Showing papers by "Jee-Hoon Jung published in 2020"

Enhanced Dual-Active-Bridge DC–DC Converter for Balancing Bipolar Voltage Level of DC Distribution System

Abstract: Conventional dual-active-bridge (DAB) dc–dc converters have a limited structure to balance the bipolar voltage level of the bipolar dc distribution system. Therefore, to regulate the bipolar voltage level, additional voltage balancers are needed for the DAB converters, which eventually requires more devices resulting in low power conversion efficiency and low power density. This article proposes an enhanced DAB dc–dc converter that can balance the bipolar voltage level without the additional voltage balancers. The bipolar voltage level can be tightly regulated under entire unbalanced load condition and even when there is no-load at one side of the dc poles. Besides, its zero-voltage-switching capability can be extended to cover the entire load range, including the no-load condition. Furthermore, the proposed converter can be operated by using a simple single phase-shift modulation. Therefore, its control algorithm can be easily implemented in digital controllers. Finally, the theoretical analysis and the effectiveness of the proposed DAB converter are validated by a 3-kW prototype converter.

Single-Stage Voltage Balancer With High-Frequency Isolation for Bipolar LVDC Distribution System

Abstract: Conventional voltage balancers for the bipolar low-voltage dc (LVdc) distribution system have been composed of multiple power stages, which degrade their power density and cost effectiveness. To minimize the power stages, this paper presents a single-stage voltage balancer with high-frequency isolation. This voltage balancer is based on the three-level dual-active-bridge converter. Furthermore, for the proposed voltage balancer, an enhanced switching modulation, using the two switching patterns $\alpha$ and $\beta$ , is proposed to fully balance the bipolar voltage level under unbalanced load condition and even for when one of the dc poles has no load. Besides, a closed-loop control system can be implemented by using output voltage information and proportional-integral controllers. Finally, experimental results using a 3-kW laboratory prototype converter verify the effectiveness of the proposed voltage balancer.

Isolated three-port DC–DC converter employing ESS to obtain voltage balancing capability for bipolar LVDC distribution system

Abstract: A bipolar low-voltage DC (LVDC) distribution system used in residential and building applications requires AC–DC converters and voltage balancers that balance the two DC bus polarities. The bipolar DC bus voltage level only relies on the voltage balancer tied with the AC grid. An isolated DC–DC converter for an energy storage system (ESS) with the voltage balancing capability is proposed to prevent the bipolar voltage level collapse caused by the failure of the grid-tied voltage balancer. The proposed converter topology is an enhanced three-port dual-active-bridge (DAB) converter which can balance the bipolar DC voltage level without complex control. Furthermore, it has less current stress in power switches than that of the conventional three-port DAB converter. The effectiveness of the proposed converter is verified with a 3-kW prototype converter.

High-gain sub-terahertz lens horn antenna with a metal guide

Abstract: In this Letter, a high-gain sub-terahertz lens horn antenna with a metal guide is proposed. In this antenna, high gain is achieved by using a metal guide and dielectric lens. The experimental results show that the impedance bandwidth of the proposed antenna is above 200 GHz, and the measured peak gain of the antenna is 39 dBi at 240 GHz.

FPGA Controller Design for High-Frequency LLC Resonant Converters

Abstract: Conventional digital controllers have limited switching-frequency resolution and computational speed. This results in a large output voltage ripple and poor dynamic performance with a low control bandwidth in high switching frequency resonant converters using an inductor-inductor-capacitor (LLC)-type resonant tank. This paper proposed a controller design based on a field programmable gate array (FPGA) for an LLC resonant converter to improve the switching-frequency resolution and dynamic performance. The improved performance is analyzed using theoretical methods compared with that of a general-purpose digital signal processor (DSP). The performance improvement is verified through circuit simulations and signal-level tests using a hardware-in-the-loop (HIL) test system.

