Physical Constraints And Stability Control Of Virtual Synchronous Generator Operating Under Weak Grid And Islanded Mode

With the increasing penetration of distributed generators(DGs)in power system,DGs based on power electronic inverter interface have been quickly developed.As an advanced control method that could bring extra inertia and damping characteristics to inverter-based DGs through imitating synchronous generator,the virtual synchronous generator(VSG)can contribute to the stability of power system.In this paper,the VSGs operating under weak grid and islanded mode is studied,and the transient characteristics of the VSGs are compared in detail,and the unstable phenomena of the two operating conditions are addressed after mathematical modeling and detailed eigenvalue analyses respectively.On this basis,the calculation method of dual physical constraints of energy margin in DC side and power margin in AC side is put forward.Combining the physical constraints with the unstable region,the stable operating boundary of VSG is obtained.The main contents are as follows:1)In this paper,mathematical models of the systems are established.The influence of VSG key parameters,e.g.,virtual inertia,damping factor,and droop coefficient on system stability is investigated,and the corresponding mathematical calculation method of unstable region is obtained.The proposed unstable region provides a theoretical basis for ensuring the stable operation of VSG.2)Considering that the output active power of VSG is restricted by the capacity margin of the converters,and the output energy is bounded by the energy margin of the energy storage,both the DC side energy storage system and the AC side power margin should be considered simultaneously when setting the inertia and damping coefficient of VSG.On the premise of stable operation of the system,this paper puts forward a double physical constraint calculation method of VSG,and obtains the operating boundary of VSG under the condition of double constraints.By analyzing the dynamic response characteristics of VSG under different virtual inertia and damping factor,the influence mechanism of constraint boundary on inertia and damping realization is obtained.3)Based on the research of stable region and physical constraints,the stability control method of VSG is presented.By real-time detecting the AC side power allowance and the DC side energy allowance,the maximum inertia that can be configured is obtained,and the unstable region is avoided effectively to ensure the stable operation of VSG.4)The digital simulation models of the VSGs operating under weak grid and islanded mode are built through PSCAD/EMTDC(?),and the relative theoretical analysis is fully and carefully validated.The simulation results verify the effectiveness of the proposed method.