Low Switching Losses Research Articles

An Efficiency-Oriented Two-Stage Optimal Design Methodology of High-Frequency LCLC Resonant Converters for Space Travelling-Wave Tube Amplifier Applications

The high-frequency LCLC resonant converters are widely used in the two-stage power converter as a dc transformer for the space travelling-wave tube amplifier applications. In the two-stage power converter, since the output voltage is controlled by a preregulator, which is the first stage, the main functions of the high-frequency LCLC resonant converter, which serves as the second stage, are to boost the input voltage and to provide galvanic isolation while keeping high efficiency. As boosting the input voltage and providing galvanic isolation can be achieved by the transformer, achieving high efficiency is most challenging. Previous studies on the LCLC resonant converter mainly focus on reducing the switching loss. However, in addition to the switching loss, the total power loss of the LCLC resonant converter contains driving and conduction loss of the main switches; core loss, copper loss, and dielectric loss of the transformer; and the conduction loss of the rectifiers. As a result, low switching loss cannot guarantee the high efficiency of the LCLC resonant converter. To solve this problem, in this paper, an efficiency-oriented two-stage optimal design methodology of the LCLC resonant converters is proposed. In the first stage, the optimal parameters of the LCLC resonant converter, which aims at minimizing the total power loss of the converter, are found from the proposed genetic algorithm + particle swarm optimization algorithm. After that, in the second stage, a single-layer partially interleaved transformer structure is proposed to realize the optimal parameters. After the transformer design is finished, the optimal LCLC resonant converter is built. The proposed efficiency-oriented two-stage optimal design method and the transformer structure are validated by simulations and experiments.

Control of Modular Multilevel Converters Using an Overlapping Multihexagon Space Vector Modulation Scheme

This paper introduces a novel space vector modulation scheme that can be applied for the control of modular multilevel cascaded converters (MMCCs) with any number of levels. This is achieved by using basic two-level or three-level hexagons to determine the switch states and the duty cycles separately within one tier of the converter which is a cascade of three-level ${H}$ -bridge, five-level flying capacitor, or neutral point-clamped inverters. Many such hexagons can be overlapped, with phase shift relative to each other, for the control of a complete MMCC, instead of extending a single hexagon to regions corresponding to the number of levels. This approach simplifies the modulation algorithm and brings flexibility in shaping the output voltage waveforms. Also, this proposed method achieves good waveform quality at low switching frequency, hence resulting in low switching losses. Simulation and experimental results are presented to verify the advantageous features of the method.

Active Gate Driver for SiC-MOSFET-Based PV Inverter With Enhanced Operating Range

For photovoltaic (PV) inverter applications, the grid code mandates reactive power support to the grid, and the amount of reactive power injection may be limited by the voltage overshoot during the switching transients of a power device. For SiCMOSFET-based PV inverters, this problem is more pronounced since the voltage and current gradient during switching transitions are much higher than a Si-based power converters. During a cloudy day when the inverter has to operate at PV panels open-circuit voltage, it becomes harder to push higher reactive power support to the grid due to the current derating of the SiC-devices at the operating dc bus voltages to keep the device within its safe operating limits with low switching losses at all operating conditions. Slowing down the switching transient could be a remedy but this also increases the converter losses. This paper demonstrates an application of a dynamic gate resistance modulation technique to keep the SiC-device within its safe operating limits while maintaining a low switching loss with minimum voltage and current overshoots. This helps to inject more power to the grid with at higher dc bus voltages without enhancement of the thermal management system. The proposed implementation also works equally well at high junction temperatures (up to T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">j</sub> = 150 °C), which further increases the operating range of the PV inverter.

Improved Proportional Base Driver for SiC BJTs

The benefits of high-power silicon carbide (SiC) bipolar junction transistors (BJTs) in terms of low conduction and switching losses, high-temperature capability, and increased reliability associated with the lack of gate oxide have been partially shadowed by the high-power consumption of its driver. This paper focuses on the optimization of SiC BJT base drivers and presents an innovative design of a proportional base current driver. The driver is a stand-alone system achieving instantaneous tracking of the collector current without the need for a current sensor and can also account for variations of the BJT’s dc current gain with the temperature. Implementation of these two features is realized by sensing the collector–emitter voltage, which is conditioned to be used as a reference voltage for a switching regulator featuring a megahertz synchronous buck converter. This leads to a variable base current that is proportional to the instantaneous collector current for the SiC BJT. The concept is validated using a 1.5-kW boost converter, which shows a significant reduction in power consumed by the driver.

