Load‐following control for dispersed generators using a PI controller

Recently, there has been growing interest in utilizing dispersed generation systems, which are grouped into micro turbine systems, co‐generation systems, and so on, as a substitute for fuel oil energy and a technology to prevent global warming. Since start‐up time of dispersed generation systems is short, it is possible to operate systems to supply load power corresponding to a demand. Moreover, PPSs (Power Producers and Suppliers) can participate in a power retail sales company, since deregulation of electric utilities was instituted in March 2000. However, PPSs have to keep instantaneous generating power commissioning rule, to maintain supply‐and‐demand balance between customer and supplier. Therefore, in this paper, we examine instantaneous generating power commissioning for dispersed generators where start‐up time is short and it is possible to operate systems to supply a power load corresponding to a demand. We adopt a PI controller as a controller. The system is composed of double control loop in inner loop and in outer loop. In inner loop electric power is controlled and in outer loop electric energy is controlled. The controller parameters are designed using the pole‐placement technique. The effectiveness of the proposed control system is confirmed by simulations. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 145(2): 58–66, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10200     

A Two‐Stage Stochastic Mixed‐Integer Programming Approach to the Smart House Scheduling Problem

A “smart house” is a highly energy‐optimized house equipped with photovoltaic (PV) systems, electric battery systems, fuel cell (FC) cogeneration systems, electric vehicles (EVs), and so on. Smart houses are attracting much attention recently because of their enhanced ability to save energy by making full use of renewable energy and by achieving power grid stability despite an increased power draw for installed PV systems. Yet running a smart house's power system, with its multiple power sources and power storages, is no simple task. In this paper, we consider the problem of power scheduling for a smart house with a PV system, an FC cogeneration system, and an EV. We formulate the problem as a mixed‐integer programming problem, and then extend it to a stochastic programming problem involving recourse costs to cope with uncertain electricity demand, heat demand, and PV power generation. Using our method, we seek to achieve the optimal power schedule running at the minimum expected operation cost. We present some results of numerical experiments with data on real‐life demands and PV power generation to show the effectiveness of our method. © 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 186(4): 48–58, 2014; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.22336     

Hierarchical decentralized autonomous control in super‐distributed energy systems

This paper deals with a decentralized autonomous control strategy of a super‐distributed energy system with a hierarchical structure in order to reduce the complexity of control. In this paper, distribution systems are assumed to be composed of multiple small‐scale power systems in which many customers with dispersed generators exist. A small‐scale power system can be considered as a unit with a generator state and a load state, or as a customer with dispersed generators. Control components of small‐scale power systems are interconnected with each other and are used to operate distribution systems. An expanded decentralized autonomous control method for a super‐distributed energy system with a hierarchical structure is proposed on the basis of the Hopfield neural network. It is demonstrated that super‐distributed energy systems with a hierarchical structure can be controlled autonomously by applying the proposed method. Copyright © 2007 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

CO2 reduction effect of the utilization of waste heat and solar heat in a city gas system

We evaluated total energy consumption and CO₂ emissions in the phases of a city gas utilization system from obtaining raw materials to consuming the product. Assuming monthly and hourly demand figures for electricity, heat for space heating, and hot water in a typical hospital, we explore the optimal size and operation of a city gas system that minimizes the life cycle CO₂ emissions or total cost. The cost‐effectiveness of conventional cogeneration, a solar heating system, and hybrid cogeneration utilizing solar heat is compared. We formulate a problem of mixed integer programming that includes integral parameters that express the state of system devices such as the on/off condition of switches. As a result of optimization, the hybrid cogeneration can reduce annual CO₂ emissions by 43% compared with the system without cogeneration. The sensitivity of CO₂ reduction and cost to the scale of the CGS is also analyzed. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 149(1): 22–32, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10369     

Evaluation of the introduction of a micro‐cogeneration system into residential houses based on monitored daily‐basis energy demand data

