Isolated Power System Research Articles

Application of electromagnetic continuous variable transmission in hydraulic turbines to increase stability of an off-grid power system

In the context of climate change, today's adoption of renewable energy sources in isolated power systems is becoming an increasingly more significant issue. Micro-hydro power plants are emerging as a mature balancing technology and a great alternative to large hydropower plants as they do not encounter population displacement and many environmental problems. It is worth noting that hydroelectric power plants combined with various sources require improvement in control laws and algorithms. Strong disturbing impacts, namely transient processes, in an isolated electric power system cause an appreciable decrease in dynamic stability. This paper presents research conducted to ensure synchronous parallel operation of permanent-magnet generators used in micro-hydroelectric power plants in an isolated power system with a controllable flexible coupling between turbine and generator. The importance of this study lies in the issue of electromechanical compatibility to be achieved in parallel operation of generators that have different parameters of time constant of mechanical inertia of rotors of electrical machines. This paper provides an overview of possible solutions to the identified problem. A concept based on a controllable flexible coupling between generator and turbine is proposed as a promising avenue to solve this problem. The mathematical models are presented along with the laws and algorithms developed for automatic control of the generator speed. Oscillograms of simulation and physical modeling presented in the final part of the paper show parallel operation of permanent-magnet synchronous generators in an isolated electric power system for various electrical distances of three-phase short circuit points.

Development of Medium-Term Water Inflow Forecasting Models for Planning Electricity Generation in Isolated Power Systems

Reliable operation of power systems with a significant share of hydropower plants (HPPs) in the energy mix depends in many respects on how accurately the water inflow is forecasted. Taken together, the water inflow prediction and optimal planning of production define energy security, ensure the possibility of protection from floods, and eliminate idle discharges at hydroelectric power plants. The solution of such problems is complicated by lack of reliable information about the water inflow, its being stochastic in nature, a variable electricity consumption pattern, and inaccurate prediction and planning models. Improvement of prediction accuracy is focused on determining the water inventory for planning prospective electricity generation at HPPs taking into account regulation in the medium term. Such regulation is necessary to meet the power system load in the load curve peak and semi-peak parts. The paper considers the problem of constructing a medium-term water inflow prediction model for planning electricity generation for a week ahead taking into account climate changes in isolated operating power systems taking as an example the electric power systems of the Gorno-Badakhshan autonomous oblast in Tajikistan. For taking into account constant climate changes, it is proposed to use an approach based on machine learning methods, which features a self-adaptation capability. Based on the results of accomplished experimental and industry-grade numerical analyses, the expediency of using a model based on an ensemble of regression decision trees has been shown.

Laboratory model of the Savonius rotor

THE PURPOSE. Increasing the efficiency and efficiency of power plants based on renewable energy sources should be carried out by improving technological, constructive, organizational, legal, technical and economic measures. Proposals are given for the development of approaches to assessing the efficiency of wind power plants based on the Savonius rotor. The design parameters are substantiated and a physical model is created for a comprehensive study and performance characteristics in laboratory conditions.METHODS. Based on the methods of physical and mathematical modeling of structures and profiles of wind turbine blades, the technical and economic indicators of various profiles of the blades of the Savonius rotor are determined.RESULTS. The theoretical substantiation of the design and various profiles of the blades of the Savonius rotor is carried out. On the basis of a comprehensive study of performance characteristics in laboratory conditions, the values of the wind energy efficiency coefficient, the rotation frequency of the wind wheel profile, and electric power were established.CONCLUSION. The results of the study can be applied to substantiate the widespread use and creation of wind power plants with a Savonius rotor to ensure high-quality and reliable power supply to remote consumers of electric energy, the creation of isolated power systems and the further development of alternative energy sources in the domestic electric power industry

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.

