ABSTRACT:
This paper proposes a hierarchical active power management
strategy for a medium voltage (MV) islanded microgrid including a multihybrid
power conversion system (MHPCS). To guarantee excellent power management, a
modular power conversion system is realized by parallel connection of small
MHPCS units. The hybrid system includes fuel cells (FC) as main and
supercapacitors (SC) as complementary power sources. The SC energy storage
compensates the slow transient response of the FC stack and supports the FC to
meet the grid power demand. The proposed control strategy of the MHPCS
comprises three control loops; dc-link voltage controller, power management
controller, and load current sharing controller. Each distributed generation (DG)
unit uses an adaptive proportional resonance (PR) controller for regulating the
load voltage, and a droop control strategy for average power sharing among the
DG units. The performance of the proposed control strategy is verified by using
digital time-domain simulation studies in the PSCAD/EMTDC software environment.
KEYWORDS:
1.
Fuel cell (FC)
2.
Multihybrid power conversion system (MHPCS)
3.
MV microgrid
4.
Supercapacitor (SC)
SOFTWARE: MATLAB/SIMULINK
CIRCUIT DIAGRAM:
Fig.
1. (a) MV microgrid consisting of two DG units. (b) Proposed structure
of
hybrid FC/SC power conversion system.
CONTROL SYSTEM:
Fig. 2. Proposed structure of the hybrid FC/SC power source.
EXPECTED SIMULATION RESULTS:
Fig.
3. Balanced load changes in feeders F3 and F1. (a) Instantaneous real and
(b)
instantaneous reactive powers of the feeders.
Fig.
4. Instantaneous voltages at the DG unit terminals during balanced load
changes
in feeder F1, (a) DG1 and (b) DG2 .
Fig.
5. Frequency of islanded microgrid during balanced load changes.
Fig.
6. Dynamic response of the DG units to balanced load changes: (a) real
power,
and (b) reactive power components.
Fig.
7. Dynamic response of DG1 units to balanced load changes: (a) FC
stack
and SC module power of first hybrid unit; (b) FC stack and SC module
power
of second hybrid unit; and (c) dc-link voltage.
Fig.
8. Unbalanced load change in feeder F1. (a) Instantaneous real and
(b)
instantaneous
reactive powers of the feeders.
Fig.
9. Dynamic response of the DG units to unbalanced load change with
conventional
PR controller: (a) real power, and (b) reactive power components
Fig.
10. Dynamic response of the DG units to unbalanced load change with
adaptive
PR controller: (a) real, and (b) reactive power.
Fig.
11. Dynamic response of DG1 units to unbalanced load change: (a) FC
stack
and SC module power of first hybrid unit; (b) FC stack and SC module
power
of second hybrid unit; and (c) dc-link voltage.
CONCLUSION:
This
paper presents a hierarchical active power management strategy for a MV
islanded microgrid considering the MHPCS. The proposed strategy includes power
management of the FC/SC hybrid system, current sharing among the MHPCS components,
voltage control of the ac-side, and power sharing among the DG units. The SC
energy storage compensates the slow transient response of the FC stack. An
adaptive PR controller and a droop controller are, respectively, used to
effectively regulate the load voltage and to share the average power among the
DG units. The performance of the proposed control strategy in both balanced and
unbalanced load switching is investigated using PSCAD/EMTDC software. The
results show that the proposed strategy:
•
enhances the dynamic response of the microgrid in fast transients;
•
accurately shares the load current among the FC/SC hybrid units;
•
robustly regulates voltage and frequency of the microgrid;
•
is able to share the average power among theDGunits even under unbalanced
conditions;
•
effectively eliminates the low frequency transient of power components; and
•
locally compensates the unbalanced loads.
REFERENCES:
[1]
N. Hatziargyriou, H. Asano, R. Iravani, and C. Marnay, “Microgrids,” IEEE
Power Energy Mag., vol. 5, pp. 78–94, Jul.–Aug. 2007.
[2]
A. G. Madureira and J. A. P. Lopes, “Coordinated voltage support in distribution
networks with distributed generation and microgrids,” IET Renew. Power
Gener., vol. 3, pp. 439–454, Sep. 2009.
[3]
Z. Jiang and R. Dougal, “A hybrid fuel cell power supply with rapid dynamic response
and high peak-power capacity,” in Proc. IEEE APEC, 2006, pp. 1250–1255.
[4]
H. Nikkhajoei and R. Lasseter, “Distributed generation interface to the certs
microgrid,” IEEE Trans. Power Del., vol. 24, pp. 1598–1608, Jul. 2009.
[5]
M. Zandi, A. Payman, J.Martin, S. Pierfederici, B.Davat, and F. Meibody- Tabar,
“Energy management of a fuel cell/supercapacitor/battery power source for
electric vehicular applications,” IEEE Trans. Veh.Technol., vol. 60, pp.
433–443, Feb. 2011.
