Implementation of Buck-Boost Converter Employed for Modulating DC-Link of Inverter Operating as AC Chopper for V/F Drive Applications

Abstract

Induction motors (IM) are the workhorse of the industries. Amongst various speed control schemes for IM, V/f and field oriented control are popularly used. In IM drive, conventional voltage source inverter (VSI) is used. Inverters are broadly used to produce variable frequency and variable output voltage for various applications like ac machines drives, uninterruptible power supplies (UPS), switched mode power sup- ply (SMPS). The proposed topology presents the two fold solution. In this solution, output voltage of converter is varied by controlling the inverter operating as ac chop- per, while fundamental frequency of converter is varied by controlling the buck-boost converter according to the reference frequency given to it. The buck-boost converter shuffles between buck mode and boost mode to produce required frequency which serves as the basic idea for proposed topology. The proposed VVVF technique eliminates the non-linearity, lower order harmonics which are generated in conventional SPWM based inverters. Elimination of lower order harmonics also reduces % THD and dv/dt. In many IM drives requiring the pure sine wave, the output of inverter is filtered out by LC filter except for high power application, which is drawback of such inverters. In this unlike conventional inverter, no LC filter is required at output. Simulation of proposed single-phase topology is carried out in MATLAB/Simulink. Such three single units are connected in h-bridge to form a three-phase system and its simulation is carried out. Hardware implementation of proposed single-phase topology is carried out using dSPACE 1104 R & D controller board in real time control.