LLC Resonant Converter Research Articles

A single‐stage bridgeless LLC resonant converter with constant frequency control based LED driver

In this article, a single-stage bridgeless LLC resonant converter with a constant frequency control method is proposed for a high-brightness light-emitting diode (LED) driver. LED strings require drivers with high power density and high efficiency. This article presents a novel LED driver circuit topology based on switch integration and the switching controlled capacitor (SCC) technique. By combining the merits of a totem-pole bridgeless boost PFC unit and a high frequency SCC-LLC half-bridge resonant converter, the proposed topology can achieve high efficiency. Due to the SCC-LLC circuit topology structure, constant frequency control of the LLC resonant converter is achieved by the regulation of the equivalent resonant capacitance. The proposed novel LED driver topology can automatically achieve soft-switching characteristics and a high power factor. The operating principle of different operation modes and the characteristics of the proposed LED driver are analysed in detail. Finally, to demonstrate the feature of the proposed topology, a 100 W/70 V laboratory prototype is built. The satisfactory experimental results correspond with the theoretical analysis and parameter design.

BurstFMControl ofLLCResonant Converter with Multiplier for High Efficiency and Low Ripple inTWTPower Supply

The burst frequency modulation (FM) control mode is applied to an LLC resonant converter with multiplier in this study for enhanced efficiency and low voltage ripple at light load. This control mode provides an effective solution to high‐voltage power supply with wide‐range loads such as the traveling wave tube (TWT) power supply. Shortages in the LLC resonant converter with multiplier at light load are analyzed and a burst FM control strategy is proposed accordingly. The principle of the LLC resonant converter with multiplier under this control mode is then analyzed in detail. A ripple control strategy and zero voltage switching (ZVS) method are proposed, where the controller is implemented by digital signal processing (DSP). The prototype of a TWT power supply based on the burst FM control mode is completed accordingly. In the burst FM control mode applied in this study, ZVS is realized from light load to full load, and the efficiency at light load is improved by 7% comparing with conventional FM mode. The voltage ripple at light load is reduced by 5 V comparing with conventional burst mode. The experimental result indicates that the proposed method is feasible and effective. © 2021 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.

High Efficiency Isolated On-Board EV Battery Charger Using LLC Resonant Converter

In this study, high efficiency design of an on-board Electrical Vehicle (EV) battery charger is presented. The presented charger has two stages where the first stage is conventional front-end boost converter and the second stage is LLC resonant converter. The basic principles of both stage are discussed and the detailed design procedures are presented in terms of wide range output voltage regulation, wide range load condition, high efficiency and high power density. The presented design approach is tested with a prototype implemented with 2.5 kW output power at 250 V-450 V output voltage range. The peak efficiency of system is obtained as 95.53% at full load condition.

An Optimized DPS Control Strategy for LCL Resonant Dual Active Bridge Converter for Wide Voltage Conversion Ratio

This article presents an improved DPS (IDPS) control strategy for LCL resonant dual active bridge converter. Due to the LCL resonant tank, the converter's working modes are analyzed by using the Fourier transform. According to the fundamental harmonics of the key waveforms, the condition of zero-voltage switching (ZVS) in different working modes is derived. The relationship between the conduction loss and load power is analyzed. To achieve ZVS with low conduction loss and seamless transitions between the forward and reverse power flow, an IDPS modulation scheme is proposed. The control strategy can cover all the load power. The conduction loss in the IDPS is compared with the enhanced DPS, which illustrates the lower conduction loss. Finally, a 1-kW experimental prototype has been built to verify the effectiveness of the IDPS control strategy.

LLC Converter Based PV Water Pumping System with Enhanced User Safety Approach

In this paper, LLC resonant converter based Photovoltaic (PV) water pumping is proposed. Commercially, the available PV based water pumping system consists of a non-isolated DC-DC converter, which is suitable for low power applications but results in a less safe operating environment for human. In the case of PV based water pumping systems, the safety of humans should be the main concern, as these systems are normally being operated by farmers, their families and it may possible that they are not that much aware of operational hazards. Therefore, this paper attempts to present an LLC converter based PV water pumping system, considering human safety as a major concern. The proposed system is simulated in MATLABenvironment and results shows that proposed system configuration has no adverse impact on system efficiency and it enhances safety for operating personals. Presented results can be further exploited for hardware verification as the future scope of this work.

