In order to discuss the resonance characteristics of grid-connected system（GCS） of large-scale new energy and half-wavelength AC transmission system（HWACTS）

combining accurate harmonic models of half-wavelength AC transmission line and transformer

we built a topology model and equivalent circuit of grid-connected of large-scale wind farms and HWACTS based on the typical topological structure of wind farms.Morever

we adopted the modal analysis method to study the resonant characteristics of the system and analyze the resonant participation factor of each node and every element’s normalized sensitivity of GCS

whose resonance center was also determined.Finally

we summarized the resonant frequency ranges corresponding to the changes of different kinds of line length

inverter parameter

and operation mode by investigating the influences of different parameters on the resonant characteristics of the system

and put forward the relatively ideal operation condition and the frequency deviations of resonance points of different operation modes.The simulation results show that the 35 kV bus is the resonant center of GCS

the resonant effect of the length change of HWTL on GCS is mainly concentrated in the low frequency（inter） harmonics.In addition

the length changes of low voltage level line

the grid-side inductance

the filter capacitor

the outer loop scale coefficient of the inverter

and the short-circuit capacity of UHV AC grid have remarkable influences on the resonance of GCS.