Identification of Two-Mass Mechanical Systems Using Torque Excitation: Design and Experimental Evaluation

This paper deals with methods for parameter estimation of two-mass mechanical systems in electric drives. Estimates of mechanical parameters are needed in the start-up of a drive for automatic tuning of model-based speed and position controllers. A discrete-time output error (OE) model is applied to parameter estimation. The resulting pulse-transfer function is transformed into a continuous-time transfer function, and parameters of the two-mass system model are analytically solved from the coefficients of this transfer function. An open-loop identification setup and two closed-speed-loop identification setups (direct and indirect) are designed and experimentally compared. The experiments are carried out at nonzero speed to reduce the effect of nonlinear friction phenomena on the parameter estimates. According to results, all three identification setups are applicable for the parameter estimation of two-mass mechanical systems.Peer reviewe

Discrete-Time Observer Design for Sensorless Synchronous Motor Drives

This paper deals with the speed and position estimation of interior permanent-magnet synchronous motor (IPM) and synchronous reluctance motor (SyRM) drives. A speed-adaptive full-order observer is designed and analyzed in the discrete-time domain. The observer design is based on the exact discrete-time motor model, which inherently takes the delays in the control system into account. The proposed observer is experimentally evaluated using a 6.7-kW SyRM drive. The analysis and experimental results indicate that major performance improvements can be obtained with the direct discrete-time design, especially if the sampling frequency is relatively low compared to the fundamental frequency. The ratio below 10 between the sampling and fundamental frequencies is achieved in experiments with the proposed discrete-time design.Peer reviewe

Sensorless self-commissioning of synchronous reluctance motors at standstill without rotor locking

This paper proposes a standstill method for identification of the magnetic model of synchronous reluctance motors (SyRMs). The saturation and cross-saturation effects are properly taken into account. The motor is fed by an inverter with a short sequence of bipolar voltage pulses that are first applied on the rotor d- and q-axes separately and then simultaneously on both the axes. The stator flux linkages are computed by integrating the induced voltages. Using the current and flux samples, the parameters of an algebraic magnetic model are estimated by means of linear least squares. The proposed method is robust against errors in the stator resistance and inverter voltage, due to the high test voltages (of the order of the rated voltage). The fitted model matches very well with the reference saturation characteristics, measured using a constant-speed method, and enables extrapolation outside the sample range. The method was tested with a 2.2-kW SyRM, whose shaft was uncoupled from any mechanical load, which is the most demanding condition for this method. The proposed method can be used for automatic self-commissioning of sensorless SyRM drives at standstill

State-space speed control of two-mass mechanical systems: Analytical tuning and experimental evaluation

This paper proposes a model-based two-degree-of-freedom (2DOF) state-space speed controller design for a two-mass mechanical system. Analytical tuning rules for a feedback gain, the reduced-order state observer, full-order state observer, and prefilter are derived. The proposed design rules enable the automatic tuning of the controller if the mechanical parameters are known. The prefilter is designed for step, ramp, and parabolic command tracking. The effects of the time delay, measurement noise, and parameter variations on controller tuning and control performance are studied by means of Nyquist diagrams, noise transfer functions, and time-domain simulations. It is shown that the full-order-observer-based controller is a preferable choice, particularly if the feedback loop is delayed and noisy. The proposed controller design is experimentally evaluated using two 4-kW servo motors coupled with a toothed belt; good reference tracking for step and dynamic commands, as well as robust and fast load-torque rejection, is demonstrated.Peer reviewe

Influence of magnetic saturation on modeling of an induction motor

This paper deals with modeling of a saturated induction machine. In control algorithms, the inverse-Γ model is widely used. However, the saturation models are typically based on the T or Γ model. Transformation between these models is easy if the machine is magnetically linear, but since the motor saturates, the modeling becomes more complex. In this paper, we study the properties of the Γ and inverse-Γ models and the transformation between these two models when the saturation is taken into account. The phenomena related to model transformation are studied by means of analytical equations. Also, the functionality of the models is studied by means of laboratory experiments.Peer reviewe

A dynamic model for bearingless flux-switching permanent-magnet linear machines

This article deals with dynamic models for three-phase bearingless flux-switching permanent-magnet (FSPM) linear machines. This machine type can be used to build a magnetically levitating long-range linear drive system, whose rail does not need any active materials apart from iron. A dynamic machine model is developed by means of equivalent magnetic models, taking into account air-gap variation and magnetic saturation. The effects of these phenomena are analyzed using finite-element method (FEM) simulations of a test machine. The parameters of the proposed model can be identified using the FEM or measured data. The model can be applied to real-time control and time-domain simulations. The model is validated by means of experiments.Peer reviewe

Levitation control for a double-sided bearingless linear motor based on feedback linearization

This paper deals with levitation control for a double-sided bearingless linear-motor system. Analytical design rules for a state-feedback gain and a state observer are derived. To decouple the production of forces in thrust- and normal-force directions, feedback-linearizing control based on the magnetic model is proposed. The proposed control design is tested in an experimental system consisting of four individually supplied linear-motor units in a double-sided configuration. The results from time-domain simulations and experimental tests suggest that the proposed control design can successfully provide smooth transition to contactless operation and retain the stable levitation during the movement in the thrust-force direction.Peer reviewe

Modeling of a bearingless synchronous reluctance motor with combined windings

This paper deals with modeling of bearingless synchronous reluctance motors with a combined winding. A method to link an existing model used for the separated windings structure to the combined winding structure is proposed. A dynamic model applicable for the purposes of time-domain simulation, model-based control design, and real-time control is presented. The finite-element method (FEM) is used to validate the proposed model and to show the feasibility of the considered slice motor type, including passive stability of axial movement and tilting, force and torque production, and ripple. Applicability of the developed model in control design is demonstrated. The model is validated by means of experiments.Peer reviewe