Transient Stability Emergency Control Research Articles

Emergency control methods for power systems based on improved deep reinforcement learning

Abstract In order to achieve fast and accurate transient stability analysis and emergency control, this paper proposes a transient stability emergency control method based on improved deep reinforcement learning. In order to fully explore the temporal and spatial variation trend of transient response, a multi-dimensional feature containing information such as transient situation energy is constructed, and the deep reinforcement learning model is transformed based on the time-space graph neural network. On this basis, an emergency control model is constructed, and the power grid knowledge is integrated into the emergency control decision-making scheme to reduce the exploration of invalid decision-making and improve the performance of the model. The effectiveness of the proposed method is verified in the IEEE-39 system.

Transient voltage stability emergency control strategy for HVDC receiving end power grid based on global orthogonal collocation

When asynchronous motors, especially double-fed asynchronous motors in large capacity pump storage are the main loads in the high voltage direct current (HVDC) receiving end power grid, the increase of the equivalent slip of asynchronous motor load may cause transient voltage instability. In order to recover the voltage rapidly in the grid, the emergency reactive power support needs to be quick and accurate. A method for transient voltage stability emergency control by temporarily reducing DC current is proposed, the inverter station is used as emergency reactive power source for the HVDC receiving end power grid. In detail, firstly, aiming at the quantitative calculation of DC current, a nonlinear optimization model with the optimization variable of DC current and the objective of minimizing energy transmission reduction of HVDC is established. Further, in order to achieve fast solution and meet the accuracy requirements, global orthogonal collocation (GOC) is incorporated into the optimization model to transform the differential equations of both objective function and constraints into algebraic equations, thus the optimization is transformed into a nonlinear programming (NLP) problem, by which the emergency control strategy, in specific, the optimal DC current control scheme is obtained. Finally, the modified IEEE 14 benchmark is used to verify the effectiveness and superiority of the proposed strategy.

Robust Transient Stability Emergency Control Considering Wind Power Uncertainties

Transient stability emergency control (TSEC) enhances power system transient stability during large disturbances but faces challenges in the high-penetration wind power grid where the wind power forecast error still cannot be ignored even with state-of-the-art forecasting methods. In this paper, the TSEC problem is modeled as robust nonlinear programming with the objective of maintaining rotor angle stability by generator tripping and load shedding while the uncertain wind power outputs are regarded as intervals. Interval programming is employed to solve the robust TSEC problem where the trajectory sensitivity analysis is applied to approximate the bounds of transient stability constraints. Numerical results on two test systems demonstrate that the proposed method improves computational efficiency and shows good performance on robustness.

Battery storage to improve the cutter negative effect transient stability control strategy

To improve the transient stability of power grid, this paper proposes an emergency control strategy considering battery storage to participate in the transient stability of power grid. The phase plane trajectory convexity is used to identify the transient stability of the power grid. After the system is unstable, the dual-machine equivalence is carried out for the multi-machine power system regulated by the energy storage power supply, and the control quantity required by the energy storage power supply to restore the system stability in the single-machine system is calculated. The effectiveness of the control strategy was verified in the EPRI-7 system. The simulation results show that the transient stability emergency control strategy with energy storage power participating in the regulation can effectively improve the transient stability, reduce the emergency control failure, and inhibit the frequency and voltage reduction.

Transient stability emergency control for AC/DC grids considering successive commutation failures

The prevalence of Line-Commutated Converter (LCC) HVDC makes the coupling and interaction phenomenon between AC system and DC system of particular complicated. There are significant challenges to determine control strategy using state-of-the-art approaches especially when discrete events (e.g. switching and state resetting) happen frequently due to successive commutation failures (CFs). An enhanced transient stability emergency control (TSEC) for AC/DC grids based on the optimal control is presented to maintain the transient stability and mitigate the successive CFs caused by AC faults. In the proposed TSEC method, an extinction advance angle constraint is added to the TSEC model to mitigate the successive CFs. The emergency power control of LCC-HVDC is employed as an additional control measure to reduce generator-tripping and load-shedding amount. The direct sequential approach is adopted to obtain the optimal solution of TSEC to improve the calculation efficiency. In the direct sequential approach, the modified adjoint sensitivity analysis (MASA) with the consideration of adjoint jump conditions is utilized to increase the gradient calculation accuracy. The effectiveness of the control strategies and the accuracy of the sensitivity calculation are verified on two test systems.

