A Transformerless Intelligent Power Substation: A three-phase SST enabled by a 15-kV SiC IGBT

The solid-state transformer (SST) is a promising power electronics solution that provides voltage regulation, reactive power compensation, dc-sourced renewable integration, and communication capabilities, in addition to the traditional step-up/step-down functionality of a transformer. It is gaining widespread attention for medium-voltage (MV) grid interfacing to enable increases in renewable energy penetration, and, commercially, the SST is of interest for traction applications due to its light weight as a result of medium-frequency isolation. The recent advancements in silicon carbide (SiC) power semiconductor device technology are creating a new paradigm with the development of discrete power semiconductor devices in the range of 10-15 kV and even beyond-up to 22 kV, as recently reported. In contrast to silicon (Si) IGBTs, which are limited to 6.5-kV blocking, these high-voltage (HV) SiC devices are enabling much simpler converter topologies and increased efficiency and reliability, with dramatic reductions of the size and weight of the MV power-conversion systems. This article presents the first-ever demonstration results of a three-phase MV grid-connected 100-kVA SST enabled by 15-kV SiC n-IGBTs, with an emphasis on the system design and control considerations. The 15-kV SiC n-IGBTs were developed by Cree and packaged by Powerex. The low-voltage (LV) side of the SST is built with 1,200-V, 100-A SiC MOSFET modules. The galvanic isolation is provided by three single-phase 22-kV/800-V, 10-kHz, 35-kVA-rated high-frequency (HF) transformers. The three-phase all-SiC SST that interfaces with 13.8-kV and 480-V distribution grids is referred to as a transformerless intelligent power substation (TIPS). The characterization of the 15-kV SiC n-IGBTs, the development of the MV isolated gate driver, and the design, control, and system demonstration of the TIPS were undertaken by North Carolina State University's (NCSU's) Future Renewable Electrical Energy Delivery and Management (FREEDM) Systems Center, sponsored by an Advanced Research Projects Agency-Energy (ARPA-E) project.

[1]  L. Heinemann,et al.  An actively cooled high power, high frequency transformer with high insulation capability , 2002, APEC. Seventeenth Annual IEEE Applied Power Electronics Conference and Exposition (Cat. No.02CH37335).

[2]  Alex Q. Huang,et al.  Comparison of the state-of-the-art high power IGBTs, GCTs and ETOs , 2000, APEC 2000. Fifteenth Annual IEEE Applied Power Electronics Conference and Exposition (Cat. No.00CH37058).

[3]  Subhashish Bhattacharya,et al.  Solid-State Transformer and MV Grid Tie Applications Enabled by 15 kV SiC IGBTs and 10 kV SiC MOSFETs Based Multilevel Converters , 2015, IEEE Transactions on Industry Applications.

[4]  Subhashish Bhattacharya,et al.  Understanding dv/dt of 15 kV SiC N-IGBT and its control using active gate driver , 2014, 2014 IEEE Energy Conversion Congress and Exposition (ECCE).

[5]  Bin Wu,et al.  High-Power Converters and AC Drives , 2006 .

[6]  Subhashish Bhattacharya,et al.  Design Considerations of a 15-kV SiC IGBT-Based Medium-Voltage High-Frequency Isolated DC–DC Converter , 2015, IEEE Transactions on Industry Applications.

[7]  S. Ryu,et al.  Experimental switching frequency limits of 15 kV SiC N-IGBT module , 2014, 2014 International Power Electronics Conference (IPEC-Hiroshima 2014 - ECCE ASIA).

[8]  Jurgen Biela.  Solid-State Transformer Based on SiC JFETs for Future Energy Distribution Systems , 2008 .

[9]  Subhashish Bhattacharya,et al.  FPGA based control board development for medium-voltage high-power three-phase dual active bridge converter , 2014, IECON 2014 - 40th Annual Conference of the IEEE Industrial Electronics Society.

[10]  Subhashish Bhattacharya,et al.  Thermal design considerations for medium voltage power converters with 15 kV SiC IGBTs , 2015, 2015 IEEE 6th International Symposium on Power Electronics for Distributed Generation Systems (PEDG).

