a lack of inertia resulting from reduced rotating mass. To address this issue, a new controller, referred to as Proportional-Fractional Integrator Plus Proportional-Derivative with Filter, PIλ(1+PDF), is designed for Load Frequency Control (LFC) with the support of a Hybrid Energy Storage System (HESS) for power systems with high-RES penetration. The HESS comprises a Superconducting Magnetic Energy Storage System (SMES) and a Vanadium Redox Flow Battery (VRFB) coupled with an Interline Power Flow Controller Flexible AC Transmission Systems (IPFC-FACTs) controller. The HESS, working in conjunction with the proposed LFC, injects virtual inertia and maintains power flow to expedite the frequency stability process. These systems are also integrated with Alternating Current (AC) and High Voltage Direct Current (HVDC) transmission lines to collectively enhance both the system's stability and the capacity of its transmission lines. To optimize the PIλ(1+PDF) controller parameters, Zebra Optimization Algorithm (ZOA) is employed utilizing an Integral Time Absolute Error (ITAE) objective function. The proposed controller is tested on a four-area power system integrated with a wind turbine, photovoltaic (PV) panels, a biodiesel generator, and a hydrogen aqua electrolyzer fuel cell, representing a high penetration of RESs in modern power systems. The results are compared with those obtained using Proportional-Integral-Derivative (PID) and Fractional Order Proportional Integral Derivative (FOPID) controllers. Sensitivity analysis and robustness tests are also performed to verify the stability of the power network by changing system parameters and under randomly chosen loading conditions. The proposed PIλ(1+PDF) controller tuned with ZOA outperforms PID and FOPID controllers by minimizing settling time for frequency changes by 62 %, eliminating overshoot, and reducing undershoots for frequency and tie-line power changes by 73 % and 55 %, respectively. Simulation results demonstrate that the proposed controller outperforms PID and FOPID controllers by effectively damping frequency and tie-line deviations, resulting in reduced frequency overshoots, undershoots, and shorter settling times.

Optimization of battery/ultra‐capacitor hybrid energy storage system for frequency response support in low‐inertia microgrid

AbstractModern power system networks are under statutory obligations to integrate renewable energy sources (RES). The primary reason is to meet ever‐increasing energy demand and also to curtail environmental pollution by greenhouse gases. However, the higher penetration of RES has the tendency of reducing inertia of overall power system network. Consequently, frequency stability is affected and deviates beyond allowable permissible limits leading to power blackouts, load shedding, and even total system failure. To address the issues associated with reduced inertia, an optimal control of hybrid energy storage system (HESS) has been proposed. HESS is basically a combination of battery and ultracapacitor, where ultracapacitor addresses rapidly varying power component by mimicking inertia while the battery compensates long‐term power variations. Thus, the HESS is effectively controlled to compensate the loss of inertia by regulating its energy flow. For the purpose of improved efficiency and better power management of the HESS, an improvised particle swarm optimization (MPSO)‐based virtual inertia control design has been proposed. The proposed MPSO is utilized to tune the gains of bidirectional dc–dc converter in such a way that improves frequency nadir with faster response to transient disturbances. This proposed method is simulated in MATLAB and its merits are validated in real time using hardware in loop. On analysing of the results, it can be observed that frequency nadir is improved by 48.96% with significant reduction in rate of change of frequency in comparison to conventional particle swarm optimization.

