Isolated AC-DC Converter Research Articles

Single-Stage Isolated AC–DC Converter Based on LCL Resonant DAB Converters With Single-Loop Control

Single-Stage Isolated AC–DC Converter Based on <i>LCL</i> Resonant DAB Converters With Single-Loop Control

A single-stage variable output AC-DC converter with PFC and soft-switching for renewable energy integration

This study introduces a versatile variable-output isolated AC-DC converter design distinguished by its incorporation of soft-switching and a novel control algorithm. The converter configuration comprises two full-bridge diode rectifiers, positioned at both input and output sides, complemented by a full-bridge isolated resonant DC–DC converter. By providing soft-switching across all semiconductor components, the proposed design could achieve a significant power density increase while still preserving the power conversion efficiency in an acceptable range. The novel control algorithm concurrently governs power factor and output voltage, employing the duty cycle as the primary control variable and the phase shift as an auxiliary parameter. Using this synergistic method fulfills more efficiency, increases power density, and improves power factor performance. The effectiveness and reliability of the converter were carefully confirmed by experiments done on a prototype, which provided the capacity to provide over 400 watts in its maximum state of operation. Notably, the converter's adaptability makes it an ideal candidate for a wide variety of applications, with a specific emphasis on integrating renewable energy sources into power systems.

Harmonic State-Space Modeling and Closed-Loop Control of Single-Stage High-Frequency Isolated DC–AC Converter

The port harmonic features of the single-phase single-stage high-frequency isolated dc-ac converter is not analyzed so far and the corresponding theoretical basis for improving the current quality is still a research gap. In this paper, a linear model in frequency domain of the single-stage high-frequency isolated dc-ac converter is originally derived based on the combined harmonic state space and extended description function modeling technique. The systematic modeling process is analyzed and the accuracy of the modeling is verified by the simulation results. Combined with the model analysis, the harmonic coupling characteristics between the ac side and the dc side are clearly presented. On this basis, this paper proposes a closed-loop control strategy to reduce the decrease of the dc-side and ac-side current quality caused by the harmonic coupling at the control level. Furthermore, this paper constructs the compound controllers based on the P-type iterative learning to suppress the harmonic currents of the dc side and the ac side, respectively. The composite controller does not distinguish the harmonic frequency. Hence, the proposed controller achieves the effective suppression of the harmonic currents in real time. The effectiveness and feasibility of the proposed control strategy are verified by the experiments.

An asymmetrical isolated AC-DC converter stationed BLDC motor drive to mitigate power quality issues

An asymmetrical isolated AC-DC converter stationed BLDC motor drive to mitigate power quality issues

An asymmetrical isolated AC-DC converter stationed BLDC motor drive to mitigate power quality issues

An asymmetrical isolated AC-DC converter stationed BLDC motor drive to mitigate power quality issues

Research on Two-stage Isolated AC–DC Converter with PSO Optimized PI Control

Research on Two-stage Isolated AC–DC Converter with PSO Optimized PI Control

Three-Phase Single-Stage Three-Port High-Frequency Isolated DC–AC Converter

Three-Phase Single-Stage Three-Port High-Frequency Isolated DC–AC Converter

A Modulation Strategy With Transformer Leakage Inductance Energy Management for a Three-Phase Matrix-Based Isolated AC–DC Converter

Three-phase matrix-based ac-dc power conversion has recently gained popularity, considering its higher conversion efficiency and power density compared to the conventional two stage solutions. In the literature, several modulation strategies have demonstrated improved total harmonic distortion (THD) of the ac current in the matrix converters through independent control of the anti-series combination of active devices that form a matrix switch (i.e., two gate drivers per matrix switch). In this paper, a matrix-based ac-dc power converter that utilizes only one gate driver per matrix switch is proposed without compromising the quality of ac current. Managing energy stored in high-frequency transformer’s leakage inductor is an issue while utilizing single driver per matrix switch. An additional short-circuit leg is proposed to circulate stored energy in the leakage inductance during zero vector periods of the proposed converter, thereby ensuring continuous path for the leakage inductor’s energy flow. Steady-state analysis of the proposed ac-dc converter along with its loss modelling are presented with necessary mathematical expressions. The presented analysis and design of the proposed converter are experimentally validated on a 2 kW hardware prototype in the laboratory environment. A pertinent comparison of the proposed matrix-based conversion methodology with the conventional matrix-based conversion strategy is also provided.

Capacitor-Voltage-Balancing Control for Isolated Medium-Voltage AC-DC Modular Matrix Converter

This paper presents a capacitor-voltage-balancing control scheme for an isolated medium-voltage AC-DC converter using level-shifted PWM control of a modular matrix converter (MMxC). The proposed isolated AC-DC converter is composed of the primary MMxC with level-shifted PWM control, high-frequency transformer, and secondary H-bridge circuits. The high-frequency transformer of the proposed circuit can be downsized because the level-shifted PWM control scheme makes the rated frequency of the high-frequency transformer equal to the switching-frequency. The proposed capacitor-voltage-balancing control can compensate for the capacitor voltage imbalance of the MMxC using the positive-sequence and negative-sequence circulating-currents with a power supply frequency and high-frequency voltage. In the proposed control system, the three feedback control systems with DC control variables can be developed to compensate for the capacitor voltage imbalance. The effectiveness of the proposed capacitor-voltage-balancing control scheme and the control systems is verified by experiments using a 200V, 5-kW laboratory prototype.

A Boost-Inductorless Electrolytic-Capacitorless Single-Stage Bidirectional Isolated AC–DC Converter

With the development of wide-bandgap devices, bidirectional isolated ac–dc converter becomes an attractive solution to realize highly compact, highly efficient power conversion for electric vehicle (EV) chargers and energy storage applications. However, in the existing literature, regardless of two-stage or single-stage isolated ac–dc converters, the circulating current in boost inductors is inversely proportional to the inductance value, resulting in large volume and high loss of the converter. In this article, a boost-inductorless electrolytic-capacitorless single-stage bidirectional ac–dc converter with high-frequency isolation is proposed. With the introduction of a center-tapped transformer, the proposed converter can achieve nearly zero circulating current without any boost inductor, thus overcoming the drawbacks mentioned above. Equivalent circuit analysis is applied to illustrate the operation principle and advantages of the proposed topology. A detailed comparison between the proposed topology and the state-of-the-art is also provided. The experimental results obtained from a 3.6 kW, 140 kHz single-phase EV charger prototype are given as the proof-of-the-concept. It is demonstrated that the proposed converter prototype realizes a peak efficiency of 96.4% with only 38 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">μ</i> H total inductance and 6.33 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">μ</i> F total capacitance.

Overview of Single-Stage High-Frequency Isolated AC–DC Converters and Modulation Strategies

The single-stage high-frequency (HF) isolated ac–dc converter has the advantages of high-power density, long life, and high efficiency. It has a broad application prospect in distributed power generation, ac microgrid, and energy storage system. In this article, its topologies are classified according to the energy storage components. The structure and operating principle of various topologies are introduced. Furthermore, the development of extended multiport single-stage HF isolated ac–dc converter is introduced. On this basis, the advantages and disadvantages, typical characteristics, cost, and power loss of various topologies are analyzed and summarized. Finally, the key issues that need to be solved are pointed out and the development trends are explored. This article aims to provide a reference for the subsequent research on single-stage HF isolated ac–dc converters and the advancement of their practicability.

Soft-Switched Integrated AC–DC Bidirectional Converter With Natural Grid Harmonic Elimination

Two-stage ac–dc converters have hard-switched ac–dc stage followed by soft-switched dc–dc stage. Since devices in the ac–dc stage are switched at low frequency (typically 10–20 kHz), bandwidth of current control loop of this stage is limited (typically less than 2 kHz). This low bandwidth current loop fails to reject current harmonic disturbances arising due to distorted grid voltages, thus necessitating multiple harmonic compensation loops or complex control algorithms for meeting IEEE Std 519-2014. Lack of soft-switching prohibits devices of the ac–dc stage from being switched at a frequency above 100 kHz and thereby attain a bandwidth of around 10 kHz for natural rejection of grid current harmonics. This article proposes an integrated three-phase bidirectional isolated ac–dc converter, where soft-switching operation is extended to devices in ac–dc stage as well. Thus, high bandwidth current loop can be achieved without reduction in efficiency. The proposed modulation scheme decouples ac–dc and dc–dc operations using <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">xor</small> logic. An iterative procedure for design of resonant tank is provided. The integration also leads to 25% fewer devices. Experiments carried out on a 5-kW prototype demonstrate that a low current total harmonic distortion, complying with IEEE standard, can be achieved with good efficiency, even under distorted grid voltages.

