Patent Publication Number: US-2017359010-A1

Title: Switched reluctance generator based automotive power generating system

Description:
TECHNICAL FIELD 
     The present disclosure relates generally to automotive power generating systems, and more specifically to an automotive power generating system including a switched reluctance generator 
     BACKGROUND 
     Certain vehicles, such as automotive vehicles, utilize hybrid electric technology including high voltage DC power generating. Due to their high power density, synchronous permanent magnet generators are used in many applications where weight and/or size are particularly important. Some power system architectures in such an example include permanent magnet generators coupled to a boost-type pulse width modulated converter (alternately referred to as an active rectifier) and a high voltage battery. In some applications, the near constant power load over the duration of the operating time can be accompanied by high peak loads during a portion of the operating time. 
     To support the peak power requirements, rechargeable high energy storage devices, such as batteries, are included within the power generating system. When peak power is required, the energy stored within the high energy storage devices supplements the energy provided by the generator. Conversely, while under a base load condition, the generator creates excess energy, and the energy is stored within the high energy storage devices. In addition to preventing battery damage and providing safe charging and re-charging, some systems are configured to absorb regenerative power from regenerative loads, such as motor drives. 
     SUMMARY OF THE INVENTION 
     In one exemplary embodiment a power generating system architecture includes a prime mover, a generator component including a switched reluctance generator, the switched reluctance generator being mechanically coupled to the prime mover and having a plurality of stator pole windings, a DC power bus connected to at least one output of the switched reluctance generator, the DC power bus including a positive bus bar and a negative bus bar, at plurality of series arranged energy storage devices connecting the positive bus bar and the negative bus bar, a plurality of state of charge modules connected to the plurality of energy storage devices, each of the state of charge modules being communicatively coupled to a generator controller, and the generator controller being configured to independently control each of the stator pole windings. 
     In another exemplary embodiment of the above described power generating system architecture the plurality of energy storage device includes at least one of a lithium ion battery and a super capacitor. 
     Another exemplary embodiment of any of the above described power generating system architectures further includes a high voltage high peak load connected between the positive bus bar and the negative bus bar. 
     Another exemplary embodiment of any of the above described power generating system architectures further includes a regenerative load connected between the positive bus bar and the negative bus bar. 
     Another exemplary embodiment of any of the above described power generating system architectures further includes a DC-DC converter connected between the positive bus bar and the negative bus bar, and including a DC power output, wherein the DC power output is connected to at least one of the generator controller and a state of charge module in the plurality of state of charge modules. 
     In another exemplary embodiment of any of the above described power generating systems the number of switched reluctance generator stator pole windings is at least equal to the number of energy storage devices, and wherein each of the energy storage devices corresponds to one of the stator pole windings. 
     In another exemplary embodiment of any of the above described power generating systems each of the energy storage devices is integrated with the corresponding stator pole winding via at least an asymmetric H-bridge. 
     In another exemplary embodiment of any of the above described power generating systems each of the asymmetric H-bridges is communicatively coupled to the controller, and is configured to convert a commanded control current for the stator pole winding into asymmetric H-bridge operations. 
     In another exemplary embodiment of any of the above described power generating systems the generator control unit includes a memory storing instructions configured to cause the generator controller to detect an imbalance in the plurality of series arranged energy storage devices, and to alter a stator pole current in at least one stator pole winding corresponding to an energy storage device that is out of balance. 
     An exemplary method for re-balancing power storage devices within a power generating system includes identifying at least one high energy storage device in a plurality of high energy storage device as having a reduced charge relative to a remained of high energy storage devices, and increasing a control current to a switched reluctance generator stator pole winding corresponding to the identified at least one high energy storage device. 
     In another example of the above described exemplary method for re-balancing power storage devices within a power generating system identifying the at least one high energy storage device includes analyzing data received from a plurality of state of charge modules using a generator controller, wherein each state of charge module corresponds to a unique high energy storage device. 
     In another example of any of the above described exemplary methods for re-balancing power storage devices within a power generating system analyzing the data comprises comparing a detected state of charge of each high energy storage device. 
