Virtual inertia with PV inverters using DC-link capacitors Eberhard Waffenschmidt, Ron S.Y. Hui EPE/ECCE 2016, Karlsruhe, Germany 5.-9.Sept. 2016 Acknowledgements to : Daniel Wagner, Markus Korbmacher, Bente Muhr, Sonny Glesmann and Nora Kovacs. TH Köln TH Köln
Sometimes 85% RE in the grid 80 9.May 2016 60 Consumption Power P / GW Export 85% 40 Conventional of the comsumption Power Solar 20 Wind Hydro Biomass Grafic: agora-energiewende 0 0:00 4:00 8:00 12:00 16:00 20:00 Time t / h 2 TH Köln TH Köln
Conventional generators will be missing 3 TH Köln TH Köln
Topology for virtual inertia PV MPP DC link Mains Power panel tracker capacitor inverter grid P(f) 4 TH Köln TH Köln
Worst case and size 5 TH Köln TH Köln
Required Energy Time t/s Contribution of 0 5 10 25 20 Germany to 0 Instantaneous Instantaneous Power P/GW Control: -0.5 Energy: Germany 2033 3700 MWs -1.0 E kin = 1.93 MWh Power: 372 MW Germany 2011 -1.5 With feed in of 80 GW: ENTSO-E 2033 -2.0 E kin = 7.4 MWh Power: -2.5 5W / kW Szenario I Energy: Few renewables -3.0 50Ws / kW dena-Studie Systemdienstleistungen 2030 6 TH Köln TH Köln
Size of electrolytic capacitors 1000 Capacitor volume V / cm³ 100 Rated 10 Capacitor Voltage 500V 1 450V 400V 200V 0.1 63V 16V Fit: V/[cm³] = 3.5 . (E/[J]) 0.72 Fit 0.01 0.001 0.01 0.1 1 10 100 1000 Energy content E / J 7 TH Köln TH Köln
Needed capacitor size for 1kW 50J 100% voltage ripple 300J 10% voltage ripple e.g. 3500µF, 400V 200 cm³ e.g. 5cm x 10cm 8 TH Köln TH Köln
Daily operation 9 TH Köln TH Köln
Voltage varitions during daily operation Definition of ∆ P ⋅ d ∆ f P = Power step = T a time constant Ta: P 0 = Power in the grid P 0 dt f f = Frequency variatrion Power into f = Grid frequency ∆ P =∆ I ⋅ U 0 C = Capacity of the capacitor the capacitor: I = Current into the capacitor Dependence of U 0 = Intermediate voltage ∆ U c ( t )= 1 ⋅ ∫ ∆ I ( t ) dt C U c = Voltage variation at capacitor voltage and current: P 0 ⋅ T a Intermediate ∆ f ∆ U c ( t )= 1 ⋅ d ⋅ ∫ dt solution: C U 0 dt f 0 Max. energy content E 0 = 1 2 2 ⋅ C ⋅ U 0 of capacitor: ∆ U c ( t ) ∆ U c ( t ) P 0 ⋅ ∆ f ∆ f = T a ⋅ 1 Solution: ⋅ ∝ U 0 2 E 0 f U 0 f Voltage variation at the capacitor is proportional to the frequency variation 10 TH Köln TH Köln
Power variation 0.4% 0.2% Relative Frequency Deviation f / fo Relative Power Deviation P/Po 0.3% 0.1% Power variation: 0.2% 0.0% ~ +/-0,1% of rated 0.1% -0.1% power 0.0% -0.2% -0.1% -0.3% Df/fo Df/fo filtered 14.8.2015, 14:00h-15:00h DP/Po -0.2% -0.4% 0 600 1200 1800 2400 3000 3600 Time t / s No significant impact on components 11 TH Köln TH Köln
Variation of intermediate voltage 0.4% 4% Voltage Deviation Uc/Uo Voltage variation: Frequency Deviation f / fo 0.3% 2% ~ +/-3.5% of nominal voltage 0.2% 0% 0.1% -2% 0.0% -4% Df/fo -0.1% -6% Df/fo filtered DUc/Uo 14.8.2015, 14:00h-15:00h -0.2% -8% 0 600 1200 1800 2400 3000 3600 Time t / s No significant impact on power stage 12 TH Köln TH Köln
Control approach 13 TH Köln TH Köln
Idea of the control Control keeps intermediate voltage at reference level Modify reference value according to Figure based on: Texas Instruments, grid frequency "Digitally Controlled Solar Micro Inverter using C2000 Piccolo Microcontroller", TMS320C2000™ Systems 2 Applications Collateral, 2014 14 TH Köln TH Köln
Realized test circuit with PFC controller Figure based on: Infineon, "Boost Controller TDA4863 - Power Factor Controller IC for High Power Factor and Low THD", Datasheet, Rev. 2, Feb. 2005. 15 TH Köln TH Köln
Measurements: Artificial frequency signal 550 160 Intermediate Voltage Control voltage (x10) 500 140 Input Power Ideal Power 450 120 400 100 350 80 Voltages / V Power / W 300 60 250 40 200 20 150 0 100 -20 50 -40 0 -60 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 Time t / s 16 TH Köln TH Köln
Conclusion 17 TH Köln TH Köln
Virtual inertia with power inverters Use intermediate voltage capacitor: Existing hardware can be used Control easily adapted 18 TH Köln TH Köln
Contact Prof. Dr. Eberhard Waffenschmidt Electrical Grids, CIRE - Cologne Institute for Renewable Energy Betzdorferstraße 2, Room ZO 9-19 50679 Cologne, Germany Tel. +49 221 8275 2020 eberhard.waffenschmidt@th-koeln.de https://www.fh-koeln.de/personen/eberhard.waffenschmidt/ 19 TH Köln TH Köln
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