Distributed Power Generation Research Articles

High-efficiency ammonia-fed solid oxide fuel cell systems for distributed power generation

Ammonia can be considered as an alternative fuel for solid oxide fuel cells (SOFCs) because it is carbon-free, it can be easily stored, and it has a high volumetric energy density. Several large-scale ammonia-fed SOFC systems have been investigated. However, small-scale systems that are applicable for distributed power generation have not been extensively studied. Therefore, we propose three small-scale ammonia-fed SOFC systems, and compare the performance of these systems with that of a standalone SOFC system. The first system is an internal combustion engine combined with an SOFC, which is termed as a SOFC-engine hybrid system. It has a simple construction and it recovers energy from anode off-gas. In the case of the second system, the water was removed from the anode off-gas to enhance the hydrogen molar fraction before supplying it to the stack. In the third system, an internal combustion engine was integrated with a recirculation SOFC system as a combination of the two above systems. An SOFC system was modeled and validated with experimental data. It was observed that the engine enhances the system efficiency by 6.2% point compared with that of the standalone SOFC system. The recirculation using a water condensation system resulted in an increase in the system efficiency to 67.4% owing to the recirculation of rich-hydrogen gas. The SOFC-engine recirculation system exhibits a higher efficiency than that of the second system. However, the maximum efficiency was 67.5%, which is slightly higher than that of the recirculation system. The obtained results proofed that NH3-fed SOFC is totally difference with others and these finding can be effectively used in further developing ammonia-fueled SOFC system.

Model Investigation of Natural Gas Engine Performance to Achieve Variable Heat/Electricity Ratios for a CCHP System by Varying Spark Ignition Timings

For electric reliability and to save energy, the distributed power generation combining cooling and heating supply called a CCHP system for architectures has many potential advantages and is widely adopted to provide electric power and to satisfy local heating and cooling loads by waste heat recovery with low carbon intensity. However, the current CCHP system usually has a fixed ratio of the power and heat due to the features of its power unit, which leads to difficulties in the load management. In this paper, based on the operation of an internal combustion engine fueled with natural gas, a novel method is proposed and studied to achieve a controllable rate of heat/power to meet different load requirements of the electricity and heat (cooling or heating loads). By varying the ignition timing of the spark ignition engine, the combustion process within the cylinder can be adjusted to occur at different crank angles so that the engine crank shaft output power (related to the generated electricity) and the heat from the exhaust gas are changed accordingly. To study the effects of ignition timing on engine power and exhaust heat energy, a two-zone model was established with a predictive combustion model. The changes in the combustion process, output power, exhaust gas temperature, and heat energy were mostly our concern. The results show that the heat/electricity ratio can be adjusted from normally 1.0 to 1.6, and they can be controlled independently under partial load operating conditions. To solve the potential thermal failure of the turbine, the extraordinarily high exhaust temperature will be adjusted by compressed air.

Research on AC/DC hybrid power supply system for easy access of distributed generation

With the development of social economy and the continuous expansion of power system construction scale, the social demand for electricity is increasing day by day. However non renewable energy is very limited, and the current energy utilization mode alone can not meet the power demand of the country's huge power consumption system. Therefore, we must be based on the current energy utilization structure and make effort to improve the utilization efficiency of renewable energy, so as to alleviate the problem of energy shortage in China. In this paper, an AC / DC hybrid power supply system is proposed, which provides an intelligent power supply platform for distributed power generation. It can be compatible with the existing low-voltage power supply system, making full use of the advantages of distributed power generation, meeting the plug and play and local consumption of electric energy. Through the local conversion of DC-DC, the system reduces the process of DC-AC-DC conversion and reduces energy consumption fundamentally. In the output control strategy, the equal current circulation suppression strategy is used to fundamentally eliminate the danger of circulation and optimize the system efficiency. Simulation experiments verify the effectiveness of the method proposed in this paper.

Reliability Analysis of MV Electric Distribution Networks Including Distributed Generation and ICT Infrastructure

In recent years, the increased distributed generation (DG) capacity in electric distribution systems has been observed. Therefore, it is necessary to research existing structures of distribution networks as well as to develop new (future) system structures. There are many works on the reliability of distribution systems with installed DG sources. This paper deals with a reliability analysis for both present and future medium voltage (MV) electric distribution system structures. The impact of DG technology used and energy source location on the power supply reliability has been analyzed. The reliability models of electrical power devices, conventional and renewable energy sources as well as information and communications technology (ICT) components have been proposed. Main contribution of this paper are the results of performed calculations, which have been analyzed for specific system structures (two typical present network structures and two future network structures), using detailed information on DG types, their locations and power capacities, as well as distribution system automation applied (automatic stand-by switching on—ASS and automatic power restoration—APR). The reliability of the smart grid consisting of the distribution network and the coupled communications network was simulated and assessed. The observations and conclusions based on calculation results have been made. More detailed modeling and consideration of system automation of distribution grids with DG units coupled with the communication systems allows the design and application of more reliable MV network structures.

