Georges Engelmann

A systematic comparison of hard- and soft-switching topologies for inductive power transfer systems

This paper provides a comparison of four series-series compensated inductive power transfer systems for contact-less vehicle charging. A systematic comparison between hard-and soft-switching topologies, as well as different operating frequencies, is performed and the impacts on system efficiency and complexity are assessed in detail. In a holistic design process each system is individually optimized for a charging power of 3kW and a variable air gap from 100mm to 170mm at a coil diameter of 500mm. It is shown that the hard-switching topologies are highly attractive in the considered power range even with state of the art semiconductors. By introducing a dual-side controlled topology a superior system efficiency is demonstrated at an operating frequency of 35 kHz.

A highly integrated drive inverter using DirectFETs and ceramic dc-link capacitors for open-end winding machines in electric vehicles

A highly integrated inverter for open-end winding machines is designed and build. This paper presents the design of a 6-phase full-bridge inverter for driving an open-end winding machine for electric vehicles. The inverter consists of six full-bridge phase modules that are arranged in a hexagonal shape inside the motor housing. DirectFETs with double-side cooling are used as switching elements. Each module has its own bank of ceramic capacitors. A low-inductive layout allows continuous operation in the nominal operating point at a dc-link voltage of 145V, which is extremely close to the breakdown voltage of the DirectFETs of 150V. In the nominal operating point with a dc-link voltage of 125V, a maximum efficiency of η = 97% is reached.

Peltier module based temperature control system for power semiconductor characterization

In the design or simulation phase of a power electronics converter, it is, among others, necessary to have accurate power semiconductor loss models. Such models can be extracted from datasheet values, but they do quite often not cover a wide variety of parameters such as dc-link voltage, temperature or even gate resistance. A double pulse test bench [1] was designed and built to measure switching losses of power semiconductors over a wide variety of different parameters. Some parameters, such as temperature or gate resistance, require additional hardware compared to setting a voltage or current level. This work will present a temperature control system installed in the afore mentioned test bench which enables automated temperature adjustment of the device under test (D.U.T.) by avoiding liquid based cooling setups. Positive as well as negative temperatures in the range of -40°C to 200°C are implemented. At first, the overall system concept and its features are presented. In a second part, focus is given to the different hardware key parts of the unit as well as insights into the temperature control. Measurement results showing the accuracy of the settled temperatures finalize this work.

Experimental analysis of the switching behavior of an IGBT using a three-stage gate driver

In this work, a gate driver with multiple stages based on switched resistors is presented. The influence of the different stages on the turn-on and on the turn-off behaviour is investigated using experimental measurements conducted on a double pulse test bench. It is shown that, compared to a single-stage reference driver, switching loss improvements are possible while maintaining the same voltage overshoot and the same reverse recovery current, thus the same device utilization. As the switching loss determination is not trivial, a dedicated section is devoted to the turn-on and turn-off loss energy calculation. The paper concludes with measurements showing switching loss improvements of 9% and 26% for a turn-on and a turn-off event, respectively, using the same voltage overshoot and reverse recovery current peaks compared to an optimized single-stage driver.

A systematic comparison of various thermal interface materials for applications with surface-mounted (DirectFET TM ) MOSFETs

Increasing power densities of power electronics with reduced volume requires increased efforts in cooling as little surface and material are available for thermal conduction. A systematic comparison of the thermal resistance of a wide selection of thermal interface materials (TIMs) ranging from solid Al2O3 to elastomeric interface materials as well as thermal greases is investigated in this work. In contrast to the ideal testing conditions used by the TIM manufacturers, a practical application setup using a surface-mounted MOSFET (DirectFETTM) pressed on a heatsink is used. Thereby, additional influences on the thermal resistance due to surface finish or non-homogeneous pressure are considered in the results. The effective contacting area as well as different pressure levels are investigated. On the basis of a B6C converter bridge, it will be shown, how the proper choice of TIM affects the mechanical and thermal design of a converter.

Experimental Investigation on the Transient Switching Behavior of SiC MOSFETs Using a Stage-Wise Gate Driver

A multiple stage gate driver for SiC MOSFETs based on a switched resistor topology is introduced and a hardware realization is presented. The measurement setup is shown in detail to highlight the quality of the shown measurement results. The evaluation of the stage-wise driver is conducted by comparing the switch and diode peak voltages as well as peak currents with regard to the switching losses to a reference driver. The switching transients are generated using a double pulse test bench. A detailed investigation on two- and three-stage operation for both, the turnon and turn-off events are presented. A variation of gate resistors and different timings is conducted for each stage and evaluated using the resulting measurements. It is shown that the drain-source peak voltage is reduced by 45% while maintaining equal turn-off losses. Analogously, a reduction of 51% of the diode peak voltage and a reduction of 50% of the peak reverse recovery current at the same time is feasible for equal turn-on losses.

Experimental comparison of voltage and current source gate drivers for IGBTs

In this work, a current source gate driver based on a switched current mirror topology for an insulated-gate bipolar transistor (IGBT) is presented. The influence of different gate current levels for the turn-on and turn-off events is investigated. Experimental measurements are conducted using a double pulse test bench. The resulting switching trajectories as well as switching losses are compared to a standard push-pull driver stage using a variation of different gate resistors. It is found that the measured switching waveforms of the standard push-pull gate driver and the current source gate driver show equal performance. Furthermore, equal switching losses are found for equal overvoltage peaks and overcurrent peaks using both driver topologies.

Field oriented modeling and control of six phase, open-delta winding, interior permanent magnet synchronous machines considering current unbalance and zero sequence currents

Industrial and academic interest on multiphase electric machines have been steadily increasing due to the advantages they provide compared to their three phase counterparts. They offer higher efficiency and better fault tolerance. The power is distributed across a larger number of machine phases and inverter legs, which allows the use of semiconductor devices with lower ratings. These advantages are especially beneficial for electric and hybrid vehicle applications. Increasing the battery pack voltage of an electric vehicle increases the cost and complexity, while decreasing the energy density of the battery pack. Therefore, electric vehicle system design may benefit on the vehicle level from a more complex drivetrain with higher dc link voltage utilization. H bridge inverters as well as multiphase machines provide increased dclink voltage utilization compared to three phase inverters and machines. A low voltage, high power drivetrain is designed for an electric vehicle using an asymmetrical six phase, open-delta interior permanent magnet synchronous machine (IPMSM) and an H Bridge inverter. Field oriented modeling and control of such a system is investigated in this paper. The sources of unbalance and zero sequence current components are explored.