Active filtering of electric power has now become a mature technology for harmonic and reactive power compensation in two-wire (single phase), three-wire (three phase without neutral), and four-wire (three phase with neutral) AC power networks with nonlinear loads. This paper presents a comprehensive review of active filter (AF) configurations, control strategies, selection of components, other related economic and technical considerations, and their selection for specific applications. It is aimed at providing a broad perspective on the status of AF technology to researchers and application engineers dealing with power quality issues. A list of more than 200 research publications on the subject is also appended for a quick reference.

A review of active filters for power quality improvement

In a world where environment protection and energy conservation are growing concerns, the development of electric vehicles (EV) and hybrid electric vehicles (HEV) has taken on an accelerated pace. The dream of having commercially viable EVs and HEVs is becoming a reality. EVs and HEVs are gradually available in the market. This paper will provide an overview of the present status of electric and hybrid vehicles worldwide and their state of the art, with emphasis on the engineering philosophy and key technologies. The importance of the integration of technologies of automobile, electric motor drive, electronics, energy storage, and controls and also the importance of the integration of society strength from government, industry, research institutions, electric power utilities, and transportation authorities are addressed. The challenge of EV commercialization is discussed.

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The state of the art of electric and hybrid vehicles

With the progressive exhaustion of fossil energy and the enhanced awareness of environmental protection, more attention is being paid to electric vehicles (EVs). Inappropriate siting and sizing of EV charging stations could have negative effects on the development of EVs, the layout of the city traffic network, and the convenience of EVs' drivers, and lead to an increase in network losses and a degradation in voltage profiles at some nodes. Given this background, the optimal sites of EV charging stations are first identified by a two-step screening method with environmental factors and service radius of EV charging stations considered. Then, a mathematical model for the optimal sizing of EV charging stations is developed with the minimization of total cost associated with EV charging stations to be planned as the objective function and solved by a modified primal-dual interior point algorithm (MPDIPA). Finally, simulation results of the IEEE 123-node test feeder have demonstrated that the developed model and method cannot only attain the reasonable planning scheme of EV charging stations, but also reduce the network loss and improve the voltage profile.

Optimal Planning of Electric-Vehicle Charging Stations in Distribution Systems

This paper summarizes diverse concepts for the next generation of power distribution system. The objective is to bring distribution engineering more closely aligned to smart grid philosophy. Issues of design, operation, and control are discussed with regard to new system theoretic as well as component/materials advances. In particular, two transmission engineering techniques are modified for use in distribution engineering: state estimation, and locational marginal pricing. The impact of electronic control in distribution systems is discussed. Because education and training have a great impact on distribution engineering, these topics are discussed as well.

The Next Generation of Power Distribution Systems

Some uncertainties, such as the uncertain output power of a plug-in electric vehicle (PEV) due to its stochastic charging and discharging schedule, that of a wind generation unit due to the stochastic wind speed, and that of a solar generating source due to the stochastic illumination intensity, volatile fuel prices, and future uncertain load growth could lead to some risks in determining the optimal siting and sizing of distributed generators (DGs) in distribution system planning. Given this background, under the chance constrained programming (CCP) framework, a new method is presented to handle these uncertainties in the optimal siting and sizing of DGs. First, a mathematical model of CCP is developed with the minimization of the DGs' investment cost, operating cost, maintenance cost, network loss cost, as well as the capacity adequacy cost as the objective, security limitations as constraints, and the siting and sizing of DGs as optimization variables. Then, a Monte Carlo simulation-embedded genetic-algorithm-based approach is employed to solve the developed CCP model. Finally, the IEEE 37-node test feeder is used to verify the feasibility and effectiveness of the developed model and method, and the test results have demonstrated that the voltage profile and power-supply reliability for customers can be significantly improved and the network loss substantially reduced.

