LLC Converter Research Articles

On-State Voltage Measurement Circuit for Condition Monitoring of MOSFETs in Resonant Converters

This work aims to estimate the Metal-Oxide-Semiconductor Field-Effect Transistor’s (MOSFET) junction temperature, guessing in real time the dynamic drain-source resistance during MOSFET operation in LLC (Inductor-Inductor-Capacitor) converters usually adopted in Switched-Mode Power Supplies. The task is accomplished using an on-state voltage measurement circuit that allows clamping of the high-voltage drain-source voltage during the off-state. The results of this method have been compared with the temperature accurately measured using a co-packed die as a thermal sensor.

Planar Magnetic Regulator Applied to an LLC Converter for CCT Control

Planar Magnetic Regulator Applied to an LLC Converter for CCT Control

병렬 운전을 통한 4kW급 인공위성용 아날로그 LLC 공진형 컨버터 개발

A modular analog LLC resonant converter capable of delivering high power for aerospace applications with zero voltage switching turn on of power semiconductors has been proposed. The LLC converter utilizes a half bridge configuration, with top and bottom switches designed by paralleling two low capacity power semiconductors suitable for use in space, thereby increasing the current capacity to enable an output of up to 1.2kW. Each LLC converter module takes in 100V power and outputs 300V in a step up DC/DC converter configuration, designed to operate with regulated voltage and current. This paper describes the operating principles and steady state analysis of the proposed DC/DC converter. To validate its effectiveness, a prototype was constructed and tested. The tests yielded a max efficiency of 95.3% and an output of approximately 4kW, demonstrating the feasibility and output performance of high efficiency, high power supplies through load sharing of multiple modules in parallel.

Design and Experimental Verification of Electric Vehicle Battery Charger Using Kelvin-Connected Discrete MOSFETs and IGBTs for Energy Efficiency Improvement

This research investigates the advantages of Kelvin-connected 4-pin discrete transistors, both MOSFETs and IGBTs, in onboard battery chargers for electric vehicles. The study compares the standard 3-pin and the extended 4-pin packages based on averaged data collected from leading manufacturers. The investigation shows significant potential power loss reduction, thermal operation mitigation, and reduced gate-drive oscillation for the 4-pin package. The benefits have been quantified by analysing the operation of actual switches in an automotive battery charger based on Boost-PFC and DC-DC LLC converters. The converters’ practical design demonstrates a procedure for integrating the Kelvin-connected package into the design methodology. The results have been verified experimentally.

A Detailed Analysis and Gain Derivation of Reconfigurable Voltage Rectifier-Based LLC Converter

In this paper, a complete analysis of an LLC resonant converter with a customized rectifier structure is presented. The converter is intended for wide, low-input, high-output voltage DC bus applications. The performance of the converter is assessed using comprehensive time-domain and fundamental harmonic approximation (FHA), which demonstrates its capacity to operate across an ample range of voltages by precisely adjusting the rectifier structure. The converter’s capability is illustrated by deriving and discussing detailed mode operation, steady-state analysis, and DC gain equations. In order to verify the theoretical analysis, a prototype with a power output of 250 watts is constructed and subjected to testing. The results of the testing demonstrate that the converter is both feasible and effective. The experimental findings illustrate its capacity to manage vast voltage ranges while upholding high efficiency. In addition, the converter utilizes a frequency switching modulation (FSM) to connect with a photovoltaic (PV) panel and control the high output voltage. This demonstrates its adaptability in renewable energy applications. The validation is in accordance with theoretical predictions, demonstrating the converter’s high-efficiency performance and versatility.

Soft‐switching boundary and piecewise control of LLC converter with hybrid modulation

AbstractThe voltage gain range of LLC converter can be effectively broadened by using the hybrid modulation of phase‐shift modulation (PSM) and pulse frequency modulation (PFM). However, the harmonic of resonant tank increases dramatically in PSM mode, and the first harmonic approximation is no longer suitable for solving the voltage gain. Moreover, the conditions for soft switching in PSM mode are not clear. Meanwhile, the small‐signal models of the converter in different modulation modes are quite different, and it is difficult for a fixed controller to ensure a good dynamic performance of the converter in both modulation modes. To address above issues, a voltage gain modeling method of PSM mode LLC converter is proposed. By establishing the function between input current and resonant current, the voltage gain model of the converter is obtained according to the power conservation. Moreover, considering the parasitic capacitance charge and resonant current commutation time, the condition for soft switching is derived. Furthermore, a control strategy of LLC converter in hybrid modulation is proposed. The piecewise proportional integral (PI) controller is adopted, and the parameters of the controller are dynamically adjusted with the modulation mode, so that the converter has excellent dynamic performance in both modes. And the hysteresis control is used to ensure the stability of mode switching. An experimental prototype with 200–340 V input and 28 V/1 kW output was built based on gallium nitride (GaN) devices. The peak efficiency was 97.82%, and the power density was 65.76 w/in3.

