Research On Distributed Two-level Control Of Island Microgrid Based On Two Kinds Of Time

Distributed generation(Distributed Generators,DGs)is a small power generation unit arranged near the user,which mainly includes solar power generation,wind power generation,biomass power generation and so on,but they all have great randomness,indirectness and volatility.It is impossible to supply electricity to power units stably and sustainably.When DGs is connected to the large power grid,it will have an impact on the large power grid and have a certain impact.In order to weaken the disadvantages of DGs direct grid connection,microgrid has been proposed as a new form of power grid.There are two kinds of operation states of microgrid:grid-connected mode and isolated island mode.When the microgrid is disturbed,it is cut off from the large power grid in an instant,and the microgrid is transformed into isolated island mode.The output voltage and frequency value of DGs will be interfered with,which deviates from their respective stable operation values.If we want to ensure the safe and stable operation of the microgrid system,weaken the impact of DGs on the large power grid,and solve the phenomenon of voltage amplitude and frequency deviation of the system,Then the output frequency and voltage amplitude of DGs must be kept near their respective reference values(ratings).In this paper,the following aspects are studied in this paper:(1)the hierarchical control of microgrid is introduced.the hierarchical control structure mainly includes the first level control(droop control,maintaining the voltage and frequency stability after the isolated island process).Two-stage control(compensation for voltage and frequency deviation caused by primary control)and three-stage control(optimal operation in isolated island and grid-connected mode and power flow control in grid-connected mode),At the same time,the traditional distributed two-level control of multi-agent system is also described.(2)aiming at the shortcomings of asymptotic synchronization and coordination of multi-intelligent system,the finite time protocol control is introduced,and the distributed secondary voltage and frequency auxiliary controller is deeply studied.Compared with asymptotic stability,finite time stability has better anti-interference performance and plug and play ability of the system.The synchronization setting time of finite time is related to the initial state.This strategy can not only ensure the sharing and allocation of active power.Moreover,the frequency and voltage of all DGs can converge to the reference value in finite time.The simulation results show that the distributed two-stage control under finite time can accurately solve the problem of global voltage regulation and accurate power allocation.And achieve good steady-state performance.(3)compared with the finite time consensus based on initial conditions,this paper also studies the distributed two-level control strategy with fixed time,which theoretically Proves that no matter what the initial conditions of the system are,Any initial state of the given system can be compensated for voltage and frequency within a fixed time,and the synchronization error can be estimated by constructing a fixed time auxiliary controller.The synchronization of fixed time terminal voltage and frequency of DGs in microgrid is realized,and the actual active power output of DGs is distributed proportionately.