Project: DC/DC converter hardware development for 20kVA single phase SST

Project Objective: The primary objective of this project is to develop a high efficiency dc-dc conversion stage of 20 kVA solid state transformer (SST) for future distribution system. In addition, this dc-dc converter is connected to the grid in the power electronics laboratory at CAPS through an active rectifier developed at MST to demonstrate the bidirectional operation of 20 kVA SST. This project supports the SST development at NSF-FREEDM ERC center led by NCSU. The FSU design using modular structure with high frequency low voltage device is an alternative approach of NCSU design of high voltage device. The dc-dc converter modules can achieve high efficiency and distributed control with plug-and-play capability.

Fig.1 presents the design of new high-frequency transformer isolated bidirectional dc-dc converter modules connected in input-series-output-parallel (ISOP) for a 20 kVA solid state transformer. The ISOP modular structure enables the use of low-voltage MOSFETs, featuring low on-state resistance and resulted conduction losses, to address medium-voltage input. Phase-shift dual-half-bridge (DHB) converter is employed to achieve high-frequency galvanic isolation, bidirectional power flow, and zero-voltage-switching (ZVS) of all switching devices, which leads to low switching losses even with high-frequency operation. Furthermore, an adaptive inductor is proposed as the main energy transfer element of phase-shift DHB converter so that the circulating energy can be optimized to maintain ZVS at light load and minimize the conduction losses at heavy load. As a result, high efficiency over wide load range and high power density can be achieved. In addition, current stress of switching devices can be reduced. The distributed control system is developed. A planar transformer adopting printed-circuit-board windings arranged in interleaved structure is designed to obtain low core and winding loss, solid isolation and identical parameters in multiple modules as shown in Fig.2. Moreover, the modular structure along with a distributed control provides plug-and-play capability and possible high-level fault-tolerance. Some significant experimental results have been shown to verify the proposed DHB dc-dc converter and control system. In particular, three papers have been published in the prestigious intentional power electronics conference.

References:

 H. Fan and H. Li, "A Novel Phase-Shift Bidirectional DC-DC Converter with an Extended High-Efficiency Range for 20 kVA Solid State Transformer," IEEE Energy Conversion Congress and Exposition, Atlanta GA, September 2010.

 

CONTACT:                                     SPONSOR:

Dr .Hui Li, Associate Professor          NSF FREEDM

hli@caps.fsu.edu  (850) 644-8573