A single-bridge interleaved three-level LLC resonant converter with current sharing capability for fuel cell system

This paper propose a wide gain single-bridge interleaved three-level LLC resonant converter with current sharing capability. This novel converter offers numerous advantages, including low cost, low current ripple, reduced voltage and current stress, widely gain range, high efficiency, good current sharing capability and versatile application scalability. Utilizing the three-level inverter + full-wave rectifier LLC converter as a representative case, the paper conducts an in-depth analysis and research on the proposed method. Finality, a 600 W experimental prototype was constructed and tested. Experimental results reveal that the proposed converter exhibits lower current ripple and a broader gain range. Moreover, the converter shows good current sharing capability (with a resonant element tolerance of 10%, the current error between the two phases does not exceed 12%) and high efficiency (peaking at 95.8%).

Integral global fast terminal sliding mode control for LLC converters

Abstract The complex characteristics of full-bridge LLC converters and PFM mode of operation result in a variety of operating modes and characteristic changes at different operating frequencies, thus increasing the difficulties in small signal characteristic analysis and good compensator design. In terms of control strategy, the traditional linear controller has limited response performance under various operating conditions such as input voltage ripple perturbation, input voltage mutation, and load mutation. To obtain greater transient response performance, stronger disturbance capability, and higher input stability of the system under different operating conditions, this paper proposes a new integral global sliding mode control law for LLC converters. In contrast to conventional control methods, the proposed control strategy exhibits enhanced dynamic response capabilities in the presence of load variations. It effectively mitigates jitter issues during steady-state operation, demonstrating a superior control performance.

A new winding structure with low common‐mode current in input series output parallel planar transformer LLC converter

AbstractMHz switches and integrated magnetic planar transformers (PT) promote the high density and miniaturization of DC/DC converters. The parasitic parameters of the PT at high frequency significantly affect the performance of converters, resulting in severe electromagnetic interference (EMI) problems. Firstly, this paper proposes a new common‐mode (CM)‐suppression winding structure for the input series output parallel (ISOP) matrix transformer LLC converter. The sources and conduction principle of CM noise are analyzed. Furthermore, this optimization based on winding shape and position is simple and feasible, suppressing the CM noise significantly. Compared with conventional multilayer winding structure, this optimization increases the current‐carrying area by 2.8%–5.9%, effectively improving the primary current distribution. In addition, the proposed structure makes the best planar windings in footprint with expanded windings, bringing the simplest layout in the primary winding. Finally, a 1 MHz 400 V/12 V 300 W LLC converter is constructed to verify the effect of this winding structure. The results show that a 40% reduction in CM current can be achieved while maintaining the current balance.

Characterization and SPICE modelling of a transformer for LLC converter based on GaN transistors

Characterization and SPICE modelling of a transformer for LLC converter based on GaN transistors

A triple‐LC‐based DC/DC converter with wide input voltage gain in both under‐resonance and over‐resonance frequency regions

AbstractIn recent years, wide voltage range DC/DC converters have been widely used in telecom power, solar generation and electric vehicle charger applications. Based on this, a new multi‐resonant converter with wide input voltage is proposed here. Compared with the traditional LLC converter, the proposed converter can maintain the output voltage within a narrow frequency regulation range in both under‐resonance and over‐resonance areas. Thus, a wide voltage range can be realized without additional switch components or complex control strategies. The topology and the corresponding working principle of the proposed converter are introduced. In addition, the equivalent model by considering the fundamental wave is established and the influence of the resonance parameters on the voltage gain characteristic is analysed in detail. With these considerations, the resonance parameters are designed. Finally, a 500 W experiment platform is established to verify the effectiveness and feasibility of the proposed converter.

Analytic discrete state-space model of LLC resonant converter

The LLC resonant converter has widely been used for having high-frequency soft-switching capability which could lead to high power density power electronic solutions, and higher power conversion efficiency at lower costs. However, the presence of excessive non-linearity resulting from power conversion through the resonant tank has led to a lack of accurate and reliable large-signal and small-signal models which limits the performance optimization. This paper presents a theoretical analysis of the LLC converter using the sampled-data modeling approach to accurately convert the continuous-time-variant state equations to discrete-time-invariant state equations and solve them using switching time-segmented boundary conditions to obtain the discrete large-signal model. The small-signal model is obtained by perturbation and linearization of the steady-state model in the vicinity of the cyclic equilibrium states of the converter. Theoretical analysis results are validated by simulating a 650W LLC converter in Matlab Simulink. Based on the provided results, the proposed steady-state and small-signal models can accurately predict the dynamic behavior of the LLC converter in different operational conditions.

