Bernd Eckardt

SiC MOSFETs in Hard-Switching Bidirectional DC/DC Converters

In this study, the necessity and beneficial characteristics of SiC power devices for novel power electronic applications are shown from an application point of view. The body diode properties of state of the art 1200 V SiC MOSFETs are discussed and the dependencies of switching speed are derived. Furthermore, the calculation of the fundamental efficiency limit of 99.67 % at the example of a bidirectional DC/DC converter operating at 100 kHz is shown.

Unidirectional fast switching non-isolated 100 kW fuel cell boost converter

This paper describes the power stage of a non-isolated unidirectional 400 V 100 kW DC-DC converter for fuel cell vehicles that reaches a switching frequency of 150 kHz with industry power modules. The power modules are equipped with custom made DCB-substrate assembled with a combination of fast 600 V superjunction Si-MOSFETs and SiC-Schottky diodes. For all other components like drivers, current sensors and the auxiliary supply converter standard products have been used to facilitate an automotive specification, and a cost efficient production. The inductors are custom-made to reduce choke losses and volume. The converter reaches an efficiency of 98 % at full load (166->400 V, 590 A lowside current). Furthermore a simple and reliable DC-link discharge unit is described that discharges with constant power and is far smaller and faster than a conventional resistor solution. Based on a constant current discharge device using a Power MOSFET in linear operation, it is extended with a small analog circuit to a roughly constant power discharge device.

Thermal characterization of an axle-twin-drive with system integrated double-inverter

Integrated drive-units for electric vehicles (EV) with combined electric machines and power electronic components offer the chance to achieve compact and cost-optimized traction systems. The demand for high power-densities and the requirement of a reliable system operation lead to the necessity of an enhanced thermal management. In the present paper, the build-up of an integrated drive-unit with 2×20 kW is described. A thermal simulation model of the used traction machines, based on Cauer-networks and parameterized with FEM-simulations and measurements, allows an analysis of transient temperature profiles for various driving situations as well as a determination of internal temperatures.

Highly filled polymers for power passives packaging

This paper presents a packaging technology for passive devices and characterization results of a demonstrator. Due to high demands on weight, cost and size this demonstrator was chosen to show the potentials of highly filled polymers for packaging solutions in power electronics especially for automotive and aerospace applications. As a demonstrator a choke for a high power multiphase 100 kW DC/DC converter was chosen. A highly filled thermal conductive thermo-plastic polymer (TC-polymer) was used to package the choke with high demands on the cooling. The TC-polymer was used to cover the total surface of the ringcore and the copper windings in one injection molding process and to realize an improved heat transport through the polymer towards the water cooled heat sink. Thermal simulations of the power losses prior to the experimental test setup showed the enormous potentials of TC-polymers. Based on these simulations different compounds of highly filled polymers with different filler fractions of 40 vol.%, 50 vol.% and 60 vol.% Al2O3 filler were produced and used to house the choke in an injection molding process. The high filler fraction and the thermal conductivity, which is one order in magnitude higher than unfilled polymers, lead to changed process conditions, compared to standard injection molding, especially with respect to temperature and pressure conditions during the molding process. The research results show restrictions and challenges in the over-molding of chokes with thermal conductive compounds, as well they revealed the viability of solution strategies. After optimizing the process, using non destructive analysis methods for the choke, it became possible to produce inductive devices with a TC-polymer package. An experimental setup with one phase of the power converter was built up to verify the simulation results. The temperature distribution of the inductive device was investigated and documented. The experiments show the extensive potentials of TC-polymers in power electronic applications.

A simple, reliable, cost and volume saving DC-link discharge device for electric vehicles

This paper describes a DC-link discharge device that is smaller and cheaper than conventional resistor or PTC-based solutions. The basic idea is to use the switching element (IGBT, Mosfet), that is usually controlling the PTC or resistor, in a linear mode and decrease the maximum power by shifting the discharge curve from an uncontrolled square voltage dependent curve to a roughly constant power characteristic. The advantages in volume and costs are described and the technical setup is explained and compared to the conventional solutions.

Galvanic isolated auxiliary power supply with high power density and efficiency

Current isolated DC/DC converters with wide input and output voltage ranges achieve power densities from 2 kW/dm3 to 5 kW/dm3. In this paper, a galvanic isolated 500 W auxiliary power supply with a power density of 9.2 kW/dm3 and peak efficiency of up to 96.1 % is presented. In the first chapter, suitable fields of application, like electrical or hybrid cars and DC-grids, are mentioned. In the second chapter, basic considerations of the converters electrical design are presented. The topology of the half bridge with center taped synchronous rectifier is shown. In the third chapter, the assembly concept is presented, by taking cost and manufacturability into account. In order to achieve these design targets, a complete planar assembled power part with PCB integrated transformer and output inductance was chosen. The converters mechanical design is described. In the fourth chapter, the cooling concept is discussed. The realization is shown by means of the power stages PCB design. The main components of the power stage are thermally characterized. The verification of the chosen cooling concept is carried out with thermal measurements. It is shown that all components are operating in their permanent allowed temperature ranges. In the last chapter, the DC/DC converter is characterized. It is shown that with different transformer designs the efficiency curve can be matched to the load profile of the desired application. With this optimization the average system efficiency can be significantly improved. Furthermore the utilization of the 500 W DC/DC converter in a 3 kW DC/DC converter system, to further improve the converter systems part load efficiency, is investigated. The ideal load distribution between the two converters or rewording phases is calculated and the achievable system efficiency is diagrammed. At light load conditions, like power safe modes, up to 25 % efficiency gains were realized.