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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%.

In this paper, a new step-down resonant modular multilevel DC/DC converter is proposed for medium-voltage applications. The proposed converter is derived from the combination of the modular multilevel converter (MMC) and resonant converter with a passive auxiliary circuit. It can achieve zero-voltage-switching (ZVS) over a wide input voltage range for all switches compared with the conventional DC/DC MMC. Specifically, the asymmetric triangular compensating current provided by the passive auxiliary circuit is first introduced to flows into the bridge arms. Then, the current bias caused by the MMC structure is eliminated in the lower side switches of the submodules to achieve ZVS. Moreover, asymmetrical pulse-width modulation is applied to double the equivalent switching frequency and obtain a high step-down ratio. In this way, the resonant current is reduced, and the conversion efficiency is improved. Besides, the simulation and experimental results of the prototype are presented to demonstrate the viability of the proposed converter. The results convincingly verify the ability of the proposed converter to offer ZVS for all the switches over a wide input voltage range.

The conventional hard-switching converters suffer from the limitations like the upper limit on switching frequency, high electromagnetic interference (EMI), more switching losses, large size, increased weight and low efficiency. To overcome these limitations, resonant converters are popularly used in chargers of electric vehicles (EVs). However, the detailed classification of resonant converters used in EVs is not sufficiently discussed in the literature. The guideline to select a resonant converter based topology required to charge an EV on the basis of its rating is not mentioned. To fill this gap, this paper presents a state-of-art literature survey of various resonant converter based topologies used in chargers of EVs. This paper focuses on a detailed classification of resonant converters used in the second stage of EV chargers. Further, it provides a guideline to designers to choose a converter topology used in the first stage and the second stage of EV charger required based on wattage, unidirectional and bidirectional power flow. Depending on the number of reactive elements present in a given resonant converter topology, these are classified as two-element, three-element, and multi-element resonant converters. Depending upon the connection of inductive (L) and capacitive (C) elements with respect to transformer winding, these converter topologies are further categorized as series, parallel (two-elements), inductor–inductor–capacitor (LLC) (three-element) and capacitor–inductor–inductor–capacitor (CLLC) (Multi-elements). However, the LLC type resonant converters offer high efficiency, zero-voltage switching (ZVS turn-on, turn-off) and low voltage stress on switches and high power density. Therefore, this paper mainly focuses on LLC type resonant converter topology. In addition, various modulation schemes and control schemes for LLC, CLLC resonant converter along with control of active power and reactive power are discussed for vehicle-2-grid (V2G) mode of operation.

The paper presents a model-based design consideration of a series single-ended transistor resonant DC-DC converter with zero voltage switching (ZVS). A characteristic of this converter is that it is highly efficient due to the resonant nature of electromagnetic processes in the power circuit and operation with soft commutations. The manuscript proposes that the determination of some of the circuit elements of the device be carried out with optimization procedures based on the application of artificial intelligence techniques. For this purpose, an objective function is used with additional constraints, such as equalities and inequalities, for both the optimization parameters and the state variables. The use of the proposed method is justified in cases where there is no methodology for the design of the specific power electronic device or there is, but it is too complicated to apply. This is usually due to the increasing complexity of power circuits and their possible modes of operation and the inevitable assumptions and limitations in the analysis and the relevant methodologies based on that analysis. In this way, a natural combination, complement and development of classical design methods with innovative ones based on the application of artificial intelligence techniques is carried out.

Deadtime is a critical design target for soft switching dc/dc converters. On the one hand, the deadtime is necessary to ensure safety operation of the devices in one switching leg; on the other hand, enough deadtime is required to achieve zero voltage switching (ZVS) operation. Due to the complexity of LLC converters, traditionally, the deadtime selection is either based on engineering experience or inaccurate analysis of converter, which leads to an unoptimized deadtime. Specifically, a large deadtime will lead to the efficiency degradation due to the body diode conduction during deadtime. The ZVS operation cannot be completely achieved with a small deadtime, which will also degrade the converter efficiency. Therefore, there is a demand for the accurate analysis of deadtime effect on LLC converters. In this paper, an accurate and in-depth analysis of deadtime effect on LLC converter is performed with the aid of time domain analysis. But the proposed adaptive deadtime strategies can also be implemented based on the experiment or simulation results for those who do not have access to time domain analysis of LLC converters. Based on the analysis, novel adaptive deadtime strategies are proposed for LLC converter. Compared with traditional fixed deadtime strategy, around 1% efficiency improvement is achieved for a 125 W experimental prototype during the whole operating range.

