Research On Power Sharing Method Of Multi-Parallel Virtual Synchronous Generator System

Microgrid provides a new way for large-scale access of distributed generation,but with the increasing permeability of renewable energy generation,the inertia of the system is reduced,which brings potential threat to the safe and stable operation of power grid.Virtual synchronous generator(VSG)can improve the stability of power grid frequency and voltage effectively by controlling microsource inverter with the characteristics of inertia,damping,active power frequency modulation,reactive voltage regulation and so on.Traditional centralized generation has the inherent advantages of large capacity,inertia sufficient,natural decoupling of power,while distributed generation capacity is generally smaller.In order to increase system redundancy for capacity expansion,distributed generation is often incorporated into the power network by decentralized access.Because of the difference of line impedance between the microsource inverter and the parallel grid,the load power cannot be accurately distributed according to the capacity of the microsource inverter,resulting in the power circulation and even the instability of the system.In this paper,the micro-source inverter controlled by virtual synchronous machine is taken as the research object,considering that the characteristics of resistive line in low-voltage distribution network can easily affect the power decoupling effect of traditional droop control.The effect of resistance inductance on power decoupling and power distribution is studied.A virtual complex impedance power allocation method based on coordinate transformation is proposed.The equivalent circuit parameters of the inverter are inversely proportional to the capacity of microsource.The power circulation between parallel operation VSG is restrained,and the problem of voltage drop of PCC point caused by traditional virtual impedance method and the stability problem of system caused by line resistance drift are avoided.Finally,the virtual synchronous machine hardware-in-the-loop simulation system is built,and the VSG single-machine characteristic experiment,the VSG double-machine parallel power distribution experiment,and the off-grid switching experiment are completed.The superiority of VSG control and the effectiveness of the proposed power allocation method are verified.