Active discharge of electric drive system

Abstract

To provide systems, devices and methods for active discharge of an electric drive system for a vehicle that performs active discharge of capacitance.SOLUTION: An electric drive system 100 for a vehicle comprises: an inverter 125 having at least one phase leg, where a first of the phase legs includes a first power switch; a DC / DC converter configured to generate an internal supply voltage that is regulated with respect to a voltage on a rail 110, 115; and a gate drive channel 150 configured to drive the first power switch into a conducting state by applying a relatively high voltage difference derived during an operation of the vehicle and to continue the driving of the first power switch with a relatively low voltage difference after a signal indicating a shutdown or fault. The DC / DC converter is configured to generate an internal supply voltage that has either a relatively high voltage difference with respect to the voltage on the rail or a relatively low voltage difference with respect to the voltage on the rail.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] Cross - reference to related applications This application claims the priority of European Patent Application No. 21157852.1 filed on February 18, 2021. European Patent Application No. 21157852.1 is incorporated herein by reference in its entirety.

[0002] The present invention relates to the active discharge of an electric drive system.

Background Art

[0003] Electric drive systems are found in electric vehicles, such as by way of example, electric cars and trucks, hybrid electric cars and trucks, and trains and trams. Electric vehicles generally include an inverter that converts a battery or other DC output into an AC signal to drive an electric motor. In these vehicles, relatively large and high - current - capacity energy - storage capacitors are commonly used as intermediate buffers between the battery and the inverter. These capacitors may be referred to as "DC - link capacitors" or "smoothing capacitors". These capacitors smooth the input voltage, provide a low - inductance current path to the inverter output stage, and store energy.

[0004] The electric drive system in a battery - powered electric vehicle is typically shut down (stopped) thousands of times over its operating life. During shutdown, the battery is isolated from the rest of the electric drive system. However, without further means, the intermediate DC - link capacitor holds charge even after being disconnected from the battery. For safety reasons, regulatory agencies often require that this charge be dissipated reasonably quickly after shutdown. For example, a typical regulatory requirement is to discharge the DC - link capacitor to a voltage of less than 60 volts within 2 seconds.

[0005] In some cases, a discharge switch and resistor may be coupled across a DC link capacitor. After disconnection from the battery, this discharge switch is switched to the conduction state, causing the DC link capacitor to discharge through the resistor. [Overview of the project]

[0006] Non-limiting and non-exclusive embodiments of the present invention will be described with reference to the following figures, where similar reference numerals in different figures indicate the same parts unless otherwise specified. [Brief explanation of the drawing]

[0007] [Figure 1] Figure 1 is a schematic diagram of the electrical drive system. [Figure 2] Figure 2 is a schematic diagram of the part of the electrical drive system in Figure 1 that is responsible for controlling the supply of power to the electric motor via the single-phase foot. [Figure 3] Figure 3 is a schematic diagram of the power regulator and the connection between the power regulator and the control device shown in Figure 1. [Figure 4] Figure 4 is a graph showing the output characteristics of IGBTs suitable for use in inverters in the drive systems of electric vehicles. [Figure 5] Figure 5 is a swimlane diagram schematically illustrating the process for the active discharge of a DC link capacitor. [Figure 6] Figure 6 is a schematic diagram of different waveforms in the electrical drive system shown in Figure 1. [Modes for carrying out the invention]

[0008] Similar reference numerals in various drawings indicate similar elements.

[0009] The following description includes many specific details to help you fully understand the present invention. However, it will be apparent to those skilled in the art that these specific details are not necessarily used to carry out the present invention. In other examples, well-known materials or methods are not described in detail to avoid complicating the understanding of the present invention.

[0010] In this specification, any reference to “one embodiment,” “an embodiment,” “an example,” or “an example” means that a particular feature, structure, or characteristic described in relation to an embodiment or example is included in at least one embodiment of the present invention. Therefore, the use of expressions such as “one embodiment,” “an embodiment,” “an example,” or “an example” in various places in this specification does not necessarily relate to the same embodiment or example. Furthermore, a particular feature, structure, or characteristic may be combined in any suitable combination and / or partial combination in one or more embodiments or examples. A particular feature, structure, or characteristic may be included in an integrated circuit, electronic circuit, coupled logic circuit, or other suitable component that provides the function described. In addition, it should be understood that the drawings provided with this specification are intended for those skilled in the art and that the drawings are not necessarily drawn to a fixed scale.

[0011] As mentioned above, regulatory bodies often require that any charge retained in the DC link capacitor after disconnection be dissipated reasonably quickly after shutdown.

[0012] In embodiments of the present disclosure, one or more power switches driving an electric motor may be used to discharge a DC link capacitor. The amount of current conducted by the power switch depends on the difference between the control terminal voltage and the reference terminal voltage of the power switch. A gate drive unit controls the voltage difference between the control terminal and the reference terminal to switch the power switch on and off and to discharge the DC link capacitor. In embodiments, the difference between the control terminal voltage and the reference terminal voltage may be varied to control the conduction of current by the power switch while the DC link capacitor is being discharged.

[0013] Figure 1 is a schematic diagram of the electrical drive system 100. The drive system 100 includes a battery 105 reversibly coupled between the high rail 110 and the low rail 115 by a switch 120. The drive system 100 further includes an inverter 125, an electric motor 130, and a gate drive channel 150. When in operation, based on the instructions of the gate drive channel 150, the inverter 125 converts the DC voltage supplied by the battery 105 into an AC voltage and supplies power to the electric motor 130. A DC link capacitor 135 is coupled between the rails 110 and 115. When the battery 105 is disconnected from the rails 110 and 115 by the switch 120, the DC link capacitor 135 discharges through the inverter 125.

