rexresearch.com
Jim MURRAY III
Elliptical Rotor Alternator / Generator / Motor
Elliptical Rotor Alternator / Generator / Motor
" Dynaflux " design reduces Lenz
Law resistance for ultra-high efficiency
WO2014070212
Controller For Toroidal Motor Having Back EMF Reduction
Controller For Toroidal Motor Having Back EMF Reduction
FIELD OF THE INVENTION
[0001] The disclosed inventions relate to the field of controllers for direct current ("DC") electric motors, and more particularly to controllers for DC motors having a toroidal stator winding and external electronic commutation to drive a rotor by interaction with a rotating magnetic field.
BACKGROUND
[0002] As described in this inventor's prior patents, conventional geometry motors are affected by Speed Voltage Back EMF that is parasitic in nature and, among other things, degrades the source potential supplied to the motor. This inventor has implemented novel geometries to reduce Speed Voltage Back EMF, such as those disclosed in co-pending application serial number 13/562,233, titled "Multi-Pole Switched Reluctance D.C. Motor with a Constant Air Gap and Recovery of Inductive Field Energy," which is hereby incorporated by reference in its entirety.
[0003] In most conventional DC motors, the energizing current to the motor is delivered via some type of commutation in communication with the motor coils. Typically, commutation may be accomplished by a mechanical commutator (e.g., commutator bars and carbon brushes), or by electronic commutation (e.g., an electronically controlled switching circuit). In most existing devices the commutator operates in conjunction with the rotor, either by being physically coupled to the rotor by a common shaft (e.g., mechanical commutation), or electronically by relying on information relating to the position of the rotor (e.g., electronic commutation).
[0004] Many drawbacks and limitations are present in existing DC motors. In addition to the above-mentioned degradation of source potential, existing designs are inconvenient for applications desiring a constant torque output with an unvarying input current. Likewise, existing designs do not lend themselves easily to creating an output horsepower that increases with the rotational speed of the rotor. Other drawbacks of traditional designs also exist. [0005] In addition, traditional controllers do not typically provide the ability to control the energizing and de-energizing of field coils in a manner that enables the creation of a rotating magnetic field. Further, traditional controllers do not typically provide for the recapture of energy due to the collapse of the magnetic field upon de-energizing and isolation of a field coil. Other drawbacks of traditional controller designs also exist.
SUMMARY
[0006] One advantage of the presently disclosed system and method is that it addresses the drawbacks of traditional systems.
[0007] Accordingly, another advantage of some embodiments of the disclosed invention is that they provide a controller for a toroidal DC motor that reduces Back EMF and, therefore, minimizes the degradation of source potential. In addition, embodiments of the disclosed invention provide a controller for a motor that provides constant torque at constant current irrespective of the speed of the rotor. Likewise, some embodiments of the disclosed inventions provide controllers for motors that output horsepower that increases with the rotational speed of the rotor.
[0008] In addition, embodiments of the disclosed controller also provide for automatic and customizable control of the associated motor's internal functions and operational characteristics, such as current limits, current switching, motor RPM, motor torque, and direction of power flow. Other advantages and features of the disclosed invention also exist and may be apparent to those of skill in the art.
[0009] Exemplary non-limiting embodiments are disclosed herein, however, it should be appreciated that other appropriate embodiments are encompassed by the present disclosure, the possible variations being too numerous to illustrate. It is understood that one skilled in the art would recognize that other potential arrangements are capable of supporting the principles disclosed herein. Other aspects and advantages of the presently disclosed systems and methods will now be discussed with reference to the drawings. BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is an overview of a DC toroid motor system in accordance with some embodiments of the disclosed inventions.
[0011] FIG. 2 shows a close-up view of some embodiments of the rotor/stator assembly 40 [toroid app fig. 3] .
[0012] FIG. 3 shows a schematic diagram of a toroid stator and rotor assembly 40 and a representation of the rotating magnetic flux lines 80 and Dead Zones 70. [toroid app fig. 6]
[0013] FIG. 4 is a schematic system overview diagram of a controller 90 in accordance with some embodiments.