In this paper, a novel soft switching push-pull LC resonant DC-DC converter for energy sources is presented. In a high step-up converter, the input of primary side possesses low voltage and high current, so the losses caused by the current account for most of the total power loss. At the same time, the high-voltage stress of the high-voltage output components on the secondary side is also a major problem. Therefore, a high-gain isolated push-pull converter with a secondary-side resonant circuit is proposed, so that the primary-side switches have zero voltage switching (ZVS) and the secondary-side diodes have zero current switching (ZCS). The push-pull structure can reduce the number of active switches, so that the total power loss on the primary side can be reduced. The converter has a resonant tank circuit arranged between the secondary side of isolation transformer and the high-voltage output rectification module. The high-voltage output rectifier module adopts a full-bridge architecture suitable for high-voltage coupling connection. The low-side power switching module adopts a push-pull architecture suitable for low-voltage and high-current applications. The resonant tank circuit uses an inductor–capacitor (LC) structure to improve the resonant tank circuit, which achieves soft switching during power transfer, increasing the efficiency of the converter and improving the electromagnetic compatibility. The main advantage of this technology is that the secondary-side leakage inductance of transformer and the resonant capacitance are connected in series to achieve ZVS for switches and ZCS for diodes. Finally, a prototype of a high-gain push-pull resonant converter was established. The converter was operated at a fixed switching frequency of 135 kHz and a duty cycle of approximately 0.5. The efficiency of the converter can reach 97.1% under experimental tests at an output voltage of 400 V and a rated output power of 500 W.

High step-down dc/dc converters are widely adopted in a variety of areas such as industrial, automotive, and telecommunication. The 48 V power delivery system becomes increasingly popular for powering high-current and low-voltage chips. The Series-Capacitor Buck (SCB) converter doubles the duty ratio and equalizes the current between the two phases. Hard switching has hindered efforts to reduce volume via increased switching frequency, although a monolithically integrated SCB converter has boosted current density. A Series-Resonator Buck (SRB) converter is realized by adding a resonant tank in series with the series capacitor Cs. All switches turn on at zero-voltage (ZVOn), and the low-side switches turn off at zero-current (ZCOff). The design of the SRB converter includes characterizing the design variables' impacts on the converter performances and designing low-loss resonant components as the series resonator. The Series-Resonator Buck converter belongs to the class of quasi-resonant converters. Its resonant frequency is higher than the switching frequency, and its waveforms are quasi-sinusoidal. This work develops a steady-state model of the SRB converter to calculate voltage gain, component peak voltages, and resonant inductor peak current. Each switching cycle is modeled based on the concept of generalized state-space averaging. The soft-switching condition of the high-side switches is derived. The ZVS condition depends on the normalized control variable and the load condition. The gain equation models the load-dependent characteristic and the peak gain boundary. The theoretical peak voltage gain of the SRB converter is smaller than the maximum gain of the SCB converter. A smaller normalized load condition results in a larger peak voltage gain of the SRB converter. The large-signal model of the SRB converter characterizes the low-frequency behavior of the low-pass filters with the series capacitor and the high-frequency behavior of the resonant elements. A design recommendation of t_off f_r

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.

In this paper, a novel and simplified model representing current-output phase-shift full-bridge DC-DC LCLC resonant converter in arc welding application is thoroughly presented. First, a switched m...

This article proposes an isolated high step-up resonant converter which is suitable for low power application. The proposed converter is simple in structure since it employs only one switch while not necessitating a clamp circuit. Also, the proposed converter is able to achieve ZCS turn- on and turn- off of the switch and ZCS turn- off of diodes using a parallel resonant circuit, resulting in high efficiency. Furthermore, the proposed converter has reduced transformer volume due to zero dc-offset current in transformer. Experimental results on 450-W prototype are provided to validate the proposed concept.

