• Journal of Power Electronics
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• v.16 no.2
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• pp.769-777
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• 2016

This work focuses on current sharing between punch-through insulated gate bipolar transistors (IGBTs) connected in parallel and evaluates the mechanisms that allow overall current balancing. Two different control strategies are presented. These strategies are based on the modification of transistor gate-emitter control voltage V_GE by using an active gate driver circuit. The first strategy relies on the calculation of the average value of the current flowing through all parallel-connected IGBTs. The second strategy is proposed by the authors on the basis of a current cross reference control scheme. Finally, the simulation and experimental results of the application of the two current sharing control algorithms are presented.

• Journal of KIISE:Software and Applications
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• v.32 no.11
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• pp.1099-1110
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• 2005

As auctions become popular, developing good agent bidding strategies has been an important focus in agent-based electronic commerce research. Especially for the continuous double auctions where no single dominant strategy is known, the agent bidding strategy has practical significance. This paper introduces an adaptive agent strategy for the countinuous double auction. The central idea is to let the agent figure out at run time when the sophisticated strategy (called the p-strategy) is beneficial and when a simpler strategy is better. Balance between exploration and exploitation is achieved by using a heuristic exploration function that trades off the expected profits and the number of tries of each strategy. We have experimentally evaluated the performance of the adaptive strategy in a wide variety of environments. The experiment results indicate that the adaptive strategy outperforms the plain p-strategy when the p-strategy performs poorly, while it performs similar to the p-strategy when the p-strategy dominates the other simple strategies.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.17 no.11
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• pp.3030-3049
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• 2023

With the development and wide application of hybrid network computing modes like cloud computing, edge computing and fog computing, the customer service requests and the collaborative optimization of various computing resources face huge challenges. Considering the characteristics of network environment resources, the optimized deployment of service resources is a feasible solution. So, in this paper, the optimal goals for deploying service resources are customer experience and service cost. The focus is on the system impact of deploying services on load, fault tolerance, service cost, and quality of service (QoS). Therefore, the alternate node filtering algorithm (ANF) and the adjustment factor of cost matrix are proposed in this paper to enhance the system service performance without changing the minimum total service cost, and corresponding theoretical proof has been provided. In addition, for improving the fault tolerance of system, the alternate node preference factor and algorithm (ANP) are presented, which can effectively reduce the probability of data copy loss, based on which an improved cost-efficient replica deployment strategy named ICERD is given. Finally, by simulating the random occurrence of cloud node failures in the experiments and comparing the ICERD strategy with representative strategies, it has been validated that the ICERD strategy proposed in this paper not only effectively reduces customer access latency, meets customers' QoS requests, and improves system service quality, but also maintains the load balancing of the entire system, reduces service cost, enhances system fault tolerance, which further confirm the effectiveness and reliability of the ICERD strategy.

• Journal of Power Electronics
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• v.14 no.6
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• pp.1119-1129
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• 2014

This study proposes a novel five-level three-phase hybrid-clamped converter composed of only six switches and one flying capacitor (FC) per phase. The capacitor-voltage-drift phenomenon of the converter under the classical sinusoidal pulse width modulation (SPWM) strategy is comprehensively analyzed. The average current, which flows into the FC, is a function of power factor and modulation index and does not remain at zero. Thus, a specific modulation strategy based on space vector modulation (SVM) is developed to balance the voltage of DC-link and FCs by injecting a common-mode voltage. This strategy applies the five-segment method to synthesize the voltage vector, such that switching losses are reduced while optional vector sequences are increased. The best vector sequence is then selected on the basis of the minimized cost function to suppress the divergence of the capacitor voltage. This study further proposes a startup method that charges the DC-link and FCs without any additional circuits. Simulation and experimental results verify the validity of the proposed converter, modulation strategy, and precharge method.

• Strategy21
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• s.38
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• pp.321-347
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• 2015

중국은 지난 10년간 아시아에서의 영향력 확대를 위한 팽창정책의 일환으로 인도양 주변 국가들과의 관계발전을 위해 국가 차원의 노력을 기울여왔다. '진주목걸이 전략(String of Pearls Strategy')으로 묘사되는 중국의 인도양 정책의 개괄적 성격에 관한 연구는 여러 학자들에 의해서 시도되어 왔으나, 인도양 주변 개별국과들과의 협력과 개입의 정도(The variation in the extent of China's Engagement and Collaboration with States along Its Indian Ocean sea lines of communication)에 영향을 미치는 구조적 요인에 대한 연구는 부재해 왔다. 이 논문에서는 인도양 주변 국가들에 대한 개입 및 관계발전을 위한 중국의 인도양정책을 국제정치학의 이론 중 '방어적 신현실주의(Defensive Neorealism)'의 이론적 틀에 근거한 '연성적 힘의 균형(Soft Balancing)'의 관점에서 고찰해 보고, 중국의 인도양 정책은 이 지역에서 중국의 팽창에 대한 미국의 견제 및 반발(Backlash)을 억제하고 중국의 에너지 안보를 보장하기 위한 전략적 정책의 결과임을 조명해 본다. 더불어 중국의 인도양 진출에 따른 미국의 정책대안을 예측해 본다. 본 연구의 목적을 위해 이론적 틀에 기반한 가설을 설정하고 인도양 주변의 11개 국가에 대한 교차 사례연구(Cross-sectional Case Analysis)를 통해 타당성을 검증한다.

