A Method for Presuming Total Output Fluctuation of Highly Penetrated Photovoltaic Generation Considering Mutual Smoothing Effect

Mutual smoothing effect of renewable energy (RE) is quite important because the amount and cost of countermeasures for maintaining soundness of power systems highly depend on evaluation of the effect. In spite of its importance, there is as yet no established method to evaluate the effect. The authors present a method for presuming the total output fluctuations of highly penetrated RE from a few measured data considering the effect. By analyzing the measured data, existing photovoltaic (PV) output fluctuations are revealed to be coherent at slower swing periods and random at faster swing periods. To represent the PV’s output fluctuation tendencies, a “Transfer Hypothesis” is introduced. A “Constant Transfer Swing Period Hypothesis” and “–20 dB/dec Slope Hypothesis” are also introduced. These hypotheses are verified by direct and indirect methods using the measured data. Only 3 sites’ data are able to presume total fluctuation of 15 sites successfully. The relationship between distance and the transfer swing period for every 2 sites out of the 15 sites agrees with these hypotheses. Finally, the authors show the total fluctuation presumption of highly penetrated PV deployment in the Hokuriku region using the proposed methods. © 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 186(3): 31–42, 2014; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.22327     

Smoothing of PV system output by tuning MPPT control

A PV system's power output is not stable and fluctuates depending on weather conditions. Using a battery is one feasible measure to stabilize a PV system's power output, but it requires additional costs and results in additional waste of used batteries. In this paper, we propose a new measure for smoothing the short‐term change in a PV system's power output, which is performed by tuning the characteristics of Maximum Power Point Tracking (MPPT) control without additional equipment. In our proposed measure, when the insolation increases rapidly, the operation point of MPPT control changes to a new point where the maximum power is not generated with the current insolation, so that the rate of increase in the PV system's power output is limited to a certain value. In order to evaluate the effect of the proposed measure on the operation of electric power systems, we evaluated the required capacity of generators for load‐frequency control (LFC). It was revealed that the additional LFC capacity is not required even in the case where penetration of PV systems reaches 5% of the utility system's total capacity if the proposed measure is applied to all PV systems. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 152(2): 10–17, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20106     

Influence of forecast accuracy of photovoltaic power output on capacity optimization of microgrid composition under 30‐minute power balancing control

A microgrid (MG) is one of the measures for enhancing the high penetration of renewable energy (RE)‐based distributed generators (DGs). If a number of MGs are controlled to maintain the predetermined electricity demand including RE‐based DGs as negative demand, they would contribute to supply–demand balancing of the whole electric power system. For constructing an MG economically, capacity optimization of controllable DGs against RE‐based DGs is essential. Using a numerical simulation model developed on the basis of a demonstrative study on an MG using PAFC and NaS battery as controllable DGs and photovoltaic power generation system (PVS) as an RE‐based DG, this study discusses the influence of the forecast accuracy of PVS output on capacity optimization. Three forecast cases with different accuracy are compared. The main results are as follows. Even with no forecast error during every 30‐minute period, the ideal forecast method, the required capacity of NaS batteries reaches about 40% of the PVS capacity for mitigating the instantaneous forecast error within 30 minutes. The required capacity to compensate for forecast error is doubled under the actual forecast method. The influence of forecast error can be reduced by adjusting the scheduled power output of controllable DGs according to weather forecasts. Besides, the required capacity can be reduced significantly if the error of balancing control in an MG is acceptable for a few percent of periods, because the total periods of large forecast error are not frequent. © 2012 Wiley Periodicals, Inc. Electr Eng Jpn, 182(2): 20–29, 2013; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.22328     

A basic study toward optimization of LFC resources in future power systems

Load frequency control (LFC) in future power systems, in which a large amount of solar photovoltaic generation is introduced, is studied. The constraints on LFC resources are classified as rate, simple, and energy limits. First, the nonlinear transfer functions of the limiters are modeled using random noise input. Second, the transfer functions of limiters are characterized by the coefficients of necessary facilities (CoNF). Third, the appropriateness of the concept and the identified value of CoNF is demonstrated through numerical simulations using a simple power system model. A way to control the contribution of existing and introduced resources to regulation of frequency fluctuation is proposed and demonstrated. © 2012 Wiley Periodicals, Inc. Electr Eng Jpn, 182(4): 47–59, 2013; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.22355     

Analysis of possible introduction of PV systems considering output power fluctuations and battery technology,employing an optimal power generation mix model

