Small Isolated Power Systems Research Articles

Wind power integration improvement in an island by installing battery energy storage systems. Case study of Lanzarote-Fuerteventura.

Some small isolated power systems have a grid infrastructure weakly meshed and stability could be seriously affected when a large amount of renewable energy is being flowed into the grid. In this paper critical clearing time (CCT) is studied along with the increase in renewable energies integration. This study considers the use of squirrel cage induction generators (SCIG) wind turbines. Battery energy storage systems (BESS) have been considered in order to overcome this kind of power system drawbacks. Thus, renewable energy integration improvement is achieved. Renewable energy improvement is analyzed by means of CCT values. Dynamic analysis is performed in order to determine CCT values taking into account voltage, system frequency and the amount of load shedding.

Operation of small isolated power system with large non-controllable RES penetration – System Operator’s experience in El Hierro Island

The Canary Islands are facing a transitiontowards renewable energy, in an attempt to build a cleaner and cheaper power system for the coming years. This transition poses a big challenge for the TSO that will face the operation of weak grids, with a large amount of non-controllable generation, in a context of reduced natural inertia. In this context the methodology and operational criteria of El Hierro’s power system, operated by the TSO, are to maximize the amount of renewable energy in a safe way, minimizing the risks associated with the unpredictability of wind-power, and to do so minimizing the electrical power generation cost. This paper shares the REE experience in the operation of a small isolated power system with large non-controllable RES that, as a result, has established a new record in 2018, where the the pumped storage hydro facility named Central Hidroeólica de El Hierro (CHE) covered the complete island’s demand during 18 consecutive days, more than two weeks where the diesel power plant was completely off and the island was therefore 100% renewable.

Virtual Synchronous Machine Control of RES Plants in Isolated Power Systems

Because of the increase in renewable energy sources (RESs) share, new control strategies of isolated power systems have been developed to improve the frequency and voltage stability of inverter-interfaced RESs. A voltage source converter (VSC) with a virtual synchronous machine (VSM) is among the most promising control schemes. This paper demonstrates how VSM control of inverter-interfaced RES can be efficiently used to improve the dynamic stability in small isolated power systems. In the proposed analysis, the RESs of a Mediterranean island are assumed interfaced to the grid by VSCs with a swing controller and a vector-current controller (VCC) with two different options for the reference current (RC) to regulate the voltage at the point of common coupling (PCC) and the real power output. The system is modelled in a PSCAD environment, and the behavior of the control is tested in the case of a phase-to-phase fault. The results of the simulations for different scenarios and values for the control parameters show the effectiveness of the control in small isolated grids. Finally, the level of grid power quality is verified via harmonic analysis of the PCC voltage.

On the road to a sustainable transport mobility in isolated power systems: The role of light-duty powertrain electrification

Plug-in vehicles are seen as a promising path to reduce the road transport greenhouse gas (GHG) emissions. However, the singularities of small isolated power systems in terms of the high dependence of fossil fuel-based generation and the relative short distances travelled do require a particular analysis to evaluate the potential emission reduction. This paper describes a simulation study for estimating the energy consumption and the corresponding Well-to-Wheels GHG emissions of different light-duty powertrain architectures subjected to real-world driving conditions, taking the island of Tenerife (Canary Islands) as a test case. The simulations have been carried out with a high-level vehicle powertrain system analysis tool, capable to estimate second-by-second vehicle energy consumption. Road gradient, GHG grid intensity and battery capacity impact on the GHG emission reduction were analysed in detail.Based on the results, the current high carbon content of the grid and the additional weight of the large battery packs limit the potential benefit of Battery Electric Vehicles (BEVs) with respect to hybrid architectures (HEV). The simulations also reveal that Plug-in Hybrid Electric Vehicles (PHEVs) currently offer a great potential to reduce the GHG emissions. Unlike other geographical areas, the high Utility Factors derived from the short distances travelled ensure the proper use of this technology.

Requirements for control strategies of grid‐connected converters in the future power system

The increasing penetration of converter-based generation in many power systems around the world has sparked a discussion about how to operate these power systems with the usual levels of efficiency, reliability and cost-effectiveness. Current grid-following converter-based generators have proven to run stably in parallel to one another, even if there are thousands of them connected in a power system, and even in very small isolated power systems with extremely low system inertia. Discussions around the necessity of additional converter performance, usually under the ‘grid-forming’ and ‘Virtual Synchronous Machines’ concepts, have recently been transferred from the academic sphere to national and international industry fora. Formal discussions have started in Great Britain, in Germany and at ENTSO-E level. However, there is still a lot of uncertainty about the real and not simulated performance of grid-forming converters, whilst the needs case for requiring this radically different control method has not been adequately justified. With the present paper we raise key questions that will serve towards an objective discussion about power system needs, grid infeed technologies and their interaction.

Optimal Planning of Isolated Power Systems with near 100% of Renewable Energy

The enhancement of economic sustainability and the reduction of GHG emissions in most of the small isolated regions strongly depends on reducing their use of imported fossil fuels. To evaluate the effectiveness of interconnecting small islands in promoting renewable penetration levels increase and cost reductions, this work proposes a multiyear expansion-planning optimization model for the Azores archipelago that considers: 1) the interconnection between the different islands using DC submarine power cables; and 2) the addition of new in-land renewable power plants. The main goal of these expansion plans is to minimize the power system's investment and operational costs. Obtained results showed that interconnections between small isolated power systems (even if not with mainland grids) strongly contribute to a to a more sustainable performance of these regions from both the economic and environmental perspectives.

Operation of small isolated power system with large non-controllable RES penetration – System Operator's experience in El Hierro Island

Operation of small isolated power system with large non-controllable RES penetration – System Operator's experience in El Hierro Island

Metaheuristic methods applied to the pumps and turbines configuration design of water pumped storage systems

Abstract The increasing penetration of fluctuating Renewable Energy Sources (RES), particularly in small isolated power systems, is raising some problems in the operational management of the system. The simpler way to solve the problem is to perform RES curtailment, but this is not the right decision from an environmental point-of-view. In this context, the storage alternative is becoming more and more a cost-effective option. This paper presents an integrated techno-economic model, whose purpose is to come up with the optimal configuration of a Water Pumped Storage System (WPSS). The expected output is the WPSS design configuration, i.e. the pump number and size and turbine number and size, which leads to the maximum Net Present Value (NPV) of the investment project. To reach the proposed objective, the model uses meta-heuristic optimization techniques, namely Particle Swarm Optimization (PSO) and Genetic Algorithms (GA), with a Unit Commitment and Economic Dispatch module (UC + ED) of the thermal-based electrical generation units, in order to calculate the system operational costs. The Terceira Island, Azores archipelago, Portugal, is the case study presented as an application of the developed model. PSO and GA converge to the same results, pointing to an optimal WPSS configuration of 2 pumps of 490 kW and 1 turbine of 500 kW, with a 263 k€ positive NPV, therefore showing the economic and technical feasibility of a WPSS, in this application.

Battery energy storage systems as a way to integrate renewable energy in small isolated power systems

Isolated power systems present high levels of Renewable Energy Sources (RES) curtailment as intermittency and isolation impose challenging difficulties regarding the integration of this energy into the electrical grid. The recent developments in electrical vehicles have decreased the kWh cost of lithium-ion batteries below a threshold value that was previously prohibitive for grid-scale applications. Therefore, the integration of RES considering the installation of a Battery Energy Storage System (BESS) into an isolated power grid is an up-to-date research topic and is assessed in this paper. The BESS is inserted into the Unit Commitment and Economic Dispatch (UC + ED) platform and regarded as another dispatchable generator. To keeps the costs down, the BESS is mainly used to provide a portion of the spinning reserve needs and secondly to alleviate the load of the thermal generators, using the free modules. The BESS configurations that maximises the economic viability and minimises the RES curtailment are presented. The results suggest that the investment in this technology may be profitable and considerably decreases the levels of RES curtailment.

A Centralized UFLS Scheme Using Decision Trees For Small Isolated Power Systems

This paper presents a centralized underfrequency load-shedding (UFLS) scheme using a decision tree to decide whether and how much load needs to be shed. UFLS schemes play an important role in protecting the integrity of small isolated power systems. Centralized UFLS schemes continuously measure and process critical system variables and act on the feeder breakers according to the system state. The decision determines the optimal amount of load to be shed by means of dichotomous tests applied to measured input variables related to the pre- and post-contingency state of the system. The applicability of the centralized UFLS scheme is shown for a Spanish small isolated power system.

