Simulation Analysis of Multi-Carrier Techniques for Three-Phase Five-Level Flying Capacitor based Front-End Converters

Abstract

In today many industries have started using variable speed drives for application like pump, fan, air conditioning system, combustion air for bioler system, water pumping system etc & Front-End Converters(FEC) 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 non- linear load draws current which has high harmonics with poor power factor, thus creating serious issue of power quality. To overcome these drawbacks one of the method used is Flying Capacitor multi-level converter. It is the most widely used topology in multi-level power conversion because it provides redundancy in switching states through which volt- age balancing can be achieved, also it eliminates the requirement of the clamping diodes and solves the problem of neutral point fluctuation which is occurred in diode clamped converter. In this project the analysis of a Three-Phase Three-level and Five-Level Flying Capacitor Front-End converter (FC-FEC) is simulated to achieve unity power factor and lower harmonic distortion. To control the gating of the converter a SPWM technique i.e. Level Shifted (LS) and Phase Shifted (PS) technique is implemented and their comparative analysis has been studied with different modulation indexes to analyse its effects on the total harmonic distortion (THD) of the line current and voltage unbalance across the clamping capacitors. A complete control scheme is simulated in MATLAB/Simulink environment in open loop system with fixed load and found the problem of unbalancing across the clamping capacitor. To overcome the above said problem a closed loop technique is also being attempted with voltage balancing scheme in different dynamic conditions. A closed loop controlling scheme is implemented with a modified PS-PWM method than an general PS-PWM method. 3-phase 230V AC supply is given on the source side and the converter has 3 clamping capacitor of 3300_F & three different volt- age rating of 75 V, 150 V & 225 V in each phase. The filter Capacitor connected at load side has capacitance 6600_F and voltage rating of 300 V. The R-L load of 10 & 1 mH is used.