Myung-Hyo Ryu

Design Methodology of Bidirectional CLLC Resonant Converter for High-Frequency Isolation of DC Distribution Systems

A bidirectional full-bridge CLLC resonant converter using a new symmetric LLC-type resonant network is proposed for a low-voltage direct current power distribution system. This converter can operate under high power conversion efficiency because the symmetric LLC resonant network has zero-voltage switching capability for primary power switches and soft commutation capability for output rectifiers. In addition, the proposed topology does not require any snubber circuits to reduce the voltage stress of the switching devices because the switch voltage of the primary and secondary power stage is confined by the input and output voltage, respectively. In addition, the power conversion efficiency of any directions is exactly same as each other. Using digital control schemes, a 5-kW prototype converter designed for a high-frequency galvanic isolation of 380-V dc buses was developed with a commercial digital signal processor. Intelligent digital control algorithms are also proposed to regulate output voltage and to control bidirectional power conversions. Using the prototype converter, experimental results were obtained to verify the performance of the proposed topology and control algorithms. The converter could softly change the power flow directions and its maximum power conversion efficiency was 97.8% during the bidirectional operation.

High-Efficiency Isolated Bidirectional AC–DC Converter for a DC Distribution System

A high-efficiency isolated bidirectional ac–dc converter is proposed for a 380-V dc power distribution system to control bidirectional power flows and to improve its power conversion efficiency. To reduce the switches’ losses of the proposed nonisolated full-bridge ac–dc rectifier using an unipolar switching method, switching devices employ insulated-gate bipolar transistors, MOSFETs, and silicon carbide diodes. Using the analysis of the rectifier’s operating modes, each switching device can be selected by considering switch stresses. A simple and intuitive frequency detection method for a single-phase synchronous reference frame-phase-locked loop (SRF-PLL) is also proposed using a filter compensator, a fast period detector, and a finite impulse response filter to improve the robustness and accuracy of PLL performance under fundamental frequency variations. In addition, design and control methodology of the bidirectional full-bridge CLLC resonant converter is suggested for the galvanic isolation of the dc distribution system. A dead-band control algorithm for the bidirectional dc–dc converter is developed to smoothly change power conversion directions only using output voltage information. Experimental results will verify the performance of the proposed methods using a 5-kW prototype converter.

Analysis of the Contactless Power Transfer System Using Modelling and Analysis of the Contactless Transformer

In this paper, the electrical characteristics of the contactless transformer is presented using the conventional coupled inductor theory. Compared with the conventional transformer, the contactless transformer has a large airgap, long primary wire and multi-secondary wire. As such, the contactless transformer has a large leakage inductance, small magnetizing inductance and poor coupling coefficient. Therefore, large magnetizing currents flow through the entire primary system due to small magnetizing inductance, resulting in low overall system efficiency. In high power applications, the contactless transformer is so bulky and heavy that it needs to be split by some light and small transformers. So, the contactless transformer needs several small transformer modules that are connected in series or parallel to transfer the primary power to the secondary one. This paper shows the analysis and measurement results of each contactless transformer module and comparison results between the series- and parallel-connection of the con tactless transformer. The results are verified on the simulation based on the theoretical analysis and the 30㎾ experimental prototype.

Effective Test Bed of 380-V DC Distribution System Using Isolated Power Converters

This paper proposes an effective test bed for a 380-V dc distribution system using isolated power converters. The proposed test-bed system is composed of a grid-interactive ac-dc converter for regulating the dc-bus voltage, a bidirectional converter for the battery power interface, a renewable energy simulator, dc home appliances modified from conventional ac components, a dc distribution panel board, and its monitoring system. This paper discusses three isolated power converters, i.e., a bidirectional ac-dc converter, a bidirectional dc-dc converter, and a unidirectional dc-dc converter for the effective power interface of a dc bus. These isolated power converters are designed using a dual-active-bridge converter and the resonant topologies of CLLC and LLC. The proposed test-bed system was implemented using a 5-kW bidirectional ac-dc prototype converter, a 3-kW bidirectional dc-dc prototype converter, and a 3-kW unidirectional dc-dc prototype converter. Finally, the performance of the test-bed system has been verified using practical experiments of load variations and bidirectional power flow, employing the prototype converters.

