Integrated PV and multilevel converter system for maximum power generation under partial shading conditions

The emerging trend towards the harnessing of the electrical power from solar energy has increased the research effort in power electronics applications. To achieve the
required voltage level, a number of photovoltaic PV sources (cells/modules) are connected in series. The major challenge here is to deal with the partial shading
problem, where the series connected PV sources are exposed to different insolation. The generated current is limited by the current of the shaded PV sources unless those
sources are bypassed by diodes, in which case the total DC voltage is reduced and the shaded sources do not contribute to the generated output power. A power electronics approach can be employed to overcome the problem, by enabling both
shaded and non-shaded sources to generate their maximum power, thereby and delivering the total generated power to the load. Thus no shaded PV source is bypassed or degrades the power extraction from the other PV sources.

This thesis investigates the PV partial shading problem of individual PV sources which are connected in series. After the review and evaluation of existing methods to
overcome this problem, the thesis employs for the first time the multilevel DC-Link inverter to deal with the problem of partial shading by using a novel control
algorithm called PV permutation algorithm. The thesis also develops a simplified generalized Integration PWM (IPWM) algorithm which can be used to control higher level inverters. An improved maximum power point algorithm “voltage-hold perturbation and observation (VH-P&O)”, which overcomes the major tracking limitations, is developed from the basic P&O algorithm.

Experimental systems of five and seven level DC-link inverters with a DC-DC buck converter system have been implemented. The digital processing unit eZdspTM
F28335 is used to control the PV systems in real time, and Matlab-Simulink Real Time Data Exchange (RTDX) is employed to display the extracted power and to control the system parameters via a designed Graphical User Interface (GUI)
window. The simulation and experimental results showed that the series connected PV sources operate at their maximum power points under partial shading conditions without affecting each other.