Conventional Generation Systems Research Articles

Biochar for Soil Improvement: Evaluation of Biochar from Gasification and Slow Pyrolysis

The growing need for food, energy and materials demands a resource efficient approach as the world’s population keeps increasing. Biochar is a valuable product that can be produced in combination with bio-energy in a cascading approach to make best use of available resources. In addition, there are resources that have not been used up to now, such as, e.g., many agro-residues that can become available. Most agro-residues are not suitable for high temperature energy conversion processes due to high alkali-content, which results in slagging and fouling in conventional energy generation systems. Using agro-residues in thermal processes, therefore, logically moves to lower temperatures in order to avoid operational problems. This provides an ideal situation for the combined energy and biochar production. In this work a slow pyrolysis process (an auger reactor) at 400 °C and 600 °C is used as well as two fluidized bed systems for low-temperature (600 °C–750 °C) gasification for the combined energy and biochar generation. Comparison of the two different processes focuses here on the biochar quality parameters (physical, chemical and surface properties), although energy generation and biochar quality are not independent parameters. A large number of feedstock were investigated on general char characteristics and in more detail the paper focuses on two main input streams (woody residues, greenhouse waste) in order to deduct relationships between char parameters for the same feedstock. It is clear that the process technology influences the main biochar properties such as elemental- and ash composition, specific surface area, pH, in addition to mass yield quality of the gas produced. Slow pyrolysis biochars have smaller specific surface areas (SA) and higher PAH than the gasification samples (although below international norms) but higher yields. Higher process temperatures and different gaseous conditions in gasification resulted in lower biochar yields but larger TSA, higher pH and ash contents and very low tar content (16-PAH). From the feedstock data looked at in more detail, a few trends could be deducted in the attempt to learn how to steer the biochar characteristics for specific uses.

Power converters, control, and energy management for distributed generation

Distributed generation (DG) is expected to play a vital role in the future to improve the quality of human life. DG and its integration to the local AC grid provide options for economical, continuous, and bidirectional power flow (utility interface). In addition, it provides a back-up to support during grid failure or blackouts. Extensive promotion of the DC grid is also proposed for the future to facilitate easy integration of renewable resources. Low-voltage DC grid derived from DG is safe and may cover a significant portion of residential load, which is mostly DC load avoiding inefficient AC/DC power supply. Vehicles in the smart grid have introduced a concept of living and mobility, i.e., sustainable living and low carbon mobility and are foreseen as a part of future microgrid. Research is needed to push and commercialize these technologies to make the environment clean by replacing conventional generation systems. This “Special Section on Power Converters, Control, and Energy Management for Distribution Generation” of the IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS, is a step forward to promote and encourage extensive investigations in the areas associated with DG. In all, 16 papers were selected, which have one or more very unique features for the proposed applications. The topics range from new high gain DC/DC converters to inverters for solar PV integration on one side and development of effective test bed to brushless generation systems for potential DG applications on the other. To facilitate an in-depth survey of the published papers, the Guest Editors will now examine one by one the different contributions by highlighting the most noteworthy developments and findings.

A Robust Frequency Control Approach in PV-Diesel Hybrid Power System

Hybrid power generation system such as photovoltaic (PV)-diesel is one of the solution to reduce operational cost of the conventional diesel generation system. However, fluctuation of PV power due to uncertainty in weather condition may generate an unstable frequency of system. Further, it may reduce the reliability of the power utility, especially when the penetration of PV power is large. Therefore, a frequency control approach that involving PV with battery supervised by neural network algorithm is proposed to generate a stable system frequency. This method can reduce the frequency deviation without smoothing PV output power. The PV panels can generate maximum power according to the weather condition and frequency deviation. The PV output power and battery output power is controlled by neural network algorithm control. The neural network algorithm control is considering frequency deviation, average insolation and change of insolation as input. The proposed method is compared with similar system but without the existence of battery as energy storage system. The simulation results show that the proposed method can generate small frequency deviation compared with system without battery.

Wind-Thermal Integrated Power System Scheduling Problem Using Cuckoo Search Algorithm

A new nature inspired metaheuristic algorithm known as the cuckoo search algorithm (CSA) is presented in this paper, to solve the unit commitment problem (UCP) for hybrid power system. The utilization of wind energy sources is increasing throughout the world. It is therefore important to develop the protocol for the integration of wind generation system with conventional thermal unit generation system. High wind penetration can lead to high-risk level in power system reliability. In order to maintain the system reliability, wind power dispatch is usually restricted and energy storage is considered for smoothing out the fluctuations. On solving UCP, the proposed binary coded CSA finds the ON/OFF status of the generating units while the economic dispatch problem (EDP) is solved using the real coded CSA. The proposed methodology is tested and validated on 3, 4, 9, 12 38 and 100 unit systems for 24 hour scheduling horizon. The effectiveness of the proposed technique is demonstrated by comparing its performance with the other methods reported in the literature.