[0014] More specifically, switch 120 is typically a mechanical switch coupled to connect battery 105 to rails 110, 115 and to disconnect battery 105 from rails 110, 115. Under normal conditions, when the vehicle including the drive system 100 is in operation, for example, when it is moving or ready to move, battery 105 is connected to rails 110, 115. Battery 105 is disconnected from rails 110, 115 during a shut-off (stop) or in the event of a very severe abnormal condition.

[0015] When the battery 105 is connected to rails 110 and 115, both the DC link capacitor 135 and the inverter 125 are biased by the battery 105. The voltage generated across the DC link capacitor 135 tends to be the same as the voltage provided by the battery 105. However, a deviation from the same value occurs because the DC link capacitor 135 allows and provides a faster charge than the battery 105. In addition, the DC link capacitor 135 is generally located closer to the power switch of the inverter 125 and at a certain distance from the battery 105. Cable inductance can result in high transient voltage events. Therefore, the DC link capacitor 135 functions to smooth the voltage across rails 110 and 115 on the inverter 125.

[0016] Each inverter 125 may include an assembly of phase legs formed by pairs of switching devices coupled in series between rails 110 and 115. Generally, the switching devices are insulated-gate bipolar transistors (IGBTs) or other power semiconductor devices. Other power semiconductor devices may include transistors such as gallium nitride (GaN)-based transistors, silicon (Si)-based transistors, or silicon carbide (SiC)-based transistors. Other transistors, such as metal-oxide-semiconductor field-effect transistors (MOSFETs) or bipolar junction transistors (BJTs), may also be used. The switching of the switching devices is driven by a gate driver circuit 140 under the control of a control device 145. The gate driver circuit 140 is configured to appropriately bias the switching devices in the inverter 125 according to control signals received from the control device 145. The control device 145 is configured to generate control signals in response to higher levels of control signals. Examples of higher-level control signals include, for example, indications that the vehicle speed can be increased or decreased. In some embodiments, a control signal from the control unit 145 may specify a switching pattern used by the gate driver circuit 140 to bias the switching devices in the inverter 125. For example, a control signal from the control unit 145 may be a pulse-width modulated switching pattern that is converted by the gate driver circuit 140 into a signal suitable for driving the switching devices in the inverter 125. In other embodiments, a control signal generated by the control unit 145 is of a higher level and is used by the gate driver circuit 140 to generate a switching pattern.The control device 145 may be implemented, for example, as a microcontroller located on the same printed circuit board (PCB) as the gate driver circuit 140. In other embodiments, the control device 145 may be implemented as a microcontroller located on a different PCB from the gate driver circuit 140. Similar to the inverter 125, the gate driver circuit 140 may be referenced to the rail 115. The control device 145 may also be referenced to the rail 115, or to a different voltage, or may include several components referenced to the rail 115 and other components referenced to a different voltage.

[0017] In either case, the gate driver circuit 140 and the control device 145 can be considered as part of a gate drive channel 150 that controls the supply of power to the electric motor 130 by appropriately driving the switches in the inverter 125. As will be described in detail below, the control device 145 may further control the switching of one or more of the switching devices in the inverter 125 in order to discharge the DC link capacitor 135 when the battery 105 is disconnected from the rails 110, 115 by the switch 120.

[0018] Figure 2 is a schematic diagram of a part of the circuit in the electrical drive system 100, specifically the part responsible for controlling the supply of power to the electric motor 130 via the single-phase foot.

[0019] More specifically, the electrical drive system 100 includes a power supply 205. Generally, the power supply 205 has an internal power supply voltage (i.e., V) between its output rails 210, 212. ISO -V COM ) is configured to generate. As shown, power supply 205 receives input rails 350, 355 and generates output rails 210, 212. In some embodiments, the high rail 110 and low rail 115 may, but not necessarily, function as input rails 350, 355. Referring to DIN72552, contacts 30 / 31 may be coupled to input rails 350, 355.

[0020] On the shown low side of the electric drive system 100, a voltage V ISO from V COM to V EE is associated with an intermediate output that is coupled to the low rail 115 of the battery 115. In the corresponding high side of the electric drive system 100 that controls the switching of the IGBT 240, the intermediate output of the second power regulator is coupled to the intermediate node, i.e., the output node 250, at the phase leg 2,60 of the inverter 125.

[0021] Returning to the shown low side of the electric drive system 100, in an example where the intermediate output 215 of the power supply 205 is coupled to the low rail 115, the voltage V ISO 210 is in a voltage range suitable for driving the power switch 245 and is referenced to the rail 115. Further, the voltage V COM 212 is selected to achieve the off-switching gate voltage of the IGBT 245. In one example, the voltage V COM 212 is low with respect to the voltage at the rail 115. In another embodiment, the voltage V COM 212 can be substantially equal to the voltage V EE 215. Thanks to the conversion result implemented by the power supply 205, the voltage difference between the high power rail 210V ISO the low power rail 212V COM and the intermediate output 215V EE can be substantially constant in the face of changes in the load state during vehicle operation. These load states include the vehicle speed and can be reflected in the switching frequency of the power switch 245. Further, the magnitude of the voltage difference between V ISO V EE and V COM is selected to provide an effective on-switching voltage and off-switching voltage for the IGBT 245. Further, V ISO V EE and V COM can be used to provide an effective power supply voltage to the internal circuit of the gate driver 140. For example, V ISO and VCOM The voltage difference between the two can be between 15V and 30V (e.g., 20 volts). While the vehicle is running, V EE and V COM The voltage difference between them can be, for example, 0 volts to 10 volts (for example, 5 volts), and therefore the voltage V at rail 212 COM This is less than or equal to the voltage at the low rail 115.

[0022] As will be described in detail below, when the battery 105 is disconnected from rails 110 and 115, the voltage difference between rails 210 and 212 can be changed to discharge the DC link capacitor 135. This change can be made by the power supply 205 based on instructions from the control unit 145. For this purpose, the control unit 145 is coupled to the power supply 205 by one or more signal lines 270, so that, for example, the control unit 145 can notify the power supply 205 of the start of an active discharge mode, and the power supply 205 can provide the control unit with information related to the change in the voltage difference between rails 210 and 212.

