Sheng-Ming Yang

Efficiency-optimized flux trajectories for closed-cycle operation of field-orientation induction machine drives

A structured design procedure for system integration is presented. A dynamic programming scheme is developed which optimizes efficiency of an induction-machine drive which is operated in closed-cycle and which has both control and state constraints. Application of rotor-flux feed-forward field-orientation control for an induction machine reduces the system equations to contain only three state variables: rotor flux, velocity, and position. Maximum stator current and rotor velocity are set as constraints. Saturation effects are modelled to provide a state-dependent constraint on the rotor-flux magnitude. Load is treated as a function of the rotor position, which is appropriate for many mechanical system applications. To optimize efficiency for closed-cycle operation of the motor, both machine losses as well as the cycle time must be minimized using an appropriate objective function. State trajectories of the system that simultaneously optimize machine efficiency and cycle time are found by dynamic programming. Flux trajectories for the optimal solution are found to vary significantly over the machine cycle. The validity of the energy optimization is investigated experimentally on a feedforward, field-oriented induction machine.<<ETX>>

Performance evaluation of a velocity observer for accurate velocity estimation of servo motor drives

Because the position transducers commonly used in industry, i.e. encoders and resolvers, do not inherently produce an instantaneous velocity measurement, some signal processing technique is generally required to improve the accuracy of velocity estimation at each sample instant. This estimated signal is then used as the velocity feedback signal for the velocity loop control. The differential position technique commonly used in industry for velocity estimation suffers from the large quantization error, therefore limits the servo control loop bandwidth. This paper presents both the theoretical analysis and the experimental verification of a scheme that uses a close loop observer for velocity estimation. The results have shown that the quantization error in the velocity feedback signal can be reduced dramatically when using a close loop observer for velocity estimation. The results also shown that at low speed, the velocity estimation could be improved with a simple compensation scheme.

Design and Implementation of a Magnetically Levitated Single-Axis Controlled Axial Blood Pump

This paper presents the design and implementation of a magnetically levitated axial blood pump. The rotor has a hollow structure for fluid flow, and the impeller is mounted on the rotor inner surface. The magnetic suspension system is realized using two passive magnetic bearings for radial direction balancing and an electromagnetic actuator for axial direction balancing. A sensor assembly for the rotors axial position control is also presented. This sensor can measure axial displacement with good accuracy. A prototype pump was built and investigated. The experimental results demonstrate successful magnetic levitation and water-pumping operations. Because radial movements were not actively controlled, noticeable oscillations existed in these directions. These oscillations were caused mainly by the radial force produced by the actuator.

A deadbeat current controller for field oriented induction motor drives

Accurate stator current control is essential in high performance field orientation-controlled induction motor drives. Any current error degrades the drives performance in the same way as an incorrectly tuned field orientation. This paper presents an efficient current control scheme that can achieve high accuracy and a fast dynamic response. This scheme uses voltage decoupling and deadbeat control loops. The decoupling controller provides the voltage needed to oppose the motors back EMF. The deadbeat controller reduces the current error as fast as possible and stabilizes the system. The control law does not require knowledge of the rotor flux and is independent of the field orientation control tuning. Good static and dynamic performances were obtained in both the simulation and experimental verifications. Because the motor leakage inductance and resistance information were required for this control method, the influence of the estimation errors for these parameters was also investigated. The results show that the leakage inductance model error might cause a current ripple. However, this parameter can be tuned to its correct value easily by inspecting the current response.

AC induction servo sizing for motion control applications via loss minimizing real-time flux control

A design procedure is presented for induction machine servo motion control applications. The approach can be used to select the minimum size machine optimally and/or to obtain optimal time performance from a given machine. The reduced-form outcome of the procedure lends itself to real-time implementation in the induction servodrive. The basis of the technique is in modeling and controlling of machine losses. The model is prepared so that trajectory modifications can be made on-site and their effects are properly accounted for in a revised optimal flux trajectory. Theoretical and experimental results demonstrate substantial performance advantages from such an approach. The validity of the design optimization was investigated experimentally on a feed-forward, field-oriented induction servo drive.<<ETX>>