A Comprehensive Overview in Control Algorithms for High Switching-Frequency LLC Resonant Converter

Abstract: An LLC resonant converter has been widely used in various industrial applications because of its high cost-effectiveness, high power conversion efficiency, simple design methodology, and simple control algorithms using a pulse frequency modulation (PFM). In addition, the soft switching capability of the LLC resonant converter is good to obtain high switching frequency operations, which can get the high-power density of the power converter. Over the past years, several studies have been conducted to improve the performance of a high switching frequency LLC resonant converter with resonant tank design, optimal power stage design, and enhanced control algorithms. This paper is the review paper in terms of the control algorithms for the LLC resonant converter. It focuses on the overview of the high switching-frequency LLC resonant converter in terms of the control algorithms. The advanced control algorithm can improve power conversion efficiency, dynamic performance, tight output voltage regulation, and small electro-magnetic interference. The operational principles of the control algorithms are briefly explained to show their own characteristics and advantages. Thereafter, the research issues for the future works will be discussed in the conclusion.

Hybrid modulation strategy of three-phase dual-active-bridge converter to improve power conversion efficiency under light load conditions in LVDC applications

Abstract: A hybrid control strategy for the three-phase dual-active-bridge (3P-DAB) converter of LVDC applications is presented to improve the power conversion efficiency under light load conditions. The 3P-DAB converter is an attractive topology for high-power applications such as railway traction and aircraft due to its inherent the zero voltage switching (ZVS) capability and reduction of conduction loss due to an interleaved structure with seamless bi-directional power transitions. However, conventional phase shift modulation (PSM) applied to a 3P-DAB converter has disadvantages such as ZVS failure under light load conditions. In this paper, an asymmetrical pulse width modulation is inserted into PSM to replace the existing modulation algorithm of a 3P-DAB converter with a simple control approach. In the proposed control, the transferred power can be calculated according to the mode changes. In addition, the soft switching area of the power switches can be expanded by the proposed hybrid control strategy. Finally, experimental results validate the proposed hybrid modulation strategy using a 3-kW prototype 3P-DAB converter.

Spread Spectrum Based Power Line Communication and EM Noise Reduction Technique for Bidirectional HB CLLC Resonant Converter

Abstract: In the previous research, the resonant converter have not integrated the EM noise reduction and the PLC capability in a single power converter. In this paper, the extension of the converter functionality is proposed with the combination of a power line communication (PLC) and the electro-magnetic (EM) noise reduction in the bidirectional halfbridge CLLC resonant converter. The designed converter shows the output voltage regulation, the PLC capability, and the EM noise reduction, simultaneously. This technical fusion using the spread spectrum technique (SST) makes design constraints to implement each functions. Therefore, the design methodology of proposed converter is necessary to implement the triple functions. The performance of the proposed triple functional converter is experimentally verified by using a 20-W prototype converter.

Input voltage selection method of half-bridge series resonant inverters for all-metal induction heating applications using high turn-numbered coils

Abstract: All-metal induction heating (IH) systems have been introduced to heat both ferromagnetic and non-ferromagnetic pots using dual resonant frequencies. They are designed for heating ferromagnetic pots using a first harmonic operation mode (FHOM) and for heating the non-ferromagnetic pots using a third harmonic operation mode (THOM). All-metal IH systems employing dual resonant frequencies consist of an IH inverter and a power factor correction (PFC) circuit to transfer desired power to pots by increasing the input voltage of the IH inverter. In this paper, the input voltage is designed to obtain an efficiency-optimized operating point. To obtain an appropriate input voltage, power loss analyses are conducted using first harmonic approximation (FHA). Based on analysis results, the input voltage of the IH inverter can be selected to improve its power conversion efficiency. A 2-kW half-bridge series resonant inverter prototype is implemented to verify the effectiveness of the proposed design by heating ferromagnetic pots using the FHOM with a 2-kW transfer power and by heating non-ferromagnetic pots using the THOM with a 1-kW transfer power.

