Implementing Multi-Criterion Logic for Improving Peak Power Tracking in Solar Pump Drive

Abstract

The disadvantage of solar energy is that the power energy is not constant throughout the day, hence during low irradiance the efficiency is as low as 9-11%. Therefore, Maximum Power Point Tracking (MPPT) is essential to Photovoltaic system as it ensures that the power converters operate at Maximum Power Point (MPP) of the solar array. Currently in solar pump drives the Perturb and Observe(P&O) algorithm is used ,in which the DC voltage is observed in a fixed sampling interval, the change in voltage(ΔV) decides the increment/decrement in speed reference, the solar pump adopts the output speed according to available DC voltage ,at steady state the operating point oscillates around the MPP and introduces disturbance and during sudden change in irradiance the tracking is not accurate and rate of tracking reduces since the operating point shift which affects the efficiency and optimum power is not being given to load. A Multi-criteria based logic is proposed based on research conducted on similar water pumping systems, the objective of this algorithm is to monitor the input current and voltage from solar array in each scan time and based on the change in input power, voltage and current the speed reference has to be determined in order to track the available peak power from the solar array Algorithms are usually implemented in two stage conversion(PV Panel -> DC/DC converter ->Inverter ->Load), the MPPT controller changes the duty cycle of DC/DC converter and tracks peak power and then inverter feeds the ac load, since DC-AC inverter with tracking algorithm is capable of doing the same along with generating variable voltage / variable frequency power supply in order to feed the pump drive this single stage conversion can be implemented at low cost, minimizing losses and reducing maintenance.