All-Silicon 99.35% Efficient Three-Phase Seven-Level Hybrid Neutral Point Clamped/Flying Capacitor Inverter

With the increasing use of photovoltaic systems, a large demand for efficient, power-dense and lightweight grid-interface inverters is arising. Accordingly, new concepts like multi-level converters, which are able to reduce the converter losses while still keeping a low construction volume, have to be investigated. The hybrid seven-level topology analyzed in this paper comprises an active neutral point clamped stage, followed by a flying capacitor stage. Compared to a pure flying capacitor converter, the combination of these two stages allows to save more than half of the capacitor volume, while still having the same requirement for the output filter stage, and hence, the same output filter volume. Moreover, the topology employs low-voltage devices and ensures low conduction and switching losses, resulting in a higher efficiency. The principle of operation of the system is briefly reviewed, and based on a detailed component modeling, an efficiency vs. power density optimization is carried out, for which switching loss measurements of state-of-the-art 200 V semiconductors are performed. From the optimization, a high-efficiency design is selected and the practical hardware realization is discussed. The simulation and optimization results are then verified by realizing an all-silicon 99.35% efficient three-phase seven-level system, featuring a volumetric power density of 3.4 kW/dm 3 (55.9 W/in 3 ), a gravimetric power density of 3.2 kW/kg, and fulfilling CISPR Class A EMI requirements. Finally, it is shown that an all-silicon realization with next generation silicon switches can achieve 99.5% efficiency with the same hardware, and 99.6% with commercial state-of-the-art GaN switches.

A Single-Stage Capacitive AC-Link AC–AC Power Converter

A single-stage three-phase ac–ac converter benefiting from a high-frequency alternating link voltage is proposed in this paper. In this converter, a very small film capacitor can transfer the energy from the input to the output, owing to the high-frequency alternating voltage of the link. This eliminates the need for large electrolytic capacitors that are typically used in dc-link ac–ac converters. Moreover, a compact high-frequency transformer at the link can replace the bulky low-frequency transformers, in case isolation is required. These features increase the power density as well as reliability of the proposed converter in comparison with the conventional dc-link converters. The number of required switches in the proposed converter is 12, which is less than the number of switches needed in matrix converters, leading to lower switching and conduction losses. Despite being single-stage, the proposed ac–ac converter is capable of both stepping up and stepping down the voltage and also frequency transformation. This eliminates the need for using cascaded power converters. In this paper, the operation principles of the proposed ac–ac converter are investigated, and variable switching frequency and fixed switching frequency control methods for operating this converter are introduced. The performance of the converter is verified through simulation and experiment.

Selective harmonics elimination in multilevel inverter by a derivative-free iterative method under varying voltage condition

Selective Harmonics Elimination Pulse width modulation (SHE PWM) presents an alternative modulation technique to operate medium voltage medium and high power converters as it reduces the switching losses. SHE PWM generates high-quality output waveform at the low switching frequency. Its application to multilevel converters furthers leads to improvement in output waveforms with lower switching losses, lesser dv/dt and lowers switching devices ratings. In this Paper SHE PWM for an asymmetrical cascaded H-bridge multilevel inverter under unequal DC voltage condition for fundamental and multiple switching cases are investigated. More harmonics can be eliminated by considering multiple switching’s. The Solution of the Nonlinear transcendental SHE equation is obtained using an advanced derivative free numerical technique which. The method is simple in implementation with fast calculations per iteration as it avoids the evaluation of Jacobian and its matrix. Also the need for precise initial guess in the proximity of actual solution is not needed as an identity matrix of the size of designed variable serves the purpose. Different inequality in the dc voltages is taken to eliminate the lower order harmonics from the output. Only exact solutions for the switching angles which ensure the complete elimination of targeted harmonics are reported. Simulation and Hardware results are presented to confirm the validity of the proposed technique.

