Penetration Level Of Renewable Energy Sources Research Articles

Ant Colony Optimization of Fractional-Order PID Controller based on Virtual Inertia Control for an Isolated Microgrid

Background: Increasing the penetration of renewable energy sources has become necessary, especially in isolated microgrids. This increase leads to a decrease in the total inertia of the microgrids, which affects microgrid stability. Moreover, voltage and frequency control in lowinertia microgrids is more difficult and sensitive. Objective: Improve low inertia isolated microgrids' dynamic response and save the microgrid stability at different contingency and uncertainty conditions. Moreover, it allows for more penetration of renewable energy sources. Method: Proposing different control strategies based on virtual inertia control. The first is a proportional- integral-derivative (PID) controller, and then, to allow for more tuning flexibility, a fractional- order proportional-integral-derivative (FOPID) controller is used. MATLAB TM/Simulink is used to compare the response of the isolated microgrid without virtual inertia control, with conventional virtual inertia control, PID-based virtual inertia control, and FOPID-based virtual inertia control. The PID and FOPID controllers’ parameters are tuned using the ant colony optimization (ACO) technique. Results: The proposed control techniques save the isolated microgrids' stability at different penetration levels of renewable energy sources and operating conditions. At the same time, the isolated microgrid without virtual inertia control or conventional virtual inertia control can not save its stability in many operating conditions. Conclusion: The proposed fractional-order proportional-integral-derivative (FOPID)-based virtual inertia control has proven its effectiveness in saving the isolated microgrid stability and gives the best controller response. FOPID-based virtual inertia control minimizes the frequency deviation with different disturbances and operating conditions.

Proactive Generation Redispatch to Enhance Power System Resilience During Hurricanes Considering Unavailability of Renewable Energy Sources

This article proposes a proactive generation redispatch strategy to enhance operational resilience of power grids during hurricanes considering unavailability and forced outages of renewable energy sources (RESs). Previous resilience enhancement strategies focus on utilizing available generation resources to enhance the performance of power grids during extreme events without proactively preparing the system for predicted events. Recent incidents have shown that unavailability and forced outages of RESs during extreme weather events can lead to catastrophic impacts. Due to spatiotemporal characteristics of hurricanes and rapidly varying component statuses, system operators need to initiate proactive actions early in time to avoid power outages and potential cascading failures. In this article, a mixed integer linear programming problem is formulated to minimize the amount of load curtailments and operational costs. The optimization problem considers the behavior of RESs and their forced outages during hurricanes. Operational generation constraints (e.g., ramping rates, minimum up/down times, and start-up/shut-down generation costs), transmission constraints (e.g., line capacity and line availability), and other system constraints (e.g., load and weather variation) are considered for the resilience enhancement approach. The importance of the proactive redispatch strategy is assessed under various penetration levels of RESs. The proposed strategy is tested on a modified version of the IEEE 30-bus system under diverse impact levels of a hurricane. The results show the effectiveness of the proactive and dynamic generation redispatch to improve power system resilience and the capability to reduce the load curtailments with limited generation resources during hurricanes by at least 40%.

Monitoring Data Factorization of High Renewable Energy Penetrated Grids for Probabilistic Static Voltage Stability Assessment

The increasing integration of large number of renewable energy sources (RESs) generates multiple kinds of uncertainties in power grids, which heavily challenges traditional deterministic approaches for voltage stability assessment (VSA). Under this circumstance, this paper proposes a high-dimensional spatial-temporal matrix factorization (STMF) approach for monitoring data to separate the deterministic part and uncertain elements caused by RESs, and presents a probabilistic index to online evaluate voltage stability. Specifically, this method explores the eigenvalue distribution of measurement data when penetrating multiple distributed wind and solar generations, as well as a learning-based STMF model is accordingly used to iteratively extract the random elements due to RESs. Unlike traditional matrix factorization approaches, this STMF method uses an adaptive and analytical model to depict the eigenvalue distribution of random components. Subsequently, a probabilistic index is designed to measure the voltage stability degree as well as provide quantiles to indicate its potential fluctuations. Numerous cases verify the effectiveness and advantages of the proposed method using different load changing models and various RES penetration levels, as well as other probabilistic and deterministic indicators are compared.

