LLC Resonant Converter Research Articles

High Efficiency LLC Resonant Converter With Wide Output Range of 200–1000 V for DC-Connected EVs Ultra-Fast Charging Stations

DC-connected ultra-fast chargers consist of isolated DC/DC converter modules to provide the required charging profile. This paper proposes a charging module that interfaces with a fixed voltage DC-bus and covers a wide variety of electric vehicles (EVs) with battery voltages ranging from 200 to 1000 V. DC/DC converters for EVs charging has been discussed several times in the literature, however the DC-connected structure with fixed DC-bus voltage is rarely considered. This paper proposes a full-bridge LLC DC/DC converter module with a configurable secondary. This configuration extends the converter’s charging voltage range without adding stress on the resonant components or operating far from the unity gain point. Due to wide output range, the converter parameters are optimized using the time-domain analytical model to cover the required range without adding unnecessary circulating current that compromises the efficiency. First, the LLC resonant converter fundamentals are briefly introduced. Then, the proposed topology operation and advantages are discussed. After which, the converter’s requirements and design method are presented, focusing on circulating current minimization. Finally, the effectiveness of the proposed converter and the optimized design strategy is verified experimentally on a 10 kW prototype with an input of 800 V and an output of 200 - 1000 V.

An Improved IPOS LLC Resonant Converter With Sub-Module Output Voltage Sharing in Low Ripple High-Voltage Applications

An Improved IPOS LLC Resonant Converter With Sub-Module Output Voltage Sharing in Low Ripple High-Voltage Applications

Variable-Frequency and Phase-Shift With Synchronous Rectification Advance On-Time Hybrid Control of LLC Resonant Converter for Electric Vehicles Charger

The <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> resonant converter has been widely used in the power supply industry, such as server power, TV power, and adapter, because this converter can realize the zero-voltage switching (ZVS) at the power <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">mosfet</small> s of the primary side. Thus, the switch losses can be decreased, and the conversion efficiency can also be improved. The electric vehicle (EV) charger has been recently widely used in research and development. However, designing <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> resonant converters for the wide battery voltage range is difficult because this converter is usually utilized in pulse-frequency modulation (PFM) to regulate the output voltage. This converter will also be limited to the low operating frequency range for the high conversion efficiency due to the switching frequency. By contrast, the phase-shift modulation (PSM) control for the wide output voltage range has been used at <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> resonant converters. However, the ZVS will be lost due to the lagging leg of the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> resonant converter when the phase-shift angle is remarkably excessive. The burst-mode control has also been proposed for the converter to regulate the output voltage and maintain high conversion efficiency at light-load conditions. Therefore, this article utilized the combination of PFM, PSM, and burst-mode control for the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> resonant converter operating at the wide output voltage range for EV charge applications. Furthermore, this article proposed a synchronous rectification advance on-time control for PFM control, which can help address the ZVS at the lagging leg when the phase-shift angle is excessive. Detailed analysis and design of this control method are also described. The performance evaluation of the proposed <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> resonant converter with hybrid control was finally realized under the following conditions: 3.75 kW, dc input voltage of 400 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DC</sub> , dc output voltage of 75–475 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DC</sub> , and maximum conversion efficiency around 97%.

High-Frequency Planar Transformer Based on Interleaved Serpentine Winding Method With Low Parasitic Capacitance for High-Current Input LLC Resonant Converter

High-Frequency Planar Transformer Based on Interleaved Serpentine Winding Method With Low Parasitic Capacitance for High-Current Input LLC Resonant Converter

Modified Two-Channel LLC Resonant Converter With Optimal Efficiency for Wide Input Voltage Applications

A modified two-channel LLC resonant converter with optimal efficiency for wide input voltage applications. The converter has the same voltage gain and power handing ability as conventional full-bridge (FB) resonant converter, but the hardware cost is lower than conventional FB resonant converter, and the operational frequency range is narrower than conventional resonant converter for the same working condition. It has the characteristics of low input impedance at low input voltage, which is used to provide high voltage gain, and high input impedance at high input voltage, which is used to provide low voltage gain, the above characteristics are analyzed and optimized to improve the efficiency for photovoltaic applications where wide voltage gain is require. A 1 kW prototype is developed, the input voltage ranges from 80 V to 200 V, the output voltage and output power are 400 V and 1 kW, the experimental result shows that the full-load efficiency can reach 96.5% over the entire input voltage range, and the peak efficiency can reach 96.9% at full-load state.

