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.