     Another example of any of the above described exemplary methods for re-balancing power storage devices within a power generating system further includes providing operational power to a generator control unit and to each of a plurality of state of charge modules from a single DC-DC converter. 
     Another example of any of the above described exemplary methods for re-balancing power storage devices within a power generating system further includes charging the at least one high energy storage device, relative to a remainder of the high energy storage devices, by altering a stator pole winding current of corresponding stator pole in a switched reluctance generator. 
     In another example of any of the above described exemplary methods for re-balancing power storage devices within a power generating system altering a stator pole winding current comprises providing a commanded stator pole winding current to a current regulator, converting the commanded stator pole winding current to asymmetric H-bridge operations using the current regulator, and generating the stator pole winding current using the asymmetric H-bridge. 
     These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  schematically illustrates a high voltage power generating system according to one example. 
         FIG. 2  schematically illustrates a control configuration for the high voltage power generating system of  FIG. 1 . 
         FIG. 3  illustrates a method for correcting an imbalance in a set of power storage devices. 
     
    
    
     DETAILED DESCRIPTION OF AN EMBODIMENT 
       FIG. 1  schematically illustrates an exemplary high voltage power generating system  100  for utilization in an automotive vehicle. The power generating system  100  includes a prime mover  110  connected to a generator system  120  via a shaft  112 . The shaft  112  translates rotational motion from the prime mover  110  to a mechanical input of the generator system  120 . In alternative examples, any other means of translating motion from the prime mover  110  to the generator system  120  can be utilized in place of the illustrated shaft  112 , with only minor alterations to the power generating system  100 . 
     In the example of  FIG. 1 , the generator system  120  includes at least one switched reluctance generator. The switched reluctance generator is connected to, and controlled by, a generator control unit  130 . The switched reluctance generator generates electrical power from the rotational energy. The generator control unit  130  is connected to a positive bus bar  142  via a first switch  132  and to a negative bus bar  144  via a second switch  134 . The positive bus bar  142  and the negative bus bar  144  form a DC power generating bus. Multiple loads are connected to the DC power generating bus including an exemplary high voltage high peak load,  150 , an exemplary high voltage regenerative load  152  and a DC-DC converter  154 . 
     The high voltage high peak load  150  is a typical automotive load that operates at (draws) a baseline energy for a majority of operations. The operations of the high voltage high peak load  150  also include occasional peak periods, where a substantially higher energy draw is required to operate the load  150 . The high voltage regenerative load  152 , similarly operates at a baseline energy draw during typical operations. In some modes, the regenerative load  152  can generate energy instead of drawing energy. These operations are referred to as being regenerative, and provide energy back to the DC bus. The DC-DC converter  154  steps down the voltage from the positive and negative voltage rails  142 ,  144  of the DC bus and provides operational energy to the generator, control unit  130 . In some examples, the DC-DC converter  154  can also be utilized to provide operational power to one or more additional components. In yet further examples, a low voltage energy storage device, or a small sized permanent magnet generator can be included within the system  100 , and provide operational power to the generator control unit  130  and similar systems in lieu of the DC-DC converter  154 . In such examples, the DC-DC converter  154  is omitted entirely, and no DC-DC converter is utilized in the charging process. 
     The illustrated high voltage high peak load  150  and high voltage regenerative load  152  are exemplary in nature. A practical system can include multiple loads of either type connected across the negative bus bar  144  and the positive bus bar  142 , and operate in the manner described herein. 
     Also connected across the positive bus  142  and the negative bus  144  is a set of high energy storage devices  160 , such as lithium ion batteries, supercapacitors, and the like. The high energy storage devices  160  are arranged in series, and are configured to supplement the power provided to the positive and negative busses  142 ,  144  when the high voltage high peak load  150  is drawing a power in excess of power generated by the generator system  120 . In contrast, when power is being provided back to the power generating system  100  by the regenerative load  152 , the power can be utilized to charge or re-charge the high energy storage devices  160 . In some alternative examples, the energy from the regenerative load  152  can be redirected to a power dissipating resistor when it is not needed to charge the high energy storage devices  160 . In yet further examples, the switched reluctance generator can be reconfigured by the generator control unit  130 , according to known techniques, to operate as a motor and provide rotational input to the prime mover  110  via the shaft  112  when the regenerative load  152  provides power back. 