[0023] At least a portion of the gate drive channel 150 is in the circuitry of the drive system 100, which is powered by rails 210 and 212. An illustrated embodiment of a portion of the gate drive channel 150 includes a gate driver 140, a pull-up transistor 225, a pull-down transistor 230, and a gate resistor 232. The gate driver 140 is configured to receive control signals and to control transistors 225, 230 according to those control signals. The pull-up transistor 225 is coupled between the high-power rail 210 and the output node 235 of the gate drive channel, and the pull-down transistor 230 is coupled between the output node 235 and the low rail 212. The gate resistor 232 conducts the drive signal from the output node 235 to the IGBT 245.

[0024] Other embodiments of this part of the gate drive channel 150 are also possible. For example, instead of including the output node 235, the gate 245 of the IGBT may be pulled up and pulled down using different channels, each containing one transistor and one gate resistor, which alternately couple the gate of the IGBT 245 to their respective rails.

[0025] The indicated portion of the electrical drive system 100 further includes one phase foot 260 of the inverter 125. The phase foot 260 includes a pair of IGBTs 240, 245 coupled in series between the positive rail 110 and the low power rail 115. The output node 250 of the inverter 125 is located between the IGBTs 240, 245 and is reversibly coupled to either the positive rail 110 or the low power rail 115 when each of the IGBTs 240, 245 is switched to the conducted state.

[0026] Note that while the control terminals (i.e., gates) of each IGBT 240, 245 are coupled to their respective parts in the gate drive channel 150, only the coupling of IGBT 245 is shown in the schematic diagram. Furthermore, the inverter 125 includes additional phase feet (for example, three or four phase feet in total).

[0027] During operation, the gate driver 140, in combination with the rest of the gate drive channel 150, coordinates the switching of IGBTs 240 and 245 and other switches at the other feet of the inverter 125 to supply power to the motor 130. When IGBT 245 is biased to the conducted state, the pull-down transistor 230 is driven to the non-conductive state by the gate driver 140 and the pull-up transistor 225 is driven to the conducted state. Conduction through the pull-up transistor 225 positively biases IGBT 245 to the low power rail 215 and puts it into the conducted state. Current can flow through the motor 130 and IGBT 245 to the low power rail 115. When IGBT 245 is biased to the non-conductive state, the gate driver 140 drives the pull-up transistor 225 to the non-conductive state and the pull-down transistor 230 to the conducted state. Conduction through the pull-down transistor 230 negatively biases the gate of the IGBT 245 to the low power rail 115 and makes it non-conductive. Power supply 205 is voltage V ISO , V EE , V COM Since it supplies this voltage, the rail 212 can negatively bias the gate of the IGBT 245, ensuring proper shut-off. However, as described above, in alternative embodiments, the voltage at rail 215 may be substantially equal to the voltage at rail 212.

[0028] For example, during vehicle operation, power supply 205 is connected to rail 210's V ISO and rail 212 V COM A 20-volt voltage difference is supplied between and V EE is V COM Let's assume it's about 5 volts higher. Therefore, V ISO and V EE The voltage difference between them is approximately 15 volts. When pull-down transistor 230 is in a conducted state and pull-up transistor 225 is not conducted, the gate of IGBT245 is V EEIt is biased 5 volts lower, and therefore lower than the emitter of the IGBT245. Off switching of the IGBT245 is guaranteed. When the pull-up transistor 225 is in a conducted state and the pull-down transistor 230 is not conducted, the gate of the IGBT245 is V EE It is positively biased by 15 volts (15 volts from the emitter of the IGBT245). The ON switching of the IGBT245 is guaranteed, and the IGBT245 conducts with a given transconductance.

[0029] Figure 3 is a schematic diagram of an embodiment of a portion of the power supply 205 and the coupling between the power supply 205 and the control unit 145. The shown embodiment of the power supply 205 is a full-bridge DC / DC converter and includes a bridge control unit 305, a transistor bridge 310, a transformer 315, a capacitor 319, and a rectifier 320. In particular, the power supply 205 is shown as a full-bridge LLC converter. Other DC / DC converter topologies are also possible. Regardless of the specific DC / DC converter topology, the power supply 205 has an internal power supply voltage V between the high power rail 210 and the low rail 212. ISO -V COM It supplies the internal power supply voltage V. In some embodiments, the internal power supply voltage V ISO -V COM This can be adjusted, but it is not always the case. Note that the voltage V at the intermediate output 215 (not shown) EE Voltage V is controlled by many different methods, including, for example, voltage dividers containing resistors, Zener diodes, and / or other elements coupled between rails 210 and 212. ISO , V COM It can be set between. More specifically, the transistor bridge 310 includes transistors 330, 335, 340, and 345 coupled between pairs of DC power rails 350 and 355. Given the turns ratio of the transformer 315, the bridge control device 305 uses the transistor bridge 310 as a full bridge, for example by a voltage mode control scheme, to create an internal power supply voltage difference V between the high power rail 210 and the low rail 212. ISO -V COMDC power rails 350, 355 supply a DC voltage at a level capable of generating [the specified voltage]. In one embodiment, the bridge control device 305 and transistors 330, 335, 340, 345 may be formed as part of an integrated circuit manufactured as either a hybrid integrated circuit or a monolithic integrated circuit. As shown, transistors 330, 335, 340, 345 are shown as n-type MOSFETs, but it should be understood that other transistors may be used.

