| Ultrasonic motor(USM)is a new type of motor,which is combined of powe electronics,new materials,new process,automatic control theory,tribology and other new high-end science.Compared to the traditional electromagnetic motor based on electromagnetic energy to get movement,USM uses the reverse piezoelectric effect of piezoelectric materials to get the ultrasonic vibration,and then achieves movement by friction.As a result,it has the advantages,such as low speed and large torque,no electromagnetic interference,self-lock while power off,to be used in many high-tech fields.These requirements then ask for the USM system to simplify its structure,to be miniaturization and flat.Though USM itself has been very tiny,its driver is needed to be miniaturized.By referring to some materials,the current situation,advantages and shortages of USM power drivers are analysed firstly in this thesis.Then the bridge driving of switching inverter mode is selected,which has the advantages of simple topology,small size,ability to drive USM directly and wide range of applications.Thus the overall architecture is determined which combines Boost converter with bridge-driver.In this means,Boost converter acts as a power supply for bridge driver to produce two square waves whose phase difference is 90 o,amplitudes are equal to the output voltage of Boost converter.Then the two square waves can be applied directly,or through the resonant network to drive USM.A Boost converter based on peak current mode(PCM)is specially designed in this thesis,which is based on the technology of Boost converter and switch inverter to drive USM.Firstly,the basic working principle and control mode of Boost converter are introduced.Secondly,the AC small signal model of PCM Boost converter with PWM control is introduced: the mature Ridley model and an improved model(applying for different loads,especially for capacitive load).Thirdly,the small signal model above is used to guide the selection of key parameters within and off chip.Fourthly,specific and important modules within and off the loop are designed,whose simulation results are also present.Finally,the simulation reults and actual testing results of Boost converter and the USM_Driver system are given.The actual circuits in this thesis are designed based on the 0.35 um BCD process.From the simulation to actual testing results,recovery time of the designed Boost converter when load step is 760 mA with almost 1A/us changing is within 20 us,which meets the requirements,the final USM driver chip works stably.This all satisfy the needing that required. |
