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Under normal operating conditions, the flow rate of a solar pump fed by a photovoltaic array follows the variations of the irradiance. However, the flow rate of a photovoltaic pumping system coupled to a water filtration unit should be constant under a constant pressure. So, the combination of solar batteries with a photovoltaic array is required. This paper presents a specific structure of the P & O algorithm for controlling a boost converter inserted between the photovoltaic array without batteries and the driving motor of a centrifugal pump. The simulation results in MATLAB/SIMULINK with ode23t solver show that blocking of the duty ratio of the control pulses of the boost converter enables to maintain a constant output voltage, even if the irradiance varies. Thus, for a duty ratio locked between 0.79 and 0.9, the output voltage of 236 V is obtained, for a flow rate of 1.08 l/s under a pressure of 5.8 bars.

A major problem concerning the operation of medium voltage power networks refers to the neutral-point grounding system. Several technical solutions are in use, none of them being completely satisfactory. One criterion to appreciate the efficiency of a grounding system is the ability of the network's protective system to accurately detect various types of faults, such as broken conductor with ground contact faults. This type of fault make a relatively important figure (3 to 10 %) in the total faults statistics for a medium voltage network. In order to detect such faults, the sensed variables are the zero-sequence voltage and the neutral-grounding current. In this paper an analytical and computational analysis is performed to see how various fault and network parameters affect these variables, assuming different grounding systems. Measurements made in two real medium voltage networks show good agreement with the theoretical results.

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