• Journal of Power Electronics
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• 제11권6호
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• pp.870-879
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• 2011

Regulated peak power tracking (RPPT) systems such as the series structure and the series-parallel structures are commonly used in satellite space power systems. However, these structures process the solar array power or the battery power to the load through two cascaded regulators during one orbit cycle, which reduces the energy transfer efficiency. Also the battery charging time is increased due to placement of converter between the battery and the solar array. In this paper a parallel structure has been proposed which can improve the energy transfer efficiency and the battery charging time for satellite space power RPPT systems. An analogue controller is used to control all of the required functions, such as load voltage regulation and solar array stabilization with maximum power point tracking (MPPT). In order to compare the system efficiency and the battery charging efficiency of the proposed structure with those of a series (conventional) structure and a simplified series-parallel structure, simulations are performed and the results are analyzed using a loss analysis model. The proposed structure charges the battery more quickly when compared to the other two structures. Also the efficiency of the proposed structure has been improved under different modes of solar array operation when compared with the other two structures. To verify the system, experiments are carried out under different modes of solar array operation, including PPT charge, battery discharge, and eclipse and trickle charge.

• 한국자동차공학회논문집
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• 제19권1호
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• pp.17-24
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• 2011

TMED(Transmission Mounted Electric Device) parallel hybrid configuration can realize EV(Electric Vehicle) mode by disengaging the clutch between an engine and a transmission-mounted motor to improve efficiencies of low load driving and regenerative braking. In the EV mode, however, jerk can be induced since there are insufficient damping elements in the drive-train. Though the jerk gives demoralizing influence upon driving comport, adding a physical damper is not applicable due to constraints of the layout. This study suggests the jerk reduction control, composed of active damping method and torque profiling method, to suppress the jerk without hardware modification. The former method creates a virtual damper by generating absorbing torque in the opposite direction of the oscillation. The latter method reduces impulse on the mated gear teeth of the drive-train by limiting the gradient of traction torque when the direction of the torque is reversed. To validate the effectiveness of the suggested strategy, a series of vehicle tests are carried out and it is observed that the amplitude of the oscillation can be reduced by up to 83%.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2011년도 전력전자학술대회
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• pp.179-180
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• 2011

This paper focuses on the Current-Voltage concurrent control method devoted to the multiple LED (light-emitting diode) string driver. Isolated DC to DC converter with cascaded chopping switch is proposed for smart lighting system such as light with sensor or back light unit of display, which need to control the current of parallel connected multiple LED stings and regulate DC voltage for micro controller for brightness control. The proposed circuit regulates the current of parallel connected multiple LED strings and additional DC voltage output simultaneously. To verify the performance, experimental results are presented based on the prototype board. 5V, 1A voltage mode electric load and two LED strings with different forward voltages are used for output loads. 23W output power is achieved and measured efficiency is in the range of 85%-87%

• 전력전자학회논문지
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• 제14권4호
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• pp.278-284
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• 2009

본 논문에서는 직류 전력을 공급하기 위한 사이리스터 컨버터의 출력 응답특성을 개선하기 위해 데이터 병렬 루프를 가지는 PID 제어 방식을 제안한다. 제안된 방식에서 사이리스터 컨버터의 점호각은 부하전류와 지령전압에 따라 결정된 점호각을 제어기와 병렬로 연결된 데이터 루프에서 발생하고, 이 점호각에 의해 발생하는 출력전압의 오차를 PID 제어기에서 보상하여 제어하는 방식이다. 제안된 방식의 실제적인 적용에서, 부하전류에 의해 병렬 데이터 루프의 점호각이 급격하게 변동하는 것을 억제하기 위해 간단한 디지털 저역통과 필터를 통하여 부하전류와 지령전압의 크기에 따라 룩-업 테이블 방식의 점호각이 결정되도록 설계하였다. 제안된 방식은 50[A]급의 사이리스터컨버터 실험을 통하여 검증하였다.

• 한국농공학회논문집
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• 제51권5호
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• pp.69-78
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• 2009

In order to improve water quality of upper watershed of Paldang reservoir, it is necessary to evaluate non-point source pollution loads and identify critical watershed pollution sources. A GIS based Soil and Water Assessment Tool was applied to evaluate model application and reliability, estimate NPS pollution load, identify critical watershed by NPS pollution sources, and suggest various best management practices for Kyongan Stream watershed. Yearly NPS pollution loads were estimated 30.0% SS, 60.1% TN and 35.4% TP, respectably. The watershed pollution load is mainly decided by precipitation condition and SS and nutrients load have a significant regression relationship. Based on 10-year average yearly NPS pollution load, critical sub-watersheds were identified. The No. 5 and 17 which have lots of relatively intensive agricultural fields and scattered industrial area were vary critical sub-watersheds and under more intensive pollution load. In order to control critical watershed, watershed best management practices such as scientific fertilizer, contour farming and parallel terrace, transferring the sloppy farmland to grass or forest and constructing a buffer zone, and constructing wetlands and retention ponds will be applied. Overall the SWAT model can be efficiently used for identification of critical sub-watersheds in order to develop a priority watershed management plan to reduce water pollutions.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2006년도 제37회 하계학술대회 논문집 A
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• pp.220-221
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• 2006