A Modulation Scheme With Full Range ZVS and Natural Power Factor Correction for Bridgeless Single-Stage Isolated AC–DC Converter

The ac side structure of a bridgeless single-stage isolated ac–dc converter reduces the number of components by sharing power switches between the bridgeless rectifier and the dual-active-bridge (DAB) dc–dc converter. However, it also makes it more difficult to achieve zero-voltage switching (ZVS) for the ac side switches. Therefore, a modulation scheme is proposed to achieve ZVS for all switches over the full ranges of the grid voltage and load. A quasi-fixed switching frequency control method is also applied, in which the switching frequency is constant during a half-cycle of the grid voltage. By adjusting the switching frequency, the grid side inductor can operate in critical conduction mode without a zero-current-detection circuit, which facilitates the ZVS realization of the ac side switches. In addition, a natural power factor correction can be realized without the grid-side current sensors. Finally, a 500 W prototype was built to validate the theoretical analysis and the effectiveness of the proposed modulation scheme.

Modeling and Compound Closed-Loop Control of Single-Phase Quasi-Single-Stage Isolated AC-DC Converter

The single-phase isolated quasi-single-stage AC-DC converter has many virtues, such as high power density and efficiency; however, its grid current closed-loop control has not been solved. This paper aims to solve the remaining gap based on a large-signal model. In this paper, the large-signal model of this converter under triple-phase-shift modulation is built for the first time. It is verified that the built model is a zero-order linear system. Based on this built model, the effect of grid harmonics on this converter grid current is analyzed. The theoretical analysis reveals that the grid voltage low-order harmonics will cause the same order grid current harmonics and only varying the parameters of the filter is not an effective method to solve this problem. For the purpose of eliminating the effect of grid voltage harmonics on the grid current and realizing the zero-error control of the fundamental component of the grid current, a grid current closed-loop control strategy based on the proportional-resonant compound odd-mode repetitive controller is proposed. The operation principle, parameter constraint, and design rule of the proposed compound control strategy are analyzed comprehensively. The theoretical analysis and the compound control strategy put forward in this paper are tested, with detailed experimental results.

A High-Efficiency Isolated PFC AC–DC Topology With Reduced Number of Semiconductor Devices

A new three-level isolated ac–dc power factor correction (PFC) topology with a minimum number of semiconductor devices is the focus of this article. This topology provides a high input power factor (PF), soft-switching, and higher efficiency than existing isolated ac–dc converters. Furthermore, the proposed circuit has lower voltage rating requirements for the secondary side devices, which leads to a lower total cost and minimizes total converter losses. This article presents a theoretical analysis describing the complete characterization of this new topology, and experimental results on a 1-kW prototype showing high PF and efficiency throughout the operating range.

A High-Power-Density High-Efficiency Soft-Switched Single-Phase Universal Input to 28-V Isolated AC–DC Converter Module Designed for Paralleled Operation

This article presents a high-power-density high-efficiency soft-switched single-phase universal input to 28-V isolated ac–dc converter module designed for parallel operation. The proposed two-stage converter utilizes a totem-pole bridgeless boost power factor correction (PFC) ac–dc converter stage followed by an isolated <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> resonant dc–dc converter stage. A comprehensive design and optimization methodology is presented that compares various designs and operating modes for the converter's power stages and selects the optimal design based on overall power density and efficiency. Additionally, a control scheme is presented for the PFC stage to minimize current distortion by accounting for various sensor, control, and gate-drive delays while ensuring zero-voltage switching (ZVS) of the transistors. Moreover, a new droop control strategy is presented, which utilizes the input current of the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> dc–dc stage to ensure equal output current distribution between paralleled modules powering a common output load. To validate the proposed design and control strategy, two 1-kW universal input to 28-V isolated ac–dc converter modules are built and tested. Each prototype converter module achieves a high power density of 84 W/in <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> and a peak efficiency of greater than 93% while ensuring a current distribution error of less than 0.3% when operating in parallel to deliver the maximum output power of 2kW.

