Low-power Motor Research Articles

Travelling wave ultrasonic motors, Part I: Working principle and mathematical modelling of the stator

Travelling wave ultrasonic motors have recently been attracting considerable attention: they may possibly soon replace—at least in certain areas—small electromagnetic motors. This development has been made possible by recent advances in power electronics, material research and digital control, which allow utilization of the piezoelectric effect for low power motors. In these motors the mechanical energy is generated with frequencies of the order of 40 kHz via piezo-elements producing bending waves in a stator, which has approximately the form of a circular plate. The rotor is then driven by the stator via contact forces, and with an extremely simple mechanism frequency reductions of 1:40 000 and more are obtained between the stator vibration and the rotor motion. As a consequence, one can work in the 40 kHz range on the electrical side, while a low frequency rotation is obtained on the mechanical side, as is desirable for many applications. In the present paper, which is the first of a series, the working principle of travelling wave ultrasonic motors is reviewed, and the main phenomena are mathematically modelled. In further papers a detailed mathematical description of the stator vibration and a first model of the contact problem will be given.

Fault Diagnosis of Electric Low-Power Motors by Analyzing the Current Signal

To detect and localize faults occurring in the rotor of universal motors analysis of the current signal in the time and frequency domain is presented. The information about the condition of the rotor is contained mainly in the periodical components of the current signal. Because these harmonics are speed dependent and the speed is not constant, digitizing synchronously with speed is carried out. The method of linear prediction is used as a spectral modeling technique in which the current spectra are modeled by all-pole spectra. The coefficients of the linear predictors are the basis for automatic fault detection and classification.

Studies on the use of conventional induction motors as self-excited induction generators

The suitability of using a normal three-phase induction motor as a capacitor self-excited induction generator (SEIG) is illustrated. The thermal limit of the stator windings being the limiting factor, the capacity of the SEIG is determined. The steady-state performance of such induction generators, maintaining a constant terminal voltage, is analyzed under resistive and reaction loads. Typical experimental results are also presented. It was found that, for low power motors, the maximum power that can be extracted as generators is 148% to 160% of the motor rating for resistive loads and 118% to 128% of the motor rating for 0.8 lagging power factor loads. Capacitive reactive volt-ampere (VAR) required to maintain constant voltage at 1.0 p.u. speed is in the range 85% to 140% of the power rating of the motor with resistive loads and 100% to 140% with lagging reactive loads.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A Method of Sensing Line Voltages for Parameter Adaptation of Inverter-Fed Induction Motor Servo Drives

Most high-performance inverter-fed induction motor drive systems require signals corresponding to the input voltages of the motor for parameter adaptation. Low-performance systems require the signals for stabilization. The voltage signals are used in the controller circuit and therefore require isolation. Isolation of the voltage signals is not a cost-effective solution in low-power motor drive systems. The fact that the base drive signals to the transistor inverter are isolated makes them the ideal choice for the reconstruction of the motor line voltages. A method of sensing line voltages from the base drive signals of the transistor inverter circuit is described. A step-by-step derivation of the voltage sensing algorithm is given which leads to a simple realization. The synthesized voltages are used in parameter adaptation for inverter-fed induction motor drives. The sensing scheme has been implemented on a laboratory prototype, providing experimental results which are presented.

Speed controllers for low-power AC motors

Speed controllers for low-power AC motors

HOMOPOLAR LINEAR SYNCHRONOUS MOTOR: STEADY STATE ANALYSIS AND EXPERIMENTAL RESULTS

ABSTRACT The main electrical and mechanical performances of a homopolar linear synchronous motor (HLSM) are calculated using classical theories which are usually applied to rotating synchronous machines. An experimental study on a low-power test motor permits the verification of theoretical results. It cranes to evidence that simple theories are applicable under certain conditions to such a motor of original conception. A full scale operational motor proposed for a combined propulsion and magnetic suspension system for high speed ground transportation is designed through extrapolation.

Ways of increasing the reliability and operating life of sintered bearings of low-power electric motors

Ways of increasing the reliability and operating life of sintered bearings of low-power electric motors