The Mechanism And Restraining Methods Research Of Low Frequency Oscillation In Interconnected Power System

With the increasing interconnection of power systems by relatively weak tie lines and lots of fast static exciters being equipped in systems, the damping of systems oscillations are severely reduced and the oscillations may sustain and even grow. They restrict the power system transfer limits, which therefore affects operational system economics and security.This paper has studied the reasons and control strategies of low frequency oscillations, presented the measurement based dynamic system identification method, and then discussed the pattern recognition of power grid's transient identification using Prony method in detail.Adding PSS in excitation system can produce additional damping torque, which may effectively damp electromechanical oscillations. When several PSS are inserted into the system, every PSS will definitely affect all electromechanical oscillation modes to some extent. So all the PSS should be coordinated to provide sufficient damping for all the electromechanical oscillation modes. Based on the present ideas, this paper has further studied the reasons of low frequency oscillations and the methods harmonizing stabilizers in multi-machine power system. We use Genetic Algorithm (GA) method to design power system stabilizers. The objective function of PSS parameters coordination is set with measuring the performance of all electromechanical modes. GA is employed to solve the optimization problem, thus can gain the PSS parameters needed. As a kind of global search method, GA almost has no limitations on the optimization problem. Because of the ability of searching in global space, GA can gain better result than conventional methods. In addition, direct adoption floating-point code for the coding of GA, this can improve computation efficiency. Adopted the VC++ establishment procedure to the above-mentioned method to carry out.The procedure is tested on New England 10-machine system, and I simulate the system with MATLAB. Case results and simulation results show all electromechanical modes in system gain satisfactory damping ratio when the PSS parameters are coordinated, this explains that the method is an effective parameters optimization method.