Method and system for detecting the electrical connection state of a high-voltage energy source with a high-voltage system of an electrically driven motor vehicle.

Abstract

Method and system (10) for detecting an electrical connection state of a high-voltage energy source (11) with a high-voltage system (12) of an electrically driven motor vehicle, in which electrical energy is transferred between the high-voltage energy source for supplying the high-voltage system with a high-voltage direct current voltage and an electric machine (14) for the electric drive of the motor vehicle by means of an inverter (13), with an electrically effective intermediate circuit capacitor (15) for the temporary storage of at least a part of the electrical energy, wherein an electrical intermediate circuit voltage (U1) applied to the intermediate circuit capacitor is detected by means of a voltage measuring device (V) and the detected intermediate circuit voltage and an actual rotational speed (n) of the electric machine are supplied to a control device (16).based on which the connection state is determined as disconnected by the control device if the detected intermediate circuit voltage and the actual rotational speed (n) are directly proportional to each other over a predetermined period of time (Δt), and otherwise the connection state is determined as closed.

Description

[0001] The invention relates to a method and a system for detecting an electrical connection state of a high-voltage energy source with a high-voltage system of an electrically driven motor vehicle.

[0002] In a high-voltage motor vehicle, such as a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (PHEV), a fuel cell electric vehicle (FCEV), or a pure electric vehicle (EV), a high-voltage system (HV system) typically serves to distribute and provide high voltage within the vehicle. This is used, for example, to supply electrical energy to an electric motor for propelling the vehicle and, if applicable, to other high-voltage components (HV components) connected to the high-voltage system. Such vehicles may have a high-voltage battery (HV battery) as a high-voltage energy source, which supplies the high-voltage system with high voltage, particularly high-voltage direct current.

[0003] High voltage is defined as a direct current voltage greater than 60 V, particularly greater than 200 V, e.g., 400 V or 800 V up to approximately 1500 V. In contrast, low voltage is defined as an electrical voltage less than or equal to 60 V, e.g., 6 V, 12 V, 24 V, 48 V, or 60 V.

[0004] In the event of a fault, it must be ensured that the high-voltage system enters a safe state. Such a state can be achieved by opening high-voltage contactors or battery contactors to isolate the HV energy source, e.g., an HV battery, from the rest of the HV system in a controlled manner.

[0005] In modern vehicle applications, the system states of a high-voltage battery are transmitted to the entire vehicle via a communication bus. This information can be used by other high-voltage components in the vehicle, such as an electric drive, to adjust their respective operating behavior in the event of faults in the high-voltage system. For example, the electrical connection status of the high-voltage battery to the high-voltage system is such essential information if the battery can be connected and disconnected from the high-voltage system via high-voltage contactors, e.g., one each for the positive (HV+) and negative (HV-) terminals of the battery.

[0006] The continuous transmission of system states requires a high level of communication between the individual vehicle components. In the event of a fault (e.g., disconnection of the high-voltage battery), it must be ensured that bus communication regarding the system state of the high-voltage battery, for example, to the electric drive, remains intact and that the relevant information can be reliably transmitted within a required timeframe. If, for example, a communication disruption occurs, a coasting operating state of the electric drive is no longer permissible. The vehicle will then no longer be able to roll.

[0007] German patent application DE 10 2015 003 446 A1 discloses a power supply device for a motor vehicle with a high-voltage system and a connected power converter, in which a protective device (high-voltage contactors) can disconnect the high-voltage battery from the high-voltage system. The document deals with the inspection of damaged switching elements of the power converter. It describes how, with the high-voltage contactors open, the electric motor can generate electrical energy through a rotary motion and feed a DC voltage into a high-voltage intermediate circuit via the inverter power electronics.The voltage present in the intermediate circuit is detected by means of a voltage sensor and evaluated by a control unit in order to detect a fault in the switching elements of the converter, since in the event of a defective switching element of the converter a voltage dependent on the speed of the electric machine is coupled into the high-voltage DC circuit via freewheeling diodes.

[0008] German patent application DE 10 2006 000 144 A1 discloses a fault diagnosis device for a vehicle with a high-voltage system, in which a DC power supply can be connected to an electrical circuit via a connection device with several relays. The device is intended to diagnose malfunctions of the relays in this connection device, in particular to detect stuck or welded relay contacts. An intermediate circuit capacitor is provided, at whose terminals a voltage is detected by means of a voltage sensor. A control unit selectively changes the switching state of the relays and evaluates the time-dependent profiles of the detected capacitor voltage in order to diagnose a relay connection fault.