Efficiency Considerations of LLC Resonant Converter for Induction Heating Application

Due to the high efficiency, high power density and low EMI provided by the LLc resonant converter, it has been widely used by researchers in many fields such as induction heating (IH). This converter is based on a resonant circuit consisting of a capacitor (Cr) and two inductors Lr, Lm operating in wide output load regulating ranges for the purpose of achieving good efficiency for very high power systems using a high operating frequency. This paper aims to present a half-bridge LLC resonant converter based on power supplies for IH applications. The analysis contains five components: half bridge inverter, resonant tank, high frequency transformer, rectifier and coil. The switching bridge generates a square waveform to excite the LLC resonant tank, which will produce a resonant sinusoidal current which is transferred to the secondary of the converter through a high-frequency transformer. as it scales the voltage up or down according to the output requirements. The load represented by the equivalent circuit of the coil and work-piece is fed by the current transformed by the rectifiers. This paper provides an improved knowledge of the control of the output power for high-temperature applications through numerical simulation Considering that the load parameters and resonant frequency vary substantially throughout the system operation. The results of testing demonstrated that the proposed scheme and assembly has good efficiency, and it is well suited for magnetic induction heating systems.

Parameters optimization design method for LLC resonant converter based on impedance model

PurposeThis paper aims to better design the resonant tank parameters for LLC resonant converter. And, it is found that under heavy load, the voltage gain is affected by junction capacitors of the primary side switching and the parasitic parameters of the secondary side diodes converted to the primary side, which will cause the voltage gain decreased when the switching frequency decreased.Design/methodology/approachThis paper proposes an optimization parameters design method to solve this problem, which was based on impedance model considering the parasitic parameters of switching devices and diodes.FindingsThe effectiveness of the proposed method is verified by impedance Bode plots and experimental results.Originality/valueFrom the perspective of impedance modeling, this paper finds the reasons for the insufficient voltage regulation capability of LLC resonant converters under heavy load and finds solutions through analysis.

Efficiency Analysis of Phase Shift LLC Resonant Converter

Compared with pulse frequency modulation, a phase-shift modulated LLC resonant converter has a wider voltage modulation range and better EMI characteristics, but the efficiency is relatively lower. In this paper, the working process and power loss characteristics of PSM LLC are analyzed, the efficiency optimization method of PSM LLC is proposed, and the relevant conclusions are verified by simulation.

A General and Automatic RMS Current Oriented Optimal Design Tool for LLC Resonant Converters

LLC resonant converters are used in renewable energy applications to achieve high power efficiency conversions between different energy sources, buses, and energy storage elements. The traditional design methods for LLC resonant converters are based on a simple frequency-domain analysis (FDA). However, the accuracy of FDA is not satisfactory, especially at wide voltage range applications. To overcome the drawbacks of the traditional FDA method in wide-range applications, in this article, the time-domain analysis (TDA) is adopted to achieve accurate analysis of LLC converters. Efficiency is normally selected as the optimization objective, where the circuit components and accurate power loss models are required beforehand. To achieve a more general optimal design method for LLC converters, a simple root-mean-square (rms) current and TDA-based optimal design method is proposed. The optimal design is achieved by minimizing the converter rms current and ensuring some key design considerations. Moreover, an automatic design tool for the proposed rms-current-based optimal design method is developed, and advanced optimization algorithms are introduced to improve the optimization speed. A 2.5-kW experimental prototype is built using the optimal circuit parameters. Experimental results under different operating conditions are demonstrated, and the results are consistent with the theoretical analysis. Efficiency comparisons between the proposed optimal design method and conventional design method are made. The proposed optimal design method can improve the converter efficiency by a maximum value of 2.14%.

