Research On The Influence Of Generator Excitation Auxiliary Functions On The Stability Of Power System

Under-excitation limiter?UEL?is a widely equipped auxiliary function of automatic excitation regulator.Its purpose are to prevent the generator from operating beyond its steady state stability limit and to prevent excessive stator end-core heating,as well as reducing the risk of malfunction of loss of field protection.However,Power system dynamic stability deterioration cases causd by UEL occurred at home and abroad.This paper focuses on UEL configuration requirements and the mechanism of system dynamic stability affected by UEL,as well as its coordination with the PSS.Firstly,this article summarizes the basic requirements for UEL configuration,such as static stability limit,stator core end fever restrictions and cooperation with the loss of field protection.The site configuration of UEL on domestic province's main power plants is investigated.The slope and intercept parameters of analysis of UEL boundary line is analyzed.The UEL boundary line coordinated with phase test curve and the loss of field protection impedance curve are checked.Secondly,the mechanism of power system dynamic stability impacted by UEL was analyzed through theoretical analysis and simulation.The extended model considering UEL is derived based the K₁-K₆ coefficient model and C₁-C₁₂coefficient model.The damping torque of generator is divided into four components according to the superposition principle.They are damping torque provided by UEL,damping torque provided by PSS,the inherent damping torque of system and damping torque related to coefficient D.The mechanism of various parts of the damping torques impacted by UEL parameters and the operating point are deduced and analyzed in detail.The results indicate that UEL boundary line with a large slope may cause damping torque provided by UEL becomes negative,UEL will worsen the positive damping torque provided by PSS in the usual case of UEL parameters.Finally,a coordinated control strategy between UEL and PSS is proposed.The strategy is to add a new PSS which is adapted to UEL.We establish the mathematical model for the parameter configuration of newly added PSS by comparing the frequency response between the original PSS and the new PSS and solve the model by particle swarm optimization algorithm?PSO?.The control structure switching between the original PSS and new PSS according to the action of UEL is designed to guarantee enough damping provided by PSS.