Patent Publication Number: US-2013234508-A1

Title: Apparatus for use in an electrical drive system, and method for operating an apparatus of this kind

Description:
This application is a National Stage completion of PCT/EP2011/069510 filed Nov. 7, 2011, which claims priority from German patent application serial no. 10 2010 062 249.4 filed Dec. 1, 2010. 
    
    
     FIELD OF THE INVENTION 
     The present invention concerns a device for the operating of an electrical drive system, as well as a method for operating the apparatus. 
     BACKGROUND OF THE INVENTION 
     The future might show, especially in the center of cities, that there will be more often so-called “zero emission zones”. These are areas in which only vehicles can drive which do not create any emission when driving. For instance, busses and delivery trucks need to be operated in a pure electric mode. 
     In vehicles with a parallel hybrid drive, besides the so called hybrid driving in which the combustion engine as well as the electric assembly drive the vehicle, there is among other things the possibility to operate exclusively with the electric machine and the combustion engine turned off, thus free of emission. To drive for a sufficient distance in a pure electric mode, sufficient electric energy has to be provided in one or several energy storage devices. 
     Also known are so-called plug-in-hybrid vehicles where their battery is not only charged through recuperation of braking energy, for instance through regenerative braking, or the combustion engine, but can also be charged in addition through the electric power grid by means of an external charging station. Plug-in-hybrid vehicles combine the advantages of electric vehicles and pure combustion engine vehicles. On one hand, one can for instance in a city, in an environmental zone, drive in pure electric mode and therefore emission and noise free, and on the other hand, longer distances can be achieved by means of a combustion engine even if the battery is at a low charge state. 
     Up to now, partially due to large development cost, there are no suitable batteries to achieve larger distances in a pure electric operation. These would have to provide a high energy content, in addition a large power capacity to guarantee the required drive dynamics in a pure electric operation. 
     The currently available batteries for hybrid vehicles are, however, designed in a way to absorb and to output recuperation energy, meaning that their life expectancy lowers drastically at large energy increases which are needed for a pure electric drive. Because these batteries are very expensive they, as single device, are not suitable to be applied continuously for a pure electric drive. 
     The state of the art therefore suggests connecting several batteries in parallel by means of the power electronics to increase the energy content and the performance ability. Such a procedure is for instance described in detail in the publication DE 10 2007 009 009 A1. The main disadvantage of a parallel circuit is, however, the control ability. Different internal resistances, due to the manufacturing or which are created by different temperatures, cause asymmetrical behavior of the batteries in an operation. These facts result in a larger decrease of the electrical distance and the powering performance. For the control, and therefore the prevention of an asymmetrical behavior of batteries which are connected in parallel, intermediate circuits are required which need to be designed physically large and heavy, to switch high currents which flow in this configuration. 
     SUMMARY OF THE INVENTION 
     Based on these facts, the present invention has the task to overcome the above mentioned disadvantages of the state of the art and to propose a device, as well as a method, which enables with little effort to run in parallel, batteries and battery systems without an intermediate circuit to an electronic inverter 
     The invention proposes a device to be used in an electric drive system, in particular in a hybrid drive system of a motor vehicle, comprising of at least a first and a second battery system configured in a parallel connection, where their load outputs are joined in a common load output, whereby each battery system has an energy storage and with it a connected pre-load circuit, whereby through an output of the pre-load circuit in each case the load output of the battery system is created, whereby the load output of each battery system, by means of the pre-load circuit, can each be connected or disconnected at the common load output, whereby the common load output is immediately then electrically coupled with an inverter input of an inverter of the device, in particular by means of an intermediate circuit capacitor. 
     In an embodiment of the inventive device, the load output of each battery system can be connected or disconnected by means of a battery management system of the battery system, whereby the battery management system controls in particular the pre-load circuit and/or a contactor. 
     In an additional embodiment of the inventive device, the battery management system is in an operational connection with a control unit of the device, in particular a hybrid control device. 
     In another embodiment of the inventive device, it is designed to alternately switch the load outputs of at least the first and/or second battery system to the common load output. 
     In accordance with the invention, a method is proposed for the operation of an inventive device, in particular in an electric drive system, and further in a hybrid drive system, whereby in a first step a first battery system, in particular depending on the load state of its energy storage, is disconnected from the common load output by means of its pre-load device, whereby in a second step a second battery system is connected to the common load output by means of its pre-load device, in particular depending of the load state of its energy storage. 