A frequency stability assessment framework for renewable energy rich power grids

The worldwide power grid is undergoing a paradigm shift due to the rise of renewable energy sources. Traditional rotating synchronous generators are being replaced by inverter-based renewable energy sources (RESs), and this trend is expected to persist in the years to come. As a result, the grid’s inertia is decreasing gradually, which presents significant obstacles to maintaining grid frequency stability. Moreover, due to the uncertainties associated with the generation of RESs and load demand, grid inertia has become a stochastic quantity. In this paper, considering the stochastic characteristics of the power generation, load demand profile and grid inertia, a framework to assess grid frequency stability with high penetration of RESs has been presented. This framework first quantifies grid frequency characteristics at different levels of RES penetration using Monte-Carlo simulation (MCS) considering the intermittent nature of RESs and load demand. This is followed by assessment of frequency stability of the power grid using proposed matrices that quantifies the amount of deviation in grid frequency and rate of change of frequency (RoCoF) outside the boundary prescribed by the grid operator. In addition, the proposed framework evaluates the sensitivity of grid frequency stability to RES penetration levels and quantifies the resiliency against contingency. Rigorous case studies on modified IEEE 39 bus test system have been presented to demonstrate the effectiveness of the proposed framework in assessing grid frequency stability.

Assessment and management of frequency stability in low inertia renewable energy rich power grids

AbstractThe integration of the renewable energy sources (RESs) into the power grid, drives a significant transformation in the conventional power generation landscape. This transition from traditional synchronous generators to inverter based RESs introduces unique challenges in maintaining the grid frequency stability due to the reduced system inertia. The inherent stochastic nature of the RES power generation, load demand, and grid inertia includes further complexity in the assessment of frequency stability. Existing studies have limitations, including neglecting the stochastic nature of RES generation and load demand fluctuations, relying on limited metrics, and lacking a comprehensive day‐to‐day assessment. To address these shortcomings of the existing approaches, this paper introduces a novel methodology for assessing frequency stability in power grids with high RES penetration. It proposes three indices for evaluating grid frequency sensitivity, resiliency, and permissibility amidst varying RES integration. Utilizing a stochastic approach, the study incorporates uncertainties in RES generation and load demand, offering a comprehensive framework for day‐to‐day frequency stability analysis. Additionally, it presents a systematic method to ascertain the necessary inertial support for maintaining desired frequency reliability in RES‐dominated grids. The effectiveness of these methodologies is validated through a case study on a modified IEEE 39‐bus test system, demonstrating their applicability in ensuring reliable grid operation under high RES scenarios.

Reactive power management considering Transmission System Operator and Distribution System Operator coordination

The increasing integration of Distribution Energy Resources (DER) in the distribution system has brought the necessity of a change in grid management and also for better coordination between the Transmission System Operator (TSO) and the Distribution System Operator (DSO). This work proposes a reactive power management model to be used by DSOs, in which reactive power flexibility from DER, and also from On-Load Tap Changer (OLTC) transformers and capacitor banks are used to handle voltage problems that may arise in both transmission and distribution grids due to the uncertain production of Renewable Energy Sources (RES). Besides, it is proposed that the DSO may provide a service to the TSO, in which the latter requests a reactive power setpoint from the first one, in the TSO-DSO boundary. Adaptive robust optimization on an Alternating Current Optimal Power Flow (AC-OPF) is modelled, ensuring that the DSO receives a feasible solution and is able to manage congestion and voltage problems. The proposed model is compared with its stochastic equivalent to assess its strengths and drawbacks. To test and validate the proposed models, a 37-bus Medium Voltage (MV) distribution grid with high RES penetration is used. An important conclusion is that, though the robust model presents a safer solution than the stochastic model, the operator must be aware of the trade-off between the desired level of robustness and the expected operating cost.

Dynamic simulation of SMR steam turbine speed response in an isolated network mode of distributed energy resources microgrids

Small modular reactors (SMRs) are being considered in combination with intermittent renewable energy sources (RESs) for microgrids applications. The high penetration of RESs poses challenges to frequency regulation in the power system, particularly when operating off-grid. To maintain the stability of the grid frequency, the SMR turbine is expected to have a high capacity for speed response. However, there have been limited studies on the performance of isolated SMR turbines. Therefore, dynamic simulations under isolated grid conditions are necessary to evaluate both turbine and SMR performance. In this study, a representative SMR model based on RELAP5 and its corresponding control system based on the SCADE program were integrated into a nuclear plant analyzer, and the simulation of two extreme cases was implemented to evaluate the performance of the turbine and the SMR. The proposed simulation modelling scheme provides valuable insights for full-range simulation modelling of SMR/RES microgrids.