This paper presents a single-phase parallel active power filter with an analog control circuit to eliminate for harmonic source currents generated by nonlinear loads. The proposed system removes the harmonic source currents by injecting a compensation current that is 180' out of phase with the load harmonic current. The detection of the load harmonics is realized by a simple new structure, referred to the Notch Filter with GIC (Generalized Impedance Converter), which has higher Q than existing harmonic detecters and a simpler structure. The compensation current is obtained using the proposed harmonic detection circuit, DC-Link voltage, and output current of the full-bridge inverter controlled current mode PWM controller. The operation of the proposed system is verified experimentally.

• 한국전기전자재료학회논문지
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• 제15권9호
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• pp.743-749
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• 2002

A 1.5V 70㏈ 100MHz CMOS class-AB complementary operational amplifier is presented. For obtaining the high gain and the high unity gain frequency, the input stage of the amplifier is designed with rail-to-rail complementary differential pairs which are symmetrically parallel-connected with the NMOS and the PMOS differential input pairs, and the output stage is designed to the rail-to-rail class-AB output stage including the elementary shunt stage technique. With this design technique for output stage, the load dependence of the overall open loop gain is improved and the push-pull class-AB current control can be implemented in a simple way. The designed operational amplifier operates perfectly on the complementary mode with 180$^{\circ}$ phase conversion for 1.5V supply voltage, and shows the push-pull class-AB operation. In addition, the amplifier shows the DC open loop gain of 70.4 ㏈ and the unity gain frequency of 102 MHz for $C_{L=10㎊∥}$ $R_{L=1㏁}$ Parallel loads. When the resistive load $R_{L}$ is varied from 1 ㏁ to 1 ㏀, the DC open loop gain of the amplifier decreases by only 2.2 ㏈.a$, the DC open loop gain of the amplifier decreases by only 2.2 dB.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제10권10호
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• pp.4787-4807
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• 2016

Although the dense interconnection datacenter networks (DCNs) (e.g. FatTree) provide multiple paths and high bisection bandwidth for each server pair, the single-path TCP (SPT) and ECMP which are widely used currently neither achieve high bandwidth utilization nor have good load balancing. Due to only one available transmission path, SPT cannot make full use of all available bandwidth, while ECMP's random hashing results in many collisions. In this paper, we present OFPT, an OpenFlow based Parallel Transport framework, which integrates precise routing and scheduling for better load balancing and higher network throughput. By adopting OpenFlow based centralized control mechanism, OFPT computes the optimal path and bandwidth provision for each flow according to the global network view. To guarantee high throughput, OFPT dynamically schedules flows with Seamless Flow Migration Mechanism (SFMM), which can avoid packet loss in flow rerouting. Finally, we test OFPT on Mininet and implement it in a real testbed. The experimental results show that the average network throughput in OFPT is up to 97.5% of bisection bandwidth, which is higher than ECMP by 36%. Besides, OFPT decreases the average flow completion time (AFCT) and achieves better scalability.

• Journal of Power Electronics
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• 제19권2호
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• pp.580-590
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• 2019

The concept of virtual synchronous generators (VSGs) is a valuable means for improving the frequency stability of microgrids (MGs). However, a great virtual inertia in a VSG's controller may cause power oscillation, thereby deteriorating system stability. In this study, a small-signal model of an MG with two paralleled VSGs is established, and a control strategy for maintaining a constant inertial time with an increasing active-frequency droop coefficient (m) is proposed on the basis of a root locus analysis. The power oscillation is suppressed by adjusting virtual synchronous reactance, damping coefficient, and load frequency coefficient under the same inertial time constant. In addition, the dynamic load distribution is sensitive to the controller parameters, especially under the parallel operation of VSGs with different capacities. Therefore, an active power increment method is introduced to improve the precision of active power sharing in dynamic response. Simulation and experimental is used to verify the theoretical analysis findings.

• Journal of Power Electronics
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• 제16권6호
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• pp.2359-2367
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• 2016

Inductive power transfer (IPT) systems have become increasingly popular in recharging electric vehicle (EV) batteries. This paper presents an investigation of a series parallel/series (SP/S) resonant compensation network based IPT system for EVs with further optimized circular pads (CPs). After the further optimization, the magnetic coupling coefficient and power transfer capacity of the CPs are significantly improved. In this system, based on a series compensation network on the secondary side, the constant output voltage, utilizing a simple yet effective control method (fixed-frequency control), is realized for the receiving terminal at a settled relative position under different load conditions. In addition, with a SP compensation network on the primary side, zero voltage switching (ZVS) of the inverter is universally achieved. Simulations and experiments have been implemented to validate the favorable applicability of the modified optimization of CPs and the proposed SP/S IPT system.