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This article presents an analysis of the different loss modes of the switching devices in a class-D series resonant converter operating with either fixed dead time or fixed duty cycle. A feasible operating region where the FETs in the inverter stage only exhibit reverse conduction losses, with no hard-switching, is identified. Furthermore, the impact of using a fixed dead time versus a fixed duty cycle is investigated. We find that using a fixed dead time is superior to using a fixed duty cycle, as a broader operating range can be achieved for the same losses, or the same operating range can be achieved with lower losses. A reduction in the reverse conduction losses of up to 59% or an expansion of the operational frequency range by 33% when using a fixed dead time is found. The modeling approach is validated on a 1-MHz prototype employing GaN switching devices. Lastly, a design example shows how the presented analysis can be used to determine the optimal fixed dead time/duty cycle for use with frequency modulation control such that the losses are minimized. [ABSTRACT FROM AUTHOR]

Zero-voltage-switching (ZVS) of dual active bridge (DAB) converter and its range extension have been studied intensively. However, this article proves that the external inductance location, i.e., placing on which side of the transformer, does affect the ZVS operation due to transformers’ parasitic capacitances, in particular, at a high switching frequency of higher than 1 MHz. Thus, this article, for the first time, gives the mathematical model of the resonant transition during the dead time and thereby analyzes partial hard switching under different modulation schemes with consideration of transformer's parasitic capacitances. From the analysis of ZVS operation, the solution of splitting the interfacing inductance and placing them on both sides of the transformer is proposed and its associated methodology of selecting these inductances is introduced. It extends the ZVS for all the switching devices and, therefore, enhances the efficiency or moves losses away from the critical semiconductor devices. Finally, the theoretical analysis is verified by the experimental results from a 1-MHz gallium nitride based DAB converter prototype. [ABSTRACT FROM AUTHOR]

With the emerging technology of wide-band-gap power semiconductors and modern ferrite materials, the switching frequency of dc–dc converters can be pushed to mega-hertz range to achieve higher power density. In order to deal with a high conduction current, multiphase converters are adopted to distribute the current for both power devices and windings. However, the current unbalance among phases may cause unexpected power loss to the converters. In this letter, the current unbalance issue is addressed by an integrated current balancing transformer for a two-phase dc–dc converter. The current of two phases in the converter can be automatically compensated to be identical by the proposed structure, which also reduces the complexity of the control system. A 1-MHz GaN-based two-phase buck converter is built to verify the proposed structure and its efficiency achieves 97.5% at 4 V/6 A output with the ZVS turn-on of the switches. [ABSTRACT FROM AUTHOR]

This paper presents design of an isolated high-step-down dc–dc converter based on a class-DE power stage, operating at a 10-MHz switching frequency using enhancement-mode gallium nitride transistors. The converter operating principles are discussed, and the power stage design rated for 20 W is presented for a step down from 200–300 V input to 0–28 V output. Commercially available magnetic materials were explored and the high-frequency resonant inductor and transformer designs using a low-loss Fair-Rite type 67 material are presented. Finite-element simulations have been performed to estimate the parameters of magnetics at 10-MHz. Experimental results are presented at 12 W, 254 V input to 22 V output and 5 W, 254 V input to 14 V output on a laboratory prototype operating at 10-MHz. At 20 W, the experimental prototype achieved an efficiency of 85.2%. [ABSTRACT FROM AUTHOR]

A new method is implemented in designing of self-oscillating loop for driving piezoelectric transformers (PT). The implemented method is based on combining both analog and digital control systems. Digitally controlled time delay through the self-oscillating loop results in very precise frequency control and ensures optimum operation of the PT in terms of gain and efficiency. Time delay is implemented digitally for the first time through a 16-b digital-to-analog converter in the self-oscillating loop. The new design of the delay circuit provides 45-ps time resolution, enabling fine-grained control of phase in the self-oscillating loop. This allows the control loop to dynamically follow frequency changes of the transformer in each resonant cycle. Ultimately, by selecting the optimum phase shift, maximum efficiency under the load and temperature condition is achievable. [ABSTRACT FROM AUTHOR]

It is well known that multilevel converters can offer significant benefits in terms of harmonic performance and reduced switching losses compared to their two-level counterparts. However, for lower voltage applications the neutral-point-clamped inverter suffers from relatively large semiconductor conduction losses because the output current always flows through two switching devices. In contrast, the T-type multilevel inverter has less conduction losses because only a single outer loop switching device is required to connect the converter output to the upper and lower dc buses, albeit at the expense of increased switching losses since these outer switches must now block the full dc link voltage. Silicon carbide (SiC) mosfet devices potentially offer substantial advantage in this context with their lower switching losses, but the benefit of replacing all switching devices in a T-type inverter with SiC mosfets is not so clear-cut. This paper now explores this issue by presenting a detailed comparison of the use of Si and SiC devices for a three-level T-type inverter operating in grid-tie applications. The study uses datasheet values, switching loss measurements, and calibrated heat sink thermal measurements to precisely compare semiconductor losses for these two alternatives for a T-type inverter operating at or near unity power factor. The results show that replacing only the dc bus connection switches with SiC devices significantly reduces the semiconductor losses, allowing either the converter power level or the switching frequency to be significantly increased for the same device losses. Hence, the use of SiC mosfets for T-type inverters can be seen to be an attractive and potentially cost-effective alternative, since only two switching devices per phase leg need to be upgraded. [ABSTRACT FROM AUTHOR]

