Kung-Yen Lee

Time Series Analysis Using Composite Multiscale Entropy

Multiscale entropy (MSE) was recently developed to evaluate the complexity of time series over different time scales. Although the MSE algorithm has been successfully applied in a number of different fields, it encounters a problem in that the statistical reliability of the sample entropy (SampEn) of a coarse-grained series is reduced as a time scale factor is increased. Therefore, in this paper, the concept of a composite multiscale entropy (CMSE) is introduced to overcome this difficulty. Simulation results on both white noise and 1/f noise show that the CMSE provides higher entropy reliablity than the MSE approach for large time scale factors. On real data analysis, both the MSE and CMSE are applied to extract features from fault bearing vibration signals. Experimental results demonstrate that the proposed CMSE-based feature extractor provides higher separability than the MSE-based feature extractor.

Online Failure Prediction of the Electrolytic Capacitor for LC Filter of Switching-Mode Power Converters

The objective of this paper is to propose a new method to detect the rise of equivalent series resistor in order to realize the online failure prediction of the electrolytic capacitor for LC filter of switching-mode power converter. Characteristics of electrolytic capacitors are introduced in this paper. Different experimental measurements are conducted and shown to illustrate the properties of electrolytic capacitors. The proposed online failure prediction method has the merits of low cost and circuit simplicity. It can be integrated within the package of the electrolytic capacitor to improve its reliability. Hardware experimental results are shown to verify the performance of the proposed method.

The AC Line Current Regulation Strategy for the Grid-Connected PV System

The ac line current regulation strategy for the grid-connected photovoltaic (GCPV) system is proposed in this paper. The power flow of the GCPV system and the operational principles of different ac line current regulation strategies are presented. In this paper, the optimal ac line current regulation is defined to be able to achieve dc-link voltage regulation in one 60 Hz ac mains cycle while minimizing the injected ac line current variation. The mathematical equations for the proposed optimal ac line current regulation strategy are derived thoroughly. The derived equations also explain the behavior of the dc-link voltage responding to the power variation of the GCPV system. As a result, the selection criteria of the dc-link capacitor can be established. Hardware experimental results have been presented to verify the validity of the proposed optimal ac line current regulation strategy.

Power loss analysis of grid connection photovoltaic systems

This paper presents power loss analysis of grid-connection PV systems, based on the loss factors of double line-frequency voltage ripple, fast irradiance variation, fast dc load variation, non-uniform solar cell characteristic, and limited operating voltage range. These loss factors will result in power deviation from the maximum power points (MPP). In the power loss analysis, both single-stage and two-stage grid connection PV systems are considered. The effects of these loss factors on two-stage grid-connection PV systems are insignificant due to an additional maximum power point tracker (MPPT), but it will reduce the system efficiency typically about 3 %. The power loss caused by these loss factors in single-stage grid-connection PV systems is also around 3 %; that is, a single-stage grid-connection PV system has the merits of saving components and reducing cost, while does not scarify overall system efficiency. Simulation results with a MATLAB software package are presented to confirm the analysis.

A simplified analog control circuit of a maximum power point tracker

This work proposes an analog maximum power point tracker (MPPT) control circuit for photovoltaic arrays. A clocked auto-oscillation method is used in this control circuit. This control principle is based on sensing the output current to achieve MPPT function. Multiplication of array voltage and current is not needed. The cost and volume of MPPT is reduced and MPPT efficiency is about 94%.

