Abstract: Traditionally, controllers for brushless, sensorless direct current (DC) motors (in, for example, Hard Disk Drive applications) would use one of the phases of the DC motor to measure a back electromotive force (back-EMF) voltage. This measurement would generally cause a discontinuity in the current waveform for a motor operating at a generally constant rotational speed (i.e., at “run speed”), which would result in poor acoustic performance (i.e., audible hum). Here, however, an integrated circuit (IC) is provided that uses coil current and applied voltage measurements to substantially maintain a predetermined phase difference between the phase of the applied voltage and back-EMF voltage, eliminating the need for a back-EMF voltage measurement and improving the acoustic performance.

Abstract: The invention relates to a method for positional recognition of a rotor of an electronically commutated electric machine, in particular an electric motor, in which a zero crossover of a voltage induced in a coil section of the rotor or stator is used for positional recognition. According to the invention, to determine the zero crossover the coil section is briefly powered down. A rotor/stator is used, comprising at least two coil sections, one of which has a lower inductance relative to the other one, and preferably only the coil section with the lower inductance is used for the positional recognition.

Abstract: In a three phase BLDC motor the rotor position is monitored by detecting the zero crossing points of the induced back EMF signals BEMF_U, BEMF_V, BEMF_W in the phase windings U, V, W. As they are illustrated, the back EMF signals are substantially sinusoidal but they may in other situations be substantially trapezoidal. The three back EMF signals are 120° out of phase with each other. In order to accurately monitor the back EMF in a phase winding, the driving waveform for each phase U, V, W includes an undriven period P close to the expected zero crossing point. The period P can be a preset part of the driving waveform or can be an interruption of the normal driving waveform in response to suitable interrupt signals. In order to determine the zero crossing points of each back EMF signal, two (or more) samples of the back EMF are taken during the undriven period P and used to interpolate the back EMF signal to determine the zero crossing point.

Abstract: The motor drive apparatus to perform vector control having excellent control performance on a motor includes an A/D converter which acquires currents flowing through a u-phase, a v-phase and a w-phase of the motor, a vector control unit which performs vector control on the motor based on d-axis motor current and q-axis motor current acquired by coordinate-converting the digitalized currents, a motor parameter and a desired angular speed of a motor rotor, a PWM generator which generates a PWM signal to drive the motor based on a motor voltage acquired by the vector control unit, and a parameter estimation unit which estimates a motor resistance, a d-axis motor inductance and a q-axis motor inductance in a direct current excitation state based on maximum peak values and minimum peak values of a d-axis motor voltage and a q-axis motor voltage and estimates a motor inductive voltage constant in a forced commutation control state.

Abstract: A method for controlling starting of a motor is described, which is mainly applicable to estimate a possible initial position of a rotor of a motor by detecting a rotor rotation signal of the motor, and find out a most possible initial position of the rotor after making statistics. In the method for controlling the starting of the motor, a starting angle position region of the motor is calculated simply by using the rotor rotation signal of the motor, without additionally arranging a Hall sensor, so as to save a cost of a Hall device and an assembling cost. Furthermore, accuracy for estimating the starting position region can be increased according to an accuracy specification of products, thereby achieving a high flexibility.

Abstract: A controller of a multi-phase electric motor includes a drive section for driving the multi-phase electric motor; a single current detection section for detecting a current value of the multi-phase electric motor; a PWM signal generation section for generating plural PWM signals of each phase within one control period based on the current value detected by the current detection section and a carrier signal; and a phase movement section for moving a phase by a predetermined amount such that frequency in change of the PWM signal of the predetermined phase generated by the PWM signal generation section is included in a non-audible range, and outputting the PWM signal which phase is moved to the drive section; wherein the phase movement section moves the phase by a predetermined amount for all the PWM signals of the predetermined phase within one control period.

Abstract: A motor speed controller and a method of controller a speed of a motor are provided. The system and method include a motor and a motor controller that monitors operation of the motor based on electromotive force (EMF) conditions of the motor. The motor controller cuts a voltage to the motor, measures an electromotive force (EMF) of the motor at a predetermined time after the cutting of the voltage to the motor, and compares the measured electromotive force (EMF) to a table.

Abstract: An apparatus and a method for driving a sensorless motor are described and shown in the specification and drawings, where the method includes steps as follows. First, a control signal is acquired, where the control signal has information of a predetermined rotational speed. Next, energy is supplied and progressively increased to the sensorless motor, so as to rotate a rotor of the sensorless motor. Then, a position of the rotor is detected. Finally, the energy is gradually regulated so that the sensorless motor is maintained at the predetermined rotational speed.

