Unfolding Bridge Research Articles

A Bidirectional Isolated Dual-Phase-Shift Variable-Frequency Series Resonant Dual-Active-Bridge GaN AC–DC Converter

This article presents a novel single-stage series resonant dual-active-bridge (SR-DAB) for grid-con- nected bidirectional ac–dc energy storage applications. The single-phase SR-DAB is connected to the grid with an unfolding bridge on the ac side. Three SR-DABs are utilized to connect to a three-phase grid. A control scheme that combines dual-phase shifts and variable frequency is proposed to achieve zero voltage switching and power factor correction over a wide range of ac and dc voltages and loads. A series of comparisons in terms of inductor root mean square current, turn- <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</small> current of all transistors are conducted at different loads to prove the advantage of the proposed converter over the traditional dual-active-bridge-based ac/dc converter. A GaN-based hardware prototype connecting the 480Y/240/208 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\Delta$</tex-math></inline-formula> three-phase grid to a 48-V battery was developed with a peak efficiency of 97.2%.

Bidirectional Grid-Connected Single-Power-Conversion Converter With Low-Input Battery Voltage

This study proposes a bidirectional grid-connected single-power-conversion converter with low-input battery voltage. The proposed bidirectional converter consists of a bidirectional dc–dc converter and an unfolding bridge, and the power conversion stage only corresponds to a bidirectional dc–dc converter. The bidirectional dc-dc converter can perform bidirectional power conversion between the low input battery voltage and a rectified sine wave due to its step-up/down voltage regulation functions. The unfolding bridge unfolds the rectified sine wave into the grid voltage and provides a current path to the grid. The study also proposes a control algorithm to regulate the grid current through a single power-processing stage. The control algorithm is comprised of a feed-forward nominal voltage compensator and a repetitive control scheme. The feed-forward nominal voltage compensator presets the operating point to lighten the burden of the grid current control, and the repetitive controller provides precise control of the grid current. Thus, the proposed bidirectional grid-connected single-power-conversion converter results in high power quality and high efficiency. Experimental results based on a 250-W prototype module are conducted to evaluate the performance of the converter and to verify the analysis.

High-Efficiency Bidirectional Grid-Tied Converter Using Single Power Conversion With High-Quality Grid Current

This paper presents a high-efficiency bidirectional grid-tied converter using single power conversion with high-quality grid current and a control system for it. The proposed converter is composed of a bidirectional flyback dc–dc converter and an unfolding bridge circuit. By adjusting the PWM signal of the flyback, the proposed converter performs bidirectional power conversion between the grid and energy storage device in only one step. The control system consists of a feed-forward controller, a linear feedback controller with a low-pass filter, and a repetitive controller. The development of the proposed control system considers the inherent dynamic characteristics of the converter, thus overcoming the constraints on designing feedback control gains originating in right-half-plane zero and LC filter dynamics. Therefore, the control system ensures desired reference tracking and disturbance rejection performances while satisfying stability requirements. In conclusion, the proposed converter can achieve high conversion efficiency through a single power conversion, and its control system makes the implementation of the single power conversion in the proposed converter feasible. The theoretical analysis for the proposed converter and its control system is described. Finally, experimental results using a 250 W prototype are represented to confirm the validity of the proposed converter and its control system.

Flyback Converter를 이용한 태양광 병렬 DC-Module 시스템

In this paper, a photovoltaic parallel dc-module system using flyback converter is proposed. Proposed PV parallel DC-module system consists of paralleled current source flyback converters which are interconnected with each other and an unfolding bridge inverter. Instead of using individual inverters like the PV AC-module, the proposed system can save installation costs by connecting multiple current source converters to a single unfolding bridge inverter. Also, because each converter in proposed system is mounted on each individual PV module like as the PV AC-module type, it is strong regarding mismatch problem among photovoltaic modules. The validity of the proposed system is confirmed through simulation and experiment results.