Novel Single-Stage Bidirectional Isolated DC–AC Converter Based on Inversely Coupled Inductor

This article proposes a novel single-stage bidirectional isolated dc–ac converter based on an inversely coupled inductor, which is feasible to be used in cascaded dc–ac solid-state transformer topologies. The topology description is presented, followed by a simple modulation scheme, then direct single-stage power transmission can be realized. The operating principles of the converter are given in detail. The steady-state and transient performance of the converter can be improved owing to the employment of an inversely coupled inductor. By combining magnetic integration technology with an inversely coupled inductor, the volume and number of magnetic components can be reduced. The detailed analysis of the duty cycle loss is carried out in this article as well. Finally, an experimental prototype is established to further verify the correctness of the proposed topology. The maximum efficiency achieved in the experimental 1-kW prototype is 94.37%.

Single-Stage Hybrid Three-Level DAB Type Resonant AC–DC Converter

In order to extend the application of single-stage dual active bridge type isolated ac–dc converter and improve its current characteristics, in this article, a novel topology with a three-level half-bridge matrix converter and a resonant tank is proposed. The operation principle and steady-state characteristics are analyzed in detail based on the PWM plus phase shift modulation. Furthermore, the relationship of the equivalent three-phase shifts to realize a minimum rms value of resonant current is introduced to enhance the operation efficiency. The proposed converter reduces the voltage stress of the power switches of the ac side matrix converter to half the ac voltage, and it is helpful to reduce the power loss and cost. Especially, it is valuable to realize the excellent high-frequency power conversion in medium-voltage applications. Furthermore, the current stress of the power switches is decreased by using the resonant tank as the temporary energy storage loop. The detailed experimental results verify the correctness and feasibility of the proposed topology and theoretical analysis.

A Control Strategy to Smooth Power Ripple of a Single-Stage Bidirectional and Isolated AC-DC Converter for Electric Vehicles Chargers

This paper proposes a single-stage AC-DC rectifier with power factor correction (PFC), high-frequency isolation and bidirectional power conversion capability for on-board battery charger (OBC) applications. The proposed converter is based on the interleaving technique and the Dual Active Bridge (DAB) operation, applying the phase-shift control to regulate the power flow. In addition to topology, this article presents a control strategy for reducing low-frequency power ripples transferred to the secondary side without any additional component and hence maintaining overall size and cost. The single-phase OBC can interchange active power with the grid to charge batteries while performing grid-to-vehicle (G2V) functionality or transferring energy back to the grid via vehicle-to-grid (V2G) mode. The theoretical analysis of the converter including modulation strategy and feedback control scheme are presented. The proposed topology and control strategy have been verified by experimental results of a 650 W SiC-based prototype.

A Single-Stage Isolated AC–DC Converter to Interlink Utility Grid and Renewable Energy Sources in a Residential DC Distribution System

This article proposes a single-stage isolated PWM rectifier topology to interlink utility grid and renewable energy sources in a 380-V dc distribution system for residential applications. The proposed topology provides both the power factor correction and output dc voltage regulation within a single power conversion stage. Furthermore, it includes an integrated flyback-based active lossless clamp (ALC) circuit to mitigate the device overvoltage issues generally noticed in the isolated single-stage PWM rectifiers. Thus, low-voltage-rating devices can be selected. The regenerative feature of the flyback ALC circuit along with soft-switching of the main converter structure helps in realizing higher efficiency. A dual-duty hybrid control algorithm is also reported to improve the converter performance. An SiC mosfet-based 1.5-kW hardware prototype is developed. The converter performance is evaluated from the experimental results obtained during both the steady state and dynamic operation. Comprehensive performance analysis and comparison study have also been presented in this article.