Research On Simplified VSG Control For Grid-connected And Off-grid Inverter

Under the background of the "double carbon" national strategic goal,there is an important trend that establishment of a new power system with new energy as the main body.To make a large number of new energy power generation connected by inverter can be connected to the grid friendly,the micro-grid inverter as the research object is taken,and the control of its off-grid connection is studied in this paper.First,the overall control strategy of grid-connected three-phase full-bridge inverter based on VSG control is described,including VSG power loop control,voltage and current loop,pre-synchronization control,and the impedance characteristics of the inverter system are analyzed when the line impedance exists in the low-voltage microgrid,aiming at the problem of output power coupling of the inverter,the method of combining virtual negative resistance with virtual inductance is designed.To ensure that the output voltage of the inverter does not fluctuate before and after grid connection while the decoupling is realized.Secondly,the input-output active power transfer function and the angular frequency-input power transfer function are derived under the condition of VSG grid-connection,and the influence of the core parameters of VSG on the dynamic performance of the system is analyzed.Then the droop control and VSG control are modeled and analyzed under different operating states,and the advantages and disadvantages of the two control systems in grid-connected and isolated operating states are expounded.A unified form based on droop control and VSG control is established,and a simplified VSG control strategy is proposed,which can achieve better control performance in grid-connected and island-based operation.Then the system design method of key control parameters is given.Finally,a PSIM simulation model and a grid-connected experimental platform for a three-phase full-bridge inverter are built.On the premise that the output voltage of the inverter remains constant before and after the grid-connected operation while the virtual negative resistance is added.Droop control,VSG control,and simplified VSG control are compared and analyzed under the island and grid-connected operation conditions.Through simulation and experimental analysis,the feasibility and effectiveness of the control strategy designed in this paper are verified.