In power systems the proper voltage ranges are predetermined in the individual voltage classes. In order to maintain the proper voltage ranges, we propose the voltage stability index VMPI (Voltage Margin Proximity Index) in this paper which defines voltage stability from the point of view of voltage magnitude limits. Many conventional papers dealing with voltage stability preventive control use control devices which take continuous values e.g. static var compensators, whereas actual power systems mainly utilize voltage control devices which take discrete values. Hence, in this paper, we propose a voltage stability preventive control using VMPI sensitivities in order to control devices which take discrete values. We generally require speed for preventive controls in order to use it on-line, however VMPI takes time due to running optimal power flow calculations. Consequently, we propose a practical voltage stability preventive control using the calculation with initial estimates of control devices and estimation of VMPI sensitivities, which require less calculation time. Simulations are run using the IEEJ west 30 machine 115 bus system to verify the effectiveness of the proposed method.
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