• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.25 no.12
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• pp.1021-1027
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• 2012

In this paper, multi-string power balancing system for streetlight was developed. Accordingly, the components of the system was developed, unit converters, MPPT control unit, a bank of Li-ion battery and controls the charging and discharging. Loss by improving the efficiency of the system through the parallel operation of the unit converter output will be reduced. And by improving the efficiency of the system through the unit converter parallel operation, output losses will be reduced. Charging and discharging efficiency of the device used in a typical solar streetlight is calculated based on the maximum power input. Because of the variation of the input power has a weakness. In this paper, flexible to changes in the input, and a system was developed to minimize the cost per watt. Measure the performance of the unit module from the system, the result was more than 91%. And the charging capacity 12 V/105 Ah, module power 180 W, respectively. Should expect to be able to improve performance through continuous monitoring in the future.

• The Transactions of the Korean Institute of Power Electronics
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• v.23 no.3
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• pp.153-160
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• 2018

Recent trends in high-power-density applications have highlighted the importance of designing power converters with high-frequency operation. However, conventional LLC resonant converters present limitations in terms of high-frequency driving due to switching losses during the turn-off period. Switching losses are caused by the overlap of the voltage and current during this period, and can be decreased by reducing the switch voltage. In turn, the switch voltage can be reduced through a series connection of four switches, and additional circuitry is essential for balancing the voltage of each switch. In this work, a three-level LLC resonant converter that can operate at high frequency is proposed by reducing switch losses and balancing the voltages of all switches with only one capacitor. The voltage-balancing principle of the proposed circuit can be extended to n-level converters, which further reduces the switch voltage stress. As a result, the proposed circuit is applicable to high-input applications. To confirm the validity of the proposed circuit, theoretical analysis and experimental verification results from a 350 W-rated prototype are presented.

• The Transactions of the Korean Institute of Power Electronics
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• v.20 no.4
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• pp.321-329
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• 2015

The static synchronous compensator (STATCOM) of cascaded H-bridge configuration accompanying multiple separate DC sides is inherently subject to the problem of uneven DC voltages. These DC voltages in one leg can be controlled by adjusting the AC-side output voltage of each cell inverter, which is proportional to the active power. However, when the phase current is extremely small, large AC-side voltage is required to generate the active power to balance the cell voltages. In this study, an alternative zero-sequence current injection method is proposed, which facilitates effective cell balancing controllers at no load, and has no effect on the power grid because the injected zero sequence current only flows within the STATCOM delta circuit. The performance of the proposed method is verified through simulation and experiments.

• Plant Journal
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• v.13 no.1
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• pp.30-36
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• 2017

During the start-up of 500 MW class coal-fired power plant, abnormal shaft vibration was occurred on bearings installed on both side of high and intermediate pressure steam turbine. Shaft vibration was analyzed to investigate the reason and find the resolution, based on well-known theory in this study. Typical vibration characteristics which occur when rotating parts contact with stationary parts were observed at the analysis of frequency, amplitude and phase angle. The reason of abnormal vibration was assumed to be rub and internal parts wear was observed during repair period. As a result of applying low speed turning and balancing for resolution of abnormal vibration, balancing was more effective for rub removal. So balancing could be excellent resolution in the case of abnormal vibration which is similar to this study.

• The Transactions of the Korean Institute of Power Electronics
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• v.9 no.2
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• pp.187-193
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• 2004

For a power source of usual electronic devices such as PDA, smart phone, UPS and electric vehicle, the battery made of serially connected multiple cells is generally used. In this case, if there are some unbalanced among cell voltages, the total lifetime and the total capacity of the battery are limited to a lower value. To maintain a balanced condition in cells, an effective method of regulating the cell voltage in indispensable. In this paper, we propose the design of a balancing circuit for electronic appliances. The balancing system was controlled by a micro-controller which enables to implement the balancing action during charging period. Proposed method has been verified by the experiment using the charger and recorder. The experimental results show that the individual battery equalization can improve battery capacity and battery lifetime and performance through an extended operational time.

