Design and Implementation of Three Level Flying Capacitor Front End Converter

Abstract

Front End Converters are generally used in adjustable-speed drives, high voltage DC transmission, switch-mode power supplies, utility interface with non-conventional energy sources etc. Earlier the rectifier conversion were carried out by diode or phase controlled rectifier which act as nonlinear load on the power utility. Such nonlinear load draws current which has high harmonics with poor power factor, thus creating serious issue of power quality. To overcome these drawbacks high power factor converters (HPFC) became the inherent part of this conversion which gives unity power factor with higher efficiency, reduced size and well-regulated dc output. Multilevel structure is gaining lot of popularity because of its excellent performance in terms of sinusoidal input current with negligible harmonic contents, unity power factor, less ripple in regulated dc output voltage. Flying capacitor multilevel converter is the most widely used topology in multilevel power conversion because it provides redundancy in switching states through which voltage balancing can be achieved, also it eliminates the requirement of the clamping diodes. In this project the performance of a Three phase three level Flying Capacitor Front End converter for high power application with bidirectional power switch will be implemented to achieve unity power factor and lower harmonic distortion. A complete simulation of the control scheme in open loop for three phase flying capacitor front end converter has been done. To control the gating of the converter different multicarrier techniques i.e. level shifted and phase shifted technique and their comparative analysis has been studied. Among the different multicarrier technique, Phase disposition multicarrier PWM technique and Phase shifted Multi carrier technique have been simulated for three phase flying capacitor converter and their detailed comparative analysis have been done. Furthermore, in order to regulate capacitor voltages of a flying capacitor converter different voltage balancing scheme have been analysed. A closed loop technique by changing the duty cycles of the switches to maintain the capacitor voltage is simulated in MATLAB/simulink for three phase flying capacitor front end converter with phase shifted multicarrier technique. For experimental verification of proposed technique dSPACE1104 controller have been used to control and monitoring of open loop system as well as closed loop balancing scheme.