Search Results (20)

This paper proposes a Boost + LLC converter-based power controller for ocean buoy tidal energy systems. To optimize output power across a wide input voltage range (40–120 V) and achieve effective power tracking control, we introduce two key innovations as follows: (1) a variable-mode inverter hybrid control strategy, combining smooth-mode switching with inverter control to enable wide gain range regulation. (2) An improved Grey Wolf Optimization (GWO) algorithm, enhanced by integrating a PSO-based elite wolf search strategy preventing local optima and maximizing power capture. Saber and Matlab simulations demonstrate that the proposed approach yields faster power tracking response and increases output power by 5–10% compared to traditional methods. The combined controller and improved GWO algorithm provide a stable and efficient solution for small-scale ocean energy systems, offering practical insights for power regulation in other marine energy sources like wave, wind, and solar. Full article

While DC/DC converters for water electrolysis systems have been widely investigated, they inherently face a critical compromise between wide voltage regulation capabilities and dynamic response characteristics. This study is based on a two-stage hybrid topology (TSIB-TPLLC) that synergistically combines a two-phase interleaved buck converter with a three-phase LLC resonant converter to resolve this challenge. The first-stage interleaved buck converter enables wide-range voltage regulation while reducing input current ripple and minimizing intermediate bus capacitance through phase-interleaved operation. The subsequent three-phase LLC stage operates at a fixed resonant frequency, achieving inherent output current ripple suppression through multi-phase cancellation while maintaining high conversion efficiency. A dual-loop control architecture incorporating linear active disturbance rejection control (LADRC) with PI compensation is developed to improve transient response compared to conventional PI-based methods. Finally, a 1.2 kW experimental prototype with an input voltage of 250 V and an output voltage of 24 V demonstrates the converter’s operational feasibility and enhanced steady-state/transient performance, confirming its suitability for hydrogen production applications. Full article

This article proposes a high-efficiency isolated three-port resonant converter for DC microgrids, combining a dual active bridge (DAB)–LLC topology with hybrid Pulse Width Modulat-Pulse Frequency Modulation (PWM-PFM) phase shift control. Specifically, the integration of a dual active bridge and LLC resonant structure with interleaved buck/boost stages eliminates cascaded conversion losses. Energy flows bidirectionally between ports via zero-voltage switching, achieving a 97.2% efficiency across 150–300 V input ranges, which is a 15% improvement over conventional cascaded designs. Also, an improved PWM-PFM shift control scheme dynamically allocates power between ports without altering switching frequency. By decoupling power regulation and leveraging resonant tank optimization, this strategy reduces control complexity while maintaining a ±2.5% voltage ripple under 20% load transients. Additionally, a switch-controlled capacitor network and frequency tuning enable resonant parameter adjustment, achieving a 1:2 voltage gain range without auxiliary circuits. It reduces cost penalties compared to dual-transformer solutions, making the topology viable for heterogeneous DC microgrids. Based on a detailed theoretical analysis, simulation and experimental results verify the effectiveness of the proposed concept. Full article

Pulse frequency modulation (PFM) is widely used in LLC resonant converters. However, in wide voltage applications, the switching frequency range is very wide, which affects the performance of magnetic components and filters. In order to achieve wide voltage gain in a narrow frequency range, this paper proposes a unified inductor type based linear resonant hybrid converter (UITBLRHC). The resonant inductor and excitation inductor are unified, and the resonant tank with equal inductance ratio is achieved. Hence, the output voltage can be adjusted within a very narrow frequency range. In addition, the parameters and operating modes of the two inductors are exactly the same. Therefore, the types of inductors can be reduced, and the magnetic flux and heat distribution between the two inductors are more uniform. Finally, an 800 W prototype was built. The proposed solution can achieve twice the voltage gain within a frequency range of 1.25 times. The experimental results prove the reliability and validity. Full article

The increasing penetration of photovoltaic (PV) systems and the need for reliable backup power solutions have led to the development of hybrid uninterruptible power supply (UPS) systems. These systems integrate PV energy storage with battery backup and grid power to optimize real-time energy management. This paper proposes an advanced energy management strategy and an artificial neural network (ANN)-based control method for PV-integrated hybrid UPS systems. The proposed strategy dynamically determines the optimal power-sharing ratio between battery storage and the grid based on real-time economic parameters, load demand, and battery state of charge (SoC). A centralized ANN-based controller ensures precise control of the LLC converter and rectifier, achieving stable and efficient power distribution. Additionally, a genetic algorithm is implemented to optimize the power sharing ratio, minimizing the LCOE under varying load and electricity pricing conditions. The proposed approach is validated through simulations, demonstrating significant improvements in cost-effectiveness, system stability, and dynamic adaptability compared to conventional control methods. These findings suggest that integrating ANN-based control with optimized energy management can enhance the efficiency and sustainability of hybrid UPS systems, particularly in fluctuating energy markets. Full article

