Research On Modulation And Control Technology Of Three Phase Current Type PWM Rectifier

The PWM rectifier uses power switching devices and pulse width modulation to overcome the problems of low power factor and high input current harmonics existing in traditional rectifiers.According to the output characteristics,it can be divided into voltage type PWM rectifier and current type PWM rectifier,current type PWM rectifier has many advantages such as wide voltage output range,internal short circuit protection,high reliability and so on.So it has been widely used in energy storage,uninterruptible power supply,new energy power generation,aerospace and induction heating and other fields.With the development of superconducting energy storage technology and the development of new power switching devices,the efficiency and power density of three-phase current type PWM rectifier are expected to be further improved,so it has wide application prospect.The modulation strategy and control strategy of three phase current type PWM rectifier are studied in this dissertation.In this dissertation,the working principle of three-phase current type PWM rectifier was analyzed first,and then the mathematical model based on static coordinate system and rotating coordinate system was established.Furthermore,the relationship between static variables,such as output voltage,active power,reactive power,power factor,and modulation ratio and switching function phase were further analyzed,and then the inherent attributes of the system were revealed.Secondly,according to the principle of SPWM modulation,the two-level logic signal of three-phase voltage type PWM rectifier was converted,and then the three-level logic signal generation technology suitable for three-phase current type PWM rectifier was obtained.On this basis,by decomposing and converting the three-level logic signal and combining with the PWM output mode of the control chip,a direct SPWM modulation mode was proposed,which realizes the same effect as the traditional two to three-level logic conversion mode,and it can eliminate the narrow pulse through the software algorithm,and effectively simplifies the system control circuit.Then the double closed-loop control strategy based on two phase synchronous rotating coordinate system was designed,and the steady-state control without static error is realized.In order to suppress the resonance of the LC filter on the AC side,by analyzing the advantages and disadvantages of the passive damping compensation method,the corresponding active damping control method was obtained by equivalent transformation of the control system block diagram on this basis,which effectively inhibits the system resonance,avoids the power loss caused by the passive damping method and improves the efficiency of the rectifier.Finally,the main circuit parameters of the system were designed.Based on the STM32F407 series of chips,the experimental prototype of the three-phase current type PWM rectifier was built.The closed-loop experimental test of the system was carried out to verify the effectiveness of the direct SPWM modulation strategy and the ability of the active damping control method to suppress the resonance.It has been verified that the three-phase current type PWM rectifier designed in this dissertation can realize stable operation per unit power factor,low input current harmonic content and the high efficiency.