Phase current determination using the on-resistance and junction temperature of a field-effect transistor
The method employs pulse width modulation and integrated freewheeling diodes in half-bridges to determine phase current efficiently, addressing the complexity and cost issues of existing methods by utilizing temperature-dependent characteristics of field-effect transistors and diodes for accurate phase current calculation.
Patent Information
- Authority / Receiving Office
- DE · DE
- Patent Type
- Patents
- Current Assignee / Owner
- SCHAEFFLER TECHNOLOGIES AG & CO KG
- Filing Date
- 2019-03-26
- Publication Date
- 2026-05-13
AI Technical Summary
Existing methods for determining phase current in inductive loads connected to a half-bridge involve additional circuitry and manufacturing costs due to the temperature-dependent resistance of field-effect transistors, which necessitate measuring the diode's forward current, increasing complexity and costs.
A method using pulse width modulation to generate phase current through a half-bridge with integrated freewheeling diodes, allowing temperature-dependent on-resistance determination of switching elements and freewheeling diodes to calculate phase current without additional circuitry, utilizing the temperature characteristics of the diodes and transistors.
This approach reduces power loss and manufacturing costs by directly measuring the voltage across existing components, providing accurate phase current determination without extra circuitry or constant current sources.
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Abstract
Description
Technical field
[0001] The invention relates to a method for determining the phase current of an inductive load connected to a half-bridge, a device for determining the phase current of an inductive load connected to a half-bridge, as well as a pre-connection unit and a computer program. Background of the invention
[0002] When driving inductive loads, the current flow in the phases is usually determined by measuring the voltage drop across a resistor in the circuit. To avoid this resistor, the associated power loss, and the corresponding manufacturing costs, components already present in the circuit can be used. For example, the voltage drop across a switching element in the half-bridge used for driving, such as a field-effect transistor, can be measured. The same current flows through this switching element as through the inductive load. Measuring the voltage across the switching element when it is switched on allows the current flow to be calculated, provided the resistance of a conducting channel of the switching element is known.
[0003] However, the resistance of the conducting channel when using a field-effect transistor (FET) as the switching element is temperature-dependent, so its temperature must first be known. This can be measured, for example, using a diode. A current is applied in the forward direction of the diode. Taking the diode's characteristic curves into account, the diode's temperature can be determined from the voltage drop across the diode at a known current. Alternatively, a body diode can be used. This is integrated into the FET and is created by an internal electrical connection between the FET's substrate terminal and the source. The diode's proximity to the conducting channel allows for a precise determination of the channel's temperature. During normal operation of the FET, the body diode is reverse-biased.
[0004] However, in this method of measuring the phase current or the temperature of the conducting channel, the current in the forward direction is extra impressed through the diode, which in turn means additional circuitry and manufacturing effort and further costs, such as for the provision of a constant current source.
[0005] DE 10 2012 109 745 A1 discloses a circuit arrangement with two field-effect transistors and a measuring circuit for measuring the forward voltage of a body diode of at least one of the field-effect transistors, which results from a predefined current flowing through the field-effect transistor.
[0006] DE 10 2017 210 457 A1 discloses a semiconductor control device with two FETs arranged side by side, the source terminals of which are connected in series. A drain terminal of one FET is connected to a high-voltage battery, and a drain terminal of the other FET is connected to a high-voltage load. A control device determines a temperature state based on a forward voltage of a body diode of the FET.
[0007] DE 10 2008 055 696 A1 discloses an electronic circuit device for detecting a detection element current through a detection element and / or a temperature in this detection element, wherein a first terminal of the detection element is connected to a first transistor element and a second terminal of the detection element is connected to a second transistor element, wherein the base terminals of the transistor elements are directly or indirectly connected to each other. Summary of the invention
[0008] It is therefore an object of the invention to provide an improved method for determining the phase current of an inductive load connected to a half-bridge.
[0009] The problem is solved by the subject matter of the independent claims. Advantageous embodiments are the subject matter of the dependent claims, the following description, and the figures.
[0010] The described embodiments apply equally to the method for determining the phase current of an inductive load connected to a half-bridge, to the device for determining the phase current of an inductive load connected to a half-bridge, to the pre-connection unit, and to the computer program. Synergistic effects can arise from various combinations of the embodiments, even if they are not described in detail.
