Henri Schneider

High Current Ripple for Power Density and Efficiency Improvement in Wide Bandgap Transistor-Based Buck Converters

With the recent development and availability of wide bandgap devices in the market, more and more power converters are being designed with such devices. Given their fast commutation, when compared to their equivalent Si-based counterparts, these new devices allow increasing the converters efficiency and/or power density. However, in order to fully avail these new devices, one should precisely know their switching characteristics and exploit it the best way possible. This paper recalls our own precise method to measure separately turn-on and turn-off energies of wide bandgap devices. This method is applied to commercially available SiC and GaN transistors and results show that they present much lower turn-off than turn-on energies. For that reason, we show that a SiC-based buck converter must have high current ripple in the output filter inductor in order to decrease transistor losses. Analysis of these losses as well as experimental results are presented. Finally, the precise design of a 2-kW SiC-based buck converter for aircraft applications is performed for different current ripples and switching frequencies. We show that current ripple higher than 250% of the dc load current significantly decreases the converters losses, and consequently allows the increase of the switching frequency, which reduces the system volume and weight.

Accurate switching energy estimation of wide bandgap devices used in converters for aircraft applications

This paper describes a method which precisely estimates switching losses of fast power semiconductors. In this method, no transistor current is measured and, consequently the switching behavior of the transistor is not changed by the measurement system. By two different measurement modes, turn-off and turn-on losses can be estimated separately, which is necessary to precisely design isolated DC/DC converters used in aircrafts. The proposed switching loss measurement method is explained and experimental results on Silicon Carbide MOSFETs verify its operation and accuracy.

Study of CVD diamond films for thermal management in power electronics

Because of its high thermal conductivity and dielectric strength, diamond is a promising material for thermal management in high voltage, high power electronics. In this paper we present our investigation of CVD polycrystalline diamond films for heat sink applications. Dielectric strength and thermal conductivity have been measured at room temperature, for either home made or commercial samples. Though the measured dielectric strength remains lower than the 10 MV/cm expected value (greatly impacted by the surface polishing), the interest of diamond is confirmed.

Reconfigurable dual active bridge converter for aircraft applications

The increase of electrical energy consumption in modern aircrafts stimulates manufactures to install a 540V DC bus in future aircrafts, together with the existing 270V and 28V DC buses. Energy transferred between the high voltage DC bus (HVDC, 270V) and the low voltage DC bus (LVDC, 28V) is made by bidirectional isolated DC-DC converters. A performing topology for these types of converters is the Dual Active Bridge (DAB) given its soft switching properties and the low number of components, which allow the converter to be highly compact. This paper introduces a new topology of DAB (named DABRSP) which uses only 4 switches at the high voltage (HV) side and can be used in 270V and 540V DC buses without oversizing switches. Oversizing is observed if regular Full Bridge (FB) or Neutral Point Clamped (NPC) converters are used in the HV side of the DAB. The proposed topology allows Zero Voltage Switching (ZVS) and Zero Current Switching (ZCS) the same way as in a typical DAB converter and it makes uses of a particular transformer to “magnetically” sum up 2-level voltages.

Double three-phase Dual Active Bridge converter for high frequency high current applications

In a world of growing need for efficient energy conversion and distributed generation, Dual Active Bridge (DAB) converters represent a prominent converter topology given its soft switching properties and the low number of components, which allow the converter to be highly compact. Depending on the operating voltages and the transferred power, large circulating currents may occur. Parallel connection of converters is a good option in high current applications in order to adapt the converters to the use of standard semiconductors. Interleaving techniques provide, to both sides of the DAB converter, the reduction of the current ripple and the increase of its frequency. As a consequence the filters associated to the converter may be reduced. This paper introduces a new topology of DAB (named DABD3) which has a double three-phase connection in the low voltage (LV) high current side of the converter. This topology allows Zero Current Switching (ZCS) in the high voltage (HV) side switches. It has the same number of switches with the same blocking voltage of a parallel association of three single phase DAB converters. However, it presents lower ripple in the DC bus current and lower switched current in the LV side, which reduces the losses of the whole system.