Patent Publication Number: US-2019184832-A1

Title: Vehicle power system with back electromagnetic field blocking

Description:
TECHNICAL FIELD 
     This disclosure relates to electric drive systems for automotive vehicles. 
     BACKGROUND 
     Hybrid-electric vehicles (HEVs) and battery electric vehicles (BEVs) may rely on a traction battery to provide power to a traction motor for propulsion, and a power inverter therebetween to convert direct current (DC) power to alternating current (AC) power. The typical AC traction motor is a three-phase motor powered by three sinusoidal signals each driven with 120 degrees phase separation. Also, many electrified vehicles may include a DC-DC converter to convert the voltage of the traction battery to an operational voltage level of the traction motor. 
     SUMMARY 
     A vehicle power system includes an electric machine configured to drive vehicle wheels, an inverter, and a switching arrangement. The switching arrangement is coupled between the electric machine and inverter, and is configured to permit current flow from the inverter to the electric machine with activation of elements of the switching arrangement, and to prevent current flow from the electric machine to the inverter without activation of the elements. 
     A vehicle power system includes an electric machine, an inverter, and a plurality of pairs, each including a switch and an associated anti-parallel diode, electrically between the electric machine and inverter. Each of the pairs is configured to permit current flow from the inverter to the electric machine with activation of the switch, and to prevent current flow from the electric machine to the inverter without activation of the switch. 
     A method for operating a vehicle power system includes, by a controller, permitting activation of switches of a switching arrangement coupled between an electric machine and inverter to permit current flow from the inverter to the electric machine, and preventing activation of the switches to block back electromagnetic fields associated with the electric machine from the inverter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1 and 2  are schematic diagrams of vehicles including electrified powertrains. 
     
    
    
     DETAILED DESCRIPTION 
     Various embodiments of the present disclosure are described herein. However, the disclosed embodiments are merely exemplary and other embodiments may take various and alternative forms that are not explicitly illustrated or described. The figures are not necessarily to scale; some features may be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one of ordinary skill in the art to variously employ the present invention. As those of ordinary skill in the art will understand, various features illustrated and described with reference to any one of the figures may be combined with features illustrated in one or more other figures to produce embodiments that are not explicitly illustrated or described. The combinations of features illustrated provide representative embodiments for typical applications. Various combinations and modifications of the features consistent with the teachings of this disclosure, however, may be desired for particular applications or implementations. 
     An input capacitor (DC capacitor) is a common element found in a DC-AC inverter. This component stores a sufficient amount of energy that can be accessed and transferred to the load during each switching cycle. The flipside of having this storage is that the stored energy can create issues if not depleted in a timely manner when the DC-AC inverter is not operational. The internal series resistance of the DC capacitor is often not large enough to dissipate the energy in a short period of time. In some circumstances, the voltage of the DC capacitor should reach 60 V in approximately 60 seconds. For this reason, there is often an additional dissipative component (e.g., resistor) in parallel with the capacitor. The value of this resistor can be calculated according to the following equation: 
         t=−RC  ln( V   acceptable   /V   max ) 
     where R and C are the resistor and capacitor values, V acceptable  is the acceptable voltage (e.g., 60 V), V max  is the maximum voltage seen by the DC capacitor, and t is the time for the DC capacitor voltage to go form V max  to V acceptable . 
     According to this equation, the smaller the resistor value, R, the shorter the discharge time, t. Thus, one may conclude that having a small resistor value, R, resolves the issue and will bring the voltage down in a reasonable time. This, however, may not be the case for the following reasons: (1) By reducing the resistor value, R, the power loss, P loss =V 2 /R, will increase for a constant voltage. Because this power loss converts to thermal load, the cooling system will work harder to remove this extra heat. (2) Since high power (high wattage) resistors are standard packs with standard values, smaller and smaller resistor values sometimes translate to more resistors in parallel, which adds to packaging complexity. 
