• Journal of Power Electronics
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• 제14권1호
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• pp.61-73
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• 2014

Multiphase machines are characterized by high power density, enhanced fault-tolerant capacity, and low torque pulsation. For a voltage source inverter supplied multiphase machine, the probability of load imbalances becomes greater and unwanted low-order stator voltage harmonics occur. This paper deals with the PWM control of multiphase inverters under unbalanced load conditions and it proposes a novel near-five-vector SVPWM algorithm based on the five-phase six-leg inverter. The proposed algorithm can output symmetrical phase voltages under unbalanced load conditions, which is not possible for the conventional SVPWM algorithms based on the five-phase five-leg inverters. The cause of extra harmonics in the phase voltages is analyzed, and an xy coordinate system orthogonal to the ${\alpha}{\beta}z$ coordinate system is introduced to eliminate low-order harmonics in the output phase voltages. Moreover, the digital implementation of the near-five-vector SVPWM algorithm is discussed, and the optimal approach with reduced complexity and low execution time is elaborated. A comparison of the proposed algorithm and other existing PWM algorithms is provided, and the pros and cons of the proposed algorithm are concluded. Simulation and experimental results are also given. It is shown that the proposed algorithm works well under unbalanced load conditions. However, its maximum modulation index is reduced by 5.15% in the linear modulation region, and its algorithm complexity and memory requirement increase. The basic principle in this paper can be easily extended to other inverters with different phase numbers.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2000년도 추계학술대회 논문집 학회본부 A
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• pp.82-84
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• 2000

This paper deals with a evaluation algorithm of interruption cost in distribution systems in the case where Dispersed Storage and Generation (DSG) systems are interconnected with the distribution systems. If DSG systems are operated as the function of the load levelling in distribution systems at the normal conditions and as the uninterruptible power supply in fault areas at the emergency conditions, the reliability improvement of the distribution systems can be expected. In other words, the benefit can be represented by the cost avoiding interruption according to the operation of DSG systems when a fault is occurred. Therefore, this paper presents the evaluation algorithm for interruption cost in order to evaluate the benefit for the uninterruptible power supply of DSG systems in a quantitative manner.

• 전기학회논문지P
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• 제63권2호
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• pp.74-80
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• 2014

Generator protection device has to detects an internal fault conditions in generator and abnormal operating conditions must be due to the hazards. Loss of excitation may cause generator itself failure as well as serious operating problem in power system, and then requires an appropriate response of generator protection device. Details modeling of generator control system and analysis of transient states in generator are important for optimal operation in power plants. In addition, the fault simulation data are also used for testing the characteristics of IED. In this paper, the hydro generator control system using PSCAD/EMTDC, visual simulation for power systems, was modeled. The generator control system which is composed of generator, turbine, exciter, governor was implemented. The parameters of generator control system model were obtained from field power plant. Loss of excitation simulations were performed while varying the fixed load. Several signals analysis were also performed so as to analyze transients phenomena.

• 전기학회논문지
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• 제57권9호
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• pp.1589-1593
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• 2008

The condition of a high voltage motor was monitored with the motor performance monitor (MPM) at the motor control center. The MPM detected defects in the rotor bar and end ring and input power according to motor and load conditions. The assessment of the condition of a coal pulverizer motor indicated it was clearly in good condition in terms of the rotor bars, over voltage, and motor performance. However, the side bands at frequency, 56.48 Hz indicated existence of rotor end-ring fault. The large torque ripple indicated abnormal operating conditions. After visual inspection, it has been observed that an impeller blade of the circulating water pump was broken off causing the irregular torque pattern.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2008년도 제39회 하계학술대회
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• pp.717-718
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• 2008

We developed the protection program for the generator fault protection system and each module of the digital protective relay H/W for loading the protection program. The protective algorithm for the generator is 51, 51G/N, 46P/N, 47P/N, 50G/N, and 32, and we developed each fault protection program. And we must design high efficiency microprocessor, CT, and PT for realtime measuring, relaying and high accuracy of measurement, also. From now on digital protective relay must be operated with integrated management systems. For this point, we must load various industrial protocol on the digital protective relay. In this research, we developed each protective relay H/W module according to above conditions. And we designed real-time operating system in order that each protective algorithm is operated with realtime processing on the H/W system.

