Design of Two Stage Single Phase Standalone Photovoltaic System with Battery Storage

Abstract

In this work, a photovoltaic system was designed that supplies a single phase standalone load at 230V, 50Hz. As PV is the only source of power and due to intermittency of solar radiation, a battery storage was added to ride through the periods of insufficient power generation by the solar arrays. Lead acid battery was chosen due to its low cost per capacity.
Also, the issue of maintaining power balance at all times is very much essential and this problem has been handled in this project in a diligent manner. For interfacing the battery to the photovoltaic system, a bidirectional DC-DC converter has been used. Maximum Power Point tracking is accomplished by a Boost converter, which also does the work of stepping up the voltage from the array into the range suitable for inverter. As the power produced by the PV array flows through the boost converter and inverter before reaching the load, it is called a two stage system. The energy balance has been accomplished without using communication infrastructure, that is all the power electronic interfaces are controlled by three independent loops. A means of knowing the exact average value of the pulsating DC bus voltage without approximations and complex computations has been demonstrated. This enables the control loops to eliminate the effect of pulsating DC bus voltage, caused by the single phase inverter, on the battery. This ensures that the battery current does not suffer from direction reversal at double the AC line frequency, especially when the PV power and load power are close enough, which is quite common in a PV system. This prevents rapid deterioration of battery lifetime.
Also, the system has been simulated in MATLAB/SIMULAINK and simulation results shows the working of Photovoltaic System.