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Maximum power point tracking (MPPT) is essential for a photovoltaic (PV) system in order to maximise the utilisation of solar energy. Under partially shaded conditions (PSC), PV strings with bypass diodes exhibit multiple peaks in the power-voltage (P-V) characteristics. Although various Global MPPT (GMPPT) algorithms have been proposed to address this issue, most of them cannot distinguish between PSC and uniform insolation, leading to the scan of the entire P-V curve under uniform insolation levels. This study introduces a general method to detect the occurrence of PSC in a PV string thereby dispensing the need to scan the entire PV curve under uniform insolation. Further, a simple technique is proposed to determine the GMPP with the minimum possible search space under PSC. The proposed algorithms for the detection of partial shading and GMPPT are validated experimentally.

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This paper presents a detailed analysis of Type-3 PLL under wide variation in input voltage and frequency. Using small signal modeling, the performance of both single loop and dual loop type-3 PLL for variation in input voltage and frequency is studied. The analysis shows that for the same bandwidth, both the single loop and dual loop Type-3 PLL exhibit similar dynamics provided the supply voltage is balanced. However, under voltage sag conditions, dual loop PLL shows improved dynamic response without affecting its stability. Further, the tracking time is reduced as the feed forward frequency is a function of supply frequency. To improve the filtering characteristics under frequency deviations, a dual loop Type 3 adaptive PLL which accurately tracks the phase and frequency of the input signal under wide frequency deviations is developed. Simulations are carried out in MATLAB and experimentally verified by implementing in ALTERA cyclone II FPGA board.

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