Research On Voltage Stability Margin Based On Dynamic Nonlinear Programming Method

With the rapid development of national economy, growing demand of energy and DC system used in long distance transmission, adversely impact the voltage stability of power system. Voltage stability margin reflects voltage stability and provides evidence for dispatchers to judge voltage stable state and provide voltage adjustment strategies. At present, the methods for calculating voltage stability margin have limitations in considering the actual operating conditions. The results can not accurately reflect the true situation. Therefore, practical solution of voltage stability margin is important to ensure power system’s voltage stability.This paper establishes the dynamic power flow model applied to the AC system and AC/DC system. The effects of load increasing modes and power flow distribution on voltage stability margin are analyzed based on the P-V curve. Voltage stability margin’s solution using normal nonlinear programming method doesn’t consider the growth mode of generators’active power outputs. A dynamic nonlinear programming method model considering the growth mode is proposed. The results of load margin calculated by the dynamic nonlinear programming method are more practical and not affected by the selection of slack node.Voltage stability margins of AC system and AC/DC system are calculated by respectively using the normal and dynamic nonlinear programming method. Results show that voltage stability margin calculated by dynamic nonlinear programming method is more reasonable and practical. Meanwhile, the effects of DC system’s control modes on voltage stability margin, and var compensator equipped in converter stations for improving voltage stability are verified effectively.This paper also calculates voltage stability margin of Liaoning power system. The effects of load increasing modes and slack node selection on Liaoning power system’s voltage stability margin are analyzed. And the results of dynamic nonlinear programming method are more favorable to actual system’s voltage stability. Voltage weak nodes are obtained by analyzing the voltage amplitude at the power limit point. And these nodes can be used as control objectives to improve the system’s voltage stability.