[0030] When using bridge 310 as a full bridge, the bridge control device 305 can switch transistors 335 and 340 to a conducted state while maintaining transistors 330 and 345 in a non-conductive state. In this configuration, the voltage difference between rails 350 and 355 minus the voltage across capacitor 319 is applied to the input winding of transformer 315. In other words, the voltage across the input winding is (assuming the voltage drop across the switch is negligible) the voltage at rail 350 minus the voltage at rail 355 minus the voltage across capacitor 319. Subsequently, the bridge control device 305 can switch transistors 335 and 340 to a non-conductive state and transistors 330 and 345 to a conducted state. In this configuration, the voltage difference between rails 355 and 350 minus the voltage across capacitor 319 is applied to the input winding. In other words, the voltage across the input winding is (similarly, assuming that the voltage drop across the switch is negligible) the voltage across rail 355 minus the voltage across rail 350, minus the voltage across capacitor 319. Thus, positive and negative pulse trains of AC current are applied to the input winding and converted into corresponding AC signals in the output winding of transformer 315 according to the turns ratio and polarity of the winding. Rectifier 320 rectifies the AC signals in the output winding to create an internal power supply voltage difference V between the high-power rail 210 and the low-power rail 212. ISO -V COM Generates.

[0031] The control device 145 is further configured to notify the bridge control device that the DC link capacitor 135 is discharged. In response, the bridge control device 305 may use the bridge 310 as a half-bridge. For example, the bridge control device 305 may alternately switch between transistors 330, 335, 340, and 345, keeping one of them in a conducted state and another in a non-conductive state, regardless of which of the transistors 330, 335, 340, and 345 is connected to the other terminals of the input winding of the transformer 315.

[0032] As an example, assume that the bridge control device 305 keeps transistor 340 in a conducted state and transistor 330 in a non-conductive state. When transistor 345 is in a non-conductive state and transistor 335 is in a conducted state, the voltage applied to the input winding of transformer 315 is the voltage difference between rails 350 and 355 minus the voltage across capacitor 319. In other words, the voltage across the input winding is the voltage at rail 350 minus the voltage at rail 355 minus the voltage across capacitor 319. In a half-bridge configuration, the voltages across capacitor 319 and the inductor of transformer 315 settle at about half the voltage difference between rails 350 and 355. This lowers the voltage across the input winding of transformer 315 and reduces the difference generated between the high-power rail 210 and the low-power rail 212. In contrast, when transistor 335 is in a non-conductive state and transistor 345 is in a conducted state, no voltage difference is applied across the capacitance and the input winding of transformer 315. Therefore, a positive pulse is converted into a corresponding AC signal in the output winding of transformer 315, and after rectification by rectifier 320, a smaller difference is generated between the high-power rail 210 and the low-power rail 212. In other words, a lower voltage across the input winding of transformer 315 results in a smaller difference being generated between the high-power rail 210 and the low-power rail 212.

[0033] As described above, the control device 145 may instruct the gate driver 140 to synchronize the switching of the switches at the base of the inverter 125 in order to supply power to the motor 130. However, the control device 145 may further control the gate driver 140 to synchronize the switching of the switches at the base of the inverter 125 in order to actively discharge the DC link capacitor 135 (Figure 1).

[0034] Referring again to Figure 2, when IGBT245 is switched to become non-conductive or non-conductive, alternating conduction through pull-up transistor 225 and pull-down transistor 230 positively or negatively biases the gate of IGBT245 with respect to the low power rail 115. The magnitude of the bias is V ISO and V EE The voltage difference between, or V EE and V COM This is the voltage difference between the two points.

[0035] When the bridge control device 305 uses the bridge 310 as a half-bridge, V ISO and V COM The voltage difference between them becomes smaller. Voltage V at low rail 212 COM is V EE The gate of the IGBT245 remains negatively biased for effective off-switching, but the impedance of the IGBT245 is increased, and the current flowing through the IGBT245 is reduced, so the voltage between the gate and emitter of the IGBT (i.e., V) remains low. GE ) is V ISO and V EE The voltage difference between these points alters the output characteristics of the IGBT245.

[0036] This change in the output characteristics of the IGBT245 can be used to actively discharge the DC link capacitor 135 without damaging the IGBT240,245. In particular, as mentioned above, the DC link capacitor 135 (and rails 110,115) maintain a high voltage after being disconnected from the battery. If the IGBT240,245 is driven with high transconductance to discharge this high voltage, this can approximate a short circuit. The current can be relatively large and can damage the IGBT240,245. In contrast, V ISO and V EE By driving at least one of the IGBTs 240, 245 with a relatively small voltage difference between them and with lower transconductance, the current can be kept low enough to avoid damage.

[0037] It should be noted that various different approaches may be used to adjust the net impedance across the phase foot 260 in order to actively discharge the DC link capacitor 135. For example, - While IGBT245 is actively switched with relatively low transconductance and higher impedance output characteristics, IGBT240 can be kept in a conducted state. - While IGBT240 is actively switched with relatively low transconductance, IGBT245 can be maintained in a conducted state. Or, - Both IGBT240 and 245 can be actively switched, provided that at least one of them has relatively low transconductance.

[0038] When both IGBT240 and 245 are actively switched, their switching is generally synchronized so that IGBT240 and 245 open and close in harmony. However, this is not always the case. For example, while IGBT240 may begin to transition to a higher conductive ON state (i.e., a state with relatively high or low transconductance), IGBT245 initially remains in a nonconductive state. IGBT245 may begin to transition to a higher conductive state at some point during or after the ON state transition of IGBT240 in order to further adjust the next impedance across the phase foot 260 to the operating state. All that is required is that a current path is formed between rails 110 and 115 with relatively low transconductance.

[0039] Furthermore, to leave no room for doubt, other phases in inverter 125 may also be involved in active discharge. In either case, a short circuit between rails 110 and 115 is avoided, with at least one IGBT acting as a more resistive element. However, that IGBT still provides a current path for the active discharge of DC link capacitor 135.

