Small-scale Power System Research Articles

Micro-combustion modelling with RBF-FD: A high-order meshfree method for reactive flows in complex geometries

New micro-devices, such as unmanned aerial vehicles or micro-robots, have increased the demand of a new generation of small-scale combustion power system that go beyond the energy-density limitations of batteries or fuel cells. The characteristics short residence times and intense heat losses reduce the efficiency of combustion-based devices, a key factor that requires of an acute modelling effort to understand the competing physicochemical phenomena that hamper their efficient operation. With this objective in mind, this paper is devoted to the development of a high-order meshfree method to model combustion inside complex geometries using radial basis functions-generated finite differences (RBF-FD) based on polyharmonic splines (PHS) augmented with multivariate polynomials (PHS+poly). In our model, the combustion chamber of a micro-rotary engine is simulated by a system of unsteady reaction-diffusion equations coupled with a steady flow passing a bidimensional stenotic channel of great slenderness. The conversion efficiency is characterized by identifying the different combustion regimes that emerged as a function of the ignition point. We show that PHS+poly based RBF-FD is able to achieve high-order algebraic convergence on scattered node distributions, enabling for node refinement in key regions of the fluid domain. This feature makes it specially well adapted to integrate problems in irregular geometries with front-like solutions, such as reactive fronts or shock waves. Several numerical tests are carried out to demonstrate the accuracy and effectiveness of our approach.

Rancang Bangun Modul Pembangkit Listrik Tenaga Surya (PLTS) Sistem Off-grid Sebagai Alat Penunjang Praktikum Di Laboratorium

This study aims to design and manufacture a practical module for a small-scale off-grid solar power system with a power capacity of 320Wp. This module consists of the main components of an off-grid type solar power system such as solar panels, Solar Charger Controller (SCC), batteries, inverters, ac/dc loads and power meter measuring instruments integrated in one module. The method used is laboratory research methods and literature study. The literature study method is to look for literature related to solar power plant as a support in making modules and laboratory methods, namely testing modules/ systems with certain conditions. Stages This research method includes identification of problems in the laboratory, literature study, design/layout of the PLTS module, determining the type and analysis of the capacity of solar panels, SCC, inverters and batteries, supplying materials/components, manufacturing modules, and testing modules in the laboratory. The output and benefits of this research are getting a practical module for the solar power plant system which makes it easier for students to understand the working principles of the PLTS system; also to optimize practicum activities in the laboratory. From the results of testing, measurement, and data analysis that have been carried out by the off-grid solar power plant (PLTS) module that has been made to function properly and works in accordance with the principle of the off-grid PLTS system, generating electricity according to the capacity of the solar panel, The solar charge controller works in accordance with its function to regulate charge and discharge of battery storage and the inverter is able to serve the load according to its capacity so that this module is ready to be used as a practical module in learning activities in the laboratory.

The stability control for isolated wind‐diesel power system based on the cross coupling effect model

In the isolated wind-diesel hybrid power system, the system voltage and frequency may be affected simultaneously by the fluctuated wind turbine output power and variable load, which can make the system crash in extreme cases without control strategy. Therefore, in order to reduce the voltage and frequency deviation caused by system power fluctuation, both the battery and super twisting algorithm sliding mode state observer (STATCOM) are equipped to adjust the active power and reactive power for load power demand in the isolated small-scale power system. Then, the system mathematical model is established which considers the cross-coupling effect exist in the small-scale power system. In order to improve the control effect of battery and STATCOM, the unified control strategy is designed for battery and STATCOM by using the super twisting sliding mode state observer and the adaptive sliding mode controller according to the constructed cross-coupling effect model. Furthermore, the parameters of controller are further optimized by using the fuzzy method. Finally, the simulation experiments are performed by the real-time digital simulator to validate the effectiveness of the proposed control strategy under different operation points.

