Improvement of AGC Strategies for Ultra-high Voltage Interconnected Power System

This paper presents an improved AGC control strategy for Ultra-high voltage (UHV) interconnected system aiming at coordination between adjustments of regional and provincial units and control of tie line power flow. Frequency regulation responsibilities are assigned among regulating zones according to disturbance type. When the disturbed zone occupies sufficient frequency regulation reserve, the generators controlled by the regional grid dispatching center and the generators controlled by provincial dispatching center located in the disturbed zone should be chosen prior to undertake frequency regulation responsibility. While the disturbance is severe, regional units located in non-disturbed zones are also involved in the regulation of UHV tie-line power to speed up the recovery of it. To avoid active power violations of inter-provinces lines, formula of ACE for provincial regulating zones is modified to restrict the fluctuation range of regional units output. As for power imbalance beyond the frequency control capability of the disturbed area, all AGC units in the network will respond to it by using the flat frequency control (FFC) scheme. In the meantime, the security of tie-line power flow is guaranteed by regional units. The proposed control strategy is applied to AGC model for Central China power grid developed in Matlab/Simulink and the effects are examined.