Method for operating an electric traction drive system and associated control device

Abstract

A method for operating an electric traction drive system (10) in which an electric motor (70) and a battery (110) for supplying the electric motor (70) are arranged, the battery module string (120) having several battery modules (130, 140), each comprising at least one battery cell, for generating an adjustable output voltage (UB) of the battery (110), which can each be connected in series to the battery module string (120) or bridged in the battery module string (120), characterized in that the battery modules (130, 140) are each monitored for proper function during operation and, if a technical fault of at least one battery module is detected, the at least one battery module (130, 140) is bridged and the traction drive system (10) is brought into a transition state in which the electric motor (70) is powered by the connected battery modules (130, 140) in such a way as to generate an adjustable output voltage (UB) of the battery (110), characterized in that the battery modules (130, 140) are each monitored for proper function during operation and, if a technical fault of at least one battery module is detected, the at least one battery module (130, 140) is bridged and the traction drive system (10) is brought into a transition state in which the electric motor (70) is powered by the connected battery modules (130, 140) in such a way that140) of the battery module string (120) is further supplied and controlled so that a currently generated torque can be maintained unchanged, wherein the electric motor (70) is designed as a three-phase machine and wherein the electric motor (70) is operated in the transition state via a field-oriented control, wherein while the traction drive system (10) is operated in the transition state, a battery diagnostic is carried out in parallel to decide whether the traction drive system (10) can continue to be operated with at least one bridged defective battery module and / or whether safety-relevant measures are initiated.

Description

[0001] The present invention relates to a method for operating an electric traction drive system in which an electric motor and a battery for supplying the electric motor are arranged. The battery module string comprises a battery module string for generating an adjustable battery output voltage. The battery module string has several battery modules, each comprising at least one battery cell, which can be connected in series with the battery module string or bridged within the battery module string. The invention further relates to a corresponding device for controlling an electric traction drive system. The invention also relates to a vehicle with an electric traction drive system, which includes an electric motor connected to a battery direct converter and the device according to the invention for controlling the electric drive system. State of the art

[0002] Batteries used in hybrid and electric vehicles are known from the state of the art and are referred to as traction batteries because they are used to power electric drives.

[0003] The schematic diagram of a prior art electric traction drive system 10, as used, for example, in electric and hybrid vehicles or in stationary applications such as rotor blade adjustment of wind turbines, is shown in the Fig. Figure 1 shows a battery (traction battery) 11 connected to a DC link, which is buffered by a capacitor 60. A pulse inverter 50 is also connected to the DC link. This inverter provides phase-shifted sinusoidal voltages for operating an electric motor 70 at three outputs via two switchable semiconductor valves 51 and two diodes 52. For the sake of simplicity, only one semiconductor valve and one diode are labeled in the drawing. The capacitance of the capacitor 60 is sufficiently large to stabilize the voltage in the DC link for the duration that one of the switchable semiconductor valves 51 is switched on. In a practical application such as an electric vehicle, this requires a high capacitance in the range of mF.

[0004] Three-phase motors are typically used as electric motors (electric machines) 70 in such traction drives 10. These are usually asynchronous motors, permanently controlled synchronous motors, or separately excited synchronous motors. Pulse converters 50 are typically used to supply the electric machine 70. In the traction applications of electric and hybrid vehicles, these converters are usually implemented with semiconductor switches 51 designed as insulated-gate bipolar transistors (IGBTs).

[0005] The one in Fig. The battery 11 shown comprises a battery module string 12 in which a plurality of battery cells 21 are connected in series and optionally also in parallel to achieve a high output voltage and battery capacity desired for a particular application. For the sake of simplicity, only one battery cell is shown with a reference symbol. A charging and disconnecting device 30 is connected between the positive terminal of the battery cells 21 and a positive battery terminal 22. Optionally, a disconnecting device 40 can also be connected between the negative terminal of the battery cells and a negative battery terminal 23.