Enhancing frequency stability in diverse power systems with conventional and renewable energy sources based on an innovative LFC and controlled energy storage integration

The rapid advancement of renewable energy sources (RESs) has led to a decrease in system inertia and an exacerbation of the instability issue. Hence, this study puts forward an approach to bolster the stability of the power grid amidst the presence of RESs and disturbances in load conditions. The strategy utilizes controlled energy storage systems, including plug-in electric vehicles and fuel cell systems, along with a secondary controller (SC). To improve the strategy's performance, novel controllers and an enhanced optimization technique are employed. The proposed controller combines proportional-integral-derivative (PID) and fractional order control methods, resulting in a new arrangement. The parameters of the controller are tuned using an improved optimization technique called an Enhanced Runge Kutta Optimizer. The effectiveness of the proposed algorithm is demonstrated through a performance comparison with conventional optimizers, using well-established mathematical equations. Additionally, the proposed controller's effectiveness is verified by comparing its performance with other controller arrangements, such as PID, combining TD-TI, and cascaded (1 + PD)-PID controllers. The performance of the system is enhanced by 66 % more with the proposed controller in SC compared to the (1 + PD)-PID controller, which is regarded as the most optimal among the controllers examined in this study. Additionally, the system's performance is improved by 44 % when the proposed strategy is implemented, as compared to the system's performance without the proposed strategy. Totally, the effectiveness of the proposed strategy is validated across various scenarios, including high penetration of RESs, significant load fluctuations, and system non-linearity.

Assessment and Enhancement of Uncertain Renewable Energy Hosting Capacity With/out Voltage Control Devices in Distribution Grids

Nowadays, with excessive integration of renewable energy sources (RESs), the distribution systems face several challenges due to exceeding the hosting capacity limit (HCL) of RESs. This article proposes a bi-stage approach to maximize the HCL considering RESs and load uncertainties. The first stage develops a multiobjective framework to adjust the system voltage profiles in a specific manner to avoid exceeding the voltage boundaries with high penetration of RESs. In the second stage, two processes are employed to maximize the HCL as the main objective function. In the first one, the photovoltaic (PV) and wind turbine (WT) plants are optimally allocated, while in the second process, a combination of three voltage control devices is proposed. A correlated multidimension probability uncertainty model is used to emulate the uncertainty of PV, WT, and load demand. Manta Ray foraging optimization (MRFO) algorithm is proposed to solve single-objective and multiobjective frameworks in the bi-stage approach considering the performance limits. The proposed approach is tested and validated on medium- and large-scale distribution systems. The effectiveness of the proposed MRFO is approved compared with two optimization algorithms. The proposed approach achieves up to 77.8% RESs integration from the total load demand for the tested systems.

Resilient virtual synchronous generator approach using DC-link capacitor energy for frequency support of interconnected renewable power systems

Modern interconnected power systems with many renewable energy sources (RESs) are more susceptible to disturbances than conventional power systems because they lack the inertia constant. Therefore, this study presents an advanced frequency control strategy for interconnected power systems considering high RESs penetration relying on the virtual inertia control (VIC) strategy-based high voltage direct current (HVDC) link, thus improving the dynamic frequency performance of future power systems. The HVDC link has been used as a DC capacitor which stores the electrostatic energy. This stored energy can supply the earliest active power support in automatic generation control system operation. Moreover, this paper develops the conventional VIC strategy based on the HVDC link by considering the dynamic behavior of a virtual rotor that mimics the inertia and damping properties of actual synchronous machines, thus stabilizing future renewable power systems. Also, this paper proposes a novel frequency control scheme based on the inertia emulation-based HVDC link and a virtual synchronous generator, which mimics the virtual rotor and virtual frequency control loops, to improve further the frequency regulation of low-inertia modern interconnected power systems. The parameters of the virtual synchronous generator scheme are optimally adjusted utilizing particle swarm optimization. The utility and superiority of the proposed VIC strategies based on the HVDC link are confirmed by contrasting them with the conventional VIC strategy relying on the HVDC link in the studied interconnected power system against various load/renewables interruptions, uncertainties, and physical restrictions. MATLAB/Simulink® software was used to simulate the results of the investigated system.

