ABSTRACT:
In this paper, a three-terminal AC/DC hybrid
microgrid with two DC terminals and one AC terminal is proposed. The proposed
system consists of cascaded H-bridge (CHB) converters based AC grid interface
and two dual active bridge (DAB) converters based DC subgrid interface that
connects two isolated DC buses. In order to reduce the number of power
conversion stages and power devices, the DAB converters are directly connected
to CHB DC rails according to the system operation requirement. To overcome the
imbalanced grid currents and DC rail voltages issues caused by this modified
system configuration with only two power conversion stages, an improved method
is proposed through the zero-sequence voltage injection in the CHB converters.
In addition, to avoid the conflicts between zero-sequence voltage injection and
the voltage/current regulation of the system, the impacts of the control
parameters to the system stability and dynamic response are investigated.
Evaluation results from both three-terminal and five-terminal hybrid AC/DC
microgrids show that the generalized effectiveness of the proposed three-phase
AC current and DC rail voltage balancing method.
KEYWORDS:
1. Three-terminal microgrid
2. Hybrid AC/DC microgrid
3. Zero-sequence voltage injection
4. Current balancing control
5. Voltage balancing control
6. Grid-voltage sags
SOFTWARE:
MATLAB/SIMULINK
CONCLUSION:
In
this paper, a multi-terminal hybrid AC/DC microgrid structure with two power
conversion stages is described in detail and a three-terminal hybrid microgrid
with two DC ports is mainly selected for case study. In order to solve the
issues of DC capacitor voltages and three-phase grid currents unbalance caused
by mismatched DC power between DC ports, an improved control method through the
adoption of zero-sequence voltage injection is developed. It has been
extensively verified that the grid current and CHB capacitor voltage balancing
control can be achieved simultaneously even in the severe case with highly
mismatched DC power, grid-voltage sags, or the changes of connection between AC
and DC subgrids.
REFERENCES:
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