Patent ID: 12194876

DETAILED DESCRIPTION

Detailed embodiments of the present disclosure are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the present disclosure that may be embodied in various and alternative forms. 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 skilled in the art to variously employ the present disclosure.

Referring now toFIG.1, a block diagram of an electrified vehicle12in the form of a battery electric vehicle (BEV) is shown. BEV12has a traction powertrain including one or more traction motors (“electric machine(s)”)14, a traction battery (“battery” or “battery pack”)24, and a power electronics module26. In the BEV configuration, traction battery24provides all of the propulsion power and the electrified vehicle does not have an engine. In other variations, the electrified vehicle may be a plug-in (or non-plug-in) hybrid electric vehicle (HEV) further having an engine.

Traction motor14is part of the traction powertrain of BEV12for powering movement of the BEV. In this regard, traction motor14is mechanically connected to a transmission16of BEV12. Transmission16is mechanically connected to a drive shaft20that is mechanically connected to wheels22of BEV12. Traction motor14can provide propulsion capability to BEV12and is capable of operating as a generator. Traction motor14acting as a generator can recover energy that may normally be lost as heat in a friction braking system of BEV12.

Traction battery24stores electrical energy that can be used by traction motor14for propelling BEV12. Traction battery24typically provides a high-voltage (HV) direct current (DC) output.

Power electronics module26is electrically connected between traction battery24and traction motor14. Power electronics module26is operable to drive traction motor14with electrical power from traction battery24for the traction motor to propel BEV12. Power electronics module26provides the ability to bi-directionally transfer energy between traction battery24and traction motor14. For example, traction battery24may provide a DC voltage while traction motor14may require a three-phase alternating current (AC) current to function. Power electronics module26may convert the DC voltage to a three-phase AC current to operate traction motor14. In a regenerative mode, power electronics module26may convert three-phase AC current from traction motor14acting as a generator to DC voltage compatible with traction battery24. In this example, power electronics module26is in the form of an inverter (or inverter system controller (ISC)).

In addition to providing electrical power for vehicle propulsion, traction battery24may provide electrical power for other vehicle electrical systems. A typical vehicle electrical system may include a DC/DC converter module28that converts the HV DC output of traction battery24to a low-voltage (LV) DC supply compatible with other low-voltage vehicle components. Other high-voltage loads, such as compressors and electric heaters, may be connected directly to the high-voltage supply without the use of DC/DC converter module28. An auxiliary battery30(e.g., a twelve-volt DC battery) is charged by DC/DC converter module28. The low-voltage vehicle components are electrically connected to auxiliary battery30.

Traction battery24is rechargeable by an external power source36(e.g., the grid). External power source36may be electrically connected to electric vehicle supply equipment (EVSE)38. EVSE38provides circuitry and controls to control and manage the transfer of electrical energy between external power source36and BEV12. External power source36may provide DC or AC electric power to EVSE38. EVSE38may have a charge connector40for plugging into a charge port34of BEV12.

A power conversion module32of BEV12, such as an on-board charger having a DC/DC converter, may condition power supplied from EVSE38to provide the proper voltage and current levels to traction battery24. Power conversion module32may interface with EVSE38to coordinate the delivery of power to traction battery24.

The various components described above may have one or more associated controllers to control and monitor the operation of the components. The controllers can be microprocessor-based devices. The controllers may communicate via a serial bus (e.g., Controller Area Network (CAN)) or via discrete conductors.

For example, a system controller48(“vehicle controller”) is present to coordinate the operation of the various components. Controller48includes electronics, software, or both, to perform the necessary control functions for operating BEV12. Controller48may be a combination vehicle system controller and powertrain control module (VSC/PCM). Although controller48is shown as a single device, controller48may include multiple controllers in the form of multiple hardware devices, or multiple software controllers with one or more hardware devices. In this regard, a reference to a “controller” herein may refer to one or more controllers.

