Abstract: Angle bounds of a normal energization of the coil of an electric motor are generated in accordance with a combination of a rotation direction and a torque direction of the electric motor. Angle bounds of the decided energization are determined based on a decision of either energization or deenergization of the coil and the detected rotation angle of the rotor. An abnormal condition is determined to exist when the angle bounds of the decided energization are not within the angle bounds of the normal energization.

Abstract: A method for monitoring motor position in a multiple phase switched reluctance motor having phase windings which are energized by a controller involves producing a signal indicative of a current delivered to an active phase winding and producing a signal indicative of a voltage across the active phase winding. A flux linkage associated with the active phase winding is then established based at least in part upon the current indicative signal and the voltage indicative signal. A position of the motor is then estimated based at least in part upon the current indicative signal and the established flux linkage.

Abstract: A circuit for controlling the operation of switched reluctance machines (i.e., motor or generator) having a plurality of phase windings. The circuit slows down the initial "turn off" of the phase windings to eliminate an abrupt reduction in the current flowing therethrough. This reduces the impulse which excites mechanical oscillations in the motor/generator, reduces switching losses in the switching transistors, and reduces the number of harmonics.

Abstract: A vehicle control device is provided that is capable of functioning as a transmission synchronizer, an electromagnetic clutch, a starter for an engine, and a generator. The device includes a first member having a plurality of inwardly extending poles and a plurality of coils that are wound upon the poles. The first member is connected to an engine output shaft for rotation therewith. The device also includes a second member that is disposed within the first member. The second member is connected to a transmission input shaft for rotation therewith. Finally, the device includes means for energizing the coils of the first member to control the operation of the control device. By controlling the energization of the coils and the relative motion of the first and second members, the control device can be used as a transmission synchronizer, a clutch, a starter for the vehicle's engine, and a generator for the vehicle's battery.

Abstract: A method for controlling a motor and a circuit for implementing the method are provided. The method includes the steps of providing current to a first phase coil of a motor and measuring the time for the current to rise between two predetermined levels. Because current rise time is proportional to phase inductance, and therefore, rotor position, the measured current rise time can be compared to a desired current rise time to determine whether conduction intervals in the motor phases are in-phase with the position of the rotor or are lagging or leading the position of the rotor. The method finally includes the step of supplying current to one of the first phase coil and a second phase coil responsive to the measured rise time in order to bring subsequent conduction intervals into phase with the position of the rotor.

Abstract: A control circuit and method for controlling a switched reluctance motor are provided. The control circuit includes a tone wheel and a Hall effect sensor for generating a position feedback signal indicative of the position of the motor. The control circuit also includes a sensing resistor for generating a current feedback signal indicative of a level of current in a phase coil of the motor. Finally, the control circuit includes first and second switches connected to opposite ends of the phase coil for controlling the level of current in the phase coil responsive to the position feedback signal and the current feedback signal.

Abstract: A three-phase reluctance motor includes, a stator having a plurality of magnetic poles around which coils corresponding to three phases are wound, a rotatable rotor having a plurality of convex poles opposed to the magnetic poles of the stator, a magnet provided on the rotor for magnetizing alternately the convex poles to N- and S-polarities in a circumferential direction, and a control circuit for magnetically exciting selectively only two of the three phases to the N- and S-polarities, respectively, and for sequentially switching two phases which are to be excited, to thereby rotate drive the rotor.

Abstract: A method for starting a polyphase DC motor having a rotor. The position of the rotor is detected by initiating current in each of the phases of the motor and measuring a time period between the initiation of current in the coil and an instant when the current exceeds a threshold current. The phase in which the current reaches the threshold in the shortest amount of time is the phase closest to the position of the rotor. A phase closest to the position of the rotor is identified in each of an odd number of trials, and a starting phase is selected as the phase identified in the majority of trials. The motor is started by providing current to the starting phase.

Abstract: A rotor position transducer for an electronically commutated electric motor has a vane mounted to rotate with the rotor and a pair of sensors, according to one embodiment. One sensor has an output coincident with positions of zero torque. The other sensor produces signals slightly in advance. Overlapping portions of the signals denote regions of different levels of torque. The second sensor output can also be used in high-speed, single-pulse control of the motor. Method embodiments and other apparatus embodiments are also disclosed.

