Reverse Recovery Current Research Articles

Bridge-arm current reduction in DC-AC inverter

ABSTRACTWhen building single-phase inverter with power Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET), switching action may cause poor reverse recovery characteristic due to body parasitic diode of MOSFET, which can produce peak current in the circuit loop and the high transient voltage and current (dv/dt, di/dt) during the turning-on period. In this article, a novel method to reduce the bridge arm current spike in DC-AC inverter is proposed. The presented method uses the improved and simplified coupled inductor which is connected between the upper and lower power devices. The parasitic capacitors of MOSFET are charged and discharged by the coupled inductor and the energy is released in the new loop; therefore, the bridge peak current is diminished. The time-domain model of transient-state analyses is given in detail. The current spike of the main switch is clamped efficiently. By increasing switching frequency, the volume of the magnetic core can be further reduced which is resulted from reduction in the reverse recovery current in parasitic diode. Because of the suppression of the spike current via the device, the switch-on loss of the power loss is reduced, and low on-state resistor of the power device can be adopted to suppress the conduction loss. The proposed approaches are validated with experimental results.

Quasi-Resonant Passive Snubber for Improving Power Conversion Efficiency of a DC–DC Step-Down Converter

A quasi-resonant passive snubber for the conventional dc–dc step-down converter is proposed. The snubber uses six passive components to achieve a zero-current turn- on and zero-voltage turn- off of the switch, and to suppress the reverse recovery current of diode. At input voltage of 200 V, output voltage of 100 V, output power of 300 W, and switching frequency of 190 kHz, the snubber increased the power conversion efficiency ηe by 2.8% and stabilized the temperature of mosfet switch at ∼68 °C. The snubber worked well for both mosfet and insulated gate bipolar transistor (IGBT) switches without increasing the voltage stress. These experimental results show that the proposed snubber is very helpful for improving ηe of a dc–dc step-down converter that operates at a high frequency.

Soft-Switching High Static Gain DC–DC Converter Without Auxiliary Switches

The development of a high static gain dc–dc converter with the integration of the voltage multiplier cell and the coupled inductors operating with soft switching is presented in this paper. The use of coupled inductors and voltage multiplier techniques allow the operation with low switch voltage and low conduction losses. The switch turn-on commutation occurs with zero current switching due to the presence of the coupled-inductor leakage inductance. The leakage inductance also reduces the reverse recovery current of all diodes. The zero voltage switching at the power switch turn-off is obtained with the inclusion of only a diode and a snubber capacitor per phase, without the use of auxiliary switches. The soft-switching range is independent of the load and is maintained even with a light load. The theoretical analysis, design procedure, and experimental results are presented in this paper. A two-phase boost converter with one voltage multiplier and coupling inductors was built with an input voltage $V_{{\text{in}}}= { \text{24 V}}$ , output voltage $V_{o}= { \text{432 V}}$ , and output power $P_{o}= { \text{400 W}}$ . The efficiency obtained is equal to 94.55% at the nominal power.

A Three-Winding Coupled-Inductor DC–DC Converter Topology With High Voltage Gain and Reduced Switch Stress

This paper presents a dc–dc boost converter topology for low input and high output voltage applications, such as photovoltaic systems, fuel cell systems, high-intensity discharge lamp, and electric vehicles. The suggested configuration consists of a three-winding coupled-inductor, a single switch and two hybrid voltage multiplier cells. Furthermore, two independent hybrid voltage multiplier cells are in parallel when the single switch S is turned on , and they are in series when the switch S is turned off . So, the advantages of the proposed converter structure are summarized as follows: 1) A coupled inductor with three windings is introduced in the presented converter structure. The two secondary windings of the coupled inductor are, respectively, used to form a hybrid multiplier cell on the one hand, on the other hand, it increases the control freedom of the voltage gain, enhances the utility rate of magnetic core and power density, and reduces the stress of power components to provide a stable constant dc output voltage. 2) The two hybrid multiplier cells can absorb synchronously the energy of stray inductance, which not only reduces the current stress of corresponding diodes, but also greatly alleviates the spike voltage of the main switch, which improves the efficiency. 3) The two hybrid multiplier cells are connected in series to supply power energy for the load, so the voltage gain is extended greatly due to this particular structure. Thus, low-voltage low-conduction-loss devices can be selected and the reverse-recovery currents within the diodes are inhibited. The operating principles and the steady state analyses of the proposed converter are discussed in detail. Finally, a test prototype has been implemented in the laboratory, and the simulated and experimental results show satisfactory agreement with the theoretical analysis.