     Also proposed is a method in which the disconnection of the first battery systems from common load output and/or the connection of the second or further the battery systems to the common load output during operation of the inverter, especially for propulsion purposes, takes place. 
     In accordance with the aspect of the invented method, one of the several battery systems is always connected at the common load output during the operation of the converter, in particular before the first step and after the second step. 
     In accordance with an additional aspect of the invented method, the connection of the battery system and the second step takes place through an increase of an inverted input voltage by means of the pre-load device of the added battery system. 
     In accordance with another aspect of the invented method, a battery system is added in the second step if its energy storage has a higher charged level than the energy storage which was connected in the first step. 
     A method is also proposed in accordance with the invention whereby, at least for the duration of the first and second step, a third of the battery systems is connected in parallel to the common load output, in particular for the stabilization of an inverter input voltage, whereby the third of the battery systems is connected or disconnected by means of its pre-load device. 
     In addition, a method is also proposed in accordance with the invention, whereby during energy feedback, via an inverter, into the common load output for the purpose of charging an energy storage, in the first step, a battery system is disconnected from the common load output, where its energy storage shows a first, large charge state, and that in the second step a battery system is connected to the common load output where its energy storage has a lower charge state compared to the energy storage of the disconnected battery system. 
     In accordance with an aspect of the inventive method, the battery system which is added in the second step is selected, depending on the load state of its energy storage, from a multitude of battery systems which can be connected to the common load output. 
     In accordance with the invention, also a motor vehicle as proposed, in particular a plug-in-hybrid motor vehicle with the inventive device. 
     Additional characteristics and advantages of the invention arise from the following description of embodiment examples of the invention, based on the figures and drawings which show the inventive details. The individual characteristics can be enabled individually or together in any combination in a variation of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiment examples of the invention are explained in the following based on the provided drawings. These show: 
         FIG. 1  as an example, a battery system forming the inventive device in accordance with a possible embodiment of the invention; 
         FIG. 2  as an example, a device to execute the inventive method in accordance with a possible embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the following description of the drawings, same elements or functions, respectively, are marked with the same reference characters. 
       FIG. 2  shows as an example and schematically an inventive device  1  for use in electric drive system  2 , in particular for a hybrid motor vehicle and more particularly for a plugin-hybrid-motor vehicle. The device  1  has an inverter  3 , in particular a voltage inverter which is provided for the connection with an electric drive assembly  4  of the drive system  2 , for instance with an induction machine. To drive the assembly  4 , the inverter  3  is operated for instance with a pulse width modulation (PWM). The inverter  3  has, besides power switches which are assembled by means of power semiconductor parts, for instance a control device for the power semiconductor parts of the power switch. 
     The device  1  according to the invention also has several, in particular similar battery systems  5   a ,  5   b ,  5   c , . . . , at least a first  5   a  battery system and a second  5   b  battery system each of which comprises or has an energy storage  6 , for instance  FIG. 1 . The energy storage  6  of a battery system  5   a ,  5   b ,  5   c  can each be configured by means of several partial energy storages  6   a ,  6   b ,  6   c , or as a single energy storage  6 . The energy storage  6  or the partial energy storages  6   a ,  6   b ,  6   c , . . . are designed as a battery cell, as an alternative for instance as a fuel cell or as a super-capacitor. Several partial energy storages  6   a ,  6   b ,  6   c , . . . can be configured for instance in parallel or, as shown, in series to create the energy storage  6 . 
     A battery system  5   a ,  5   b ,  5   c , . . . , in accordance with the invention, is designed in particular with an energy storage  6  as an accumulator, in particular as a traction battery. The stored energy is available at an output  7  of the energy storage  6 , i.e. between the electrical connections, whereby each battery system  5   a ,  5   b ,  5   c , . . . in particular provides a DC voltage. 
     A battery system  5   a ,  5   b ,  5   c , . . . has for instance a housing  8  in which its components are protected and isolated against environmental conditions, respectively, and each has also an electrical output, i.e. a load output  9 , through which the energy of the energy storage  6  is withdrawn, i.e. an output at the load side. The load output  9  is each in particular configured by means of two connection terminals  10  of a battery system  5   a ,  5   b ,  5   c , . . . which can, for instance, extend out from the housing  8 . 
