• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.29 no.9
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• pp.42-50
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• 2015

The Buck-Boost converter consisted of two switches is more expensive than the conventional Buck converter, because of the increase of the components. However, it can control the DC voltage depending on the requested load voltage without additional circuits, because it can control the voltage under the relatively wide range of the load. Additionally, it can control the output voltage constantly under the variation of the input voltage. In the paper two control loops consisted of current and voltage control are designed. When two controllers are operated at the same time the problem of the output voltage is occurred. Therefore, the solution of the output voltage problem is proposed. Finally, the validity of the proposed scheme is investigated with simulated and experimental results for a prototype system rated at 1kVA.

• Journal of Power Electronics
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• v.16 no.5
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• pp.1725-1734
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• 2016

This paper presents a novel seven-level (7L) voltage source converter for high-power medium-voltage applications. The proposed topology is an H-bridge connection of two nested neutral-point clamped (NNPC) converters and is referred to as an HNNPC converter. This converter exhibits advantageous features, such as operating over a wide range of output voltages, particularly for 10-15 kV applications, without the need to connect power semiconductors in series; high-quality output voltage; and fewer components relative to other classic seven-level topologies. A novel sinusoidal pulse width modulation technique is also developed for the proposed 7L-HNNPC converter to control flying capacitor voltages. One of the main features of the control strategy is the independent application of control to each arm of the converter to significantly reduce the complexity of the controller. The performance of the proposed converter is studied under different operating conditions via MATLAB/Simulink simulation, and its feasibility is evaluated experimentally on a scaled-down prototype converter.

• Journal of Power Electronics
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• v.17 no.6
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• pp.1391-1401
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• 2017

In this paper, a secondary resonance half-bridge dc-dc converter with an inductive output filter is presented. The primary side of such a converter utilizes asymmetric pulse width modulation (APWM) to achieve zero-voltage switching (ZVS) of the switches, and clamps the voltage of the switch to the input voltage. In addition, zero current switching (ZCS) of the output diode is achieved by a half-wave rectifier circuit with a filter inductor and a resonant branch in the secondary side of the proposed converter. Thus, the switching losses and diode reverse-recovery losses are eliminated, and the performance of the converter can be improved. Furthermore, an inductive output filter exists in the converter reduce the output current ripple. The operational principle, performance analysis and design equation of this converter are given in this paper. The analysis results show that the output diode voltage stress is independent of the duty cycle, and that the voltage gain is almost linear, similar to that of the isolation Buck-type converter. Finally, a 200V~380V input, 24V/2A output experimental prototype is built to verify the theoretical analysis.

• Journal of Electrical Engineering and Technology
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• v.11 no.6
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• pp.1634-1644
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• 2016

In this paper, a current-fed two-inductor bi-directional DC/DC converter using resonance (CF-TIBCR) and its design method are proposed. The CF-TIBCR has characteristics of low current ripple and a high current rating because of two separated inductors. Also, it achieves zero voltage switching for all switches and zero current switching for switches of a low voltage stage by using the resonant tank. Besides, a voltage spike problem in conventional current-fed converters is solved without the need for an additional snubber or clamping circuits. As a result, the CF-TIBCR features high step-up and high efficiency. Since the proposed converter has difficulty achieving the soft-switching condition when the converter requires the low voltage transfer ratio, a method that varies the number of resonant cycles is adopted to extend the output voltage range with satisfying the soft-switching condition. The principles of the operation characteristics are presented with a theoretical analysis, and the proposed converter is verified through results of an experiment using a laboratory prototype.