• Smart Structures and Systems
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• 제29권6호
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• pp.785-790
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• 2022

Condition monitoring of permanent magnet synchronous motors (PMSMs) and detecting faults such as eccentricity and demagnetization are essential for ensuring system reliability. Motor current signal analysis is the most commonly used precursor for detecting faults in the PMSM drive system. However, the current signature responds sensitively to the load and temperature of the motor, thereby making it difficult to monitor faults in real- applications. Therefore, in this study, a condition monitoring methodology that detects motor faults, including their classification with standstill conditions, is proposed. The objective is to detect and classify faults of PMSMs by using programmable inverter without additional sensors and systems for detection. Both DC and AC were applied through the d-axis of a three-phase motor, and the change in incremental inductance was investigated to detect and classify faults. Simulation with finite element analysis and experiments were performed on PMSMs in healthy conditions as well as with eccentricity and demagnetization faults. Based on the results obtained from experiments, the proposed method was confirmed to detect and classify types of faults, including their severity.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1999년도 추계학술대회 논문집 학회본부 A
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• pp.113-115
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• 1999

A more reliable relaying algorithm for detecting a high impedance fault (HIF) requires fault currents at the relaying point containing information of various HIF characteristics as well as load conditions. As HIF characteristics, there are buildup, shoulder, nonlinearity and asymmetry. This paper presents a modeling method of a HIF in a distribution system using EMTP. In order to represent HIF characteristics, the proposed method uses two time-varying resistances. The first TVR models nonlinearity and asymmetry using voltage as the input. The second TVR models buildup and shoulder using time information as the input. The proposed method is implemented in EMTP.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2007년도 추계학술대회논문집
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• pp.891-894
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• 2007

This study presents fault diagnosis of low speed bearing using support vector machine (SVM). The data used in the experiment was acquired using acoustic emission (AE) sensor and accelerometer. The aim of this study is to compare the performance of fault diagnosis based on AE signal and vibration signal with same load and speed. A low speed test rig was developed to simulate various defects with shaft speeds as low as 10 rpm under several loading conditions. In this study, component analysis was also performed to extract the feature and reduce the dimensionality of original data feature. Moreover, the classification for fault diagnosis was also conducted using original data feature without feature extraction. The result shows that extracted feature from AE sensor gave better performance in faults classification.

• 전력전자학회논문지
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• 제26권2호
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• pp.150-157
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• 2021

Nowadays, a DC microgrid that can link various distributed power sources is gaining much attention. Accordingly, research on fault situations, such as line-to-line and line-to-ground faults of the DC microgrid, has been conducted to improve grid reliability. However, the blackout of an AC system and the oscillation of a DC bus voltage have not been reported or have not been sufficiently verified by previous research. In this study, a 20 kW DC microgrid testbed using a power HIL simulation technique is proposed. This testbed can simulate various fault conditions without any additional grid facilities and dangerous experiments. It includes the blackout of the DC microgrid caused by the AC utility grid's blackout, a drastic load increment, and the DC bus voltage oscillation caused by the LCL filter of the voltage source converter. The effectiveness of the proposed testbed is verified by using Opal-RT's OP5707 real-time simulator with a 3 kW prototype three-port dual-active-bridge converter.

• 한국안전학회지
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• 제12권3호
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• pp.166-172
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• 1997

배전선로에서 지락사고가 발생할 경우 신속한 검출은 감전사고 예방, 전기화재 방지 및 전력설비의 최적 운용에 있어서 중요하다. BEF(Back-fed Earth Fault)는 일종의 배전선로 지락사고로 부하측이 지락되는 경우이며 지락전류가 매우 작기 때문에 전류 검출에 의하여 배전 계통을 보호하기는 어려우나 배전 자동화 지역에서는 UVR(Under Voltage Relay)을 이용하여 보호한다. 그러나 배전 자동화가 되지 않은 지역에서는 UVR에 의해 보호가 불가능하므로 BEF의 특성을 해석하여 경제적으로 BEF를 방지하여야 한다. 본 논문에서는 RTDS, EMTP 시뮬레이션, ETSA의 실증 시험 데이터를 비교, 검토하여 기준 영상전류치를 설정하고, 이를 적용하여 측정된 영상 전류와 설정된 기준치를 비교하여 3상-단일 접지 배전 시스템의 정상 상태와 BEF의 구분이 가능한 BEF검출 알고리즘을 제안하였다. 다양한 조건에서 ETSA의 현장 시험에 적용하여 검토한 결과 3상-단일 접지 배전 시스템에서 제안된 BEF 검출 알고리즘의 타당성이 입증되었다. 따라서 본 알고리즘을 적용하여 배전선로를 운용하면 BEF에 의한 재해의 예방이 가능하리라 사료된다.