SiC-based unidirectional solid-state transformer concepts for directly interfacing 400V DC to Medium-Voltage AC distribution systems

400 V DC distribution networks present a promising solution for supplying high-power DC loads such as information processing systems, transportation battery charging facilities and DC micro grids, among others. For these applications, high transmission efficiency, reliability and controllability are mandatory. With the current technology, these loads are fed from PWM rectifiers which are connected to the three-phase Low-Voltage (LV) distribution grid (400 V AC in Europe). The LV grid itself is supplied via Low-Frequency Transformers (LFT) from the Medium-Voltage (MV) grid, providing galvanic isolation and the required voltage step down. This paper presents three unidirectional AC/DC SiC-based Solid-State Transformer (SST) topologies with direct connection to the MV grid, which avoid the utilization of the aforementioned LFT by integrating a Medium-Frequency (MF) conversion stage, thus increasing the efficiency and power density of this supply system. The SST topologies are compared by means of a chip area-based comparative evaluation. Finally, the most suited among the presented topologies is Pareto-optimized, achieving a total MV AC to 400 V DC efficiency of 98.3 %. It is shown that the optimized SST features 40 % less overall losses compared to state-of-the-art solutions.

[1]  S. Allebrod,et al.  New transformerless, scalable Modular Multilevel Converters for HVDC-transmission , 2008, 2008 IEEE Power Electronics Specialists Conference.

[2]  Florian Krismer,et al.  Modeling and optimization of bidirectional dual active bridge DC-DC converter topologies , 2010 .

[3]  Johann W. Kolar,et al.  Component cost models for multi-objective optimizations of switched-mode power converters , 2013, 2013 IEEE Energy Conversion Congress and Exposition.

[4]  Johann W. Kolar,et al.  The Essence of Three-Phase PFC Rectifier Systems—Part II , 2013, IEEE Transactions on Power Electronics.

[5]  J. W. Kolar,et al.  Design of a minimum weight dual active bridge converter for an Airborne Wind Turbine system , 2012, 2012 Twenty-Seventh Annual IEEE Applied Power Electronics Conference and Exposition (APEC).

[6]  Juan C. Vasquez,et al.  Advanced LVDC Electrical Power Architectures and Microgrids , 2015 .

[7]  Toit Mouton,et al.  Natural balancing of the two-cell back-to-back multilevel converter with specific application to the solid-state transformer concept , 2009, 2009 4th IEEE Conference on Industrial Electronics and Applications.

[8]  Frank Bodi,et al.  380/400V DC powering option , 2011, 2011 IEEE 33rd International Telecommunications Energy Conference (INTELEC).

[9]  Marcelo Lobo Heldwein,et al.  Modular multilevel converter based unidirectional medium/high voltage drive system , 2013, IECON 2013 - 39th Annual Conference of the IEEE Industrial Electronics Society.

[10]  Toit Mouton,et al.  Solid-state transformer topology selection , 2009, 2009 IEEE International Conference on Industrial Technology.

[11]  J. Kolar,et al.  Optimal inductor design for 3-phase voltage-source PWM converters considering different magnetic materials and a wide switching frequency range , 2014, 2014 International Power Electronics Conference (IPEC-Hiroshima 2014 - ECCE ASIA).

[12]  Prasad Enjeti,et al.  Medium voltage power distribution architecture with medium frequency isolation transformer for data centers , 2014, 2014 IEEE Applied Power Electronics Conference and Exposition - APEC 2014.

[13]  Rainer Marquardt,et al.  A new AC/AC-multilevel converter family applied to a single-phase converter , 2003, The Fifth International Conference on Power Electronics and Drive Systems, 2003. PEDS 2003..

[14]  R. Ayyanar,et al.  Common duty ratio control of input series connected modular DC-DC converters with active input voltage and load current sharing , 2003, Eighteenth Annual IEEE Applied Power Electronics Conference and Exposition, 2003. APEC '03..

[15]  A. Pratt,et al.  Evaluation of 400V DC distribution in telco and data centers to improve energy efficiency , 2007, INTELEC 07 - 29th International Telecommunications Energy Conference.

[16]  Gonzalo Abad,et al.  Modular Multilevel Converter With Different Submodule Concepts—Part I: Capacitor Voltage Balancing Method , 2013, IEEE Transactions on Industrial Electronics.

[17]  Alireza Nami,et al.  Current source modular multilevel converter for HVDC and FACTS , 2013, 2013 15th European Conference on Power Electronics and Applications (EPE).

[18]  J. Kolar,et al.  Theoretical Converter Power Density Limits for Forced Convection Cooling , 2005 .

[19]  Mahmoud Samiei Moghaddam,et al.  Look up table based control of multi-level AC/AC converters with strategy of DC link balancing , 2010, 2010 Joint International Conference on Power Electronics, Drives and Energy Systems & 2010 Power India.

[20]  Johann W. Kolar,et al.  Solid-State-Transformers: Key Components of Future Traction and Smart Grid Systems , 2014 .

[21]  Andreas Lindemann,et al.  A Theoretical and Experimental Analysis of N+1 and 2N+1 Phase-Shifted Carrier-Based PWM Strategies in Modular Multilevel Converters , 2014 .

[22]  Juan C. Vasquez,et al.  Advanced LVDC Electrical Power Architectures and Microgrids: A step toward a new generation of power distribution networks. , 2014, IEEE Electrification Magazine.

[23]  Johann W. Kolar,et al.  Braking chopper solutions for Modular Multilevel Converters , 2011, Proceedings of the 2011 14th European Conference on Power Electronics and Applications.

[24]  J. Kolar,et al.  Scaling and balancing of multi-cell converters , 2014, 2014 International Power Electronics Conference (IPEC-Hiroshima 2014 - ECCE ASIA).