Small Disturbance Stability Analysis And Optimal Control Of DC Distribution System

The DC distribution system has the characteristics of good controllability,high reliability,and no need to consider power and frequency issues.It has received extensive attention from academia and industry at home and abroad.However,the DC distribution system is a typical power electronic system,which lacks rotational inertia and is vulnerable to disturbance and instability.How to improve the stability of DC distribution system has become a hot research topic.At present,there are few studies on the optimization of droop coefficient.This paper studies this problem.Through the perturbation analysis of the droop coefficient,combined with matrix perturbation theory,the corresponding optimization method is proposed.The main work of this paper is summarized as follows:Firstly,the influence form and degree of droop coefficient perturbation of DC distribution system on system state matrix are analyzed.A small disturbance model of DC distribution system is established.By writing the state space equation,the system state matrix is derived.It is found that the system state matrix has the characteristics of block and sparsity.The matrix perturbation theory is used to analyze the droop coefficient of each module.The influence characteristics of droop coefficient on each module of system state matrix are obtained.It provides a theoretical basis for the droop coefficient optimization process.Secondly,an optimization method of droop coefficient of energy storage converter based on matrix perturbation theory is proposed.A comprehensive objective function for multiple operating scenarios is established,taking into account the requirements of small disturbance stability,damping ratio and stability margin of the system.The SQP method is used to find the optimal solution within the threshold range.The parameters,characteristic solutions and objective functions of each module of the DC distribution system are updated until the termination condition is satisfied to obtain the optimal value of the droop coefficient.In the optimization process,the method of matrix perturbation theory is combined.The first-order perturbation term of the system characteristic matrix is solved directly.This method can guarantee the calculation accuracy and can be solved directly and quickly.Finally,the effectiveness of droop coefficient optimization based on matrix perturbation theory is verified by Simulink time domain simulation and RTBox experimental platform.Finally,an optimization design method of droop coefficient for multi-terminal DC distribution system based on perturbation theory is proposed.The objective function based on asymptotic stability,stability margin and damping ratio is established.When analyzing the droop coefficient optimization problem,the traditional eigenvalue analysis method and matrix perturbation theory are combined.According to the maximum perturbation range of the droop coefficient,the coordinated optimization of the droop coefficient is realized by controlling the eigenvalues.The proposed method can obtain the system eigenvalues more quickly under the premise of satisfying the solution accuracy,and also avoids the repeated formation of the system state matrix and the repeated solution of the eigenvalues in the solution process.Finally,the DC distribution system model with DC/AC inverters and DC/DC converters is built on the RTBox semi-physical experimental platform to verify the effectiveness of the proposed optimization method.In this paper,a small disturbance model of DC distribution system is established.Combined with the matrix perturbation theory,the droop coefficient is analyzed.The influence characteristics of droop coefficient on the state matrix of each module of the system are obtained.The droop coefficient optimization method based on perturbation theory is proposed to improve the stability and damping ratio of the system.