Research On Stability-oriented Optimal Control For Microgrid Based On The Matrix Perturbation Theory

Microgrid is a small power supply and distribution network,which connects multiple loads and multiple power units with energy storage systems together by power electronic converter interface.However,on the basis of the stability,optimal control for microgrid has become an important research issue due to the inherent intermittency and randomness of power units.On the basis of careful analysis and summary for existing method of improving the small signal stability,Small signal model is established firstly and the stability boundary of dominant control parameters is gotten in this paper.Stability-oriented optimal control method for microgrid is presented based on the matrix perturbation theory secondly.Lastly,the simulation results proves the effectiveness of the proposed control strategy in this paper.Firstly,in this paper,the background and structure of microgrid are summarized.The importance of microgrid stability and analysis methods of small signal stability are expounded.And existing methods for stability-oriented optimal control method are summarized.Matrix perturbation theory and optimization algorithms are also introduced simply.And small signal model for the whole microgrid is established.Secondly,based on the example of this paper,the circuit parameters and measured variable value are collected into the coefficient matrix to solve the characteristic value and analyze the stability.The root locus diagram with droop coefficient for active and reactive power,and voltage controller and current controller parameters changing are drawn respectively.The dominant control parameters are found out,and then the correctness of the dominant control parameters which are gotten by the analysis for root locus diagram is verified by analyzing the characteristic value sensitivity.Stability boundary of dominant control parameters is solved by combining the root locus diagram with the data of characteristic value from MATLAB.Thirdly,the principle of optimal control is expounded in detail.The optimal control model for the first time,including small signal stability,damping ratio and stability margin is built.Because the optimal algorithm needs iteration during execution,the coefficient matrix needs to be formed repeatedly and the characteristic values need to be solved repeatedly.That results in a mount of computation,and the influence form of parameter perturbation on the system is also not clear.Therefore,the optimal control model for the first time is solved by the matrix perturbation theory combined with artificial fish optimal algorithm.The result for optimization for the first time is verified through characteristic value distribution and the histogram of damping ratio.In order to improve small signal stability further,the voltage amplitude and frequency deviation need to be reduced because the droop control is a kind of deviating regulation.Therefore,optimal control model again is established and solved by artificial fish algorithm.Finally,simulation model of microgrid with the proposed optimal control strategy for stability in this paper is established in MATLAB/SIMULINK.In the simulation,with public load disturbance and local load disturbance respectively,initial simulation model without joining optimization,simulation model of only joining optimal control for the first time and simulation model of joining optimal control again and optimal control for the first time are operated.The simulation results proves the validity and effectiveness of the proposed control strategy in this paper.And a PC interface of real-time monitoring is also made by upper computer software of VC++.