Development of a controlled rectifier for variable power factor operation using pulse width modulation

Abstract

Generally uncontrolled rectifier is made of diodes and controlled rectifiers are made of thyristors. Both these types of rectifiers distorts the input current in a way that the shapes of the current are nonsinusoidal. These distortion of the current increases the harmonic terms. In other words, there remains total harmonic distortion or THD in the current. These THD not only degrades the power factor but also degrades the power quality of the grid. In recent years, these THD have become significant because of the increase of use of rectifier based electrical and electronic devices. To eliminate the THD, Space Vector Pulse Width Modulated (SVPWM) rectifier has been proposed over conventional rectifiers. But the pulse generation is very complex for this kind of rectifier. This thesis analyzes the SVPWM rectifier and proposes a new hybrid scheme to generate real time PWM patterns. Because of the new scheme the rectifier will be a fully functional device which will draw sinusoidal input current in phase with input voltage. By modifying the timing of the pulses, the pulses can be lagged or lead from the original time. By thus, the device is also capable of drawing leading or lagging current. This capability gives the devices functionality as a reactive power compensator at some extents. The goal of this thesis is to develop a prototype of the rectifier. At first, simulation will be done in MATLAB Simulink. After that, microcontroller and Look Up Table (LUT) based hybrid circuit to generate real time PWM patterns will be interfaced with proper switches to conduct the work.