This paper presents an evaluation of the impact of extensive introduction of photovoltaic (PV) systems and stationary battery technology into the optimal power generation mix in the Kanto and Kinki regions. The introduction of solar PV systems is expected to be extensively deployed in the Japanese household sector and utility companies in order to address the concerns of energy security and climate change. Considering this expected large‐scale deployment of PV systems in electric power systems, it is necessary to investigate the optimal power generation mix which is technologically capable of controlling and accommodating the intermittent output‐power fluctuations inherent in PV systems. Against this background, we develop both a solar photovoltaic power generation model and an optimal power generation mix model, including stationary battery technology, which can be used to explicitly analyze the impact of PV output fluctuations at a detailed time interval resolution such as 10 minutes for 365 consecutive days. Simulation results reveal that PV introduction does not necessarily increase battery technology due to the cost competitiveness of thermal power plants in the load‐following requirement caused by PV systems. Additionally, on the basis of sensitivity analysis on PV system cost, dramatic cost reduction proves to be indispensable for PV to supply bulk electricity similarly to thermal and nuclear power plants. © 2012 Wiley Periodicals, Inc. Electr Eng Jpn, 182(2): 9–19, 2013; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.22329     

Characteristics evaluation of a CO2‐capturing power generation system with reheat cycle utilizing regenerative oxygen‐combustion steam‐superheater

A new CO₂‐capturing power generation system is proposed that can be easily realized by applying conventional technologies. In the proposed system, the temperature of medium‐pressure steam in a thermal power plant is raised by utilizing an oxygen‐combusting regenerative steam‐superheater. The CO₂ generated by combusting the fuel in the superheater can be easily separated and captured from the exhaust gas at the condenser outlet, and is liquefied. The superheated steam is used to drive a steam turbine power generation system. Using a high‐efficiency combined cycle power generation system as an example, it is shown that the proposed system can increase the power output by 10.8%, and decrease the CO₂ emissions of the entire integrated system by 18.6% with a power generation efficiency drop of 2.36% compared with the original power plant without CO₂ capture, when the superheated steam temperature is 750 ^°C. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 165(1): 35–41, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20575     

A study on voltage rise control effect by leading power factor operation of PVs considering tap change of distribution transformer

The voltage rise problem in distribution networks has been discussed as the foremost concern against the penetration of large amounts of photovoltaics (PVs). As a solution of such a problem, using voltage regulation facilities such as SVC (Static Var Compensator) or Loop power flow controller has been proposed. However, this might require major investments in the distribution network and that means the cost would be imposed on the nation. In this paper, the authors focus on the latent ability of the present distribution network and PVs to find solutions to the problem and propose a low‐cost solution to mitigate the voltage rise by using constant leading power factor operation of PVs. The distribution voltages are calculated in the case of increasing highly penetrated PVs, where it is very important to make an aggregated model of the distribution networks including loads and PVs. The authors aggregate many loads and PVs by using an aggregation method called “Y‐connection.” As a result of simulation with the aggregated realistic model of distribution networks, the authors confirmed that using a combination of leading power factor operation with $Q = - 0.2P$ and the LDC of the distribution transformer makes it possible to maintain adequate voltage without voltage regulation facilities such as SVC. © 2012 Wiley Periodicals, Inc. Electr Eng Jpn, 180(3): 46–54, 2012; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21276     

Optimal Weekly Operation Scheduling of Pumped Storage Hydropower Plant Considering Optimal Hot Reserve Capacity in a Power System with a Large Penetration of Photovoltaic Generation

In recent years, a large amount of photovoltaic (PV) generation capacity has been installed in power systems. However, the power output from the PVs is random and intermittent in nature. Therefore, PV generation poses many challenges to power system operation. To estimate the impact of these issues on power system operation, we propose an optimal weekly demand and supply simulation method considering large penetration of PV generation. In this paper, an operation scheduling method considering optimal hot reserve capacity is studied. The effectiveness of the proposed method is shown by using Monte Carlo simulation.     

太阳能电源热源一体化系统的设计与开发

从外观结构、能量流向及控制电路等方面设计了太阳能电源热源一体化系统。本系统具有可移动性,配备了滚轮且模拟光源可拆卸,可以在室外工作,在没有任何外接电源的情况下进行太阳能的相关应用。本系统结合了太阳能发电和太阳能发热两方面的技术,其中太阳能电源部分用于为自身供电并可对外输出电能,太阳能热源部分用于产生热能。通过实验测试结果可知,本系统每年可产生691kWh的电能和3047.8kWh的热能。本系统由于可移动且不需外接电源等特点,可满足偏远地区或孤岛等无电网地区的日常生活对热水与电力的需求,也可用于太阳能方面的实验测试。     

Potential evaluation of energy supply system in grid power system,commercial, and residential sectors by minimizing energy cost

