ABSTRACT:
The conventional over/under voltage, over/under frequency based anti-islanding protection scheme presents significant nondetection zone (NDZ) under critical loading conditions of distribution networks. To overcome this challenge, a unique hybrid technique has been proposed in this article for the anti-islanding protection of distributed generators (DGs). The algorithm requires the injection of an active oscillatory disturbance signal of very small magnitude through the current control loop along the direct axis of the synchronously rotating reference frame of the converter. Small signal stability analysis of the system is carried out to analyze the effect of such active signal injection having different frequencies. The anti-islanding protection algorithm first involves the superimposition of d-axis voltage. Thereafter, two novel indexes are proposed based on which the trip signal logic is developed for the protection scheme. The methodology has been found to detect an unintentional islanding scenario within 90 ms from the initiation instant. The efficacy of the proposed hybrid anti-islanding protection scheme is tested under various abnormal operating conditions by performing simulations on the CIGRE LVtest system. Experimental validation of the proposed methodology has also been carried out in Controller Hardware-in-the-Loop (CHIL) platform using Typhoon HIL 602+ and Speedgoat baseline real-time target machine.
KEYWORDS:
1.
Active
disturbance injection
2.
Anti-islanding
protection
3.
Distributed
generators (DGs)
4.
Small signal stability
5.
Superimposition
SOFTWARE: MATLAB/SIMULINK
CONTROL DIAGRAM:
Fig. 1. Control strategy adopted for the DGs with signal injection through direct axis current control loop.
EXPECTED SIMULATION RESULTS:
Fig. 2. Performance of the proposed scheme under zero power mismatch condition.
Fig. 3. Performance of the proposed scheme under different types of load Switching
Fig. 4. Performance of the proposed scheme under unbalanced loading condition
CONCLUSION:
Small
signal stability analysis-oriented design of a hybrid real-time anti-islanding
protection scheme has been proposed and successfully demonstrated in this
article. The prominent features of the proposed method can be listed as
follows.
1)
Faster detection time of an unintentional islanding event compared to most of
the proposed methods in literature even under the worst case scenario.
2)
The selection of amplitude of the disturbance signal has been done considering
the negative impact on power quality. On the other hand, the frequency of the
active disturbance signal has been selected in such a way that it avoids any
kind of excitation of the modes of the system thereby causing instability.
3)
Due to the superimposition of the d-axis voltage, the effects due to transients
are nullified and the methodology preserves both security and dependability
attribute.
4)
Although the theoretical analysis has been carried out in the standard IEEE
1547 test system, the protection technique proposed in this article is
generalized and can be applied for DGs in any distribution networks.
The efficacy of the proposed algorithm is evaluated under various operating conditions by conducting simulations on the CIGRE LV distribution network. Further, the real-time performance evaluation of the proposed algorithm has been carried out in the CHIL platform using Typhoon HIL 602+ and Speed goat baseline real-time target machine on standard IEEE 1547 test system under various operating conditions. It has been observed that the algorithm is robust under different operating scenarios and is able to preserve its desired functionality in most of the cases.
REFERENCES:
[1]
F. Blaabjerg, Y. Yang, D. Yang, and X. Wang, “Distributed power generation systems
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[2]
UL Standard for Safety for Inverters, Converters, Controllers, and
Interconnection System Equipment for Use with Distributed Energy Resources,
UL 1741, 2010.
[3]
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[4]
F. Noor, R. Arumugam, and M. Y. Vaziri, “Unintentional islanding and comparison
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[5]
S. Dutta et al., “Shifting of research trends in islanding detection
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