Digital motion control techniques for electrical drives

Sammanfattning: Digital motion control area toady is a well-established one,which is believed to be first initiated by power electronicengineers in the early seventies. Modern digital controltheory, advances in digital signal processor andmicrocontroller technology and recent developments in powerelectronic devices have made this field a very competitive one.The objective of this thesis is to present some digital motioncontrol techniques that can be applied for electrical drives.This is done by investigating two motion control problemsassociated with electrical drives; namely, precision motioncontrol and sensorless motion control.Application of digital motion control techniques for preciseeccentric rotor positioning of an induction machine with ActiveMagnetic Bearings (AMB) is the first application problemaddressed in the thesis. The final goal is to prepare aflexible test rig for the study of acoustic noise in standardinduction machines with rotor eccentricity. AMB control hasbeen a challenging task for the control engineers since itsinvention. Various types of control techniques - both analogand digital - have been attempted with a lot of success overthe past years. In the application area of rotating machines,the whole concept of AMB control means stabilizing the rotor ofthe machine in the exact center of the radial AMBs andmaintaining that position under magnetic disturbance forcesexerted on it by the stator under running condition. The aim ofthe first part of the thesis is to present several digitalmotion control techniques that would give the user theflexibility of moving the rotor to any arbitrary position inthe air gap and maintaining that eccentric position.The second part of the thesis dealt with sensorless controlof Permanent Magnet Synchronous Motors (PMSM) for high-speedapplications. Conventional PMSM drives employ a shaft-mountedencoder or a resolver to identify the rotor flux position. Itis advantageous to eliminate the shaft-mounted sensor byincorporating sensorless control schemes for PMSM drive systemsdue to many reasons. A sensorless control scheme must besufficiently robust and less computationally heavy for it to besuccessful. However, reliable performance of a sensorlesscontrol drive strategy is always an integration of many digitalmotion control techniques. Implementation of fast currentcontrol by overcoming sampling delay in the discrete system isa key issue in this respect. Suitable speed control with areliable controller anti-windup mechanism is also essential.Compensation techniques for the inverter non-idealities mustalso be incorporated to achieve better performance. In thispart of the thesis, all these aspects of a well performingsensorless control strategy for a PMSM are investigated.Frequency dependent machine parameter variation, which is asignificant practical problem against achieving the expectedperformance of these control strategies, is also addressed.Most of the problems addressed in the thesis are related toimplementation issues of a successful control method. Theapproach in this work is to find solutions to those applicationissues from the automatic control theory.Keywords:Eccentric rotor positioning, modeling,integrator anti-windup, bumpless transfer, identification,periodic disturbance cancellation, sampling delay compensation,cascaded control, speed and position estimation, compensationsfor non-idealities, parameter estimation, start-uptechnique