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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]

The momentum toward high efficiency, high frequency, and high power density in power supplies limits wide use of conventional wire-wound magnetic components. This paper gives an overview of planar magnetic technologies with respect to the development of modern power electronics. The major advantages and disadvantages in the use of planar magnetics for high-frequency power converters are covered, and publications on planar magnetics are reviewed. A detailed survey of winding conduction loss, leakage inductance, and winding capacitance for planar magnetics is presented so power electronics engineers and researchers can have a clear understanding of the intrinsic properties of planar magnetics. [ABSTRACT FROM AUTHOR]

Electrical power systems in future uninterruptible power supplies or electrical vehicles may employ hybrid energy sources, such as fuel cells and supercapacitors. It will be necessary to efficiently draw the energy from these two sources as well as recharge the energy storage elements by the dc bus. In this paper, a bidirectional isolated dc-dc converter controlled by phase-shift angle and duty cycle for the fuel-cell hybrid energy system is analyzed and designed. The proposed topology minimizes the number of switches and their associated gate driver components by using two high-frequency transformers that combine a half-bridge circuit and a full-bridge circuit together on the primary side. The voltage doubler circuit is employed on the secondary side. The current-fed input can limit the input current ripple that is favorable for fuel cells. The parasitic capacitance of the switches is used for zero voltage switching (ZVS). Moreover, a phase-shift and duty-cycle modulation method is utilized to control the bidirectional power flow flexibly and it also makes the converter operate under a quasi-optimal condition over a wide input voltage range. This paper describes the operation principle of the proposed converter, the ZVS conditions, and the quasi-optimal design in depth. The design guidelines and considerations regarding the transformers and other key components are given. Finally, a 1-kW 30~50-V-input 400-V-output laboratory prototype operating at 100-kHz switching frequency is built and tested to verify the effectiveness of the presented converter. [ABSTRACT FROM AUTHOR]

An important distortion mechanism in hysteretic self-oscillating (SO) class-D (switch mode) power amplifiers - carrier distortion - is analyzed and an optimization method is proposed. This mechanism is an issue in any power amplifier application where a high degree of proportionality between input and output is required, such as in audio power amplifiers or xDSL drivers. From an average-mode point of view, carrier distortion is shown to be caused by nonlinear variation of the hysteretic comparator input average voltage with the output average voltage. This easily causes total harmonic distortion figures in excess of 0.1-0.2%, inadequate for high-quality audio applications. Carrier distortion is shown to be minimized when the feedback system is designed to provide a triangular carrier (sliding) signal at the input of a hysteretic comparator. The proposed optimization method is experimentally proven in an audio power amplifier leading to THD figures that are comparable to the state of the art. Experimental hardware is a hysteretic SO bandpass current-mode-controlled single-ended audio power amplifier capable of 45 W into 8 Ω or 80 W into 4 Ω from a ±34 V supply with less than 0.03% THD from 100 Hz to 6.7 kHz. Carrier distortion is shown to account for this limitation in THD performance. [ABSTRACT FROM AUTHOR]