Method and device for identifying single defective semiconductor switch

Abstract

The invention relates to a method for identifying individual semiconductor switches (210, 340) of a half-controlled H-bridge (100) having a permanent conduction defect for setting an excitation current of an externally excited synchronous machine (10), in which a target excitation current as a function of a request (21) and the measured excitation current are detected in order to determine an adjustment deviation, and outputs a fault signal (31) when the adjustment deviation exceeds an adjustment deviation threshold value (960). Furthermore, for improvement, the actual duty cycle of the control signal is compared with a standard duty cycle for the target excitation current value, which standard duty cycle corresponds to the currently measured excitation current value. If the set duty cycle deviates from the determined standard duty cycle (1070) or the standard duty cycle range (1080) due to the absence of knowledge of the resistance of the field winding (460), a fault signal (31) is also output. The invention also relates to a control device (1200) having a corresponding detection device (1240).

Description

Technical Field

[0001] The invention relates to a method for identifying individual semiconductor switches having a permanent conduction defect of a half-controlled H-bridge for setting the field current of an externally excited synchronous machine. The invention also relates to a control device having a detection device for identifying individual semiconductor switches having a permanent conduction defect of such a half-controlled H-bridge for setting the field current. Background Art

[0002] The semi-controlled H-bridge circuit, also referred to as the semi-controlled H-bridge, is often used as a control circuit for generating the excitation current of an externally excited synchronous machine. Figure 1 Schematically shown in FIG. 1 . The circuit 100 comprises a bridge branch 200 and a further bridge branch 300. The one bridge branch 200 comprises a semiconductor switch 210, which is also denoted by the abbreviation T1. A diode 230 polarized in the cut-off direction and also referred to as D3 is connected in series with the semiconductor switch 210. The other bridge branch 300 comprises a further diode 320 arranged in the cut-off direction, which is also referred to as D2. In the other bridge branch 300, a further semiconductor switch 340 (also referred to as T4) is arranged in series with the further diode.

[0003] A load branch 400 is formed between a connection point 250 of one bridge branch 200, between a semiconductor switch 210 and a diode 230, and another connection point 350 of another bridge branch 300, between another diode 320 and another semiconductor switch 340. The load branch comprises an excitation winding 460, for which an ohmic winding resistance 465 and a winding inductance 467 are shown as an equivalent circuit. In addition, in the load branch, a current measuring device 480 is constructed in series with the excitation winding 460. The current measuring device 480 is designed to measure the excitation current I exc . Excitation voltage U exc The bridge branch 200 and the other bridge branch 300 are connected to the supply voltage U at the ends 201, 301. DC The intermediate circuit capacitor 500 is connected to the positive pole 51 of the bridge branch 200 and is connected to the negative pole 52 of the supply voltage at the opposite ends 202, 302. The intermediate circuit capacitor 500 is arranged in parallel with the bridge branch 200. The supply voltage U DC In addition, a current measuring device 180 is provided, which can measure the total current I flowing through the half-controlled bridge circuit 100 DC The voltage measuring device 190 is designed in parallel with the intermediate circuit capacitor 500 and measures the supply voltage U DC .

[0004] In order to realize the excitation current I according to a request from the driver, for example, in a vehicle driven by an externally excited synchronous machine exc , semiconductor switches T1, T4; 210, 340 are controlled by pulse width modulation control signals respectively. When semiconductor switches are mentioned below, one semiconductor switch 210, T1 and another semiconductor switch 340, T4 are meant. When one of the semiconductor switches is mentioned, this can be one semiconductor switch 210, T1 or another semiconductor switch 340, T4.

[0005] The control signals 611 and 621 have the same frequency but are offset from each other by half a period T. PWM (See Figure 2 ). When not only one semiconductor switch 210, T1 is turned on, but also another semiconductor switch 340, T4 is turned on at the same time, current flows through the half-controlled semiconductor bridge.

[0006] The control signals each have the same duty cycle, which is 50% or greater. The duty cycle is understood to be the period T of the signal at which the control signal is at a level that switches the controlled corresponding semiconductor switch 210, 340 to the on state. PWM The greater the pulse width of the control signal, the longer the time period during which current can be fed into the excitation winding 460.

[0007] exist Figure 2 In the figure, five graphs 610-650 are schematically shown in sequence, and the graphs are respectively relative to time 601 with a period T of the pulse width modulation signal. PWM The top two graphs 610, 620 indicate pulse width modulated control signals 611 and 621 for controlling one semiconductor 210, T1 and another semiconductor 340, T4. Levels 612, 622 are plotted relative to time 601. Since the semiconductor switch 210, T1 is closed and turned on when the control signal 611 has a level of 1, and is closed and blocked when the level is 0, the graph 610 and similar graphs 620 can also be interpreted as state diagrams, and the control signals 611, 621 can be interpreted as state curves of the corresponding semiconductor switches T1, 210 and T4, 340. The excitation voltage 631 is plotted in the graph 630. In the time range 635 where the two control signals have a level of 1, a drop corresponding to approximately U on the excitation winding occurs. HV A positive voltage is shown in the diagram 640. A changing excitation current 641 is shown. When both semiconductor switches 210, 340, T1, T4 are turned on, the excitation current rises sharply over time and falls slightly more slowly in the range where at least one of the semiconductor switches 210, 340 is in the closed state.

[0008] In the last diagram 650 , the total current I flowing through the half-controlled half-bridge is plotted against time 601 . DC 651.

[0009] In the illustrated variant according to the prior art, the two control signals 611 , 621 are offset by half a period T PWM / 2. This offers the advantage that the current fed into and out of the intermediate circuit capacitor 500 remains low. In addition, the frequency of the current ripple in the active semiconductor switch is twice the switching frequency of the individual semiconductor switches, which is advantageous for the ripple of the excitation current. In addition, the power losses are evenly distributed on the semiconductor switches and the diodes, respectively. In addition to the center-positioned pulse width modulation shown here, edge-related pulse width modulation can also be used, in which the control signals 611, 621 are also offset by half a pulse width modulation period.

