Research On Voltage Control Strategy Of Low Voltage Microgrid

In recent years,successive large-scale power outages,natural disasters and global energy bottlenecks have made the disadvantages of interconnected power grid gradually exposed.The traditional power system urgently needs to be integrated with renewable energy and the auxiliary power grid with sustainable development appears.Distributed generation possesses the characteristics of environment friendliness,high energy efficiency and flexible installation.Microgrid,as an effective carrier of distributed power,has become an effective way to fully utilize renewable energy.Reasonable voltage control is an important guarantee for the stable operation of the microgrid system.According to the adjusting ability and task,the microgrid voltage control includes primary voltage control and secondary voltage control.This article focuses on the secondary voltage control.Firstly,it introduces the operation mode of low-voltage microgrid and the control strategy of micro-source.The control of microgrid includes master-slave control and peer-to-peer control.The control strategies of micro-source includes PQ control,V / f control and droop control.Secondly,this paper studies the control of microgrid voltage under master-slave control,and proposes a secondary voltage control strategy based on sensitivity.The strategy transforms voltage control into an optimization problem.By solving the optimization equation,a voltage control scheme with optimal voltage regulation is obtained.In the optimization model,the voltage energy function is used as an assessment index of the voltage regulation effect,which can not only reflect the overall voltage level of the system but also precisely control the individual bus voltage by adjusting the voltage weight coefficient.At the same time,taking into account the high impedance characteristics of AC lines in low voltage microgrids,a voltage sensitivity matrix is established to couple the bus voltage with the DG active power function and call active resources for voltage regulation.Finally,the control of the secondary voltage of the microgrid under the peer-to-peer control is studied.Based on different voltage-regulating purpose,threestrategies are proposed: direct voltage control,indirect reactive power control and voltage/reactive power hybrid control.Three voltage control strategies are modeled and simulated respectively.The research shows that during the secondary voltage regulation,the direct voltage control strategy can quickly restore the microgrid voltage to the rated value,but lacks the control of the reactive power.The indirect reactive power control strategy can achieve the power allocation reasonable.However,the higher voltage control accuracy can not be achieved.The voltage/reactive hybrid control strategy can adjust the reactive power distribution coefficient to ensure the rationality of power distribution in the microgrid.At the same time,the voltage control coefficient in the strategy is adjusted to further improve the voltage control accuracy of the microgrid system.