A CLL resonant converter with transformer–inductor-integrated magnetics is proposed. The CLL resonant converter is derived by placing the resonant inductor of an LLC resonant converter on the secondary side of the transformer. In comparison with an LLC resonant converter, the circulating current associated with the magnetizing current of the transformer is removed from the resonant inductor. More importantly, the phase difference between the flux in the magnetic cores of the transformer and the resonant inductor becomes larger. Therefore, the flux of the transformer and inductor can be cancelled with each other, resulting in a reduced loss and volume of the magnetic core. A novel structure is proposed to integrate the transformer and inductor with integrated winding structures. Detailed analysis and optimized design of the integrated transformer–inductor are presented. The effectiveness and feasibility of the proposed solutions are verified with simulation and experimental results.

Emerging wide bandgap devices are extending the operating frequency range and power handling capability of solid state based resonant power converter solutions. Presently, resonant power converters for industrial induction heating are using vacuum-tubes, achieving efficiencies of 50–60 %. By replacing the prevalent vacuum tube technology with a solid state based solution, the efficiency of the industrial induction heating processes is expected to be increased. A design of a Class-E Push-Pull resonance converter using silicon carbide MOSFETs is proposed. A prototype, operating at 2.5 MHz, has been built showing a proof-of-concept of the topology at 4 kVA, achieving an efficiency of 91.8 % with a representative industrial induction heating load.

An interleaved LCLC resonant converter with accurate current balancing performance over a wide input voltage range is proposed. Resonant tank components have slight tolerances that can unbalance load sharing between paralleled phases. Because of the steep voltage gain curve of the LCLC resonant tank, most conventional current sharing approaches might not be effective. In the proposed converter, the impedances of the resonant tanks are matched by a switch-controlled capacitor (SCC) that is in series with the resonant capacitor resulting in precise load current balancing between phases. The impact of various unbalanced situations on the interleaved LCLC resonant converter is investigated, a minimum operating angle for the SCC circuit is identified, the basic accuracy of SCC current balancing via digital control is investigated, and a control strategy is proposed to perform the current sharing. Computer simulation results and experimental results from a GaN-based prototype validate the performance of the proposed interleaved LCLC converter with precise current sharing over a wide input voltage range from 250 to 400 V. Using enhancement mode GaN and benefiting from the interleaving feature, a high conversion efficiency is achieved on a two-phase 1 kW LCLC converter with peak efficiency of 96.7%.

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.

This article proposes an ultrawide output range ${LLC}$ resonant converter based on adjustable turns ratio transformer and reconfigurable bridge. Due to the reconfiguration of the transformer by two four ${\bf -}$ quadrant switches, the transformer exhibits three different effective turns ratios, which correspond to three output ranges. Moreover, in case of lower output voltage, the primary side is reconfigured as a half-bridge to further extend the output voltage range. The design of resonant tank parameters is less constrained by the voltage gain requirement. The switching frequency range in each mode can be squeezed close to the resonant frequency, which contributes to an improved soft switch performance. The operational principles, design considerations, and mode transition are analyzed. A 4 A rated prototype that converts 390 V input to a 60–450 V output is designed and tested to validate the concept. A smooth mode transition is achieved without transient issues. The design prototype demonstrates 97.50 $\%$ peak efficiency and good overall efficiency performance over this ultrawide output range.

For applications with hold-up time requirements, the LCLC converter can achieve a wider voltage gain range than the LLC converter without degrading the normal operation efficiency due to its variable-magnetizing-inductor (VML) structure, which is formed by an inductor and an additional capacitor. However, the wide gain range achieved by the VML is at the expense of a high resonant voltage stress of the VML’s capacitor, which affects the converter volume/cost. Hence, to solve the contradiction between wide gain range and low capacitor voltage stress when the VML technique is adopted for hold-up operation, this paper proposes a novel C-LLC-LL converter. Specifically, the VML is arranged into a novel C-dual-LL structure. By relying on the unique output voltages relation between C-dual-LL’s two branches, the reduced voltage stress of the VML’s capacitor and the expanded voltage gain range can be simultaneously realized. To evaluate the feasibility of the proposed solution, a comprehensive analysis is conducted, and experimental results obtained from a 500-W C-LLC-LL prototype are also provided.

This article presents a reconfigurable voltage multiplying rectifier (RVMR) to improve the performance of an LLC resonant converter for wide output voltage applications. The RVMR can operate as voltage-doubler mode or voltage-quadrupler mode according to the primary switching strategy. Two operation modes split a wide output voltage range into two narrow ranges. Therefore, the RVMR enables the LLC resonant tank to be designed in a narrow output voltage range, which results in a narrow switching frequency range, high efficiency, and high power density. A smooth mode transition can be achieved by adopting a phase-shift control to general pulse frequency modulation control without any additional switch. The proposed RVMR LLC converter can improve its efficiency by 2.9% and reduce component volume by 26% compared to the conventional full-bridge LLC resonant converter. A 750-W prototype with 400 V input, 100–300 V output voltage, and 2.5 A max output current has been built and tested to verify the effectiveness of the proposed converter.