In order to reduce CO₂ emission from residential sectors in Japan, PEFC with high efficiency and low environmental impact is expected as one of the promising micro‐cogeneration (µCGS) systems. However, the energy demands in houses largely differ from each other and the profiles are also changed every day. Thus, when µCGS is actually introduced, it is necessary to examine the equipment capacity and operation of µCGS in each house. In this paper, the optimization model is developed in order to evaluate the µCGS based on daily‐basis demand data. Using actually monitored energy demand data in four households, the differences between using daily‐basis data and using the monthly‐average data are evaluated from viewpoints of economic and environmental performance of µCGS systems. Moreover, by adding the penalty factor to disposal heat of µCGS, it is seen that system configuration and system operation of µCGS can attain CO₂ reduction and energy conservation as well as cost reduction. ©2008 Wiley Periodicals, Inc. Electr Eng Jpn, 166(4): 20–30, 2009; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20653     

Proposal and Evaluation of a New‐Type Cogeneration System for Energy Saving and CO2 Emission Reduction

The paper proposes a cogeneration system which generates four types of energy or material resources: electricity, steam, hot water, and freshwater. The proposed system can capture CO₂, and be constructed on the basis of a combined cycle power generation system which consists of a gas turbine and a back‐pressure extraction turbine. In the proposed system, power is produced by driving the gas turbine system. High‐pressure saturated steam with medium temperature is produced in the heat recovery steam generator by using gas turbine exhaust gas, and then superheated with a regenerative superheater in which the fuel is burned by using oxygen instead of air for driving the steam turbine generator. Water and CO₂ are recovered from the flue gas of the regenerative superheater. It has been estimated that the proposed system has a net power generation efficiency of 41.2%, a heat generation efficiency of 41.5%, and a total efficiency of 82.7%. Freshwater of 1.34 t/h and CO₂ of 1.76 t/h can be recovered. It has also been shown, when a case study was set and evaluated, that the proposed system can save 31.3% of energy compared with the conventional energy supply system, and reduce CO₂ emission by 28.2% compared with the conventional cogeneration system. Copyright © 2007 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Influence of the Emissions Trading Scheme on generation scheduling

The paper investigates the effects of emissions constraints and Emissions Trading Scheme (ETS) on the generation scheduling outcome. ETS is a cap-and-trade market mechanism that has been introduced in European Union in order to facilitate CO₂ emissions management. This scheme gives generators certain amount of CO₂ allowances which they can use to cover emissions produced during energy generation. In a current setting, most of the allowances are given for free. However, under ETS generators also have an opportunity to buy and sell CO₂ allowances on the market. Since generation power outputs are bounded by the amount of CO₂ emissions that they are allowed to produce over time, it is becoming increasingly important for generating units to manage their allocations in the most profitable way and decide when and how much of permissions to spent to produce electricity. The method proposed here allows for modeling of this new limitation by including costs of buying and selling of CO₂ allowance in the generation scheduling procedure. It also introduces additional emissions constraints in the problem formulation. Although CO₂ permissions and energy are traded in separate markets, the proposed formulation permits analysis on how emission caps and emission market prices can influence market outcome. The method is illustrated on a 5-unit system. Given examples compare (i) a base-case when all generators have made a decision to use portions of their total free allocations that do not cause any shortfall during the investigated time period; (ii) two cases when the least expensive generators’ decisions on the amount of free allowances they are willing to use during the considered period are insufficient. In all cases generators also submit prices at which they expect to be able to “top-up” or sell allowances on the market, however, only in the second and third case the “buying” option becomes active and affects generation scheduling and total costs.In addition, the paper investigates how aggregation of emissions allowances of generators belonging to the same company can affect market clearing.     

Energy Economics of a Modern Suspension Preheater Plant Compared to a Modern Plant Incorporating Cogeneration

The rising cost of fuel experienced over the past several years has caused the cement industry to look for more energy efficient systems for producing cement. Probably the most popular system has been the suspension preheater, frequently coupled with a roller mill, a flash calciner, or both. While these systems have yielded greatly improved fuel efficiencies, they have also contributed to higher consumption of electrical energy. This, coupled with the rapid rise in cost of electrical energy, has led to a renewed interest in cogeneration, wherein the heat contained in the kiln off-gases is used to produce steam to run turbine generators, thereby increasing the use of lower cost fuel energy while decreasing the use of higher cost purchased electric power energy. The production cost of a suspension preheater is different than for a plant utilizing cogeneration, so the production cost per ton of the two systems is compared, and the differences are used to determine the feasibility of cogeneration for a specific set of conditions. Two cogeneration cases will be examined. One is a plant utilizing generated power from waste heat only, all of which is consumed by the plant. The other is a plant which not only utilizes waste heat power but also produces for sale back to the utility company.     

