G. T. Heydt

Harmonic Power Flow Studies Part I - Formulation and Solution

The conventional Newton-Raphson power flow study has been reformulated to permit the inclusion of nonlinear loads. These loads give rise to harmonic signals which propagate throughout the power system. The reformulation is based on the reduction to zero of the mismatch active power and reactive voltamperes, the imbalance current at harmonic frequencies, and the mismatch apparent Voltamperes. Conclusions on the existence of positive, negative, and zero sequence signals are made for harmonic frequencies. The harmonic power flow study formulation is illustrated for a three phase full wave bridge rectifier. A companion paper presents a discussion of the actual computer implementation and several practical examples.

Identification of harmonic sources by a state estimation technique

A reverse power flow procedure is described to identify the sources of harmonic signals in electric power systems. Methods have been reported elsewhere to analyze the propagation of these harmonics signals throughout the network. Here the reverse problem of how to identify the source (and potentially the type) of harmonic signals is considered. Line and bus data at several points in the network are used with a least-squares estimator to calculate the injection spectrum at buses suspected of being harmonic sources. When energy at harmonic frequencies is found to be injected into the network at a bus, that bus is identified as a harmonic source. >

Dynamic state estimation of power system harmonics using Kalman filter methodology

A Kalman filter is used to obtain the optimal estimate of the power system harmonic content. The measurements are simulated by adding Gaussian noise to the power system voltage and line flows at different harmonies obtained from a harmonic load flow program (HARMFLO). The effect of load variation over a one day cycle on the power system harmonics and standard are presented. The test results on the IEEE 14 bus system are included. The main difference in this approach from static estimation methods is that this method is dynamic and has the capability of tracking harmonic content versus time. >

The Impact of Electric Vehicle Deployment on Load Management Straregies

The future penetration of electric vehicles into the transportation sector is unknown. However, if off peak recharging of electric vehicles is employed, considerable improvement in daily load factor is possible. Similarly, load management methods to shift peak load to off-peak periods will also improve load factor. The impact of electric vehicle deployment on load management strategies primarily occurs in two areas: (i) reduction in effectiveness of load factor improvement of either electric vehicle deployment or load management strategies due to the action of the other and (ii) inadvertent addition to peak demand by electric vehicle load. These and other factors are considered in this paper and several practical considerations of recharging of electric vehicles are summarized.

Probabilistic Methods For Power System Dynamic Stability Studies

In this paper, several sources of uncertainty in electric power systems are incorporated into the dynamic stability analysis of the system. Operating point stability is considered, with the system model written in state variable notation. The sensitivites of the eigenvalues of the associate matrix are used to calculate the statistics of eigenvalue locations. When the uncertainties considered are approximated by the multivariate normal distribution, the probability of dynamic stability is computed using the generalized tetrachoric series. The principle advantages of this method over multiple runs of a deterministic stability study are rapid calculation times and the availability of consistently calculated probability of operating point stability figures.

Harmonic Power Flow Studies - Part II Implementation and Practical Application

This is a companion paper to a paper of the same title, Part I, in which the eLectric power flow problem is reformulated to account for harmonic signals which arise from nonLinear loads. In this paper, implementation and practical applications are discussed. The problem of initialization of bus voltages (including harmonics) is considered and convergence of the algorithm is assessed from the theoretical viewpoint and from the results of actual studies. The principal content of this paper is two examples both containing nonlinear loads (rectifiers).

Fast Transient Security Assessment

The growth of large interconnected power systems demands a high degree of security for normal operation. This requirement emerges from the fact that the possible disturbances in large power systems could have catastrophic results. Therefore it is the duty of power system control center to retain the operating point within secure boundaries. In order to control the security of system, one has to monitor and analyze the level of system security and enhance it in case it does not fulfill the system security requirement. The pattern recognition technique which is proposed in this paper is a method suitable for fast, on-line. security assessment. Most of the literature in this area concerns the use of steady state variables for identification purposes; the use of transient measurements, however, has been found to be better suited for the fast classification of operating points with minimal error. One of the salient conclusions of this paper is that the pattern recognition technique is a serious candidate for on-line applications. This favorable conclusion is based on the inclusion of transient state variables in the feature vector.

A hybrid nonlinear-least squares estimation of harmonic signal levels in power systems

It is expected that guides and recommended practices will be adopted in the United States for the limitation of harmonic currents and voltages in electric power systems. A method of using measurements and topological/mathematical methods to identify signal levels that do not comply with these guides and standards is described. The methodology is based on measurements, state estimators, and system modeling. An illustration of its application is given. A hybrid nonlinear-least-squares method is used for state estimation. This estimation theory is used to calculate (estimate) bus voltages and line currents which cannot be (or are not) measured directly. The basis for the least-squares estimator is the Kirchhoff current law, and the basis for the nonlinear technique is minimum mismatch power. >

An assessment of ocean thermal energy conversion as an advanced electric generation methodology

The history of ocean thermal energy conversion (OTEC), a process that employs the temperature difference between surface and deep ocean water to alternately evaporate and condense a working fluid, is reviewed. In the open-cycle OTEC configuration, the working fluid is seawater. In the closed-cycle configuration, a working fluid such as propane is used. OTEC is assessed for its practical merits for electric power generation. Because rather large amounts of seawater and working fluid are required, the energy requirements for pumping them may be greater than the energy recovered from the OTEC engine itself. The concept of net power production is discussed. The components of a typical OTEC plant are described with emphasis on the evaporator heat exchanger. Operation of an OTEC electric generating station is discussed, including transient operation. Recent experiments and efforts at the National Energy Laboratory-Hawaii (NELH) are summarized. Remarks are made on bottlenecks and the future of OTEC as an advanced electric generation methodology. >

Transient stability assessment by pattern recognition in the frequency domain

A pattern recognition methodology is presented which utilizes spectral monitoring of electromechanical oscillations to assess the transient stability of interconnected power systems. The proposed frequency-domain approach permits definitive recognition of unstable dynamic modes. This is used to design an adaptive linear classifier which, in the developmental implementation, virtually eliminates both false dismissals and false alarms. The result is an accurate and reliable decision-making system which performs transient stability monitoring and assessment in real time. >