Research On Control Technology Of Bus Voltage For DC Microgrid

Due to the flexible and convenient consumption of local energy,distributed generation has gradually become an important way to efficiently utilize the new energy.All kinds of new energy generation devices directly connect to the grid,which may cause many adverse effects such as the safe operation.DC microgrid has the advantages such as high energy utilization and not considering synchronization problems in the integration of new energy and new load.It has become effective network architecture to connect the distributed new energy generation device to the intelligent distribution system.The reactive power and frequency parameters do not exist in DC microgrid system;the primary goal of the safe operation of the system is maintaining the stability of bus voltage.The imbalance of the source and load power in DC microgrid will lead to the disturbance fluctuation of the bus voltage,and the wide access of all kinds of power electronic devices may also cause the oscillating fluctuation of the bus voltage.The instability of bus voltage will threaten the normal operation of equipment,deteriorate the quality of power supply and reduce the reliability of power supply.Therefore,the research on control technology of bus voltage for DC microgrid is great significance.DC microgrid bus voltage is usually maintained by a distributed generation unit with constant voltage control mode in the system,and droop control is an important way of power sharing among the constant voltage control units.The problems of the traditional droop control technology are power sharing precision and voltage droping which is analyzed in this paper.It studies the refined principle of the variable droop coefficient using to improve power sharing precision and the variable droop intercept adopted to restrain voltage droping.An improved droop control method based on voltage droping compensation and power sharing compensation is put forward in this paper.The simulation results show that the refined droop control technique can improve the power sharing precision between the constant voltage control units and effectively suppress the bus voltage droping.Bus voltage signal is effective information to intuitively reflect the internal power flow in DC microgrid.To achieve efficient utilization of various new energy sources,this paper proposes a coordinated control strategy among distributed generations based on bus voltage signal and regulate the voltage stability of the bus bus.According to the control strategy,the DC voltage of the microgrid bus is divided into four levels,and each level corresponds to a working mode of the system.Under the working modes,the bus voltage can be maintained by different distributed generation units,and the grid converter of each distributed generation unit will adopt the corresponding control strategy according to the operating targets under different modes.The simulation results show that the above coordinated control strategy can effectively improve the energy utilization and maintain the bus voltage constant.The constant power load in the DC microgrid has the characteristic of negative impedance,which will reduce the damping of the system and make the bus voltage oscillate when the load power is greatly disturbed.In this paper,a steady state mathematical model of a DC microgrid is established,and the running characteristics of constant voltage control unit and constant power are analyzed.The asymptotic stability region of the system is studied by Lyapunov method.To suppress the bus voltage oscillation caused by the damping of the system,a method of restraining the voltage oscillation of the bus based on the dual active damping is proposed by introducing the virtual resistor and the virtual generator.The simulation results show that dual active damping control technology can guarantee voltage stability of DC microgrid bus under severe disturbance of load power.