Feeding Partial Power into Line Capacitors for Low Cost and Efficient MPPT of Photovoltaic Strings Ali Elrayyah Mohammed Badawey Yilmaz Sozer Qatar Environment and Energy Research Institute (QEERI) Doha, Qatar Electrical and Computer Engineering Department The University of Akron Akron-OH, USA Electrical and Computer Engineering Department The University of Akron Akron-OH, USA aelrayyah@qf.org.qa mob4@zips.uakron.edu ys@uakron.edu Abstract—In PV strings, a number of PV modules are connected in series where the same current passes over all of them. To allow the maximum power points of the PV modules to be tracked individually, DC/DC converter known as optimizers could be used to interface each PV module with string. Processing the entire PV power by the optimizers increases the cost and degrades the system efficiency. In this paper, a method is proposed to have partial processing of the PV power using DC/DC converters which feed their output into capacitors connected in the same string of the PV modules. To further decrease the system cost and improve the efficiency, more than one PV modules can feed their partial power into the same capacitor. As the number of PV modules that share the same capacitor increases, the system cost decreases further. The validity of the proposed method is verified through simulation studies and hardware experimentation. Keywords—PV strings; partial power processing; maximum power point tracking I. INTRODUCTION Recently, a significant growth is witnessed in the energy supplied to utility grids from renewable energy sources (RESs). This growth is motivated by various economic, environmental and technical benefits provided by deploying distributed energy sources (DESs) and RESs. Among RESs, solar PV is receiving a lot of interest and as its cost continues to drop; its installations are increasing all over the world. Power electronics converters are used to perform the required conversion for the DC power produced by the PV modules to the AC form that suits the voltage and current in the grid power lines. It is always desirable to keep the system cost low and one of the approaches to achieve that is by interfacing a number of PV modules with the grid trough the same power electronics converter. This approach is effective as several PV modules are usually interfaced with utility grids at the same location. The common practice is to connect the modules in series forming what is called PV strings before it get attached to the DC/AC power electronics inverter. This approach helps also in raising up the DC voltage to a level that allows smooth interfacing with the grid. Factors such as manufacturing variability, shading and accumulation of dirt/dust may lead serially connected PV modules to have different maximum power point (MPP) characteristics [1-2]. Accordingly, the current that passes over each module needs to be controlled separately to ensure that the MPPs of the individual PV modules are tracked. Among available technologies, two kinds of systems are used to track the MPPs of individual PV modules which are the microinverters and the DC power optimizers. Microinverters convert the DC power produced by a single PV module to an AC power that is supplied to the grid. DC power optimizers use DC/DC converters to interface the PV modules to the string. But as stated before, DC power optimizers could be more preferred for utility scale application as they reduce the cost and support the high voltage required for utility-tied inverters [3]. Figure 1 shows the use of DC power optimizers to interface PV modules with input side of a DC/AC inverter. As the PV modules have different MPP currents, the DC power optimizers, which are DC/DC converters, process these current to match the string current at their outputs. Figure 1. Using DC power optimizers to interface PV module to a single inverter This research is sponsored by Qatar Environment and Energy Research Institute for the project # GC5004 . 978-1-4673-9550-2/16/$31.00 ©2016 IEEE 392