Abstract: An electronically commutated motor (ECM) often employs a Hall sensor for reliable operation. Even when a Hall sensor is omitted from a motor having a plurality of stator winding phases (24, 26) and a permanent-magnet rotor (22), one can reliably detect direction of rotation of the rotor by the steps of: (a) differentiating a voltage profile obtained by sampling either (1) induced voltage in a presently currentless phase winding or (2) voltage drop at a transistor, through which current is flowing to a presently energized phase winding, and (b) using such a differentiated signal (du—24?/dt, du—26?/dt) to control current flow in an associated phase winding. In this manner, one obtains reliable commutation, even if the motor is spatially separated from its commutation electronics.

Abstract: A motor driving method for driving a direct-current (DC) motor, designed for avoiding a reverse current induced by the Back Electromotive Force (BEMF), includes providing a driver circuit for driving the DC motor; comparing a signal level of a terminal of the DC motor and a predetermined voltage value to produce a comparing result; and controlling a specific lower gate switch to avoid the occurrence of a reverse current of the DC motor according to the comparing result.

Abstract: A motor control device with which both high-accuracy current detection and improvement in voltage utilization factor are achieved is provided. When an ON time of any one of low potential side switching elements corresponding to respective phases in a driving circuit is shorter than a detection time of a current value, a microcomputer estimates a phase current value of a current undetectable phase based on current values of two phases other than the current undetectable phase corresponding to the said FET. Then, at the time of current detection using the blind correction, during current detection for two phases, other than the current undetectable phase, based on which the blind correction is performed, motor control signals for maintaining switching states of a switching arm corresponding to the current undetectable phase are output.

Abstract: Systems and methods of controlling a permanent magnet motor without a mechanical position sensor are provided. In accordance with one embodiment, a motor control system includes an inverter configured to receive direct current (DC) power and output a power waveform to a permanent magnet motor, driver circuitry configured to receive control signals and drive the inverter based upon the control signals, a current sensor configured to determine a sampled current value associated with the power waveform, and control circuitry configured to generate the control signals based at least in part upon a comparison of a flux-producing component of the sampled current value and a flux-producing component of a command reference current value.

Abstract: A control apparatus for an induction motor is provided and includes a rotating-speed locked loop and a feed-forward magnetizing-axis angular position emulator. The rotating-speed locked loop emulates a speed control loop of the induction motor for producing an emulated torque current and an emulated rotor angular speed. The feed-forward magnetizing-axis angular position emulator receives the emulated torque current and the emulated rotor angular speed for producing a feed-forward estimated magnetizing-axis angular position, wherein according to the feed-forward estimated magnetizing-axis angular position, a first voltage controlling the induction motor is transformed from a synchronous reference coordinate system of the induction motor to a static reference coordinate system of the induction motor, and a two-phase current detected from the induction motor is transformed from the static reference coordinate system to the synchronous reference coordinate system.

Abstract: Methods, system and apparatus are provided for sensorless control of a vector controlled motor drive system that includes an electric motor used to drive an auxiliary oil pump.

Abstract: To estimate a fluctuation component of the torque generated at the motor accurately, a motor control device (3) which controls a motor with a stator having armature winding and a rotor having a permanent magnet is provided to include a torque fluctuation component estimation unit for estimating a torque fluctuation component generated at the motor based on flux-linkage of the armature winding and an armature current that flows the armature winding. The torque fluctuation component estimation unit estimates the torque fluctuation component (Trp) based on an inner product (Fd·id+Fq·iq) of a flux-linkage vector which is a vectorial representation of the flux-linkage and a current vector which is a vectorial representation of the armature current.

Abstract: An apparatus for starting a direct current brushless motor and a method thereof are provided. The direct current brushless motor comprises a plurality of windings. The control apparatus comprises a sense amplifier, a differential circuit, and a control circuit. The sense amplifier is configured to detect a first back electro-motive force of a non-electrified first winding. The differential circuit is configured to calculate a differential value of the first back electro-motive force. The control circuit is configured to provide a current to two of the windings and to switch the current to another two of the windings to start the direct current brushless motor.

