Hierarchical Power Balance Coordinated Control Of Renewable Energy Microgrid

As one of the most effective forms of distributed new energy power generation management,microgrid has been widely concerned and studied by countries all over the world.The intermittent and uncertainties of new energy sources such as photovoltaics will have an impact on power supply stablization and power quality of the microgrid.New energy power generation is usually integrated into the power grid with power electronic power devices as an interface.How to control the grid-connected converter to achieve power balance in the microgrid and ensure that the frequency/amplitude of voltage is within the specified range,meeting the user's safe power demand is an important issue.This paper studies a hierarchical control scheme to achieve power balance control of the microgrid,which mainly includes the following contents:Firstly,starting from the background of the problem,the background of the new energy microgrid is introduced.The research status of the microgrid control method is analyzed and the centralized,autonomous and hybrid control schemes are compared.In order to reduce communication dependence and increase the flexibility of "plug and play" of the power generation equipment,hybrid control scheme is determined to be the research direction.In view of the power shortage/overdue caused by the intermittent and uncertainties of new energy power generation,the energy structure of the combination of distributed power source and the energy storage device is used to achieve the “cut the peaks and fill the valley” function of power in the network,and a hierarchical control method is determined.In the system,the solar-storage system constitutes a virtual synchronous machine inverter to participate in frequency modulation;the photovoltaic inverters without energy storage battery does not participate in frequency modulation,and the maximum power tracking method is used to realize grid-connected running;the energy storage unit is designed to realize power balance of the islanded microgrid,and it is connected to the grid through PQ control.The model and transfer function of the underlying controller are analyzed.The droop control curve and its inertia time constant characteristics of the virtual synchronous machine are studied.The suppression effect of the virtual synchronous machine method on the frequency disturbance is analyzed.The voltage frequency/amplitude response of the designed underlying control system of the virtual synchronous machine to the system load change and the disturbance suppression of frequent load changes are verified by simulation.The framework of the global physical quantity monitoring of the central controller is analyzed.The control curve of the power balance based on enregy storage unit with dead zone is studied.The switching point of the ESU working state is clearly defined,which is used to realize the function that is similar to the secondary frequency modulation of the traditional power system.The function constitutes a hierarchical control capable of cooperating with the source-storage as required by the MGCC's instructions.By using two microgrid model benchmarks(0.4kV,20 kV Benchmark)proposed by CIGRE,the International Council on Large Electric systems,the hierarchical control method is simulated and analyzed based on various scenarios.Finally,the rationality and effectiveness of this method are further proved through the physical platform experiment.A small-capacity microgrid platform was built,and the experimental verification of the system's regulation was completed.