[0006] The disconnect and charge device 30 and the disconnect device 40 each comprise a contactor 31 or 41, respectively, which are designed to disconnect the battery cells 21 from the battery terminals 22 and 23 in order to de-energize the battery terminals 22 and 23. Otherwise, due to the high DC voltage of the series-connected battery cells 21, there is a significant risk to maintenance personnel or other persons. The charge and disconnect device 30 also includes a charging contactor 32 with a charging resistor 33 connected in series with the charging contactor 32. The charging resistor 33 limits the charging current for the capacitor 60 when the battery 11 is connected to the DC link. For this purpose, the contactor 31 is initially left open, and only the charging contactor 32 is closed.When the voltage at the positive battery terminal 22 reaches the voltage of the battery cells 21, the contactor 31 can be closed and, if necessary, the charging contactor 32 can be opened. The contactors 31, 41, and the charging contactor 32 significantly increase the cost of a battery 11, as high demands are placed on their reliability and the currents they must handle.

[0007] If a technical problem occurs in the traction battery of such a traction drive, which could either directly lead to the failure of a battery cell or, if the battery continues to operate, to a safety-relevant, unsafe state, the battery management system brings the battery into a safe state. According to the state of the art in lithium-ion battery systems, this state is achieved by disconnecting the battery from the DC link by opening the contactors of the charging and disconnecting device.

[0008] The traction drive's control system must then cope with the situation where the battery is no longer available as an energy storage device. Depending on the electric motor's operating state, the control system essentially only ensures that the pulse inverter or inverter is not damaged. Inverter damage can be caused, for example, by an excessively high voltage increase in the DC link. Consequently, the control system can no longer take into account the traction drive's dynamically appropriate behavior, or, theoretically, it can no longer even establish such behavior due to the battery disconnection.

[0009] As a consequence, the traction drive delivers undesirable or even impermissible torques from a driving dynamics perspective, particularly sudden, large negative torques. This must then be managed within the overall design of such a vehicle's traction drive system through additional measures, such as a mechanical freewheel. These additional measures are complex and highly undesirable, as they are only needed in the event of a technical fault in the battery and are therefore typically never used.

[0010] In the applicant's earlier patent application, file number DE 10 2010 041 014 A1, a battery system with a battery having a step-adjustable output voltage was described. The block diagram of a drive system (traction drive) 10 with such a battery 110 is shown in the Fig. Figure 2 shows that the battery 110 is composed of several battery modules 130, 140 arranged in a single battery module string 120, with battery cells connected in series and / or parallel. The battery modules 130, 140 can be connected or bridged in the battery module string 120 by means of their respective associated coupling units. Systems with such batteries 110 are also referred to as battery direct converters (DICOs) 110. These can convert the batteries shown in the Fig. Replace the traction battery shown in section 10.

[0011] The possible course of the output voltage UB of the in the Fig. The battery direct converter 110 shown in the 2 is in the Fig. Figure 3 shows the output voltage UB, which is the voltage generated by the battery module string 120. Fig. Figure 3 shows the dependence of the output voltage UB on the number k of battery modules 130, 140 connected to the battery module string 120. The battery modules 130, 140 connected to each battery module string 120 each have the same module voltage UM. The output voltage UB of the battery module string 120, shown as a function of the connected number k of battery modules 130, 140, is linear and follows the relation UB = k·UM, where 1 < k < n. Here, n is the maximum number of battery modules 130, 140 that can be connected to the battery module string 120. The maximum output voltage UB of the battery module string 120 can then accordingly assume the value n·UM.

[0012] Document DE 10 2011 004 248 A1 discloses a circuit arrangement with a multi-stage converter for generating an AC output voltage (Vac). The multi-stage converter consists of several converter stages connected in series. Each converter stage has: input terminals, output terminals, and a switching arrangement between the input and output terminals to generate a pulse-width modulated output voltage with a variable duty cycle, depending on the control signal.

[0013] Document US 5,670,861 A discloses a circuit and method for monitoring and controlling a long battery chain, particularly for electric vehicles. The modular, safe, and efficient battery management system maximizes the lifespan and performance of batteries in electric vehicles.