Impact of DC 48 V on Automotive Power Supply Systems: Comparison with DC 42 V and Future View under DC 60 V

In the twenty‐first century, rapid advances are being made in the electric propulsion of vehicles as a countermeasure of global warming. In addition, CO₂ emissions from all vehicles are to be stringently regulated to 95 g/km by 2020. Thus, most automakers around the world have had to develop not only hybrid electric vehicles, but also conventional internal combustion engine with energy‐saving technology. Battery technology (Li‐ion) and semiconductor technology (SiC and GaN) for automotive power supply systems have proceeded to the mass‐production stage. In 2011, Verband der Automobilindustrie (German OEMs and suppliers) announced the adoption of DC 48 V for the market of 2020. In this paper, we analyze the needs and impact of DC 48 V and compare it with DC 42 V (current technology). We also try to portray the future view under DC 60 V for automotive power supply systems.     

DC‐linked hybrid generation system with an energy storage device including photovoltaic generation and gas engine cogeneration for residential houses

For the past few years, hybrid generation systems including solar panel and gas cogeneration have been used for residential houses. Solar panels can generate electronic power at daytime but not at night. But the power consumption of residential houses usually peaks in the evening. The gas engine cogeneration system can generate electronic power without such a restriction, and it also can generate heat power to warm up a house or to produce hot water. In this paper we propose a solar panel and gas engine cogeneration hybrid system with an energy storage device, combined by a DC bus. If a blackout occurs, the system still can supply electronic power for special house loads. We propose a control scheme for the system related to the charging level of the energy storage device and the voltage of the utility grid, which can be applied to both grid‐connected and standalone operation. Finally, we report experiments designed to demonstrate system operation and calculations for loss estimation. © 2012 Wiley Periodicals, Inc. Electr Eng Jpn, 182(4): 29–46, 2013; Published online in Wiley Online Library ( wileyonlinelibrary.com ).DOI 10.1002/eej.22321     

A multi‐objective optimization model for determining urban energy systems under integrated energy service in a specific area

The integrated energy service system for a specific area is supposed to deliver electric and thermal energy in an integrated manner for the purpose of reducing cost, primary energy consumption, and CO₂ emission. Under an assumption of the service system, this paper develops a multi‐objective optimization model for determining urban energy systems. Considering the various energy system alternatives, such as photovoltaic generations for residential houses and fuel‐cell cogenerations for business and commercial customers, the model determines the share of the energy system alternatives in order to minimize the above three indices. As numerical examples, this paper illustrates trade‐off analyses in the case when the proposed model is applied to a 2 km × 2 km square area in Osaka. Finally, this paper illustrates the role of various energy system alternatives from CO₂ reduction and fossil energy reduction points of view. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 147(3): 20–31, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10275     

A method for compensating customer voltage drops due to nighttime simultaneous charging of evs utilizing reactive power injection from battery chargers

When we consider global warming, the reduction of CO₂ emissions is one of the most important issues which require urgent solutions. One option is to integrate low‐CO₂‐emission generators to the grid as much as possible. Another option is to replace ine?cient vehicles based on internal‐combustion engines with electric ones (EVs). Due to the latter, we can easily predict that most consumers will charge EVs' batteries during nighttime. Thus, excessive voltage drops due to nighttime simultaneous charging are expected to be a possible future problem. This paper proposes a method for compensating the voltage drops by injecting reactive power from EV battery chargers. © 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 184(1): 19–29, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.22390     