Abstract: A switching circuit for a reluctance machine includes one or more half-bridge converter modules including serially connected switches connected between power rails +V.sub.dc and -V.sub.dc. A pair of capacitors are also connected between the power rails, and the phase winding of the machine is connected at one end between transistors and at the other end between the capacitors. The switches act as separate power circuits, alternately conducting to excite the phase winding either during alternate phase conduction periods or during alternate groups of phase periods. The half-bridge modules are commercially readily available as cost-effective preassembled items.

Abstract: In a switched reluctance motor and control system for such a motor, a rotor comprises four salient poles each having a width of about 50-degrees, and a stator has six salient poles each having a width of about 30-degrees. One Excitation winding is mounted around each stator salient pole and these are connected in series. An excitation drive circuit supplies a dc excitation current to each excitation winding to excite the motor in accordance with an excitation command signal. A torque-current drive circuit renders a current, whose magnitude in accordance with a torque command, to flow into torque windings mounted one round on each of the six stator salient poles successively according to the angle of rotation of the rotor.

Abstract: Disclosed is a current controlling apparatus of a switched reluctance motor (SRM) having an inverter unit for variably switching the excitation state of each phase of the polyphase stator: generates a current controlling signal so that a current error between a current commanded by a current command unit and a current which is actually applied to the SRM can be compensated; and performs a pulse width modulation after receiving the current controlling signal and then supplies to the inverter unit, thereby enhancing efficiently the operating characteristic of the SRM by minimizing the current error. In other words, the current control apparatus in the SRM which searches for a current error by comparing a current controlling signal commanded by a current command unit with a current actually applied to the SRM and then operates the SRM by a current adjacent to the command current by compensating a current value corresponding to the compared current error.

Abstract: A reluctance machine including a plurality of phase windings where each phase winding comprises a plurality of fractional-pitched coils. The reluctance machine may be coupled to a drive that can energize one, two or more of the phase windings to provide output torque that is derived from: (i) the self-inductances of the phase windings; (ii) a combination of the self-inductances of the phase windings and the mutual inductances between the phase windings; or (iii) the mutual inductances between the phase windings.

Abstract: A current transducer includes a current transformer in which the conductor carrying the current to be monitored constitutes the primary. The transformer secondary is wound on a toroidal core. The transformer is operated below its cut-off frequency such that the output from the secondary is proportional to the differential of the current in the primary. The secondary output is integrated by an integrator to provide a measure of current in the primary and the integrator is initialized at predetermined intervals. A current measuring device for an electric machine, for example a reluctance machine, includes at least one of the current transducers.

Abstract: A circuit and method for controlling a switched reluctance motor are provided. The circuit includes a phase coil and a switch that controls a current in the phase coil responsive to a hysteresis control signal. The circuit also includes a current sensor that measures the level of current in the phase coil and a comparator that compares the measured current level to a predetermined upper hysteresis current level. The circuit further includes a hysteresis control signal generating circuit that generates the hysteresis control signal responsive to the comparison signal and a timing signal that comprises a series of timing pulses. The hysteresis control signal assumes a first logic level whenever the measured level of current in the phase coil exceeds the predetermined upper hysteresis current level, thereby opening the switch and allowing current to dissipate from the phase coil.

Abstract: The control of the current in a PWM mode through independently controlled windings of a multi-phase motor driven in a "bipolar" mode is implemented by employing only two sense resistors and related control loops. This is so regardless of the actual number of windings of the motor.

Abstract: A driving circuit for a multi-phase switched reluctance (SR) machine, wherein a reduced number of wire connections between the machine and driving circuit are needed. In addition, one embodiment of the driving circuit requires the use of fewer individual diodes for the circuit design. The reduction in the number of wire connections and diodes provides greater reliability, improved efficiency, and lower production costs.

Abstract: A method for controlling the average voltage applied to a phase winding of a reluctance machine during periods of current increase, stable current control, and current decrease to improve machine efficiency and thereby reduce acoustical noise produced by the machine and unwanted vibration. According to one aspect, a method is provided whereby a maximum duty cycle is selected and voltage is applied to the phase winding during the period of current increase according to the maximum duty cycle until the current reaches a desired peak current value and thereafter the voltage applied to the phase winding is equal to the lesser of the voltage required to keep the phase current at the predetermined peak current value or the voltage corresponding to the maximum duty cycle.

