Series Resonant DC-DC Converter Research Articles

Experimental investigation of bidirectional series resonant DC-DC converter in different operating modes

This paper presents a study of bidirectional series resonant DC/DC converter. The main operating modes of the converter with phase-shift control technique are observed. An experimental survey with a laboratory model of such type of converter working over the resonant frequency is made. The functionality of the studied device operating in a wide area of loading is demonstrated with waveforms of the main parameters. The conducted measurements are used to build the experimental output characteristics of the converter. A similarity of the experimental results with the theoretical are denoted, and the ability to achieve current source characteristics for the whole range of loading is proven. The possibility of the studied converter for operation both in forward and reverse modes of energy flow is proved, which positions the device as an appropriate variant for implementation in the storage system control area.

Self-Healing Photovoltaic Microconverter With Zero Redundancy and Accurate Low-Cost Fault Detection

This paper studies a zero-redundancy fault-tolerant dc-dc series resonant converter (ZR-SRC) for residential photovoltaic (PV) applications. This converter can handle faulty conditions on-the-fly using topology morphing control without increasing the number of components. Furthermore, it can withstand a single fault in both input and output bridge semiconductors, i. e., up to two semiconductor faults. The proposed dc-dc converter could increase the availability of residential photovoltaic-powered dc microgrids. Comprehensive fault diagnosis and localization algorithms are proposed for MOSFETs on both sides of the ZR-SRC. The paper proposes а short-circuit fault (SCF) detection in the input-side MOSFETs using the existing PV voltage measurements, decreasing the converter cost and size. The open-circuit fault (OCF) in the output-side MOSFETs is detected by sensing the voltage of the bottom two switches sharing the same ground with the dc bus. In addition, the post-fault operation of the converter is thoroughly analyzed. Recommendations for the PV power clipping are given to ensure the safe operation of the converter after a fault. A 300 W experimental setup is built to demonstrate the feasibility and performance of the proposed fault-tolerant converter.

Zero-Backflow Power Control Scheme of Dual Bridge Series Resonant DC–DC Converters With High-Accuracy Time Domain Modeling

In the fundamental harmonic approximation (FHA) modelling of dual bridge series resonant DC-DC converters (DBSRCs), the approximation error of the FHA model will lead to low accuracy of optimization schemes, which will reduce the efficiency of DBSRCs. In this paper, firstly, the time domain analysis (TDA) modelling of the DBSRC is adopted, which can describe the characteristics of the DBSRC accurately. Secondly, the extended phase shift (EPS) modulation based on the TDA modelling is discussed, and the backflow power model with the TDA of the DBSRC is developed. On this basis, a zero-backflow power optimization scheme is proposed. In addition, the effects of dead time are analyzed and the compensation method is proposed. The proposed backflow power optimization method with dead time compensation can achieve zero-backflow power and improve the efficiency of the DBSRC. Especially, the proposed method with TDA modelling is more excellent when DBSRC operates in wide voltage range conditions. Finally, a comprehensive experiment comparison of DBSRC under the minimum current trajectory (MCT) with FHA modelling and the proposed method with TDA modelling is discussed. The experimental results have verified the effectiveness of the proposed scheme.

Single-Phase Grid-Forming Strategy with Power Decoupling Implementation for Electrolytic-Capacitor-Free EV Smart Battery Charger

Smart Battery Chargers (SBCs) implementing grid-forming (GFM) control strategies are a promising solution to provide voltage and frequency support, increasing the grid reliability. Typically, GFM studies consider inverters with high DC-link capacitance. Therefore, there is a research gap in two-stage DC-AC converters with small DC-link capacitance implementing GFM strategies. This article proposes a novel approach to implement a GFM control strategy along with active power decoupling (APD) in an isolated, single-phase, electrolytic-capacitor-free two-stage DC-AC structure. The structure is composed of a voltage source inverter (VSI), DC-linked by film capacitors, with a dual-active-bridge series-resonant (DABSR) DC-DC converter. High DC-link ripple is allowed and managed by the APD. Hence, electrolytic capacitors are avoided, increasing the converter lifetime. In the proposed approach, the VSI implements the GFM strategy, operating in the four quadrants of the active and reactive power plane. However, the DABSR allows galvanic isolation, average DC-link voltage control, and suppression of the low-frequency ripple on the battery current, minimizing the impact in the battery lifetime. Design criteria are given for the DC-link voltage controller, active-reactive power controllers, inner inverter controllers, and APD technique. The control strategy is validated for vehicle-to-grid and stand-alone vehicle-to-home applications, using hardware-in-the-loop for a 2kW test setup.

