چكيده به لاتين
ABSTRACT
Simple structure and operation, high efficiency, inherent short-circuit protection and regenerative capability are the most important advantages of load-commutated inverters (LCI’s) which have made them a prevalent industrial choice to drive wound-field synchronous machines (WFSM’s) in high-power (higher than 1 Megawatt) applications such as pumps, fans, compressors, gas-turbine starters, etc.
In this thesis, a comprehensive study is carried out on the modeling and control of different possible configurations of LCI-fed WFSM drives. The existing industrial topologies of this type of drives are limited to three- or asymmetrical six-phase cases. In this thesis, an investigation is also made on the possibility of employing symmetrical multiphase LCI-fed WFSM drives, e.g., symmetrical five-phase case. In order to provide a background for a more accurate comparison between the symmetrical and asymmetrical multiphase LCI-fed drive operation, first, an approach based on magneto-static finite element analysis (FEA) is introduced to compute magnetizing and leakage inductances matrices considering the space harmonics. Then, an algorithm based on switching functions is proposed to estimate different quantities of the drive, specifically electromagnetic torque, at steady-state. At each point, the validity of the proposed methodologies is assessed against experiments. The results are next utilized to compare the performance of LCI-fed symmetrical five-phase and asymmetrical six-phase WFSM drives from the view-point of torque ripples and stator copper losses.
Contrary to the conventional industrial approaches in controlling LCI-fed WFSM drives, field-oriented control in stator flux reference frame is proposed. Afterwards, the integral-proportional (PI) regulators of the control system are adjusted according to the analogy between this drive and the phase-controlled dc-machine drive. Furthermore, an improved flux observer is recommended to estimate the rotor position without the need for encoder.
Finally, a novel multilevel current-source inverter based on thyristor devices is proposed. Simulation studies and experimental results reveal that the three-phase LCI-fed drive related drawbacks such as poor starting performance, torque ripples, low power factor and quasi-square waveform of the stator current are improved remarkably by employing the proposed configuration.
