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EDNE MAY 2015

Power conversion New demands on DC-link power capacitors By J.Konrad, M. Koini, M. Schossmann, M. Puff, EPCOS OHG Following the trends in power electronics both automotive and industry applications need compact, reliable and cost effective components to reach the major targets of increased power density and miniaturisation. Key technologies such as fast switching semiconductors are already successful . Since electronic components and their characteristics become more and more complex, design solutions have to be found on the system level and in addition, the interaction of active and passive devices needs to be understood in detail. The DC-link capacitor – as part of the commutation loop and especially during semiconductor switching – has a lasting effect on the behaviour and efficiency of the application. Different power electronic designs use low inductive assemblies of semiconductors and DC-link capacitors to lower the voltage overshoot during turn-off 4. In most cases, system designers have to deal with capacitors of large volume and with large commutation loops. The “CeraLink” capacitor technology which is described in this paper and was introduced earlier in 1 and 2, shows high capacitance density as well as a very low self-inductance to keep the commutation loop inductancelow. DC-link capacitors in power electronics DC-link capacitors are used in most power converters to stabilise the DC-link voltage by balancing the interim difference between the input source and the output load. The voltage ripple needs to be minimised to avoid electrical stress to the source and semiconductors as well as to comply with EMI requirements. It also acts as energy storage during the hold-up time. Besides its major function, a DC-link capacitor should contribute to fast and efficient switching of the semiconductor by minimising the necessary space. To a large extent, the packaging and outline of a motor inverter is defined by the DC-link capacitor size 3. Therefore high capacitance density is a major key parameter in any effort to decrease the inverter volume and to increase the power density. Together with a high current handling capability, a low self-inductance and an optimised connection technique, a compact DC-link is a desirable attribute. This principle is also true for other power electronic converters, Figure 1. principle block picture and size comparison of a motor inverter (source: Volkswagen AG 3) where a miniaturisation of the DC-link capacitor is needed. Additionally, robustness requirements must be fulfilled for defined stresses (thermal, electric, environmental, and mechanical). Therefore, new developments in DC-link capacitor technologies have to focus on the demands of next generations of power electronics. Device characteristics: Ceramic material The continuation of this paper describes a new capacitor technology, “CeraLink”, that contains lead-lanthanum-zirconate-titanate ceramic (PLZT) as dielectric material (1, 2). Download PDF of Article Find DC-link capacitors on EETsearch 27 EDN Europe | MAY 2015 www.edn-europe.com


EDNE MAY 2015
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