Martin März

Novel cost-efficient contactless distributed monitoring concept for smart battery cells

The market breakthrough of electric vehicles is mainly delayed by the still too high costs of the battery system. The novel distributed battery cell monitoring and management concept presented in this paper allows a significant reduction of the final battery pack costs. Further, due to economies of scale, it provides reduced development costs and much lower time-to-market. The proposed concept provides a contactless cost-efficient data transmission interface with capacitive coupling, thus making the development of a battery monitoring circuit for each battery module type needless. The costs are mainly reduced thanks to the high volume manufacturing approach of novel smart battery cells integrating all the sensors of the monitoring electronics together with passive cell balancing and cell heating function. This paper describes the possibilities offered by the proposed concept and shows implementation examples of such a contactless distributed battery cell monitoring.

Thermal management in high-density power converters

This paper gives an overview of basic principles of the thermal management in high density power converters. Methods for heat removal on a device and circuit board level are discussed. New packaging technologies for discrete power semiconductors as well as multifunctional board integration techniques are included. A view is given on future 3D integration techniques that take into account the poor thermal conductivity especially of the passive component materials. With these techniques much higher power densities are possible. Some examples of prototype systems are presented, together with the achieved technical data.

Overview of different topologies and control strategies for DC micro grids

Overview, comparison and evaluation of common DC micro grid design considerations. The focus of this paper is to explore the main differences and advantages/disadvantages of various topologies and control strategies for DC micro grids. The requirements of various application areas can strongly influence the individual system design. Control strategies, single- or two-phase designs, earthing concepts, system voltages and power levels are discussed as well.

Full SiC DCDC-Converter with a Power Density of more than 100kW/dm3

This Paper describes a non-isolated bidirectional full SiC 800V 200kW DCDC-converter power stage for electric and hybrid vehicles that reaches a power density of more than 100 kW/dm3 at a switching frequency of 200 kHz. The high power density is achieved by the use of SiC-MOSFETs sintered on custom made Si3N4 DCB-substrates controlled by custom made extremely flat drivers and a resulting very low inductive DC-link connection. All passive components like inductors and capacitor boards are custom made in order to keep all parasitic effects as low as possible. The power is subdivided on six interleaved phases to reduce the required capacitor ripple current capability.

Modelling and measuring complex impedances of power electronic converters for stability assessment of low-voltage DC-grids

Interconnecting power converters within a low voltage DC grid can be a challenging task since these devices are rarely tested under final operating conditions during their development process in conjunction with converters from different manufacturers, different kinds of loads and appropriate grid impedances. In the worst case, stationary oscillations might occur in the grid setup for which the actual reason is hard to determine and solving the problem will require time-consuming trial and error means. Therefore, theoretical knowledge about how power converters react on grid-side disturbances is crucial for a preliminary analysis of the static and dynamic performance of low-voltage DC grids before plugging the devices together. Based on these considerations general guidelines for the dimensioning of control loops and grid-side capacitors of power converters can be derived. The following outlines describe the fundamentals of power converter behavior when exposed to disturbances occurring on the output current, e. g. from load steps. Another focus lies on shaping grid-side impedances of converters to avoid stability issues. Furthermore, a method to measure the impedances of interest is thoroughly described. All obtained results are verified in a brief case study.

Energy distribution with DC microgrids in commercial buildings with power electronics

This paper describes the application of a distributed DC microgrid in a commercial environment as well as the current state of the art and standardization efforts. The introduced grid features various sources and loads being interconnected with a 380 VDC bus. Here, focus lies on the implementation of a DC fast charge station for electro mobility into a DC grid as well as to elaborate the advantages compared to charging from the AC grid. Additionally, the application of DC nanogrids in workplace environments and their combination with a superordinate DC microgrid is presented. The benefits offered by nanogrids compared to conventional AC power supply in an office are discussed as well. Finally, the hardware to realize a DC microgrid within one electrical cabinet is introduced. Its versatility to fulfill a wide range of functions in the grid is shown as well.

Analytical Solution of Thermal Spreading Resistance in Power Electronics

A good understanding of thermal spreading resistance is crucial for thermal management in power electronics. In this paper, an analytical solution is developed for the determination of thermal spreading resistance with a heat source placed on a three-layer substrate, wherein the same footprint is assumed for different layers. An approximate approach is then proposed based on the analytical model when the substrate has unequal layer dimensions. Both the analytical model and the approximate approach are validated by comparing results with numerical simulations, and quite good agreement is observed. Moreover, to further improve the thermal performance of a power module, a new material with high thermal conductivity is used as an additional heat spreader. Parametrical study of the effect of such a heat spreader is carried out. Results show that the material holds promise for application in power electronics.

Fundamental efficiency limits in power electronic systems

In this paper, the efficiency limits of power electronic converters are investigated from a semiconductor point of view. The approach is presented on the example of a hard switching half bridge while taking Si, SiC and GaN devices into account. Beside parasitic effects of the semiconductors itself, further converter non-idealities and limits from a thermal point of view are discussed. All in all, the obtained results act as a design guideline and allow for an easy comparison of different semiconductor technologies.

An advanced voltage droop control concept for grid-tied and autonomous DC microgrids

Droop Control has been a well-established control technique both in AC and DC power distribution grids for many years, because it provides a simple way to equally distribute the load current between remote power sources. With the increasing demand for low voltage DC microgrids supplying high-reliability equipment, like servers in data centers, to work both grid-tied and autonomously without a connection to the AC mains and fueled only by local renewable and conventional power sources, voltage droop control is facing new challenges. With power equipment being delivered from several manufacturers the demand for a communication less control scheme that only uses the voltage at the terminal point or the converter output current as an indicator how the control set point should be changed in order to satisfy the energy demand of the loads arises. In consequence, the commissioning time of the DC microgrid is greatly reduced since all components can be simply plugged together without the need for adaptions. An outline for such an inherently autonomous voltage droop control scheme to keep the system voltage within a narrow band of ± 10 % of its 380 VDC nominal value is given in the following paper by describing voltage droop control modelling basics and the selection of characteristic droop curves for different kinds of power sources as well as by giving simulative results from a small-scale DC microgrid.

Polymer bonded soft magnetics for EMI filter applications in power electronics

In this study, polymer bonded soft magnetic materials (PBSMM) were investigated for the application as a magnetic core and electromagnetic shielding material in inductive devices for EMI filter applications. The nature of switch mode power converters makes them a potential source of EMI noise emission. EMI filters are generally necessary to ensure electromagnetic compatibility of converters to the other electronic equipment. Conventional discrete EMI filters usually comprise passive components with different volume and form factors. The manufacturing of conventional inductive components requires different processing and packaging technologies, of which many include cost intensive processing steps. Due to the parasitics of the discrete components and their interconnections the effective filter frequency range is limited. As a result discrete EMI filters are usually not integrable into an arbitrary formed volume and show relative high production costs. This study aims on solving this issue by the integration of inductive EMI filter components using polymer bonded soft magnetics. PBSMMs were produced using thermoplastic polyamide 6 matrix materials. The filler materials were chosen from the wide range of different soft magnetics. The magnetic properties were characterized using injection molded ring core test specimens and a computer controlled hysteresis recorder as well as an impedance analyzer. Inductive devices with PBSMM as magnetic core have great potentials in automotive applications that have to meet a high geometric flexibility and highest power densities.