Research of p‐i‐n Junctions Based on 4H‐SiC Fabricated by Low‐Temperature Diffusion of Boron

Novel method of boron diffusion at low temperatures between 1150 and 1300°C is used for the formation of both p‐i SiC junction and i‐region in one technological process. As the junction formation conditions in this method are essentially different from those in the conventional diffusion (low temperatures and process of diffusion are accompanied by formation of structure defects), it is of special interest to identify advantages and disadvantages of a new method of diffusion. Developed SiC p‐i‐n junction diodes have fast switching time, and the duration of the reverse recovery current is less than 10 ns with a breakdown voltage of 120–140 V. Fabricated diodes possess capability to operate at temperatures up to 300°C. As the temperature of diffusion process is lower than the melting temperature of silicon, this new technology allows fabrication of diodes on the base of SiC/Si epitaxial structures.

Simulation Study of a Power MOSFET with Built-in Channel Diode for Enhanced Reverse Recovery Performance

A new silicon power MOSFET architecture is proposed by introducing a built-in channel diode through a dummy MOS gate electrically coupled to the source. The oxide thickness of the channel diode is reduced to obtain a desired turn-ON voltage and attenuate the minority carrier injection from the PN junction body diode. Consequently, the proposed MOSFET is able to deliver superior reverse recovery characteristics, including reductions in reverse recovery charge ( $Q_{\sf RR}$ ) and peak reverse recovery current ( $I_{\mathrm{ RRM}}$ ) by a factor of ~4.2 and ~2.6, respectively. The breakdown voltage (232 V) of the proposed MOSFET is the same as the conventional MOSFET. The on-resistance of the proposed MOSFET (8.5 $\text{m}\Omega \cdot \text {cm}^{{2}}$ ) is only slightly increased compared with conventional MOSFET (8.0 $\text{m}\Omega \cdot \text {cm}^{{2}}$ ). The gate-to-drain charge ( $Q_{\sf GD}$ ) and gate charge ( ${Q} _{\mathsf {G}}$ ) are reduced by a factor of ~7.2 and ~3.9, respectively. Significantly improved figures of merit ( ${R} _{ON} \times {Q}_{\mathsf {G}}$ and ${R} _{ON} \times {Q}_{\mathsf {GD}}$ reduced by a factor of ~3.7 and ~6.8, respectively) are obtained in the proposed MOSFET. The device concept and characteristics are systematically analyzed with numerical TCAD simulations.

Multi-Phase Modular Drive System: A Case Study in Electrical Aircraft Applications

In this article, an advanced multiphase modular power drive prototype is developed for More Electric Aircraft (MEA). The proposed drive is designed to supply a multi-phase permanent magnet (PM) motor rating 120 kW with 24 slots and 11 pole pairs. The power converter of the drive system is based on Silicon Carbide Metal Oxide Semiconductor Field-Effect Transistor (SiC MOSFET) technology to operate at high voltage, high frequency and low reverse recovery current. Firstly, an experimental characterization test is performed for the selected SiC power module in harsh conditions to evaluate the switching energy losses. Secondly, a finite element thermal analysis based on Ansys-Icepak is accomplished to validate the selected cooling system for the power converter. Thirdly, a co-simulation model is developed using Matlab-Simulink and LTspice® to evaluate the SiC power module impact on the performance of a multiphase drive system at different operating conditions. The results obtained show that the dynamic performance and efficiency of the power drive are significantly improved, which makes the proposed system an excellent candidate for future aircraft applications.