Optimal design and techno-economic analysis of an autonomous small isolated microgrid aiming at high RES penetration

Electrification demand in small isolated power systems is typically covered by autonomous power stations, mainly diesel-generators. The technical constraints introduced by diesel-generators along with the high cost of storage options confine the penetration of renewable energy sources (RES) in these systems. This paper examines the possibility of utilizing a RES-hybrid system for a small Greek island by exploring three different case scenarios. The first two include system configurations with gradual conventional fossil-fuel power reduction while in the third one we investigate if a nearly 100% renewable system is feasible. Techno-economic analyses ensure the technical feasibility of the systems and address their economic viability. Results showed that the conventional fossil-fuel power required for the first and the second scenario could be decreased 52% and 74% compared to the existing system and the system's overall by 17% and 26% respectively. RES-penetration reached 68% (first-scenario) and 74% (second-scenario) while the NPC value was calculated to 1.84 and 2.25 million euro respectively. A nearly 100% renewable energy system (third scenario) could be technically feasible but it would require the installation of enormous RES equipment capacity dramatically increasing the total cost. Finally, the social aspect and local acceptability of RES-projects in Greece are discussed.

Adaptive Neuro-Fuzzy Synchronization in Isolated Power Systems with High Wind Penetration

Isolated power systems (IPSs) worldwide are traditionally powered by diesel generators that are very expensive to run and produce harmful emissions. In order to mitigate these problems, wind turbines are being introduced into existing IPSs. Although this integration has been reasonably effective at reducing running costs and emissions, high levels of wind penetration cause large system frequency variations, resulting in a prolonged synchronization process for newly dispatched diesel generators. Long synchronization can compromise the stability of a small IPS. This paper examines the diesel synchronization problem using a real IPS as a case study and offers a solution by introducing the concept of predictive synchronization based on adaptive neuro-fuzzy systems. Simulation results demonstrate a significant reduction in diesel generator synchronization times.

Reducing Under-Frequency Load Shedding in Isolated Power Systems Using Neural Networks. Gran Canaria: A Case Study

Small isolated power systems often experience generator outages, which are responsible for the activation of the under-frequency load shedding scheme with the corresponding negative impact on electricity consumers and, hence, market loss. There are three main causes of this problem: the power system's low inertia, the speed governors' low capacity, and a poor size-ratio between generator and system. The most extensive research line in this area is focused on the optimization of the load shedding scheme, which is a partial solution. Another research line is presented to solve the problem from the point of view of the system operator. This paper proposes an online method to predict and correct possible load shedding by redistributing load dispatching. This proposal uses artificial intelligence techniques, in particular neural networks, and a special-purpose power system simulator. In order to evaluate the proposal, the achieved solution is applied to a real case study: the island of Gran Canaria. This application shows the improvement that might be achieved by implementing this simple method. The method proposed in this paper is strongly recommended for regions that have suitable geographical sites as well as energy problems similar to those of the Canary Islands (see tech. rep. “Map of the Canary Islands Power Systems” by Red Electrica de Espana).

INTEGRACIÓN DE AEROGENERADORES SÍNCRONOS MULTIPOLOS EN SISTEMAS ELÉCTRICOS AISLADOS CONSIDERANDO LA MÁXIMA DURACIÓN DE CORTOCIRCUITO

Global installed capacity of renewable energy has experienced a higher increase in recent years, especially wind power. It is expected that this trend will continue. Large amounts of wind power can be introduced in continental power systems. However, in small isolated power systems, such as those in islands, penetration of wind power can show some problems. These problems are related to the characteristics of the small isolated power systems and those related to the wind power. An example of this is the variability of the power generated by wind turbines.

Critical Clearing Time and Wind Power in Small Isolated Power Systems Considering Inertia Emulation

The stability and security of small and isolated power systems can be compromised when large amounts of wind power enter them. Wind power integration depends on such factors as power generation capacity, conventional generation technology or grid topology. Another issue that can be considered is critical clearing time (CCT). In this paper, wind power and CCT are studied in a small isolated power system. Two types of wind turbines are considered: a squirrel cage induction generator (SCIG) and a full converter. Moreover, the full converter wind turbine’s inertia emulation capability is considered, and its impact on CCT is discussed. Voltage is taken into account because of its importance in power systems of this kind. The study focuses on the small, isolated Lanzarote-Fuerteventura power system, which is expected to be in operation by 2020.

