Research On Power Sharing Among The Parallel Inverters In Low-Voltage Micro-grid Which In Islanding Operation

Distributed generation systems based on renewable energy sources have been experiencing rapid development in recent years.As well,a more recent concept called microgrid is developed by grouping a cluster of loads and paralleled DG units in a common local area.In the islanding operation of a microgrid,its DG units are governed by droop control algorithms so they can operate with enhanced reliability in a de-centralized fashion without any communication.However,the coupling between the active and the reactive power of the droopcontrolled inverters is critical in the low-voltage microgrid.Therefore,new control methods for the grid elements in islanded microgrids need to be developed.To tackle this issue,a novel frequency-voltage frame transformation is proposed to improve the system stability and offset the power coupling in a low-voltage grid.The proposed control strategy can not only effectively decouple the real and reactive power but also can improve the system transient and stability performance.Primary control is dominated by droop control.However,droop control suffers from steady state frequency and voltage deviation subsequent to a change in system loads.Secondary control is responsible for voltage and frequency restoration by providing the set points for the primary control.The Secondary level control requires communication links and/or centralized and distributed control structures,which make the control more complex and expensive.Therefore,a novel power sharing approach is proposed based on the utilization of a dynamic feedback incorporating washout filters.Similar to the droop control,the proposed approach does not require communication but unlike droop control it can prevent voltage and frequency deviations.The proposed approach eliminates the need for the secondary level control,which is utilized for voltage and frequency restoration.The proposed approach eliminates the need for the secondary level control,which is utilized for voltage and frequency restoration.