Transient stability assessment with time-adaptive method based on spatial distribution

Adaptive cost-sensitive assignment method for power system transient stability assessment

In this paper, an online power system transient stability assessment (TSA) problem is mapped as a two-class classification problem and a novel data mining algorithm the core vector machine (CVM) is proposed to solve the problem based on phasor measurement units (PMUs) big data. First of all, an offline training, online application framework is proposed, which contained four sub-steps, namely features selection, offline training, online application, and assessment evaluation. First, 24 features are selected to present the system status. Then in the offline training procedure, the PMU big data is generated by time domain simulation, and a CVM model is trained and tested. In the online application procedure, an interface between PMU data center and feature calculation program is set up to collect real time specific PMU big data and the CVM trained is applied to the TSA problem. Last but not least, the evaluation indices are calculated. Compared with other support vector machines, the proposed CVM based assessment algorithm has the higher precision, meanwhile, it has the least time consumption and space complexity. As long as online PMU big data are received, TSA can be done simultaneously. Case studies on the IEEE New England 39-bus system, and real systems in China and the U.S., exhibit the speed and effectiveness of the proposed algorithm.

Recently, data-driven methods have been widely assessed by researchers in the field of power system transient stability assessment (TSA). The differences in prediction difficulty among the samples are ignored by most previous studies. To address this problem, anchor loss (AL) is introduced, which can dynamically reshape loss values based on the prediction difficulty of samples. Thereby, easy samples are suppressed by reducing their loss values to avoid being paid too much attention when they are misclassified. Meanwhile, hard samples are emphasized by increasing their loss values, in order to be predicted correctly as much as possible. On basis of the AL, historical information in the model training process is considered. A novel loss function named historical information anchor loss (HIAL) is designed. The loss values can be adaptively rescaled according to the previous prediction results as well as the prediction difficulty of samples. Finally, the HIAL is combined with the deep brief network (DBN) and applied in the IEEE 39-bus system, and a realistic system is produced to verify its effectiveness. By incorporating prediction difficulty and historical training information, the accuracy (with a reduction in misjudgment rate exceeding 30%) and convergence speed of the TSA model can be significantly improved.

In order to maintain the stable operation of power systems, quick and accurate transient stability assessment (TSA) after the fault clearance is important. Machine learning methods have been widely used in the transient stability analysis of power systems. However, how to make good use of time series data of PMUs and effectively balance the contradiction between rapidity and accuracy brings new challenges to TSA. To address this problem, we propose an anti-jitter dynamic evaluation method based on long-short term memory (LSTM) network. In this model, the trajectory cluster characteristics of generators power angles after fault clearance are taken as inputs, and an improved LSTM is used to learn the nonlinear mapping relationship between the input characteristics and the transient stability. Meanwhile, by the use of sliding time windows and anti-jitter mechanism, a hierarchical real-time prediction framework is constructed to effectively utilize the time series data of PMUs. The case studies on two systems indicate that the proposed method has superior evaluation accuracy and general performance. In addition, the proposed method can effectively evaluate the stability margin or instability degree of samples, which provides reliable reference information for emergency control.

In recent years, the power system transient stability assessment (TSA) based on a data-driven method has been widely studied. However, the topology and modes of operation of power systems may change frequently due to the complex time-varying characteristics of power systems. which makes it difficult for prediction models trained on stationary distributed data to meet the requirements of online applications. When a new working situation scenario causes the prediction model accuracy not to meet the requirements, the model needs to be updated in real-time. With limited storage space, model capacity, and infinite new scenarios to be updated for learning, the model updates must be sustainable and scalable. Therefore, to address this problem, this paper introduces the continual learning Sliced Cramér Preservation (SCP) algorithm to perform update operations on the model. A deep residual shrinkage network (DRSN) is selected as a classifier to construct the TSA model of SCP-DRSN at the same time. With the SCP, the model can be extended and updated just by using the new scenarios data. The updated prediction model not only complements the prediction capability for new scenarios but also retains the prediction ability under old scenarios, which can avoid frequent updates of the model. The test results on a modified New England 10-machine 39-bus system and an IEEE 118-bus system show that the proposed method in this paper can effectively update and extend the prediction model under the condition of using only new scenarios data. The coverage of the updated model for new scenarios is improving.

Deep Neural Network (DNN) has been introduced to power system transient stability assessment (TSA) and achieved quite remarkable success. However, since the DNNs are ‘blackbox’ models, it is very hard to reveal misbehaviors of the DNNs and repair them to get better performance. To address these challenges, this paper proposes to use Arachne, a fresh program repair technique for DNNs, to repair TSA DNNs. Arachne can fix DNN's specific misclassifications at little cost to overall accuracy. In TSA, missed detections is more severe to the system than false alarms due to the conservation requirements. Case studies have demonstrated the usefulness of the proposed method.

