ABSTRACT:
This paper presents a unified control strategy that
enables both islanded and grid-tied operations of three-phase inverter in
distributed generation, with no need for switching between two corresponding
controllers or critical islanding detection. The proposed control strategy
composes of an inner inductor current loop, and a novel voltage loop in the synchronous
reference frame. The inverter is regulated as a current source just by the
inner inductor current loop in grid-tied operation, and the voltage controller is
automatically activated to regulate the load voltage upon the occurrence of
islanding. Furthermore, the waveforms of the grid current in the grid-tied mode
and the load voltage in the islanding mode are distorted under nonlinear local
load with the conventional strategy. And this issue is addressed by proposing a
unified load current feedforward in this paper. Additionally, this paper presents
the detailed analysis and the parameter design of the control strategy.
Finally, the effectiveness of the proposed control strategy is validated by the
simulation results.
KEYWORDS:
1.
Distributed
generation (DG)
2.
Islanding
3.
Load current
4.
Seamless
transfer
5.
Three-phase
inverter
6.
Unified control
SOFTWARE: MATLAB/SIMULINK
Fig.
1. Overall block diagram of the proposed unified control strategy.
EXPECTED SIMULATION RESULTS:
Fig.
2. Simulation waveforms of load voltage vC a , grid current iga,
and inductor current iLa when DG is in the grid-tied mode
under condition of the step down of the grid current reference from 9 A to 5 A
with: (a) conventional
voltage
mode control, and (b) proposed unified control strategy.
Fig.
3. Simulation waveforms of load voltage vC a , grid current iga,
and inductor current iLa when DG is transferred from the
grid-tied mode to the islanded mode with: (a) conventional hybrid voltage and
current mode control, and (b) proposed unified control strategy.
CONCLUSION:
A
unified control strategy was proposed for three-phase inverter in DG to operate
in both islanded and grid-tied modes, with no need for switching between two
different control architectures or critical islanding detection. A novel
voltage controller was presented. It is inactivated in the grid-tied mode, and
the DG operates as a current source with fast dynamic performance. Upon the
utility outage, the voltage controller can automatically be activated to
regulate the load voltage. Moreover, a novel load current feed forward was
proposed, and it can improve the waveform quality of both the grid current in
the grid-tied mode and the load voltage in the islanded mode. The proposed unified
control strategy was verified by the simulation results.
REFERENCES:
[1] R. C. Dugan and T. E. McDermott,
“Distributed generation,” IEEE Ind. Appl. Mag., vol. 8, no. 2, pp.
19–25, Mar./Apr. 2002.
[2]
R. H. Lasseter, “Microgrids and distributed generation,” J. Energy Eng.,
vol. 133, no. 3, pp. 144–149, Sep. 2007.
[3]
C. Mozina, “Impact of green power distributed generation,” IEEE Ind. Appl.
Mag., vol. 16, no. 4, pp. 55–62, Jul./Aug. 2010.
[4]
IEEE Recommended Practice for Utility Interface of Photovoltaic(PV) Systems,
IEEE Standard 929-2000, 2000.
[5]
IEEE Standard for Interconnecting Distributed Resources with Electric Power
Systems, IEEE Standard 1547-2003, 2003.
