Power Quality 向上을 위한 Wavelet Transform을 利用한 高調波 除去 技法에 관한 硏究

박성원 성균관대학교 대학원 1997 국내석사

In recent years, electric power quality(PQ) has become an important issue in power systems. This is due to the fact that usage of power electronics equipments and electronics-based loads which are sensitive to power quality disturbances has been increased, and thus normal operations in industrial and commercial facilities are becoming more vulnerable to the electric power quality disturabances. For improvement of power quality, this thesis presents a new approach to cancel the harmonic of various types of electric power quality disturbances using discrete wavelet transform. This method is to decompose a given disturbance signal into other signals which represent a smoothed version and a detailed version og the original signal. The decomposition is performed using multiresolution signal decomposition techiques. The result shows that the discrete wavelet transform was able to detect the electric power quality disturbances and to remove the harmonic of electric power quality disturbances.

位相面軌跡을 利用한 電力系統 故障檢出 및 故障形態 判別에 관한 硏究

신,영철 成均館大學校 1998 국내석사

Energy efficient C-dump 컨버터에 의한 SRM 구동시스템의 고성능 제어

정동효 成均館大學校 大學院 2002 국내박사

Adjustable speed drives for automotive engine cooling application employ DC, BLDC or switched reluctance motors. The traditional brushed DC motor is not suitable for many of these adjustable speed applications because of the wear associated with the brushes, lower overall power density, and EMI problems associated with converter arcing. Field weakening in the BLDC motor is sometimes attempted through phase advance of the current waveform, yet this tends to introduce substantial torque ripple. The simplicity of construction and lack of costly permanent magnets imply that the SRM would be much less expensive to produce in the quantities that DC or induction motor. An important difference between the SRM and BLDC motors is their behavior at high speeds. The SRM is reasonably good at behaving as a constant power motor above base speed. The BLDC motor, on the other hand, often loses power output capability rapidly as the speed increases. With an increase of electronic devices in automobiles, an emphasis has been placed on conducted mode noise issues for among others reasons, safety. Energy efficient C-dump converter, derived from the conventional C-dump converter, are proposed switched reluctance motor(SRM) drive for automotive engine cooling application. The proposed converter overcomes the limitation of conventional C-dump converter, and could reduce the overall cost of the SRM drive. The development of advanced power electronic switching devices has enabled high frequency switching operation and has improved the performance for driving SRM. EMI evaluation is performed by using a spectrum analyzer across the line impedance stabilization network(LISN) for DC, BLDC motor and switched reluctance motor. As conducted emission testing to the CISPR25 standard was specified at a constant speed and constant high speed, the conducted emission in the model were simulated at these speed and compared with experimentally obtained results. This thesis also considers the experimental results of conducted mode noise from a 12V, 250W, 6/4 pole switched reluctance motor for use in an understood automotive engine cooling application. Simulation and experimental results obtains on a laboratory prototype are finally presented to evaluate the performance of the SRM drive in the terms of conducted mode noise compared to DC and BLDC motor drive.

單相 PWM인버터를 이용한 직류 스폿용접기의 定電力制御에 관한 硏究

김재문 성균관대학교 대학원 1995 국내석사

In recent years, there is increasing interests in spot welder with industrial growth of automobile. It makes autowelding and short-time welding possible. Conventional spot welders using AC source bring about the depreciation of welding products, because constant current control makes its workpiece spattered during welding process. In this paper, the constant power control strategy using PI controller is proposed to improve the quality of the welding products. PI controller is implemented by 16bit one-chip 80C196KB microcontroller. In comparison with AC spot welder, the DC spot welder with high frequency PWM inverter is lighter in its size and weight than that of AC spot welder, which is more reliable and obtains high efficiency. Simulation and experimental results show that DC spot welder with single phase PWM inverter is effectively controlled by the constant power control method in very short-time.

