Abstract
Microgrid integration and fault protection in complex network scenarios is a coming challenge to be faced with new strategies and solutions. In this context of increasing complexity, this paper describes two specific overload control strategies for four-wire inverters integrated in low voltage four-wire alternating current (AC) microgrids. The control of grid-tied microgrid inverters has been widely studied in the past and mainly focused on the use of droop control, which hugely constrains the time response during grid-disconnected operation. Taking into account the previous knowledge and experience about this subject, the main contribution of these two proposals regards providing fault current limitation in both operation modes, over-load capability skills in grid-connected operation and sinusoidal short-circuit proof in grid-disconnected operation. In the complex operation scenarios mentioned above, a hybrid combination of AC droop control based on dynamic phasors with varying virtual resistance, and voltage/frequency master voltage control for grid-(dis)connected operation modes are adopted as the mechanism to enhance time response. The two proposals described in the present document are validated by means of simulations using Matlab/Simulink and real experimental results obtained from CENER (The National Renewable Energy Centre) experimental ATENEA four-wire AC microgrid, obtaining time responses in the order of two-three grid cycles for all cases.
Highlights
In the coming years, it is expected that classical electrical grids will drive forward to a smarter, more flexible, reliable, efficient and bidirectional format leading to a more complex framework
To avoid over-modulation situations in the DC–alternating current (AC) stage, a preventive controller is suggested at the higher level of the DC–DC control scheme in order to provide an increment of ubus, ∆ubus, to the rated DC-link voltage
This section focuses on demonstrating by the use of simulations the virtual resistance contribution to a fast and seamless transference between operation modes, the power over-load supervisor operation, and the fault current limitation strategy for an ideal (
Summary
It is expected that classical electrical grids will drive forward to a smarter, more flexible, reliable, efficient and bidirectional format leading to a more complex framework. The main contribution of the present paper is the demonstration by simulation and real results of the advantages and flexibility of a fast time response hybrid combination of voltage control techniques that ensures proper FCL capabilities introducing two strategies for this purpose: one for each operation mode. This allows for applying specific control strategies and solutions in a context of increasing complexity scenarios avoiding the use of generic solutions that are not always the most appropriate ones.
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