Control strategy of low voltage microgrid based on equivalent reference current control

Taking the low voltage microgrid with multiple distributed generations as research subject, this paper proposed equivalent reference current control method which is suitable for two operation modes of microgrid based on PQ control method and V/f droop control method. For the amplitude and frequency of voltage, the deviation value between reference value and actual value is introduced respectively into dq axis component of the reference current, distributed generation(DG) have corresponding operation characteristics in two operation modes of microgrid by controlling the deviation value. In the islanded operation mode, DG share the power proportional according to their rating power by different coefficients of the deviation and provide voltage and frequency support for the microgrid; in the grid-connected operation mode, the coefficient of deviation is set to zero to eliminate the influence of deviation on output power and achieve the goal of constant power output. In addition, the reference power transition link which is conducive to smooth reconnection is introduced by controlling the deviation while interconnecting to the distribution grid. This proposed control method can avoid the switch of control methods and insure the smooth transition when operation modes change, and can also effectively improve the dynamic adjustment performance of voltage and frequency in island mode, and achieve the direct power control in grid-connected mode. At the same time, the grid synchronization controller based on this control method is designed to achieve the smooth reconnection of the microgrid. Through three detailed case studies, being operating in grid-connected mode, operating in island mode, and switching operation modes, the feasibility and effectiveness of the proposed control strategy are validated by Matlab/Simulink, and two parallel three-phase inverters system is implemented for the experimental demonstration.