High-Efficiency Quad-Mode Parallel PV Power Optimizer for DC Microgrids

The paper introduces a new parallel photovoltaic (PV) power optimizer intended for direct integration of PV modules into a dc bus or microgrid. The topology is derived from a typical galvanically isolated buck series resonant dc-dc converter (SRC) to the buck-boost SRC recently proven as a parallel PV power optimizer (PO). By applying the topology morphing control, this two-mode converter is extended to the quad-mode parallel PV PO. Its operation modes defined by changing modulation of switches are detailed, and gain expressions are provided. The proposed concept provides enhanced performance in the region where global power maximum could occur due to partial shading. Accordingly, a significant efficiency improvement is achieved at voltages below the nominal value that targets the most probable PV module operating point without shading. An experimental prototype was built to demonstrate the benefits of the proposed quad-mode PV PO and compare it to the existing two-mode buck-boost SRC. Thermal stress analysis is supported with power loss breakdown calculations to demonstrate component thermal stresses in critical operating points.

Soft Switched Current Fed Dual Active Bridge Isolated Bidirectional Series Resonant DC-DC Converter for Energy Storage Applications

This paper proposes a high-frequency isolated current-fed dual active bridge bidirectional DC–DC series resonant converter with an inductive filter for energy storage applications, and a steady-state analysis of the converter is carried out. The performance of the proposed converter has been compared with a voltage-fed converter with a capacitive output filter. The proposed converter topology is operated in continuous conduction mode with zero circulation current (ZCC), less current stress and high efficiency. The conditions required for soft switching are determined, and it is found that the converter operates with soft switching of all switches for a wide variation in load and input voltage without loss of duty cycle. Current-fed converters are suitable for low-voltage renewable energy applications because of their inherent boosting capability. An inductive output filter is chosen to make the output current ideal for fast charging and high-power-density battery storage applications. Simple single-phase shift control is used to control the switches. The performance of the converter is studied using PSIM simulation software. These results are confirmed by an experiment on a 135 W converter on an OPAL-RT real-time simulator. The maximum efficiency obtained in simulation is 96.31%. Simulation and theoretical results are given in the comparison table for both forward and reverse modes of operation. A breakdown of the losses of this converter is also presented.

Design and Control of Series Resonant DC-DC Converter for DC Wind Turbines

High power reliability and high energy density are always in demand, and this is driving the evolution of power conversion technologies. People have begun to examine the potential positions of dc systems in both current and future power equipment due to the rise in the use of renewable energy and the implementation of energy storage in recent decades. Because of its efficiency and power density, dc voltage representation has found use in a wide range of fields, including data centres, the aerospace industry, and dc micro-grids. Resonant DC-DC converters, with their gentle switching and minimal EMI, provide a promising solution to these problems. Finding and examining the various modes of operation of the converter while employing the pulse-removal approach is the primary objective of this study. The new method of operation utilises variable frequency and variable phase displacement in sub-resonant mode, which promises to reduce the transformer size while also facilitating the soft-switching change of the insulated gate bipolar transistors (IGBTs) and line frequency diodes on the rectifier side. The pulse elimination approach, a revolutionary mode of operation for the converter, involves phase and frequency shift modulation at varying rates. Using the results of MATLAB/SIMULINK simulations, the suggested control technique may be utilised to establish the baseline switching function configuration necessary to attain high power efficiency.

Design and Control of Series Resonant DC-DC Converter for DC Wind Turbines

High power reliability and high energy density are always in demand, and this is driving the evolution of power conversion technologies. People have begun to examine the potential positions of dc systems in both current and future power equipment due to the rise in the use of renewable energy and the implementation of energy storage in recent decades. Because of its efficiency and power density, dc voltage representation has found use in a wide range of fields, including data centres, the aerospace industry, and dc micro-grids. Resonant DC-DC converters, with their gentle switching and minimal EMI, provide a promising solution to these problems. Finding and examining the various modes of operation of the converter while employing the pulse-removal approach is the primary objective of this study. The new method of operation utilises variable frequency and variable phase displacement in sub-resonant mode, which promises to reduce the transformer size while also facilitating the soft-switching change of the insulated gate bipolar transistors (IGBTs) and line frequency diodes on the rectifier side. The pulse elimination approach, a revolutionary mode of operation for the converter, involves phase and frequency shift modulation at varying rates. Using the results of MATLAB/SIMULINK simulations, the suggested control technique may be utilised to establish the baseline switching function configuration necessary to attain high power efficiency.

