Study On The Influence Of New Energy On Low Frequency Oscillation Of Power Grid And Its Suppression Strategy

Due to the advantages of mature technology and abundant resources,wind power,photovoltaic and other new energy develop rapidly,and the proportion of grid-connected new energy based on converters gradually increases.However,the converter side is decoupled from the grid side frequency,which is more likely to cause low-frequency oscillation when the grid is subject to small disturbance.Because the grid-side converter has the characteristics of easy control of output power and fast response time,the low frequency oscillation can be suppressed by adjusting the additional output power of the new energy grid-side converter.Therefore,this paper analyzes the basic principle of additional power output of new energy converters to suppress low frequency oscillation and the influence of conventional sag control and improved sag control on low frequency oscillation of power grid.Meanwhile,based on the improved sag control,a maximum additional power injection control is proposed.Finally,considering the output power characteristics of different new energy units,a coordinated control strategy of maximum additional power injection control mode and improved sagging control mode is proposed.The main work contents include:(1)Based on the fuzzy theory of adding active and reactive power for restraining low frequency oscillation in the network,this paper presents a linear model for an infinite bus system including the new energy station was established.By constructing the standard Heffron-Phillips model,the action path of the additional power droop control was analyzed.The torque analysis of the additional power is carried out based on the damping torque method.(2)Firstly,based on the classical electric torque method,the dynamic characteristics of the power grid are analyzed by conventional droop control.In order to solve the problem that the traditional droop control can not increase the inertial level,a modified drop control method is put forward.By introducing the differential link of the speed feedback link,the improved droop control can not only improve the inertia level of the system.It also provides the system with greater damping capacity than conventional droop control.(3)In view of the improved droop control,the additional output power may exceed the capacity limit of the converter when the droop coefficient approaches infinitesimal,a new energy station maximum additional power injection control mode considering the capacity limit of the converter is proposed.Aiming at the problems such as unstable output power of new energy or the need to keep active power reserve for a long time when the active power output of wind power and photovoltaic power is used to suppress the oscillation in low frequency oscillation,moreover,the low-frequency vibration suppressing capability of a simple energy storage plant might not be sufficient because of the limited energy storage capability,a coordinated control strategy of new energy unit and energy storage is proposed...