Abstract
Microgrids (MGs) are regarded as the best solution for optimal integration of the renewable energy sources into power systems. However, novel control strategies should be developed because of the distinct inherent feature of MG components in comparison to conventional power systems. Although the droop-based control method is adopted in the MG to share power among distributed generation units, its dependency to grid parameters makes its implementation not as convenient as that in conventional power systems. Virtual impedance has been proposed as the complementary part of droop control in MGs. In this study, adaptive virtual impedance is designed considering its effects on the system performance in the MG including: (i) decoupling active and reactive power control by making the grid X / R ratio high, (ii) maximum transferable power through the feeder, (iii) stability concern and (iv) precise reactive power sharing in different operating modes as well as smooth transition from connected mode to islanded mode (IM). To this end, a novel method is proposed to determine the reactive power reference of distributed generation (DG) units according to their contribution in reactive power sharing in IM. In addition, simulation in MATLAB/Simulink environment is conducted to assess the performance of the control system.
Highlights
Modern life requirements in terms of providing clean and economically efficient electrical energy have encouraged power engineers to integrate renewable energy sources (RESs) into distribution networks and close to load centres
The centralized control systems are based on high-bandwidth communication links, which collect data from each distributed generation (DG) unit to the MGCC and send the set points determined by the MGCC to DG units
This paper addresses active and reactive power sharing issues in decentralized droop controlled MGs
Summary
Modern life requirements in terms of providing clean and economically efficient electrical energy have encouraged power engineers to integrate renewable energy sources (RESs) into distribution networks and close to load centres. The virtual impedance is adjusted within the obtained permitted range adaptively to achieve the following targets: 1) reference tracking in CM where the issue is to deliver the pre-set reactive power determined by the MGCC, 2) smooth transition between CM and IM, 3) accurate reactive power sharing in IM, where the problem is to implement precise reactive power sharing, according to assigned droop gains, by means of voltage regulation to prevent circulating current among power converters To this end, first a novel decentralized method is developed to specify the reactive power reference for each DG unit according to their contribution in supplying the reactive power.
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