**Author details**

116 An Update on Power Quality

use of the PI controller to zero)

PI controller to zero)

**8. Conclusions** 

**Figure 46.** Difference between load voltage magnitude and nominal value (this amount is decreased by

**Figure 47.** Difference between load voltage and source voltage phases (this amount decreased by use of

In this research different approaches for reference generation of UPQC have been proposed. Based on the general equations of Fourier transform, its response settling time is one cycle. In this research for increasing the response speed and improving the control system capabilities in dynamic conditions, very fast Fourier transform approach has been proposed for balanced three phase systems. In the proposed approach, settling time of the response could be reduced to one twelfth of a cycle. In the proposed approach, there were two data window lengths, T/12 and T/2. In the sag, swell, and load change conditions, control system was switched to T/12 for obtaining fast response. Then for improving the proposed approach responsibility in filtering of unwanted steady state oscillation, control system was switched to T/2 for obtaining no oscillated response. In these states, fast response in dynamic conditions as well as good response in the steady state conditions would be possible. In this research for the detection of the source voltage sag, swell, and load change conditions, derivative of the first order magnitude of the voltage and current signal, were compared to a constant value. This was based on the fact that in these conditions voltage or current magnitude generally changes rapidly. Proposed control approach was simulated in MATLAB/SIMULINK software. Voltage sag, swell, and harmonics were compensated by Ahad Mokhtarpour

*Department of Electrical Engineering, Tabriz Branch, Islamic Azad University, Tabriz, Iran* 

Heidarali Shayanfar *Department of Electrical Engineering, South Tehran Branch, Islamic Azad University, Tehran, Iran* 

Seiied Mohammad Taghi Bathaee *Department of Electrical Engineering, K.N.T University, Tehran, Iran* 
