(1990). ENERGY FUNCTION ANALYSIS FOR POWER SYSTEM STABILITY. Electric Machines & Power Systems: Vol. 18, No. 2, pp. 209-210.

Energy function analysis for power system stability

Power system emergency control is generally regarded as the last safety net for grid security and resiliency. Existing emergency control schemes are usually designed off-line based on either the conceived “worst” case scenario or a few typical operation scenarios. These schemes are facing significant adaptiveness and robustness issues as increasing uncertainties and variations occur in modern electrical grids. To address these challenges, this paper developed novel adaptive emergency control schemes using deep reinforcement learning (DRL) by leveraging the high-dimensional feature extraction and non-linear generalization capabilities of DRL for complex power systems. Furthermore, an open-source platform named Reinforcement Learning for Grid Control (RLGC) has been designed for the first time to assist the development and benchmarking of DRL algorithms for power system control. Details of the platform and DRL-based emergency control schemes for generator dynamic braking and under-voltage load shedding are presented. Robustness of the developed DRL method to different simulation scenarios, model parameter uncertainty and noise in the observations is investigated. Extensive case studies performed in both the two-area, four-machine system and the IEEE 39-bus system have demonstrated excellent performance and robustness of the proposed schemes.

Adaptive Power System Emergency Control Using Deep Reinforcement Learning

This paper presents new results on the applications of reachability methods and computational tools to a twoarea power system in the case of a cyber attack. In the VIKING research project a novel concept to assess the vulnerabilities introduced by the interaction between the IT infrastructure and power systems is proposed. Here we develop a new framework and define a systematic methodology, based on reachability, for identifying the impact that an intrusion might have in the Automatic Generation Control loop, which regulates the frequency and the power exchange between the controlled areas. The numerical results reveal the weaknesses of the system and indicate possible policies that an attacker could use to disturb it.

Cyber attack in a two-area power system: Impact identification using reachability

The objective of power system controls is to keep the electrical flow as well as voltage magnitudes within acceptable limits in spite of the load and network topology changes. The control of voltage level is accomplished by controlling the production, absorption as well as flow of reactive power at various locations in the system. This paper presents an approach to determine a real-time system protection scheme to prevent voltage instability and maintain a desired amount of post-transient voltage stability margin (an index of system security) following the occurrence of a contingency by means of reactive power control. This approach is based on the model predictive control (MPC) theory. According to an economic criterion and control effectiveness, a control switching strategy consisting of a sequence of amounts of the shunt capacitors to switch is identified for voltage restoration. The effect of the capacitive control on voltage recovery is measured via trajectory sensitivity. The sensitivity of voltage stability margin with respect to the capacitive control is used to construct a security constraint for post-fault operation in the MPC formulation. The efficacy of the proposed approach is illustrated through applications to the WECC system for enhancing the voltage performance and to the 39-bus New England system for preventing voltage collapse.

/pdf/model-predictive-control-based-real-time-power-system-4t14lrpzh3.pdf

Model Predictive Control-Based Real-Time Power System Protection Schemes

This paper presents a numerical procedure for the reachability analysis of systems with nonlinear, semi-explicit, index-1 differential-algebraic equations. The procedure computes reachable sets for uncertain initial states and inputs in an overapproximative way, i.e. it is guaranteed that all possible trajectories of the system are enclosed. Thus, the result can be used for formal verification of system properties that can be specified in the state space as unsafe or goal regions. Due to the representation of reachable sets by zonotopes and the use of highly scalable operations on them, the presented approach scales favorably with the number of state variables. This makes it possible to solve problems of industry-relevant size, as demonstrated by a transient stability analysis of the IEEE 14-bus benchmark problem for power systems.

/pdf/reachability-analysis-of-nonlinear-differential-algebraic-2yw59xsgct.pdf

Reachability Analysis of Nonlinear Differential-Algebraic Systems

http://home.eng.iastate.edu/~rkumar/PUBS/power-reach.pdf

Reachability analysis based transient stability design in power systems

This paper proposes an optimization-based method of planning reactive power control for electric transmission systems to endow them with the capability of being reconfigured to a secure configuration under a list of contingencies. The overall objective function is to minimize the installation cost of new controls such as mechanically switched capacitors, while satisfying the requirements of voltage stability margin and voltage magnitude under a contingency list. The backward/forward search algorithm with linear complexity is used to select candidate locations for switched capacitors. Optimal locations and amounts of new switch controls are obtained by solving a sequence of mixed integer programming problems. The modified New England 39-bus system and a North American power system with 6358 buses are adopted to illustrate the effectiveness of the proposed method.

Planning Reconfigurable Reactive Control for Voltage Stability Limited Power Systems

This paper presents a reachability based method to compute the stability region of a stable equilibrium point and uses it to design controls for transient stability of power systems. First, a Hamilton-Jacobi-Isaacs (HJI) partial differential equation (PDF) is obtained for the propagation of the backward reachability set of a nonlinear system. This computation when used to obtain the backward reachable set of a stable equilibrium point yields its stability region. Using the stability regions of various discrete controls (also called modes) transient stability design is performed. For example the effectiveness of a control can be verified by checking whether a post-fault initial state is in the stability region of the system with that control switched on. We illustrate our method by applying it to a single-machine infinite-bus system equipped with series and shunt capacitive compensation.

/pdf/power-system-transient-stability-design-using-reachability-1gxemsz63l.pdf

Power system transient stability design using reachability based stability-region computation

This paper proposes a new optimization based algorithm to plan the minimum amount of switched shunt and series capacitors to restore the voltage stability of a power system after severe contingencies. Through parameterization of severe contingencies, the continuation method is applied to find the critical point. Then, the backward/forward search algorithm with linear complexity is used to select candidate locations for switched shunt and series capacitors. Next, a mixed integer programming formulation is proposed for computing locations and amounts of switched shunt and series capacitors to withstand a planned set of contingencies. A linear programming formulation is utilized to further refine the compensation amounts. The approach is illustrated using the New England 39-bus system.

Licheng Jin

Papers

Model Predictive Control-Based Real-Time Power System Protection Schemes

Reachability analysis based transient stability design in power systems

Planning Reconfigurable Reactive Control for Voltage Stability Limited Power Systems

Power system transient stability design using reachability based stability-region computation

Planning minimum reactive compensation to mitigate voltage instability