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Nordic Workshop on Power and Industrial Electronics NORPIE 2004 Trondheim, 14-16 June

Nordic Workshop on Power and Industrial Electronics NORPIE 2004 Trondheim, 14-16 June. Dimensioning of a Current Source Inverter for the Feed-in of Electrical Energy from Fuel Cells to the Mains Malte Mohr , Friedrich W. Fuchs Chair for Power Electronics and Electrical Drives

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Nordic Workshop on Power and Industrial Electronics NORPIE 2004 Trondheim, 14-16 June

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  1. Nordic Workshop on Power and Industrial ElectronicsNORPIE 2004 Trondheim, 14-16 June Dimensioning of a Current Source Inverter for the Feed-in of Electrical Energy from Fuel Cells to the Mains Malte Mohr, Friedrich W. Fuchs Chair for Power Electronics and Electrical Drives Christian-Albrechts-Universität zu Kiel, Germany

  2. Outline 1. Introduction 2. Fuel cell 3. Demands on the inverter 3.1 Current source inverter (CSI) 3.2 Dimensioning/optimisation 3.3 Laboratory test setup 4. Conclusion

  3. 1. Introduction • Fuel cells convert chemical energy directly into electrical energy. • Fuel cells have a high electrical efficiency. • Application in decentral power generation. • Fuel cells deliver dc-current. • Power electronics converts it into ac-current. • A current source inverter fulfils the requirements for operation at fuel cells.

  4. 2. Fuel cell V [V] J [A/cm2]

  5. V-I characteristic curve of a single fuel cell: 2. Fuel cell • voltage depends significantly on current V[V] J[A/cm2]

  6. characteristic curve at full fuel supply V-I characteristic curve of a single fuel cell: 2. Fuel cell • voltage depends significantly on current • maximum current depends on supplied fuel V[V] J[A/cm2]

  7. characteristic curve at partial fuel supply V-I characteristic curve of a single fuel cell: 2. Fuel cell • voltage depends significantly on current • maximum current depends on supplied fuel V[V] J[A/cm2]

  8. V-I characteristic curve of a single fuel cell: 2. Fuel cell • voltage depends significantly on current • maximum current depends on supplied fuel • operation in the linear part of the characteristic curve V[V] J[A/cm2]

  9. operating point at partial load operating point at full load V-I characteristic curve of a single fuel cell: 2. Fuel cell • voltage depends significantly on current • maximum current depends on supplied fuel • operation in the linear part of the characteristic curve V[V] J[A/cm2]

  10. 3. Demands on the inverter The inverter has to • draw well smoothed dc-current from the fuel cell to prevent damages of the cell, • have low harmonics in the mains current, • adapt the varying fuel cell voltage to the mains voltage, • feed in active power, • be efficient, • be economical.

  11. 3.1 Current source inverter (CSI) Current source inverter (CSI): meets the demands increases the voltage towards the mains

  12. 3.1 Current source inverter (CSI) • higher efficiency of the inverter system at higher dc input voltages • input voltage is limited: Vdc < Vline , depending on ac-filter values • load range is limited if the system is optimised for high input voltages • Losses of the current source inverter depend on the current Id

  13. 3.2 Dimensioning/optimisation stack with higher system voltage stack with lower system voltage maximum inverter input voltage maximum inverter current Efficiency dependend on input dc voltage:

  14. 3.2 Dimensioning/optimisation maximum inverter input voltage maximum inverter current Efficiency dependend on input dc voltage: transmitted power at high system voltage transmitted power at moderate system voltage transmitted power at low system voltage

  15. 3.2 Dimensioning/optimisation Load range dependend on input dc voltage: • full load range • lower input voltage • low efficiency • moderate load range • moderate input voltage • better efficiency • no load range • high input voltage • best efficiency

  16. 3.2 Dimensioning/optimisation • rated inverter power increases proportional to the input dc current • reducing the power range yields to better efficiency and less rated inverter power

  17. 3.2 Dimensioning/optimisation Simulation of the current source inverter with Simplorer® vline Id Id* I, V iline t • rise time < ¼ periode of the mains • inverter much faster than fuel cell

  18. 3.3 Laboratory setup circuit diagram of the laboratory setup:

  19. power circuit with low leakage inductance measuring and control devices overvoltage protection 3.3 Laboratory setup

  20. 3.3 Laboratory setup input dc-current, output ac-current and output ac-voltage; inverter at ohmic-inductive load, open-loop controlled

  21. 4. Conclusion The current source inverter is suitable to convert electrical energy from fuel cells to feed in the mains, has poor utilisation and poor efficiency at low dc-input voltages. • Limitation of power range enhances efficiency and inverter utilisation. • In principle the CSI is suited for higher system voltages and therefore higher power ratings.

  22. Nordic Workshop on Power and Industrial ElectronicsNORPIE 2004, 14-16 June Dimensioning of a Current Source Inverter for the Feed-in of Electrical Energy from Fuel Cells to the Mains Malte Mohr, Friedrich W. Fuchs Chair for Power Electronics and Electrical Drives Christian-Albrechts-Universität zu Kiel, Germany

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