Research On Adaptability Of Relay Protection For Transmission Lines Of Large-scale Wind-solar Hybrid Power Generation System

Large-scale wind-solar hybrid generation systems generally consist of a combination of full-power inverter-type power sources(permanent magnet synchronous Generator,PMSG and photovoltaic power generation,PVG)and partial-power inverter-type power sources(doubly-fed induction generator,DFIG).The hybrid operation combines the fault characteristics of some power inverter-type and full-power inverter-type power supplies.Taking into account the interaction between different types of units,it shows more complex transient characteristics.Large-scale wind-solar hybrid generation systems have different types of units that use different control strategies,unsynchronized entry failure control strategies,and the number of units that enter the fault control strategy under different fault types is also different,which poses more severe challenges to the line protection devices.Comprehensively considering the principles of reliability,selectivity,sensitivity and quickness of relay protection,the differential protection,distance protection,phase selection components and direction components of the large-scale wind-solar hybrid generation system are studied.Part of the power inverter type power supply(DFIG)is p.u.t into the crowbar circuit during the fault,which causes the stator current frequency shift.In a large-scale wind-solar hybrid generation systems when the DFIG account is relatively large,Current frequency offset will reduce the calculation accuracy of the outgoing line protection based on Fourier algorithm.The transient fault characteristics of DFIG after the grid fault crowbar circuit is p.u.t into operation are studied.After the voltage drops deeply,the AC component of the decayed speed frequency in the stator fault current is the main component in the initial stage of the fault.It is proposed to remove the crowbar circuit to restore the excitation after the attenuation of the AC component of the attenuated speed frequency is completed,which can improve the low voltage ride-through performance and improve the reliability of the protection based on the 50 Hz frequency.The protection of the outgoing line of the large-scale wind-solar hybrid generation systems based on the principle of mutation is studied.By establishing an equivalent impedance model,it is revealed that the characteristics of the equivalent power supply potential and internal impedance during the fault period depend on the fault control strategy,which is very different from the traditional power supply.By studying the characteristics of the impedance waveform of the equivalent positive sequence mutation in the wind-solar hybrid generation systems,a new type of transmission line longitudinal protection based on the impedance waveform correlation structure is proposed.By calculating the Pearson correlation coefficient of the equivalent positive-sequence mutation impedance waveform extracted from the protection installations on both sides of the transmission line,it is possible to effectively distinguish between internal and external faults.The applicability of longitudinal protection based on the correlation of impedance waveforms is studied.