Research On Multi-Level Distributed Cooperative Control Of AC/DC Hybrid Microgrid

With the continuous increase in the proportion of distributed power sources,one of the effective solutions to reasonably accept its high proportion of access to the grid is to build an AC/DC hybrid microgrid that integrates the characteristics of AC and DC microgrid operation and regulation.Complex communication conditions,different line impedances and environmental disturbances and disturbances can easily bring about communication delay,unstable voltage and frequency,and poor system power distribution.In particular,in islanded operation mode of AC/DC hybrid microgrid,different line impedances and system communication delay can easily lead to the fluction or even instability of AC/DC hybrid microgrid,which would affect the flexible and stable operation of the hybrid microgrid.Therefore,the control strategy of AC/DC hybrid microgrid has broad technical prospects and research value.In order to effectively solve the control problems of system,such as voltage,frequency regulation and power proportional distribution,and to make up for the shortcomings of communication delay under complex communication conditions,this thesis propounds a multi-level distributed cooperative control strategy of AC/DC hybrid microgrid,which is based on the consensus theory considering communication delay and adaptive virtual impedance control.Firstly,the interlinking converter of the AC/DC hybrid microgrid control strategy is propounded,which is based on the principle of droop characteristics.The traditional droop control principle and the mathematical model of the interlinking converter are analysed and introduced.On the basis of this,the control strategy of the interlinking converter is established,which is adopted to maintain the power flow between AC/DC sub networks and the stability of bus voltage,realize the cooperative operation between the sub networks and the power sharing of hybrid microgrid.Secondly,the adaptive virtual impedance control strategy is propounded to meet the needs of system power proportional distribution.The limitations of traditional droop control and the principle of virtual impedance are analyzed.With that in mind,adaptive virtual impedance control strategies for the AC side subnet and the DC side subnet are designed,which is adopted to reduce the influence of different line impedances,and lay the foundation for the proportional distribution of system power of the distributed secondary control.Finally,a multi-level distributed cooperative control strategy for AC/DC hybrid microgrid is propounded.On the basis of the principle of droop control,this thesis propounds the primary droop control strategy.And a multi-loop control structure including voltage,current and power controllers is designed,which is adopted to realize the rapid response to voltage and frequency changes of primary control layer.The principle of the consensus algorithm is analyzed,and the consensus theory considering the communication delay is proposed to overcome the influence of the system communication delay.The distributed secondary control strategy is propounded to adjust the voltage and frequency deviation caused by the differential regulation of the primary control layer,and according to the compensation effect of the adaptive virtual impedance to achieve the proportional distribution of the system power.Furthermore,The multi-level distributed cooperative control is realized by the hierarchical autonomy and vertical cooperation among different levels.And through simulation analysis,the control effect and performance of the propounded control strategy are verified.