Space vector pulse width modulation for Two-Phase voltage source inverter with reduced number of static switches

Abstract

This thesis is concerned with the application of space vector pulse width modulation (SVPWM) technique to the control of the two-phase full bridge voltage source inverter (VST) having reduced number of switches. SVPWM gives higher fundamental component amplitude, provides more efficient use of DC supply voltage and generates less harmonic distortion in the output voltages and currents than other PWM techniques. It is a different approach, which is based on the space vector representation of the voltages in the complex plane and it refers to a special way of determining the switching sequence. The desired two-phase output voltages are represented by a reference voltage vector, which is used for modulation process. For the two-phase inverter output, selection of four active space voltage vectors produces a square envelope for the reference voltage vector. When the desired outputs are two-phase sinusoidal voltages with 90-degree phase shift, reference vector becomes a revolving vector with the same frequency of output voltage. For a chosen number of PWM carrier pulses in one fundamental period, the position of the reference voltage vector can be calculated by using a very simplified formula, which makes the implementation faster. Between asymmetric and symmetric SVPWM only symmetric one is considered so that the harmonic contents are minimized. Two different timing sequences and corresponding switching states are proposed for this symmetric technique. For the implementation of space vector PWM, three level switching patterns are determined by using software. For real time application these theoretically determined switching signals for the six power transistors of an inverter are generated by a digital signal processor (DSP) kit and finally the two-phase output voltages are applied to a balanced two-phase load. A high performance data acquisition card is used to acquire the experimental data of real time PWM patterns and the load voltages. The experimental results are found good and in agreement with the theoretical results. Mathematical analysis along with theoretical and experimental performance of the proposed inverter are presented. Distortion factor (OF) shows that the output voltage quality is good enough to apply in any type of practical two-phase load.