Snubber Capacitor Research Articles

Soft-Switched Modulation Technique for a Single-Stage Matrix-Type Isolated DC–AC Converter

This paper proposes a soft-switched modulation technique with synchronous rectification for an isolated single-stage single-phase matrix-type dc–ac converter. The dc side consists of a full bridge inverter, and the ac side is a 2×2 matrix converter-based cycloconverter. The proposed unipolar modulation strategy provides zero current switching/zero voltage switching (ZVS) for the ac side devices and ZVS-on for the dc side devices. It also allows natural commutation of the current flowing through the secondary side leakage inductor of the isolation transformer and the grid inductor during unity power factor (UPF) condition, thus eliminates the requirement of snubber circuit. An improved soft-switched flyback-based regenerative snubber circuit is also presented for non-UPF operation. Proposed snubber circuit recycles the energy stored in the snubber capacitors in every switching cycle. A guideline to design snubber circuit along with a comparative study is discussed in this paper. Performance of the proposed hybrid modulation technique is evaluated in an SiC mosfet based 1.2-kW dc–ac converter prototype. A detailed analysis of the converter performance has been presented in this paper considering the circuit non-idealities.

A Zero-Voltage and Zero-Current Switching Interleaved Two-Switch Forward Converter With Passive Auxiliary Resonant Circuit

This article presents an interleaved two-switch forward dc/dc converter with zero-voltage and zero-current switching, which adopts a coupled inductor and a snubber capacitor. The proposed converter can realize soft operation for main power switches by using the coupled inductor, snubber capacitance, the leading switches' parallel capacitances, and the transformer leakage inductance. Compared with the initial converter that uses a coupled inductor, during the freewheeling stage, the proposed converter has significant performance in reducing the primary circulating current that flows through the power elements. More importantly, the proposed converter can eliminate the problems in the rectification diodes such as voltage stress, parasitic ringing, and reverse recovery. Based on the equivalent circuits in different operation modes, the operation principle and the soft-switching requirement of the converter are discussed. Besides, the design criteria for the key parameter are given in this article. The practical effectiveness of the proposed converter was validated by the simulation results and experimental results of prototype using the power mosfet.

High-Performance Active-Clamped Isolated SEPIC PFC Converter With SiC Devices and Lossless Diode Clamp

An isolated active-clamped single-ended primary-inductor converter (SEPIC) power factor correction (PFC) converter based on SiC devices is presented. The impact of the resonant inductance on the switch voltage stress and range of zero-voltage switching is analyzed. Analytical expressions for the operating points of the switches over the line cycle are derived and used to evaluate the switching loss. Resonant inductance and snubber capacitance are chosen based on the analysis to reduce the switching loss without overstress of the switches. Lossless diode clamp circuits are designed for the output diode so that the peak voltage and extra losses due to device parasitics-induced oscillation are significantly reduced. The analysis is validated with a 2-kW single-phase PFC rectifier module with a peak efficiency of 96.56% at the 200-kHz switching frequency, total harmonic distortion (THD) < 2%, and power density of 58 W/in3.

High-efficiency Bidirectional Buck–Boost Converter for Residential Energy Storage System

This paper proposes a bidirectional dc–dc converter for residential micro-grid applications. The proposed converter can operate over an input voltage range that overlaps the output voltage range. This converter uses two snubber capacitors to reduce the switch turn-off losses, a dc-blocking capacitor to reduce the input/output filter size, and a 1:1 transformer to reduce core loss. The windings of the transformer are connected in parallel and in reverse-coupled configuration to suppress magnetic flux swing in the core. Zero-voltage turn-on of the switch is achieved by operating the converter in discontinuous conduction mode. The experimental converter was designed to operate at a switching frequency of 40–210 kHz, an input voltage of 48 V, an output voltage of 36–60 V, and an output power of 50–500 W. The power conversion efficiency for boost conversion to 60 V was ≥98.3% in the entire power range. The efficiency for buck conversion to 36 V was ≥98.4% in the entire power range. The output voltage ripple at full load was &lt;3.59 Vp.p for boost conversion (60 V) and 1.35 Vp.p for buck conversion (36 V) with the reduced input/output filter. The experimental results indicate that the proposed converter is well-suited to smart-grid energy storage systems that require high efficiency, small size, and overlapping input and output voltage ranges.

