Research On Controllably Inductive Power Filtering Method For Power Quality Comprehensive Management

For industry rectifier system,the diode or thyristor based rectifiers are now widely used,which causes a series of power quality issues,such as harmonic pollution,low power factor and operation loss of the transformer.This thesis presents a controllably inductive power filtering(CIPF)method with the new filtering mechanism.First,by comparing the existing harmonic suppression method,the thesis reveals the advantages of inductive filtering method on the harmonic elimination and the reduction of transformer loss.By means of the basic study on the CIPF system,it indicates that the filtering system can realize the bi-directional suppression of the harmonic currents from the non-linear load side and the gird side,and dampen the harmonic resonance.Moreover,the experimental results verify the above theoretical analysis.The major work and the innovative achievement in this thesis are summarized as follows:(1)The special operating mechanism of the CIPF method is revealed in theory.First,the equivalent circuit model and the mathematical model are established and the mathematical expression which is used to reflect the influence of the non-linear load and the background harmonic on the grid-side current is deduced.Based on the mathematical expression,the special impedance matching condition and the requirement for control coefficient setting can be obtained.Furthermore,this section studies the harmonic bi-directional suppression in term of the mathematical expression and the sensitivity analysis,which revealed the ability of harmonic suppression and resonance damping.(2)The system stability of the CIPF system is theoretically and preliminarily analyzed.Comprehensively considering the practical control and detecting algorithm,and the influence of time delay,the system transfer functions of each components are obtained.According to the deduced mathematical expression for the grid-side current,the close loop model of the CIPF system is established,and the bode diagram and the Nyquist diagram of the open loop transfer function are plotted,respectively.Then,the system stability under different harmonic damping coefficients is discussed.Based on the stability analysis,we can obtain the setting requirement of the controller parameter,which is helpful for the efficient and stable operation of the CIPF system.(3)A virtual impedance comprehensive control(VICC)strategy for the inductive power filtering system is proposed.To efficiently utilize the control potential of the voltage-source inverter and seek a control algorithm that suit the CIPF system,the VICC strategy is designed.The conventional harmonic detecting algorithm is no longer suitable for the CIPF system.Based on the study on the existing harmonic detecting algorithm,the selective harmonic detecting and control method,and the related dc voltage regulation method are proposed.The proposed harmonic control method effectively improves the filtering performance and reduces the capacity of the inverter.Moreover,the proposed zero-impedance control is designed to satisfy the impedance matching condition for implementing the inductive filtering.The zero-impedance control can improve the frequency selectivity of the passive device and create a virtual single tuned filter at specific harmonic frequency.(4)The CIPF prototype is developed in the laboratory.To validate theoretical research of the CIPF method,a experimental prototype is established in the laboratory.According to the practical experience during the development of the prototype,this section introduces the overall structure,the wiring scheme,the program implementation and system debugging.At last,the working performance of the CIPF prototype is tested to verify the theoretical analysis.The experimental results shows that the CIPF method has advantages on harmonic bi-directional suppression,resonance damping,reactive compensation and reduction of transformer loss.This thesis performs the preliminary study on the CIPF method,reveals the special operating mechanism,and constructs the basic theory and application research system.The research establishes the foundation for the further study on the CIPF system.The research achievements further deepen the inductive filtering theory,and lead a new way for the harmonic suppression and reactive compensation.