Energy management of community energy storage in grid-connected microgrid under uncertain real-time prices

Although several energy management schemes are developed in the literature, they are not thoroughly examined in order to reduce the impact of uncertain power generation, demand and electricity prices to minimise the operating cost of a small-scale power system. This paper investigates energy management schemes under uncertain environments and proposes a scheduling scheme to minimise the operating cost of a grid-connected microgrid. Optimisation problems are formulated as real-time scheduling approaches, and are solved by developing modified particle swarm optimisation (MPSO) algorithms. The modification in the MPSO algorithm is performed through structural change in incorporating a mechanism that regulates the selection procedure for decision variables. The effectiveness of the proposed algorithm is justified by comparing the results with other recent algorithms. All the algorithms are separately tuned using the Taguchi technique to demonstrate a fair comparison in solving the scheduling problem. The scheduling program demonstrates superior performance in all cases, including when there is uncertainty in prediction, as compared to other energy management approaches, although solutions have significant deviations due to prediction errors. It is also shown that the proposed MPSO algorithm for the scheduling program can save 16.80 per cent operational cost as compared to the PSO algorithm.

Cooperative Frequency Control of a Small-Scale Power System between Diesel Engine Driven Adjustable Speed Generator and Battery

This paper proposes the application of an adjustable speed diesel engine-driven power plant employing a doubly-fed induction generator to an isolated small-scale power system including renewable power sources. This type of power plant can contribute to fast and flexible power balancing regulation under vacillating power supply such as wind, solar and other renewable power sources. Installation of a battery system is also considered, which can assist in coordinating the power plant to augment renewable power sources in the isolated power system.

Proposed energy management for a decentralized DC-microgrid based PV-WT-HESS for an isolated community

Microgrids are small-scale power systems destined to supply isolated villages and optimum utilization of renewable energies. For this reason, this paper presents a DC-MG of 150 Kwp to feed an island village. The configuration of the proposed system consists of four interconnected sub-sections supplied by the centralized unit through PV and Wind Distributed Energy Resources DERs, in addition to the supercapacitor storage device. In the other hand, internal batteries of each sub-section cover its load demand separately, where electrical and chemical storage devices can be advantageous hybrid energy storage system HESS for the system. Thus, the control structure of the DC-MG is based on current hysteresis method to assure the charge/discharge operation and the stability of the DC-bus voltage, then a proposed management strategy to manage the shared energy of the DCMG system. The system behavior is tested under variable parameters and conditions using Matlab/Simulink.

Game-theoretic robust optimization for a small-scale integrated power system

The dispatch of an integrated power system involves how to balance the interests of all participants and alleviate the negative effects of uncertainties. In this paper, a game-theoretic robust optimization approach for a small-scale integrated power system is proposed. This optimization approach consists of two stages, i.e. the day ahead dispatch stage and the realtime feedback correction stage. In the day ahead dispatch stage, a game theory based optimal algorithm is established to address the issue that participants in the power system have distinct objectives and their interests are in conflict. Using the gaming results of the day ahead dispatch, a realtime feedback correction algorithm is implemented to enhance the robustness of the power system against the uncertainties of renewable energy resources (RERs) and loads. It is shown that with the communication between the power plant, microgrids and independent end users, the Nash equilibrium can be reached after several iterations and the scheduling plan of each participant is obtained. Meanwhile, with the error prediction over a certain period prescribed in the future, the negative effects of uncertainties are extensively reduced. A small-scale power system is used as a case to illustrate the effectiveness of the proposed optimization approach.

Field Test of Wind Power Output Fluctuation Control Using an Energy Storage System on Jeju Island

At present, renewable energy installations are expanding to solve both environmental problems and expensive energy fuel import prices in isolated areas. However, in a small-scale power system, rapid output fluctuations of renewable energy may cause power quality problems such as voltage and frequency fluctuations in the power system. To solve this problem, the local government of Jeju Island in South Korea implemented a megawatt (MW)-class pilot project to stabilize the output power of wind turbines using an energy storage system (ESS). In this project, a 0.5 MWh lithium-ion battery was connected to a 3 MW wind turbine via 1 MW power conversion system (PCS). In this paper, the field test results were divided into four categories as follows. First, the performance of stabilizing the output of the wind turbine using ESS was confirmed. Second, the control performance of the ESS was confirmed when the wind turbine suddenly stopped due to an accident. Third, it was confirmed that the ESS discharged energy into the power system after the stabilization of the wind turbine output. Fourth, the reasons for the failure of the ESS to control output stabilization of the wind turbine were analyzed through MATLAB simulation.

