Method for monitoring actuation device of electric motor

Abstract

The invention relates to a method for monitoring a control device (150) of an electric motor, a plurality of switching elements (159) being provided in the control device (150), a switching time being measured in at least one of the switching elements (159), and a state of the control device (159) being evaluated on the basis of the measured switching time.

Description

Technical Field

[0001] The invention relates to a method for monitoring an actuation device of an electric motor and to an arrangement for carrying out the method. Background Art

[0002] Various devices for driving electric motors are known. In principle, such a driving device comprises an arrangement of switching elements, wherein the arrangement is also referred to as an inverter or output stage and has at least one half-bridge having a first switching element and a second switching element connected in series with the first switching element. The first switching element is typically referred to as a high-side (HS) switching element and the second switching element as a low-side (LS) switching element.

[0003] A method for operating a control device for controlling an electric motor is known from the publication DE 102020203016 A1. The control device comprises at least one half-bridge having a first switching element and having a second switching element connected in series with the first switching element. The half-bridge operates with a first dead time in a first switching process in which the first switching element is disconnected and the second switching element is closed. In addition, the half-bridge operates with a second dead time in a second switching process in which the second switching element is disconnected and the first switching element is closed. An output current caused by the operation of the half-bridge and / or an output voltage caused by the operation of the half-bridge are monitored, wherein a first switching variable related to the turn-off time of the first switching element and / or the turn-on time of the second switching element is obtained from the output current and / or the output voltage, and the duration of the first dead time is dynamically adapted according to the first switching variable. In addition, a second switching variable related to the turn-off time of the second switching element and / or the turn-on time of the first switching element is obtained from the output current and / or the output voltage, and the duration of the second dead time is dynamically adapted according to the second switching variable. In particular, this can also be performed as a function of current, voltage and / or temperature.

[0004] In modern power electronics, for example inverters or power converters or power control units, such as drives of electric BDC motors (BDC: brushless direct current) electronic output stages are used in order to drive and control or regulate the current.

[0005] One of the main problems in output stages is the high failure rate during operation, which can be caused by thermal or mechanical loads, electrical overload or by aging.

[0006] This results in a fault in the output stage in each case, wherein the only reaction to this event is to initiate a faulty operation of the output stage or to switch off the output stage. For safety-critical applications, there is only one possible option for reacting after a fault in the output stage, which can lead to potential dangers for the user. Therefore, components are often overdesigned in order to minimize the risk of potential dangers. However, this is associated with high costs.

[0007] A fault in the power unit or in the power component can only be detected if the functionality is impaired. The system can therefore only react to a fault or defect, which can lead to potential dangers for the user. Until now, it has been impossible to generate a warning of an impending system failure for power electronic components. The only possible solution is to set up a damage counter for the component over temperature or time or temperature deviation, which can excessively limit the operating time.

[0008] In order to prevent components of the output stage, such as MOSFET, IGBT, etc., from overheating and thus being damaged, temperature-detecting components, such as diodes on the chip of the components of the output stage or temperature-dependent elements, such as NTC, PTC, diodes, etc., which are hermetically mounted on one or more components of the output stage, are used to measure the temperature of the device, since most faults are caused by excessive temperatures of the chip, and this can be detected using such measures. Nevertheless, since the measuring or detection element measures the temperature of the chip passively, not all faults can be detected by such a measuring or detection element. Therefore, if only some units are damaged and cause a cascading fault or failure of the MOSFET, it is unlikely that the measuring element will detect the fault in advance and the system will be able to react appropriately. Summary of the invention

[0009] Against this background, a method is described having the features of claim 1 and an arrangement according to claim 10. Embodiments are derived from the dependent claims and from the description.

[0010] The method described is used for monitoring an actuation device of an electric motor, wherein a plurality of switching elements, for example MOSFETs, are provided in the actuation device. The switching times are then measured in at least one of the switching elements. The state of the actuation device is evaluated based on the measured switching times. This means that the measured switching times, for example, allow conclusions to be drawn about the switching element whose switching times are measured and thus also about the state of the output stage in which the switching element is located and even about the state of the entire actuation device. Typically, only one half-bridge can be monitored per signal.