Abstract: To estimate an initial magnetic pole position, estimated control axes corresponding to the d-axis and q-axis are set as the ?-axis and ?-axis, and a with high frequency rotation voltage or alternating voltage on the ?? coordinate system applied to the motor. A high frequency current ih flowing in the motor is then extracted from a detected motor current (armature current) and a direct current component (ih?×ih?)DC of a product of the ?-axis and ?-axis components of the high frequency current ih is derived. Alternatively, the ??-axis component ich? and the ??-axis component 66 of the high frequency current ih that are shifted by ?/4 in electric angle from the ?-axis and the ?-axis are used to obtain a direct current component of their product (ich?×ich?)DC. The magnetic pole position is then estimated by computing the axial error ?? between the ?-d axes utilizing the direct current components.

Abstract: A method for estimating a rotor position in an electrical machine is provided. The method is applicable to electrical machines that have magnetic saliency. The method includes extracting the rotor position from a demodulated output signal generated in response to an injected high frequency carrier signal and determining a position error compensation based upon a demodulation delay and a velocity or rotational frequency of the electrical machine. The method also includes estimating the rotor position by applying the position error compensation to the extracted rotor position.

Abstract: An inverter device, a motor driving device, a refrigerating air conditioner, and a power generation system, which can reduce the recovery loss thereof, are obtained. A plurality of arms that can conduct and block current are provided. At least one of the plurality of arms includes: a plurality of switching elements each having a parasitic diode and being connected in series with each other; and a reverse current diode connected in parallel with the plurality of switching elements.

Abstract: A method for starting a brushless DC motor. A rotor is aligned with a stator in accordance with a predetermined phase. After alignment, the rotor is positioned in accordance with another phase, two phases are skipped, a timer is set to a first count time, and the rotor is aligned with the stator in accordance with a third phase. Then the timer is restarted and the rotor is aligned with the stator in accordance with a fourth phase. After a first delay, first back electromotive force value is stored. The timer is stopped when the first back electromotive force value substantially equals a peak amplitude of opposite polarity. The timer is updated to a second count time that is substantially equal to a time at which the second timer was stopped. The process is repeated until the rotor has a position and a velocity that are suitable for normal operation.

Abstract: An alternating-current motor control apparatus includes a stator frequency computing unit configured to compute a stator frequency of a motor magnetic flux; a torque error computing unit configured to compute a torque error by using the motor magnetic flux, an estimated current, and a motor current; and a speed estimator configured to estimate a speed of the alternating-current motor by using the stator frequency and the torque error. The speed estimator includes a proportional controller configured to reduce the torque error to zero, and an adaptive filter configured to eliminate a high-frequency component of the torque error.

Abstract: A control system includes a position control module, a power control module, and a diagnostic module. The position control module applies a driving current for positioning a rotor of a motor at one of first and second positions. The power control module applies a first voltage to one of first and second phases of the motor to generate a first current after the position control module applies the driving current to position the rotor at the first position. The power control module applies a second voltage to one of the first and second phases to generate a second current after the position control module applies the driving current to position the rotor at the second position. The diagnostic module determines when the rotor is restricted from rotating based on the first and second currents.

Abstract: Disclosed is a method for detecting the current position of a rotor, in particular the angle of rotation of the rotor, an electromotor and a method for detecting the speed and/or the angle of rotation of an electromotor. The speed of the electromotor is hereby implied inter alia from the number of zero crossings of a comparison signal of the armature resistances or respectively conductances determined continuously in time and the average values of the armature resistances or respectively conductances determined continuously in time.

Abstract: A speed estimation method for determining the speed of a sensorless permanent magnet brushless motor having one or more phases driven by one or more stages of an inverter, each stage including high- and low-switches connected in series across a DC Bus and having a respective common switched node, the respective switched node being coupled to a respective motor phase terminal.

Abstract: A motor rotation irregularity detection circuit includes a first integrator for integrating a rotation detection signal that is output from a driver of a sensor-less motor; a differentiator for outputting a difference between a binary signal based on the integral in the first integrator and the rotation detection signal; a second integrator for integrating an output signal of the differentiator; a comparator for making a comparison between the integral in the second integrator and a reference voltage to output an irregularity detection signal; and an output terminal for outputting a signal coming from the comparator.

Abstract: In a driving apparatus for a three-phase synchronous motor, in which a battery is connected between a neutral point of a stator coil and a negative-pole bus, a control circuit acquires three-phase AC currents. The control circuit checks whether a neutral-point electric current is contained in an electric current detected by an electric current detecting section. Based on the check result, the control circuit checks whether electric current values for three-phases containing the neutral-point electric current are set together or electric current values for three-phases excluding the neutral-point electric current are set together to acquire the three-phase AC currents for driving the motor.

