Power Dispatch Optimization Model For Grid Resilience Enhancement And Its Evaluation Method

The power system is an important infrastructure that supports social and economic development and guarantees people's reasonable living standards.Power security is an important part of national security.In recent years,extreme natural disasters have occurred frequently,seriously threatening the safe operation of power grids.In order to assess the ability of the grid to cope with extreme natural disasters,the concept of resilience is introduced into the grid.Research on the assessment methods and improvement measures of grid resilience to improve the safe and reliable operation of the grid in extreme natural disasters is essential for the normal development of modern society.Power dispatch optimization is a key part of power system operation control and plays an important role in the safe and economic operation of the power grid.Based on this,this thesis investigates the power dispatch optimization model for improving grid resilience and its evaluation method.It should be noted that grid resilience behaves differently under different natural disasters,so the type of disaster targeted should be clearly defined when studying grid resilience.Among all extreme natural disasters,typhoon disaster is one of the most serious and frequent disasters that threaten the safe operation of China's power grid.Therefore,this thesis investigates power dispatch optimization models that consider the impact of typhoon disasters on overhead transmission lines of power grids to improve the ability of power grids to withstand typhoons.The main contents and main contributions of this thesis are summarized as follows:(1)A grid resilience assessment method considering transmission line cascading overload outages under typhoon hazards is proposed.First,the wind-induced outage model and overload outage model of overhead transmission lines are developed,and then,a grid resilience assessment model based on the OPA cascading failure simulation model is proposed.Finally,eight resilience assessment metrics are defined in terms of the number of outage lines,and the maximum and average load loss percentages to quantitatively describe the distribution of blackout sizes during typhoon disasters and compare the resilience of different systems or the same system under different operation strategies.In the case study,by comparing with the current resilience assessment model that only considers wind-induced outages on overhead transmission lines,it is found that the resilience assessment method proposed in this thesis fully takes into account the risk of possible cascading failures on transmission lines during typhoon disasters,which can better reflect the impact of extreme disasters on the grid and help grid dispatchers to develop more resilient power dispatch schemes.(2)From the perspective of preventing outages caused by overloads,a new Q_(N-k)-1contingency set generation method is proposed,and a unit commitment optimization model considering the security constraints of Q_(N-1)-1 and Q_(N-2)-1 outages of the affected lines is developed.The considered security constraints can minimize the fully loaded lines(line flow exceeding the normal limit)after N-1 or N-2 outages on one hand,and keep the remaining lines of the grid from being overloaded(line flow exceeding the long-term emergency limit)on the other hand,avoiding cascade overload outages to a certain extent.A decomposition algorithm based on the line outage distribution factor is proposed to address the difficulty of solving the security-constrained unit commitment problem with a large number of N-k and Q_(N-k)-1 security constraints.The effectiveness of the model and algorithm is verified by simulations of the modified IEEE 30-bus and 118-bus systems.The power dispatch scheme obtained from the proposed model is evaluated and compared with the power dispatch scheme obtained from the traditional security-constrained unit combination models by using the resilience assessment method and indexes given in Chapter 2.The case studies show that the proposed model can reduce the probability of overload outages caused by wind-induced outages of transmission lines under typhoon disasters,thus reducing the amount of load loss and improving the resilience of the grid against typhoons.(3)A multi-objective DC optimal power flow model that takes into account the loading rate of the affected lines and the uniformity of the loading rate of all lines is proposed.Since the objective function and constraints of the proposed model are built based on the absolute value function,it is a nonlinear optimization problem,which is difficult to be solved directly using existing commercial optimizers.In this thesis,a method is given to transform it into a mixed-integer linear programming problem by introducing auxiliary variables and auxiliary constraints,and a two-stage optimization method is proposed for the problem of too many integer variables in large system applications.Simulations performed on the modified IEEE30-bus and 118-bus systems verify the effectiveness and efficiency of the model and solution method.The power dispatch scheme obtained from the proposed model is evaluated and compared with the power dispatch scheme derived from the traditional security-constrained optimal power flow model by using the resilience assessment method and metrics proposed in Chapter 2.The case studies show that,compared with the traditional N-k security-constrained optimal power flow model,the proposed model improves the grid resilience through the grid power flow distribution without generating planned load shedding,which provides a normal power supply to the consumer before outages occur.(4)A robust N-k security-constrained DC optimal power flow model with coordination of preventive control and corrective control is proposed to address the problems that the traditional corrective security-constrained optimal power flow model is not reliable enough and the preventive security-constrained optimal power flow model is too conservative.A solution method is designed based on the column and constraint generation algorithm.The optimization results of the proposed model include not only a power dispatch scheme for the base state but also the maximum load shedding required to adjust the line flow below the long-term emergency limit under contingency conditions,which provides a reference for the grid operators to develop disaster prevention and mitigation strategies.Simulations performed on the modified IEEE 30-bus and 118-bus systems verify the effectiveness of the models and solution methods.Resilience assessment simulations show that,compared with the traditional corrective control model,the power dispatch scheme obtained from the proposed model is much more resilient;compared with the traditional preventive control model,the model has a relatively higher resilience assessment index,but reduces the amount of planned load shedding at base state.This enables the system to ensure power supply at the base state,and achieve a compromise between operational cost and operational risk.