[0011] Furthermore, it should be noted that all embodiments of the present invention relating to a method can be carried out in the described sequence of steps. However, this need not be the only possible and necessary sequence of steps of the method. The methods described herein can be carried out in a different sequence of disclosed steps without deviating from the corresponding embodiment of the method, unless expressly stated otherwise below.
[0012] According to a first aspect of the invention, a method for determining a phase current of an inductive load connected to a half-bridge is specified, the method comprising the following steps: A first step comprises generating the phase current through the inductive load connected to the half-bridge by means of pulse width modulation, wherein a first switching element and a second switching element of the half-bridge are alternately switched on, wherein a passive freewheeling phase is provided between a switch-on phase of the first switching element and a switch-on phase of the second switching element and / or between the switch-on phase of the second switching element and the switch-on phase of the first switching element, in which both switching elements are switched off, wherein in the switch-on phase of the first switching element the phase current flows through the first switching element, wherein in the switch-on phase of the second switching element the phase current flows through the secondA switching element is operated, wherein the first switching element has a first integrated freewheeling diode and the second switching element has a second integrated freewheeling diode, and wherein, during the passive freewheeling phase, the phase current flows through one of the two freewheeling diodes. A second step comprises detecting a first voltage applied to one of the two switching elements during the turn-on phase of the corresponding turned-on switching element. A third step comprises determining an on-resistance of the turned-on switching element based on a first temperature of the turned-on switching element and a predetermined first temperature characteristic of the turned-on switching element. A fourth step comprises determining the phase current through the turned-on switching element from the determined on-resistance and the first voltage. A fifth step comprises determining a direction of the phase current during theThe passive freewheeling phase and the determination of the freewheeling diode through which the phase current flows are described. A sixth step involves detecting a second voltage applied to the freewheeling diode through which the phase current flows. A seventh step involves determining a second temperature of the freewheeling diode through which the phase current flows, based on the detected second voltage, the phase current, and a predetermined second temperature characteristic of the freewheeling diode through which the phase current flows. An eighth step involves equating the first temperature of the switching element with the second temperature of the freewheeling diode integrated into the corresponding switching element.
[0013] In the first step of the method according to the invention, a phase current is generated through the inductive load by switching the switching elements of the half-bridge that drives the load. For the sake of simplicity, the following description assumes a positive phase current direction, meaning the phase current flows from the half-bridge through the inductive load. However, the method can also be applied to a negative phase current direction with appropriate adjustments to the terminology. Regardless of the phase current direction, only the temperature of one of the switching elements can be determined. Pulse width modulation can be used to generate the phase current, allowing the switching elements to be either on or off. This avoids unnecessary power loss in the increased resistance of a partially switched element.
[0014] In one embodiment of the invention, the phase current in the passive freewheeling phase is a freewheeling current of the inductive load.
[0015] Freewheeling current is a current that continues to flow after an external voltage applied to an inductive load is switched off. It can be caused by the field energy stored in the magnetic field of the inductive load. Such a freewheeling current has a continuous curve; changes in current intensity are therefore not abrupt.
[0016] In one embodiment of the invention, the first and second switching elements are each a field-effect transistor with a source, a gate and a drain, in which a channel is switched, wherein the source is internally connected to a substrate of the field-effect transistor, and wherein the freewheeling diode is a body diode of the field-effect transistor.
[0017] Of the four electrical terminals of a field-effect transistor (FET)—source, drain, gate, and substrate—two, namely the substrate and source, are internally connected. This reduces the number of electrical terminals, but it also necessitates the presence of a diode integrated into the FET, which is arranged in parallel with the conducting channel. This diode is called a body diode. In one direction of current flow at the drain of the FET, the body diode does not affect the transistor's operation because it is reverse-biased. In a second direction of current flow at the drain, the FET is bypassed by the forward-biased body diode, allowing a freewheeling current to flow through it. In particular, a MOSFET or any other suitable type of FET with an insulated gate can also be used as the FET.
[0018] In one embodiment of the invention, the on-resistance of the switching elements and the freewheeling diodes depends on the temperature.
