Rong-Ceng Leou

Stochastic Analyses of Electric Vehicle Charging Impacts on Distribution Network

A stochastic modeling and simulation technique for analyzing impacts of electric vehicles charging demands on distribution network is proposed in this paper. Different from the previous deterministic approaches, the feeder daily load models, electric vehicle start charging time, and battery state of charge used in the impact study are derived from actual measurements and survey data. Distribution operation security risk information, such as over-current and under-voltage, is obtained from three-phase distribution load flow studies that use stochastic parameters drawn from Roulette wheel selection. Voltage and congestion impact indicators are defined and a comparison of the deterministic and stochastic analytical approaches in providing information required in distribution network reinforcement planning is presented. Numerical results illustrate the capability of the proposed stochastic models in reflecting system losses and security impacts due to electric vehicle integrations. The effectiveness of a controlled charging algorithm aimed at relieving the system operation problem is also presented.

An economic analysis model for the energy storage systems in a deregulated market

Recent developments and advances in energy storage technologies are making the application of energy storage technologies a viable solution to power applications. The energy storage systems can store energy previously, and then release it in the proper time. Due to their flexibility, it is suitable to apply this technology to deregulated power markets. Therefore, this paper will build the economic analysis model for the energy storage systems in a deregulated power market. The costs including installing energy storage systems and operation & maintenance expense and the revenues containing energy price arbitrage, reducing transmission access cost, and deferring facility investment are considered in this paper. All these factors are evaluated by present worth value. Due to complexity of this problem, this paper proposes a method combining the genetic algorithm with linear program (GALP) to determine the best capacity and operating status of the energy storage system.

Optimal Charging/Discharging Control for Electric Vehicles Considering Power System Constraints and Operation Costs

With the popularization of electric vehicles (EVs), the influence on power systems is receiving increasing attention. According to statistics, EVs are in a parking state for more than 90% of the time, thus, the electric energy of the EVs accumulated by aggregators can be used to support the operation of power systems. This paper takes reducing operation costs as the objective function and considers the constraints of EVs and power systems to establish the optimal charging/discharging control of electric vehicles, which meet the operational safety of power systems and convenient driving. The influence on operation costs, peak load, and loss for the proposed charging/discharging two-way control, charging-only control, and free charging modes of EVs are compared. The influence of battery charging and discharging efficiency on these results is also discussed in this paper.

A power quality monitoring system based on J2EE architecture

Due to the rapid development of the industry, the requirement of the power quality is more rigorous than ever. In spite of a short period of time of power outage, it may lead to a large amount of loss. Recently, many companies perform power quality site surveys. Power quality monitoring becomes one of the major services of the power company for his customers. A good understanding of the power quality can help power companies choose correct instruments to improve the power quality. In order to construct a good and flexible power quality monitoring system, this paper designs a power quality database system according to the monitoring data from feeders, and builds an information technology system based on J2EE (Java 2 platform, enterprise edition) architecture.

The optimal portfolio of the day-ahead market and real-time market for the load serving entities

With the deregulation of the electric utilities, load serving entities face more financial risk. Load serving entities serve retail customers by contracts, which are structured to shield the customers from any fluctuation from the wholesale price of electricity. The financial risk from the wholesale market must therefore be absorbed by the load serving entities. This paper will consider that the load serving entities obtain power energy by participating in the day-ahead market, real-time market, and electricity contracts, and propose an investment model for load serving entities to determine their ratios. Therefore, this paper will build a mathematic model to determine the optimal portfolio that load serving entities invest in the day-ahead market and real-time market with or without the electricity contracts. These results will help the load serving entities to find a balance between the benefit and risk.

RFID-based autonomous mobile car

Radio Frequency Identification (RFID) system is looked upon as one of the top ten important technologies in the 20th century. Industrial automation application is one of the key issues in developing RFID. Therefore, this paper designs and implements a RFID-based autonomous mobile car for more extensively application of RFID systems. The microcontroller of Microchip PIC18F4550 is used to control the autonomous mobile car and to communicate with RFID reader. By storing the moving control commands such as turn right, turn left, speed up and speed down etc. into the RFID tags beforehand and sticking the tags on the tracks, the autonomous mobile car can then read the moving control commands from the tags and accomplish the proper actions. Due to the convenience and non-contact characteristic of RFID systems, the proposed mobile car has great potential to be used for industrial automation, goods transportation, data transmission, and unmanned medical nursing etc. in the future. Experimental results demonstrate the validity of the proposed mobile car.

Analysis of PEV charging impact on distribution transformer aging for charging station transformer design

As plug-in electric vehicles (PEVs) are expanding, there is a growing need for widely distributed publicly accessible charging stations that supply electric energy for the recharging of the PEVs. In the charging station design, the proper distribution transformers that delivery reliable power from utility to the station are essential and important. To ensure economic and reliable operation of the charging station, the paper proposes a methodology for the PEVs charging station transformer design. A set of dynamic thermal energy models that describe the relationship between the transformer winding temperature and charging station load profile is derived according to ANSI/IEEE standards. The base load, PEVs demand, power quality, ambient temperature, transformer rating and connection all are taken into account. The models are then used to analyze PEVs charging impact on transformer loss-of-life and determine the proper transformer capacity and connection. The proposed method provides a better knowledge of the transformer effects and can be used for evaluating the level of PEVs that might be accepted on a distribution transformer. The models developed can also be used for determining proper transformers in the design of charging station distribution systems. The field testing results of a practical charging station for PEVs pilot projects in Taiwan confirm the validity of the proposed method.

A Multiyear Transmission Planning Under a Deregulated Market

In a deregulated market, transmission planning plays an essential role on providing a fair and competitive environment. Due to different market architectures, this kind of planning is different from that of monopoly power industry. This paper proposes a multiyear transmission model under a deregulated market. This model considers investment costs, operation costs, and load curtailment costs for different load scenarios. In order to deal with this complex model, a genetic algorithm is used to solve this problem

The estimation of interharmonics by group frequencies

In this paper, an innovative concept, group frequency (GF), is proposed to facilitate the analysis of power system interharmonics as well as conventional integer harmonics. The concept is applied in the analysis of load currents of integral cycle controllers (ICCs) and other controlled power applications. A GF can be generalized for the analysis of load currents or voltages of other power devices. One of the advantages of the GF is that a large number of frequency components of a load voltage or current are simplified to a few frequency components without significantly changing the power quality impact of the load current or voltage.

Harmonic current characteristic analysis for wind turbines

This paper analyzes the harmonic current characteristic of wind turbines. Field measurement, data sorting, and analysis are conducted for wind turbine. Most wind turbines at present use a power converter and are equipped with harmonic filters, the control results of these equipments will become highly stochastic as wind speed changes. Even if there is a slight difference in the wind speed, harmonic output of wind turbine will be quite different. If harmonic currents are segmented and the probability density distributions are calculated, then different viewpoints as can be observed. Although harmonic currents of the wind turbine are stochastic, the probability density distributions are close to normal distribution. A stochastic harmonic current predictor is then proposed in this paper based on the probability density distributions of harmonic current. Test results show that the harmonic currents of a wind turbine in long-term operation can be effectively analyzed by the established probability density distributions.