Method to actively hold electric motor position, electric motor, and motorized drive roller assembly

Abstract

A method for controlling an electric motor can include selectively directing, with a controller and a plurality of half-bridges, current through a plurality of coils of a stator of the electric motor whereby a rotor of the electric motor is driven in rotation. The rotor can have at least one permanent magnet defining a rotor magnetic field axis and each coil can define a respective coil magnetic field axis when energized. The method can also include holding, with the controller, after the selectively directing, the rotor in a first angular position. The holding can include closing a high-side switch of a first half-bridge or a low-side switch of a second half-bridge while pulsing open and closed the other. An electric motor operable to execute the method and a motorized drive roller incorporating the electric motor are also disclosed.

Description

METHOD TO ACTIVELY HOLD ELECTRIC MOTOR POSITION, ELECTRIC MOTOR, AND MOTORIZED DRIVE ROLLER ASSEMBLYBACKGROUND1. Field

[0001] The present disclosure relates to a system of electric supply and / or of control for one or more electric motors, particularly to hold a position of a rotor of an electric motor.2. Description of Related Prior Art

[0002] CN102714480 discloses an Inductance parameter identification method of synchronous motor and implementation system thereof. The method comprises: applying a three- phase balance high frequency voltage or current signal to the synchronous motor; sampling a feedback high frequency current or voltage of the synchronous motor; extracting positive sequence and negative sequence component amplitude of the feedback high frequency current or voltage which has the same frequency of the injecting voltage or current; and calculating to get d-axis inductance Ld and q-axis inductance Lq of the synchronous motor. Identification of the d-axis inductance and q-axis inductance of the synchronous motor can be implemented more accurately on a general inverter on the basis of non-increase of hardware cost. The method and system have the following advantages of implementing easily, not high demand for the motor feedback current sampling accuracy, and controlling easily for the frequency and amplitude of the high frequency voltage signal injected into the motor, and identifying to get the d-axis inductance and q-axis inductance of the motor directly no matter the motor shaft is in a free state, or in a hold tight stage, which do not affect accuracy of identification.

[0003] CN107994828 discloses Permanent magnet synchronous motor quadrature-direct axis inductance measurement method. The method comprises the steps of fixing quadrature-axis or directaxis current of the permanent magnet synchronous motor on a certain current point, injecting symmetrical direct-axis or quadrature-axis square wave reference voltage into the quadrature-axis or direct-axis to change the quadrature-direct axis current, and obtaining the change relation of the direct-axis or quadrature-axis inductance on the quadrature-axis or direct-axis current point along with the injected direct-axis or quadrature-axis current and the equivalent voltage value of the nonlinear factor of an inverter; obtaining the direct-axis or quadrature-axis inductance value of the permanent magnet synchronous motor, which changes along with saturation, of all current points at the corresponding rotor position according to the change relation and the equivalent voltage value;according to the method for measuring the alternating current and direct current axis inductance of the permanent magnet synchronous motor at different rotor positions considering the influence of the saturation effect and the nonlinear factors of the inverter, the motor inductance values at different saturation degrees are identified by obtaining the one-to-one correspondence of the motor alternating current and direct current axis inductance and all alternating current and direct current axis current combinations, the influence of the nonlinear factors of the inverter is identified and compensated, and the inductance measurement precision can be improved.

[0004] CN108988722 discloses a kind of measuring method of the ac-dc axis inductance characteristic curve of permanent magnet synchronous motor. The measuring method can recognize axis inductor and d-axis inductance of the permanent magnet synchronous motor under different magnetic saturation degree, overcome the influence of the conduction voltage drop of switch element and dead time effect to output voltage in inverter, improve the signal -to-noise ratio of cunent sample, inductance identification precision is improved, the inductance characteristic curve of d-axis and quadrature axis is drawn according to inductance identification result.

[0005] CN117175999 discloses a household appliance and control method of permanent magnet synchronous motor. The household appliance comprises: a housing; the permanent magnet synchronous motor is arranged in the shell and is used for controlling the rotating speed according to the voltage signal; a controller configured to: determining the actual rotor position of the permanent magnet synchronous motor; injecting positive and negative alternating voltage signals under a rotor coordinate system of the permanent magnet synchronous motor according to the actual rotor position, and acquiring direct-axis high-frequency current and quadrature-axis high-frequency current under the rotor coordinate system; determining a gain coefficient according to the direct-axis high- frequency current and the quadrature-axis high-frequency current; and injecting voltage into the permanent magnet synchronous motor according to the gain coefficient. The invention can reduce the influence of parameter change of the permanent magnet synchronous motor and the frequency and amplitude change of the injection voltage signal on the determination of the actual rotor position of the motor, thereby improving the self-adaptive capacity of high-frequency square wave injection on the permanent magnet synchronous motor with different parameters.

[0006] EP4160903 discloses a control method and related device for drive motor of automobile, and transmission gearbox of automobile. A stator of the drive motor includes a first phase winding, a second phase winding, and a third phase winding. The method includes: obtaining a position of a rotor of the drive motor, where the first phase winding is connected in parallel to the second phase winding, the first phase winding is connected in series to the third phase winding, andthe second phase winding is connected in series to the third phase winding; and the drive motor is in a boost charging mode, and is configured to charge a power battery of the automobile after boosting a charging voltage; and if the position of the rotor is not a first target position, supplying a first current to the drive motor, so that a magnetic field generated by the stator adjusts the position of the rotor to the first target position, to make a locked-rotor torque of the drive motor be zero. In this embodiment of this application, the locked-rotor torque of the drive motor can be released.

[0007] US20140327379A1 discloses a position sensorless drive system and method for permanent magnet motors. An embodiment includes a square wave voltage source connectable to an input of a permanent magnet motor. At least one current sensor is connectable to the motor, wherein the current sensor is configured to sense the current in at least one power line to the motor in response to the square wave input to the motor. The position of the rotor relative to the stator may be determined based on the current resulting from the square wave voltage.

[0008] WO2018102872A1 discloses a sensorless ac motor controller. The controller including: a power converter driving the AC electric motor; a feed forward converter that derives voltage values provided to the power converter; and a load model unit configured to derive an applied rotor speed used for an input to the feed forward converter, wherein the applied rotor speed is derived using a stabilising speed correction value with a substantially zero average value.

[0009] The background description provided herein is for the purpose of generally presenting background context of the disclosure. Work of the presently named inventor, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.SUMMARY

[0010] This section provides a simplified summary in order to provide a basic understanding of some aspects described herein. This summary is not an extensive overview and is not intended to identify “key” or “critical” elements of the present disclosure or to delineate the scope of the various aspects described herein. The purpose of this portion of the document is to present some concepts in a simplified form as a prelude to the more detailed description that is presented later.

