Hyung-Soo Mok

Design of current controller for 3-phase PWM converter with unbalanced input voltage

Generally current controllers of three-phase PWM power converters have been implemented in the synchronous frame because the synchronous frame controller can eliminate steady state error and has fast transient response by decoupling control. However most of such controllers have been designed under balanced input voltage. Therefore such designed current controllers showed undesirable current control characteristics under unbalanced conditions because the current reference is distorted by the second order harmonic voltage due to negative sequence. In this paper, a current controller for a PWM power converter, considering unbalanced input voltage, is designed and verified by both simulation and experiment.

A new instantaneous output current control method for inverter arc welding machine

According to the adoption of inverter circuit topology for welding machine area, the improvement of welding performance con be achieved. However conventional CO/sub 2/ inverter arc welding machine uses the constant voltage characteristics. So the metal transfer is performed under nonoptimum conditions in view of spatter generation. In this paper the new control algorithm is proposed for welding machine, which is the instantaneous output current control method using single chip microprocessor. But the optimum waveform of welding current is still uncertain, as a first step for figuring out the optimized waveforms, this study was performed, and as a result of performance test of the proposed system, it was demonstrated that all of the waveform variation parameters could be set individually and the generated spatter is reduced compared to conventional inverter arc welding machine.

300V DC feed system for Internet data center

Internet Data Centers (IDC), as essential facilities for modern IT industry, typically have scores of MW of concentrated electric loads. Uninterruptible Power Supplies (UPS) are necessary for the power feed system of IDCs because of stable power requirement. Thus, conventional AC power feed systems of IDCs have three cascaded power conversion stages such as (AC-DC), (DC-AC), and (AC-DC), which results in very low conversion efficiency. On the contrary, DC power feed systems need just a single power conversion stage (AC-DC) supplying AC mains power to DC server loads, which gives comparatively high conversion efficiency and reliability [5]. This paper compares the efficiencies between 220V AC power feed system and 300V DC power feed system on equal load conditions which were established in Mok-Dong IDC of Korea Telecom Co. Ltd. (KT). Experimental results show that the total operation efficiency of the 300V DC power feed system is around 15% higher than that of the 220V AC power feed system.

Simulation based Power Electronics Education in Korea

This paper covers various power electronics education in Korea. In broad concept, they are composed of two methods, i.e. power electronics education in college as a part of formal curriculum and on-the-job (or field) training in industrial field to develop experienced engineers. In this paper, the simulation based education example of power electronics for students in the department of electrical engineering and engineers in companies is introduced. And also it is shown some practical attempts, which are called industrial electronics competition program sponsored by KIPE, to increase the interests of engineering students on power electronics.

3D education system of DC motor drive using RecurDyn and CoLink

An increasing number of schools and industrial workplaces has recently applied theory-based computer simulation to their education system for electric drives, making computer simulation an essential element of the program. This paper introduces an education system for motor drive using the dynamic 3D analysis simulation tools RecurDyn and Colink to provide more accurate analyses and realistic training.

A Comparative Study on the Electric Power Efficiency of IDCs with AC and DC Distribution Systems

급격한 IT 산업 발전의 산물인 인터넷데이터센터(IDC)는 서버 시스템이 집적된 고밀도 디지털 부하로 구성되는 특징을 가지고 있다. IDC의 디지털 부하 특성을 고려하여 직류배전시스템을 도입하는 경우 전력 변환 체계의 단순화로 효율 향상의 가능성이 일부 제기되어 왔으나, 국내 IDC 환경에서의 효율성이 검증된 사례는 없었다. 본 논문에서는 교류배전방식을 적용한 KT 분당 IDC와 직류배전방식을 적용한 KT 남수원 IDC의 전력 효율을 비교 분석함으로써 국내 IDC 배전체계의 직류화에 따른 효율 개선 효과를 제시하였다. DC 48[V]를 배전하였을 때 직류배전 방식의 효율이 13.2[%] 높은 것으로 도출되었으며, DC 380[V]의 공급을 가정하였을 때에는 25[%] 이상의 효율 향상을 기대할 수 있었다.

A New Automatic Synchronous Switch Post Regulator for Multi-Output Converters

A New Automatic Synchronous Switch Post Regulator for Multi-output converters is proposed. Additional PWM circuit for regulation of auxiliary output voltage is useless so that different from existing SSPR or synchronous switch. Also have the advantages of high efficiency, low part-count, tight regulation and low cost. For experimental verification 25W two-output flyback converter is conducted.

A novel pulse power supply for magnetron using high voltage capacitor embedded high frequency transformer

This paper described that novel high voltage capacitor (HVC) embedded high frequency transformer and novel inverter power supply topology for driving magnetron in microwave oven. This transformer is used to achieve down-sizing, low-cost and efficiency improvement. Proposed transformer has HVC in its secondary winding. Therefore, this transformer does not need external high voltage capacitor which used in conventional power supply. As use of this transformer, output voltage is shifted from ground to above 2000 [V] and efficiency of microwave oven can be improved. The weight of proposed transformer is about one sixth of conventional one and efficiency is improved by seven percent compared to the efficiency of the conventional system.

Digital Control Strategy for Single-phase Voltage-Doubler Boost Rectifiers

In this paper, a digital controller design procedure is presented for single-phase voltage-doubler boost rectifiers (VDBR). The model derivation of the single-phase VDBR is performed in the s-domain. After that the simplified equivalent z-domain models are derived. These z-domain models are utilized to design the input current and the output dc-link voltage controllers. For the controller design in the z-domain, the traditional K-factor method is modified by considering the nature of the digital controller. The frequency pre-warping and anti-windup techniques are adapted for the controller design. By using the proposed method, the phase margin and the control bandwidth are accurately achieved as required by controller designers in a practical frequency range. The proposed method is applied to a 2.5 kVA single-phase VDBR for Uninterruptible Power Supply (UPS) applications. From the simulation and the experimental results, the effectiveness of the proposed design method has been verified.

Load sharing improvement in parallel-operated lead acid batteries

A battery is the device that transforms chemical energy into direct-current directly without a mechanical process. Unit cells are connected in series to obtain the necessary voltage, while being connected in parallel to organize capacity for load current and to decrease the internal resistance for corresponding the sudden shift of the load current. Because the voltage drop in parallel battery sets in unequal, low efficiency of power converter and system shutdown may result. However, when the system is being driven in parallel, a circular-current can be generated. The charging current differs in each battery set because the system, including batteries, rectifiers and loads, are connected in parallel, making the charge voltage constant. It is shown that, as a result, the new batteries are heated by over-charge and over-discharge, and the over charge current increases rust of the positive grid and consequently shortens the lifetime of the new batteries. The difference between the new batteries and old ones is the amount of internal resistance. In this paper, the authors detect the unbalance current using a microprocessor and achieve current balance by adjusting the resistance of each battery set. The internal resistance of each set becomes constant and the charge and discharge currents are balanced by inserting an external resistance into the system and calculating the change of internal resistance.