Conference Paper

Highly efficient SiC inverter for aircraft application with innovative thermal management

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Power electronic systems for aircraft applications gain more and more interest due to increasing gravimetric power density on power stage level by utilizing advantages of WBG devices. However, the overall system design has to be optimized, including housing, mechatronic design and thermal management. This paper presents the power stage design of a highly efficient SiC drive inverter with fail-operational capabilities for a small electric aircraft utilizing only the laminar flow given by the air speed on the surface and thermal capacities of the inverter housing for cooling means.

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... The first concept of the Alice aircraft by Eviation had wingtip motors that moved heat to the streamlined surface of the nacelle where it was convected away Zivan (2019). Another example of an electric aircraft that uses this basic form of a heat exchanger is the aircraft concept by iSight of Fraunhofer, which mounts the hot motor controller components directly on the motor nacelle Bentheimer et al. (2019). The X-57 high lift motor also uses this method to cool both the high lift motors and their motor controllers . ...
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Electrified aircraft benefit from the versatile ways electric motors can be integrated with an airframe. However, thermal management is needed to move waste heat out of the motors because the heat is not expelled with the exhaust as in a conventional engine. Plate-fin, fin, and surface heat exchangers are incorporated as air-side heat exchangers for electrified aircraft thermal management systems. Typically, analytic tools are used to design heat exchangers within these categories. However, analytic tools lack the fidelity required for detailed shaping and assessment of general heat exchanger configurations. Tools based on first principles, such as finite element analysis or computational fluid dynamics, can verify heat exchanger performance but are too costly to use in a manual design loop. Shape optimization can be used with first-principles-based models to design heat exchangers without limiting the geometry to those previously well studied. In this work, we apply this methodology to design a heat sink for the high-lift motor of an electric technology demonstrator, the X-57 Maxwell. We use a gradient-based optimizer to modify the thickness distribution of the heat sink to find designs that minimize drag while meeting the heat load constraint. To model the heat transfer from the motor, we use both convection-only and conjugate heat transfer models and compare the resulting differences in the optimized shapes. We found that the convection-only model under-predicted heat rejection and thus led to larger than necessary heat sinks when used in optimization. To study the effect of the heat load on the design, we compare the heat sinks designed for the baseline motor and heat sinks designed for less efficient motors. Our study results show how the heat exchanger’s geometry changes from uniformly thick to designs with fins as the heat load increases. Furthermore, we found that the variation in drag across designs is driven by differences in the pressure drag due to flow separation. Finally, we conclude with a comparison of the optimized designs to those representing more simple fin designs and find that the optimized designs have fins that are shifted forward to reduce the adverse pressure gradient, which mitigates separation on the aft part of the fin. The developed shape optimization method could also be applied to improve other heat exchangers, specifically those designed to reject relatively low amounts of heat.
Conference Paper
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There is a growing need for highly efficient, power dense DC-AC converters to support a number of future more electric aircraft technologies. SiC has been identified as a potential technology to improve the efficiency of these converters. To analyse the semiconductor losses, this paper presents the semiconductor loss equations for the two-level converter (2LC), three-level neutral point clamped converter (3LNPCC) and the three-level T-Type converter (3LTTC). Based on the equations and current datasheet information, it is identified that SiC technology offers significant reductions in losses compared with traditional Si devices. The paper also discusses a number of hybrid device combinations to achieve the benefits of high efficiency in SiC technology and low cost of Si technology. Based on the semiconductor losses the converter efficiencies in the SiC 2LC and the 3LTTCs are about 3-4 % higher than in the Si 2LC for a 42 kW three phase converter operating at a 25 kHz switching frequency.
This paper presents and evaluates three accurate (20 %) calorimetric switching loss measurement methods, which are capable of measuring hard- and softswitching losses at high speed (20-25 min/point) compared to other calorimetric methods. A comprehensive switching loss measurement data accuracy analysis is done, setting the benchmark for the accuracy analysis of switching loss data. The high accuracy in the switching loss data is obtained by a high ratio of switching losses to total measured losses in the Device Under Test. This is achieved by using a full-bridge configuration, where the conduction losses are reduced up to 80% in the Device Under Test by utilizing the duty cycle as an additional degree of freedom compared to a half-bridge configuration. Furthermore, the proposed calorimetric methods yield more reliable switching loss data than electrical methods, particularly than the double pulse test. Switching loss data is presented for the 900V, 75 A, 10m SiC MOSFETs from CREE, that are one of the first discrete SiC MOSFETs to come with a TO-247-4 package.
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This paper proposes a digital PWM control technique for a segmented permanent magnet synchronous motor with multi-phase interleaved PWM inverters. A segmented motor with its segmented stator windings can be connected and excited by segmented PWM converters using multiphase interleaved PWM techniques. A phase shedding control strategy is developed for efficiency optimization when operating in light load condition. A digital PWM modulator with adjustable switching frequency and phase shift has been realized with FPGA. Analysis oriented simulation has been carried out for the loss analysis of the multiphase interleaved PWM inverter. Experimental verification has been carried out to show the improvement of the proposed digital PWM technique.
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In automotive industry space is extremely limited. The efficient and fast control of electric motors is a key technology to save energy and space. This paper shows strategies to improve energy consumption of a redundant Voltage Source Inverter (VSI) and an associated double three-phase Permanent Magnet Synchronous Motor (PMSM). Focus is to significantly reduce the DC link power dissipation of the power electronics to extend life time or to reduce the capacity and thus the size required to install the capacitors. In particular, shifted control technique and in addition phase displacement are developed and implemented on a drive unit used in automotive application to control the multi-phase system. Analytical calculations show that these strategies reduce the DC link capacitor effective current value. The conventional three-phase PMSM is compared with the double three-phase PMSM run with the new control strategies.
Record-low 10mΩ SiC MOSFETs in TO-247, rated at 900V
  • V Pala
  • G Wang
  • B Hull
  • S Allen
  • J Casady
  • J Palmour
V. Pala, G. Wang, B. Hull, S. Allen, J. Casady and J. Palmour, "Record-low 10mΩ SiC MOSFETs in TO-247, rated at 900V," 2016 IEEE Applied Power Electronics Conference and Exposition (APEC), Long Beach, CA, 2016, pp. 979-982.
A segmented traction drive system with a small dc bus capacitor
  • G J Su
  • L Tang
G. J. Su and L. Tang, "A segmented traction drive system with a small dc bus capacitor," 2012 IEEE Energy Conversion Congress and Exposition (ECCE), Raleigh, NC, 2012, pp. 2847-2853.