[0010] It is important when controlling the semiconductor switches 210, T1; 340, T4 that the voltage at the field winding changes and is equal to the positive supply voltage, for example the traction network voltage, or to the negative sum of the forward voltages of the diode and the semiconductor (approximately -2 V to -3 V) each time one of the semiconductor switches 210, T1 or 340, T4 is switched on or off. The current then undergoes a series of exponential functions and rises relatively steeply in the case of a positive voltage at the field winding, limited by the inductance 367, and falls relatively slowly in the short-circuit phase, i.e. when the semiconductor switch is closed.

[0011] The description so far presupposes that the two semiconductor switches 210, T1; 340, T4 are correctly switched according to the control signals 611, 621. Since the field winding 460 is usually designed as the rotor of a synchronous machine and usually has a large inductance 467, in the event of a fault, it is necessary to short-circuit the field winding 460 by one of the two semiconductor switches (one semiconductor switch 210, T1 or the other semiconductor switch 340, T4). Due to the current direction, the corresponding diode 320 or 330 of the other bridge branch 200, 300 is conductive. If no short circuit occurs, energy will flow from the large inductance of the field winding of the rotor into the intermediate circuit of the inverter. If, in the case of regeneration, the battery contactor opens relatively simultaneously with the short circuit, including immediately before or immediately after the short circuit, and the converter is therefore no longer connected to the traction network battery, the capacity of the conventional intermediate circuit capacitor 500 is usually insufficient to prevent overvoltage from damaging the main inverter and / or the H-bridge circuit described here and possibly other high-voltage (HV) components. Therefore, it makes sense to determine in advance whether one of the semiconductor switches is defective.

[0012] For a fault situation in which one of the two semiconductor switches remains permanently open despite being controlled, the excitation current I excwill drop to 0 in a short period of time (usually a few hundred milliseconds). If both switches are permanently turned on, the supply voltage U DC Permanently as field winding U exc The voltage applied causes a sharp increase in the current through the field winding. Overcurrent detection can reliably detect this fault and shut down the supply voltage. A more difficult and critical situation is that one of the two semiconductor switches 210, 340 no longer switches and remains in a permanently on state and is therefore defective, while the other semiconductor switch still switches normally. The cause of this defect may lie in the control circuit or may also lie in a defect in the semiconductor switch 210 or 340 itself.

[0013] DE 10 2014 102 869 A1 describes that a first switching element is provided in a rotating electrical machine for stopping the supply of a current for excitation, which excites a field winding. A detector detects, based on a voltage at a control terminal of the current for excitation, how the current for excitation is supplied to the field winding via the control terminal of the current for excitation. An abnormality determiner determines, based on a detection result of the detector and a voltage induced on a stator winding of at least a single phase, whether an abnormality exists in at least one second switching element connected to an output terminal of the stator winding of at least a single phase. A second drive controller controls the drive of the first switching element based on the determination result of the abnormality determiner. Summary of the invention

[0014] The object of the invention is to specify a method and a device with which the identification of a single defective semiconductor switch in a half-controlled H-bridge for an externally excited synchronous machine can be detected in a simpler manner, wherein one of the semiconductor switches has a permanent conduction defect.

[0015] According to the invention, this object is achieved by a method having the features of the invention and by a control device having the features of the invention. Advantageous embodiments emerge from the exemplary embodiments.

[0016] The invention is based on the idea of ​​identifying and utilizing deviations in a regulator in order to identify a defective state of a single semiconductor switch. In particular, a method for identifying a single semiconductor switch with a permanent conduction defect in a semiconductor switch of a half-controlled H-bridge for setting an excitation current of an externally excited synchronous machine is implemented, wherein the half-controlled H-bridge circuit has a bridge branch, another bridge branch, and a load branch, wherein the one bridge branch has a semiconductor switch T1 and a diode D3 connected in series in the reverse direction, the other bridge branch includes another diode D2 connected in series with another semiconductor switch T4 in the reverse direction, and the load branch includes an excitation winding of the externally excited synchronous machine, wherein the load branch connects a connection point between a semiconductor switch T1 and the diode D3 in the one bridge branch to another connection point between another diode D2 and another semiconductor switch T4 in the other bridge branch, and wherein a load branch for measuring the current excitation current is arranged in the load branch. A current measuring device for a magnetizing current; wherein a semi-controlled H-bridge circuit is coupled to a control device, the control device comprising an excitation current regulator, which generates two pulse width modulated control signals of the same frequency and phase-shifted by half a period for controlling a semiconductor switch and a further semiconductor switch, so that the excitation current flowing through the load branch can be adjusted according to requirements (command variable) by pulse width modulation of the control signal, wherein the duty cycle in normal operation is limited to a range of 50% to 100%, wherein the duty cycle is the ratio of the time pulse width of the signal level that puts the controlled semiconductor switch into the conducting state to the period of the control signal, and wherein the load branch comprises a current measuring device in order to measure the excitation current, which is used as a feedback signal (regulation variable) by the excitation current regulator, wherein the method comprises the following steps:

[0017] The excitation current is detected, a target excitation current according to the requirement is compared with the excitation current measured and detected by the current measuring device to determine the regulation deviation, and the regulation deviation is compared with a regulation deviation threshold, and a fault signal is output if the regulation deviation differs from the regulation deviation threshold by more than a tolerance range.