[0014] FIG. 5 illustrates a schematic diagram for a coil switch 400 in accordance with some disclosed embodiments.
[0015] FIG. 6 shows a coil switch 400 functional diagram displaying only the parts which are used for one of the two magnetic polarities in accordance with some embodiments.
DETAILED DESCRIPTION
[0016] In the following detailed description, reference is made to the accompanying drawings that form a part hereof, and in which are shown by way of illustration specific embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized and that various changes may be made without departing from the spirit and scope of the present invention. The following detailed description is, therefore, not to be taken in a limiting sense.
[0017] The operation of a DC Motor of standard design requires that sets of magnetic field producing coils be electro-mechanically, or electronically switched, so as to secure an output torque and continuous rotary motion. This is typically achieved by timing the switching of the coils, such that the coil windings spend a maximum amount of time beneath the magnetic poles of the motor such that the electromagnetic force (F) described by the Lenz force relationship,
[0018] F = Bel, [0019] (where B is the magnetic field, I is the length of the conductor, and I is the current) can be fully exploited. However in the invention herein disclosed, two opposing magnetic fields are created within the toroidal windings of the stator, and come together at two points (i.e., 180 mechanical degrees apart) where they exit the confines of the stator iron, traverse the air gap, and enter the rotor structure which is positioned across a diameter of the toroid. Accordingly, the reluctance forces associated with this rotor structure will cause the rotor to align itself with the flux lines, producing a torque, and providing a closed path for the flux, to travel through the rotor, cross the air gap on the other side, and return to the stator, thus, allowing each flux line to return to its associated coil group. This is discussed in more detail with reference to FIG. 3 below. Thus, a very large value of restoring torque may exist within the motor, rotor, and drive shaft whether rotation ensues or not. Rotation is a secondary feature of this arrangement, and is determined by the switching frequency of the windings. Therefore, when rotation is desired, a switching sequence is initiated which turns off and isolates one coil in one coil group, while simultaneously turning on one coil in the other complementary coil group. This action will advance the position of the rotor by 360/n degrees, where n is the total number of coils arranged around the periphery of the toroidal stator. The switching sequence is repeated for the next adjacent set of coils in each group and rotation may be sustained at a speed related to the rate of switching.
[0020] The areas where the rotating flux field dynamically interacts with the windings are at the two positions where the flux exits out of the stator and enters the rotor, and exists out of the rotor and enters the stator. Therefore, depending upon the arc length required by the physical dimensions of the rotor, a certain number of windings are electronically eliminated from the overall circuit within these two regions, thereby providing a "Dead Zone," or an isolated segment at each end of the rotor's immediate position, thereby insuring that speed-related Back EMF will be kept to an absolute minimum.
[0021] Therefore, a motor operating in accordance with this scheme, will sustain a rotating field of flux 80, and a rotating Dead Zone 70, which possess the same angular velocity, but not necessarily the same phase relationship. Depending upon the load applied to the motor, the Dead Zone 70 may be advanced or retarded with respect to the rotor's position, in order to minimize any flux coupling between the rotating field and the DC windings. Additional features and aspects of a toroidal motor system are disclosed in greater detail in concurrently filed, related application serial no. xx/xxx,xxx, titled "Toroidal Motor Design Having Back EMF Reduction."
[0022] FIG. 1 is an overview of a DC toroid motor system in accordance with some embodiments of the disclosed inventions. As shown, some embodiments may comprise a DC toroid motor 10 further comprising an appropriate power supply 20. Of course, the particular power supply 20 may vary in accordance with factors such as the intended use of the motor 10, the environment motor 10 is intended to operate in, the desired electric inputs, the desired torque outputs, the desired RPM, or the like.
[0023] Some non-electronically controlled embodiments of motor 10 may comprise a commutator 30 assembly. As shown, some embodiments may comprise a commutator 30 that is located apart from the rotor/stator assembly 40. Further, in embodiments where commutator 30 comprises an electro-mechanical device, a powered driver 32 may also be included. Powered driver 32 may comprise any suitable motor, or other prime mover, capable of imparting the desired rotational motion to commutator 30.