Optimal Siting and Sizing of Distributed Generators in Distribution Systems Considering Uncertainties

In this paper we use the results of simulations to predict the net harmonic currents produced by large numbers of single-phase desktop computers in a facility, such as a commercial office building. We take into account attenuation due to system impedance and voltage distortion, as well as diversity in harmonic current phase angles due to variations in power and circuit parameters. Using experimental and published data we establish ranges of circuit parameters for an equivalent 120 V, 100 W "base computer unit" and branch circuit, update our computer modeling code (described in previous papers) to iteratively handle the interaction between current and voltage harmonics, and use the code to predict the net harmonic injection currents at the point of common coupling (PCC) represented by a shared transformer connected to a stiff power system. The key contributions of this paper are: providing estimates of the net harmonic current injection due to distributed single-phase computer loads in Amps/kW, as well as in percent of fundamental current, for a wide range of system loading and voltage distortion conditions; and illustrating that the reduction in harmonic currents due to phase angle diversity (expressed in Amps/kW) is relatively independent of system loading, whereas the reduction due to attenuation increases significantly with system loading. >

Predicting the net harmonic currents produced by large numbers of distributed single-phase computer loads

This paper describes the effect of supply voltage harmonics on the response of single-phase capacitor-filtered diode bridge rectifier loads. A complete analytical model for calculating the current harmonics of these loads, when energized by nonsinusoidal supply voltages, is presented. The model is then used to investigate the effect of supply voltage harmonics on current harmonics. The key findings of the paper are as follows: (1) the phase angles of supply voltage harmonics determine whether or not these harmonics increase or decrease current distortion. In general, a peaked voltage wave increases input current distortion, whereas a flattened wave has the opposite effect. Because of this complex relationship, voltage crest factor is a much better predictor of total harmonic current distortion than is total harmonic voltage distortion. (2) The current harmonics created by these loads produce voltage harmonics that tend to have a partial self-compensating effect on the current harmonics. >

Effect of supply voltage harmonics on the input current of single-phase diode bridge rectifier loads

This paper presents a method for predicting the net harmonic currents produced by a large number of electric vehicle (EV) battery chargers. The problem is stochastically formulated in order to account for randomness in individual charger start-time and battery state-of-charge. The authors introduce a model that allows for partial harmonics cancellation due to diversity in magnitudes and phase angles. A general solution technique is presented along with an example using data from a commercially available EV charger. Their results show that a limiting distribution of 7-10 chargers is adequate for accurately predicting harmonic injection currents using the central limit theorem. They also show that the expected values of net harmonic currents are considerably less than the peak values that would have been realized if the same number of chargers were operated in unison.

A statistical method for predicting the net harmonic currents generated by a concentration of electric vehicle battery chargers

This paper presents a statistical method for predicting the effect that widespread electric vehicle (EV) battery charging will have on power distribution system harmonic voltage levels. The method uses a statistical model for nonlinear load currents to generate the probabilities of specific harmonic voltage levels. The statistical model for the harmonic currents produced by a concentration of EVs accounts for partial harmonics cancellation introduced by uncertainty and variation in charger start-time and initial battery state-of-charge. A general solution technique is presented along with several examples using data from a commercially-available EV charger and an actual power distribution system. The results show that there is a definite threshold penetration below which EV charging has negligible impact on the number of buses whose voltage total harmonic distortion (THD/sub V/) exceeds 5%. During the late evening of a summer day, the authors' example distribution system can accommodate EV penetration levels as high as 20%. A similar analysis of the system in the spring or fail indicates that the system can accommodate a 15% EV penetration before THD/sub V/ exceeds 5% at an unacceptable number of buses.

A statistical analysis of the effect of electric vehicle battery charging on distribution system harmonic voltages

The concept of "standards" is introduced for the design of power acceptability curves. The power acceptability curves are aides in the determination of whether the supply voltage to a load is acceptable for the maintenance of a load process. The construction of the well-known Computer Business Equipment Manufacturing Association (CBEMA) power acceptability curve is discussed, and issues of 3-phase and rotating loads are discussed.

R.S. Thallam

Papers

Predicting the net harmonic currents produced by large numbers of distributed single-phase computer loads

Effect of supply voltage harmonics on the input current of single-phase diode bridge rectifier loads

A statistical method for predicting the net harmonic currents generated by a concentration of electric vehicle battery chargers

A statistical analysis of the effect of electric vehicle battery charging on distribution system harmonic voltages

The design of power acceptability curves