[0018] If a certain threshold value of the control deviation is exceeded, it can be assumed that one of the semiconductor switches is switching correctly, but the other semiconductor switch is defective, or is in a permanently conductive state, at least if the excitation current is still measured and has not decayed completely to 0. Therefore, if the control deviation occurs above the control deviation threshold value, a fault signal is output, which indicates that one of the semiconductor switches in the permanently conductive state is defective.

[0019] Accordingly, a control device having a detection device is implemented, wherein the detection device is used to identify a single semiconductor switch with a permanent conduction defect in the semiconductor switches of a half-controlled H-bridge, wherein the half-controlled H-bridge is used to set the excitation current of an externally excited synchronous machine, wherein the half-controlled H-bridge includes a bridge branch, another bridge branch, and a load branch, wherein the one bridge branch has a semiconductor switch T1 and a switching diode D3 connected in series in the cut-off direction, the other bridge branch includes another diode D2 connected in series with another semiconductor switch T4 in the cut-off direction, and the load branch includes the excitation winding of the externally excited synchronous machine, wherein the load branch connects a connection point between a semiconductor switch T1 and the diode D3 in the one bridge branch and another connection point between another diode D2 and another semiconductor switch T4 in the other bridge branch, and wherein a current measuring device for measuring the current excitation current is arranged in the load branch; wherein the control device includes an excitation current regulator, which is designed to generate two A control signal of pulse width modulation of the same frequency and with a phase shift of half a period is used to control a semiconductor switch and another semiconductor switch, so that the excitation current flowing through the load branch can be adjusted according to requirements (command variable) by pulse width modulation of the control signal, wherein the duty cycle in normal operation is limited to a range of 50% to 100%, wherein the duty cycle is the ratio of the time pulse width of the signal level that puts the controlled semiconductor switch into a conducting state to the period of the control signal, and wherein the load branch includes a current measuring device to measure the excitation current, which is used as a feedback signal (control variable) by an excitation current regulator, wherein the detection device is designed to detect the excitation current measurement value of the current measuring device, and compare the target excitation current value required by the excitation current regulator with the detected excitation current measurement value to determine the control deviation, and compare the control deviation with a control deviation threshold value, and output a fault signal if the control deviation differs from the control deviation threshold value by more than a tolerance range.

[0020] The detection device is preferably implemented using a program-controlled processor and a program memory in which a program code is stored, and when the program code is executed on the processor, the steps of the method described here are implemented in conjunction with the half-controlled H-bridge described here. As a result, a control device that can detect faults of semiconductor switches can be formed in a simple manner. Since the duty cycle of each control signal is limited to at least 50%, the regulator can no longer adjust the required small excitation current in a suitable manner. Since the excitation winding is supplied with voltage for half the duration of each period of the control signal, a minimum current is present in the excitation winding.

[0021] However, the diagnosis can also be extended or improved to other areas. To this end, in one embodiment of the invention, it is provided that the supply voltage U applied to the half-controlled H-bridge is detected.DC , and for the supply voltage U DC A standard duty cycle for a target excitation current value is determined, which corresponds to the currently measured excitation current value for the possible minimum resistance of the load branch, and a fault signal is output if the currently set duty cycle is less than the determined standard duty cycle. The standard duty cycle required to generate a specific excitation current depends largely on the ohmic resistance of the excitation winding. For example, this resistance value may fluctuate due to manufacturing tolerances. Another important influencing factor is the temperature of the excitation winding, which is usually formed in the rotor of the synchronous machine. Taking into account the fluctuation range of the resistance of the excitation winding, it is possible to estimate how large the duty cycle is required to obtain a specific target excitation current value at a given size of the supply voltage. The simplest estimate assumes that if both semiconductor switches of the half-controlled H-bridge are functioning properly, the minimum duty cycle for the possible lowest resistance value must be exceeded. This duty cycle that determines the target excitation current value is called the standard duty cycle. If the set duty cycle of the excitation current regulator is lower, this is a reliable sign that one of the semiconductor switches has a permanent conduction defect.

[0022] In one embodiment, it is considered that the duty cycle can be estimated for a certain target current based on the fluctuation range of the resistance of the load branch and the fluctuation range of the rotor resistance at a given supply voltage. This results in a standard duty cycle range, i.e., a range within which the duty cycle set for a currently detected excitation current value or a target excitation current value in the case of a properly functioning semiconductor switch can lie. Depending on the actual resistance of the load branch or the excitation winding, which largely determines this resistance, different duty cycles may be required in a properly functioning H-bridge circuit (in which the two semiconductor switches are correctly switched) in order to generate the corresponding excitation current.

[0023] Therefore, in one embodiment, it is provided that the supply voltage U DC , and determining a standard duty cycle range for the excitation current value or the target excitation current value measured relative to the currently set duty cycle on the one hand and for the detected supply voltage on the other hand, the standard duty cycle range includes the following duty cycles, which correspond to the currently measured excitation current value or the required target excitation current for possible different load branch resistances, and checking whether the currently set duty cycle is within the standard duty cycle range, and detecting a short-circuited switch if the currently set duty cycle is not within the determined standard duty cycle range.

[0024] As mentioned above, due to manufacturing tolerances and / or due to the lack of knowledge of the actual field winding temperature, the possible fluctuation range of the resistance may be quite large. In field windings with aluminum or copper as the main component, the resistance changes by about 4 parts per thousand (α = 4x10 -3 / K). The resistance of the field winding can be estimated according to the following formula:

[0025] R exc (θ) = R exc,nom ·(1+α(θ min -20℃))·(1±δ)

[0026] It is assumed here that the standard resistance of the excitation winding R exc,nom is the resistance of the field winding at 20°C. Assume that the manufacturing tolerance δ is about 20% in accordance with reality. With a standard resistance value R at 20°C ext,nom The resistance of the field winding is about 0.6·R ext,nom To about 2·R ext,nom For example, in a case with a standard resistor R exc,nom = 10Ω (10 ohms) in the field winding, the resistance range is approximately from R exc,nom =6Ω(6 ohms) changes to the maximum value R exc,max =20Ω (20 ohms). Here, for the minimum value assumption, the lowest temperature is θ min = -40°C. For the maximum rotor temperature θ max Assuming a value of 180°C (θ max =180°C).