Instantaneous Shaft Radial Force Control with Sinusoidal Excitations for Switched Reluctance Motors

In general, unbalanced radial force acting on rotor shaft is undesirable since it causes vibrations. Due to its special structure, the shaft radial force and torque of a three-phase 12/8 switched reluctance motor can be separately controlled by proper selection of pole currents of the energized phase. In this paper, a sinusoidal current excitation scheme is proposed for the torque and radial force control of a 12/8 pole SRM. When controlled with the selected sinusoidal currents the SRM can produce the desired shaft radial force in any direction of the rotational plane without disrupting the rotational torque. Also, since the pole currents are individually controlled a more sophisticated phase commutation strategy is proposed for smoother torque and radial force ripples. The proposed schemes were verified experimentally.

An Approach to Producing Controlled Radial Force in a Switched Reluctance Motor

Unbalanced radial force acting on a rotor shaft is undesirable because it causes motor vibrations. However, motor vibrations can be reduced with intentionally produced shaft radial force which cancels the existing unbalanced radial forces due to a nonuniform air gap or external load. Due to its special structure, the shaft radial force and torque of a switched reluctance motor (SRM) can be separately controlled when all pole currents are controlled independently. However, control of SRM radial force is rarely discussed in the existing literature. This paper presents a scheme that produces a controlled radial force for a 12/8-pole SRM. In this scheme, mutual inductances between stator poles are included in the control model. The motor torque is controlled with the conventional method, i.e., all poles in the conduction phase are energized with the same current to produce the desired torque. Two extra poles from the descending-inductance phase are energized to produce the desired radial force. The cross-coupling torque produced by the force producing poles is compensated. The experimental results have verified that when controlled with the proposed scheme, the SRM was able to produce a controlled radial force when at standstill or running, and subjected to a load torque.

Observer-based inertial identification for auto-tuning servo motor drives

In servo motor drive applications variation of inertia degrades drives performance. Motor response is affected not only by external disturbance input but also by mechanical parameters such as inertia and friction. These factors must all be considered in order for accurate inertia identification and drive tuning. In this paper, an observer-based auto-tuning scheme for servo motor drives is presented. This scheme is consisted of a state estimator to estimate motor disturbance and two adaptive controllers to separately adjust drive inertia and friction to their correct value. The servo control loop is tuned automatically with the inertia found. The experimental results show that this auto-tuning scheme can achieve good performance and that the scheme is able to estimate the mechanical parameters accurately.

Generation of Parametric Kinematic Error-Correction Functions from Volumetric Error Measurements

A rapid arid convenient means of acquiring a knowledge of the kinematic errors of a machine or mechanism can be helpful in the diagnosis of the source of these errors and in their mechanical or software correction. However, direct measurement of kinematic errors is often difficult and time consuming. Volumetric error measurements are often more easily made. It therefore is desirable to be able to obtain parametric functions describing kinematic errors from volumetric error measurements rather than by measuring the kinematic errors themselves. Three phases in the generation of kinematic error functions from volumetric error measurements are described in this paper: establishing a kinematic model, acquisition of volumetric error measurements, and determination of the parametric error functions from the volumetric error measurements. These functions can be used to diagnose the source of errors. They also represent kinematic errors in a compact form suitable for software-based real-time error correction in machine motion controls.

Adaptive fuzzy logic-based velocity observer for servo motor drives

As the position transducers commonly used in industry do not inherently measure an instantaneous velocity, signal processing is generally required to improve the accuracy of velocity estimation at each sampling instant. This estimated signal is then used as the velocity feedback for the velocity loop control in servo motor drives. In this paper, an adaptive fuzzy logic-based observer is proposed to estimate velocity from the measured motor position. The proposed observer has a structure similar to that of the conventional state observer except that the state feedback is replaced with a fuzzy logic feedback. The observer has two adaptation mechanisms: the first one is used to vary the fuzzy output, and the second one is used to identify the motor parameters. The experimental results show that the noise in the estimated velocity caused by the quantization of the measured position can be reduced dramatically with the proposed observer. In addition, the observer has good transient responses in both normal and in low speeds.