Research On Minitype High Performance PM AC Servo System

With the development of microelectronics technology, power electronics,computer technology, control technology and motor manufacturing technology, asthe important drive parts of digital control machine tools, industrial robots, largescale integrated circuit manufacturing and aerospace field application, permanentmagnet AC servo system has been applied broadly in modern industry automationmanufactures.Sponsored by National High Technology Development (863Program) Project,guided by the fast and stable tracking requirements of humanoid robot joint drivesystems, we deeply study the robot integrated joint drive system design approach,including the permanent magnet AC servo control strategies and the minitype highperformance AC servo system development. Specifically include the following:The inner current loop bandwidth constraints the dynamic response of theservo system. This paper presents a bandwidth expansion strategy of the currentloop. In digital control AC servo system, there are two major factors restrictingcurrent loop bandwidth, switching frequency and digital delay which means thesum of time durations of A/D sampling, algorithm execution and PWM duty cycleupdate delay. The switching losses will rise with the switching frequency increase.So expanding the current loop bandwidth is necessary, without changing theswitching frequency. The delay effects of current sampling and duty cycle updatewere analyzed and the bandwidth expansion strategy is proposed. Double statorcurrent sampling and double PWM duty cycle update are achieved in a carrierperiod. The current loop bandwidth can be extended more than one timetheoretically and the dynamic performance of servo system is improved.The predictive current control for permanent magnet synchronous motor(PMSM) digital control system is studied and an improved robustness predictivecurrent control algorithm is proposed. The traditional deadbeat predictive controlalgorithm, based on Lagrange interpolation formula, has fast dynamic response andconstant switching frequency and is suitable for digital implementation. However, itis sensitive to motor inductance mismatch. So an improved deadbeat predictivecontrol algorithm is proposed. The current offset constraint and output voltageprediction method are modified. The relationship between algorithm stability andmotor inductance mismatch is analyzed using root locus method. In case if theinductance mismatch occurs, the system remains stable. The actual motor currentcould follow the reference current and the closed-loop control is achieved. Therobustness of the algorithm is improved. In order to ensure speed response follow the command rapidly, withoutovershoot and oscillations occurring in the dynamic process, we propose a speedcontrol loop IP regulator parameter design method. The proportional action isrelocated into the feedback path to constitute integral-proportional (IP) regulator.Taking stability and following performance into account, the speed controllerdesign method is derived, and the anti-windup strategy is considered. The inertiaidentification is adopted to achieve controller parameters tuning. The speed controlstrategy has fast response without overshoot and oscillation, and improves anti-disturbance performance.The requirements for humanoid robot joint servo system are small size, lightweight, high response speed and high control precision. Aiming at these technicalrequirements, the minitype high performance servo system design method isproposed. The minitype AC servo system is consisting of high power densitypermanent magnet motor, minitype servo driver and magnetic encoder. The keytechnologies in the miniaturization design of the servo driver are researched,including power supply system, voltage and current detection, mechanical structuredesign and other aspects. The design method and solution of each function moduleare given. The thermal design of the minitype servo driver is implemented to ensurethe reliability of the system. The thermal analysis model is established, and thestructure is optimized based on simulation.Two types of minitype servo drivers have been developed after the aboveresearch work. And the system hardware and software have been designed.Experimental results show that the minitype AC servo system has small volume,light weight, good control performance, high power density, strong universality andother characteristics. It is applicable for the humanoid robot integrated joint drivesystem. And the research has built a stable base for the independent innovation andindustrialization of minitype servo control technology.The content in this paper is an important part of National High TechnologyDevelopment (863Program) Project (High Performance Humanoid Robot SenseControl Unit and System: High-speed High-precision Integrated Joint). The projecthas been checked and accepted by National863expert group and has achieved ahigher rating in September,2011.