Condicionamento de potÃncia de uma motobomba em um sistema de bombeamento fotovoltaico atravÃs de um conversor de frequÃncia

AUTOR(ES)
DATA DE PUBLICAÇÃO

2004

RESUMO

Frequency converters (FC), usually applied in industrial applications, are being adopted in practice, to drive photovoltaic pumping systems (PVPS), substituting equipment (inverters), specially designed for that purpose. However, the information available, regarding the operation of FC for applications of that nature is small or almost inexistent. This work has as main objectives the evaluation of the experimental characteristics of a FC and the determination of the best fixed operating voltage. With that information we can then evaluate the possibilities that the FC offers in substitution of inverters specifically dedicated to photovoltaic applications. In the first part of this work a general description of a traditional PVPS is given. All components that integrate the system and the main functions are detailed. After that, general information is presented, regarding frequency converters, its basic operational modes and configurations needed to operate a PVPS. Experimental tests were accomplished, at first, with a pumping system specifically designed for photovoltaic applications and then, with the same pumping system but with its inverter substituted by the FC, both systems working in independent situations. Another test has been carried out using the FC with a conventional centrifugal pump, acquired in the local market. The objective of this experiment was to evaluate the technical viability of this kind of coupling. In all the tests, the same amount of modules, but with different configurations in order to match the inverter and FC voltage inputs, have been used. Measurements allowed to obtain the characteristic curves, water flow rate versus solar irradiance, for each one of the pumping systems analyzed. Those informations were used to estimate the daily, long term average water volume, pumped by each one of the tested systems, through the statistical method of utilizability. Comparing the long term water volume supplied by the system with the FC with the one supplied by the specific photovoltaic system, we evaluated the potential of the FC technology. The smallest difference found between the average water volume pumped by both systems is around 8.5 %. This value was verified for the system operating with 285 V. Using the conventional motor pump, results show an average pumped water volume around 35 % smaller, when compared to the specific photovoltaic pumping system. The difference of 8.5 %, in the first case, is due to the operational mode of the FC, fixed voltage, versus the operational mode of the photovoltaic inverter that follows the maximum power point. In the second case, the performance of the conventional motorpump, designed to work on higher manometric heads than the ones used in the experiments, contributes to increase the difference in pumped water volume from 8.5 % to 35 %. We conclude, finally, that, in terms of cost-benefit relations, the frequency converter presents effective possibilities to substitute, in practice, the specific equipment used in photovoltaic applications. Improvements on the FC operational mode can still be introduced, reaching similar performance to the one obtained from equipment specially designed for photovoltaic applications.

ASSUNTO(S)

bombeamento fotovoltaico coversor de frequÃncia engenharia nuclear potencia motoboma

ACESSO AO ARTIGO

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