Flexible Power Point Tracking for Solar Photovoltaic Systems using Secant Method
Abstract : Grid-connected photovoltaic (PV) systems impose challenges like voltage fluctuations, low system inertia and power quality issues. The need to tackle these challenges led to the introduction of flexible power point tracking (FPPT), where the PV power output is controlled by an energy management system (EMS), rather than solely operating the PV systems on the maximum power point (MPP). The requirement of fast transient response implies that algorithms such as the one proposed in this paper are desirable. The proposed algorithm uses the secant method to achieve significantly improved results in comparison to the existing methods. The method also simplifies the prediction of variations during changes in the environment and power reference, hence, results in reduced oscillation around the set-point and faster convergence. Experimental validation is presented in this paper for supporting the claims. The results in terms of accuracy, convergence rate, steady state oscillations and cumulative error are bench-marked against one of the most recent FPPT methods.
? The flexibility of the proposed adaptive FPPT algorithm has been demonstrated experimentally on a 3-kVA laboratory setup under different conditions.
? The tracking error of the proposed algorithm has been reduced significantly in all experimental tests, while the settling has also been decreased.
? The results demonstrated the applicability and effectiveness of the proposed FPPT algorithm as an additional function for existing MPPT algorithms in GCPVPPs.
? Therefore, the existing maximum power point tracking algorithms in GCPVPPs, should be replaced by flexible power point tracking (FPPT) algorithms in GCPVPPs in order to comply with these demands.
? It is known that the irradiance and cell temperature do not have a significant effect on the panel voltage around the MPP .Therefore, the parameters corresponding to the reference curve are selected to initiate the FPPT process.
? It should be noted that the issues arising from this assumption will be addressed in the following subsections of the paper.A power tolerance, dp is provided as a stopping condition for the proposed FPPT algorithm.
? The need to tackle these challenges led to the introduction of flexible power point tracking (FPPT), where the PV power output is controlled by an energy management system (EMS), rather than solely operating the PV systems on the maximum power point (MPP).
• Improving the conversion efficiency by means of this method only requires a cheap thermometer besides the essential sensing tools of P&O.
• It has been shown that the proposed ER method ensures a fast convergence speed in response to the rapidly changing atmospheric conditions.
• The variable perturbation step searching applied in ER not only accelerates the tracking speed, but also provides a way for eliminating the oscillations in steady state.
• As long as the power varies exceeding the predetermined tolerance t, which indicates the changes of I-V characteristic, MPP estimation process is reactivated and a new searching iteration begins. The flow chart of the proposed ER method.
? The various performance parameters for the comparison of the secant method and the adaptive voltage-step-based P&O algorithm.
? An extra measurement was taken in order to discern environmental changes, which affects the PV performance. Convergence needs to be faster as the power reference may vary frequently, and the effect of environmental changes should also be considered.
? It can be seen that the secant method showcases better performance on both sides of operation than the adaptive step P&O method.
? Its execution is also simple, as there is no need for evaluating any derivatives or additional functions.Overall, the proposed secant-method-based FPPT algorithm showcases better performance than any other FPPT algorithm available in the literature.
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