Control software development for three phase grid connected inverter

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Futó András
Department of Automation and Applied Informatics

The dependency on renewable energies in generating energy is instantly increasing due to decaying of conventional energy sources and increasing demand. Distributed generation provides multiple energy sources that integrate with electrical grid and support electrical loads with secure and reliable energy source. However, matching energy from different sources is a challenging task which requires a strict and efficient control schemes. Electrical power inverters play a vital role in harmonizing different types of energy into the grid by converting DC quantities to AC quantities and achieving a stabilized power flow between the distributed generator and the grid. Several studies have been carried out to apply different control strategies to perform efficient control of the inverter. In this thesis, a software for controlling such an inverter is developed using C programming language. The control scheme is based on PI controller whose parameters can be monitored and tuned in real-time manner. Linear PI controller for current and voltage is designed. Moreover, a software phase locked loop SPLL is also designed and programmed to efficiently synchronize the inverter to the gird. Control strategy is evaluated through an experimental circuit composed of a three-phase inverter, a dc source, and three-single phase transformers connected to the main grid. Additionally, active and reactive power flow between the inverter and the grid is illustrated through an oscilloscope and current props to ensure the effectiveness of the controlled inverter. Finally, harmonic content of the inverter output waveforms is calculated and compared to the main standards concerning integration of distribution generation into electrical grid.


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