energies Article SiC-Based High Eﬃciency High Isolation Dual Active Bridge Converter for a Power Electronic Transformer Mariam Saeed * , María R. Rogina , Alberto Rodríguez , Manuel Arias and Fernando Briz Department of Electrical Engineering, University of Oviedo, 33204 Asturias, Spain; rodriguezrmaria@uniovi.es (M.R.R.); rodriguezalberto@uniovi.es (A.R.); ariasmanuel@uniovi.es (M.A.); fernando@isa.uniovi.es (F.B.) * Correspondence: saeedmariam@uniovi.es Received: 30 January 2020; Accepted: 1 March 2020; Published: 5 March 2020   Abstract: This paper discusses the beneﬁts of using silicon carbide (SiC) devices in a three-stage modular power electronic transformer. According to the requirements to be fulﬁlled by each stage, the second one (the DC/DC isolation converter) presents the most estimable improvements to be gained from the use of SiC devices. Therefore, this paper is focused on this second stage, implemented with a SiC-based dual active bridge. Selection of the SiC devices is detailed tackling the eﬃciency improvement which can be obtained when they are co-packed with SiC antiparallel Schottky diodes in addition to their intrinsic body diode. This eﬃciency improvement is dependent on the dual active bridge operation point. Hence, a simple device loss model is presented to assess the eﬃciency improvement and understand the reasons for this dependence. Experimental results from a 5-kW Dual Active Bridge prototype have been obtained to validate the model. The dual active bridge converter is also tested as part of the full PET module operating at rated power. Keywords: SiC devices; antiparallel diode; dual active bridge; power electronic transformer; high-frequency transformer 1. Introduction A line-frequency transformer (LFT) is a key element in transmission and distribution for traditional centralized generation-based systems. Their main functionality is to interface diﬀerent voltage levels in the grid [1]. LFTs are a well-established, relatively cheap, and reliable technology. However, they fail to cope with modern grid demands, such as the integration of distributed resources and energy storage systems, as well as power ﬂow control. The power electronic transformer (PET), also called a solid-state transformer (SST), was introduced in 1970 [2]. It is considered an alternative to LFT, as it connects two AC voltage ports while providing galvanic isolation [1]. PET is a semiconductor-based energy conversion system based on fast-switching devices, which potentially enables a signiﬁcant reduction in volume and weight [3]. Moreover, thanks to the controllability of the power devices, the PET provides additional functionalities, such as reactive power, harmonics and imbalances compensation, ride-through capabilities, and smart protections. The power semiconductor technology used in PETs has been traditionally based on Silicon (Si). However, the fast advances in wide-band-gap (WBG), specially the Silicon Carbide (SiC), power semiconductors has attracted the attention to their use in the medium voltage (MV) modular three-stage PETs [4], mainly due to their high blocking voltage along with their superior switching behavior [5,6]. Several examples of using SiC devices in diﬀerent PET topologies exist in literature [7–13]. In the majority of applications, 1.2/1.7 kV commercial SiC MOSFETs are used for LV side devices, while for HV side, 10 kV non-commercial MOSFETs are used [6,8]. In some works, SiC was used in all the PET stages, such as in the TIPS (transformer-less intelligent power substation), which is an all-SiC Energies 2020, 13, 1198; doi:10.3390/en13051198 www.mdpi.com/journal/energies