Abstract: A switched reluctance motor driven by a two-phase source, includes a stator having an even number of evenly-spaced, like stator poles defining a gap between each stator pole; windings for each of the two phases of the motor wound about stator poles that are circumferentially separated by a winding and an associated stator pole of a different phase; and a rotor mounted for rotation relative to the stator, the rotor having an even number of rotor poles, the rotor poles being dimensioned such that when the phases are alternately energized, the rotor poles operatively interact with the stator poles such that the motor advances sequentially to a first state wherein one-third of the rotor poles are magnetically coupled to a like number of the stator poles, to a second state wherein two-thirds of the rotor poles are magnetically coupled to a like number of stator poles and to a third state wherein all of the rotor poles are magnetically coupled to a like number of stator poles.

Abstract: An electrical machine includes a stator and a rotor. The stator includes on its internal face at least one induction winding housed in a pair of recesses and a series of housings for excitation means. The rotor does not have windings and includes teeth for establishing variable magnetic fluxes in the induction winding. The excitation brings into play permanent magnets adapted to establish a closed circumferential magnetic flux in the stator and excitation windings locally establishing an adjustable magnetic flux in the reverse circumferential direction. The rotor teeth are adapted to effect a flux commutation in the stator and the, or each, permanent magnet occupies an angular position located between the angular positions of the two arms of a common induction winding. In this way an alternating magnetic flux is produced in the induction winding or windings during the rotation of the rotor.

Abstract: A control circuit for a motor having at least two windings is used to optimize noise reduction by controlling the deenergization of each winding in a two-stage decay. The duration of the two-stage decay and particularly the first decaying current portion is controlled by a controller operatively coupled to a switch device. The duration of the first decaying current portion is varied between the various phases of the motor to provide optimum noise reduction.

Abstract: A switched reluctance machine includes a first element having a plurality of uniform poles and a second element having a first pole and a second pole. The first pole has a wide face and the second pole has a narrow pole face. The first and second elements are disposed for movement relative to each other such that the wide and narrow poles are moveable in spaced relation to the plurality of uniform poles.

Abstract: An improved commutation control method precisely controls commutation in a switched reluctance machine with a relatively low resolution position encoder and a low cost micro-processor based controller. The control method involves the formation of a motor position signal having logic level transitions, or edges, that define base commutation signals for commutating the motor phase windings in sequence with no phase advance. When no phase advance is desired, the controller turns the phase windings on and off in time with the respective base commutation signals. When phase advance is desired, the controller turns each of the windings on and off relative to the base commutation signal for the preceding phase winding. More specifically, the turn-on and turn-off points for phase advance control are timed to occur a delay time after the edges of the base commutation signal for the preceding phase.

Abstract: A motor controller controls the operation of an electric motor (28). The motor controller includes sensors (30, 97, 102) for sensing at least one dynamic operating characteristic of the motor and for providing a signal indicative of the at least one sensed dynamic motor operating characteristic. A variable gain regulator (190) receives a current command request signal having a value and provides a motor current control signal having a value functionally related to the value of the received current command request signal and a gain control value. A gain scheduler (196) is operatively coupled to the variable gain regulator (190) and to the sensor (30, 97, 102) for providing the gain control value to the variable gain regulator (196) in response to the sensed at least one dynamic motor operating characteristic to thereby control the amount of gain of the variable gain regulator (190).

Abstract: A switched reluctance motor having a rotor and a stator is provided the motor includes means for adjusting a relative angle between a switch turn-off angle at which a switch for supplying power to a coil is turned off, and a tooth overlap angle at which a tooth portion of the rotor and a tooth portion S of the stator are overlapped according to a predetermined calculation. The switched reluctance motor has reduced vibration and noise levels, thereby increasing their application.

Abstract: A switched reluctance electrical machine system including a switched reluctance machine, a rechargeable DC energy store and principle voltage terminals connectable to an external power source. The switched reluctance machine comprises a rotor, a stator and windings wherein the windings include at least two closely-coupled coils and a power converter for controlling current flow in the windings. The power converter has first and second circuits. The first circuit contains one of the closely-coupled coils and the principle voltage terminals while the second circuit contains the other of the closely-coupled coils and the energy store. A first switching arrangement is connected in series with the coils in the first circuit and a second switching arrangement is connected in series with the coils in the second circuit.

