Geum-Bae Cho

Switched-Inductor Quasi-Z-Source Inverter

This paper deals with a new family of high boost voltage inverters called switched-inductor quasi-Z-source inverters (SL-qZSIs). The proposed SL-qZSI is based on the well-known qZSI topology and adds only one inductor and three diodes. In comparison to the SL-ZSI, for the same input and output voltages, the proposed SL-qZSI provides continuous input current, a common ground with the dc source, reduced the passive component count, reduced voltage stress on capacitors, lower shoot-through current, and lower current stress on inductors and diodes. In addition, the proposed SL-qZSI can suppress inrush current at startup, which might destroy the devices. This paper presents the operating principles, analysis, and simulation results, and compares them with those of the SL-ZSI. To verify the performance of the proposed converter, a laboratory prototype was constructed with 48 Vdc input and an ac output line-to-line voltage of 120 Vrms. The simulation and experimental results verified that the converter has high step-up inversion ability.

Performance analysis of the DTC using a closed loop stator flux observer for induction motor in the low speed range

Direct torque control (DTC) of an AC motor has the fast torque and flux dynamic responses even though it has very simple scheme to implement. However, DTC do not show good performance at low speed range with conventional open loop stator flux observer when stator resistance varied. Therefore, authors propose a new nonlinear stator flux observer in order to estimate the stator flux of induction motor at low speed and show its simulation results.

Isolated High Step-Up DC–DC Converter Based on Quasi-Switched-Boost Network

In this paper, a new isolated high step-up dc-dc converter is proposed based on the quasi-switched-boost network. The proposed converter has the following features: 1) continuous input current; 2) reduced turn ratio of the isolated transformer; 3) increased reliability, as it can operate in either short-circuit mode or open-circuit mode without causing damage to the power converter; and 4) unchanged primary and secondary voltage waveforms of the transformer, although the shoot-through duty cycle is variable. Compared to the quasi-Z-source-based isolated dc-dc converter, the proposed converter uses fewer passive components. The operating principles, analysis, parameter design guideline, and comparison with the quasi-Z-source-based isolated dc-dc converter are presented. A 450 W prototype is built to test the proposed converter. The proposed converter is applicable for distributed power generation applications where a varying low dc input voltage is converted to a high stabilized dc output voltage with a galvanic separation requirement.

A Study of the PV System for Optimum Design Methods With Loss Parameter Compensation

Photovoltaic systems utilize the infinite clean energy of the sun, without creating any air pollution or noise and mechanical vibration. A PV system operates without the need of fuel, rotation surfaces, high temperatures or high pressures. It is therefore to do maintain and simple to install as well as having a long life cycle. The global market for PV systems continues to grow rapidly by 30[%] per year. This paper suggests a new design method for the PV system installation that will allow to the improvement of system efficiency. This method is in accordance with the loss parameter compensation method designed for the PV systems and investigated through simulation and practical experimentation. It was applied to an interconnected 10[㎾] grid PV system and was demonstrated in the field. Features such as solar array, KS, system efficiency, performance and stability were considered. Through the proposed optimal parameter design method, the features of the system were studied, and the 10[㎾] PV system was demonstrated and analyzed.

Speed control of AC servo motor using neural networks

Recently intelligent control has received increased attention in various applications. With PID controllers, it is difficult to obtain gain suitable to the load because of disturbances, parameter variations and measurement noise. In order to reduce mechanical parameter variations, and to obtain good dynamic performance, PID controllers and neural network controllers for AC servomotor control are investigated. The microprocessor provides an output to the difference in command. The servo system improves the characteristics of speed control. When the motor is running at the same speed as set by the reference signal, the speed encoder also provides a signal of the same frequency. From the viewpoint of wide control range, a good dynamic performance and a cost effective approach, the NNE of an adaptive neural network controller is used to identify the parameters and characteristics of the AC servomotor. To train the controller, the weights are dynamically adjusted using the backpropagation algorithm. Neural networks are used so PID control can control, efficiently, the speed of the AC servomotor. Finally experimental results prove the excellent performance of this control system.

Analysis of Property for White and RGB Multichip LED Luminaire

LEDs are increasingly used for many applications including automotive, aviation, display, transportation and special lighting applications. Generally, the RGB multichip LED luminaire applied to signboard, emotional lighting system and display device and the white LED luminaire applied to general lighting system. white LED spectra for general lighting should be designed for high luminous efficacy as well as good color rendering. This paper describes characteristics of LED luminaire white LED and RGB multichip LED. Two type of LED luminaire prototype used experiment physical, electrical and optic test and performance analyzed. RGB multi-chip and phosphor-type white LED luminaire were analyzed by experiment on their color characteristics and luminous efficacy of radiation, distribution curve, and electrical characteristics. Research work is in progress to develop an improved performance for optic and electrical works well for two type of LED luminaires.

Performance assessment of 3kW grid-connected PV Systems in Korea

In this paper, for the field test of the first photovoltaic (PV) systems in Korea, the performance of a 3kW grid-connected PV systems for house, separately installed in the solar energy demonstration research complex, had been analyzed for the four years from January 2003 to December 2006.

A novel detecting noise reduction scheme for voltage-regulated current-fed power filter

Active power filters have been developed to solve the harmonics disturbance problems on power system networks. Particularly for current-type active power filters, a voltage regulation scheme is considered to control the voltage of capacitor at the input side of a nonlinear load. For precise control, the value of voltage drop at the AC side must be included. Because of the reactance of the filter, external noises are added to the detected voltage drop signal and hence the resultant signals will be seriously distorted, particularly where an electronic differentiator is used. To reduce these noises, a novel detected noise reduction scheme with an observer based algorithm is proposed. The designed observer algorithm is applied and then investigated by digital simulation. Also the experimental results are shown to verify the validity of proposed scheme.

A study on the reduction of in-rush current for energy saving of single phase induction motor

In this paper, an analog controller is proposed to reduce in-rush current that happens during starting of a single phase induction motor within 200% of rated current depending on an international standard. The soft start method is used as the main conventional method that reduces inrush current and controls the input current through the main winding control. Capacitor starting of a single phase induction motor requires large starting torque. If the input electric power is less, the starting torque decreases and because starting time is delayed, electric power loss increases. Therefore, this paper discusses improved reduction of starting torque at main winding control which controls the auxiliary winding that is paralleled with the main winding that uses an electrical starting switch, and leads to energy saving during starting.

Se-loss-induced CIS Thin Films in RTA Process after Co-sputtering Using CuSe2 and InSe2 Targets

Chalcopyrite CuInSe2 (CIS) thin films were prepared without Se- / S-containing gas by co-sputtering using CuSe2 and InSe2 selenide-targets and rapid thermal annealing. The grain size increased to a maximum of 54.68 nm with a predominant (112) plane. The tetragonal distortion parameter η decreased and the inter-planar spacing d(112) increased in the RTA-treated CIS thin films annealed at a 400°C, which indicates better crystal quality. The increased carrier concentration of RTA-treated p-type CIS thin films led to a decrease in resistivity due to an increase in Cu composition at annealing temperatures ≥ 350°C. The optical band gap energy (Eg) of CIS thin films decreased to 1.127 eV in RTA-treated CIS thin films annealed at 400°C due to the improved crystallinity, elevated carrier concentration and decreased In composition.