Abstract: An electric motor drive system having current detecting sections for detecting the currents flowing into electric motors, speed variation calculating sections for calculating the speed variation estimating values for the electric motors in accordance with the motor currents detected by the current detecting sections and the current command values for the motors corresponding to the detected currents and a speed uniformizing voltage compensating section for delivering the values that serve to compensate the amplitudes of the voltages applied to the electric motors in such a manner that the speed variation estimating values calculated by the speed variation calculating sections become equal to a predetermined value.

Abstract: In a motor control apparatus, apparatus all switching devices of all phases of an inverter are kept fixed at OFF in accordance with a value of an all-OFF control pulse signal Poff outputted by a pulse generator. The pulse generator generates at least twice a pulse causing an induced voltage detection signal Pdet to change to an H level. A terminal voltage of a motor is inputted in accordance with the value of the induced voltage detection signal Pdet. Data of the sampling round in which amplitude of the induced voltage signal is great and the signal is not in saturation is selected from the data so inputted and a rotor position is estimated.

Abstract: A control system for an electric motor is arranged to determine the position of the motor from at least one electrical parameter by means of a position determining algorithm. It is further arranged to monitor at least one algorithm parameter defined by the algorithm and if the monitored parameter meets a predetermined fault condition to generate a fault indication.

Abstract: A brushless motor control device according to the present invention drives a brushless motor including a stator having coils of three phases U, V, and W and a neutral line, and a sub coil provided in any one phase of the phases U, V, and W, for detecting a voltage induced in the coil of the one phase, and the brushless motor control device carries out a conduction control function, for the respective phase coils of the brushless motor, that performs a 120° conduction when a rotation speed of the brushless motor is lower than or equal to a predetermined rotation speed, and that performs a 180° conduction when the rotation speed is higher than or equal to the predetermined rotation speed, and the brushless motor control device includes a motor control unit that controls the brushless motor based on information of the rotor stop position when activating the brushless motor, controls the brushless motor based on the first rotor position information when in the 120° conduction, and controls the brushless motor bas

Abstract: Electric drive units comprising a common active part having a stator and a rotor, which has windings and/or permanent magnets for a drive function and an energy transmission function, enable the rotor winding that is provided for energy transmission to be used to allow position detection at a low additional cost. For this purpose, a power converter in the rotor, which provides the output of electrical energy for the energy transmission function, impresses an alternating voltage into the rotor winding, said voltage being detected in the stator and allowing the rotor position to be determined.

Abstract: A back electromotive force detection circuit detects a zero-crossing point by comparing a back electromotive force Vu in at least one coil of a motor with a center tap voltage at a common node of the coils, and outputs a back electromotive force detection signal. A switching control circuit controls switching states of multiple switching circuits based upon the back electromotive force detection signal, thereby adjusting the current flowing through the coils. A window generating circuit outputs a window signal at a predetermined level during a period obtained by multiplying the cycle of the back electromotive force detection signal by a predetermined coefficient before the detection of the zero-crossing point. The switching control circuit stops the switching operation during a period in which the window signal is maintained at the predetermined level, thereby setting the state to the high impedance state that corresponds to a non-driving period.

Abstract: An energization signal generating circuit respectively compares back electromotive forces generated in coils of each phase of a motor with a midpoint voltage of each phase, and generates energization signals. A pulse signal generating circuit generates a pulse signal in which duty ratio is controlled according to torque. A ramp signal generating circuit divides, into a plurality of times, a period of a frequency generation signal obtained by synthesizing the energization signals, and, for each divided time unit, generates a ramp signal in which pulse width gradually changes, and which has a frequency the same as the pulse signal. An output circuit supplies a drive current to the coils of each phase, based on the energization signals, the pulse signal, and the ramp signal.

Abstract: An electrical machine having a stator and a rotor. The stator includes a core and a plurality of windings disposed on the core in a multiple-phase arrangement. The rotor is disposed adjacent to the stator to interact with the stator. A method of operating the motor includes applying a pulsed voltage differential to first and second terminals of the windings resulting in movement of the rotor; monitoring the back electromotive force (BEMF) of the windings to sense rotor movement; after the applying and monitoring steps, monitoring the BEMF of the windings to determine whether the rotor is rotating in a desired direction, and electrically commutating the motor when the rotor is rotating in the desired direction and zero or more other conditions exist.

