Chun-Chang Liu

A new method for calculating loss coefficients [of power systems]

A method is proposed which avoids many limitations associated with traditional B-coefficient loss coefficient calculation. The proposed method, unlike the traditional B-coefficient method, is very fast and can handle line outages. The method utilizes network sensitivity factors which are established from DC load flow solutions, Line outage distribution factors (ODFs) are formulated using changes in network power generations to simulate the outaged line from the network. The method avoids the use of complicated reference frame transformations based upon Krons tenser analysis. The necessity of data normalization used in least squares and the evaluation of the slope of /spl theta//sub j/ versus PG/sub n/ is not necessary with the proposed method. Using IEEE standard 14-bus and 30-bus systems, the methods results are compared against results obtained from an AC load flow program (LFED). The methods solution speed is compared to that of the LFED method, the base case database method and the conventional B-coefficient method based on A/sub jn/-factor. The proposed method is easy to implement and, when compared to other methods, has exhibited good accuracy and rapid execution times. The method is well suited to online dispatch applications. >

An output feedback static var controller for the damping of generator oscillations

Abstract The damping of electromechanical oscillations of synchronous generators using an output feedback static var controller is investigated in this paper. An eigenstructure assignment technique is applied to design this controller. The designed controller is simple in structure and easily implemented by a proportional-integral (PI) controller. Eigenvalue analyses and time domain simulations under different loading conditions are both performed in order to demonstrate the effectiveness of the proposed controller.

An improved minimizing algorithm for the summation of disjoint products by Shannon's expansion

Abstract This paper presents a new method, the SLR algorithm, of representing the reliability formula of network system in the form of the near smallest number of sdp terms. The virtue of SLR lies in its ability to express the Boolean function in sdp form on the basis of Shannons expansion theorem, reducing the number of sdp terms to the near smallest by choosing the most appropriate variable xi. While the Abraham algorithm and its successors obtain relatively short sdp forms of the Boolean functions of coherent network systems, this new method generates shorter disjoint product terms than any other known sdp method. Because the system reliability formula is considerably reduced in the number of terms, there will be sharp computational saving in processing larger paths of complex networks. Its ease of full documentation is a further positive feature for reliability analysts.

Analysis of the performance of induction watthour meters in the presence of harmonics (a new model approach)

Abstract A quasilinear model is developed to investigate the registration error of an induction watthour meter in the presence of harmonics. The registration error is determined by all the frequency responses of the harmonic components, the distortion factors of voltage and current harmonics, and the harmonic power factors; their relationship is clearly expressed in a simple error function by using the model, which provides a firm analytical basis to describe all the phenomena of the frequency response and harmonics response of the meter. All the meter parameters in the model are measurable; the measurement principles and procedures are also described in this paper. The presented model is more general, simple and parameter measurable than those of past studies. Its capability and accuracy have been verified by comparing experimental and computation results for typical single-phase and three-phase induction watthour meters.

Improvements on the line outage distribution factor for power system security analysis

Abstract This paper presents two sensitivity factors in terms of the generation shift distribution factor (GSDF) to improve some defects of the conventional formula for the line outage distribution factor (ODF). The sensitivity factors are established by using the concepts of generation change and power injection to simulate the outaged line flow and one of them is then applied to the case of line addition. A transfer factor is derived to calculate the power flow of the added line very quickly from the relationship between the ODF and the GSDF. The proposed method has been tested by means of a standard system. Compared with the conventional ODF in the line outage case and with DC load flow in the line addition case, the proposed method has good accuracy and a fast execution time. This method is very suitable for real-time security assessment and contingency analysis of power systems.

A multiobjective optimization approach to loading balance and grounding planning in three-phase four-wire distribution systems

Abstract This paper proposes a multiobjective optimization approach to loading balance and grounding planning. A new formulation is presented of the optimal loading balance and grounding planning problem in three-phase four-wire distribution systems. This formulation is a multiconstraint, multiobjective and nondifferentiable optimization problem with both equality and inequality constraints. It encompasses four desired objectives related to investment, operational efficiency, security, and pollution of the system. A method based on simulated annealing was used to determine (i) the phase load pattern, (ii) the locations of the neutral to be grounded, and (iii) the types of numbers of ground electrodes to be installed such that the desired objective functions are minimized while the load variation and system operation constraints are met. The ϵ-constraint method was incorporated in the method to solve the multiobjective problem. A salient feature of the method is that it allows designers to find a desirable, global, noninferior solution of the problem.

Real-time line flow calculation using a new sensitivity method

Abstract This paper presents an injected power shift distribution factor to improve the deficiencies of conventional sensitivity methods. A modified two-step technique, combining the generalized generation shift distribution factor and the proposed injected power shift distribution factor, is developed to consider the nonconformity of the demand change. Line flows can be obtained directly without running a load flow program when the system operating point is shifted to a new one. The derivation is performed in an integral form to replace an incremental form reported in the literature and the solution algorithm is described. The potential performance of the proposed method is demonstrated by means of a standard system. Compared with the exact solution of the fast decoupled load flow calculation, the proposed method has a lower execution time and high solution accuracy. This method is very suitable for real-time application in power system operation.

Harmonic compensation of induction watthour meter performance

Abstract This paper analyzes the variation of the registration error of an induction watthour meter (IWHM) with respect to those parameters concerning the harmonic characteristics of the load and harmonic performance of the IWHM. Based on an analysis of the results of error variation, two types of compensation methods, namely, meter external methods and meter internal methods, are proposed to improve the accuracy of the IWHM when operated in harmonic situations. The meter external methods are related to the harmonic characteristics of the load, while the meter internal methods are associated with the harmonic performance of the IWHM. Each compensation method is comprised of several measures. This paper presents these measures for each compensation method, and gives detailed illustrations of the practical aspects for each measure. The feasibility of each compensation method is assessed, and some useful suggestions for utilities, users and manufacturers of IWHMs are offered. The study results show that the registration error due to constant single power harmonic interference can be fully compensated. When multiple power harmonics exist, however, the compensation, in general, can only focus on the main harmonic component to reduce the registration error to as low as possible. The effectiveness of those compensation methods which are feasible has been confirmed by the experimental results.

On-line economic dispatch using a new loss coefficient formula

Abstract This paper presents an on-line economic power dispatch method by calculating the B -coefficients from the network sensitivity factors. The sensitivity factors are established from a new line flow solution based on the DC load flow model. The derivation of a new loss coefficient formula is performed and the solution algorithm is described. Many assumptions in the use of the conventional loss coefficients are eliminated. Example systems are tested to demonstrate the performance of the proposed method. Compared with the exact solution of the optimal load flow method and the computational rapidity of the base-case database method, the proposed method has good accuracy and a fast execution time. This method is very suitable for on-line application in the economic operation of power systems.

An improved minimizing algorithm for sum of disjoint products by Shannon's expansion

Abstract This paper presents a new method, the Schneeweiss-Liu revised (SLR) algorithm, to represent the reliability formula of a network system in the form of the nearly smallest number of the sum of the disjoint product (sdp) terms. The virtue of the SLR algorithm lies in its ability to express the Boolean function in sdp form on the basis of Shannons expansion theorem, reducing the number of sdp terms to the nearly smallest by choosing the most appropriate variable xi. While the Abraham algorithm and its successors obtain relatively short sdp forms of the Boolean functions of coherent network systems, this new method generates shorter disjoint product terms than any other known sdp method. Because the number of terms in the system reliability formula is considerably reduced, there will be sharp computational saving when processing larger paths of complex networks. The ease of full documentation with this method is a further positive feature for reliability analysts.