[0011] A method for controlling an electric motor can include selectively directing, with a controller and a plurality of half-bridges controlled by the controller, current through a plurality of coils of a stator of the electric motor whereby a rotor of the electric motor is driven in rotation about a central axis of the rotor. Each of the plurality of half-bridges can be connected directly to a high-side of one of the plurality of coils. Respective low-sides of the plurality of coils can be interconnected through one of a Y connection and a delta connection. The rotor can have at least one permanent magnet defining a rotor magnetic field axis Each of the plurality of coils can define a respective coil magnetic field axis when energized. The method can also include holding, with the controller, after the selectively directing, the rotor in a first angular position about the central axis of the rotor relative to the stator. The holding can include opening a plurality of respective high-side switches of the plurality of half-bridges. The holding can also include opening a plurality of respective low-side switches of the plurality of half-bridges. The holding can also include closing at least one of a high-side switch of a first half-bridge of the plurality of half-bridges and a low-side switch of a second half-bridge of the plurality of half-bridges while pulsing open and closed the other of the high-side switch of the first half-bridge and the low-side switch of a second half-bridge.

[0012] According to other features, the method can also include sensing, with a sensor, voltage at a position between a high-side switch of a third half-bridge and a low-side switch of the third half-bridge while both of the high-side switch of the third half-bridge and the low-side switch of the third half-bridge are open. The sensing can occur over time and during the closing while pulsing. The holding can further comprise comparing, with the controller, a waveform of the voltage sensed over time by the sensor during the sensing against a predetermined voltage over time waveform. The holding can also further comprise determining, with the controller, a difference between the sensed voltage over time waveform and the predetermined voltage over time waveform. The difference can be further defined as one of a difference between respective rise times of the waveforms, a difference between respective maximum values of slopes of the waveforms, a difference between respective peak values of the waveforms, and a difference between respective time durations above a predetermined voltage of the waveforms.

[0013] In other features, the closing while pulsing can include pulsing, with the controller, the other of the high-side switch of the first half-bridge and the low-side switch of a second half-bridge in an open and closed cycle at a frequency of between 20 kHz - 100kHz. A closed portion of the open and closed cycle can have a duration of between 0.75 pS - 5 pS. The holding can further comprise changing, with the controller, in response to the difference, the duration of the closed portion of the open and closed cycle. The holding can further comprise changing, with the controller, in response to the difference, the frequency of the open and closed cycle. The duration of the closed portion of the open and closed cycle can correspond to 2 - 35 watts of power.

[0014] According to additional features, the opening of the plurality of respective high-side switches of the plurality of half-bridges can further comprise opening, with the controller, a high-sideswitch of the second half-bridge while the second half-bridge is connected directly to a high-side of a second coil of the plurality of coils. The opening of the plurality of respective high-side switches of the plurality of half-bridges can also further comprise opening, with the controller, a high-side switch of a third half-bridge of the plurality of half-bridges while the third half-bridge is connected directly to a high-side of a third coil of the plurality of coils. The opening the plurality of respective low-side switches of the plurality of half-bridges can further comprise opening, with the controller, a low-side switch of the first half-bridge while the first half-bridge is connected directly to a high-side of a first coil of the plurality of coils. The opening the plurality of respective low-side switches of the plurality of half-bridges can also further comprise opening, with the controller, a low-side switch of the third half-bridge. The closing while pulsing can further comprise closing, with the controller, the low-side switch of the second half-bridge. The closing while pulsing can also further comprise pulsing the high-side switch of the first half-bridge between open and closed conditions, whereby, when the high-side switch of the first half-bridge is in the closed condition, current flows through the first coil and the second coil when the high-side switch of the first half-bridge is closed.

[0015] According to other features, the selectively directing can be further defined wherein a first number of the plurality of half-bridges and a second number of the plurality of coils are multiples of three.

[0016] In other features, the method can also include determining, during the holding, with the controller, the first angular position the rotor. The method can also include second selectively directing, after the holding, with the controller and the plurality of half-bridges controlled by the controller, current through the plurality of coils of the stator of the electric motor whereby the rotor of the electric motor can be driven in rotation about the central axis of the rotor. The second selectively directing can be based at least in part on the determining.

[0017] An electric motor can include a stator, a rotor, a plurality of half-bridges, and a controller. The stator can have a plurality of coils with respective low-sides and high-sides. The low- sides of the plurality of coils can be interconnected through one of a Y connection and a delta connection. Each of the plurality of coils can define a respective coil magnetic field axis when energized. The rotor can be positioned at least partially within the stator and can have a central axis and at least one permanent magnet. The at least one permanent magnet can define a rotor magnetic field axis. The plurality of half-bridges can each be connected directly to one of the high-sides of the plurality of coils. The controller can be configured to selectively direct current through the plurality of coils by selectively opening and closing low-side switches and high-side switches of the plurality of half-bridges whereby the rotor is driven in rotation about the central axis. The controller can alsobe configured to hold the rotor in a first angular position about the central axis relative to the stator. The controller can be configured to hold the rotor by opening a plurality of the high-side switches. The controller can be configured to hold the rotor also by opening a plurality of the low-side switches. The controller can be configured to hold the rotor also by closing at least one of the high-side switch of a first half-bridge of the plurality of half-bridges and the low-side switch of a second half-bridge of the plurality of half-bridges while pulsing open and closed the other of the high-side switch of the first half-bridge and the low-side switch of the second half-bridge.

[0018] In other features, the electric motor can further comprises a sensor. The sensor can be arranged and configured to sense voltage at a position between the high-side switch of a third halfbridge of the plurality of half-bridges and the low-side switch of the third half-bridge. The sensor can also be configured to communicate a signal corresponding to sensed conditions to the controller.

[0019] According to additional features, the controller can be further defined as configured to compare a waveform of the voltage sensed over time by the sensor against a predetermined voltage over time waveform. The controller can be further defined as configured to identify a difference between the waveform of the voltage sensed over time and a predetermined voltage over time waveform. The controller can be further defined as configured to pulse the other of the high-side switch of the first half-bridge and the low-side switch of the second half-bridge in an open and closed cycle having a frequency of between 20 kHz - 100kHz, wherein a closed portion of the open and closed cycle has a duration of between 0.75 pS - 5 pS. The duration of the closed portion of the open and closed cycle can correspond to 2 - 35 watts of power.