[0024] Some embodiments also may comprise a number of conductors 42 in electrical communication with stator coils and commutator 30 contacts. For clarity, the figures only illustrate a single conductor 42, but, of course, as many conductors 42 as desired may be implemented. In addition, any suitable connection mechanisms may also be implemented, such as ribbon cables, multi-conductor cables, modular connectors, connection busses, or the like. Likewise, any suitable conductors 42 are possible and may vary with the intended use, power, speed, number of coils, or environment considerations. Likewise, any suitable connection scheme for conductors 42 (e.g., a connection bus) may be implemented. Controller 90 and energy recapture 100 are discussed below and may also be provided in some embodiments.
[0025] FIG. 2 shows a close-up view of some embodiments of the rotor/stator assembly 40. As shown, conductors 42 carry input power from the contacts 38 to the toroidal stator 44 and may be connected to the stator coils in any suitable configuration as discussed in more detail below (again, for clarity, only one conductor 42 is shown). As shown, toroidal stator 44 is generally annular in shape and arranged to allow rotor 46 to rotate within the center space of the toroid. [0026] As shown in FIG. 2 some embodiments of rotor 46 may comprise an un-excited (e.g., coil-less) rotor 46. For some embodiments rotor 46 may be generally rectangular with ends shaped to conform to a curvature that generally matches the curvature of the inner circle of the toroid stator 44 to ensure a constant air gap, and allow free rotation. Other embodiments may include coils (not shown) on rotor 46 in order to, among other things, provide a mechanism for increasing motor 10 torque output.
[0027] Other shapes and configurations for rotor 46 are also possible. For example, rotor 46 may comprise a disc of varying magnetic permeability. A portion of such a disc may include a relatively high permeability material that provides a preferential flux path through the rotor 46. Other shapes and configurations for rotor 46 are also possible.
[0028] In some embodiments, it may be preferable to couple motor 10 with other machines, instruments, or devices, therefore, output coupler 48 may be provided on a shaft coupled to rotor 46. Output coupler 48 may comprise one or more pulleys, gears, shafts, or other couplers.
[0029] A variety of connection schemes for stator coils 50 are possible. For example, a series connection for stator coils 50 may be implemented, meaning that each coil is connected to the next in a series fashion.
[0030] In addition, the motor 10 may be configured for parallel connection of stator coils 50 in accordance with some embodiments. Parallel connection in the present disclosure means that each stator coil 50 is independently connected to a DC power supply (e.g., supply 20) so that it may be independently energized to create a resultant magnetic field.
[0031] Control of the switching of the various power cycles for the coils 50 may be achieved in any suitable manner. For example, controller 90 may contain an electronic control circuit that gives separate, customizable control over the energizing of each coil 50 as described herein.
[0032] Further, in accordance with the disclosure herein, the magnetic field flux lines 80 (and Dead Zones 70) may be controlled using controller 90 so that at any given time a portion of the stator coils are energized with one polarity (e.g., positive) and the other, complementary, portion are energized with the opposite polarity (e.g., negative). Likewise, by disconnecting and isolating a member, or members, of a specific coil group, a rotating Dead Zone 70 may be created in accordance with the principles outlined herein.
[0033] The switching performed by controller 90 is performed so that no current is allowed to flow through the coil 50 windings which lie between each group of "active" coils. This selective form of switching, then creates a series of "inactive and isolated coils" which constitute two Dead Zones 70 located 180 mechanical degrees apart on the stator 44, and which rotate in synchronism with the rotor 46. These traveling Dead Zones 70 then represent windows for the flux 80 to pass through with minimal, if any, inducing of a Back EMF Voltage, or a Back Torque, either of which could reduce motor 10 performance.
