Abstract
The heuristic perturb-and-observe-based maximum-power-point tracking (MPPT) algorithm of photovoltaic (PV) generator is still the most popular technique in use, despite the broad spectrum of developed other MPPT algorithms. The correct direction of the next perturbation step requires that the previous perturbation is settled down properly and the applied perturbation step size is large enough to overcome the PV-power changes induced by the varying irradiation level and/or the power-grid-originated PV-voltage ripple. The requirements for the minimum perturbation step size are well defined in the available literature. The design equations to predict the PV-power settling time are derived by assuming that the PV-interfacing converter operates in continuous conduction mode (CCM). A large perturbation step size may drive the interfacing converter to enter into discontinuous conduction mode (DCM), which will delay the PV-power settling process and destroy the validity of the predicted settling times. In order to avoid confusing the MPPT process, the maximum perturbation step size has to be limited as well. This paper provides theoretical foundations for the proper design of the maximum step size based on the DC-DC interfacing-converter dynamic behavior. The theoretical findings are validated with experiments as well as by simulations by means of a boost-type DC-DC converter and real PV panel.
Highlights
Broad spectrum of maximum-power-point (MPP) tracking algorithms ranging from the simple passive methods to the application of artificial intelligence is available as discussed in [1,2,3,4,5,6]
The purpose of the simulations was to verify the behavior of the transients, when the interfacing converter operates in conduction mode (CCM) as well as to study the inductor-current behavior, when the maximum step size is applied in different operational regions of the PV generator
The perturb and observe (P&O)-based MPP-tracking control is already well mastered with design formulas, which are developed assuming the interfacing converter to operate in CCM
Summary
Broad spectrum of maximum-power-point (MPP) tracking algorithms ranging from the simple passive methods to the application of artificial intelligence is available as discussed in [1,2,3,4,5,6]. The correctly selected perturbation frequency, which guarantees that the PV voltage and current measurements are performed at the moment when the PV power transient is properly settled down [10,12,13,24], the correctly selected minimum perturbation step size to producing high enough PV-power variation, which overcomes the combined power changes induced by the irradiation change during the perturbation interval and the PV voltage/current ripple [10,12,13,24] It was recently pointed out in [29] that it is necessary to select correctly the maximum perturbation step size to keep the PVG-interfacing converter to operate and keep on operating in continuous conduction mode (CCM) during the perturbation process.
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