Research On DC Bus Voltage Control Strategy Of AC/DC Micro-Grid

The continuous consumption of primary energy such as coal,oil and natural gas has caused serious pollution to environment.In this context,countries around the world are actively developing and utilizing renewable clean energy such as water,solar energy and wind energy.Renewable energy can be connected to the large power grid through the micro-grid.AC/DC micro-grid has the advantages of both AC micro-grid and DC micro-grid,which is an important form of power system development in the future.In the grid-connected AC/DC micro-grid,AC micro-grid can effectively guarantee the stability of AC bus voltage because of the support from the large power grid connected.However,due to the large number of distributed energy sources featured with intermittent and random characteristics,like wind power and photovoltaic,the stability of bus voltage in DC micro-grid is usually poor.so the So the stability control of DC bus voltage is significant for safe and stable operation of AC/DC micro-grid.In this paper,the stability control of DC bus voltage in AC/DC micro-grid is studied as follows:Firstly,the basic topology of AC/DC micro-grid is introduced in detail,and the operation modes of various topologies are analyzed.On this basis,the modeling analysis of interconnected converter and energy storage system in AC/DC micro-grid is studied,which provides a theoretical basis for the following proposed control strategy.Secondly,in view of the voltage fluctuation of DC bus caused by power fluctuation in the DC micro-grid from isolated AC/DC micro-grid,a DC bus voltage stability control method based on multi-working-mode energy storage device is proposed.In the proposed method,the energy storage device is connected to the DC bus through bidirectional DC/DC converter,and the traditional constant voltage charge/discharge control strategy of battery is improved.The threshold action voltage is added to allow that the battery’s charging/discharging action can be carried out after self-checking of the working mode.The proposed control strategy can effectively control the DC bus voltage in the DC micro-grid,at the same time,the frequent charging/discharging action of the battery interface is avoided and its service life can be prolonged.The simulation results show that the energy storage device can determine the charging/discharging state of the battery according to the fluctuation of DC bus voltage.Besides,the DC voltage is controlled within a reasonable fluctuation range,and the charging/discharging times of the battery are significantly reduced.Finally,the DC bus voltage stability control method of AC/DC micro-grid in grid-connected mode is studied.Firstly,the design method of traditional PI controller-based DC bus voltage control system of interconnected converter is introduced in detail.Limitation that hardware cost brought from PI plus power disturbance feedforward control strategy is pointed out,and the DC bus voltage control strategy based on Active Disturbance Rejection Control(ADRC)for the interconnected converter is then proposed.Based on the dynamic equation of DC side voltage of interconnected converter,the extended state observer(ESO)is constructed,which can accurately estimate the total disturbance of DC voltage control system,and significantly improve the control performance of interconnected converter for DC bus voltage without increasing the hardware cost of control system.The parameter selection of extended state observer and its influence on disturbance estimation performance are studied;Based on the extended state observer,the design method of active disturbance rejection controller for DC bus voltage is studied,and the tuning principle of control parameters is introduced;aiming at easing the contradiction between the disturbance rejection capability and the high-frequency noise suppression characteristics in conventional constant parameter ESO based ADRC(CESO-ADRC)controller,an adaptive observation parameters ESO based active disturbance rejection controller(AGESO-ADRC)further is proposed,which improves the adaptability of ADRC to noise environment when applied to interconnected converters.Simulation results verify the correctness and effectiveness of the proposed control strategy.