The I-U characteristics of any solar module are a highly nonlinear relation that depends on solar insolation level (G) as well as on the module surface temperature (T). At a fixed value of G, the module terminal voltage decreases nonlinearly as the load current increases. Most of previous work related to investigating the photovoltaic (PV) array performance is depending on a nonlinear mathematical equation relating the module voltage with its current. Therefore, it is difficult to determine the operating point analytically.
It is known that most of operating points lies in the range between the no-load voltage (Uoc) and the maximum power point voltage (Umpp). In this paper, an approach is presented to obtain approximate closed-form expressions for the I-U characteristics of any PV array in the range from no-load condition up to the maximum power point condition. The technique presented allows direct method to predict the operating conditions of PV arrays when feeding loads, such as DC motors, without using tedious and time consuming iterative techniques.
The approximated I-U characteristics are compared with the corresponding exact characteristics and very close agreement was obtained. To validate the proposed closed form expressions when DC motors are fed from a PV array, the torque speed characteristics of different types of DC motors fed from a PV array are obtained and compared with its corresponding exact characteristics. The difference between the exact and the approximate characteristics is very small.
|