[0027] Therefore, in the embodiment of measuring the temperature of the excitation winding in the load branch, a decisive improvement can be achieved. Therefore, in a further embodiment, it is provided that the temperature of the excitation winding in the load branch is detected and the resistance of the excitation coil is calculated based on the detected temperature in order to limit the standard duty cycle range.

[0028] A further improvement can be achieved if the resistance of the load branch is calibrated under known temperature conditions of the field winding in order to compensate for uncertainties in the resistance of the load branch due to manufacturing tolerances.

[0029] However, it is usually difficult to measure the temperature of the field winding using sensors, since the sensors are implemented in the rotor. Therefore, in one embodiment, it is provided that the temperature of the field winding is predicted continuously and iteratively based on a temperature model, which takes into account the measured and detected field current and the duration between the measurements. If the distance is small enough, the temperature of the field winding can be predicted very well from this. For further improvement, other provided measured values, such as the ambient temperature, the stator temperature, possible coolant temperature, etc., can be detected and included. The temperature determined using the temperature model is then used to limit the standard duty cycle range, thereby enabling reliable detection of defective semiconductor switches, especially also at high currents, wherein the standard duty cycle range also includes a plurality of duty cycles.

[0030] The starting temperature of the temperature model can be derived from the detected ambient temperature or other measured or calculated temperatures after a longer standstill of the machine.

[0031] This ensures that the temperature model is always optimally adapted to the actual temperature of the field winding.

[0032] Another possibility of determining the resistance of the field winding as accurately as possible, either additionally or alternatively, is to calculate the resistance of the load branch from the detected supply voltage and the detected field current, which are measured for the duty cycle last set in the associated standard duty cycle range. This duty cycle enables the identification of defective, permanently conducting semiconductor switches as quickly as possible even in the case of the required large field current. Even in the case of the required high current for the field current, the field current regulator must reduce the duty cycle relative to the standard duty cycle, which corresponds to the correct resistance value under the condition of a known supply voltage if one of the two semiconductor switches fails. Here, it is utilized that the time scale of the temperature-dependent change of the resistance of the field winding is greater than the time constant of the current regulation. On the contrary, in these cases, the control variable field current will not deviate. Therefore, monitoring the duty cycle enables more reliable detection of defective semiconductor switches.

[0033] Especially for the situation that the excitation winding must be short-circuited in the event of a fault, it is particularly advantageous to know the faulty, permanently closed semiconductor switch. In this case, it must be avoided that the semiconductor switch that is functioning properly is closed to cause a short circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The present invention will be described in more detail below with reference to the accompanying drawings. In the accompanying drawings:

[0035] Figure 1 shows a schematic diagram of a half-controlled H-bridge for generating an excitation current;

[0036] Figure 2 Different diagrams are shown, which are plotted against time in units of the time per pulse width period, wherein the control signal of the semiconductor switch, the voltage dropped across the excitation coil, the change in the excitation current and the total current flowing through the entire circuit are respectively graphically shown;

[0037] Figure 3 shows the case where one of the semiconductor switches has a permanent conduction defect Figure 2 Comparable charts;

[0038] Figure 4shows a graph of the actual field current plotted against the target field current, once for a case where both semiconductor switches are switching correctly and once for a case where one of the semiconductor switches has a permanent conduction defect;

[0039] Figure 5 A schematic diagram showing the duty cycle of different resistances of the field coil winding plotted against a target field current is shown;

[0040] Figure 6 A schematic diagram of a motor vehicle with an externally excited synchronous machine is shown, which is controlled by means of a half-controlled H-bridge via a control device having a detection device for detecting semiconductor switches with a permanent conduction defect, and

[0041] Figure 7 A schematic diagram of a flow chart of a method for identifying a semiconductor switch having a permanent conduction defect is shown. DETAILED DESCRIPTION

[0042] exist Figure 3 In the above description Figure 2 Similarly, the signal curves and the measured variables determined or derived therefrom are shown for the operation of a half-controlled H-bridge, wherein one of the semiconductor switches (not limited to the Figure 1 The other semiconductor switch 210, T1 of the versatility) has a permanent conduction defect. In the diagram 820, the level 822 of the control signal 821 for another semiconductor switch 340, T4 is plotted in the period length of the pulse width modulated control signal relative to time 801. In the case of a properly functioning semiconductor switch 100, the diagram can also be understood as a state diagram of another semiconductor switch 340, T4. In the case of level 0, the semiconductor switch 340, T4 is disconnected, that is, not conducting, and correspondingly in the case of level 1, it is turned on and closed. The diagram 810 correspondingly shows a control signal 811 of a semiconductor switch 210, T1, which is shown as a dotted line. The level 812 is plotted relative to time 801. The switching state 813 of a semiconductor switch 210, T1 is shown as a solid line. The one semiconductor switch is permanently conducting, which corresponds to level 1. The third diagram 830 shows the voltage U dropped on the excitation coil 460. exc 831. Since one semiconductor switch 210, T1 is permanently turned on and a minimum duty cycle of 50% is set for the control signal 811 of the other semiconductor 340, T4, the supply voltage U DC is applied to the excitation winding 460 at least half of the time.

[0043] This results in a minimum excitation current I exc_min Flows in the field winding 460. The fourth graph 840 shows the field current I excThe amplitude of the current 841 fluctuates. Compared with the normal operating state, the frequency of the current change is halved. The fifth graph 850 shows the total current I DC 851.