A vision of an electric power architecture for the next generation

Since the present hierarchical power grid structure and AC interface are mature and rigid, a new electric power system architecture is proposed here to save the earth by making use of renewable energy sources. The architecture consists of a new concept and a historical technology, that is, a network of many “electric clusters” with a DC interface. The cluster includes dispersed electric power generators, electric appliances, electric storage, and “electric power routers.” The router is equipment to resourcefully route electrical energy between neighboring clusters and to manage electrical energy in the cluster. The transfers of electrical energy (between clusters and within clusters) and the generation of electricity from renewal energy sources (such as sunlight, wind, tides, and biogas) are intermittent and have very wide dynamic ranges, so that the interface must make use of DC. When we achieve an energy society with this architecture, we will be able to reduce energy consumption, greenhouse gas emissions, and materials use. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 150(1): 18–25, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20039     

Evaluation of a plug‐in hybrid electric vehicle considering power generation best mix

In the transport section, it is necessary to reduce the amount of CO₂ emissions and oil dependence. Bio fuels and fuel cell vehicle (FCV), electric vehicle (EV) and plug‐in hybrid electric vehicle (PHEV) are expected to reduce CO₂ emissions and oil dependence. We focus on PHEV. PHEV can reduce total energy consumption because of its high efficiency and can run with both oil and electricity. Introduction of PHEV reduces oil consumption, but it also increases electricity demands. Therefore, we must evaluate PHEV's CO₂ reduction potential, not only in the transport section but also in the power grid section. To take into account the distribution of the daily travel distance is also very important. All energy charged in the PHEV's battery cannot always be used. That influences the evaluation. We formulate the total model that combines passenger car model and power utility grid model, and we also consider the distribution of the daily travel distance. With this model, we show the battery cost per kWh at which PHEV begins to be introduced and oil dependence in the passenger car section is to be reduced to 80%. We also show PHEV's CO₂ reduction potentials and effects on the power supply system. © 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 171(2): 12–22, 2010; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20920     

基于振荡能量消耗的发电机阻尼评估方法

为了准确评估多机电力系统中发电机的阻尼特性,提出了一种基于发电机振荡能量消耗的阻尼评估方法。首先,推导了基于6阶电气参数模型发电机的振荡能量流的表达式,克服了现有基于4阶电气参数模型的振荡能量流存在保守性的不足。其次,建立了基于振荡能量消耗的模式阻尼贡献指标,提出了基于发电机响应和特征值/特征向量的指标计算方法,评估了多机系统中发电机的阻尼特性。模式阻尼贡献指标物理意义明确,所有发电机的指标之和即为振荡模式的衰减因子。最后,4机2区域系统的分析结果验证了所提方法的准确性和有效性。     

A method for load frequency control using battery in power system with highly penetrated photovoltaic generation

It is generally believed that large battery systems will be needed to store surplus electric energy due to the high penetration of renewable energy (RE) such as photovoltaic generation (PV). Since the main objective of high penetration of RE is to reduce CO₂ emissions, reducing kWh output of thermal generation that emits large amounts of CO₂ in power systems should be sufficiently considered. However, thermal generation plays an important role in load frequency control (LFC) of power systems. Therefore, if LFC could be performed with batteries and hydropower generation, the kWh output of thermal generation could be reduced significantly. This paper presents a method of LFC using batteries in a power system with highly penetrated PVs. An assessment of the effect of the proposed method considering mutual smoothing effect of highly penetrated PVs is made. © 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 184(4): 22–31, 2013; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.22425     

Life cycle CO2 emissions of a photovoltaic/wind/diesel generating system

A photovoltaic/wind/diesel generating system with a battery (PWD system) is discussed from the viewpoint of total CO₂ gas emissions during system lifetime. The total emissions are the sum of the emissions occurring at manufacturing and operating. First, the manufacturing CO₂ emissions of the photovoltaic generator and the wind turbine generator are calculated by “the process analysis method.” This method considers the material used in each generator, its weight and its CO₂ emission rate. On the other hand, the manufacturing CO₂ emissions of the diesel generator and the battery are calculated using “the interindustry (input‐output) table.” Second, the PWD system is operated on a computer so that the fuel consumption of the diesel generator is a minimum assuming that hourly series data of electric load, insolation intensity, wind speed, and air temperature are known during the year. And CO₂ emissions occurring at system operation are obtained from the annual fuel consumption of the diesel generator. The results show that CO₂ total emissions of the PWD system are lower than those of the conventional diesel generator system. The CO₂ total emissions reach a minimum when the photovoltaic/wind generating ratio is 50/50. The CO₂ emissions of manufacturing decrease with increasing of the wind generating ratio from 100/0 to 0/100. The CO₂ total emissions decrease as the natural energy ratio increases. It is, however, saturated to about 60% when the ratio is more than 60%. And the CO₂ total emissions increase with increasing of the battery capacity. It is concluded that the PWD system plays an important role in decreasing considerably the CO₂ total emissions while the total system cost is high under the present price circumstances. © 2001 Scripta Technica, Electr Eng Jpn, 138(2): 14–23, 2002     

