Mechanism Analysis Of Fault Current Limiter On Suppressing Multiple HVDC Commutation Failure And Its Multi-objective Allocation Optimization

When short-circuit fault of the DC inverter side occurs in AC/DC hybrid power system with multi-infeed direct current(MIDC),on one hand,it will bring the problem of short-circuit current exceeding standard,on the other hand,the continuous decrease of the AC system voltage may cause concurrent commutation failure of multi high-voltage direct current(HVDC)s,which will lead to the transient stability problem of the sending system in severe cases.Fault current limiter(FCL)can not only limit the short-circuit current effectively,but also has the effect of inhibiting DC commutation failure.In this dissertation,the method of installing FCLs near the short circuit zone is proposed to research the effects on suppressing commutation failure and transient instability of the system under the relative motion between clusters caused by unbalanced power.Besides,an optimal allocation method is proposed by using FCL to suppress the commutation failure.Specific research is carried out as follows:1)The mechanism and influence factors of DC commutation failure are summarized,and the characteristics of multi-infeed HVDC commutation failure are also studied.2)Influence mechanism of FCLs on suppressing single and multiple DC commutation failure is analyzed respectively.In addition,theoretical analysis of the impacts of multiple HVDC commutation failure on the stability of the sending system under different power flow directions with FCLs inserted is also discussed,using the extended equal area criterion(EEAC)theory.3)Based on PSD-BPA software platform,simulation is carried out taking the "North China-Central China-East China" power grid as the object case system.Results demonstrate that,the introduction of FCLs can not only suppress commutation failure effectively,but also reduce the risk of multiple HVDC commutation failure.At the same time,it can alleviate the power imbalance and the transferred system flow caused by the concurrent commutation failures,which can significantly increase the transmission capacity of the regional section and improve the transient stability of the system.4)A FCL optimal allocation method is proposed,taking suppressive effects on commutation failure into account,which can be applied in practical engineering.