On the Practical Evaluation of the Switching Loss in the Secondary Side Rectifiers of LLC Converters

The switching loss of the secondary side rectifiers in LLC resonant converters can have a noticeable impact on the overall efficiency of the complete power supply and constrain the upper limit of the optimum switching frequencies of the converter. Two are the main contributions to the switching loss in the secondary side rectifiers: on the one hand, the reverse recovery loss (Qrr), most noticeably while operating above the series resonant frequency; and on the other hand, the output capacitance (Coss) hysteresis loss, not previously reported elsewhere, but present in all the operating modes of the converter (under and above the series resonant frequency). In this paper, a new technique is proposed for the measurement of the switching losses in the rectifiers of the LLC and other isolated converters. Moreover, two new circuits are introduced for the isolation and measurement of the Coss hysteresis loss, which can be applied to both high-voltage and low-voltage semiconductor devices. Finally, the analysis is experimentally demonstrated, characterizing the switching loss of the rectifiers in a 3 kW LLC converter (410 V input to 50 V output). Furthermore, the Coss hysteresis loss of several high-voltage and low-voltage devices is experimentally verified in the newly proposed measurement circuits.

Hybrid Dual-Loop Control for Current Regulation and Low-Frequency Ripple Rejection in Led Drivers

This paper presents a new hybrid dual-loop control system for the DC/DC LLC resonant converter, operating as a downstream DC/DC converter in a two independent stage offline LED driver. The outer loop employs a PI controller to maintain the average LED current regulated at the reference value and reject parametric variation. The inner loop implements an adaptive periodic disturbance rejection (APDR) subsystem, thus conceiving the hybrid PI\&APDR controller. The APDR subsystem is designed to strictly reject the bus voltage ripple and limit its transmission to the LED current. Experimental results show the proposed controller feasibility in achieving good tracking behavior, reduced output current ripple under different bus voltage ripple amplitude and frequency, robustness against parametric variations, and simple implementation and design. For the sake of completeness, the proposed PI&APDR is compared with the conventional proportional resonant controller employing experimental results and extra analysis based on simulations.

A Novel Design Approach for LLC Resonant Converters in Off-line LED Driving Applications

A Novel Design Approach for LLC Resonant Converters in Off-line LED Driving Applications

An Electrical Isolated DC Power Supply with Two Ports Based on LLC Resonant Converter

A modified LLC resonant converter is proposed for isolated dc power supply where two ports are needed. The converter can supply different dc voltages for two isolated loads, and the resonant parameters of two LLC channels can be designed as different. The topology of the proposed LLC resonant converter is introduced, the voltage gain is detailed discussed. A simulation model is built to verify the correctness of the proposed LLC resonant converter`s theory. The simulation results verify that the converter can supply two different dc voltages, and the voltages can keep steady even the load states are changed suddenly.

An Effective Integration of APM and OBC With Simultaneous Operation and Entire ZVS Range for Electric Vehicle

This article proposes an effective integration of APM and OBC providing simultaneous operation without an extra circuit and entire ZVS range of all switches. The integrated circuit of the proposed charger is configured by combining high voltage-side switch legs of the LLC resonant converter of OBC and the PSFB converter of APM. In the simultaneous mode, by operating the common leg as a lagging leg of the phase-shift full bridge (PSFB) converter, the conduction losses of the common leg switches are decreased due to current cancellation effect, and the lagging leg switches of the PSFB converter achieve entire ZVS operation. Further, in the APM standalone mode, entire ZVS operation of the lagging leg switches is also secured by utilizing the magnetizing current of the LLC resonant converter. As a result, the proposed integrated charger achieves comprehensive improvement in terms of efficiency as well as volume and cost. A laboratory prototype combining a 3.7-kW LLC resonant converter with a 1-kW PSFB converter is built and tested in order to verify the performance and theoretical claims.

