| Under the dual pressure of energy demand and environmental issues,the concept of microgrid is proposed to take advantage of distributed generation and reduce the negative influence on power supply reliability and power quality,when distributed generations are connected to the power grid.With the DC load becoming more and more common,the DC microgrid with lower loss and stronger controllability has a strong development potential,and related research become more and more.DC microgrid is divided into two operating modes:islanding and grid-connected.It is necessary to realize stable operation in two modes and smooth switch between two modes.So it is important to research stability control strategy of DC micro grid.DC microgrid stability control is divided into two elements,one is DC microgrid energy coordination management strategy,and the other is DC bus voltage stability control strategy.Firstly,the concept of DC microgrid is introduced and the development status and stability control status of DC microgrid are summarized.Then typical micro source is selected.The mathematical model of photovoltaic cells is established,based on the output characteristic curve of photovoltaic cells,the maximum power point of photovoltaic cells is traced by using perturbation and observation method.The general mathematical model of the battery is established,and the charging and discharging control of the battery is realized based on the small-signal analysis of Buck-Boost circuit.Applying the Parker transform to the bidirectional DC/AC mathematical model,the decoupling control of constant DC bus voltage of bidirectional DC/AC converter is realized.Secondly,taking DC microgrid energy management strategy as the research object,DC microgrid master-slave control stratrgy is analyzed in detail.When the battery is the main power supply under normal operation,the energy coordination management of islanding and grid-connected is analyzed,and the energy management is researched when the battery is out of service.On the premise that the output value of each converter does not reach respective limit value,four operation modes are simulated and analyzed:normal grid-connected,islanding,switch between grid-connected and islanding,grid-connected without battery.The feasibility of master-slave control strategy is verified.The traditional PI control can not satisfy the stability of DC bus voltage under large disturbance.So backstepping sliding mode control based on state feedback linearization for bidirectional Buck-Boost converter is proposed.The simulation shows that the response speed is fast and the stability region of the system is enlarged.Adaptive backstepping sliding mode control for bidirectional DC/AC converter is proposed.This method can track the uncertain parameters of the system well,and has the characteristics of fast response and smaller maximum deviation.The robustness of the system has been improved. |
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