A Magnetic Coupling Based Gate Driver for Crosstalk Suppression of SiC MOSFETs

Silicon carbide (SiC) devices have attracted widespread attention because of their superior characteristics. However, not only the higher slew rate of drain–source voltage but also the higher slew rate of reverse recovery current can result in a more serious crosstalk problem than Si-based devices in a half-bridge application. Crosstalk suppression should be integrated into the gate driver to ensure the safe operation of SiC devices. Therefore, a specific mathematical analysis is done in this paper to figure out the crosstalk phenomenon. The limitations of the existing suppression methods are illustrated. Thus, a gate driver based on the magnetic coupling is proposed to ensure the gate–source voltage within the safe range, even when the positive and negative spurious pulse voltages appear. The proposed gate driver uses three ring transformers to insulate the control signal and driver power supply. So, it is feasible to drive a half-bridge circuit in the medium or high power applications. By saving optical couplers and isolated drive power supplies, the gate driver can realize fully galvanic isolation and generate the positive and negative gate–source driving voltage simply. The results derived from the proposed mathematical analysis and the effectiveness of the proposed driver in suppressing the spurious pulse voltage are verified by the experiments.

Switching performance of quasi-vertical GaN-based p-i-n diodes on Si

The switching performance of GaN-based p-i-n diodes on Si was investigated for the first time. A double-pulse test circuit using an inductive load was utilized to evaluate the diode's switching characteristics. When the GaN diode was switched from an on-state with IF = 450 mA to an off-state with VR = −200 V (dIF/dt = 16 A/μs), the peak reverse recovery current (Irr) and time (trr) was measured to be 19.4 mA and 7.1 ns, respectively. The amount of charges stored in the drift region and the turn-off energy was extracted to be 0.14 nC and 0.054 μJ, respectively. The carrier lifetime under high-level injection conditions in GaN was estimated to be 0.6 ns. The reverse recovery characteristics of the GaN diodes showed little sensitivity to elevated temperatures up to 150 °C. During the forward recovery (from off-state with VR = −190 V to on-state with IF = 450 mA), the GaN diode exhibited a negligible voltage overshoot. In comparison to a commercial fast recovery-Si diode, the superior reverse and forward recovery performance of GaN-based p-i-n diodes indicates their practicality in fast switching applications and reliability at high temperatures.

A Novel Interleaved Nonisolated Ultrahigh-Step-Up DC–DC Converter With ZVS Performance

This paper presents an interleaved nonisolated dc-dc converter with high-voltage gain and zero-voltage switching (ZVS) performance. Both coupled inductor and voltage multiplier cell techniques are used to increase the voltage gain. The ZVS circuit is composed of an active clamp which is in series with the output filter capacitors. This will give rise to further extension of the voltage gain. Applying the interleaving technique at the input of the converter, the ripple of the input current is reduced. Due to the leakage inductances of coupled inductors, the diodes are turned-off under zero-current switching condition. Hence, the reverse current recovery problem is alleviated. The steady-state analysis of the proposed converter is also presented. Finally, a 900-V to 415-W laboratory prototype is implemented to validate the performance of the proposed converter.

Fast Switching 4H-SiC P-i-n Structures Fabricated by Low Temperature Diffusion of Al

P-i-n 4H-SiCAl diode structures are fabricated by a new approach which is low temperature diffusion of aluminium (Al) in SiC using flow of vacancy defects from surface into volume of crystal. In conventional diffusion in SiC, the operating temperature is usually >2050°C while, in this approach, the diffusion temperature is between 1150 and 1300°C. As the conditions of formation of junction in this method essentially differ from conventional diffusion (low temperature and process of diffusion are accompanied by forming structure defects), it is interesting to identify the advantages and disadvantages of a new method of diffusion. Fabricated p-i-n structures have low breakdown voltage between 80 and 140 V (due to the influence of dislocations and micropipes) and are capable of operating at temperatures up to 300°C. Structure has fast switching time and duration of the reverse recovery current less than 10 ns. We believe that because of low diffusion temperature, the concentration of nitrogen related trapping levels is relatively low and as a result the fast switching time is observed in our samples. It has been shown that this low temperature diffusion technology can be used to fabricate p-region and high resistive i-region of SiC diode in single-step process.