Characteristics Analysis and Design of a Resonant dc–dc Converter With ZCS and Short-Circuit Fault Current Limiting Capability

The series resonant dc-dc converter (SRC) which features zero current switching (ZCS) and open-loop control is widely used for providing galvanic isolation and voltage scaling. However, output short-circuit (OSC) fault is a challenge for SRC because it will cause dramatically high current in the low-impedance resonant tank. To address this issue, a resonant full-bridge dc-dc converter only using small dc-side capacitors to resonate with the resonant inductor Lr is proposed. Under normal condition, ZCS can be achieved. When OSC fault occurs, the output dc-side capacitor can be bypassed by the anti-paralleled diodes of the full bridge and the resonant current can be limited automatically by the resonant inductor Lr without additional control. The operation principle of the converter under normal and faulty condition is analyzed. Based on these analyses, the switching frequency to achieve ZCS is designed. The resonant inductor Lr and dc-side resonant capacitors Cr design considerations are provided. The ZCS characteristics and the current limiting capability of the converter are verified on an experimental prototype.

Transient Modulation for the Step-Load-Change Process in a Dual-Bridge Series Resonant Converter

A phase-shifted dual-bridge series resonant DC-DC converter (DBSRC) is a competitive candidate for applications of an energy storage system. At the request of a step-load-change command such as the start-up and power-level change, the converter may suffer from large-amplitude transient oscillations due to improper transient modulation. Furthermore, the DC bias current and overshoot current/voltage in the resonant tank and transformer caused by oscillations may result in transformer saturation and poor dynamic performance. To solve these problems, two fast transient modulation (FTM) methods are proposed in this paper. First, based on the steady-state analysis of the converter with phase-shift control, the current and voltage trajectory of the resonant capacitor can be obtained. Then, the detailed principles of two FTM methods are explained for achieving a smooth transition. Through the adjustment of the durations of the adjacent switching intervals temporarily, the transient trajectory can be predicted and is expected to match the destination trajectory within one switching period. Consequently, the proposed FTM methods enable the converter to move from one steady state to another instantly and the step-load-change transition can be an overshoot-free procedure. Finally, both simulation and experimental tests prove that the two modulation methods can effectively eliminate DC bias current and overshoot current/voltage in the DBSRC transient process and obtain a fast transient response.

Grid-connected photovoltaic system with power smoothing

This paper analyzes the power smoothing of grid-connected photovoltaic (PV) systems under fast irradiance changes. The analyzed converter is composed of a triple active bridge series-resonant (TABSR) DC-DC converter cascaded with a voltage source inverter (VSI). Two controlled variables are considered: battery current and the PV voltage. The TABSR DC-DC converter is modeled as controlled current sources for the battery and the PV ports. The ramp rate (RR) control algorithm is used to smooth the PV output power profile enhancing the power delivered to the grid. Four ramp rates (10%, 5%, 2% and 1%) are used to evaluate the RR control algorithm and the battery state of charge (SOC) response. Therefore, the battery can be sized appropriately. Real data for irradiance and temperature in an overcast day is used to verify the effectiveness of the proposed system.

Reliability Evaluation of Isolated Buck-Boost DC-DC Series Resonant Converter

This paper investigates the reliability of an isolated buck-boost DC-DC converter (IBBC) based on the configuration of a series resonant converter (SRC). Two approaches are employed to predict the IBBC reliability, which are based on the MIL-HDBK-217F handbook and FIDES guide. The latter approach can take into account how the failure rate of the converter components based on the physics of failure is influenced by a varying yearly mission profile. To do this, the thermal loading of each IBBC component is obtained, taking into account the photovoltaic (PV) mission profile of the solar irradiance and ambient temperature. In such a case, the PV module is operating at the maximum power point (MPP) and the IBBC transfers this power into the DC microgrid (MG). Second, the component-level failure rate is calculated with both reliability assessment approaches, to evaluate the converter-level failure rate. Therefore, the converter reliability can be defined while taking the serial reliability connection of the converter components into account. The reliability analysis is carried out using a cloud Python engine installed and running in a Google Colaboratory notebook. The results indicate that the primary semiconductors are the most vulnerable component in the IBBC. The <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$B_{10}$</tex-math></inline-formula> lifetime of the case-study IBBC calculated using the MIL-HDBK-217F and FIDES approaches is 14.80 and 23.20 years, respectively. This indicates that, when compared to the methodology from the MIL-HDBK-217F handbook, the approach from the FIDES guide can provide a more accurate prediction for the IBBC lifespan considering the real field mission profile.

