Research On Fast Corrective Control Strategy Considering The Synergy Of Multiple Flexible Control Measures

Corrective control is an important way to eliminate line overloads.It is essential for ensuring safe operation of the power grid.with the development of UHV AC and DC transmission technology and the application of flexible AC transmission systems(FACTS),the power of transmission lines has been greatly improved,making the power flow transfer caused by grid faults more serious,may cause overload of other lines or even cascading failures.Meanwhile,with the energy transformation,the access of high proportion of renewable energy makes the operation mode of power grids more changeable,the system operational safety is more challenged,and the corrective control(CC)strategy is put forward higher requirements.On the one hand,the complexity of the power grid is improved,and the CC strategy based on the direct current(DC)power flow model is more and more difficult to meet the accuracy requirements.On the other hand,the variety of operating modes puts higher demands on the rapidity of making CC scheme.At the same time,however,the application of FACTS,VSC-HVDC and other equipments,as well as the development of integrated electricity and gas systems(IEGS),which is expected to become a new carrier of energy transmission,have provided new ideas for CC strategy.It is of great significance to fully exploit the controllable resources of modern power grids and utilize the complementary characteristics of multiple energy sources to study the fast CC strategy with high accuracy and low control cost.In order to quickly eliminate the line overloads of power grid,from the perspective of the rapidity,accuracy and low cost of the corrective control scheme,this paper fully coordinate the use of controllable resources such as thyristor controlled series compensation(TCSC),VSC-HVDC,transmission switching(TS),and multi-energy complementary,carried out an in-depth study on fast corrective control strategy considering the synergy of multiple flexible control measures,from the following four aspects:(1)Aiming at the problem of high control cost caused by conventional corrective measures,a CC strategy considering TCSC and VSC-HVDC adjustment is proposed.The TCSC compensation degree and DC power are adjusted to quickly improve the power flow distribution,and to reduce the control cost.Firstly,it is deduced that the sensitivity of the TCSC compensation level to the active power flow of the AC line will change with the change of TCSC compensation level,thus it is difficult for sensitivity method to guide TCSC adjustment.This paper proposed a CC strategy by constructing a CC optimization model that takes into account the adjustment of TCSC and VSC-HVDC,and solving it with anintelligent optimization algorithm.Furthermore,in order to reduce decision variables and improve calculation speed,a heuristic search method based on affinity propagation(AP)clustering is proposed to automatically identify the generators and load nodes with the best adjustment effect on the overloaded lines.The verification results of the modified IEEE30-bus benchmark show that TCSC and VSC-HVDC can significantly reduce the load shedding of CC,and the heuristic search method can effectively improve computation efficiency and the operability of the CC scheme.(2)Aiming at the problem that conventional CC strategy is difficult to balance rapidity and accuracy,a second order cone programming(SOCP)based CC strategy considering adjusting TCSC and voltage source converter based multi-terminal HVDC(VSC-MTDC)is proposed to quickly and accurately obtain CC schemes.Firstly,the SOCP-based power flow model for grid with TCSC and VSC-MTDC is derived based on AC power flow model.Further,in order to ensure the accuracy of the relaxed model,an additional constraint of power loss is proposed.On this basis,taking TCSC compensation degree,DC power,generator power(continuous type)and load cut-off state(0-1 binary type)as decision variables,and the minimum load shedding and generator adjustment as the objective function,a CC optimization model based on mixed integer second order cone programming(MISOCP)is proposed.Aiming at improving the calculation efficiency of MISOCP,a two-stage fast solution method based on relaxation-correction is proposed,and the MISOCP model is transformed into SOCP model.The verification results of the modified IEEE30-bus benchmark show that the SOCP-based CC strategy greatly improves the generation speed of CC schemes under the premise of accurately responding to the preset power flow adjustment requirements.(3)Aiming at the problem that the DC power flow model based CC strategy considering TS is not accurate enough,a MISOCP based CC strategy considering TS and adjustment of multiple fast corrective measures is proposed.Firstly,the key points of the MISOCP power flow optimization model construction and acceleration solution method considering TS are analyzed.On this basis,the AC power flow model based MISOCP power flow model for power grid with changeable topology,TCSC and VSC-MTDC is derived,and the corresponding CC model considering TS and TCSC,VSC-MTDC adjustment is constructed.Furthermore,to improve the computational efficiency of MISOCP model,a heuristic double acceleration solution strategy is proposed.It consists of a heuristic line selection strategy to reduce the number of 0-1 binary variables based on comprehensive influence index of line outage,and an accelerated solution strategy for inducing objective function.Finally,based on the modified IEEE 57-bus benchmark,the effectiveness of theproposed method is verified,and the superiorities of the proposed method in terms of adjustment effect,computation efficiency and accuracy are verified.(4)For the safe operation of IEGS with power grid as the core,considering the complementary relationship between energy transmission networks,an IEGS convex power flow model is constructed based on MISOCP power grid model,and a coordinated CC strategy considers the two-way coupling relationship of electricity and gas networks is proposed.Firstly,for the gas network,it is analyzed that the SOCP-based power flow model is not tight enough,thus to make it tighter,for one-way or two-way flow of natural gas in the pipeline,improved one-way and two-way convex model of the gas network are proposed.Then,for the power grid,in order to further reduce the load shedding,a frequency relaxation strategy considering the generator and load active power-frequency regulation characteristics is proposed,and a corresponding flexible power flow convex model is constructed.On this basis,a coordinated CC optimization model considering the electric-gas two-way coupling relationship is constructed.The modified IEGS example(formed by the IEEE 118-bus grid and the Belgian 20-node natural gas network)shows that the proposed coordinated CC strategy is highly flexible,and the grid-gas network coupling helps reduce the load shedding amount and wind curtailment.