     The above issues may be exacerbated during flat tow. In this case, the back electromagnetic fields generated by the motor may charge the DC capacitor. This charge should be dissipated once the vehicle stops. If we assume that the DC capacitor is 1000 uF, the required resistor value to deplete the DC capacitor charge may be 26 kΩ, which may result in approximately 13 W of continuous power loss. Heat may build up as a result, particularly in circumstances in which the cooling system is not operable, such as during flat tow. Some vehicle manufacturers approach the flat tow issue by specifying trailer tow requirements instead. In such cases, the discharge resistors may be designed for normal operation only. 
     The above issues may also be exacerbated during downhill travel as back electromagnetic fields generated by the motor may charge the DC capacitor. Some vehicle manufacturers use specific switching algorithms to circulate current trough the motor windings to dissipate the power. Although this methodology may be effective, it may increase losses due to switching. Here, various arrangements of diodes and/or switching elements are contemplated that block reverse currents from unwanted charging. 
     With reference to  FIG. 1 , vehicle  10  includes electrified powertrain  12 , controller  14 , transmission  16 , and wheels  18 . The electrified powertrain  12  includes traction battery  20 , inverter  22 , switch pack  24 , and electric machine  26 . As indicated by heavy solid line, the electric machine  26  is mechanically coupled with the transmission  16 , and the transmission  16  is mechanically coupled with the wheels  18 . Thus, mechanical power developed by the electric machine  26  can be transferred to the wheels  18  via the transmission  16 . 
     The inverter  22  includes capacitor  28  and switches  30 ,  32 ,  34 ,  36 ,  38 ,  40 . Each of the switches is paired with a corresponding anti-parallel diode  31 ,  33 ,  35 ,  37 ,  39 ,  41  respectively. The capacitor  28 , switches and diodes  30 - 41  are arranged in usual fashion with the capacitor  28  being electrically in parallel with the traction battery  20 , and electrically between the traction battery  20  and switches and diodes  30 - 41 . In this example, the electric machine  26  is a three-phase electric machine. As such, the switch pack  24  includes a trio of switches  42 ,  44 ,  46  each paired with a corresponding anti-parallel diode  43 ,  45 ,  47  respectively. 
     Each of the three pairs of switches and anti-parallel diodes is electrically in series with a phase of the electric machine  26  and a mid-point of a leg of the inverter  22 . This arrangement permits the switch pack  24  to permit AC current flow between the inverter  22  and electric machine  26  with selective activation of the switches  42 ,  44 ,  46 . The controller  14 , for example, may control the inverter  22  and switch pack  24  during a propulsion mode such that current from the traction battery  20  flows through the activated switch  40 , the anti-parallel diode  47  to a phase of the electric machine  26 , and through the activated switches  42 ,  30  returning to the traction battery  20  without activation of the switch  46 . The controller  14 , for example, may control the inverter  22  and switch pack  24  during a regenerative mode such that current from a phase of the electric machine  26  flows through the activated switch  46  and the anti-parallel diode  41  to the traction battery  20 , and the anti-parallel diodes  31 ,  43  returning to the electric machine  26 . These methodologies can, of course, be extended to all the phases. This arrangement also permits the switch pack  24  to prevent current flow from the electric machine  26  to the inverter  22  without activation of the switches  42 ,  44 ,  46  by virtue of the anti-parallel diodes  43 ,  45 ,  47 . This, for example, may be responsive to a tow mode or downhill travel mode. Thus, this arrangement permits the switch pack  24  to passively block currents associated with back electromagnetic fields associated with the electric machine  26  from the inverter  22 . 
     The switch pack  24  may also be used in concert with the inverter  22  and electric machine  26  to discharge the capacitor  28 . The controller  14 , for example, may operate the switches  30 ,  40 ,  42  such that current circulates between the inverter  22  and windings of the electric machine  26 . 
     The inverter  22 , in certain examples, may include a resistor  48  in parallel with and electrically between the traction battery  20  and capacitor  28 . Thus the controller  14 , for example, may operate the inverter  22  and switch pack  24  to direct current from the motor  26  to the resistor  48  to discharge the same assuming for example that the usual contactors (not shown) between the traction battery  20  and inverter  22  are open. 