능동 클램프 ZVS 플라이백 컨버터용 고역률 정류기에 관한 연구

안정준 성균관대학교 대학원 2001 국내박사

Many conventional switching power supplies in plasma etching equipment and drive circuit for plasma display panel TV operate by rectifying the input ac line voltage and filtering it with large electrolytic capacitors. This process involves both nonlinear and storage elements and results in undesirable ride effects such as the generation of distorted input current waveform rich harmonics. The resulting input power factor is also poor(0.65 or less) further, the input current has the shape of narrow pulses, which in turn increases its rms. To correct the power factor and reduce high harmonic current contents, passive circuits (using only resistors, capacitors and inductors) or active circuits (typically switching-mode power conditioning circuits) can be used. Several switching regulator topologies are suitable for power factor improvement and harmonic current reduction. Despite the improved performance of the existing boost topology, that is, single phase boost converter, there are several disadvantages associated with this approach. I) The required switching frequency of the boost switch is high. This in turn increases the switching losses and lowers the efficiency. II) The diode is in the series path the power flow and contributes to voltage drop, increased power loss, and reduced reliability. III) Special design of the dc side inductor is necessary to carry dc current as well as high frequency ripple current. IV) At any given instant, three semiconductor device drops exist in the power flow path. In response to these concerns, this dissertation proposes and investigates an alternative power factor correction and harmonic current reduction topology for single phase semibridge converter fed from single phase ac mains. The advantages of the proposed approach are as follows: I) Improved characteristics in terms of high input power factor and sinusoidal shape of the input current. II) At any given instant, only two semiconductor device drops exist in the power flow path. III) The rms current rating of the boost switches is low. IV) The location of the boost inductor on the ac side contributes to reductions in EMI interference. In order to reduce the size of energy accumulation devices, the converter needs a high switching frequency but it causes to higher voltage stress and further higher switching loss at the main switch of the converter. And, owing to resonance between the leakage inductance of the transformer and the parasitic capacitor of the switch, the noise is increased and the reliability of the switch is decreased after all. In this dissertation, active clamped ZVS PWM converter with input power factor correction in ac main is presented. These converter reduce the voltage stress of the switches by using the active clamp technique. In addition, zero voltage switching makes it possible to operate at high switching frequency, resulting in the high power density. To verify validity of the proposed converter, the lOOkHz, 48V, 300W converter are designed and tested. In the future, this converter will be apply to the discharge drive circuit for PDP TV.

Wavelet 變換을 利用한 高抵抗 地絡事故 檢出 및 故障點 推定에 관한 硏究

변성현 成均館大學校 1998 국내석사

신경회로망을 이용한 전력계통 안정화 장치에 관한 연구

조필훈 성균관대학교 대학원 1995 국내석사

In power system, low frequency oscillation become a major concern for many years. In order to depressure low frequency oscillation, the power system stabilizer(PSS) parameters must be adjusted when there is a change in power system conditions. This paper presents the application of neural network to tunning the PSS parameters. To training neural nework, generator real power(P) and reactive power(Q) are chosen as the input signal and the output is the desired PSS parameters. A popular type of neural network, the multi-layer perceptron with error-back-propagation training method, is employed. The neural network, once trained, can yield proper PSS parameters under any generator loading condition. Simulation results show that the neural network based power system stabilizers yield better dynamic performance than conventional power system stabilizations in the sense of having large damping in respons to a step disturbance.