Distributed carbon-aware energy trading of virtual power plant under denial of service attacks: A passivity-based neurodynamic approach

With the popularity of distributed power generation units, traditional consumers become prosumers. Meanwhile, the emerging information and communication technology brings new opportunities to the energy trading service by providing various platforms. Thus, the energy trading problem of prosumers quickly ascends to the spotlight. Nevertheless, the personalized small-scale prosumers bring challenges of coordinated operation, supply-demand balance and carbon emission control. In this paper, based on an edge-cloud platform, a distributed carbon-aware energy trading mechanism is proposed for coordinating the prosumers within the virtual power plant. Moreover, the personalized characteristics including generation cost and the carbon emissions are handled without revealing the private information under the distributed formulation. In this way, the coordination effects of the prosumers are fully explored, and a multi-agent network is employed to achieve the supply-demand balance and the carbon emission awareness. Moreover, to deal with the denial of service attacks in the cyber layer, a passivity-based neurodynamic approach is proposed, which is resilient to denial of service attacks. A set of realistic case studies on energy trading problem under denial of service attacks are given, demonstrating the effectiveness of the proposed mechanism in coordinated operation, supply-demand balancing and carbon-awareness under denial of service attacks.

A robust controller design procedure for LCL‐type grid‐tied proton exchange membrane fuel cell system in harmonics‐polluted network

AbstractProton exchange membrane fuel cell (PEMFC), due to its high efficiency and good stability, is one of the most efficient and effective sources of alternative renewable energy. The LCL filters are utilized to attenuate the harmonics caused by inverter‐based distributed power generation systems (DPGS). In this paper, a systematic robust control design is presented for an LCL‐type grid‐tied PEMFC inverter. The proposed nested control includes the capacitor current feedback and the outer grid current loops, considering the computational delays. The proposed control results in more accurate and realistic modeling to transfer the power of PEMFC and inject a high‐quality current into a weak and harmonics‐polluted network. Also, by utilizing the proposed method, the computational delays that affect the damping capability are eliminated, and the performance of the control system is improved. In addition, designing a virtual series and parallel impedances strengthens the phase and amplitude of the inverter output impedance. As a result, the robust operation of the inverter for significant changes in network impedance is improved, and the system well attenuates the mains voltage harmonics. The simulation results in Matlab/Simulink environment confirm the performance of the control system and the suitable quality of the injected current of the PEMFC system into the weak and harmonic‐polluted network.

Perspective of new distributed grid connected roof top solar photovoltaic power generation policy interventions in India

The building integrated rooftop solar photovoltaic (PV) systems, contribute significantly to the decentralised power generation. In this study a detailed analysis of the new distributed power generation policy from roof top PV systems, in India, is carried out along with identifying policy interventions required for its successful implementation. A contrasting perspective of decentralised power generation analysis is presented for roof top power generation enhancement and solar industry growth in India. As a case study, the implementation of roof top PV power generation in India is presented which faces a number of challenges including resistance from energy distribution companies (DISCOMs). The electricity tariff analysis is also carried out, to suggest corrective measures. The novelty of the study is that it identifies solar tariff, benchmark cost, energy subsidy pattern, release methodology and lack of incentives to DISCOMs as crucial parameters to be addressed for roof top PV promotion. The study is of importance and of interest for the effective implementation of distributed renewable power generation in the residential sector for solar industry and DISCOM growth in India and other countries worldwide.

Decoupled fractional-order harmonic filter for power quality enhancement of grid-connected DG units

The global expansion of power electronics interfaced distributed generator (DG) units has led to the incrementation of nonlinear loads in the distribution systems, which may impose negative effects on the power quality. To maintain the desired power quality while actively compensating the harmonics in the presence of frequency deviations, this work proposes a decoupled closed-loop fractional-order current controller that incorporates the harmonic alleviation with the DG power generation function. Accordingly, an optimal fractional-order proportional–integral–derivative (FOPID) is designed to control the DG unit fundamental current, while compensating the local nonlinear load harmonic current (LHC) effects. A noteworthy contribution of this paper is that the optimal control scheme delivers the desired performance without the need for LHC detection and effectively reduces the operational cost. Another contribution is the implementation of an optimal FOPI-based control scheme in the outer power control loop to extract the fundamental current reference with no phase-locked loop (PLL) components. This offers comprehensive solutions with several improvements, such as eliminating the power tracking steady-state error under fundamental current tracking errors and preventing harmonic disturbances from being imposed on the harmonic control by the power control part. The feasibility and effectiveness of the proposed power control scheme are validated in comparison with the conventional PI approach.

