Recently, medium voltage SiC devices have been developed which can be used for grid tie applications at medium voltage. Two such devices -15 kV SiC IGBT and 10 kV SiC MOSFET have opened up the possibility of looking into different converter topologies for medium voltage distribution grid interface. These can be used in medium voltage drives, active filter applications or as the active front end converter for Solid State Transformers (SST). Transformer-less Intelligent Power Substation (TIPS) is one such application for these devices. TIPS is proposed as a 3-phase SST interconnecting 13.8 kV distribution grid with 480 V utility grid. The Front End Converter (FEC) of TIPS is made up of 15 kV SiC IGBTs.This paper focuses on the advantages, design considerations and challenges associated with the operation of converters using these devices keeping TIPS as the topology of reference.

Basic power topology for a Solid State Transformer (SST) with new 15kV SiC IGBT devices is discussed. It is difficult to build high efficient, light weight, magnetically isolated solid state transformer for high voltage (13.8 kV) grid connectivity with existing Si 6.5kV rated IGBTs and diodes. Existing state of the art high voltage (6.5kV), high speed power devices (IGBT) cause considerable amount of loss (switching and conduction loss). With the advent of SiC devices these limitations are largely mitigated and this provides the motivation for new power topologies. The targeted efficiency of the proposed SST is 98%.Simulation results for a 1 MVA proposed SST topology is presented. I.

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Medium Voltage (MV) SiC devices have been developed recently which can be used for 3-phase, MV grid tie applications. Two such devices-15 kV SiC IGBT and 10 kV SiC MOSFET have opened up the possibilities of looking into different converter topologies for MV distribution grid interface. These can be used in MV drives, active filter applications or as the active front end converter for Solid State Transformers (SST). Transformerless Intelligent Power Substation (TIPS) is one such application for these devices. TIPS is proposed as a 3-phase SST interconnecting 13.8 kV distribution grid with 480 V utility grid. It is an all SiC devices based multi-stage SST. This paper focuses on the advantages, design considerations and challenges associated with the operation of converters using these devices keeping TIPS as the topology of reference. Efficiency of TIPS topology is also calculated using the experimentally measured loss data of the devices and the high frequency transformer. Experimental results captured on a developed prototype of TIPS along with its measured efficiency are also given.Index Terms-Active front end converter, medium voltage grid tie application, silicon carbide, solid state transformer. NOMENCLATUREZ out rect (s) FEC closed loop output impedance in forward direction Z in dab (s) DAB closed loop input impedance in forward direction V dc rect FEC dc bus voltage V dc dab DAB dc bus voltage C dc MV side dc bus capacitance m FEC modulation index K v , T v FEC dc bus voltage controller gain, time constant K i , T i FEC current controller gain, time constant ω ibw FEC current control loop bandwidth L s , R s FEC line inductance and resistance per phase i load rect FEC load current i d FEC d-axis current i d1 DAB d-axis current L m , C p , R c DAB magnetizing inductance with its parasitic capacitance and resistance C m DAB primary winding mutual capacitance L l1 , C 1 , R 1 DAB leakage inductance with its parasitic capacitance and resistance L f 1 , R df 1 DAB filter inductance and its parasitic resistance L s1 , R s1 DAB secondary inductance and its series resistance φ DAB phase angle N DAB turns ratio K v1 , T v1 DAB dc bus voltage controller gain, time constant K i1 , T i1 DAB current controller gain, time constant T f DAB feedback path time constant V dc low DAB low voltage side dc bus voltage i load dab DAB load current C dc low , E SR DAB low voltage side dc bus capacitor and its ESR R load dab DAB parallel load model

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