How Can EVs Support High RES Penetration in Islands

The electrification of the transportation sector contributes to a cleaner environment in non-interconnected island (NII) systems or standalone islands. Moreover, e-mobility can significantly contribute to achieving very high renewable energy source (RES) penetration levels in islands, allowing a reduction both in the emissions due to the conventional generation and the system’s cost. Ιncreased RES penetration, however, can pose technical challenges for an island’s system. In order to overcome these challenges, new technologies like grid-forming converters are important. Moreover, the provision of new ancillary services in relation to battery storage systems might be considered, while novel control and protection schemes are needed to ensure secure operation. E-mobility can also contribute to solving technical problems that arise from very high RES penetration by providing frequency containment reserves or reactive power compensation. Since EV charging demand introduces modifications in the system’s load curve, e-mobility may affect the power grid for long-term planning and short-term operation, i.e., line loading and voltages. The application of specifically developed smart charging methodologies can mitigate the relevant grid impact, while effective exploitation of EV–RES synergies can achieve higher RES penetration levels. This paper examines how e-mobility can contribute to increasing RES penetration in islands while considering the technical issues caused. In particular, this paper takes into account the distinct characteristics of NIIs towards the identification of solutions that will achieve very high RES penetration while also addressing the relevant technical challenges (voltage control, frequency control, short circuit protection, etc.). The effect of e-mobility in the power grid of NII systems is evaluated, while smart charging methodologies to mitigate the relevant impact and further increase RES penetration are identified.

Optimal Scheduling of Distribution Network With Autonomous Microgrids: Frequency Security Constraints and Uncertainties

Widespread integration of autonomous microgrids (MGs) into the distribution network (DN) makes the scheduling of distribution systems challenging. Especially, the uncertainties of renewable energy sources (RESs) and load demand put the MG frequency at the risk of violation for its low inertia and the high penetration of RESs. To address the schedule problems associated with uncertainties and frequency security, a day-ahead scheduling optimization model is proposed based on the chance-constrained programming (CCP) theory. The frequency security constraints and uncertainties of RESs/load demand associated with MGs are considered during the development of the proposed model. The total operation cost of the distribution system consisting of DN and MGs is minimized, while the MG frequency deviations caused by uncertainties are restricted in the predefined safe range by the proposed CCP-based model. Besides, a linearization method is presented and used to transform the proposed model into a mixed-integer linear program to determine the efficiency of the CCP-based model. Finally, numerous case studies are conducted to illustrate the effectiveness and good scalability of the proposed model and understand the advantages of using the model. The RT-LAB hardware-in-loop tests are carried out to study the real-time performance under the scheduling solved by the proposed model. Simulation and experimental results validate that the proposed model can be used to minimize the total operation cost of the DN system integrated with MGs while ensuring that the MG frequency deviations are operated within an acceptable range.

Multi-stage Co-planning Model for Power Distribution System and Hydrogen Energy System Under Uncertainties

The increased deployment of electricity-based hydrogen production strengthens the coupling of power distribution system (PDS) and hydrogen energy system (HES). Considering that power to hydrogen (PtH) has great potential to facilitate the usage of renewable energy sources (RESs), the coordination of PDS and HES is important for planning purposes under high RES penetration. To this end, this paper proposes a multi-stage co-planning model for the PDS and HES. For the PDS, investment decisions on network assets and RES are optimized to supply the growing electric load and PtHs. For the HES, capacities of PtHs and hydrogen storages (HSs) are optimally determined to satisfy hydrogen load considering the hydrogen production, tube trailer transportation, and storage constraints. The overall planning problem is formulated as a multistage stochastic optimization model, in which the investment decisions are sequentially made as the uncertainties of electric and hydrogen load growth states are revealed gradually over periods. Case studies validate that the proposed co-planning model can reduce the total planning cost, promote RES consumption, and obtain more flexible decisions under long-term load growth uncertainties.