Switching and Conduction Loss Reduction of Dual-Buck Full-Bridge Inverter Through ZVT Soft-Switching Under Full-Cycle Modulation

Based on the no blanking time characteristic, voltage error does not occur in the pulsewidth modulated output stage of dual-buck full-bridge inverter (DBFBI), resulting in lower total harmonic distortion (THD) of the output current. The two main modulations applied in the topology are half-cycle modulation and full-cycle modulation. Compared with the half-cycle modulation, the full-cycle modulation does not have the zero-crossing problem, but the inverter requires a bias current to guarantee better output waveform. The circulation current loop caused by bias current has a great influence on inverter efficiency. This article proposes a novel zero voltage transition (ZVT) soft-switching topology to increase efficiency by reducing the switching losses and conduction losses resulting from low bias current. The advantages of the DBFBI are included in the proposed inverter. The soft-switching condition is achieved by the snubber cells, and the energy stored in the passive snubber capacitors can be transferred effectively. The topology deduction, operating principles, and design guidelines are presented in detail. An 800-W experimental prototype operating with a 100-kHz switching frequency is implemented to verify the theoretical result.

Wide-Range ZVS Control Technique for Bidirectional Dual-Bridge Series-Resonant DC–DC Converters

For high-voltage and high-power bidirectional dc–dc converters, soft switching of all active power devices is mandatory to ensure the high efficiency and reliability. This paper describes a control technique for wide-range zero-voltage switching (ZVS) implementation of dual-bridge series-resonant dc–dc converters. The proposed control technique integrates variable-frequency modulation (VFM) and phase-shift modulation (PSM), in which the former effectively achieves the ZVS for both step-down and step-up operation, while the latter is employed to further extend the power transmission capability. The proposed technique is built on the time-domain analysis of the ZVS condition. A closed-form solution is formulated that guarantees the sufficient ZVS commutation current at switching instants, accounting for the presence of switches parasitic and/or snubber capacitances, while maintains the rms tank current at near-to-minimum levels. Furthermore, a compensation strategy for the effect of conduction losses is presented achieving better switching behavior and higher efficiency. Compared with the minimum rms current trajectory modulation, lower switching losses, enhanced efficiency, and mitigated voltage ringings are obtained. Effectiveness of the proposed technique is verified by means of a 800 W experimental prototype. Closed-loop operation with the proposed VFM+PSM controller is also implemented and experimentally tested.

Quasi-Resonant Voltage Doubler With Snubber Capacitor for Boost Half-Bridge DC–DC Converter in Photovoltaic Micro-Inverter

This paper proposes a quasi-resonant boost half-bridge dc–dc converter with high power conversion efficiency and a wide input voltage range for a photovoltaic micro-inverter. The proposed converter has a combined structure of a boost-integrated half-bridge converter on the primary side of the transformer and a voltage doubler with a snubber capacitor on the secondary side. By using the quasi-resonance techniques, it achieves zero-voltage switching (ZVS) turn- on and low turn- off losses for the switches, as well as ZVS turn- on for the diodes. In addition, the proposed converter has no dc-magnetizing current for the transformer due to the dc-blocking capacitor, and it doubles the voltage gain with half the voltage stress of diodes through the voltage doubler. The effectiveness of the converter was verified with a 300-W prototype with an input voltage range of 13–50 V, an output voltage of 400 V, and a switching frequency of 50 kHz. The experimental results show that the converter had more than 90.0% power conversion efficiency for the output power range of ∼300 W, and its maximum power conversion efficiency was 97.5% for an output power of 160 W.

