Implementation of space-vector-modulation in a three-phase VSI type grid connected inverter

Abstract

The motivation behind this thesis is to generate AC signal of varying amplitude and frequency from a constant DC source. The device which is used to obtain this kind of action is known as inverter. At present, the inverter is classified into three ways i.e. square wave inverter, modified sine wave inverter or quasi sine wave inverter and pure sine wave inverter. The first two classifications of inverter have seldom used and have very limited applications. Nowadays, the pure sine wave inverter is more demanding because of the requirement of high efficiency and reliability. On the contrary, it is more complex to implement. The main focus of this thesis is the implementation of space vector-pulse-width-modulation (SVPWM) which is one of the algorithm of different pulse-width-modulation techniques. It is applicable for three phase voltage-source- inverter for controlling induction and synchronous machine. In this technique, the reference vector of varying amplitude and direction continually revolve around the hexagon with a fixed sampling frequency generating a gate pulses for the 12 power switches used in neutral-point-converter. The space-vector-pulse-width-modulation is advantageous over carrier based pulse-width-modulation. The properties which are used to analyze the performance of different pulse width modulation methods are total harmonic distortion (THD) and the amplitude of fundamental component. Better utilization of DC bus voltage makes the space-vector-pulse-width-modulation better than the carrier based pulse-width-modulation. This thesis explains the concept, theory and implementation of three level space-vector pulse-width modulation using MATLAB/Simulink environment. It also incorporates the waveform of 7-segment, 9 segment and 13-segment switching pattern to avoid the problem of harmonics. The concept of DC-neutral-point-potential control has also been developed. To support the theory, gating signal pattern has been drawn and some mathematical calculations have been performed. To get the clear picture of voltage measurement at each output stage, the derivation of line-to-line voltages and line-to- neutral voltages are also taken into account along with the calculation of duty cycle of switches.