A Comprehensive Study of HVDC Link with Reserve Operation Control in a Multi-Infeed Direct Current Power System

The Korean government is targeting the development of a renewable energy penetration of 30–35% by 2040 of the total generation. These conditions will decrease network stability due to a lack of inertia, especially in isolated systems, such as Jeju Island. HVDC systems with several balancing arrangements of reserve operation are used to maintain variability and uncontrollability of RES penetration. This paper presents the fast frequency reserves of HVDC control systems for frequency stability enhancement in the isolated power system by using a combined frequency containment process with grid stability standards. A new MIDC reserve operation control with angle and voltage deviation at the bus converter was developed to provide a faster and more appropriate balancing arrangement compared to the other concept. In addition, two layers of energy and transfer-capacity flexibility were considered to prevent the need to hunt for that balancing arrangement, as well as low nadir frequency, unavailability of the reserve and other constraints caused by each region having a different network size, HVDC interconnection capacity, and type. The proposed control schemes were verified by simulations on the Korean power system model implemented in PSS/E for different sizes of disturbance.

Use of smart grid based wind resources in isolated power systems

The optimization of both power consumption and balance of Smart Grid is required for online power control considering the use of alternative energy sources. A concept of “generating consumers” has been introduced for active consumers, leading to flexibly regulating the power flows, equalizing the load schedule, and minimizing the financial costs of consumed power. This study aimed to develop a new mathematical model of optimal both power consumption and balance considering the participation of “generating consumer” in the form of wind resources, which presents the intelligent system with a bidirectional power flow. The approach proposes a priority system to choose the optimal generation source, minimizing its material and financial costs based on the particle swarm optimization algorithm and holon concept. A high potential of own wind sources has been examined in a coastal zone of the Far East and on the Russky and Popov Islands. As result, Russky Island doesn't receive any additional income (max −433 EUR) since its power consumption cannot be covered even with bidirectional power flows while the Popov Island gains income (max 468 EUR) due to existing power excess. The efficiency of the developed software has been validated by using the gradient descent algorithm.

Coordinating Energy Resources in an Islanded Microgrid for Economic and Resilient Operation

Microgrids with advanced management and control strengthen power system reliability and resilience. In normal operation, economy and reliability are the objectives. However, for adverse events, economy would not be the top concern and focus moves to resiliency and providing energy to critical loads. The resource dispatch strategy in normal economic mode would not be suitable for resilient mode given adverse events. In this work, an energy resource coordination strategy is proposed for a hydro–diesel-battery islanded microgrid, which improves distribution system resiliency by preevent control and switching to resilient mode from economic mode. Resiliency metric is used to verify and quantify the effectiveness of the selected strategy among available ones. Real-time resiliency management system (RT-RMS), a real time resilience management and visualization tool is developed and the resiliency driven resource coordination is integrated into it. Finally, a 14-nodes isolated power system model and a simplified 55-nodes real-world islanded microgrid model are used for validation and demonstrate the effectiveness of proposed resource coordination method.

Specifics of hydropower plant management in isolated power systems

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Data-driven energy management of isolated power systems under rapidly varying operating conditions

We propose an energy management algorithm for isolated industrial power systems that integrate uncertain renewable generation and energy storage. The proposed strategy is designed to ensure sustainable and cost-effective operations by managing the energy flows in the grid, and is structured so to cope with: (1) high levels of renewable power penetration, and (2) load profiles characterized by non-smooth patterns and irregular events (i.e., events such as those occurring from connections/disconnections of large scale equipment, or from large wind speed ramps). The proposed algorithm leverages a stochastic economic model predictive control (MPC) scheme capable of dealing simultaneously with the dispatch and scheduling of the local generation units. More precisely, the scheme embeds a mixed-integer linear programming (MILP) optimal control policy formulation together with a stochastic programming approach. Moreover, the optimization problem accounts for multiple techno-economical objectives, such as minimization of operational costs, battery degradation, and non-utilized energy. We test the algorithm on a case study of an isolated offshore Oil & Gas platform producing energy onsite with conventional gas turbines and a local wind farm, while integrating a battery energy storage system. The results show that the proposed approach can issue ensemble predictions that successfully capture the potential irregular variations just by using recent past information of the associated random variable, even when no particular sudden events are anticipated in the near-future (i.e., step changes/trend reversals). In this way, the approach provides useful future information for the optimal management of the grid. This effect is numerically quantified via simulations that compare the performance of the proposed stochastic optimization approach against its deterministic MPC version in several realistic operating conditions. The empirical results suggest that the stochastic version leads to better scheduling of the conventional generators, with up to 12.86% reductions of the operating cost, 2.56% reduction in fuel consumption and emissions, and 35.29% reduction in status transitions (on/off) of the gas turbines, while keeping dumped energy and battery degradation as low as possible.