태양광 병렬 DC-Module형 에너지 저장장치를 위한 양방향 컨버터 제어기법

In this paper, a control method of bidirectional converter for photovoltaic parallel DC-Module energy storage system(ESS) is proposed. The proposed bidirectional converter is connected in parallel with DC link which is located between current source flyback converters and unfolding bridge. Because output current of converters are rectified sinusoidal waveform, bidirectional converter requires suitable control method. Therefore, a theoretical analysis of the proposed control method is provided. Also, the validity of the proposed one is confirmed through experiment results.

A Single-Phase Bidirectional AC/DC Converter for V2G Applications

This paper presents a single-phase bidirectional current-source AC/DC converter for vehicle to grid (V2G) applications. The presented converter consists of a line frequency commutated unfolding bridge and an interleaved buck-boost stage. The low semiconductor losses of the line frequency commutated unfolding bridge contribute to the comparatively good efficiency of this converter. The buck and boost operating modes of the interleaved buck-boost stage provide operation over a wide battery voltage range. The interleaved structure of the interleaved buck-boost stage results in lower battery current ripple. In addition, sinusoidal input current, bidirectional power flow and reactive power compensation capability are also guaranteed. This paper presents the topology and operating principles of the presented converter. The feasibility of the converter is validated using MATLAB simulations, as well as experimental results.

Two‐switch flyback inverter employing a current sensorless MPPT and scalar control for low cost solar powered pumps

Flyback inverter is known as a low cost solution for photovoltaic (PV) ac module application. This study presents a two-switch flyback inverter followed by a low frequency unfolding bridge for fractional horse power water pumping systems. This topology mitigates the problem of high-voltage transients at switch turn off which commonly exists in single switch flyback inverters. Moreover, the proposed control strategy achieves an integration of a novel sensorless maximum power point tracking (MPPT) algorithm as well as a constant v / f control for the efficient utilisation of both the PV panel and the motor. The proposed control algorithm minimises the cost and simplifies the control strategy. The validity and capability of the proposed method are verified by both simulation and practical results of a DSP-based two-switch flyback solar micro inverter for a fractional horsepower water pumping system.

Bidirectional Single Power-Conversion DC–AC Converter With Noncomplementary Active-Clamp Circuits

This paper presents a bidirectional single power-conversion dc–ac converter with noncomplementary active-clamp circuits. The proposed converter comprises a bidirectional flyback converter and an unfolding bridge. In order to interface the grid with a low-voltage energy storage through only single power-conversion, the bidirectional flyback converter transforms the low voltage directly into the folded grid voltage and regulates the folded grid current. The proposed converter adopts noncomplementary operation strategy for the active-clamp circuits. By using this strategy, the bidirectional flyback converter not only avoids the voltage spike but also minimizes the power losses by the circulating energy. Thus, with single power-conversion and noncomplementary active-clamp circuits, the proposed converter obtains high power efficiency. To facilitate the bidirectional single power-conversion, a novel control algorithm is developed. With this control algorithm, the proposed converter ensures high grid power quality and seamless mode transition. The proposed bidirectional dc–ac converter is theoretically analyzed in detail. The experimental results based on a 250-W prototype are provided to evaluate its performance.

Designing a Single-Stage Inverter for Photovoltaic System Application

This paper focuses on a full-bridge high-frequency isolated inverter which is proposed for distributed photovoltaic power supply application. The researched system consists of a full-bridge high-frequency DC/DC converter with the proposed symmetric phase-shift modulation algorithm to achieve the ZVS switching function and a line frequency unfolding bridge. It replaces the traditional two stages of independent control algorithms with a one-stage control to obtain high conversion efficiency. A TMS 320F2812 digital signal processor-based control technique is used to achieve the desired algorithm function for the grid-connected photovoltaic power system application. The researched system can have two operating methods depending on the applied situation. Finally, a prototype of 300 W with the maximum power point function is settled to verify the proposed idea.