ABSTRACT:
In this paper a nested power-current-voltage control
scheme is introduced for control of single phase power inverter, integrating small-scale renewable
energy based power generator in a microgrid for both stand-alone and
grid-connected modes. The interfacing power electronics converter raises
various power quality issues such as current harmonics in injected grid current,
fluctuations in voltage across the local loads, voltage harmonics in case of
non-linear loads and low output power factor. The proposed nested proportional
resonant current and model predictive voltage controller aims to improve the
quality of grid current and local load voltage waveforms in grid-tied mode simultaneously
by achieving output power factor near to unity. In stand-alone mode, it strives
to enhance the quality of local load voltage waveform. The nested control
strategy successfully accomplishes smooth transition from grid-tied to
stand-alone mode and vice-versa without any change in the original control structure.
The performance of the controller is validated through simulation results.
KEYWORDS:
1.
Microgrid
2.
Stand-alone mode
3.
Grid-connected mode
4.
Voltage harmonics
5.
Current harmonics
6.
Proportional resonant control
7.
Model predictive control
SOFTWARE: MATLAB/SIMULINK
BLOCK DIAGRAM:
Fig.
1. Block diagram of MPVC scheme
EXPECTED SIMULATION RESULTS:
Fig.
2(a). Steady state grid voltage, load voltage and grid current waveforms with
resistive load
Fig.
3(b). Steady state grid voltage, load voltage and grid current waveforms with
non-linear load
Fig.
4. THD values of voltage and current waveforms in grid connected mode
Fig.
5(a). Steady state grid voltage, load voltage and filter current waveforms with
resistive load
Fig.
6 (b). Steady state grid voltage and load voltage waveforms with non-linear
Load
Fig.
7. THD values of load voltage waveform in stand-alone mode
Fig.
8(a). Transient state grid voltage, load voltage and grid current waveforms
with
change in active power reference
Fig.
9(b). Transient state grid voltage, load voltage and grid current waveforms with
change in reactive power reference
Fig.
10(c). Grid voltage, load voltage and grid current waveforms during voltage
Sag
(a) Transfer
from stand-alone to grid-tied mode
(b)
Transfer from grid-tied to stand-alone mode
Fig.11.
Grid voltage, load voltage, filter inductor current, grid current
Waveforms
(a)
Transfer
from stand-alone to grid-tied mode
(b)
Transfer from grid-tied to stand-alone mode
Fig.12.
Grid current tracking error waveforms
CONCLUSION:
In
this paper, a nested proportional resonant current and model predictive voltage
controller is introduced for control of single phase VSI integrating a RES
based plant in a microgrid. This strategy improves the quality of local load
voltage and grid current waveforms with both linear and non linear loads. A
non-linear load such as the diode bridge rectifier introduces voltage
harmonics, but this scheme is successful in achieving low THD values for
inverter local load voltage and grid current simultaneously. Simulation results
validates the outstanding performance of the proposed controller in both steady
state and transient state operations. A smooth transfer of operation modes from
stand-alone to grid-tied and vice versa is also achieved by the nested control
scheme without changing the control algorithm.
REFERENCES:
[1]
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[2]
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[3]
F. Blaabjerg, R. Teodorescu, M. Liserre, and A. V. Timbus, “Overview of control
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[4]
Q. C. Zhong and T. Hornik, "Cascaded Current–Voltage Control to Improve
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Electron., vol. 60, no. 4, pp. 1344- 1355, April 2013.
[5]
Y Zhilei, X Lan and Y Yangguang, "Seamless Transfer of Single-Phase Grid-Interactive
Inverters Between Grid-Connected and Stand-Alone Modes," IEEE Transactions on Power
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