Research on Economic Evaluation Methods of Offshore Oil Multi-Platform Interconnected Power System Considering Petroleum Production Characteristics

Offshore oil multi-platform interconnected power system is developing rapidly. The proposal of an effective economic evaluation method that fits the actual production situation of offshore oilfields is very meaningful for the planning and construction of multi-platform interconnected power systems. This article proposes the electric depreciation, depletion, and amortization (DD&A) barrel oil cost S and maximum expected benefit per unit power generation Ie as economic indicators, considering the actual production characteristics and life cycle of the oil field. In order to build a complete economic evaluation system, this article also introduces the N−1 pass rate ηN−1, voltage qualification rate γ, power supply reliability ASAI (Average Service Availability Index), and other reliability indicators to evaluate the offshore power system. When calculating the weight of the indicators, analytic hierarchy method (AHP) was applied to calculate subjective weights, and an entropy method was applied to calculate objective weights. To unify the two weights, the ideal point method is proposed to obtain compound weights. Finally, this article selects an offshore oil field in Bohai Bay, China as example, and analyses short-term small-scale, long-term large-scale, and actual power system as calculation examples in different planning periods. The analysis result verifies the effectiveness of the economic evaluation method.

Experimental investigation of a novel micro gas turbine with flexible switching function for distributed power system

Micro gas turbine (MGT) is widely used in small-scale distributed power systems because of its low emissions and fuel flexibility. However, the under-utilization of its exhaust heat and the low electric efficiency are the main bottlenecks that restrict its application. Additionally, the flexible switching between the power generated by the MGT and the power grid is also a key factor for keeping the secure operation of a distributed power station. Therefore, this paper conducted some experimental investigations of a 30 kW MGT to provide reference solutions for the above issues. This MGT is located at Shanghai Jiao Tong University (SJTU), which is designed by the Gas Turbine Research Institute of SJTU, and is manufactured by a turbo-machinery factory in Chongqing, China. The demonstration prototype is mainly composed of a single stage centrifugal compressor, a radial turbine, a combustor, a high-speed permanent magnet generator, and a control system. The results show that the MGT can achieve steady operation at a low rotational speed from 10000 r/min to 34000 r/min in the case of using oil lubricated bearings, which can greatly reduce the economic cost compared with the use of air bearings. At the same time, the ignition success rate of combustion chamber (CC) reaches 98% at a low rotational speed, and a wide range of stable combustion area can be obtained, because of the novel design method of combustor by referencing the way applied in an axial flow aero-engine. The MGT generating set can achieve functions, such as starting up, ignition, stable operation, loaded operation, grid-connection and stopping. This system also can realize flexibly switching from the start motor mode to the generator mode, and from grid-connected mode to off-grid mode, because the innovative multi-state switching control system is adopted. The above research work can make our state master independent intellectual property rights of micro gas turbine, rather than continue to be subject to the technological monopoly of the developed states, which can provide theoretical and experimental support for the industrialization of MGT in China.

Accelerated Distributed Hybrid Stochastic/Robust Energy Management of Smart Grids

The uncertainties of renewable energy, loads, and electricity prices pose significant challenges to the economical and secure energy management of smart grids. In this article, a hybrid stochastic/robust (HSR) optimization method is developed to minimize the overall cost of all units. The proposed approach takes advantage of stochastic programming, robust optimization, and distributed optimization methods while considering various system constraints. First, stochastic electricity price scenarios are selected by the Latin hypercube sampling method. Second, the uncertainties of renewable energy generation and loads are managed by the proposed robust optimization method under each price scenario. Then, an improved distributed optimization method is proposed to solve the formulated HSR optimization problem, which considerably enhances the convergence with the accelerated gradient method. Numerical case studies of both small-scale and large-scale power systems demonstrate the accuracy, effectiveness, and scalability of the proposed distributed HSR approach. Additionally, the optimality and convergence of this proposed distributed algorithm are mathematically proven and analyzed.

