Fault handling in an electric machine of a hybrid drive

Abstract

Method for fault handling in an electric machine (30) of a hybrid drive, comprising the steps: Determine whether at least one operating parameter of the electrical machine (30) is above an associated operating parameter limit value; Activating a supply connection of the electrical machine (30) for a time interval assigned to the operating parameter, after it is detected that at least one operating parameter is above the assigned operating parameter limit value; and Short-circuit the supply connection to ground after the time interval has elapsed.

Description

State of the art

[0001] The invention relates to hybrid vehicles with a synchronous electric motor. To prevent permanent damage to the vehicle and the synchronous motor, the operation of the synchronous motor is monitored and, in the event of a fault, it is short-circuited to ground. According to the prior art, therefore, when a fault is detected, the current connection of the synchronous motor is directly connected to ground.

[0002] However, such a procedure can lead to permanent damage to the synchronous motor in the case of some types of faults and can also negatively affect the driving operation of the vehicle powered by the hybrid drive.

[0003] Documents DE 198 35 576 A1 and DE 10 2005 035 055 A1 disclose methods for the safe operation of electrical machines. Disclosure of the invention

[0004] The invention is based on the consideration that measures taken in the event of a fault should depend on the type of fault occurring in the electric machine of a hybrid drive. According to one aspect of the invention, when certain types of faults occur, the electrical connection of the electric machine is not immediately grounded after the fault occurs, but is first disconnected for a specific period of time, i.e., decoupled from the electrical connection, in order to interrupt the current flow. It has been recognized that damaging current spikes can occur during short circuits, particularly of synchronous motors, which can be avoided if the electrical connection of the synchronous motor is first disconnected before the short circuit.Although short-circuiting to ground is absolutely necessary to bring the electric machine, especially a synchronous motor, into a safe state, the safe operation of the hybrid drive in the event of a fault is not negatively affected if the power supply to the synchronous motor is disconnected for a short period of time, i.e., for example, a few microseconds, between the occurrence of the fault and short-circuiting to ground.

[0005] To detect faults, preferably at least one current sensor and / or at least one voltage sensor is used, measuring the current flowing into the electric machine and the voltage applied to the power supply of the electric machine or to the electric machine itself. Preferably, the power supply is provided by a pulse inverter, the output voltage of which is measured.

[0006] According to a further aspect of the invention, it is checked whether the current flowing into the electric machine exceeds a limit, and / or whether the output voltage of the electric machine's power supply exceeds a maximum voltage, i.e., a limit value. According to the invention, if the current flowing into the electric machine exceeds a limit value, i.e., if a phase overcurrent fault occurs, the connection of the electric machine is disconnected for a longer period of time before it enters a short-circuit state, in contrast to the case where a voltage exceeding a limit value is present at the terminals of the electric machine or at the power supply of the electric machine, i.e., when an overvoltage fault occurs.

[0007] Phase overcurrent faults or overvoltage faults can occur if the power supply to the electric machine is defective, if a fault occurs within the electric machine itself, if the mechanical load on the output of the electric machine exceeds a limit, or if similar faults occur. If the electric machine has multiple phases and thus multiple electrical connections, each input is preferably monitored with regard to the applied voltage and the current flowing through it. If a fault occurs on one phase, the entire electric machine is preferably short-circuited to ground after a short free-running period, according to the procedure described above.

[0008] Current and voltage can be measured digitally or analogously. For example, a voltage sensor, particularly a direct tap of the applied voltage, is fed to an evaluation element that outputs a signal when a threshold voltage is exceeded. This can be achieved, for example, using a comparator or a suitably configured operational amplifier. The current is preferably measured by incorporating a sense MOSFET into the power supply, at whose sense output the current flowing through the output stage can be detected. Alternatively or in combination with this, the magnetic field generated by the current can be measured, for example, using Hall sensors or magnetoresistive resistors to measure the static magnetic field, or using inductors to measure the dynamic magnetic field.Furthermore, shunt resistors can be used, across which a voltage drop proportional to the current flowing through them can be applied. The measured current and / or voltage values ​​can be processed further in analog or digital form.

