Abstract:
A 2-phase switched reluctance device topology includes a switched reluctance device having first and second phase coils. Each of the first and second phase coils has a first terminal and a second terminal. The first terminal of each of the first and second phase coils is electrically coupled between two switching elements of a first pair of switching elements. The second terminal of the first phase coil is electrically coupled between two switching elements of a second pair of switching elements. The second terminal of the second phase coil is electrically coupled between two switching elements of a third pair of switching elements. Each switching element includes a first electrode, a second electrode, and a control electrode, wherein the control electrode is communicatively coupled to a switch controller that operates the switching element. Each switching element also includes a diode communicatively coupling the first electrode to the second electrode.

Description:
TECHNICAL FIELD 
       [0001]    The present disclosure relates generally to switched reluctance devices and, more particularly, to a 2-phase switched reluctance device and associated control topologies. 
       BACKGROUND 
       [0002]    Switched reluctance (also known as variable reluctance) machines are becoming increasingly popular in automotive and industrial applications due, in large part, to their lower cost, increased reliability, and greater power/weight ratio when compared with other conventional motor/generator types. For example, because they do not require expensive “rare-earth” magnets like their permanent-magnet counterparts and do not use brushes or split-rings that are prone to failure after prolonged or extended use like wound-rotor AC induction motors, they may be less expensive to manufacture and provide increased reliability. Furthermore, unlike AC induction machines, switched reluctance machines do not require rotor conductors, which may substantially increase the weight of the machine, the inertia of the rotor, and the difficulty in the cooling of the rotor. 
         [0003]    Although switched reluctance machines provide certain cost and reliability advantages over other types of machines, they require separate control systems for exciting the electromagnetic field associated with the machine. These control systems may be customized based on the desired operational and/or design characteristics associated with a particular machine. For example, in many cases control systems are customized based on the number of poles and/or phase coils of the machine. 
         [0004]    One such system is described in U.S. Pat. No. 6,054,819 (“the &#39;819 patent”) to Pengov on Apr. 25, 2006. The system of the &#39;819 patent describes a driving circuit that includes a plurality of switching elements and freewheeling diodes configured to provide a switching solution for operating a switched reluctance machine. The system of the &#39;819 patent may be expandable to accommodate multiple phases by cascading an additional switch and diode with the base system, thereby enabling motor control capabilities for any multi-phase switched reluctance machine. 
         [0005]    Although the system of the &#39;819 patent may provide one control system solution for a multi-phase machine, it may include several disadvantages. Specifically, the configuration options for machines that employ the control system of the &#39;819 patent may be limited and inflexible. For example, because the system is adapted for use with a particular machine design, only one wiring configuration may be supported. As a result, should one or more of the switches or diodes fail, maintenance or replacement of the control system may be required. Furthermore, because the system may not be re-configured “on the fly,” applications requiring different and/or alternative wiring schemes associated with the machine may not be supported by the system of the &#39;819 patent. Thus, in order to provide increased system flexibility, a universal control system that provides multiple wiring solutions for switched reluctance machines may be required. 
         [0006]    The presently disclosed 2-phase switched reluctance device and control topologies are directed toward overcoming one or more of the problems set forth above. 
       SUMMARY OF THE INVENTION 
       [0007]    In accordance with one aspect, the present disclosure is directed toward a 2-phase switched reluctance device. The device topology may include a switched reluctance device including first and second phase coils, each of the first and second phase coils including a first terminal and a second terminal. The first terminal of each of the first and second phase coils may be electrically coupled between two switching elements of a first pair of switching elements. The second terminal of the first phase coil may be electrically coupled between two switching elements of a second pair of switching elements. The second terminal of the second phase coil may be electrically coupled between two switching elements of a third pair of switching elements. Each switching element may include a first electrode, a second electrode, and a control electrode, wherein the control electrode is communicatively coupled to a switch controller that operates the switching element. Each switching element may also include a diode communicatively coupling the first electrode to the second electrode. 