An approach of controlling the inverter-based generator for use in an islanded microgrid

The controls of power generation by the inverter-based generator are proposed in this work. The proposed control adjusts the active power output by varying the phase angle instead of the conventional frequency variation. The benefit of operating the network by a fixed frequency is that it eradicates the problems associated with the frequency deviation. The PID controls with recommended gain adjustment are proposed to control the power generation. The power generation schemes are adapted from the classical power generation by the synchronous generator, where the modes of operation are Swing, PV and PQ mode. The proposed three modes of operation are adequate to operate fully in a small-scale power system such as in an islanded microgrid. A case study of operating the proposed controls in a microgrid by simulation is used to demonstrate the feasibility of implementation of the controls.

Development of a hardware-in-the-loop simulator for small-scale concentrated solar combined heat and power system

• A HiL framework of a novel integrated solar mCHP plant is developed. • The HiL simulator is designed in Matlab/Simulink and coupled with the real controller of the plant. • The HiL simulator is used for control algorithms optimization and control strategy definition. • Optimal proportional and integral gains of the PI-based control are assessed for all the diverters. • The best control strategy to assure constant inlet temperature at the ORC consists in acting on the aperture of a diverter. In this work a hardware-in-the-loop (HiL) simulator of a novel micro combined heat and power system is presented and its use for control algorithm optimization is demonstrated and discussed. The plant under investigation consists of a concentrated Linear Fresnel Reflectors solar field, a 2 kWe/18 kWt Organic Rankine Cycle unit and an advanced latent heat thermal energy storage tank equipped with reversible heat pipes as developed by a consortium of universities and companies within the EU funded project Innova Microsolar. A smart control unit manages their integration and monitors the operation of each subsystem. In order to support the optimization of the control algorithms and the definition of the best control strategy of the micro-CHP plant at different working conditions, a simulation framework based on Matlab/Simulink has been developed by the authors and connected to the real control unit according to a HiL approach. Ad-hoc models of the different subsystems together with those of the components (i.e. valves and variable speed pumps) regulating the plant operation have been included. The use of the HiL simulator has permitted to optimize the control logic of the integrated plant prior to its future commissioning, thus helping to overcome some of the technical and reliability issues occurring during the setup of the real system. In particular, the HiL has allowed: (i) to define the proportional and integral gains of the diverters in order to assure a robust and fast response of the plant during the switch among the different operation modes; (ii) to prove the limits of acting on the oil pump flow rate in assuring the nominal oil temperature at the inlet of the ORC unit, due to the inherent fluctuations caused by this control strategy; and (iii) to assess the best control strategy which is obtained by acting on the aperture of the diverter which controls the oil mass flow rate to the ORC unit. Hence, the scientific approach here proposed can be extended also to many other complex energy conversion systems in order to significantly reduce the potential critical issues during their commissioning.

Characteristics of a Sinusoidally-Distributed Cylindrical-Rotor Self-Excited Single-Phase Synchronous Generator

The small-scale power systems favor the installation of self-excited synchronous generators due to their simple construction. Many configurations were reported in the literature but there have been always two issues: voltage regulation (VR) and total harmonic distortion (THD) of the output voltage. This paper presents an experimental investigation to improve the performance of single-phase, self-excited, synchronous generator (SPSESG) in terms of the VR and THD. The applied modification is the implementation of sinusoidally-distributed stator windings which implies a different number of turns in each slot. A typical lab single-phase synchronous machine was rewound with the proper number of turns in each slot and then tested against resistive, resistive-inductive, resistive-capacitive, and dynamic loads (induction motor). The experimental results proved that the modified generator performance has significantly improved in terms of the VR and THD. The worst VR was recorded in the case of dynamic load and it was 6.5 %. While the highest THD was 4.5 %, at no load. These figures are much better than other configurations reported in the literature.

