| As the most representative and multiplex device of Flexible A.C. Transmission System (FACTS), the Unified Power Flow Controller (UPFC) is one of the research focuses in FACTS recently. UPFC has the characteristic functions as follows: fast and dynamical adjusting the parameters of electricity transmission system, such as voltage, impedance, phase angle, real power and reactive power; expanding the capacity of electricity transmission; improving the stability of power system and optimizing the operation of power system. Based on the comprehensive intelligent control theories, UPFC intelligent control methods were presented in this thesis. Firstly, control scheme of UPFC were described. UPFC consisting of shunt converter and series converter provides shunt compensation and serial compensation for power system. Based on the equivalent circuits of the shunt compensation and the series compensation, the paper investigated the basic relationship between shunt compensation control and serial compensation control, and corresponding control schemes. Consequently, Hierarchic Control Architecture was proposed for UPFC. Based on the CC-PWM converter, intelligent current control method for UPFC power converter was described in the thesis. To meet up the deficiency of the general hysteresis current controller and sinusoid band hysteresis current controller, a band-variable fuzzy hysteresis current control method was presented which regulates the band of hysteresis automatically using fuzzy reasoning on the basis of the value and the mutative direction of control current error. As a result, control precision and dynamic performance of the current are improved. PI regulation law is one of the common methods applied in linear current controller of the power converter while its adaptive performance is poor. To improve adaptive capacity of the current controller, fuzzy adaptive PI current controller and fuzzy neural networks adaptive PI current controller were proposed to adjust the parameters of PI controller automatically according to the running status of the converter. UPFC DC voltage control is the precondition to realize serial compensation control. Intelligent method for DC voltage control was investigated deeply in the paper. Firstly, the double closed-loop control structure of UPFC current and voltage was analyzed comprehensively, and then decoupled-control for inner current loop was achieved by state-feedback and input forward-feed. Consequently, practical design method for UPFC double closed-loop control was derived. In the thesis, combining the fuzzy control and neural control with PID control, adaptive fuzzy PI control and adaptive neural cell PID control were proposed for UPFC DC voltage control. Simulation results have demonstrated the significant performance of proposed method. Power flow control is one of the basis functions of UPFC series compensation control, intelligent power flow control method was studied in the paper. Based on the equivalent circuit of series compensation, this thesis established a closed-loop dynamic structure of UPFC power flow control, which realized the decoupled-control of the active power and reactive power using multi-variable decoupling theory. As the dynamic performance of normal PI control is poor because of the character of transmission lines, this thesis presented an adaptive fuzzy PI control method for UPFC power flow control which takes the transition time, the error and the sum of the last two errors as inputs. Consequently a three-input and two-output fuzzy controller was build to adjust the PI parameters automatically. Simulation results showed that the fuzzy adaptive PI controller has better response performance on the condition of no overshoot. In addition, application of neural network in the UPFC power flow control was also investigated in this paper. Integrating the fuzzy control with neural network control, fuzzy neural networks control and recurrent fuzzy neural networks control method for UPFC power flow control was presented. Simulation results showed that the proposed neural network control method can overcome the disturbance of induction feature of transmission lines and improve dynamic response speed of UPFC power flow control.
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