         [0008]    According to another aspect, the present disclosure is directed toward a method for operating a 2-phase switched reluctance device having first and second phase coils wherein each of the first and second phase coils may include a first terminal and a second terminal. The method may include electrically coupling the first terminal of each of the first and second phase coils between two switching elements of a first pair of switching elements. The method may also include electrically coupling the second terminal of the first phase coil between two switching elements of a second pair of switching elements. The method may further include electrically coupling the second terminal of the second phase coil between two switching elements of a third pair of switching elements. Each switching element may include a first electrode, a second electrode, and a control electrode, wherein the control electrode is communicatively coupled to a switch controller that operates the switching element. Each switching element may also include a diode communicatively coupling the first electrode to the second electrode. 
         [0009]    In accordance with yet another aspect, the present disclosure is directed toward a machine comprising a power source and a switched reluctance device operatively coupled to the power source including first and second phase coils. Each of the first and second phase coils may include a first terminal and a second terminal. The first terminal of each of the first and second phase coils may be electrically coupled between two switching elements of a first pair of switching elements. The second terminal of the first phase coil may be electrically coupled between two switching elements of a second pair of switching elements. The second terminal of the second phase coil may be electrically coupled between two switching elements of a third pair of switching elements. Each switching element may include a first electrode, a second electrode, and a control electrode, wherein the control electrode is communicatively coupled to a switch controller that operates the switch. Each switching element may also include a diode communicatively coupling the first electrode to the second electrode. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  provides a diagrammatic illustration of an exemplary disclosed machine employing a 2-phase switched reluctance device consistent with certain disclosed embodiments; 
           [0011]      FIG. 2  provides an exemplary illustration of a 2-phase switched reluctance machine in accordance with certain disclosed embodiments; 
           [0012]      FIG. 3  provides an exemplary illustration of a 3-phase power converter for a switched reluctance machine, in accordance with the disclosed embodiments; 
           [0013]      FIGS. 4A and 4B  provide schematic illustrations of a first exemplary switched reluctance motor topology consistent with the disclosed embodiments; 
           [0014]      FIG. 5  provides a table illustrating alternative switched reluctance motor topologies consistent with the exemplary embodiment illustrated in  FIGS. 4A and 4B ; 
           [0015]      FIGS. 6A and 6B  provide schematic illustrations of a second exemplary switched reluctance motor topology consistent with the disclosed embodiments; and 
           [0016]      FIG. 7  provides a chart illustrating alternative switched reluctance motor topologies consistent with the exemplary embodiment illustrated in  FIGS. 6A and 6B . 
       
    
    
     DETAILED DESCRIPTION 
       [0017]      FIG. 1  provides an illustration of an exemplary machine  100 , consistent with certain disclosed embodiments. Machine  100 , as the term is used herein, refers to any fixed or mobile machine that performs some type of operation associated with an industry such as mining, construction, farming, transportation, manufacturing, energy exploration or any other industry. Non-limiting examples of fixed machines include an engine system operating in an off-shore plant environment (e.g., off-shore drilling platform), a stationary generator set for generating electricity, a turbine operating in a power plant environment, and any other type of fixed machine. Non-limiting examples of mobile machines include commercial and/or passenger vehicles, cranes, excavators, backhoes, haulers, dumpers, tractors, marine vessels, aircraft, mining vehicle, earth moving machines, loggers, and any other type of moveable machine. Machine  100  may be driven by a combustion engine, a turbine, or an electric motor. The types of machines listed above are exemplary only and not intended to be limiting. Furthermore, it is contemplated that although  FIG. 1  is illustrated as a track-type tractor, it may include any suitable type of machine operable to perform a desired task. As illustrated in  FIG. 1 , machine  100  may include, among other things, a power source  101 , a motor  105 , a switched reluctance machine  110 , and a power converter  120 . 
         [0018]    Power source  101  may include any device configured to output energy for use by machine  100 . For example, power source  101  may include an internal combustion engine that operates on diesel fuel, gasoline, natural gas, or any other type of fuel. Alternatively and/or additionally, power source  101  may include any type of device configured to output mechanical and/or electrical energy such as, for example, a fuel cell, battery, turbine, alternator, transformer, or any other appropriate power output device. 
