Research On The Influence Of Virtual Control Technology On Small Signal Stability Of Power System

With the arising attention to the environmental problems and the improvement of people's environmental awareness,more and more low pollution and sustainable clean energy has been developed rapidly.For example,wind power is a kind of clean energy that uses the kinetic energy of the wind to generate electricity.But the access of large scale wind power has caused an impact on the stability of the power system.Since the wind generator requires power electronic converters to connect to the grid,the output power of a wind turbine can not respond to the changes of the frequency of the system.The large amplitude fluctuation of the system frequency caused by the rise of the wind power permeability will seriously affects the stability of the system.In order to solve this problem,virtual inertial control is applied to wind turbines,and the power fluctuation of the system is balanced by using the kinetic energy of the wind rotor,providing a dynamic active power support for the system.In addition,the wind turbines with converter connected to the power grid do not possess the inertia and damping as the traditional synchronous generators do.Therefore,the stability of the high wind power penetration system is strongly affected by power fluctuations and system failures.Therefore,virtual synchronous machine control technology is applied to simulate the dynamic response of synchronous machines,so as to cope with transient stability and dynamic stability of the power grid.This paper mainly studies the influence of wind turbine on the stability of small interference in power system after the application of the above virtual control technologies.First,the thesis introduces the research background and significance,the development status of wind power domestic and abroad,the types of wind turbines,the control modes and the electrical mathematical models of all parts.The analysis method of small disturbance stability in wind power system is studied,and the linearization model of the power system with wind turbine is set up.Then,the thesis introduces the basic concept and principle of virtual inertia control,puts forward the damping torque analysis model of the wind generator under the virtual inertia control method,and analyses the mechanism of the influence of the virtual inertia control to the damping characteristics of the oscillating modes.Besides,the factors that affect the effect of virtual inertia control on the damping of oscillation mode have been researched,including wind turbine access position,synchronous machine inertia and the inertia of the system,the distribution of the damping of synchronous machines,and examples were used for verification.The thesis illustrates the validity of the equivalence of a wind farm with a wind turbine.Also a new way called residue method was put forward to forecast the changing trend of oscillation mode after applying the virtual inertia control to the wind generator.Finally,the basic concepts and principles of the additional virtual synchronizer control for wind turbines are studied,and the damping torque analysis model of wind generator under virtual synchronous machine control is put forward.A numerical example of a single machine infinite bus system is given.The thesis analyses the influence mechanism of the virtual synchronous machine control of the wind turbine to the small signal stability,and the factors that influence the control effect of the virtual synchronous machine to the oscillation modes,including virtual inertia,active power virtual damping coefficient,and verifies the results of theoretical analysis in numerical examples.