[0019] The switching elements and freewheeling diodes, being semiconductor components, exhibit temperature-dependent characteristics. In a field-effect transistor (FET) used as a switching element, the electrical resistance of the conducting channel between source and drain depends not only on the voltage applied to the gate but also on the temperature of the conducting channel. In particular, the temperature of the conducting channel can change due to a current flowing through it, as the power dissipation across the channel's resistance causes it to heat up. The FET's body diode also exhibits a temperature-dependent characteristic, allowing its temperature to be determined from the current flowing through it and the voltage drop across the body diode.
[0020] In one embodiment of the invention, the direction of the phase current during the passive freewheeling phase is determined by means of a voltage level at a node between the two switching elements of the half-bridge.
[0021] The two switching elements of the half-bridge are electrically connected. The inductive load can also be connected at these connection points. The phase current through the inductive load can either flow from this connection point through the inductive load, which is considered the positive current direction. Alternatively, the phase current can flow from the inductive load to the connection point, which is considered the negative current direction. The two outer terminals of the half-bridge are advantageously connected to the poles of a DC voltage source, with one of the poles, for example, the negative pole in one embodiment of the invention, being grounded. The direction of the phase current can then be determined by measuring the voltage at the connection point of the switching elements relative to, for example, ground.For example, a positive phase current is present at a negative voltage at the junction point, and a negative phase current at a positive voltage.
[0022] In one embodiment of the invention, the switching elements are a high-side switching element or a low-side switching element of the half-bridge.
[0023] The high-side switching element is the element of the half-bridge that is connected to the positive terminal of a DC voltage source. The low-side switching element, on the other hand, describes the element connected to the negative terminal of the DC voltage source, which may also be grounded.
[0024] In one embodiment of the invention, the magnitude of the phase current through the inductive load during a cycle, represented by the switch-on phase of the first switching element, the passive freewheeling phase and the switch-on phase of the second switching element, is predicted according to a model.
[0025] The method according to the invention uses a predetermined relationship between the current flowing through the conducting channel of a switching element and the current flowing through the corresponding freewheeling diode. As a first approximation, a change in the current during a cycle, particularly between a switching element's on-phase and an adjacent passive freewheeling phase, can be neglected due to the current-conserving effect of the inductive load. However, for example, the current's time course can also be estimated using a model calculation to obtain more accurate results. Parameters for this model calculation can include the phase current itself, the inductance of the inductive load, or resistances and applied voltages in the circuit.
[0026] Another aspect of the invention comprises a device for determining the phase current of an inductive load, wherein the device has: a first switching element with an integrated first freewheeling diode and a second switching element with an integrated second freewheeling diode, wherein the first switching element and the second switching element are part of a half-bridge for controlling the inductive load.Furthermore, the device comprises a voltage measuring device designed to detect voltages applied to the switching elements, and a control device designed to switch the switching elements, determine the temperature of at least one freewheeling diode, determine the temperature of at least one switching element based thereon, determine the on-resistance of the at least one switching element based thereon and a predetermined first temperature characteristic, and determine the phase current of the inductive load through the at least one switching element based thereon, wherein the control device is designed to determine the temperature of the freewheeling diode based on a measured voltage, a predetermined second temperature characteristic, and a freewheeling current of the inductive load.
[0027] In this device, two switching elements, each with an integrated freewheeling diode, form a half-bridge. A connection node, to which an inductive load is connected, is located in the middle of the half-bridge between the two switching elements. The half-bridge can be connected to a DC voltage source, such that each switching element is situated between one of the DC voltage source's poles and the connection node. A voltage measuring device determines the voltages applied to the switching elements. The control device is designed to switch the switching elements, for example, according to pulse-width modulation, such that a phase current flows through the inductive load.Because the control device is designed to further process the voltages measured by the voltage measuring device in the various operating states using the temperature characteristics of the switching elements and the freewheeling diodes, the control device can determine the temperature of the freewheeling diode through which the phase current flows. Based on this temperature, the control device can determine the on-resistance of the switching element and the current through the switching element.
[0028] Another aspect of the invention comprises a pre-assembly unit for determining the phase current of an electric motor, wherein the pre-assembly unit has three devices according to one of the previous embodiments, wherein the inductive load is a winding of the electric motor, wherein the pre-assembly unit is designed to operate an electric motor with three-phase alternating current, and wherein the pre-assembly unit is designed to determine the phase current of three phases of the electric motor with the devices according to one of the previous embodiments.
