Abstract
Medium-voltage dc (MVdc) grids are attractive for electric aircraft and ship power systems, battery energy storage system (BESS), fast charging electric vehicle (EV), etc. Such EV or BESS applications need isolated bidirectional MVdc to low-voltage dc (LVdc) or LVac converters. However, the existing Si-based solutions cannot fulfill the requirements of a high-efficiency and robust converter for MVdc grids. This article presents a 5-kV SiC-based universal modular solid-state transformer (SST). This universal current-source SST can interface either an LVac or LVdc grid with an MVdc grid in single-stage power conversion, while the conventional dual-active bridge (DAB) converter needs an additional inverter. The proposed SST module using 3.3-kV SiC MOSFETs and diodes is bidirectional and can serve as a building block in series or parallel for higher voltage higher power systems. The topology of each module is based on the soft-switching solid-state transformer (S4T) with reduced conduction loss, which features reduced electromagnetic interference electromagnetic interference (EMI) through controlled dv/dt, and high efficiency with full-range zero-voltage switching for main devices and zero-current switching for auxiliary devices. Operation principle of the modular S4T (M-S4T), capacitor voltage balancing control between the cascaded modules, design of components including a medium-voltage (MV) medium-frequency transformer (MFT) to realize a 50-kVA, 5-kV dc to 600 V dc or 480 V ac M-S4T are presented. Importantly, the MV MFT prototype achieves very low leakage inductance (0.13%) and 15-kV insulation with coaxial cables and nanocrystalline cores. The proposed universal modular SST is compared against the DAB solution and verified with dc-dc and dc-ac simulation and 4-kV experimental results. Significantly, the MV experimental results of a modular dc transformer with each module at MVdc are rarely covered in the literature and reported for the first time.
| Original language | English |
|---|---|
| Article number | 9380936 |
| Pages (from-to) | 11326-11343 |
| Number of pages | 18 |
| Journal | IEEE Transactions on Power Electronics |
| Volume | 36 |
| Issue number | 10 |
| DOIs | |
| State | Published - Oct 2021 |
| Externally published | Yes |
Funding
Manuscript received September 25, 2020; revised November 23, 2020 and January 30, 2021; accepted March 1, 2021. Date of publication March 17, 2021; date of current version June 30, 2021. This work was supported in part by the Power America Institute and in part by the Center for Distributed Energy, Georgia Institute of Technology. This paper was presented in part at the IEEE ECCE 2018. Recommended for publication by Associate Editor M. Liserre. (Corresponding author: Liran Zheng.) The authors are with the School of Electrical and Computer Engineering, Georgia Institute of Technology, Atlanta, GA 30332 USA (e-mail: [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]).
| Funders | Funder number |
|---|---|
| Center for Distributed Energy | |
| Power America Institute | |
| Georgia Institute of Technology |
Keywords
- Current-source converter (CSC)
- Dc transformer (DCT)
- High-frequency link (HFL)
- Input-series output-parallel (ISOP)
- Isolated bidirectional DC-DC converter (IBdc)
- Medium-voltage direct-current network
- Power electronic transformer (PET)
- Zero-current switching (ZCS)
- Zero-voltage switching (ZVS)