Research on power consumption distribution characteristics of a water-lubricated twin-screw air compressor for fuel cell applications

The water-lubricated twin-screw air compressor is very suitable for applications in high-pressure PEMFCs in distributed power generation, for it can provide absolutely oil-free air. Power consumption distribution is a significant characteristic for clarifying the influence mechanism of water injection and lubrication, which could provide the optimizing direction for performance enhancement. Hence, a mathematical model is constructed in this paper, aiming to analyze the power consumption distribution in different positions of the compressor at different rotating speed, including indicated power of dry air, water vapor and liquid water, friction power in the rotor chamber, friction power of radial journal bearings, thrust bearings and the lip seal. Results show that thrust bearings account for the largest amount of total power loss by over 52%, followed by indicated power of liquid water, radial journal bearings, while the indicated power of water vapor, friction powers in the rotor chamber and of the lip seal are minor power losses. This is very different from the common oil-injected twin-screw compressors, in which the friction power in the rotor chamber is also the dominant power loss. It illustrates the advantage of the low friction coefficient of water for sealing clearances in the water-lubricated twin-screw air compressor.

A Novel Method of Islanding Detection in a Distributed Power Generation System Integrated with Photovoltaic-Array

Wydawnictwo SIGMA-NOT wydaje czasopisma fachowe informujące swoich czytelników o najnowszych osiągnięciach naukowych i nowoczesnych rozwiązaniach technicznych w Polsce i na świecie, popularyzuje problemy techniczne oraz poszerza wiedzę i kulturę techniczną.

Feasibility of hybrid wind and photovoltaic distributed generation and battery energy storage systems under techno-economic regulation

The Brazilian electric energy compensation system (EECS) states that 100% of the energy generated and inserted into the grid should be returned to prosumers as credits to their energy bill. Ongoing regulatory changes propose that compensation should only be provided for the energy cost (43%). From this perspective, with awareness of the complementarity between wind and solar sources, energy storage systems (ESS) applied to hybrid distributed generation (DG) can become attractive. This study aimed to assess the economic feasibility of hybrid DG power plants with battery banks. Stochastic analyses were carried out by varying nine of the variables (nominal power, solar radiation, wind speed, electricity demand, energy tariffs, discount rate, battery bank investment, and solar and wind installation costs) in three types of hybrid power plants (micro, mini, and small). All scenarios presented a high probability of viability. The main conclusions are as follows. The complementarity of the sources yields benefits to the system: batteries have a high investment cost, which require incentives for their insertion in the DG as a decrease in battery cost or a specific subsidy. The regulatory framework should consider the possibility of payout for the benefits provided by the use of an ESS for DG, i.e., energy storage is directly related to the smart grid concept.

Performance study on a thermoelectric generator with exhaust-module-coolant direct contact

The Automotive Thermoelectric Generator (ATEG) aims to recycle the heat in vehicle exhaust, and transforms it into electricity. This paper proposes a specific structure of an automotive direct contact thermoelectric generator (ADCTEG) system. With no space among the TEMs, exhaust gas and coolant water, this automotive direct-contact configuration works in favor of system integration, minimizing the contact thermal resistance, and maximizing thermal efficiency. In this new TEG system, the thermoelectric modules (TEMs) expose the hot side surface on the automotive waste gas, while another surface directly contact with the cooling water. For the purpose of revealing output characteristics of the ADCTEG and the heat transfer performance, several numerical simulations and bench test are carried out to predict the temperature distribution, flow field and output power generation. Meanwhile, the influence of experimental parameters on ADCTEG power generation performance is studied also, the output characteristics of ADCTEG under vehicle on-board environment are discussed. The net output power of ADCTEG under different engine rotation speed is calculated. The researches on output characteristics of liquid–solid–gas ADCTEG system has guiding significance for the structure design of heat exchanger and the optimization design of thermal resistance and heat transfer of the system, and also has reference value for the potential application of automotive TEG.