An Open-Loop Start-up Method for LLC Resonant Converter with Fixed Frequency and Variable Duty Cycle

An open-loop start-up method with fixed frequency and variable duty cycle for LLC resonant converter is proposed in this paper. The start-up method adopts pulse width modulation (PWM) technology to control LLC resonant converter with fixed switching frequency and variable duty cycle. Compared with conventional start-up method that uses a relative high switching frequency to start-up the converter with closed control loop, the proposed start-up method can reduce the start-up frequency, then the switching loss and driving loss during the start-up process can be reduced. Moreover, the proposed method can fast start-up the converter with low device`s electrical stress. Because high start-up frequency is no need for the proposed start-up method, then the hardware cost of driving chip can be decreased. The theory and the logic of the proposed start-up method is detailed analysed in this paper. The correctness and effectiveness of the proposed start-up method are verified by the built simulation results.

Interleaved Single-Stage LLC Converter Design Utilizing Half- and Full-Bridge Configurations for Wide Voltage Transfer Ratio Applications

Automotive on-board dc-dc converters are required to operate over a wide input and output voltage range depending on the state of charge of the input and the output battery. Conventionally, the unidirectional power transfer between these batteries is enabled by a two-stage converter concept. A first-stage nonisolated dc-dc converter regulates the input voltage of the galvanically isolated second-stage dc-dc converter such that the second-stage converter operates in its optimum operating point. This article presents a single-stage interleaved LLC resonant converter of 3.6 kW for this purpose. While LLC converters are usually not suitable to cover such a wide voltage range (the input voltage between 240 and 420 V and the output voltage between 8 and 16 V), this LLC converter is operated in a full-bridge mode for large gains and in a half-bridge mode for low gains. For intermediate gains and loads, the LLC employs the phase-shift mode. To operate the interleaved LLCs at equal switching frequencies enabling output current ripple cancellation to reduce the output capacitor, again, the phase-shift mode is utilized to balance the power transfer during the full-bridge mode while the asymmetrical duty-cycle mode is proposed for power balancing during the half-bridge mode. This article analyzes the converter design for these modes of operation and provides a comprehensive design procedure allowing the designer to simultaneously analyze all stress values for various resonant tank designs. A 3.6-kW prototype employing Si superjunction MOSFETs achieves a power density of 2.1 kW/L. The maximum efficiency reaches 96.5%, while for most operating points, it is kept well above 90%. The experimental measurement results validate the analysis and show that phase-shift operation and asymmetrical duty-cycle modulation can be utilized for power balancing for full-bridge and half-bridge configurations, respectively, such that a much smaller output capacitor can be employed.

Design of a LLC Resonant Converter for Powering a PEM Electrolyzer

This paper proposes the design of a LLC resonant converter to supply a proton exchange membrane (PEM) electrolyzer. The PEM requires a low voltage with high current, a reduced output voltage ripple, and an overdamped dynamic behavior of the converter to avoid voltage overshoots. The designed converter allows satisfying the design constraints, minimizing switching and reverse recovery losses; the efficiency is influenced mainly by the output rectifier's conduction losses.

Closed loop analysis of Dual Bridge Converter with 4- levels

Abstract: A dual bridge (DB) LLC resonant converter for dc-dc conversion with closed loop is proposed in the system. The model is capable of delivering very low voltage, with a variable input dc fluctuations in the source side. The new PWM technique used helps the bridge output robust. The proposed model works only in 4 modes of operation. DB LLC converter uses different phase shift for each individual switches with different duty ratios. The model is simulated with 160V/200V DC input and 24V output with 20A i.e. 480W is provided to verify the operation. Keywords: Dual Bridge, LLC resonant converter, Closed loop operation, Boost converter.

Design of LLC Resonant Type Full-Bridge DC-DC Converter

In order to develop and utilize renewable energy reasonably, the problems such as the increasingly intensive power load, insufficient power supply capacity and short power supply radius in major cities should be overcome. In this paper, a LLC resonant DC-DC converter is proposed for low voltage distribution network. Firstly, the energy transmission model and mathematical model of DC-DC converter under different modes are analysed. Secondly, the parameters of the resonator are designed. Finally, the simulation platform is built, and the simulation and experiment of DC-DC converter under different working conditions are carried out to verify the correctness of the proposed scheme.