[0009] Against this background, the invention aims to provide technical solutions that reliably detect the electrical connection status of a high-voltage energy source with the high-voltage system of an electrically powered vehicle and ensure safe operation of the vehicle even in the event of malfunctions. Furthermore, the invention aims to improve component protection, particularly for components of an electric drive system.

[0010] This problem is solved by a method having the features of claim 1 and by a system having the features of claim 6. Further particularly advantageous embodiments of the invention are disclosed in the respective dependent claims.

[0011] It should be noted that the features listed individually in the claims can be combined with one another in any technically meaningful way (even across category boundaries, for example between method and apparatus) and demonstrate further embodiments of the invention. The description further characterizes and specifies the invention, particularly in conjunction with the figures.

[0012] It should also be noted that the conjunction “and / or” used herein, which stands between two features and links them together, is always to be interpreted in such a way that in a first embodiment of the object according to the invention only the first feature may be present, in a second embodiment only the second feature may be present, and in a third embodiment both the first and the second feature may be present.

[0013] The use of the term "approximately" herein is intended to include a tolerance range that a person skilled in the art in this field would consider customary. In particular, the term "approximately" is to be understood as a tolerance range of the relative quantity of a maximum of + / -20%, preferably a maximum of + / -10%.

[0014] The invention relates to a method for detecting the electrical connection state of a high-voltage energy source (e.g., a high-voltage battery) with a high-voltage system (HV system) of an electrically powered motor vehicle (e.g., HEV, PHEV, FCEV, EV), in which electrical energy is transferred between the high-voltage energy source, which supplies the high-voltage system with a high-voltage direct current, and an electric machine (e.g., a permanent magnet synchronous machine, PSM) for the electric drive of the motor vehicle by means of an inverter (e.g., a pulse inverter), with an electrically effective intermediate DC link capacitor for the temporary storage of at least a portion of the electrical energy. An intermediate DC link voltage applied to the DC link capacitor is detected by means of a voltage measuring device (e.g., a voltage sensor). A control device (e.g.,The detected DC link voltage and the actual rotational speed of the electric machine are supplied to a microcontroller, microprocessor, or similar device. Based on these values, i.e., the DC link voltage and the actual rotational speed, the control unit determines the connection state as disconnected if the detected DC link voltage and the actual rotational speed are directly proportional to each other over a predetermined period; otherwise, the connection state is determined as closed.

[0015] The direct proportionality of two quantities exists when the ratio of these quantities, i.e., their quotient, remains constant within the considered time period. Comparing the measured DC link voltage and the actual rotational speed of the electric machine thus indirectly allows for inferences about the electrical connection state of the high-voltage (HV) power source with the HV system, i.e., whether, for example, the high-voltage or battery contactors of an HV battery are open or closed. The actual electrical connection state is a safety-relevant system state for the safe operation of the HV system.

[0016] The direct proportionality of the measured DC link voltage and the actual speed of the electric machine during the disconnected connection state is based on the EMF voltage (electromotive force, EMF) generated by the electric machine, which is proportional to the speed of the machine and is the only voltage applied to the DC link capacitor in the disconnected connection state.

[0017] The invention enables the inverter to no longer rely on intact bus communication from another vehicle component (e.g., a high-voltage device) to receive this system state information, which would otherwise be dependent on the current switching state of high-voltage contactors or battery contactors. Furthermore, an uncontrolled disconnection of the high-voltage power source from the high-voltage system, e.g., due to a broken cable, can also be reliably detected. In any case, the inverter is able to maintain a safe operating state of the electric drive or electric machine, depending on the detected connection state of the high-voltage power source.

[0018] This offers, among other advantages, that in the event of a malfunction in the vehicle or the high-voltage system, e.g., due to open high-voltage contactors and / or a communication failure between high-voltage components resulting in an integrity status of the high-voltage system that cannot be received via a communication bus signal, the electric motor's freewheeling function can be maintained and the vehicle's rolling capability maximized. Furthermore, the electric drive can continue to operate without torque loss, and thermal power losses from the electric motor can be minimized.

[0019] The actual rotational speed can be recorded directly at the electric machine (e.g., at a rotor) using a suitable speed sensor.

[0020] Alternatively or additionally, the actual rotational speed can be determined indirectly via a recorded wheel rotation speed of a wheel of the motor vehicle driven by the electric machine and a previously known transmission ratio between the electric machine and the driven wheel.

[0021] In a preferred embodiment, the predetermined time duration is selected from a range between approximately 0.1 s and 2 s, more preferably between approximately 0.5 and 1.5 s. This ensures that the detection of the severed electrical connection between the HV power source and the HV system is possible shortly after the event occurs, and that any transient transient processes in the HV system resulting from the sudden electrical interruption have subsided sufficiently to allow for a reliable assessment.

