Supplying micro-grids with stationary fuel cell systems

1
Supplying micro-grids with stationary fuel cell
systems
Prof. Dr.-Ing. G. Balzer, Dipl.-Ing. D.
Audring Darmstadt University of
Technology Department of Electrical Power Systems
2
Structure

• Examined micro-grid
• Short-circuit performance
• Disconnection from power system
• Conclusions

3
Examined micro-grid

• Micro-grid is supplied by one fuel cell
• Fuel cell sets voltage and frequency of
  micro-grid
• Induction motor and two loads are connected to
  micro grid
• Network connection is simulated for back-up power
  supply using a disconnecting switch

4
Short-circuit performance

• Fuel cell acts as a voltage source with limited
  current output
• This leads to low short-circuit current at
  micro-grid
• Selectivity with over-current protection is
  difficult to achieve

5
Short-circuit performance

• Short-circuit currents are limited by inverter
• Transformation ratio and vector group of
  inverter-transformer influences short-circuits at
  micro-grid

6
Short-circuit performance
7
Disconnection from power system

• Short-circuit at power system leads to voltage
  drop at connected micro-grid
• Induction motor slows down
• Induction motor must be re-accelerated after
  disconnection from network
• Power quality is poor during disconnection and
  not acceptable for PC etc.

8
Conclusions

• Main characteristic of micro-grid supplied by
  fuel cell is low short-circuit current
• Selectivity with over-current protection is
  difficult to achieve
• Transformation ratio and vector group of
  inverter-transformer is to consider for
  calculation of short-circuit currents at
  micro-grid
• Disconnection from power system due to
  short-circuit has to carried out fast to reduce
  voltage disturbances at micro-grid