In this article, a resonant converter based on a series-parallel self-adjusting rectifier structure is proposed. By changing the driving signal of the switch, the converter has four working modes: full-bridge structure frequency modulation control, full-bridge structure phase-shift control, half-bridge structure frequency modulation control and half-bridge structure phase-shift control. The newly proposed resonant converter retains the soft switching characteristics of the LLC resonant converter and the mode switching can be completed only through software control without adding additional switches. Different modes correspond to different gain ranges. By changing the control strategy of the modes, the newly proposed converter can meet the design requirements of wide output. Finally, an experimental prototype with an input voltage of 25 V and an output voltage of 9 V to 35 V is built. The experimental results prove the correctness of the wide output characteristics of the converter proposed in the article and, in the four operating modes, it can realize zero-voltage turn-on of the active switch on the primary side and zero-current turn-off of the rectifier diode on the secondary side, which preserves the high efficiency of the resonant converter.

Refereed/Peer-reviewed This paper proposes a quasi-resonant step-up DC-DC converter to provide the DC-link voltage for piezoelectric transmitters (PZETs). The resonance not only provides a soft-switching condition for the converter switches, but also helps to decrease the converter element sizes for marine applications. Operation modes of the proposed converter are discussed. The current and voltage of the converter components are derived analytically, and hence the converter gain is obtained. The performance of the proposed high-step-up, high-power density converter is examined through a comprehensive simulation study. The simulation results demonstrate the soft-switching operation and short transient time required for the converter to reach the reference output voltage. The converter output voltage remains unchanged when an inverter with a passive filter is placed at its output while supplying the PZET. The proposed DC-DC converter is prototyped to validate the converter gain and soft-switching operation experimentally. The converter gain and soft-switching results in simulation are well matched with those of the experimental tests. The converter efficiency in three different switching frequencies is obtained experimentally. The power density of the proposed topology is determined via the designing of a printed circuit board. The experimental results demonstrate the appropriate gain and efficiency of the converter in the tested power range.

The active clamp flyback (ACF) converter is gradually becoming popular in the application field of low or medium output power range due to its advantage of soft switching and high conversion efficiency. An asymmetric half-bridge (AHB) flyback converter has been proposed in previous studies. The main advantages of the AHB flyback are the same number of components as the ACF converter and the soft switching technique. In this paper, an AHB flyback converter with constant off-time (COT) plus pulse frequency modulation (PFM) is proposed, so that the resonant time is not affected by the input voltage and load, and can achieve a wide range of zero voltage switching (ZVS) operating range. Compared to pulse width modulation (PWM), the PFM control with COT can make the system more stable. Finally, a prototype circuit with a specification input of 48 V to an output of 2.5 V/8 A is made for verification.

There are many different derivatives of the variable and fixed frequency switching control techniques used in the control of load resonant converters. In this study; among these techniques frequency modulation (FM), phase shift modulation (PSM) and pulse density modulation (PDM) are applied separately to series resonant converter (SRC). The techniques are examined and compared in many respects. An experimental setup was built, which consists of a 400W converter (with the input voltage of 200 V and the output voltage of 36V), a control circuit and a resistive load to verify the theoretical studies. The converter is controlled by FM, PSM and PDM separately for 120 kHz basic operating frequency and different output currents. The experimental results are compared in terms of efficiency, output voltage ripple, soft switching, switch voltage and ease of application and hardware. The comparison results are presented. It is observed that FM has better performance than the other two techniques in many aspects.

