Hybrid micro-grids require harmony operation
of renewable energy resources based voltage source inverters
(VSIs) in grid-tied as well as islanded modes. In this paper, the
modeling, analysis, and control strategy of VSIs based
autonomous micro-grid are developed. An integrated control
system for autonomous micro-grid is carried out including two
control levels. The primary control level is comprised of the
current and voltage inner control loops, the virtual inductor
loops, and the droop control loops. This control level is
necessary to regulate voltage and frequency, and also to
achieve accurate power sharing among the paralleled
distributed generators (DGs). However, the secondary control
level is employed to eliminate the voltage magnitude and
angular frequency deviations produced by primary control
level. The parameters of secondary controllers are optimized
using particle swarm optimization technique to achieve good
dynamic and steady state performance for micro-grid voltage
and frequency. Two micro-grid structures are modeled and
simulated in MATLAB environment to accomplish this study.
The first structure consists of only one distributed generation
unit, while the second contains four DGs. Each structure is
tested with and without secondary control level under the load
variations to confirm the robustness of the control system. The
results of the traditional and optimized secondary controllers
are compared. |