[0040] Furthermore, as described later, the switching patterns of one or both of the IGBTs 240 and 245 during active discharge can be defined by the control device 145, by the gate drive unit 140, or by both the control device 145 and the gate drive unit 140.

[0041] Figure 4 is graph 400, which shows the output characteristics of IGBTs suitable for use in inverters in electric vehicle drive systems, such as IGBT240 and 245. The positions along the x-axis in graph 400 represent the voltage difference between the collector and emitter of the IGBT (i.e., V), expressed in volts. CE ) represents the collector current (i.e., I) expressed in amperes. The position along the y-axis represents the collector current expressed in amperes. C ) represents the different curves 405, 410, 415, 420, 425, and 430, each representing a different voltage (i.e., V) between the gate and emitter of the IGBT.GE ) is related to. For example, curve 405 is related to V GE When V is 19 volts CE and I C Curve 410 shows the relationship between V GE When V is 17 volts CE and I C Curve 415 shows the relationship between V GE When V is 15 volts CE and I C Curve 420 shows the relationship between V GE When V is 13 volts CE and I C Curve 425 shows the relationship between V GE When V is 11 volts CE and I C Curve 430 shows the relationship between V GE When V is 9 volts CE and I C This shows the relationship between V. GE As the value decreases, the slopes of curves 405, 410, 415, 420, 425, and 430 become smaller, and the resistance of the IGBT increases.

[0042] Generally, graphs such as Graph 400, provided by IGBT suppliers, can be easily used to adjust the voltages and values ​​of different components for a particular operating environment.

[0043] Figure 5 is a swimlane diagram schematically representing process 500 for the active discharge of a DC link capacitor. In the context of the electrical drive system described above, actions in the control unit lane may be performed by the control unit 145, actions in the bridge control unit lane may be performed by the bridge control unit 305, and actions in the gate driver lane may be performed by the gate driver 140. While process 500 may be performed in the context of these specific components, process 500 can be further adapted to other electrical drive systems. For example, in some embodiments, one physical device may provide functions assigned to different control units. For instance, a bridge control unit and a gate driver may be mounted on a single printed circuit board. Nevertheless, the process and / or logic may be considered separately.

[0044] In step 500, the control device may signal the start of the active discharge mode in step 505. The control device may signal the start of the active discharge mode in response to one or more higher level signals, such as a signal indicating the termination of device operation or a signal indicating the occurrence of a very severe abnormal condition. The start of the active discharge mode can be signaled by many different methods. For example, a signal at a special active discharge terminal may indicate the start.

[0045] As described above, in some embodiments, a control signal from the control unit may specify a switching pattern used by the gate driver to bias the switching devices in the inverter. In these embodiments, such a control signal is terminated before the start of the active discharge mode. In some embodiments, the termination of the switching pattern may signal the start of the active discharge mode.

[0046] In some embodiments, the bridge control unit and gate driver may be implemented in a single physical device, for example, they may be implemented on a single gate driver printed circuit board. In another embodiment, the bridge control unit and gate driver may be formed as part of an integrated circuit manufactured as either a hybrid integrated circuit or a monolithic integrated circuit. In such cases, the start of the active discharge mode may be signaled using the same terminal that transmits a control signal specifying how the switching device in the inverter is biased. For example, after the appropriate absence of a control signal, a special active discharge mode start signal may be sent by the control unit to the combined bridge control unit / gate driver device.

[0047] In response to receiving a signal indicating the start of the active discharge mode, the bridge control unit may, at 510, switch the transistor bridge from full-bridge drive to half-bridge drive. As described above, this results in a decrease in the output voltage of the DC / DC converter. The bridge control unit may, at 515, continue driving the transistor bridge as a half-bridge. In one example, the bridge control unit may drive the transistor bridge as a half-bridge while monitoring the output of the DC / DC converter. This monitoring may depend on the components in the DC / DC converter involved in output regulation; that is, no further components or modifications to the DC / DC converter are required.

[0048] Furthermore, in 520, the bridge control device can identify undervoltage conditions at the DC / DC converter output. Generally, DC / DC converters monitor for undervoltage conditions without requiring the DC link capacitor to be actively discharged. This is done to identify potential anomalies and to ensure proper calculation of the electrical drive system. In some embodiments, this same function may be relied upon in an active discharge mode, and no further components or modifications to the DC / DC converter are required. However, the time required for the DC / DC converter output voltage to drop below the undervoltage threshold can vary between different DC / DC converters, typically requiring a time between 1 and 10 milliseconds.

[0049] At 525, the control device 145 receives a signal indicating an undervoltage condition. In response, at 530, the control device notifies the gate driver unit to start active discharge switching. As described above, in some embodiments, the control signal from the control device may specify a particular switching pattern used by the gate driver circuit. In such embodiments, the control device may notify the start of active discharge by transmitting an active discharge switching pattern. For example, the active discharge switching pattern may be a pulse-width modulated pulse train. The pulses for active discharge may have a higher frequency / shorter duration than the pulses in the switching pattern used during vehicle operation.

[0050] As another example, in some embodiments, the control signal generated by the control device 145 is at a higher level and is used by the gate driver circuit 140 to generate an active switching pattern during active discharge.

[0051] In yet another different example, in some embodiments, the active discharge switching pattern is partially determined by the control device 145 and partially determined by the gate driver circuit 140. For example, the control device 145 may transmit an indication of when one or both of the IGBTs 240 and 245 switch to the conduction state, without any associated indication of when the IGBTs 240 and 245 switch to the non-conduction state. Rather, the timing of when the IGBTs 240 and 245 switch to the non-conduction state may be determined by the gate driver circuit 140.

