Research On Continuous Power Flow For Hybrid AC/DC Microgrid

The AC/DC hybrid microgrid refers to a microgrid that contains AC bus and DC bus and interconnected converters that connect the AC bus and DC bus,and can supply power directly to AC loads or DC loads.Continuous power flow(CPF)can solve the singular problem of nonlinear equations well,and it is a powerful tool for calculating static voltage stability analysis of power systems.The operation mode of the AC/DC hybrid microgrid is flexible and diverse,and there is a coupling relationship between the AC and DC power under the operation of the interconnected converter,which makes the CPF calculation in different operation modes different from the single power supply microgrid.This paper studies the continuous power flow calculation of AC-DC hybrid microgrid,the main work is as follows:1)The operation modes of hybrid AC/DC microgrid system is analyzed,and a continuous power flow algorithm based on Accelerated LM Algorithm with Non-monotone Linear Search(ALMNL)is proposed.Four basic operation modes of AC/DC hybrid microgrid are analyzed.Combined with the distributed generator(DG)device and the overall control method of microgrid,six types of operation systems under different operation modes of AC-DC hybrid microgrid are formed and analyzed.The mathematical model of CPF and its main calculation links are given,and a continuous power flow algorithm based on Accelerated LM Algorithm with Non-monotone Linear Search is proposed to reduce the amount of calculation and increase the convergence speed.The CPF calculation simulation analysis of AC and DC microgrid system is carried out.2)When the change load is on one side,a continuous power flow calculation method of AC/DC hybrid microgrid based on unidirectional prediction and correction is proposed,taking into account the impact of intermittent DG output uncertainty.The CPF model of the AC-DC hybrid microgrid is established,and the optimal scenario generation method based on Wasserstein distance is used to construct the discrete optimal scenario of wind power and photovoltaic output.A CPF method based on unidirectional prediction and correction is proposed for different areas where the changing load is located: only the subsystem where the changing load is located is required for prediction and correction calculation,while the subsystem without changing load is solved for conventional power flow calculation.The key of the initial point and correction calculation is the solution of the deterministic power flow equations,and the CPF calculation is performed on the droop coordinated control AC-DC hybrid microgrid example system to verify the correctness and effectiveness of the proposed method.3)Under the condition that both AC and DC sides have varying loads,a bidirectional prediction and correction method for AC/DC hybrid microgrid continuous power flow is proposed.Based on the analysis of CPF of AC/DC hybrid microgrid system under the change load on both sides,the load static characteristics in line with the actual operation are studied,and the unified continuous power flow calculation model of AC/DC hybrid microgrid under different operation modes is formed.In order to verify the correctness and validity of the proposed method,the CPF calculation is carried out for the AC-DC hybrid microgrid with variable load on both sides.4)A method of CPF calculation for microgrid based on Chord method is proposed.Aiming at the problem of large calculation amount and singularity of voltage stability critical point,the improved iterative Chord method is applied to the CPF calculation of microgrid,and the convergence speed of the algorithm near the singularity point is analyzed.According to the constraints of microgrid system in the process of load growth,the constraints of different node types and their corresponding node type conversion methods are analyzed,and the influence of node type conversion on continuous power flow calculation is considered.The proposed method is used to calculate the CPF of microgrid system to verify its correctness and effectiveness.