[0034] As with any magnetic field, the flux lines 80 created by the energized coil 50 windings will travel from one pole to the other (e.g., North to South). Rotor 46, which for some embodiments may comprise steel or some other magnetically responsive material, provides a preferred path for the flux lines to travel through, and complete the magnetic circuit, but in so doing, will align the rotor 46 so that the end faces of the rotor line up with the Dead Zones 70 created in the coil 50 windings. This is illustrated in FIG. 3 which shows a schematic diagram of a toroid stator and rotor assembly 40 and a representation of the rotating magnetic flux lines 80 and Dead Zones 70. As shown, rotor 46 may be generally rectangular with ends shaped to conform to a curvature that generally matches the curvature of the inner circle of the toroid stator 44 to ensure a constant air gap 76, and allow free rotation. At the instant depicted in FIG. 3, active coils 50 on the "left half of the toroid stator 44 generate magnetic flux lines 80 that cross air gap 76, enter the rotor 46 through Dead Zone 70a, traverse the rotor 46, and exit the rotor 46 and cross air gap 76 through Dead Zone 70b to complete the magnetic circuit. Likewise, active coils 50 on the "right half of the toroid stator 44 traverse a corresponding route on the other side of the toroid stator 44.
[0035] In the above-described manner, the Back EMF due to rotation of the rotor 46 in the presence of the stator 44 magnetic field is reduced by controlling the characteristics of the rotor 46 and coil 50 interactions. Creation of the Dead Zones 70 insures that no current is present in the adjacent coil 50, and consequently minimal, or no, Back EMF Voltage or magnetic field is generated in that coil 50, when rotor 46 is adjacent to the coil 50. [0036] Such an arrangement creates a motor 10 that delivers constant torque at varying rotor 46 speeds. Furthermore, the torque is adjustable by changing the input current, and, thus, the magnitude of the resultant stator 44 magnetic field. At a given current setting the motor 10 output torque will remain relatively constant irrespective of speed. Further, motor 10 output horsepower (HP), can be determined from:
[0037] HP = (Torque x speed)/K, where K is constant that depends upon the units used.
[0038] It is apparent that for embodiments of motor 10 that the HP increases as RPM increases, and output torque will stay constant for a given current (and magnetic field strength), thus, horsepower can be varied with the speed of the rotor 46 which is determined by the switching frequency, or by changing the current at a given speed. Other advantages also exist.
[0039] For some embodiments, parallel configuration of the toroidal stator coils 50 enables fine tuning and customization of the resultant magnetic field, the Dead Zones 70, and the relative motion of both. In such a manner, it is possible to customize or adapt the motor 10 operative characteristics to suit the intended use, environment, or other parameters. Such control parameters may employ high speed adjustments made by micro-processors imbedded within the electronic control circuitry of controller 90.
[0040] Turning now to FIG. 4, additional detail of controller 90 is disclosed. FIG. 4 is a schematic system overview diagram of a controller 90 in accordance with some embodiments. As shown, the embodiments of controller 90 may comprise 4 main elements: low voltage power supplies 404, high voltage power supplies 406, a system controller 402, and coil switches 400.
[0041] As disclosed herein, toroid motor 10 comprises multiple coils 50 which are sequentially turned on and off, so as to produce a rotating magnetic flux field 80. In some embodiments, a first group of multiple coils 50 are turned on as group, causing all to have the same magnetic polarity (e.g., North). This first group of multiple coils 50 may have a second, complimentary, group of multiple coils 50 containing an equivalent number of coils 50 as the first group, yet connected to create the opposite magnetic polarity (e.g., South), and located on an opposite side of the stator 40. This "equal and opposite" arrangement of the coils may be maintained by the controller 90 during operation. Also, as shown in FIG. 3, the Dead Zones 70 at the points between where the magnetic polarity changes, may be created by controller 90 switching off and isolating a predetermined number of coils 50. By sequentially energizing (and de-energizing and isolating) successive coils 50, the magnetic flux field 80, and Dead Zones 70, can be made to rotate around the stator 40.
[0042] Some embodiments of the controller 90 may create two Dead Zones 70 and two sections of energized stator coils 50, one of each magnetic polarity. Of course, it is also possible for the toroid motor 10 to have more than two Dead Zones 70 and more than two complementary sections of energized sequential coils. Likewise, it is possible to vary the width of the Dead Zones 70 (e.g., by de-energizing, disconnecting, and isolating more, or fewer, coils 50), or to change the arc length of the Dead Zones (e.g., asymmetric, symmetric, etc.). Other configurations are also possible.