Mathematical simulation of an automatic steam turbine control system

The paper considers the construction of a mathematical model for an electrohydraulic system to control automatically the Т-63-13,0/0,25 product manufactured by JSC Kaluga Turbine Plant. Mathematical simulation of control systems makes it possible to improve considerably the quality of control, that is, the accuracy and reliability of such systems, as well as to accelerate greatly the development and calculation of the control system and the parameters of its individual components. The T-63-13,0/0,25 mathematical model of the ASTCS allows estimating the effects of design parameters during any load dropping (in a range of 0 to 100%) and the quality of control for the monitored parameters both in the process of operation as part of an isolated power system (generator output, frequency) and an integrated power system (generator output). A mathematical representation has been developed in the model for the control units, the T-63-13,0/0,25 product model, and the electronic controlling part of each of the control units. It has been proposed that pulse-width modulation be used to control the synchronous motors which makes it possible to control the synchronous machine shaft speed by changing the supply voltage frequency. To this end, the control system’s model uses a frequency converter which is proposed to be used in the real control system. The developed control system with one adjustable steam extraction in the T-63-13,0/0,25 steam turbine is coupled and autonomous, that is, each of the two meters for the turbine’s controlled parameters has effect on both steam distribution systems such that a deviation for one of the controlled parameters does not lead to excitations in the other.

Fuzzy Logic-Based Load Frequency Control in an Island Hybrid Power System Model Using Artificial Bee Colony Optimization

This study presents the implementation of Artificial Bee Colony (ABC) optimization in an island hybrid power system model using fuzzy logic-based load frequency control. The Island Hybrid Power System considered in this study consisted of various generation units and an energy storage system. The optimized control parameters of PID using ABC were used in an intelligent fuzzy logic controller. The profiles (power & Frequency) of isolated hybrid power system were improved using a Super Conducting Magnetic Energy Storage (SMES) System. Individual controllers were used for wind turbine and diesel generators to control the power output for balancing the demand (frequency change control). Comparative analysis of power and frequency with the help of various classical and intelligent control configurations is presented. The outcome of the study shows that a minimum deviation in frequency and power is obtained through the proposed Intelligent Fuzzy Control approach for the considered isolated power system model.

Frequency control strategy for coordinated energy storage system and flexible load in isolated power system

The isolated power system has a simple structure with small inertia and no support from the large-scale power system, so the frequency stability problem is more prominent. A frequency control method based on coordinated control of flexible loads (FL) and energy storage systems (ESS) is proposed in this paper. The ESS adopts the droop control considering the state of charge (SOC) to quickly respond to the system frequency deviation and provide fast frequency support. Based on the load power–voltage sensitivity, the FL participates in frequency control by adjusting the load voltage and thus the load demand. Based on the two frequency regulation resources, the active–reactive cooperative control strategy is proposed to adopt the fast response characteristics of ESS to cooperate with the synchronous unit to prioritize frequency regulation and enable the FL reactive control strategy when the system disturbance is larger than the primary frequency regulation capacity of the synchronous unit. The effectiveness of the proposed control strategy for isolated power systems is verified by building a modified IEEE33 node islanding system simulation in the real-time digital simulator (RTDS).