Evaluation of Residential PV‐EV System for Supply and Demand Balance of Power System

In recent years, there has been a growing interest in ecofriendly technologies such as residential photovoltaic (PV) systems and electric vehicles (EVs). PV systems and EVs will contribute to reducing CO₂ emissions in the residential sector and the transportation sector, respectively. In spite of that, high penetration of PV systems into the power grid can cause grid voltage and frequency stability problems. Also, the growth of the EV market will create an extra electricity load (for charging the EV fleet), leading to an increase in power utility fuel costs. In this research, we proposed the usage of the PV‐EV system as a method of mitigating the impact the spread of residential PV systems and EV on the power grid. We built an PV‐EV system simulation model and investigated the PV‐EV system contribution to the balance of power supply and demand and to reducing the total cost of the household under different electricity pricing scenarios. We also evaluated the effect of uncertainty in the forecasting of load and PV output on the performance of the PV‐EV system.     

Proposal and evaluation of a gas engine and gas turbine hybrid cogeneration system in which cascaded heat is highly utilized

A high‐efficiency cogeneration system (CGS) is proposed for utilizing high‐temperature exhaust gas (HTEG) from a gas engine (GE). In the proposed system, for making use of heat energy of HTEG, H₂O turbine (HTb) is incorporated and steam produced by utilizing HTEG is used as working fluid of HTb. HTb exhaust gas is also utilized for increasing power output and for satisfying heat demand in the proposed system. Both of the thermodynamic characteristics of the proposed system and a gas engine CGS (GE‐CGS) constructed by using the original GE are estimated. Energy saving characteristics and CO₂ reduction effects of the proposed CGS and the GE‐CGS are also investigated. It was estimated that the net generated power of the proposed CGS has been increased 25.5% and net power generation efficiency 6.7%, compared with the original GE‐CGS. It was also shown that the proposed CGS could save 27.0% of energy consumption and reduce 1137 t‐CO₂/y, 1.41 times larger than those of GE‐CGS, when a case study was set and investigated. Improvements of performance by increasing turbine inlet temperature were also investigated. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 166(3): 37– 45, 2009; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20708     

Generator cars with hybrid power plants

Centralized power supply systems for passenger and special trains with generator cars (GCs) are characterized by a lower specific weight and cost of equipment and lower service and repair expenses, as well as the possibility of using the standard general-purpose electrical apparatus. Their disadvantages include a large amount of noxious atmospheric emissions when diesel generators with a load less than the rated value are in operation and a high noise level. This hinders the operation of GCs at stations and depots and in tunnels. Designing combined power systems in which alternative energy sources, particularly as regards electrochemical generators (ECG) characterized by the absence of noxious atmospheric emissions, low noise level, higher efficiency increasing with the loads lower than the rated ones are used along with diesel generators is a method of improving the ecological performance of generator cars. The power control methods, the principles of control system construction, and the variants of the structure and an ECG energy channel operating with a voltage inverter in parallel to a synchronous generator are discussed in this article. The possibility of controlling the active and reactive powers of the ECG energy channel within a wide range by changing the modulation coefficient and the initial phase of the master effect of the voltage inverter is shown. A block diagram of the control system providing high speed and satisfactory quality of the transient processes in the energy system with the GC is proposed. The mathematical modeling method is used to indicate the possibility of ensuring a satisfactory quality of electric energy on the channel output (the total harmonic distortion does not excess 10–12%) with a rather high efficiency (80–88%) over the total power range.