Optimal Sizing and Sitting of Distributed Generation in Distribution Network considering Power Generation Uncertainty

This paper presents an application of the recent metaheuristic Geometric Mean Optimizer (GMO) for the allocation of renewable energy sources (RES), including wind turbine (WT) and biomass-based Distributed Generation (DG) units in the distribution network (DN). The primary objective function is to minimize the total power and energy losses. The Weibull probability distribution function (PDF) is employed to describe the uncertainty of wind speed. The high penetration of RES with intermittent availability and demand variations has introduced many challenges to DN, such as power fluctuations, voltage rise, high losses, and low voltage stability. Therefore, the use of dispatchable biomass is considered to smooth out supply fluctuations and maintain supply continuity. A standard IEEE 69-bus test system is used to verify the performance of the proposed approach. The simulation results and comparison with other techniques demonstrate the significant energy loss reduction achieved by the proposed technique.

Comparative Performance of DVR and STATCOM for Voltage Regulation in Radial Microgrid with High Penetration of RES

In recent years, the penetration of renewable energy sources (RES) in microgrids and distribution system feeders has increased manifold. Moreover, the advancement of power electronics-based devices in the distribution system has significantly increased the number of sensitive loads. Variations in the voltage under intermittent RES create functional problems with sensitive loads, necessitating voltage regulators (VR) installation. In this paper, two custom power devices: dynamic voltage restorer (DVR) and static synchronous compensator (STATCOM), used for voltage regulation in a microgrid, are investigated under different operating conditions. The efficacy of DVR and STATCOM for voltage regulation in an 11-node radial microgrid with high penetration of RES is simulated under a MATLAB Simulink environment. Furthermore, the simulated microgrid voltage profile results are analyzed to evaluate the efficacy of both voltage regulators.

Under voltage load shedding and penetration of renewable energy sources in distribution systems: a review

ABSTRACT The growing energy demand and the emerging environmental concerns across the globe caused increasing penetration of renewable energy sources (RESs) in distribution systems. One of the major issues faced by modern distribution systems with high RESs penetration is voltage instability. Generally, voltage instability can lead to voltage collapse, which is one of the key drivers for blackout incidents around the world. Under voltage load shedding (UVLS) schemes are usually executed as the final option to prevent a large-scale blackout or voltage collapse. But ever-increasing integration of RESs in distribution systems creates an additional threat to the existing UVLS schemes. Therefore, new UVLS methods are necessary to provide the appropriate corrective scheme for distribution systems, particularly when connected with RESs. This paper reviews and updates the recent UVLS methods emphasizing on distribution network application. In addition, the contributions and limitations of the conventional, adaptive, and computational intelligence techniques of UVLS are highlighted. Moreover, this paper provides an overview of the voltage stability indices applied for UVLS methods. Also, at the end of this review article, the further research directions to improve the safety of modern distribution systems during emergencies using UVLS are drawn as the conclusion.