[0009] According to a preferred embodiment of the invention, the detected digital or analog values ​​of continuous current or voltage signals are compared by an error detection circuit with a respective limit value. If the respective value exceeds the limit value, the error detection circuit preferably outputs a voltage level that differs from the voltage level output when the respective value is below the limit value. For example, a high-level signal (HIGH signal) can be output when the limit value is exceeded, while a low-level signal, for example a LOW signal, is output otherwise. Such a conversion of continuous-value signals into discrete error signals facilitates further processing by one or more corresponding timer circuits.

[0010] In a further embodiment of the invention, a timer circuit is connected downstream of the fault detection circuit, which, depending on the fault signal and its level and depending on a time constant, switches off the electrical machine before it is short-circuited.

[0011] The time constant can be implemented by connecting a comparator input to an RC circuit, so that a level change from 0 to 1, i.e., from a low level to a high level, only affects the comparator output when the capacitor reaches a corresponding voltage level. Other implementation options include LC or LR circuits as networks that determine the time constant, in combination with digital logic circuits in CMOS or TTL technology, such as AND, OR, or XOR gates, or in the form of logic gates connected via the networks as a monostable multivibrator. The circuits that determine the time constant can also include a temperature compensation element, which at least partially compensates for the time constant's dependence on the temperature of the components used.Furthermore, elements can be provided to compensate for the dependence on the operating voltage of the circuit, for example, voltage regulators. The circuit that defines the time interval can also be a digital circuit, for example, a timer (especially a quartz crystal) and a counter, whereby the elapsed time or the reaching of the end of the time interval is determined by comparing the counter value with a predetermined value.

[0012] These circuits can be built from individual components, or integrated circuits such as freely programmable circuits, for example ASICs or field-programmable memory chips, can be used. Instead of a quartz crystal, a flip-flop or another signal source with a constant frequency can be used as the time generator. The time interval thus provided between fault detection and short-circuiting of the electric motor is preferably a few microseconds, for example between 0.1 and 10 microseconds, preferably between 1 and 5 microseconds. Furthermore, the time constant is preferably configured such that if a phase overcurrent fault occurs and subsequently an overvoltage fault occurs, for example within the time interval assigned to the phase overcurrent fault, then the time interval between detection of the overvoltage fault and short-circuiting has a length corresponding to the overvoltage fault.

[0013] To implement freewheeling and short-circuiting to ground, the electric machine is preferably connected to the power supply via a power switching device. Depending on freewheeling or short-circuit signals, this device interrupts the current flow to the electric machine or short-circuits the electric machine's current input, preferably to ground. Parts of the power switching device can also be implemented in the power supply, for example, as an additional emergency stop input that disconnects the power supply's output stages from the output or connects the output of the output stages to ground. According to a further embodiment of the invention, the power switching device can be linked to overload protection devices that protect the electric machine.

[0014] In a further embodiment of the invention, the time intervals depend not only on the types of faults but also on other operating parameters of the hybrid drive, for example, the speed of the vehicle driven by the hybrid drive, the operating mode of an internal combustion engine provided in the hybrid drive, or other safety-relevant operating parameters such as the temperature of the drive components. According to a further embodiment of the invention, the time interval between fault detection and short-circuiting is extended until the current present at the terminals of the electric machine falls below a limit value.

[0015] It is evident to a person skilled in the art that the above-mentioned measures for determining the time constant can be combined, and that the measures for controlling and carrying out the short-circuiting and interrupting of the power supply can be combined with each other. Brief description of the drawings

[0016] Exemplary embodiments of the invention are shown in the drawings and explained in more detail in the following description.

[0017] They show: Fig. 1 a circuit diagram of an electric drive with the monitoring circuit according to the invention and Fig. 2 an embodiment of the monitoring circuit according to the invention. Designs

[0018] In the Fig. Figure 1 shows an electric drive in the form of a circuit diagram implementing the monitoring circuit according to the invention. The depicted electric drive is designed to implement the fault handling method according to the invention. The electric drive comprises a voltage source 10 that supplies voltage to a pulse inverter 12. This inverter generates a pulse-width modulated output voltage from the input voltage, which supplies an electric machine 30 via a network 20. The pulse inverter is controlled by a drive controller (not shown), which controls the operation of the electric machine 30. The network 20 includes a voltage sensor 40 that measures the output voltage of the pulse inverter.Alternatively or in combination with this, the pulse inverter can output an internal voltage or a corresponding voltage signal via a terminal 42, which represents an internal voltage linked to the output voltage or the output voltage itself. The network 20 further comprises a current sensor 50, which measures the phase current flowing to the electric machine 30 and outputs a corresponding current signal. To monitor the operation of the electric machine 30, a monitoring circuit 60 according to the invention is provided, which detects a voltage signal from the voltage sensor 40 and a current signal from the current sensor 50. To detect these signals, the monitoring circuit 60 has a voltage input 62 and a current input 64.