[0022] Further advantageous embodiments provide that, after determining the disconnected connection state, a freewheeling operating state of the electric machine, in which it (alone) induces the DC link voltage, is maintained. This allows the vehicle to roll even in cases where communication between different high-voltage components is impossible due to a fault. In addition to the improved rolling capability and torque neutrality of the electric drive, the electric machine and the inverter are also protected from damage caused by overload.

[0023] In this sense, another advantageous embodiment of the invention provides that the freewheeling operating state is maintained as long as the DC link voltage induced by the electric machine remains below a predetermined limit value; otherwise, the electric machine is actively short-circuited by means of the inverter, and the freewheeling operating state is terminated. This limit value can, for example, be a hazardous voltage, typically 60 VDC. Actively short-circuiting the electric machine controlled by the inverter means that the inverter deliberately establishes an electrical connection between the electrical phases of the machine, thus placing the machine into a defined short-circuit state. For this purpose, circuit breakers (e.g., DC circuit breakers) can be used.The inverter's IGBTs or MOSFETs are controlled to supply current to the electric machine in such a way that the machine's phases are short-circuited, consequently generating a braking torque and dissipating energy. Active short-circuiting (ACS) is a deliberately controlled operating state of the electric machine via the inverter's power electronics.

[0024] In a further embodiment, after determining the disconnected connection state, an actual vehicle speed is determined based on the actual rotational speed of the electric motor and a known gear ratio between the electric motor and a wheel of the vehicle driven by the electric motor, with a known wheel circumference. This allows monitoring of the vehicle's subsequent speed after the electrical connection is disconnected. The safety of the freewheeling operating state is further enhanced.

[0025] Furthermore, the invention relates to a system for detecting an electrical connection state of a high-voltage energy source (e.g., high-voltage battery) with a high-voltage system of an electrically driven motor vehicle (e.g., HEV, PHEV, FCEV, EV), which comprises an inverter for the controlled transfer of electrical energy between the high-voltage energy source for supplying the high-voltage system with a high-voltage direct current and an electric machine for the electric drive of the motor vehicle with an electrically effective intermediate circuit capacitor for the temporary storage of at least a part of the electrical energy to be transferred, a voltage measuring device for detecting an intermediate circuit voltage applied to the intermediate circuit capacitor, and a control device which is configured toto receive the detected DC link voltage and the actual rotational speed of the electric machine and, based on these, to determine the connection state as disconnected if the detected DC link voltage and the actual rotational speed are directly proportional to each other over a predetermined period of time, and otherwise to determine the connection state as closed.

[0026] It is understood that, with regard to system-related definitions of terms as well as the effects and advantages of system-related features, full reference can be made to the disclosure of analogous definitions, effects, and advantages of the method according to the invention, and vice versa. A repetition of explanations of analogous features, their effects, and advantages can therefore be omitted in favor of a more concise description, without such omissions being to be interpreted as a limitation of any of the disclosed subject matter of the invention.

[0027] In an advantageous embodiment, the control unit is an integral part of the inverter, i.e., it forms a functional and, if necessary, structural unit with the inverter. However, the invention is not necessarily limited to this, so the control unit can be provided separately from the inverter and need not form a structural unit with it.

[0028] The inverter is preferably designed as a pulse inverter (PWR).

[0029] The electric machine is preferably a permanent magnet synchronous machine (PMSM).

[0030] Further features and advantages of the invention will become apparent from the following description of exemplary embodiments of the invention, which are not to be understood as limiting and are explained in more detail below with reference to the drawing. The drawing schematically shows: Fig. 1 a speed-voltage diagram of an EMF voltage of a permanent magnet synchronous machine (PMM); Fig. 2. A time-dependent speed and voltage profile to illustrate a method for detecting an electrical connection state of a high-voltage energy source with a high-voltage system of an electrically driven motor vehicle according to an embodiment of the invention; and Fig. 3 a system for detecting an electrical connection state of a high-voltage energy source with a high-voltage system of an electrically driven motor vehicle according to an embodiment of the invention.

[0031] In the different figures, parts of equal value with regard to their function are always provided with the same reference symbols, so that they are usually only described once.

[0032] Fig. 1 establishes a relationship between the rotational speed n of an electric machine, e.g., a permanent magnet synchronous machine (PMSM), and an electrical voltage U generated by an electromotive force (EMF) of the electric machine. EMK as in Fig. As can be seen in section 1, the EMF voltage U EMK proportional linearly to the rotational speed n.