     It is provided, in accordance with  FIG. 2  of the invention, that at least a first and a second battery system  5   a ,  5   b  are connected in parallel to create the inventive device, in particular more than two battery systems  5   a ,  5   b ,  5   c , . . . , whereby the load outputs  9  of the battery systems  5   a ,  5   b ,  5   c , . . . are joined in a common load output  11 , i.e. electrically. Such a created common load output  11  is, according to the invention, directly energetically or rather immediately, connected with the inverter input  12  of the inverter  3  of the device, meaning without the power electronics which is connected between the common load output  11  and the inverter  3 . 
     An intermediate circuit capacitor  13  is implemented at the input  12  of the inverter  3  for the energy coupling, in particular by means of at least one intermediate circuit capacitor  13 . The coupling element or intermediate circuit capacitor  13 , respectively, is especially provided to store the energy, or to intermediately store it, which is provided by means of the common load output  11 , to provide the inverter  3  with energy, as needed, to drive an electric drive assembly, for instance with a required voltage level. The coupling element  13  is in particular connected between the input terminals  3   a  of the inverter  3 . 
     In addition, each battery system  5   a ,  5   b ,  5   c , . . . has, in accordance with the invention, a pre-charging circuit  14  which can be, in particular, an integral part of each battery system  5   a ,  5   b ,  5   c , . . . or be assigned to it. The pre-charging circuit  14  is hereby utilized to limit the high charging current which is present at the coupling or rather the energy storage element  13  which is positioned at the common load output  11 . By means of each pre-charging circuit  14 , the inverter input voltage can be selectively raised to the voltage level of a battery system  5   a ,  5   b ,  5   c , . . . which needs to be connected electrically with the common load output  11 , without a defect. 
     In accordance with the invention, a pre-charging circuit  14  is, in each case, coupled with the energy storage  6  of the battery system  5   a ,  5   b ,  5   c  . . . , i.e. electrically, wherein, by way of an output  14   a  of the pre-charging circuit  14 , the load output  9  of a battery system  5   a ,  5   b ,  5   c , . . . is, in each case, created. The pre-charging circuit  14  has, in a commonly known art, a pre-charging and a main contactor  15 ,  16 , as well as a pre-charging resistor  17 , whereby by way of the contactors  15 ,  16  the load output of each battery system  5   a ,  5   b ,  5   c , . . . can each be connected into or disconnected from the common load output  11 , i.e. by opening of the contactors  15 ,  16  and the closing of, for instance, one of the contactors  15  or  16 , respectively. The implementation of an additional contactor into the battery system  5   a ,  5   b ,  5   c , . . . can also be provided, for instance  FIG. 1 . 
     Thus and by means of the pre-charging circuit  14 , the respective load output of each of the battery systems  5   a ,  5   b ,  5   c , . . . can be added to or disconnected in a simple manner at the load output  11 . For the control of each pre-charging circuit  14  of a battery system  5   a ,  5   b ,  5   c , . . . , the invention provides, in each case, a battery management system  18  or battery control device, respectively, for each battery system  5   a ,  5   b ,  5   c , . . . which becomes for instance an integral part therewith. A battery management system  18  controls adding another load output  9  to the common load output  11 , or disconnection from the load output  11 , respectively, by means of at least one contactor  15 ,  16  of the respective pre-charging circuit  14  whereby, for the addition, first the pre-charging contactor  15  can be closed and the main contactor  16  can be bypassed, i.e. the addition of a battery system  5   a ,  5   b ,  5   c , . . . at the common load output  11  takes place after the pre-charging. 
     For a specifically targeted addition or disconnection of battery systems  5   a ,  5   b ,  5   c , . . . to a common load output  11 , it is provided in this invention that a battery management system  18 , in each case, interacts with a control device  19  of the device  1 , in particular, interacts with a hybrid control system. By means of the control device  19 , switching signals are communicated to the battery management system to open and close the contactors  15 ,  16 , so that the addition or disconnection of the respective load output  9  can be performed in a simple manner. The signals of the control device  19  are communicated, for instance via a Bus  20 , to the respective battery management systems  18 . In particular, such a designed device  1  enables the connection or disconnect of the load outputs  9  of different battery systems  5   a ,  5   b ,  5   c , . . . to alternate at the common load output  11  or the inverter  3 . 