[0052] In some embodiments, a desaturation protection function in the gate driver circuit 140 may be used to specify when the IGBTs 240 and 245 are switched to a non-conductive state. In this context, desaturation protection is a function implemented by the gate driver circuit to protect the driven switches (e.g., IGBTs 240 and 245) from currents that could, for example, damage the device. An overcurrent or short circuit is detected in the protected device, and in response, the device is switched to a non-conductive state. It is generally important that the device is switched to a non-conductive state as quickly as possible. For this purpose, desaturation protection is usually implemented by a gate driver circuit directly coupled to the device and can respond without delay.

[0053] In the context of active discharge, the gate driver circuit 140 may provide desaturation protection and monitor the voltage across one or both of the IGBTs 240 and 245. Typically, the driver circuit 140 compares the voltage across one or both of the IGBTs 240 and 245 to a threshold to determine whether a desaturation or short-circuit condition exists. If the voltage across the IGBTs 240 and 245 is greater than the threshold, the gate driver circuit triggers IGBT protection and switches the IGBTs off. This process may be used during active discharge to specify when the IGBTs 240 and 245 are switched off. In particular, the gate driver circuit 140 switches the IGBTs 240 and 245 off in response to the detection of a desaturation / short-circuit condition.

[0054] This approach can offer several advantages. For example, desaturation protection is generally already present in modern gate driver circuits. Furthermore, since desaturation protection relies on detecting current or voltage within the driven switch, using desaturation protection to define part of the active discharge switching pattern intrinsically adjusts the active discharge switching pattern not only for the driven switch but also for its operating state (e.g., temperature).

[0055] In either case, the process proceeds further to block 532, where an active discharge switching pattern is realized by a gate driver driving the switching of transistors to the ON and OFF states according to the active discharge switching pattern.

[0056] Either or both of the control unit and the gate driver may monitor the voltage across the DC link capacitor during active discharge. In 535, it is determined whether the DC link capacitor is sufficiently discharged. If the DC link capacitor is not sufficiently discharged, the control unit 145 continues to provide the active discharge switching pattern. If the DC link capacitor is sufficiently discharged, in 540, the termination of the active discharge mode is notified. In the shown embodiment, the control unit determines that the DC link capacitor is sufficiently discharged and notifies both the bridge control unit and the gate driver of the termination of the active discharge mode. In an embodiment where the gate driver determines whether the DC link capacitor is sufficiently discharged, the gate driver notifies the bridge control unit and the control unit of the termination of the active discharge mode. In either case, in 550, the active discharge switching scheme is terminated. After the active discharge scheme is terminated, in block 545, the bridge control unit performs DC / DC conversion and V ISO -V COM For generation, it can switch from a half-bridge to a full-bridge, and the gate driver terminates the control to switch the transistor on and off according to an active discharge switching scheme.

[0057] Figure 6 is a schematic diagram of different waveforms in the electrically driven system 100. All waveforms are shown as a function of time and span a window, during which the voltage across the DC link capacitor 135 is actively discharged. For example, the waveforms may span a short window during a shutdown or response to a very severe abnormal condition and immediately following them.

[0058] Waveform 605 represents the signals to start and end the active discharge mode. In the context of Figure 2, the active discharge control signal may be transmitted from the control unit 145 to the power supply 205 via a communication line assigned to carry the signals to start and end the active discharge mode, for example. Waveforms 610 and 615 represent the voltages applied by the bridge control unit to two control terminals of the transistors in the transistor bridge, which is both full-bridge (before T2) operation and half-bridge (between T2 and T4) operation. Waveform 620 represents the voltage V on the high power rail. ISO Voltage V at rails 210 and 212 COM This represents the voltage difference between the two. Waveform 625 represents the voltage across the DC link capacitor 135. Waveform 630 represents the drive voltage applied to the control terminal of IGBT 245 (or another IGBT involved in the active discharge of the DC link capacitor 135).

[0059] Before time point T1, waveform 605 indicates that the bridge control device causes the bridge to operate as a full bridge, i.e., out of active discharge mode. As a result, the bridge control device causes the transistors in the transistor bridge to operate as a full bridge. For example, waveform 610 may represent the drive signal applied to the control terminal of transistor 335, and waveform 615 may represent the drive signal applied to the control terminal of transistor 345. Transistors 335 and 345 are alternately switched between the conducted and non-conductive states and participate in generating the AC signal applied to transistor 315. As shown in waveform 620, the voltage V on the high power rail... ISO Voltage V at rails 210 and 212 COM A regulated and relatively high voltage difference is generated between them. As shown in waveform 630, the gate-to-emitter voltage of IGBT245 (or other IGBTs involved in the active discharge of DC link capacitor 135) is continuously pulled up and pulled down. As shown, the drive of IGBT245 does not need to be continuous. For example, when an electric vehicle is in an "idling state", the motor 130 does not need to be driven.

[0060] At time T1, the control device 145 starts the active discharge mode by, for example, transitioning waveform 605 to the high state. In the illustrated embodiment, the control device 145 maintains waveform 605 in the high state throughout the active discharge mode. Other provisions for notifying the start and end of the active discharge mode are also possible.

[0061] After the delay, the bridge control device starts to operate the bridge as a half-bridge, that is, in the active discharge mode. While the transistors in the bridge driven by waveform 610 are maintained in the conducting state, the transistors driven by waveform 615 are maintained in the non-conducting state. The other transistors in the bridge can be alternately switched by a technique similar to the switching in waveforms 610 and 615 before T1.

[0062] In response to the switching to operation as a half-bridge, the magnitude of the voltage generated by the DC / DC converter (that is, the voltage V at the high power rail ISO 210 and the voltage V at the low rail 212 COM The voltage difference between) becomes smaller. This further reduces the voltage difference between the voltage V at the high power rail ISO 210 and the voltage V at the intermediate output 215 EE That is, the gate-to-emitter voltage of the voltage of the IGBT 245 or other IGBTs involved in the active discharge of the DC link capacitor 135 is reduced.