[0020] A motorized drive roller (MDR) can include a roller and an electric motor. The electric motor can be operably coupled with the roller to rotate the roller. The electric motor can include a stator, a rotor, a plurality of half-bridges, and a controller. The stator can have a plurality of coils with respective low-sides and high-sides. The low-sides of the plurality of coils can be interconnected through one of a Y connection and a delta connection. Each of the plurality of coils can define a respective coil magnetic field axis when energized. The rotor can be positioned at least partially within the stator and can have a central axis and at least one permanent magnet defining a rotor magnetic field axis. The roller can be coupled with the roller to drive the roller in rotation. The plurality of half-bridges can each be connected directly to one of the high-sides of the plurality of coils. Each of the plurality of half-bridges can have a respective low-side switch and a respective high-side switch. The controller can be configured to selectively direct current through the plurality of coils by selectively opening and closing the low-side switches and the high-side switches whereby the rotor is driven in rotation about the central axis. The controller can also be configured to hold therotor in a first angular position about the central axis relative to the stator. The controller can also be configured to hold the rotor by opening a plurality of the high-side switches. The controller can also be configured to hold the rotor by also opening a plurality of the low-side switches. The controller can also be configured to hold the rotor by also closing at least one of the high-side switch of a first half-bridge of the plurality of half-bridges and the low-side switch of a second half-bridge of the plurality of half-bridges while pulsing open and closed the other of the high-side switch of the first half-bridge and the low-side switch of the second half-bridge.

[0021] According to other features, the MDR can further comprises a sensor. The sensor can be arranged and configured to sense voltage at a position between the high-side switch of a third halfbridge of the plurality of half-bridges and the low-side switch of the third half-bridge. The sensor can also be configured to communicate a signal corresponding to sensed conditions to the controller.

[0022] In other features, the controller can be further defined as configured to compare a waveform of the voltage sensed over time by the sensor against a predetermined voltage over time waveform. The controller can be further defined as configured to identify a difference between the waveform of the voltage sensed over time and a predetermined voltage over time waveform. The controller can be further defined as configured to pulse the other of the high-side switch of the first half-bridge and the low-side switch of the second half-bridge in an open and closed cycle having a frequency and each cycle having a closed portion and an open portion of different durations. The duration of the closed portion of the open and closed cycle can correspond to 2 - 35 watts of power.BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The detailed description set forth below references the following drawings:

[0024] Figure l is a schematic of an electric motor according to an exemplary embodiment of the present disclosure;

[0025] Figure 2 is a graph showing exemplary voltage waveforms; and

[0026] Figure 3 is a schematic representation of a conveyor system that can incorporate an electric motor according to one or more embodiments of the present disclosure.DETAILED DESCRIPTION

[0027] The present disclosure, as demonstrated by the exemplary embodiment described below, provides rotor position feedback to a hold a rotor in a parked position and then drive the electric motor. The feedback can be used to control motor power and torque and adjust forces as necessary to selectively drive a rotor in rotation, such as, by way of example and not limitation, arotor engaged with a roller of a motorized drive roller assembly (an “MDR”) or fan blade of a fan assembly. Energy consumption and holding power performance of an embodiment of the present disclosure can be similar to an arrangement including an extraneous sensor.

[0028] An embodiment of the present disclosure can utilize data generated by a sensor that can be already built onto the drive circuit board of the motor. Thus, in one or more embodiments of the present disclosure, no extraneous / supplemental / addition sensor(s) need be added to the motor if current and / or voltage measurement can be derived from a circuit board of the motor. At least some embodiments of the present disclosure can thus obviate the need for relatively higher cost, more invasive sensors that would need to be placed in or on the mechanical assembly of the motor, like magnetic hall sensors, encoders, resolvers, GMR rotational sensor, AMR position sensor, etc.

[0029] MDRs in conveyance applications can be required to resist motion and hold packages in place when not in “motoring mode” (a motor of the MDR driving a roller of the MDR in rotation). Applications also exist in other electric motor driven fields such as air-moving where it may be required to prevent a fan from spinning under the force of external air flow. Embodiments of the present disclosure include any application and / or operating environment where it is advantageous for the motor to hold position and not spin while consuming a minimum amount of power applies.

[0030] “Hold position” functionality can be an expected functionality by default on drive rollers in one or more operating environments. When a system controller of a conveyance application commands a roller to stop, system preference may be that the roller is expected to brake, stop quickly (such as between 100 -300 mS), and then hold a fixed rotational position. Even along sections of the conveyance application that are sloped the roller is expected to hold packages to a predetermined weight limit in place. Also, if a package in an upstream, adjoining section of the conveyance application is pushed into a package on the stopped section, the stopped rollers can be expected to actively resist the motion. A specific MDR does not “know” where it is positioned along the path formed by the conveyance application, so this “stop and hold” function can be required on all rollers of all MDRs.

[0031] The inventor has observed that MDRs currently found in the art use some sort of rotor position sensor for producing feedback to execute the hold function. The present disclosure advantageously eliminates the sensor and thus enhances reliability and manufacturing ease, as well as reduces cost. The inventor has also observed that one approach applied in the art to execute a hold function is to drive motor winding current causing the motor to lock with motion-opposing torque available. However, the inventor has further observed that this leads to undesirable powerrequirements and causes an MDR to overheat quickly and also reduces overall system efficiency leading to increased energy costs in the end application.

[0032] Knowing rotor position at zero and / or low speeds can also be advantageous for motor starting, particularly starting with torque / load requirements. The present disclosure provides further benefits of detecting rotor position and then aligning the stator magnetic vector to create torque and rotation. Applying the method disclosed herein again on the new position and then again adjusting the vector could be used to start motor rotation from zero rotations per minute (RPM) with significant torque, all without the need for a shaft position sensor.

[0033] The present disclosure provides the functionality of delivering hold position performance without the need for a rotor position sensor. Inductance is measured while exerting a holding torque on the rotor. Applications utilizing inductive sensing require high motor inductances, but the present disclosure utilizes low inductances, typical of low voltage.

[0034] Referring now to Figure 1, an exemplary electric motor 10 includes a stator 12. The exemplary stator 12 has a body 14 defining a plurality of posts, such as posts 16, 18, and 20. The exemplary stator 12 also has a plurality of coils, such as coils 22, 24, and 26. Each of the exemplary coils 22, 24, 26 is wound around one of the exemplary posts 16, 18, 20. It is noted that stators of embodiments of the present disclosure are not limited to three posts / coils. Stators utilized in one or more embodiments of the present disclosure can include posts / coils in multiples of three, as in the exemplary embodiment, or in multiples of other numbers.

[0035] Each of the exemplary coils 22, 24, 26 has a respective low-side and a respective high- sides. For example, the exemplary coil 22 has a low-side referenced at 28 and a high-side referenced at 30, the exemplary coil 24 has a low-side referenced at 32 and a high-side referenced at 34, and the exemplary coil 26 has a low-side referenced at 36 and a high-side referenced at 38. The low-sides of coils can be interconnected through one of a Y connection and a delta connection. The low-sides 28, 32, 36 of the exemplary coils 22, 24, 26 are interconnected through a Y connection. The connection is represented by a circle referenced at 40. While a Y connection is applied in the exemplary embodiment, a delta connection could be applied in one or more other embodiments of the present disclosure.

