Hybrid voltage stability assessment (VSA) for N− 1 contingency

Abstract

With the growing deployment of phasor measurement units (PMUs), measurement-based voltage stability assessment (VSA) that estimates the system Thevenin equivalent has been widely discussed in recent years. This approach attracts favorable attentions mainly for its simplicity and great potential in real-time applications, as opposed to the continuation power flow (CPF) method which is model-based VSA. However, the existing measurement-based VSA deals with the normal case, but not any contingency case because there is no measurement data for a contingency case which is hypothetical. With this motivation, a hybrid VSA method is proposed based on both model-based and measurementbased techniques. First, an enhanced model-based sensitivity analysis estimating the postcontingency status is proposed, and then it is combined with the measurement-based Thevenin equivalent approach. The proposed sensitivity analysis has the feature of simplicity, which is aligned with the measurement-based Thevenin equivalent. Test results with the IEEE 14, 39, and 118-bus system show that the proposed sensitivity is highly accurate in estimating N-1 contingency system variables and the proposed hybrid VSA method for N-1 contingency captures the insecure contingencies successfully. The proposed method greatly broadens the practical application of PMUs for VSA under N-1 contingency.

Sensitivity Based Thevenin Index for Voltage Stability Assessment Considering N-1 Contingency

“…Still, the proposed approach gives more accurate results in predicting the post-contingency VSI. For contingency 1-5, the average error σ is 24.82% by using the method in [16]. This value decreases to 4.25% by leveraging the proposed approach.…”

“…Under the normal load level, no alarms will be triggered for bus 14 since the predicted post-contingency VSIs are all below 0.45. Also, the proposed approach outperforms the method in [16] for better estimation of the post-contingency VSI. Next, we test the proposed approach for the peak load condition.…”

“…To both accurately estimate the post-contingency states and the voltage stability margin, it is paramount to predict the possible PV-PQ transitions. The piecewise linear sensitivity method [16] is used to predict the Q limits violation. First, a K factor which reflects the severity of reactive power violation at a PV bus is defined as follows…”

“…We compare the accuracy of the proposed approach with the method in [16]. Note that the VSI adopted in [16] is based on the voltage magnitude deviation proposed in [10]. To accommodate the comparison, we shift the VSI to Z th / Z L .…”

“…To accommodate the comparison, we shift the VSI to Z th / Z L . Nevertheless, we leverage the same method as given in [16] to identify the post-contingency TE. The last row in Table I, i.e., σ, denotes the average relative error (averaged among all load buses) of the two approaches with respect to the benchmark results.…”