[0044] exist Figure 4 In the example, the excitation current I exc，ist 910 as the ordinate, using the target current I exc，soll 920 as the horizontal axis. First, I exc,ist with I exc,soll The relationship of 930 graphically shows the case where the two semiconductor switches are switched correctly (solid line 930). The actual current and the target current correspond to each other. The case where one of the two semiconductor switches (without limiting the general applicability of one semiconductor switch 210, T1) has a permanent conduction defect is shown by means of the dashed line 940. In the embodiment shown, a minimum excitation current of slightly less than 20 A is achieved at a minimum duty cycle of 50% for the other semiconductor switch (here the other semiconductor switch 340, T4).

[0045] As with any regulation, a certain deviation of the actual variable from the target variable must be tolerated in order to obtain a functioning regulation. This tolerable regulation deviation is limited by a regulation deviation threshold 960. If a larger regulation deviation 970 occurs in the case of a static or slowly changing target variable, the detection device can determine that one of the semiconductor switches is defective. In the example shown, such a regulation variable deviation greater than the regulation deviation threshold occurs for all requests for field currents that result in a target field current in the range of 0 to approximately 17.5 A. Figure 4 980 is also shown for an incredibly large control deviation. The half-controlled H-bridge cannot generate an excitation current in this range, since the minimum current is already slightly below 20 A. For target currents above the threshold of 17.5 A, a defect in one of the semiconductor switches cannot be detected based on the control deviation. Only at target currents below 17.5 A does a detectable control deviation occur.

[0046] In the example shown, however, in the range above 17.5 A, detection is possible at least in many cases if the duty factor of the field current regulator is also evaluated.

[0047] exist Figure 5 , the duty cycle 1010 is graphically plotted against the target current 1020. The dashed line with short dashed line elements indicates the duty cycle 1030 for the target current when the field winding has a minimum resistance and the two semiconductor switches are switching correctly. Accordingly, the duty cycle 1030 for generating the target current I is 1010 when the two semiconductor switches are functioning properly and the field winding has the maximum possible resistance. exc，sollThe required duty cycle 1040 is drawn as a dashed line with long dashed elements. For example, a target current of 25 A corresponds to a duty cycle 1070 between about 59% and about 82.5%, depending on the current resistance value of the excitation winding. Therefore, if a duty cycle outside this standard duty cycle range 1080 (indicated by the hatched line) is determined, the detection circuit can determine from this that one of the semiconductor switches (in the specific example, one semiconductor switch 210, T1) is defective. The duty cycle 1050 is shown as a solid line, which is necessary to produce the target current if one of the two semiconductor switches (in the specific example, one semiconductor switch 210, T1) has a permanent conduction defect and the resistance of the excitation winding or load branch is minimal. In the example shown, in the case of the minimum resistance value of the excitation winding, the minimum current is greater than the range shown in the diagram, in the case of this minimum current, the other semiconductor switch 340, T4, which is functional, switches at a duty cycle of 50%. Therefore, in the case of a minimum resistance value of the field winding, the set duty cycle of the field current regulator is always 50% and is therefore lower than the standard duty cycle 1030 for the minimum resistance, which is set for the case where the two semiconductor switches 210, 340, T1, T4 are correctly switched. Therefore, a fault can be detected in any case if the set duty cycle is lower than the standard duty cycle for the minimum resistance corresponding to the corresponding target current of the currently measured field current.

[0048] The duty cycle 1060 of the target current to be set for the case where one of the two semiconductor switches 210, 340, T1, T4 (in this case, one semiconductor switch 210, T1) has a conduction defect and the excitation winding has a maximum resistance is also shown in a dot-dash line. It can be seen that if the resistance is not sufficiently known, the duty cycle 1060 obtained for the large current is partially located in the standard duty cycle range 1080.

[0049] It is therefore advantageous to limit the field winding 460 or the load branch 400 (see Figure 1 ) to limit the standard duty range. In some embodiments, this can be done by measuring and detecting the actual temperature of the field winding 460, which is related to the resistance value. In other embodiments, the temperature and thus the resistance of the field winding are determined by temperature modeling. For example, the measured field current and the power loss across the ohmic resistance 465 derived therefrom are used to continuously model the heating of the field coil 460 during operation.

[0050] It is also advantageous to calibrate the resistance value of the field coil at a known temperature. This can be done, for example, at the end of the belt of a production line for externally excited synchronous machines. Recalibration can also be carried out after a longer downtime when the machine is not in operation. In motor vehicles, it is usually common to measure the ambient temperature, so that the value of the ambient temperature measured here can be detected by a detection device and used as the initial temperature in the modeling with respect to the temperature of the field winding.

[0051] Furthermore, in other embodiments, the resistance value can additionally or alternatively be continuously determined based on the measured and detected total current and supply voltage. Thus, the resistance finally determined for a trusted duty cycle (i.e., a duty cycle indicating that both semiconductor switches are functioning properly) can be used as the resistance value for determining the standard duty cycle. When one of the semiconductor switches has a permanent conduction defect, the excitation current increases, and the excitation current regulator tracks the excitation current by reducing the duty cycle of the two control signals. The temperature rise of the excitation winding caused by the increase in the excitation current is slower than the speed at which the current regulation adjusts the duty cycle. Therefore, even at high currents, a fault in one of the semiconductor switches due to its permanent conduction can be identified based on the knowledge of the resistance according to the deviation of the set value from the standard set value.

