Transient Stability Of Power Angle In Interconnected Systems With Virtual Inertia And Integrated Control

The application of virtual inertia in power system with high wind penetration can improve frequency stability,but the transient stabi lity of power angle will be significantly affected due to the change of inertia distribution.Therefore,the current inertia control still has the risk of power oscillation.In order to prevent the virtual inertia from affecting first-swing stability and damping characteristics,this paper analyzes the transient stability mechanism of the interconnected power system with controlled inertia.The main research results are listed as follows.Firstly,a dynamic model of the interconnected system connected to a group of variable-speed wind turbines is established,and transient energy function of the equivalent system with virtual inertia is derived.Based on the extended equal-area criterion(EEAC),the influence mechanism of virtual inertia on transient energy conversion is analyzed.It is concluded if first swing direction of power angle is different,the influence of virtual inertia on transient angle stability is also different.Secondly,a linearized model of the interconnection system with wind power is established.Based on the different time scale,the integral manifold method is used to reduce the order of state equations.Utilizing the eigenvalue analysis method,the influence of virtual inertia modulated in different power-generating areas on the damping characteristics is then analyzed.Based on the DIgSILENT/PowerFactory,the modal analysis for a system with two regions and four generators is performed,and the effect of virtual inertia on the power oscillation mode has been verified.Thirdly,according to the research conclusions,a cooperative virtual inertia control strategy based on doubly-fed wind turbines is proposed.By rationally configuring the control parameters of the virtual inertial controllers in different power generation areas,the transient stability of power angle could be enhanced.For the area where the damping is weakened,a variable inertia control strategy is adopted to accelerate the oscillating attenuation for the power angle and improve the friendliness of wind power grid connection.Fourthly,a simulation model of an interconnected power system with wind power is established,and experimental verification is performed on a hardware-in-the-loop platform based on RT-LAB.The results show that the flexible inertia control can maintain the frequency adjustment function,improve the transient stability of power angle,and damp the subsequent oscillations effectively.