Analysis and Modeling of SiC JFET Bi-Directional Switches Parasitic Oscillation

Silicon carbide (SiC) junction field-effect transistor (JFET) based bi-directional switches (BDSs) have great potential in the construction of several power electronic circuits, including matrix converters, multi-level converters, solid state breakers, and so on. Parasitic oscillation in SiC JFET-based BDSs has direct impact on the stability and reliability of these circuits. Proper handling of parasitic oscillation becomes highly critical. This paper focuses on the parasitic oscillation suppression in SiC JFET-based BDSs. A parallel snubber capacitor or a series ferrite ring was often used to damp parasitic oscillation in switching circuits in the literature. However, conventionally, the snubber capacitance was obtained by time-consuming and labour-intensive trial-and-error methods. The main contribution of this study is to derive the simplified equivalent transient circuit of the SiC JFET-based BDS considering all parasitic elements and quantitatively define the reasonable range of the snubber capacitance. And the combined effect of the selected snubber capacitance and the selected ferrite ring is investigated. In the end, simulation and experimental results validate the effectiveness of the proposed method.

A Simple Approach to Enhance the Effectiveness of Passive Currents Balancing in an Interleaved Multiphase Bidirectional DC–DC Converter

This paper studies the high power density bidirectional dc–dc converter with interleaving, soft-switching, and near critical conduction mode (near-CRM) operation. Systematic design and control methods are proposed to enhance the effectiveness of passive currents balancing between multiple interleaved phases without using individual phase current feedbacks. This paper first analyzes the zero voltage turn- on operation, including the turn- off energy diversion by the added snubber capacitor and the turn- off resonance models. Second, the intrinsic inverse co-relation between the phase current deviation and the resulting effective duty cycles variation is quantitatively formulated and modeled as a closed-loop mechanism that balances the currents passively. Then, the design constraints of the system parameters including the snubber capacitance, dead time, and valley currents of the near-CRM mode are formulated to guarantee the effectiveness of counteracting the current unbalance. Finally, a variable switching frequency control is proposed to actively control the valley current and maintain the current balancing effectiveness throughout the operating range. An IGBT-based 20-kW three-phase interleaved prototype with the maximum efficiency of 99.1% is constructed to verify the proposed design and control methods.

Pseudo-Full-Bridge Inverter With Soft-Switching Capability for a Quarter-Phase Ultrasonic Motor

This paper presents a high-efficiency inverter with the aid of the soft-switching technology, which is accomplished by the resonance of the in-series inductance with the snubber capacitance. The equivalent circuit of the quarter-phase ultrasonic motor is initially deduced, based on which the topology along with the operations of the novel inverter is subsequently presented. The configuration of the new quarter-phase inverter shows its uniqueness in terms of the shared arms and the especially designed snubber capacitance in comparison with the existing inverters. The circuit analysis infers that the dead time of the inverter is the key factor to arrive at the zero-voltage-switching or the zero-current-switching operations. Experimental measurements have demonstrated that the efficiency of the whole drive increases by a factor of 1.25 after replacing the traditional inverter with the proposed one. It should also be noted that the proposed inverter in association with the design method of the dead time not only can work for the quarter-phase ultrasonic motor, but also can be applicable for other kinds of quarter-phase devices. The soft-switching operations are achieved in the quarter-phase inverter for the first time, whose amplitudes of the output voltage and switching frequency are not required to be constant any more.

Voltage Overshoot Suppression for SiC MOSFET-Based DC Solid-State Circuit Breaker

The transient overvoltage and oscillation phenomena, which are caused by its high switching speed in a solid-state dc circuit breaker based on the silicon carbide (SiC) metal–oxide–semiconductor field-effect transistor (MOSFET), are a crucial problem. This paper presents a simple and reliable method to manage such a problem. An equivalent circuit model for SiC MOSFET is primarily established. The influence of stray inductance in energy absorption loop on the turn-off characteristics of the dc circuit breaker is then analyzed. Subsequently, possible typical overvoltage suppression methods, such as using a resistor–capacitor snubber circuit and increasing gate resistance and parallel capacitance between the gate and source, are simulated and analyzed. Thereafter, a peak voltage suppression method that does not sacrifice the fast switching capability of SiC MOSFET is proposed based on different amounts of energy absorbed by metal oxide varistors (MOVs) with varying voltage levels. A basic principle for selecting a snubber MOV is proposed based on the voltage ratio of a snubber and an energy-absorbing MOV. Finally, the feasibility of the proposed method is verified via a small-scale principle prototype.