자속-차전류 특성을 이용한 전력용 변압기의 보호계선 알고리즘

박재세 成均館大學校 大學院 2003 국내박사

The power transformer is an important piece of equipment in transforming and delivering power in a power system. It shows a lower accident ratio than other system equipment, but once an accident occurs, it causes long-term operation failure and economic loss. It brings high and serious spillover effects. Therefore, protective relaying, which detects internal faults in a power transformer, is highly important. The most widely used primary protection for the internal fault detection of power transformers is current percentage differential relaying. However, the harmonic component could be decreased by magnetizing inrush when there have been changes to the material of the iron core or its design methodology. The higher the capacitance of the high voltage status and underground distribution, the more the differential current includes the second harmonic component during the occurrence of an internal fault. Therefore, the conventional harmonic restraint methods need modification. Therefore, this study proposes an advanced protective relaying algorithm for enhanced power transformer protection. This algorithm enables a clear distinction of the disturbance status of the internal fault of the power transformer and non-internal fault magnetizing inrush and other disturbances. It does this by analyzing RMS fluctuation of terminal voltage from electric power data, instantaneous value of the differential current, RMS changes, harmonic component analysis of differential current and slope analysis of flux-differential characteristic. This improved algorithm, suggested in this study, was closely examined and compared with other various algorithms, such as the fuzzy logic based algorithm, the discrete wavelet transform based algorithm, the conventional current percentage differential relaying algorithm in the various categories of fault detecting timing, feature extraction and others. The protection method of utilizing the Turbo C programming language and MS-Excel could help solve problems with power transformer protection by examining case studies of data collected by WatATP 99 software and MS-Excel. Below are some results : (1) This study proposed advanced algorithm that can clearly determine internal faults and magnetizing inrush of the power transformer, through numerical analysis by using the terminal voltage and input / output currents. (2) The proposed algorithm imported the flux-differential slope characteristic, thus improving and solving the previously existing problems with conventional 2nd harmonic component restraint RDR algorithms, which cause specific magnetizing inrush, and malfunctioning of the internal fault trip. (3) The proposed technique does not solely rely on the inclusion ratio of the second harmonic component when determining the existence of magnetizing inrush. Because of this, it can prevent malfunctioning of current percentage differential relaying, which has built-in second harmonic component protection. This malfunctioning could be created by improvements in the iron core material and system environment changes. (4) The Proposed algorithm enables magnetizing inrush detection within (roughly) 1.5 periods and it can detect internal faults within 0.5 period. (5) When compared with the fuzzy relaying, DWT relaying and conventional RDR relaying algorithms, this new advanced algorithm excelled not only in the relay operation time of protection relaying, but also in other comparison criteria. (6) This paper proposed the appropriate performance evaluation method for digital protective relaying by examining the weakness and strength of the digital filter, which aims to protect the power transformer; by studying the digital protective relaying and by using theoretical analysis. As stated above, this study proposed a protection technique, which is a numeric algorithm that utilizes terminal voltage and input/output current. This enables real-time detection and processing along with hardware application of the protective relaying. The magnetizing inrush discrimination and internal fault detection of this advanced algorithm showed fast and reliable performance. In the future, studies on and consideration of the over-excitation status should be continued. by comparing and analyzing the field test data This advanced technique and performance evaluation when used with many other algorithms will shorten the time and cost in adapting to and developing a new and better algorithm. We aim to apply this technology in integrative protection equipment development, which is the key technology for intelligent electronic devices in next-generation substation automation systems.

단일 프로세서를 이용한 전력용 변압기의 다기능 디지털 보호계전기 설계

권기백 成均館大學校 大學院 2002 국내박사

As electrical power system has become complicated and enlarged to cope with the increasing electric demand, it has to be expected that higher speed, higher reliability, higher function and higher arithmetic ability in protective relay should be realized. Therefore, in this papers, We studied system requirement specification, hardware design and implementation, protective algorithm and software design method to implement multi-function digital protective relay which has high trust and high function of protection as well as control and metering for power transformers. The main contents and results are as follows. ① Hardware design ·Multifunction protective relay for transformer is implemented by TMS320C32-50[MHz], which is the specific processor for digital signal processing, as a result, it is completed by the wide improvement of arithmetic capability of protective relay. ·Input circuit considering characteristic of CT is designed, and analog filter LPF of RC network is designed by simulation, to filter the DC offset component and high harmonic. ·Using 16 channel MUX and 16 bits A/D converter, analog input parts contributed high level of analog input to precise data acquisition from small signals to large signals. ·In the process of A/D conversion end signal by using DMA controller that transfer blocks of data to any location in the memory map without interfering with CPU operation, CPU utilization is increased effectively, as a result it made possible real time using a single processor. ② Software design ·Percentage differential relaying element which have the 2nd harmonic restraint characteristic was used as main protective algorithm in the protective relaying algorithm of the trans-former, and an overcurrent, ground overcurrent relaying element which has an instantaneous and time delay characteristic was used as back up protective algorithm. ·Software reliability was improved as developing and separating application software and hardware control software on a real time kernel. ·Software of protective relay is designed using object oriented UML, as a result, this improves reliability on specification, document and visuality. ·Reliability is proved by testing operating value, operating time, reset value, reset time, phase characteristic and harmonic characteristic of a percentage differential relaying element using protective relay tester. ·Reliability is proved testing operating value and operating time, reset value and reset time of an overcurrent, ground overcurrent relaying element using protective relay tester. We hope that contents of this paper are based on the stone of basic theoretical and technical information to develop a number of digital protective relays. We are looking forward to be the chance to develop a transformer multifunction protective relay for the purpose of practical products. In addition, if a communication module is used effectively, it will be possible to apply to automation of power systems, and remote monitoring and control.

GA를 이용한 TCSC 적용 LQ 제어기의 가중행렬 선정 및 설계

김학만 성균관대학교 1997 국내박사