ABSTRACT:
Control
strategies of distributed generation (DG) are investigated for different
combination of DG and storage units in a microgrid. This paper develops a
detailed photovoltaic (PV) array model with maximum power point tracking (MPPT)
control, and presents real and reactive power (PQ) control and droop control
for DG system for microgrid operation. In grid-connected mode, PQ control is
developed by controlling the active and reactive power output of DGs in
accordance with assigned references. In islanded mode, DGs are controlled by
droop control. Droop control implements power reallocation between DGs based on
predefined droop characteristics whenever load changes or the microgrid is connected/disconnected
to the grid, while the microgrid voltage and frequency is maintained at appropriate
levels. This paper presents results from a test microgrid system consisting of
a voltage source converter (VSC) interfacing with a DG, a PV array with MPPT,
and changeable loads. The control strategies are tested via two scenarios: the
first one is to switch between grid-connected mode and islanded mode and the
second one is to change loads in islanded mode. Through voltage, frequency, and
power characteristics in the simulation under such two scenarios, the proposed
control strategies can be demonstrated to work properly and effectively.
KEYWORDS:
1.
Distributed generation
2.
PV
3.
Microgrid
4.
Droop control
5.
PQ control
SOFTWARE: MATLAB/SIMULINK
BLOCK
DIAGRAM:
Fig. 1. Schematic of the microgrid.
CONTROL SYSTEM:
Fig. 2. Schematic of the PQ control.
Fig. 3. Schematic of the droop control.
EXPECTED SIMULATION RESULTS:
Fig. 4. PQ control under grid-connected
mode.
Fig. 5. Droop control for switching
modes.
Fig. 6. Droop control for varying load.
CONCLUSION:
In
this paper a detailed PV model with MPPT, and PQ and droop controllers is
developed for inverter interfaced DGs. The use of PQ control ensures that DGs
can generate certain power in accordance with real and reactive power
references. Droop controller is developed to ensure the quick dynamic frequency
response and proper power sharing between DGs when a forced isolation occurs or
load changes. Compared to pure V/f control and master-slave control, the proposed
control strategies which have the ability to operate without any online signal
communication between DGs make the system operation cost-effective and fast
respond to load changes. The simulation results obtained shows that the proposed
controller is effective in performing real and reactive power tracking, voltage
control and power sharing during both grid-connected mode and islanded mode. To
fully represent the complexity of the microgrid, future work will include the
development of hierarchical controllers for a microgrid consisting of several
DGs and energy storage system. The function of primary controller is to assign optimal
power reference to each DG to match load balances and the secondary controllers
are designed to control local voltage and frequency.
REFERENCES:
Barsali,
S., Ceraolo M., Pelacchi, P., and Poli, D. (2002). Control techniques of
dispersed generators to improve the continuity of electricity supply. IEEE
Conf., Power Engineering Society, vol.2, pp.789-794.
Cai,
N., and Mitra J. (2010). A decentralized control architecture for a microgrid
with power electronic interfaces. IEEE conf., North American Power Symposium,
pp. 1-8.
Chen,
X., Wang, Y.H., and Wang, Y.C. (2013). A novel seamless transferring control
method for microgrid based on master-slave configuration. IEEE Conf., ECCE
Asia, pp. 351-357.
Cho,
C. H., Jeon, J.H., Kim, J.Y., Kwon, S., Park, K., and Kim, S. (2011). Active
synchronizing control a microgrid. IEEE Trans., Power Electron., vol.
26, no. 12, pp. 3707-3719
Choi,
J.W. and Sul, S.K. (1998). Fast current controller in three-phase AC/DC boost
converter using d-q axis crosscoupling. IEEE Trans., Power Electron., vol.13,
no.1, pp. 179-185.
