Study Of PWM Power Amplifier In DC Servo System

In high precision DC servo system, the PWM power amplifier based on power electronic devices is mainly used. It can realize the wide range control of speed and position and has excellent capabilities. But the power electronic devices in PWM power amplifier are working in the on-off state, easily producing the over-voltage and over-current phenomena. Under tht condition the power electronic devices are bearing higher dv/dt, di/dt and more energy losses, influencing itself capability and life-span. At the same time, the dv/dt, di/dt also cause the severe electromagnetism disturbances, such as the disturbances in the photoelectric theodolite will make the other systems working improperly. So the research of EMC and reliability of PWM amplifier has the important engineering meaning.The components, working principle, advantages and defects of PWM power amplifier are introduced briefly in the dissertation. The working characteristics of H-bridge PWM power amplifier in double-polarity mode is analyzed qualitatively and qualitatively and the conclusion that fluctuant magnitude and continuousness of armature current are the essential parameters which can be used to evaluate PWM control modes. Then with regard to EMC, reliability and control flexibility of PWM power amplifier, the following contents are studied.To improve the control flexibility of PWM power amplifier and realize all kinds of PWM control mode, a PWM controller is designed based on CPLD by using VHDL, which has the features of low cost, high reliability and integration.The EMC of DC PWM power amplifier is analyzed and several measures to restrain the disturbances of PWM power amplifier are put forward. Based on the PWM power amplifier in existence, the RCD snubber circuit experiment is carried out and the result shows that the RCD snubber circuit can restrain the voltage surge and the disturbances of dv/dt, di/dt.The PWM power DC-DC convenor based on IPM-IGBT is developed. The measuring circuit and restraining circuit of pump voltage are also designed. The entire system has the advantages of simple circuit,small size and high reliability.