A comparative study of MPPT methods for distributed photovoltaic generation

Abstract

Photovoltaic (PV) energy generation is becoming an increasingly prevalent means of producing clean, renewable power. PV is renewable, reliable, and domestically secure. One of the most important components of PV systems is the inverter technology that converts the direct current (DC) power output from the PV panel or array to alternating current (AC) used on both the individual end-user and centralized grid levels. The large variety of inverters share the same general goal: to allow for the most efficient and stable transfer of as much power as possible. One specific means of accomplishing this goal is the inclusion of a Maximum Power Point Tracking (MPPT) DC-DC converter. The purpose of MPPT is to ensure that the PV panel or array is always producing power as near to the knee of its I-V curve as possible. This extracts the maximum amount of power at any given time. In constantly sunny situations, there is little impact on overall performance of a particular MPPT design on the PV system, as only small voltage differences due to the particular construction of each panel effects the overall voltage outputs. However, cloud cover changes the output from a PV panel drastically with reduced solar irradiation causing the current of the solar panel to drop. It is postulated herein that the stability and quality problems created by central MPPT during periods of differing solar irradiation on various panels could be solved with a system of MPPT distributed on each panel. These would then feed collectively to a central inverter. To test these systems, a PSCAD model was developed for both centralized and distributed MPPT systems, and the solar irradiation was randomly varied. This allowed for observation of the stability and quality of the output voltage for each system.