Simple power electronic controller for photovoltaic fed grid-tied systems using line commutated inverter with fixed firing angle

A power electronic interface with maximum power point tracking (MPPT) for grid connected photovoltaic (PV) systems using an integrated cascade boost converter (ICBC) and line commutated inverter (LCI) has been proposed. The variable dc voltage of the PV array is fed as input to the ICBC and the output voltage of the ICBC is maintained constant with the firing angle of the LCI being fixed at an appropriate value greater than 90°. The interesting feature of this scheme is that, it is not mandatory that the constant dc-link voltage should be more than the peak value of the grid voltage. As the array voltage is now boosted and fixed at the dc link, any variation in the PV output power is reflected in the variation of the dc-link current and hence only one parameter (the dc-link current) sensing is required for the MPPT. Furthermore, the proposed controller has made it possible to dispense with the step up transformer between the LCI and the utility grid. The complete scheme has been constructed and experiments have been conducted on an 84 V, 10 A PV array feeding power to a three-phase 230 V utility grid and the experimental results are compared with the MATLAB simulation results. The steady-state analysis of the overall system and the experimental results confirm the validity of the proposed controller and the efficacy of the analysis.