Rotor angle stability-constrained dispatch and control of large-scale wind penetrated power system

• Main Author: Yuan, Heling
• Other Authors: Xu Yan
• Format: Thesis-Doctor of Philosophy
• Language: English
• Published: Nanyang Technological University 2022
• Subjects: Engineering::Electrical and electronic engineering
• Online Access: https://hdl.handle.net/10356/162119
• Institution: Nanyang Technological University

With the development of technology and the requirement of environment, the penetration of renewable energy resources in power systems has dramatically increased recently. Though wide use of wind power is beneficial to environment and economy, it could bring technical issues to power system stability due to its intermittency and uncertainty as well as non-synchronous nature. In general, four main effects on power system transient stability are: 1) wind generation has no contribution to system inertia and system with synchronous generators replaced by wind turbines will lead to reduction of inertia, 2) power electronics converter-based interfacing is added when wind turbines are implemented, which will change the dynamic behavior of the system, 3) power dispatch of synchronous machines will change fast to compensate wind power variation, 4) the magnitude and direction of power flows will fluctuate quickly and randomly in the transmission lines. Hence, it is an essential and significant problem to maintain system’s stability with high level wind power penetration. Transient stability assessment (TSA) is conducted to determine if the system is stable. If the system is found to be unstable, transient stability control action needs to be conducted to retain the stability of the system. Generally, control actions can be mainly divided into two categories: preventive control (PC) and emergency control (EC), depending on its implementation time. Based on Extended Equal Area Criterion (EEAC) method, which can provide stability level and classify critical machines (CMs) and non-critical machines (NMs) and sensitivity concept of generators, a new PC approach is proposed to optimally balance the wind power variation by rescheduling synchronous generators while maintaining the transient stability for credible contingencies. The whole problem is formulated as a linear programming (LP) problem with stabilization constraints, which is computationally efficient and transparent to solve. Furthermore, by adding EC (such as load shedding) to maintain transient stability, a coordination method of generation rescheduling and load shedding is proposed for the enhancement of transient stability while considering uncertain wind power output. For the sake of minimizing the total coordination cost, a bi-level optimization model is developed. Firstly, A risk coordination parameter is defined to adjust the total coordination cost on the upper level and the lower level is for generation rescheduling and load shedding. Then, uncertain wind power output is strategically selected as a small number of testing scenario and solved in load shedding model. Finally, golden section search method is applied to solve the bi-level problem. The proposed method is validated on the New-England 39-bus system. The efficiency, economic optimality, and stability robustness are demonstrated. However, the scenario-based uncertainty model cannot guarantee the full robustness, i.e., 100% robustness against wind power uncertainties. In current research, robust optimization has been demonstrated as an effective approach to deal with uncertainties and ensure the robustness. Hence, a robust optimization approach for coordinating generation dispatch and emergency load shedding (ELS) against transient instability under uncertain wind power output is developed. The problem is modelled as a two-stage robust optimization (TSRO) model considering transient stability constraints, where the first-stage is to optimize the generation dispatch (PC) before a contingency and the second-stage decision is the ELS (EC) after the contingency occurrence under the worst case of wind power variation. To solve this TSRO problem, a solution algorithm which integrates TSA and transient stability constraint construction in a column and constraint generation (C&CG) framework is proposed. The proposed method is validated on the New-England 39-bus system and the Nordic32 system, which shows high computational efficiency and stability robustness against uncertain wind power over conventional deterministic methods. In addition, there will be a conflict between the economic and stability objectives in high wind penetrated power systems. Meanwhile, transient stability and small signal stability may have positive/negative correlations subjected to generation dispatch. Hence, a multi-objective optimal power flow (OPF) method that can compromise these objectives while considering wind power uncertainties is employed to achieve the trade-off among the generation cost, transient stability, and small signal stability. The model is solved by a mature multi-objective evolutionary algorithm (MOEA) and the proposed method is tested on a New-England 10 machine 39 bus system. The Pareto solutions have verified the optimality, effectiveness, and robustness of the proposed method.