A Study On The Multi-terminal Unified Power Flow Controller

To control the complex powers emanating from a bus in power system, there are two solutions. The obvious solution is to equip each of the N lines radiating from the node with its own Unified Power Flow Controller (UPFC). The next evolution of the idea is to equip with a Multi-terminal UPFC (M-UPFC). To simplify the research, this thesis treats the Two-terminal UPFC (M-UPFC) (when N=2) as the investigative target mainly. A throughout analysis and study is conducted to modeling and designing of the controller with the T-UPFC. The relative model and control projects are presented and examined by simulation.The M-UPFC needs high power rate because it is generally used in high voltage transmission lines. Based on the study of the high-power converters, a suited inverter (diode-clamping multilevel inverter) is selected. The topology of the diode-clamping multilevel inverter is also inproved in the thesis.A switching function mathematical model of this device is constructed by introducing the concept of switching function. It has more generality than the output and the topological model with the consideration of the internal switching character and the physical course of the T-UPFC.The dynamic model of the T-UPFC was constructed which considers the process of the T-UPFC's internal modulation and converters, the process of charge and discharge of DC capacitance.This paper applies Fuzzy Neural Network(FNN) based on the Improved Genetic Algorithm(IGA) to the T-UPFC.Because FNN can be used without the specific model of the object, and it stores useful information as distributed manner, we usually make use of the topological structure and weights of neural network to realize nonlinear mapping, which make those weights full of meaning, also reserve the training algorithm of the IGA. As it is known, we hope to get the universal best answer,so in the processing of weight training, we adopt IGA to avoid the defect of BP algorithm which is very easy to get into the local best answer and the defect of the Traditional Genetic Algorithm(TGA) which is very easy to get into premature convergence.The simulation results verify the efficiency of the T-UPFC designed in this paper. It can damp the subsequent swing quickly under serious power oscillation circumstance to enhance the system dynamic stability apparently.