Artificial intelligence-based approaches to control the neutral current compensator and implementation of power quality conditioner for power quality enhancement | Original Article

ABSTRACT:

Power electronic components and electronic converters gave birth to numerous new applications, offering unmatched comfort, flexibility and efficiency to the customers. Owing to the improvement in technologies, large number of harmonics are introduced and they degrade the performance of the three-phase four-wire distribution system. These effects of distortion also affect the point of common coupling where other loads are connected to the system. A lot of measures and mitigating techniques have been presented in the literature but each has its own drawbacks like circuit complexity, lack of reducing lower order harmonics, occurrence of resonance problems with line impedance, etc. To overcome these defects, the thesis proposes two techniques to improve the power quality of the system. The first method aims at designing a Neutral Current Compensator and the second method involves designing of Unified Power Quality Conditioner. The neutral conductor of three-phase four-wire distribution systems have been widely employed to deliver electric power to single-phase or three-phase loads. The neutral conductor usually carries the zero-sequence current due to the unbalanced loading among phase conductors. As more and more electronic equipment such as computers, copy machines and adjustable speed drives are being used, the harmonic currents drawn by their rectifier front ends also become significant. Especially, the zero-sequence triple (3rd, 9th, etc) harmonics accumulate in the neutral conductor, resulting in overloading of the neutral conductor and the distribution transformer. Survey results in United States have indicated that 22.6 of the sites have neutral current exceeding the phase currents. In order to alleviate the effects of neutral current, the thesis proposes a new technique based on neutral current compensator. The neutral current compensator is a series active filter which is connected in series with the neutral conductor. The main objective of this compensator is to eliminate the harmonic component present in the neutral conductor there by overloading and overheating in the neutral conductor can be eliminated. By eliminating the harmonic distortion in the neutral, the phase current distortion is also reduced to a considerable extent. Rotating unit vector-based hysteresis controller is used to extract the harmonic component in the neutral conductor. The proposed method implements back propagated artificial neural network, fuzzy logic controller techniques and fuzzy solar PV based hysteresis controllers. The MATLAB simulation software is used to model and simulate the circuits. The hardware model is also implemented for the compensation of the neutral current harmonics to validate the simulation results. The effects of nonlinear loads also have a high impact on the load voltage distortion and load current distortion. Consequently, the current drawn by the loads has a high harmonic distortion level. If this level continues, then it affects the performance of the system by causing over heating of the conductors and degrades the efficiency. The thesis prescribes a model of Unified Power Quality Conditioner to overcome these potential problems. Synchronous Reference Frame controller is used to extract the reference signals for the series and shunt inverter of unified power quality conditioner. The conventional Proportional Integral (PI) controllers, genetic algorithm-based tuning of PI controllers and particle swarm optimization-based tuning of PI controllers are implemented for maintaining constant voltage across the input of inverter circuit. Hysteresis current and voltage controllers are used to generate the switching signals for the series and shunt inverters. Fuzzy logic controller is implemented to control the upper and lower band of the hysteresis controller. Among the various techniques stipulated, the PSO tuned PI controller with fuzzy hysteresis controller provides good dynamic response by reducing the harmonic distortion in the load current and load voltage, thereby balancing the unbalanced loads.