The under-excitation limiter(UEL)

as a limit part of the excitation system

has an important influence on the stability of the system. However

due to the unrational parameter setting of UEL

the positive damping effect provided by the power system stabilizer(PSS)is weakened after UEL acts. This causes the oscillation and even the serious fault of the generator frequently in the actual operation of the power grid. Based on the extended Heffron-Phillips model

a simplified model with PSS and UEL for excitation system is derived. The frequency response method is used to draw the Bode diagram of the open-loop transfer function of PSS and UEL. The frequency band of UEL and PSS is analyzed

and a specific parameter setting program of UEL is given

which can make UEL and PSS coordinated. Taking the data of Yunnan power grid for example

the single-machine infinite-bus system is developed to verify the correctness of the theory in simulation software of PSASP and MATLAB. The simulation results show that

after the UEL parameter is set by the frequency response method

the UEL action will not affect the output of the PSS

and UEL and PSS can cooperate to ensure the steady-state operation of the system.