DC-Link Modulated Pure Sine Wave Inverter Fed Induction Motor Drives

Abstract

At the present time inverters are used to produce variable frequency and variable output voltage in induction motor drive. Researchers have endeavored many Pulse Width Modulation (PWM) techniques to improve quality of output voltage and current profile to boost the efficiency of overall induction motor drive. In this kind of drives the output of inverter is filtered out by LC filter before it is fed to induction motor, this serve as biggest drawback for such inverters.

In proposed topology the variable output voltage and frequency is achieved by controlling duty cycle of semiconductor switch i.e. MOSFET of buck-boost converter. As the output voltage of buck boost converter is unipolar, H-Bridge inverter is required to make final output bipolar. The voltage across the output capacitor of buck- boost converter serves as d.c. link voltage to the H-bridge inverter. It is very lucid that if the buck - boost is operated by constant duty cycle it will produce constant output voltage at output capacitor which is in turn serves as DC link to inverter. The diagonally opposite switches of H-bridge inverter are triggered simultaneously and the upper switches of different legs are switched in 180° phase shifted mode resulting in inverter to produce bipolar square wave at output. Duty cycle of buck - boost is varied in such way that it produces voltage at capacitor which follows rectified sine reference and inverter switches are synchronized with rectified sine reference which result in production of sine voltage waveform at output of inverter. This serves as basic idea for proposed topology, in this unlike conventional inverters no LC filter are required at output.

Simulation task for proposed idea has been carried out in MATLAB simulink (The Product of MathWorks Inc.) for single as well as three phase system. For real world implementation, the rectified sine reference generation and controlling of buck boost converter is achieved by ARM Cortex M-3 Controller on NXP LPC1768(Product of NXP Inc. A company founded By Philips) prototyping board.