[0011] Based on the fact that temperature and other fault mechanisms can lead to increased switching times, the idea is to monitor the switching times of the switching element. If the measurement of the switching times shows high values ​​for the switching times based on the measured currents and voltages, this indicates that the MOSFET or the thermal cooling path of the MOSFET is damaged, more precisely due to increased temperatures. Such increased temperatures can also be caused by other components. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Further advantages and embodiments of the invention are apparent from the description and the drawings.

[0013] It goes without saying that the features mentioned above and those yet to be explained below can be used not only in the respectively specified combination but also in other combinations or alone without departing from the scope of the present invention. Among them:

[0014] Figure 1 The diagram shows the course of a signal for illustrating the HS turn-off behavior in the case of a defective MOSFET;

[0015] Figure 2 The diagram shows the course of a signal for illustrating the HS turn-off behavior in the case of an intact MOSFET;

[0016] Figure 3 The circuit diagram shows a half-bridge with a call path and the entire control device.

[0017] Figure 4 The circuit diagram shows a single HS / LS switch with a call path.

[0018] Figure 5 The diagram shows the curve of the signal when measuring the switch-off time in the case of a HS MOSFET / IGBT.

[0019] Figure 6 A comparison between call signals from a set of call signals is shown graphically with respect to temperature. DETAILED DESCRIPTION

[0020] The invention is schematically illustrated in the drawings based on exemplary embodiments and is described in detail below with reference to the drawings.

[0021] Figure 1The switching behavior of a damaged HS-MOSFET is shown in diagram 10. The HS-MOSFET is damaged, for example, by mechanical damage, in this case by overloading and thus deep crack formation in the chip. The time t [s] is plotted on the abscissa 12 of the diagram 10 and the voltage [V] is plotted on the ordinate 14 thereof, in which the U at the HS-MOSFET is shown. DS 20. U at LS-MOSFET DS 22. U at HS-MOSFET GS 24 and U at LS-MOSFET GS The trend of 26.

[0022] Figure 2 The switching behavior of an undamaged HS-MOSFET is shown in diagram 50. The time t [s] is plotted on the abscissa 52 of the diagram 50 and the voltage [V] is plotted on the ordinate 54 thereof, wherein the U DS 60. U at LS-MOSFET DS 62. U at HS-MOSFET GS 64 and U at LS-MOSFET GS The trend of 66.

[0023] As can be seen, the gate plateau voltage of a damaged MOSFET increases, which leads to increased switching times of the switching device, in this case the MOSFET.

[0024] To measure the switching times, for example, the phase feedback signal or the call path signal can be measured, which can be used Figure 3 This is performed by the switching circuit shown in FIG.

[0025] Figure 3 A half bridge is shown on the left, which is generally designated by reference numeral 100. The half bridge 100 comprises a HS-MOSFET 102 and a LS-MOSFET 104. Furthermore, the diagram shows a voltage for a battery V BAT A connection 110 for ground, a connection 112 for ground, a gate connection 114 for HS-MOSFET 102, a gate connection 116 for LS-MOSFET 104, a source connection 118 for HS-MOSFET 102 and a source connection 120 for LS-MOSFET 104. MOSFETs 102, 104 thus act as switching elements.

[0026] The diagram furthermore shows an output 122 for a control signal for a consumer and an output 124 for state feedback, a so-called call path 124 .

[0027] A first curve 130 shows the course of a square wave signal applied to the gate terminal 114 of the HS-MOSFET 104. A further curve 132 shows the course of a square wave signal applied to the call path 124. An arrow 140 shows the time difference between the two curves 130, 132 when switched off, and an arrow 142 shows the time difference between the two curves 130, 132 when switched on.

[0028] exist Figure 3 The right side of the diagram shows a control device for controlling an electric motor in a block diagram, wherein the control device is generally denoted by reference numeral 150. The control device 150 includes a microcontroller 152, a gate driver unit (GDU) 154, a signal conversion-feedback switching circuit 156, and an output stage 158, in which at least one half bridge 100 and thus a switching element 159 are arranged.

