Research On Transient Stability Of Power Climbing Control For Grid-Forming Inverter

At present,Chinese energy revolution is to build a new power system with clean,low carbon,safe and efficient clean energy as the core.As distributed energy is connected to the power grid through low inertia and damped power electronic equipment,the supply and demand form of the system changes,and it becomes an inevitable trend for new energy to participate in the system regulation.At peak loads,the grid-forming inverters are required to conduct high power scheduling to ensure the balance of supply and demand in the power system.If the output power of the grid-forming inverter cannot follow the change of the reference active power,the power imbalance will cause system instability.Therefore,it is very important to study the transient stability of inverter under high power scheduling.In this thesis,the transient stability of the grid-forming droop control inverter single-machine infinite-bus system with grid support under different power scheduling and limit power scheduling is studied.Firstly,based on the mathematical model of the grid-forming droop control inverter single-machine infinite-bus system,the output power characteristics are analyzed.Combined with the P-δ curve,the output power characteristics and critical stability point of the inverter are analyzed under the changes of reactive current,grid voltage and line reactance,and the transient stability of the inverter under the changes of the active power droop coefficient,reactive power droop coefficient and reference active power value in droop control.Secondly,based on the equal area criterion,the transient stability of grid-forming inverter under power scheduling is analyzed.In order to maintain the stable operation of the power system during the transient process of reaching the critical stable point of grid-forming inverter,based on the constraint of transient stability,two control schemes of variable step size power climbing and constant step size power climbing are proposed.The reference active power with inertia and integral link to simulate the above two control schemes,which can reduce the response time and overshoot and improve the transient stability of grid-forming inverters in high power scheduling.In addition,based on the output power expression of the grid-forming inverter,the influence of the active power scheduling on the output reactive power of the inverter is analyzed.Aiming at the problem of large reactive power loss under high power scheduling,a reactive power compensation scheme is proposed.By compensating the output delayed reactive power of grid-forming inverter,the transient stability of the system is improved.Combined with the phase trajectory,the transient stability of the compensated and uncompensated inertia climbing schemes under the same power scheduling condition is directly compared.Finally,base on RTDS and LAUNCHXL-F28379 D hardware-in-the-loop experimental platform,the grid-forming droop control inverter single-machine infinite-bus system is built,and the transient stability of the grid-forming inverter based on power climbing control under power scheduling was experimentally verified.