[0036] The exemplary electric motor 10 also includes a rotor 42. The exemplary rotor 42 is positioned at least partially within the exemplary stator 12. The exemplary rotor 42 has a central axis referenced at 44. A rotor in embodiments of the present disclosure has at least one permanent magnet. The exemplary rotor 42 is schematically shown as a single permanent magnet, however it is noted that the present disclosure is not limited to a single permanent magnet or any particular number ofpermanent magnets. The exemplary rotor 42 defines a magnetic field axis referenced at 46. In one or more embodiments of the present disclosure, a roller can be coupled with a roller of an MDR assembly to drive the roller in rotation. Figure 3 schematically shows a conveyance system 48 that is configured to move packages. The exemplary conveyance system 48 includes a plurality of rollers, such as a roller referenced at 50. The exemplary electric motor 10 is incorporated to the exemplary conveyance system 48 and the rotor 42 (not visible in Figure 3) of the exemplary electric motor 10 can drive the roller 50 in rotation to move packages or be held in position to deter / prevent packages from moving.

[0037] Referring again to Figure 1, the exemplary electric motor 10 also includes a plurality of half-bridges, such as exemplary half-bridges 52, 54, 56. It is noted that embodiments of the present disclosure are not limited to electric motors having any particular number of half-bridges. The high- sides of the exemplary half-bridges 52, 54, 56 are connected to an exemplary direct current (DC) bus rail referenced at 58. The low-sides of the exemplary half-bridges 52, 54, 56 are connected to a DC bus return referenced at 60. A source of DC power is referenced at 62 provides electric power to the exemplary half-bridges 52, 54, 56.

[0038] Each of the exemplary half-bridges 52, 54, 56 includes a high-side switch and a low- side switch. The exemplary half-bridge 52 includes an exemplary high-side switch 64 and a low-side switch 66. The exemplary half-bridge 54 includes an exemplary high-side switch 68 and a low-side switch 70. The exemplary half-bridge 56 includes an exemplary high-side switch 72 and a low-side switch 74. It is noted that in various embodiments of the present disclosure many different switch combinations are possible with various switches locked on or off or cycling (PWM-ing).

[0039] Each of the exemplary half-bridges 52, 54, 56 is connected directly to one of the high- sides of the exemplary coils 22, 24, 26. The exemplary half-bridge 52 is connected directly to the exemplary high side 30 of the exemplary coil 22. The exemplary half-bridge 54 is connected directly to the exemplary high side 34 of the exemplary coil 24. The exemplary half-bridge 56 is connected directly to the exemplary high side 38 of the exemplary coil 26.

[0040] The exemplary electric motor 10 also includes a controller. An exemplary controller is referenced at 76. The exemplary controller is configured to control the switches 64, 66, 68, 70, 72, 74 to open or close. When a particular one of the switches 64, 66, 68, 70, 72, 74 is open, current does not flow through that switch. When a particular one of the switches 64, 66, 68, 70, 72, 74 is closed, current flows through that switch. It is noted that a representation of communication / signal lines is not included in Figure 1 to enhance the clarity of Figure 1, but the exemplary controller 76 is connected to all of the exemplary switches 64, 66, 68, 70, 72, 74 whereby a control signal can be sentby the exemplary controller 76 to any one or more of the exemplary switches 64, 66, 68, 70, 72, 74 to close and thereby permit the flow of current. When a control signal is not being received from the exemplary controller 76, an exemplary switch 64, 66, 68, 70, 72, 74 will be open and thereby prevent the flow of current. An exemplary controller that can be utilized, after appropriate programming to accomplish the activity set forth herein, is a circuit board that includes a Texas Instruments TMS320F000137 microcontroller.

[0041] The exemplary controller 76 is configured to selectively direct current through the plurality of exemplary coils 22, 24, 26 whereby the exemplary rotor 42 is driven in rotation about the central axis 44 of the exemplary rotor 42. The exemplary controller 76 selectively directs current through the plurality of exemplary coils 22, 24, 26 by selectively closing and opening the exemplary switches 64, 66, 68, 70, 72, 74. The exemplary switches 64, 66, 68, 70, 72, 74 are closed and opened to selectively energize the exemplary coils 22, 24, 26. Each of the exemplary coils 22, 24, 26 generates a magnetic field with a respective coil magnetic field axis when energized by the flow of current. The exemplary controller 76 thus selectively energizes the exemplary coils 22, 24, 26 to generate successive magnetic fields that interact with the magnetic field generated by the rotor 42 to drive the rotor 42 in rotation. By way of example and not limitation, a conveyance system such as the exemplary conveyance system 48 is operating in a transporting mode when the exemplary controller 76 is selectively directing current through the plurality of exemplary coils 22, 24, 26 and thereby driving the exemplary rotor 42 in rotation about the central axis 44. When the exemplary controller 76 is selectively directing current through the plurality of exemplary coils 22, 24, 26, whereby rotor 42 is rotating, the electric motor 10 can be viewed as operating in a “running” or “operating” mode.

[0042] The exemplary controller 76 is also configured to hold the exemplary rotor 42 relative to the exemplary stator 12. In an MDR application, this functionality prevents or at least inhibits a package from moving along a conveyance path defined by a conveyance system. When it is desired to switch the conveyance system from transporting operation to holding operation, an angular position exemplary rotor 42 can be held. The angular position exemplary rotor 42 corresponds to the orientation of the exemplary magnetic field axis 46 of the exemplary rotor 42 in a plane normal to the exemplary central axis 44 of the exemplary rotor 42. The schematic illustration of the exemplary stator 12 and exemplary rotor 42 in Figure 1 is in such a plane. When the exemplary controller 76 is controlling the plurality of exemplary coils 22, 24, 26, whereby the rotor 42 is held in position, the electric motor 10 can be viewed as operating in a “hold” or “fixed” mode.

[0043] In one exemplary approach of practicing the present disclosure, the exemplary controller 76 can control the exemplary switches 64, 66, 68, 70, 72, 74 to hold the exemplary rotor 42 in a first angular position about the exemplary central axis 44 relative to the exemplary stator 12 by opening a plurality of the high-side switches. The exemplary first angular position is shown in Figure 1. In the exemplary approach, the exemplary controller 76 can open the high-side switch 68 of the half-bridge 54. As noted above, the exemplary half-bridge 54 is connected directly to the exemplary high-side 34 of the exemplary coil 24. “Opening” a switch for the exemplary holding of the rotor 42 can mean ceasing the transmission of the control signal to close if the signal is currently being transmitted and / or maintaining the switch in the open orientation (by the omission of the control signal) if already open. In the exemplary approach, the exemplary controller 76 can also open the exemplary high-side switch 72 of the exemplary half-bridge 56. As noted above, the exemplary halfbridge 56 is connected directly to the high-side 38 of the exemplary coil 26.

[0044] Further in the exemplary approach, the exemplary controller 76 can open the exemplary low-side switch 66 of the exemplary half-bridge 52. Further in the exemplary approach, the exemplary controller 76 can open the exemplary low-side switch 74 of the exemplary half-bridge 56. Thus, the third motor phase, of which the exemplary half-bridge 56 is part, is thus left floating since both switches 72, 74 are open.

