Optimal Operation Of New Energy Power System Considering Inertia Demand

Building new power system driven by "double carbon" goals has become the energy power development strategy of our country.The pace of green and low-carbon transformation of power grids has been accelerating,and new energy power generation represented by wind and solar power has been developed on a large scale.Wind and solar power generation is weakly connected to the system through power electronic converters,and a large number of new energy sources are connected to the grid for power generation,making conventional synchronous units gradually replaced,and the inertia level of the power system continues to decline.As the first line of defense to maintain the frequency safety of the power system,the decrease in the level of inertia has brought serious challenges to the safe operation of the power system.In addition,due to the large scale of wind and solar power bases being far from the load center,most of them are transmitted to the load center through ultra-high voltage direct current,which makes the uneven distribution of inertia in the power system prominent.After being disturbed,the frequency change of the system has obvious spatial distribution characteristics,making the frequency security problem of the power system more complex.Therefore,this paper studies the inertia evaluation and optimal operation of new energy power systems.Firstly,the inertia resources of both sides of source and demand are evaluated.On the source side,the energy sources and inertia characterization methods of inertia support for conventional units are analyzed.In addition,the mechanism of providing inertia for new energy power generation through virtual synchronous generator technology is analyzed,and its support capacity is characterized by virtual inertia constants;On the demand side,the method of zonal inertia evaluation is used to quantify the inertia support capacity of the demand side.Firstly,perform correlation analysis on the measured data to achieve power system zoning,and then evaluate the inertia of each region based on the rotor motion equation.Finally,obtain the total inertia of demand side,establish the relationship between the load power and the inertia of demand side,providing a basis for the operation model.The analysis of numerical examples proves that the evaluation results of the proposed zonal inertia evaluation method are more accurate.Secondly,the optimal operation model of new energy power systems considering inertia demand is studied.Based on the dynamic frequency response of the power system,the spatial distribution characteristics of dynamic frequency are modeled according to the power allocation mechanism when the power system is disturbed,and then the inertia demand constraints are established based on the system’s requirements for two key indicators,namely,the rate of change of frequency and the frequency nadir.Finally,with the goal of minimizing the power generation,start-up cost and wind abandonment cost of the system,and taking into account constraints such as inertia demand and the technical and economic characteristics of units,an optimal operation model for new energy power systems considering inertia demand is established.The results of numerical examples show that the established optimization operation model can provide the optimal output mode of the units while ensuring system frequency safety.It also indicates that considering the inertia support capacity of the demand side in the optimized operation model can bring significant economic benefits.The results provide a reference for developing the power generation operation mode considering frequency safety in new energy power system.Finally,taking inertia resources as an auxiliary service,the pricing method of inertia services is studied.Based on the established optimal operation model considering inertia demand constraints,the nodal inertia service is priced based on the corresponding shadow price of inertia demand constraints.To this end,the startup and shutdown variables are first relaxed,and the inertia demand constraint is transformed into a second-order cone form.Then,the dual variable of the inertia demand constraint is used to price the nodal inertia service.Finally,numerical tests are conducted on the IEEE-39 bus system and the Northwest China power grid system.The results show that the proposed inertia pricing method can establish a reasonable price for inertia service,which is helpful to motivate inertia resources to provide auxiliary services.