Data-informed scenario generation for statistically stable energy storage sizing in isolated power systems

We consider the problem of how to generate uncertainty scenarios to be used in energy storage sizing problems in isolated power systems. More precisely, we consider storage sizing formulations where both loads and generation are stochastic, where no closed form analytical expression is available, and where the presence of multiple discrete random variables makes the sizing problem mixed integer and with combinatorial search spaces. We thus propose and characterize a data-driven scenarios selection strategy that mitigates the computational issues associated with these types of storage sizing problem formulations while guaranteeing statically stable optimal solutions. Specifically, the approach works by first learning the distribution of the uncertainties of the loads and generation starting from field data, and then generating, through the learned distribution, an optimal set of uncertainty scenarios that are subsequently used in a two-stage stochastic programming reformulation of the original sizing problem. The workflow does not impose arbitrary structures to the correlation among the uncertainties, nor does it lump these in a single parameter; thus, it is suitable for systems with any load characteristics. Moreover, the approach ensures to reach a solution that is statistically close to the one that would be computed if the original problem was solvable and not computationally intractable. As a case study, we analyze the problem of designing an energy storage system for a wind powered oil and gas platform to minimize the expected daily system operational costs. Numerical simulations showed that the proposed methodology leads to higher quality solutions compared with other scenario selection strategies. This reveals realistic estimations of the expected benefits, while also highlighting the risk-management limitations, when solving the risk-constrained version of the problem.

Potential of Organic Rankine Cycle for waste heat recovery from piston engine-based power plants in isolated power systems

Waste Heat Recovery with Organic Rankine Cycle (ORC) in piston engine-based power plants placed in isolated systems is addressed in this paper. The power plant subjected to study is located in La Palma, Canary Islands, considered a representative example of small-to-medium isolated power system where the diesel engine is the solely or the main conventional technology for generation. In those systems, the power plant load control to cover the grid demand results in a noticeable variability of the available heat. This challenge is addressed in this paper through a performance and economic evaluation of an intermediate thermal energy storage system. A techno-economic analysis of the proposed power plant is performed taking as input the annual exhaust thermal energy available. The ORC-Diesel unit interaction is studied by means of an in-house developed plant load management model. An annual power plant fuel economy gain and pollutant emission reduction between 5% and 7% is estimated. In addition, the extra power and spinning reserve provided by the ORC allows the power plant to reduce its operational cost through the reduction of the number of diesel units starts. • Waste heat recovery assessment from power plants in isolated power systems. • Efficiency increase and emission abatement due to the additional energy generated. • Additional power and spinning reserve allows diesel units disconnection. • Economically attractive solution, with payback times lower than 5 years.

Hybrid frequency control strategies based on hydro‐power, wind, and energy storage systems: Application to 100% renewable scenarios

Over the last two decades, variable-speed wind turbines (VSWTs) have gradually replaced conventional generation. However, the variable and stochastic nature of wind speed may lead to large frequency deviations, especially in isolated power systems with high wind energy integration, where this integration causes a lack of inertia. This paper proposes a hybrid hydro-wind-flywheel frequency control strategy for isolated power systems with 100% renewable energy generation, considering both variable wind and a generator tripping. VSWTs and flywheels include a conventional inertial frequency control. The frequency control strategy involves VSWTs rotational speed and State of Charge (SOC) of flywheels variations that may affect the wear and tear of mechanical elements and reduce the efficiency of the frequency control action. The hydro-power controller also tracks the VSWTs' rotational speed deviation and the flywheel SOC to modify the generated power accordingly. This hybrid frequency strategy significantly reduces frequency excursions, the rotational speed deviations of VSWTs and the SOC of flywheels. To reduce the hydro-power plants' wear, an additional control strategy is proposed by the authors and evaluated. Results from a case study based on an isolated power system located in El Hierro (Canary Islands, Spain) are included, and extensively discussed in the paper.

Comparison and Influence of Flywheels Energy Storage System Control Schemes in the Frequency Regulation of Isolated Power Systems