This paper presents a comparative evaluation of the loss and thermal performance of two advanced three-level inverter topologies, namely the partial silicon carbide (SiC) T-Type and the Hybrid-neutral-point-clamped (NPC), both of which are aimed at reducing the high switching losses associated with a conventional Si T-Type inverter. The first solution directly replaces the 1200 V primary Si IGBT switches with lower loss 1200 V SiC MOSFETs. The second solution strategically adds 600 V CoolMos FET devices to the conventional Si T-Type inverter to reduce the primary commutation losses. Semiconductor loss models, experimentally verified on calibrated heat sinks, are used to show that both variations can significantly reduce the semiconductor losses compared with the Si T-Type inverter. The results show that both alternatives are attractive if high efficiencies and reduced thermal stress are major requirements for the converter design. [ABSTRACT FROM PUBLISHER]

This paper presents the design, modeling, and control of an isolated dc-dc three-port converter (TPC) based on an interleaved-boost full-bridge converter with pulsewidth modulation (PWM) and phase-shift control for hybrid renewable energy systems. In the proposed topology, the switches are driven by phase-shifted PWM signals, where both phase angle and duty cycle are the controlled variables. The power flow between the two inputs is controlled through the duty cycle, whereas the output voltage can be regulated effectively through the phase shift. The primary-side MOSFETs can achieve zero-voltage-switching (ZVS) operation without additional circuitry. Additionally, due to the ac output inductor, the secondary-side diodes can operate under zero-current-switching (ZCS) conditions. In this study, the operation principles of the converter are analyzed and the critical design considerations are discussed. The dynamic behavior of the proposed ac-inductor-based TPC is investigated by performing state-space modeling. Moreover, the derived mathematical models are validated by simulation and measurements. In order to verify the validity of the theoretical analysis, design, and power decoupling control scheme, a prototype is constructed and tested under the various modes, depending on the availability of the renewable energy source and the load consumption. The experimental results show that the two decoupled control variables achieve effective regulation of the power flow among the three ports. [ABSTRACT FROM PUBLISHER]

This paper deals with a thorough analysis of zero-voltage switching, especially for bidirectional inductorless piezoelectric transformer-based switch-mode power supplies with a half-bridge topology. Practically, obtaining zero-voltage switching for all of the switches in a bidirectional piezoelectric power converter is a difficult task. However, the analysis in this paper will be convenient for overcoming this challenge. The analysis defines the zero-voltage region indicating the operating points whether or not soft switching can be met over the switching frequency and load range. For the first time, a comprehensive analysis is provided, which can be used as a design guideline for applying control techniques in order to drive switches in piezoelectric transformer-based converters. This study further conveys the proposed method to the region where all the switches can obtain soft switching. Moreover, the analysis can be applied to other types of resonant converters with or without piezoelectric transformers. Experimental and simulation results are provided verifying the performed analysis. [ABSTRACT FROM AUTHOR]

Soft switching is required to attain high efficiency in high-frequency power converters. Piezoelectric-transformer-based converters can benefit from soft switching in terms of significantly diminished switching losses and stresses. Adequate dead time is needed in order to deliver sufficient energy to charge and discharge the input capacitance of piezoelectric transformers in order to achieve zero-voltage switching. This paper proposes a method for detecting the optimum dead time in piezoelectric transformer-based switch-mode power supplies. The provision of sufficient dead time in every cycle of the switching period results in the quick start-up of resonant current inside the transformer. The new method is implemented by dynamically detecting the optimum dead time for each resonant cycle and results in reduced energy loss and, consequently, increased efficiency in the converter during initialization time and steady-state operation. The theory of optimum dead time operation is also discussed in this paper. Experimental results and simulation are provided to show the implementation of the concept. [ABSTRACT FROM AUTHOR]

This paper presents a digital control technique to achieve valley switching in a bidirectional flyback converter used to drive a dielectric electroactive polymer-based capacitive incremental actuator. This paper also provides the design of a low input voltage (24 V) and variable high output voltage (0–2.5 kV) bidirectional dc–dc flyback converter for driving a capacitive incremental actuator. The incremental actuator consists of three electrically isolated mechanically connected capacitive actuators. It requires three high-voltage (HV) (2–2.5 kV) bidirectional dc–dc converters to accomplish the incremental motion by charging and discharging the capacitive actuators. The bidirectional flyback converter employs a digital controller to improve the efficiency and charge/discharge speed using the valley switching technique during both charge and discharge processes, without the need to sense signals on the output HV side. Experimental results verifying the bidirectional operation of a HV flyback converter are presented using a 3-kV polypropylene-film capacitor as the load. The energy-loss distributions of the converter are presented when 4- and 4.5-kV HV mosfets are used on HV side. The flyback prototype with a 4 kV mosfet demonstrated 89% charge energy efficiency to charge the capacitive load from 0 V to 2.5 kV, and 84% discharge energy efficiency to discharge it from 2.5 kV to 0 V. [ABSTRACT FROM AUTHOR]

