Performance Comparison Between Bipolar and Unipolar Switching Scheme for a Single-Phase Inverter Based Stand-alone Photovoltaic System

Abstract

This paper presents a comparative experimental study of bipolar and unipolar switching schemes of a single-phase inverter based stand-alone PV system. The single-phase inverter is connected with the PV string and DC-DC converter in subsequent arrangement along with maximum power point tracking (MPPT) for optimum power generation in autonomous mode despite of changing irradiance condition. The steady-state and transient behaviour of both incremental conductance (INC) and variable step-size incremental conductance (VSSINC) MPPT algorithms are analyzed thoroughly. The sinusoidal pulse width modulation (SPWM) technique is incorporated to create the proper gate signals for the inverter switches. The inherent harmonic component in output inverter voltage is somewhat reduced by choosing a high frequency carrier signal and an LC filter is designed to eliminate the higher order harmonics. A laboratory setup for the dual-stage stand-alone PV system is developed using a boost converter, 1 − ϕ inverter and the control schemes are implemented using the dSPACE RTI1103 digital controller. The INC and VSSINC MPPT results are presented at varying irradiation. The functionality of the bipolar and unipolar SPWM are observed at an irradiation of 210 W/m2 which confirms that the unipolar SPWM gives superior performance than bipolar SPWM switching.