[0014] The document KOURO, S. [et al.]: Recent Advances and Industrial Applications of Multilevel Converters. In IEEE Transactions on Industrial Electronics, Vol. 57, 2010, No. 8, pp. 2553-2580. IEEE Xplore [online] DOI: 10.1109 / TIE.2010.2049719, in: IEEE provides an overview of classic and new multilevel converter topologies, as well as modulation methods and control strategies.

[0015] Document DE 10 2010 062 478 A1 discloses a method and a device for operating an electric machine, particularly in a motor vehicle powertrain. The torque monitoring takes into account the degradation of the electric machine in order to avoid false alarms and premature system failure.

[0016] Document DE 10 2010 041 014 A1 discloses a battery system with a variably adjustable intermediate circuit voltage for electric vehicles. By selectively switching individual battery modules on and off within a battery module string, the voltage of the DC intermediate circuit can be varied and thus adapted to the respective operating state of the electric motor.

[0017] Document DE 10 2011 054 146 A1 discloses a fault-tolerant architecture for battery systems, particularly for electric vehicles. The invention describes bypass circuits that make it possible to bypass individual cells or modules in the event of failure or performance loss in order to maintain the functionality of the overall system.

[0018] Document US 2009 / 0206679A1 discloses a device, a system, and a method for automatically replacing a defective battery in a battery-powered electrical device, such as an electric vehicle. Disclosure of the invention

[0019] According to the invention, a method for operating an electric traction drive system is provided, in which an electric motor and a battery for supplying the electric motor are arranged. The battery comprises a battery module string which, for generating an adjustable output voltage, includes several battery modules, each comprising at least one battery cell. These modules can be connected in series with the battery module string or bypassed within the battery module string. During operation of the traction drive system, the battery modules are monitored for proper function. If a technical fault in at least one battery module is detected during monitoring, that battery module is immediately bypassed.In addition, the traction drive system is transferred into a transitional state in which the electric motor is supplied and controlled by the connected battery modules of the battery module string in such a way that a currently generated torque can be maintained unchanged.

[0020] An electric motor designed as a three-phase machine is adjusted in the transition state by means of a field-oriented control to continue operating the drive system with a constant torque.

[0021] After the drive system has been brought into the transition state, a battery diagnosis is carried out according to the invention, on the basis of which it is decided whether the drive system will continue to be operated by means of the battery with the failed and bypassed battery module and / or whether further safety-relevant measures are initiated.

[0022] According to the invention, a device for controlling an electric traction drive system is further provided, in which an electric motor and a battery for supplying the electric motor are arranged. The battery has a battery module string for generating an adjustable output voltage, comprising several battery modules, each containing at least one battery cell, which can be connected in series with the battery module string or bypassed within the battery module string. The device is designed to monitor the battery modules for proper function during operation and, if a technical fault in at least one battery module is detected during monitoring, to control the traction drive system in such a way that the at least one battery module is bypassed and the traction drive system is brought into a transitional state.In this transitional state, the traction drive system is operated in such a way that the electric motor continues to be supplied and controlled by the connected battery modules of the battery module string in a manner that allows the currently generated torque to be maintained unchanged.

[0023] The invention relates in particular to batteries that are operated in conjunction with a battery direct converter and are connected to a DC circuit of an inverter.

[0024] In traction drives for electric and hybrid vehicles, the traction batteries can therefore preferably be designed as direct battery converters. The voltage of the DC link can thus be adjusted in steps between 0 V and the maximum possible output voltage, which is reached when all battery modules are connected. If a technical fault occurs in one of the battery modules of the direct battery converter, such as the sudden failure of at least one of its battery cells or the malfunction of at least one of its battery cells, which could lead to a safety-relevant condition of the affected battery module if continued operation occurs, this battery module is bypassed by its associated coupling unit. This battery module is then no longer available to the battery of the direct battery converter for supplying or receiving electrical energy.The battery cells of the affected battery module are not negatively affected by continued operation of the remaining, still functional battery modules in such a way that a safety-relevant condition arises in the faulty battery module. Therefore, the remaining battery modules can continue to supply the traction drive after a technical defect has been detected in one of the battery modules.

