A Study On Intelligent Detection And Control Approaches Of Distortion Currents For Active Power Filters

Active Power Filter (APF) is one of the most promising methods to solve theharmonic problem, which can be used for integrated compensating harmonic,reactive currents. The detection and control methods of distortion currents for APFare key factors affecting not only the compensation performance of APF, but also theextension application. Artificial intelligence techniques have become essential to thedetection and control for distortion currents of power system. The thesis studies newintelligent detection and control approaches of distortion currents for active powerfilters to satisfy the diverse requirements for APF to apply in the modern powersystem.An adaptive detecting approach of the harmonic currents based on Hopfieldneural network (HNN) optimum theory is proposed in this paper. Instead of trainingthe network, the basic principle of neural network is applied to determine adaptivelythe magnitude and phase of the fundamental and each of the harmonic currentcomponents in real time. A new method for estimation of power frequency based onquadrature phase-locked loop (QPLL) concept is used to Hopfield neural network.The QPLL--HNN harmonic estimation system can be applied to the precisefrequency and each of the harmonics for power system. The computer simulationsresults show that the methods have some advantages, such as real time, highaccuracy, adaptability to load currents, etc.The new intelligent hysteresis control methods based on Genetic Algorithm andneural network to compensate currents for active power filters are proposed in thepaper. Genetic algorithm (GA) is employed to optimize the switching instants inmain circuit to minimize total harmonic distortion in the power system as well asdecrease operating frequency of APF greatly. A hysteresis controller is realized by aback propagation neural network and the digital signal processor. The controller hasa high performance in response of current and robustness and insensitivity to theparameter changes. The simulations and experiments results prove the effectivenessof the control strategy.A shunt active power filter (APF) as harmonic generator taken to the dc link ofthe inverter eliminates harmonic wave generated by the inverter, so implement anew type of electrolytic capacitorless inverter circuit with harmonic compensation inthis paper. Control is mixed by Fuzzy logic control and hysteresis control, whichmade APF generate the harmonics current compensated accurately. The system isinvestigated analytically as well as experimentally. The obtained results arepresented to prove the correctness of the proposed method.