Detects the fault and separates the faulted section so that the rest of the system keeps operating. System consists of one master controller, two slave controllers, and freewheeling branches between each line and ground. slave controllers read the current at each end of the bus segment and send it to the master controller.

1. Final Presentation
on Project
Submitted by
Suraj Shrestha
72/MSDG/217
Title:
Fault Detection and Isolation in Low-
Voltage DC-Bus Microgrid System

2. Contents of presentation
1. Introduction
2. Literature review
3. Objective
4. Methodology
5. Simulation
6. Results
7. Conclusion
8. Application

3. 1. Introduction
Fig.1 LVDC microgrid system
Advantages DC
• the dc power is based on the constant peak
voltage
• can deliver power 2 times that of an ac
system with the same cable
• do not suffer from the skin effect
• small-scale distributed power system consisting of distributed energy sources and
loads
• can be readily integrated with the renewable energy sources.
• LVDC is a new concept in distribution, suitable for offices with computer loads and
isolated power system and rural power system
1.1 Low Voltage DC Microgrid

4. Introduction contd…
1.2 Fault protection of LVDC system
a) Line to ground fault b) Line to line fault
• protection of dc distribution systems has posed many challenges
• AC CB mechanisms, which rely on the natural zero crossing of the ac current to open the
circuit, are inadequate to interrupt dc currents..
• Due to the limitations of fuses and traditional ac CBs in dc systems, a solid-state CB has
become a valid option for dc power system protection eg. IGBT

5. 2. Literature review
• A short-circuit current calculation method for low-voltage dc microgrid is
proposed in reference [1] paper, using a line model of bipolar which includes π
type equivalent circuits, solidstate bidirectional switches with snubber circuits
and freewheeling branches
• A noval scheme to detect the fault in the bus between devices and to isolate the
faulted section is developed in reference [2] paper, in the a loop-type dc-bus-
based microgrid system,

6. 3. Objective
• To develop a novel method to detect and isolate the fault in a Low Voltage
DC bus segment

7. 4. Methodology
4.1 Presented Protection scheme
Note: Protection Controller in segment B and C are omitted
• detects the fault and separates the faulted section
so that the rest of the system keeps operating
• The loop-type dc bus is used for robustness
• Entire loop will be divided into a series of
segment consisting of section of bus and a
segment controller, between subsystems.
• System consists of
• Two slave controllers
• To read the current at each end of the
bus segment and send it to the master
controller
• One master controller
• Send command according to Slave
controllers reading
• freewheeling branches between each line and
ground.

8. Methodology contd….
4.2 Implementation of the protection scheme
• Configuration of Segment A
• Semiconductor-based bidirectional switches
S1x
• segment separation
• Diodes D2x
• for and fault current freewheeling
• normal operations,
• switches S1x closed
• diodes D2x are open
• At fault, the master controller detects it using
the information from the slave controllers and
opens switches.
• Diodes are conducting at the same time to form
a freewheeling path for fault currents so that the
switches can open and the fault current can be
extinguished through resistors
Note: Arrows denote the switching action when a fault is detected

9. Methodology contd….
Fig. Line-to-ground fault between point A and G Fig. Isolated line-to-ground fault

10. 5. Simulation
5.1 Simulation Parameter

11. Simulation contd…
5.2 Simulation Circuit for Ling to ground Fault

12. Source Side
Load Side
Segment C
Segment B
Without Protection
Simulation contd

13. Source Side
Load Side
Segment C
Segment B
With Protection
Simulation contd…

14. 6. Result
Fig. Source-side fault current
Expected Actual Outcome
Time
Current

15. Result contd…
Fig. Load side fault current
Expected Actual Outcome
Time
Current

16. Result contd…
Fig. Load voltage Without Protection Fig. Load Voltage After clearing Fault
Time
Voltage
Time
Voltage

17. Result contd…
Fig. Segment B voltage After Clearing Fault Fig. Segment C Voltage After clearing Fault
Time
Voltage
Time
Voltage

18. Result contd…
Fig. Freewheeling branch Current
Time
Current

19. 7. Conclusion
• presented protection scheme consists of segment controllers capable of detecting
abnormal fault current in the bus and separating the faulted segment to avoid the entire
system shutdown

20. 8. Application
• The scheme can be applied to dc power systems, such as Green Buildings, with
sustainable energy resources and data centers with a server array

21. References
[2] Fault Detection and Isolation in Low-Voltage DC-Bus Microgrid System
Jae-Do Park, Member, IEEE, and Jared Candelaria, Student Member,
IEEE, IEEE TRANSACTIONS ON POWER DELIVERY, VOL. 28,
NO. 2, APRIL 2013
[1] A Short-circuit Current Calculation Method for Low-Voltage DC
Microgrid, Xiaoli Lai, Fei Liu , Kai Deng, Qi Gao, Xiaoming Zha
978-1-4799-6768-1/14/$31.00 ©2014 IEEE

22. Thank you