     Connected to, and monitoring, each of the high energy storage devices  160  is a state of charge module  162 . The state of charge modules  162  include sensors for detecting current, voltage, temperature, and the like of each of the high energy storage devices  160 . The sensed values are then communicated to the generator control unit  130  which determines a current state of charge of the high energy storage device  160  based on the sensed values according to any known state of charge determination technique. In alternative examples, each state of charge module  162  can include a processor and determine the state of charge of the corresponding high energy storage device  160  independently. In such an example, only the state of charge is communicated to the generator control unit  130 . 
     As described above, the generator system  120  includes a switched reluctance generator. Each of the high energy storage devices  160  is integrated with the switched reluctance generator and is configured to be charged by a corresponding switched reluctance generator channel. 
     With continued reference to  FIG. 1 ,  FIG. 2  schematically illustrates the integration of a single high energy storage device  160  with a channel of the switched reluctance generator within the generator system  120 . The high energy storage device  160  is integrated with a switched reluctance generator stator winding  210  via an asymmetric H-bridge  220  circuit. Also included within the integration between the high energy storage device  160  and the switched reluctance generator channel is a current regulator  230  that is communicatively coupled to the generator control unit  130 , and configured to regulate the current through the switched reluctance generator stator winding  210  by manipulation of the asymmetric H-bridge  220 . 
     The current in the stator winding  210  is controlled by the generator control unit  130  in response to the information received from the state of charge module  162  corresponding to the high energy storage device  160  in the switched reluctance generator channel  200 . By controlling the current passing through the switched reluctance generator stator pole winding  210 , the generator control unit  130  controls the power provided to the corresponding high energy storage device  160 , thereby enabling the generator control unit  130  to charge or re-charge each of the high energy storage devices  160 . As each high energy storage device  160  is within its own channel  200 , and corresponds to a unique stator winding  210 , the generator control unit  130  is capable of charging or re-charging each high energy storage device  160  independently of each other high energy storage device  160 . 
     In some circumstances it is possible for one or more of the high energy storage devices  160  to discharge more, or less, energy during a peak load than a remainder of the high energy storage devices  160 . This results in the overall state of charge of the high energy storage devices  160  being different, and is referred to as an imbalance in the state of charge. By independently controlling the current through each switched reluctance generator stator winding  210 , the generator control unit  130  is able to actively correct an imbalance without overcharging or undercharging the high energy storage devices  160 . 
     With continued reference to  FIGS. 1 and 2 ,  FIG. 3  illustrates a method for re-balancing high-energy storage devices  160  within a DC power generating system including a switched reluctance generator. Initially, the generator control unit  130  detects an imbalance between the state of charge within the set of series arranged high energy storage devices  160  in a “Detect Imbalance” step  310 . 
     Once an imbalance has been detected, the generator control unit  130  determines an appropriate control current for each stator winding of the switched reluctance generator in a “Determine Appropriate Charge Profile” step  320 . As each high energy storage device  160  is connected to a single corresponding stator winding  210 , the provision of distinct control currents to each stator winding  210  provides a distinct charging profile to the corresponding high energy storage device  160 , allowing the high energy storage devices  160  to be simultaneously re-balanced. 
     Once the generator control unit  130  has determined the appropriate charge profile for each high energy storage device  160 , the generator control unit  130  independently controls each of the stator windings  210  in an “Independently Control Stator Windings” step  330 . The independent control charges the high energy storage devices  160  and re-balances the charge. 
     In some examples, the state of charge modules  162  can continuously monitor the state of charge of their corresponding high energy storage devices  160  during the charging process, thereby allowing the generator control unit  130  to adapt the charging profile of one or more high energy storage devices  160  on the fly. 
     While described above in reference to a DC power generating system for an automotive vehicle, one of skill in the art having the benefit of this disclosure will understand that the principles and configurations described herein can be applied to any DC power generating system and are not limited in application to automotive vehicles. 
     It is further understood that any of the above described concepts can be used alone or in combination with any or all of the other above described concepts. Although an embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.