Shih-Kuen Changchien

Apply rough set and GM(h,N) model to analyze the influence factor in gas breakdown

In power system field, to study the characteristics of the gas breakdown is essential and of importance in designing the protection of high voltage system as well as to the power system reliability. Hence, in this paper, the major purpose is to propose a refined mathematical approach based on rough set method and GM(h,N) method to find the priority of influence factor in gas breakdown. And also created rough set and GM(h,N) toolbox based on Matlab, which to help the complex calculation and analysis. As the result, we not only can get the rank of influence factor in gas breakdown, but also provides a new idea for extension the applications of rough set and GM(h,N) method.

Optimal Design of DC-DC Converter with LC Snubber by Hybrid Method

In this paper, it is first proposed that genetic algorithm and Taguchi method can be employed in the optimal design of DC-DC converter with LC snubber. The purpose of this optimal design is to lower the spike voltage Vdsp of power switch and hence reduce the cost in manufacturing circuit. It is great educational value for students and engineers. For the first step, we investigate the circuit parameters which will affect Vd and subsequently converge the range of circuit parameter value by means of genetic algorithm, and conduct the optimal design of prototype converter with Taguchi method. Compared with spike voltage Vdsp of non-optimal design circuit, the effect of optimal design is revealed. In suppressing spike voltage, the Vdsp measured from optimal design circuit is 115 V, and is actually 28.1% reduced. Therefore, using genetic algorithm and Taguchi method in the optimal design of converter with LC snubber is a more economic, practical and efficient of circuit design, which meanwhile can be easily applied to other electronic circuits and accomplish the optimal design of various quality characteristics.

Implementation and Study of Constant-Frequency LLC Resonant Converter

This chapter presents an LLC resonant converter with constant frequency. Since LLC resonant converters possess the advantages of high efficiency and low electromagnetic interference, they are widely used in many applications. However, the EMI filter design becomes more complex because of the variable-frequency operation of LLC resonant converter. Therefore, in this chapter, a circuit configuration of a buck converter cascade an LLC resonant converter, buck-fed LLC resonant converter, is proposed to complete constant-frequency operation and simplify the EMI filter design. The buck converter is applied in the proposed converter as the input source for the LLC resonant converter. In addition, by adjusting the output voltage of the buck converter, the output regulation and constant-frequency operation of the proposed converter can be achieved. Finally, a prototype of the buck-fed LLC resonant converter with input voltage 380–400 V and output 24 V/10 A is implemented. The experimental results demonstrate the feasibility of the proposed converter.

Design of the Chaotic Secure Communication Time-delay System by LMIs Method

In this paper, we utilize a proper Lyapunov function and Lyapunov theorem, combined with LMIs method, in order to design a controller L, which ensures the synchronization between the transmission and the reception ends of the chaotic secure communication system with time-delay of output state. Meanwhile, for the purpose of increasing communication security, we encrypt and decrypt the original to- be-transmitted message with the techniques of n-shift cipher and public key. The result of simulation shows that the proposed method is able to synchronize the transmission and the reception ends of the system, and moreover, to recover the original message at the reception end. Therefore, the method proposed in this paper is effective and feasible to apply in the chaotic secure communication system.

Optimal Design of Lossless Passive Snubber for DC/DC Converters

This paper presents an optimal design of lossless passive snubber for DC/DC converters, which offers an efficient and best design method. The proposed method can not only reduce the spike voltage Vdsp of a power switch in the circuit, but also raise the conversion efficiency of the converter. In this paper, we have used Taguchi method to create the optimal design of LC lossless snubber. It can overcome the chaotic drawback of trial-and-error method, the bias of one-factor-at-a-time experiments, and the disadvantage of too many trials for full-factorial experiments. In Taguchi method, the voltage V ds of power switch and source side current Iin are the quality characteristics of the circuit, and the snubber inductor L c, snubber capacitor CL, transformer leakage inductor Le, and switching frequency f are control factors which influence the circuit quality characteristics. According to the control factors and levels, this paper used an orthogonal array L9 (34) to implement experiments, and made a factor response table and graph. Eventually, the optimal values of the control factors Lc, CL, Le and f were decided and then increased ratio of S/N to 16.8%. The simulation results demonstrated that the proposed method applying to optimal design of LC lossless snubber circuit was feasible and efficient