Control of a Three-phase Shunt Active Power Filter for Unbalanced Conditions
Type of DegreePhD Dissertation
Electrical and Computer Engineering
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The awareness of the quality and reliability of the power system has been increased in recent years due to several reasons. The excessive increasing of the applications of power electronics devices on the grid causes power quality problems including harmonic distortion and unbalancing in the power system. The unbalanced loading and the variations in the loads cause system imbalance. Harmonic distortion and system imbalance weaken the system and make it unstable and unsecured. Several devices have been introduced for solving power quality problems. Problems such as imbalance and harmonics can be corrected using filters. Because of the increasing of nonlinear loads, the active power filter (APF) have been preferable over passive filters. The shunt APFs are controlled to eliminate power quality problems related to source current. However, some control systems do not operate effectively under unbalanced power system operation. The extraction of the positive and negative sequence components is important for the control system of shunt APFs. Traditional extraction methods have weak performance under unbalanced conditions. Therefore, a new extraction method is introduced. It operates under any power system conditions, and is intended to extract the positive and negative sequence components from the measured signals. The analysis and evaluation demonstrate the capability of this extraction method. An improved control method based on instantaneous real and reactive power theory (IRPT) is proposed. Using the proposed extraction method allows the control system to operate under different power system conditions. Several simulation and experimental tests are presented to validate the work of this control method. Moreover, the system frequency could fluctuate due to changes in the power system. For that, the proposed control method was examined under frequency change. A frequency detection method was designed using the proposed extraction filter. It is aimed to measure the frequency and allow the control system to adapt the system frequency. Several simulation and experimental tests were performed to validate the operation of the proposed control methods. Finally, a voltage sensorless control method is presented. It is intended to reduce the number of the measured signals. The proposed extraction method is used with the source current. The simulation and experimental results show the operation of this control technique.