• Proceedings of the IEEK Conference
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• 2000.07a
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• pp.314-317
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• 2000

Cluster system provides attractive scalability in terms of computation power and memory size. With the advances in high speed computer network technology, cluster systems are becoming increasingly competitive compared to expensive parallel machines. In parallel processing program, each task load is difficult to predict before running the program and each task is interdependent each other in many ways. Load imbalancing induces an obstacle to system performance. Most of researches in load balancing were concerned with distributed system but researches in cluster system are few. In cluster system, the dynamic load balancing algorithm which evaluates each processor's load in runtime is purpose that the load of each node are evenly distributed. But, if communication cost or node complexity becomes high, it is not effective method for all nodes to attend load balancing process. In that circumstances, it is good to reduce the number of node which attend to load balancing process. We have modeled cluster systems and proposed marginal dynamic load balancing algorithms suitable for that circumstances.

• Journal of Electrical Engineering and Technology
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• v.12 no.1
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• pp.29-38
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• 2017

This paper presents a study on the state-of-charge (SOC) reference based active cell balancing in real-time. The optimal references of SOC are determined by using the proposed active cell balancing system with the bidirectional DC/DC converters via the dual active bridge (DAB) type. Then, the energies between cells can be balanced by the power flow control of DAB based bidirectional DC/DC converters. That is, it provides the effective management of battery by transferring energy from the strong cell to the weak one until the cell voltages are equalized to the same level and therefore improving the additional charging capacity of battery. In particular, the cell aging of battery and power loss caused from energy transfer are considered. The performances of proposed active cell balancing system are evaluated by an electromagnetic transient program (EMTP) simulation. Then, the experimental prototype is implemented in hardware to verify the usefulness of proposed system.

• Journal of Power Electronics
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• v.14 no.2
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• pp.315-323
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• 2014

An optimized space vector pulse width modulation (SVPWM) method with common mode voltage elimination and neutral point potential balancing is proposed for an open-end winding induction motor. The motor is fed from both of the ends with two neutral point clamped (NPC) three-level inverters. In order to eliminate the common mode voltage of the motor ends and balance the neutral point potential of the DC link, only zero common mode voltage vectors are used and a balancing control factor is gained from calculation in the strategy. In order to improve the harmonic characteristics of the output voltages and currents, the balancing control factor is regulated properly and the theoretical analysis is provided. Simulation and experimental results show that by adopting the proposed method, the common mode voltage can be completely eliminated, the neutral point potential can be accurately balanced and the harmonic performance for the output voltages and currents can be effectively improved.

• The Transactions of the Korean Institute of Power Electronics
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• v.23 no.5
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• pp.313-320
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• 2018

This study proposes a new voltage balancer with bidirectional DC-DC converter function. The proposed balancer can serve as a voltage balancer and a bidirectional DC-DC converter. Thus, the balancer can be applied to battery management systems or fast chargers in electric vehicles (EVs) charging stations while balancing bipolar DC bus voltages. The proposed system has unlimited voltage balancing range unlike the conventional voltage balancing control using a three-level DC-DC converter. A comparison of the voltage balancing range between the proposed and conventional scheme is explored to confirm this superiority. Simulation and experimental results are provided to validate the effectiveness of the proposed system.

• Journal of Power Electronics
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• v.17 no.6
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• pp.1625-1636
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• 2017

A power electronic transformer (PET) based on the cascaded H-bridge (CHB) and the isolated bidirectional DC/DC converter (IBDC) is capable of accommodating a large scale battery energy storage system (BESS) in the medium-voltage grid, and is referred to as a power electronic transformer based battery energy storage system (PET-BESS). This paper investigates the PET-BESS and proposes a coordinative control strategy for it. In the proposed method, the CHB controls the power flow and the battery state-of-charge (SOC) balancing, while the IBDC maintains the dc-link voltages with feedforward implementation of the power reference and the switch status of the CHB. State-feedback and linear quadratic Riccati (LQR) methods have been adopted in the CHB to control the grid current, active power and reactive power. A hybrid PWM modulating method is utilized to achieve SOC balancing, where battery SOC sorting is involved. The feedforward path of the power reference and the CHB switch status substantially reduces the dc-link voltage fluctuations under dynamic power variations. The effectiveness of the proposed control has been verified both by simulation and experimental results. The performance of the PET-BESS under bidirectional power flow has been improved, and the battery SOC values have been adjusted to converge.