Capacitance Optimization of Protective Snubber Capacitors in an Electric Power Converter

This article considers an approach to capacitance optimization of snubber capacitors in power converters based on series connection of power semiconductor devices (PSDs) by selecting their parameters. Studies of PSD parameters in the state of high conductivity revealed their high scatter. This results in significant temperature variations of their semiconductor structures. To decrease overvoltage amplitude in devices and to optimize the parameters of protective snubber circuits, it is required to provide the closest thermal modes of operation of series PSDs. The thermal processes in PSDs were studied using an electrothermal model that is distinguished from those previously developed in Multisim environment in that the initial data are acquired during testing of devices. The experimental results demonstrated that, by selection of electric and thermal parameters, it is possible to decrease the capacitance of snubber capacitors by an order of magnitude. This will allow one to decrease significantly the loss in PSD semiconductor structures when toggling them from low to high conductivity and to minimize the weight and dimensions of gate units.

Design of a Proportional Resonant Controller with Resonant Harmonic Compensator and Fault Ride Trough Strategies for a Grid-Connected Photovoltaic System

This paper presents the design and analysis of a proportional resonant controller with a resonant harmonic compensator and switch-type fault current limiter, as a fault-ride through strategy for a three-phase, grid-connected photovoltaic (PV) system under normal conditions and asymmetrical faults. The switch-type fault limiter comprised of current-limiting inductors, a bridge rectifier, a snubber capacitor, linear transformers, and energy absorption bypass. Furthermore, a critical and analytical comparison of switch-type fault limiters is carried out, with the conventional crowbar as the fault-ride through strategy, in combination with a conventionally tuned proportional integrator controller. The designed fault-ride through strategies with proportional integrator and proportional resonant controllers with resonant harmonic compensators are tested at the point of common coupling of the photovoltaic system and at a distance of 19 km from the point of common coupling, in order to analyze the impacts of fault parameter with respect to location. A MATLAB/Simulink model of a 100 kW three-phase grid-connected photovoltaic system is used for analysis. The simulation results of the proposed switch-type fault limiter with proportional resonant controller effectively validate the stable, ripple-free, and robust response compared to all other configurations. In addition, it is also verified that the grid faults on the PV system have a significant impact on fault type, and less impact on fault location.

Improved High Step-Up Z-Source DC–DC Converter With Single Core and ZVT Operation

A previously proposed high step-up dc–dc converter based on Z -source circuit is improved such that conduction losses of the converter and current stress of its power switch are reduced. The improved converter contains only one magnetic core and all of the inductors are coupled. It is shown that using one core allows us to use windings with lower copper resistance that results in reducing resistive losses of the coupled inductors. Also, by rearranging two diodes of the converter, the switch current and its conduction loss are reduced. In addition, a previously proposed auxiliary circuit for zero-voltage-transition operation is employed with a minor modification that makes it possible to use a relatively large snubber capacitor that significantly decreases current–voltage overlap of the main switch at turn-off instant. Improvement in the overall efficiency of the presented structure over the existing high step-up Z -source converter is demonstrated by implementing a 100-W prototype of each converter for 30- to 300-V voltage conversion.

RCD snubber design based on reliability consideration: A case study for thermal balancing in power electronic converters

In a turn-off RCD snubber, the capacitor value is usually optimized in order to minimize the power dissipated in the switch and snubber circuit. However, it may not be the best value of the snubber capacitor from the reliability point of view. In this paper, the capacitor value is optimized based on reliability considerations. Proposed method presents a new design to achieve the maximum reliability for the set of switch and its snubber. Mathematical analysis of the proposed method is conducted in MATLAB environment. Also, the experimental results are presented for validity of the theoretical analysis.

Analysis and Suppression of Unwanted Turn-On and Parasitic Oscillation in SiC JFET-Based Bi-Directional Switches

Silicon Carbide (SiC)-based Bi-Directional Switches (BDS) have great potential in the construction of several power electronic circuits including multi-level converters, solid-state breakers, matrix converters, HERIC (high efficient and reliable inverter concept) photovoltaic grid-connected inverters and so on. In this paper, two issues with the application of SiC-based BDSs, namely, unwanted turn-on and parasitic oscillation, are deeply investigated. To eliminate unwanted turn-on, it is proposed to add a capacitor (CX) paralleled at the signal input port of the driver IC (integrated circuit) and the capacitance range of CX is also analytically derived to guide the selection of CX. To mitigate parasitic oscillation, a combinational method, which combines a snubber capacitor (CJ) paralleled with the JFET (Junction Field Effect Transistor) and a ferrite ring connected in series with the power line, is proposed. It is verified that the use of CJ mainly improves the turn-off transient and the use of a ferrite ring damps the current oscillation during the turn-on transient significantly. The effects of the proposed methods have been demonstrated by theoretical analysis and verified by experimental results.