     In the inventive method, to operate the device  1 , in particular, in the electric drive system  2 , a first of the battery systems  5   a ,  5   b ,  5   c , . . . , for instance the battery system  5   a , is disconnected, in a first step, especially depending on the charge state of its energy storage  6 , from the common load output  11  by means of the pre-charging device  14 . When operating the inverter  3  for a drive purpose, meaning to support the assembly  4  at the load side, that battery system  5   a  which needs to be disconnected has a low charge level, it is for instance lower than a pre-determined threshold. The load state is especially monitored by the battery management system  18  of the battery system  5   a , and is for instance communicated, via the bus  20 , to the control device  19 . 
     In a second step, a second battery system,  5   a ,  5   b ,  5   c , . . . , for instance  5   b , is connected to the common load output  11  in this inventive method, by means of its pre-charging device  14 , again particularly depending of the charge state of its energy storage  6 . During the operation of the inverter  3  especially for the purpose of driving, based on charge states communicated to the control device  19  of the additional energy storages  6 , which are monitored by means of the respective battery management systems  18 , and their additional battery systems  5   a ,  5   b ,  5   c , . . . , the control device  19  selects a battery system  5   d , where its energy storage  6  has a high charge state, in comparison to the additional battery systems  5   a ,  5   c ,  5   d, . . . .    
     The selected battery system  5   a ,  5   b ,  5   b , . . . , for example the battery system  5   b , gets connected by means of its load output  9  to the common load output  11 , whereby the added connection utilizes the pre-charging possibility by means of the pre-charging contactor  15  and the pre-charging resistor  17 , meaning that the additional battery system is additionally connected in the second step through an increase of the inverter input voltage by means of the pre-charging device  14  of the battery system  5   b  which is, for instance, to be added. 
     Therefore by means of the inventive method, a drained battery or energy storage  6 , respectively, can be disconnected in a simple manner electrically from the inverter  3 , and the new battery or energy storage  6 , respectively, can be added in a simple manner for the additional drive of the electric assembly  4 . 
     It is in particular provided in the invention that in each case exactly one of several battery systems  5   a ,  5   b ,  5   c , . . . during the operation of the inverter  3  connected to the common load output  11 , in particular, before the first step, meaning before disconnecting the first battery system  5   a  and after the second step, meaning after adding the second or additional battery systems  5   b ,  5   c , . . . , respectively. Thus, different charge states of different battery systems  5   a ,  5   b ,  5   c , . . . do not influence the battery cluster and power electronics, besides the inverter  3 , can be omitted. An electronic drive system  2  or the inverter  3 , respectively, is hereby always precisely energized by the connected energy storage  6 . 
     In accordance with the invention, switching between a first and a second battery system  5   a ,  5   b ,  5   c , . . . is carried out during the operation of the inverter  3 , preferably in a situation at which no or only a little amount of torque is required for the assembly  4 . The reason for this is that a reliable torque cannot be delivered during the switch. The disconnection of the battery systems  5   a ,  5   b ,  5   c , . . . and the connect of an additional battery system  5   a ,  5   b ,  5   c , . . . takes place for example, during the hybrid drive, during a change of load, during a shift, in a still-stand phase, at a low torque requirement for the e-machine or the assembly  4 , respectively. 
     In a variation of the inventive method, in particular when the inverter  3  is operating for the purpose of a drive, it is provided that before a first of the battery systems  5   a ,  5   b ,  5   c , . . . , for instance  5   a  is disconnected, an additional or third, respectively, of the battery systems  5   a ,  5   b ,  5   c , . . . , for instance  5   c , is connected, in the first step, in parallel to the common load output  11 , whereby the third battery system  5   c  during or after the connection of a second of the battery systems  5   a ,  5   b ,  5   c , . . . , for instance  5   b , is disconnected from the common load output  11 , whereby the third battery system  5   c  in particular is connected or disconnected by means of its pre-charge device  14 . At least for the duration of the first and second steps, the third battery system  5   c  is hereby connected to the common load output  11 . 