Demand Side Flexibility Potential and Comfort Performance of Non-Residential Buildings

The need to create and maintain a sustainable indoor environment is now more than ever compelling. Both the legislation framework concerning the energy performance of buildings, as determined in its evolution through the EU Directives 2010/31/EU, 2012/27/EU and 2018/844/EU, and the European strategic plans towards green buildings, denote the need of sustainability and comfort of indoor environment for the occupant. Moreover, the EU Directive 2018/2001 sets the renewable energy target of at least 32% for 2030, denoting that the high renewable energy sources penetration level leads to challenges in the design and control of power generation, transmission and distribution. Demand side management may be able to provide buildings with the energy flexibility needed, in order to utilize the intermittent production of Renewable Energy Sources in a much more efficient and cost-effective way. The flexibility potential of installed building systems is investigated, while considering the effects on the indoor environment conditions and the perceived comfort. The implemented Demand Response (DR) control strategy shifts loads by changing heating system set point temperatures, based on market clearing prices of the day ahead market. The results indicated a reduction in energy consumption and energy costs, while maintaining indoor environment quality at satisfactory levels.

Probabilistic multi-stability operational boundaries in power systems with high penetration of power electronics

This paper presents a framework for defining multi-stability operational boundaries of power systems under varying penetration levels of power electronic interfaced generation and uncertain system’s loading. Boundaries are established considering the small-disturbance and large-disturbance rotor angle stability, as well as the frequency and voltage stability of the system. Estimating system’s operational boundary from multi-stability perspectives will provide invaluable information on how to best operate the system and how to mitigate certain condition that leads to instability especially in the current deregulated market and high penetration of power electronic interfaced generations. A singular stability assessment and its subsequent operational boundary may be valid only for a specific stability study and those may not be true for other types of stability. This paper illustrates the proposed framework in a modified New England Test System using a probabilistic approach. The impact of these varying loading conditions and renewable energy sources penetration levels are quantified on a per-stability-type basis and then aggregated into the multi-stability perspective. The established multi-stability operational boundary is heavily influenced by the frequency and large-signal disturbance rotor angle stability. A significant improvement in the system’s operational stability boundaries, particularly for voltage stability and small disturbance rotor angle stability, occur when the voltage source converter high voltage direct current’s ability to independently control active and reactive power via VDC-Q control is fully utilized.

재생에너지 확대에 따른 국내 계통관성 별 적정 예비력 평가

As the penetration level of renewable energy sources (RESs) increases, the decrease in the system inertia and spinning reserves will be one of the major challenges for the secure operation of power systems. Recently, in order to secure power system frequency within the limit defined in the grid code, accurate analysis on the frequency responsive reserves is getting important. In this study, method of evaluating the minimum level of inertia along with the required reserves to secure system frequency is developed. Furthermore, maximum allowable penetration level of RESs is analyzed in order to secure frequency after a sudden loss of a single generator unit. And with the evaluated minimum inertia for the secure frequency, this study shows the amount of the increased generation and the system frequency response in the time frame after a single generator or two generator units are tripped off. In the developed method, increase in RES penetration is illustrated as a negative load while considering the merit order of conventional generators. A case study is conducted on the future Korean power system of 2024.

Impact of Forecast Uncertainty on Wind Farm Profitability

Abstract The great amount of support schemes that initially fueled the fast and often uncontrollable, renewable energy sources (RESs) growth have been strongly reduced or revoked in many countries. Currently, the general trend is to try to equate RESs to traditional power plants. From the energy market point of view, this entails exposing RESs to market competition and mechanics. For example, it could be requested that RESs submit a production schedule in advance and are financially responsible for any deviation from it. This could push the wind farm (WF) operators to make accurate forecasts, thus fostering the electric system resiliency and an efficient use of balancing resources. From the forecasting point of view, this is not a trivial problem since the schedule submission is often due 10–12 h before the actual delivery. Since forecast errors are unavoidable, the submitted schedule could turn out to be infeasible, thus forcing the WF to adopt correcting actions, which are generally costly. This study estimates the revenue reduction that would affect a WF operating in the energy market due to forecast errors. To do this in a realistic way, a case study is selected, and realistic forecast scenarios are generated by using a copula approach. Relevant forecast error features, like autocorrelation and dependency on forecasted power level and forecast lead time, are modeled. The revenue reduction due to balancing actions is calculated on an annual basis, by using typical days. These were derived through a clustering procedure based on production data. Losses ranging from 5% to 35% have been found, depending on the days and market prices. A sensitivity analysis to the costs of balancing actions is performed. The effect of different market architectures and different RESs penetration level is considered in the analysis. Finally, the effectiveness of two techniques (i.e., curtailment and batteries) to reduce forecast error impact in highly penalizing market environments is assessed.

