Modeling of Step-up Grid-Connected Photovoltaic Systems for Control Purposes

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

Modelo matemático de sistemas fotovoltaicos para búsqueda distribuida del punto de máxima potencia

“…La energía solar es una fuente limpia y renovable de electricidad con bajo impacto ambiental, disponibilidad en el sitio de consumo y sostenibilidad [1]. La energía del sol se convierte en energía eléctrica mediante el efecto fotovoltaico utilizando celdas solares.…”

“…Por tanto, la energía eléctrica generada por un PV debe convertirse a niveles de voltaje CA con la mayor eficiencia posible. Esta transformación CC/CA se debe realizar utilizando circuitos de electrónica de potencia que permitan extraer la máxima potencia de la disponible en el PV [1]- [3].…”

“…Adicionalmente, la potencia producida por el PV depende de las condiciones de irradiación solar, la temperatura a la que se encuentra y la impedancia de la carga en terminales del PV [1], [3]. Para maximizar la extracción de energía es posible modificar la impedancia de la carga, generalmente utilizando un convertidor CC/CC.…”

“…Esta inconveniente se soluciona conectando en serie los módulos para proveer el voltaje requerido [1], [3], [6]. Pero, es común que diferentes PV en el arreglo experimenten diferentes niveles de irradiación solar debido a cuerpos externos que generen sombras, generando un efecto conocido como "mismatching" [6], [7].…”

Auto-tuning of PV controllers to improve the speed response and stability of the P&O algorithm

“…Photovoltaic modules (PVM) transform sunlight into electricity (Esram & Chapman, 2007), (Jiménez, Cadavid, & Franco, 2014), and there exists an optimal operation point for each environmental condition in which the PVM produces maximum power, named Maximum Power Point (MPP). Figure 1 shows the power profile of a BP585 PV module (Trejos, Gonzalez, & Ramos-Paja, 2012) under two different irradiance levels S 1 and S 2 , the change in the MPP depending on such environmental conditions can be observed.…”