This study reviews advancements in high-frequency converters for renewable energy systems and electric vehicles, emphasizing their role in enhancing energy efficiency and sustainability. Using the PRISMA 2020 methodology, 73 high-quality studies from 2014 to 2024 were synthesized to evaluate innovative designs, advanced materials, control strategies, and future opportunities. Key findings reveal significant progress in converter topologies, such as dual active bridge and LLC resonant designs, which enhance efficiency and scalability through soft-switching. Wide-bandgap semiconductors, including silicon carbide and gallium nitride, have driven improvements in power density, thermal management, and compactness. Advanced control strategies, including adaptive and AI-driven methods, enhance stability and efficiency in microgrids and vehicle-to-grid systems. Applications in photovoltaic and wind energy systems demonstrate the converters’ impact on improving energy conversion and system reliability. Future opportunities focus on hybrid and multifunctional designs that integrate renewable energy, storage, and electric mobility with intelligent control technologies like digital twins and AI. These innovations highlight the transformative potential of high-frequency converters in addressing global energy challenges driving sustainable energy and transportation solutions. This review offers critical insights into current advancements and pathways for further research and development in this field. Full article

Aiming at the problem of the circuit operating frequency changing beyond the regulation range and zero switching not being guaranteed when the input voltage range of the LLC resonant converter is large, a hybrid control technology with a variable structure and variable mode is proposed in this paper to realize the wide input range of the LLC resonant converter. Depending on the input voltage range, this technology can ensure the frequency range of the circuit and meet the realization conditions of zero voltage switching (ZVS) in different modes. The test results show that the circuit can control the frequency at 0 kHz~200 kHz, the phase shift range is 0~2π/5, the maximum voltage gain multiple is 3.3 times, and the control mode is three PWM hybrid switching control. Full article

This paper presents a hybrid control strategy for the LLC resonant converter in X-ray machines, addressing the limitations of voltage gain range under Pulse Frequency Modulation (PFM) and dynamic response under Phase Shift Modulation (PSM). The strategy employs an improved fruit fly optimization algorithm (IFOA) to optimize PI control and integrate Hybrid Phase-Shifted and Frequency-Modulated control. It dynamically adjusts the switching frequency and phase shift angle to maintain output stability and efficiency, ensuring optimal operation under rated conditions. A Matlab-based system simulation model confirmed the stability and accuracy of the IFOA in controlling the converter. Subsequent prototype testing validated the strategy’s effectiveness in reducing conduction losses, enhancing overall efficiency, and demonstrating practical feasibility and superiority. Full article

In this paper, a hybrid control method with adaptive phase-shifting modulation (PSM) and pulse-frequency modulation (PFM) is proposed to optimize the steady-state performance of an LLC resonant converter in wide voltage-gain range application. For the primary-side switches under the hybrid control method, zero-voltage switching (ZVS) performance is maintained over wide voltage-gain range and the turn-off loss is reduced; therefore, the converter reconciles wide voltage-gain range and high efficiency. Mode characteristics under different phase-shifting-angle-θ and switching-frequency-fs combinations is analyzed, and then the soft-switching characteristic is revealed. By introducing time domain analysis, the turn-on current of the primary-side switches is calculated, and thus the ZVS boundary of different θ and fs combinations is inferred. In addition, to acquire the optimum steady-state operation of the converter, the turn-off current is calculated; by making the converter work near to the minimum turn-off current operating point, the turn-off loss can be reduced greatly. With the principles of achieving ZVS performance and minimizing turn-off current, the phase-shifting angle θ of PSM is designed to be adaptive to the reference output voltage, no additional circuits are needed, and the two control degrees (θ and f_s) are simplified to one (f_s). The simulation and experiment are developed to verify the feasibility and effectiveness of the hybrid control method; the results show that ZVS performance is maintained at wide voltage-gain range and the turn-off current of the hybrid control method is reduced to that of the single PFM, and thus the turn-off loss is reduced. The efficiency comparison validates the fact that the hybrid control method has less power loss than single PSM and single PFM. Full article

LLC resonant converters are prone to generating a large inrush current during the start-up process, which will cause damage to the resonant elements and threaten the safe operation of the circuit. In this study, we investigate the soft-start method to suppress the inrush current of an LLC resonant converter. Based on the traditional frequency-decreasing method, we integrate PWM control to broaden the output voltage gain range during the start-up. Additionally, to ensure the smooth establishment of the output voltage, the controller performs the closed-loop control of the duty cycle and frequency in sequence based on the rate of output voltage rise. A prototype experiment based on STM32F334C8T6 is established to experimentally validate the presented soft start-up method. The experiment results indicate that the soft start-up method improves the start-up performance, reduces the maximum inrush current by 47.5% compared with that of the frequency-decreasing method, and builds up the output voltage quickly. The start-up process is smooth, which improves the reliability of the LLC resonant converter. Full article

