LLC Resonant Converter Research Articles

An Input-Series-Output-Parallel Cascaded Converter System Applied to DC Microgrids

Direct current transformer (DCT) is a key piece of equipment in direct current (DC) microgrids, and the mainstream topologies mainly include LLC resonant converter (LLC) and dual active bridge (DAB). In this paper, a novel bi-directional buck/boost + CLLLC cascade topology is proposed for the input-series-output-parallel cascade converter system of a DC microgrid. To solve the problem that frequency variation causes the converter to deviate from the optimal operating point, resulting in low efficiency, and the inability to achieve a soft switching function. The CLLLC converter operates near the resonant frequency point as a DCT, only providing electrical isolation and voltage matching, while the buck/boost converter controls the output voltage and the voltage and current sharing of each module. Compared to other cascaded converter systems, the cascaded converter proposed in this paper has high efficiency, simplifies the parameter design, and is suitable for wide input and wide output operating conditions. The system adopts a three-loop control strategy, establishes the small-signal modeling of the system, and its stability is verified by theoretical analysis and simulation. The simulation and experimental results verify the correctness of the proposed cascaded converter based on buck/boost + CLLLC and the effectiveness of the control strategy.

Research on the development and intelligent application of power environmental protection platform based on big data

Abstract In order to improve the practical effect of the power environmental protection platform, this paper combines the big data technology to develop and design the power environmental protection platform. In this paper, a power factor correction (PFC) and resonant half-bridge joint controller is used to combine the traditional two-level topology into one-level topology. Moreover, this paper adopts a fixed frequency half-bridge LLC resonant converter with a simple control circuit to obtain a stable resonant half-bridge controller with a fixed output voltage. The choice of this overall power topology architecture can not only meet the design requirements, save costs and simplify the control of the circuit, but also improve the efficiency of the whole machine and the performance of the power environmental protection platform. The experimental research shows that the power environmental protection platform based on big data proposed in this paper can effectively improve the effectiveness of power environmental protection strategies.

An adaptive synchronous rectifier driving strategy for unregulated LLC resonant converter

AbstractLLC resonant converters are widely adopted in many different industrial applications due to their high efficiency operation. To further improve LLC resonant converters' efficiency, the secondary unregulated diode rectifier is replaced by the synchronous rectifier (SR). In many applications, LLC converter is designed to operate at resonant frequency to maximize the system efficiency and act as a DC transformer (DCX). The SR driving signal is set as the same as the primary driving signal to work in an open‐loop mode. However, the resonant frequency will deviate due to the tolerance, working environment, and ageing effect of circuit components, which will lead to the degradation of the system efficiency and output voltage variation. Unfortunately, most of the existing techniques cannot be simply adopted in SR LLC DCX. Therefore, an adaptive SR driving strategy that can compensate the circuit components' variations is necessary for SR LLC DCX. Inan adaptive SR strategy based on the constant voltage gain characteristic at resonant frequency point is proposed. The proposed strategy is applicable for all different scenarios with easy implementation and low cost.

An Electrolytic-Capacitor-Less PFC LED Driver With Low DC-Bus Voltage Stress for High Power Streetlighting Applications

This paper presents a single-stage, soft-switching, high power factor, flicker-free LED driver without any electrolytic capacitors for streetlighting application. The proposed LED driver consists of a buck-boost type power factor correction (PFC) circuit integrated with an asymmetric half-bridge LLC resonant converter. The buck-boost type PFC circuit provides a high power factor, low input current harmonics, and low dc bus average voltage. Unlike other methods that use the first harmonic approximation (FHA) analysis or the differential equations in time domain to analysis the LLC circuit, in this paper, a Fourier series-based analysis is proposed. The proposed method provides better accuracy in comparison with the FHA while being simpler than the time domain analyze method. The half-bridge LLC resonant converter is designed such that ZVS is obtained for the entire input voltage range (185 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$-$</tex-math></inline-formula> 265 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$V_{rms}$</tex-math></inline-formula> ), and for 20% to 100% of the full-load power. In addition, a magnetic integration technique is utilized to increase efficiency and reduce converter size. The designed control system enables lowering the output current ripples without using any electrolytic capacitors. To verify the feasibility of the proposed LED driver, a 200 W prototype is implemented. The proposed LED driver achieves maximum efficiency of 94.6%, high PF, and a maximum of 15% output current ripples.

Accurate Analysis Method and Voltage Gain Curve Derivation Algorithm Based on Time-Domain Analysis for High-Efficiency LLC Resonant Converter Design

An accurate analysis method for an LLC resonant converter and a time-domain analysis (TDA)-based voltage gain curve derivation algorithm are proposed in this paper. When applied to an LLC resonant converter, the TDA method can obtain high-accuracy current and voltage waveforms by solving nonlinear equations for circuit parameters through operation-mode analysis. An LLC resonant converter operating mode classification algorithm was proposed based on the results of this analysis. The circuit voltage and current values in the steady state were quickly and precisely derived using this algorithm. An accurate power-loss analysis is required to design a high-efficiency converter. Therefore, TDA is a powerful tool for designing an LLC resonant network. The proposed TDA-based LLC resonant converter analysis and voltage gain curve derivation algorithm provides high-accuracy voltage, current value estimation and voltage gain curves for all switching-frequency ranges. The effectiveness of the proposed algorithm is verified using a 500 W LLC resonant converter prototype experiment.

Analysis &amp; Simulation of Different LLC Converter Topologies

There is an expanding trend in electric vehicle (EV) technologies because of finite fuel sourcesand environmental concerns. One of the essential barriers in EVs commercialization is the charging ofbatteries. The inductor-inductor-capacitor (LLC) resonant converter appears the most appealing design dueto its advantages, such as small electromagnetic interference, obtaining high-power density, ability to bedesigned at very high switching frequencies, operation for wide input and output voltage range with narrowswitching frequency variation, and high efficiency. This study compares different topologies of LLCresonant converter that can be adapted as battery charger of electric vehicle. The schematics of topologies,detailed design calculation of the parameters, simulation results of topologies to show the circuitperformance are presented, respectively. The simulation model is realized for whole examined topologieswith a proportional integral controller to obtain constant output voltage using MATLAB. LLC resonantcircuit is designed for the input voltage range of 305-345V, output voltage range of 36-58V, and outputpower of 700W. Analytical and simulation results are included in this study to illustrate the performancedifferences among the presented topologies of LLC resonant converter in terms of structure, efficiency, anddynamic response at sudden load changes.

Bidirectional half‐bridge LLC resonant converter with automatic current sharing characteristic

SummaryA bidirectional half‐bridge (BHB) LLC resonant converter with automatic current sharing characteristics is proposed in this paper for high‐power bidirectional energy storage applications. With the help of magnetizing inductance of transformer, all MOSFETs on the primary and secondary sides can realize zero‐voltage switching. By grouping the secondary windings of the transformer, excellent current sharing can be achieved in both forward and backward operation modes even if there is a 10% error of the resonant parameters. Due to the half bridge structure in both primary and secondary sides, the number of switches is reduced. And the resonant capacitance is small, which is conducive to integrate into the isolation transformer. Thus, the power density and overall efficiency of the proposed converter can be improved. Whether the converter is in forward or backward operation mode, the PWM control strategy is consistent, and it is not required to control the power flow by regulating the phase shift angle of primary and secondary sides, which makes the control strategy of the proposed converter easier. Finally, an 850 W experimental prototype is established to verify the superiority of the proposed circuit. Under the full load condition, the measured peak efficiency is 98.11% and 97.11% in the forward and backward operating modes, respectively.

PI_BPNN controller for transient response improvement of LLC resonant converter

PI_BPNN controller for transient response improvement of LLC resonant converter

Voltage-Mode Variable-Frequency Controlled LLC Resonant Power Factor Correction Converter and Its Accurate Numerical Calculation Analysis

LLC resonant converter is a good candidate for single-stage ac–dc converter, which can realize both functions of power factor correction (PFC) and output voltage regulation, and contribute to the improvement of conversion efficiency and power density. However, voltage mode (VM) controlled single-stage half-bridge LLC PFC converter has the disadvantages of large dead-zone of input current and hard-switching operation, since there is no current control. Besides, the voltage ripple of input filter brings asymmetrical operation of the converter between the positive and the negative half-switching cycle. In order to solve these problems, this article presents a modified numerical calculation method, which can realize accurate characterization of the asymmetrical behavior of resonant current and voltage. Based on that, the switching frequency of LLC resonant converter for unity power factor (PF) is derived. A method of fitting the switching frequency is proposed to simplify the circuit implementation. A 250-W/48-V prototype has been built to verify the analysis results. Experimental results show that the proposed voltage-mode variable-frequency (VM-VF) controlled LLC resonant PFC converter can achieve high efficiency of up to 94.08% and power factor of 0.95 over the input voltage range of 180–260 VAC.

Optimal Design of a Matrix Planar Transformer in an LLC Resonant Converter for Data Center Applications

The 48-V bus converter has been gradually adopted in intermediate bus architecture. The ever-growing development of data centers consumes significant power, thereby pushing power converters to be more efficient. This article focuses on the optimization of the transformer for an LLC resonant converter used in data centers, which is the second stage operating as a dc transformer to realize the isolation and a fixed voltage step-down ratio. The front stage is a multiphase buck converter. The magnetic core geometry reported in this article for the LLC enables a single turn for both primary and secondary windings. Compared with the previous research, the improved interleaving winding scheme benefits from reduced conduction path, lower ac resistance, and smaller core volume. Ansys 3D simulation performs the design and optimization of the magnetic core. The proposed magnetic core, winding layout, and design optimization are verified in the 30-/5-V 660-W LLC resonant converter. It has higher current stress but achieves a higher efficiency of 97.7%, better thermal performance, and lower components count than the state of the art.

Current Sharing Control of Multi-Input Modular DC-DC Converter Using Unregulated LLC Resonant Converter

By applying an unregulated LLC resonant converter to a multi-input modular DC-DC converter (MIMC), the LLC converter can be operated at an optimal frequency while achieving power source flexibility. However, the output characteristics of an LLC converter are easily affected by the resonance parameter, and when connected in parallel, the output current is unbalanced. In this paper, we propose a current sharing control method to solve the current imbalance problem, and automatically balance the output current of each module. The effectiveness of the proposed current sharing control method is verified by simulations and experiments.

A Burst Mode and Variable Frequency Voltage Sharing Control Mechanism for an Adjustable High Voltage Pulsed Converter

This article presents a modular adjustable high-voltage pulse (MAHVP) generation system. The proposed MAHVP generation system uses a combination of full-bridge LLC resonant converters whose input terminals are connected in parallel and whose output terminals are in series to boost the output voltage; input parallel output series configuration efficiently increases the power holding capabilities of the overall system. The MAHVP generation system uses a novel burst mode and variable frequency voltage sharing (BMVFVS) control mechanism, the BMVFVS control mechanism senses the type of load if the MAHVP generation system needs to operate at a heavy load, it uses the variable frequency voltage sharing method to divide the power equally between the modules to enhance the overall performance. For light load conditions, the MAHVP generation system operates in burst mode, and the BMVFVS control mechanism combined with the frequency modulation technique is used to control the amplitude and pulsewidth of the output voltage smoothly and efficiently. A hardware prototype of 2.4 kW is developed, and experimental results are taken to verify the feasibility and validity of the proposed system, the maximum output voltage of the developed two-module prototype is tested up to 6 kV at the high efficiency of 97%.

A Novel Dead Time Design Method for Full-Bridge LLC Resonant Converters with SiC Semiconductors

As third-generation semiconductors become commercial, SiC semiconductors are gradually becoming more widely used in LLC resonant converters. The efficiency of the LLC resonant converter is improved by employing soft switching. However, when designing LLC resonant converters, semiconductors are usually regarded as ideal devices, and their turn-on and turn-off times are neglected. Furthermore, the method of designing the dead time relies on engineering experience and lacks precise theoretical foundations. In order to overcome the shortcomings of the current empirical method and to improve the generality and practicality of the dead time design method, a novel method for calculating the dead time of full-bridge LLC converters is proposed through theoretical research based on the operating principle of full-bridge LLC converters and the conditions for implementing soft switching. The method takes into account the switching characteristics of semiconductors and the on-state delay time of their body diodes, stray inductance, drive circuits, and errors arising from the first harmonic approximation (FHA) and improves the accuracy of the dead time calculation. It can implement good soft switching with full-bridge LLC converters, reduce switching losses, and improve system efficiency. Finally, the simulation experiment and the 2 kW experimental prototype are built to verify the effectiveness of the proposed method.

An improved time‐domain analytical method for LLC resonant converters and dead time designs for zero‐voltage switching

AbstractIn this paper, an improved time‐domain analytical method for LLC resonant converters is proposed. Unlike traditional time‐domain analytical methods, the resonant current in the dead time is derived by considering the equivalent capacitances of the switching devices and the transformer. The equivalent output capacitance of the primary‐side switch is calculated by using a two‐segment fitting approach. The equivalent capacitance of the transformer is calculated by using the six‐capacitor model. The current increment method is used to calculate the initial value of the magnetizing current and to determine the numerical calculation conditions for the proposed time‐domain expressions. Finally, the dead time ranges for zero‐voltage switching of the converter are derived based on the improved time‐domain method. Experiments were carried out with a 10 kW LLC resonant converter. The lower limit of the dead time calculated with the proposed method is closer to the experimental results than the values of two conventional methods.

An LLC Resonant Half-Bridge Converter Optimal Design Using First Harmonic Approximation: A Complete Step-by-Design

There are several industrial uses for LLC resonant converters. The outcome of the converter is greatly influenced by the design and analysis methodologies used. An LLC resonant converter has been designed based on first harmonic approximation (FHA) modelling, and an optimal design technique has been provided in this work. The goal of this research is to provide a thorough design technique for an LLC resonant converter, based on rigorous quantitative analysis of the circuit’s steady-state performance. This study uses FHA technique, which greatly facilitates the model of the system, resulting in a linear circuit that can be analyzed using a standard complex ac-circuit analysis. The FHA methodology is used to establish circuit characteristics and to estimate the outcomes. Although half-bridge power converters are frequently employed in isolated, converters with high-voltage inputs, and medium-power applications are frequently constructed with resonant switching to increase efficiency, a feature that adds complexity but also provides various performance benefits. Two major benefits of the LLC resonant architecture are the soft-switching capabilities of the Power MOSFETs and secondary rectifiers, as well as the ability to operate at zero load. Additionally, the LLC resonant converter is simulated and the results are confirmed using PSIM.

Inserted-Shunt Integrated Planar Transformer With Low Secondary Leakage Inductance for LLC Resonant Converters

The leakage inductance of an integrated transformer is usually utilized as the series inductor of an <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> topology. However, leakage inductance exists on both primary and secondary sides of an integrated transformer and secondary leakage inductance leads the control and design of the converter to difficulty. In this article, a novel topology forinserted-shunt integrated transformers is proposed that has low secondary leakage inductance. The inserted shunt of the proposed topology is not segmental and can be located conveniently within the transformer. In addition, the inserted shunt does not require low permeability core material, simplifying its manufacture. The design and modeling of the proposed transformer topology are presented and verified by finite-element analysis and experimental implementation. The proposed topology is also compared with a recently published inserted-segmental-shunt integrated transformer. It is shown that the proposed transformer provides higher efficiency and lower ac resistance. Finally, an <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> resonant converter is implemented to examine the performance of the proposed integrated transformer in practice.

Design and Analysis of ANN Control based LLC Resonant Converter

Abstract: In this, artificial neural network controller is designed for LLC resonant converter for voltage regulation. The performance of the proposed converter with proportional-integral (PI) controller and ANN controller are analysed from the simulation results. A voltage mode control is provided to get regulated load voltage irrespective of the changes in supply. ANN controller is used for the voltage mode control and the efficiency of the proposed ANN controller is estimated and comparison is made with conventional PI controller. The simulation work is done with MATLAB/Simulink software

Performance Comparison Analysis of a High Voltage DC LLC Resonant Converter for Telecom and Datacenter Applications

Intermediate Bus Architecture (IBA) is used for power distribution in information communication technology (ICT) equipment due to the flexibility of its power distribution and cost-effectiveness compared to centralized or DC-mediated power. The reason for IBA's good performance in this context is its greater reliability and efficient Intermediate Bus Converter (IBC). Existing IBAs comprise low-voltage systems with multiple power, resulting in power loss. This study outlines the need for a high-voltage DC-to-DC converter to solve the problems associated with conventional 48 VDC converters. A 300 W LLC series resonant converter is utilized for the design and analysis of converter efficiency and losses across various input voltages. The results indicate that the maximum converter efficiency is &gt;92% at full load. MATHCAD is used to analyze the performance of the LLC converter and understand the suitable operating zones for zero-voltage-switching. The LLC converter's efficiency is investigated for multiple input voltage ranges. The LLC converter is designed and developed in MATLAB and the results of the simulation are presented. Trade-offs in the LLC converter's design are also discussed, with the goal of operating the converter in an optimal manner and achieving the maximum possible efficiency.

Long Life Power Factor Corrected LED Driver with Capacitive Energy Mechanism for Street Light Applications

Conventional switch-mode LED drivers have problems such as poor performance in harmonic distortion, flickering, power factor correction, stresses on the switches, high switching losses, large size, and high cost. To resolve these problems, we propose a long-life LED driver with the ability of power factor correction. The proposed system is based on the integration of a half-bridge LLC resonant converter and two boundary-conducted boost converters. Both boost converters share a common inductor designed in such a way that both boost converters work in boundary conduction mode to attain the natural power factor correction. Half-bridge LLC resonant converter has soft switching characteristics, which assure the zero-voltage switching (ZVS) of primary-side switches and zero-current switching (ZCS) of diodes on the secondary side. This significantly reduces switching losses and improves the overall efficiency of the system. Voltage divider capacitors are used on the input side, which minimizes the bus voltages. The proposed system has two identical secondary windings with a coupled inductor to eliminate the mismatch between them, which powers two independent LED strings. The simulation of a 100-watt 240 V AC converter yields the approximate sinusoidal shape of the input current. It shows that the switches on the primary side are operated in ZVS and the diodes in ZCS. At 240-volt AC input, the efficiency is 87.4%, the total harmonics distortion (THD) is 10.98%, and the power factor (PF) is 0.98.

Improved Multiphase Interleaved LLC Resonant Converter With Virtual Controllable Voltage Sources

In this article, a simplified virtual controllable voltage sources (SVCVSs) structure for multiphase ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$n \ge3$ </tex-math></inline-formula> ) interleaved LLC resonant converter has been proposed. The SVCVS in each phase is constructed by single auxiliary winding of transformer of the nearby as the phase number is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\ge 3$ </tex-math></inline-formula> , hence printed circuit board (PCB) layout of the improved multiphase interleaved LLC resonant converter becomes much simpler. The feasibility of the multiphase interleaved LLC resonant converter with SVCVSs has been illustrated by vector diagrams, and a family of topologies has been derived. Finally, the 12-V/60-A three-phase interleaved LLC converter with VCVSs/SVCVSs has been tested based on a laboratory built-up prototype. Experimental results show that the three-phase converter with SVCVSs can achieve close output current ripple but higher efficiency than the converter with VCVSs.