• The Transactions of the Korean Institute of Power Electronics
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• v.13 no.2
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• pp.88-95
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• 2008

This paper proposes a fast fault detection algorithm under open-circuit fault of a switch for a brushless DC(BLDC) motor drive system. This proposed method is configured without the additional devices for fault detection and identification. The fault detection and identification are achieved by a simple algorithm using the operating characteristic of the BLDC motor. After the fault identification, the drive system is reconfigured for continuous operation. This system is reconfigured by four-switch topology connecting a faulty leg to the middle point of DC-link bidirectional switches. This proposed method can also be embedded into existing BLDC motor drive systems as a subroutine without excessive computational effort. The feasibility of a the proposed fault detection algorithm is validated in simulation and experiment.

• Journal of Power Electronics
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• v.18 no.2
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• pp.627-639
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• 2018

The fact that the reliability of IGBTs has become a more and more significant aspect of power converters has resulted in an increase in the research on the open circuit (OC) fault location of IGBTs. When an OC fault occurs, a zero-current phenomena exists and frequently appears, which can be found in a lot of the existing literature. In fact, fault variables have a very high correlation with the zero-current interval. In some cases, zero-current interval actually decides the most significant fault feature. However, very few of the previous studies really explain or prove the zero-current phenomena of the fault current. In this paper, the zero-current phenomena is explained and verified through mathematical derivation, based on two-level and three-level NPC static var generators (SVGs). Mathematical models of single OC fault are deduced and it is concluded that a zero-current interval with a certain length follows the OC faults for both two-level and NPC three-level SVGs. Both inductive and capacitive reactive power situations are considered. The unbalanced load situation is discussed. In addition, simulation and experimental results are presented to verify the correctness of the theoretical analysis.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.60 no.5
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• pp.1073-1077
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• 2011

The breaking capacity of circuit breakers could be no more increased in the electric power system. This is because the fault current increases due to continuous increases in electric power demand and facilities. To solve the problem, it is necessary to come up with an alternative. The superconducting fault current limiter (SFCL) has received an attention among various alternatives. The SFCL effectively reduce a fault current in cooperation with a power circuit breaker. A various types of the SFCL are suggested and a study on them have been progressed. As a result of it, the SFCL can be applyed to the electric power system in the near future. But, a study on recovery behaviors of the SFCL is not enough for applying to the electric power system. If the superconducting elements do not completely recover to the superconducting state after fault operation, it might be a breakdown of the superconducting elements due to heavy power burden and it gives an bad influence on the working of other electric devices. Additionally, the distribution power system has reclosing operation such as open-0.3sec-closed/open-3min-closed/open procedure. So we need to study more about improvement of the recovery behaviors of the SFCL. In this paper, we analyzed the recovery behaviors of a flux-coupling type SFCL according to reclosing operation when a single line-to-ground fault occurred and we compared recovery behaviors of the SFCL with and without a neutral line between secondary reactors and superconducting elements. Also, the flux-coupling type SFCL has advantageous for increases of capacity by controlling the variation in turn ratios between two reactors. Consequently, when the number of turns of the secondary reactors increased, the power burden of the superconducting elements was bigger due to the increase of impedances of the secondary reactors. To distribute the power burden, two superconducting elements connected in series and the balanced quenching of the superconducting elements was induced by connecting a neutral line.

• Journal of Power Electronics
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• v.16 no.3
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• pp.1087-1096
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• 2016

This paper reports an investigation conducted on two diagnostic methods based on the switching voltage pattern of IGBT open-circuit faults in voltage-source inverters (VSIs). One method was based on the bridge arm pole voltage, and the other was based on bridge arm line voltage. With an additional simple circuit, these two diagnostic methods detected and effectively identified single and multiple open-circuit faults of inverter IGBTs. A comparison of the times for the diagnosis and anti-interference features between these two methods is presented. The diagnostic time of both methods was less than 280ns in the best case. The diagnostic time for the method based on the bridge arm pole voltage was less than that of the method based on the bridge arm line voltage and was 1/2 of the fundamental period in the worst case. An experimental study was carried out to show the effectiveness of and the differences between these two methods.

