Electromechanical And Electromagnetic Hybrid Simulation For Power System With Static Var Compensator

With the rapid development of modern power systems, many new power electronic devices such as HVDC links and FACTS devices have been widely applied in system operations and control. HVDC transmission system has advantages in high voltage power transmission, network connecting between different power systems. FACTS equipment can improve power transmission capacity, enhance the stability and security of power systems without changing greatly the configuration and frameworks of power grids. Therefore, more emphasis has been placed on the research of these power electronic devices and their controllers. In order to study the effects of the protection and control of these devices in a system disturbance or an internal fault caused by the breakdown of semiconductor switches, electromagnetic transient program (EMTP) is widely used to simulate the waveforms with detailed 3-phase transient models of power networks. However, an implementation of a complete EMTP simulation for a large entire power system is usually very difficult due to the limitation of practical computer storage and computation time. On the other hand, transient stability program (TSP) can efficiently simulate the performance of an extensive interconnected power system including HVDC and FACTS devices based on the single-phase quasi-steady state representations. However, the fast transient responses for HVDC and FACTS systems in waveform and the internal fault of power electronic devices can not be simulated in detail.To compromising the advantages of both TSP and EMTP, hybrid simulation algorithms have been proposed in this thesis. The entire power system is divided into two subsystems, the detailed subsystem and external subsystem according to different research interest. The detailed subsystem is defined to include HVDC or FACTS devices while the remaining parts of the power network are named as the external subsystem. The bus at which these two subsystems interact is designed as interface bus. The hybrid methods use interactive execution of EMTP for detailed analysis of HVDC links and/or FACTS devices and TSP for the external AC system. As TSP utilizes relatively larger integration time-step (usually 0.02 second) than that of EMTP, which typically requires time-step of 50 microseconds, the hybrid algorithm has relatively high efficiency in computations and requires less computer storage. And the hybrid approach can also simulate the fast response in three-phase waveform for HVDC or FACTS devices.This paper studies the new techniques to enhance the accuracy of the conventional hybrid methods. An improved new TSP/EMTP hybrid algorithm dynamically considering the effect of the frequency deviation in the interface between TSP/EMTP is proposed. The instantaneous frequency of interface bus, one of interfacing variables obtained by TSP simulation, is utilized as the frequency of the Norton equivalent source in EMTP simulation and calculated dynamically after each step of TSP simulation according to the new techniques developed in this paper. The 3-generator and 9-bus IEEE system and New England system are introduced to demonstrate the effectiveness of the new hybrid simulation algorithm dynamically considered the effect of frequency deviation caused by system disturbance. Simulation results clearly show that the new hybrid simulation algorithm can effectively improve the accuracy of TSP/EMTP hybrid simulation.