Research On Multi-String Maximum Power Point Tracker For Grid-connected PV System

The output of photovoltaic (PV) array is influenced by the environmental factors such as irradiation and temperature. Maximum Power Point Tracker (MPPT) is usually used in PV systems to track the maximum power point and match the array and the loads. A multi-string MPPT for small-scale grid-connected PV system is presented in the thesis. This thesis analyzes the advantages and disadvantages of traditional mountain climbing and incremental conductance (Inc Cond) algorithm ,and simulates them by MATLAB,then proposes a varied-step events-record algorithm. The experiment results show that this algorithm can track the maximum power point fast and exactly. Multi-String maximum power point tracker can track each sting's maximum power point, so it can solve the mismatch of multi strings. A 3 kW Multi-String MPPT composed of two Boost converters is presented. The system adopts digital and analog hybrid control method. The MCU PIC16F877 completes the MPPT algorithm, and a PWM IC TL598 is used to control the Boost converter. The MCU can send data to a personal computer (PC) by serial communication, so we can analyze the data in a PC. The experimental results illustrate that the hardware and software design is feasible and satisfactory.