The Application Of Nonlinear Equivalent Principle In Continuous Power Flow Calculation Considering Generator Current Constraints

The method of Continuous power flow is one of the important methods of static voltage stability analysis in power system.It can accurately calculate the margin of system voltage stability.Continuous power flow(CPF)algorithm is an improved flow algorithm by introducing the parameter into a one-dimensional correction equation to solve the problem of Jacobi matrix singularity.In the continuous power flow calculation,when in the restraint of reactive power,the PV nodes is converted to PQ nodes.The traditional processing method is only to take the reactive power as a limiting condition and has nothing to do with the node voltage.However,in the actual operation of the system,with the increase of the load power,generator reactive power limits does not ensure that value is equal to the constraints,but it changes along with the change of voltage.Therefore,the voltage stability margin calculated by considering only reactive power constraints is larger.For these reasons,this paper puts forward a control flow algorithm by thinking about both the generator stator currents constraints and rotor current constraints.This algorithm is used for the more preciseness of generator reactive power support ability,and it can solve the current problem,which is that the reactive power of the generator changes over voltage.For not satisfying the stator current and rotor current constraints conditions of the generator node,the solution is to carry on the node type convertion with using two types of extension node which are named as P-I_a(Active power and stator current constraints)node and P-E_q(Active power and rotor current constraints)node.When the stator current or rotor current is limited,to establish a function relationship about the injection node power and the node voltage,Furthermore,to fix the Jacobi matrix related parameters.With the increase of the load,the Jacobi matrix of power flow equation will be gradually singular to make power flow calculation no longer convergence,thus it is unable to accurately obtain the voltage stability limit,and the workload of calculating the voltage stability power flow limit will be bigger.therefore,the article presents a nonlinear equivalent method for analysising the static voltage stability.This method both avoids the repeated iterative calculating power flow equation and resolves the problem that the regular power flow is without solution at the point of collapse and have no reliable convergence around the point of collapse.Through the higher-order derivative of the injection system power parameter in power flow equations and the compound function chain derivation rule,the nonlinear equivalent model of node voltage and load current about the current mode is established.That power limit criterion shows that a necessary condition for reaching the critical state of the system is a dynamic equivalent impedance module exactly equal to the static load equivalent impedance module.With the nonlinear equivalent model of voltage and current as well as the limit current criterion,we can rapidly forecast the power flow limit of system in an initial state,and accurately predict the calculation step of the continuous power flow.In NewEngland10 machine 39 node simulation,we can verify the correctness and effectiveness of the application of nonlinear equivalent,considering both generator stator constraints and rotor current constraints.