Abstract:
An electrical system for a vehicle includes a power source providing electrical power to a first and a second electrical motor. Each motor has two or more windings, and each winding has a first end and a second end. A boost link such as a battery or capacitor is configured to store electrical energy for subsequent retrieval and use by either electrical motor. A first inverter circuit includes a first grouping of switches, wherein each of the first group of switches couples one of the first ends of the windings to the power source. A second inverter circuit includes a second group of switches, each coupling one of the second ends of the windings to the boost link. A controller is coupled to activate each of the first and second groups of switches to thereby allow the electrical energy to be placed on and retrieved from the boost link.

Description:
TECHNICAL FIELD 
     The present invention generally relates to electric motors, and more particularly relates to boost systems for electric motors found in, for example, hybrid vehicles. 
     BACKGROUND 
     In a DC-driven electric motor system, such as a hybrid vehicle system with one or more electrical motors, the power of the system is typically increased by enlarging the motor, adding additional magnets to the motor, or boosting the available DC voltage with, for example, a conventional boost DC-DC converter. However, a larger motor typically takes up additional space, additional magnets generally provide additional complexity and weight, and boosting the available DC voltage generally burdens the motor with a higher current rating. Hence, extra power provided by conventional boosting techniques is typically offset by one or more disadvantages. 
     More recently, inverter circuits have been designed to increase the power provided within an electric motor system. A conventional six-switch, three-leg inverter topology, for example, can increase the power of a system that includes one or more three-phase motors where the DC link is connected across a line-to-line portion of the three-phase motors. Even this topology, however, typically has limitations on its ability to increase available power and/or to decrease the current rating of the inverter. 
     Accordingly, it is desirable to provide an improved inverter topology for obtaining boost power from a multi-motor system without adding complexity to the system or increasing the motor size. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background. 
     BRIEF SUMMARY 
     According to various exemplary embodiments, an electrical system for a vehicle suitably includes a power source providing electrical power to a first and a second electrical motor. Each motor has two or more windings, and each winding has a first end and a second end. A boost link such as a battery or capacitor is configured to store electrical energy for subsequent retrieval and use by either electrical motor. A first inverter circuit includes a first grouping of switches, wherein each of the first group of switches couples one of the first ends of the windings to the power source. A second inverter circuit includes a second group of switches, each coupling one of the second ends of the windings to the boost link. A controller is coupled to activate each of the first and second groups of switches to thereby allow the electrical energy to be placed on and retrieved from the boost link. Other exemplary embodiments encompass techniques for boosting the power in a multi-motor electrical system. 
     This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the detailed description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       The present invention will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and 
         FIG. 1  is a circuit diagram of an exemplary multi-motor electrical system having boost features; 
         FIG. 2  is a circuit diagram showing one circuit path for transferring electrical energy from the power source to the boost link; 
         FIG. 3  is a circuit diagram showing one circuit path for retrieving electrical energy stored on the boost link to an electrical motor; 
         FIG. 4  is a circuit diagram showing an alternate circuit path for retrieving electrical energy stored on the boost link; and 
         FIG. 5  is a circuit diagram showing another alternate circuit path for retrieving electrical energy stored on the boost link. 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     The following description generally relates to methods and systems for storing and boosting the electrical power available in a multi-motor electrical system such as that found on many hybrid automobiles, trucks and other vehicles. In this regard, the following detailed description is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, brief summary or the following detailed description. 
     The following description refers to elements or nodes or features being “connected” or “coupled” together. As used herein, unless expressly stated otherwise, “connected” means that one element/node/feature is directly joined to (or directly communicates with) another element/node/feature in a mechanical, logical, electrical or other appropriate sense. Likewise, unless expressly stated otherwise, “coupled” means that one element/node/feature is directly or indirectly joined to (or directly or indirectly communicates with) another element/node/feature in a mechanical, logical, electrical or other appropriate sense. The term “exemplary” is used in the sense of “example,” rather than “model.” Further, although the figures may depict example arrangements of elements, additional intervening elements, devices, features, or components may be present in a practical embodiment of the invention. 
     With reference now to the drawing figures and initial reference to  FIG. 1 , an exemplary electrical system  100  suitable for use in an automobile, truck or other vehicle suitably includes a power source  108  coupled with two or more electrical motors  102 ,  104 . Each motor  102 ,  104  includes two or more inductive windings  151 - 153 ,  154 - 156  that are switchably coupled back to power source  108  via inverter circuits  162 ,  168  (respectively). The opposite ends of each winding  151 - 153 ,  154 - 156  are switchably coupled to a boost link  110  via inverter circuits  164 ,  166  (respectively). In practice, the various switches in inverter circuits  162 ,  164 ,  166 ,  168  receive control signals  112  from controller  106  to place each of the various switches into an appropriate conducting or non-conducting state. By switchably connecting boost link  110  to power source  108  through the windings of motors  102  and  104 , then, extra power from boost link  110  can be stored and subsequently applied at appropriate times to either motor  102 ,  104 . 