Economic Power Dispatch using Hybrid Particle Swarm Optimization with Simplex Search Method

This paper presents the solution of economic power dispatch (EPD) in thermal power plants using the hybridization of particle swarm optimization (PSO) and simplex search method (SSM). EPD is obtaining the best generating schedule to supply the power demand and covering the transmission losses with minimum overall fuel cost. Physical constraints like valve point loading effects, ramp rate limits and prohibited operating zones are also included with basic EPD problem to increase the practicability in the problem. As PSO performs well in finding the global best solution and SSM in finding the local best solution, thus their combination improves the overall minimum results obtained for the generation fuel cost objective function. The performance of the proposed methodology is tested on different test systems having categories of small-scale, medium-scale and large-scale power system problems. The results obtained are then compared with other reported methods to show the superiority of the proposed algorithm.

A New Bat Optimization Algorithm to Solve EPD Problem Solving with Transmission Loss

The economic power dispatch (EPD) is an integral part of the power system, and the major roles and purpose of its use are for achieving a reliable and efficient operation out of power system generation networks, and this operation should be obtained by minimizing the generator fuel cost. Getting optimal solutions to EPD problem requires efficient optimization algorithms. Novel Bat Algorithm (NBA) is one of the most recent methods and it has already proven its efficiency and reliability for solving the EPD problem. This paper proposes Novel Bat Algorithm (NBA) in order to solve the EPD problem based on the large scale power system. The NBA has proved its efficiency and it gave a perfect performance for small-scale systems compared with the original Bat algorithm (BA), because of considering the Doppler Effect and assumed that bat can move between various habitats. The study of the EPD for large-scale power systems is more important than study it for small ones, because all power systems in countries are considered large networks. This is why all modern studies focus on the study of EPD for large systems. To test the performance of NBA during small and large scale power system, we have applied it to many systems, including 3-thermal units, 6-thermal units, 31-Iraqi thermal units and IEEE 40-thermal units respectively, with transmission losses and generator limits, and we have made a comparison of the obtained results of NBA with other optimization methods. The Iraqi thermal units have been utilized as a new data.

Techno-economic evaluation and technology roadmap of the MWe-scale SOFC-PEMFC hybrid fuel cell system for clean power generation

This paper proposes a novel hybrid fuel cell power generation system with high efficiency. The thermo-economic modeling of the MWe-scale systems using different fuels is conducted to evaluate the economic feasibility under the subsidy policy of Eastern China. This work aims to develop the technology roadmap for this kind of clean power system. It is found that the energy efficiency of the natural gas and biogas fed systems could reach up to 64% and 63.5% respectively, thus they are efficient and cost-optimal for the hybrid system while liquefied petroleum gas and water gas yield low efficiency and high electricity cost. Moreover, under the subsidy policy, the biogas-fed hybrid system is more suitable for a small-scale power system, while the natural gas-fed system is preferable for the large-scale case. The specific electricity cost of small-scale biogas hybrid fuel cell power plant is 0.365 CNY/kWh, lower than the present feed-in-tariff price 0.475–0.704 CNY/kWh of other biogas plants in China. Also, the cost of 0.345–0.347 CNY/kWh of large-scale natural gas-fed hybrid system is much lower than the on-grid electricity price 0.7655 CNY/kWh in Shanghai. These results reveal that the proposed hybrid fuel cell power system is efficient and economically feasible. The payback period and annual return on investment are 0.8–1.2 year and 11–12%, respectively.

