Converter: step-down technology

As a result of an electronic design constraint, most of the DC-DC (or MPPT) converters operate on "step-down" principle. This means that without transformer, they cannot deliver a voltage greater than the input voltage.

Therefore in a pumping system, the PV-array MPP voltage should rise over the voltage required by the pump at the desired flow rate, at any time. Otherwise, even when the available power is sufficient, the pump operating voltage will adjust until reaching the corresponding (I, V) point on the PV array characteristics, reducing the effective useful power.

This "step-down" limitation can be taken into account by the simulation only when the voltage behavior of the pump is well defined. With pumps specified only by power curves, it is neglected.

NB: This means that when using standard pumps designed for 230VAC grid operation, the PV array should deliver at least 325V to the inverter for obtaining undistorted sinus at the pump (unless special step-up inverter, or inverter with transformer, is used).