     Power source  108  is any battery, generator, fuel cell or other source of electrical energy. Generally, power source  108  corresponds to a conventional hybrid vehicle battery or series of batteries providing direct current (DC) to system  100 . Although both motors  102 ,  104  are shown coupled to the same power source  108  in  FIG. 1 , in practice each motor  102 ,  104  could be coupled to a separate power source with or without a common electrical reference (e.g. ground). Protective capacitors  114  and/or  116  may be coupled in parallel or otherwise in communication with power source  108 . Such capacitors, when present, can provide signal filtering (e.g. to smooth current ripple) and/or other effects. 
     Each motor  102 ,  104  is any type of induction motor or the like having any number of inductive windings (e.g. windings  151 - 153  and  154 - 156 ) corresponding to any number of electrical phases. The embodiment shown in  FIG. 1 , for example, has three electrical phases, although equivalent embodiments could make use of two, four or any other number of inductive phases. Motors  102 ,  104  operate according to conventional electrical principles. By alternately connecting the various windings  151 - 156  to power source  108 , for example, various electrical paths can be formed and altered as appropriate to generate mechanical torque applied to any number of wheels, flywheels or other mechanical loads. 
     Inverter circuits  162 ,  164 ,  166  and  168  suitably include any number of transistors, switching elements, relays or other switches  121 - 144  that are capable of coupling one or more ends of windings  151 - 156  to each other, to power source  108  and/or to boost link  110  as appropriate. In various embodiments, switches  121 - 144  are implemented with insulated gate bipolar transistors (IGBTs), metal oxide semiconductor field effect transistors (MOSFETs), and/or the like. Such transistors typically provide a common terminal (e.g. a base or gate terminal) that can be driven to a relatively high or low voltage to thereby enable electrical conductivity between the remaining terminals of the device. Examples of “double-ended” inverter circuitry and various methods of operating such circuits are contained in U.S. Pat. No. 7,154,237, though any other inverter circuitry and/or operating techniques could be equivalently applied in alternate embodiments. For convenience, circuits  162  and  168  may be described herein as a single inverter, since both of these circuits are primarily concerned with coupling motor windings  151 - 156  to either side of power source  108 . Similarly, circuits  164  and  166  may be referenced as a single inverter since both of these circuits are primarily concerned with the sides of windings  151 - 156  that are not directly coupled to power source  108 , but rather may be coupled to boost link  110 . 
     Controller  106  is any device, module, circuitry, logic and/or the like capable of providing control signals  112  to the various components of inverter circuits  162 - 168 . Controller  106  may be implemented with a conventional microprocessor or microcontroller, for example, which would typically include software or firmware instructions stored in volatile or non-volatile digital memory. In other embodiments, controller  106  is implemented with programmed gate arrays, look-up tables or other logic circuitry of any kind. Although not shown in  FIG. 1 , controller  106  may be physically coupled to switches  121 - 144  via any type of multiplexing/de-multiplexing or other decoding circuitry to reduce the number of logic pins or other outputs on controller  106  used to provide signals  112 . 
     Boost link  110  is any device, module or other structure capable of storing and releasing electrical energy. In various embodiments, boost link  110  is a capacitor (e.g. a so-called “super-capacitor” having a capacitance on the order of 0.5-20 Farads or so). In other embodiments, boost link  110  is implemented with a battery, fuel cell, flywheel or the like. Boost link  110  is capable of being charged and discharged through the various windings  151 - 156  to increase or decrease the relative voltage applied across the winding during operating of motors  102 ,  104 . In the embodiment shown in  FIG. 1 , for example, electrical energy can be applied from power source  108  to boost link  110  via any winding  151 - 156  through activation and deactivation of various switches  121 - 144  in inverter circuits  162 - 168 . 
