A grid tied photovoltaic (PV) power conversion topology is presented in this study with a novel scheme of resynchronization to the grid. This scheme serves the purpose of supplying continuous power to the load along with feeding power to the grid. The control approach helps in mitigation of harmonics and improving the power quality while extracting the optimum power from the PV array. Depending on the availability of grid voltage, the proposed configuration is controlled using three approaches, defined as grid current control, Point of Common Coupling (PCC) voltage control and intentional islanding with re-synchronisation.
A simple proportional integral controller manages the grid current, load voltage, battery current and DC Direct Current (DC) link voltage within these modes. Moreover, a control scheme for quick and smooth transitions among the modes is described. The robustness of the system under erratic behaviour of solar insolation, load power and disturbances in grid supply makes it a suitable choice for a residential application. The control, design and simulation results are presented to demonstrate the satisfactory operation of the proposed system.
Fig. 1 Proposed system topology
EXPECTED SIMULATION RESULTS:
Fig. 2 Performance of the system under grid isolation
GCC to PVC, (b) Harmonic spectrum of grid current (ig), (c) Harmonic spectrum of load voltage (vL)
Fig. 3 Performance of the system under grid reconnection
(a) Mode change from PVC to IIRS, (b) Grid voltage (vg) vs. load voltage (vL) during
Fig. 4 Performance of the system for insolation change from 1000 W/m2
The proposed scheme has combined the solar PV power generating unit to single-phase grid with a unique feature of resynchronization of grid to the system after overcoming the grid failures. The ability of the system to generate maximum power for varying insolation, feeding active power to the grid as well as load and store/extract power to/from the battery has been validated by the dynamic performance. This helps in increasing the efficiency of the system.
The scheme has utilised minimum number of switches resulting in lower switching losses. The VSC has the ability to diminish the switching harmonics in grid current and load voltages resulting in <5% THD as demanded by the IEEE 519 standard. The system has ability to re-synchronise with the grid within five cycles of grid voltage for any phase difference. This helps in achieving the fast time response of the system, thus making it a suitable choice for residential applications. The obtained results have authenticated the robustness and feasibility of the proposed system under various disturbances.
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