Development of a 3 kW double-acting thermoacoustic Stirling electric generator

In this paper, a double-acting thermoacoustic Stirling electric generator is proposed as a new device capable of converting external heat into electric power. In the system, at least three thermoacoustic Stirling heat engines and three linear alternators are used to build a multiple-cylinder electricity generator. In comparison with the conventional thermoacoustic electricity generation system, the double-acting thermoacoustic Stirling electric generator has advantages on efficiency, power density and power capacity. In order to verify the idea, a prototype of 3kW three-cylinder double-acting thermoacoustic Stirling electric generator is designed, built and tested. Based on the classic thermoacoustic theory, numerical simulation is performed to obtain the thermodynamic parameters of the engine. And distributions of key parameters are presented for a better understanding of the energy conversion process in the engine. In the experiments, a maximum electric power of about 1.57kW and a maximum thermal-to-electric conversion efficiency of 16.8% were achieved with 5MPa pressurized helium and 86Hz working frequency. However, we find that the mechanical damping coefficient of the piston is dramatically increased due to the deformation of the cylinder wall caused by high thermal stress during the experiments. Thereby, the system performance was greatly reduced. Additionally, the performance differences between three engines and three alternators are significant, such as the heating temperature difference between three heater blocks of the engines, the piston displacement and the output electric power differences between three alternators. These problems need further investigation. This work presents a new thermal-to-electric conversion technology, which can be utilized in many energy area, such as solar energy, industrial waste heat and so on.

MPPT Control Method Using Boost Type DC-DC Converter for PV Generation System with Mismatched Modules

Nowadays in a household PV generation system, it is generally connecting PV modules in series and then output to the power-conditioner. However, when PV modules are mismatched, it will lead to a wrong maximum power point tracking (MPPT) to all modules and a power decreasing of the whole system. Aiming at this problem, this paper presents the idea which improves the MPPT without changing the conventional power-conditioner, by adding a boost type DC-DC converter behind each module. Simulations of PSIM and experiments are taken to prove this theory. The result shows that, by this idea, the generated power of the conventional PV generation system can be greatly increased under the condition of mismatch.

Developing Educational Smart Grid Laboratory for the UAEU

The goal of this paper is to present the first stage of developing an educational laboratory to teach smart grid design and implementations for both under graduate and graduate levels. Hampden 180 simulator that represents conventional generation, transmission, and distribution power system is integrated with intelligent electronic devices and tied together in an architecture that provides reliable and fault-tolerant protection, control and monitoring. The upgraded laboratory will demonstrate high level of functionality and satisfying the design and operation objectives of smart grid metering, protection, control, monitoring and communication. Part 2 of this paper will discuss and present the implementation stage.

Seasonal shifting of surplus renewable energy in a power system located in a cold region

The Fukushima nuclear disaster in 2011 changed Japan's strategy for reducing CO₂ emissions. The government is now placing more emphasis on the development of nonCO₂-emitting distributed generation systems such as wind, solar, and tidal power to reduce greenhouse gas emissions and guarantee electricity supply in the case of a natural disaster. This paper proposes a strategy for the exploitation of wind, solar, and tidal resources in a cold region in Japan by utilizing surplus energy from the summer and spring during winter. It also aims to determine the most favorable energy mix of these renewable sources and storage system types. The study is performed by calculating hourly demand and renewable energy supply for the city in one year, which is based on actual data of demand, solar irradiation, wind speeds, and tidal current speeds. The costs of the components of the renewable power plants and storage systems are considered, and different proportions of generation outputs are evaluated with different types of storage systems. According to results, the configuration containing the hydrogen storage system using organic chemical hydride methylcyclohexane (OCHM) is the most economical but is still more expensive than one using a conventional generation system. Moreover, we confirm that the cost of CO₂ emissions is the key element for leveling the playing field between conventional and renewable generation from an economic perspective. The cost of CO₂ emissions to public health as well as those costs related to the interruption of services during a catastrophe must be carefully calculated with other issues from conventional power projects to perform a precise comparative evaluation between both types of generation systems.