[11]  D.M. Divan,et al.  A three-phase soft-switched high power density DC/DC converter for high power applications , 1988, Conference Record of the 1988 IEEE Industry Applications Society Annual Meeting.

[12]  Bin Wu,et al.  High-Power Converters and ac Drives: Wu/High-Power Converters and ac Drives , 2006 .

[13]  Subhashish Bhattacharya,et al.  Start-up scheme for solid state transformers connected to medium voltage grids , 2015, 2015 IEEE Applied Power Electronics Conference and Exposition (APEC).

[14]  S. Ryu,et al.  Silicon carbide power MOSFETs: Breakthrough performance from 900 V up to 15 kV , 2014, 2014 IEEE 26th International Symposium on Power Semiconductor Devices & IC's (ISPSD).

[15]  Subhashish Bhattacharya,et al.  Medium voltage power converter design and demonstration using 15 kV SiC N-IGBTs , 2015, 2015 IEEE Applied Power Electronics Conference and Exposition (APEC).

[16]  Rik W. De Doncker,et al.  Dynamic and Balanced Control of Three-Phase High-Power Dual-Active Bridge DC–DC Converters in DC-Grid Applications , 2013, IEEE Transactions on Power Electronics.

[17]  Jun Wang,et al.  Smart grid technologies , 2009, IEEE Industrial Electronics Magazine.

[18]  Subhashish Bhattacharya,et al.  Stability analysis of the high voltage DC link between the FEC and DC-DC stage of a transformer-less intelligent power substation , 2014, 2014 IEEE Energy Conversion Congress and Exposition (ECCE).

[19]  Subhashish Bhattacharya,et al.  Transformer less Intelligent Power Substation design with 15kV SiC IGBT for grid interconnection , 2011, 2011 IEEE Energy Conversion Congress and Exposition.

[20]  G. K. Moghaddam,et al.  Design considerations and performance evaluation of 1200 V, 100 a SiC MOSFET based converter for high power density application , 2013, 2013 IEEE Energy Conversion Congress and Exposition.

[21]  Subhashish Bhattacharya,et al.  Design considerations and development of gate driver for 15 kV SiC IGBT , 2014, 2014 IEEE Applied Power Electronics Conference and Exposition - APEC 2014.

[22]  J. W. Kolar,et al.  Medium frequency transformers for solid-state-transformer applications — Design and experimental verification , 2013, 2013 IEEE 10th International Conference on Power Electronics and Drive Systems (PEDS).

[23]  S. Bhattacharya,et al.  Ultra high voltage IGBTs in 4H-SiC , 2013, The 1st IEEE Workshop on Wide Bandgap Power Devices and Applications.

[24]  Wensong Yu,et al.  Design and operation of A 3.6kV high performance solid state transformer based on 13kV SiC MOSFET and JBS diode , 2014, 2014 IEEE Energy Conversion Congress and Exposition (ECCE).

[25]  Subhashish Bhattacharya,et al.  Experimental validation of the steady state and transient behavior of a transformerless intelligent power substation , 2014, 2014 IEEE Applied Power Electronics Conference and Exposition - APEC 2014.

[26]  Brett Hull,et al.  Progress in Silicon Carbide Power Devices , 2006, 2006 64th Device Research Conference.

[27]  Subhashish Bhattacharya,et al.  Design, measurement and equivalent circuit synthesis of high power HF transformer for three-phase composite dual active bridge topology , 2014, 2014 IEEE Applied Power Electronics Conference and Exposition - APEC 2014.

[28]  David E. Grider,et al.  10 kV, 120 A SiC half H-bridge power MOSFET modules suitable for high frequency, medium voltage applications , 2011, 2011 IEEE Energy Conversion Congress and Exposition.

[29]  Subhashish Bhattacharya,et al.  Characterization of 15 kV SiC n-IGBT and its application considerations for high power converters , 2013, 2013 IEEE Energy Conversion Congress and Exposition.

[30]  Subhashish Bhattacharya,et al.  A unified control scheme for harmonic elimination in the front end converter of a 13.8 kV, 100 kVA transformerless intelligent power substation grid tied with LCL filter , 2014, 2014 IEEE Applied Power Electronics Conference and Exposition - APEC 2014.