An IPAVSG Control Strategy for Microgrid With Multi-Parallel VSG System

Virtual synchronous generator (VSG) is widely used in various distributed power generation systems due to great simulated inertia and damping support performance. However, when the microgrid (MG) composed of multi-parallel VSG is in both grid-connected and islanded modes with various large disturbances, the control strategy with fixed parameters cannot guarantee the stable operation of the MG under all disturbances. To this end, an improved parameter-adaptive virtual synchronous generator (IPAVSG) control strategy is proposed in this paper to ensure that the virtual inertia and damping are adaptively optimized with the system operating state during the disturbance process. Therefore, the dynamic performance of the power frequency regulation and transient stability are significantly improved. Meanwhile, in order to realize the output active power of each VSG is distributed among the loads according to the ratio of its rated capacity, the active power decoupling control is designed to eliminate the influence of the virtual damping on the output active power of the VSG in islanded MG. The effectiveness and practicability of the proposed control strategy are verified through several experiments.

An Effective Non-Square Matrix Converter Based Approach for Active Power Control of Multiple DGs in Microgrids: Experimental Implementation

In this paper, a new modulation strategy based on the carrier-based switching strategy for the non-square direct matrix converters (MC) is proposed to control the active power of distributed generation (DG) units. In this strategy, the active power of DGs is controlled by the central input current control of the non-square direct MC independent from the voltage and frequency. Conventionally, each DG has a converter, and for supplying a load with N number of DGs, N number of converters are needed and each converter has its own modulation switching and control strategy to control the power output of each DG. Needless to say, in a microgrid with N number of DGs, the control strategy of each converter has more complex structure than that of a microgrid with one converter, and surely the former strategy entails more volume and price. Using the proposed converter in this paper, it is possible to supply a load with N number of DGs through one converter. Also, the power outputs of all DGs are controlled by a central control strategy. The proposed central control strategy is described and simulated for a typical microgrid. Experimental and simulation results validate the effectiveness of the proposed converter and the proposed strategy. The results demonstrate the applicability and efficiency of the system and verify the theoretical analysis.

Economic aspects of introducing pumped-storage hydroelectric power plants into the mine dewatering system for distributed power generation

The paper examines the pumped hydroelectric energy storage potential of mine dewatering system for power generation in a distributed power system. Based on the water inflows that can be used to fill the drainage basins, the following options for pumped-storage hydroelectric power plants (PSHPP) are considered: when groundwater is discharged from only one mine, one hydraulic turbine is installed on the horizon below the surface; with additional discharge of groundwater from neighboring mines – installation of two or four hydraulic turbines at the drainage stages closest to the surface. Comparison was made with grid only system. It is based on net present value (NPV) and levelized cost of energy (LCOE) criteria. Variable parameters were hydraulic turbine water flow and mine power consumption. Also, for a certain combination of parameters, the optimal mine power system was determined. The area of use of the PSHS is estimated. It was found that the smallest economic effect is achieved when the power generation of one hydraulic turbine is close to the power consumption. The area of expedient use of the PSHPP within the limits of parameter variation is 17.2%, 19.6% (base and peak costs of power). This is because power generation drops when the water flow decreases. It does not cover the needs of the mine and there is a power shortage. Thus, the mine power system autonomy is very low. With an increase in water inflow and the number of hydraulic turbines, first up to two and then up to four units, the area of expedient use of PSHPP increases to 51.5%, 55.9% and 50.6%, 72.8%, respectively. However, with low energy consumption and a low water flow, it is still rational to receive electricity from the grid. This is due to a sharp drop in the efficiency of hydraulic turbines and high costs for maintenance and repair of PSHPP equipment, which are not comparable to the cost of purchasing power. So it was noted that with the base cost of electricity and an increase in the number of hydro turbines from two to four, the area of conditions under which the use of PSHPP is justified even decreased by 0.9%. At peak cost, the area increases by 16.9%. The mine power system autonomy is not achieved. In general, the efficiency of using PSHPP for mine dewatering systems is high, but the feasibility of their use should be studied for specific conditions of use.

Forecast Method of Distributed Photovoltaic Power Generation Based on EM-WS-CNN Neural Networks

In order to cope with the challenges of dispatching of power grids brought by large-scale distributed photovoltaic power generation related to production and consumers, a maximum expected sample weighted convolutional neural network (EM-WS-CNN) is proposed to forecast the distributed photovoltaic output. First, the distance correlation coefficient and the principal component analysis method are used to extract the comprehensive meteorological factors from the original meteorological data, and then the 6 statistical indexes of the comprehensive meteorological factors and historical power data are used as the clustering characteristics. The historical data are divided into different weather types by using the maximum expectation clustering, and the training samples are weighted based on the membership matrix. Finally, the weighted training data are used to construct the EM-WS-CNN model. In the experimental analysis, the above-mentioned method is compared with the CNN model, and the results show that the proposed method has higher accuracy and robustness.

