Simulink modelling of LV photovoltaic grid-connected distributed generation

EU Governments are working towards increasing the amount of renewable energy sources in order to reduce the environmental impact of energy generation (Directive 2001/77/CE). Further, recent technical developments (e.g. fuel-cells, micro CHP using novel turbines or Stirling engines and photovoltaic (PV) devices integrated into the fabric of buildings) and the liberalisation of the electricity market encourage the use of renewable resources in terms of distributed generation (DG) and CHP units. On the other hand, the presence of large amount of DG can have a negative impact on distribution networks, which are designed and operated as passive networks supplied by planned centralized generation. In LV distribution networks the effect of grid-connected PV DG units is worth to be investigated as such systems have a natural inclination to be easily integrated into high density urban LV distribution networks. If a large capacity of PVDG is to be connected in the future, then it will be necessary to account for consequences on important technical aspects, some of which related to power quality supplied to customers (voltage variations, protection, harmonic distortion, etc.) [1]. In order to study the effects of PVDG on distribution operation, the present paper deals with the development of PV units models suitable for large scale systems studies, for both steady state and transient analysis. The first section presents a general description of grid-connected PV systems to introduce the system modelling. The second section discusses the basic PLL concept and design criteria for grid-connected PV applications. In the third section modelling of the current reference generator of single-phase inverters based on the PLL technique is dealt with. The models have been developed by means of Simulink
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(Dynamic System Simulation for MATLAB
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). Finally, as an example of the application of the models developed, the fourth section presents a study which shows the effect of grid-connected PV units on feeders voltage profile in a LV distribution network.