Increased renewable energy penetration in isolated power systems has a clear impact on the quality of system frequency. The flywheel energy storage system (FESS) is a mature technology with a fast frequency response, high power density, high round-trip efficiency, low maintenance, no depth of discharge effects, and resilience to withstand continuous charge-discharge cycling without lifetime degradation. These FESS properties allows to effectively address the frequency quality problem. This study analyzes the contribution of a FESS to reducing frequency deviations in an isolated system that combines a diesel plant, wind farm, and pump-storage hydropower plant based on the El Hierro power system. This study approaches this analysis by comparing six different FESS governor control schemes (GCSs). Of these six GCSs, the nonlinear proportional variant (NLP <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\mathrm {V}}$ </tex-math></inline-formula> ) is a singular contribution based on the NLP scheme previously developed by the same researchers. Different governor’s parameter settings for the FESS GCSs were also compared, obtained from the proposed tuning methodology that considers the renewable energy generation distribution, frequency impact, and lifetime degradation of diesel, hydraulic groups, and flywheels. The GCSs were compared in terms of average frequency deviation, Zenith and Nadir frequency difference, wear and tear of diesel electromechanical elements and Pelton turbine nozzles, flywheels cycles per hour, and FESS average state of charge. The results show that including a FESS plant considerably improves frequency regulation. The tuning criteria and GCSs have a clear influence on the results, with NLP and NLP <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</sub> GCSs offering relevant improvements in frequency deviations.

Оперативное прогнозирование потребления мощности в изолированных энергосистемах

Ensuring stable power supply and proper electric power quality while continuously managing the production, transmission and distribution of electricity is the main goal of the dispatch center of any power system, including an isolated one. Continuous management is based on an electric power regime planning process. According to its results, the dispatch center sends to the electric power industry entity the planned dispatch schedule of the power generation, transmission and consumption in an hourly (half-hour) breakdown, which has to be received by the managed entity 8–10 hours before the onset of the planned day. In the operational management of the electric power regime, the dispatch center operators on duty adjust (update) the values of the planned dispatch schedule. Active power consumption in the power system is one of the most significant parameters being updated. The possibilities of improving the accuracy of operationally forecasting active power in isolated power systems are investigated taking the Kaliningrad power system as an example. The existing power consumption forecasting methods are analyzed. The influence of power plant auxiliaries on the total active power consumption in the power system is studied. Methodological principles for operational forecasting of power consumption have been developed and proposed, which are recommended for inclusion in regulatory documents as a methodology. The proposed methodology is based on a mathematical model that takes into account the consumed power variation rate on a typical day, forecasted meteorological data and the dependence of power consumption for power plant auxiliaries on the composition of the generating equipment switched in operation.

Impact of Energy Policies on the Transition to Zero-Emission Mobility in Isolated Power Systems: Tenerife Island Test Case

Impact of Energy Policies on the Transition to Zero-Emission Mobility in Isolated Power Systems: Tenerife Island Test Case

Reduction of operational restrictions of the transmission system in electrical systems through facts implementation

Operational constraints cause an increase in complexity, operating cost, and environmental and socioeconomic impact on electrical systems; operational constraints can be due to power flow, voltage, or frequency deviations. These restrictions force the grid operator to perform unplanned actions. This article identifies the various Alternating Current Flexible Transmission Systems (FACTS) devices with their characteristics, attributes, and implementation methods to lessen operating constraints on isolated and relatively small transmission systems with frequent power flow limit violations and voltage deviations. The case study is carried out in the National Interconnected Electric System (SENI) of the Dominican Republic, where the Fast Stability Voltage Index is used as an indicator to see the impact of the implementation of FACT to mitigate the operational restrictions of the electric system. Simulations are performed in the PowerFactory DIgSILENT software to obtain the results when modeling the interconnected FACTS devices on the transmission lines. The use of FACTS reduces the loadability of transmission lines, which is an essential factor in the emergence of power flow control and voltage constraints in isolated power systems.

A Market Assessment of Distributed Battery Energy Storage to Facilitate Higher Renewable Penetration in an Isolated Power System

Power systems with a high share of renewables require additional ancillary services to operate safely and reliably. System operators are introducing schemes to attract investment in technology which will provide ancillary services. Battery storage can provide some of these services but investment in equipment is required. This study investigates the potential benefits of energy storage and tests the market arrangements to attract investment. The study uses a combination of numerical and system analyses to test the financial performance. A dynamic economic dispatch model was used to evaluate the system costs and emission levels. A unit commitment model was used to measure the reserve cost. Both models use real-time load data for a region in the Irish electricity market. The ancillary service revenue is modelled based on actual renewable levels for the Irish system. The frequency and rate of change of frequency response are evaluated by introducing a disturbance to the system model with and without energy storage. The results were used to test investment opportunities using established financial appraisal techniques.