Fractional Order Notch Filter for Grid-Connected Solar PV System with Power Quality Improvement


 Power Quality This paper deals with the development of fractional order notch filter (FONF) for a grid-connected solar photovoltaic (PV) system. The developed FONF control approach is used to estimate fundamental active constituents from the distorted load currents and hence gating pulses for operating voltage source converter (VSC) are used in the PV system. This control approach for the grid-connected solar PV system is designed to achieve several purposes such as feeding active power demand of load/grid and counter current related power quality issues at common connecting point.


The power quality issues taken into consideration are harmonics distortion, reactive power burden on the system and unbalancing of connected loads. The FONF based control proposes a modified structure of an integer order notch filter. The integer order filters have limitation due to fixed integrator and differentiator term. In FONF, the power of integrator used in a notch filter, can be modified according to the application required for obtaining accurate response of the system.


A prototype of the grid-connected solar PV system is developed in the laboratory using IGBTs based VSC and dSPACE MicroLabBox (DS-1202) to demonstrate the behaviour of the FONF based control. Simulation and experimental results are obtained for steady state and unbalanced loads with variation in solar irradiance. The harmonic distortions in the system are observed as per the IEEE-519 standard.


  1. Solar photovoltaic generation
  2. Fractional order control
  3. Notch filter
  4. Harmonics
  5. Power quality



Fig. 1 System configuration of grid connected solar PV system.


Fig. 2 Bode plot comparison of IONF (α=1, β=1, ξ=0.1 and α=1, β=1, ξ=1) and FONF (α=1.2, β=0.8, ξ=0.5) with different values of fractional parameters.

Fig. 3 Comparative performance of IONF and FONF in converging active weight component.

Fig. 4 Convergence of fundamental active components using FONF, NLMS and NLMF under (a) steady state and (b) unbalanced loading conditions.

Fig. 5 Harmonic spectra of (a) grid current iga using FONF (b) grid current iga using NLMS (c) grid current iga using NLMF (d) load current ila.

Fig. 6 Harmonic spectrum of grid current with different frequency components using FONF controller.

Fig. 7 Harmonic spectrum under nonlinear load with R-C parallel branch using FONF controller (a) grid current, iga (b) load current, ila.


A three-phase grid connected solar photovoltaic system with FONF based control has been proposed in this work. The FONF control has been designed to accomplish twin functions of the grid-connected PV system viz. delivering active power to the load/grid and alleviating current related power quality issues at PCC. Numerous power quality issues such as harmonics distortion in the grid current, reactive power demand of the load and unbalancing load currents have been solved by the developed control system.


The FONF control has been found suitable in terms of its flexibility to alter power of integrator used in the notch filter and asymmetrical gain response curve, which is not possible in case of integer order notch filter. It has been observed from the Bode plot that sharpness of developed FONF does not alter by increasing the value of damping ratio once fractional gains are appropriately decided. Moreover, this control presents fast response when compared with integer order notch filter.


Performances of FONF controller have been confirmed at steady state and unbalanced load along with variation in solar irradiance considered. Experimental results demonstrate performance of FONF controller in maintaining 3.2% THD in the grid current, which is in accordance with the IEEE-519 standard for the grid interfaced PV system.


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