[0045] Further in the exemplary approach, the exemplary controller 76 can close at least one of the exemplary high-side switch 64 of the exemplary half-bridge 52 and the low-side switch 70 of the exemplary half-bridge 54 while pulsing open and closed the other of the exemplary high-side switch 64 of the exemplary half-bridge 52 and the low-side switch 70 of the exemplary half-bridge 54. “Closing” a switch for the exemplary holding of the rotor 42 can mean starting the transmission of the control signal to close if the signal is not then currently being transmitted and / or maintaining the switch in the closed orientation (by the maintaining of the control signal) if already closed. In the exemplary approach, by way of example and not limitation, the exemplary controller 76 can close the low-side switch 70 of the exemplary half-bridge 54 and pulse open and closed the high-side switch 64 of the exemplary half-bridge 52. In other embodiments of the present disclosure, the pulsing could be done in another way, such as pulsing the low side switch and closing the high-side switch.

[0046] Figure 1 illustrates the respective magnetic field axes when the exemplary controller 76 is controlling the exemplary switches 64, 66, 68, 70, 72, 74 to hold the exemplary rotor 42 in the first angular position about the exemplary central axis 44 relative to the exemplary stator 12 when executing the exemplary hold approach. The exemplary flow of current during the closed portion of the pulse of exemplary switch 64 is referenced by arrows 78. The magnetic field axis of the exemplarycoil 22 in response to current flowing according to arrows 78 is referenced at 80. The magnetic field axis of the exemplary coil 24 in response to current flowing according to arrows 78 is referenced at 82. The magnetic fields represented by the magnetic field axes 80, 82 interact with the magnetic field of the exemplary rotor 44 to hold the rotor 44 in the position shown in Figure 1. This is shown, by way of example and not limitation, by the orientation of the magnetic field axis 46 positioned midway between the magnetic field axes 80, 82, angularly about the axis 44.

[0047] In one or more embodiments of the present disclosure, by way of example and not limitation, the exemplary controller 76 can pulse whichever switch is pulsed in an open and closed cycle at a frequency of between 20 kHz - 100kHz, such as 40kHz corresponding to a period of 25 pS. Motor drive switching frequencies can be in the range 2kHz to 200kHz. When the rotor 42 is stationary, there is no opposing BEMF present and so very short voltage pulses can be applied to keep current under control (under a limit). The resulting waveform measured on the open coil / phase can fall off quite fast, such as in 2.5 pS. There would then be a portion of dead time before the next pulse. For example, there can be 22.5 pS of essentially off time before the graph would repeat in one or more embodiments of the present disclosure. A closed portion of the open and closed cycle / period, or the “switch on” time, can have a duration of between 0.75 pS - 5 pS. An open portion of the open and closed cycle / period, or a “switch off’ time, can have a duration of between 20 pS - 24.25 pS. Thus, the cycle can have a closed portion and an open portion of different durations in one or more embodiments of the present disclosure. The inventor has found that a relatively short pulse at regular intervals can cause significant current to flow in the windings that are energized to generate stator magnetic fields to hold the rotor 42 in position.

[0048] In the exemplary embodiment of the present disclosure, the duration of the closed portion of the open and closed cycle corresponds to approximately 2 - 35 watts of power. In the exemplary embodiment, the running power of the electric motor 10 is typically 10 - 35 watts. Peak power when the electric motor 12 is operating is typically around 75 watts. For example, when the electric motor 10 is part of an MDR, peak power can be employed to accelerate packages from a standstill. The power utilized while holding the rotor 42 can start at 2 watts. If there are no forces acting to rotate the rotor 42, 2 watts can maintain the rotor 42 in a held or parked position. If there are forces acting to rotate the rotor 42, up to about 15 watts can be utilized to maintain the rotor 42 in the held / parked position, thus partially overlapping the running power range. Additionally, in the exemplary embodiment, the hold power can be between 2.6% - 20% of the peak power and can be between 8% - 66% of the mean of typical running power. Of course, the amount of power utilized during holding can be minimized to only the amount of power required at any particular moment.

[0049] The exemplary electric motor 10 also includes an exemplary sensor 84. The exemplary sensor 84 is arranged physically and configured to sense voltage at a position between the exemplary high-side switch 72 of the exemplary half-bridge 56 and the exemplary low-side switch 74 of the third exemplary half-bridge 56. The exemplary sensor 84 can sense the voltage during the hold mode, while both switches 72, 74 are open and the switch 64 is being pulsed. The exemplary sensor 84 can also be configured to communicate a signal corresponding to sensed conditions to the exemplary controller 76. It is noted that, in one or more embodiments of the present disclosure, the sensor need not be extra or added piece of hardware. Voltage sensing on the terminals of a motor is included in many if not most motor designs.

[0050] The exemplary controller 76 can change one or more parameters of the open and closed cycle in response to conditions sensed by and received from the sensor 84. The exemplary controller 76 can compare the conditions sensed by and received from the sensor 84 against predetermined data. By way of example and not limitation, the exemplary controller 76 can compare a waveform of the voltage sensed over time by the exemplary sensor 84 during the hold mode against a predetermined voltage over time waveform.

[0051] Figure 2 is a graph correlating time along the x-axis and voltage of the open motor phase along the y-axis. The voltage of the open motor phase is sensed by sensor 84 and communicated to the controller 76 in the exemplary embodiment of the present disclosure. The open motor phase includes the half-bridge 56 and the coil 26 in the exemplary embodiment of the present disclosure. The shaded portion of the graph corresponds to the closed portion of the open and closed cycle of pulsing and the unshaded portion of the graph corresponds to the open portion of the open and closed cycle of pulsing. A typical switch-on time, the shaded area of the graph, can be under 1 gS. The waveform in the graph that is referred to as “parked” corresponds to the rotor 42 held in the fixed position shown in Figure 1. The waveform in the graph that is referred to as “+12 Deg” corresponds to the rotor 42 shifted from the fixed position shown in Figure 1 toward alignment with a first of the axes 80, 82. The waveform in the graph that is referred to as “-12 Deg” corresponds to the rotor 42 shifted from the fixed position shown in Figure 1 toward alignment with a second of the axes 80, 82. The positions of the rotor 42 corresponding to the +12 Deg and -12 Deg can be undesirable and can be caused, by way of example and not limitation, when momentum of a relatively heavy package urges the roller 50 (and thus the rotor 42) to move from the hold / parked position.

[0052] It is noted that the voltage waveforms shown in Figure 2 are a result of the changing phase inductances. Voltage at the exemplary coil / phase 26 starts at zero at the beginning of the hold mode. At every pulse, a measurement of the voltage at the exemplary coil 26 can be made through asimple resistive network at relatively high speeds, such as 5 MHz by way of example and not limitation. As current grows during the pulse when the exemplary switch 64 is closed, the terminal voltage at the exemplary coil 26 also increases. The voltage at the exemplary coil 26 is further responsive to the inductances in the first and second exemplary coils / phases 22, 24. The inductances of each of the first and second exemplary coils / phases 22, 24 are affected by the current flowing through them (strength, frequency) and also by the magnetic field generated by the permanent magnet(s) of the rotor 42.

