Research On Comprehensive Controls For Enhancing Static Voltage Stability Of Power Systems

The safe and stable operation of the power system is an essential guarantee for maintaining the development of the national economy and people’s livelihood.With the continuous expansion of the power system scale and the increasing of power load,the problem of voltage stability of the power system has become increasingly prominent.Many large-scale power outages have been caused by voltage stability problems on a global scale,causing substantial economic losses and severe social impacts.Therefore,it is of great significance to take effective enhanced control measures to improve the static voltage stability of the power system.Previous studies,adopt a single control measure to improve the load margin of the power system,which often contains too many control quantities and has a limited effect on optimizing the load margin.In practice,system operators often prefer to adjust fewer control variables to keep the system within the voltage stability expectation domain,so it is especially important to improve the static voltage stability of power systems by adopting a small number of control variables and integrating multiple control measures.It conducts an in-depth study on the comprehensive control strategy for power system voltage stability based on these situations in this dissertation.The main contents include:There are a large number of control variables in the power system.To quickly screen out the control variables that effectively improve the system load margin,this dissertation introduces the calculation of the continuous power flow method and sensitivity method,and derives the formula for calculating the sensitivity between the load margin and each control variable.To reduce the 0/1 variables corresponding to each control measure in the optimization model proposed in this dissertation,the sensitivity is used as an indicator to measure the optimization effect of each control measure on the system load margin,and the set of candidate variables that effectively improve the load margin is quickly screened out.To achieve the goal of enhancing the static voltage stability of the power system by synthesizing multiple control measures,a method of source-network coordination optimization is proposed to improve the load margin of the power system in this dissertation.This method constructs an optimization model of the core backbone grid of the power network through transformer tap adjustment and transmission line switching.On this basis,the active power output adjustment of the generator is introduced to improve the system load margin.In the optimization of the power network structure,the load margin of the system meets the set upgrading requirements as the target,and the constraints include the maximum number of adjustable transformers and the maximum number of switching lines,the transformer tap adjustment and switching lines are calculated based on the sensitivity method,and finally determine the load margin under the optimization of the power network structure.In the calculation of generator active power output adjustment,to minimize the workload of operators,a generator optimal adjustment model that integrates economy and static voltage stability is proposed in this dissertation.The model aims to minimize the number of generators involved in the adjustment and minimize the cost of power generation.The constraints include that the system load margin meets the set lifting requirements and the safe operation of the power system.The mathematical essence of the problem is a multi-objective nonlinear mixed integer programming problem.To solve the above problem,the linear sensitivity method is used to quickly estimate the generator that needs to adjust the output,and the integer programming problem that minimizes the number of controls is solved.Then,aiming at the minimum power generation cost,the linear programming method is used to solve the adjusted output value of each generator.Finally,the specific set of generators to be adjusted and their adjustment amounts are determined.Numerical studies are carried out in IEEE 39-bus and IEEE 118-bus power systems to verify the effectiveness of the proposed method.