Abstract
This paper identifies the partial shading problem of a PV module using the one-diode model and simulating the characteristics exhibiting multiple-peak power output condition that is similar to a PV array. A modified particle swarm optimization (PSO) algorithm based on the suggested search-agent deployment, retracking condition, and multicore operation is proposed in order to continuously locate the global maximum power point for the PV system. Partial shading simulation results for up to 16 modules in series/parallel formats are presented. A distributed PV system consisting of up to 8 a-silicon thin film PV panels and also having a dedicated DC/DC buck converter on each of the modules is tested. The converter reaches its steady state voltage output in 10 ms. However for MPPT operation, voltage, and current measurement interval is set to 20 ms to avoid unnecessary noise from the entire electric circuit. Based on the simulation and experiment results, each core of the proposed PSO operation should control no more than 4 PV modules in order to have the maximum tracking accuracy and minimum overall tracking time. Tracking for the global maximum power point of a distributed PV system under various partial shading conditions can be done within 1.3 seconds.
Highlights
In a centralized photovoltaic system, the total power generated by the entire array of PV modules is reduced due to panel’s mismatch, degradation, or partial shading conditions
Latest research works on different maximum power point tracking (MPPT) techniques include Cuckoo search method [1], MPPT based on the bypass diodes working mechanism [2], colony of flashing firefly method [3, 4], modified incremental conductance algorithm [5], voltage interval regularity method [6], artificial bee colony method [7], particle swarm optimization and related methods [8,9,10,11,12,13], random search method [14], and radial movement optimization [15]
In a distributed PV system, each module is usually controlled by a local DC/DC converter having its maximum power point tracker, and the effect of partial shading can be limited to module level instead of the entire system
Summary
In a centralized photovoltaic system, the total power generated by the entire array of PV modules is reduced due to panel’s mismatch, degradation, or partial shading conditions. In such a case, the power characteristic curve for the entire PV array exhibits multiple maxima power points making the maximum power point tracking (MPPT) algorithm more difficult to find its global extreme value. Multivariable maximum power point tracking method ( known as the distributed MPPT or DMPPT) has an advantage over the classical distributed MPPT algorithm by using only one set of current and voltage data. Following the work of [22], a DMPPT algorithm based on panel level DC/DC converter control using embedded microcontroller is possible.
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