Influence of PWM Methods on Semiconductor Losses and Thermal Cycling of 15-kVA Three-Phase SiC Inverter for Aircraft Applications

Abstract

This paper presents the influence of different pulse width modulation (PWM) methods on losses and thermal stresses in SiC power modules used in a three-phase inverter. The variation of PWM methods directly impacts instantaneous losses on these semiconductors, consequently resulting in junction temperature swing at the fundamental frequency of the converter's output current. This thermal cycling can significantly reduce the lifetime of these components. In order to determine semiconductor losses, one needs to characterize SiC devices to calculate the instantaneous power. The characterization methodology of the devices, the calculation of instantaneous power and temperature of SiC dies, and the influence of the different PWM methods are presented. A 15-kVA inverter is built in order to obtain experimental results to confirm the characterization and loss calculation, and we show the best PWM methods to increase efficiency and reliability of the three-phase inverter for specific aircraft applications.Electronics 2020, 9, 620 2 of 18The authors in References [5,6] performed precise loss calculations in power converters based on the double pulse method (DPM) and the modified opposition method (MOM), respectively, to measure switching energy. Since the MOM method gives more precise results, especially for very fast components such as SiC and GaN, this method is used in the work presented here.Therefore, this paper aims to recall and give more details to explain the approach to precisely calculate losses in three-phase inverters using experimental data from an accurate characterization of switching energies of wide bandgap (WBG) components. This approach was first presented in Reference [6], and it allows us to show the influence of different pulse width modulation (PWM) methods on losses of a three-phase inverter with floating neutral point.PWM methods are used to optimize certain characteristics of the power converter. Some of them were created in the 1970s and 1980s to reduce losses in three-phase inverters [7]. They are based on preventing switching when the converter current is high, in each phase. Optimal PWM methods can be created, as shown in Reference [8], even for SiC-based power converters. However, the aim here is, unlike other papers, not to reduce losses, but to show the influence of PWM methods and other converter parameters on SiC-based converter losses, specifically on the temperature variation in SiC dies, which is directly related to the power module reliability.Although WBG components such as silicon carbide (SiC) or gallium nitride (GaN) transistors have higher performance than their silicon (Si) counterparts, their reliability data are either reduced or non-existent. Some works showed reduced reliability on SiC dies, when compared to Si-based switches, due to degradation of the oxide-semiconductor interface [9] or the body diode characteristics [10]. The lack of reliability data and the general feeling in the community about the low reliability of these components are hindering their use and consequ...

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