[0019] The network 20 further comprises a controllable freewheeling switch 70 and a controllable short-circuit switch 80. The switches can be implemented as relays, MOSFETs, IGBTs, or equivalent power components. The controllable freewheeling switch 70 is located between the output of the pulse inverter and the electric machine 30 to interrupt the power supply to the electric machine 30 in the event of a fault. Fig. Figure 1 shows the controllable freewheeling switch between the current sensor 50 and the pulse inverter 12. However, this switch can also be connected in series between the current sensor 50 and the electric machine 30. In normal operation, the controllable freewheeling switch 70 is closed, allowing current to flow from the pulse inverter 12 to the electric machine 30. The controllable freewheeling switch 70 has a control input with which the switching state of the controllable freewheeling switch 70 can be controlled, and which is connected to the monitoring circuit 60 via a freewheeling output 66. If the monitoring circuit detects a corresponding fault, it can interrupt the current flow between the pulse inverter and the electric machine 30 by controlling the controllable freewheeling switch, according to the method according to the invention.Similarly, the controllable short-circuit switch 80 has an input that is connected to an output 68 of the monitoring circuit according to the invention. If the monitoring circuit detects a fault, it can control the controllable short-circuit switch 80 via the short-circuit output 68 to short-circuit the input of the electric machine 30. Preferably, the monitoring circuit 60 comprises a logic circuit that ensures that the short-circuit switch 80 only short-circuits or is controlled to short-circuit when the controllable freewheeling switch is open. Fig. In the first embodiment, the controllable short-circuit switch 80 is connected directly in parallel to the electric machine 30. Alternatively, it can also be connected to the electric machine via the current sensor 50. In another embodiment, the short-circuit switch is connected directly in parallel to the output terminals of the pulse inverter.

[0020] The electric machine 30 is preferably a synchronous machine, for example a synchronous machine with a permanent magnet as excitation, wherein, alternatively, the electric machine 30 can also be a separately excited synchronous machine, a DC motor, or an asynchronous motor. The power supply 10 is preferably the battery of a hybrid drive and can be provided by means of high-capacity lead-acid batteries or by means of suitable equivalent electrical energy storage devices. Furthermore, the power supply 10 can be provided by means of a battery with a high capacity or by means of suitable equivalent electrical energy storage devices. Fig. The circuit shown in Figure 1 includes overload protection. The voltage output 42 of the pulse inverter can output an internal current signal or other operating parameters in combination with, or as an alternative to, the internal voltage signal. The signals output by the voltage sensor 40 and the current sensor 50 can be analog voltage signals, analog current signals, or their digital equivalents. In a further embodiment, the current sensor 40 and / or the voltage sensor 50 can also include a comparator circuit that compares the detected voltage or current with a setpoint and therefore outputs a signal corresponding to the exceedance of the respective setpoint.

[0021] The inventive concept can be provided by the monitoring circuit 60, but also by a monitoring circuit comprising a voltage sensor and / or a current sensor, whereby such an implementation may further include the controllable freewheeling switch and / or the controllable short-circuit switch, or not. According to a further embodiment of the invention, the monitoring circuit according to the invention can also include the controllable pulse inverter 12 or the voltage and current sensors provided therein.

[0022] The Fig. Figure 1 shows a single-phase electric drive with the monitoring circuit according to the invention in a single-phase configuration. Alternatively, the electric machine can also be multi-phase, wherein preferably each phase has a corresponding controllable freewheeling switch and a corresponding controllable short-circuit switch, which are connected to one or more monitoring circuits according to the invention. In a multi-phase configuration with several monitoring circuits, these are preferably interconnected to transmit fault signals, for example, phase overcurrent signals and / or overvoltage signals, which are assigned to one or more phases.

