Control Strategy Of Energy Storage Power Station To Suppress Continuous Commutation Failure Of DC System

In recent years,the energy development strategy of "power transmission from West to East,mutual supply between of North and South,and national interconnection" is proceeding steadily,and HVDC transmission technologies with the advantages in long-distance and large-capacity transmission have developed rapidly.In this context,the problem of commutation failure cannot be neglected,which is one of the common faults in the LCC-HVDC system.The implementation of inappropriate measures after the first commutation failure may cause successive and multiple commutation failures.Continuous commutation failure will cause HVDC unipolar or bi-polar blocking,which threatens the safe and stable operation of the power system seriously.Therefore,it is of practical importance to study effective measures to suppress continuous commutation failure.First,the mechanism of the commutation failure of HVDC sytem is analyzed in detail.Based on it,the major influencing factors of the commutation failure are summarized and analyzed theoretically.Through the statistical analysis of the commutation failure in the HVDC systems in operation,it is pointed out that the AC system failure is the main reason for the commutation failure.Therefore,it is reasonable to impose a short-circuit fault at the receiving converter bus to initiate the HVDC commutation failure.Furthermore,the fundamental principles of suppressing commutation failure based on reactive power compensation are explained,and the advantages and disadvantages of different reactive power compensation device s are summarized.Then,the equivalent method based on Thevenin’s theorem is utilized to establish the equivalent model for the large-capacity energy storage power station,which can help to reduce the difficulty of modeling and increase the speed of simul ation.The main circuit and control circuit of the energy storage power station which has been equivalent are studied comprehensively.Furthermore,in order to suppress the HVDC continuous commutation failure,an emergency reactive power support control strategy for energy storage power station is proposed in this thesis.The control strategy of fixed period comparison constitutes the control strategy of the bidirectional DC-DC converter of the energy storage power station,and the control strategy of the DC-AC converter of the energy storage station is composed of the following parts: the voltage and current inner loop control;the active and reactive power outer loop control where reactive power control is prior to active power control.The proposed strategy can control reactive power exchange between the energy storage station and HVDC system in real time according to the voltage variation of the receiving converter bus,and it is conducive to support the transient voltage of the converter bus at fault time,thus suppressing the continuous commutation failure of HVDC system.Finally,the PSCAD/EMTDC platform is utilized to build the simulation model containing energy storage power station modules on the basis of the standard HVDC transmission system.In addition,the effectiveness of the proposed control strategy for the energy storage power station to provide emergency reactive power support has been verified.The simulation results confirm that the proposed strategy can effectively reduce the occurrence of continuous commutation failures to a certain extent.Furthermore,the model is modified to study the impact on the effect of suppressing continuous commutation failure if the capacity or location of the energy storage power station changes.The simulation results show that the energy storage power station needs to have sufficient capacity to suppress the continuous commutation failure of HVDC system.The larger the value of the voltage stability factor of the bus in where energy storage power station locat es,the more obvious the effect on suppression of continuous commutation failure.The findings of the research can provide certain guiding ideas for the capacity selection and placement of energy storage power stations.