Referring now toFIG.2, with continual reference toFIG.1, a schematic diagram of the traction powertrain of BEV12and a powertrain control module60for the traction powertrain is shown. Powertrain control module60(or “powertrain controller”) is considered as being implemented by controller48.

As indicated, the traction powertrain includes traction motor14, traction battery24, and inverter26. As shown inFIG.2, the traction powertrain further includes a DC-link capacitor62. DC-link capacitor62is disposed between traction battery24and inverter26. Particularly, DC-link capacitor62is connected between a positive bus68and a negative bus70of the traction powertrain and is connectable in parallel with traction battery24through a pair of switches64and66. Switches64and66have an opened state and a closed state for selectively coupling traction battery24to positive bus68and negative bus70. DC-link capacitor62is a relatively large energy storage capacitor employed by inverter26to maintain a desired DC input voltage from traction battery24to the inverter and to absorb switching related ripples.

As shown inFIG.2, inverter26includes a plurality of power switches (not labeled; circuit symbols shown) arranged in a bridge configuration. Particularly, in this example, there are six power switches with respective pairs of the power switches being respectively arranged in three phase legs. Powertrain controller60controls the power switches to switch on and off in a desired manner for inverter26to drive traction motor14with electrical power from traction battery24via DC-link capacitor62. Each power switch may be an insulated-gate bipolar transistor (IGBT) (IGBT symbols shown inFIG.2) or another type of semiconductor power switch (e.g., MOSFET). Each power switch has a control terminal (e.g., a gate) coupled to a respective driver circuit72of powertrain controller60. Powertrain controller60further includes a control unit (e.g., a motor-generator control unit (MGCU))74. Driver circuits72are controlled by control unit74which generates switching commands according to various operating modes of inverter26.

Referring now toFIG.3, with continual reference toFIG.2, a flowchart80describing operation carried out by powertrain controller60for controlling inverter26is shown. The operation includes a normal operation and an active discharge operation. In the normal operation, powertrain controller60controls inverter26to drive traction motor14with electrical power from traction battery24via DC-link capacitor62in order for the traction motor to propel BEV12. In the active discharge operation, powertrain controller60controls inverter26in a manner causing DC-link capacitor62to discharge.

Pursuant to the normal operation, for example, powertrain controller60performs pulse-width modulation (PWM) control of the power switches of inverter26, as indicated by process block82. As such, PWM control signals having a controlled duty cycle are applied by control unit74to the gates of the power switches via respective driver circuits72. In this way, inverter26is controlled to operate in a normal PWM torque control mode to drive traction motor14with electrical power from traction battery24via DC-link capacitor62in order for the traction motor to propel BEV12.

A check is continually performed to determine whether an active discharge event of DC-link capacitor62is desired, as indicated by decision block84. If no, then the normal operation continues per process block82. If yes, then the normal operation ceases and the active discharge operation commences.

As the active discharge operation involves discharging DC-link capacitor62, traction battery24is to be disconnected from the DC-link capacitor for the active discharge operation to occur. The active discharge operation may thus commence while switches64and66are opened with DC-link capacitor62thereby being disconnected from traction battery24.

Pursuant to the active discharge operation, for example, powertrain controller60controls the power switches of inverter26to supply electrical current from DC-link capacitor62to the traction motor load in a manner that causes the torque of traction motor14to be zero, as indicated by process block86. For example, powertrain controller60can pulse-width modulate the power switches of inverter26according to an algorithm that pushes a zero-torque current which results in zero motor torque while dissipating charge on DC-link capacitor62. More generally, powertrain controller60applies an appropriate “discharge pulse” to the gates of the power switches of inverter26to cause the inverter to operate in a manner causing DC-link capacitor62to discharge. In this way, powertrain controller60controls inverter26to operate in a manner causing DC-link capacitor62to discharge.

A check is continually performed to determine whether DC-link capacitor62has been discharged, as indicated by decision block88. If no, then the active discharge operation continues per process block86. If yes, then the active discharge operation is terminated.