If the economic activity in the commercial and residential sector continues to grow, improvements in energy conversion efficiencies of energy supply systems is necessary for CO₂ mitigation. In recent years, the electricity driven hot water heat pump (EDHP) and the solar photovoltaic (PV) have been commercialized. The fuel cell (FC) of co‐generation system (CGS) for the commercial and residential sector will be commercialized in the future. Copyright © 2004 Wiley Periodicals, Inc. The aim is to indicate the ideal energy supply system of the users sector, which manages both the economical cost and CO₂ mitigation, considering the grid power system. In this paper, cooperative Japanese energy supply systems are modeled by linear programming. It includes the grid power system and energy system of five commercial sectors and a residential sector. The demands of sectors are given by the objective term for 2005 to 2025. Twenty‐four‐hour load for each three annual seasons are considered. The energy systems are simulated to minimize the total cost of energy supply, and to mitigate the CO₂ discharge. As a result, the ideal energy system at 2025 is shown. The CGS capacity grows to 30% (62 GW) of the total power system, and the EDHP capacity is 26 GW, in commercial and residential sectors. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 160(2): 9–19, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/ eej.20361     

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     

Evaluation of output and unit cost of power generation systems utilizing solar energy under various solar radiation conditions worldwide

Characteristics and economics of three power generation systems which utilize solar energy were investigated and compared for systems located in five different regions. The three systems investigated were a solar thermal system, a solar photovoltaic system, and a CO₂‐capturing hybrid power generation system utilizing solar thermal energy (referred to as the hybrid system) which has been proposed by the authors. The net generated power energy and the net exergetic efficiency of the hybrid system have been estimated to be larger and higher, respectively, than those of the others. Economic evaluation reveals that the unit cost of generated power energy of the solar thermal system changes most widely corresponding to the change in solar radiation condition and that the cost of the hybrid system changes the least. In general, the most economical system has been estimated to be the solar thermal system in a location which is superior in solar condition and to be the hybrid system in a not so good solar condition. The solar photovoltaic system has the possibility of being the most economical if its construction cost is greatly improved, though the hybrid system is still the most economical under considerably worse solar conditions such as in Osaka. © 1999 Scripta Technica, Electr Eng Jpn, 127(3): 1–12, 1999     

Optimized coordinated control of LFC andSMES to enhance frequency stability of areal multi-source power system consideringhigh renewable energy penetration

With rapidly growing of Renewable Energy Sources (RESs) in renewable power systems, several disturbances influence on the power systems such as; lack of system inertia that results from replacing the synchronous generators with RESs and frequency/voltage fluctuations that resulting from the intermittent nature of the RESs. Hence, the modern power systems become more susceptible to the system instability than conventional power systems. Therefore, in this study, a new application of Superconducting Magnetic Energy Storage (SMES) (i.e., auxiliary Load Frequency Control (LFC)) has been integrated with the secondary frequency control (i.e., LFC) for frequency stability enhancement of the Egyptian Power System (EPS) due to high RESs penetration. Where, the coordinated control strategy is based on the PI controller that is optimally designed by the Particle Swarm Optimization (PSO) algorithm to minimize the frequency deviations of the EPS. The EPS includes both conventional generation units (i.e., non-reheat, reheat and hydraulic power plants) with inherent nonlinearities, and RESs (i.e., wind and solar energy). System modelling and simulation results are carried out using Matlab/ Simulink® software. The simulation results reveal the robustness of the proposed coordinated control strategy to preserve the system stability of the EPS with high penetration of RESs for different contingencies.     

Computation of locational and hourly maximum output of a distributed generator connected to a distribution feeder

Recently, the total number of distributed generation such as photovoltaic generation systems and wind turbine generation systems connected to a distribution network has drastically increased. Distributed generation using renewable energy can reduce the distribution loss and emission of CO₂. However, the distribution network with the distributed generators must be operated while maintaining the reliability of the power supply and power quality. In this paper, the authors propose a computational method to determine the maximum output of a distributed generator under operational constraints [(1) voltage limit, (2) line current capacity, and (3) no reverse flow to bank] at arbitrary connection points and hourly periods. In the proposed method, a three‐phase iterative load flow calculation is applied to evaluate the above operational constraints. The three‐phase iterative load flow calculation has two simple procedures: (Procedure 1) addition of load currents from the terminal node of the feeder to root one, and (Procedure 2) subtraction of voltage drop from the root node of the feeder to terminal one. In order to check the validity of the proposed method, numerical simulations are performed for a distribution system model. Furthermore, the characteristics of locational and hourly maximum output of a distributed generator connected to a distribution feeder are analyzed using several numerical examples. © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 167(2): 38–47, 2009; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20610     

Dynamic behavior of an island power system with variable‐pitch wind turbines under high renewable energy penetration and high wind speed

High penetration of renewable energy in a power system may cause the problem of power dispatching and stability. The detailed dynamic behavior analysis for such a system is therefore important to the planning and operation of the power system. This study discussed the dynamic characteristics of an island power system with variable‐pitch wind turbines under high wind speed and high small hydraulic output power. The system primarily consisted of three diesel engine power generation systems, three constant‐speed variable‐pitch wind turbines, a small hydraulic induction generation system, and lumped static loads. The maximum penetration of renewable energy in this system could reach almost 60%. Detailed models based on MATLAB/Simulink were developed to cater for the dynamic behavior of the system. The results suggested that this island power system can operate stably in this operational mode with the help of variable‐pitch wind turbines. This study can serve as an important reference for planning, operation, and further expansion of island power systems. Copyright © 2014 John Wiley & Sons, Ltd.     