• Proceedings of the KIPE Conference
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• 2001.10a
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• pp.369-373
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• 2001

Multilevel inverter has attracted great interest in high-voltage high-power field because of its less distorted output. In this paper, a direct torque control (DTC) technique based on a three-level neutral-point-clamped (NPC) inverter is presented. In order to solve the intrinsic neutral-point voltage-balancing problem and to obtain a high performance DTC, a special vector selection method is introduced and the concept of virtual vector is developed. By using the proposed PWM strategy, a MRAS speed sensor-less DTC drive can be achieved without sensing the neutral-point voltage, The strategy can be verified by simulation and experimental results.

• Journal of Power Electronics
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• v.16 no.5
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• pp.1735-1742
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• 2016

This paper proposes an interleaved five-level boost converter based on a switched-capacitor network. The operating principle of the converter under the CCM mode is analyzed. A high voltage gain, low component stress, small input current ripple, and self-balancing function for the capacitor voltages in the switched-capacitor networks are achieved. In addition, a three-loop control strategy including an outer voltage loop, an inner current loop and a voltage-balance loop has been researched to achieve good performances and voltage-balance effect. An experimental study has been done to verify the correctness and feasibility of the proposed converter and control strategy.

• Structural Monitoring and Maintenance
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• v.2 no.2
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• pp.133-143
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• 2015

Civil engineering infrastructure is aging and requires cost-effective maintenance strategies to enable infrastructure systems operate reliably and sustainably. This paper presents an approach for determining risk-cost balanced repair strategy of corrosion damaged reinforced concrete structures with consideration of uncertainty in structural resistance deterioration. On the basis of analytical models of cover concrete cracking evolution and bond strength degradation due to reinforcement corrosion, the effect of reinforcement corrosion on residual load carrying capacity of corroded reinforced concrete structures is investigated. A stochastic deterioration model based on gamma process is adopted to evaluate the probability of failure of structural bearing capacity over the lifetime. Optimal repair planning and maintenance strategies during the service life are determined by balancing the cost for maintenance and the risk of structural failure. The method proposed in this study is then demonstrated by numerical investigations for a concrete structure subjected to reinforcement corrosion. The obtained results show that the proposed method can provide a risk cost optimised repair schedule during the service life of corroded concrete structures.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.10 no.9
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• pp.4023-4043
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• 2016

Network virtualization has been regarded as a core attribute of the Future Internet. In a network virtualization environment (NVE), multiple heterogeneous virtual networks can coexist on a shared substrate network. Thus, a substrate network failure may affect multiple virtual networks. In this case, it is increasingly critical to provide survivability for the virtual networks against the substrate network failures. Previous research focused on mechanisms that ensure the resilience of the virtual network. However, the resource efficiency is still important to make the mapping scheme practical. In this paper, we study the survivable virtual network embedding mechanisms against substrate link and node failure from the perspective of improving the resource efficiency. For substrate link survivability, we propose a load-balancing and re-configuration strategy to improve the acceptance ratio and bandwidth utilization ratio. For substrate node survivability, we develop a minimum cost heuristic based on a divided network model and a backup resource cost model, which can both satisfy the location constraints of virtual node and increase the sharing degree of the backup resources. Simulations are conducted to evaluate the performance of the solutions. The proposed load balancing and re-configuration strategy for substrate link survivability outperforms other approaches in terms of acceptance ratio and bandwidth utilization ratio. And the proposed minimum cost heuristic for substrate node survivability gets a good performance in term of acceptance ratio.

• Journal of Electrical Engineering and Technology
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• v.7 no.1
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• pp.1-8
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• 2012

The current paper presents a novel control strategy of a three-phase, four-wire Unified Power Quality (UPQC) to improve power quality. The UPQC is realized by the integration of series and shunt active power filters (APF) sharing a common dc bus capacitor. The realization of shunt APF is carried out using a three-phase, four-leg Voltage Source Inverter (VSI), and the series APF is realized using a three-phase, three-leg VSI. To extract the fundamental source voltages as reference signals for series APF, a zero-crossing detector and sample-and-hold circuits are used. For the control of shunt APF, a simple scheme based on the real component of fundamental load current (I $Cos{\Phi}$) with reduced numbers of current sensors is applied. The performance of the applied control algorithm is evaluated in terms of power-factor correction, source neutral current mitigation, load balancing, and mitigation of voltage and current harmonics in a three-phase, four-wire distribution system for different combinations of linear and non-linear loads. The reference signals and sensed signals are used in a hysteresis controller to generate switching signals for shunt and series APFs. In this proposed UPQC control scheme, the current/voltage control is applied to the fundamental supply currents/voltages instead of fast-changing APF currents/voltages, thus reducing the computational delay and the required sensors. MATLAB/Simulink-based simulations that support the functionality of the UPQC are obtained.