         [0019]    Switched reluctance machine  110  may be operatively coupled to power source  101  and may be configured to convert at least a portion of the power output associated with power source  101  into electrical energy. For example, switched reluctance machine  110  may include a power converter  120  for sequentially energizing phase coils in order to produce an electromagnetic field electrical energy from. Switched reluctance machine  110  may also include a power converter configured to control the switched reluctance machine and produce electric power at various voltage and/or current levels. 
         [0020]    Motor  105  may be operatively coupled to switched reluctance machine  110  and configured to provide mechanical force for performing a task associated with machine  100 . Motor  105  may receive electrical energy from switched reluctance machine  110  to produce torque output for performing work. For example, motor  105  may be coupled to a transmission (not shown) for providing output torque to a shaft to move one or more traction devices to propel machine  100 . Although motor  105  may be described as a drive for one or more traction devices (not shown), it is contemplated that motor  105  may be used in any application of machine  100  that may require mechanical energy to operate. Motor  105  may include any type of motor such as, for example, a switched reluctance motor (similar to switched reluctance device  110 ), an AC induction motor, a synchronous motor, a brushless DC motor, or any other suitable type of motor. 
         [0021]    It is contemplated that, in certain cases, switched reluctance machine  110  may be configured to operate as a motor for receiving electrical energy and converting a portion of the electrical energy to mechanical energy for use by one or more components, such as power source  101 , associated with machine  100 . For example, in situations where switched reluctance machine  110  is not providing electrical power, it may be operated as a motor for supplying mechanical power for machine  100 . This power may be provided to power source  101  for operating parasitic power source loads and/or reducing fuel consumption. According to one embodiment, switched reluctance device  110  may include any type of motor or generator that is configured to unidirectional power flow. 
         [0022]    As illustrated in  FIG. 2 , switched reluctance machine  110  may include a stator  111  electromagnetically coupled to an actuator  112  and separated by an air gap  115  over which an electromagnetic field is induced. Switched reluctance machine  110  may also include phase coils  114  substantially wound around poles  113  for supplying electrical energy to induce an electromagnetic field between stator  111  and actuator  112 . It is also contemplated that switched reluctance machine  110  may include any appropriate type of motor for providing mechanical energy output, such as a linear motor, a stepper motor, or any other type of motor that is operated with uni-directional current flow within the coils of the motor. Alternatively and/or additionally, switched reluctance machine  110  may include an electric generator for providing a electric power output. 
         [0023]    Stator  111  may include a high magnetic permeability metallic core, such as, for example, iron, cobalt, nickel, or any other high permeability metal or alloy thereof, configured to promote a magnetic flux proportional to a magnetizing current. For example, stator  111  may include an iron core of particular size, shape, and dimension so as to maximize the magnetic flux density given the size and configuration of actuator  112 . Although stator  111  is illustrated as a substantially circular stator for use with a rotor, it is contemplated that stator  111  may include a linear stator for use with a linear motive bar, as in, for example, a linear motor or as a platter configuration as used in an axial flux designed motor. 
         [0024]    Actuator  112  may include a metallic core operatively coupled to stator  111  and configured to move relative to stator  111  in the presence of a magnetic field. For example, as illustrated in  FIG. 2 , actuator  112  may include a substantially round core disposed within stator  111  and configured to rotate within stator  111  in the presence of a generated electromagnetic field. Although actuator  112  is illustrated as a rotor in one exemplary embodiment, actuator  112  may include a metallic beam configured to move linearly with respect to stator  111 , as in a linear motor. Actuator  112  may include high magnetic permeability metallic structure such as, for example, iron, cobalt, nickel, or any other such type of appropriate material. 
         [0025]    Poles  113  may include salient metallic structures that may protrude from stator  111  to provide a highly concentrated magnetic flux density to provide greater electromagnetic interaction with actuator  112 . Poles  113  may be constructed of a high relative permeability metal such as, for example, iron, cobalt, nickel, or any other such material. The number of poles  113  may be selected based on the desired speed and torque relationship depending upon the prospective use of the motor during the design stages. Although switched reluctance machine  110  is illustrated as an eight pole machine, it is contemplated that more or less poles may be provided depending on the desired performance of switched reluctance machine  110 . 