[0025] If a technical fault occurs in the battery of the battery direct converter, the traction drive powered by it is reliably and precisely guided into a special transition state thanks to the invention, until a battery diagnosis and a fault assessment have been carried out. In this transition state, the drive can continue to operate with the current torque that the drive delivered to the shaft before the technical problem occurred. The torque remains constant in this transition state, and the drive can continue to respond to the torque commands transmitted by the driver via the accelerator pedal. From a driving dynamics perspective, this represents a significant improvement over the situation known from the prior art.After assessing the fault, the powertrain can then be put into a kind of "fault state" in which the faulty battery module is no longer involved in powering the drive, but the drive can continue to operate with reduced performance, such as a lower electric range.

[0026] The additional measures required in the prior art with regard to the drive function, such as the implementation of mechanical freewheels, which are generally only needed and used when a battery fault occurs, can thus be omitted. The inventive method and the corresponding device do not require any additional hardware and can therefore be implemented without corresponding additional costs for the manufacture of the inventive drive systems. The transitional operation is maintained until a fault diagnosis can determine whether and, if so, how the traction battery can continue to be operated without safety risks and, in particular, with reduced performance.

[0027] According to the invention, the drive is advantageously always operated in such a way that the drive's operation is ensured even if any battery module of the battery direct converter suddenly fails. This measure can affect the permissible maximum voltage that the three-phase drives require at their terminals to maintain their operation. Furthermore, it determines at which speeds an asynchronous machine enters so-called field weakening mode and no longer delivers its maximum possible torque to the shaft. If a fault occurs in a battery module, the drive can also adjust the voltage conditions at the machine's terminals required for the controlled operation of the electric motor by bridging this faulty battery module.

[0028] The three-phase motor is then operated via a so-called field-oriented control system, familiar to those skilled in the art, in such a way that the torque demand specified by the driver via the accelerator pedal is met. The driver is therefore initially unaware that one of the battery modules has failed due to a technical problem and has been bypassed. During the transition phase, a battery diagnostic test and an assessment of the battery's condition determine whether the technical problem affects only one battery module or the entire battery.

[0029] According to the invention, if the drive system continues to be operated by means of the battery with the failed and bypassed battery module after the battery diagnostics according to the invention have been carried out, the battery can continue to operate the drive system with a correspondingly reduced output voltage. In other words, if the battery diagnostics determine that the traction drive system can continue to be operated, then the traction drive system is brought into an operating state in which the electric motor continues to be supplied with an output voltage that is reduced by the value of the battery module voltage corresponding to the bypassed defective battery module.

[0030] Alternatively, a sufficient number of additional battery modules can be connected to replace at least one bypassed defective battery module. Using this approach, the electric motor can continue to be supplied with an unchanged or only slightly reduced output voltage.

[0031] This also means that, depending on the result of the battery diagnostics performed, a decision can be made as to whether the traction drive will continue to operate with the exclusion of only the one faulty battery module, or whether further measures to ensure safety, such as switching off other battery modules, warning the driver or reducing the performance of the drive, must be initiated.

[0032] Based on the current state of the battery, even the sudden failure of two or more battery modules can be reliably managed. This simply requires maintaining a sufficiently high voltage reserve during operation of the drive system compared to the maximum available voltage.

[0033] In a particularly advantageous embodiment of the invention, if the drive system continues to be powered by the battery with the failed and bypassed battery module, and subsequently another battery module fails, the drive system continues to operate by means of a correspondingly repeated process. This means that the previously described method according to the invention remains applicable even if the battery already has a defective module, but the rest of the battery continues to operate. For this purpose, the battery management system or the control system of the drive simply needs to take into account that the available maximum voltage, the storage capacity, and the performance of the battery are adapted to the conditions resulting from the failure of a battery module.

[0034] Using the method and device according to the invention, a situation in which at least one battery module fails can be reliably controlled in such a way that the drive is reliably transferred into a transitional state in which it is still possible to respond to current torque specifications of the driver.

[0035] According to a further aspect of the invention, an electrical battery system is created that comprises a battery module string with several battery modules, each containing at least one battery cell. The battery modules can each be connected in series to the battery module string or bridged within the battery module string, so that a variable output voltage of the battery can be set.