Traditional machine learning models are subject to changes in the data distribution. Once the topology of power grid changes, the distribution of power grid data will change, resulting in the consequence that the former transient stability assessment model based on machine learning is no longer applicable and needs to be retrained. However, the power network after the topology changes cannot provide enough data for the training of the new model. To solve the problem above, this paper proposes a method of power system transient stability assessment based on transfer learning, which fully taps the potential of past data and assists a small amount of newly acquired data in training the model. The simulation results on the CEPRI36 system show that the proposed method can effectively improve the accuracy of original classification models, especially for weak classifiers with insufficient generalization ability. The disadvantage of transfer learning lies in the long training time, which still needs to be improved.

Machine learning approaches have exhibited high potential in power system transient stability assessment (TSA), yet their initial preparation stages of stability knowledge base generation (SKBG) based on time-domain simulations often undergo high computational costs. In fact, how to ease the heavy computational burden of SKBG without sacrificing the reliability is still a significant challenge. To address this problem, this paper develops a semi-supervised ensemble learning (SSEL) framework for reliable SKBG acceleration, without additional need for computing hardware upgrading. In particular, it performs detailed simulations for a minority of cases and fast simulations for the majority ones to reduce the total computation time. Considering the absence of stability status information of those fast simulated cases, an SSEL scheme is systematically designed to reliably label their stability status. Before implementing SSEL, two concise feature descriptors are first introduced to efficiently extract transient features from multiplex system trajectories. Then, all the cases are characterized in a unified feature space, whereby a series of semi-supervised support vector machines are trained in randomly formed subspaces. Afterward, these single machines are systematically combined to derive an enhanced SSEL model, which is able to make reliable and robust labeling decisions. Further, a backtrace strategy is carefully devised for SSEL, so as to maintain the high reliability of SKBG. Test results on the IEEE 39-bus system and the realistic GD Power Grid in South China illustrate the excellent performances of the proposed framework on SKBG acceleration.

Taking full advantage of synchrophasors provided by GPS-based wide-area measurement system (WAMS), a novel VBpMKL-based transient stability assessment (TSA) method through multifeature fusion is proposed in this paper. First, a group of classification features reflecting the transient stability characteristics of power systems are extracted from synchrophasors, and according to the different stages of the disturbance process they are broken into three nonoverlapped subsets; then a VBpMKL-based TSA model is built using multifeature fusion through combining feature spaces corresponding to each feature subset; and finally application of the proposed model to the IEEE 39-bus system and a real-world power system is demonstrated. The novelty of the proposed approach is that it improves the classification accuracy and reliability of TSA using multifeature fusion with synchrophasors. The application results on the test systems verify the effectiveness of the proposal.

Convolutional neural network-based power system transient stability assessment and instability mode prediction

Spatial-temporal adaptive transient stability assessment for power system under missing data

Transient stability assessment (TSA) based on machine learning techniques is a classical problem of classification. In this paper, a new transient stability assessment model using the weighted random forest (WRF) is proposed. Random forest, which runs fast and can scale to very high dimensional datasets, is one of the most popular methods applied to TSA after faults occurred. However, in the actual operation of modern power system, unstable samples constitute only a very small minority of the cases. Besides, the traditional random forest algorithm does not work very well on imbalanced data. To tackle the problem, weighted random forest is adopted to lean the interest towards to the correct classification of rare class, and improve the prediction performance. Case study on the New England 39-bus test power system exhibits that WRF has better performance than the original random forest.

In machine learning-based transient stability assessment (TSA) problems, the characteristics of the selected features have a significant impact on the performance of classifiers. Due to the high dimensionality of TSA problems, redundancies usually exist in the original feature space, which will deteriorate the performance of classification. To effectively eliminate redundancies and obtain the optimal feature set, a new feature reduction method based on neighborhood rough set and discernibility matrix is proposed in this paper. First, 32 features are selected to structure the initial feature set based on system principle. An evaluation index based on neighborhood rough set theory is used to characterize the separability of classification problems in the specified feature space. By constructing the discernibility matrix of input features, a feature selection strategy is designed to find the optimal feature set. Finally, comparative experiments based on the proposed feature reduction method and several common feature reduction techniques used in TSA are applied to the New England 39 bus system and Australian simplified 14 generators system. The experimental results illustrate the effectiveness of the proposed feature reduction method.

Transient voltage stability assessment of renewable energy grid based on residual SDE-Net

This paper proposes an improved LSSVM power system transient stability evaluation method. According to the Bayesian nonlinear hierarchical framework, the automatic selection of parameters is implemented to improve the sensitivity of LSSVM classifier model to parameter and improve the accuracy of transient stability assessment Firstly, the original feature set related to the system stability is calculated by the wide area measurement information. The feature selection method is used to compute the feature, and the optimal feature set which is strongly related to the stability of the power system is determined. The training set and the test set are divided into Mapped to high-dimensional space, so that the nonlinear and linear classification of the transformation. Then, the optimal parameters of LSSVM are determined by Bayesian nonlinear hierarchical model, and the fast transient stability is determined. Finally, the validity and accuracy of the evaluation model are verified by IEEE-39 node system and actual system.