Fabian Denk

Switching speed-control of an optimized capacitor-clamped normally-on Silicon Carbide JFET cascode

This paper presents the results of controlling the switching speed (dv/dt) of an optimized version of the capacitor-clamped normally-on Silicon Carbide (SiC) JFET cascode. The cascode circuit is an easy way to employ the normally-on SiC JFET in a normally-off configuration using a low-voltage Silicon (Si) MOSFET in series connection. The traditional cascode circuit exhibits some disadvantages, namely limited control of the switching speed and high frequency oscillations on the drain-source-voltage of the low-voltage Si MOSFET. The optimized capacitor-clamped cascode reduces the oscillations and enables control of the voltage and current slopes as well as implements a protection of the JFET gate. The theoretical background of the capacitor-clamped cascode and the control of voltage slope are explained and investigated experimentally.

Integrated PFC and series resonant frequency converter analysis and control

A control algorithm for an integrated power factor correction (PFC) and series resonant converter (SRC) using only two switches is presented, allowing to open loop control the AC input current and the DC output current independently. The theory for this approach is analyzed in time domain and a novel approach for open loop regulation is presented and verified. The software defined power (SDF) control algorithms determines the switching frequency and duty cycle of the converter.

Investigations of SMPD SiC-MOSFET phase-leg modules for MHz inverters

In this work we present results of investigations on the usability of ISOPLUS SMPD SiC-MOSFET phase-leg modules for medium-frequency resonant inverters. These modules combine excellent thermal performance, very low parasitic inductances and good switching performance with the benefits of surface-mountable packages. In the first step, a SPICE and a thermal simulation of a half-bridge inverter using the SMPD module and one using discrete SiC-MOSFETs in TO-247 package was performed. Here, the semiconductor losses of the discrete devices were 2.5 times higher than the one of the SMPD module. In the second step, a modular prototype of a resonant MHz half-bridge inverter with the SMPD module was built. A short circuit test and efficiency measurements with an ohmic load showed an excellent switching performance of the SMPD SiC-MOSFET phase-leg module in the MHZ range. With the inverter prototype, an efficiency of > 95% was measured, at a switching frequency of 2.01 MHz and an output power of 5.6 kW delivered to the load resistor.