بررسي پديده رزونانس در اتصال آرايه هاي منابع تجديدپذير بر اينورتر به شبكه

چكيده انگليسي :

Investigation of resonance in networks with multiple inverter based renewable energy systems Fariba Asghari f asghari@ec iut ac ir Date of Submission January 14 2014 Department of Electrical and Computer Engineering Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language Farsi Supervisor Hamidreza Karshenas karshen@cc iut ac ir Abstract This thesis is concerned with resonance phenomenon in distribution power grids when multiple grid connected Photovoltaic PV inverters are installed in the vicinity of each other This situation can happen for example in roof top ac module installations where a large number of PV inverters are connected to the grid Using renewable and clean energy sources such as wind and solar has been growing rapidly in recent years due to fossil energy crisis and rising level of greenhouse gases In this regard PV energy harvesting has become very popular due to many factors such as its scalability and the possibility to use roof top PV panels in any size and number Inserting solar energy to ac grid through PV process always involves a solid state inverter due to the fact that PV energy is dc while almost all grids are ac Such an inverter always includes a passive filter at its output in order to attenuate the current harmonics generated by inverter and prevent their injection to grid In the areas where there is a large penetration of such inverters into distribution grid the aggregation of inverters and the fact that their output filter appear in parallel with each other can change the resonance behaviour of the network leading to unwanted voltage amplifications due to resonant phenomenon The resonance occurs as a result of interaction between the aggregated filter capacitors and grid reactance In this thesis analytical studies are presented in order to investigate this phenomenon A comprehensive modelling of a network with multiple grid connected inverters is derived This model is obtained by modelling the inverter as a controlled current source i e its Norton equivalent circuit The first stage of studies is carried out by considering only the effect of passive components on frequency response The frequency response of such a network with LCL output filter is obtained In the second stage the complete inverter including its control system is taken into consideration In this regard various types of controllers used in single phase grid connected inverters are investigated Single phase inverters are chosen in these studies as most ac modules are single phase Two important types of controllers that are investigated are proportional resonance PR and deadbeat DB controllers The effect of different parameters such as the number of inverters the impedance of connecting lines and controller structure and parameters on the resonance behaviour of network is shown It is shown that with certain number of parallel inverters the possibility of occurring resonance at characteristic harmonics of network becomes high The studies in this thesis are carried out by two different approaches and verified by each other In one approach the s domain transfer function of multi inverter system is derived and low damped poles are recognised In another approach the time domain simulation of the same multi inverter system is performed The agreement between the results of these two approach shows the validity of modelling The studies are concluded by proposing improved controllers with the aim of mitigating resonance Keywords Grid connected inverter Resonance Photovoltaic systems LCL filter

اصغري، فريبا

بررسي پديده رزونانس در اتصال آرايه هاي منابع تجديدپذير بر اينورتر به شبكه

اينورتر متصل به شبكه , سيستم هاي فتوولتايي , فيلترLCL