High-Power-Density DC–DC Converter Using a Fixed-Type Wireless Power Transmission Transformer with Ceramic Insulation Layer

In this study, we propose the use of a short-distance and fixed-type wireless power transmission transformer via a half-bridge LLC resonant converter. A ceramic insulating layer was used instead of an air gap, meaning that the heat generated from the transformer core and the PCB winding was quickly transferred to the external metal case, with the ceramic insulating layer acting as a heat pipe. In order to stabilize the output voltage, we proposed the use of IR photo tunnel technology, and it was applied to two ceramic insulating layers so that the voltage error signal of the secondary output voltage could be transmitted as light to the primary side. As a result, it was possible to physically separate the primary and secondary sides of the power circuit centering on the ceramic insulating layer. The experiment was carried out with the input voltage of 400 V, the output voltage of 54 V, the maximum output power of 1 kW, and the switching frequency of 1.3 MHz or higher. As a result, the maximum operating frequency was 1.83 MHz, and the output voltage stability to the load was 0.49% or lower. The power density of the experimental circuit was 380 W/in3 or higher, and the maximum power conversion efficiency was approximately 93% or higher.

Dynamic improvement for phase-shift LLC resonant converter based on disturbance observer

LLC resonant converters have been widely used in DC/DC conversion because of their high efficiency. However, the converters are highly nonlinear, making it hard to use typical linear control methods. This paper proposes a disturbance-observer-based control approach, which achieves better performance compared with the conventional PI controller. First, according to the extended describing function (EDF) method, the small-signal model of the phase-shift LLC resonant converter is established, which is further simplified to a third-order system. Then, the disturbance-observer-based control is presented, which incorporates a disturbance observer (Dob) to estimate the uncertain effects resulting from external disturbances, circuit parameters variation and model mismatch, and compensate for them in a feedforward way. The main advantage of this control structure is that it can improve the stability and dynamic response simultaneously, where the Dob optimizes the dynamic responses and the PI controller is designed to satisfy the stability requirement. Finally, a 600 W simulation model is built in MATLAB/Simulink to verify the proposed control method, whose superiority over the classic PI controller is proved by the simulation results.

Analysis of an LLC–DAB integrated DC–DC converter topology with low loss and low cost

AbstractThis paper proposes an LLC‐DAB integrated high‐frequency isolated DC–DC converter topology structure to reduce the loss and cost of the DC power distribution system. Furthermore, the complexity and efficiency of the system also can be improved. The proposed converter consists of a DAB converter and two input‐parallel‐output‐parallel half‐bridge LLC resonant converters. It provides two DC voltage level buses, namely the HVDC bus and the LVDC bus. Compared with the typical converter topology of the DC power distribution system, the number of power semiconductors of the proposed converter topology is reduced by sharing the power semiconductors of the DAB converter and LLC resonant converter. As a result, with the number of power semiconductors decreasing, the cost and loss of the system are reduced. Moreover, the proposed converter can control the flow direction of power conversion and supply power to the loads. The single‐phase‐shift modulation method is adopted for the DAB converter, and two LLC resonant converters operate as the DC transformer under resonant frequency with open‐loop control. The operation principles and characteristics of the proposed converter are discussed. Finally, the simulation is carried out and an experimental prototype is developed to verify the effectiveness of the proposed topology.

In-Depth Design and Multiobjective Optimization of an Integrated Transformer for Five-Phase LLC Resonant Converters

