Performance and design of an electromagnetic sensor for brushless DC motors

Abstract

The electromagnetic position sensing device described in the paper operates both at standstill and running speeds by detecting the phase change of the second harmonic component of induced voltage in pickup coils around a stator of magnetically nonlinear material. The magnetic circuit associated with each pickup coil is excited by a high frequency sinusoidal current and has a magnetic bias that is switched by the position of a simple magnet attached to the rotor of the machine. Results are presented from a prototype device and signal processing is considered to the point where three logic position signals are available, as in Hall effect units. An analytical treatment of the device is given such that geometrical optimisation is possible. List of principal symbols b0 = bias flux density in active zones b S = bias flux density averaged over unit breadth X B,, B , = instantaneous flux density in outer and inner D = breadth of winding slot e, = instantaneous standardised output of one unit e s 2 , E,, = instantaneous and peak values of second harmonic standardised EMF induced in a pickup coil, respectively H , , H , =instantaneous magnetic field in outer and inner zones, respectively i, I = instantaneous and peak excitation currents, respectively J, J^ = instantaneous and peak drive current densities averaged over winding slot, respectively 57. = maximum current density in winding slot area L = axial length of unit L = length of winding slot MI, M, = gradients of line segments on B / H characterNd NO t = time X Y a @ 0 zones, respectively istic operative at time t = number of turns in exciting coil of a unit = number of turns in a pickup coil = total breadth of a unit = breadth of outer zone = fraction of winding slot allotted to pickup coil = total magnet flux passing through a unit = angular frequency of excitation current Paper 7198B (Pl), first received 25th September 1989 The authors are with the Department of Electrical Engineering, University of Manchester, Manchester M13 9PL, United Kingdom 174 1 introductionThe range of applications for brushless DC motors continues to increase and with it the need for these motors to operate in more hostile environments. The usual rotor position sensing device incorporated in these motors is a Hall effect ring [l] where three suitably positioned semiconductor devices detect rotor position via the influence either of a special switching magnet on the rotor or of the main rotor poles. The motor volume that must be allotted to the Hall effect ring is often brought into question, particularly for very small motors. However, sometimes of greater significance is the suitability of these devices in terms of reliability in environments involving high temperatures, high vibration levels and ionising radiation. Whether or not the Hall effect device is criticised on a volume or a reliability basis, the search for an alternative unit continues. If a unit independent of the main magnetic circuit of the motor is considered, there are several alternative systems possible [ 1, 21 involving ...

Sensorless control of PM synchronous motors and brushless DC motors - an overview and evaluation

“…The second harmonic of the measured signal is used to estimate the rotor position. In [18], these coils are placed in an additional stator lamination with equally spaced slots. It is possible to create machine saliency attaching small metal pieces to the surface of the magnets [19].…”

Novel Electromagnetic Rotor Position Sensor for Brushless DC Machine in Aviation and Aerospace Industry

“…In the last several decades, the brushless DC machine (BLDCM), taking the advantages of small volume, light-weight, reliable operation, and efficient energy-saving, is gradually used in many aviation and aerospace industry applications such as the all electric aircraft electromechanical actuation system, the space robot actuation system, the lunar roving vehicle wheel and steering drive, and so on [1][2][3][4][5][6][7]. As a synchronous AC machine, rotor position sensor is an essential part of the BLDCM to produce torque and generate power.…”

“…The environment temperature may even exceed 160 degrees Celsius and reach 200 degrees Celsius. Moreover there all or partially exist mechanical vibration, electromagnetic interference, dust and oil pollution [1][2][3][4][5][6][7].…”

“…The state-of-the-art technology can merely extend semiconductor operating temperature to 150 degrees Celsius, which means that the traditional hall-effect sensor, the photo-electronic sensor and the giant-magnetic-resistance sensor will all fail to function properly [1][2][3][4][5][6][7]. Although the resolver can withstand the above severe conditions, there are still some deficiencies.…”

“…With a relatively high frequency sinusoidal current injected into the excitation coils, the induced voltage of the pickup coils was modulated by the machine rotor position. Reference [6] proposed another method with a lot improvement. The excitation and pickup coils were set in the sensor by independent notches along the outer circumference of the stator core and a salient permanent magnetic rotor was used.…”