[0029] The ballast is designed to determine the phase current in, for example, the three phases of a three-phase motor. It features three of the devices described above, with one of the three phases of the electric motor connected to each device as an inductive load. The phase current of each phase is determined as previously described. The ballast can simultaneously function as an inverter, generating three-phase alternating current from the direct current of the DC voltage source.
[0030] Another aspect of the invention comprises a computer program which, when executed on a processor, causes a device according to one of the preceding embodiments to perform a method according to one of the preceding embodiments, wherein the execution of the method steps according to one of the preceding embodiments is assigned to either an ASIC or a microcontroller, wherein the method steps are of detecting a first voltage applied to one of the two switching elements during the turn-on phase of the corresponding turned-on switching element, determining the phase current through the turned-on switching element based on the determined turn-on resistance and the first voltage, determining a direction of the phase current during the passive freewheeling phase, and determining the freewheeling diode through which the phase current flows.The process of detecting a second voltage across the freewheeling diode carrying the phase current and determining a second temperature of the freewheeling diode carrying the phase current, based on the detected second voltage, the phase current, and a predetermined second temperature characteristic of the freewheeling diode carrying the phase current, is assigned to the execution by the ASIC, and the process steps of determining an on-resistance of the switched-on switching element based on a first temperature of the switched-on switching element and a predetermined first temperature characteristic of the switched-on switching element, and equating the first temperature of the switching element with the second temperature of the freewheeling diode integrated into the corresponding switching element, are assigned to the execution by the microcontroller.
[0031] The execution of the computer program implementing the method according to the invention can be distributed across different components according to a suitable hardware / software partitioning. For example, steps S2, S4, S5, S6, and S7 described in the claims can advantageously be executed on an ASIC, while steps S3 and S8 are executed on a microcontroller. The execution of step S1 can be further divided so that the microcontroller handles the pulse-width modulation, while the ASIC controls the switching elements. However, any other type of partitioning can also be implemented, distributing the execution of the method steps across different hardware components.
[0032] Further embodiments of the invention are explained below with reference to the following drawings: Brief description of the characters Fig. Figure 1 shows a schematic diagram of a half-bridge. Fig. Figure 2 shows a schematic setup of a device according to the invention for determining the phase current of an inductive load connected to a half-bridge. Fig. Figure 3 shows the time course of the phase current and the control voltages at the first and second switching element of the half-bridge and the different operating states. Fig. Figure 4a shows the voltages measured at the junction during the different operating states with positive phase current direction. Fig. Figure 4b shows the direction and path of the phase current in the case of a positive phase current direction. Fig. Figure 5a shows the voltages measured at the junction during the different operating states with negative phase current direction. Fig. Figure 5b shows the direction and path of the phase current in the case of a negative phase current direction. Fig. Figure 6 shows a block diagram of the inventive method for determining the phase current of an inductive load connected to a half-bridge. Detailed description of the figures
[0033] Fig. Figure 1 shows a schematic diagram of a half-bridge. The half-bridge comprises a first field-effect transistor 110 with an integrated first body diode 111 and a second field-effect transistor 120 with an integrated second body diode 121. Each of the field-effect transistors 110, 120 has three electrical terminals: source, gate, and drain. The first source 112, the first drain 113, and the first gate 114 are the terminals of the first field-effect transistor 110, and the second source 122, the second drain 123, and the second gate 124 are the terminals of the second field-effect transistor 120. In the n-type, self-blocking field-effect transistors shown here, current flow from drain to source can be controlled by applying a control voltage to the gate. Without a control voltage applied to the gate, the transistor is off; a depletion region 115, 125 prevents current flow from drain to source.Applying a control voltage to the gate creates an electrically conductive channel in the semiconductor material of the field-effect transistor between the drain and source. Current can now flow from drain to source with low electrical resistance. When current direction is specified, it refers to conventional current direction. For example, the body diode 111, 121 is formed by an internal electrical connection between the substrate of the field-effect transistor 110, 120 and its associated source 112, 122. During normal operation of the field-effect transistor, the body diode is reverse-biased, so the actual function of the field-effect transistor is not affected. However, current can still flow from source to drain through the body diode.Due to the internal structure of the field-effect transistor, the diode in the semiconductor material of the field-effect transistor is located in close proximity to the depletion region 115, 125, so that a similar temperature can be assumed for the body diode 111, 121 and the depletion region 115, 125. Therefore, a measurement of the body diode temperature allows conclusions to be drawn about the temperature of the depletion region of the respective field-effect transistor. The temperature of the depletion region influences the resistance of the field-effect transistor between drain and source.