• Proceedings of the KIEE Conference
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• 2004.11d
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• pp.83-88
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• 2004

As the electric system is getting larger to meet the increasing demand for electric power, the rating of power apparatus is becoming inevitably higher in its working voltage and larger in its capacity. According to KEPCO reports, power transformers in the KEPCO system have undergone troubles such as winding short insulation breakdowns every year since 1981. the cause of this troubles were high one line grounding fault currents in KEPCO systems that had direct grounding systems. KEPCO has installed the NGR(neutral grounding reactor) to lower this fault current and reduced winding short insulation breakdowns in power transformers. But when a circuit breaker opened a no load bus, some trips of circuit breakers for protecting transformer have occurred by mal-operation of 59GT(overvoltage ground relay) that detect disconnection of NGR. Therefore, in this paper, we analyzed the cause and examined the effect of time delav circuit to prevent wrong operation of 59GT.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.32 no.3
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• pp.232-239
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• 2008

The position sensors used in a magnetic bearing system are desirable to provide some degree of fault-tolerance as the rotor position is necessary for the feedback control to overcome the open-loop instability. In this paper, we propose an inductive position sensor that can cope with a partial fault in the sensor. The sensor has multiple poles which can be combined to sense the in-plane motion of the rotor. When a high-frequency voltage signal drives each pole of the sensor, the resulting current in the sensor coil contains information regarding the rotor position. The signal processing circuit of the sensor extracts this position information. In this paper, we used the magnetic circuit model of the sensor that shows the analytical relationship between the sensor output and the rotor motion. The multi-polar structure of the sensor makes it possible to introduce redundancy which can be exploited for fault-tolerant operation. The proposed sensor is applied to a magnetically levitated turbo-molecular vacuum pump. Experimental results validate the fault-tolerance algorithm.

• The Journal of the Acoustical Society of Korea
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• v.14 no.2E
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• pp.43-49
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• 1995

In this paper a space search technique is used to detect and locate the faults of the circuit interconnections. The circuit interconnections are represented by the tree structure and the tree space is searched to detect and locate the open faults of the circuit interconnections. The breadth search is used to detect the open faults and reduce the space size. The depth search is used to locate the open faults.

• The Transactions of the Korean Institute of Power Electronics
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• v.16 no.5
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• pp.457-465
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• 2011

The fault analysis and detecting algorithm for a 3 phase diode rectifier is proposed. The 3 phase dioderectifier is used for the AC power rectifier of the PWM inverter. The input power or diode faults cause theripples of the DC voltage, degradation of the control performance and life shortening of the DC link capacitor.In this paper, the ripple of the DC voltage is mathematically analyzed for the earth fault of input power andopen circuit fault of the diode, respectively. The fault detection and type of fault can be obtained by comparingthe average DC voltage and the instant DC voltage which is sampled with 6 times of grid frequency. Theproposed method can be easily applicable and doesn't require additional circuit. The experimental and simulationresults are presented to verify the validity of the proposed method.

• Journal of Power Electronics
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• v.9 no.3
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• pp.377-385
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• 2009

In this paper, a diagnosis method for switch open-circuit faults in three-phase PWM inverters is proposed, which employs support vector machine (SVM) as classifying method. At first, a discrete wavelet transform (DWT) is used to detect a discontinuity of currents due to the fault, and then the features for fault diagnosis are extracted. Next, these features are employed as inputs for the SVM training. After training, the SVM produces an optimized boundary which is used identifying the fault. Finally, the fault classification is performed online with instantaneous features. The experimental results have verified the validity of the proposed estimation algorithm.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.64 no.3
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• pp.498-504
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• 2015

This paper proposed an Spread Spectrum Time Domain Reflectometry (SSTDR) using time-frequency correlation analysis in order to have more accurate fault determination and location detection than classical SSTDR despite increased signal attenuation due to the long distance to cable fault location. The proposed method was validated through comparison with classical SSTDR methods in open- and short-circuit fault detection experiments of low-voltage power cables. The experimental results showed that the proposed method can detect correlation coefficients at fault locations accurately despite reflected signal attenuation so that cable faults can be detected more accurately and clearly in comparison to existing methods.