The active discharge operation is applicable for rapidly discharging DC-link capacitor62when shutting down the electric drive system of the traction powertrain. A shutdown of the electric drive system can be initiated by various events. During such a shutdown, traction battery24is quickly isolated from the rest of the electric drive system by opening switches64and66. However, a HV electric charge will remain on DC-link capacitor62. As such, DC-link capacitor62should be discharged to a certain level within a specific time.

During the normal operation, powertrain controller60receives electrical power from auxiliary battery30in order for the powertrain controller to perform the normal operation in controlling inverter26. An issue is that during certain shutdown events, the flow of electrical power from auxiliary battery30to powertrain controller60is disrupted whereby the powertrain controller receives no electrical power from the auxiliary battery. As such, powertrain controller60is unable to perform the active discharge operation in controlling inverter26unless the powertrain controller is electrically powered by another source. Further, in order for DC-link capacitor62to be discharged to the certain level within the specific time, powertrain controller60should immediately proceed with the active discharge operation as soon as a shutdown event occurs.

In accordance with the present disclosure, powertrain controller60is configured (i) to be electrically powered by an electrical power source on-board the powertrain controller (i.e., an electrical power source other than auxiliary battery30) during a shutdown event such that the powertrain controller can perform the active discharge operation in controlling inverter26and (ii) to immediately proceed with the active discharge operation as soon as the shutdown event occurs to thereby be in the best position to discharge DC-link capacitor62to the certain level within the specific time.

Regarding the feature (i), powertrain controller60includes a low-voltage (e.g., twelve-volt) super capacitor which electrically powers the powertrain controller as soon as the powertrain controller stops receiving a sufficient level of electrical power from auxiliary battery30. Powertrain controller60will stop receiving a sufficient level of electrical power upon certain shutdown events occurring. As such, the super capacitor electrically powers powertrain controller60during the active discharge operation whereby the powertrain controller is operable to perform the active discharge operation during a shutdown event.

Regarding the feature (ii), powertrain controller60includes a comparator which is used to trigger the powertrain controller to perform the active discharge operation upon detecting a shutdown event. Particularly, the comparator continually compares the level of electrical power (if any) received by powertrain controller60from auxiliary battery30with a predetermined threshold level. The received electrical power being less than the threshold level is indicative of a shutdown event occurring. This is because the flow of electrical power from auxiliary battery30to powertrain controller60will be disrupted during a shutdown event. The disruption results in the received electrical power being less than the threshold level. Upon the received electrical power becoming less than the threshold level, the comparator triggers powertrain controller60to perform the active discharge operation. In this way, the comparator is used to detect for a shutdown event and, upon detecting a shutdown event, the comparator is used to trigger powertrain controller60to perform the active discharge operation. Consequently, powertrain controller60immediately proceeds with the active discharge operation as soon as a shutdown event occurs to thereby be in the best position to discharge DC-link capacitor62to the certain level within the specific time.

Referring now toFIG.4, with continual reference toFIGS.2and3, a circuit diagram of the traction powertrain and powertrain controller60is shown. Traction battery24, DC-link capacitor62, inverter26, and traction motor14of the traction powertrain are shown. The power switches of inverter26are shown with MOSFET symbols. Gate drivers72and control unit74of powertrain controller60are also shown.

As further shown inFIG.4, powertrain controller60is connected to auxiliary battery30to receive electrical power from the auxiliary battery in order to control inverter26. Particularly, powertrain controller60further includes a DC/DC converter96which converts the electrical power from auxiliary battery30into a sufficient power level for use by control unit74and gate drivers72in controlling inverter26.

As noted above, during the normal operation, the electrical power flow from auxiliary battery30to powertrain controller60is not disrupted and is at a sufficient level for the powertrain controller to be electrically powered in order to control inverter26. However, as further noted above, during certain shutdown events in which the active discharge operation is desired, the electrical power flow from auxiliary battery30is disrupted and is not at a sufficient level for powertrain controller60to be electrically powered in order to perform the active discharge operation.

