Research On The Detecting Algorithm For The Batteries’ Capacity In Stand-alone Photovoltaic System

In recent years, solar photovoltaic technology has been rapidly developed. Due to low cost and high reliability, the battery is widely used in stand-alone photovoltaic system. Battery is an energy storage device in stand-alone photovoltaic system. The calculation of State Of Charge (SOC) of battery leads to inaccurate overcharge and over discharge, which will shorten the service life of battery. In this thesis, the method of battery capacity detection for stand-alone photovoltaic system is studied.1. The basic principle of battery work is studied; the characteristics of charge and discharge and the parameters of the battery SOC were analyzed. Many conventional on-line measurement algorithms of battery capacity are studied.2. The advantages and disadvantages of Many conventional SOC algorithms are compared. This thesis proposes an improved Kalman filter SOC algorithm which is based on the combination of ampere-hour method and open-circuit voltage method. The algorithm is based on the ampere-hour method, and uses the open-circuit voltage method to estimate the initial value of SOC, The initial value of SOC and real time value is corrected by using the Kalman filter algorithm.3. The algorithms is simulated in Matlab/Simulink. The simulation results show that the algorithm reduces the initial value estimation error and the current cumulative error, and improves the accuracy of the SOC estimation of the battery. The service life of the battery is prolonged, and the stability of the photovoltaic system is improved.4. An experimental platform of stand-alone photovoltaic system is designed in this thesis. The effectiveness of proposed control algorithm is verified by the experimental results.