Abstract: A reluctance motor/generator system in which a winding failure event in one channel of a multiple channel multiple phased stator assembly is accommodated by removal of the failed winding from the reluctance motor/generator machine's electrical circuit using electrical switching and an acceptance of reduced machine output capability. This electrical switching also accomplishes a reversal of magnetic polarity in poles of one remaining normal channel of the machine. The magnetic polarity reversal as accomplished electrically largely excludes secondary magnetic flux from stator poles carrying the failed winding and its associated phase windings of the channel and thereby precludes electrical energy generation in the failure event pole. In the thus achieved channel-removed mode of machine operation, a different more elongated magnetic flux path through the machine rotor and stator elements becomes active and provides reduced but usable electrical output from the machine.

Abstract: A method and apparatus for controlling the average voltage applied to a phase winding of a reluctance machine during a period of current increase, controlling the current when a desired current is reached, and controlling the voltage applied during a period of current decrease, to improve machine efficiency and thereby reduce acoustical noise produced by the machine, and unwanted vibration. The apparatus comprises circuitry and associated elements which are operable to switch the phase winding into circuits which apply either a positive DC voltage, a zero voltage, or a negative DC voltage, to increase, maintain, or decrease the current in the winding. The timing and the rate of the switching is controlled as a function of the angular position and speed of a rotor of the reluctance machine, the torque output of the machine, and the desired speed or torque.

Abstract: A method for powering an electronically switched variable reluctance polyphase electric motor from a rectified voltage source, including for each phase, magnetizing sequences during which the rectified voltage is applied to each phase and demagnetizing sequences during which the inverse of the rectified voltage is applied to each phase. The method further includes sensing disturbances in the current from the rectified voltage source and in response thereto, free-wheel sequences during which the magnetic energy currently stored in at least one of the phase is substantially maintained therein.

Abstract: A method for powering an electronically switched variable reluctance motor (100) from a single-phase AC voltage source (17) is disclosed. Each phase of the motor is sequentially subjected to a magnetizing sequence, a demagnetizing sequence and an energy transfer to a storage capacitor (C) common to all the phases. Feedback sequences (R) in which the energy stored in the storage capacitor (C) is returned to the rectifier stage (15) are performed by controlling a chopping switch (TH) connected in series to the storage capacitor (C). The method includes a step of monitoring the energy returned to the rectifier stage (15) in order to correct instability in the rectified power supply current (Ia) relative to a reference current wave, and modulating the cyclical chopping ratio around a substantially constant mean value. The method is useful for powering household appliances.

Abstract: A method and circuit for detecting a locked rotor in a switched reluctance motor are provided. The method includes the step of measuring, at a predetermined frequency, the time required for a current in the motor to rise or fall between predetermined current levels to thereby obtain a plurality of sample rise or fall times. The method further includes the step of comparing first and second sample times of the plurality of sample times to obtain a time comparison value that is indicative of a change in position of the rotor. Because current rise and fall times are indicative of, and vary with, rotor position, a comparison of multiple rise or fall times may be used to indicate a change in position of the rotor and, therefore, whether the rotor is in motion or is locked. The method may finally include the step of comparing the time comparison value to a predetermined reference value that is indicative of a locked rotor.

Abstract: An electric power starter/generator system for converting electrical energy from a remote dc electrical power source coupled to a dc distribution bus to mechanical energy to start a turbine engine in a start mode, and for converting mechanical energy from the turbine engine to electrical energy to power utilization equipment connected to the dc bus in a generate mode, comprises a switched reluctance machine, an inverter having a dc input/output coupled to the dc distribution bus, and at least a first and a second switch coupling each of the machine's phase windings to the dc bus, and at least a first and a second diode for cross-cupling each of said phase windings to the dc bus, and a controller coupled to the inverter for monitoring and controlling system performance during the start mode and the generate mode of system operation.

Abstract: An energization controller for an electric motor eliminates the possibility that a motor driver may be destroyed when the electric motor rotates in the opposite direction from its driving direction.

Abstract: An apparatus for controlling an electric assist steering system (10) having an electric assist motor (26) operatively connected to a steerable member. Energization of the motor provides steering assist to the steering member. The apparatus includes a steering torque sensor (27) for sensing applied steering torque and providing a torque signal indicative thereof. A first switching device (72) is operative coupled between one terminal of the electric assist motor (26) and a first terminal of a source of electrical energy. A second switching device (98) is operative coupled between a second terminal of the electric assist motor and a second terminal of the source of electrical energy. A controller (76) periodically switches the first and second switching devices between ON and OFF conditions so that the ON condition of each the first and second switching devices is less than one-hundred percent of a period and a portion of the ON condition of the first and second switching devices overlap.

