Abstract
This paper presents modeling approaches for step-up grid-connected photovoltaic systems intended to provide analytical tools for control design. The first approach is based on a voltage source representation of the bulk capacitor interacting with the grid-connected inverter, which is a common model for large DC buses and closed-loop inverters. The second approach considers the inverter of a double-stage PV system as a Norton equivalent, which is widely accepted for open-loop inverters. In addition, the paper considers both ideal and realistic models for the DC/DC converter that interacts with the PV module, providing four mathematical models to cover a wide range of applications. The models are expressed in state space representation to simplify its use in analysis and control design, and also to be easily implemented in simulation software, e.g., Matlab. The PV system was analyzed to demonstrate the non-minimum phase condition for all the models, which is an important aspect to select the control technique. Moreover, the system observability and controllability were studied to define design criteria. Finally, the analytical results are illustrated by means of detailed simulations, and the paper results are validated in an experimental test bench.
Highlights
Power generation systems based on alternative energy sources have become stronger options to address the continuous power demand and the initiative to reduce the use of fossil fuels
The applicability of the proposed modeling approach to real cases was demonstrated by experimentally validating the application example previously presented
A bulk voltage composed by both DC and 100 Hz components was adopted to put in evidence the system capability to operate with small non-electrolytic capacitors
Summary
Power generation systems based on alternative energy sources have become stronger options to address the continuous power demand and the initiative to reduce the use of fossil fuels. One of the most suitable option concerns photovoltaic (PV) modules, for low power levels [1]. The innovation on photovoltaic energy and power electronics fields makes this technology an important research area, in modeling and control techniques. The design of a controller capable of rejecting disturbances on the PV module (PVM) and the load represents one of the main challenges in the implementation of this kind of systems, where it is essential to select an appropriate model for the PVM, the power electronics interface, and the disturbance sources. In [4], the single diode PVM model and the diode equivalent circuit are discussed, and a piecewise linear model is proposed. In [5] a simplified model is proposed using only parameters provided by manufacturer’s specifications to avoid the use of numerical methods
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