| With the rapid development of power grid cross-regional interconnection and power market,it has brought significant economic benefits,and it also brings serious challenges to the safe and stable operation of power system.The optimization of reactive power flow in power systems is one of the effective means to coordinate the economic and safe operation of power systems.The traditional reactive power optimization mainly aims to reduce the system active power loss,ensure that the voltage value of each bus meets the requirements,and improve the economical operation of the system.It is suitable for the system with sufficient margin of transmission capacity.However,due to the increasing demand for load,the proportion of long-distance transmission continues to increase.With the system load increased,the transmission capacity of the system is likely to be close to its operating limit,which makes it easy to induce a grid collapse accident characterized by voltage collapse.At the same time,while adjusting the reactive power control device to reduce the network loss,it will inevitably change the reactive power distribution of the system and affect the voltage stability margin of the system.Therefore,it is necessary to consider the voltage stability margin of the system during the reactive power optimization process.Therefore,this paper has carried out related research on reactive power optimization of power system considering static voltage stability margin.The main contents include:(1)A linear search-trust region algorithm is proposed to improve the computational process of the linear programming method for solving the reactive power optimization model.This paper introduces the research status and solving algorithm of reactive power optimization in power system,the research status and analysis methods of voltage stability,and the research status of reactive power optimization considering voltage stability.For the nonlinear model of traditional reactive power optimization,the linear programming algorithm is widely used to solve the problem.The objective function and constraints are linearized by the sensitivity matrix,in which the correlation sensitivity coefficient of the transformer tap is deduced in detail.A linear search-trust region algorithm is proposed to determine the search direction and step size of each iteration in linear computation,which is helpful to improve the computational speed and convergence efficiency.The effectiveness of the algorithm is verified by Ward&Hale 6 system.(2)Establish a multi-objective reactive power optimization model considering the constraint of voltage stability margin,based on the relationship between reactive power reserve and voltage stability and the relationship between voltage stability margin and reactive power control variables.The reactive power sensitivity of the generator to load is proposed,and the weight coefficient of each generator is obtained.The direct method is used to derive the sensitivity coefficient of the static voltage stability margin to each reactive control device,and the voltage stability margin is directly added to the constraint as an inequality constraint.The maximum of the system reactive spare capacity is also added as one of the objective functions.The model is linearized according to the sensitivity matrix,and the linear model is solved by the linear search-trust region algorithm proposed in(1).Case study verifies the correctness of the model and the effectiveness of the algorithm.(3)Propose a calculation method of static voltage stability margin considering optimal reactive power support.The effect of the automatic voltage control system(AVC)system on the system voltage is not considered in the process of calculating the static voltage stability margin using the conventional continuous power flow method.Reactive power optimization is an important part of the AVC system.The various reactive power control devices ensure that the voltage is within the specified range and affect the voltage stability margin.The PV curve obtained by the conventional continuous power flow through the estimation-correction method shows that as the power of the specified load bus increases,the voltage of each bus has a downward trend.Since the AVC is not considered to support voltage of the bus,the calculation result is slightly conservative.Therefore,an improved continuous power flow method is proposed to calculate the static voltage stability margin.Case study verifies the correctness of the proposed model and the necessity of considering reactive power optimization configuration in the calculation process of the continuous power flow. |
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