Dynamic Economic Dispatch With Maximal Renewable Penetration Under Renewable Obligation

This paper presents a multi-objective dynamic economic dispatch model with renewable obligation requirements. The two objective functions that are presented in this paper aim to increase the level of renewable energy sources in the grid while minimising the total operating cost and respecting the spinning reserves required to maintain continuity of supply. The proposed model incorporates thermal power plants, photovoltaic and wind power plants into the grid. The paper presents a Pareto optimal solution which is a compromise between maximising the renewable energy source generation while minimising the operating costs. A renewable obligation policy is implemented in the proposed model to ensure that renewable energy source generators are utilised and any failure to attain the required renewable obligation is penalised in line with the renewable obligation framework. The proposed model is modified into a single objective optimisation problem and numerical tests are performed on the modified IEEE 24 RTS system and IEEE 118 bus system to test the effectiveness of the model. A comparative study evaluates the impact of the proposed model on the traditional dynamic economic dispatch in terms of the achieved renewable energy source penetration level and economic performance. The numerical simulations show that the proposed model is robust and can attain high renewable energy source penetration levels.

Demand response-integrated economic dispatch incorporating renewable energy sources using ameliorated dragonfly algorithm

This paper presents an integrated demand response (DR) and dynamic economic dispatch (DED) model consisting of renewable energy sources (RESs) and shunt FACTS (flexible AC transmission systems) devices with focus on reducing thermal energy consumption. RESs are environment friendly and can be located close to the load centers, which helps in reducing T&D losses as well as harmful emissions. DR helps in reducing peak power consumption and generation cost of thermal power plants. Shunt FACTS device, static synchronous compensator (STATCOM), helps in improving voltage profile of the network. Analyses are carried out using the proposed ameliorated dragonfly algorithm (ADFA). The efficiency of developed ADFA is proved by comparing the obtained results with many other methods. Static economic dispatch is carried out on 6-, 17- and 40-thermal generator test systems using ADFA, and the results are compared with other existing methods available in the literature. Further, DED is carried out on 6- and 17-thermal generator test systems. Later, a DED is performed on a real-time 17-thermal generator (South Indian 86-bus system) system for four seasons. Solar irradiance and wind speed are modeled using beta distribution and Weibull distribution functions by collecting the historical data of the test system. The developed demand response program is implemented on a real-time 17 thermal unit and 86-bus test system located in Tamil Nadu, southern part of India. The developed DR model alters time-independent loads so that burden on generating stations during the peak load is minimized. The effect of DR, RES and STATCOM in the test system is studied individually. Further, a comparative analysis considering DR, RES and STATCOM together is presented. The results obtained are promising, and it can be interpreted that by using the developed model there will be improvement in the penetration levels of RES which in turn reduces the demand for thermal energy.

Optimization of virtual inertia considering system frequency protection scheme

In applying virtual synchronous generator (VSG) to solve low inertia problem due to high renewable energy sources (RESs) penetration in the power system, selecting proper value for its parameters is important to maintain frequency stability of the system subject to dynamic events and contingencies. For this purpose, several methods have been proposed. However, in those methods, VSG parameters are selected without considering system frequency protection scheme. Therefore, the setting of the existing frequency protection scheme might be inadequate for the application in low inertia condition. In this paper, a method to select proper virtual inertia constant of VSG by taking the system frequency protection scheme into account is proposed. The dynamic change of the virtual inertia constant is shown under different system inertia and penetration level of RESs. Using the proposed method, optimal virtual inertia support from VSG for different system inertia condition could be achieved in line with the existing system frequency protection scheme and thus, the reconfiguration of the existing frequency protection scheme is not necessary for the application in low inertia condition.

Self-Adaptive Virtual Inertia Control-Based Fuzzy Logic to Improve Frequency Stability of Microgrid With High Renewable Penetration

Maintaining frequency stability of low inertia microgrids with high penetration of renewable energy sources (RESs) is a critical challenge. Solving this challenge, the inertia of microgrids would be enhanced by virtual inertia control-based energy storage systems. However, in such systems, the virtual inertia constant is fixed and selection of its value will significantly affect frequency stability of microgrids under different penetration levels of RESs. Higher frequency oscillations may occur due to the fixed virtual inertia constant or unsuitable selection of its value. To overcome such a problem and provide adaptive inertia control, this paper proposes a self-adaptive virtual inertia control system using fuzzy logic for ensuring stable frequency stabilization, which is required for successful microgrid operation in the presence of high RESs penetration. In this concept, the virtual inertia constant is automatically adjusted based on input signals of real power injection of RESs and system frequency deviations, avoiding unsuitable selection and delivering rapid inertia response. To verify the efficiency of the proposed control method, the contrastive simulation results are compared with the conventional method for serious load disturbances and various rates of RESs penetration. The proposed control method shows remarkable performance in transient response improvement and fast damping of oscillations, preserving robustness of operation.