Solugas – Operation Experience of the First Solar Hybrid Gas Turbine System at MW Scale

CSP hybridisation is one of the most promising concepts for cost reduction and dispatchability, and also one of the most competitive with conventional electricity generation systems. The Solugas project, first solar hybrid system topped with a gas turbine at megawatt scale, was commissioned in May 2012 in Abengoa's Solúcar Platform near Seville.Numerous operation objectives of the project have been tackled since the operation started and the project is running for several hundred solar operation hours already, yet for the technology assessment the stable operation and evaluation of long time behaviour are crucial. In 2012 the maximum receiver outlet temperature objective was achieved: the temperature of the heat transfer medium -pressurised air- has been heated up to 800°C in one receiver, reaching a temperature gradient of almost 500K.Current objectives include obtaining the tubular receiver efficiency accurately and optimisation of plant operation and control, in order to be able to characterise the behaviour of the plant and the production of the future plants.

Distributed energy resource system optimisation using mixed integer linear programming

In this study a mixed integer linear programming (MILP) model is created for the design (i.e. technology selection, unit sizing, unit location, and distribution network structure) of a distributed energy system that meets the electricity and heating demands of a cluster of commercial and residential buildings while minimising annual investment and operating cost. The model is used to analyse the economic and environmental impacts of distributed energy systems at the neighbourhood scale in comparison to conventional centralised energy generation systems. Additionally, the influence of energy subsidies, such as the UK's Renewable Heat Incentives and Feed in Tariffs, is analysed to determine if they have the desired effect of increasing the economic competitiveness of renewable energy systems.

DFIG 풍력터빈이 연계된 전력계통의 CCT 영향분석

풍력발전시스템은 기존의 발전시스템과 매우 다르다. 그러므로 전력계통에 풍력시스템을 연계하기 위해서는 동적특성에 대한 연구가 필요하다. 풍력발전기의 안정도해석은 전력계통의 운영에 있어서 중요 쟁점이다. 기존의 동기발전기만으로 구성된 전력계통의 위상각 안정도는 풍력발전기가 포함되면 그 결과가 달라진다. 즉, 풍력터빈에 연계된 발전기는 대부분 비동기인 유도발전기이기 때문이다. 위상각의 동기화 여부로 판별하는 위상각 안정도는 임계고장제거시간(CCT)을 계산하여 평가한다. 계통해석용 풍력터빈의 모델은 다양하여 그 해석에 어려움이 있으나 지금은 크게 4가지 타입으로 표준화가 되어있다. 본 논문에서는 PSS/E-32에서 제공하는 풍력터빈의 3번째 표준모델인 DFIG(Doubly-Fed induction Generator)모델을 이용하여 풍력단지가 연계된 전력계통의 CCT를 풍력단지의 위치와 용량을 고려하여 분석한다. Wind generation systems are very different in nature from conventional generation systems. Therefore it is necessary to research dynamic characteristics of wind generation systems connected to a power system. The stability analysis of wind turbine generator is an important issue in the operation of the power system. The result of angular stability of the power system that consists of only synchronous generators is different from that of the power system including wind turbine generators. This is due to the fact that generators connected to wind turbines are generally induction generators. The angular stability assessing synchronization of generators is determined by its corresponding critical clearing time(CCT). Wind turbine models for the analysis of power system are varied and difficult to use, but now these are standardized into four types. In this paper, the analysis of the CCT of the power system connected to wind farm considering the location and capacity is performed by using DFIG(Doubly-Fed induction Generator) wind turbine built-in type3 model in PSS/E-32.

National electricity planner and use of distributed energy sources in India

Abstract Indian electricity supply system mostly consists of a centralized, large and conventional generation system. Gradually, as the scenario of huge increase in demand as compared to generation was imposed on the system, the electric utilities have been restructured in various ways. With the restructuring process, the system operators are planning to implement alternative energy resources in the system. Nowadays, these resources are being utilized through small and modular energy conversion systems, known as distributed generation (DG) based on conventional and renewable energy resources. By implementing DG in the system, the environmental impact has been reduced along with the enhancement of reliability and quality in the power supply. Therefore, it is very important to choose DG at various locations in a country like India, because of varying weather conditions and resource availability. Determining DG options at different locations depends upon various attributes like economic, technical, environmental and resource availability, etc. Sometimes, it becomes difficult in part of authorities to arrive at a suitable decision on choosing the type of DG technology for a particular region or area. Overall Indian power system is divided into five broad regional grids viz., northern regional grid (NRG), eastern regional grid (ERG), southern regional grid (SRG), north eastern regional grid (NERG), western regional grid (WRG), operated and maintained by the respective regional load dispatch centers (RLDCs). The main objective of this work is to determine various DG technology options in each of the five regions in India with consideration of the above mentioned attributes. Analytic hierarchy process (AHP) has been used to identify the relative importance of the chosen attributes at various regions. Based on this, suitable DG options are determined.