Grid Integration of Single-Stage SPV-STATCOM System Using Symmetric Cascaded Five-Level VSC

This work proposes a dual-function single-stage solar photovoltaic (SPV) grid-tied system with STATCOM (static compensator) capabilities using a three-phase five-level cascaded VSC (voltage source converter) operating at low switching frequency with low total harmonic distortion (THD) and low switching losses. The proposed SPV-STATCOM system works in three modes: i.e. Mode-1, in which only an active power is transferred to the grid, Mode-2, in which both active and reactive power are supplied to the grid and Mode-3, in which only reactive power is supplied to the grid, thereby utilizing the full capabilities of the SPV system. An incremental conductance algorithm is used to track power from SPV array which is fed to the grid. To synchronize the VSC to the grid, a decoupled current controller with feed-forward term and double decoupled synchronous reference frame phase-locked loop (DDSRF-PLL) is used. The use of a single-stage five-level cascaded VSC offers the advantages of low switching losses and the operation at high power and high voltage which results in an improvement in quality of power of the system. The simulated results demonstrate the system design and control scheme under varying conditions.

High‐power‐density high‐efficiency LLC converter with an adjustable‐leakage‐inductance planar transformer for data centers

LLC converters can achieve high efficiency, high- power density, wide gain range, and galvanic isolation. This study presents a high-power-density and high-efficiency LLC converter with an adjustable-leakage-inductance planar transformer for the DC-DC conversion in data center power supplies. A planar transformer with adjustable leakage inductance is modelled and developed to provide an accurate design for resonant frequency and voltage gain. A detailed power loss analysis is performed. Furthermore, a thermal model is provided to aid in heat sink design. GaN devices are used in the converter to achieve high-switching frequency and low-switching loss. A 450 kHz, 360-400 V DC input, 12 V DC output, 750 W LLC converter prototype with an adjustable-leakage-inductance planar transformer is built and tested. The power density of the system is 15.4 W/cm 3 including an auxiliary power supply. The peak efficiency of the overall system is over 95%.

Multicell-to-Multicell Equalizers Based on Matrix and Half-Bridge LC Converters for Series-Connected Battery Strings

Due to the low switching loss, compact size, and low price, the LC series resonant converter (LCSRC) as an energy carrier is promising in battery equalizers. However, the conventional equalizers based on LCSRC only can realize the one-cell-to-one-cell balancing for a high-voltage series-connected battery pack, causing a low equalizing speed and efficiency. Therefore, two direct multicell-to-multicell (MC2MC) balancing topologies based on matrix LC converter and half-bridge LC converter are proposed, respectively, which achieve the direct energy transfer from a consecutive more-charged-cell group to a consecutive less-charged-cell group, significantly improving the equalizing speed and efficiency. An analytical model for the LCSRC is developed to provide a guidance for the optimal design of the proposed equalizers. The prototypes for the proposed two balancing topologies are constructed. The MC2MC balancing performances are verified though the comparative experimental results at different initial voltage distributions. In particular, the proposed equalizers simultaneously achieve the fast balancing speed and high equalization efficiency. The measured peak efficiency is about 87.9% at the four-cell-to-four-cell equalization.

Hybrid periodic carrier frequency modulation technique based on modified SVPWM to reduce the PWM noise

This study proposed a hybrid periodic carrier frequency modulation (HPCFM) technique based on the modified space vector pulse-width modulation (SVPWM) for two-level three-phase voltage source inverters to eliminate the PWM noise. Owing to PWM technique and switching losses considerations, ear-piercing high-frequency acoustic noise from motor is common. The proposed HPCFM technique is able to remove the high-frequency unpleasant acoustic noise more effectively than conventional PCFM with lower switching losses and shorter frequency range. In addition, the PWM harmonics in phase voltage and phase current are reduced significantly. Furthermore, the HPCFM method is simple to implement and does not employ additional circuits in drive system. The effectiveness of the proposed approach has been confirmed by detailed experimental results.

