Analysis of Three-Phase Grid-Tied Thyristor Based Inverter for Solar PV Applications

In the early phases of ac to dc inverters/ converters which were line commuted, the line current was square in shape. It contained higher order harmonics which generates electromagnetic induction which in turn causes heating of the core of power transformers or distribution transformers. Simple pulse width modulation based inverters which uses MOSFET/IGBT has high switching loss, and it has quite low reliability and the power handling capability in comparison to using thyristor/SCR. In case of thyristor-based inverters, pulse width modulation in not feasible due to commutation circuits. In dc to ac conversion, it is desired that the output waveform resembles a sine wave as much as possible and harmonic content must be low. In this paper, a multilevel inverter topology has been presented in which switching angle has been controlled and three phase ac to dc converter circuits are used in inversion mode. Since there is natural commutation, there is no requirement of a separate circuit for synchronization. In this paper, simulation is performed for grid tied three-phase 12 pulse converters. The solar PV systems are incorporated for DC source. The converter is analyzed by varying DC source voltage, Inductance and varying the switching angles so that the total harmonic distortion is reduced.