• Journal of Power Electronics
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• v.17 no.6
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• pp.1433-1444
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• 2017

A family of non-isolated DC-DC three-port converters (TPCs) that allows for a more flexible power flow among a renewable energy source, an energy storage device and a current-reversible DC bus is introduced. Most of the reported non-isolated topologies in this area consider only a power consuming load. However, for applications such as hybrid-electric vehicle braking systems and DC microgrids, the load power generating capability should also be considered. The proposed three-port family consists of one unidirectional port and two bi-directional ports. Hence, they are well-suited for photovoltaic (PV)-battery-DC bus systems from the power flow viewpoint. Three-port converters are derived by combining different commonly known power converters in an integrated manner while considering the voltage polarity, voltage levels among the ports and the overall voltage conversion ratio. The derived converter topologies are able to allow for seven different modes of operation among the sources and load. A three-port converter which integrates a boost converter with a buck converter is used as a design example. Extensions of these topologies by combining the soft-switching technique with the proposed design example are also presented. Experiment results are given to verify the proposed three-port converter family and its analysis.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.58 no.2
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• pp.301-307
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• 2009

In the paralleled converter module with peak current mode control, current imbalance appears when the voltage controllers with integral control of converter module are not exactly identical. In this paper, the voltage controller is designed to equal the current command of each converter module using the current command bus. The current balance controller is also proposed to balance the average currents of converter modules with imbalaced inductance. It is designed to have good transient response. Proposed method is implemented with the paralleled 2-module and 4-module boost converters with imbalanced inductance. Experimental results verify the performance of current share during both steady and transient states of converter.

• The Transactions of the Korean Institute of Power Electronics
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• v.26 no.4
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• pp.285-293
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• 2021

An optimal operation method based on weighted efficiency for a two-stage boost converter is proposed in this study. Detailed loss analysis of the converter is performed to derive the optimal operation method according to the load and input voltage fluctuations, and the optimal DC-bus voltage is derived by applying the weighted efficiency method. The proposed method can satisfy optimal efficiency in the main operation region without a complicated control method. Using 1kW typical two-stage boost converter and is verified three types of weighted efficiency formulas and loss analysis are utilized to derive high-efficiency optimal DC-bus voltage from each load range.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.25 no.3
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• pp.40-49
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• 2011

This paper presents novel circuit topology of half-bridge soft-switching PWM inverter type DC-DC high power converter for DC bus feeding power plants. The proposed DC-DC power converter is composed of a typical voltage source-fed, half-bridge high frequency PWM inverter with a high frequency planar transformer link PWM control scheme and parallel capacitive lossless snubbers. The operating principle of the new DC-DC converter treated here is described by using switching mode-equivalent circuits, together with its unique features. All the active power switches in the half-bridge arms and input DC bus lines can achieve ZCS turn-on and ZVS turn-off commutation transitions. The total turn-off switching losses of the power switches can be significantly reduced. As a result, high switching frequency IGBTs can actually be selected in the frequency range of 40[kHz] under the principle of soft-switching. The performance evaluations of the experimental setup are illustrated practically.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.64 no.1
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• pp.29-34
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• 2015

DC bus electrolytic capacitors are used in variety of equipments as smoothing element of the power converters because it has high capacitance for its size and low price. It is responsible for frequent breakdowns of many static converters and inverter drive systems. Therefore it is important to diagnosis monitoring the condition of an electrolytic capacitor in real-time to predict the failure of power converter. In this paper, the on-line remote diagnosis monitoring system for DC BUS electrolytic capacitors of power converter using low-cost type Zigbee communication modules is developed. To estimate the health status of the capacitor, the equivalent series resistor(ESR) of the component has to be determined. The capacitor ESR is estimated by using RMS computation using AC coupling method of DC link ripple voltage/current. The Zigbee communication-based experimental results show that the proposed remote DC capacitor diagnosis monitoring system can be applied to DC/DC converter and UPS successfully.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.58 no.4
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• pp.404-409
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• 2009

A DC power system has many loads with various functions. In particular, these sizable loads take the form of power electronic converters. When they are tightly regulated, the loads appear as constant power loads and result in negative incremental input impedance. Under certain conditions the effect of such loads on the power system is causes instability. In this paper, converter with a large storage capacitor and a lag compensator is proposed as a DC bus conditioner to mitigate the voltage transients on the bus. In addition, the proposed control approach has the advantage of performing both the functions of mitigating the voltage bus transients and maintaining the level of energy stored. Simulation and experimental results showed that the proposed control method was operated well in a small-scale DC power system that contained subsystems with constant power characteristics, such as DC/DC converters and electrical drives.

