Optimization Design Of Controller For Damping Power Oscillations In The Power System By UPFC

The research and application of FACTS device now has become one of the hotspots along with the promotion of AC-DC hybrid transmission system. With the help of FACTS technology, our AC transmission system will become more controllable, effective, economic and security. As a typical representation of the third generation of FACTS devices, Unified Power Flow Controller (UPFC) is the most complex and the most powerful devices in this family, it can adjusting basic parameters of the system (voltage, current, circuit equivalent impedance, etc.) to achieve functions such as shunt compensation, series compensation and phase shift only by changing the control law with a unified device. Because of the multi-use technology advantage of UPFC, research on the theory and development of the actual device has large market prospect and practical significance.The UPFC controller designed in this paper is used to solve issues about the power system voltage, the power flow control and the stability of the power system.Firstly, this paper briefly introduces the principle, equivalent structures of series and shunt side and operation mode of UPFC. And a flow and voltage control strategy based on proportion-integral PI control for the UPFC shunt-series VSCs is proposed, which the shunt side of the UPFC is mainly used to control both the voltage of the AC system where the UPFC is connected as well as the voltage of the DC capacitor, and the series side of the UPFC is used to control the active and reactive power flow of the transmission line. The result of simulation of the controller in Matlab/Simulink shows that the load flow and voltage can be adjusted quickly and efficiently by UPFC.Secondly, the parameters of the PI controller is obtained through experience tuning method which is time wasting and can not get the best performance of the controllers. So this paper optimizes PI parameters of the controller based on particle swarm optimization algorithm, in order to improve the tracking ability for instructions of UPFC. Simulation model built in Matlab has verified the steady-state control performance of the algorithm. And comparison with non-optimized PI controller, the simulation results show that the optimized PI controller can tracking steady flow control better and dynamic performance simulation also indicates that the controller can oscillate damping against the fault effectively.Finally, in order to improve the dynamic performance of UPFC, the additional damping controller based on fuzzy control is established on the series side of UPFC, which uses the generator speed difference as the input signal. The detailed derivation of fuzzy interrogation table and fuzzy control rules are listed in the paper. The effectiveness of the proposed control strategy are validated, and compared with no additional damping controller and an additional damping controller based on the principle of PSS, results shows that after adding additional damping controller, system shows better dynamic performance, including voltage control, power flow adjustment, and oscillate damping against the fault.