ABSTRACT:
This paper proposes a control strategy for an islanded microgrid
to effectively coordinate hybrid power source (HPS) units and to robustly
control individual interfaced inverters under unbalanced and nonlinear load
conditions. Cascaded H-bridge (CHB) multilevel inverters are flexibly deployed
in order to enhance the power quality and redundancy. The HPS employs fuel cell
(FC) as the main and super capacitors (SC) as complementary power sources. Fast
transient response; high performance; and high power density are the main
characteristics of the proposed HPS system. The presented control strategy consists
of a power management strategy for the HPS units and a voltage control strategy
for the CHB multilevel inverter. A multi proportional resonant (multi-PR)
controller is employed to regulate the load voltage at unbalanced and nonlinear
load conditions. The proposed multi-PR controller includes a fundamental voltage
controller with harmonic compensators. Digital time domain simulation studies
in the PSCADIEMTDC environment are given to verify the overall proposed system
performance.
KEYWORDS:
1.
Hybrid power source
2.
Fuel cell
3.
Supercapacitor
4.
CHB multilevel inverter
5.
Multi-PR
SOFTWARE: MATLAB/SIMULINK
CIRCUIT DIAGRAM:
Fig. I. Proposed structure of the hybrid FC/SC power source.
CONTROL SYSTEM
Fig. 2. Proposed control strategy of hybrid FC/SC power source
EXPECTED SIMULATION RESULTS:
Fig. 3. Microgrid response to unbalanced and nonlinear load
changes;
(a) Instantaneous real and reactive power. (b)
Positive-sequence, negativesequence,
and harmonic components of load
Fig. 4. (a) Instantaneous current waveforms, (b) switching
patterns of the
output voltage, and (c) voltage waveforms of each phase of the
DG unit's
CHB inverter due to the nonlinear load connection.
Fig. 5. (a) Instantaneous current waveforms, (b) switching
patterns of the
output voltage, and (c) voltage waveforms of each phase of the
DG unit's
CHB inverter due to the single-phase load disconnection.
Fig. 6. (a) voltage THD, and (b) voltage unbalance factor at DG
unit
terminal.
Fig. 7. The dc-link voltage waveforms to the unbalanced and
nonlinear
load changes.
Fig. 8. Dynamic response of the DG unit to load changes:
currents of FC
stacks and SC units of each HPS, (a) phase a, (b) phase b, and
(c) phase c.
CONCLUSION:
This paper presents an effective control strategy for an
autonomous microgrid considering the HPS and CHB multilevel inverter under
unbalanced and nonlinear load conditions. The proposed strategy includes power
management of the hybrid FC/SC power source and the CHB multilevel inverter
voltage control. The main characteristics of the proposed HPS are high
performance; high power density; fast transient response. Furthermore, a
multi-PR controller is presented to regulate the voltage of the CHB multilevel
inverter in the presence of unbalanced and nonlinear loads. The performance of
the proposed control strategy is investigated using PSCADIEMTDC software. The
results show that the proposed strategy:
• robustly regulates the voltage of the microgrid under unbalanced
and nonlinear load conditions;
• reduces THD and improves power quality by using CHB multilevel
inverters;
• enhances the dynamic response of the microgrid;
• accurately balances the dc-link voltage of each H-bridge cell;
and
• effectively manages the power among the power sources in the
HPS system.
REFERENCES:
[l] W. Liu, J. F. Chen, T. Liang, and R. Lin,
"Multicascoded sources for a high-efficiency fuel-ceU hybrid power system
in high-voltage application," IEEE Trans. Power Electron., vol. 26, pp.
931-942, Mar. 2011.
[2] IEEE Recommended Practice for Electric Power Distribution
for Industrial Plants. ANSIIIEEE Std. 141, 1993.
[3] IEEE Recommended Practices and Requirements for Harmonic
Control in Electrical Power System. IEEE Std. 519, 1992.
[4] J. Pereda and J. Dixon, "23-level inverter for electric
vehicles using a single battery pack and series active filters," IEEE
Trans. Veh. Techno!., vol. 61, pp. 1043-1051, Mar. 2012.
[5] A. Ghazanfari, M. Hamzeh, H. Mokhtari, and H. Karimi,
"Active power management of multihybrid fuel celIlsupercapacitor power
conversion system in a medium voltage microgrid," IEEE Trans. Smart Grid,
vol. 3, pp. 1903-1910, Dec. 2012.
