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
Fig. 1 Compact
hybrid AC/DC microgrid system
Fig. 2 AC bus
voltage and current of A phase in grid-connected mode
Fig. 3 SOC of the
battery in grid-connected mode
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
Fig. 6 DC bus
voltage with the influence of solar irradiance variation
and pulse load
Fig. 7 SOC of the battery in islanded mode
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
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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