[0023] The Fig. Figure 2 shows a preferred embodiment of the monitoring circuit according to the invention. The Fig. The monitoring circuit shown in section 2 includes an overvoltage input 110, which is detected by a digital level change when the voltage of the pulse inverter exceeds a threshold value. To provide a signal detectable by input 110 from the analog voltage signal, a comparator can be used that compares an analog voltage signal with a threshold value, or the voltage signal can be directly fed to the input of a digital logic element, which, due to its digital nature, also has a switching threshold.

[0024] Similarly, the in Fig. The monitoring circuit shown in Figure 2 has a phase overcurrent input 120, which preferably receives digital signals whose levels represent a phase overcurrent fault. The overvoltage input 110 is connected, via logic NAND gates, to a first comparator 130 and a first RC network 140, which together define a time constant. The overvoltage input 110 is connected to the first RC network 140 via logic NAND gates, the NAND gates 150 providing a reset input 155 that allows the overvoltage input 110 and the comparator 130, including the first RC network 140, to be reset.

[0025] The phase overcurrent 130 is connected to a second comparator 170 via a second RC network 160. Both the first comparator 130 (OPEN COLLECTOR) and the second comparator 170 (OPEN CORRECTOR) each have at least one pull-up resistor at their outputs.

[0026] When the level of the overvoltage input 110 and / or the phase overcurrent input 130 changes, the respective capacitance 144, 164 is first charged via the respective resistor 142, 162 of the respective first or second RC network. The first RC network thus comprises a first resistor 142 and a first capacitance 144, whereas the second RC network comprises a second resistor 162 and a second capacitance 164. The rate of change during a level change of the respective first or second RC network is therefore determined by the resistance value of the respective first or second resistor 142 or 162 and the first or second capacitance 144, 146 charged by it. The first or second RC network is also connected to the positive input of the first or second comparator 130, 170. The first comparator 130 and the second comparator 170 are each equipped with at least one pull-up resistor on the output side.

[0027] The output signals of the first and second comparators 130 and 170 are combined via summing NAND gates 180. The output signal of the summing NAND gate is fed via a NAND gate stage to a total summing NAND gate 190, which also receives a signal from a reset conditioning gate 200. The reset conditioning gate 200 is also a NAND gate that combines the phase overcurrent signal with the input signal of the first RC network 140.

[0028] The summation NAND gate 190 outputs a signal that controls the controllable freewheeling switch. The implementation of the summation NAND gate thus corresponds to the freewheeling output 66 of the Fig. 1.

[0029] In the Fig. 2 corresponds to the freewheeling signal 110, the output of the total summing NAND gate 190, and forms in the Fig. In the illustrated version 1, the control signal of the controllable freewheeling switch 70 is shown, which is controlled by the output 66 of the circuit 60.

[0030] Preferably, the monitoring circuit comprises the Fig. 2. Furthermore, a control circuit for the controllable short-circuit switch, which detects the occurrence of an overvoltage fault or a phase overcurrent fault and, upon the occurrence of at least one of these faults, closes the controllable short-circuit switch 80 via a control signal when the freewheeling signal returns to the inactive state. The freewheeling signal returns to the inactive state when it was previously triggered by the occurrence of one of the faults and the time interval provided by the monitoring circuit, which is triggered by the occurrence of a phase overcurrent fault or an overdrive fault, has expired or is expiring.

[0031] Preferably, the monitoring circuit comprises Fig. 2 furthermore a separate power supply circuit for the NAND gates used and the first and second comparator 130, 170, which smooths a voltage originating from a vehicle electrical system by means of smoothing devices and / or control devices and removes voltage spikes by means of filtering.

[0032] According to a further explanation of the in Fig. In the invention shown in Figure 2, the signal output of the NAND gate 190 is connected to a power stage and / or a level converter to directly control the controllable freewheeling switch and / or the controllable short-circuit switch. Furthermore, the reset input 155 can be connected not directly to a reset signal, but via another RC network, preferably with a corresponding comparator or NAND gate circuit, to apply a predetermined delay to a reset signal output to the monitoring circuit. Furthermore, the monitoring circuit can be... Fig. 2. Proceed with an input for a release signal that resets the entire circuit to a state that prevails during normal operation.

