Ching-Tzong Su

Variable scaling hybrid differential evolution for solving network reconfiguration of distribution systems

This paper presents an effective method-variable scaling hybrid differential evolution (VSHDE)-for solving the network reconfiguration for power loss reduction and voltage profit enhancement of distribution systems. The network reconfiguration of distribution systems is to beneficially recognize load transfers so that the objective function composed of power losses is minimized and the prescribed voltage limits are satisfied. The variable scaling factor based on the 1/5 success rule is used in the VSHDE method to overcome the drawback of the fixed and random scaling factor and alleviate the problem of the selection of a mutation operator in the hybrid differential evolution (HDE). One three-feeder distribution system from the literature and one practical distribution network of Taiwan Power Company (TPC) are used to compare the performance of the proposed method with the HDE, genetic algorithms (GAs), and simulated annealing (SA). Numerical results show that the performance of the proposed method is better than the other methods.

New approach with a Hopfield modeling framework to economic dispatch

This paper presents a new Hopfield model based approach for the economic dispatch problem of power systems. To solve the economic dispatch problem using the Hopfield model, an energy function composing power mismatch, total fuel cost and the transmission line losses is defined. The weighting factors associated with the terms of the energy function can be either appropriately selected or directly estimated in the proposed model. Which, however, are determined by trial and error in the conventional Hopfield method. To minimize the value of the energy function, the computational procedures including a series of adjusting the weighting factor associated with the transmission line losses and updating the unit generations and power losses are carried out. Because the weighting factors are governed by some relationships developed, adjustment of the weighting factor is much simpler and more effective in steadily achieving solutions than adjustment of the /spl lambda/-multiplier in the lambda-iteration method for economic dispatch problems. Computational results reveal that this approach can find accurate solutions more simply and fast compared with the conventional lambda-iteration method.

Ant direction hybrid differential evolution for solving large capacitor placement problems

This paper presents an ant direction hybrid differential evolution (ADHDE) with integer programming which is effective and efficient for solving large capacitor placement problems in distribution systems. The use of proper mutation operator in hybrid differential evolution (HDE) can accelerate the search of a global solution. However, the selection of mutation operator depends on the problem. In this study, the ADHDE method utilizes the concept of ant colony search to search the proper mutation operator to accelerate searching out the global solution. Various-scale application systems are used to compare the performance of the proposed method with HDE, simulated annealing, and ant system. Numerical results show that the performance of the proposed ADHDE method is better than the other methods. Also, the ADHDE method is superior to some other methods in terms of solution power loss and costs.

A fast-computation Hopfield method to economic dispatch of power systems

This paper develops a direct-computation Hopfield method for solving the economic dispatch (ED) problems of thermal generators. The method employs a linear input-output model for neurons. Formulations for solving the ED problems are explored. Through the application of these formulations, direct computation instead of iterations for solving the problems becomes possible. Unlike the usual Hopfield methods which select the weighting factors of the energy function by trials, the proposed method determines the corresponding factor using formulation calculation. Hence, it is relatively easy to apply the proposed method. The effectiveness of the developed method is identified through its application to two example power systems. Computational results show that the method has excellent performance, and that it is superior to other methods in many respects.

A new fuzzy-reasoning approach to optimum capacitor allocation for primary distribution systems

This paper presents a fuzzy-reasoning method to optimum shunt capacitor placement and sizing for the radial distribution systems. In the method, capacitor allocation is applied to correct voltage and reduce power loss for a given load pattern. The problem of capacitor allocation includes the location, type (fixed or switched), and size of capacitor. Hence it is a combinatorial optimization problem with multiple objectives. A simple algorithm is presented for optimal capacitor placement and sizing problem of distribution systems having concentrated loads. Two membership functions are defined for voltage and power loss, respectively. Results are obtained through applying a simple min-operation. The method proposed is simple, straightforward, and effective.

Feeder reconfiguration and capacitor setting for loss reduction of distribution systems

Abstract The stress to elevate overall efficiency has forced utilities to look for greater efficiency in electric power distribution. This study presents an effective approach to feeder reconfiguration and capacitor settings for power-loss reduction and voltage profile enhancement in distribution systems. The optimization technique of simulated annealing (SA) can be relied on to solve the problem efficiently. The merit of the method is that it can provide a global or near-global optimum for feeder reconfiguration and capacitor settings. The objective of this study is to recognize beneficial load transfer, to take the objective function composed of power losses be minimized and voltage limits be satisfied. The proposed approach is demonstrated by employing an IEEE illustrative example. Computational results show that by taking into account feeder reconfiguration and capacitor settings simultaneously, one can minimize losses more efficiently than by considering them separately.

Fuzzy-Based Voltage/Reactive Power Scheduling for Voltage Security Improvement and Loss Reduction

This paper presents a new approach using fuzzy set theory for voltage and reactive power control of power systems. The purpose is to find a solution that takes both voltage security enhancement and loss reduction into account for an electric power system. The approach translates violation levels of buses voltage and controlling ability of controlling devices into fuzzy set notations using a linearized model. A feasible solution set that achieves voltage improvement is first attained using the max-min operation of fuzzy sets. The final solution, which takes power loss reduction into account, is then determined employing the min-operation on the feasible solution set previously obtained. A modified IEEE 30-bus test system is used to demonstrate the application of the proposed approach. Simulation results show that the approach is efficient, simple, and straightforward.

A new fuzzy control approach to voltage profile enhancement for power systems

This paper presents a new approach using fuzzy set theory for voltage and reactive power control of power systems. The purpose is to enhance voltage security of an electric power system. The violation bus voltage and the controlling variables are translated into fuzzy set notations to formulate the relation between voltage violation level and controlling ability of controlling devices. A feasible solution set is first attained using the minimum operation of fuzzy sets, then the optimal solution is quickly determined employing the maximum operation. A modified IEEE 30-bus test system is used to demonstrate the application of the proposed approach. Simulation results show that the approach is efficient and has good flexibility and adaptability for voltage-reactive power control.

A Hopfield network approach to economic dispatch with prohibited operating zones

This paper presents a Hopfield model to solve the power system economic dispatch (ED) problem with some of the units having prohibited operating zones. In the proposed method, the authors introduce an equilibrium point, lying in the interior of a prohibited zone, which will divide the prohibited zone into the left and the right prohibited zones referred to this point. In this way, in order to prevent the unit from operating into prohibited zone, they incorporate the novel countermeasures into the proposed Hopfield model. Through case studies of a system with 15 units, they prove the possibility of application of the Hopfield model to a practical ED problem mentioned above. Computer simulations manifest that not only this proposed model itself is much simpler but also its computation results are very close to those of the conventional methods.

Modified differential evolution method for capacitor placement of distribution systems

Optimal capacitor placement determines the size and location of capacitors to be installed on a radial distribution feeder. The capacitor placement problem is a combinatorial optimization problem having an objective function composed of power losses and capacitor installation costs subject to bus voltage constraints that are commonly solved by employing mathematical programming methods. This paper presents a new capacitor placement method which employs modified mixed integer hybrid differential evolution (MIHDE) method and sensitivity factor of buses for a given load pattern of distribution systems. The sensitivity factors help reduce the number of alternatives to be examined and MIHDE finds the optimal solution. The proposed approach is demonstrated by employing an application example. Numerical results show that the proposed method can achieve an optimal solution as the exhaustive search can but with much less computational time. This method is especially beneficial for capacitor placement of large distribution systems.