Heterojunction Diode Shielded SiC Split-Gate Trench MOSFET With Optimized Reverse Recovery Characteristic and Low Switching Loss

A split-gate SiC trench MOSFET with a hetero-junction diode (HJD) is proposed and numerically analyzed in this paper. The proposed structure features the HJD to effectively suppress the turn-on of the parasitic body diode and reduce the depletion region in the JFET area. A P+ shielding layer surrounding the HJD and the gate oxide layer is used to alleviate the concentration of the electric field under the gate trench and improve the switching performance. As a result, not only the breakdown voltage is increased by 20.8% at the same level of the on-state resistance but also the miller charge and the switching loss of the proposed structure are reduced by 52% and 39.1%, respectively when compared with those of the conventional SiC trench MOSFET.

Multiple-Output ZVS Resonant Inverter Architecture for Flexible Induction Heating Appliances

Flexible cooking surfaces have changed the domestic induction heating product paradigm enabling the use of a wider range of cookware materials, shapes, and positions. In order to implement such systems, multiple-output resonant inverters featuring high-performance and high-efficiency operation while achieving a cost-effective implementation are required. This paper proposes a multiple-output zero-voltage-switching resonant inverter for flexible induction heating appliances. The proposed converter features a matrix structure, enabling a cost-effective implementation with a reduced number of power devices while achieving high performance and low switching losses. It has been tested by means of an experimental prototype featuring 48 induction heating coils, proving the feasibility of the proposed approach.

Operation of a Bidirectional Series-Resonant Converter With Minimized Tank Current and Wide ZVS Range

Due to wide soft-switching operation range, high-frequency isolated resonant converters are featured with low switching losses. Therefore, it is meaningful to minimize the resonant tank current in an isolated resonant converter in order to enhance the overall system efficiency. In this work, a bidirectional series-resonant converter under phase-shifted modulation combined with a modified pulsewidth modulation gating scheme is addressed. The modified pulsewidth modulation gating scheme is helpful to keep more switches operating in zero-voltage switching (ZVS) at light load. According to the steady-state analysis with the fundamental harmonic approximation approach, a specified control strategy with minimum rms tank current based on three control dimensions is proposed in closed form. The validity of the proposed control strategy is verified through experimental tests. The pulsewidth of modulated voltage using the modified gating scheme is larger than that of the conventional pulsewidth modulation voltage, which compensates for the effects of more high-order harmonics on rms current. Therefore, compared with existing control strategies for minimum current operation, the proposed control strategy demonstrates comparable performance in depressing conduction loss and wider soft-switching range in high load range. And it is able to achieve higher efficiency at light load, thanks to more switches working in ZVS.

Design of a 1-MHz High-Efficiency High-Power-Density Bidirectional GaN-Based CLLC Converter for Electric Vehicles

In this paper, a bidirectional CLLC converter operating at MHz-level switching frequency is proposed to achieve high power density and high efficiency. An optimized stacked printed circuit board winding based planar transformer with adjustable leakage inductance is modeled and designed for the proposed converter. It is enabled using gallium nitride devices to achieve fast switching with low switching losses. A detailed power loss model is established for the efficient thermal design of the converter. A proof-of-concept hardware of 3.3 kW, 400–450 VDC input, 250–420 VDC output CLLC converter with 1 MHz operating frequency is built and tested over a wide range of loading conditions. The power density of the system is 9.22 W/cm3 (151.1 W/in3) and the peak efficiency achieves over 97%.

An Improved 4H-SiC Trench-Gate MOSFET With Low ON-Resistance and Switching Loss

In this paper, an improved 4H-SiC U-shaped trench-gate metal–oxide–semiconductor field-effect transistors (UMOSFETs) structure with low ON-resistance ( ${R}_{ \mathrm{\scriptscriptstyle ON}}$ ) and switching energy loss is proposed. The novel structure features an added n-type region, which reduces ON-resistance of the device significantly while maintaining the breakdown voltage ( ${V}_{\textsf {BR}}$ ). In addition, the gate of the improved structure is designed as a p-n junction to reduce the switching energy loss. Simulations by Sentaurus TCAD are carried out to reveal the working mechanism of this improved structure. For the static performance, the ON-resistance and the figure of merit (FOM $= {V}_{\textsf {BR}}^{\textsf {2}}/{R}_{ \mathrm{\scriptscriptstyle ON}}$ ) of the optimized structure are improved by 40% and 44%, respectively, as compared to a conventional trench MOSFET without the added n-type region and modified gate. For the dynamic performance, the turn-on time ( ${T}_{ \mathrm{\scriptscriptstyle ON}}$ ) and turn-off time ( ${T}_{ \mathrm{\scriptscriptstyle OFF}}$ ) of the proposed structure are both shorter than that of the conventional structure, bringing a 43% and 30% reduction in turn-on energy loss and total switching energy loss ( ${E}_{\mathbf {SW}}$ ).