Abstract: A flux regulated permanent magnet brushless motor has a stator having an inner peripheral bore. A permanent magnet rotor is mounted within the inner peripheral bore. A control winding is supplied to a DC current to regulate flux of the machine. A small AC current is also supplied and an output is sensed to determine a position of the permanent magnet rotor.

Abstract: A controller outputting voltage instructions for drive control of an electric rotating machine adds, by using adders, position estimation voltage instructions for estimating the rotor position generated by a position estimation voltage generator, to drive voltage instructions, and outputs the resultant signals as voltage instructions. A position estimation device includes current extractors for extracting position estimation currents having the same frequency components as that of the position estimation voltage instructions, from electric rotating machine currents detected by a current detector, a position estimation current amplitude calculation section for calculating position estimation current amplitudes from the position estimation currents; and an estimation position calculation unit for calculating an estimated position of the electric rotating machine, based on the position estimation current amplitudes.

Abstract: A system. The system includes a first module, a second module communicably connected to the first module, a third module communicably connected to the first module, and a fourth module communicably connected to the third module. The first module is configured for determining an angle. The angle is defined by a first rotating reference frame having an axis aligned with a permanent magnet flux of a permanent magnet motor, and a vector of a motor magnetizing flux of the permanent magnet motor. The second module is configured for defining a second rotating reference frame having an axis aligned with the vector, and for transforming a two-phase set of direct currents from the first rotating reference frame to the second rotating reference frame. The first and second rotating reference frames are synchronized. The third module is configured for generating a first direct current reference signal associated with the second rotating reference frame.

Abstract: A motor control device has a three-phase bridge circuit, a driving circuit, and a microcomputer. The three-phase bridge circuit has three pairs of MOSFETs for U, V, and W phases of a three-phase AC motor as a control target. The microcomputer has a dead time set value storage unit and a PWM signal generation unit. The PWM signal generation unit generates a PWM signal with a dead time including a response characteristics of the pair of MOSFETs for each of U, V, and W phases of the AC motor based on a three-phase voltage instruction value supplied from an outside device and the dead time set value stored in the dead time set value storage unit. The PWM signal generation unit outputs the PWM signal for each phase to the driving circuit. This independently adjusts the dead time for the MOSFETs for each phase.

Abstract: A brushless motor includes: a permanent magnet; a driving coil moving relative to the permanent magnet; a sensor coil disposed to the permanent magnet so as to generate a sensor coil induced voltage having a same phase of a driving coil induced voltage generated in the driving coil; and a driving circuit applying a driving voltage to the driving coil, the driving voltage having a same phase of the sensor coil induced voltage generated in the sensor coil.

Abstract: An electronically commutated motor (ECM) often employs a Hall sensor for reliable operation. Even when a Hall sensor is omitted from a motor having a plurality of stator winding phases (24, 26) and a permanent-magnet rotor (22), one can reliably detect direction of rotation of the rotor by the steps of: (a) differentiating a voltage profile obtained by sampling either (1) induced voltage in a presently currentless phase winding or (2) voltage drop at a transistor, through which current is flowing to a presently energized phase winding, and (b) using such a differentiated signal (du—24?/dt, du—26?/dt) to control current flow in an associated phase winding. In this manner, one obtains reliable commutation, even if the motor is spatially separated from its commutation electronics.

Abstract: A control system for an electric motor is arranged to determine the position of the motor from at least one electrical parameter by means of a position determining algorithm which is reliant on movement of the motor to determine the motor position, and to start up the motor from rest by applying voltages to the motor that are independent of the position of the motor.

Abstract: A disk drive is disclosed comprising a disk, a head actuated over the disk, and a spindle motor for rotating the disk, wherein the spindle motor comprises a plurality of windings. During a spin-up operation of the disk, a sinusoidal driving signal is applied to each winding of the spindle motor for a spin-up interval, wherein during at least eighty percent of the spin-up interval the sinusoidal driving signals are applied to the windings of the spindle motor open loop.

Abstract: An inverter control circuit controls transistors based on comparison of a voltage command wave with a carrier wave, when a magnitude of a voltage vector is equal to or less than a peak value of the carrier wave. The voltage command wave is a wave, which is offset to a maximum value side from a reference potential of the carrier wave so that a maximum value of the voltage command wave equals a peak value of the carrier wave. The inverter control circuit makes an on-period of the transistor on a positive bus side longer than that of the transistor on a negative bus side by using the command voltage. The amount of electricity charged in a capacitor is reduced in comparison with a case in which the voltage command wave is used. Thus, thermal loss of a stator coil and a diode on the positive bus side is reduced.