Variable Frequency Phase-Shift Modulation Symmetrical Series-Resonant Bidirectional DC-DC Converter—Analysis and Verification of ZVS Performance and Reactive Power Minimization—

Variable Frequency Phase-Shift Modulation Symmetrical Series-Resonant Bidirectional DC-DC Converter—Analysis and Verification of ZVS Performance and Reactive Power Minimization—

Topology-Level Power Decoupling Three-Port Isolated Current-Fed Resonant DC-DC Converter

In order to solve the problems of existing three-port isolated dc-dc converter such as power decoupling and the nonzero instantaneous power of the standby port, a three-port isolated bidirectional current-fed series-resonant dc-dc converter is proposed in this article. The operational principle and general transfer power expressions of various ports are analyzed with the duty-cycle plus phase-shift control. Then, the power decoupling at the topology level is realized by setting the switching frequency equal to the resonant frequency of the resonant tank on the high-voltage side; thus, the transfer power of the two ports on the low-voltage sides can be controlled independently. Moreover, it is proved that the proposed converter realizes the zero instantaneous power of the standby port. On this basis, an optimized modulation strategy by taking the minimum root mean square value of the resonant current as the objective function is presented. The exact relationship between the desired transfer power and various phase shifts is accordingly obtained. The detailed experimental results verify the correctness of the proposed converter and corresponding modulation strategy.

Wide Range Series Resonant DC-DC Converter with a Reduced Component Count and Capacitor Voltage Stress for Distributed Generation

This paper proposes a galvanically isolated dc-dc converter that can regulate the input voltage in a wide range. It is based on the series resonance dc-dc converter (SRC) topology and a novel boost rectifier. The proposed topology has a smaller number of semiconductors than its SRC-based existing topologies employing an ac-switch in the boost rectifier. The proposed dc-dc converter comprises only two diodes and one switch at the output side, while the existing solutions use two switches and two diodes to step up the voltage. The proposed converter boosts the input voltage within a single boosting interval in the positive half-cycle of the switching period. In addition, the resonant current in the negative half-cycle is sinusoidal, which could enhance the converter efficiency. The resonant capacitor voltage is clamped at the level of the output voltage. Therefore, the voltage stress of the capacitor could significantly reduce at various input voltage and power levels. This makes it perfect for distributed generation applications such as photovoltaics with wide variations of input voltage and power. The converter operates at the fixed switching frequency close to the resonance frequency to obtain the maximum efficiency at the nominal input voltage. The zero-voltage switching (ZVS) feature is achieved in the primary semiconductors, while the diodes in the output-side rectifier turn off at nearly zero current switching. The mathematical model and design guidelines of the proposed converter are discussed in the paper. The experimental results confirmed the theoretical analysis based on a 300 W prototype. The maximum efficiency of the converter was 96.8% at the nominal input voltage, and the converter has achieved a wider input voltage regulation range than that with the boosting cell comprising an ac-switch.

An Overview and Comprehensive Comparative Evaluation of Constant-Frequency Voltage Buck Control Methods for Series Resonant DC–DC Converters

The paper focuses on galvanically isolated series-resonant dc-dc converters with a low quality factor of a magnetically integrated resonant tank. These converters can be controlled at a constant switching frequency to achieve the input voltage buck regulation. The paper compares various buck control methods, such as conventional pulse-width modulation, hybrid pulse-width modulation, shifted pulse-width modulation, hybrid shifted pulse-width modulation, improved shifted pulse-width modulation, asymmetrical pulse-width modulation, pulse-width modulation, and hybrid pulse-width modulation applied to the series-resonant dc-dc converter. The study considers step-up implementation of the series-resonant dc-dc converter topology with the voltage doubler rectifier, which makes it suitable as a front-end dc-dc converter for the integration of renewable energy sources in dc microgrids. The voltage buck control methods considered were compared analytically in terms of the cumulative power losses calculated theoretically. The theoretical results were compared with the experimental measurements to confirm the calculations and benchmark the voltage buck control methods. The experimental validation was performed using a 250 W prototype that demonstrated the hybrid PSM achieves the best performance. The experimental results were found in good agreement with analytically predicted values of the power loss.