Analysis of Steady-State Characteristics of LLC Resonant Converters

Analysis of Steady-State Characteristics of LLC Resonant Converters

Constant DC‐bus critical conduction mode Zeta converter fed primary‐side regulated LLC resonant converter in LED lighting applications

AbstractThis paper deals with a two‐stage high‐power light‐emitting diode (LED) driving solution for an isolated LED load. The first‐stage DC–DC power conversion is using a nonisolated Zeta converter operating in critical conduction mode to reduce component stress and switching power loss. This power stage is accountable for the power factor correction (PFC) under the universal AC voltage operation and developed a constant DC‐bus voltage for the second stage. In the second stage, half‐bridge LLC resonant converter is dedicated to deliver ripple‐free DC voltage to an isolated LED load. A new primary‐side regulation (PSR) technique is implemented in series with the resonant tank to reduce the component counts in the feedback loop. The stability of the DC‐bus voltage is verified by the state‐space analysis for the critical conduction mode (CrCM) Zeta converter. A 150 W load is driven by a prototype with a nearly unity power factor (PF) and low harmonics distortion in the input current.

A Novel Analysis Method and Corresponding Voltage Regulation Strategy for LLC Resonant Converter

At present, intermittent control is a main method to solve the problem of pumping output voltage with light load of LLC resonant converter, which can not only solve the problem of high pumping output voltage, but also, to a certain extent, improve the efficiency of light load to a certain extent when converter is operating. However, in extremely light‐loading, especially in no‐ loading, with the intermittent cycle increasing and the low‐frequency ripple being introduced, which cannot meet the demand of high‐quality output voltage, and is not conducive to the converter's stable operation. Due to the extremely small power transferred by the converter, in this case, efficiency is not the main factor considered. In this paper, a voltage regulation strategy based on energy feedback is proposed for LLC resonant converter in extremely light‐loading. The output voltage is controlled by adjusting the feedback energy to the source. Compared with the uncontrollable burst off mode of the intermittent control, the proposed control method can effectively improve the output voltage quality due to the controllability in voltage drop mode and the independence from the load. It also can eliminate low frequency ripple and extend battery charging life. The output voltage ripple is minimized by optimizing the duty cycle and the phase shift angle. The correctness and feasibility of the proposed method are verified by experiments. © 2021 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.

Fully FPGA‐based implementation of a modified control strategy for power electronic transformer in railway traction applications

AbstractDue to its several advantages (especially low volume and weight), power electronic transformer has gained notable attraction in railway applications. The main focus of this work is devoted to development a fully filed programmable gate array (FPGA)‐based control platform for power electronic transformer in the aforementioned application. Due to the parallel processing of FPGAs that results in a faster control algorithm execution, reliable operation (which is of major importance in traction applications) is guaranteed. For this purpose, an input series output parallel power electronic transformer structure is built, and various considerations for reliable and stable operation of the power electronic transformer in traction applications, such as safe start‐up and bidirectional power flow, along with the required control and pulse generation schemes, have been designed and implemented in a Xilinx FPGA control platform. Moreover, a modified control algorithm is proposed for controlling the power electronic transformer in a simple and more reliable manner. This control scheme is developed based on the output voltage of the DC–DC–LLC resonant converter, and can effectively control the sum of rectifier DC‐link voltages and track the input sine reference current, with a lower number of required sensors. Finally, the effectiveness of the proposal has been tested from various aspects by experimental tests.

LLC Converter Based PV Water Pumping System With Enhanced User Safety Approach

In this paper, LLC resonant converter based Photovoltaic (PV) water pumping is proposed. Commercially, the available PV based water pumping system consists of a non-isolated DC-DC converter, which is suitable for low power applications but results in a less safe operating environment for human. In the case of PV based water pumping systems, the safety of humans should be the main concern, as these systems are normally being operated by farmers, their families and it may possible that they are not that much aware of operational hazards. Therefore, this paper attempts to present an LLC converter based PV water pumping system, considering human safety as a major concern. The proposed system is simulated in MATLABenvironment and results shows that proposed system configuration has no adverse impact on system efficiency and it enhances safety for operating personals. Presented results can be further exploited for hardware verification as the future scope of this work.