Research On Microgrid Power Control Strategy Based On Virtual Impedance

With the development of power electronics technology,microgrid is supplemented by centralized power generation,and its distributed power generation technology is becoming mature.However,the power sharing problem of the microgrid is easily affected by the impedance of each distributed power line in the system,so that the power is not shared proportionally.This topic studies the microgrid power control strategy based on virtual impedance,which enables the power of each distributed generation in the microgrid to be proportionally shared.First of all,this paper analyzes the communication mode between distributed generation and realizes cooperative control of the voltage and frequency of each distributed generation.The distributed generation is analogized to the form of an agent,so the knowledge of algebraic graph theory and Laplacian matrix is first introduced.The multi-agent network system consistency protocol is introduced,which proves the convergence of dynamic consistency theory.In the case of a communication delay in a multi-agent network system,the stability of the system under the maximum delay that can be tolerated is demonstrated.Secondly,the mathematical model of distributed generation is established.Based on the consensus algorithm,a distributed cooperative control strategy of voltage and frequency is established.Considering the traditional hierarchical control,for the conventional droop control,the microgrid cannot achieve the limitation of power proportional sharing.For the frequency deviation from the rated value,the secondary distributed cooperative control strategy is adopted to realize the frequency recovery of each distributed power source to th e rated value,and the active power of each distributed power source is proportionally shared;for the voltage deviation from the rated value,a dynamic consensus distribution is adopted.The average voltage recovery control algorithm causes the output vol tages of the distributed power sources to converge to the average voltage,and the reactive power of each distributed generation is proportionally shared.Then,a distributed adaptive virtual impedance control system based on consensus algorithm is designed.The reason why reactive power can not be shared proportionally is analyzed,which is caused by unbalanced line impedance between distributed generation.On the basis of conventional droop control,virtual impedance control is added to achieve better decoupling of active and reactive power.A distributed adaptive virtual impedance control system based on dynamic consensus algorithm is designed.The control strategy can dynamically adjust the line impedance among distributed generation without knowing the impedance in the line.The reactive power of each distributed generation is shared proportionally.Finally,considering the unbalanced or non-linear load in the microgrid,the negative sequence power and harmonic power will appear in the grid.The adaptive virtual impedance control strategy is adopted to add the negative sequence and harmonic power to the active frequency droop control loop.At this time,the active power cannot be proportionally shared.The value of the adaptive virtual impedance is calculated by using the change value of the active power at this time,and the virtual impedance at the fundamental negative frequency and the harmonic frequency is dynamically adjusted.The simulation results show that the negative sequence and harmonic power are proportionally shared when the line impedance is unknown.