Abstract:
This thesis is concerned with the improvement of current controllers for use with voltage
source inverters. Analysis of hysteresis current controller (HCC) is presented. The common
problems of non-uniform and burst switching of scalar type controllers (hysteresis
current controller and ramp comparison controller (!tCC)) are addressed. An improved
model of HCC, referred to as PRC is proposed for uniform switching frequency operation.
Theoretical basis is established where, an add-on function of programmed amplitude and
slope can keep the switching frequency of HCC to a predefined value. In addition to uniform
switching frequency operation, the proposed model has significant improvement on
the total harmonic distortion coefficient. Analysis of the predictive controller is also made
in this research. The shoot through current behavior of predictive controller is improved
by the use of a voltage vector limiter. A generalized approach is proposed for the design
of the proposed predictive controller with inductive load. Separate schemes are proposed
for implementation of PRC and predictive controllers based on general purpose PC architecture.
Incorporating the merits of both PRC and predictive controller, a new and novel
current controller (referred to as NEW-CC) is developed in this work. This controller
operates on regular sampled basis and predicts pulse widths of individual phases once
on each carrier period. The load parameters are tracked on each fundamental as well as
carrier cycles. Uniform switching as well as shoot through current limiting is achieved in
this new controller. The performance of this new controller is compared with the other
current controllers and is found to give better performance. The new current controller
has lower total harmonic distortion than other current controllers. This controller do not
have sub-harmonics in the load current spectrum as is normally encountered in scalar type
current controllers at large bands. The new current controller has been experimentally
tested. Its performance is in good agreement with the theoretical results.
