In this paper, three-phase, four-wire shunt active power filter (SAPF) is utilized to mitigate system harmonics of distorted voltage source for unbalanced and nonlinear loads. Basically, the source voltage should be pure sinusoidal waveform to get a good mitigation of source current harmonics. In this under study system, the source voltage is assumed to be harmonic distortion non-sinusoidal voltage source. The phase locked loop (PLL) control circuit is wielded for extracting the fundamental component of the distorted source voltage to use it as an input signal to the SAPF control. Another input signal to the SAPF is the distorted load current. The SAPF control system uses (p-q) theory to calculate the optimum instantaneous current to be injected by the SAPF to mitigate the source current harmonics even the source voltage is harmonic distorted. MATLAB/SIMULINK software package is utilized to simulate the system under study. The effect of SAPF is tested when it’s used with and without the PLL control circuit. The simulation results show that, the THD of source current when using the PLL control circuit is improved to comply with the harmonic limits given in the IEEE 519-1992 and IEC 61000-4-7 standards.

The power quality improvement faces different significant problems due to the wide use of power electronics and voltage instability. To overcome these different power quality problems, an active power filter is used. The active power filter in general has four main categories, shunt, series, unified power quality conditioner and hybrid active power filter. The shunt active power filter is usually used to mitigate source current harmonics and compensate reactive power for power factor improvement. The series active power filter is usually used to mitigate voltage problems (sags, swells, transients, dips, distortions….). The unified power quality conditioner is used for all voltage and current problems. In this paper, the three phase three-wire series active power filter is utilized alone to mitigate all power system problems (voltages and currents) for this case study, such as voltage sag, voltage swell, voltage harmonics, and source current harmonics to comply with the harmonics limits given in IEEE 519-1992, and IEC 61000-4-7 standards. The source current harmonic problem mainly exists due to, 1) distorted voltage source, and 2) non-linear loads. The series active power filter can effectively eliminate the source current harmonics in case of distorted voltage source. Consequently, the series active power filter can be used alone as a power quality improvement for all voltage and current problems as mentioned in this case study.

Power quality improvement faces different and significant problems due to voltage instability and the wide use of electronic power devices. To overcome these different power quality problems, an active power filter is used. The active power filter, in general, has 4 main categories- shunt, series, unified power quality conditioner, and hybrid active power filter. The shunt active power filter is usually used to mitigate source current harmonics and compensate reactive power for power factor correction. The series active power filter is usually used to mitigate voltage problems (sags, swells, transients, dips, distortions, harmonics, etc.). The unified power quality conditioner is a combination of the shunt active power filter and the series active power filter; it is used to mitigate all voltage and current problems, compensate voltage, current system harmonics, and reactive power compensation, and mitigate voltage dips, voltage sags, voltage swells, and voltage phase shift. In this paper, the 3-phase 3-wire unified power quality conditioner is utilized to mitigate all power system problems (voltages and currents) and discuss the effect of the shunt and series active power filter separately on source voltage and source current waveforms. This case study shows that the source voltage distortion can be mitigated by using the series active power filter alone, but the source current distortion cannot be mitigated without using both the series and shunt active power filter. The source current harmonic problem mainly exists due to 1) distorted voltage sources, and 2) non-linear loads. Therefore, the unified power quality conditioner must be used to mitigate source current distortions in the case of the distorted voltage source, to comply with the standard limits IEEE 519, IEC 555, and IEC 61000. HIGHLIGHTS The UPQC is used to mitigate all voltage and current problems and improve all power system quality The SEAPF eliminates all voltage problems The SHAPF has no effect on source voltage The SHAPF eliminates source current harmonic distortion GRAPHICAL ABSTRACT