Open loop control of a stepping motor with step loss detection and stall detection using back-EMF based load angle estimation

Stepping motors are the most used electrical machines for low power positioning. The drive controls the machine so that the rotor performs a fixed angular displacement after each step command pulse. Counting the step command pulses enables open-loop positioning. The vast majority of the stepping motor systems is driven in open-loop. When the rotor hits an obstacle stall occurs. Step loss due to overload is another typical problem with stepping motor driven systems. Both phenomena are not detected in open-loop which causes loss of synchronism. In this paper, a sensorless load angle estimator is used to detect step loss and stall. This algorithm is based on the typical stepping motor drive algorithms and does not depend on mechanical load parameters. The method therefore has a broad industrial relevance

Robust sensorless load angle control for stepping motors

In industry, the bulk of the stepping motors is driven in open loop full-step mode with maximum current to avoid step loss. This results in noisy operation due to torque ripples and a poor energy-efficiency. To tackle these problems the current current level at which the stepping motor is driven can be reduced to an optimal level. In this paper, a sensorless load angle controller is proposed and implemented to optimise the drive current level. However, reducing the current level results in a diminished torque margin for load disturbances. In this paper, a countermeasure to enhance the robustness of the sensorless load angle controller against torque disturbances is proposed and assessed trough measurements

Impact of harmonic voltage distortion on the voltage sag behavior of adjustable speed drives

The behavior of adjustable speed drives under voltage sag conditions and supplied form non-sinusoidal voltage waveforms has received little attention in recent years. This paper shows that voltage harmonic distortion has a major impact on the drive behavior. The impact of voltage sag conditions, including harmonics is represented by means of voltage tolerance curves. To overcome the impact, a fast field weakening control scheme for field oriented induction motor drives is analyzed

Advanced nonlinear modelling techniques for switched reluctance machines

This paper gives an overview of different modelling techniques to describe the nonlinear behaviour of both saturated switched reluctance machine (SRM) and power electronic converter. The current research contributes by comparing the de-coupled single-phase superposition method (lookup-tables) with a coupled analysis between drive model in Matlab/Simulink® and finite element model of the SRM motor. Experimental characterization techniques as well as finite element techniques are used to obtain the single-phase flux-linkage data. Transient electromagnetic analysis using the finite element method,coupled with a drive model and optimization strategy in Matlab/Simulink®, results in a more accurate SRM modelling. These results are more accurate because the mutual coupling between different phases is taken into account. Using this direct coupling, a complete analysis of the motor behaviour (local saturation, iron losses, …) can be modelled with the finite element software, keeping the complex drive and control strategy in Matlab/Simulink®.At every time step of the discrete solver, data is exchanged between the drive model and the coupled electric circuit of the finite element analysis.Simulation results are compared with measurements offlux-linkage, torque, phase current and iron losses. Pro’s and contra’s of the coupled and de-coupled modelling technique are discussed

Frequency response functions and modal parameters of a rotating system exhibiting rotating damping

In the analysis of the stability threshold speed caused by rotating damping in rotating machinery, there is a lack of experimental data. This stability threshold speed can be found theoretically by means of a linear speed dependent model. The accuracy of the model depends highly upon the linearity and especially on the damping type that has been chosen. In this paper, the theoretical model and the importance of the stability analysis is discussed together with an experiment to validate the model. A rotating shaft is used to extract frequency response functions at different speeds. The shaft is excited with an automated impact hammer and the response is measured by eddy current probes. From these frequency response functions, the poles are extracted and compared to the poles derived from the model. It is found that the imaginary part of the poles, or the Campbell diagram, agrees quite well. The decay rate plot shows a similar increase as from the model, but there seems to be an extra stabilizing effect that is not accounted for in the model

Modeling of the behavior of AC undervoltage relays during voltage dips

This paper proposes a dynamic model for the behavior of an AC undervoltage protection relay during voltage dips. The behavior is expressed by means of standardized voltage tolerance curves and highly depends on the point on-wave (phase angle) of the dip initiation. Using the model, it can be explained that AC undervoltage relays are much more sensitive to voltage dips of e.g. 50% Urated than to short interruptions (0% Urated), caused by the magnetic behavior. The model takes into account the electrical, magnetic and mechanical system equations. An experimental set-up with a programmable power source as dipgenerator is build to validate the model. Finally, a complete weaving machine is represented to analyze the influence towards voltage dip immunity by adding an undervoltage protection relay

Calorimetric efficiency determination of power electronic variable speed drives

A calorimeter test bench for the efficiency and power loss determination of power electronic variable speed drives is presented. The balanced calorimetric setup with air as the cooling medium is proposed to test small electronic drives for AC motors in a power range from 1 kW up to 7,5 kW. The construction, the required measurement equipment, the measurement procedure and especially the measurement results and uncertainty are important aspects of this test bench and are discussed in this paper. The device under test is a 2,2kW drive which is measured using both the input-output method and the calorimetric method. The test results are compared and conclusions are made concerning usability, repeatability and accuracy of the test bench. The overall goal is to further examine and optimize the calorimetric approach and to be able to obtain more accurate and comparable test results of very high efficient frequency converters. This setup reaches an uncertainty of ±2,39% or ±1,48W on the power loss at full load and speed using the calorimetric method