Abstract
Global maximum power point tracking (GMPPT) refers to the extraction of the maximum power from photovoltaic (PV) modules in real time under changing ambient conditions. Due to the installation of PV systems in densely built-up areas, partial shading scenarios are commonplace. Commercially established GMPPTs suffer from low tracking speeds and inefficiency. A novel GMPPT algorithm is proposed here based on the rectangular power comparison (RPC), which exploits the fundamental relationship between the shading factor, the bypass diode voltage and the global maximum power point. The entire theoretical formulation of RPC is presented systematically for the first time. This method boasts of increased conversion speeds owing to the precomputation of the module voltage versus the shading factor correlations using the regression of diode model from the experimentally obtained bypass diode characteristics. The proposed method is simple to implement with the computational complexity of order $n$ , which represents the number of uniquely shaded PV modules in a series string. The proposed approach addresses the much-needed intersection problem between the distributed and centralized PV systems and therefore targets PV strings which are most common in residential and small to medium scale commercial PV installations world over. The proposed approach is validated with the in-house developed prototype hardware set-up and software control implementation giving a 99% tracking efficiency with a recorded tracking time of 10 ms. The experimental results show 50 times improvement in speed and 95% increase in power gain as compared to the other popular existing methods namely scanning based GMPPT and local MPPT methods respectively, with negligible computational burden and less than 0.5% added cost to the conventional PV energy conversion system.
Highlights
As photovoltaics are entering mainstream energy conversion, the challenges associated with this promising renewable energy resource are entering the lime light
Partial shading reduces the output of the PV systems but if long operations are continued under this condition, without bypass diode protection, The associate editor coordinating the review of this manuscript and approving it for publication was Haris Pervaiz
To get the reliability of centralized inverters and maximum power extraction efficiency of distributed MPPTs having one power converter per PV module, we propose a hybrid approach which incorporates merits of both methods without suffering from their limitations
Summary
As photovoltaics are entering mainstream energy conversion, the challenges associated with this promising renewable energy resource are entering the lime light. The last class of GMPPT includes control-based methods such as constant input power control [35], but this method suffers from power loss due to a low voltage operation when power command exceeds the instantaneous system availability Second such method is introduced in [6] where proportional-integral (PI) controllers are used in each distributed inverter to track individual peaks of each PV module, leading to increased component count and reliability issues. The basis of the proposed RPC approach is the evaluation of the relative powers and irradiances of different modules in a PV string using the module voltage information and the string current, which are monitored for shading detection These measured voltages further specify the shading factor by using the bypass diode characteristics regression model, which are first time applied for global maximum power point tracking. PLMPP, i is expressed as Pi in the text to follow, where i is defined as the index of the local maximum power point which varies from 1 for uniform irradiance to n for all uniquely shaded PV modules, each having a bypass diode across it
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