Study On Control Strategies Of AC Excited Generator And Its Excitation Power Supply

The Alternating Current Excited Generator (ACEG), which has features of variable speed constant frequency operation, superior steady-state and transient-state operation characteristics, is especially suitable for the renewable energy generation system such as hydropower generation with variable water head, pumping storage generation and wind-power generation. The appropriate excitation control strategy and excellent excitation power supply should be used to realize the good regulation performance, agility and reliability of operation for ACEG system. The control strategies of the ACEG and its excitation power supply under the grid normal operation condition and grid short-circuit fault condition have been deeply studied in this dissertation.Firstly, the decoupling excitation control strategy based on the full fuzzy controller is proposed, and the decoupling excitation control system of ACEG based on the full fuzzy controller is established and analyzed in detail. Both the simulation and experiment results are used to validate the respectively control ability of active power, reactive power and rotor speed for ACEG system used full fuzzy controller, and the variable speed constant frequency generation can also be realized. The system has strong robustness and good dynamic and static performance.The reason of the DC-link voltage fluctuation within a back-to-back PWM converter controlled by the traditional vector control strategy has been analyzed in detail, and an improved back-to-back PWM converter control strategy based on the rotor-side converter instantaneous power feedback control has been proposed. Both the simulation and experiment results are used to validate the proposed method. The stable control ability of the DC-link voltage can be effectively improved when regulating the generator and it improves the dynamical response ability and stability of the ACEG system.The transient physical process of the ACEG and the reason for the rotor over current or over voltage at that time of a grid fault process are deeply analyzed. An improved excitation control strategy is proposed for the rotor side converter in ACEG to allow the system to ride through the grid short-circuit fault. In order to avoid the over current in the rotor during the fault, the rotor current AC components produced by the stator currents at 50Hz have been successfully restrained and the stator resistance is also used to realize the decay of DC component of the stator current during the grid fault process. The proposed control strategy is validated by the simulation results under the grid symmetrical and unsymmetrical fault conditions. The rotor excitation converter has been successfully protected during the grid fault and it improves the fault ride-through ability of the ACEG generation system.It is the key point that the grid-side converter and rotor-side converter in a back-to-back PWM converter should be accurately controlled to realize the fault ride-through control of ACEG during the grid short-circuit fault. An improved control strategy of the grid-side converter for grid fault is analyzed and proposed in detail and the proposed control strategy is validated by the simulation results. The DC-link voltage of excitation power supply can be stably controlled during the fault, and the effect of ride-through control for the generator can be improved. Furthermore, the DC-link capacitor can also be protected and the system stability can be improved during the fault.An experimental ACEG excitation control system excited by back-to-back PWM converter is established. The excitation control of ACEG and the operation performance of the back-to-back PWM converter in the ACEG variable speed constant frequency generation have been deeply studied by experiment, and some valuable conclusions have been achieved.