High voltage pulse power supply using Marx generator & solid-state switches

High voltage pulse power supply using Marx generator and solid-state switches is proposed in this study. The Marx generator is composed of 12 stages and each stage is made of IGBT stack, two diode stacks, and capacitor. To charge the capacitors of each stage in parallel, inductive charging method is used and this method results in high efficiency and high repetition rates. It can generate the pulse voltage with the following parameters: voltage: up to 120 kV, rising time: sub /spl mu/S, pulse width: up to 10 /spl mu/S, pulse repetition rate: 1000 pps. The proposed pulsed power generator uses IGBT stack with a simple driver and has modular design. So this system structure gives compactness and easiness to implement total system. Some experimental results are included to verify the system performances in this paper.

Optimized Design of Bi-Directional Dual Active Bridge Converter for Low-Voltage Battery Charger

This paper proposes an optimized design of dual active bridge (DAB) converter for low voltage charger. Among various bi-directional DC/DC converters, DAB converter is a high efficiency buck and boost bi-directional DC-DC converter isolated by a high frequency transformer. Battery voltage varies according to the charging status of the battery and the parameters of the DC/DC converter are the same regardless of the battery voltage. When the battery voltage is high, the soft switching (ZVS) region is reduced compared to the low battery voltage. In this paper, variable switching frequency is adopted in order to maximize soft-switching (ZVS) region at the high battery voltage. The same power can be obtained at the same duty regardless of the battery voltage using the variable switching frequency. The proposed method is applied to a 5kW prototype dual active bridge converter, and the experimental results are analyzed and verified.

Analysis of the contactless power transfer system using modelling and analysis of the contactless transformer

In this paper, the electrical characteristics of the contactless transformer is presented using conventional coupled inductor theory. Compared with the conventional transformer, a contactless transformer has large airgap, long primary wire and multi-secondary wire. So contactless transformer has large leakage inductance, small magnetizing inductance and poor coupling coefficient. Therefore, large magnetizing current flows through entire primary system due to small magnetizing inductance and the overall system efficiency will be low. In high power applications, contactless transformer is so bulky and heavy that it should be split by some light and small transformers. So contactless transformer needs several small transformer modules which are connected series or parallel to transfer the primary power to the secondary one. This paper shows analysis and measurement results of the each contactless transformer module and comparison results between series-connection and parallel-connection of the contactless transformer. The results are verified on the simulation based on the theoretical analysis and the 30 kW experimental prototype

Electrolytic capacitor-less, non-isolated PFC converter for high-voltage LEDs driving

This paper introduces electrolytic capacitor-less, non-isolated power factor corrected converters for high-voltage LEDs driving. To increase lifetime of the power supply, electrolytic capacitor is substituted to small polyester film capacitor and to insure input power factor(PF) higher than 0.9, conventional Boost and Buck-Boost PFC converters are chosen to drive high voltage LEDs driving due to its simplicity and low cost. The converters operate in boundary mode condition between CCM and DCM to achieve soft switching and high efficiency. 20W Boost and Buck-Boost PFC converters were designed and tested to drive 400V and 200V LEDs each with 0.2uF polyester film capacitor and through experiment 0.99 PF and over 92% efficiency were achieved at full load.

High voltage pulse generator using boost converter array

Using boost converter array consists of IGBTs, diodes and L-C circuits, novel repetitive impulse voltage generator was developed. In the presented circuits, high voltage pulse is generated by series-connection of capacitors and IGBTs. Therefore, the high voltage pulse is obtained by circuit configuration without any high voltage pulse transformer and high voltage DC source. Especially, the proposed circuit can operate up to several kHz and have high reliability and longer life than conventional ones. It also gives voltage balance of IGBTs automatically. So, the difference of characteristics of IGBTs and a drive signal does not cause severe problems. To verify the proposed circuit, a 2 kV and 40 A pulse generator is manufactured and tested.

Development of a photovoltaic simulator with novel simulation method of photovoltaic characteristics

This paper propose photovoltaic simulator with a novel simulation method of Photovoltaic (PV) characteristics. The equation of photovoltaic characteristic is very complex and non linear system. So it is too difficult to implement a PV simulator using this method. To overcome this problem, this paper describe simple novel method using only photovoltaic voltage, current curve from PV modules databook on standard test condition. The prototype PV simulator is introduced to experimentally verify the proposed method.