Transient Frequency Stability Emergency Control for the Power System Interconnected With Offshore Wind Power Through VSC-HVDC

For the power system interconnected with the large-scale offshore wind power through VSC-HVDC, such as SZ power grid, it may be engaged with transient frequency stability and lack of related control due to the randomness, fluctuation and intermittence of the wind. This paper proposes a transient frequency control strategy for the power system interconnected with offshore wind power through VSC-HVDC based on sensitivity. Firstly, the structure of SZ power grid and the calculation method of transient frequency stability index are introduced, and the transient frequency problems existing in SZ power grid are explored. Secondly, the mathematical formulation for the transient frequency control is described, including the objective function and the constraints. Furthermore, a transient frequency emergency control strategy based on special sequence and the sensitivities is proposed, which includes thermal units regulation, wind power regulation, DC modulation and load shedding. Finally, the effectiveness of the proposed control strategy is verified by simulation in SZ power grid.

An Efficient Parallel Sequential Approach for Transient Stability Emergency Control of Large-Scale Power System

Generator-tripping and load-shedding are important emergency control measures to maintain the transient stability of the power system. In this paper, emergency control is modeled as a large-scale optimal control problem. An efficient parallel sequential approach, which consists of preprocessing layer, simulation layer, and optimization layer, is proposed to solve the problem. In the preprocessing layer, power system partitioning is performed to construct a Jacobian matrix of double-layered bordered block diagonal (BBD) structure, control variable selection and initialization are designed to reduce computation cost and improve convergence. In the simulation layer, the differential algebraic equations are solved in parallel with the sensitivity analysis by reusing the LU-factorizations. Based on the BBD structure of Jacobian matrix, a parallel block algorithm is proposed to further accelerate computation speed. In the optimization layer, the resulting nonlinear programming problem is efficiently solved by predictor–corrector interior point method. The efficiency and practicality of the proposed approach are verified by numerical experiments on three test systems.

Transient Stability Emergency Control Using Asynchronous Parallel Mixed-Integer Pattern Search

Special protection schemes (SPSs) are designed to monitor system conditions and apply control to avoid system collapse when subjected to a disturbance. Transient stability emergency control (TSEC) is a practical and effective SPS mechanism that utilizes generator tripping and load shedding as control actions to maintain system synchronism during severe contingencies, but faces significant challenges when it comes to a real-world grid of significant scale and complexity. In this paper, considering the characteristic of different control measures, TSEC problem is modeled as a mixed-integer nonlinear optimization problem with differential algebraic equation constraints. The proposed mixed-integer pattern search approach is able to obtain an optimal strategy without explicit derivative information of various complex component models. Furthermore, asynchronous parallelism is exploited and implemented to improve work-load balance and accelerate search procedure. Case studies on three different scale systems, including a real-world electric grid in China demonstrate that the proposed approach is promising to obtain TSEC strategy for large-scale power systems.

An Efficient Optimal Control Method for Open-Loop Transient Stability Emergency Control

With the expansion of modern power systems, the stability issues become more and more prominent. Transient stability emergency control is usually designed in open-loop schemes and applies proper actions to avoid system collapse when transient stability cannot be guaranteed in serious contingencies. Taking transient stability and economic efficiency of power system into consideration, the emergency control problem can be modeled as an optimal control problem, which is computational expensive. In this paper, an optimal control method with constraint aggregation is proposed to reduce computational complexity. The yield nonlinear problem is a fairly small-scale optimization problem which can be efficiently solved by predictor–corrector interior point method. The adjoint sensitivity analysis (ASA) is employed to evaluate the first-order derivative while Broyden–Fletcher–Goldfarb–Shanno (BFGS) algorithm is used to obtain the second-order derivative. Besides, very dishonest Newton (VDHN) method and reusage of LU factorization results are explored to accelerate the forward and backward integration phase of ASA, respectively. The proposed approach is tested on four cases with different scales, and shows its potential in computational efficiency.

Development of a WAMS based test platform for power system real time transient stability detection and control

The real-time transient stability detection and emergency control technology based on wide area response has become a hot research area in power system stability studies. Several different technologies have been proposed, but lots of problems remain to be solved before they can be applied in practice. A wide area measurement system (WAMS) based test platform is developed for transient stability detection and control. The design as well as main function modules of the platform are introduced. In addition, three generator power angle prediction methods and six response based transient instability detection technologies are given. Results of engineering application demonstrate that the developed test platform can provide a real-time operation environment, which can effectively compare and analyze the validity and practicability of these transient stability detection technologies. Based on the measured perturbed trajectories from actual power systems or the Real-Time Digital Simulators (RTDS), the platform can realize the assessment and visual result presentation of various responses from different transient instability detection technologies. The test platform can be applied to different power systems and it is convenient to embed new transient instability detection modules. Meanwhile some deficiencies and shortcomings in engineering application are pointed out and corresponding suggestions are given. In conclusion, the hardware and software structure, function modulus and engineering applications are presented. The application in actual power systems shows that it has a good application perspective.

