Improved control of a photovoltaic pumping system by DTC-SVM to optimize the water flow

This paper deals with two different techniques of vector method-related direct torque control: the conventional (DTC-C) and the space vector modulation (DTC-SVM). Both are used for an induction motor in the photovoltaic pumping system. Based on instantaneous space vector theory, and with an optimal selection of the space voltage vectors in each sampling period, the DTC achieves effective control of the stator flux and torque. Consequently, the number of space voltage vectors and switching frequency directly influence the performance of the DTC control system, giving an advantage for a rotor position free control system. In order to improve the efficiency of the photovoltaic generator, maximum power point tracking techniques are investigated. The incremental conductance (Inc-MPPT) algorithm is applied to the system with variable temperature and irradiance conditions. DTC associated with Inc-MPPT allows the system to operate at its maximum power, with a good performance and fast response without overshoot. Comparing the two control techniques of torque, it appears that DTC-SVM optimizes not only the photovoltaic conversion efficiency but also the losses in the induction motor, and it improves the water flow quantity.

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