Abstract:
Power electronic converters have become quite popular to meet the industrial demand
for better utilisation of renewable power. Among the power electronic converters, AC AC converters are potential candidate for wind energy systems, where a low voltage
variable speed generator feeds power to the higher voltage fixed frequency grid. Broadly
AC-AC converters can be classified into two types, one with energy storage elements
and another without energy storage elements which is knows as matrix converters (MC).
Converters with energy storage such as diode bridge cascaded voltage source inverter
and voltage source back to back converter are the standard solutions adopted by the
industries. Aiming to reduce the usage of energy storage elements and improve the
input switching characteristics, matrix converters are evolved. Matrix converters are
considered as a futuristic converter with many desirable features like input power factor
control, high power density, high efficiency and extended life time. On the other
side, matrix converters have restriction in terms of performance parameters such as
voltage transfer ratio, reactive power transfer capability and susceptibility to changes
in dynamic conditions. To cater the above limitations in matrix converters, researchers
have proposed inclusion of passive elements in matrix converters, which leads to hybrid
matrix converters.
In this thesis, a proposition has made to investigate an ultra sparse matrix con verter (USMC) topology. The USMC is a specific version of matrix converter char acterised by reduced number of semiconductor switches. For enhancing the operating
range of USMC, the concept of switched capacitor and switched boost networks are
integrated at the DC link section of USMC. Since the established modulation scheme
for USMC cannot be applied to switched capacitor ultra sparse matrix converter (SC USMC). Therefore a modulation technique is developed to achieve high voltage gain byproper placement of switching states within a switching cycle. The SC-USMC has ad ditional advantage of producing balanced output voltage even under unbalanced input
supply. The second version of USMC-switched boost ultra sparse matrix converter (SB USMC) is proposed with shoot through immunity, which produces higher voltage gain
with lesser number of passive elements. A modulation technique is developed to reduce
the current ripple of the inductor.
To improve the output total harmonic distortion (THD) and voltage gain char acteristics of USMC, a three level Z source based sparse matrix converter is proposed
which has multi voltage levels along with boosted output voltage. This converter has
advantage of less number of switching devices compared to multi level matrix convert ers. In order to control it, a modulation technique has been developed with careful
insertion of shoot through period without tampering the multi level behaviour.
Comprehensive analytical derivations and simulation results are carried out to
investigate the operation of the proposed converters. Performance of the proposed
converters is then compared with conventional converters. The operation of the three
converters are also validated experimentally using laboratory prototype.