[0043] For some embodiments, the system controller 402 may control the low voltage 404 and high voltage 406 power supplies, and the coil switches 400 in order to achieve the desired motor torque and RPM at optimal efficiency. System controller 402 may comprise any suitable system controller such as a microprocessor, or other central processing unit (CPU). Of course, more than one processor, integrated processors, or other combinations of processing may also be implemented.
[0044] Some embodiments of system controller 402 may also include a communications channel to receive a signal indicative of feedback from the motor 10 related to a shaft speed, a shaft position, or the like. The feedback signal may be generated in any suitable fashion. For example, feedback signal may be created via a shaft encoder 408 or other shaft position sensor. The feedback signal may, among other things, be used to keep the motor 10 within certain operational specifications.
[0045] In some embodiments, low voltage power supplies 404A and 404B may be used to hold the active motor coils 50 at an electric current level which is controlled by the system controller 402. For the embodiment shown in FIG. 4, two supplies 404 are used; one supply 404 for each coil 50, although the disclosure is not so limited and other types of supply 404 may be implemented. Thus, for some embodiments, low voltage supply 404 A may energize one coil 50 (e.g., to a North polarity) in the first group of active coils, and supply 404B may energize the complementary coil 50 (e.g., to a South polarity) in the second group of active coils 50.
[0046] Similarly, some embodiments may also comprise high voltage power supplies 406 A and 406B which may be used to quickly raise motor coils 50 up to the electric current level that the low voltage supplies 404 are set to hold. For the embodiment shown in FIG. 4, two supplies 406 are used; one supply 406 for each coil 50, although the disclosure is not so limited and other types of supply 406 may be implemented.
[0047] FIG. 5 illustrates a schematic diagram for a coil switch 400 in accordance with some disclosed embodiments. The coil switches 400 for a toroid motor 10 may preferably perform the following functions: (1) energize a coil 50 with the appropriate (e.g., North or South) polarity, for a particular coil 50 in a particular direction, and then switch to the opposite polarity every 180 degrees of rotation; (2) provide a relatively short duration high voltage pulse in order to generate the flux lines 80 quickly around the subject coil 50 (for higher RPM); and (3) capture any recoverable energy when the coil 50 is turned off and isolated. In some embodiments, the controller 90 will include as many coil switches 400 as there are coils 50 in stator 40. Other configurations are also possible.
[0048] As also shown in FIG. 5, for some embodiments, the main output section of the entire switch 400 may contain six separate switching positions, which may consist of more than one transistor at each position in order to increase current flow capability. In FIG. 5, these switch positions are labeled Ql through Q6.
[0049] In some embodiments, three switches may be used to energize each motor coil at a given time in order to provide the desired North or South polarity. For example, Ql, Q3 and Q5 may be used for one polarity, and Q2, Q4 and Q6 are used for the opposite, complementary, polarity.
[0050] FIG. 6 shows the coil switch 400 functional diagram displaying only the parts which are used for one of the two magnetic polarities in accordance with some embodiments. For these embodiments, a sequence of operation to turn a coil 50 completely on, hold it on, and then turn it off and isolate it while re-capturing inductive energy for a given polarity, is as follows.
[0051] First, Ql and Q3 turn on in order to make the holding voltage and current available to the coil 50. The low voltage power supply 404 may be set so as to provide the given current for a desired motor 10 torque, and at a voltage which will sustain that current by counteracting the inevitable resistive losses in the system. This voltage is lower than the fast rise voltage. [0052] After Ql and Q3 are turned on, Q5 turns on for a relatively small amount of time in order to provide a short high voltage pulse that causes the coil's 50 magnetic flux lines 80 to rise quickly. Some embodiments may also comprise Dl which is a blocking diode that allows the voltage on the B side of the coil 50 to go negative with respect to ground A and Q3 without causing current flow.
[0053] When it is time to turn off and isolate the coil 50, Ql is turned off first. The flyback action caused by flux lines 80 leaving the coil 50 causes the voltage on the A side of the coil 50 to go negative, forward biasing D5 in order to capture the coil's 50 inductive energy. In this embodiment, CI represents a capacitor which may be used to capture this fly-back energy for later use. Of course, other capture and storage devices may also be used.
