asokatechnologies@gmail.com 09347143789/09949240245

Search This Blog

Friday, 14 June 2019

A Unified Control Strategy for Three-phase Inverter in Distributed Generation



ABSTRACT:  
This paper presents a unified control strategy that enables both islanded and grid-tied operation of three-phase inverter in distributed generation (DG), 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 (SRF). 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 grid-tied mode and the load voltage in islanding mode are distorted under nonlinear local load with the conventional strategy. And this issue is addressed by proposing a unified load current feed forward in the paper. Additionally, the 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 and experimental results.
KEYWORDS:
1.      Distributed generation
2.      Three-phase inverter
3.      Islanding
4.      Unified control
5.      Seamless transfer
6.      Load current
SOFTWARE: MATLAB/SIMULINK
CIRCUIT DIAGRAM:





Fig. 1 Schematic diagram of the distributed generzation based on the proposed control strategy.

 EXPECTED SIMULATION RESULTS:

Fig. 2 Bode plot of the transfer function from load current to grid current with
and without the load current feedforward, when DG operates in grid-tied
mode.

Fig. 3 Simulation waveforms of load voltage vCa, grid current iga and inductor
current iLa when DG is in grid-tied mode under condition of the step down of
the grid current reference from 9A to 5A with: (a) conventional voltage mode
control, and (b) proposed unified control strategy.


Fig. 4 Simulation waveforms of load voltage vCa, grid current iga and inductor
current iLa when DG is transferred from grid-tied mode to islanded mode with:
(a) conventional hybrid voltage and current mode control, and (b) proposed
unified control strategy.

CONCLUSION:

A unified control strategy is proposed for three-phase inverter in DG to operate in both islanded and grid-tied mode, with no need for switching between two different control architectures or critical islanding detection. A novel voltage controller is presented. It is inactivated in 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 feedforward is proposed, and it can improve the waveform quality of both the grid current in grid-tied mode and the load voltage in islanded mode. The proposed unified control strategy is verified by the simulation and experimental 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.