Solid-State Transformer and MV Grid Tie Applications Enabled by 15 kV SiC IGBTs and 10 kV SiC MOSFETs Based Multilevel Converters

Abstract

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

Solid State Transformers Topologies, Controllers, and Applications: State-of-the-Art Literature Review

“…The three-stage conversion topology shown in Figure 1c was presented in [1,[27][28][29][30][31]. The first stage utilizes an AC/DC rectifier aimed at regulating the voltage across the HV DC link, shaping the input current [30,32], and achieving bi-directional power flow and reactive power compensation [33] as well as harmonic elimination [34][35][36]. While the second stage includes a high frequency, the DAB is required to regulate the active power flow, provide galvanic isolation, and control the voltage at the LV DC bus [33].…”

“…A major advantage of multi-stage topologies is the inclusion of a low voltage DC link as reported in [30,33,39,40] in which DC loads, distributed generators, and energy storage devices can be directly connected to the SST without the need for an AC conversion stage. This is optimal for a multiport SST serving a mixture of AC devices and DC applications such as hybrid microgrids, solar PV, DC bus home, data centres [41][42][43], and optimised fast chargers of energy storage devices [3].…”

Active Hybrid Solid State Transformer Based on Multi-Level Converter Using SiC MOSFET

“…Hence, it can operate for using only half of the tap voltage. All power semiconductor switches are applied with SiC MOSFETs and SiC Energies 2019, 12, 66 4 of 15 schottky diodes to reduce the switching losses and to implement high efficiency and power density [7]. The design and implementation of power stage was verified through electrical insulation test and thermal simulation.…”

“…If the transformer turn ratio is N : 1, then the secondary side voltage is equal to Equation (6) and the range of the compensable secondary side voltage is V inv /N. The magnitude of the inverter duty reference, DC link voltage, and output voltage of the inverter are D re f _inv and V DC , V inv are given by Equation (7). As a result, D re f _inv of the inverter for controlling the V sec is finally summarized as in Equations (8), (9) and (10).…”

“…Nevertheless, SST has the disadvantage that the converter must be configured towards high voltage power semiconductor switches in order to cope with the high distribution gri d voltage. Recently, high voltage rated power semiconductor switches over 15 kV have been studied, but these are difficult to use commercially [7][8][9][10]. Therefore, in order to apply the commercial power semiconductor switches, cascaded multi-module structure in which power modules are connected in a series or parallel is forced.…”