| The development and construction of islands and remote areas rely on reliable power supply.Microgrid technology is one of the core key technologies for the orderly control of distributed new energy equipment and efficient energy utilization in islanded power systems in remote areas.Islanded microgrids have characteristics such as small system capacity,weak overcurrent capability of power electronics equipment,diverse operating modes,strong coupling between multiple units,etc.At the same time,due to factors such as harsh environments,extreme weather,and improper personnel operation,islanded microgrids often face large disturbance shocks.Disturbances include short circuit faults,heavy overload,and sudden changes in output of new energy units,which cause serious transient stability operation problems such as synchronous instability,voltage instability,and frequency instability.This paper focuses on the transient synchronization stability problem of islanded microgrids considering microsource control switching.This paper aims to solve problems such as transient synchronization stability modeling,analysis,transient stability evaluation,and control of islanded microgrids.The main research results are summarized as follows:(1)Various types of voltage control inverter power control loops make it difficult to analyze the impact of different power control loop parameters on the transient synchronization stability of inverters.This paper reveals the equivalent relationship between different power control loops,and proposes a large-signal unified model for transient synchronization stability of voltage control inverters.The effects of various power control loop parameters on the transient synchronization stabilit y of voltage control inverters are also compared and analyzed.There are many types of voltage-controlled inverter’s control in islanded microgrids.There are also many parameters that affect the transient synchronization stability of inverters,which makes it difficult to analyze the transient synchronization stability of various voltage-controlled inverters.By comparing the characteristics of active/reactive power control loops,a unified model considering different active/reactive power control loops are established.Then a large-signal unified model for transient synchronization stability of voltage control inverters is established.On this basis,the impact of power control loops’ parameters on the first swing stability and global stability of inverters is analyzed.The study shows that increasing the damping coefficient of the inverter helps to improve its transient synchronization stability.Increasing the virtual inertia of the inverter can improve its first swing stability but will reduce its global stability.(2)Current-limiting control strategies makes the analysis of the mechanism of transient synchronization instability complex.This study addresses the problem of non-linear changes in transient synchronization characteristics of inverters caused by current-limiting control strategies.The impact of three different current-limiting control strategies on the transient synchronization stability of voltage-controlled inverters is compared and analyzed.The main control parameters affecting the transient synchronization stability of inverters are also analyzed.For inverters using mode-switching current limiting control strategy,an equivalent analysis model considering mode-switching control was established.Then the transient synchronization characteristics of the inverter under different operating m odes were analyzed.Additionally,for inverters using virtual impedance current limiting control strategy,an analysis model and power angle curve considering virtual impedance control were established.Then the influence trend and characteristics of virtual impedance control on the transient rotor angle operation of the inverter were analyzed.Finally,the impact of current limiter on the transient power angle operation of inverters is compared.The research found that reducing the reference active pow er can improve the transient synchronization stability of inverters using different current-limiting control strategies.For inverters with current limiter or virtual impedance control,the shorter the fault duration,the better the transient synchronization stability of the inverter.For inverters using mode-switching control,the fault duration has nothing to do with its transient synchronization stabi lity.(3)Aiming to solve the problem of singularity in the inverters’ model caused by current-limiting control and the conservatism in the stability domain evaluation of traditional Takagi–Sugeno(TS)fuzzy method,this study proposes an active TS fuzzy transient stability domain evaluation method for islanded microgrids.Firstly,the mechanism of the singularity problem in microgrids’ model caused by current-limiting control strategy is revealed.A smooth processing method for inverters’ model considering current-limiting control strategy is proposed.Secondly,based on this method,the model of a micogrid with virtual impedance current limiting control and current limiter control is established.Finally,the reasons for the conservatism in the traditional TS fuzzy transient stability domain evaluation method for islanded microgrids are analyzed.Then an active search-based TS fuzzy transient stability domain evaluation method is proposed,which does not require determining the parameters search direction when evaluating the attraction domain.The proposed method effectively reduces conservatism of the evaluated attraction domain.(4)In response to the problem of rapid parameter changes in islanded microgrids caused by current-limiting control and the difficulty of fast transient synchronization stability control,a decentralized robust control method for transient synchronization stability in islanded microgrids is proposed.Firstly,a decentralized coordination control architecture for islanded microgrids based on multi-agent ideas is proposed,and then a transient power controller suitable for transient stability regulation of inverters is proposed based on this architecture.The impact of transient power controller parameters on the transient synchronization stability of inverters is analyzed,and the parameter selection range of the transient power controller is determined.Considering the impact of current-limiting control strategy on the islanded microgrid model,a feedback linearization decentralized robust control model for microgrids considering uncertain parameters is establish ed.Then a corresponding decentralized robust controller design method is proposed.This method ensures effective current limiting of inverters while achieving decentralized robust control of transient synchronization stability in islanded microgrids.This paper focuses on the analysis and control issues of transient synchronization stability in islanded microgrids considering microsources control switching.This paper carries out four specific research contents: large-signal unified modeling of inverters,transient synchronization stability analysis of inverters,transient stability domain evaluation,and decentralized robust control of islanded microgrids.The relevant conclusions provide research ideas and technical solutions for the analysis,optimization,and control of transient stability of islanded microgrids under microsource control switching conditions. |
PDF Full Text Request