[0063] By time t3, the voltage generated by the DC / DC converter has dropped below the undervoltage level 640. In some embodiments, the undervoltage level 640 can remain the same in both the active discharge mode and other (e.g., operating) modes. The same function can be relied upon and no further components or modifications to the DC / DC converter are required.

[0064] After the voltage generated by the DC / DC converter drops below the undervoltage level 640 at T3, the gate-to-emitter voltage of the IGBT, i.e., waveform 630, becomes pulsed with pulse train 635, each pulse train 635 being just enough to bias the IGBT 245 into a conducted state with limited transconductance. The voltage across the DC link capacitor 135, i.e., waveform 625, discharges. Then, at time t4, the voltage across the DC link capacitor 135 has dropped to a sufficiently low level that the active discharge using pulse 635 can be considered terminated. The control device 145 signals the end of the active discharge mode, for example, by transitioning waveform 605 to a low state.

[0065] After the active discharge mode ends, the vehicle may, for example, completely shut down or even resume operation. For example, to shut down, the bridge control unit may allow the operation of the transistor bridge to end. Generally, the voltage across the DC link capacitor 135 may continue to decrease over time due to power consumption by other components. Alternatively, to resume operation, the bridge control unit may resume operating the bridge as a full bridge.

[0066] As mentioned above, waveforms 605, 610, 615, 620, 625, and 630 only occur during and immediately after shutdown, or in response to and immediately after a very severe abnormal condition, within a short window.

[0067] The above description of examples shown relating to the present invention, including matters described in the abstract, is not intended to be exhaustive or to be a limitation to the disclosed forms themselves. While specific embodiments and examples of the present invention are described herein for illustrative purposes only, various equivalent modifications are possible without departing from the broader spirit and scope of the invention. Indeed, it is understood that specific and exemplary voltages, currents, frequencies, output range values, times, etc., are presented for illustrative purposes and other values ​​may be used in other embodiments and examples as taught in the present invention. For example, instead of controlling the impedance output characteristics of a power switch in an inverter, the impedance output characteristics of a power switch in a DC / DC converter connected to rails 110, 115 may be controlled and used to discharge a DC link capacitor 135. Such a DC / DC converter may be used to power other components in a vehicle.

[0068] In consideration of the detailed description above, these modifications may be applied to examples of the present invention. The terms used in the claims described below should not be construed to limit the present invention to the specific embodiments disclosed in the specification and claims. Rather, the scope must be defined entirely by the claims described below, and the claims must be construed in accordance with established principles of claim interpretation. Accordingly, this specification and the figures should be considered illustrative and not limiting.

[0069] Although the present invention is defined in the claims, it should be understood that the present invention may be defined by the following examples instead.

[0070] Example 1. An electrical drive system for a vehicle, comprising: an inverter including at least one phase foot, wherein the first phase foot of the phase foot includes a first power switch; a DC / DC converter configured to generate an internal power supply voltage regulated to a voltage in a rail configured to be coupled to a DC power supply, wherein the DC / DC converter is configured to generate an internal power supply voltage having a relatively high voltage difference to the voltage in the rail or a relatively small voltage difference to the voltage in the rail; and a gate drive channel configured to drive a first power switch into a conducted state by applying a relatively high voltage difference derived from the internal power supply voltage during the operation of the vehicle, wherein the gate drive channel is configured to continue driving the first power switch using a relatively small voltage difference derived from the internal power supply voltage after a signal indicating vehicle shutdown or abnormality.

[0071] Example 2. The electrical drive system according to Example 1, comprising a DC / DC converter, a transistor bridge, and a coupled bridge control device configured to receive a discharge command and, in response to the discharge command, to switch from driving the transistor bridge as a full bridge to driving the transistor bridge as a half bridge.

[0072] Example 3. The electrical drive system according to Example 1 or Example 2, wherein the gate drive channel is configured to pulse drive a first power switch after a signal indicating vehicle shutdown or malfunction.

[0073] Example 4. The electrical drive system according to Example 3, wherein the gate drive channel is configured to pulse drive a first power switch over a time window defined in relation to the time required to discharge the capacitance coupled across the phase feet of the inverter.

[0074] Example 5. An electrically driven system according to any one of Examples 1 to 4, wherein the DC / DC converter further comprises a capacitor and a transformer including input and output windings, and the capacitor is coupled to the input winding of the transformer.

[0075] Example 6. An electrically driven system according to any one of Examples 1 to 5, wherein the first phase foot of the phase foot comprises a second power switch, and the gate drive channel is further configured to drive the second power switch over a time window.

[0076] Example 7. The electrical drive system according to Example 6, wherein the gate drive channel is configured to drive a second power switch with a transconductance higher than the transconductance of the first power switch over a time window.

[0077] Example 8. A vehicle equipped with an electrical drive system as described in any one of Examples 1 through 7.

[0078] Example 9. A control system configured to control a power switch having a first terminal, a second terminal and a control terminal, wherein the conductance between the first terminal and the second terminal of the power switch corresponds to the difference between the voltage at the control terminal and the voltage at the second terminal, and the control system comprises a power capacitor coupled between the positive rail and the negative rail of the control system, and a DC / DC converter configured to detect a discharge command in the control system, wherein the discharge command causes the power capacitor to start active discharge, and the DC / DC converter is configured to switch from generating an internal power supply voltage with a relatively large voltage difference to generating a power supply voltage with a relatively small voltage difference, and the DC / DC converter is configured to output a signal indicating that the internal power supply voltage has fallen below a threshold, and a switch control device coupled to receive a signal indicating that the internal power supply voltage has fallen below a threshold, wherein the switch control device is configured to control the difference between the voltage at the control terminal and the voltage at the second terminal based on a power supply voltage with a relatively small voltage difference in response to the signal indicating that the internal power supply voltage has fallen below a threshold.