The LLC resonant converter is a popular, variable switching frequency dc--dc converter that may be controlled using two methods: charge and frequency control. In this article, the application of LLC resonant converters to input-parallel, output-parallel system is studied. In this respect, the models of output-port I-V characteristics and small-signal output impedance of the charge controlled LLC converter are proposed. In addition, a mathematical framework is developed for droop-based paralleled dc--dc systems. It distinctly identifies the output dc voltage and circulating current modes of stability, even in systems comprising of nonidentical converters. The developed model and the analytical framework are utilized to study the two modes of stability in droop-based parallel-connected LLC converters. It finds the circulating current mode instability for both the charge and frequency control methods, despite a stable output dc bus voltage. The instability inhibits fast response and high closed-loop bandwidth, eroding the reported advantages of the charge control method over frequency control. Further investigation into the output port I-V characteristics reveals the superiority of charge-controlled LLC converters in paralleled systems than the conventional frequency-controlled converters. A novel application of “common inner reference” based “automatic load sharing” strategy is developed and uniquely applied to the charge controlled system. In addition, the effects of component tolerance and communication delay on this strategy are also briefly explored. The theoretical output-port models and the stability analyses of parallel-connected LLC resonant converters are validated through experiments on a hardware prototype. Further, the supplementary video files illustrate the advantage of the charge control method over frequency control in such system. Finally, the proposed automatic load sharing strategy is validated in steady-state and through a step-change in load.

An interleaved LLC half-bridge series resonant converter having an integrated transformer includes a power supply, a magnetic core, a first converter, a second converter and an output load circuit. The magnetic core has first and second outer columns and a center column. The first converter includes a first switch circuit, a first resonant tank, a first transformer, and a first rectifier circuit. The first transformer is coupled to the first resonant tank and includes a first primary winding wound on the first outer column and a first secondary winding wound on the second outer column. The second converter includes a second switch circuit, a second resonant tank, a second transformer and a second rectifier circuit. The second transformer is coupled to the second resonant tank and includes a second primary winding wound on the first outer column and a second secondary winding wound on the second outer column.

This article presents a wind switched-reluctance generator (SRG) based microgrid (MG) with plug-in energy support mechanism. First, the wind SRG is properly designed and controlled. By applying the dynamic commutation shift and robust voltage control, it has the generated voltage with fast tracking and regulation responses under varying driven speed and load. Then, the MG common dc-bus voltage is established via a reconfigurable interleaved boost converter. The working cell number can be automatically changed to possess high efficiencies over wide power range. To enhance the voltage regulating characteristics, the feedback controller is augmented with an adaptive command feedforward controller and a robust tracking error cancellation controller. A bidirectional Capacitor-inductor-inductor-capacitor (CLLC) resonant converter and a bidirectional single-phase three-wire (1P3W) load inverter are constructed for powering loads and conducting grid-connected operation. As the wind energy input is deficient and even the wind turbine is halted, the inherent SRG followed boost converter can be reconfigured to form an interleaved boost switch-mode rectifier. The possible harvested single-phase ac and dc sources can be plugged into the MG for achieving energy support. The operation characteristics of the MG and the smooth transfer between all constituted power stages are demonstrated experimentally.

In this article, a reconfigurable nonisolated buck–boost (BB) integrated full-bridge series resonant converter (FBSRC) based light emitting diode (LED) driver is proposed for wide input voltage automotive lighting applications. The proposed LED driver is derived by the integration of BB operation with FBSRC. It can be reconfigured into three different resonant converter topologies such as BB integrated FBSRC, BB integrated half-bridge series resonant converter (BB-HBSRC), and conventional HBSRC and, hence, produces three levels of voltage gains. By transformation from one topology to other based on the input voltage range and with asymmetrical pulsewidth modulation control, it can operate for wide input voltage range while maintaining the soft switching. The main advantages of the proposed configuration are smooth transformation into three different topologies without any additional switching devices, no topological transitions within a switching cycle in steady state, use of simple proportional–integral controller, soft switching, and wider voltage gain with buck/boost operation. In addition, dimming control is also achieved using pulsewidth modulation technique. Detailed theoretical analysis of the proposed converter is presented. To verify the analysis and performance, a prototype of 22.7 W, 22.5 V LED driver is designed, simulated, and tested for a wide input voltage range of 18 to 120 V.

