• 전기학회논문지
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• 제57권2호
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• pp.155-163
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• 2008

This paper presents a novel framework for analysis of power system wide-area blackout based on so called fault cascading scenarios. For a given power system operating state, "triggering" faults or a "seed faults" are chosen based on the probabilities estimated from the hazard rates. The fault probabilities reflect both the load and the weather conditions. Effects of hidden failures in protection systems are also reflected in establishing the fault propagation scenarios since they are one of the major causes for the wide-area blackouts. A tree type data structure called a PS-BEST(Power System Blackout Event Scenario Tree) is proposed for construction of the fault cascading scenarios, in which nodes represent various power system operating states and the arcs are the events causing transitions between the states. Arcs can be either probabilistic or deterministic. For a given initial fault, the total probability of leading to wide-area blackout is estimated by aggregating the individual probability of each fault sequence route leading to wide-area blackout. A case study is performed on the IEEE RTS-79(24 bus) system based on the fault data presented by the North American Electrical Reliability Council(NERC). Test results demonstrate the potentials and the effectiveness of the proposed technique for the future wide-area blackout analysis.

• 유공압시스템학회논문집
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• 제8권4호
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• pp.17-23
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• 2011

Proportional control solenoid is a type of modulating valve that can continuously control the valve position with magnetic force of solenoid. Recent microcontroller based digital servocontroller for proportional valve is being developed toward the smart valve with additional features such as enhanced control algorithm for finer process and intelligent on-board diagnosis for maintenance. In this paper, development of servocontroller network control with CAN bus which is free from problems of security and network traffic jam is presented. Design of network control system includes modes of communication between master and slave, assignment of 29bit message identifier and message objects, transaction of communication sequence, etc. Monitoring function and control experiments for remote valve through CAN network prove the extended function of smart valve control system.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2006년도 춘계학술대회논문집
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• pp.340-343
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• 2006

As the needs of consumer on ride comforts increase and the reduction of road traffic noise tightened step by step, the power unit noise emitted by cars has been reduced. It has been found that tire noise dominates noise produced by the power-train when vehicles are driven at high speeds. Therefore, in these days, tire/pavement noise is concerned. Tire/pavement noise is affected by pavement type and vehicle???s transmission loss. Tire noise mechanism is produced by several mechanisms. The sound of tire can propagate either through the air or through the structure of vehicle. Pattern noise is the result of pressure variations through the air to the interior side of vehicle. Especially, on smooth asphalt the periodicity of tread design, pitch sequence is important factor, which have an influence on the reduction of tire noise.

• 대한수학회지
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• 제45권2호
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• pp.513-525
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• 2008

Using known properties of superquadratic functions we obtain a sequence of inequalities for superquadratic functions such as the Converse and the Reverse Jensen type inequalities, the Giaccardi and the Petrovic type inequalities and Hermite-Hadamard's inequalities. Especially, when the superquadratic function is convex at the same time, then we get refinements of classical known results for convex functions. Some other properties of superquadratic functions are also given.

• Journal of Advanced Marine Engineering and Technology
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• 제17권3호
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• pp.60-69
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• 1993

The speed control associated with dc servo motors for direct-drive applications of mobile robot is considered in this study. Robot is moved by power wheeled steering of two dc servo motors mounted to it. In order to cooperate with micro-computer and to achieve the high-performance operation of dc servo motor, speed control system is composed of a digital Phase Locked Loop and H-type drive circuit. And the motor is driven by Pulse Width Modulations. In controlling PWM, it is modified to compose of H-type drive circuit with feedback diodes and switching transistor and design of control sequence so that it may show linear characteristics. As a result, speed characteristics of motor showed linear features. In order to get data on design of PLL control system, the parameters of 80[W[ motor & robot device is measured by simple software control. The PLL speed control system is schemed and designed by leaner drive circuit and measured parameters. A complete speed control system applied to 80[W] dc servo motor showed good linearity, stability and high response. Also, it is verified that the PLL speed control system has good compatibility as a mobile robot driver.

• 전력전자학회논문지
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• 제18권1호
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• pp.26-36
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• 2013

This paper presents a simple and cost-effective stand-alone rapid battery charging system of 30kW for electric vehicles. The proposed system mainly consists of active front-end rectifier of neutral point clamped 3-level type and non-isolated bi-directional dc-dc converter of multi-phase interleaved half-bridge topology. The charging system is designed to operate for both lithium-polymer and lithium-ion batteries. The complete charging sequence is made up of three sub-interval operating modes; pre-charge mode, constant-current mode, and constant-voltage mode. The pre-charge mode employs the stair-case shaped current profile to accomplish shorter charging time while maintaining the reliable operation of the battery. The proposed system is specified to reach the full-charge state within less than 16min for the battery capacity of 8kWh by supplying the charging current of 78A. Owing to the simple and compact power conversion scheme, the proposed solution has superior module-friendly mechanical structure which is absolutely required to realize flexible power expansion capability in a very high-current rapid charging system.