Continuous Conduction Mode Soft-Switching Boost Converter and its Application in Power Factor Correction

Continuous conduction mode (CCM) boost converters are commonly used in home appliances and various industries because of their simple topology and low input current ripples. However, these converters suffer from several disadvantages, such as hard switching of the active switch and reverse recovery problems of the output diode. These disadvantages increase voltage stresses across the switch and output diode and thus contribute to switching losses and electromagnetic interference. A new topology is presented in this work to improve the switching characteristics of CCM boost converters. Zero-current turn-on and zero-voltage turn-off are achieved for the active switches. The reverse-recovery current is reduced by soft turning-off the output diode. In addition, an input current sensorless control is applied to the proposed topology by pre-calculating the duty cycles of the active switches. Power factor correction is thus achieved with less effort than that required in the traditional method. Simulation and experimental results verify the soft-switching characteristics of the proposed topology and the effectiveness of the proposed input current sensorless control.

An isolated AC module for photovoltaic energy conversion

ABSTRACTIn this paper, an isolated ac module with pseudo dc-link and galvanic isolation is proposed for photovoltaic energy conversion. The studied grid-tie ac module can individually extract the maximum solar power from each photovoltaic panel and transfer to ac utility system. It consists of an interleaved active-clamping single-ended primary-inductive circuit (SEPIC) with a secondary voltage doubler, a full-bridge polarity selector operating under line frequency to achieve high efficiency. For the studied topology, key features such as reduced input current ripple, zero-voltage switching (ZVS) of primary switches, low reverse-recovery current of the output diodes, and lower switch voltage stress are obtained. Also, to reduce input current ripple, an interleaved control strategy is adopted. A simple control strategy is proposed to generate a rectified sinusoidal waveform voltage at the pseudo dc-link capacitors and achieve the high maximum power point tracking (MPPT) accuracy. The operation principles and design considerations of the studied ac module are analyzed and discussed. A prototype with 25–60 V dc input, 110 V/60 Hz ac output and 150 W power rating has been constructed for verifying the feasibility of the proposed ac module.

Low Reverse Recovery Charge 30 V Power MOSFET With Double Epi Structure for DC–DC Converters

Low reverse recovery charge solutions are proposed for 30 V power MOSFETs featuring a double epi structure. The parallel connection of a MOSFET and a Schottky barrier diode (SBD) is used to reduce the recovery charge. The breakdown voltage of the SBD area must be enhanced in order to integrate the MOSFET and the SBD on a single chip. Thus, we studied two types of devices using a double epi structure for enhancing the breakdown voltage of the SBD area. One is an integrated single-chip device and the other is an integrated unit cell device. The integrated unit cell device exhibited lower reverse recovery currents than the integrated single-chip device did during the simulations that were conducted. However, the loss calculation of the integrated unit cell device resulted in an increase in loss because of the diode characteristics needed for the greater barrier height of the p−-layer. Therefore, the integrated single-chip device was experimentally investigated. As a result, the surge voltage of the device was reduced by 58%, which enabled for the use of a lower voltage device and a reduction in the device loss.

Valve saturable reactor iron losses of ultrahigh‐voltage direct current converter

Thyristor-based line-commutated converters (LCCs) are widely used to achieve AC/DC and DC/AC power conversions in UHVDCs (ultrahigh-voltage direct currents) transmission. Valve saturable reactors are used to protect power thyristors. To improve the efficiency of bulk electricity transmission over long distance, the operating voltage and current of UHVDCs and therefore the thermal stresses applied to the valve saturable reactors have steadily increased over the last decades. Valve saturable reactor iron losses were studied by accounting for the reverse recovery characteristics of the valve thyristors and the non-linear characteristics of the saturable reactors. The impact of UHVDC current on valve saturable reactor iron losses was quantified and verified. The valve saturable reactor iron losses of an LCC are generated not only at the turn-on and turn-off periods of the valve, but also at the off-state of the valve. The amount of the losses are affected by the AC busbar stray capacitances of the converter, the valve firing and extinction voltages, the rates of change of valve commutation current, and the reverse recovery current of the valve thyristors. The conclusion obtained will help to understand better the forming mechanism of valve saturable reactor iron losses and optimise the valve saturable reactor design.

