Abstract
To achieve high efficiency and power density, silicon carbide (SiC)-based Inductor-Inductor-Capacitor (LLC) resonant converters are applied to the DC/DC converter stage of a solid-state transformer (SST). However, because the input voltage of an SST is higher than the rated voltage of a commercial SiC device, it is essential to connect SiC devices in series. This structure is advantageous in terms of voltage rating, but a parasitic capacitance tolerance between series-connected SiC devices causes voltage imbalance. Such imbalance greatly reduces system stability as it causes overvoltage breakdown of SiC device. Therefore, this paper proposes a switching scheme to solve the voltage imbalance between SiC metal-oxide-semiconductor field-effect transistors (MOSFETs). The proposed scheme sequentially turns off series-connected SiC MOSFETs to compensate for the turn-off delays caused by parasitic capacitor tolerances. In addition, dead-time selection methods to achieve voltage balance and zero voltage switching simultaneously are provided in detail. To verify the effectiveness of the proposed scheme, experiments were conducted on a 2 kW series-connected SiC MOSFET LLC resonant converter prototype.
Highlights
Due to the recent interest in smart grid, distributed power system, and renewable energy, researches have been actively conducted to replace large and heavy line-frequency transformers
Equation (29) indicates that charge supplied by the magnetizing current ILm,pk should be larger than the charge necessary for fully charging and discharging the output capacitance of all switches in the dead-time
This paper proposes a switching scheme to overcome voltage imbalance in series-connected silicon carbide (SiC)
Summary
Due to the recent interest in smart grid, distributed power system, and renewable energy, researches have been actively conducted to replace large and heavy line-frequency transformers. A solid-state transformer (SST) proposed as a solution is a power converter that converts the magnitude or type of voltage using a power semiconductor and a high-frequency transformer [1,2,3,4]. An SST consists of an AC/DC rectifier stage, a DC/DC converter stage, and a DC/AC inverter stage. The DC/DC converter stage enables DC voltage conversion, high power density, and galvanic isolation by using a high-frequency transformer. The most commonly used topology for the DC/DC converter stage is a dual active bridge (DAB) [5,6,7,8], which exhibits characteristics of galvanic isolation and high power density, and can achieve zero-voltage switching (ZVS) without additional circuit. Due to a high turn-off current, the turn-off loss is large and it is difficult to guarantee
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