| The phase angle control of the Two-Level Sinusoidal Pulse Width Modulation (SPWM) strategy has been studied in Part I of this thesis, and applied to a new voltage-source type PWM High Voltage Direct Current (HVDC) transmission system. The PWM-HVDC station exercises direct control over the voltage phase angle, the amplitude and the frequency at the ac terminals using the phase angle lock loop (PLL) control of the SPWM. The parallel connection of multi-terminal PWM-HVDC stations can be achieved through simple local feedback control. The feasibility studies for the system, based on laboratory experiments and numerical analysis, are reported in the thesis.; In Part II of the thesis, the Three-Level SPWM technique has been studied and applied to the controls of a 3-chase, 6-valve, current-source PWM rectifier. A new Dynamic Three-Level SPWM strategy together with its Decoupler Pre-Processor has been proposed. The strategy enables each of three phase currents of the converter to be controlled independently and linearly, so that the dynamic feedback can be channelled. The Pole Placement control method has been implemented successfully, using a real-time digital control scheme. The scheme also succeeds in active filtering. The experimental results are obtained from a 1-KVA size laboratory model with a real-time controller using three TMS320C25 DSPs. The three DSPs operating in parallel are necessary to compute the feedback algorithms with minimum delays so as to ensure sufficient frequency bandwidth. |