Wide Input Voltage Range Operation of the Series Resonant DC-DC Converter with Bridgeless Boost Rectifier

The series resonant DC-DC converter (SRC) can regulate the input voltage in a wide range at a fixed switching frequency. In this work, the bridgeless rectifier, which is utilized intensively in the applications of the power factor correction, has been integrated into the SRC as a voltage step-up cell at the output-side of the SRC. It is shown that the conventional overlapping pulse-width modulation (PWM) of the two metal oxide semiconductor field-effect transistors MOSFETs in this rectification cell limits the input voltage regulation range of the converter due to excessive power losses in abnormal operating conditions. The abnormal operating conditions occur when the instantaneous voltage across the resonant capacitor is larger than the secondary voltage of the isolation transformer. This happens at high values of the DC voltage gain, i.e., low input voltages and high currents, which causes the resonant current to flow in the reverse direction in the same half-cycle through a parasitic path formed by overlapping PWM of the rectifier MOSFETs. The abnormal operation results in additional conduction loss in the converter as the MOSFETs of the bridgeless boost rectifier turn on at high current at the beginning of each half of the switching period. Accordingly, the overall efficiency of the converter significantly deteriorates. This paper proposes the hybrid PWM aiming to improve the efficiency of the SRC with a bridgeless boost rectifier in a wide input voltage regulation range. The converter swaps between the overlapping and the proposed short-pulse PWM schemes to drive the MOSFETs in the bridgeless boost rectifier. The transition between the two PWM schemes is defined according to the boundary condition that relies upon the operating point of the converter power and the input voltage. The proposed hybrid PWM scheme is analyzed and compared to the overlapping PWM at different levels of the input voltage and the load power. A 300 W prototype was studied in the laboratory to show the feasibility of the proposed hybrid PWM scheme with the closed-loop control system to switch between the two PWM schemes.

Design and Implementation of Series Resonant DC-DC Converter

The resonant DC-DC converter is known as advantageous over conventional DC-DC converter in terms of efficiency. This is primarily because the resonant converter operates at soft switching mode. In this paper, we report our work on the design and implementation of a series resonant DC-DC converter with full-bridge switching. The developed converter consisted of two main parts, namely the PWM signal-generating circuit as the driver for MOSFET and converter primary circuit. The first part was implemented by using Arduino UNO R3, whose output was amplified with IR2110 optocoupler. The latter was made up of full-bridge inverter, which employs MOSFET as the electronic switches, resonance circuit, and full-bridge uncontrolled rectifier. Performance of the developed converter was tested by supplying input voltage ranging from 20 to 30 V. It was shown that the converter functioned as a step-down “DC” transformer, i.e. voltage reducer. The maximum output voltage level obtained was half of the input, which was achieved at switching frequency of 40 kHz and efficiency of 50%. The converter was also tested to supply practical electrical load. In this case, a 12-V electric drill was put in place. The drill worked well, and a converter efficiency of 43% could be calculated during this operation.Keywords : DC-DC Converter, Series Resonance and Switching

Unified Boundary Control With Phase Shift Compensation for Dual Bridge Series Resonant DC-DC Converter

Unified Boundary Control With Phase Shift Compensation for Dual Bridge Series Resonant DC-DC Converter

Voltage Regulation of DC-DC Series Resonant Converter Operating in Discontinuous Conduction Mode: The Hybrid Control Approach

Dynamic modeling and control of dc-dc series resonant converter (SRC) especially when operating in discontinuous conduction mode (DCM) is still a challenge in power electronics. Due to semiconductors switching, SRC is naturally represented as a switched linear system, a class of hybrid systems. Nevertheless, the hybrid nature of the SRC is commonly neglected and it is modeled as a purely continuous dynamics based on the sinusoidal approximation and averaging. However, an SRC may be purposely designed to operate in DCM so the sinusoidal approximation is no longer acceptable. Therefore, it is essential to analyze the stability using a more sophisticated model. This paper presents a novel hybrid control strategy for the output voltage regulation of the SRC operating in DCM. Neither sinusoidal nor averaging is used. The stability of the closed-loop system is systematically fulfilled by satisfying some linear matrix inequalities. The proposed hybrid control approach has simple hardware implementation which does not require fast sampling of the resonant tank waveforms and external voltage-controlled oscillator. A prototype of the SRC is constructed and the hybrid controller is realized on a TMS320F2812 DSP core. The effectiveness of the proposed method is verified by simulation and experimental results.