tantalum capacitors decreases rapidly with increasing frequency. Therefore, MLCCs can support large ripple currents and breakdown voltage tolerance and also ...
2018 International Conference on Computing, Mathematics and Engineering Technologies – iCoMET 2018
Review on Present and Future Integration Techniques for Capacitors in Motor Drives Rooh Ul Amin Shaikh
Ayesha Saeed
Rajesh Kumar
Department of Electrical & Electronic Engineering, The University of Nottingham, UK
Department of Electrical Engineering, NED University of Engineering & Technology, Pakistan
Department of Electrical Engineering, University of Tun Hussein Onn, Malaysia
Abstract— The structural and functional integration of passive components, power electronic converters, heat sinks and mechanical sub-systems is required to make an efficient and power dense electric motor-drive system which is essential for traction, aerospace and marine applications. The Integrated Motor Drives (IMD) has been at focal point with growing interest in power electronics research industry over past few years. Passive components such as filter inductors and capacitors entail significant amount of space in aerospace and automotive drive systems and have added penalties of high losses and weight. The integration of passive components in such systems offer many benefits such as power dense design, reduction in cost, mass, size and eases the manufacturing processes. This paper continues with reviewing available capacitor technologies and their thermal capabilities, selection and sizing of capacitors for drives, a brief overview of filter inductor integration already designed and presents some potential future approaches on integrating the output filter capacitor in the same PMSM drive. Keywords—Integrated Motor Drive (IMD), PMSM, Filters, Inductor, Capacitor.
I. INTRODUCTION Passive assemblies (inductors, capacitors) impose an obstruction to meet an ever increasing high power density demands in power electronic systems for electric drives employed in More Electric Aircrafts (MEA), Electric Vehicles (EV), Hybrid Electric Vehicles (HEVs), Marine Applications etc. which require close physical and functional integration of various electrical and mechanical sub-systems for reduced weight, size and costs targets. The assemblage of passives for power electronic systems is voluminous due to sizeable and disjunctive modules coming from different manufacturers with distinct technologies and large number of miscellaneous packaging parts, thus lending them geometrically un-optimized for high power density integration. Passive components for the filters usually occupy tremendous space of the whole drive system employed in
electric transportation applications. This is because they are separately conceived and devised after other drive components such as converters, gate driver circuits, control circuits and machine itself have been developed leading to distinct subsystems which calls for novel integration approaches [1, 2, 3]. II. LITERATURE REVIEW A. Capacitors for Drive Applications In VSI drives, capacitor (both for dc-link and output filter) presents to be one of the expensive and massive passive components. In power converters, its main function is to stabilize the dc bus voltage and to counterbalance the load difference between the input source and the output. They do so by absorbing the large ripple currents and restraining the voltage transients which occur due to switching action of the converter and thus providing a low impedance path for the switching harmonics. They can also be used to smooth battery current if used for traction drives. However, for large scale application of IMDs, one of the existing challenges among others is the designing of capacitors under high temperature and high frequency operations for use in power electronics in DC-link filters and AC filters. The main capacitor types available requiring research attention in Integrated Drives include: Ceramic Capacitors, Multi-layer ceramic capacitors, Electrolytic capacitors, Film Capacitors. The ideal requirements for Integration in a Drive System expects capacitors to possess high capacitance, compactness, operation at high temperatures, high voltage and/or current ratings, high energy densities and low cost to meet the challenges of increased power densities, thermal management and manufacturing for economically Integrated Drive systems. It is merely impossible to expect a passive component to have all such attributes, hence a trade-off has to be established between the applications and attributes. In the previous research undertaken, some novel approaches have been worked out to integrate the output filter inductor in a Permanent Magnet Synchronous Motor (PMSM) while leaving the filter capacitor and damping resistor outside the machine. This section highlights the properties, current trends and
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advancements in aforementioned capacitor types used for filters in terms of thermal capabilities, operation, ratings and their pros and cons with respect to drive applications. 1) Ceramic Capacitors Ceramic Capacitors are the most widely used components in modern electronics which can be used in high voltage and high temperature applications. The plenty of ceramic compositions and their manifold dielectric behavior have made them pervasive in many extreme environments. Custom-made ceramic capacitors also exist to cover potential gaps in other capacitor technologies such as high voltage capacitors with ratings from 50-100 kV [4]. High temperature ceramic capacitors that can bear temperatures up to 250℃ can be found. The disadvantages are low energy density, high costs and brittle nature, therefore the catastrophic failures requires extra caution in circuit design. Shocks and vibrations are usually notable in traction drives which raise reliability concerns over their mechanical firmness [1]. CeralinkTM is now developing an advanced ceramic capacitor technology which can operate both as dc-link and
TABLE I.
Dielectrics
Class I
Class II
Dielectric Constant Low (5 to few hundreds)
High (1000 to > 20000)
snubber capacitor as a compact element by locating the capacitor in close proximity with the semiconductor switch in the converter design. It is made with anti-ferroelectric material that can offer high capacitance at operating voltages, low losses at high temperatures and low parasitic values of Equivalent Series Resistance (ESR) and Equivalent Series Inductance (ESL) [5]. It has magnificent lifetime at temperatures above 125 ℃ due to high insulation level where hardly other capacitors can be used [6]. This technology can save the space in converter and increase power density. Some commercially available wide dielectrics for ceramic capacitors fabrication along with their properties are listed in Table I. 2) Multi-layer Ceramic Capacitors (MLCCs) MLCCs are distinguished for their high capacitance and compactness [7], high energy density, very high ac current ratings, high temperature operation up to 200℃ [1], and is the dominant form of ceramic capacitors. They feature small size, low cost, large capacitance per unit volume and is very little affected by environmental factors [8]. MLCCs are now acquiring wide spread attention in aerospace electronic equipment and automotive applications.
CERAMIC DIELECTRICS AND THEIR PROPERTIES
Dissipation Factor Low (
