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Friday, 16 March 2018

Fuzzy logic controller for five-level shunt active power filter under distorted voltage conditions


In this paper, a five-level inverter is used as a shunt active power filter (APF), taking advantages of the multilevel inverter such as low harmonic distortion and reduced switching losses. It is used to compensate reactive power and eliminate harmonics drawn from a diode rectifier feeding a RL load under distorted voltage conditions. The active power filter control strategy is based on the use of self tuning filters (STF) for reference current generation and a fuzzy logic current controller. The use of STF instead of classical extraction filters allows extracting directly the voltage and current fundamental components in the a-J3 axis without phase locked loop (PLL). This study is divided in two parts. The first one deals with the harmonic isolator which generates the harmonic reference currents. The second part focuses on the generation of the switching pattern of the inverter by using a fuzzy logic controller applied and extended to a five level shunt APF. The MA TLAB Fuzzy Logic Toolbox is used for implementing the fuzzy logic control algorithm. The obtained results show that, the proposed shunt active power filter controller has produced a sinusoidal supply current with low harmonic distortion and in phase with the line voltage.
1.      Active filter
2.      Harmonics isolator
3.      Distorted voltage conditions
4.      Self-tuning filter
5.      Fuzzy logic control and PWM control



Fig1.power system configuration


Fig. 2. Supply voltage Vs waveform

Fig. 3. Supply current Is waveform without filtering.

Fig. 4. Supply current Is waveform with filter.

Fig. 5. Active filter current If

Figure 6. APF output voltage Vab (line to line) for a five-level with

Fig. 7. DC voltage of the condensers Vdc

This paper has discussed the control and performance improvement of a shunt active power filter under distorted voltage conditions, using a fuzzy logic controller for a five level shunt active power filter based on the optimization of the reference current generation and using a modified version of the p-q theory and PDPWM to generate switching signals. Simulation results have shown high performances in reducing harmonics and power factor correction. The use of the Self-tuning filter leads to satisfactory improvements since it perfectly extracts the harmonic currents under distorted conditions. With the fuzzy logic control, the active filter can be adapted easily to more severe constraints, such as unbalanced conditions. In addition, results have demonstrated the major advantages of using STF and fuzzy logic controller in filter control. The Five-level APF provides numerous advantages such as improvement of supply current waveform, less harmonic distortion and possibilities to use it in high power applications. As final conclusion, the obtained results showed that, the proposed active power filter controller have provided a sinusoidal supply current with low harmonic distortion and in phase with the line voltage.
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