The hybrid AC/DC microgrid is considered to be the more and more popular in power systems as increasing DC loads. In this study, it is presented that a hybrid AC/DC microgrid is modelled with some renewable energy sources (e.g. solar energy, wind energy), typical storage facilities (e.g. batteries), and AC, DC load, and also the power could be transformed smoothly between the AC and DC sub-grids by the bidirectional AC/DC converter. Meanwhile, coordination control strategies are proposed for power balance under various operations. In grid-connected mode, the U–Q (DC bus voltage and reactive) or PQ method is adopted for the bidirectional AC/DC converter according to the amount of exchange power between AC and DC system in order to improve the DG utilisation efficiency, protecting the converter and maintain the stable operation of the system. In islanded mode, V/F control is applied to stabilising the entire system voltage and frequency, achieving the power balance between the AC and DC systems. Finally, these control strategies are verified by simulation with the results showing that the control scheme would maintain stable operation of the hybrid AC/DC microgrid.

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Coordination control of hybrid AC/DC Microgrid
ABSTRACT:
The hybrid AC/DC microgrid is considered to be the more and more popular in power systems as
increasing DC loads. In this study, it is presented that a hybrid AC/DC microgrid is modelled
with some renewable energy sources (e.g. solar energy, wind energy), typical storage facilities
(e.g. batteries), and AC, DC load, and also the power could be transformed smoothly between the
AC and DC sub-grids by the bidirectional AC/DC converter. Meanwhile, coordination control
strategies are proposed for power balance under various operations. In grid-connected mode, the
U–Q (DC bus voltage and reactive) or PQ method is adopted for the bidirectional AC/DC
converter according to the amount of exchange power between AC and DC system in order to
improve the DG utilisation efficiency, protecting the converter and maintain the stable operation
of the system. In islanded mode, V/F control is applied to stabilising the entire system voltage
and frequency, achieving the power balance between the AC and DC systems. Finally, these
control strategies are verified by simulation with the results showing that the control scheme
would maintain stable operation of the hybrid AC/DC microgrid.
SOFTWARE: MATLAB/SIMULINK

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BLOCK DIAGRAM:
Fig. 1 Compact hybrid AC/DC microgrid system

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EXPECTED SIMULATION RESULTS:
Fig. 2 AC bus voltage and current of A phase in grid-connected mode
Fig. 3 SOC of the battery in grid-connected mode

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Fig. 4 Power of wind, DC side power flowed into AC side and the output
of battery in grid-connected mode
Fig. 5 PV output power versus 50*solar irradiation in islanded mode

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Fig. 6 DC bus voltage with the influence of solar irradiance variation
and pulse load
Fig. 7 SOC of the battery in islanded mode

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Fig. 8 AC bus voltage and current of A phase in islanded mode
Fig. 9 Power of wind, DC side power flowed into AC side and the output
of battery in islanded mode

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CONCLUSION:
In this paper, the coordination control strategies are proposed for the hybrid AC/DC microgrid,
operating in grid-connected mode and islanded mode. The control strategies are verified with
Matlab/ Simulink under various operations and load conditions. The simulation results show that
the control strategies of the hybrid AC/DC microgrid system are efficient. In grid-connected
mode, both the bidirectional AC/DC converter and the batteries can keep the DC bus voltage
stable, and ensure the converter smoothly operates in U–Q or PQ methods under the various
solar irradiation conditions. In islanded mode, the AC bus voltage and frequency are provided by
bidirectional AC/DC converter, the battery is to maintain DC bus stability and system power
balance under pulse load and various solar irradiation conditions.
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