| The energy consumption by industrial departments of our country account for nearly two-thirds of total energy consumption, and now the ratio of power energy in the terminal consumption is continuously increasing. The distribution grid of industrial enterprise is the important link of power consumption and energy conservation. For many years, our country paid insufficient attention to the field of industrial electricity, while energy management of some enterprise were even still in the extensive stage, such as electrical equipment aging, low technical content, low utilization rate of load, non-effective operation and low reliability of energy-saving equipment. All of them can lead to much power loss and severely limit the improvement of production efficiency. Therefore, in order to improve power efficiency and power quality of electrical equipments, building up a green, effective and safe enterprise distribution power grid become an inevitable choice in solving the consumption and shortage contradiction. And it has been becoming increasingly prominent in the rapid development process of our economic and social.At present, the key technologies and sets of power electronics equipments in high energy-consuming metallurgy industry are still immature. Mostly the development of power conversion technology is just focused on a single equipment, so energy-saving effect is limited. According to the bottleneck problems of power conversion and power quality control of distribution power grid, based on the support of Graduate Innovation Fund Project in Hunan Province and the national "863" plan project, in this paper it interprets the intension of high-efficient power conversion and its control. Around multi-functional PWM rectifier, two-phase orthogonal inverter, multi-parallel dc switching power supply and other aspects, the related theory and method of high-efficient power conversion and its control are researc hed in depth. The research covers the working mechanism analysis, mathematical modeling, control algorithm, optimal design, and the key technical problems of engineering application and other aspects, and it can form a basic research method and technical s olution of high-efficient power conversion and control method. The research achievements and key points are mainly embodied in the following aspects:(1) A multi-functional composited-type PWM rectifier and its control method are studied, which can both realize PWM rectification and compensate reactive power & harmonics at the same time. For harmonic suppression, a harmonic comprehensive control method based fundamental dq rotating coordinates is proposed, turning the characteristic 6k ± 1 harmonics into a kind of 6k harmonics. So the number of harmonic resonant controllers has reduced greatly, and it can reduce the complexity of control system. In order to guarantee the stability operation of PWM rectifier under the unbalanced grid voltage, a current com bined control method based dq rotating coordinates is proposed, which can realize the comprehensive control of positive-sequence and negative-sequence current in positive-sequence dq rotating coordinate. And the proposed controller combines the feedforward con trol and feedback control, which can improve the response performance of system.(2) To meet high-power applications at the middle/high-voltage grid, a kind of three-level PWM rectifier with LC series filter is put forward. It can realize the effective integration of PWM rectification and power compensation function. On the basis of the analysis of working principle and operation performance, the parameters design method for minimizing the operation voltage is deeply studied. In order to reduce power switches of PWM converter, a three-phase two-leg PWM rectifier is studied, the switching mathematical model is established. And then the dc-link ripples and their analytical expressions are deduced. According to this analysis, a composite control method composed of feedforward control and feedforward decoupling based feedback control is put forward, which can realize the independent control of two legs of PWM rectifier and tracking the reference nearly without errors.(3) For the special needs of metallurgical el ectromagnetic stirring, a two-phase orthogonal power supply composed of PWM rectifier and three-leg inverter is studied. Firstly, the power balance mathematical model of system is established, and then the mathematical expression of dc-link 2nd harmonic ripple is deduced. According to this analysis, a composite control method of former PWM rectifier is proposed, which can improve the power quality of power supply. For the latter three-leg inverter, a current composite control method composed of feedforward control and PR iterative-type feedback control is put forward on the basis of load model, which can effectively improve the dynamic output performance and meet the frequent alternating rotation requirement of electromagnetic stirrer.(4) In order to meet the high-power dc power supply requirements in electrochemistry, a multiple-parallel high-frequency switching power supply based on PWM rectifier is studied. For the multiple-parallel system, firstly, the main factors which cause the current-sharing error are analyzed. The virtual-impedance based dynamic and static current-sharing control method of dc/dc converter under voltage and current control modes are put forward respectively. The current-sharing error feedback control is used to enhance the current-sharing impedance, which can effectively improve the current-sharing performance, and the output feedforward approach is adopted to improve the dynamic performance of system. Secondly, the s domain control model of multiple-parallel system under two kinds of control modes are set up, and the stability of multiple-parallel system is analyzed. The result shows that it has stronger current-sharing performance and stable performance for current closed-loop control mode.(5) According to the actual engineering bac kground, several key problems in engineering application of two-phase orthogonal inverter for electromagnetic stirring and high-current switching power supply for electrolytic copper-foil are researched. According to the requirements of special-steel smelting, firstly, the mathematical model of electromagnetic stirror is analyzed. And then a 300 k VA two-phase orthogonal power supply and its parameter design method are studied. The design of hardware control circuit and software system based on DSP controller is described. According to the engineering background of electrolytic copper-foil, a 50 k A high-frequency switching power supply and the design of main circuit parameters are studied. The design of hardware control circuit and software system based on DSP controller is described. Finally, the devices are running normally with good effect. The enterprise‘s product quality is improved, and energy-saving effect is obvious.According to the power conversion, energy conservation demand of enterprise ‘ power grid, the high-efficient multifunctional PWM rectifier, two-phase orthogonal inverter, multi-parallel dc power supply and their control methods are researched deeply, which can overcome the limitation of single power electronics equipment, and realized the high-efficient power conversion and power quality control of distribution grid, etc. On the basis of the research of high-efficient power conversion and its control method, it can provide certain reference value for the research of other power quality control equipments, and is propitious to the practical process of power electronic system.Through the successful development of metallurgy special power supply and its engineering application, it can not only meet the demand for high-quality special steel and ultra-thin copper-foil, and reduce the production cost of metallurgy manufacturing enterprises. Meanwhile it can improve the international competitiveness, and has great significance to national economy and national defense construction. |
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