Research On The Converting System Based On The Injected Harmonic Current Of Rectifier Transformer

Traditional converting system which uses a large number of non-linear power electronic components has a large number of harmonic current which inject to the power grid, therefore, it causes to decline the power quality and increase the loss. In order to suppress harmonic current and improve power factor, the traditional filtering scheme uses passive filter in the side of grid, however, passive filter can only compensate for fixed-frequency harmonic current and may appear the resonance, at the same time, it is easily affected by the impedance of power grid. But active power filter is not been used in large-scale domain because of the limit of the price, the device's capacity, voltage's grade and others. The hybrid active filter which combines its respective advantages of active filter and passive filter has become the major focus of the research on the suppressing harmonic current and the compensation of reactive power.This thesis combines with the topic of the Green Energy-saving DC Station which is the key science & technology project of 06GK1003-1 in the Eleventh Five Year Plan of Hunan Province. The study focuses on the following aspects:(1) A new filtering scheme which combines with the technology of the novel inductive filter and hybrid active power filter is presented in the paper. The working principle and general structure of the new converting system based on the novel rectifier transformer are introduced in the thesis. The filtering principle of the new converting system is derived from its equivalent mathematical model.(2) An overview of the various detection method of harmonic current which has been divided into two broad categories according to the definition of the power and the theories of digital signal processing is given in this paper. Because of the relay protection and the imbalance of the system, the detection method of harmonic current based on double-dq transformation is proposed. Its schematic diagram and formula are given. The novel all-digital phase-locked loop which can track grid's frequency in real time is proposed. Through the analysis of the simulation and experimental results, it is demonstrated that the principle of the novel all-digital phase-locked loop is correct and feasible.(3) The various control strategies of active power filter are overviewed. Refer to the method of the switching function, the mathematical model of the new converting system is derived. The advantage and disadvantage of the fuzzy control, PI control and repetitive control are detailedly analysed and compared. The comprehensive control technology of the current's waveform based on fuzzy+ PI+ repetitive control is proposed. The strategy and parameters of control are given. The simulation models of the comprehensive control is illustrated in Matlab. It is demonstrated that the control's technique has a good steady-state accuracy and dynamic performance by the results of the simulation.(4) The new converting system's overall structure and program are proposed, the novel rectifier transformer and the circuit of the hybrid active filter are designed. The design's parameters are given. The simulation models of the new converting system is illustrated in Matlab. The simulation's study is more in-depth. It is demonstrated that it is feasible by the results of the simulation. It also shows that the control technology of the current's waveform based on fuzzy+ PI+ repetitive control is better than the PI+ repetitive control, and the PI+ repetitive control is better than the pure PI control. It can be especially applied for the applications with large disturbances.