[0079] Example 10. The control system according to Example 9, wherein the DC / DC converter comprises a transistor bridge and a bridge control device coupled to receive a discharge command, the bridge control device configured to switch in response to the discharge command from driving the transistor bridge as a full bridge to driving the transistor bridge as a half bridge.

[0080] Example 11. A control system described in any one of Examples 9 through 10, wherein the discharge command is a shutdown command.

[0081] Example 12. A control system according to any one of Examples 9 to 11, wherein the switch control device is configured to receive high-level commands by converting them into switching patterns for controlling the difference between the voltage at a control terminal and the voltage at a second terminal.

[0082] Example 13. A control system according to any one of Examples 9 to 12, wherein the DC / DC converter is configured to output an undervoltage signal indicating that the internal power supply voltage has dropped below a threshold.

[0083] Example 14. A control system according to any one of Examples 9 to 13, wherein the power switch is part of the phase foot of an inverter that includes multiple phase foots.

[0084] Example 15. A vehicle equipped with a control system described in any one of Examples 9 through 14.

Claims

1. 1. A control system configured to control a power switch having a first terminal, a second terminal and a control terminal, wherein a conductance between the first terminal and the second terminal of the power switch is responsive to a difference between a voltage at the control terminal and a voltage at the second terminal, the control system comprising: a power supply capacitor coupled between a high rail and a low rail, the power switch being coupleable between the high rail and the low rail and drivable to discharge the power supply capacitor; 1. A DC / DC converter configured to generate an internal power supply voltage, comprising: A switch controller may control a difference between the voltage at the control terminal of the power switch and the voltage at the second terminal of the power switch based on the internal power supply voltage; The DC / DC converter is configured to detect a discharge command in the control system, the discharge command indicating that an active discharge of the power supply capacitor is to be initiated, and in response to receiving the discharge command, the DC / DC converter: generating the internal power supply voltage with a relatively large voltage difference suitable for driving the power switch with a high mutual conductance; generating the internal power supply voltage with a relatively small voltage difference suitable for driving the power switch with low transconductance, and keeping a current discharging the power supply capacitor sufficiently low to avoid damage to the power switch; It is configured to switch the DC / DC converter is further configured to output an undervoltage signal indicating that the internal power supply voltage has dropped below a threshold, the undervoltage signal indicating an abnormal potential condition in the DC / DC converter; the power supply capacitor; a switch control device coupled to receive the under-voltage signal indicating that the internal power supply voltage has dropped below the threshold after the DC / DC converter has received the discharge command and switched to generating the internal power supply voltage with the relatively small voltage difference, wherein in response to receiving the under-voltage signal, the switch control device is configured to specify an active discharge switching pattern to be used by a gate driver circuit to control the difference between the voltage at the control terminal of the power switch and the voltage at the second terminal of the power switch based on the internal power supply voltage with the relatively small voltage difference; Equipped with Control system.

2. The DC / DC converter, A transistor bridge; a bridge controller coupled to receive the discharge command, the bridge controller configured to switch from driving the transistor bridge as a full bridge to driving the transistor bridge as a half bridge in response to the discharge command; Equipped with The control system of claim 1 .

3. The discharge command is a shutdown command. The control system of claim 1 .

4. the switch control device is configured to receive high level commands and to convert the high level commands into a switching pattern for controlling the difference between the voltage at the control terminal and the voltage at the second terminal. The control system of claim 1 .

5. the switch control device comprising a gate driver circuit including a desaturation protection circuit, the desaturation protection circuit specifying when conduction of the power switch ceases during the active discharge; The control system of claim 1 .

6. the power switch is part of a phase leg of an inverter including a plurality of phase legs; The control system of claim 1 .

7. The control system is housed in a vehicle. The control system of claim 1 .

8. A vehicle equipped with a control system described in any one of claims 1 to 7.

9. 1. An electric drive system for a vehicle, the electric drive system comprising: A control system according to claim 1; an inverter including at least one phase leg, a first phase leg of the at least one phase leg including the power switch; Equipped with the DC / DC converter is configured to generate the internal power supply voltage regulated relative to a voltage at a rail configured to be coupled to a DC power source, the DC / DC converter being configured to generate the internal power supply voltage with the relatively large voltage difference relative to the voltage at the rail or the relatively small voltage difference relative to the voltage at the rail; the switch control device is part of a gate drive channel configured to drive the power switch into a conductive state by applying the relatively large voltage difference derived from the internal power supply voltage during operation of the vehicle, and configured to continue driving the power switch using the relatively small voltage difference derived from the internal power supply voltage after a signal indicating a shutdown or fault of the vehicle. Electric drive system.

10. the gate drive channel configured to pulse the power switch after the signal indicating the shutdown or fault of the vehicle.

10. The electric drive system of claim 9.

11. the gate drive channel is configured to pulse the power switch for a duration defined relative to a time required to discharge a capacitance coupled across the at least one phase leg of the inverter.

11. The electric drive system of claim 10.

12. the gate drive channel comprises a gate driver circuit including a desaturation protection circuit, the desaturation protection circuit specifying when conduction of the power switch ceases during pulse driving; 11. The electric drive system of claim 10.

13. The DC / DC converter, A capacitor; a transformer including an input winding and an output winding, the capacitor being coupled to the input winding of the transformer; Further comprising:

10. The electric drive system of claim 9.

14. the first phase leg of the at least one phase leg includes a second power switch; the gate drive channel is further configured to drive the second power switch for a sustained period.

10. The electric drive system of claim 9.

15. the gate drive channel is configured to drive the second power switch with a transconductance higher than a transconductance of the power switch for the duration.

15. An electric drive system according to claim 14.

16. The electric drive system is housed in a vehicle.

10. The electric drive system of claim 9.

17. A vehicle comprising an electric drive system as described in any one of claims 9 to 16.

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