[0029] Signal is the PWM signal U for HS-MOSFET PWM,HS 160. PWM signal U for LS-MOSFET PWM,LS 162. Signal U for the gate of HS-MOSFET GATE,HS 164. Signal U for the source terminal of HS-MOSFET SOURCE,HS 166. Signal U for the gate of LS-MOSFET GATE,LS 168. Signal U for the source terminal of LS-MOSFET SOURCE,LS 170, corresponding to the signal U SOURCE,HS 166 phase signal U PHASE 172 and signal U PFB , phase readback signal 174. This is a signal 124 adapted to the logic voltage, which can have a significantly higher voltage.

[0030] Figure 4 The call path for a single HS / LS switch, for example for an n-channel MOSFET, is shown. It is also possible to use a p-channel MOSFET. Figure 3 As in , the diagram shows LS switch 200 and HS switch 202 together with connections and control signals and signals on the call paths.

[0031] If a longer switching time is imposed at a phase by means of a switching circuit, a measuring device, such as a microcontroller, can measure the switching time of the phase. Thus, if, for example, the THS_OFF time is longer than expected for the provided state, this indicates an overheating temperature or a malfunction of the device.

[0032] Figure 5 Shows different signal trends, namely U GS,HS 250, UGS,LS 252.U DS,LS 254.U DS,HS 256,U PWM,HS 258.U PWM,LS 260, U PFB 262. The double arrow indicates the duration, i.e. the set dead time T Dead,set 270. Time T HS,off 272. Time T LS,on 274 and unused dead time T Dead,unused 276.

[0033] Thus, a measuring device, for example a microcontroller controlling the inverter, can detect the fault before it leads to a complete failure of the inverter and can initiate suitable counter measures. The overtemperature can be detected based on the fact that the threshold voltage increases with temperature and the resulting increase in the switching time can be measured or estimated at the same current and the same voltage. Figure 6 This can be seen in the chart in .

[0034] The temperature [° C.] is plotted on the abscissa 302 of the diagram 300 and the switching time difference [%] is plotted on the ordinate 304 thereof. Figure 6 The diagram shows a comparison between the call signals over the temperature, wherein the curve of the acquired values ​​is respectively shown together with the curve of the linear interpolation.

[0035] The diagram shows a first trend 310 with a difference of 1A from interpolated trend 312 , a second trend 314 with a difference of 2A from interpolated trend 316 , a third trend 318 with a difference of 5A from interpolated trend 320 , and a fourth trend 322 with a difference of 10A from interpolated trend 324 .

[0036] If the measured switching time exceeds the calculated switching time at the maximum permissible temperature, a fault or overtemperature can therefore be detected. For example, a switching time of 850 ns is calculated at a current of 50 A and a drain-source voltage of 13 V is calculated at a temperature of 175° C. If the measured switching time under these conditions is higher than this 850 ns, this indicates that the switching device has an overtemperature or is damaged.

[0037] It is now possible to warn the user of a faulty device, thereby preventing a potentially dangerous situation before the device fails completely. It is also possible to put the device into emergency operation before a defect occurs.

[0038] Some definitions are given below:

[0039] The switching time is the time between the change in the signal at the input, that is, at the gate, which sends the command to the output stage, and the change in the signal at the output U DS , that is, the duration between the points in time at which the drain-source-voltage changes, the operating time delay.

[0040] The duration between switching of the half-bridge is:

[0041] UDS_Highside-off and UDS_Lowside-on are called the dead time of the falling edge, and

[0042] UDS_Highside_off and UDS_Highside_on are called the dead time of the rising edge.

[0043] The basic idea is to calibrate the switching time of each MOSFET / IGBT of the power device once for a specified current or multiple specified currents, voltages (plurality) and chip temperature and to permanently or occasionally recalculate or determine the switching time (plurality) of the power device (plurality) during normal operation.