Power electronics is a fast-developing technology within the electrical engineering field. This paper presents the results and experiences gained from applying design-oriented project-based learning to switch-mode power supply design in a power electronics course at the Technical University of Denmark (DTU). Project-based learning (PBL) is known to be a motivating problem-centered teaching method that not only places students at the core of teaching and learning activities but also gives them the ability to transfer their acquired scientific knowledge into industrial practice. Students choose a specification to implement from various power converter application projects, such as a fuel cell power conditioning converter, a light-emitting diode (LED) driver or a battery charger. The students select the topology, design magnetic components, calculate input/output filters and design closed-loop controllers necessary to fulfill the requirements listed in the chosen specification and thus meet the project's goals. This paper presents the course teaching plan and teaching methods, assessment method and student feedback. [ABSTRACT FROM PUBLISHER]

With the advancement of material science, various smart materials with intrinsic capacitive property are emerging. The high-voltage (HV) power electronics converters with bidirectional energy flow functionality for supplying the capacitive load are highly demanded. A switching cycle-based analytical model of an HV bidirectional converter driving capacitive load is beneficial in thoroughly understanding the operational behavior, investigating the energy efficiency, and optimizing the design. In this paper, an HV bidirectional flyback converter for capacitive load is generally discussed in terms of configuration and working principle. Considering the parasitic elements as well as the core loss effect, the converter is modeled with analytical formulas for one switching cycle. The comparison between the model-based calculation results and prototype experiments-based measurement results are used to validate the analytical model. [ABSTRACT FROM AUTHOR]

This paper presents the design of a resonant converter with a switching frequency in the very high frequency range (30-300 MHz), a large step down ratio (ten times), and low output power (1 W). Several different inverters and rectifiers are analyzed and compared. The class E inverter and rectifier are selected based on complexity and efficiency estimates. Three different power stages are implemented; one with a large input inductor, one with a switch with small capacitances, and one with a switch with low on-resistance. The power stages are designed with the same specifications and efficiencies from 60.7-82.9% are achieved. [ABSTRACT FROM AUTHOR]

This letter presents a new zero-voltage-switching (ZVS) isolated dc–dc converter which combines a boost half-bridge (BHB) cell and a full-bridge (FB) cell, so that two different type of power sources, i.e., both current fed and voltage fed, can be coupled effectively by the proposed converter for various applications, such as fuel cell and supercapacitor hybrid energy system. By fully using two high- frequency transformers and a shared leg of switches, number of the power devices and associated gate driver circuits can be reduced. With phase-shift control, the converter can achieve ZVS turn-on of active switches and zero-current switching (ZCS) turn-off of diodes. In this letter, derivation, analysis, and design of the proposed converter are presented. Finally, a 25–50 V input, 300–400 V output prototype with a 600 W nominal power rating is built up and tested to demonstrate the effectiveness of the proposed converter topology. [ABSTRACT FROM AUTHOR]

A new pulse width modulation (PWM) strategy which is an alternative approach of the discontinuous PWM (DPWM) for a three-level neutral-point-clamped (NPC) inverter is developed and presented in this paper. The proposed PWM scheme not only takes advantage of the special properties available in NPC inverters, but also reduces the switching loss of the inverter along with an inherent neutral point (NP) voltage control. Based on a circuit-level decoupling concept, the NPC inverter can be decoupled into two three-level Buck converters in every defined operating section, and thereby the controller design can be simplified. The salient features of the proposed scheme, as compared with the existing carrier-based DPWM strategies, are: 1) its reduced computational processing time, 2) its capability to balance the dc-link voltage without any additional control, and 3) its reduced complexity, e.g., only one carrier wave needed for pulse width modulating. Same as a space-vector modulation, the maximum modulation index, 1.1547, can be attainable by the proposed scheme. Moreover, compared to conventional continuous sinusoidal PWM, using this technique proposed here, the switching losses of the devices can be reduced by one third. In order to explain the operation of this topology properly, the decoupling principle including the driving signal synthesis and the NP potential variation are analyzed in detail in this paper. Finally, the viability and performance of the proposed modulation scheme are shown through simulation and experimental results in a laboratory prototype. [ABSTRACT FROM PUBLISHER]

Most switched mode power supplies provide a regulated voltage at their output. However, there are applications requiring a controlled current. Among others are battery chargers, test equipment for converters driven by solar cells, and LED drivers. This paper describes a dc–dc power converter realizing such a current source. The converter is based on a boost converter, supplied by a voltage source and acting as a current source. The boost converter can increase the output voltage above the input voltage. The converter provides a high control bandwidth based on a self-oscillating current loop. As additional practical features, soft start and output overvoltage limitation are included and described in this paper. The modulator, the control, and the power stage are described in detail and verified by the experiment. [ABSTRACT FROM AUTHOR]