[0052] exist Figure 6 1 is schematically shown in FIG. 2 . The motor vehicle has an externally excited synchronous machine 10 as a drive machine. Two important influencing variables for determining the target excitation current are the current machine speed, which is proportional to the driving speed, and the torque requested by the driver (referred to here as request 21). The excitation current for the excitation winding, which is usually arranged in the rotor, is provided by a semi-controlled H-bridge circuit 100, which is controlled by a control device 1200. The electrical energy comes from a traction battery 50, which is connected to the H-bridge circuit 100, among other things. The traction battery 50 has a positive pole 51 and a negative pole 52. The control device 1200 detects the driver's request 21, for example, via an accelerator pedal 20. The control device 1200 includes a detection device 1240, which is designed to detect a single defective semiconductor switch in the semi-controlled H-bridge circuit 100 and output a fault signal 31. The fault signal can be output, for example, via a control lamp in the instrument cluster or any other display device 30 in the vehicle. Fault signal 31 can also be output as an electrical signal or a radio signal for further processing in control device 1200 or another control unit of motor vehicle 1. Control device 1200 is usually designed as a component of a pulse-controlled inverter for controlling an externally excited synchronous machine.

[0053] The same technical features as in the other figures are provided with the same reference numerals and are not explained in detail here. In particular, the H-bridge circuit 100 is substantially the same as Figure 1The H-bridge circuit 100 shown is identical. Additionally, only the temperature sensor 490 is shown, which determines the field winding temperature T exc The excitation winding temperature is provided as a temperature signal 491 .

[0054] The control device 1200 includes an excitation current regulator 1220. The excitation current regulator has a regulator unit 1221, which outputs a target current I depending on the detected demand signal. exc，soll The signal generating device 1222 of the field current regulator 1220 generates a control signal StS T1 and StS T4 The control signals are pulse width modulated control signals whose phases are shifted by half a pulse width period. The control signals control the semiconductor switches T1, 210 and T4, 340. The two semiconductor switches are designed as IGBTs, for example. DC Initially, the average voltage drops across the field winding. Here, TV is the duty cycle. This results in an average excitation current Here, R exc represents the ohmic resistance of the load branch or field winding 460. By means of the detected measured field current I which is detected as a control variable by the control device 1200 and its field current regulator 1220 exc , the excitation current I can be adjusted accordingly according to the requirement signal 21 or the requirement exc .

[0055] Combine the following Figure 7 The detection unit 1240 is described more precisely by referring to the schematic flow chart of the method for detecting a semiconductor switch with a permanent conduction defect in a half-controlled H-bridge 100. In 2010, the detection device detects the target value I of the excitation current. exc，soll On the other hand, the measured actual value I of the current measuring device 480 is detected in 2020 exc . In 2030, the detection device compares the two values ​​and forms a control deviation from this. In 2040, the control deviation is compared with a control deviation threshold and a check is performed to determine whether the control deviation threshold is exceeded. It is understood by a person skilled in the art that the amount of the control deviation is compared with the control deviation threshold. If there is a deviation above the control deviation threshold, a fault signal is generated and output in 2050, which can be provided as an electronic signal to other control devices or other control devices (not shown) and / or output on the display device 30. If the control deviation is not determined, the supply voltage U is detected by the detection device in 2060. DC Together with the detected excitation current I excAs well as one or more specifications about the resistance value of the load branch 400 or the field winding 460, in particular the resistance value of the ohmic resistor 465, it is possible to determine the duty cycle which is to be set by the field current regulator in order to generate the corresponding field current I exc Such a duty cycle is referred to as a standard duty cycle. If the resistance value of the load branch 400 is only inaccurately known, a standard duty cycle range can also be determined, which includes duty cycles that are set at different possible resistance values ​​in order to generate the currently measured excitation current I exc . In 2080, the detection device 1240 also detects the current duty cycle. In 2090, the determined standard duty cycle or the determined standard duty cycle range is compared with the actual duty cycle, and a check is made as to whether the actual duty cycle is consistent with the standard duty cycle. Here, for example, it is checked whether the actual duty cycle is lower than the minimum possible standard duty cycle. If this is the case, a fault signal is also output in 2050. Otherwise, the method is implemented iteratively. In order to improve the detection accuracy, the method may include optional method steps. For example, if the temperature measuring device 490 is arranged at the excitation winding and provides a temperature signal T exc 491, this can be detected by the detection device in 2100. Excitation winding R exc The detected resistance value can then be used in method step 2070 to determine a standard duty cycle or a standard duty cycle range. Alternatively or additionally, the total current I flowing through another current measuring device 180 of the H-bridge circuit can also be detected by the detection device in 2110. DC Together with the detected supply voltage U DC , the current resistance of the excitation winding can be calculated from this in 2120, wherein this determination is only performed when the actual duty cycle is determined for the duty cycle in the iterative implementation of the method in method step 2090, and the actual duty cycle is consistent with the standard duty cycle. There are also alternative possibilities to derive the resistance value of the excitation winding in a computational manner based on available electrical measurement variables. One or more resistance values ​​of the load branch 400 or the excitation winding 460 determined in this way are also used to determine the standard duty cycle, in order to be able to better determine this value or to limit the standard duty cycle range.

[0056] Alternatively or additionally, the knowledge of the resistance value of the load branch 400 can be improved by calibrating the resistance value at a known temperature of the field winding. This can be done, for example, at the end of the belt of the production line in 2130. Alternatively or additionally, the calibration can be carried out or repeated in 2140 after a longer downtime of the externally excited synchronous machine 10. For this purpose, for example, the currently measured ambient temperature T umg. Other signals, such as the coolant temperature, the operating state of a cooling device such as a fan, etc., can also be detected in 2160. In one embodiment, the different values ​​detected in this way are used to model the temperature of the excitation winding in 2170. In addition to the information from the calibration, the information from the ambient temperature and the information from other signals and information indicating the operating state of the vehicle, in particular the measured excitation current value and the time information are also used for modeling in order to calculate the heating of the excitation winding in 2180 based on the ohmic losses generated in the excitation winding and then calculate the resistance therefrom. The modeled resistance value changed in this way is of course included in the subsequent modeling, because this resistance value largely determines the heat losses in the excitation winding.