[0044] In order to estimate the switching times from the feedback signal, the known currents must be:

[0045] flows into the output stage in order to measure the switch-on and switch-off times of the LS switches,

[0046] from the output stage in order to measure the switch-on and switch-off times of the HS switches.

[0047] The required known current can be generated by the output stage itself or by an external source. The applied voltage can also be measured in order to increase the accuracy.

[0048] Requirements for half bridge:

[0049] The dead time between HS-switching and LS-switching is set to be greater than the necessary minimum dead time.

[0050] The dead time for the falling edge and the dead time for the rising edge should be determined individually for each half-bridge.

[0051] Require:

[0052] The switching times of the MOSFET / IGBT should be determined at least at one temperature. This can also be performed at several temperatures. The measurement(s) are used as reference value(s).

[0053] The switching time of the MOSFET / IGBT should be determined at least at one current. This can also be done at several currents. The measurement(s) is used as reference value(s).

[0054] The switching time of the MOSFET / IGBT should be determined at at least one voltage. It is also possible to carry out this at several voltages. The measurement(s) are used as reference value(s).

[0055] A phase feedback signal should be provided for a logic circuit. This should be done, for example, for a comparator in order to be able to read out the phase feedback signal for an internal measuring device, for example for a microcontroller or the like.

[0056] The difference between the set signal and the signal read back is measured, for example, by a microcontroller.

[0057] The switching time is the duration, the operating time delay, between the command being sent to the input of the output stage, that is to say the signal change at the gate, and the load voltage changing.

[0058] The advantages of the described method embodiment compared to earlier solutions are:

[0059] Earlier solutions were only able to detect overtemperatures in switching devices by measuring the temperature of the switching element using a separate measuring device.

[0060] Known systems can only detect a fault when a device fails and affects the system. Now it is possible to detect a component before it is damaged.

[0061] The new approach makes it possible to identify faults before they have disruptive effects on the system.

[0062] This enables appropriate countermeasures to be initiated before a disturbance in the system presents a potential danger to the user.

[0063] Aging effects of the thermal connection between each individual component of the output stage and the heat sink can be detected by comparison with a temperature model relating to the lifetime.

[0064] Early warnings can be generated before the run is completed.

[0065] The safety margin due to overdesign can be reduced to a minimum.

[0066] There is no need to implement a fault counter which would unduly limit the lifetime.

[0067] Increased safety for the user and increased system availability are achieved.

[0068] More failure modes can be detected than when temperature alone is used.

[0069] The general advantages of the method are independent of the internal or external sensors used.

[0070] Digital measurement of the feedback signal edge instead of the signal with small level and high impedance of the analog thermal sensor, such as the measurement of the parasitic body diode, can be achieved. This is also robust in terms of electromagnetic compatibility.

[0071] If phase / load feedback monitoring is implemented, the method can then be used for each individual power device in each half-bridge B2 , B4 , B6 , . . . or in an individual power switch.

[0072] A simple measuring switch circuit can be used.

Claims

1. A method for monitoring a control device (150) for an electric motor, wherein: A plurality of switch elements (159) are arranged in the control device (150). measuring a switching time in at least one of the switching elements (159), and A state of the actuation device (159) is evaluated based on the measured switching times.

2. The method according to claim 1, which is performed in order to detect a fault in the control device (150).

3. The method according to claim 2, wherein: If a fault is identified, the user is warned.

4. The method according to claim 2 or 3, wherein: If a fault is detected, an emergency run is initiated.

5. The method according to any one of claims 1 to 4, wherein: The measured switching times are compared with the other times.

6. The method according to claim 5, wherein: The other time is obtained by calculation.

7. The method according to any one of claims 1 to 6, wherein: The switching times are determined by means of the measured call path signal.

8. The method according to any one of claims 1 to 7, wherein: The determined switching times are taken into account via the measured current and the measured voltage.

9. The method according to any one of claims 1 to 8, wherein: MOSFETs (102, 104) are used as switching elements.

10. An arrangement of an actuation device (150) for monitoring an electric motor, the arrangement being designed to carry out a method according to any one of claims 1 to 9.

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