The input-parallel output-parallel (IPOP) connected converter system allows the use of a low-power converter module for high-power applications. However, mismatches in the IPOP circuit parameters cause uneven current sharing between the constituent modules, which makes the IPOP system unreliable for practical use. Different techniques have been proposed so far; however, they cause an increase in magnetic volume, cost, component count, and complexity of the IPOP system. In this article, a reliable and efficient magnetic integration technique is proposed for the current sharing requirements of the IPOP system based on LLC resonant converter modules. The proposed integrated magnetic current balancing transformer (ICBT) based IPOP LLC resonant converter modules ensures both the input current sharing and output current sharing between constituent LLC modules, under the open-loop condition quite effectively. The proposed ICBT is the resonant inductors of LLC resonant converter modules, coupled to perform the function of current balancing as well as generates enough leakage inductances for resonance operation, simultaneously. Thus, it can reduce the overall magnetic volume and improves power density of the IPOP LLC modules. Moreover, the current sharing performances of the proposed ICBT in both the steady-state and dynamic-state are analyzed based on the magnetic and electrical model. To validate the performance of the proposed ICBT based IPOP two LLC modules, a 2.6-kW hardware prototype was designed, fabricated, and tested successfully.

Synchronous rectification (SR) is the key to achieve high efficiency for high output current LLC resonant converters. Recently proposed methods for SR control do not offer a complete solution for industrial applications. The drain-to-source voltage sensing based methods cannot utilize the full benefits of SR due to the field-effect transistor (FET) package stray inductance. The adaptive SR control methods suffer from the variable on time and cannot reach the minimum power loss. This research aims for a high-performance SR control strategy that not only has good steady-state performance but also works reliably during transients. This article introduces an analytic–adaptive method for SR control that delivers accurate adjustment for both turn on and turn off moments of SR FETs below and above resonance. The proposed method takes into account the stray inductance of SR FETs; hence, it enables full efficiency gain of SR. The feasibility of implementation for the proposed method integrated with closed-loop control is experimentally validated on a 300 W 390/12 V half-bridge LLC resonant converter with 93.66% peak efficiency.

Common-mode (CM) noise cancellation method is an attractive approach to reduce the original CM noise in power converters, which helps to shrink the size of electromagnetic interference filter. Traditional CM noise cancellation method cancels the CM noise current by adding a branch consisted of a compensation voltage source and a compensation capacitor, which generates a cancellation current and nullifies the noise current. As the duality, the voltage cancellation method is also feasible for reducing the CM noise, which has not been investigated in dc–dc converters. In this article, a common-mode voltage cancellation (CMVC) method is proposed, which cancels the CM voltage of the converter by inserting compensation voltage source into the input power cord. The requirement for achieving CMVC is that the cancellation voltage and the parasitic capacitances in the circuit are matched. The applications of CMVC method in basic nonisolated and isolated dc–dc converters are presented, and the considerations for practical applications of this method are discussed. Finally, a buck converter and a half-bridge LLC resonant converter prototype are built, and the proposed method is verified by experiment, respectively.

LLC resonant converters have been widely used in many different industrial applications. Analysis and design methodologies have great effect on the converter performance. Accordingly, a complete step-by-step optimal design methodology based on time-domain analysis has been proposed for an LLC resonant converter in this article. The proposed design methodology is implemented under the worst operation condition, and the following considerations are included to obtain the suitable design area: operation mode; voltage stress for resonant capacitor; zero voltage switching operation for primary switches; and resonant tank root-mean-square current. Then, by finding all possible design candidates and comparing them based on the power loss model, the optimized design candidate can be found. Compared with the existing design methodologies, the proposed one has the advantages of high accuracy and small computation requirement, which makes it application in industry possible. Finally, a 192-W experimental prototype was built to validate the effectiveness of the proposed design methodology. In addition, a MATLAB graphical user interference program was built based on the proposed design methodology to visualize and facilitate the design process for engineers.

Recently, omnidirectional wireless power transfer (WPT) systems have been studied intensely, due to their improved flexibility as compared to their planar counterparts. The LCCL-LC resonant converter topology is selected due to its current source characteristics in this article. The system frequency is pushed to megahertz (MHz) to increase the spatial charging freedom. In a megahertz WPT system, the reactance of the full bridge rectifier can no longer be neglected; therefore, an analytical model of the full bridge rectifier input impedance is built. Furthermore, zero-voltage switching (ZVS) of the switching devices is essential in reducing the switching loss and noise in a megahertz system. A design methodology of the LCCL-LC circuit is proposed to achieve the ZVS operation in the case of one transmitter and one receiver. Then, the ZVS analysis is extended to the scenario of multiple transmitter coils and one receiver coil. Finally, a 6.78-MHz wireless charging system is built according to the proposed design methodology. Experimental results validate the accuracy of the ZVS analysis, and the ZVS operation is well achieved under different coupling and load conditions. The peak system efficiency of 82% at 5-W output power is achieved.