[0053] It is also noted that the parked waveform can be stored in a memory of the exemplary controller 76 or a memory accessible by the exemplary controller 76. It is also noted that the parked waveform can be determined / derived for an electric motor during development and testing of that electric motor. Differently constructed motors and motors having different physical geometries would likely have different parked waveforms. The inductance of any coil / phase / winding of a motor is also affected by the amount and shape of steel in the magnetic circuit. It is also noted that a particular electric motor may have more than one parked waveform and so sensed voltage waveforms can be compared against more than one predetermined waveform. The amount of steel that is present in the magnetic circuit can change with rotational position of the rotor 42, thus changing the inductance of the coil of the open phase, resulting in different parked waveforms. The minimum and maximum inductances are commonly known as D and Q axis inductance or Ld and Lq. “D” stands for direct axis and “Q” stands for quadrature axis. The wave form will change based on the parked position and a user could park the rotor at different angles.

[0054] The exemplary controller 76 can, during the hold mode, determine a difference between the sensed voltage over time waveform and the predetermined voltage over time waveform. In response to a determination of a difference, the exemplary controller 76 can alter one or more parameters of open and closed cycle to increase a level of torque acting on the rotor 42 by the magnetic fields generated by the energized coils. By way of example and not limitation, a difference that prompts a change to one or more parameters of open and closed cycle can be a difference between respective rise times of the waveforms. The rise time is the duration of time that voltage is increasing to a maximum value. In Figure 2, the rise time of the predetermined, parked waveform and the +12 Deg waveform is about 1 pS, while the rise time of the -12 Deg waveform is less than 1 pS. Other differences that can prompt one or more changes can be a difference between respective maximum values of slopes of the respective waveforms (a first derivative of the each waveform), a difference between respective maximum values of the squared component (a second derivative of the each waveform), a difference between respective peak values of the waveforms, a difference betweenrespective durations between peak and fall time, a difference between respective derivate and a second derivative of the falling waveform after the driving pulse has ended, and a difference between respective time durations above a predetermined voltage.

[0055] In response to determining / identifying a difference between the sensed voltage over time waveform and the predetermined voltage over time waveform, the exemplary controller 76 can change one or more parameters of the open and closed cycle. By way of example and not limitation, the exemplary controller 76 can change the duration of the closed portion of the open and closed cycle. In other words, in the exemplary embodiment, the switch 64 can be held closed for a longer period of time. Thus, the driving pulse duration is increased to drive more current and expend more power to hold the rotor 42 stationary. Applying this approach, a relatively small amount of power is used, which keeps drive temperatures under control, but can be automatically increased as required to hold heavy loads and generate relatively high torques up to the power rating of the motor, such as, for example 35 watts. In one or more embodiments of the present disclosure, the exemplary controller 76 can change the frequency of the open and closed cycle, such as for some type of power loss optimization. Also, the frequency can be fixed in one or more embodiments of the present disclosure and the 'on’ time of the switch (the duty cycle) can be altered. One good example of changing the frequency would be to keep the switch ‘on’ time fixed and alter the frequency of the pulses to change power as more pulses per time means more hold power and torque. This would have the advantage that the pulse would always be the same and possibly lead to more stability in the waveform shown in Figure 2. The changes can be implemented in the pulse following the pulse in which the difference was identified.

[0056] The description above is of an exemplary approach to controlling the exemplary switches 64, 66, 68, 70, 72, 74 to hold the exemplary rotor 42 in the first angular position about the exemplary central axis 44 relative to the exemplary stator 12. In one or more embodiments of the present disclosure, any motor phase (or combination of all three phases) may be used to drive current and generate the desired field axis(es). High-side and / or low-side switches or both may be pulse width modulated to control current flow through the windings / coils in one or more embodiments of the present disclosure. At some point during approaches different from the exemplary approach detailed above, one or more switches on the same high or low side can be pulsed and other, “opposite side” switch or switches can be held closed to generate one more fixed, stator magnetic field axes. In one or more embodiments of the present disclosure, all three phases could be used to drive current and then feedback from one or more phase after a current pulse could be used to determine the alignment / position of the exemplary rotor 42. Different switching patterns will affect the decay rateof the current and how the measurement of current must be achieved. For example, switching patterns that allow decaying current flow to charge de bus capacitors will result in faster current decay rates than a switching pattern that recirculates current through switches or diodes (or a combination) and only decay energy through losses.

[0057] In addition, the angular position of the rotor 42 when the transition between the operating mode and the hold mode occurs is not limiting on the present disclosure. It is possible that the rotor 42 may be rotated forward or backward slightly during the transition. It is not necessary to know the angular position of the rotor 42 when the transition between the operating mode and the hold mode starts.

[0058] The exemplary controller 76 can identify the position of the exemplary rotor 42 at zero speed, such as when the exemplary rotor 42 is in an “initial” position. An initial position of the exemplary rotor 42 can be defined the first time the exemplary motor 10 is operated and can also be defined after the exemplary rotor 42 has been operated for a particular period of operation and before a subsequent period of operation. Identification of the initial position can be advantageous for motor starting, particularly starting with torque / load requirements. As set forth above, one or more parked waveforms can be stored in a memory of the exemplary controller 76 or a memory accessible by the exemplary controller 76. These stored, parked waveforms can be determined / derived for an electric motor during development and testing of that electric motor and stored in memory. Each stored parked waveform can correspond to a particular angular position of the exemplary rotor 42. During holding, the controller 76 can control current after a particular period of operation and before a subsequent period of operation such that the sensed voltage waveform is fully or substantially aligned with one of the stored, parked voltage waveforms, which corresponds to the exemplary rotor 42 being held in a known / parked position. The action of holding the position of the rotor 42 in the parked position occurs prior to the subsequent period of operation and therefore the controller 76 also advantageously provides the benefit of identification of the initial position the exemplary rotor 42 when the subsequent period of operation is to commence.

[0059] Embodiments of the present disclosure can be applied in electric motors in which Ld and Lq are equal and in electric motors in which Ld and Lq are not equal. Also, it is noted that it is not necessary that the controller 76 know the particular angular position of the rotor 42 when it stops rotating at the end of a first instance of selectively directing current (a first period of operation) in order to hold the rotor 42 in the particular position that it comes to rest at after operation is paused. However, the controller 76 can determine the particular angular position of the rotor 42 while the rotor 42 is being held based on the sensed voltage waveform(s). It is noted that the holding processof closing a switch of one phase while pulsing an “opposite-side” switch of another phase can be varied, such as utilizing different pairs of switches across the different phases, to generate more than one voltage waveform while the rotor 42 is held in the parked position and these voltage waveforms can be used by the controller 76 to determine the particular angular position of the parked position. Prior to starting a second instance of selectively directing current (a second period of operation subsequent to the first period of operation), the controller 76 can resume directing current for motor operation based in part on the particular angular position of the current parked position. For example, the controller 76 can initially direct current through the phase(s) such that the initial torque acting on the rotor 42 is maximized.

