Research On Dual Current Feedback Control And Bus Voltage Control Strategy Of Grid-Connected Converter For DC Microgrid

DC microgrid through the converter connecting the distributed power supply,energy storage device and terminal load,which without a large number of DC-AC converter relative AC microgrid and reduced the use of the converter number in the system to improve the efficiency of power transmission.DC microgrid uses the DC transmission does not exist phase synchronization,harmonic and reactive power loss and so on,has the widespread attention of people.Among them,the bidirectional grid-connected converter,as the key interface between the DC microgrid and the AC grid,can realize the bidirectional power flow and the stable control of the DC bus voltage.Taking good control of it is one of the essential conditions to maintain the normal operation of the DC microgrid.Firstly,the traditional droop control of the grid-connected converter is improved to simplify the structure of the DC bus voltage control.Secondly,aiming at the resonant problem of LCL type grid-connected converter,a dual current feedback control is proposed to effectively suppress the resonant problem.Finally,in order to improve the anti-interference ability of the DC microgrid,an improved virtual inertia control is introduced into the control structure of the grid-connected converter to make the DC bus voltage have certain inertia when it is subjected to shock response.The specific research contents of this paper are as follows:In the first part,an improved droop control is proposed in view of the complicated design process of the traditional droop control and double closed loop control for grid-connected converter.The method by simultaneous both sides ac/dc converter power equal and traditional droop control equation of the dc bus voltage and current converter side of quadratic function relation,and according to the quadratic function equation of alternatives to traditional droop control and voltage loop,save voltage loop PI regulator to reduce the parameter design and adjustment process,simplify the control structure.The simulation and experimental models of the DC microgrid under grid-connected operation mode are built to verify the effectiveness of the proposed improved droop control structure.In the second part,compared with L-type and LC type filters,LCL filter has better high frequency harmonic suppression ability.However,due to its own third-order structure,it will cause resonance phenomenon in the circuit and amplify the harmonic amplitude at a specific frequency,which will threaten the safe and stable operation of grid-connected converter in serious cases.In order to reduce the adverse effect of this phenomenon in the grid-connected operation of micro grid,a dual current feedback control strategy is proposed.Based on the indirect current feedback control of grid-connected converter,an active damping loop with grid-connected current feedback considering delay was added to analyze its damping equivalent characteristics,expand the effective working area of active damping,and improve the resonance suppression effect in weak current network.Finally,the dual current feedback control is validated in simulation and experiment.In the third part,the Virtual Synchronous Generator(VSG)principle of the Virtual DC Machine(VDCM)control and the Virtual inertia control applied to the grid-connected converter make the DC bus voltage has a certain inertia.It can reduce the voltage amplitude fluctuation of the bus when the power mutation occurs in the DC microgrid and improve the anti-interference ability of the microgrid.However,VDCM is applied to bidirectional DC/DC converters,and VSG-like virtual inertia control applied to grid-connected converters has the problem of amplitude sharp drop in the initial stage of system operation,so the range of rotational inertia is limited.Therefore,based on the VDCM control principle,an improved virtual inertia control strategy applied to grid-connected converters is proposed in this paper,so that a certain amount of inertia can be added to the microgrid during operation,and the amplitude drop phenomenon does not exist in this method.Compared with the traditional droop control,the simulation and experiment are carried out to verify its effectiveness.