Power Quality in Microgrids Including Supraharmonics: Issues, Standards, and Mitigations

A microgrid (MG) is a small-scale power system with a cluster of loads and distributed generators operating together through energy management software and devices that act as a single controllable entity with respect to the grid. MG has become a key research element in smart grid and distribution power systems. MG mainly contains different renewable energy sources (RESs) that use various technological advancements, such as power electronics-based technologies. However, it has an unstable output, thereby causing different types of power quality (PQ) events. As a result, standards and mitigation methods have been developed in recent years. To mitigate PQ issues due to MG integration, various methods and standards have been proposed over the last years. Although these individual methods are well documented, a comparative overview had not been introduced so far. Thus, this study aims to fill the gap by reviewing and comparing the prior-art PQ issues, solutions, and standards in MGs. We compare the main issues related to voltage sag, voltage swell, voltage and current harmonics, system unbalances, and fluctuations to ensure high-quality MG output power. The new technologies associated with MGs generate harmonics emission in the range of 2–150 kHz, thereby causing a new phenomenon, namely, supraharmonics (SH) emission, which is not sufficiently covered in the literature. Therefore, the characteristics, causes, consequences, and measurements of SH are highlighted and analyzed. The mitigation strategies, control, and devices of PQ issues are also discussed. Moreover, a comparison is conducted between the most popular devices used to mitigate the PQ issues in MG in terms of cost, rating, and different aspects of performance. This review study can strengthen the efforts toward the mitigation and standards development of PQ issues in MG applications, especially SH. Finally, some recommendations and suggestions to improve PQ of MG, including SH, are highlighted.

Accurate Study and Evaluation of Small PV Power Generation System Based on Specific Geographical Location

As an important new energy, solar energy has been extensively used in the world and different types of solar energy systems have been used in different fields. The photovoltaic power generation system has obvious advantage and high stability compared with other energy systems. Furthermore, the small-scale photovoltaic power generation system has a wider application in the field of power generation due to the performance of high efficiency. In this paper, the optimization research and system evaluation of small-scale photovoltaic power system have been studied in different areas by simulation and experimental methods. Based on the determination of photovoltaic model system, four typical geographical locations are selected and PVsyst is applied to the simulation study. The annual power output is 4829 kWh, 3489 kWh, 4455 kWh, 2766 kWh and the solar energy utilization efficiency is 14.91%, 14.79%, 17.66%, 15.77% for Mexico City, Xinyang, Changchun and London respectively from the simulation results. The results show that the radiation conditions, the optimum tilt angle, the minimum spacing and different geographical locations are the main reasons for the difference of power generation and solar energy utilization efficiency. Subsequently, Changchun is selected as the experimental area to carry out experimental research and verify the conclusion of the simulation study. The volt ampere characteristic curve and power output curve show that the photovoltaic system has no defects, hot spots, partial shading and damage. The annual total power generation of Changchun is 4119 kWh. Hence, the simulation results are in good agreement with the experimental results. Consequently, the application of small photovoltaic power generation system requires to fully consider the regional conditions and key parameters (optimum tilt angle, minimum spacing, etc.) to obtain better power generation efficiency.

Optimal Reactive Power Dispatch Using Chaotic Bat Algorithm

In this paper, the chaotic bat algorithm (CBA) is applied to solve the optimal reactive power dispatch (ORPD) problem taking into account small-scale, medium-scale and large-scale power systems. ORPD plays a key role in the power system operation and control. The ORPD problem is formulated as a mixed integer nonlinear programming problem, comprising both continuous and discrete control variables. The most outstanding benefit of the bat algorithm (BA) is its good convergence for optimal solutions. The BA, however, together with other metaheuristics, often gets stuck into local optima and in order to cope with this shortcoming, the use of the CBA is proposed in this paper. The CBA results from introducing the chaotic sequences into the standard BA to enhance its global search ability. The CBA is utilized to find the optimal settings of generator bus voltages, tap setting transformers and shunt reactive power sources. Three objective functions such as minimization of active power loss, total voltage deviations and voltage stability index are considered in this study. The effectiveness of the CBA technique is demonstrated for standard IEEE 14-bus, IEEE 39 New England bus, IEEE 57-bus, IEEE 118-bus and IEEE 300-bus test systems. The results yielded by the CBA are compared with other algorithms available in the literature. Simulation results reveal the effectiveness and robustness of the CBA for solving the ORPD problem.