High-power isolated dc–dc converters are preferred in the medium-voltage cascaded H-bridge (CHB) photovoltaic (PV) generation systems due to high power density and galvanic isolation. However, high-power transformers in dc–dc converters can result in high power losses and poor heat dissipation due to thick isolation materials. The three-phase LLC (3P-LLC) converter has been reported suitable for high power applications. Comparing to the single-phase counterpart, the 3P-LLC converter employs three discrete transformers, leading to a larger core area for better heat dissipation. To further increase the power density and the heat dissipation capability of resonant converters, increasing the phase number and integrating magnetic components are considered. This work proposes a five-phase LLC (5P-LLC) resonant converter for the CHB PV application. To increase the power density, a five-phase magnetic integrated transformer (5P-MIT) is proposed and designed with an optimal limb structure to avoid local flux saturation. To further increase the power density, reduce the transformer losses, and enhance the heat dissipation capability, multiobjective optimization is developed to meet multiple design requirements simultaneously. A design case is studied to show the advances of the proposed 5P-MIT. To further investigate the proposed 5P-LLC, a down-scaled prototype is developed with a 5P-MIT. Experiments are conducted to verify the analyses and the functionality.

Steady-State Analysis and Optimal Design of an LLC Resonant Converter Considering Internal Loss Resistance

In this paper, a steady-state model of an LLC resonant half-bridge converter with internal loss resistance is proposed, in order to maximize power conversion efficiency, and steady-state characteristic equations of DC voltage gain and input impedance are derived for the optimal design of the converter. First, to confirm the validity of the steady-state characteristic equation and the optimal design process, a prototype converter with a maximum output of 2 kW was designed. Through comparison of simulation, calculation, and experimental results obtained from the prototype test, it is shown that the calculation results proposed in this paper were closer to the experimental results than the calculation results obtained under the lossless condition. In addition, the relationship between the switching frequency and the load current of the prototype was compared, in order to determine the operating range of the switching frequency, which is important in the converter design stage. In this case, it was confirmed that the calculated value reflecting the internal loss showed a close result. In conclusion, we confirm the usefulness of the analysis results reflecting the internal loss resistance proposed in this paper and the optimal design process.

Control Strategy of Half-Bridge Three-Level LLC Resonant Converters With Wide Output Voltage Range

A half-bridge three-level LLC (HBTL-LLC) resonant converter has low voltage stress, high power density, and a large range of soft switching, so it is widely considered and applied, but there are problems such as a small adjustable range of output voltage and difficulty in implementing soft switching. In this article, based on the detailed analysis of the working principle of an HBTL-LLC resonant converter, a three-stage hybrid control strategy is proposed: frequency modulation (FM) control is used when the gain is high, and phase shift control is used when the gain is low. If the phase shift angle achieves the critical value of the soft switch and the gain is still high, variable-frequency burst control is used to expand the adjustment range of the output voltage and improve the power efficiency at low voltage output. Finally, a 500-V, 15-A prototype was designed and analyzed and experimented. The results verified the feasibility and effectiveness of the proposed three-stage hybrid control strategy.

Fixed-Frequency Phase-Shift Modulated Capacitor-Clamped LLC Resonant Converter for EV Charging

<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> resonant converter has been widely employed in electric vehicle (EV) charging applications. However, conventional frequency-modulated <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> converters generally demand a wide frequency variation range and are difficult to scale up, while the traditional phase-shifted (PS) <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> converters have the issues of ease of losing soft-switching condition and high turn- <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</small> current. In response to these challenges, this article proposes a new method for EV charging applications based on the capacitor-clamped <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> converter topology and fixed-frequency PS modulation. Compared with traditional PS <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> converters, the proposed method can achieve 1) smaller phase shift variation range, 2) lower turn- <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</small> current, and 3) wider soft switching range, resulting in higher efficiency. An 825-W prototype with 200 V input and 125–210 V output range verified the features of the proposed idea, and the efficiency reaches 97.82% at the maximum output power.

Development of a Resonant Auxiliary Power Supply Control Algorithm and Resonant Destruction Detecting for Railway Vehicles

In this paper, the method and a control algorithm for detecting resonant destruction of a resonant auxiliary power supply for railway vehicle are proposed. It is essential to reduce the weight of the electric equipment attached to the lower part of the railway vehicle because it greatly affects the life of the railway vehicle, such as wheel and bearing. In order to reduce the weight and volume of the auxiliary power supply, in the case of windings, high-speed switching should be performed by lowering the input voltage. Therefore, in this paper, the auxiliary power supply control algorithm using an LLC resonant converter to reduce the weight of auxiliary power supply for railway vehicle is proposed, and the method of detecting resonant destruction due to device failure of a resonant converter is proposed. The proposed algorithm steps down the wire voltage using an input buck converter for high-speed switching, and the inverter input voltage is controlled through the LLC resonant converter. In addition, ZVS (Zero Voltage Switching) is operated to minimize the loss of the resonant converter, and the optimal design of the resonant tank is also proposed. In order to detect resonant destruction, a detection method formulated by analyzing the resonant current peak value for the load capacity is proposed. The algorithm proposed in this paper is verified by simulation and experiment.

