Mixed third-fourth order generalised integrator based PLL for grid integration of solar photovoltaic systems

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ABSTRACT Increasing energy demand and the need for reduction in carbon emissions has necessitated the grid integration of solar photovoltaic (PV) systems, which are being widely employed in the tropical region. In a single-stage PV system, a voltage source inverter (VSI) is used to interface the PV panels with the grid. For the control and grid synchronisation of this VSI, an instantaneous phase angle of the fundamental positive sequence component (FPS) of grid voltage needs to be determined. Generalised integrator-based phase-locked loops (PLLs) are widely employed for this determination. This paper proposes a new orthogonal signal generator (OSG) for a generalised integrator-based PLL, known as mixed third-fourth order generalised integrator-based PLL (MTFOGI-PLL). The proposed MTFOGI offers fast dynamic response, better filtering and dc-offset rejection capability. The reported PLL is implemented as a part of the voltage-oriented control of the grid-tied PV system. The MTFOGI-PLL based operation of the grid-tied PV system is analysed under ideal and non-ideal grid conditions. From the results, it is observed that the proposed PLL accurately extracts the FPS voltages under different operating conditions resulting in the functioning of the grid-tied PV system as per the grid codes.