A UFLS Scheme for Small Isolated Power Systems Using Rate-of-Change of Frequency

This letter presents a centralized underfrequency load-shedding (UFLS) scheme using the initial rate-of-change of frequency (ROCOF) to decide whether and how much load needs to be shed. The applicability of the centralized UFLS scheme is shown for a Spanish small isolated power system.

Sizing and Controller Setting of Ultracapacitors for Frequency Stability Enhancement of Small Isolated Power Systems

This paper studies the impact of the size and controller settings of an ultracapacitor (UC) on frequency stability. Underfrequency load-shedding (UFLS) schemes play an important role in protecting the system against frequency instability and their performance is used as a measure for the enhancement of frequency stability thanks to the UC. To this end, a simplified but still accurate model of the UC is developed. In addition, a meaningful procedure is proposed to size the UC's power and energy storage capacities in function of the system parameters and operation constraints in order to improve frequency stability. Finally, the impact of the UC on the UFLS scheme is studied for many generation dispatch scenarios and for all possible single generating unit outages of a Spanish isolated power system. An analysis with respect to the UC's control parameters and its size in terms of power and energy storage capacities is carried out, too. Appropriate control parameter settings improve the UC's impact on frequency stability.

Energy storage systems for frequency stability enhancement in small-isolated power systems

Frequency stability is one of the most relevant issues in operation of small isolated power systems. High penetration of renewals may significantly affect frequency stability of isolated power systems since renewable energy sources connected to the grid through power electronic interfaces do not provide either inertia or primary frequency regulation. This paper describes a research and demonstration project led by Endesa aimed at testing the state of the art of energy storage systems in isolated power system. Power systems of the Spanish Canary Islands will be used as test bench. The paper shows the contribution of La Palma ultra-capacitor and La Gomera flywheel to frequency stability and control enhancement.

An ultra-capacitor for frequency stability enhancement in small-isolated power systems: Models, simulation and field tests

The most relevant issue in operation of isolated power systems is frequency stability. Frequency stability is concerned with the ability of generators to supply the loads at an acceptable frequency after a disturbance. Frequency stability is governed by the kinetic energy stored in the generator-prime mover rotating masses and the prime mover frequency primary regulation. If frequency excursions are not within +/−2.5Hz range, cascade tripping of the remaining generators can occur because of generator over/under frequency protections tripping. Energy storage systems can contribute to frequency stability enhancement if their discharging is governed by a frequency controller.Endesa is leading a research project on testing the state of the art of energy storage systems for several applications (peak-shaving, voltage control, frequency control) in several isolated power systems of the Canary Islands. Several applications are being investigated. One of them consists on the application of a 4MW–5s ultracapacitor (UC) for frequency stability enhancement of the La Palma power system.This paper reports the dynamic model developed for time domain simulation and controller design of frequency stability, and field tests undertaken to validate models and the controller settings. A simple but still accurate model is presented. The proposed model takes into account the UC’s state of charge (SoC) and it represents the dynamics of the power electronics by means of a non-linear first-order model. The frequency control consists of droop control and inertia emulation. Ramp rate limits, power limits and SoC are also taken into account in the frequency control. In comparison with the recorded field tests, the proposed model is able to accurately represent the response of the UC for the purpose of frequency stability analysis.

Real power and frequency control of a small isolated power system

This paper describes the dynamic analysis of a small isolated power system comprising a wind turbine generator and a diesel generator. The analysis is carried out in time domain considering simplified models of the system components by taking into account the wind turbine pitch controller and the diesel engine speed governor. Wind disturbance model consisting components of gusting of wind, rapid ramp changes and random noise. The wind generator is always operated with its rated power and the additional power required by the load is supplied by the diesel generator. For better dynamic performances of wind–diesel system under wind and load disturbance conditions, two control schemes are used. In the first case, a proportional–integral (P–I) controller and in the second case a proportional–integral–derivative (P–I–D) controller are used. Gain parameters of these controllers are optimized using genetic algorithm (GA) and Particle swarm optimization (PSO) considering two different objective functions and the results are compared. The sensitivity analysis of the wind diesel system is carried out for parameter uncertainties and the stability of the system is analyzed using D-stability criterion. Analysis is also carried out to examine the effect of power injection to a 69 bus radial distribution network by wind–diesel isolated system.