Environmental assessment of CCHP (combined cooling heating and power) systems based on biomass combustion in comparison to conventional generation

Biomass CCHP (combined cooling heating and power) systems based on biomass combustion have already demonstrated their benefits in some operating conditions. However, their environmental and energy performance might not always be better than that of conventional stand-alone generation systems. In order to assess the possible benefits, these plants are evaluated by means of Life Cycle Assessment (LCA) methodology to provide some guidelines regarding their environmental feasibility. A thermodynamic model, which considers the integration of different sizes of cogeneration and cooling units, was developed to contribute to properly defining the life cycle inventory stage. Moreover, the model outputs were used to develop a primary energy savings ratio (PESR) analysis and compare its results with those of the LCA.The LCA results show that, whereas small plant cooling-to-heating ratios cause CCHP plants based on biomass combustion to be environmentally feasible (they imply environmental benefits compared to conventional average stand-alone generation), high plant cooling-to-heating ratios in fact cause them to be environmentally unfeasible. Results also allow us to state that the use of the PESR by itself might not be adequate to assess the steady-state performance of this type of plant because, in some circumstances, it might limit the plant's feasibility when environmental benefits could still be achieved.

Development of sustainable energy on generation system leads to eco-friendly society

Abstract The utilization of wind energy sources is increasing throughout the world. It is therefore important to develop the protocol for the integration of wind generation system with conventional thermal unit generation system. High wind penetration can lead to high-risk level in power system reliability. In order to maintain the system reliability, wind power dispatch is usually restricted and energy storage is considered for smoothing out the fluctuations. This article proposes a novel methodology that employs fuzzified binary real coded artificial bee colony (BRABC) algorithm for solving multi-objective unit commitment problem (MOUCP) for hybrid generation system. Here three conflicting functions such as fuel cost, emission and reliability level of the system are considered. These functions are formulated as a single objective optimization problem using fuzzy set theory. Also the fuzzy membership design variables are tuned using real coded artificial bee colony (ABC) thereby requirement of expertise for setting these variables are eliminated. The proposed method is validated on different test system and results are compared with the existing literature.

Operational Adequacy Studies of Power Systems With Wind Farms and Energy Storages

In a power system with high renewable power penetration, uncertain and intermittent characteristics of renewable energy resources become major concerns of system planning and operation. In such a power system, conventional thermal or hydro units have to be dispatched, shut down or started up more frequently to incorporate load, renewable resource variation and system failures. Slow ramp up (or down) of conventional units may cause energy shortage (or surplus) in power systems with high wind power penetration or in isolated micro grids with limited dispatchable capacity. This paper proposes a technique to evaluate operational reliability and energy utilization efficiency of power systems with high wind power penetration. The ramp rate of a conventional generator and energy storage system (ESS) are considered in the proposed technique. The effect of slow ramp-up rate or fast reduction of wind speed on system reliability is measured by the expected energy not supplied. A new index designated as the expected energy not used is proposed and formulated to represent energy surplus due to fast increase of wind speed and slow ramp down of conventional units. The IEEE-RTS is used to illustrate the applications of the proposed method.

Study of the Critical Fault Clearing Time for the Super High Voltage Cable-Wound Generator System

The super high voltage generator, the stator winding of which is made of high voltage power cable, can be connected to the power grid directly. In this paper, the first super high voltage generator prototype at home is taken as an example, the equivalent circuits of the super high voltage generator system is proposed from the static power characteristic when the system transmission line is broke down because of the single phase to ground fault, phase to phase fault and two phases to ground fault. And the power expressions are also presented, and then the power angle and speed of the super high voltage cable wound generator are simulated with the improved Euler algorithm, and the critical fault clearing times of three faults are obtained. At the same time, the critical fault clearing time of a typical conventional synchronous generator system is also calculated and compared with the super high voltage cable wound generator system, and it is found that the dynamic stability margin of the super high voltage cable wound generator system is higher than that of conventional generator system.

