Shunt active power filter with modified synchronous reference frame technique and fuzzy logic current controller for harmonic mitigation

Harmonics is a power quality problem which represents a steady-state problem. It leads to a number of issues, ranges from equipment mal-function, which result to overheating of rotating machinery and random tripping of relays for protection of devices. Shunt active power filter (SAPF) has been the most popular choice to address harmonic disturbances in power system networks. For efficient compensation, SAPF greatly depends on fast and accurate detection of reference harmonic current. To generate the reference signals, modified synchronous reference frame (MSRF) technique is chosen. Low pass filter (LPF) has always been used to separate fundamental from harmonic components, and it provides adequate and reasonable results in harmonic mitigation. However, there is need for improvement due to presence of unwanted low order harmonics that cannot completely be eliminated by LPF. Meanwhile, generation of compensation current by SAPF is also depending on switching strategy. Sinusoidal PWM is used with fuzzy controller for better output performance. However, if the number of membership functions is too large, due to hardware limitations such as memory, speed and cost, all sets of rules cannot adequately be implemented in a complex system. Also, there is no certainty that the rules are defined correctly with no confliction between each other at certain situations. Furthermore, the ability to select an optimized subset of fuzzy rules is a major challenge in designing the control system. Therefore, in this research work, two modifications have been introduced to address the mentioned issues. First, harmonic extraction using SRF for three-phase three-wire system introduces a band pass filter, and second, simple three membership functions in fuzzy logic controller for inputs and five outputs are designed to improve performance of the switching algorithm. The SAPF was simulated in Matlab-Simulink platform and further verified with laboratory prototype. The simulation and experimental results show ability of the proposed algorithms to accurately estimate harmonic reference signal which was utilized in switching pulses for the SAPF. The performance index is the THD which is clearly shown to be improved from 23.99 % to 0.92 % for RL nonlinear load and for the RC nonlinear load from 35.46 % to 1.49 %. From both results, the proposed algorithms show good performances when compared with the conventional algorithms. The THDs were reduced to acceptable level in conformity with the available standard.

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