The Research On Theory And Applications Of Novel Converter Transformer And Its Filter System

To implement the industrialization of the patent of invention and the patent of utility model:"Self-Coupled Compensating and Suppressing Harmonic Converter Transformers", it's funded by the key science & technology project 05GK1002-1 of the Tenth Five Year Plan and 06GK1003-1 of the Eleventh Five Year Plan of Hunan Province. Under the background of the key science & technology project, the dissertation completes a part of this project and establishes the theoretical analytical system of novel converter transformer and its filter system (Novel System for short) in HVDC transmission system. This theoretical and analytical system includes the following:Combining the developing policy"transmitting the electricity from the west areas to east China, mutual suppling between north and south, entire country interconnecting network and power market"of our country's power industry in twenty years, it states the present application and development status of HVDC and UHVDC transmission technique in our country, and also points out that it's necessary and feasible to develop UHVDC transmission technique in our country. However there are some problems in the traditional HVDC transmission system: unfavorable filtering effect, increasing the burden to converter transformer, etc.The functions, technical characteristics and types of structure are analyzed. Firstly the mathematical model of traditional converter transformer is established; based on which the influence of different impedances of two bridges on commutated voltage is analyzed, and harmonic characteristics of converter transformer's windings current is analyzed under two conditions of considering the commutated impedance and ignoring it; and the windings capacity is calculated; then the connection scheme of traditional converter transformer and its filtering, reactive power compensation are presented.The vector relation between transformer windings'voltage is analyzed. Firstly four possible types of structure are stated and the self-coupling and compensating functions of novel system are analyzed. Taking the single-phase harmonic suppression transformer for example, its mechanism of harmonic suppression and the harmonic characteristics of novel system is analyzed; its design capacity is calculated, then the simulation models of novel converter transformer and traditional one are established, the simulating results verify the idea of inductive filtering.A systematic analysis method is proposed, which is based on multi-winding transformer theory, combining the magnetomotive balance, Kirchhoff's law and the voltage, current equations of loop circuit, and the mathematical model of novel system is established; and the matrix relations between load current and windings current and between the voltage of valve port and the primary phase voltage are analyzed; and the influence of asymmetry primary voltage on operational characteristics is discussed; also the voltage loss is calculated; its nodal admittance matrix in phase coordinates is derived, which can be easy-to-use in systematic model establishment.Aiming at the features of novel system, a three-phase testing method of commutated impedance is proposed. Firstly the commutated impedance is calculated using one-phase and three-phase testing methods; then the calculating result of commutated impedance based on mathematic model is presented. The results show that they are all coincident. so the reliability of novel system's mathematical model is verified; in the last, the impedance of filter branch how to influence the commutated impedance is analyzed.A novel converter– Filter Commuated Converter (FCC) is creatively proposed. Firstly the reactive power compensation ratio at the valve side (for short: compensation ratio) is defined; then the compensation ratio how to influence voltage loss of valve side, the commutated impedance, without-load line voltage at the valve side, DC voltage, the commutated angle and power factor etc are analyzed; moreover based on which, the equivalent Graetz bridge circuit model and DC side model of FCC are established, which provide the theoretical principle for further research on FCC. According to the mechanism of commutation failure and the factors influencing it, the every variable how to influence the commutation failure is analyzed, and the sensitivity of every variable to switch-off angle is analyzed when the inverter adopts FCC; furthermore, the method is put forward to mitigate the commutation failure.Through summarizing the designing method of traditional filters, the parameters'designing steps of single-tuned, double-tuned, two-order high pass filters and capacitor are presented. Based on the mechanism of harmonic suppression, the designing method of filters under harmonic suppression transformer is proposed, and the parameters'designing steps of single-tuned and double-tuned filters are stated; Similarly based on the design parameters of research platform of novel DC transmission system which will be done, the system's filter and reactive power compensation equipments is integrative designed, and the parameters are pointed out in detail.The designing idea of research platform of novel DC transmission system is stated, including the system structural frame and functions of every subsystem; in the last, based on the platform, the tests are done about the compensation factor how to influence the commutated impedance, line voltage without load, harmonic current analysis in the windings with zero compensation factor, DC side voltage, commutation angle and effect comparison of harmonic suppression with novel filtering methods and traditional ones; the results further verify superior operational characteristics and filtering effect of novel system.The novel system takes advantage of electromagnetic induction of transformer, the functions of harmonic suppression and reactive power compensation of filters, which eliminates the drawbacks of the traditional scheme. Due to the superior operational characteristics and filtering effect of novel system, it is inevitable that the novel system has a greatly prospect. The research platform provides exploring product for further spreading application in these areas including the metro, chemical and metal industry etc.