Inertia Allocation Mechanism And Stability Analysis Of Network Based Onactive Support Of New Energy

With the large-scale new energy access to the power system,the VSC of the inverters in the system increases gradually,and the inertia intensity decreases,resulting in the reduction of frequency support capacity,affecting the normal and stable operation of the power system.After active support control,VSC new energy unit has inertia support capability similar to traditional synchronous generator,which can improve the frequency stability of the system.At the same time,compared with traditional synchronous generator,VSC new energy unit has variable inertia characteristics because of its adjustable parameters.Therefore,according to the actual demand of the system response,combined with the characteristics of network inertia center,the frequency stability of the system can be further improved by flexibly setting the inertia of each unit.The main content of thesis is based on the control strategy of active support of new energy.The small disturbance stability of two-zone system with different control strategies for VSC with different proportion of new energy is analyzed.Considering the dynamic regulation effect of active support control with different parameters,the inertia flexible control method is adopted to improve the frequency stability of two-zone system.Firstly,the basic principle of active support control is described in detail.Compared with PQ control and droop control,the active support control has better frequency support ability.A small disturbance model of active support control VSC grid-connected and two-machine system is established.Combined with the actual simulation system,it is verified that increasing the virtual inertia time constant of active support VSC reduces the stability of the system,and increasing the damping coefficient improves the stability of the system.Secondly,aiming at the regional interconnected system,the state equation of the two-zone system is deduced.Combined with PQ control and active support mathematical model,the state equation of the two-zone system with VSC new energy unit is deduced.Using software simulation method,modal analysis of the two-zone system is carried out from three aspects: participation factor,damping ratio and oscillation frequency.It is verified that the active support control of VSC has the effect of increasing the damping ratio of the system and improving the regional oscillation mode under different proportion of new energy.Combined with time domain simulation,it is further shown that active support control can improve system stability.Finally,the inertia allocation characteristics of the network with active support VSC are studied,the expression of the inertia center position of the two-zone system is derived,and the frequency distribution characteristics of interconnected lines are analyzed.A four-machine two-zone system model is built in Digsilent/PowerFactory software.It is verified that the active support VSC inertia flexible control method can improve the frequency stability of the system by adjusting the center of inertia to the load disturbance point.At the same time,adding inertia control equipment in the weak inertia region will increase the inertia intensity of the weak inertia region,and the center of inertia will shift to the weak inertia region,thus improving the frequency stability of the system.