A Damping Scheme for Switching Ringing of Full SiC MOSFET by Air Core PCB Circuit

In this paper, a resonant damping circuit to suppress the switching ringing of full SiC mosfet is proposed. It reveals that the ringing phenomenon caused by parasitic impedances of switching circuit can be damped out using air core PCB transformer which has a properly designed secondary side circuit. The design method for PCB transformer and the secondary circuit are developed considering the physical dimension applied to the PCB transformer inserted between full SiC mosfet module and snubber capacitor. Experimental results using 1200 V–180 A full SiC mosfet module validate the design method and the performance of the proposed air core PCB circuit. Thanks to the damping circuit, the resonant component due to the switching ringing has been reduced to a half compared to that of system without damping circuit.

Selection of Inductor and Snubber Capactor to Optimize the Size and Efficiency of DC-DC Switching Power Converter

This paper presents a selection of inductor and snubber capacitor in non-isolated synchronous DC-DC switching power converter. The circuit is made to operate in Synchronous Discontinuous Conduction Mode (SDCM)/Forced Continuous Conduction Mode (FCCM) of operation for minimum inductor value, to reduce the size, weight and cost of the converter. The turn off loss of the switch induced by SDCM of operation is minimized by connecting snubber capacitor across the transistor switch. Before the switch is turned ON, snubber capacitor requires certain amount of energy must be stored in the inductor to discharge the capacitor energy [1]. The question is how much capacitor and inductor value is required. A series of MATLAB script are executed to find minimum inductor value for FCCM of operation and to select snubber capacitor for maximum efficiency. Complementary gate signals are used to control the ON and OFF of main and auxiliary switch. SDCM of operation due to complementary control gate signal scheme, minimum turn on loss of the transistor switch and low diode reverse recovery loss are achieved. Thus the Zero Voltage Resonant Transition (ZVRT) of transistor switch is realized, both turn on and turn off loss is minimized and also removes the parasitic ringing in inductor current.

Nonisolated Single-Switch Two-Channel LED Driver with Simple Lossless Snubber and Low-Voltage Stress

In two-channel light-emitting diode (LED) driver, capacitive-current-balancing method is the simplest and the most effective way to equally balance the current in each channel due to its simplicity. As a result, the capacitive balancing method was used with flyback or tapped-boost converters in low-power LED applications. Since flyback and tapped-boost converters suffer from a snubber loss and a high-voltage stress on the switching devices, conventional approaches use additional passive components, resulting in the limitations on the cost and power density. In this paper, a new converter topology for low-power two-channel LED application has been proposed. The proposed converter uses the blocking capacitor and the output capacitor as a snubber capacitor so that it has a low-voltage stress without using the additional components. Although the blocking capacitor plays a role as a snubber capacitor, the current balancing characteristic is still preserved. Furthermore, the proposed converter has a high efficiency since it minimizes the number of semiconductor components in the current paths. The effectiveness of the proposed converter has been verified with an offline 3.3 Vdc input and 11.55 W rated output prototype.

Regenerative‐passive snubber two‐switch forward converter

A regenerative-passive snubber (RPS) for pulse-width modulation (PWM) two-switch forward converter (TSFC) is presented. The RPS circuit is recycled the magnetic energy stored in the transformer leakage inductor and is achieved zero voltage switching turn off of power switches. Moreover, the RPS provides the resonant path formed by snubber capacitors and the snubber inductor to achieve zero current switching (ZCS) turn on of switches. In addition, the output diodes turn on/off under ZCS. The proposed RPS-PWM TSFC is analysed and experimental result for a 160 W, 300 kH prototype at the output voltage of 32 V are obtained to verify the theoretical analysis.