Optimal power flow considering voltage stability with significant wind penetration

Abstract

Voltage stability evaluation is one of the major issues in the power system operation and control. One reason is that there is an enormous number of voltage collapses which frequently occurs. The principal objective of this thesis is to choose appropriate criteria for voltage stability evaluation in optimal power flow (OPF) approach considering the worst contingency or the congested condition. Voltage stability can be affected by several elements and control ways which operate on different time scales. In particular, the role of wind power generation, demand response (DR), over excitation limiter (OXL), energy storage system (ESS) and on-load tap changer (OLTC) are significant. The proper modelling of these elements and control ways as well as using in an OPF approach should be analyzed in longterm voltage stability. First, an impedance-based (IB) index is presented in this thesis that can evaluate unstable behavior of the power system with doubly-fed induction generator (DFIG) wind farms integration. A model for DFIG capability curve limits is presented that can be integrated to the internal circuit of the generator. Furthermore, the OLTC model was added to this index. The index uses the concept of coupled single-port circuit. The OPF with new IB-index constraint is implemented to show the performance of the index. This study also introduces a multi-objective stochastic optimal power flow (SOPF) approach with the presence of uncertain wind power generations. The multi-objective SOPF investigates the operating cost, voltage stability and emission effects as the objective functions. The effect of the DR program is considered in this study. The fuzzification technique is used to normalize all objective functions in the multi-objective SOPF. A line voltage stability index (LVSI) is presented and compared with other LVSIs. The proposed multi-objective SOPF is also carried out with different existing LVSIs as the objective functions. Following the voltage stability assessment, the frequency control is also considered in the SOPF. In this case, the frequency restoration scheme cooperates with DR and spinning reserve to stop a frequency drop in contingency events. This scheme is defined in three levels. Furthermore, an extended-L (EL) index is used to evaluate voltage stability analysis. Several frequency and voltage constraints are added in the SOPF approach. The EL-index considers a generator equivalent model (GEM). In addition, energy storage systems (ESSs) are considered in this SOPF approach. Those approaches are analyzed in detail and they are tested and validated on several case studies. The results show that the proposed approaches operate successfully.

Date	18 Jul 2017
Original language	American English
Awarding Institution	École de technologie supérieure
Supervisor	Louis-A. Dessaint (Supervisor)