• 한국신재생에너지학회:학술대회논문집
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• 2007.11a
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• pp.293-296
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• 2007

본 논문에서는 UPS 기능을 갖는 단상 태양광 발전 시스템을 제안하였다. 제안하는 시스템은 태양광 어레이 (photovoltaic array)에서 최대전력을 얻기 위해 MPPT (maximum power point tracking)를 수행하는 컨버터, 계통전원 상태나 태양광 발전량에 상관없이 부하에 정현파 전압을 공급하는 인버터, 태양광 어레이에서 발전된 잉여전력을 계통으로 전달하거나 부하에 필요한 전력을 dc bus로 공급하는 인버터, 정전시 dc bus에 전력을 공급하는 양방향 컨버터 (bidirectional converter)로 구성된다. 제안하는 시스템은 발전된 전력을 계통으로 전달할 뿐만 아니라, UPS (uninterruptible power supply)기능도 수행하는 시스템으로 계통전압이 불안정하거나 정전시에도 부하에 안정적이고 깨끗한 전압을 항상 공급할 수 있다. 각각의 인버터, 컨버터, 및 양방향 컨버터는 dc bus를 공유하며, dc bus의 전압에 따라 동작상태가 결정이 된다. dc bus중심의 제어는 dc bus전압을 안정적으로 유지시키며, 부하에 걸리는 전압의 변동을 최소로 하고 시스템의 디자인 및 제어를 단순화한다. 모든 알고리즘과 제어기를 하나의 마이크로 컨트롤러로 구현하였고 제안된 시스템의 우수성을 실험을 통해 검증하였다.

• The Transactions of the Korean Institute of Power Electronics
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• v.26 no.4
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• pp.263-270
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• 2021

Active AC/DC converters with PWM operation are utilized to regulate rectified DC bus voltage of a permanent magnet synchronous generator in the maritime DC power system. A DC bus voltage regulation strategy that exploits the six-step operation is proposed in this study. Compared with that of the PWM operation, switching loss of the converter can be significantly reduced under the six-step operation. Moreover, conduction loss can also be reduced due to the high modulation index and reduced flux-weakening current of the six-step operation. A controller is used for the proposed DC bus voltage regulation strategy to verify its validity with the simulation and experimental setup. The simulation and the experimental test results showed that the converter loss reduces to a maximum of 70% and 19%, respectively.

• Journal of Power Electronics
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• v.12 no.4
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• pp.567-577
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• 2012

This paper introduces a new scheme to balance the DC bus voltages of a cascaded H-bridge converter which is used as a Distribution Static Synchronous Series Compensator (D-SSSC) in electrical distribution network. The aim of D-SSSC is to control the power flow between two feeders from different substations. As a result of different cell losses and capacitors tolerance the cells DC bus voltage can deviate from their reference values. In the proposed scheme, by individually modifying the reference PWM signal for each cell, an effective balancing procedure is derived. The new balancing procedure needs only the line current sign and is independent of the main control strategy, which controls the total DC bus voltages of cascaded H-bridge. The effect of modulation index variation on the capacitor voltage is analytically derived for the proposed strategy. The proposed method takes advantages of phase shift carrier based modulation and can be applied for a cascaded H-bridge with any number of cells. Also the system is immune to loss of one cell and the presented procedure can keep balancing between the remaining cells. Simulation studies and experimental results validate the effectiveness of the proposed method in the balancing of DC bus voltages.

• Proceedings of the KIPE Conference
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• 2001.10a
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• pp.523-528
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• 2001

This paper deals with two non-conventional HVDC system, that are, the Capacitor Commutated Converter (CCC) in which series capacitors are included between the converter transformer and the valves, and the Controller Series Capacitor Converter (CSCC), based on more conventional topology, in which series capacitors are inserted between the AC filter bus and the AC network. The simulation waveforms show that if these compare to conventional HVDC, these HVDC systems have many advantages in steady-state and transient performance.