[0033] Fig. Figure 2 presents a time-dependent rotational speed and voltage profile to illustrate a method for detecting an electrical connection state of a high-voltage energy source with a high-voltage system of an electrically driven motor vehicle according to an embodiment of the invention. Fig. Figure 3 represents an exemplary associated system 10 according to one embodiment of the invention. Reference will be made hereafter to the Fig. 2 and Fig. 3 taken.

[0034] In Fig. Figure 3 shows the system 10 essentially comprising a high-voltage energy source 11, e.g., a high-voltage battery for providing a high-voltage direct current, a high-voltage system 12 of an electrically driven motor vehicle (not shown in detail) supplied by the high-voltage energy source 11, an inverter 13, an electric machine 14 for the electric drive of the motor vehicle (here a permanent magnet synchronous machine, PSM), a DC link capacitor 15, and a control unit 16. The inverter 13 serves for the controlled transmission of electrical energy between the high-voltage energy source 11 and the electric machine 14 with the electrically effective interposition of the DC link capacitor 15 for the temporary storage of at least a portion of the electrical energy to be transmitted.Furthermore, a voltage measuring device V is provided for detecting an electrical intermediate circuit voltage U1 applied to the intermediate circuit capacitor 15. As in . Fig. As shown in Figure 3, the control unit 16 receives the DC link voltage U1 and the actual rotational speed n of the electric machine 14, as measured by the voltage measuring device V. The control unit 16 is configured to determine the connection state as disconnected based on the measured DC link voltage U1 and the actual rotational speed n of the electric machine 14 if the measured DC link voltage U1 and the actual rotational speed n remain constant for a predetermined time period Δt (see Figure 3). Fig. 2) behave directly proportionally to each other, and otherwise determine the connection state as closed. The determined connection status can be provided by the control unit 16 to other vehicle components via an output signal 17, but is not necessarily limited to this.

[0035] The conversion of the high-voltage direct current supplied by the high-voltage system 12 into an alternating voltage supplied to the machine 14 is carried out in a manner known per se by means of power switches 18 (e.g. MOSFETs), of which in Fig. The six circuit breakers shown are used to control the current supply to three electrical phases of the machine 14. The number and arrangement of the circuit breakers 18 are not necessarily limited to the number and arrangement shown, but may differ.

[0036] The control of the circuit breakers 18 can be performed by the control unit 16, but is not necessarily limited to this. In this case, the control unit 16 can be considered a functional and, if applicable, also a structural component of the inverter 13. Alternatively, the inverter 13 can have a separate control unit (not shown) for controlling the circuit breakers 18.

[0037] In Fig. Figure 3 further shows that the high-voltage energy storage device 11 can be electrically connected to or disconnected from the high-voltage system 12 by means of two high-voltage contactors 19 (one for each pole of the HV energy source). A separate control unit (not shown) may be provided for this purpose.

[0038] Based on Fig. 2 The functional principle according to the invention is described in more detail below. Fig. Figure 2 represents both the actual rotational speed n of the electric machine 14 and the DC link voltage U1 along the ordinate. Time t is plotted along the abscissa.

[0039] In an initial time interval between t0 and t1, during which the HV contactors 19 are closed and the HV energy source 11 is electrically connected to the HV system 12 (i.e., the system is considered closed), the electric machine 14 operates normally and in a controlled manner via the inverter 13. It can be observed that during this interval, the actual rotational speed n of the machine 14 and the DC link voltage U1 are not directly proportional to each other due to a dynamic load on the HV energy storage device in the charging and discharging directions, respectively.

[0040] At time t1, the HV contactors 19 are opened, for example, due to a fault in the HV system 12. The opening of the HV contactors 19 typically results in a voltage jump in the HV DC link, i.e., at the DC link capacitor 15, either upwards or downwards, since the HV voltage level is no longer determined by the HV power source 11 or the HV battery with its cell interconnection. During this transient transition phase between t1 and t2, the following occurs: Fig. 2 several possible voltage waveforms of the intermediate circuit voltage U1, exemplified as U1 1 , U1 2 , U1 3 and U1 4 illustrated. For example, the DC link voltage U1 increases. 1 immediately after opening the HV contactor 19, the voltage jumped up, whereas the intermediate circuit voltages U1 2 , U1 3 and U1 4 Remove after opening, e.g. abruptly as with U1 3 or essentially continuously as with U1 2 and U1 4 .

