DC Transformers in DC Distribution Systems
Abstract
:1. Introduction
2. Features of DCTs in MLVDC Distribution Systems
2.1. High Dynamic Performance and Bidirectional Power Flow
2.2. HighFrequency Isolation
2.3. High Voltage Gain and High Power Ratings
3. Typical Topologies of DCTs in MLVDC Distribution Systems
 (1)
 InputSeries–OutputParallel (ISOP) structure;
 (2)
 Modular Multilevel Converter (MMC);
 (3)
 Hybrid structure.
3.1. ISOP Topology
3.2. MMC Topology
3.3. Hybrid Topology
4. Control Strategies
4.1. SteadyState Control Strategy
 (1)
 All modules are selfcontained and standardized;
 (2)
 Ease of expanding the power capacity;
 (3)
 High redundancy.
4.2. TransientState Control Strategy
4.3. Cascaded System Control Strategy
5. Engineering Application
 (1)
 Pure PV accesses scenario
 (2)
 Hybrid PV, ESS, and various industrial load access scenarios
 (3)
 Charging pile accesses scenario
 (4)
 Residential, commercial, data center, and other application access scenario
6. Challenges and Future Works
6.1. Challenges
 (1)
 Design and manufacture of highfrequency transformers
 (2)
 Limitations of DCT efficiency optimization algorithm
 (3)
 Immature FRT method
 (4)
 Disadvantages at device level
 (5)
 Cascaded instability
6.2. Future Works
 (1)
 Improve the design theory and manufacturing method of highfrequency transformers under highvoltage and highpower conditions by analyzing the loss characteristics of magnetic core winding and the aging mechanism of insulation materials under harsh conditions, exploring the highprecision measurement method of parasitic parameters.
 (2)
 Establish a complete and accurate loss model, exploring the core factors affecting the operation efficiency and proposing a global efficiency improvement method for DCTs.
 (3)
 Carry out indepth research on the fault characteristics of DCTs, including analyses of the operation mechanism of DCTs under fault states, characterization of the operation boundary, and study of the FRT strategy.
 (4)
 Develop the application of widebandgap (WBG) power devices in DCTs. SiC power devices have apparent advantages in switching speed, onstate resistance, and switching losses; developing highvoltage SiCMOSFETs can reduce the number of modules in an ISOP.
 (5)
 Develop an impedance sweep tool for DCTs. Recently, many equipment manufacturers have focused on developing a specialized impedance analysis tool to obtain the input/output impedance by frequency sweeping [77]. In addition to this, equipment that can automatically design a reasonable LC filter and reshape the impedance to achieve stabilization is also a research hotspot.
7. Conclusions
Author Contributions
Funding
Data Availability Statement
Conflicts of Interest
References
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Topologies  Features 
ISOP 

MMC 

Hybrid Topology  Combination of the above advantages and disadvantages. 
Methods  Features 
OVR–IVS control 

OVR–IVS–OCS control 

Decentralized OVR–IVS control 

Droop control 

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Chen, Y.; Zhang, Y. DC Transformers in DC Distribution Systems. Energies 2023, 16, 3031. https://doi.org/10.3390/en16073031
Chen Y, Zhang Y. DC Transformers in DC Distribution Systems. Energies. 2023; 16(7):3031. https://doi.org/10.3390/en16073031
Chicago/Turabian StyleChen, Yangfan, and Yu Zhang. 2023. "DC Transformers in DC Distribution Systems" Energies 16, no. 7: 3031. https://doi.org/10.3390/en16073031