设计以MCS - 51单片机的PWM兼容控制器.docxVIP

附录ADesign of PWM Controller in a MCS-51 Compatible MCUA.1 AbstractThis paper presents a design of Pulse-Width Modulated (PWM) controller module in a MCU based on MCS-51 structure. The design can generate 2-channel programmable periodic PWM signals. These output PWM signals from MCU can be used for a variety of applications including motor control. The function of the design allows users to select independent or complementary inversion timing relationships between 2 PWM wave forms. The latter mode selection also includes optional dead time function to support driving H-bridges and inverters. Therefore, users can control the output PWM signals through setting the duty-cycle registers.After the successful simulation at the front end, practicalexperiments made on a NIOS development board verify the design.A.2 IntroductionPWM technology is a kind of voltage regulation method by controlling the switch frequency of DC power with fixed voltage to modify the two-end voltage of load. This technology can be used for a variety of applications including motor control, temperature control and pressure control and so on. In the motor control system shown as Fig. 1, through adjusting the duty cycle of power switch, the speed of motor can be controlled. As shown in Fig. 2, under the control of PWM signal, the average of voltage that controls the speed of motor changes with Duty-cycle ( D = t1/T in this Figure ),thus the motor speed can be increased when motor power turn on, decreased when power turn off.Fig A1 PWM control block diagramFig A2 The Relationship between Voltage of Armature and Duty-cycleTherefore, the motor speed can be controlled with regularly adjusting the time of turn-on and turn-off. There are three methods could achieve the adjustment of duty cycle: (1)Adjust frequency with fixed pulse-width. (2) Adjust both frequency and pulse-width. (3) Adjust pulse-width with fixed frequency. Generally, there are four methods to generate the PWM signals as the following: