Modeling and Control of Three-Level Boost Rectifier Based Medium-Voltage Solid-State Transformer for DC Fast Charger Application

This paper presents modeling, control, and system design of three-level boost (TLB) rectifier based medium-voltage (MV) solid-state transformer (SST) for dc fast charger application. In order to operate at MV with 1.2-kV SiC devices, the target system is configured by input-series output-parallel (I...

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Bibliographic Details
Published in:IEEE transactions on transportation electrification 2019-12, Vol.5 (4), p.890-902
Main Authors: Lee, Moonhyun, Yeh, Chih-Shen, Yu, Oscar, Kim, Jong-Woo, Choe, Jung-Muk, Lai, Jih-Sheng
Format: Article
Language:English
Subjects:
Adaptive control
Balancing
Control
Control design
Control systems
Control theory
Converters
dc fast charger
Electric bridges
Electric potential
Feedback control
Feedforward control
Feedforward systems
Modelling
Modules
Prototypes
Rectifiers
Silicon carbide
Solid state
solid-state transformer (SST)
system modeling
Systems design
three-level boost (TLB) rectifier
Topology
Transformers
Transportation
Voltage
Voltage control
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Summary:This paper presents modeling, control, and system design of three-level boost (TLB) rectifier based medium-voltage (MV) solid-state transformer (SST) for dc fast charger application. In order to operate at MV with 1.2-kV SiC devices, the target system is configured by input-series output-parallel (ISOP) multimodule structure. Each module adopts TLB to front-end rectifier and stacked half-bridge LLCs to back-end isolated dc-dc converters. Operation principles of TLB rectifier and LLC converters are analyzed to derive an equivalent model of the entire system. Based on the detailed derivation, this paper aims to achieve three performance criteria, including bus voltage regulation, input current regulation, and voltage balancing. Basic feedback control loops are designed to control TLB's output voltage and input current in an average manner, based on the derived system model. Then, ideal TLB duty-ratios in both continuous/discontinuous conduction modes are analyzed and duty-ratio feedforward control is proposed to improve the low quality of input current due to inherent feedback control limitations. For voltage balancing, system design approaches are used in the SST prototype. With the proposed control and system design, a prototype of four-module-stacked TLB SST was built and tested up to 3.8-kVrms and 16-kW conditions.
ISSN:2332-7782
2577-4212
2332-7782
DOI:10.1109/TTE.2019.2919200