[0036] According to the invention, the battery can in particular be a lithium-ion battery.

[0037] Furthermore, according to the invention, a vehicle is provided which has an electric traction drive system in which an electric motor and a battery for supplying the electric motor are arranged. The battery has a battery module string with several battery modules, each comprising at least one battery cell, to generate an adjustable output voltage. The battery modules can be connected in series with the battery module string or bridged within the battery module string. The traction drive system in the vehicle also includes the control device according to the invention.

[0038] Advantageous embodiments of the invention are specified in the dependent claims and described in the description. Drawings

[0039] Exemplary embodiments of the invention are explained in more detail with reference to the drawings and the following description. The drawings show: Fig. 1 the basic circuit diagram of a traction drive known from the prior art with an electric motor which is connected to a battery with a battery module string formed from several battery cells, Fig. 2 the basic circuit diagram of a traction drive known from the prior art with an electric motor which is connected to a battery with a battery module string consisting of several battery modules, each with at least one battery cell, wherein, for the purpose of generating an adjustable output voltage, the battery modules of the battery are designed to be connected in series or bridged with the battery module string, Fig. 3 a possible course of the output voltage of the in the Fig. 2 shown battery depending on the number of battery modules connected to the battery module string, and Fig. 4 a schematic diagram of a traction drive according to a first embodiment of the invention with an electric motor which is connected to a battery with a battery module string consisting of several battery modules, each with at least one battery cell, wherein the battery modules are designed to be connected in series or bridged to the battery module string in order to generate an adjustable output voltage of the battery. embodiment of the invention

[0040] In the Fig. Figure 4 shows the basic circuit diagram of a traction drive 10 according to a first embodiment of the invention.

[0041] The traction drive comprises a battery (traction battery) 110, which is connected to a DC link buffered by a capacitor 60. A pulse inverter 50 is also connected to the DC link. This inverter provides phase-shifted sinusoidal voltages for operating the electric motor 70 at three outputs via two switchable semiconductor valves 51 and two diodes 50. According to this embodiment, the electric motor 70 is designed as a three-phase motor.

[0042] The battery 120 comprises a battery module string 12 with several battery modules 130, 140 arranged in the battery module string, which are made up of battery cells connected in series and / or parallel. For the sake of simplicity, the following were used in the Fig. Figure 4 shows only two battery modules 130 and 140. The battery modules 130 and 140 can be connected or bridged in the battery module string 120 by means of their respective coupling units (not shown separately). A charging and disconnecting device 30 is located between the positive terminal of an uppermost battery module 130 and a positive battery terminal 22. This device is similar to the charging and disconnecting device shown in the... Fig. 1 is configured, switched. Optionally, a disconnecting device 40, such as the disconnecting device from the Fig. 1 is configured, can be switched. Systems with such batteries 110 are, as already mentioned, referred to as battery direct converters (DICO) 110.

[0043] The traction drive 110 according to the invention further comprises a control device 200, which is electrically connected to the respective terminals of the battery modules 130, 140. The control device 200 is also configured to measure the voltages of the individual battery modules 130, 140. Furthermore, the control device 200 is designed so that if, during the operation of the traction drive system 10, a battery module 130, 140 connected to the battery module string 120 fails or a defect of the battery module is detected, the electric motor 70 continues to be supplied by means of the battery 110 but without the failed and bypassed battery modules 130, 140, and the electric motor 70 is adjusted via the control line 210 so that the drive system 10 is brought into a transitional state in which the drive system 10 initially delivers an unchanged torque as before the failure of the at least one battery module 130, 140.

[0044] According to the in Fig. In the embodiment shown in Figure 4, this is achieved in particular by adjusting or controlling the electric motor 70, which is designed as a three-phase machine, here: an asynchronous machine, by means of a field-oriented control.

[0045] Furthermore, the control device 200 of the particular embodiment shown here is configured to perform a battery diagnosis during the period in which the drive system 10 is in the transition state, and to decide whether the traction drive 10 continues to operate with at least one failed and bypassed battery module 130, 140 and / or whether other safety-related measures are initiated. Preferably, the control device 200 includes a battery diagnostic unit for this purpose.

