Research And Design Of Excitation Control Method For Brushless Cascade Synchronous Generator Unit

Excitation Control System is an important component of micro-turbine power system, and has a direct impact on the output voltage indicator of the generator unit.The background of this thesis is the micro cascade brushless synchronous generator excitation control system developed coordinately by Northeastern University and another company. Sampling of AC voltage and current of the synchronous generator is firstly researched in this thesis. After the transfer functions of every stage of the 3-stage synchronous generator unit are deduced, according to the physical analysis of the stages, the continuous state space model of brushless synchronous generator is built. Besides, the impact of the load on mathematical model on the condition of island operation is analyzed deep. Based on this model above, a double-loop PID controller based on output voltage and excitation current is designed, not only simulated but also tested on field. To improve the robustness of this system, an excitation controller based on sliding mode adaptive algorithm is designed, and simulated, which proves that the performance index of this controller reaches the designing requirement, and quickness and overshoot of this controller is better than the PID controller.In this thesis, the main job could be shown as follows:(1)Various methods of sampling, such as the three-point sampling method, Fourier sampling method, DC sampling method and other AC sampling methods are analyzed deep and simulated, thus the optimal method, which is three point sampling method, is obtained. After the correction of the AD part of DSP2812 is designed, hardware and software based on this method is designed, and actual waveform and sampling digital values are obtained.(2) The mathematical models of every stage of the synchronous generator unit are built on the basis of the real condition of islanding operation, including BUCK circuit and filter circuit, thus the whole mathematical model is built, which is a six-order system.(3) According to the actual parameters given by the partner company and the rebuilt per-unit system, transfer functions and space state functions of every stage of the unit are obtained, and the space state model of the three-level brushless alternator synchronous generator unit is derived.(4) Double closed loop PID controller is designed using the frequency domain correction method, and is simulated by means of SIMULINK and PSB, which proves the efficiency of the controlling system scheme. Besides, based on the continuous controller above, a discrete PID controller is designed and a field test based on this controller is conducted.(5) A sliding mode controller is designed based on a first-order filter and synchronous generators unit, and to verify the correctness of this very method, a simulation is conducted by means of SIMULINK based on discrete transfer function.