Power Savings with all SiC Inverter in Electric Traction applications

The advantage of Silicon Carbide (SiC) based devices are less thermal management requirements and smaller passive components which result in higher power density. SiC devices have higher blocking voltages, lower on-state resistance and switching losses and higher thermal conductivity and operating temperatures. SiC devices can operate at higher voltages, higher frequencies and higher junction temperatures than comparable Si devices, which results in significant reduction in weight and size of the power converter and increase in system efficiency.

A Soft-Switching Step-Down PFC Converter With Output Voltage Doubler and High Power Factor

In this paper, a new soft-switching bridgeless single-phase power factor correction (PFC) converter is presented and analyzed. Employing an auxiliary switch, the input current dead angle that is the main drawback of the existing buck-type PFCs is omitted, and thus, the power factor (PF) is improved, which is the main contribution of the paper. Proposed PFC converter operates under discontinuous conduction mode (DCM) and draws sinusoidal input current from power supply inherently. All switches and diodes are turned on and off under soft switching, which leads to low switching losses and elimination of diode reverse recovery problems. Also, minimum numbers of semiconductor devices are in the power flow path that reduce the conduction losses. A 120-W laboratory prototype is implemented and experimental results verify the validity of theoretical analysis and show efficiency of 92.1%. In addition, total harmonic distortion (THD) of 3.3% is achieved and the input current harmonics complies with IEC61000-3-2 Class D requirements.

Characterization analysis and gate driver design for 1200 V 10 A SiC MOSFET

Silicon carbide (SiC) metal-oxide-semiconductor field-effect transistor (MOSFET) can work at high switching frequency with low switching loss compared with Si insulated gate bipolar transistor (IGBT). Although Si IGBT and SiC MOSFET have the same MOS-gate structure, the transient characteristics and the gate driver requirements for Si IGBT and SiC MOSFET are different. In order to fully utilize the advantages of SiC MOSFET, the gate driver of SiC MOSFET needs to be optimized to meet some special driving requirements. The paper aims to analyze the characteristics for the new generation of wide band gap semiconductor device SiC MOSFET and proposes a novel gate driver for SiC MOSFET. Meanwhile, the driving protection circuit of SiC MOSFET is also investigated. The performances of the proposed gate driver have been experimentally evaluated by double pulse test (DPT). In addition, the effect of different external capacitors [Formula: see text] and external driving resistances [Formula: see text] on the switch characteristics of SiC MOSFET is analyzed in detail.

SiC + Si three‐phase 48 V electric vehicle battery charger employing current‐SVPWM controlled SWISS AC/DC and variable‐DC‐bus DC/DC converters

Wide-bandgap (WBG) devices such as SiC and GaN switches are regarded as next-generation power semiconductors, due to their superior performance over conventional Si devices, for instance, a low switching loss and high thermal conductivity. Its bottleneck, however, is the high cost, which is critical for renewable energy and automotive industries. This study adopts SWISS AC/DC rectifier topology for the three-phase 380-480 VAC along with an isolated DC/DC converter, indicating such topology can maximise the advantages of Si (low conduction loss) and SiC (high switching loss), altogether thereby yielding the high performance and low cost. A novel space-vector pulse width modulation (SVPWM) was proposed to control such a current-source power factor correction, where only two SiC devices were adopted for the DC-bus voltage control. The closed-loop control of the grid current is realised for the unity power factor. Such topology further allows the DC-bus voltage to be varied with the output voltage, thereby minimising the system loss. A final prototype was built to charge a 48 V battery at 11 kW. Experimental results validated the effectiveness of such battery charger design.