Study On The Technique Of Back-to-Back Converter

With the development of power electronic devices and the continuous improvement of a variety of motor control theory, motor control performance is greatly improved. The general-purpose converter that has simple structure and simple control method is still the most widely used kind of converter at present.As the general-purpose converter usually employs uncontrolled diode rectifier, there are unavoidably a lot of shortcomings of it, such as a large number of input current harmonics, low energy efficiency, denial of four-quadrant operation, etc.The PWM rectifier technology, of which the uncontrolled diode rectifier is replaced by a controlled IGBT is used in this paper in order to overcome these shortcomings.The converter employs such topology not only has the characteristics of high power factor, low harmonic pollution, two-way flow of energy, but also ensure the system of good static and dynamic performance and reliability.First, several major topological structures of the current source and voltage source back-to-back PWM inverter are discussed in this paper. The advantages and disadvantages of these topological structures are also analyzed.Second, the PWM rectifier which is the most important component of PWM inverter that usually has two components of PWM rectifier and PWM inverter is the research focus in this paper. The working principle of PWM rectifier is introduced, and the mathematical model of the PWM rectifier in two-phase rotating coordinate system is deduced in details. The control strategy of three-phase voltage rectifier is analyzed in this paper, and a double-loop structure control system that has outer loop of voltage and the inner loop of current is designed. The space vector pulse width modulation (SVPWM) based on switching model is introduced, and the design method of the inductance and capacitance values in voltage PWM rectifiers is given as well.Third, the dead time effect in induction motor control is analyzed and the judgments principle of the current direction based on the power factor angle is presented. The dead time compensation strategy of SVPWM for the three-phase voltage PWM inverter is given in this paper, the availability of which is proved under different frequencies in experiments.Finally, the circuit design which uses TMS320F2812 as a core control chip is introduced. Using MATLAB software, the simulation study of PWM rectifier and back-to-back PWM converter is proceeded, in which the feasibility of the strategy is proved. The experimental platform, under which many experiments are proceeded, is established based on the results. The experiments of PWM rectifier and back-to-back PWM inverter are proceeded, in which the result of waveforms proves the correctness and the practicality of back-to-back PWM inverter technology and PWM rectifier technology.