[0046] Thus, according to the invention, a method and a control device are created with which an electric drive system having a battery direct converter can advantageously be transferred into a transition state in which there is no reduction of the current torque.

Claims

[1] Method for operating an electric traction drive system (10) in which an electric motor (70) and a battery (110) for supplying the electric motor (70) are arranged, the battery module string (120) having several battery modules (130, 140) each comprising at least one battery cell, which can each be connected in series to the battery module string (120) or bridged in the battery module string (120) to generate an adjustable output voltage (UB) of the battery (110), characterized bythat the battery modules (130, 140) are each monitored for proper function during operation and, if a technical fault in at least one battery module is detected, at least one battery module (130, 140) is bypassed and the traction drive system (10) is switched to a transition state in which the electric motor (70) continues to be supplied and controlled by the connected battery modules (130, 140) of the battery module string (120) in such a way that a currently generated torque can be maintained unchanged, wherein the electric motor (70) is designed as a three-phase machine and wherein the electric motor (70) is operated in the transition state via a field-oriented control, wherein, while the traction drive system (10) is operated in the transition state, a battery diagnostic is carried out in parallel to decide,whether the traction drive system (10) can continue to be operated with at least one bypassed defective battery module and / or whether safety-relevant measures are initiated. [2] Method according to claim 1, wherein, if it has been decided according to the battery diagnosis that the traction drive system (10) can continue to be operated, the traction drive system (10) is brought into an operating state in which the electric motor (70) continues to be supplied with an output voltage (UB) which is reduced by the voltage value of a battery module voltage corresponding to the bypassed defective battery module (130, 140). [3] Method according to claim 1, wherein, if it has been decided according to the battery diagnosis that the traction drive system (10) can continue to be operated, a sufficient number of further battery modules (130, 140) are connected to replace the at least one bridged defective battery module (130, 140) so that the electric motor (70) continues to be supplied with an unchanged or less reduced output voltage (UB). [4] Method according to claim 2 or 3, wherein if a further battery module (130, 140) fails, the method according to one of claims 1 to 3 is repeated accordingly, wherein, based on a corresponding further battery diagnostic step, a decision is made as to whether the further battery module (130, 140) is to be bypassed or not. [5] Device (200) for controlling an electric traction drive system (10) in which an electric motor (70) and a battery (110) for supplying the electric motor (70) are arranged, which has a battery module string (120) with several battery modules (130, 140), each comprising at least one battery cell, for generating an adjustable output voltage (UB) of the battery (110), which can each be connected in series to the battery module string (120) or bridged in the battery module string (120), characterized bythat the device (200) is configured to monitor the battery modules (130, 140) for proper function during operation and, if a technical fault of at least one battery module is detected during monitoring, to control the traction drive system (10) in such a way that the at least one battery module (130, 140) is bypassed and the traction drive system (10) is brought into a transitional state in which the electric motor (70) continues to be supplied and controlled by the connected battery modules (130, 140) of the battery module string (120) in such a way that a currently generated torque of the electric motor (70) can be maintained unchanged, wherein the device (200) is configured to operate the electric motor (70) according to a field-oriented control, and the device (200) has a battery diagnostic unit and is configured toWhile the traction drive system (10) is operated in the transition state, a battery diagnostic is carried out in parallel to decide whether the traction drive system (10) can continue to be operated with at least one bypassed defective battery module and / or whether safety-relevant measures are initiated. [6] Battery system comprising a battery (110) comprising a battery module string (120) with several battery modules (130, 140), each comprising at least one battery cell, which can be connected in series to the battery module string (120) or bridged in the battery module string (120) to generate an adjustable output voltage (UB) of the battery (110), and comprising a device (200) according to claim 5. [7] Vehicle with an electric traction drive system (10) in which an electric motor (70), a battery (110) provided for supplying the electric motor (70), which has a battery module string (120) with several battery modules (130, 140) each comprising at least one battery cell, which can each be connected in series to the battery module string (120) or bridged in the battery module string (120), and a device (200) according to claim 5 are arranged for generating an adjustable output voltage (UB) of the battery (110).

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