A method for evaluating effects of energy efficiency improvement on carbon dioxide emission reduction

Global warming due to increasing atmospheric carbon dioxide (CO₂) is a matter of serious concern. Energy efficiency improvement has been considered to be the most effective strategy for reducing CO₂ emissions. The acceleration of R&D for energy technologies which have large effects on CO₂ emission reduction should be effective in abating global warming. In this study, the author proposes a method for evaluating the effects of energy efficiency improvement on CO₂ emission reduction. This method utilizes a compact energy system model combined with analytical calculations. Using this method, effects of energy efficiency improvement in Japan in the year 2030 are analyzed. Energy efficiency improvement in thermal power generation, nuclear power generation, and heat utilization are especially effective for reducing CO₂ emissions. The author estimates that CO₂ emissions per capita can be stabilized at the present level by energy efficiency improvement.     

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     

An Evaluating Model of Photovoltaic Power Output Variations for an Energy System Planning in an Urban Area

This paper presents a mathematical model to evaluate the power output variations from photovoltaic systems (PV) in collaboration with an energy system planning in an urban area, and applied the model to a demonstrating energy system. The evaluating model is developed from per-floor area PV power output variations on the basis of the past 1 year of actual solar insolation. The evaluation of the power variations is represented in terms of a per-floor area standard deviation curve. In case of considering two alternatives, battery-less and battery-installed PV systems, a correlative coefficient curve is calculated, then a total standard deviation curve representing the total PV power variations can be formulated on the basis of a random variable (RV) model. The model is applied as a tool to evaluate the power variation in an energy system. The energy system planning demonstration approaches the optimal planning by minimizing total cost under CO₂ emission reduction and the power variation constraints. The results show the impacts of the constraint of power variation that limit the installation of PV system. The constraint results the increase of the proportion of PV system with battery installation against PV system without battery installation. Consequently, the constraint also degrades the maximum potential of the entire system to reduce CO₂ emission corresponding to the decrease of PV system. © 2009 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Proposal and characteristics evaluation of a CO2-recovering hybrid power generation system utilizing solar thermal energy

A CO₂-recovering hybrid power generation system utilizing solar thermal energy is proposed. In the system, relatively low temperature saturated steam around 220°C is produced by using solar thermal energy and is utilized as the working fluid of a gas turbine in which generated CO₂ is recovered based on the oxygen combustion method. Hence, solar thermal utilization efficiency is considerably higher as compared with that of conventional solar thermal power plants in which superheated steam near 400°C must be produced for use as the working fluid of steam turbines; the requirement for solar radiation in the location in which the system is constructed can be significantly relaxed. The proposed system is a hybrid energy system using both the fossil fuel and solar thermal energy, thus the capacity factor of the system becomes very high. The fuel can be used exergetically in the system; i.e., it can be utilized for raising the temperature of the steam heated by utilizing the turbine exhaust gas more than 1000°C. The generated CO₂ can be recovered by using an oxygen combustion method, so that a high CO₂ capturing ratio of near 100 percent as well as no thermal NO_x emission characteristics can be attained. It has been shown through simulation study that the proposed system has a net power generation efficiency of 63.4 percent, which is higher than 45.7 percent as compared with that of the conventional power plant with 43.5 percent efficiency, when the amount of utilized solar energy is neglected and the temperature of the saturated steam is 220°C.     

Development of a city‐type compact wind power generation system

It is necessary to use renewable energy, such as photovoltaic, wind power, and biomass energy, from the viewpoint of CO₂ regulation and environmental protection of the Earth. In recent years, the tendency is toward larger wind power generation systems to achieve cheaper electricity. Generators having capacities of 1500 kW to 2000 kW tend to dominate the market. However, a large wind power generation system has limitations in terms of location and can be installed only in the suburbs. At the same time, a city‐type compact wind power generation system, designed for city needs, has more flexibility and can be installed in the residential areas of a city. In this paper, we introduce an original control operation system called a “pump‐up” operation system, designed to effectively use the city wind, and report the results of its field test. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 158(2): 56–63, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20440