         [0026]    Phase coils  114  may include one or more wires associated with poles  113  and configured to induce a magnetic flux within poles  113 . Phase coils  114  may be constructed of any material that has a substantially high conductivity such as copper, iron, steel, aluminum, or any other suitable material for conducting current. Further electric conductors may be substantially wound around poles  113  to maximize the current-induced magnetic flux within poles  113 . 
         [0027]    Phase coils  114  may be arranged in phases such that, when phase coils  114  are energized, the magnetic flux generated within poles  113  cooperate to provide maximum rotational force on actuator  112 . For example, in one embodiment, phases may be arranged such that phase coils  114  associated with pairs of poles  113  that are diametrically opposed induce a uniform, symmetric magnetic field to move actuator  112 . Although switched reluctance machine  110  is illustrated as a symmetric motor, it is contemplated that asymmetric configurations may be realized with phase coils  114  arranged to provide a uniform magnetic field for moving actuator  112 . 
         [0028]    According to one embodiment, switched reluctance machine  110  may include one or more internal cooling devices  116  for extracting heat associated with switched reluctance machine  110 . For example, internal cooling devices  116  may include thermally conductive elements, such as metallic materials that, when placed in proximity to a heat source, may facilitate dissipation of heat from the heat source. Alternatively and/or additionally, internal cooling devices  116  may include one or more cooling circuits for circulating a cooling medium, such as, for example, ethylene glycol, propylene glycol, water, air, gel coolants, or any other suitable cooling medium. It is contemplated that the internal cooling devices  116  may be coupled to an external heat transfer device (not shown), such as a radiator, fan, or other device for dissipating the heat collected by internal cooling devices  116 . According to one embodiment, internal cooling devices  116  may be coupled to a coolant reservoir (not shown) for storing a cooling medium associated with internal cooling devices  116 . It is contemplated that internal cooling devices  116  may include any cooling feature that may be adapted to cool switched reluctance machine  110 . 
         [0029]    As illustrated in  FIG. 3 , power converter  120  may include one or more components configured to energize multiple phases of an electric machine using a single power supply device. For example, power converter  120  may be electrically coupled to switched reluctance machine  110  and configured to sequentially provide electric current for energizing phase coils  114 . Power converter  120  may include one or more switching devices  121   a - f , one or more switching diodes  125   a - f , voltage input terminals  126  for receiving a input power, and a shunt capacitor  127  reducing AC and other high-frequency signals associated with the input power. 
         [0030]    Switching devices  121   a - f  may each include one or more electrical devices configured to provide one or more current flow paths associated with power converter  120 . Each of switching devices  121   a - f  may include two operational states: an “on” state whereby the switching device permits a flow of current through the device, and an “off” state whereby the switching device prevents the flow of current through the device. Switching devices  121   a - f  may each include a solid-state semiconductor switching device such as, for example, an insulated gate bipolar transistor (IGBT) switch, a CMOS switching element, a MOSFET switch, or any other suitable type of switching element. According to an exemplary embodiment, switching devices may include insulated gate bipolar transistors due to their high current handling capability. Furthermore, although switching elements  121   a - f  are illustrated as npn devices, it is contemplated that switching devices may include pnp devices, n-channel devices, p-channel devices or any other suitable type of semiconductor switching element. 
         [0031]    Switching devices  121   a - f  may each include, among other things, a first electrode  122 , a second electrode  123 , and a control electrode  124 . Switching devices  121   a - f  may each be actuated by the application of control signals to control electrode  124  by a switch controller  128 . For instance, switch controller  128  may provide a signal corresponding to an “on” state to control electrode  124 , thereby inducing a conduction channel in the switching device and permitting current flow through the device. Similarly, switch controller  128  may provide a signal corresponding to an “off” state to control electrode  124 , thereby removing off the conduction channel and preventing the flow of current through the device. 