Transient Stability Emergency Control Research Based on Critical Machine Unit

Self-healing ability is the basic requirement of smart grid. When a fault occurs, the control system should analysis transient stability on line and offer control measures quickly. This paper presents a fast and accurate transient stability emergency control measure. Based on the wide-area measures system, the sensitivity of critical-machine-unit stability index to controlled parameter is derived, and as one of transient stability constraints, sensitivity equation is incorporated into the nonlinear optimization algorithm to obtain the required emergency control amount. The method is simple and quick; the smallest cutting amount ensures load power supply, the simulation verifies the method’s superiority.

Study on power system transient instability detection based on wide area measurement system

AbstractIn this paper, a method, which is essential in initiating emergency control measures, is proposed for fast and accurate online detection of transient instability based on real‐time measurement. Under a certain disturbance, the candidate critical cluster (CC) of power system is predicted and refreshed at each sampling step. The method identifies the loss of synchronism at each time step by observing the geometric characteristic of the post‐fault trajectory of the generalized one‐machine equivalent system. Unlike the previous extended equal‐area criterion method, it is unnecessary to calculate the unstable equilibrium point (UEP) during instability detection in this method and some limitations caused by the time‐invariant assumption are also eliminated. Simulations are carried out on the IEEE 50 generator test system and a real power system. The simulation results indicate that the proposed method has the features of reliability and effectiveness in identifying the loss of synchronism with inter‐area mode. Copyright © 2008 John Wiley & Sons, Ltd.

A novel optimization method of transient stability emergency control based on practical dynamic security region (PDSR) of power systems

This paper proposes a novel optimization method of transient stability emergency control based on a new concept of the so-called extended practical dynamic security region (EPDSR) defined in this paper and four experiential laws about the EPDSRs found from a number of studies in real power systems. In this method, the effect of a control action is represented by the displacement of EPDSR’s critical hyper-plane boundary in the direction of its outer normal vector. If an unstable contingency occurs, appropriate emergency control actions are triggered so that the enlarged EPDSR can cover the current operating point. Based on these ideas, a mathematics model of emergency control strategy is developed for minimizing its total cost and guaranteeing power system transient stability. The simulation results on the 10-generator, 39-bus New-England Test System as well as other real power systems have shown the validity of this method.

Optimal placement of rotor angle transducers for power system stability

An optimal placement method of rotor angle transducers for power system stability is presented in this paper. For angle stability, information content of generator rotor angle responses to disturbances is an appropriate performance criterion of placement sites. To maximize information content, the method consists of three steps: clustering, grouping and selecting. After distinct dynamic scenarios are extracted by a hierarchical agglomerative clustering technique, a coherency identification step is implemented to form candidates and then placement sites are determined using Gram determinant as the information content measure. The proposed method is applied to a transient stability emergency control scheme in a practical power system. Simulation results demonstrate its rationality.

Generalized one-machine equivalents in transient stability studies

We consider an emerging class of hybrid methods which basically reduce a multimachine power system into a one-machine infinite bus (OMIB) equivalent and then apply the suitably adapted equal-area criterion. A time-domain transient stability program is used to refresh the OMIB parameters at each time step to arrive at "generalized" OMIBs. The scheme is able to provide accurate real-time transient stability assessment under any power system modeling, any stability scenario and any instability mode. On the other hand, similar generalized OMIBs may potentially be designed for real-time transient stability emergency control, by using real-time measurements. The purpose of this letter is to highlight some unique enhancements to the class of methods offered by the generalized OMIB concept.

A Method for Real-Time Transient Stability Emergency Control

Abstract We propose a method able to perform real-time transient stability emergency control. It relies on real-time measurements that it processes in such a way so as to infer multimachine power system stability from a one-machine equivalent. More precisely, the method attempts to : (i) assess in real-time the system stability; (ii) appraise the severity of instability, whenever detected; (iii) identify the location and size of corrective actions to be taken (e.g. how much generation to shed and (out of) which generator(s)). The use of the one machine equivalent is crucial to the method; in particular, it makes it able to predict (in)stability, to provide margins and to identify critical machines, in virtually negligible computing times even in comparison with the very short durations of transient stability phenomena. In this paper, a generation shedding scheme is further proposed. This, together with the overall transient stability emergency approach are illustrated on the Hydro-Quebec EHV power system.