Abstract: A commutation controller for a switched reluctance machine has separate timer circuits for determining the firing signals for motoring and generating modes. Each timer circuit comprises a ramp generator and a pair of comparators which denote the ON- and OFF-angle as the ramp output passes preset thresholds applied to the comparators. A multiplexer selects the output from one of the motoring and generating timers according to the mode of machine operation. By producing timing signals for the motoring and generating modes separately and continuously, a transition between motoring and generating modes can be carried out smoothly without timing error.

Abstract: A hybrid single-phase variable reluctance motor system has a stator (1) having a pair of oppositely disposed salient main poles (4) provided with main windings (12) and at least one pair of oppositely disposed salient auxiliary poles (5, 6) provided with auxiliary windings (13, 14) and disposed intermediate the main poles (4) on the stator (1). Furthermore the motor system has a rotor (2) having a pair of oppositely disposed salient poles (7) without windings. Additionally the motor system includes a control circuit (11) for rotating the rotor (2) during normal running by supplying current pulses to the main stator windings (12) in synchronism with rotation of the rotor (2) and for rotating the rotor (2) on starting by supplying current pulses to both the main and auxiliary stator windings (12, 13, 14) in synchronism with rotation of the rotor (2).

Abstract: A motor monitoring and control circuit calculates a value parameter for a position of the motor at given instants. The same parameter (which may be position or speed of a rotor) is then measured at subsequent instants. These values are used to compute a future value of the parameter. The motor monitoring and control circuit is advantageous in that it can be used for any type of motor and can be easily and quickly fitted to a motor without the need for expensive and time consuming initial measurements and computations of characteristic properties of the motor in order to calibrate it. Similarly, automatic compensation is made during operation.

Abstract: An system for minimizing the output torque ripple effect in a switched reluctance electric motor operating in phase overlap mode positions at least one compensating coil such that, when energized, the magnetic flux of the field created by current flowing through the compensation coil couples and opposes the magnetic flux created in the main winding of compensation coil.

Abstract: A switched reluctance machine controller derives an error signal from the difference between a current reference and the phase winding current. The error signal is applied to a pair of hysteresis circuits which define adjacent hysteresis bands above and below the reference current. The magnitude of the hysteresis bands may vary as a function of the current reference. The outputs of the hysteresis circuits are received by control logic which permits current to be applied to the phase winding when the current is below the hysteresis bands, removes current from the phase winding when the current is above the hysteresis bands and allows the phase winding current to freewheel when the current is between the upper and lower hysteresis limits. The power device used for freewheeling alternates between an upper power device and a lower power device.

Abstract: A hysteresis current controller includes a hysteresis current control device which has an adjustable hysteresis band. A feedback signal indicative of current in the load is compared with a current demand signal to produce an error signal which is received by the hysteresis control device. The switching output of the hysteresis control device is monitored to derive a signal indicative of its frequency which is used in a control loop to vary the hysteresis band to maintain the switching frequency output substantially constant.

Abstract: The invention provides a controller for specifying a drive voltage for synchronous motors relative to a desired speed profile. The controller senses motor current and optionally senses motor rotational position. A motor torque reference is first determined to balance (a) an estimated motor load torque, (b) the reference speed profile, and (c) a filtered incremental friction. A reference torque is then determined for the operating speed, and a reference current is determined to produce the reference torque. A primary voltage module then determines a primary voltage as a function of the calculated motor torque and the reference motor current to create a reference current at the operating speed. An incremental voltage module determines an incremental voltage based on an incremental resistance and an incremental back EMF of the motor. The primary and incremental voltages are then summed specify the applied voltage to drive the motor to the reference speed profile.

Abstract: A method for controlling the current profile for current supplied to each phase of a poly-phase switched reluctance motor when a respective phase of the motor is active. The interval each motor phase is active is determined as a function of motor operating conditions, as is a desired profile of current flow into and out of a phase winding (W) associated with the phase. The current profile has an initial portion (Z1) in which current flows into the winding from an initial value current value to a peak current value (I.sub.p). It also has a terminal portion (Z3) including current cut-off to the winding with current in the winding being either stored or dissipated prior to the phase becoming inactive. There may also be an intermediate portion (Z2) occurring between attainment of the peak current and the beginning of the terminal portion of the current profile.