Real-time test-bed system development using power hardware-in-the-loop (PHIL) simulation technique for reliability test of DC nano grid

Abstract: Since various power sources such as renewable energy and energy storage systems (ESSs) are connected to the DC grid, the reliability of the grid system is significant. However, the configuration of an actual DC grids for testing the reliability of the grid system is inconvenient, expensive and dangerous. In this paper, a test-bed system made up of a 20-kW DC nano grid and a control algorithm considering an external grid based on power hardware-in-the-loop (PHIL) simulation are proposed to demonstrate the reliability of the DC grid. Using the PHIL simulation technique, target grids can be safely implemented with laboratory-level instruments and simulated by real-time simulators, which emulates grid operations that are similar to the actual grid. In addition, using the proposed control algorithm, the operations of grid-connected converters are demonstrated according to the grid-connected or islanding modes. Finally, the reliability of the simulated DC nano grid and the effectiveness of the grid-connected converter are verified using the PHIL simulation system with 3-kW prototype converters.

Wireless Power Transfer System with Reduced EMI Emission Employing Spread Spectrum Technique

Abstract: Wireless power transfer (WPT) system based on a magnetic resonance between WPT coils has high parasitic capacitance due to the magnetic shielding materials of the coils. It induces high conductive electromagnetic interference (EMI) which travels along with the capacitive coupling. To reduce the EMI emission from the wireless charger, a WPT system with a spread spectrum technique (SST) is proposed in this paper for the EV charging application. The proposed wireless charger can reduce the peak and quasi-peak values of the EMI by spreading them into wide bandwidth. Moreover, it adopts the bridgeless rectifier at the secondary side, which can control the output voltage even though its operating frequency changes due to the SST. The performance of the proposed wireless charger including the output voltage regulation and EMI reduction capabilities are evaluated using simulation results based on PSIM software.

Analysis and Design of Three-Phase Buck Rectifier Employing UPS to Supply High Reliable DC Power

Abstract: In the DC distribution system, to step down the DC voltage level from the AC grid voltage, the conventional topologies require multiple power conversion stages and bulky line-frequency transformers, which degrade their power density and cost-effectiveness. In addition, the conventional topologies suffer from a shoot-through problem resulting in their low system reliability. In this paper, to overcome the above issues, systematic design approaches of a three-phase buck rectifier with an uninterruptible power supply (UPS) and a protection algorithm are proposed to obtain the high reliability of the DC distribution system, which can deal with fault conditions and can regulate the output voltage level. It only requires a single stage of the three-phase buck rectifier. Also, a thyristor switch is added without any commutation circuits to cut off the output from the fault circuit. The shoot-through faults do not occur in the buck rectifier, leading to high reliability. A dual-active-bridge (DAB) DC-DC converter is applied as the UPS to supply the electric power from the battery when the buck rectifier is shut down under the fault conditions. Finally, the protection algorithm is proposed to detect the fault conditions and to regulate the output voltage level.

Practical Controller Design of Three-Phase Dual Active Bridge Converter for Low Voltage DC Distribution System

Abstract: In a low voltage DC (LVDC) distribution system, isolated bi-directional DC-DC converters are key devices to control power flows. A three-phase dual-active-bridge (3P-DAB) converter is one of the suitable candidates due to inherent soft-switching capability, low conduction loss, and high-power density. However, the 3P-DAB converter requires a well-designed controller due to the influence of the equivalent series resistance (ESR) of an output filter capacitor, degrading the performance of the 3P-DAB converter in terms of high-frequency noise. Unfortunately, there is little research that considers the practical design methodology of the 3P-DAB converter’s controller because of its complexity. In this paper, the influence of the ESR on the 3P-DAB converter is presented. Additionally, the generalized average small-signal model (SSM) of the 3P-DAB converter including the ESR of the capacitive output filter is presented. Based on this model, an extended small-signal model and appropriate controller design guide, and performance comparison are presented based on the frequency domain analysis. Finally, experimental results verify the validity of the proposed controller using a 25 kW prototype 3P-DAB converter.