This letter proposes a voltage balancing method for series-connected power devices in an LLC resonant converter. Series connection of power devices can allow an LLC resonant converter to operate in high-voltage applications. One key problem of series-connected power devices is the voltage imbalance due to device parameter deviations and gate drive delays. To achieve voltage balancing, an auxiliary module (AM) is connected in parallel with each power device. Each AM consists of a capacitor and an auxiliary switch with an antiparallel diode. The AM operates as a clamping circuit and voltage among the series-connected power devices can be shared evenly if the AM capacitor voltages are well-balanced. The AM capacitors are charged during the asynchronous period of the series-connected power devices. The excess energy of AM capacitors can be released by the freewheeling current during dead time in an LLC converter. By assigning a pulsing gate signal to AMs with higher voltages in every switching cycle, the AM capacitor voltages can be balanced. The proposed method will not induce additional power loss and does not affect the normal operation of power devices. Experimental results are provided to verify the effectiveness and feasibility of the proposed method.

The concept of vehicle-to-grid has received considerable attentions over the past decade. Electric vehicle (EV), a common load of dc microgrids, can serve as distributed energy storage system to improve the reliability and stability of the dc microgrid, support integration of renewable energy source, and improve the overall system efficiency. In order to achieve bidirectional power transmission between the dc microgrid and EV, this article proposes a novel three-level CLLC resonant converter for off-board EV charger. By adding resonant CLLC components and by combining the working modes of the two three-level full bridges, the proposed converter adapts to the wide voltage range of EV, from 200 to 700 V. An equivalent circuit model with first harmonic approximation approach is established to analyze the frequency characteristics of the resonant converter. Moreover, an algorithm of working mode selection is proposed on the principle of minimum transformer RMS current. Finally, a 3.5 kW hardware prototype was built to verify the feasibility and the advantage of the three-level CLLC resonant converter. The efficiency of the proposed converter changes little over a wide output voltage range, and the flying capacitor voltages of the proposed converter are balanced well.

This letter proposes a high output voltage dc–dc converter topology with series stacked converter modules. To implement the proposed modular dc–dc converter structure, output voltage balancing of the modules and simplification of the control circuitry were considered the major design objectives. To achieve voltage balancing between the modules, we proposed a split-secondary transformer winding structure and distributed connections to the rectifier circuit blocks. Each transformer includes two secondary windings, with each wire pair connected to a different rectifier circuit. Consequently, one rectifier receives ac power simultaneously by sharing the secondary windings fed from two different transformers. The proposed method was verified using a modular LCC resonant converter, which is widely employed in high-voltage applications. As a result, the control circuit was simplified by using a single controller to regulate the total output voltage and by applying a compact sensing circuit referenced to the output voltage of the module placed at the lowest grounding point.

Here, a novel DC–DC converter based on a series‐resonant inverter and a multi‐stage current‐driven rectifier for the active balance charger of lithium‐ion series batteries is proposed. In the proposed topology, diodes are placed in a current‐driven half‐wave rectifier to regulate the voltage at the terminals of the batteries. The proposed balance charger has been compared with the Cockcroft–Walton voltage multiplier, DC–DC multilevel boost converter, chain structure using an additional capacitor, and series‐resonant voltage multiplier topologies. The cost of the proposed topology has not increased in comparison to other topologies and can be made modularly and more stages can be increased by adding capacitors and diodes. The experimental results are obtained from charging six lithium‐ion series batteries, of which one of them has been damaged. All topologies balance and charge the rest of the batteries despite the damaged battery. The results show that the proposed topology for the converter has reduced the average balancing and charging time by 40.77% and 13.33%, respectively, compared to other topologies. Therefore, the energy losses of the proposed topology are less than the other topologies. Also, the higher energy efficiency of the proposed topology is expected due to the faster‐balancing speed.

This article investigated two cases of impulse transformer location selection in the DC-DC type two-step resonant converter, which fully segregates processes of taking and transferring energy between the input and its load. The electromagnetic processes during energy taking/transferring were studied, including active and static losses in the converter elements. Based on the suggested analytical-numerical method, the criteria for selecting the impulse transformer optimal transformation ratio, from the system efficiency point of view, was derived. The proposed optimization technique can be applied to a wide variety of input and output parameters. References 3, Figures 7.