[0033] The in Fig.The circuit shown in Figure 2 can be implemented using discrete components or integrated circuits. Alternatively or in combination, a programmable logic device, for example an ASIC, an FPGA, or a microcontroller, can implement the inventive method or monitoring circuit. If a microcontroller or a CPU is used, the monitoring circuit preferably comprises non-volatile memory containing software modules that implement at least part of the monitoring circuit. In the case of such a digital implementation, a digital equivalent in the form of a counter and a clock generator can be used instead of an RC circuit to determine time intervals.In general, time intervals can be determined by counting discrete events, energy transfer processes such as those that occur when charging capacitors or generating a magnetic field in a coil, and by passing digital (or analog) signals through discrete elements, for example logic gates, where their total chain propagation time determines the time interval.

[0034] The current and / or voltage sensors used can also include analog-to-digital converters for interference-free transmission, which convert the detected current or voltage signal into a digital value. Alternatively, or in combination, the current and / or voltage sensors can also include active amplifiers that amplify the detected signal and thus modify transmission interference. The output signals of the current and / or voltage sensors can be analog and at least partially linear, digital in the form of binary values, or in the form of pulse widths or frequency-modulated signals. Furthermore, the current and / or voltage sensors can be identical to the current and / or voltage sensors of the electric machine, which are used for precise control of the machine during normal operation. Alternatively, the current and / or voltage signals can originate from the output stage that drives the electric motor, instead of from the sensors.

Claims

[1] Method for fault handling in an electric machine (30) of a hybrid drive, comprising the steps: Determine whether at least one operating parameter of the electrical machine (30) is above an associated operating parameter limit value; Activating a supply connection of the electrical machine (30) for a time interval assigned to the operating parameter, after it is detected that at least one operating parameter is above the assigned operating parameter limit value; and Short-circuit the supply connection to ground after the time interval has elapsed. [2] Method according to claim 1, wherein the operating parameters comprise a current flowing to the supply terminal and / or an output voltage of a control device connected to the supply terminal of the electrical machine (30), wherein the time interval associated with the current can be selected independently of the time interval associated with the output voltage. [3] Method according to claim 2, wherein the time interval associated with the current is greater than the time interval associated with the output voltage. [4] Method according to claim 2 or 3, wherein the current supply is interrupted for the time interval associated with the voltage before the electrical machine (30) is short-circuited when the current and simultaneously or subsequently the output voltage exceeds the respective operating parameter limit. [5] Method according to any of the preceding claims, wherein the electrical machine (30) is a synchronous machine with excitation winding and / or with permanent magnet and the control device comprises a pulse inverter (12) which generates the current and the output voltage. [6] Monitoring circuit (60) for monitoring an electric machine (30) of a hybrid drive, comprising a freewheeling output (66), a short-circuit output (68), a timer circuit and at least one detection input (62; 66) for at least one operating parameter, wherein the monitoring circuit (60) is configured to output a freewheeling signal via the freewheeling output when a limit value associated with the at least one operating parameter is exceeded, and the timer circuit provides for each of the at least one operating parameter a time interval which begins when the limit value is exceeded and at the end of which the short-circuit output (68) outputs a short-circuit signal. [7] Monitoring circuit according to claim 6, wherein the freewheeling output (66) and the short-circuiting output (68) are configured to control a control device that supplies current to the electric machine (30), which uses the freewheeling signal to disconnect the supply terminals of the electric machine (30) and the short-circuiting signal to connect the supply terminals of the electric machine (30) to ground. [8] Monitoring circuit according to claim 6 or 7, wherein the at least one operating parameter comprises a current with which the electrical machine (30) is supplied and a voltage which is applied to the electrical machine (30), wherein the time interval which is assigned to the current is greater than the time interval which is assigned to the voltage. [9] Monitoring circuit according to claim 8, wherein the time interval corresponds to the time interval associated with the voltage when the detection input detects that the current limit and then the voltage limit are exceeded simultaneously or successively. [10] Monitoring circuit according to one of claims 6-9, wherein the detection input is a serial or parallel input (110; 120) for at least one operating parameter in digital or analog form, and the timer circuit comprises: an analog circuit with an operational amplifier (130, 170), a comparator, and / or a monostable flip-flop circuit, as well as an RC, an LR or an LC network (140, 160), or a digital circuit with a timer, a counter and a counter value comparator.

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