Study On Theory And Key Technology Of High Performance Rectifier System

With the increasing depletion of fossil fuels and exacerbation of environmental pollution, electric energy as the most convenient, valuable and green energy plays an important role to develop and promote the modernization of the entire human civilization. United Nations Millennium Assembly determined that the global economy should choose the low-carbon and sustainable way. Under this background, how to improve energy efficiency and enhance power quality control and management has increasingly gained the attention of governments of all countries. For some high energy-consuming areas such as metallurgy and chemical industries, the high-power rectifier system with diodes or thyristors is now widely employed, but there are huge energy loss, low power factor and severe harmonic pollution and other negative issues. Therefore, the research and development of new high performance rectifier system (HPRS) and its control technologies is extremely important for the realization of energy saving, emission reduction and efficiency promotion goals.With high operating performance, the proposed HPRS, which can synchronously complement electrical energy transformation, harmonic suppression and reactive power compensation, is a new-type high-power rectifying supply system. Based on inductive filtering method, the basic theory, key technologies and engineering application of HPRS in12-pulse form are mainly researched in this thesis. The major work and the innovative achievement in this thesis are summarized as follows:1) The operating mechanism of HPRS is analyzed and the decoupling circuit model is established. First, the whole system electromagnetic constraint equations associated with the transformer are presented. Then, under the symmetric condition of power supply system with HPRS, the system single-phase decoupling model is established and its single-phase equivalent circuit equations are derived. Based on these equations, the operating mechanism of the inductive filtering system is analyzed, and the conditions of inductive filtering needed to meet and the principle of reactive power compensation are also discussed. Meanwhile, according to the system symmetrical feature of physical structure, the system decoupling model is simplified. With the simplified model, it has the advantage to fully characterize complex electromagnetic relationship of the system by using a simple form, which lays the theoretical foundation for the follow-up study of operating characteristics, the optimization design of components and verification work. 2) The steady-state operating characteristics of HPRS are studied. The characteristic equations of each port of the system under the fundamental and harmonic operating conditions are derived, which aims at the performance improvement with inductive filtering technology. At the same time, with the new-type rectifier transformer, the HPRS’s performance on harmonic suppression, reactive power compensation and commutation process is separately investigated. For the same operating conditions of fundamental and harmonics environment, the comparative study is done between the HPRS and the conventional one which with filtering device on the network side. From the simulation and experimental results, it is concluded that HPRS is superior to conventional rectifier system and better meet the performance requirements.3) The study on the design, selection and detail parameter optimization of L-C filtering device of HPRS is done. Considering the actual conditions, each filtering configuration is evaluated and the multi-objective optimization mathematical model for the filtering parameters design is established. An improved particle swarm optimization algorithm based on vector evaluation method is put forward for the parameters optimization of the chosen filtering scheme. Examples analysis, simulation and experimental results show that the optimized filter can satisfy with the pre-design requirements and performed a good filtering effect, especially to deal with the currents amplification phenomenon of5th and7th harmonic at the system grid-side. The method of filtering scheme selection and its filtering parameters optimization will provide design guidance for the engineering application of HPRS, and it also can provide reference for other power filters design.4) The potential efficiency promoting methods for the HPRS is further excavated. By using the energy monitoring system and the optimization control technology, the overall efficiency of HPRS can be further enhanced. During the development of new energy-saving technology for high-power rectifier system, it urgently needs to employ an efficiency monitoring system in order to achieve accurate power measurement and give appropriate efficiency assessment for each component or energy-saving technology. For the proposed efficiency monitoring system, a current inversion algorithm is proposed to solve the accurately measurement problem for heavy direct current. Meanwhile, in order to improve system power quality and coordination between the thyristors and the voltage regulating devices, an expert cooperative control algorithm model is proposed for the rectifier control. The test results of this control algorithm showed that it can improve the adjustment efficiency of both thyristors and voltage regulator and guarantee the firing angle of the thyristors keeping within optimal adjustment range.5) The system efficiency of HPRS’s engineering application is tested and analyzed. By taking one electrolysis rectifier system as a typical case, the background of HPRS’s application, the wiring scheme of main circuit and its design parameters are introduced. Then, based on these measured data got by field test, the items about system harmonics, power factor and power consumption of each component are analyzed. The analysis demonstrates that HPRS possesses good characteristics on operating efficiency and power quality, which provides engineering examples to promote the application of inductive filtering technology in other fields.In summary, the HPRS’s working mechanism, the main circuit topology, analytical mathematical model, the system equivalent circuit, the filtering parameter optimization design and the system collaborative control algorithms based on experts arbitration are conducted in this thesis. The basic theory and key technology of HPRS, which has the characteristics of power saving and efficiency promoting, is initially set up, it lay the theoretical and technical foundation for the application of HPRS in high power current conversion areas such as electric railway traction systems, HVDC, etc. The research results and engineering application cases of HPRS can also provide a useful reference for the development of high performance commutation equipments in other areas.