Research On Voltage Control Strategy Of Microgrid Under Unbalanced Conditions

Microgrid can integrate distributed energy and maximize the economic benefit of distributed generation.In the three-phase islanded microgrid,the occurrence of asymmetric loads causes the unbalanced voltage of the microgrid,and much negative-sequence load current can also affect the stability and dynamic performance of the system.The main contents of this paper are as follows:(1)The topic background and research significance are elaborated.The basic concepts and research status of microgrid are summarized.The microgrid inverter control strategy based on droop control strategy is analyzed,and the mathematical model of the microgrid inverter is established.The control methods of unbalanced microgrids are introduced.(2)Voltage unbalance compensation of microgrid and the principle of negative-sequence load current are analyzed in detail.The influence of negative-sequence inverter output impedance is the main factor of voltage unbalance factor and negative-sequence load current distribution,this paper proposes a distributed microgrid voltage unbalance hierarchical optimization control strategy.This strategy comprises the negative-sequence virtual conductance-negative-sequence reactive power G-Q-droop control layer and the second negative-sequence voltage of coordinated optimization control layer.The negative virtual conductance is added on the inverter output negative-sequence virtual conductance to achieve implement the output voltage asymmetry degree and improve the precision of the negative-sequence current distribution load coordination optimization.And through the MATLAB/Simulink simulation model validation algorithm is effective.(3)The negative-sequence small signal model of the microgrid that consists of multiple inverters is established.The important parameters effect the stability and dynamic performance of the microgrid system are analyzed in detail,providing the basis for controller parameters selection.(4)Based on SpaceR,a semi-physical real-time simulation platform for microgrid is set up,and experimental verification is carried out on the unbalance voltage layered optimization control algorithm proposed in this paper on the experimental platform.