Research on MPPT and Single-Stage Grid-Connected for Photovoltaic System

System JUI-LIANG YANG, DING-TSAIR SU, YING-SHING SHIAO Department of Electrical Engineering National Chang-hua University of Education Bao-Shan Campus, Address: No.2, Shi-Da Road, Changhua City 520 REPUBLIC OF CHINA.(TAIWAN) [email protected], [email protected], [email protected] http://www.ncue.edu.tw Abstract: This paper proposes a grid-connected photovoltaic (PV) system that is consisted of a boost converter with maximum power tracking, battery charge controller, inverter, and the related control circuits. A sliding mode controller is designed for controlling the boost converter to output the maximum power of the solar cells. A control strategy is proposed of a Maximum Power Point Tracking (MPPT) impendence adapter coupling a photovoltaic generator to a battery. The proposed strategy is based on the sliding mode control theory of continuing systems to permit a direct control of power converter. The PV generator price is even relatively high, so the user is interested of the optimal coupling of PV generator to electromechanical loads. In fact, this system uses the optimal coupling in order to have maximum power during the whole operating period. A grid-connected inverter is designed to transform the maximum output power into the load and utility. The real power control is using zero-cross and phase-lock circuits that control the inverter output voltage which is phase lead and synchronized with the utility. A digital circuit is used to detect the phase angles of the load voltage and current to control the inverter output amplitude to achieve the reactive power load compensation. A monitor circuit is designed to detect the voltage and frequency variation in the utility. When the photovoltaic system encounters a voltage and frequency deviation, the monitor circuit immediately disconnects the photovoltaic system from the utility to prevent the island effect. The proposed system is implemented by using OP amplifiers and micro controller (PIC16F877A). Both the simulation and experimental results using MATLAB show the sliding mode controller for maximum power tracking has good performance. The phase and amplitude control experiments achieve the real and reactive power control. The island effect experiments demonstrate evidence of the solar cell system protection ability illustrating the proposed grid-connected photovoltaic system has good operating performance.