Kohji Higuchi

Power control of single-phase voltage source inverter for grid-connected photovoltaic systems

This paper presents the design and analysis of both the active and reactive power control of a single-phase voltage source inverter (VSI) for grid-connected photovoltaic (PV) system. The proposed method is based on vector control of power by decoupling control of the active and reactive current components to feed the active and reactive power to the grid. The aim of this research is to control power factor at grid, to improve overall efficiency of transferring power of PV to alternate current power conversion into the grid, and to decrease phase current distortion of VSI. In this work, mathematical model of system has presented in details. The results of simulations of PV system 1kW connected to grid 220V, 50 Hz using MATLAB/Simulink software are also discussed. Simulation results have shown that the grid input power factor is nearly unity, and the distorting of phase current of the proposed system has been reduced, causing the total harmonic distortion for various power conditions falls within 5%.

A NEW DESIGN OF ROBUST DIGITAL CONTROLLER FOR DC-DC CONVERTERS

Abstract Robust DC-DC converters which can cover extensive load changes and also input voltage changes are needed. In this paper, we propose a new method for designing good approximate 2-degree-of freedom (2DOF) digital controller which makes the control bandwidth wider, and at the same time makes a variation of the output voltage very small at sudden changes of resistive load. The proposed approximate 2DOF digital controller is actually implemented on a DSP and is connected to a DC-DC converter. Experimental studies demonstrate that this type of digital controller can satisfy given specifications.

A match of X-ray teeth films using image processing based on special features of teeth

This paper presents a match of X-ray teeth films using image processing based on special features of teeth. This method will help the dental doctors to match simply a pair of teeth using the special features of the teeth films. Teethpsilas pictures are scanned and adjusted by a scanner and a computer, respectively, as well as then they are converted into binary code and decoded to the direction code (chain code). The chain code of each picture is compared with the statistical chain code. Therefore, the percentage of the same chain code is approximately 90% (i.e. matching same patterns) for the comparison of one root to one root (7 times) and two roots to two roots (7 times) while the percentage of the same chain code is reduced at relatively below 50% (i.e. matching different patterns) for comparison of one root to two roots (2 times).

Automatic Prediction System of Dengue Haemorrhagic-Fever Outbreak Risk by Using Entropy and Artificial Neural Network

Predicting Dengue Haemorrhagic Fever outbreak is obviously urgent in order to control and prevent a widespread of the fever in advance. However, the prediction of Dengue Haemorrhagic Fever outbreak needs the analysis from experts which is inconvenient and costly. An automatic prediction system should be developed. This paper proposes an automatic prediction system of Dengue Haemorrhagic-Fever outbreak risk by using entropy technique and artificial neural network. In this system, the information extraction is preprocessed prior to the prediction in order to reduce data redundancy and retain only those relevant data. First, the external factors such as temperature, relative humidity, and rainfall are considered during the information extraction. Then, a supervised neural network is deployed to predict the possible risk of Dengue Haemorrhagic Fever outbreak. To evaluate the performance of proposed system, the experiments based on the condition of weather data and Dengue Haemorrhagic Fever cases from January 1999 until December 2007 were conducted. Our prediction achieves 85.92% accuracy compared to the actual data.

Robust control of PWM power amplifier by approximate 2-degree-of-freedom digital controller with bumpless mode switching

Robust PWM power amplifiers whose transient response characteristics do not deteriorate against extensive load changes and/or direct-current power-supply voltage changes are needed. In this paper, a digital robust controller with bumpless mode switching for PWM power amplifiers which can satisfy such demands and can extend the range of capacitive load wider is proposed. It is necessary to measure the value of load to implement this bumpless mode switching automatically according to the load range. Thus, the method of estimating capacitive load is shown. Although it is necessary to use current for estimating capacitive load, it is expensive if a current sensor is used. Therefore, an easy current estimating method which can be performed more cheaply is shown. The current estimated by this method is used for capacity estimation and current feedback. The bumpless mode switching is automatically performed by estimating a capacitive value, without specifying the value of capacitive load beforehand. That is, the value of capacitive load is estimated during DDC execution, and the control mode is automatically switched bumplessly according to this estimated value. The digital controller equipped with capacity estimation and the bumpless mode switching is realized by a DSP. An experiment shows that the digital controller with the proposed bumpless mode can satisfy larger specifications.