[0057] Both the field current regulator 1220 and the detection device 1240 are preferably implemented by means of a program-controlled microprocessor 1260 on which a program code 1270 stored in a memory device 1250 is executed. It should be understood that other embodiments may also have dedicated circuits for implementing the field current regulator and / or the detection device.

[0058] Parameters or value tables used by the detection device to calculate the standard duty cycle or the standard duty cycle range can also be stored in the memory 1250. In particular, the standard duty cycle is calculated according to a parameterized formula, in which one parameter is the resistance value of the load branch or the excitation coil, and the target current to be set is included as a function variable. However, in other embodiments, the target duty cycle can also be determined according to a table stored in the memory.

[0059] If a defect is determined, for example, by an unexpectedly large control deviation or an accompanying unbelievable duty cycle, the defective semiconductor of the two semiconductors can be identified by detecting the occurrence of a positive field current change during a switching cycle when the semiconductor switch should be switched off. Due to the offset of the control signal and the requirement that the duty cycle is in each case greater than 50% during normal operation, it is ensured that if the semiconductor switch is functional, the field current does not increase positively immediately after switching off one of the semiconductor switches, but if the semiconductor switch has a permanent conduction defect, an increase in the field current occurs. Therefore, in order to identify which semiconductor switch is defective, in one embodiment, it is checked whether a positive increase in the field current change occurs after the nominal switching time for switching off one of the semiconductor switches. If this is the case, the semiconductor switch that should be switched off at this nominal switching time is defective.

[0060] A person skilled in the art will appreciate that only exemplary embodiments are described here and, in particular, the additional current measuring device 180 or the temperature sensor 490 are not necessary for all embodiments of the present invention.

[0061] Reference numerals list

[0062] 1 Motor Vehicle

[0063] 10 Externally excited synchronous machine

[0064] 20 Driving pedals

[0065] 21 Driving Requirement Signal

[0066] 30 Display device

[0067] 31 Fault signal

[0068] 50 Traction Battery

[0069] 51 positive electrode

[0070] 52 Negative electrode

[0071] 100 H-bridge circuit

[0072] 180 Another current measuring device

[0073] 190 Voltage measuring device

[0074] 200 Bridge Branch Road

[0075] 201 End of bridge branch 200

[0076] 202 The opposite end of the bridge branch 200

[0077] 210, T1 semiconductor switch

[0078] 230, D3 diode

[0079] 250 connection points

[0080] 300 Another Bridge Branch

[0081] 301 The end of another bridge branch 300

[0082] 302 The opposite end of the other bridge branch 300

[0083] 320, D2 another diode

[0084] 340, T4 another semiconductor switch

[0085] 350 connection points

[0086] 400 Load branch

[0087] 460 Field winding

[0088] 465 ohm winding resistance

[0089] 467 Winding Inductance

[0090] 480 Current measuring device

[0091] 490 Temperature Sensor

[0092] 491 Temperature signal

[0093] 500 Intermediate circuit capacitor

[0094] 601 Time

[0095] 610 Chart

[0096] 611 Control signal (T1)

[0097] 612 Level

[0098] 620 Charts

[0099] 621 Control signal (T4)

[0100] 622 Level

[0101] 630 Charts

[0102] 631 Excitation voltage

[0103] 640 Charts

[0104] 641 Excitation current

[0105] 650 Charts

[0106] 651 Total current

[0107] 801 Time

[0108] 810 Chart

[0109] 811 Control signal (T1)

[0110] 812 Level

[0111] 813 Switching state (of defective semiconductor switch)

[0112] 820 Charts

[0113] 821 Control signal (T4)

[0114] 822 Level

[0115] 830 Charts

[0116] 831 Excitation voltage

[0117] 840 Charts

[0118] 841 Excitation current

[0119] 850 Charts

[0120] 851 Total current

[0121] 910 Excitation current

[0122] 920 Target current

[0123] 930 solid line

[0124] 940 dotted line

[0125] 960 Adjustment Deviation Threshold

[0126] 970 Adjustment Deviation

[0127] 980 Incredibly large range of regulation deviations

[0128] 1010 Duty Cycle

[0129] 1020 Target current

[0130] 1030 Duty cycle for minimum resistance of a properly functioning semiconductor switch

[0131] 1040 Duty cycle for the maximum resistance of a properly functioning semiconductor switch

[0132] 1050 Duty cycle with minimum resistance and defective semiconductor switch

[0133] 1060 Duty cycle with maximum resistance and defective semiconductor switch

[0134] 1070 (standard) duty cycle (relative to excitation current 25A)