     The architecture of  FIG. 1  is but one example. Others, of course, are also contemplated. The electric machine  26  may have a different number of phases. And the switch pack  24  may include a corresponding different number of switches and anti-parallel diode pairs. Possible switch types include IGBTs, MOSFETs, thyristors, etc. 
     The architectures contemplated herein may be implemented within a variety of vehicle configurations.  FIG. 2 , for example, depicts an electrified vehicle  54  that includes one or more electric machines  56  mechanically coupled to a hybrid transmission  58 . The electric machines  56  may operate as a motor or generator. In addition, the hybrid transmission  58  is mechanically coupled to an engine  60  and a drive shaft  62  that is mechanically coupled to the wheels  64 . 
     A traction battery or battery pack  66  stores energy that can be used by the electric machines  56 . The vehicle battery pack  66  may provide a high voltage direct current (DC) output. The traction battery  66  may be electrically coupled to one or more power electronics modules  68  that implement the architectures discussed above. One or more contactors  70  may isolate the traction battery  66  from other components when opened and connect the traction battery  66  to other components when closed. The power electronics module  68  is also electrically coupled to the electric machines  56  and provides the ability to bi-directionally transfer energy between the traction battery  66  and the electric machines  56 . For example, the traction battery  66  may provide a DC voltage while the electric machines  56  may operate with a three-phase alternating current (AC) to function. The power electronics module  68  may convert the DC voltage to a three-phase AC current to operate the electric machines  56 . In a regenerative mode, the power electronics module  68  may convert the three-phase AC current from the electric machines  56  acting as generators to the DC voltage compatible with the traction battery  66 . 
     The vehicle  54  may include a variable-voltage converter (VVC) (not shown) electrically coupled between the traction battery  66  and power electronics module  68 . The VVC may be a DC/DC boost converter configured to increase or boost the voltage provided by the traction battery  66 . By increasing the voltage, current requirements may be decreased leading to a reduction in wiring size for the power electronics module  68  and the electric machines  56 . Further, the electric machines  56  may be operated with better efficiency and lower losses. 
     In addition to providing energy for propulsion, the traction battery  66  may provide energy for other vehicle electrical systems. The vehicle  54  may include a DC/DC converter module  72  that converts the high voltage DC output of the traction battery  66  to a low voltage DC supply that is compatible with low-voltage vehicle loads. An output of the DC/DC converter module  72  may be electrically coupled to an auxiliary battery  74  (e.g., 12V battery) for charging the auxiliary battery  74 . The low-voltage systems may be electrically coupled to the auxiliary battery  74 . One or more electrical loads  76  may be coupled to the high-voltage bus. The electrical loads  76  may have an associated controller that operates and controls the electrical loads  76  when appropriate. Examples of electrical loads  76  may include a fan, an electric heating element, and/or an air-conditioning compressor. 
     The electrified vehicle  54  may be configured to recharge the traction battery  66  from an external power source  78 . The external power source  78  may be a connection to an electrical outlet. The external power source  78  may be electrically coupled to a charger or electric vehicle supply equipment (EVSE)  80 . The external power source  78  may be an electrical power distribution network or grid as provided by an electric utility company. The EVSE  80  may provide circuitry and controls to regulate and manage the transfer of energy between the power source  78  and the vehicle  54 . The external power source  78  may provide DC or AC electric power to the EVSE  80 . The EVSE  80  may have a charge connector  82  for plugging into a charge port  84  of the vehicle  54 . The charge port  84  may be any type of port configured to transfer power from the EVSE  80  to the vehicle  54 . The charge port  84  may be electrically coupled to a charger or on-board power conversion module  86 . The power conversion module  86  may condition the power supplied from the EVSE  80  to provide the proper voltage and current levels to the traction battery  66 . The power conversion module  86  may interface with the EVSE  80  to coordinate the delivery of power to the vehicle  54 . The EVSE connector  82  may have pins that mate with corresponding recesses of the charge port  84 . Alternatively, various components described as being electrically coupled or connected may transfer power using a wireless inductive coupling. 