• 전력전자학회논문지
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• 제20권1호
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• pp.1-10
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• 2015

This paper proposes a control algorithm for permanent magnet synchronous generators with a back-to-back three-level neutral-point clamped voltage source converter in a medium-voltage off-shore wind power system under unbalanced grid conditions. Specifically, the proposed control algorithm compensates for unbalanced grid voltage at the PCC (Point of Common Coupling) in a collector bus of an off-shore wind power system. This control algorithm has been formulated based on symmetrical components in positive and negative synchronous rotating reference frames under generalized unbalanced operating conditions. Instantaneous active and reactive power is described in terms of symmetrical components of measured grid input voltages and currents. Negative sequential component of AC input current is injected into the PCC in the proposed control strategy. The amplitude of negative sequential component is calculated to minimize the negative sequential component of grid voltage under the limitation of current capability in a voltage source converter. The proposed control algorithm enables the provision of balanced voltage at the PCC resulting in the high quality generated power from off-shore wind power systems under unbalanced network conditions.

• 전력전자학회논문지
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• 제16권3호
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• pp.283-292
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• 2011

본 논문에서는 기존의 멀티레벨 인버터와는 달리 DC링크단에 스위치를 설치함으로써 성능을 향상시킨 새로운 형태의 H-브리지 멀티레벨 인버터를 제안한다. 제안된 방식은 계통 연계형 단상 멀티레벨 인버터로서 기존의 단상인버터에 비하여 출력 전압 파형이 정현파에 가깝고, 고압 대용량 시스템용 멀티레벨 인버터로의 확장도 용이할 뿐만 아니라 직렬연결을 통하여 간단히 전압레벨을 확장할 수 있다는 장점을 갖는다. 동일한 5레벨의 경우 기존의 H-브리지 직렬형이나 NPC형 멀티레벨 인버터는 가제어 스위치가 8개 사용되는 반면에 제안한 멀티레벨 인버터는 가제어 스위치가 6개 사용되기 때문에 회로 구성이 간단하여 신뢰도가 높고 경제적인 구현이 가능하고 스위칭 손실이 줄어서 효율이 향상되는 특징이 있다. POD 변조기법을 기반으로 하여 반송파 신호 하나만을 사용하는 새로운 PWM 방법을 제시하였으며 DC링크 커패시터 전압의 균형을 위한 스위칭 시퀀스에 대해서도 검토하였다. 제안된 토폴로지의 타당성을 시뮬레이션과 실험을 통하여 확인하였다.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2005년도 제24회 춘계학술대회논문집
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• pp.92-95
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• 2005

본 연구는 기존의 폭발볼트와는 달리 작동에 필요한 전원의 공급 없이 수행하면서, 또한 지연기능까지 포함한 비전기식 지연형 폭발볼트에 관한 것이다. 즉 비전기식 작동방법을 이용하여 전원 공급 장치를 없앨 수 있기 때문에 분리장치의 소형화가 가능해졌고, 이를 위하여 기존 폭발볼트의 작동 메카니즘과는 다른 새로운 개념의 메카니즘을 적용하였고, 또한 지연기능을 추가하기 위하여 작동메카니즘 개발과 별도로 지연장치를 개발하였다. 전원을 사용하지 않고 작동하는 착화장치를 설계하기 위하여 폭발볼트가 결합된 비행체에서 발생하는 공기의 저항력을 이용하였다. 고속으로 비행하는 발사체의 속도를 줄이고 안전한 착륙을 위한 낙하 시스템의 설계에 고려될 수 있는 장치라고 생각된다.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2011년도 전력전자학술대회
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• pp.429-430
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• 2011

This paper presents a simple and cost-effective stand-alone rapid battery charging system of 30kW for electric vehicles. The proposed system mainly consists of active front-end rectifier of neutral point clamped 3-level type and non-isolated bi-directional dc-dc converter of multi-phase interleaved half-bridge topology with coupled inductors. The charging system is designed to operate for both lithium-polymer and lithium-ion batteries. The complete charging sequence is made up of three sub-interval operating modes; pre-charging mode, constant-current mode, and constant-voltage mode. The pre-charging mode employs the staircase shaped current profile to accomplish shorter charging time while maintaining the reliable operation of the battery. The proposed system is able to reach the full-charge state within less than 16min for the battery capacity of 8kWh by supplying the charging current of 67A. The optimal discharging algorithm for Vehicle to the Grid (V2G) operation has been adopted to maintain the discharging current of 1C. Owing to the simple and compact power conversion scheme, the proposed solution has superior module-friendly mechanical structure which is absolutely required to realize flexible power expansion capability in a very high-current rapid charging system.