     In the embodiment shown in  FIG. 1 , each of the windings  151 - 156  can be switchably coupled to either the positive or negative terminals of power source  108  by inverter circuits  162  and  168 , respectively, thereby allowing either full rail voltage (e.g. the full voltage applied by power source  108 , B + , B − , ground, or any other applied voltage) to be applied in either direction across any winding  151 - 156 . Switches  121 - 123 , for example, switchably couple windings  151 - 153  (respectively) to the positive voltage (or primary) side of power source  108 , while switches  124 - 126  couple windings  151 - 153  (respectively) to the opposite (e.g. negative or reference) side of power source  108 . Similarly, switches  139 - 141  switchably couple windings  154 - 156  to the positive voltage side of power source  108 , and switches  142 - 144  couple windings  154 - 156  to the negative side of power source  108 . To apply a positive or negative voltage across any particular winding  151 - 156 , then, one or more switches associated with the winding can be activated. To couple winding  153  to the positive side of power source  108 , for example, switch  123  is activated, while switches  121  and  122  typically remain closed to prevent current from entering coils  152  and  151 , respectively. Similarly, winding  154  can be coupled to the opposite side of power source  108  by activating switch  142 . Again, any of the windings  151 - 156  on either motor  102 ,  104  can be coupled to either the primary or opposite side of power source  108  by simply actuating and/or de-actuating the various switches  121 - 126  and  139 - 144 . 
     The opposing ends of the windings  151 - 156  can be similarly coupled to each other in any type of arrangement (e.g. a wye-junction) as appropriate through actuation and de-actuation of switches  127 - 138 . Activating switches  127 ,  128  and  129 , for example (or switches  130 - 132 ) would place the three windings  151 - 153  in motor  102  into a “wye” arrangement. The various switches  127 - 138  in inverter circuits  154 ,  166  are also able to switchably couple windings  151 - 156  to boost link  110  as appropriate. 
     By placing electrical energy on boost link  110  during motor operation, energy can be stored for subsequent retrieval by either motor  102 ,  104 . The various motor windings  151 - 156  thereby serve to separate two effective power sources (i.e. source  108  and boost link  110 ), which in turn allows boost link  110  to serve as a source of additional voltage applied across any winding  151 - 156 . Either motor  102 ,  104  may provide power to boost link  110  through conventional pulse width modulation methods, for example, and stored power is subsequently available to either motor  102 ,  104  to create positive or negative torque. Various techniques for placing and retrieving electrical energy from boost link  110  are described below. 
     Referring now to  FIG. 2 , an exemplary technique for placing electrical energy on boost link  110  suitably involves placing boost link  110  into a circuit with power source  108 . By activating switches  123 ,  124 ,  127  and  132 , for example, a current path is formed from the primary terminal of power source  108  through winding  153  and boost link  110 , returning through winding  151  to the opposing side of power source  108 . Note that any other current path through any two windings  151 - 156  could be used in the alternative, including any of the paths shown in  FIGS. 3-5 . As boost link  110  is switched into the circuit, charge is stored as appropriate. The stored charge is then available for discharge and/or recharge during subsequent operation of motors  102 ,  104 . 
       FIGS. 3 and 4 , for example, show exemplary techniques for coupling boost link  110  into a circuit that includes windings  155  and  156  of motor  104 . These circuits could be timed to charge boost link  110 , or to discharge energy previously stored in any way.  FIG. 3 , for example, shows switches  134 ,  136 ,  140  and  144  activated to create a circuit  302  from power source  108  through winding  155  to boost link  110 , with a return path through winding  156  back to power source  108 . If boost link  110  had been previously charged, the energy on the boost link could be discharged across winding  156 , thereby increasing the voltage across the winding and resulting in additional torque produced by motor  104 . 
       FIG. 4  shows a similar circuit  402 , with switches  133  and  137  activated in place of switches  134  and  138 ; switches  140  and  144  remain activated as in  FIG. 3 . In the  FIG. 4  arrangement, however, the energy applied by boost link  110  is reversed, thereby serving to reduce the voltage across winding  156  (or, alternatively, to increase the voltage across winding  155 ). 
     With final reference now to  FIG. 5 , switches  121 ,  125 ,  129  and  131  are shown activated to create a circuit  502  through windings  152  and  153  for charging and/or discharging boost link  110 . As noted above, any number of circuits for charging and/or discharging the energy stored on boost link  110  could be formulated and applied during motor operation. Each of these circuits can be created through simple application of control signals  112  to the switches  121 - 144 . The switches may be activated and/or de-activated through simple application of proper voltages to the base or gate terminals of transistor switches, for example, or according to any other technique. Digital instructions in software, firmware or any other format can therefore be executed within controller  106  to create appropriate control signals  112 , to control the timing and sequencing of such signals  112 , and to otherwise direct the operation of system  100  as appropriate. 
     The techniques described above may be applied in any number of environments and applications. In the vehicle context, boost circuitry can be readily deployed in a hybrid vehicle to allow for “boosting” and/or “bucking” of voltage between electric motors. Similar concepts may be readily applied in the context of any automotive, transportation, aerospace, industrial and/or setting as appropriate. 
     While several exemplary embodiments have been presented in the foregoing detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing the exemplary embodiment or exemplary embodiments. It should be understood that various changes can be made in the function and arrangement of elements without departing from the scope of the invention as set forth in the appended claims and the legal equivalents thereof.