DCM Frequency Control Algorithm for Multi-Phase DC-DC Boost Converters for Input Current Ripple Reduction

In this paper, a discontinuous conduction mode (DCM) frequency control algorithm is proposed to reduce the input current ripple of a multi-phase interleaved boost converter. Unlike conventional variable duty and constant frequency control, the proposed algorithm controls the switching frequency to regulate the output voltage. By fixing the duty ratio at 1/N in the N-phase interleaved boost converter, the input current ripple can be minimized by ripple cancellation. Furthermore, the negative effects of the diode reverse recovery current are eliminated because of the DCM characteristic. A frequency controller is designed to employ the proposed algorithm considering the magnetic permeability change. The proposed algorithm is analyzed in the frequency domain and verified by a 600 W three-phase boost converter prototype that achieved 57% ripple current reduction.

Integrated Three-Voltage-Booster DC-DC Converter to Achieve High Voltage Gain with Leakage-Energy Recycling for PV or Fuel-Cell Power Systems

In this paper, an integrated three-voltage-booster DC-DC (direct current to direct current) converter is proposed to achieve high voltage gain for renewable-energy generation systems. The proposed converter integrates three voltage-boosters into one power stage, which is composed of an active switch, a coupled-inductor, five diodes, and five capacitors. As compared with conventional high step-up converters, it has a lower component count. In addition, the features of leakage-energy recycling and switching loss reduction can be accomplished for conversion efficiency improvement. While the active switch is turned off, the converter can inherently clamp the voltage across power switch and suppress voltage spikes. Moreover, the reverse-recovery currents of all diodes can be alleviated by leakage inductance. A 200 W prototype operating at 100 kHz switching frequency with 36 V input and 400 V output is implemented to verify the theoretical analysis and to demonstrate the feasibility of the proposed high step-up DC-DC converter.

Passive Lossless Snubbers Using the Coupled Inductor Method for the Soft Switching Capability of Boost PFC Rectifiers

In order to minimize switching losses for high power applications, a boost PFC rectifier with a novel passive lossless snubber circuit is proposed. The proposed lossless snubber is composed of coupled inductors merged into a boost inductor. This method compared with conventional methods does not need additional inductor cores and it reduces extra costs to implement a soft switching circuit. Especially, the proposed circuit can reduce the reverse recovery current of output diode rectifiers due to the coupling effect of the inductor. During turn-on and turn-off operating modes, the proposed PFC converter operates under soft switching conditions with high power conversion efficiency. In addition, the performance improvement and analysis of the operating effects of the coupled inductors were also presented and verified with a 3.3 kW prototype rectifier.

SiC Based Single Chip Programmable AC to DC Power Converter

A single chip Programmable AC to DC Power Converter, consisting of wide band gap SiC MOSFET and SiC diodes, has been proposed which converts high frequency ac voltage to a conditioned dc output voltage at user defined given power level. The converter has high conversion efficiency because of negligible reverse recovery current in SiC diode and SiC MOSFET. High frequency operation reduces the need of bigger size inductor. Lead inductors are enough to maintain current continuity. A complete electrical analysis, die area estimation and thermal analysis of the converter has been presented. It has been found that settling time and peak overshoot voltage across the device has reduced significantly when SiC devices are used with respect to Si devices. Reduction in peak overshoot also increases the converter efficiency. The total package substrate dimension of the converter circuit is only 5 mm × 5 mm. Thermal analysis performed in the paper shows that these devices would be very useful for use as miniaturized power converters for load currents of up to 5-7 amp, keeping the package thermal conductivity limitation in mind. The converter is ideal for voltage requirements for sub-5 V level power supplies for high temperatures and space electronics systems.

Research on Reverse Recovery Transient of Parallel Thyristors for Fusion Power Supply

In nuclear fusion power supply systems, the thyristors often need to be connected in parallel for sustaining large current. However, research on the reverse recovery transient of parallel thyristors has not been reported yet. When several thyristors are connected in parallel, they cannot turn-off at the same moment, and thus the turn-off model based on a single thyristor is no longer suitable. In this paper, an analysis is presented for the reverse recovery transient of parallel thyristors. Parallel thyristors can be assumed as one virtual thyristor so that the reverse recovery current can be modeled by an exponential function. Through equivalent transformation of the rectifier circuit, the commutating over-voltage can be calculated based on Kirchhoff's equation. The reverse recovery current and commutation over-voltage waveforms are measured on an experiment platform for a high power rectifier supply. From the measurement results, it is concluded that the modeling method is acceptable.