Research On Virtual Inertial Control And Autonomous Current Sharing Strategy Of DC Microgrid Optical Storage Converter

Because of its excellent renewable energy acceptance,DC microgrids do not need to consider issues such as reactive power control and frequency tracking compared to AC micro grids,and the DC bus is directly connected to the DC load,eliminating the need for intermediate AC/DC links,and the control method is more simplicity,so it has attracted widespread attention in recent years.Different from the traditional AC large-inertia power network dominated by rotating devices such as steam turbines,the DC microgrrid formed by power electronic converters is a low-inertia system,which has "rigidity" and insufficient inertia.Therefore,this paper proposes a DC microgrid optical storage converter Virtual inertia control,which simulates the inertial response process of the rotor speed to power fluctuations,which improves the DC bus inertia and enhances the reliability of the DC microgrid power supply.There are multiple converters in parallel operation mode in DC microgrid.The traditional droop control takes into account the influence of line impedance and the converter output power is uneven.An independent current sharing strategy for parallel converters is proposed to realize the power sharing control of parallel converters.The details are as follows:Part one,the traditional P-U droop control in DC microgrid only has drooping characteristic and a lack of inertia,which are unable to reject voltage fluctuation.The sudden fluctuation of the power in the n etwork will have an adverse impact on the voltage,which could cause voltage overshoot.In order to suppress the voltage fluctuations and improve the transient behaviors of the bus voltage,a virtual DC motor control strategy based on the P-U droop characteristics is proposed.By mimicking the mechanical inertia characteristics of the DC motor to adjust the P-U droop control loop,the large inertia an d the high damping output characteristic of the DC motor can be realized in the DC VSC.The specific mechanism of the VDCM control is analyzed in this paper,and the effectiveness of the proposed method is verified by the comparative simulation and experiment test with the traditional P-U droop control base on the micro-grid experiment platform.Part two,traditional DC microgrid parallel converters use droop control to distribute the output power of the converter,but due to the influence of line impedance,the droop characteristics are offset,resulting in uneven output power distribution of each converter,and the excessive operating conditions of the converter increase,which reduced converter life.In order to avoid excessive operation of the converter and realize the power sharing control of the DC microgrid parallel converter,an autonomous current sharing strategy for the DC microgrid parallel optical storage converter is proposed.By adding a virtual impedance compensation link,the output power of the converter is adjusted according to the output electrical characteristics of the converter,so that the output power of each converter is autonomously divided.In the virtual impedance compensation process,the power sharing characteristics of the converter in constant voltage operation mode and droop operation mode are analyzed,and the specific mechanism of autonomous current sharing strategy operation is clarified.A simulation and experiment of a DC microgrid parallel converter is established to verify the effectiveness of the proposed autonomous current sharing strategy for the parallel converter.