A low power clock generator with adaptive inter-phase charge balancing for variability compensation in 40-nm CMOS

Abstract. Power dissipation besides chip area is still one main optimization issue in high performance CMOS design. Regarding high throughput building blocks for digital signal processing architectures which are optimized down to the physical level a complementary two-phase clocking scheme (CTPC) is often advantageous concerning ATE-efficiency. The clock system dissipates a significant part of overall power up to more than 50% in some applications. One efficient power saving strategy for CTPC signal generation is the charge balancing technique. To achieve high efficiency with this approach a careful optimization of timing relations within the control is inevitable. However, as in modern CMOS processes device variations increase, timing relations between sensitive control signals can be affected seriously. In order to compensate for the influence of global and local variations in this work, an adaptive control system for charge balancing in a CTPC generator is presented. An adjustment for the degree of charge recycling is performed in each clock cycle. In the case of insufficient recycling the delay elements which define duration and timing position of the recycling pulse are corrected by switchable timing units. In a benchmark with the conventional clock generation system, a power reduction gain of up to 24.7% could be achieved. This means saving in power of more than 12% for a complete number-crunching building block.

Characteristics and Economics Evaluation of an H2O Turbine Reheat Cycle Power Generation System Based on Oxy-Combustion Method for Utilizing Exhaust Gas of Large Scale MCFC

AbstractA large scale MCFC (48 MW) was adopted to construct a high-efficiency and economic power generation system without CO2 emission for utilizing its exhaust gas. A conventional steam turbine power generation system (STPS) is evaluated and the net generated power increase rate (NPIR) is estimated to be 8.22% and the STPS is economically feasible. A new CO2-capturing repowering system with reheat cycle is proposed: in the proposed system, saturated steam produced at a HRSG by using the MCFC exhaust gas is utilized as a main working fluid of a gas (H2O gas) turbine, and the temperature of the steam is raised by combusting fuel in a combustor by using pure oxygen instead of air. It is estimated that the NPIR of the proposed system is 24.4%, and the CO2 reduction amount is 27.0 kt-CO2/y, compared to that (9.09 kt-CO2/y) of the STPS, and that the proposed system surpasses the STPS in terms of economics.

Performance evaluation of a fuel processing system based on membrane reactors technology integrated with a PEMFC stack

The development of fuel cells is promised to enable the distributed generation of electricity in the near future. However, the infrastructure for production and distribution of hydrogen, the fuel of choice for fuel cells, is currently lacking. Efficient production of hydrogen from fuels that have existing infrastructure (e.g., natural gas, gasoline or LPG) would remove a major drawback to use fuel cells for distributed power generation. The aim of this paper is to define the better operating conditions of an innovative hydrogen generation system (the fuel processing system, FP) based on LPG steam reforming, equipped with a membrane shift reactor, and integrated with a PEMFC (Proton Exchange Membrane Fuel Cell) stack of 5 kWel. With respect to the conventional hydrogen generation systems, the use of membrane reactors (MRs) technology allows to increase the hydrogen generation and to simplify the FP-PEMFC plant, because the CO removal system, needed to reduce the CO content at levels required by the PEMFC, is avoided. Therefore, in order to identify the optimal operating conditions of the FP-PEMFC system, a sensitivity analysis on the fuel processing system has been carried out by varying the main operating parameters of both the reforming reactor and the membrane water gas shift reactor. The sensitivity analysis has been performed by means of a thermochemical model properly developed. Results show that the thermal efficiency of the fuel processing system is maximize (82.4%, referred to the HHV of fuels) at a reforming temperature of 800 °C, a reforming pressure of 8 bar, and an S/C molar ratio equal to 6. In the nominal operating condition of the PEMFC stack, the FP-PEMFC system efficiency is 36.1% (39.0% respect to the LHV).

Biomass direct chemical looping process: A perspective

Abstract This paper provides a perspective on the biomass direct chemical looping (BDCL) scheme which directly converts biomass into hydrogen and/or electricity with CO 2 capture. The discussion involves the preliminary design, potential challenges, and feasibility assessments in the BDCL process. Description of the BDCL process and the characteristics of biomass are provided in order to discuss potential advantage and disadvantage that may occur in this system. The feasibility of employing the BDCL process based on preliminary studies relative to competing biomass technologies and conventional fossil fuel conversion schemes is also discussed based on the perspective of energy conversion efficiencies, and economic analysis. Biomass has proven to be less efficient and more cost intensive compared to the current fossil fuel processes, due to its relatively low energy density, high moisture content and distributed-resource. However, the BDCL process has the potential to compete against conventional energy generation systems via its high conversion efficiency. A preliminary economic analysis demonstrates that BDCL system integrated with CCS to receive carbon credit is capable of producing electricity at a competitive price to the current fossil fuel processes.