         [0032]    Diodes  125   a - f  may be operatively coupled to each of switching devices  121   a - f  to provide a reverse flow path of current between first electrode  122  and second electrode  123 . For example, diodes  125   a - f  may each be coupled between the first electrode  122  and the second electrode  123  associated with its respective switching devices  121   a - f . By providing a reverse flow path of current, diodes  125   a - f  may protect the corresponding switching devices  125   a - f  from potential damage from the buildup of high reverse voltage potentials. In addition, diodes  125   a - f  may provide a conduction path for energy flow back to the DC source when switched reluctance machine  110  is generating power. According to one embodiment, each of diodes  125   a - f  may be included with a corresponding switching devices  121   a - f  as part of a single integrated switching element. Alternatively, switching devices  121   a - f  and diodes  125   a - f  may be separate, standalone components. 
         [0033]    Power converter  120  embodies a standard 3-phase power converter for use with many types of 3-phase industrial machine. As illustrated in  FIG. 3 , switching devices  121   a - f  are arranged as three pairs of series-connected switching devices, with each pair arranged in parallel with each other pair. Each pair comprises a first switching element (e.g.,  121   a ,  121   b , and  121   c , respectively) and a second switching element (e.g.,  121   d ,  121   e , and  121   f , respectively). The first electrode  122  of each of the first switching elements may be electrically coupled to a first DC voltage potential. The second electrode  123  of each of the first switching elements may be electrically coupled to the first electrode  122  of the respective second switching elements forming a contact node PC-A, PC-B, and PC-C, respectively, providing three connection points for the field winding in a typical 3-phase machine wiring configuration. The second electrode of each of the second switching elements may be coupled to a second DC voltage potential. According to one embodiment, the first DC voltage potential may be greater than the second DC voltage potential. 
         [0034]      FIGS. 4A and 4B  illustrate one exemplary switched reluctance machine topology for operating a 2-phase switched reluctance machine, such as switched reluctance machine  110 , using a 3-phase universal power converter, such as power converter  120 . As illustrated in  FIGS. 4A and 4B , phase coils  114  may include first and second phases A and B, respectively, with each phase coil including positive and negative terminals. In this configuration, the positive terminal of phase coil A may be electrically coupled to contact node PC-A, while the negative terminal of phase coil B may be electrically coupled to contact node PC-C. The negative terminal of phase coil A and the positive terminal of phase coil B may each be electrically coupled to contact node PC-B. 
         [0035]    In order to maximize efficiency, first and second phase coils associated with switched reluctance machine  110  must be operated alternately (i.e., phase coil A may not conduct current while phase coil B is conducting current). Thus, to operate switched reluctance machine  110 , each phase is individually excited. As illustrated in  FIG. 4A , for example, phase A is excited by placing switching devices  121   a  and  121   e  in the “on” state, enabling current flow through switching device  121   a , through phase coil A, and through switching device  121   e . This current flow induces a electromagnetic field around the poles associated with phase coils A, which attracts the poles of actuator  112 . Once the poles of the actuator  112  are nearly in line with the poles of the stator (i.e., maximum torque position), switching devices  121   a  and  121   e  are placed in the “off” state. Because phase coil A is essentially a large inductor, a current flow path for discharging phase coil A may be provided to quickly eliminate any residual current that may be stored in the coils, thereby limiting the resistance associated with actuator  112  due to any electromagnetic field that may be produced by the residual current. This current flow path may be provided by diodes  125   b  and  125   d . It is contemplated that the switched reluctance machine  110  may be configured to generate output power by turning on switching devices  121   a  and  121   e  slightly before alignment and, subsequently turning them off slightly after alignment. After switching devices  121   a  and  121   e  have been turned off, switched reluctance machine  110  may continue to generate current through diodes  125   d  and  125   b  until poles are aligned. 
         [0036]    As illustrated in  FIG. 4B , once switching devices  121   a  and  121   e  have been placed in the “off” state, switching devices  121   b  and  121   f  may be placed in the “on” state. As a result, switching devices  121   b  and  121   f  provide a current flow path through phase coil B, which energizes the stator poles associated with phase coil B. This current flow induces an electromagnetic field around the stator poles, which attracts the poles of actuator  112 , producing torque and facilitating angular rotation. When the poles of actuator  112  become nearly aligned with the poles of the stator, switching devices  121   b  and  121   f  are placed in the “off” state, the residual current in phase coil B discharges through diodes  125   e  and  125   c , discharging the electromagnetic field associated with the stator poles of phase coil B. 