[0034] Fig. Figure 2 shows a schematic diagram of a device 100 according to the invention for determining the phase current of an inductive load 160 connected to a half-bridge. The inductive load 160 is connected to the half-bridge, which consists of the first switching element 110 and the second switching element 120, at node 190. The second terminal of the inductive load 160 can be connected to a star point 170, another half-bridge, or the supply voltage, or it can be grounded. A second and a third inductive load, such as in a three-phase motor, can also be connected to this star point 170. In this embodiment, two voltage measuring devices 130, 140 measure the voltage applied to the first and second field-effect transistors 110, 120, which is also the voltage applied to the first and second body diodes 111, 121. The half-bridge can be connected to a DC voltage source 180.A control device switches the first and second switching elements 110, 120, receives the measured values from the voltage measuring devices 130, 140, and calculates the phase current and the temperature of the junctions 115, 125 of the first and / or the second field-effect transistor 110, 120. The control device can also be divided into two or more components.
[0035] Fig. Figure 3 shows the time course of the phase current and the control voltages at the first and second switching elements 110, 120 of the half-bridge and the different operating states. I_Phase represents the phase current, U_GS,HS the gate voltage at the high-side switching element, U_GS,LS the gate voltage at the low-side switching element, and t is the time. I., II., and III. indicate the first, second, and third operating states, respectively. By switching the switching elements 110, 120 of the half-bridge, which controls an inductive load 160, a phase current is generated through the inductive load 160 in the first step of the method according to the invention. For the sake of simplicity, a positive direction of the phase current is assumed in the following description; that is, the phase current flows from the half-bridge through the inductive load 160. However, the method can also be applied to a negative phase current direction with appropriate adjustments to the designations.For each phase current direction, however, only the temperature of one of the switching elements 110, 120 can be determined. Pulse width modulation can be used to generate the phase current, allowing the switching elements to be either on or off. This avoids unnecessary power loss in the increased resistance of a partially switched switching element. While the on-phase of the first switching element 110 causes an increase in the phase current, the phase current decreases during the passive freewheeling phase. The inductance of the inductive load 160 ensures a steady current profile over time by counteracting changes in the current.Three operating states are defined by additional switching phases of the second switching element 120 during the switching phase of the first switching element 110. These states are characterized by the switching of the switching elements 110 and 120 and the resulting paths of the phase current: In the first operating state, the first switching element 110 is switched on, so that the phase current flows through the conducting channel 115 of the first switching element 110. In the second operating state, both the first and second switching elements are switched off. However, the phase current is maintained by the connected inductor and now flows through the freewheeling diode 121, which is integrated into the second switching element 120. In the third operating state, the second switching element 120 is switched on, so that the phase current now flows through the conducting channel 125 of the second switching element 120.A fourth operating state, occurring between the third and first operating states of a subsequent iteration of the process, corresponds to the second operating state in terms of switching state and current flow. It is important to note that only either the second or the fourth operating state is necessary. In the second step, a first voltage applied to the second switching element 120 is detected in the third operating state. The on-resistance of the second switching element 120 is determined using a predetermined first temperature characteristic and temperature of the second switching element 120. In the fourth step, the phase current through the second switching element 120 is determined based on the calculated on-resistance and the measured first voltage. The direction of the phase current is determined in the fifth step, which takes place in the second operating state.This can be done by determining a voltage level measured at the junction 190 between the two switching elements 110 and 120. In the present case of positive phase current direction, this means that the phase current flows through the freewheeling diode 121 of the second switching element 120 in the second operating state. In the sixth step, the second voltage applied to the freewheeling diode 121 of the second switching element 120 is measured. In the seventh step, a second temperature of the second freewheeling diode 121 is determined based on the measured second voltage and a predetermined second temperature characteristic of the second freewheeling diode 121. In the eighth step, the second temperature of the freewheeling diode 121 of the second switching element 120 is used to deduce the first temperature of the conducting channel 125 of the second switching element 120.Due to the close proximity of the conducting channel and the freewheeling diode, it is advantageous to assume an almost identical temperature. With this updated value of the first temperature of the conducting channel 125 of the second switching element 120, the procedure can then be repeated. However, it should be noted that the sequence of steps described here can also be different. In particular, it is not to be understood as restrictive. Furthermore, in the described cyclic sequence of steps, the process can be restarted at the first step after the execution of the eighth step.