Multi-Stage Expansion Planning of Distribution Network Considering Distributed Power Generation

With the gradual increase in the penetration rate of distributed power sources, in view of the planning problem of coordinating the location and capacity of distributed power sources with the grid frame and transformers of the distribution network, a distribution network that takes into account distributed power sources is proposed. Aiming at the lowest cost of investment, maintenance, energy production, energy loss, and load loss penalty, and considering the power flow constraints, planning and operation constraints of each planning stage, a multi-stage expansion planning model for the distribution network is established. The mixed-integer linear programming algorithm is used to solve the problem, and the optimal planning scheme at each stage is obtained. The simulation results show that the multi-stage expansion planning method for coordinating distributed power and distribution network proposed in this paper can prevent the problems of isolated nodes and transmission nodes, improve the reliability of the planning scheme, and have good economic benefits.

Selective Harmonic Elimination in a Cascaded Multilevel Inverter of Distributed Power Generators Using Water Cycle Algorithm

This research paper proposes the application of a meta-heuristic algorithm, namely the water cycle algorithm (WCA), for optimizing the performance of a multi-level inverter for a distributed energy resources-based smart grid system. The aim is to find the optimal switching angles to achieve selective harmonic elimination. To exhibit the effectiveness of the proposed algorithm and evaluate the results, a three-phase seven-level cascaded multilevel inverter (CHBMLI) is used. This paper demonstrates the efficacy of the proposed algorithm by performing a rigorous comparison with existing meta-heuristic algorithms. Independent sample t-tests for different population sizes are demonstrated, which reflect the better performance of the proposed algorithm’s results. For the comparison, crucial parameters for optimization, including population size and number of iterations, are kept the same for the proposed WCA and other algorithms. Since we are solving a minimization problem, a lower fitness value is focused. In our research paper, we show how the proposed algorithm attains a lower fitness value and fast rate of convergence. For different values of the modulation index, WCA performs better than particle swarm optimization (PSO) and the firefly algorithm (FA). For a particular case of a modulation index value of 0.8, the minimum value found by WCA over 50 samples is 0.0001, whereas that of PSO and FA are 0.0223 and 0.0433, respectively, which shows that WCA has better accuracy. The results clearly present that the proposed algorithm provides a competitive percentage of elimination of selected harmonics when compared with other meta-heuristic algorithms.

A two-level power management strategy in a DC-coupled hybrid microgrid powered by fuel cell and energy storage systems with model predictive controlled interface converter

This paper intends to present a DC-coupled hybrid microgrid, including proton exchange membrane fuel cell (PEMFC), battery bank, and supercapacitor, which is suitable for applications such as distributed power generation and the power system of vessels. In the proposed configuration, the PEMFC serves as the main energy source, and supercapacitor and battery bank are as energy storage systems. A comprehensive model of the 6 kW PEMFC, including the dynamic model along with the electrical model, is presented. Three DC-DC converters, consisting of an inter-leaved boost with voltage multiplier converter (IBVM) connected to the fuel cell and two bi-directional converters connected to the storage devices are employed. Additionally, an AC-DC converter is utilized to ensure stable AC voltage supply, proper power flow, and DC-link voltage control. Moreover, this paper provides a two-level power management strategy (PMS) to control and optimally distribute power between the components of the hybrid microgrid. The proposed strategy is divided into device-level and system-level controls. At the device-level control, a decentral-ized model predictive control strategy (MPC) without using any proportional-integral-derivative (PID) controllers is proposed to control the different modules of the hybrid microgrid. Also, at the system-level control, a rule-based strategy is developed to optimally distribute power between power sources and ensure stable operation under different operation modes. The simulation results in Matlab/Simulink environment are given to verify the effectiveness of the PEMFC model, the chosen converters, the proposed control methods, and the proposed hybrid microgrid.

Optimal Topology Design for Distributed Generation Networks Considering Different Nodal Invulnerability Requirements

Distributed generators and microgrids are of great importance for the stable operation of power systems when failures occur. The major work of this paper is proposing an optimal topological design model of preset connection lines, aiming at a distributed power generation network based on different nodal invulnerability requirements. Moreover, the important innovation of this paper lies in that the perspective is shifted from the system to an individual node of a different type. When a node malfunction occurs, the faulty node can be connected to its neighbor nodes by closing a switch to achieve energy exchange. The distributed generation network consists of a series of nodes that can realize self-sufficiency and can be classified into three types with different levels of importance according to their tasks. The nodes of different types must meet different requirements of destructibility. In this paper, a mixed-integer linear programming model is formulated to solve the optimal topology design problem. In addition, this paper also analyzes the influence of changing nodal power generation capacity and nodal type, and the simulation results show the practicability of the proposal.