Accordingly, as further shown inFIG.4, powertrain controller60further includes a super capacitor (C1)90and a charger sub-circuit94. During the normal operation, charger sub-circuit94is configured to charge super capacitor90with electrical power from auxiliary battery30. Charger sub-circuit94limits the charge current in charging super capacitor90. For example, super capacitor90is charged to the charge level of auxiliary battery30(e.g., twelve volts). In turn, when the active discharge operation is required and powertrain controller60is not electrically powered by auxiliary battery30, super capacitor90provides the electrical power for the powertrain controller to operate. Super capacitor90is relatively small but has a capacitance in several farads. That capacity can store the electrical energy for use by gate drivers72, control unit74, and DC/DC converter96during a discharge pulse duration for the active discharge operation.

As further shown inFIG.4, powertrain controller60further includes a comparator (COMP)92. As noted above, comparator92is used to (i) detect a shutdown event by virtue of being used to detect that the electrical power flow from auxiliary battery30to powertrain controller60is disrupted and is not at a sufficient level for the powertrain controller to be electrically powered in order to control inverter26and to (ii) trigger the powertrain controller (now being electrically powered by super capacitor90in order to control the inverter) to perform the active discharge operation upon detecting the shutdown event.

In further detail, as further shown inFIG.4, powertrain controller60further includes, in the electrical configuration shown inFIG.3, low-voltage active switches Q1 and Q2, resistors R1, R2, R3, and R5, a diode D1, a connection Vbahead of diode D1 (auxiliary battery side), a connection X0to control unit74, and a Zener diode Z1. Powertrain controller60may be implemented with a printed circuit board (PCB). In such case, the noted electrical elements of powertrain controller60as well as drivers72, control unit74, super capacitor90, comparator92, charger sub-circuit94, and DC/DC converter96are arranged on the PCB.

During the normal operation, the LV battery voltage Vb(e.g., 12 V) is present and super capacitor90voltage Vcis charged to the 12 V battery voltage. That means:Vb≥7.5 V (7.5 V is a predetermined voltage level used by comparator92)X0=0 (or low level)Q1=OFFQ2=OFF

Consequently, powertrain controller60will continue the normal operation in controlling inverter26(i.e., the powertrain controller will not apply a discharge pulse to the power switches of inverter26pursuant to the active discharge operation).

However, during a shutdown event, the LV battery voltage Vbwill be 0 V, which is below the 7.5 V threshold. Then X0will be equal to 1 or high level to trigger control unit74to control gate drivers72to apply the discharge pulse to the power switches of inverter26pursuant to the active discharge operation. That means:Vb<7.5 VX0=1 (or high level)Q1=ONQ2=ON

Consequently, switches Q1 and Q2 turn ON whereby super capacitor90provides electrical power for gate drivers72, control unit74, and DC/DC converter96to operate, powertrain controller60will apply a discharge pulse to the power switches of inverter26pursuant to the active discharge operation. That is, the discharge pulse is applied over the motor inverter and windings.

The width of the discharge pulse is adjustable and is set by control unit74. For example, the width of the discharge pulse can be 200 μ-sec, 400 μ-sec, etc. (i.e., as long as needed for DC-link capacitor62to be discharged). For the discharge pulse, a discharge pulse command control motor inverter operating at zero-torque condition (e.g., Iq=0 A and Id=100 A) may be implemented. During discharge, powertrain controller60may implement a traction motor Id-Iqcurrent closed control loop to control the discharge current. During discharge, the actual Id-Iqcurrent will track the Id-Iqreference so traction motor BEMF (back electromotive force) cannot affect the discharge operation.