[0060] What has been described above includes examples of the subject innovation. It is, of course, not possible to describe every conceivable combination of components or methodologies for purposes of describing the disclosed subject matter, but many further combinations and permutations of the subject innovation are possible. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein is intended merely to be illustrative and does not pose a limitation on the scope of any innovation disclosed herein unless otherwise claimed. The word “exemplary” is used to mean serving as an example, instance, or illustration. Any aspect or design described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other aspects or designs. Rather, use of the word “exemplary” is intended to present concepts in a concrete fashion. Further, any statements set forth within the Detailed Description of this document and addressing a prior art device(s) are the observations of the inventors and such statements themselves are not prior art or admissions as to what is prior art.

[0061] As used herein, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Unless indicated otherwise by context, the term “or” is to be understood as an inclusive “or.” Terms such as “first”, “second”, “third”, etc. when used to describe multiple devices or elements, are so used only to convey the relative actions, positioning and / or functions of the separate devices, and do not necessitate either a specific order for such devices or elements, or any specific quantity or ranking of such devices or elements. Use of the terms “about” or “approximately” are intended to cover values that are above and / or below a stated value or range, or within manufacturing tolerances, as would be understood by one having ordinary skill in the art in the respective context. In some instances, this may encompass values in a range of approx. + / -10%; in other instances there may be encompassed values in a range of approx. + / -5%; in yet other instances values in a range of approx. + / -2% may be encompassed; and in yet further instances, this may encompass values in a range of approx. + / -!%.

[0062] It will be understood that the terms “comprises” and / or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof, unless indicated herein or otherwise clearly contradicted by context. Recitations of a value range herein, unless indicated otherwise, serves as a shorthand for referring individually to each separate value falling within the stated range, including the endpoints of the range, each separate value within the range, and all intermediate ranges subsumed by the overall range, with each incorporated into the specification as if individually recited herein. Unless indicated otherwise, or clearly contradicted by context, methods described herein can be performed with the individual steps executed in any suitable order, including: the precise order disclosed, without any intermediate steps or with one or more further steps interposed between the disclosed steps; with the disclosed steps performed in an order other than the exact order disclosed; with one or more steps performed simultaneously; and with one or more disclosed steps omitted, unless expressly contradicted by the text herein or context.

[0063] While the present disclosure has been described with reference to one or more exemplary embodiments, it is to be understood that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the present disclosure. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the present disclosure without departing from the essential scope thereof. Therefore, it is intended that the present disclosure not be limited to a particular embodiment disclosed herein as the best mode contemplated for carrying out this present disclosure, but that the present disclosure will be viewed as covering any embodiment falling within the scope of the appended claims. Various aspects or features described herein may be implemented as a method, apparatus, or article of manufacture using standard programming and / or engineering techniques.

[0064] Also, the right to claim for patent coverage a particular sub-feature, a sub-component, or a sub-element of any disclosed embodiment, singularly or in one or more sub-combinations with any other sub-feature(s), sub-component(s), or sub-element(s), is hereby unconditionally reserved by the Applicant. Also, particular sub-feature(s), sub-component(s), and sub-element(s) of one embodiment that is disclosed herein can replace particular sub-features, sub-components, and subelements of another embodiment disclosed herein or can supplement and be added to another embodiment unless expressly indicated otherwise by the drawings or this specification. The inventor also assert that any of the claims set forth after this detailed description can be combined with any other claim or claims regardless of whether or not there is a direct line of dependency, unless there isan express indication in this text or the drawings unambiguously indicating that such a combination is not possible. The order of the claims and the lines of dependency are irrelevant to the various ways that the features, elements, sub-elements, components, sub-components, etc. of the present disclosure can be combined and thus claimed. Further, the doctrine of claim differentiation is to be applied in construing the appended claims. Further, the use of the word “can” in this document is not an assertion that the subject preceding the word “can” is unimportant or unnecessary or “not critical” relative to anything else in this document The word “can” is used herein in a positive and affirming sense and no other motive should be presumed. More than one patentable “invention” may be disclosed in the present disclosure and it is noted that an “invention” is defined by the content of a patent claim and not by the content of descriptive text or drawings.

Claims

CLAIMSWhat is claimed is:

1. A method for controlling an electric motor comprising: selectively directing, with a controller and a plurality of half-bridges controlled by the controller, current through a plurality of coils of a stator of the electric motor whereby a rotor of the electric motor is driven in rotation about a central axis of the rotor, each of the plurality of halfbridges connected directly to a high-side of one of the plurality of coils, respective low-sides of the plurality of coils interconnected through one of a Y connection and a delta connection, the rotor having at least one permanent magnet defining a rotor magnetic field axis, and each of the plurality of coils defining a respective coil magnetic field axis when energized; and holding, with the controller, after said selectively directing, the rotor in a first angular position about the central axis of the rotor relative to the stator by: opening a plurality of respective high-side switches of the plurality of half-bridges, opening a plurality of respective low-side switches of the plurality of half-bridges, and closing at least one of a high-side switch of a first half-bridge of the plurality of halfbridges and a low-side switch of a second half-bridge of the plurality of half-bridges while pulsing open and closed the other of the high-side switch of the first halfbridge and the low-side switch of a second half-bridge.

2. The method of claim 1 further comprising: sensing, with a sensor, voltage at a position between a high-side switch of a third half-bridge and a low-side switch of the third half-bridge while both of the high-side switch of the third halfbridge and the low-side switch of the third half-bridge are open, said sensing occurring over time and during said closing while pulsing.

3. The method of claim 2 wherein said holding further comprises: comparing, with the controller, a waveform of the voltage sensed over time by the sensor during said sensing against a predetermined voltage over time waveform; and determining, with the controller, a difference between the sensed voltage over time waveform and the predetermined voltage over time waveform.

4. The method of claim 3 wherein the difference is further defined as one of a difference between respective rise times of the waveforms, a difference between respective maximum values of slopes of the waveforms, a difference between respective peak values of the waveforms, and a difference between respective time durations above a predetermined voltage of the waveforms.

5. The method of claim 3 wherein said closing while pulsing further comprises: pulsing, with the controller, the other of the high-side switch of the first half-bridge and the low-side switch of a second half-bridge in an open and closed cycle at a frequency of between 20 kHz - 100kHz, wherein a closed portion of the open and closed cycle has a duration of between 0.75 pS - 5 pS.

6. The method of claim 5 wherein said holding further comprises: changing, with the controller, in response to the difference, the duration of the closed portion of the open and closed cycle.