[0041] In Fig. 2. All depicted intermediate circuit voltages U1 run through this line. 1 , U1 2 , U1 3 and U1 4 From time t2 at the latest, the DC link voltage U1 is directly proportional to the actual rotational speed n, i.e., the DC link voltage U1 corresponds to the EMF voltage U1. EMK This voltage is caused by the electromotive force (EMF) of machine 14. After the HV contactors 19 open, this voltage is the only voltage present at the DC link capacitor 15.

[0042] If, during the predetermined time period Δt, which may be approximately 1 s, the direct proportionality between the intermediate circuit voltage U1 and the actual rotational speed n of the electrical machine 14 is given, the control device 16 determines the connection state as disconnected.

[0043] This information can subsequently be used to establish a suitable safe state for the electric drive or electric machine 14, e.g., to establish or maintain a freewheeling state for the machine 14 despite a disconnected connection. Overall, the invention achieves increased rolling capability of the vehicle and torque neutrality of the electric drive, as well as improved component protection, in particular of the electric machine 14 and the inverter 13. REFERENCE MARK LIST: 10 System 11 High-voltage energy storage 12 High-voltage system 13 inverters 14 Electric Machine 15 Intermediate circuit capacitor 16 Control unit 17 Output signal 18 circuit breakers 19 High-voltage contactors n Actual rotational speed PSM permanent magnet synchronous machine t time t0 First time point t1 Second time point t2 Third time point Δt duration U voltage U EMK EMF voltage U1 DC link voltage U1 1 First waveform of an intermediate circuit voltage U1 2 Second waveform of an intermediate circuit voltage U1 3 Third course of an intermediate circuit voltage U1 4 Fourth phase of an intermediate circuit voltage V Voltage measuring device

Claims

Method for detecting an electrical connection state of a high-voltage energy source (11) with a high-voltage system (12) of an electrically driven motor vehicle, in which electrical energy is transferred between the high-voltage energy source (11) for supplying the high-voltage system (12) with a high-voltage direct current voltage and an electric machine (14) for the electric drive of the motor vehicle by means of an inverter (13), with an electrically effective intermediate circuit capacitor (15) for the temporary storage of at least a part of the electrical energy, wherein an electrical intermediate circuit voltage (U1) applied to the intermediate circuit capacitor (15) is detected by means of a voltage measuring device (V) and the detected intermediate circuit voltage (U1) and an actual rotational speed (n) of the electric machine (14) are supplied to a control device (16).based on which the connection state is determined as disconnected by means of the control device (16) if the detected intermediate circuit voltage (U1) and the actual rotational speed (n) are directly proportional to each other over a predetermined period of time (Δt), and otherwise the connection state is determined as closed. Method according to claim 1, wherein the time duration (Δt) is predetermined from a range between 0.1 s and 2 s, preferably between 0.5 and 1.5 s. Method according to claim 1 or 2, wherein, after determining the disconnected connection state, a freewheeling operating state of the electrical machine (14) in which it induces the intermediate circuit voltage (U1) is maintained. Method according to claim 3, wherein the freewheeling operating state is maintained as long as the intermediate circuit voltage (U1) induced by the electric machine (14) is below a predetermined limit value, and otherwise the electric machine (14) is actively short-circuited by means of the inverter (13) and the freewheeling operating state is terminated. Method according to one of the preceding claims, wherein, after determining the disconnected connection state, an actual vehicle speed is determined based on the actual rotational speed (n) of the electric machine (14) and a previously known transmission ratio between the electric machine (14) and a wheel of the motor vehicle driven by the electric machine (14) with a previously known wheel circumference. System (10) for detecting an electrical connection state of a high-voltage energy source (11) with a high-voltage system (12) of an electrically driven motor vehicle, comprising an inverter (13) for controlled transmission of electrical energy between the high-voltage energy source (11) for supplying the high-voltage system (12) with a high-voltage direct current and an electric machine (14) for the electric drive of the motor vehicle with an electrically effective intermediate circuit capacitor (15) for the temporary storage of at least a part of the electrical energy to be transmitted, a voltage measuring device (V) for detecting an intermediate circuit voltage (U1) applied to the intermediate circuit capacitor (15) and a control device (16) which is configuredto receive the detected intermediate circuit voltage (U1) and an actual rotational speed (n) of the electrical machine (14) and, based on these, to determine the connection state as disconnected if the detected intermediate circuit voltage (U1) and the actual rotational speed (n) are directly proportional to each other over a predetermined period of time (Δt), and otherwise to determine the connection state as closed. System according to claim 6, wherein the control device (16) is part of the inverter (13). System according to claim 6 or 7, wherein the electrical machine (14) is a permanent magnet synchronous machine (PSM).

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