Abstract: A PWM modulation unit modulates a three-phase voltage instruction, which is input, on the basis of a PWM method, and outputs a gate signal to each phase switching element of an inverter. A high-frequency component arithmetic unit calculates, at each time of switching of the inverter, a high-frequency component of a current occurring due to a voltage which is determined by the PWM modulation unit and is output from the inverter. An index arithmetic unit calculates, as an index R proportional to a rotational phase angle estimation error, from the high-frequency component of the current. A rotational phase angle estimation unit executes an estimation arithmetic operation of the rotational phase angle by using the index R. The invention provides a synchronous motor sensorless control apparatus which enables stable driving with simple adjustment, and does not cause an extreme increase in amount of arithmetic calculations.

Abstract: Switching elements are driven by a control signal outputted from a control circuit, so that a rotating magnetic field is generated from a stator coil to rotate a rotor of a synchronous electric motor. The control signal is generated through use of a selected modulation scheme, which is selected from a plurality of modulation schemes. The control circuit determines which one of the modulation schemes is used as the selected modulation scheme based on a sensed voltage value of a voltage sensor, which senses an output voltage of a power supply device.

Abstract: The position of a rotor of a motor is determined. The motor includes the rotor and a stator and the stator includes a plurality of coils. The rotor further includes at least one rotating magnetic field device. When the rotor is moving below a threshold speed, the current in each of the plurality of coils of the stator is measured. A pre-programmed data structure is accessed. The pre-programmed data structure stores a plurality of stator currents associated with a plurality of predetermined rotor positions. A first absolute position of the rotor is determined from the data structure according to the measured current from each of the plurality of coils. When the rotor is moving above the threshold speed, one or more rising or falling edges of magnetic field strength associated with the at least one rotating magnetic field device of the rotor are sensed. At least one timing aspect of the rising and falling edges of magnetic field strength are compared to determine a second absolute position of the rotor.

Abstract: The synchronous motor driving apparatus including position sensors provided in the synchronous motor, a current polarity detection circuit for detecting the polarities of the currents in the respective phase windings of the synchronous motor, an inverter driving the synchronous motor, a motor speed calculation unit calculating the rotational speed of the synchronous motor depending on the output signals from the position sensors, a speed control unit outputting a first voltage adjusting component (q-axis current command value Iq*) to cause the rotational speed of the synchronous motor to approach a speed command value and a phase control unit outputting a second voltage adjusting component (d-axis current command value Id*) to cause the phase differences between the phases of the position sensor signals and of the currents in the respective phase windings of the synchronous motor to become a predetermined value.

Abstract: A method and system for an engine starter/generator is provided. The starter/generator system includes a three phase squirrel cage induction machine, a three phase inverter/converter electrically coupled to the three phase squirrel cage induction machine. The starter/generator system also includes a bidirectional DC-DC converter electrically coupled to the three phase inverter/converter, and a digital control board configured to sensorlessly determine a rotor angle from a plurality of phase currents to the induction machine during a start mode. During the start mode, logic in the digital control board configures the starter/generator system into a combination of an induction motor, a three phase DC-AC inverter, and a DC-DC boost converter, and during a generate mode, the logic in the digital control board configures the starter/generator system into a combination of an induction generator, a three phase AC-DC converter, and a DC-DC buck converter.

Abstract: A flux switching electric motor (102) is disclosed. The motor comprises a rotor (104), a stator (106), field windings (124, 126) and armature windings (128, 130). #A microcontroller (134) controls supply of electrical current to the field and armature windings. A rotor position sensor includes a divider for (i) receiving an input signal dependent upon the rate of change of current in at least one field winding, (ii) receiving an input signal dependent upon the voltage across at least one armature winding, current through which causes at least part of the current in the field winding, and (iii) providing the microcontroller (134) with a control signal which is dependent upon the ratio of the input signals received by the divider.

Abstract: Methods and apparatus are provided for aligning a control reference axis with a magnetic north of a permanent magnet motor. The method includes the steps of injecting a predetermined stator current on an estimated reference axis of the permanent magnet motor and introducing predetermined error on the estimated reference axis. The method further includes the steps of determining if a speed of the permanent magnet motor is greater than a predetermined threshold speed and setting the control reference axis to 180° added to the estimated reference axis if the speed of the permanent magnet motor is greater than the predetermined threshold speed or setting the control reference axis to the estimated reference axis if the speed of the permanent magnet motor is less than or equal to the predetermined threshold speed.