W.T. Yang

Two-level optimal output feedback stabilizer design

Design of two-level system stabilizers is considered using an optimal reduced-order model whose state variables are torque angles and speeds. The reduced-order model retains their physical meaning and is used to design a two-level linear feedback controller that takes into account the realities and constraints of the electrical power systems. The two-level control strategy is used, and a global control signal is generated from the output variables to minimize the effect of interaction. The effectiveness of this controller is evaluated, and an example, the multimachine system, is given to illustrate the advantages of the proposed method. The responses of the system with the two-level scheme and optimal reduced order scheme are included for comparative analyses. >

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 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.

Power system feedback stabilizer design via optimal subeigenstructure assignment

Power system stabilizer (PSS) design is addressed using an optimal reduced order model whose state variables are torque angles and speeds. System damping can be improved by using eigenvalue assignment, and the coordination of stabilizers can be achieved through eigenvector assignment by maintaining system mode shapes. The proportional-integral PSSs are derived by the optimal reduced order model. The effectiveness of the stabilizer is evaluated. By using the output feedback only, the result of eigenstructure assignment is more stable and much better than the assignment method based on the whole system model. Examples, a single-machine to infinite bus system and a multimachine system, are given to illustrate the advantages and effectiveness of the proposed approach. Results based on the whole system model are included for comparative analyses. >

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.

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.

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.

An improved minimizing algorithm for the sum of disjoint products with the inversion of a single variable

Abstract This paper presents a new method, the ALL algorithm, of representing the reliability formula of network system in the form of the near smallest number of sdp terms. The main feature of the ALL is its ability to properly arrange the order of minimal paths as well as to apply inversion to products of single variable. While the Abraham algorithm and its successors yield relatively short sdp forms of the Boolean functions of coherent network systems, this new method generates shorter disjoint products than any other known sdp method. Because the system reliability formula is considerably reduced in the number of terms, there will be a sharp decrease both in computation time and in rounding errors.