Unit Commitment Strategy Of Power System Considering Wind Turbine Overspeed Load Reduction And Inertia Control

China’s wind power resources are quite rich,and has a greater value of use,with the promotion of wind power technology,wind power in the power system in the proportion of increasing.Within the power grid,frequency is a key factor in evaluating power quality of the power grid.If the power grid is suddenly interrupted,the balance between generating and absorbing energy will be out of balance.The power supply shortage caused by this phenomenon will lead to the decrease of the power grid frequency.Large-scale integration of wind power into the power grid leads to a reduction in the equivalent moment of inertia of the system.In addition,conventional wind turbines do not have spare capacity for primary frequency modulation and do not provide inertial support to the power system.Therefore,it is far from enough to maintain the system frequency stability by relying only on the frequency modulation ability of traditional thermal power units.Traditional unit commitment plans do not include system frequency dynamic constraints.Under this background,in the study of large-scale wind power grid-connected power system unit commitment optimization,the problem of system dynamic frequency stability under disturbance has become an important topic.This dissertation mainly proposes a unit combination model that considers wind turbine overspeed reduction and inertia control and takes into account the system frequency dynamic constraints.The main research contents of this paper are as follows:Firstly,the composition and working principle of DFIG are studied,the dynamic model of DFIG is deduced and established,the principle of wind power frequency regulation is analyzed,and the maximum power operation curve at different wind speeds is obtained,and the virtual inertia control method is compared with overspeed The load shedding control method is combined,and the virtual inertia time constant definition is used to quantitatively analyze the size of the virtual inertia time constant under different load shedding amounts of the wind turbine.Then model the multi-machine system with fan frequency modulation,and derive the lowest frequency expression after disturbance.Through expression analysis,it can be seen that the minimum value of the system frequency increases with the increase of the system inertia time constant and adjustment power.Improving the system inertia level and frequency modulation capability has a positive effect on the safety and stability of the frequency.The participation of wind turbines in system frequency modulation can reduce the traditional power system’s requirements for inertia and primary frequency modulation,and improve the system unit regulation power and inertia level,thereby improving system dynamic frequency stability.Next,build a unit commitment optimization model that considers dynamic frequency constraints,and use multivariate piecewise linearization technology to solve the problem of highly nonlinear characteristics of frequency constraints;finally,a 10-unit system with wind power gridconnected as an example is calculated and analyzed to verify that wind turbines participate in frequency modulation Feasibility in unit commitment decision-making.The comparison with the traditional unit commitment results shows that the model satisfies the economy while improving the system stability.