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A direct current brushless electric motor has a rotor, and a stator with inwardly extending teeth, between each pair of which a winding slot is defined. The radially inward face of each tooth has a dummy slot shaped so the reluctance forces between rotor and stator due to the presence of the dummy s

A direct current brushless electric motor has a rotor, and a stator with inwardly extending teeth, between each pair of which a winding slot is defined. The radially inward face of each tooth has a dummy slot shaped so the reluctance forces between rotor and stator due to the presence of the dummy slots are the same as those due to the winding slots. Motor control means incorporate a current feedback loop based on the incoming phase of each phase combination in the phase energization sequence in a driving mode and phase changeover may be initiated by Hall devices, two for each transition point, underlying the axial ends of the rotor magnets. The control means may incorporate a pulse width modulation power supply permitting the establishment of bias currents under motor standstill conditions.

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A brushless d.c. drive system, comprising a multiphase motor having a stator, a rotor and a plurality of phase windings; control means for energizing said phase windings in paired combinations and in a predetermined sequence during system operation, two phase windings being energized in each paired

A brushless d.c. drive system, comprising a multiphase motor having a stator, a rotor and a plurality of phase windings; control means for energizing said phase windings in paired combinations and in a predetermined sequence during system operation, two phase windings being energized in each paired combination; sensor means for indicating rotor disposition at each of a plurality of rotational dispositions of the rotor relative to the stator, each said disposition corresponding to a transition from energization of one said paired combination of the phase windings of the motor to energization of a further paired combination of the phase windings, one of the phase windings of a paired combination of phase windings energized prior to each said transition being de-energized at said transition and a further winding being energized at said transition to define a new paired combination of phase windings, and the energization of the other of said phase windings of said paired combination of phase windings energized prior to said transition being maintained through said transition and subsequent thereto in said new paired combination; current sample means for providing a signal indicative of the actual current present in each phase winding; means for establishing a current error signal by comparison of a required current signal with said signal indicative of actual current present in one of the phase windings of an energized paired combination of phase windings; means for regulating the current flowing in the phase windings, when energized, in dependence on said current error signal; and means for transferring the establishment of said current error signal from comparison of said required current signal with said signal indicative of actual current present in the phase winding whose energization is maintained at each said transition from one said paired combination of phase windings to another of said paired combinations of phase windings, to comparison of said required current signal with said signal indicative of actual current present in the phase winding being energized at said transition, the current present in said phase winding being energized being, at least initially, substantially zero, so that the current error signal is, at least initially, of relatively large magnitude, and thus demands a large phase current. A brushless d.c. drive system, comprising a multiphase rotational motor having a stator, a rotor and a plurality of phase windings, control means for energizing said phase windings in paired combination and in a predetermined sequence during system operation, and sensor means associated with said control means for indicating rotor disposition at each of a plurality of rotational dispositions of the rotor relative to the stator, each said disposition corresponding to a transition from energization of one said combination of the phase windings of the motor to energization of a further combination of the phase windings, one said winding being de-energized at each said transition and a further winding being energized, and the disposition of the rotor for transition between any two phase combination in one direction of rotation being rotationally displaced from its disposition for transition between the same two phase combinations in the opposite direction of rotation. A brushless d.c. motor, comprising a stator having a plurality of windings and formed from a multiplicity of laminations, and a rotor having a plurality of poles defined by axially extending permanent field magnets, the rotor being rotationally mounted within the stator and being substantially surrounded by the stator, a plurality of Hall effect devices being mounted on the stator at one axial end of the motor and positioned at a plurality of locations around a circumferential path in the vicinity of axial end regions of said axially extending permanent field magnets, said axially extending permanent field magnets serving also as triggering magnets for the Hall effect devices, and each of said devices being activated when there is a respective predetermined angular relationship between the rotor and the stator, the stator laminations having axially outwardly directed axial end faces, and the axial end regions of the axially extending permanent field magnets having axially outwardly directed axial end faces, the axial end face of the stator lamination at the axial end of the motor at which the Hall effect devices are mounted and the axial end faces of the permanent magnet axial end regions at said axial end of the motor being disposed in a substantially common radial plane extending at right angles to the axis of rotation of the rotor, the windings having winding end portions extending axially outwardly of said stator lamination axial end face at said axial end of the motor at which the Hall effect devices are mounted so that annular space is defined radially inwardly of the winding end portions and axially outwardly of the axial end faces of the axially extending permanent field magnet end regions, mounting means for the Hall effect devices extending through said annular space to support said Hall effect devices in dispositions which are radially inwardly of and underlie said axial end regions of said axially extending permanent field magnets. A pulse width modulation power suppply for a two-terminal inductive load, having two switches and control means for regulating the on and off periods of each switch to control current magnitude and direction in said load, the on period of each switch being phase displaced relative to the on period of the other switch under zero net current conditions and of sufficient duration for overlap periods to be established between the on periods of the switches, a forward current pulse being established by a first said overlap period and a reverse current pulse being established by a second said overlap period, so that equal and opposite alternating current pulses flow through said load under said zero net current conditions. A brushless d.c. drive system comprising a three phase rotational motor, control means for energizing the phase windings of the motor, and means for applying a signal indicative of a parameter of motor performance to said control means, said control means including means for connecting the phase windings of said motor either for energization in paired combinations or for single-phase energization, in dependence on said motor performance parameter, without interruption of motor rotation, and said control means being adapted to energize said windings, in each case, in a respective predetermined sequence, wherein said parameter of motor performance is speed, the system includes means for monitoring motor speed, and the control means includes a comparator for detecting whether or not motor speed exceeds a preset speed to provide an input to said means for connecting the phase windings either for energization in paired combinations or for single-phase energization so that said phase windings are connected for energization in paired combinations when motor speed is less than said preset speed and are connected for single-phase energization when motor speed exceeds said preset speed.