Abstract
A method to design a sliding-mode control of a photovoltaic system based on a flyback converter is proposed. First, the photovoltaic system is modeled to design the sliding-mode controller and to select the parameters of a maximum power point tracking algorithm. Then, the detailed design of the sliding-mode controller is presented, which includes the establishment of the sliding surface. The transversality, reachability, and equivalent control tests are also developed. Because the power extraction of the PV system is carried out through a P&O MPPT algorithm, the selection of the perturbation magnitude, the perturbation period, and the maximum switching frequency is integrated into the control design. Additionally, since the derivative of the MPPT output could prevent the achievement of the reachability test, a filter to limit that derivative is also integrated into the design process. The whole method is illustrated in an application example where the data of a BP585 PV module and a real flyback converter are used. Once the parameters were obtained, circuital simulations performed in PSIM validated the intended operation of a PV system composed of a PV module and a flyback converter, which is connected to a source that produces the perturbations of an AC grid.
Highlights
An integrated design procedure for the sliding-mode control of the first-stage flyback that belongs to a PV system was presented and validated in this paper
Specific attention was put on the Sliding Mode Control (SMC) design; the basic concepts of the sliding-mode controller applied to power converters were presented
Because the power extraction had to be implemented with a maximum power point tracking algorithm, the MPP tracking (MPPT) output was filtered to limit its derivative
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. This dc/dc converter is used to implement the MPPT algorithm, which usually generates a voltage or current reference to find and track the MPP of the module Such reference is tracked by a control system to improve the MPPT dynamic response and reject the 100 Hz or 120 Hz voltage oscillations reflected in the PV module from the grid [13]. The paper has four main contributions: (1) The proposed SMC controller guarantees the system stability for any operating point and the desired dynamic performance for the tracking of the PV module voltage reference. (3) The proposed design procedures of the SMC and the first-order filter, as well as the implementation details, facilitate the application of the proposed controller for any (i.e., existing or new) flyback converter used in grid-connected PV systems with microinverters or distributed. MPPT systems. (4) The paper provides formal stability tests through the analysis of the transversality, reachability, and equivalent control conditions
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