Transient Stability Analysis and Design of VSGs with Different DC-link Voltage Controllers

Virtual synchronous control has been widely studied for the advantages of emulating inertia for voltage source converters(VSCs).A constant dc-link voltage is usually assumed in existing literature to estimate transient stability of virtual synchronous generators(VSGs).However,actual power supply in the dc-side of VSGs is limited and different dc-link voltage controllers are needed to achieve power balance between DC side and AC side.Addition of dc-link voltage controller has great influence on transient behavior of VSGs,which has not been investigated by previous research.To fill this gap,this paper gives insights into the effect of dc-link voltage dynamics on transient stability of VSGs.First,two typical kinds of VSGs with dc-link voltage controllers are introduced.Then,mathematical models considering dc-link dynamics are established and the effect of dc-link voltage controllers on transient synchronization stability of VSGs is revealed through equal area criterion(EAC).It is found that dc-link voltage controller would reduce stability margin of VSGs and design-oriented transient stability analysis is carried out quantitively using critical clearing time(CCT).Finally,simulation results are given to validate correctness of theoretical analysis.