| Three-phase AC-to-DC converters are increasingly designed to ensure a high power quality and a good DC voltage regulation performance. Nevertheless, problems related to their control process still exist. Although the hysteresis-based control is widely used in power electronics applications, it suffers from major drawbacks due to the dependency of the switching frequency on the system parameters, the operating conditions and time. Another control approach known as the Pulse-Width-Modulation (PWM) technique offers a fixed-switching-frequency operation and appears, therefore, more suitable for these applications. Nevertheless, its implementation requires basically the knowledge of a mathematical model that represents accurately the converter. The availability of such models is yet limited to DC-DC and AC-DC bidirectional converters. This thesis extends well-known modeling techniques, using averaging approach, to unidirectional three-phase rectifiers. For this purpose, two topologies are considered: the current injection rectifier and the three-switch three-level rectifier. These topologies are characterized both by a low number of active switches, simple control, low cost, high robustness and high efficiency.; Systematically designed control laws, given by the well-developed control theory, are then applied to the proposed models. The validity of the models and the performance of the control system are verified either numerically, using computer simulation tools, or experimentally through real-world measurements.; This report is divided into five chapters. In chapter 1, a review of the most popular high power quality boost-type rectifiers is presented, and the advantages of the unidirectional three-phase topologies are emphasized. In chapter 2, a comparative study of control techniques, control laws and modeling approaches is elaborated. In chapter 3, a linear control scheme is developed for a two-stage single-phase boost rectifier. The performance of the converter in the steady state and transient regimes is analyzed. The input impedance and audio-susceptibility of the converter are also computed and analyzed. In chapter 4, the modeling of a current-injection three-phase rectifier is proposed. A small-signal representation is developed and the corresponding transfer functions are computed and validated, firstly, by numerical simulations using the Power System Blockset of Matlab/Simulink and, secondly, through experimental results obtained from a 2 kW-laboratory prototype. The proposed model is then used in the design of several control schemes, which are implemented separately. A comparative evaluation of the applied control laws shows the superiority of the nonlinear multiple loops approach over the other ones. Finally, in chapter 5, a new modeling approach and a nonlinear control scheme are proposed for the three-switch three-level three-phase rectifier. The performance of the controlled converter is analyzed numerically. |