Abstract: A method for estimating and controlling the rotor position of a SRM comprises the steps of sampling phase currents and estimating phase fluxes from at least one excited phase of the SRM, sampling phase currents and estimating phase inductances from at least one unexcited phase of the SRM, and estimating the rotor position by determining a rotor position that is common to the estimated phase flux and the estimated phase inductance solutions to predetermining flux and inductance models. The estimation of rotor position can be less sensitive to measurement noise by applying a least squares technique. Once the rotor position has been estimated by the above method, the position of the rotor can be controlled so as to provide an overall effective control of the SRM. In particular, once the position of the rotor is estimated, the excitation provided to the motor is then adjusted to urge the rotor from its current position, velocity or torque toward a desired position, velocity or torque.

Abstract: An apparatus for sensing the position of a switched reluctance motor (SRM) is provided, which detects a relative position of a rotor through concentric slit groups formed along different concentric circumferences of a sensor plate and compensates the position of the rotor through a compensating slit which is formed on the sensor plate, thereby effectively preventing the distortion of the position detection pulse from being accumulated and spread by restricting bad influences caused by the distortion of the position detection pulse generated by partial reasons to a relevant position. As a result, since it is possible to prevent the distortion of the position detection pulse from being accumulated and spread by restricting bad influences caused by the distortion of the position detection pulse generated by partial reasons to the relevant position, the rotating torque ripple and noise can be reduced, thereby maximizing the efficiency of the SRM.

Abstract: A motor control system selectively energizes a motor winding to maximize the motors efficiency and output torque under conditions of varying rotor speed, winding temperature, and supply voltage. Motor output requirement values and sensor output is used to develop independent parameters in the translation and dilation domain from which optimal turn-on and turn-off or "conduction angles" are developed. The optimal conduction angles are processed by circuitry to generate actuation signals that selectively control the delivery of energy to the motor winding.

Abstract: A switched reluctance motor drive includes a noise reduction circuit configured to control the decay of current when a motor phase is switched from active to inactive. The current decay is controlled to occur in two stages: a first portion and a second portion. The first portion is controlled by alternately activating and deactivating one of the two switches in the two switch drive topology to obtain a current profile conforming to a predetermined profile. The current decay in the second portion of the inactive interval occurs by keeping both switches off so that it decays naturally. The duration of the first portion of the inactive interval is different for each motor phase, as is the duty cycle of the switch gating signal driving the switch that is alternately activated and deactivated. The scheme reduces the acoustic noise generated during operation of the motor.

Abstract: It is an object of this invention to attain reliable starting characteristics and stable rotation performance of a motor in a motor of a phase synchronization driving type.

Abstract: A reluctance machine system including a reluctance machine having a stator including at least one phase winding and a rotor defining rotor poles and inter-pole gaps, where permanent magnet inserts are positioned within the inter-pole gaps to interact with the currents in the phase windings to provide permanent magnet torque and to improve the machine's performance.

Abstract: An improved portable wood planing machine for the surface planing of wooden planks or boards is provided. The machine has a switched reluctance motor. In an exemplary embodiment, the planing machine includes a carriage assembly locking mechanism for locking the carriage assembly relative to a plurality of vertical support columns to thereby vertically fix the carriage assembly. In one form, the carriage assembly locking mechanism includes a plurality of levers which cooperate to engage the support columns of the carriage assembly. The exemplary embodiment further includes a depth stop adjustment mechanism which allows the operator to accurately select a minimum workpiece depth from one or more predetermined depths and a material removal indicator assembly operable for enabling the user of the planing machine to accurately determine the amount of material to be removed during each pass of the workpiece.

Abstract: A control circuit (10) for controlling the residual or tail current decay in a single phase or polyphase SRM winding when a phase is switched from active to inactive. A Hall-effect type sensor (30) senses rotor position of the SRM. Current flows through a winding (W) of the motor when the motor phase winding is active; and, current flow into the winding decays to zero when the phase becomes inactive. Semiconductor switches (22) direct current flow into the winding when the phase is active and then redirect residual energy in the winding between an energy recovery circuit and an energy dissipation circuit when the phase becomes inactive. A PWM signal generator (44) provides PWM operating signals to the switches to control current flow first into the winding and then between the recovery and dissipation circuits. A control module (42), or microprocessor (52) with a PWM output, is responsive to rotor position information for controlling operation of the PWM signal generator.