In further detail, one pulse of 200 or 400 μ-sec at 100 A are examples. In reality, the time duration of the discharge pulse and current amplitude can be adjusted by calibration according to specific vehicle condition such as capacitance and DC-bus voltage, etc. Further, before the discharge circuit starts to discharge the DC bus capacitor energy, a controller (e.g., a battery electronic control module (BECM)) usually has opened contactors64and66, so traction battery24disconnects from DC-link capacitor62. For example, when the actual battery voltage Vbis lower than the minimum full function voltage of 7.5 V, then powertrain controller60will not be in the normal vehicle operation state and the BECM will open the contactors. For the proposed discharge strategy, it is capable of long time discharging, because inverter and motor windings can dissipate heat to keep their temperatures low. The proposed discharge strategy utilizes the traction motor's current closed-loop control to maintain discharge current, so the back EMF (BEMF) of the traction motor, even if more than a trivial amount, will not affect DC-link capacitor discharging.

In further detail, the arrangement of comparator92allows changes of the actual battery voltage Vbin a relatively wide range and bypasses oscillating between ON and OFF. In this example, the minimum full function voltage for powertrain controller is 7.5 V. Accordingly, comparator92compares the actual battery voltage Vbwith the reference voltage 7.5 V (from Vc, Zener diode Z1, and resistor R5). If the actual battery voltage Vbis greater than the reference voltage 7.5 V, then the actual battery voltage Vbkeeps providing electrical power and the normal operation of inverter26is not affected. If the actual battery voltage Vbis smaller than the reference voltage 7.5 V, then the connection X0becomes high level and switch Q1 turns ON whereby super capacitor90provides electrical power for gate drivers72, control unit74, and DC/DC converter96to operate. The actual battery voltage Vbkeeps smaller than the reference voltage 7.5 V and the connection X0keeps high level to maintain switch Q1 at ON state while the voltage Vcprovides the electrical power for powertrain controller60to operate as the diode D1 blocks current flow into the auxiliary battery side.

Referring now toFIGS.5A,5B,5C, and5D, with continual reference toFIG.4, circuit diagrams of respective charger sub-circuit versions94a,94b,94c, and94dare respectively shown. As shown, charger sub-circuit94can use discrete components (versions94aand94b) or integrated chip (IC) devices (versions94cand94d).

Charger sub-circuit version94ashown inFIG.5Alimits inrush current by charging capacitor C2. As capacitor C2 charges, the voltage Vgsof switch Q3 increases and allows switch Q3 to turn on slowly. The capacitance of capacitor C2 and the voltage Vgscharacteristic of switch Q3 determine how switch Q3 quickly turns on. Zener diode Z2 prevents switch Q3 from exceeding its maximum rating.

Charger sub-circuit version94bshown inFIG.5Buses PNP switch Q4 and resistor R6 to achieve current sensing and limiting. When current flows through resistor R6 and switch Q3, the voltage across resistor R6 creates the Vbebias for switch Q4. If the current is too high, then switch Q4 turns on and limits conduction of switch Q3 by reducing Vgsof switch Q3.

Charger sub-circuit versions94cand94dshown inFIGS.5C and5Duses few external components by using IC devices. Charger sub-circuit version94cdoes not use a current sensing resistor to limit inrush current. Charger sub-circuit versions94duses a current sensing resistor R6 to limit current.

As described, powertrain controller60implements an active discharge circuitry for discharging a DC-link capacitor of a traction powertrain of an electrified vehicle. In this regard, powertrain controller60can cause inverter26to be operated in a manner in which DC-link capacitor62is discharged to a certain level within a specific time upon commencement of certain shutdown events. Powertrain controller60may meet the certain level and specific time requirements by discharging a main capacitor through the inverter and motor windings within any additional HV level components. Super capacitor90is used to energize the powertrain controller60during a shutdown event. This makes powertrain controller60relatively reliable. Further, powertrain controller60does not use a thermal management strategy such as for preventing overheating of a discharge resistor as no discharge register is utilized. Powertrain controller60just uses LV components which are relatively simple to package.

While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the present disclosure. Rather, 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 present disclosure. Additionally, the features of various implementing embodiments may be combined to form further embodiments of the present disclosure.