     In some configurations, the electrified vehicle  54  may be configured to provide power to an external load. For example, the electrified vehicle may be configured to operate as a back-up generator or power outlet. In such applications, a load may be connected to the EVSE connector  82  or other outlet. The electrified vehicle  54  may be configured to return power to the power source  78 . For example, the electrified vehicle  54  may be configured to provide alternating current (AC) power to the electrical grid. The voltage supplied by the electrified vehicle may be synchronized to the power line. 
     Electronic modules in the vehicle  54  may communicate via one or more vehicle networks. The vehicle network may include a plurality of channels for communication. One channel of the vehicle network may be a serial bus such as a Controller Area Network (CAN). One of the channels of the vehicle network may include an Ethernet network defined by the Institute of Electrical and Electronics Engineers (IEEE) 802 family of standards. Additional channels of the vehicle network may include discrete connections between modules and may include power signals from the auxiliary battery  74 . Different signals may be transferred over different channels of the vehicle network. For example, video signals may be transferred over a high-speed channel (e.g., Ethernet) while control signals may be transferred over CAN or discrete signals. The vehicle network may include any hardware and software components that aid in transferring signals and data between modules. The vehicle network is not shown but it may be implied that the vehicle network may connect to any electronic module that is present in the vehicle  54 . A vehicle system controller (VSC)  88  may be present to coordinate the operation of the various components. 
     As depicted, the vehicle  54  may include the power conversion module  86  for transferring power from the external power source  78  to a high-voltage bus of the vehicle  54 . The vehicle  54  also includes the DC/DC converter module  72  for converting the voltage of the high-voltage bus to a voltage level suitable for the auxiliary battery  74  and low-voltage loads  90  (e.g., around 12 Volts). The vehicle  54  may further include additional switches, contactors, and circuitry to selectively select power flow between the traction battery  66  to the DC/DC converter  72  and/or between the power conversion module  86  and the traction battery  66 . To reduce cost and packaging complexities, it may be desired to combine the power conversion module  86  and the DC/DC converter module  72  into a single, integrated unit. An integrated unit may help to enhance hardware utilization of the components and reduce the number of active and passive components that are present in the vehicle. Further, the integrated unit may have improved cooling capabilities. In addition, the packaging space required may be reduced. 
     The processes, methods, logic, or strategies disclosed may be deliverable to and/or implemented by a processing device, controller, or computer, which may include any existing programmable electronic control unit or dedicated electronic control unit. Similarly, the processes, methods, logic, or strategies may be stored as data and instructions executable by a controller or computer in many forms including, but not limited to, information permanently stored on various types of articles of manufacture that may include persistent non-writable storage media such as ROM devices, as well as information alterably stored on writeable storage media such as floppy disks, magnetic tapes, CDs, RAM devices, and other magnetic and optical media. The processes, methods, logic, or strategies may also be implemented in a software executable object. Alternatively, they may be embodied in whole or in part using suitable hardware components, such as Application Specific Integrated Circuits (ASICs), Field-Programmable Gate Arrays (FPGAs), state machines, controllers or other hardware components or devices, or a combination of hardware, software and firmware components. 
     The words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the disclosure and claims. As previously described, the features of various embodiments may be combined to form further embodiments that may not be explicitly described or illustrated. While various embodiments may have been described as providing advantages or being preferred over other embodiments or prior art implementations with respect to one or more desired characteristics, those of ordinary skill in the art recognize that one or more features or characteristics may be compromised to achieve desired overall system attributes, which depend on the specific application and implementation. These attributes include, but are not limited to cost, strength, durability, life cycle cost, marketability, appearance, packaging, size, serviceability, weight, manufacturability, ease of assembly, etc. As such, embodiments described as less desirable than other embodiments or prior art implementations with respect to one or more characteristics are not outside the scope of the disclosure and may be desirable for particular applications.