[0135] 1080 standard duty range

[0136] 1200 Control Device

[0137] 1220 Field Current Regulator

[0138] 1221 Adjustment device

[0139] 1222 Signal Generating Device

[0140] 1240 Detection Device

[0141] 1250 Memory

[0142] 1260 Microprocessor

[0143] 1270 Program Code

[0144] 2000 Flowchart of a method for detecting defective semiconductors

[0145] 2010–2180 Methods and Steps

Claims

1. A method for identifying a single semiconductor switch having a permanent conduction defect in a semiconductor switch (210, 340) of a half-controlled H-bridge (100), the half-controlled H-bridge being used to set an excitation current of an externally excited synchronous machine, wherein: The half-controlled H-bridge (100) comprises a bridge branch (200) having a semiconductor switch T1 (210) and a diode D3 (230) connected in series in a blocking direction, and a further bridge branch (300) comprising a further diode D2 (320) connected in series with a further semiconductor switch T4 (340) in a blocking direction, and A load branch (400), the load branch comprising an excitation winding (460) of the externally excited synchronous machine, wherein the load branch (400) connects a connection point (250) between a semiconductor switch T1 (210) and a diode D3 (230) in the one bridge branch (200) and another connection point (350) between another diode D2 (320) and another semiconductor switch T4 (340) in the other bridge branch (300), And wherein a current measuring device (480) for measuring a current excitation current is arranged in the load branch (400); The half-controlled H-bridge (100) is coupled to a control device (1200), the control device comprising an excitation current regulator (1220), the excitation current regulator generating two pulse width modulated control signals (611, 621) of the same frequency and with a half-cycle phase shift, for controlling the one semiconductor switch T1 (210) and the other semiconductor switch T4 (340), so that the excitation current flowing through the load branch (400) can be modulated according to the pulse width of the control signal (611, 621). The invention relates to a load branch (400) for controlling a field current, wherein the duty cycle in normal operation is limited to a range of 50% to 100%, wherein the duty cycle is the ratio of the time pulse width of a signal level (612, 622) which puts the correspondingly controlled semiconductor switch (210, 340) into a conducting state to the period of the control signal (611, 621), and wherein the load branch (400) comprises a current measuring device (480) for measuring an excitation current, which is used as a feedback signal by the excitation current regulator (1220), Wherein, the method comprises the steps of: Detect the excitation current and target excitation current, comparing the target excitation current according to the requirement with the excitation current measured and detected by the current measuring device to determine the regulation deviation, and comparing the regulation deviation to a regulation deviation threshold, and If the control deviation exceeds the control deviation threshold value, a fault signal is output.

2. The method according to claim 1, characterized in that Detecting the supply voltage U applied to the half-controlled H-bridge (100) DC , and for the supply voltage U DC A standard duty cycle of a target excitation current value is determined, the standard duty cycle corresponding to the currently detected measured excitation current value for the possible minimum resistance value of the load branch (400), and a fault signal is output if the currently set duty cycle is less than the determined standard duty cycle.

3. The method according to claim 1, characterized in that Detection supply voltage U DC , and determining a standard duty cycle range (1080) for the excitation current value measured relative to the currently set duty cycle and the detected measured supply voltage, the standard duty cycle range including the following duty cycles, which correspond to the currently measured excitation current value for possible different resistance values ​​of the load branch, and checking whether the currently set duty cycle is within the standard duty cycle range (1080), and if the currently set duty cycle is not within the determined standard duty cycle range (1080), a short-circuited semiconductor switch is detected.

4. The method according to any one of the preceding claims, characterized in that The measured temperature of the field winding (460) in the load branch (400) is detected and the resistance of the field winding is calculated based on the measured temperature so as to limit a standard duty cycle range (1080).

5. The method according to any one of the preceding claims, characterized in that The resistance of the load branch is calibrated under known temperature conditions of the field winding (460) to compensate for uncertainty in the resistance of the load branch due to manufacturing tolerances.

6. The method according to any one of the preceding claims, characterized in that The temperature of the field winding (460) is predicted continuously and iteratively based on a temperature model that takes into account the measured field current and the duration between measurements.

7. The method according to claim 6, characterized in that After a relatively long standstill of the externally excited synchronous machine, an initial temperature of the temperature model is derived from a measurement of the ambient temperature.

8. The method according to any one of the preceding claims, characterized in that The resistance of the load branch (400) is calculated from the detected supply voltage and the detected excitation current, which are measured for the duty cycle last set in the associated standard duty range (1080).

9. A control device (1200) having a detection device (1040) for identifying a single semiconductor switch having a permanent conduction defect among semiconductor switches (210, 340) of a half-controlled H-bridge (100), the half-controlled H-bridge being used for setting an excitation current of an externally excited synchronous machine, wherein: The half-controlled H-bridge (100) has a bridge branch (200) having a semiconductor switch T1 (210) and a diode D3 (230) connected in series in a blocking direction, and a further bridge branch (300) comprising a further diode D2 (320) connected in series with a further semiconductor switch T4 (340) in a blocking direction, and A load branch (400), the load branch comprising an excitation winding (460) of the externally excited synchronous machine, wherein the load branch connects a connection point (250) between a semiconductor switch T1 (210) and a diode D3 (230) in the one bridge branch (200) and another connection point (350) between another diode D2 (320) and another semiconductor switch T4 (340) in the other bridge branch (300), And wherein a current measuring device (480) for measuring a current excitation current is arranged in the load branch (400); The control device (1200) comprises an excitation current regulator (1220), which is designed to generate two pulse width modulated control signals (611, 621) of the same frequency and with a half-cycle phase shift, for controlling the one semiconductor switch T1 (210) and the other semiconductor switch T4 (340), so that the excitation current flowing through the load branch (400) can be adjusted according to requirements through the pulse width modulation of the control signals (611, 621), wherein wherein the duty cycle in normal operation is limited to a range of 50% to 100%, wherein the duty cycle is the ratio of the time pulse width of the signal level (612, 622) which puts the correspondingly controlled semiconductor switch (210, 340) into the conducting state to the period of the control signal (611, 621), and wherein the load branch (400) comprises a current measuring device (480) for measuring the excitation current, which is used as a feedback signal by the excitation current regulator (1220), It is characterized in that The detection device (1040) is designed to detect the excitation current measurement value of the current measuring device (480) and compare it with the target excitation current value required by the excitation current regulator (1220) to determine the regulation deviation, and compare the regulation deviation with a regulation deviation threshold, and output a fault signal if the amount of the regulation deviation exceeds the regulation deviation threshold.

10. The control device (1200) according to claim 9, characterized in that: The detection device (1240) comprises a program-controlled processor and a program memory with a program code, wherein the steps of the method according to any one of claims 1 to 8 are carried out when the program code is executed on the processor.

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