Research On Current Limiting&Sharing Control And Virtual Inertia Control Of Inverter In Microgrid With Generators

With the growing penetration of distributed generation,the microgrid will gradually connect with the main network through the distribution network,which has the characteristics of low voltage,small capacity,flexible and changeable,and is different from the traditional vertical control and energy circulation structure.Among them,the low-voltage transmission environment leads to the change of power distribution mode in units and the failure of traditional inverter control.At the same time,the inverter is the main interface of the interconnection of all subnets,resulting in the lack of inertia of the system and the instability after disturbance.In order to ensure the reliable operation of the system,the traditional transient current limiting& sharing control and virtual synchronous generator(VSG)control of the inverter are improved.First of all,the power transmission characteristics of low-voltage microgrid are analyzed.It is found that it is contrary to the droop control(primary frequency modulation),which leads to the failure of traditional droop power control and endangers the stability of the system.In this case,the actual power is orthogonal transformed and decoupling droop control is proposed to realize the power distribution of parallel units in proportion to droop coefficient.In addition,the power climbing speed of the droop control inverter is faster than that of the synchronous generator in the microgrid,and the load carrying capacity of the inverter is limited.Considering the resistance inductive transmission line of the low-voltage microgrid,according to the over limit of the inverter output current and the scheduling command of the central controller,this paper constructs an adaptive virtual impedance control under the decoupling droop control of the inverter and power angle coordinated control according to its varying intensity,which improves the power sharing degree and current limiting stability of theinverter.Secondly,droop control or VSG control can simulate inertia of any size under ideal source,but the source side cannot respond to transient load in time to maintain DC bus voltage stability.Therefore,only through the improvement of the algorithm can not fundamentally improve the ability of the inverter to bear the transient load.In view of the essential reason that the inverter output lacks inertia,this paper configures the inertia energy in the DC side of the inverter from the hardware,and improves the disadvantages of the traditional virtual synchronous generator on algorithm.The Buck Boost converter powered by lithium battery cooperates with the improved virtual synchronous machine(IVSG)strategy proposed in this paper to provide inertial energy and the reference of frequency and enhance the inertial capability of the inverter.Finally,the small signal analysis of the above models is carried out,the stability of the selected parameters and control strategy is verified by means of root locus,and the microgrid simulation model based on MATLAB/ Simulink is built,and the improved control strategy and structure are verified and analyzed.Based on the DSP TMS320F28335 development board,the inverter experiment platform is built,the main circuit,control circuit and software control system are designed in detail,and the control strategy of transient steady-state current limiting&sharing in the microgrid with synchronous generator proposed in this paper is verified.