Research on Wide Input Voltage LLC Resonant Converter and Compound Control Strategy

This paper presents a wide input voltage vehicle DC/DC converter based on an LLC resonant converter for a 48 V light hybrid power system. According to the design requirements of on-board DC/DC converters and an analysis of their system characteristics, a full-bridge LLC resonant converter is employed with a zero-voltage activation of the switching transistors through resonant elements. In terms of the control strategy, the unsatisfactory high-frequency regulation gain of an LLC resonant converter is analyzed under the frequency modulation (FM) control strategy. In addition, to accommodate wide input voltage operating conditions, a composite control strategy is proposed by combining the advantages of the frequency modulation control strategy and phase shift control strategy, analyzing their control principles, and discussing the selection of the control mode switching point. By modeling LLC resonant converters with simulation software, the obtained results verify the effectiveness of the composite control strategy for LLC resonant converters. An experimental platform based on the TMS320F28335 controller, which can achieve stable operation with an input voltage in the range of 300 V–600 V and an output voltage of 48 V, is then built. The experimental results verify the feasibility of the design.

Design and Analysis of LLC Resonant Converter With Valley Switching Control for Light-Load Conditions

The LLC converter has been widely used in the power supply industry for its high conversion efficiency. When the output load is low, the LLC resonant converter will substantially increase the operating frequency, thereby reducing the conversion efficiency and exceeding the limited operating frequency of the specification. Thus, burst-mode control is applied to increase the ability of regulation at light-load conditions. Even so, the switching period of power switches still occurs at a high switching frequency. Burst-mode control will also result in an extremely low-frequency output voltage ripple. In this study, a valley switching control (VSC) for the LLC resonant converter at light-load conditions is proposed. The VSC control strategy maintains the output voltage by modulating the pulsewidth signals of drivers and achieves valley switching by modulating the switching frequency. Thus, the VSC strategy can reduce the operating frequency compared with the frequency modulation strategy. Compared with burst-mode operations, the proposed VSC effectively reduces the switching loss and has the advantage of high-frequency output voltage ripple. The VSC increases the efficiency and the power quality of the converter. Detailed analysis and design of the proposed method are described. Experimental results are recorded for a prototype converter with a dc input voltage of 400 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$V_{\mathrm {DC}}$ </tex-math></inline-formula> , an output voltage of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$48~V_{\mathrm {DC}}$ </tex-math></inline-formula> , and an output current of 12.5 A.

Integration of Three-Phase LLC Resonant Converter and Full-Bridge Converter for Hybrid Modulated Multioutput Topology

A multioutput dc–dc topology based on hybrid modulation of pulse frequency modulation and the phase shift is proposed in this article. The proposed hybrid modulated multioutput converter is derived from the integration of a three-phase LLC resonant converter and the full-bridge converter. With the hybrid modulation, the multioutput is controlled independently free from cross-regulation and isolated from each other. With the three-phase interleaving operation, the resonant currents can be reduced, and thus, the efficiency will be improved. Furthermore, the output current ripple of the main output voltage is reduced; as a consequence, the lifetime of the output filter capacitor is extended, and the reliability is reinforced. What is more, the number of the power switches is reduced, and the zero-voltage switching of the power switches can be achieved within the entire load range by the proposed integrated topology. All the abovementioned features of the proposed converter will lead to a compact, efficient, and cost-effective design. Finally, a 1.4-kW triple-output laboratory prototype is built and tested to validate the feasibility and effectiveness of the proposed converter.