7. The method of claim 5 wherein said holding further comprises: changing, with the controller, in response to the difference, the frequency of the open and closed cycle.

8. The method of claim 5 further comprising: consuming, with the electric motor, during said holding, 2.6% - 20% of a peak power consumed during said selectively directing.

9. The method of claim 1 wherein: said opening the plurality of respective high-side switches of the plurality of half-bridges further comprises: opening, with the controller, a high-side switch of the second half-bridge while the second half-bridge is connected directly to a high-side of a second coil of the plurality of coils, and opening, with the controller, a high-side switch of a third half-bridge of the plurality of half-bridges while the third half-bridge is connected directly to a high-side of a third coil of the plurality of coils; said opening the plurality of respective low-side switches of the plurality of half-bridges further comprises: opening, with the controller, a low-side switch of the first half-bridge while the first halfbridge is connected directly to a high-side of a first coil of the plurality of coils, and opening, with the controller, a low-side switch of the third half-bridge; and said closing the at least one of a high-side switch of the first half-bridge and the low-side switch of the second half-bridge while pulsing open and closed the other of the high-side switch of the first half-bridge and the low-side switch of a second half-bridge further comprises: closing, with the controller, the low-side switch of the second half-bridge, and pulsing the high-side switch of the first half-bridge between open and closed conditions, whereby, when the high-side switch of the first half-bridge is in the closed condition, current flows through the first coil and the second coil when the high-side switch of the first half-bridge is closed.

10. The method of claim 1 wherein said selectively directing is further defined as: selectively directing, with a controller and a plurality of half-bridges controlled by the controller, current through a plurality of coils of a stator of the electric motor whereby a rotor of the electric motor is driven in rotation about a central axis of the rotor, each of the plurality of halfbridges connected directly to a high-side of one of the plurality of coils, respective low-sides of the plurality of coils interconnected through one of a Y connection and a delta connection, the rotor having at least one permanent magnet defining a rotor magnetic field axis, and each of the pluralityof coils defining a respective coil magnetic field axis when energized, and wherein a first number of the plurality of half-bridges and a second number of the plurality of coils are multiples of three.

11. The method of claim 1 further comprising: determining, during said holding, with the controller, the first angular position the rotor; and second selectively directing, after said holding, with the controller and the plurality of halfbridges controlled by the controller, current through the plurality of coils of the stator of the electric motor whereby the rotor of the electric motor is driven in rotation about the central axis of the rotor, each of the plurality of half-bridges connected directly to the high-side of one of the plurality of coils, respective low-sides of the plurality of coils interconnected through one of the Y connection and the delta connection, the rotor having at least one permanent magnet defining the rotor magnetic field axis, and each of the plurality of coils defining the respective coil magnetic field axes when energized, said second selectively directing based at least in part on said determining.

12. An electric motor comprising: a stator having a plurality of coils with respective low-sides and high-sides, wherein said low-sides of the plurality of coils are interconnected through one of a Y connection and a delta connection, and wherein each of the plurality of coils defines a respective coil magnetic field axis when energized; a rotor positioned at least partially within said stator and having a central axis and at least one permanent magnet defining a rotor magnetic field axis; a plurality of half-bridges each connected directly to one of said high-sides of said plurality of coils; and a controller configured to: selectively direct current through said plurality of coils by selectively opening and closing low-side switches and high-side switches of said plurality of half-bridges whereby said rotor is driven in rotation about said central axis, and hold said rotor in a first angular position about said central axis relative to said stator by: opening a plurality of said high-side switches, opening a plurality of said low-side switches, andclosing at least one of said high-side switch of a first half-bridge of said plurality of halfbridges and said low-side switch of a second half-bridge of said plurality of halfbridges while pulsing open and closed the other of said high-side switch of said first half-bridge and said low-side switch of said second half-bridge.

13. The electric motor of claim 12 further comprising: a sensor arranged and configured to sense voltage at a position between said high-side switch of a third half-bridge of said plurality of half-bridges and said low-side switch of said third half-bridge and also configured to communicate a signal corresponding to sensed conditions to said controller.

14. The electric motor of claim 13 wherein said controller is further defined as configured to: compare a waveform of the voltage sensed over time by said sensor against a predetermined voltage over time waveform; and identify a difference between the waveform of the voltage sensed over time and a predetermined voltage over time waveform.

15. The electric motor of claim 14 wherein said controller is further defined as configured to: pulse the other of said high-side switch of said first half-bridge and said low-side switch of said second half-bridge in an open and closed cycle having a frequency of between 20 kHz - 100kHz, wherein a closed portion of said open and closed cycle has a duration of between 0.75 gS - 5 pS.

16. The electric motor of claim 15 wherein the electric motor is configured to utilize during the holding of said rotor an amount of power between 8% - 66% of a mean of typical running power during the selectively directing of current.

17. A motorized drive roller (MDR) comprising: a roller; and an electric motor operably coupled with said roller to rotate said roller, said motor including: a stator having a plurality of coils with respective low-sides and high-sides, wherein said low-sides of the plurality of coils are interconnected through one of a Y connection and a delta connection, and wherein each of the plurality of coils defines a respective coil magnetic field axis when energized, a rotor positioned at least partially within said stator and having a central axis and at least one permanent magnet defining a rotor magnetic field axis, said roller coupled with said roller to drive said roller in rotation, a plurality of half-bridges each connected directly to one of said high-sides of said plurality of coils and each having a respective low-side switch and a respective high-side switch, and a controller configured to: selectively direct current through said plurality of coils by selectively opening and closing said low-side switches and said high-side switches whereby said rotor is driven in rotation about said central axis, and hold said rotor in a first angular position about said central axis relative to said stator by: opening a plurality of said high-side switches, opening a plurality of said low-side switches, and closing at least one of said high-side switch of a first half-bridge of said plurality of half-bridges and said low-side switch of a second half-bridge of said plurality of half-bridges while pulsing open and closed the other of said high-side switch of said first half-bridge and said low-side switch of said second half-bridge.

18. The MDR of claim 17 wherein the electric motor further comprising: a sensor arranged and configured to sense voltage at a position between said high-side switch of a third half-bridge of said plurality of half-bridges and said low-side switch of said third half-bridge and also configured to communicate a signal corresponding to sensed conditions to said controller.

19. The MDR of claim 18 wherein said controller is further defined as configured to: compare a waveform of the voltage sensed over time by said sensor against a predetermined voltage over time waveform; and identify a difference between the waveform of the voltage sensed over time and a predetermined voltage over time waveform.

20. The MDR of claim 19 wherein said controller is further defined as configured to: pulse the other of said high-side switch of said first half-bridge and said low-side switch of said second half-bridge in an open and closed cycle having a frequency and each cycle having a closed portion and an open portion of different durations.

21. The MDR of claim 20 wherein the duration of the closed portion of the open and closed cycle corresponds to 2 - 35 watts of power.

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