     The integration of a third of the battery systems  5   a ,  5   b ,  5   c , . . . which in particular has an energy storage  6  in the form of a special pre-load battery, into the parallel circuit or the battery cluster, respectively, it is hereby provided that during a switch between a first and a second battery system, i.e. a disconnection of the first and a connection of the second of each to the common load output  11 , is inserted and connected so as to stabilize the intermediate circuit which is established by means of the intermediate circuit capacitor  13 . Thus, the reduction of load at the inverter  3  during execution of the switch is significantly lower. The third pre-load battery system, for instance  5   c , is for instance an energy storage  6  with a low energy content in comparison to the additional energy storages of the traditional battery systems  5   a ,  5   b ,  5   d , . . . , but a particularly large pre-load resistor  17 . 
     The energy back-feed from the inverter  3  into the common load output  11  or during recuperation, respectively, it is provided, in the first step for the purpose for the charging of an energy storage  6 , to disconnect a first battery system  5   a ,  5   b ,  5   c , . . . , for instance  5   a , from the common load output  11 , when its energy storage  6  has a high load state in comparison to the load state of traditional energy storages  6  of additional battery systems  5   b ,  5   c ,  5   d , . . . . The disconnected battery system  5   a  has been previously—for instance for drive purposes—connected to the common load output  11  due to its large energy storage load state. 
     In the second step, a second one or an additional one, respectively, of the other battery systems  5   a ,  5   b ,  5   c , . . . , for instance  5   b , is connected at the common load output  11 , and its energy storage  6  has a lower charge in comparison to the energy storage  6  of the disconnected battery system  5   a . The battery system  5   a  which needs to be connected is again selected by the control device  19  in conjunction with the battery management system  18 , i.e. depending on the load state of the energy storage  6  and added, in particular, by means of the pre-charge circuit  14 . The selected battery system  5   b  is, in particular, the one having the lowest charge state in the energy storage  6  where having the lowest has the lowest charge state in comparison to the others. 
     It is hereby provided, in accordance with the invention, to sequentially charge or rather connect or disconnect the energy storages  6  of each of the battery systems  5   a ,  5   b ,  5   c , . . . meaning, starting with the one which has the lowest charge state—in particular to prevent a total discharge—and ending with the one which has the largest charge state. Hereby, it is also provided to connect in each case exactly one energy storage  6 , prior to each disconnection or after each connection to the common load output  11 . 
     Charging of the energy storages  6  takes place at the time—in case the recuperated energy is not sufficient—for instance during a hybrid drive through a load point shifting. When the inventive method is applied in a plugin-hybrid vehicle, the charging of the energy storages  6 , in particular the battery cells, can also take place at an electrical outlet, also sequentially as previously described. 
     It is provided in this invention to keep the bus load on the bus  20  low, in particular with a CAN-bus, even with a multitude of participating battery systems  5   a ,  5   b ,  5   c , . . . . Hereby, the energy storages  6 , which are not needed and which are physically disconnected from the common load output  11 , are operated in a sleep mode. In this sleep mode the respective battery system  5   a ,  5   b ,  5   c , . . . transmits with its assigned ID a limited amount of information, for instance its actual charge state (SOC) and, if needed, status information such as voltage, temperature, State of Health. The “sleeping” energy storages  6  or batteries, respectively, need to change into the regular operating mode for the addition on demand, meaning that they need to continually listen, while in the sleep mode, for a wake-up signal on the bus  20 . 
     It is in particular provided in the invention to execute the first step and the second step several times consecutively, whereby the first step and the second step each alternate. Hereby, exactly one energy storage  6  is connected to the common load output  11  after each switch. If required, the suitable energy storage  6  can in each case be connected with the inverter  3 . 
     REFERENCE CHARACTERS 
     
         
         
           
               1  Device 
               2  Electric Drive System 
               3  Inverter 
               3   a  Input Terminals Inverter 
               4  Electric Drive Assembly 
               5   a ,  5   b ,  5   c , . . . Battery System 
               6  Energy Storage 
               6   a ,  6   b  Partial Energy Storage 
               7  Output Energy Storage 
               8  Housing 
               9  Load Output Battery System 
               10  Terminals Battery System 
               11  Common Load Output 
               12  Input Inverter 
               13  Intermediate circuit capacitor 
               14  Pre-charging Circuit 
               14   a  Output Pre-Charging Circuit 
               15  Pre-Charging Contactor 
               16  Main Contactor 
               17  Pre-Charging Resistor 
               18  Battery Management System 
               19  Control Device 
               20  Circuit