Modified Grid-Connected CSI for Hybrid PV/Wind Power Generation System

The principle of a power conditioning unit for hybrid PV/wind power generation system is proposed. The proposed power conditioner is based on the current source inverter (CSI) topology. All energy sources are connected in parallel with a DC-bus through the modified wave-shaping circuits. To achieve the unity power factor at the utility grid, the DC-link current can be controlled via the wave-shaping circuits with the sinusoidal PWM scheme. In this work, the carrier-based PWM scheme is also proposed to minimize the utility current THD. The power rating of the proposed system can be increased by connecting more PV/wind modules through their wave-shaping circuits in parallel with the other modules. The details of the operating principles, the system configurations, and the design considerations are described. The effectiveness of the proposed CSI is demonstrated by simulation results.

A carrier-based unbalanced PWM method for four-leg voltage source inverter fed asymmetrical two-phase induction motor

This paper presents a carrier-based unbalanced PWM method for two-phase four-leg voltage source inverter and its realization for asymmetrical two-phase induction motor. A modulation strategy is developed to synthesize unbalanced two-phase output voltage waveforms based on the unipolar modulation technique with open-loop V/f control. The proposed control scheme allows independent magnitude controllability and quadrature phase angle for unbalanced two-phase output voltages. Thus, the modulation algorithm makes the four-leg voltage source inverter inequitable with unbalanced two-phase loads. Simulation and experimental results confirm the feasibility of the control method for the inverter.

An improved soft-switching single-phase inverter for small grid-connected PV-system

In order to increase the conversion efficiency of grid-connected PV-systems, a high-efficiency PV power inverter with simple control methodology is required. To satisfy this requirement, an improved single-phase inverter using soft-switching technique is proposed. The proposed power inverter circuit is composed of a ZVT-PWM boost dc-dc converter and a LLCC resonant inverter. The dc-link voltage amplitude is controlled by ZVT-PWM boost dc-dc converter with soft-switching transition for all active switches. The stable sinusoid ac output voltage is inverted from dc-link voltage via a LLCC resonant inverter. The effectiveness of the proposed grid-connected inverter for small PV system is verified by simulation results.

Robust control of PWM power amplifier by approximate 2-degree-of-freedom digital controller with mode switching

Robust PWM power amplifiers whose transient response characteristics do not deteriorate against an extensive load change and/or direct-current power-supply voltage change are needed. In this paper, a digital robust controller with mode switching for PWM power amplifiers which can satisfy such demands is proposed. First, a nominal model of PWM power amplifiers which consists of a PWM signal generating part, an electric power conversion part and a LC filter is derived from the linear approximation. The controlled objective is described by the discrete-time systems with consideration of the input dead time. It is shown that a digital controller can be designed by the same way as the previously proposed digital controller and then the load range spreads more by mode switching. A DSP is implemented to the digital controller with mode switching. It is shown from an experiment that mode-switched digital controllers are realizable.

VT-AMDF, a pitch detection algorithm

This paper proposes a VT-AMDF pitch detection algorithm which based on average magnitude difference function (AMDF). Time processing is important when implement in real time system. In order to decrease computational time and complexity of pitch detection, the VT-AMDF uses only 55% of total time intervals. The method can reduce the computational time 1.3, 1.4, 4.8 and 5.4 times, compared with original AMDF, autocorrelation function (ACF), normalized square difference function (NSDF) and YIN, respectively. The experiments evaluate on seven words in five different tones of Thai isolated word. The results show that the gross error of VT-AMDF is 3.88%, which is more than original AMDF 0.48 and YIN 0.22, but less than ACF 0.54 and NSDF 1.47.