         [0037]    According to the embodiments illustrated in  FIGS. 4A and 4B , only four switching devices ( 121   a ,  121   b ,  121   e  and  121   f ) are used and only four diodes ( 125   b ,  125   c ,  125   d , and  125   e ) are used. As a result, those of ordinary skill will realize that additional wiring configurations may be implemented that use different combinations of switching elements and diodes. Other permutations and combinations of wiring topologies consistent with the embodiments illustrated in  FIGS. 4A and 4B  are illustrated in the chart of  FIG. 5 . As illustrated in  FIG. 5 , multiple wiring topologies may be realized using 3-phase power converter  120  to energize 2-phase switched reluctance machine  110 , that utilize four switching devices and four diodes. 
         [0038]      FIGS. 6A and 6B  illustrate an exemplary disclosed configuration in which only three switching devices and three diodes are used. According to this embodiment, positive terminals of phase coil A and phase coil B may be electrically coupled to PC-A, while the negative terminals of phase coils A and B may be coupled to PC-B and PC-C, respectively. 
         [0039]    According to this embodiment, switching devices  121   a  and  121   e  may be placed in the “on” state to energize phase coil A. Once switching devices  121   a  and  121   e  are placed in the “off” state, the residual current may be discharged through diodes  125   d  and  125   b . Similarly, switching devices  121   a  and  121   f  may be placed in the “on” state allowing energizing current to flow through phase coil B. When switching devices  121   a  and  121   f  are placed in the “off” state, the residual current may be discharged through diodes  125   d  and  125   c.    
         [0040]      FIGS. 6A and 6B  illustrate only one configuration where switched reluctance machine  110  may be electrically coupled to power converter  120  such that only three switching devices and three diodes may be required to operate switched reluctance machine  110 . It is contemplated that additional switch topologies may be provided that use three switching devices and three diodes of power converter, and that those skilled in the art will recognize that additional wiring topologies may be implemented without departing from the scope of the present disclosure. For example,  FIG. 7  provides a table illustrating alternative wiring topologies using 3-phase power converter  120  to energize 2-phase switched reluctance machine utilizing only three switching devices and three diodes. 
       INDUSTRIAL APPLICABILITY 
       [0041]    Although the configurations and topologies associated with the disclosed 2-phase switched reluctance machine are illustrated and described in connection with the motor operation of the machine, it is contemplated that these configurations and topologies may also be applied to the operation of the machine as a generator. Indeed, the only difference between the motor and generator operation of 2-phase switched reluctance machine  110  lies in the timing and sequencing of the operations of switching devices  121   a - f.    
         [0042]    The presently disclosed 2-phase switched reluctance device and its associated topologies may have several advantages. First, the disclosed machine topology may significantly reduce the time associated with power converter repair and/or replacement, in the event of a failure. For example, the 2-phase switched reluctance machine topologies provide multiple wiring configuration schemes. As a result, should one or more of the switching devices and/or diodes fail or otherwise become inoperable, the motor topology may be easily re-configured by simply re-wiring the phase coils to the power converter. This may substantially reduce the time and cost associated with replacement of the power converter. 
         [0043]    Additionally, the disclosed switched reluctance machine topology may provide increased flexibility. For example, power converter  120  associated with the 2-phase switched reluctance machine topology may be universally used with any 2- or 3-phase industrial machine, reducing the need for customized or specialized power converter design. Furthermore, because power converter  120  may be used in almost any 2- or 3-phase commercial or industrial machine, the costs associated with stocking and maintaining associated with repair and/or replacement parts for separate power converters may be significantly reduced. 
         [0044]    It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed 2-phase switched reluctance device and associated control topologies. Other embodiments of the present disclosure will be apparent to those skilled in the art from consideration of the specification and practice of the present disclosure. It is intended that the specification and examples be considered as exemplary only, with a true scope of the present disclosure being indicated by the following claims and their equivalents.