Current Balancing Control Method With Reduced Number of Current Sensors for Interleaved LLC Converters

Current Balancing Control Method With Reduced Number of Current Sensors for Interleaved LLC Converters

An ISOP LLC Converter With Changeable Equivalent Magnetizing Inductance Utilizing Coupled Inductor for Ultrawide Input Voltage Range Application

An ISOP LLC Converter With Changeable Equivalent Magnetizing Inductance Utilizing Coupled Inductor for Ultrawide Input Voltage Range Application

A Holistic Design Optimization Method for LLC Converters in Light Electric Vehicle Chargers

A Holistic Design Optimization Method for <i>LLC</i> Converters in Light Electric Vehicle Chargers

Study of an LLC Converter for Thermoelectric Waste Heat Recovery Integration in Shipboard Microgrids

Static waste heat recovery, by means of thermoelectric generator (TEG) modules, constitutes a fast-growing energy harvesting technology on the way towards greener transportation. Many commercial solutions are already available for small internal combustion engine (ICE) vehicles, whereas further development and cost reductions of TEG devices expand their applicability at higher-power transportation means (i.e., ships and aircrafts). In this light, the integration of waste heat recovery based on TEG modules in a shipboard distribution network is studied in this work. Several voltage step-up techniques are considered, whereas the most suitable ones are assessed via the LTspice simulation platform. The design procedure of the selected LLC resonant converter is presented and analyzed in detail. Furthermore, a flexible control strategy is proposed, capable of either output voltage regulation (constant voltage) or maximum power point tracking (MPPT), according to the application demands. Finally, both simulations and experiments (on a suitable laboratory testbench) are performed. The obtained measurements indicate the high efficiency that can be achieved with the LLC converter for a wide operating area as well as the functionality and adequate performance of the control scheme in both operating conditions.

Design of 3-level LLC converter voltage controller for wide input voltage fluctuations

The auxiliary power supply unit for railway vehicles delivers various power to the passenger car. Maintaining isolation between the catenary power line and the auxiliary power in the compartment is typically essential. To ensure electrical isolation, an efficient LLC resonant converter is utilized among isolated DC-DC converters. Generally, LLC resonant converter primarily employ PFM control method. However, there is a limitation in increasing the switching frequency at high input voltages, making it difficult to handle wide input voltage fluctuations from the overhead catenary power line. To overcome this limitation, the PFM control method is introduced alongside the existing PFM control method, resulting in the presence of two controllers. However, since these two controllers regulate the output voltage differently, there is a potential for output voltage overshoot due to significant input voltage fluctuations. This paper proposes a method that combines PFM and PWM controllers, along with feed-forward compensation, to address these issues. The effectiveness of this proposed method is validated through PSIM simulation and experimentation.

Lower-Height-Oriented Magnetic Integration Design for Onboard Power Converter of Electric Vehicles

With the development of electric vehicles (EVs), EV onboard power converters are expected to pursue higher power density and lower height. Compared with active power devices, passive magnetics seems to be the main restriction for higher efficiency and power density. In the power distribution system, two-stage configurations of Buck+LLC converter is widely employed in various electronic equipment, which requires multiple magnetics. On this basis, the integration of two Buck+LLC converters has been studied to reduce the overall cost and improve the power density. Firstly, the two buck converters are interleaved and operate in critical mode (CRM) to reduce current ripple and realize soft switching. Hence, the two buck inductors can be negative-coupled with each other and integrated into one magnetic core to achieve lower switching frequency and smaller volume. In addition, the two LLC dc transformers are also integrated with only one switching leg and one magnetic core. By extending the effective area and canceling the high-frequency magnetic flux, the loss and volume of both the integrated buck inductors and integrated LLC transformers are reduced significantly. Detailed integration methods and parameter design processes are presented. A 700 W, 150-350 V-to-12 V dual-output dc-dc converter with 500 W/in <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> power density is demonstrated to verify the effectiveness and feasibility of the proposed methods.

A partial energy current‐sharing method for interleaved LLC converter with phase shift current balance module

AbstractA partial energy current‐sharing method for an interleaved LLC resonant converter with a phase shift current balance module (CBM) is presented in this paper. The current sharing is achieved by controlling the phase shift angle of the bridge in the CBM. The proposed method maintains excellent soft‐switching performance, minimizes power losses, and ensures high overall efficiency as only partial energy is processed. This method simplifies current sharing in the resonant converter by using phase shift control, making it easy to implement and extend to multiple phases. A 500‐kHz two‐phase interleaved LLC prototype was built to validate the effectiveness of this method in achieving current balancing.

Reliable and optimal design of variable inductor integrated LLC converter

AbstractThe variable inductor integrated LLC (VI‐LLC) converter is able to operate at constant switching frequency and avoid wide variable frequency range and thus emerged in recent years. However, VI‐LLC converter suffers two reliability problems. First, coupling between the main winding and the control winding of variable inductor (VI) causes negative effects on the converter, which are few considered in the literature. Second, parameter fluctuation (PF) of resonant elements has negative effects on operation and gain reliability of VI‐LLC converter, causing unreliable operation and voltage gain deviation. To solve the above problems, in this paper, a reliable and optimal design methodology of VI‐LLC converter is proposed. First, the coupling effects of VI are introduced and analyzed, with a coupling index proposed to quantify and reduce the coupling effects. Then, negative effects on VI‐LLC converter caused by PF are visualized and eliminated with the filtered parameter space and the redetermined variation range of VI. Based on the above consideration, a reliable final parameter space considering PF effects and the coupling problem is established. Finally, the efficiency space referring to the final parameter space is established based on the loss model of VI‐LLC converter to determine the optimal design candidate. Experimentation has shown a good agreement with theory and proven validity of the proposed design methodology.