Abstract
The AC/DC hybrid microgrid (MG) has been widely promoted due to its high flexibility. The capability to operate in islanding mode is an appealing advantage of the MG, and also sets higher requirements for its control system. A droop control strategy is proposed on account of its distinguishing feature of automatic power sharing between distributed generations (DGs), but it introduces some drawbacks. Therefore, distributed cooperative secondary control is introduced as an improvement. In order to optimize the active power sharing in AC/DC hybrid microgrids, a number of cooperative control strategies have been proposed. However, most studies of AC/DC hybrid microgrids have mainly focused on the control of the bidirectional converter, ignoring the effects of secondary control within subnets, which may make a difference to the droop characteristic. This paper extends the cooperative control to AC/DC hybrid microgrids based on normalizing and synthesizing the droop equations, and proposes a global cooperative control scheme for AC/DC autonomous hybrid microgrids, realizing voltage restoration within AC and DC subnets as well as accurate global power sharing. Ultimately, the simulation results demonstrate that the proposed control scheme has a favorable performance in the test AC/DC hybrid system.
Highlights
For the sake of improving the capacity of the power grid to penetrate distributed generations (DGs) as well as promoting the intelligent process of the grid, the concept of a microgrid (MG) has been put forward
This paper extends the cooperative control to AC/DC hybrid microgrids based on normalizing and synthesizing the droop equations, and proposes a global cooperative control scheme for AC/DC
When a planned or spontaneous event leads to the off−grid of a MG, it can still work in an autonomous state, but at this point, no external power grid can provide reference for the system frequency and voltage of the point of common coupling (PCC), setting higher requirements for the control system
Summary
For the sake of improving the capacity of the power grid to penetrate distributed generations (DGs) as well as promoting the intelligent process of the grid, the concept of a microgrid (MG) has been put forward. Fanghong Guo et al [10] designed an efficient secondary controller with the superiority of less information transmission and demonstrated its excellent performance in DC microgrids These above−mentioned studies only focused on one separate microgrid, while the control of hybrid microgrids needs to consider the coordination between. This paper extends the distributed cooperative control to AC/DC hybrid microgrids based on normalizing and synthesizing the droop equations, establishes the power sharing relationship between the subnets and proposes a control strategy for the AC/DC autonomous microgrid. The primary control adopts droop control and the secondary control is introduced to implement voltage restoration and proportional power sharing between DGs. In addition, the controller of the bidirectional converter compares the power demand on AC and DC sides to determine the reference of transmission power. The simulation results on MATLAB/Simulink demonstrate that the proposed control scheme has a favorable performance in the test AC/DC hybrid system
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