Risk-averse Volt-VAr management scheme to coordinate distributed energy resources with demand response program

Distributed energy resources (DERs), such as renewable energy sources (RESs) and energy storage systems (ESSs), are inevitable parts of future power grids. However, the high penetration of RESs may cause voltage violation issues in distribution levels. To this end, the application of the Volt-VAr management (VVM) scheme is highlighted. This paper aims to maintain voltage levels within standard ranges with optimal coordination of different resources at minimum operational costs and voltage deviation. In more detail, this article develops a new VVM in distribution networks to effectively coordinate novel smart grid technologies such as PV inverters, time of use demand response program (TOU-DRP), energy storage systems (ESSs) with traditional devices, including on-line tap changer transformer (OLTC) and switchable capacitor banks (SCBs). Because the coordinated VVM is a bi-objective model that minimizes both operating cost and voltage deviation, it is proposed to use the ε-constraint technique to identify optimal Pareto solutions. To handle the uncertainty related to RESs and load demands, a robust technique based on information gap decision theory (IGDT) is also utilized. The formulation is configured as a mixed-integer linear program (MILP) and solved by CPLEX. It was implemented on the 118-bus distribution network under various conditions. The simulation results clearly show that the coordination of DERs and traditional devices has a significant impact on maintaining voltage levels within permissible ranges while minimizing operational costs. A higher degree of uncertainty radius can also be obtained if DRP participates in the VVM scheme.

Modified Cascaded Controller Design Constructed on Fractional Operator ‘β’ to Mitigate Frequency Fluctuations for Sustainable Operation of Power Systems

The demand for energy is increasing at an abrupt pace, which has highly strained the power system, especially with high share of power generation from renewable energy sources (RES). This increasing strain needs to be effectively managed for a continuous and smooth operation of the power system network. Generation and demand exhibit a strong correlation that directly creates an impact on the power system frequency. Fluctuations and disruptions in load frequency can manifest themselves as over-voltages and physical damages in the power grid and, in the worst case, can lead to blackouts. Thus, this paper proposed an effective solution to mitigate the load frequency problem(s), which is initiated by the changing load demand under high penetration of RES. This paper presented an improved cascaded structure, the proportional integral with a fractional operator coupled with proportional derivative PI−FOP+PD. The proposed FOP+PD modifies the (1+PD) controller by introducing fractional properties that improve its tracking efficiency and mitigate frequency fluctuations taking minimal time. The introduction of FOP β diversifies its tracking and overall controlling ability, which translates it as a significant controller. The controller optimal parameters are extracted by deploying a dragonfly search algorithm (DSA). The study of the results illustrates that the proposed design displays efficient performance under any disturbance or uncertainty in the power system.

Impact of high penetration of renewable energy sources on grid frequency behaviour

With the emergence of renewable energy sources (RESs), the power grid all over the world is going through a paradigm shift. Traditional rotating synchronous generators are being replaced by inverter-based RESs, and this trend is expected to continue in the coming years. Consequently, the inertia of the grid is gradually decreasing, which can pose significant challenges on grid frequency stability. This paper assesses the impact of integration of inverter-based RESs on grid frequency response through eigenvalue analysis of low-inertia power grids. Also, this study quantifies this impact by analysing sensitivity of the grid frequency, RoCoF, frequency nadir and frequency stability on the penetration level basis of RESs. Case studies on the modified IEEE 39 bus test system have been presented to demonstrate the effectiveness of the proposed approach in analysing the impact of high penetration of RESs on frequency stability.

Impact Assessment of Different Battery Energy Storage Technologies in Distribution Grids with High Penetration of Renewable Energies

The need for increasing further the penetration of Renewable Energy Sources (RESs) is demanding a change in the way distribution grids are managed. In particular, the RESs intermittent and stochastic nature is finding in Battery Energy Storage (BES) systems its most immediate countermeasure. This work presents a reality-based assessment and comparison of the impact of three different BES technologies on distribution grids with high RES penetration, namely Li-ion, Zn-Air and Redox Flow. To this end, a benchmark distribution grid with real prosumers’ generation and load profiles is considered, with the RES penetration purposely scaled up in such a way as to violate the grid operational limits. Then, further to the BES(s) placement on the most affected grid location(s), the impact of the three BES types is assessed considering two Use Cases: 1) Voltage & Congestion Management and 2) Peak Shaving & Energy shifting. Assessment is conducted by evaluating a set of technical Key Performance Indicators (KPIs), together with a simplified economic analysis.