Analysing economic and environmental sustainability related to the use of battery and hydrogen energy storages for increasing the energy independence of small islands

Energy costs, carbon dioxide emissions, security of supply and system stability are common challenges in small islands. Many European islands have become pilot sites of energy innovation, but this green transition goes slowly in other ones usually not connected to the national grid. This study investigates the economic and environmental sustainability related to the integration of hydrogen and batteries storage in small islands, considering at the same time the use of the stored hydrogen for fuelling Fuel Cell Electric Vehicles and Hydrogen Compressed Natural Gas vehicles to meet electricity and public transportation demand of islands, so as to increase the Renewable Energy Sources penetration level. Selecting the island of Favignana (Italy) as case study, HOMER software has been used to carry out the energy analysis of different scenarios, in order to identify the most effective energy solution from both technological and economical point of views. Using economic and environmental indicators, the outcomes show that the implementation of a hybrid storage system with batteries and electrolyser can be an adequate and reliable option for increasing energy independency of small island and decarbonizing transport sector optimizing economic and environmental sustainability.

Quantification of Intra-hour Security-Constrained Flexibility Region

Rapid growth of renewable energy sources (RES) in the generation capacity mix poses substantial challenges on the operation of power systems in various time scales. Particularly in the intra-hour time scale, the interplay among variability and uncertainty of RES, unexpected transmission/generation outages, and short dispatch lead time cause difficulties in generation-load balancing. This paper proposes a method to quantify the intra-hour flexibility region. A robust security-constrained multiperiod optimal power flow model is first constructed to quantify the frequency, magnitude, and intensity of insufficient flexibility. The randomness of RES is captured by uncertainty sets in this model. The N-k contingency, spinning reserve, and corrective control limit constraints are included. This model is then cast into a two-stage robust optimization model and solved by the column-and-constraint generation method. The emergency measures with a least number of affected buses are derived and subsequently assessed by the postoptimization sensitivity analysis. Finally, the operational flexibility region is determined by continuous perturbation on the RES penetration level and the forecast error. The IEEE 14-bus system and a realistic Chinese 157-bus system are used to demonstrate the proposed method.

An Improved Dispatch Strategy of a Grid-Connected Hybrid Energy System with High Penetration Level of Renewable Energy

As more and more renewable energy sources (RES) integrated into the conventional distribution system, how to make the current electric grid more reliable and efficient is becoming an important topic the world must face. In order to achieve these goals, grid-connected hybrid energy systems (HES) which contain battery energy storage systems (BESS) and many other advanced technologies have been developed and applied. Many benefits of BESS, such as high density of energy and power, have fast response in energy time-shift, frequency regulation, and so on. This paper focuses on the fluctuation alleviation and power quality improvement of grid-connected HES with high penetration level of RES. A multistage dispatch strategy of BESS for HES is proposed in this paper to mitigate the randomness and intermittence of the power flowed in HES because of high penetration level of RES integration. Four other conventional strategies are also discussed for evaluating the performance of the method proposed in this paper. Detailed cases and corresponding discussions are implemented, and the results show that the method proposed in this paper is more effective and robust than the other conventional strategies.

An Online Mechanism for Incorporating Demand Side Flexibility into the Smart Grid

We propose an incentive compatible (IC) online mechanism for market integration of a flexible demand side in a smart grid with significant contribution from renewable energy sources (RES). This mechanism relies on the notion of energy services (Schweppe et al., 1989), i.e., combinations of appliances and associated time-wise load shifting potential. We compare this online mechanism over several metrics to an idealistic offline and online social planner. We find that the cost of establishing incentive compatibility in terms of social welfare is especially low in settings with high flexibility. This is a very positive result as we cannot expect classic welfare maximization approaches to compute realistic outcomes given self-interested agents. Under the IC mechanism, providing consumption flexibility decreases individual agents' payments and increases their chances of allocation. The presented online IC mechanism addresses a major obstacle for smart grid adoption, namely the lack of incentives fostering demand side flexibility. We see sufficient flexibility as an essential component in future power systems to facilitate higher RES penetration levels. Furthermore, we show that the classic paradigm of centralized control of flexible energy services offers only little societal benefits under our assumptions and can thus be replaced by a decentralized mechanism ensuring incentive-compatibility, scalability as well as robustness.

A Wind-Hydro-Pumped Storage Station Leading to High RES Penetration in the Autonomous Island System of Ikaria

Pumped storage is generally viewed as the most promising technology to increase renewable energy source penetration levels in power systems and particularly in small autonomous island grids, where technical limitations are imposed by the conventional generating units. The Hybrid Power Station (HPS) of Ikaria Island, Greece, which is currently in the construction stage, will be one of the first wind-hydro-pumped-storage hybrid stations in the world. In this paper, the HPS is described and a suitable operating policy is introduced, both for the HPS and the overall generation system of Ikaria, taking into consideration the existing regulatory framework for HPS in isolated island grids. Based on the proposed policy, the operation of the Ikaria Island system is simulated on an annual basis, in order to quantify the expected benefits from the operation of the HPS.