[0054] After the fly-back energy dissipates out of the coil 50, Q3 is then turned off, and the coil switch 400 is again ready to perform an identical operation but with the North and South poles reversed, by using Q2, Q4, Q6, D2, and D6.
[0055] As also shown in FIG. 4, embodiments of the controller 90 may also communicate with a recaptured energy system 100. The concepts of recapturing energy from the collapse of the magnetic flux 80 fields in each coil 50, has been previously disclosed in copending application serial number 13/562,233, titled "Multi-Pole Switched Reluctance D.C. Motor with a Constant Air Gap and Recovery of Inductive Field Energy," which is hereby incorporated by reference in its entirety.
[0056] In brief, each collapsing flux 80 field in coil 50 produces an electrical output pulse which represents the re-captured field energy. These pulses may be then directed by the coil switches 400 of controller 90 to a recaptured energy system 100, and then may be stored, for example, in a capacitor bank or other storage that comprises part of recapture system 100. In some embodiments, energy from this recapture system 100 could be removed if desired, and used to supply power to external appliances (not shown).
[0057] In some embodiments, recapture system 100 may operate in "Open System Operation," which means that energy recaptured from the motor's inductive components during its operation, will be applied to a capacitive storage element, and then utilized to supply power to some electrical load external to the motor itself, such as a lamp, a resistor, a pump, etc. Of course, any suitable external load may be powered in this manner. [0058] Likewise, power inverters or other devices can be used to convert the recaptured power to alternating current (AC). Unconverted direct current (DC) power from recapture system 100 may be used to power DC loads. Other configurations of Open System Operation are also possible.
[0059] In addition, some embodiments may be designed for "Closed System Operation," which means that energy recaptured from the motor's inductive components during its operation, will be applied to a capacitive storage element in recapture system 100 and then utilized to send power back to the motor power supply by means of a DC to DC converter operating in conjunction with an electronic feedback controller, or the like. Other configurations of Closed System Operation are also possible.
[0060] The torque and speed characteristics of the motor disclosed here -in are quite straight forward. Because there is little or no Back EMF, the torque is proportional to the applied current regardless of the angular speed. The RPM is dependent upon the effectiveness of the switching frequency, which controls the movement from one coil 50 set to the next.
Accordingly, the inductive reactance of the individual coil 50 windings become a limiting factor where speed is concerned, as said reactance will impede or limit the rise time of the magnetic field for a given voltage selection. However, this impedance becomes a matter of engineering design choice because of the effects which are brought to bear by the toroidal coil 50 windings.
[0061] The geometry of the toroid 40 tends to create a condition which is very natural to the confinement of a magnetic field. This property may be exploited by running the flux 80 density up close to saturation, which not only produces high torque in the rotor 46, but which also drives down the inductive reactance of the coil 50 windings in much the same way as experienced in a saturable reactor. One result of applying this concept may be the approach of the coil 50 windings to a pure resistive impedance as the flux 80 density approaches saturation, and an associated diminution of the coil 50 rise-time. Therefore, as impedance (Z) approaches resistance (R) in value, the time (t) will become very small, and allows switching speeds of a very high order indeed. The above-described properties and parameters also results in the formation of a substantially square wave current.
[0062] Such an arrangement also allows for reasonably constant torque at any current (I) setting, with I being limited mostly by the value of resistance (R), and a variable speed function which will support a wide range of angular speeds and high values of acceleration. Under such conditions, the shaft horsepower is substantially linear at a given value of current, with angular velocity being the independent variable. Thus, a graph of shaft horsepower versus RPM is expected to be almost linear in nature.
[0063] Although inductive reactance is greatly reduced by the use of controlled saturation of the back iron, it cannot be eliminated completely, especially when lighter torque settings are arranged. Accordingly, where there is inductance (L) and current (I), there will be stored energy (E) in keeping with the relationship E = 1⁄2 LI <2>. Therefore, when coil 50 windings collapse their magnetic fields at the start of each Dead Zone 70, the stored field energy will be converted back into electrical energy in very short intervals of time, and provisions, as described herein, preferably exist to contend with this recaptured power.
[0064] While the invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof.