Bidirectional Resonant Converter Research Articles

Bidirectional Resonant Converter for DC Microgrid Applications

A bidirectional resonant converter is presented and verified in this paper for an electric vehicle battery charger/discharger system. The presented circuit can achieve forward and backward power operation, low switching losses on active devices, and wide output voltage operation. The circuit structure of the presented converter includes two resonant circuits on the primary and secondary sides of an isolated transformer. The frequency modulation approach is adopted to control the studied circuit. Owing to the resonant circuit characteristic, active devices for both forward (battery charge) and backward (battery discharge) power operation can be turned on at zero voltage switching. In order to implement a universal battery charger for different kinds of electric vehicle applications, the DC converter is demanded to have a wide output voltage range capability. The topology morphing between a full bridge resonant circuit and half bridge resonant circuit is selected to obtain high- and low-output voltage range operations so that the 200–500 V output voltage range is realized in the presented resonant converter. Compared to the conventional bidirectional converters, the proposed can be operated under a wide voltage range operation. In the end, a 1 kW laboratory prototype circuit is built, and experiments are provided to demonstrate the validity and performance of the presented bidirectional resonant converter.

Bidirectional Soft Switching Push–Pull Resonant Converter Over Wide Range of Battery Voltages

This article presents a bidirectional soft-switching push-pull resonant converter that is highly efficient over a wide range of battery voltages. It is derived by integrating a current-fed push-pull circuit and an active voltage doubler circuit with a bidirectional switch. The converter operates as a pulsewidth modulation (PWM) current-fed push-pull resonant-boost converter in the forward direction, but as a PWM half-bridge resonant converter in the backward direction. The most attractive feature of the proposed converter is that, by employing the bidirectional switch and corresponding switching modulation, it can achieve almost ZVS at turn-off instants under wide variations of battery voltages. Therefore, the proposed converter achieves high efficiency even during high-frequency operation. Moreover, no instantaneous reactive current flows through the circuit under wide variations of battery voltages and loads. Furthermore, the proposed bidirectional resonant converter has a high conversion ratio in both power flow directions without using a transformer that has high turns-ratio. The operating principles and characteristics of the proposed bidirectional resonant converter are presented in detail. Experimental results using a 1-kW prototype verified the feasibility and efficiency of the proposed converter.

Design of an Isolated Bidirectional Symmetric Resonant Converter

An isolated type bidirectional resonant converter is presented in this paper. Using a dual active bridge as the main topology and integrating symmetric resonant mechanism, the developed converter features an isolated type bidirectional resonant converter with bidirectional power conversion and electrical isolation capabilities to ensure working security and stability. The application of a symmetric resonant scheme enables the control range of input and output voltages to be widened and achieves soft switching during bidirectional power conversion. A converter design process covering all the bases is exhibited in this work. With the digital signal processor (DSP) TMS320F28335 being employed as the control core, the developed isolated bidirectional resonant converter can effectively handle the power conversion between the simulated 400 V DC grid and the energy storage battery ranging from 280 to 403 V. Based on a 1 kW capacity design, the test data reveal that the forward conversion efficiency from grid to battery can reach 93.25%, and the reverse conversion efficiency from battery to grid is as high as 94.60%.

Highly Efficient Bidirectional Current-Fed Resonant Converter Over a Wide Voltage Gain Range

In this article, we propose a current-fed bidirectional resonant converter that has minimal switching loss over a wide voltage gain range. The proposed bidirectional resonant converter employs a double current-fed structure at the low-voltage side and an active voltage doubler with a bidirectional switch at the high-voltage side.The converter operates as a pulsewidth-modulation (PWM) double current-fed resonant converter in the forward mode and a PWM half-bridge resonant converter in the backward mode. By incorporating a bidirectional switch across center nodes of the active voltage doubler, the converter achieves almost zero-voltage switching at the turn-off instant, thereby, incurring little switching loss at all active switches. The proposed topology exhibits a high conversion ratio with low transformer turns-ratio and a low current ripple at the low-voltage side. The operating principles and theoretical derivations of the converter are discussed in detail. The performance of the proposed bidirectional converter are verified using a prototype that has 48-72-V low voltage, 380-V high voltage, and 1-kW output power.

Bidirectional Resonant CLLC Charger for Wide Battery Voltage Range: Asymmetric Parameters Methodology

The CLLC bidirectional resonant converter has significant potential in battery chargers and dc microgrids, due to its bidirectional power transfer capability. To ensure uniform characteristics for bidirectional operation, secondary LC resonant tank components are usually designed to equal the primary LC components after reflection. This conventional design method is regarded as the symmetric design. It is used in applications where wide voltage regulation is not required, such as CLLC dc transformers. However, for bidirectional battery charger applications, the battery has a wide voltage range variation, and gain requirements during charging and discharging are different. These asymmetric characteristics could lead to undesirable large switching frequency range if a conventional symmetric CLLC design is employed. To address this issue, a detailed asymmetric parameters methodology (APM) is proposed in this article. It can design gain curves for charging and discharging modes separately. This enables overlapping of the switching frequency range for both modes, thereby reducing the bidirectional frequency range variation. It brings lower switching loss caused by excessive high frequency, and relieve the extra conduction loss and current stress of power switches as well. Finally, a detailed analysis of the proposed APM is provided and validated with simulations and experiments.

SiC-Based Bidirectional Multilevel High-Voltage Gain Switched-Capacitor Resonant Converter with Improved Efficiency

This paper presents the research results of the bidirectional multilevel resonant switched capacitor converter (MRSCC). The converter can achieve a high voltage ratio in multilevel topology, which limits the voltage stress on switches and is able to operate with high power efficiency. The converter can be applied as an interconnector between DC voltage systems used for various applications. This paper presents a method that significantly improves the efficiency of the MSRCC through topology modification. Furthermore, the feasibility of the converter was demonstrated with the use of SiC and Si MOSFET switches, together with suitable passive components. It was demonstrated that the proposed modification of the topology makes the converter very efficient in SiC-based ones and can significantly improve the efficiency of Si MOSFET converters. The series of test results of the SiC-based converter is a novel aspect presented in this paper and shows promising achievements of efficiency. The results were obtained from the laboratory setup of 5 kW and 0.5/2 kV MRSCC. To demonstrate the bidirectional operation of the converter, a back-to-back setup (0.5/2/0.5 kV) was used. It also demonstrates that such a high-voltage gain converter can be accurately tested with the use of laboratory equipment with a typical voltage range.

Removal of Instantaneous Reactive Power From High-Conversion-Ratio Bidirectional Resonant Converter With Balanced Capacitor Voltage

This article presents bidirectional operation of a resonant converter that features high step-up/down capability, high efficiency, and balanced capacitor voltage. When transferring power in the backward direction, the original converter may suffer from significant reverse current due to large fluctuation of the resonant capacitor voltage. By applying the right amount of phase in the pulsewidth-modulation signal, we can remove the instantaneous reactive power generated during the backward operation. We first derive the nominal duty ratio of the secondary side in terms of the backward voltage gain, then derive the threshold load level, above which the instantaneous reactive power appears, and compute the required amount of phase shift to remove it. We also analyze the sensitivity of the required amount of phase with regard to resonant tank parameters. A 400-W prototype converter has been built to demonstrate the performance of the proposed converter.

Bidirectional Resonant DC-DC Converter for Microgrid applications

This paper presents a non-isolated bidirectional soft-switching dc-dc converter for DC microgrid energy storage synchronization. To assist the soft switching of switches and diodes, the LCL resonant circuit is applied and an input end half-bridge boost converter is enforced. Using the voltage doubler circuit introduced on the output side, a voltage gain of 2X is achieved. Through the non-isolated circuit, the total voltage gain is obtained. The capacitive divider halves the voltage on the greater hand. The circuit performs a high frequency ripple of low output voltage. Diodes guarantee zero voltage Turn ON for switches and zero current turn ON and turn OFF during buck / boost operation Although no internal snubber circuits are available, the circuit ensures low voltage stress across semiconductor systems.

A bidirectional resonant converter based on wide input range and high efficiency for photovoltaic application

<span lang="EN-US">This work highlights a modular power conditioning system (PCS) in photovoltaic (PV) applications which consists with a DC-DC converter. The converter is able to regulate and amplify the input DC voltage produced by the PV panal. The implementation of Mosfet as bidirectional switch on the converter yields greater conversion ratio and better voltage regulation than a conventional DC-DC step up converter and PWM resonant converter. It also reduces the switching losses on the output DC voltage of the converter, as the MOSFET switches on primary winding of converter switch on under ZVS conditions. The proposed resonant converter has been designed, with the modification of series resonant converter and PWM boost converter that utilizes the high frequency of AC bidirectional switch to eliminate the weaknesses of used converters. The topology of the proposed converter includes the mode of operations, designing procedure and components selection of the new converter elements. This topology provides a DC output voltage to the inverter at range of about 120Vac-208 Vac. </span>

Reactive Power Elimination for High Conversion-Ratio Bidirectional Resonant Converter

This article presents a reactive power elimination method for high conversion-ratio bidirectional resonant converter with ripple-free current at the low voltage side. When transferring power in the backward mode operation, the converter with heavy loads suffers from significant reverse current that generates reactive power. By adjusting the right amount of phase of the pulsewidth modulation signals, we can eliminate the reverse current and the corresponding reactive power. We derive the voltage gain, calculate the right amount of phase, and identify the load threshold, above which the reverse current appears. We use a 600 W converter prototype to demonstrate the performance of the proposed converter.

High-Frequency Bidirectional Resonant Converter for High Conversion Ratio and Variable Load Operation

Applying RF circuit design techniques to dc–dc resonant converters has enabled switching frequencies well beyond 10 MHz, leading to higher power densities and faster transient response. Synchronous rectification is advantageous for low-voltage high-power applications but is challenging to implement in a high-frequency (HF) dc–dc converter. This article proposes an HF/very HF (VHF) resonant converter structure in which the rectifier and the inverter switches can be driven with the same gate signal. The presented structure enables efficient bidirectional power delivery in the HF/VHF range for applications that require a large voltage conversion ratio. A 64-MHz, 12-W, 36–12-V prototype converter verifies the operation of the structure. This article further explores an interleaved architecture of the same circuit to improve efficiency and transient performance. Finally, a 13.56-MHz 210–30-V prototype converter with 90% peak efficiency at 200 W demonstrates the advantages of the interleaved architecture.

High-Frequency PCB Winding Transformer With Integrated Inductors for a Bi-Directional Resonant Converter

The momentum toward high power density high-efficiency power converters continues unabated. The key to reducing the size of power converters is high-frequency operation and the bottleneck is the magnetic components. With the emerging widebandgap devices, the switching frequency of power converters increases significantly, to hundreds of kilohertz, which provides us the opportunity to adopt printed circuit board (PCB) winding planar magnetics. Compared with the conventional litz-wire-based magnetics, planar magnetics can not only effectively reduce the converter size, but also offer improved reliability through automated manufacturing process with repeatable parasitics. Another way to reduce the number of magnetic components and shrink the size of power converters is through the magnetic integration. In this paper, a novel PCB winding based magnetic structure is proposed to integrate both inductor and transformer into one component. In this structure, the inductor value can be easily controlled by changing the cross-sectional area of the core or the length of the air gap. A 6.6-kW 500-kHz CLLC resonant converter prototype with 98% efficiency and 130-W/in3 (8 kW/L) power density is built to verify the feasibility of the proposed PCB winding based magnetic structure.

Double Voltage Rectification Modulation for Bidirectional DC/DC Resonant Converters for Wide Voltage Range Operation

It is difficult to achieve wide voltage range for full-bridge-based bidirectional resonant dc/dc converter due to the large resonant current caused by the small magnetizing inductance. A half-bridge modulation was proposed to extend the output voltage range by offering an additional step-down voltage step of 0.5 normalized gain. But in backward operation, the converter cannot provide the two-times step-up voltage gain to match the forward 0.5 step-down voltage gain, which disables the converter to truly work bidirectionally with large voltage range. This paper proposes a double voltage rectification (DVR) modulation on the rectification side to achieve twice the voltage gain for the backward direction to effectively widen the operation voltage range, which matches the ratio of the two dc port voltages where the half-bridge modulation is used in the forward direction. In the DVR modulation, the operation of the input-side resonant tank is the same as that of the conventional modulation. The switches on the input side still turn on with zero-voltage switching (ZVS), and the body diodes on the rectification side still turn off with zero-current switching. Moreover, the turning on and off of the mosfets on the rectification side are also ZVS, which causes no additional losses and guarantees high-frequency operation. The rotational operation of the rectification-side switches improves the thermal balance condition, enlarging the power capacity and improving the reliability of the converter. A smooth transition method between the two modulations is also proposed, which still guarantees ZVS turning on for the rectification-side switches. The symmetrical CLLLC resonant converter is taken as an example to illustrate the operation principle and features of the proposed modulation. And other bidirectional resonant converters for the DVR modulation are also presented. Finally, a 3-kW bidirectional CLLLC resonant converter prototype with 100-kHz resonant frequency is built to verify the proposed modulation.

Bidirectional DC resonant converter with magnetic-coupling current balance

ABSTRACTThis paper studied a bidirectional frequency-control dc converter with magnetic-coupling to achieve 1) current balance on low voltage side, 2) low switching losses on power devices, and 3) bidirectional power transfer capability. The developed circuit is basically constructed by half-bridge circuits on input and output sides. LLC resonant tank with frequency-control is used to obtain low switching losses on power devices. Magnetic-coupling element is used to achieve current balance on low voltage side. Synchronous rectifiers are employed on low voltage and high current side to decrease power losses and increase circuit efficiency. The effectiveness of the studied circuit is verified from a 720 W laboratory prototype.

Analysis and Design of a 1-MHz Bidirectional Multi-CLLC Resonant DC–DC Converter With GaN Devices

A 1-MHz half-bridge high-gain multi- CLLC bidirectional resonant converter with (gallium nitride) GaN field effect transistor (FETs) and integrated planar magnetics is proposed in this paper. It presents excellent gain characteristic and high power density, which is very suitable for a distributed energy storage system. The operation principle, topology features, and parameter design method of the converter are discussed in detail. The improved winding method of integrated planar magnetics is also elaborated. And then, a 400-W prototype is established and the corresponding experiments are carried out in 1 MHz. Finally, the accuracy and correctness of the theory are verified and the highest efficiency of the converter can reach 94.3%.

Family of isolated bidirectional resonant converters with duty‐cycle control and automatic power flow transition

This study proposes a family of duty-cycle controlled bidirectional resonant converters and its uniform modulation schemes. This family of converters is composed of a current-fed stage, a transformer with LC resonant tank and a voltage-fed stage. Therefore, high-voltage gain and low-current ripple can be achieved. With the proposed uniform modulation schemes, automatic forward and backward mode transition is realised. Furthermore, the voltage gain is only determined by the duty cycle, independent of load and power flow direction, thus simple control can be adopted and voltage can be regulated in a wide range. Zero-voltage switching of all switches can be achieved over a wide load range. The operation principle and analysis of one of the converters are presented as an example. Design considerations are provided. Experimental results are shown to verify the theoretical analysis.

Bidirectional Resonant Converter with Half-Bridge Circuits: Analysis, Design, and Implementation

A soft-switching dc–dc converter with bidirectional power flow capability is studied in this paper for energy storage units or electric vehicle applications. The circuit topology of the studied converter is constructed using a dual half-bridge circuit with split capacitors. A series resonant tank with frequency control modulation is employed in the proposed circuit to realize the soft switching characteristics of active devices. Synchronous-rectifier-based Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFETs) are used on the low-voltage side to lessen conduction loss on the power semiconductors. The benefits of the studied circuit are bidirectional power flow capability, high efficiency, low switching loss, and simple circuit structure. The achievability of the developed converter is demonstrated from test results with a scaled-down laboratory prototype.

A Bidirectional Resonant DC–DC Converter Suitable for Wide Voltage Gain Range

This paper proposes a new bidirectional resonant dc-dc converter suitable for wide voltage gain range applications (e.g., energy storage systems). The proposed converter overcomes the narrow voltage gain range of conventional resonant dc-dc converters, and meanwhile achieves high efficiency throughout the wide range of operation voltage. It is achieved by configuring a full-bridge mode and a half-bridge mode operation during each switching cycle. A fixed-frequency phase-shift control scheme is proposed and the normalized voltage gain can be always from 0.5 to 1, regardless of the load. The transformer root-mean-square (rms) currents in both the forward and reverse power flow directions have a small variation with respect to the voltage gain, which is beneficial to the conduction losses reduction throughout a wide voltage range. Moreover, the power devices are soft-switched for minimum switching losses. The operation principles and characteristics of the proposed converter are firstly analyzed in this paper. Then the analytical solutions for the voltage gain, soft-switching, and rms currents are derived, which facilitates the parameters design and optimization. Finally, the proposed topology and analysis are verified with experimental results obtained from a 1-kW converter prototype.

Modeling and Controller Design of a Bidirectional Resonant Converter Battery Charger

In this paper, a controller design methodology is proposed for a CLLLC -type bidirectional resonant converter. The soft switching of all devices in this topology and the very high operating frequency lead to increased overall system efficiency. However, the dynamic nature of this converter is highly dependent on loading conditions, which proves challenging when designing the voltage and current closed-loop controllers. System instability is mainly due to the high-Q resonant peaking, which is observed in the open-loop bode-plots. In this paper, the controller design methodology is proposed, which accounts for the dynamics behavior due to load variations. The controller stability will be evaluated against the entire range of operating switching frequency. Both battery charging and regeneration modes will be described and analyzed. The focal contribution of this paper will focus on defining the worst operating scenarios for the converter using system-level modeling and analysis. In addition, the controller will be defined based on these operating points. To validate and verify the controller design methodology proposed, a 3.5-kW converter is designed with the appropriate output voltage and current loop controllers. The step response verified a stable system designed and thus proving the proposed controller design methodology.

Bidirectional Resonant DC-DC converter for Microgrid Applications

<p>This paper proposes a non-isolated soft-switching bidirectional dc/dc converter for interfacing energy storage in DC microgrid. The proposed converter employs a half-bridge boost converter at input port followed by a LCC resonant tank to assist in soft-switching of switches and diodes, and finally a voltage doubler circuit at the output port to enhance the voltage gain by two times. The LCC resonant circuit also adds a suitable voltage gain to the converter. Therefore, overall high voltage gain of the converter is obtained without a transformer or large number of multiplier circuit. For operation in buck mode, the high side voltage is divided by half with capacitive divider to gain higher step-down ratio. The converter is operated at high frequency to obtain low output voltage ripple, reduced magnetics and filters. Zero voltage turn-on is achieved for all switches and zero current turn-on and turn-off is achieved for all diodes in both modes i.e., buck/boost operation. Voltage stress across switches and diode is clamped naturally without external snubber circuit. An experimental prototype has been designed, built and tested in the laboratory to verify the performance of the proposed converter.</p>