Converter: step-down technology

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

Therefore, in a pumping system, the PV-array MPP voltage must be higher than the voltage required by the pump at the desired flow rate at all times. Otherwise, even when sufficient power is available, the pump operating voltage will adjust to the corresponding (I, V) point on the PV array characteristics, reducing the effective useful power.

This "step-down" limitation can be accounted for in the simulation only when the pump's voltage behavior is well defined. For pumps specified only by power curves, it is neglected.

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