Power Quality Assessment of Voltage Positive Feedback Based Islanding Detection Algorithm

ABSTRACT:

Islanding refers to a condition where distributed generators (DGs) inject power solely to the local load after electrical separation from power grid. Several islanding detection methods (IDMs) categorized into remote, active, and passive groups have been reported to detect this undesirable state. In active techniques, a disturbance is injected into the DG’s controller to drift a local yardstick out of the permissible range. Although this disturbance leads to more effective detections even in well-balanced island, it raises the total harmonic distortion (THD) of the output current under the normal operation conditions. This paper analyzes the power quality aspect of the modified sliding mode controller as a new active IDM for grid-connected photovoltaic system (GCPVS) with a string inverter. Its performance is compared with the voltage positive feedback (VPF) method, a well-known active IDM. This evaluation is carried out for a 1 kWp GCPVS in MATLAB/Simulink platform by measuring the output current harmonics and THD as well as the efficiency under various penetration and disturbance levels. The output results demonstrate that since the proposed disturbance changes the amplitude of the output current, it does not generate harmonics/subharmonics. Thereby, it has a negligible adverse effect on power quality. It is finally concluded that the performance of the sliding mode-based IDM is reliable from the standpoints of islanding detection and power quality.

KEYWORDS:

  1. Islanding detection method (IDM)
  2. Power quality
  3. Sliding mode controller
  4. Total harmonic distortion (THD)
  5. Voltage positive feedback (VPF)

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Fig. 1. Sliding mode MPPT technique. (b) Schematic diagram.

EXPECTED SIMULATION RESULTS:

Fig. 2. Effect of VPF and proposed schemes on THDI with different percentages of nominal power.

Fig. 3. Average THDI for different disturbance sizes. (a) Modified sliding mode. (b) Classic VPF.

CONCLUSION:

In this paper, the influence of the classic VPF and modified sliding-mode IDM on the GCPVS’s power quality and efficiency has been evaluated. The study has been done for a 1 kWp PV system with string inverter. The simulation results show that, while the THD of output current in the proposed IDM is smaller than the simple VPF, both methods render acceptable power quality in a wide range of system operation. This proper performance has been achieved due to the variation of the current magnitude rather than the angle or frequency. This magnitude variation is realized in VPF and the proposed method in the current and voltage control loops (MPPT), respectively. The simulations also confirm that the acceptable THDI and harmonics are guaranteed in multi-GCPVSs connection situation even at low power generation levels as the worst scenario. Since the new technique tries to deviate the system from its MPP condition, the effect of embedded disturbance on the efficiency is also performed. In this regard, the simulations are carried out and a negligible reduction in MPPT and inverter efficiencies (less than 0.04%) has been demonstrated in the proposed method. This occurs since MPP can be gained at a small bound around ref. It has been finally concluded that the modified sliding mode controller has the advantages of the conventional VPF scheme in islanding detection as well as a higher power quality in the production of energy.

REFERENCES:

[1] A. Jäger-Waldau, “PV status report 2017,” Publications Office of the European Union, Luxembourg, 2018.

[2] M. Sandhu and T. Thakur, “Harmonic minimization in a modified cascaded multilevel inverter for islanded microgrid using two switching techniques,” International Journal of Grid and Distributed Computing, vol. 10, no. 12, pp. 11-20, Dec. 2017.

[3] S. Natarajan and R. S. R. Babu, “Reduction of total harmonic distortion in cascaded H-bridge inverter by pattern search technique,” International Journal of Electrical and Computer Engineering (IJECE), vol. 7, no. 6, p. 3292, Dec. 2017.

[4] A. Luo, Q. Xu, F. Ma et al., “Overview of power quality analysis and control technology for the smart grid,” Journal of Modern Power Systems and Clean Energy, vol. 4, no. 1, pp. 1-9, Jan. 2016.

[5] A. Khamis, H. Shareef, E. Bizkevelci et al., “A review of islanding detection techniques for renewable distributed generation systems,” Renewable and Sustainable Energy Reviews, vol. 28, pp. 483-493, Dec. 2013.

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