Long-term Voltage Stability Analysis And Control Considering Events Sequence

The power system complexity increases because of the increasing size of the power system, combined AC and DC transmission systems, smart grid and distributed power grid, which to some extent may also lead to potential instability problems of large-scale power system. Several times of large blackouts indicated that there is a relatively long voltage drop process from the initial state to the unstable state. This article focuses on the long-term voltage stability analysis. In this paper a long-term voltage stability analysis model is proposed to study the long-term voltage instability mechanism, and a long-term prevention and control voltage stability model is proposed to get a more effective voltage control strategy.Generally speaking, the action of various components of power system such as OLTCs, exciter limiters and load variation need to be considered in long-term power system dynamics analysis. This article focuses on the voltage instability caused by system control measures (OLTC and over-excitation limit, etc.) and discrete events (branch load encroachment) driven by load variation, and to develop more effective voltage control strategy.Long-term power system dynamics analysis should make a trade-off between result precision and time consumption. Time-domain analyses of power systems simulate the operation of the grid by solving differential-algebraic equations, the long computation time is not conducive to rapid real-time analysis, although the result is more accurate. A temporal power flow method (TPF) driven by load variation is proposed which tracks system evolving states interwoven by continuous dynamics and discrete events. Feasible operating states are solved by using predictor and corrector, events are triggered which involves OLTCs, exciter limiters and branch load encroachment, etc. Upon detecting instability or collapse, the routines are stopped. The corresponding relationship between load and events obtained using continuation method is mapped to the load curve. Through TPF method, the load margin and time margin from the current operating states to the network decomposition or the critical point can be predicted. Simulation results on the New England 39-bus system verify the effectiveness of the proposed method.In order to prevent the system voltage instability incidents, there is need to form effective prevention and control model to get the appropriate prevention and control strategy. The model needs to ensure the accuracy of the calculation and the requirements of the online application. Blackouts model based on self-organized criticality theory to long-term instability analysis of the power system focuses on the evolution of the grid, including the expansion of generators, line expansion and load growth. A more practical prevention and control model temporal optical power flow is proposed in this article. This model uses two-level time frames, the upper frame which includes load forecasting and voltage posture regulating is used for contingency filtering, selection of voltage trend regulating node and setting the voltage constraints range, the lower carries on optical power flow calculation of the actual load with the use of various parameters obtained from the upper frame. This model can not only meet the target of reducing the power loss but also consider the balanced distribution of reactive power, so more accurate control strategies can be formulated to avoid the potential impact on long-term voltage stability due to improper control strategy. The IEEE 30-bus system is used to verify the effectiveness of the proposed method.