• 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 international Conference on Electrical Machines and Systems
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• v.2 no.2
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• pp.225-231
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• 2013

Low voltage ride through capability augmentation of a hybrid micro-grid system is presented in this paper which reflects enhanced reliability in the system. The control scheme involves parallel connected multiple ac-dc bidirectional converters. When the micro-grid system is subjected to a severe voltage dip by any transient fault single power converter may not be able to provide necessary reactive power to overcome the severe voltage dip. This paper discusses the control strategy of additional power converter connected in parallel with main converter to support extra reactive power to withstand the severe voltage dip. During transient fault, when the terminal voltage crosses 90% of its pre-fault value, additional converter comes into operation. With the help of additional power converter, the micro-grid system withstands the severe voltage fulfilling the grid code requirements. This multiple converter scheme provides the micro-grid system the capability of low voltage ride through which makes the system more reliable and stable.

• Journal of Power Electronics
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• v.8 no.1
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• pp.60-73
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• 2008

In this paper a three-phase ac-to-dc resonant converter with high input power factor and isolated output is proposed. To improve the input power factor of the converter, high frequency current is injected into the input of the three-phase diode bridge rectifier. It is injected through an impedance network consisting of a series of L-C branches from the output of the high frequency three-phase inverter. A narrow switching frequency variation is required to regulate the output voltage. A design example with different design curves is illustrated along with the component ratings. Experimental verification of the converter is performed on a prototype of 3 kW, 1000 V output, operating above 300 kHz. Experimental results confirm the concept of the proposed converter. Narrow switching frequency variation is required to regulate the output voltage.

• Journal of Power Electronics
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• v.18 no.4
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• pp.1223-1234
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• 2018

In this paper, a new three-port multidirectional DC-DC converter is proposed for integrating an energy storage system (ESS) to a bipolar DC microgrid (BPDCMG). The proposed converter provides a voltage-balancing function for the BPDCMG and adjusts the charge of the ESS. Thanks to the multi-functional operation of the proposed converter, the conversion stages of the system are reduced. In addition, the efficiency and weight of the system are improved. Therefore, this converter has a significant capability when it comes to use in portable BPDCMGs such as electric DC ships. The converter modes are analyzed and small-signal models of the converter in each of the independent modes are extracted. Finally, comprehensive simulation studies are carried out and a BPDCMG laboratory prototype is implemented in order to verify the performance of the proposed voltage balancer using the burst mode control scheme.

• Proceedings of the KIEE Conference
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• 2007.11c
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• pp.108-111
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• 2007

A novel voltage sag compensator with hi-directional DC/DC converter of Electric double layer capacitor is proposed. Recently, the double-layer capacitor which is drawn attention as a new energy storage element has a lot of advantage such as no maintenance, long lifetime and quick charge/discharge characteristics with large current. This DC/DC converter is used to control the charging current to the double-layer capacitor and also used to keep the DC link voltage constant for discharge of the double-layer capacitor. Therefore, the proposed DC/DC converter has the high-efficiency controller, dynamic compensator of voltage sag is driven by this converter. Finally, experimental results show the validity of the control scheme and the ability of the dynamic voltage compensator.

• Journal of Power Electronics
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• v.19 no.1
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• pp.201-210
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• 2019

This paper proposes a multimode hybrid control strategy that can achieve zero-voltage switching of primary switches and zero-current switching of secondary rectifier diodes in a wide input voltage range for full-bridge LLC resonant converters. When the input voltage is lower than the rated voltage, the converter operates in Mode 1 through the variable-frequency control strategy. When the input voltage is higher than the rated voltage, the converter operates in Mode 2 through the VF and phase-shift control strategy until the switching frequency reaches the upper limit. Then, the converter operates in Mode 3 through the constant-frequency and phase-shift control strategy. The secondary-side diode current will operate in the discontinuous current mode in Modes 1 and 3, whereas it will operate in the boundary current mode in Mode 2. The current RMS value and conduction loss can be reduced in Mode 2. A detailed theoretical analysis of the operation principle, the voltage gain characteristics, and the realization method is presented in this paper. Finally, a 500 W prototype with 100-200 V input voltage and 40 V output voltage is built to verify the feasibility of the multimode hybrid control strategy.