Enhanced Switching Pattern to Improve Cell Balancing Performance in Active Cell Balancing Circuit Using Multi-Winding Transformer

Abstract: Cell balancing performance is an important factor in determining the operational efficiency of the active cell balancing circuit. Thus, this study approached this need by developing an enhanced switching pattern. The circuit is designed to transfer energy between arbitrary source and target cells. It has been operated in flyback and buck-boost modes according to the position of the source and target cells. In this circuit, the coupling coefficient of the transformer considerably affects the balancing performance of the flyback operation. The energy transferred to the non-target cell is increased by the low-coupling coefficient due to the leakage inductance. Therefore, the high energy transfer ratio cannot be achieved using conventional switching patterns. In this paper, a new flyback switching pattern is proposed, which can minimize the effect of the coupling coefficient in the cell balancing operation. The proposed switching pattern uses the cells which do not participate in the balancing process to control the voltage applied to each winding, which results in a high energy transfer ratio irrespective of the coupling coefficient. In addition, an enhanced operating method has been proposed to improve the cell balancing speed by reducing the energy transfer path in specific cell conditions. The performance of the proposed switching pattern was verified in a 15 W cell balancing circuit.

Practical Design Methodology of IH and IPT Dual-Functional Apparatus

Abstract: A domestic induction heating (IH) apparatus uses series resonance to transfer the electric energy to the IH vessel. Similarly, an inductive power transfer (IPT) utilizes the resonance to transfer power to the secondary side. Therefore, the IPT function can be integrated into the IH apparatus by sharing the IH power stage as the primary side of the IPT. In this article, a practical design methodology of the IH and IPT (IH-IPT) dual-functional apparatus is proposed. The design considerations of the IPT mode are discussed, such as the power stage design limitation and practical implementation to increase the compatibility to the IH apparatus. Moreover, the design methodology of the IPT mode is provided based on the design considerations. The validity of the proposed design methodology is evaluated through experimental results with an IH-IPT prototype.

Effective in‑laboratory test method for PV power generation with enhanced PV emulation accuracy

Abstract: Photovoltaic (PV) systems require outdoor experiments to verify their functionality and reliability. However, outdoor experiments require complicated experimental set-ups including PV panels, power conversion circuits and controllers. In addition, the experimental data obtained from such systems can be easily affected by environmental conditions such as weather, temperature and season. Recently, PV emulation methods have been proposed that can emulate PV characteristics in the laboratory by connecting a DC supply to PV modules in parallel. However, the voltage characteristics of the conventional PV emulator are different from those of real PV panels, which degrades the accuracy of the PV emulator. This paper proposes an effective PV emulation method with accuracy improvements at the maximum power point of the PV panel, which is based on a simple circuit analysis. Using the proposed PV emulation method, the performance verification of a target PV system can be easily and accurately obtained. The proposed emulation method for PV power generation is experimentally verified by comparisons between it, the conventional emulation method and results obtained from outdoor experiments.

Power Hardware-in-the-Loop Simulation for DC Microgrid Reliability Test

Abstract: As the efficient usage of energy in the grid becomes more important than before, diverse power sources, such as distributed renewable energies, are linked to DC microgrid. Therefore, the reliability test of the entire microgrid is essential. However, configuring the real DC grid to test its reliability takes a lot of time and cost. In this paper, a 20-kW DC microgrid is modeled by using the Power Hardware-in-the-Loop (PHIL) simulation technique, which verifies the feasibility of the DBS algorithm. Through the PHIL simulation test technique, the proposed testbed can simulate the overall operation of the DC microgrid. Furthermore, depending on the DC bus voltage, the operations of the grid-connected converter can be verified, and the DC bus voltage control ability through seamless mode transition can be validated under the grid failure. Finally, the proposed testbed shows the reliability of the DC microgrid using the PHIL simulation tests with a 3-kW prototype converter.