This paper presents a 250 kHz bidirectional battery charger circuit using a GaN HEMT. The charger is subjected to a high-/low-side constant voltage at 200 V/20 V. The charger circuit is a hybrid of the LLC and flyback circuit topologies. Both the power output analysis and efficiency control of this circuit are simplified when the magnetization current is minimized using the low-resistance GaN HEMT. The switching frequency is controlled to match the series resonance in a way that is analogous to conventional LLC circuit controls, while the duty ratio that determines the power output and the dead time, which determines the zero voltage switching, is controlled in an analogous manner to the flyback circuit control. The charging and discharging modes were altered by applying a double-throw relay that changes the transformer turn ratio, which is different from conventional LLC designs using the switching frequency adjustment. A nominal turn ratio with N_p = 35 and N_s = 3.5 for a 200 V/20 V converter can only produce an internal series resonance with no current flowing in any charging direction. The proposed circuit using a transformer with multiple windings (N_p = 35, N_s,F = 4, and N_s,R = 3) was fabricated to deliver 125 W output power from the power grid battery to the vehicle battery in the forward (charging) mode and 90 W in the reverse (discharging) mode. The conversion efficiency was calculated to be as high as 97% in the forward mode and 95% in the reverse mode. The high conversion efficiency is due to the characteristics of the GaN HEMT, including low resistive and switching losses. The equations derived in this paper associate these losses with the series resonant frequency and power conversion rate, which highlight the advantages of using a GaN HEMT in this CLLC design. Full article

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. Full article

This paper proposes a photovoltaic (PV) string-level isolated DC–DC power optimizer with wide voltage range. A hybrid control scheme in which pulse frequency modulation (PFM) control and pulse width modulation (PWM) control are combined with a variable switching frequency is employed to regulate the wide PV voltage range. By adjusting the switching frequency in the above region during the PWM control process, the circulating current period can be eliminated and the turn-on period of the bidirectional switch of the dual-bridge LLC (DBLLC) resonant converter is reduced compared to that with a conventional PWM control scheme with a fixed switching frequency, resulting in better switching and conduction loss. Soft start-up control under a no-load condition is proposed to charge the DC-link electrolytic capacitor from 0 V. A laboratory prototype of a 6.25 kW DBLLC resonant converter with a transformer, including integrated resonant inductance, is built and tested in order to verify the performance and theoretical claims. Full article

A hybrid PWM converter is proposed and investigated to realize the benefits of wide zero-voltage switching (ZVS) operation, wide voltage input operation, and low circulating current for direct current (DC) wind power conversion and solar PV power conversion applications. Compared to the drawbacks of high freewheeling current and hard switching operation of active devices at the lagging-leg of conventional full bridge PWM converter, a three-leg PWM converter is studied to have wide input-voltage operation (120–600 V). For low input-voltage condition (120–270 V), two-leg full bridge converter with lower transformer turns ratio is activated to control load voltage. For high input-voltage case (270–600 V), PWM converter with higher transformer turns ratio is operated to regulate load voltage. The LLC resonant converter is connecting to the lagging-leg switches in order to achieve wide load range of soft switching turn-on operation. The high conduction losses at the freewheeling state on conventional full bridge converter are overcome by connecting the output voltage of resonant converter to the output rectified terminal of full bridge converter. Hence, a 5:1 (600–120 V) hybrid converter is realized to have less circulating current loss, wide input-voltage operation and wide soft switching characteristics. An 800 W prototype is set up and tested to validate the converter effectiveness. Full article

A new hybrid high-frequency link pulse-width modulation (PWM) converter using voltage balance capacitor and current balance magnetic coupling is proposed to realize low freewheeling current loss and wide load range of soft switching operation. Series-connected H-bridge converter is adopted for high voltage applications. In addition, a voltage balance capacitor and a current balance magnetic coupling core are employed for achieving voltage and current balance. To extend zero-voltage switching (ZVS) range of switches at lagging-leg of phase-shift PWM converter, soft switching LLC converter is linked to the lagging-leg of phase-shift PWM converter. Therefore, the wide ZVS load operation is realized in the presented hybrid converter. The other high freewheeling current disadvantage in conventional phase-shift PWM converter is improved by a snubber circuit used on low-voltage side. Thus, the primary current during the freewheeling state is decreased and close to zero. In addition, the conduction losses on primary-side components of studied converter are reduced. The secondary-sides of phase-shift PWM converter and LLC resonant converter are series-connected to achieve power transfer between input and output sides. Experimental results using a laboratory prototype are provided to demonstrate the effectiveness of the studied circuit and control algorithm. Full article