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Power Electronics in Photovoltaic Power Systems M.Sc. Tuomas Messo, 7.11.2013 Contents 1.Scale and cost of PV generation 2.Power electronics as a part of PV systems 3.Grid interfacing 4.Maximum power point tracking 5.Research in DEE 7.11.2013 2 Cost of PV electricity The cost of PV electricity has been coming down due to increased volume and more efficient technology Grid parity will be likely to happen in the near future 7.11.2013 3 Small-scale PV production Roof-top mounting, TUT, DEE, (Sähkötekniikan Laitos) 13.1 kW peak power 69 PV modules 190 watts each Research plant Benefits Feed-in tarif (e.g., Germany) Own supply of electricity Challenges Partial shading Snow and ice 7.11.2013 4 Small-scale PV production Modules need to be completely clean from ice to work efficiently Ice creates a partial shade 7.11.2013 5 Building-integrated PV production CIS Tower in Manchester, UK 7,244 PV modules 80 watts each 391 kW peak power Benefits Cut-down electricity cost Large facades are already available Challenges Losses due to partial shading http://www.sharpmanufacturing.co.uk/ 7.11.2013 6 Large-scale PV production (PV plants) Waldpolenz Solar Park, Germany 52 MW peak power 153,650 PV modules 220 hectares Investment cost 130 M€ Benefits No pollutants Profitable investment? Challenges Large power fluctuations Maintenance (dust, ice) Locating a fault http://michaeltomczyk.com/images/juwi_waldpolenz_450.jpg 7.11.2013 7 PV production In short The peak power of a PV plant can be almost anything Different power scales face different problems Power electronics are needed in all of them www.abb.com www.sma.com 7.11.2013 8 Contents 1.Scale of PV generation 2.Power electronics as a part of PV systems 3.Grid interfacing 4.Maximum power point tracking 5.Research in DEE 7.11.2013 9 Power Electronics in Photovoltaics Voltage of the PV module has to be at the MPP to extract maximum power The operating voltage can be determined using a power electronic device H. Häberlin, Photovoltaics System Design and Practice 7.11.2013 10 Power Electronics in Photovoltaics The DC electricity produced by PV modules has to be transformed into AC in grid-connected PV power systems DC-AC transformation is done using a device called an inverter www.abb.com 7.11.2013 11 Power Electronics in Photovoltaics The inverter acts as an interface between the grid and the PV modules Grid Load 7.11.2013 12 Power Electronics in Photovoltaics The inverter is required to shut down if a grid fault occurs ride-through capability inject high quality current be reliable operate at the MPP be cheap 7.11.2013 13 Power Electronics in Photovoltaics PV inverter manufacturers ABB SMA Siemens Danfoss Vacon kW range MW range 7.11.2013 14 Contents 1.Scale of PV generation 2.Power electronics as a part of PV systems 3.Grid interfacing 4.Maximum power point tracking 5.Research in DEE 7.11.2013 15 Grid Interfacing Different architectures exists Central 3-phase inverter String inverter Multistring inverter Module-integrated inverter S. Kjaer et. al., “A Review of Single-Phase Grid-Connected Inverters for Photovoltaic Modules”, IEEE Trans. Industry applications 7.11.2013 16 Grid Interfacing The inverter should work with good efficiency η PAC PDC This means that the inverter is designed to have small losses Early 90’s transformer inverter. Modern transformerless inverter. H. Häberlin, Photovoltaics System Design and Practice 7.11.2013 17 Grid Interfacing New type of inverters based on SiC devices have efficiencies up to 99.5 % Not much room for improvement there C. Ho et. al., “Practical Design and Implementation Procedure of an Interleaved Boost Converter Using SiC Diodes for PV Applications”, IEEE Trans. Power Electronics 7.11.2013 18 Reliability Lifetime of a PV module is more than 20 years Nobody knows the exact lifetime of a PV inverter (less than 10a) G. Petrone et. al., “Reliability Issues in Photovoltaic Power Processing Systems”, IEEE Trans. Industrial Electronics H. Häberlin, Photovoltaics System Design and Practice 7.11.2013 19 Reliability Significant amount of PV energy can be lost if the system is not designed properly H. Häberlin, Photovoltaics System Design and Practice 7.11.2013 20 Contents 1.Scale of PV generation 2.Power electronics as a part of PV systems 3.Grid interfacing 4.Maximum power point tracking 5.Research in DEE 7.11.2013 21 Maximum Power Point Tracking PV inverter controls the voltage of the PV generator to extract maximum power Inverter A keeps disconnecting and inverter B fails to track the MPP voltage “Choosing the right inverter”, Photon International 7.11.2013 22 Maximum Power Point Tracking MPPT efficiency should be very close to 100% for modern inverters. MPPT efficiency should be checked for different power levels. The example inverter shown below exhibits superior MPPT efficiency in high power conditions and very poor efficiency in low power conditions. H. Häberlin, Photovoltaics System Design and Practice 7.11.2013 23 Maximum Power Point Tracking MPP can be traced by sweeping the voltage of the PV generator but then power is lost Does it matter if the efficiency of inverter is 99 or 99.5% if power is lost during the sweep? H. Häberlin, Photovoltaics System Design and Practice 7.11.2013 24 Maximum Power Point Tracking MPPT can get confused when irradiance changes H. Häberlin, Photovoltaics System Design and Practice 7.11.2013 25 Maximum Power Point Tracking Selecting the right parameters for the MPPT-algorithm is crucial H. Häberlin, Photovoltaics System Design and Practice 7.11.2013 26 Contents 1.Scale of PV generation 2.Power electronics as a part of PV systems 3.Grid interfacing 4.Maximum power point tracking 5.Research in DEE 7.11.2013 27 Research in DEE Modeling and control of power electronic converters in PV applications Optimization of MPP-tracking algorithms Modeling and operation of PV generators in real conditions Conventional two-level three-phase inverter. Three-phase Z-source inverter. 7.11.2013 28 Research in DEE Outcomes: Component sizing Reliable control design Identifying potential stability issues T. Messo et. al.,”Minimum dc-link capacitance requirement of a twostage photovoltaic inverter”, Energy Conversion Congress and Exposition, 2013 7.11.2013 29 Interested in power electronics? DEE-32000 Tehoelektroniikan perusteet, 5 op DEE-33020 Tasa- ja vaihtosuuntaajat, 5 op DEE-33030 Sähkömoottorikäytöt, 5 op DEE-33040 Sähkömoottorikäyttöjen laboratoriotyöt, 3 op DEE-34000 Taajuudenmuuttajat, 5 op DEE-34030 Tehoelektroniikan suunnitteluprojekti, 5-8 op DEE-33106 Switched-mode Converters, 5 op DEE-34106 Converter Dynamics and EMC, 5 op DEE-53116 Solar Power Systems, 4 op 7.11.2013 30 Opintosuunnistus 14.11 Ohjelma: – 10.15 tietoisku salissa SF213 Sähkövoimatekniikan ja Tehoelektroniikan opiskelusta – n. 10.45 labrakierrokset, esittelyssä mm. • • • • • aurinkovoimala tuulivoimalasimulaattori sähköauto RTDS-verkkosimulaattori suurjännitelaboratorio 7.11.2013 31 http://solarbackpacking.com/ Thank you! 7.11.2013 32