An Investigation on Barrier Inhomogeneities of 4H-SiC Schottky Barrier Diodes Induced by Surface Morphology and Traps

The correlation between barrier inhomogeneities of 4H-SiC Schottky barrier diodes (SBDs) and surface defects and traps for SBDs fabricated with and without chemical-mechanical polishing (CMP) is investigated. 60% of the barrier inhomogeneities of SBDs with invisible surface defects are eliminated when CMP is applied in the refabrication. About 40% of SBDs with carrots inside the active areas exhibit double barriers without using CMP. This excludes that carrots are a cause of barrier inhomogeneities. However, none of the barrier inhomogeneities of the SBDs with carrots can be eliminated by using CMP. Most barrier inhomogeneities of SBDs with various surface defects inside the active areas can be improved by CMP. The difference between the high and low barrier heights of an SBD with CMP was reduced to about 0.02-0.06 eV. Therefore, the leakage current induced by barrier inhomogeneities is also reduced by CMP. Moreover, SBDs with a resistive termination extension (RTE) have a higher barrier height than SBDs without RTE, and there is no direct evidence to show that the inclusion of RTE can induce barrier inhomogeneities.

Design and implementation of a push-pull phase-shifted bi-directional inverter with a dsPIC controller

This paper presents design and implementation of a bi-directional inverter, including a high frequency transformer, a push-pull switch configuration at the dc side, a cycloconverter at the ac side, and a dsPIC controller. The dc/ac conversion is achieved with a phase-shifted control strategy. In addition, this topology also can achieve an ac/dc conversion with the PFC function. In this circuit, the dsPIC realizes almost all functions, including generation of PWM signals, A/D conversion, phase shift, circuit protection, and PFC during ac/dc conversion. The proposed bi-directional inverter can reduce weight, size and volume significantly as compared to a conventional low frequency transformer approach. Experimental results obtained from a prototype with a dc side voltage of 48V, an ac side voltage of 110Vrms, and power rating of 500W have verified its feasibility.

Design and Fabrication of 4H–SiC Lateral High-Voltage Devices on a Semi-Insulating Substrate

Design and fabrication of 4H-SiC lateral high-voltage devices on semi-insulating substrates based on the charge compensation principle have been investigated in this work. In the simulation, field plates are critical in relieving the electric field crowding at junction corners at high reverse biases. By incorporating field plates with proper lengths, the breakdown voltage (BV) of a single-zone reduced-surface-field (RESURF) device with a 100- μm drift region can be improved from 3360 to 5880 V. The BV can be further enhanced to 8000 V by using a two-zone RESURF structure. The reduction in BV by 10% charge imbalance variation is also improved from 49% for a single-zone structure to 36% for a two-zone structure. Simulation also shows that oxide charges and other surface charges will offset the optimized charge imbalance conditions and, therefore, should be considered in design if the amount is significant. A 4H-SiC JFET with a two-zone RESURF region was fabricated to demonstrate the advantages of lateral devices based on these concepts. The fabricated lateral 4H-SiC JFET has a BV of 4200 V and a specific on -resistance of 454 mΩ·cm2. The figure of merit is as high as 38.8 MW/cm2.

Counter-Doped JTE, an Edge Termination for HV SiC Devices With Increased Tolerance to the Surface Charge

In this paper, a comparison of different techniques for SiC high-voltage devices is performed using numerical simulations. In particular, the method of counter doping (CD) introduced in the junction termination extension (JTE) region to create a multizone termination effect is investigated. Simulation shows that compared with the other edge termination techniques, CD-JTE greatly reduces the sensitivity of breakdown voltage (BV) to JTE doses and surface charges. The multizone CD-JTE with outer rings shows that for a 30-μm thick epi-layer, 90% of the theoretical BV is achievable with a wide tolerance of 11 × 1012/cm2 to the JTE dose and 85% of the theoretical BV with an increased tolerance of 6.19 × 1012/cm2 to the positive surface charges, both superior to other JTE structures investigated in this paper.

A method for assessing patent similarity using direct and indirect citation links

Assessing patent similarity is a fundamental and critical step in patent citation analysis. When evaluating a similarity among two patents, considering both direct and indirect citation links leads to more precise similarity assessment. This study proposes a method for assessing patent compound similarity that includes direct and indirect similarities. Given a direct similarity matrix that represents a patent citation network, the method calculates indirect similarity matrices and then obtains a compound similarity matrix. Keyword analysis in the text mining is employed to obtain a similarity for a pair of patents. In addition, two criterion are proposed for validating the compound similarities for the patent citation network.