Measurment based voltage stability monitoring and control

Abstract

A measurement base voltage stability monitoring and control scheme having a means for measuring current and voltage phasors at a boundary bus of a load center; and an equivalent network having a fictitious bus with an aggregate load representative of all loads of the load center. The scheme further includes a computing device to calculate a voltage stability margin index based on the aggregate load of the fictitious bus and compare the voltage stability margin index to a pre-set threshold. The computing device causes an action to take place based on the comparison between the voltage stability margin index and the pre-set threshold.

What is claimed is: 
     
         1 . A method of controlling voltage stability at load center, comprising the steps of:
 (a) measuring current and voltage phasors at a boundary bus of a load center;   (b) determining a maximum power transfer from an external system to the load center; and   (c) determining a voltage stability margin index using the maximum power transfer and comparing the voltage stability margin index to a pre-set threshold such that an action representative of the comparison may be initiated.   
     
     
         2 . The method according to  claim 1 , further including the step of creating a fictitious boundary bus and aggregating all loads of the load center to the fictitious boundary bus. 
     
     
         3 . The method according to  claim 2 , further including the step of determining an equivalent of the external system using an aggregated voltage and an aggregated current of the fictitious boundary bus. 
     
     
         4 . The method according to  claim 1 , further including the step of providing a warning message to a grid operator to indicate a level of the stability margin. 
     
     
         5 . A method of controlling voltage stability at load center, comprising the steps of:
 (a) providing a voltage stability monitoring scheme having:
 (i) a means for measuring current and voltage phasors at a boundary bus of a load center; and 
 (ii) an equivalent network having a fictitious bus to represent total power transferred to the load center; 
   (b) measuring current and voltage phasors at the boundary bus of the load center;   (c) using a calculated voltage and a calculated line current from the equivalent network to estimate a Thevenin equivalent representative of an external system;   (d) calculating a maximum power transfer from the external system to the load center using the Thevenin equivalent;   (e) determining a voltage stability margin index using the calculated maximum power transfer;   (f) comparing the voltage stability margin index to a pre-set threshold; and   (g) taking an action representative of the comparison between the voltage stability margin index and the pre-set threshold.   
     
     
         6 . The method according to  claim 5 , further including the step of calculating the voltage of the equivalent network using 
       
         
           
             
               
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         7 . The method according to  claim 5 , further including the step of calculating the total power transferred to the load center using 
       
         
           
             
               
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         10 . The method according to  claim 5 , further including the step of calculating the voltage stability margin index for active power, reactive power, and apparent power. 
     
     
         11 . The method according to  claim 5 , further including the step of using a Kalman filter to estimate the Thevenin equivalent. 
     
     
         12 . The method according to  claim 5 , further including the step of sending a signal to activate a minimum amount of load shedding at a substation.