[0036] Fig. Figure 4a shows the voltages measured at node 190 during the various operating states with positive phase current direction. U_GND represents the voltage at ground potential, U_DH the drain-high-side voltage at drain 113 of the first switching element 110. U_SH is the source-high-side voltage that can be measured at node 190. U_SD,LS is the voltage measured between source 122 and drain 123 of the low-side switching element 120 in the second operating state.
[0037] Fig. Figure 4b shows the direction and path of the phase current with a positive phase current direction. In the first operating state, the phase current flows through the conducting channel of the first switching element 110 from drain 113 to source 112. In the second operating state, the phase current flows through the body diode 121 of the second switching element 120 from source 122 to drain 123. And in the third operating state, the phase current flows through the conducting channel of the second switching element 120 from source 122 to drain 123. A voltage measuring device determines the voltages applied to the switching elements. This can be done, for example, by measuring the voltage between node 190 and a reference point, such as a terminal of the DC voltage source 180. If the voltage of the DC voltage source 180 is known, the voltages applied to the switching elements 110 and 120 can then be calculated.On the other hand, the voltage measuring device can have two separate voltmeters 130, 140, each of which measures the applied voltage at one of the two switching elements 110, 120. Since the freewheeling diode integrated in the switching element is arranged in parallel to the conducting channel of the switching element, the voltage measured at the switching element corresponds to both the voltage at the conducting channel and the voltage applied to the freewheeling diode. The control device 150 is designed to switch the switching elements according to, for example, pulse width modulation, such that a phase current flows through the inductive load 160.By separately switching on one or the other switching element, as well as by phases in which both switching elements 110, 120 are switched off, the phase current can flow alternately either through one switching element, through the other switching element, or through one of the two freewheeling diodes 111, 121, thereby defining different operating states. Since the control device 150 is designed to further process the voltages measured by the voltage measuring device in the different operating states using the temperature characteristics of the switching elements 110, 120 and the freewheeling diodes 111, 121, the control device 150 can determine the temperature of the freewheeling diode through which the phase current flows. For an integrated freewheeling diode such as a body diode, this temperature is a measure of the temperature of the conducting channel 115, 125 of the switching element.Based on this temperature, the control device can determine the on-resistance of the switching element and the current through the switching element. This current is equal to the phase current through the inductive load 160. According to the invention, the phase current maintained by the inductive load when one and / or the other switching element is switched off, which is thus a freewheeling current of the inductive load, is used to measure the voltages across the current-carrying components.
[0038] Fig. Figure 5a shows the voltages measured at node 190 during the various operating states with negative phase current direction. U_GND represents the voltage at ground potential, U_DH the drain-high-side voltage at drain 113 of the first switching element 110. U_SH is the source-high-side voltage that can be measured at node 190. U_SD,HS is the voltage measured between source 112 and drain 113 of the high-side switching element 110 in the second operating state.
[0039] Fig. Figure 5b shows the direction and path of the phase current in the case of a negative phase current direction. In the first operating state, the phase current flows through the conducting channel of the first switching element 110 from source 112 to drain 113. In the second operating state, the phase current flows through the body diode 111 of the first switching element 110 from source 112 to drain 113. And in the third operating state, the phase current flows through the conducting channel of the second switching element 110 from drain 123 to source 122.
[0040] Fig.Figure 6 shows a block diagram of the inventive method for determining the phase current of an inductive load connected to a half-bridge. The diagram illustrates the cyclic sequence of the individual steps of the method. The numbering of the steps is only exemplary; a different step can be chosen as the starting point when carrying out the method. Since each step refers back to a result from previously performed steps, a suitable starting value can be defined before the first execution of the inventive method. For example, an ambient temperature can serve as the starting value, the same value of which can also be assumed for the temperature of the junction of the first field-effect transistor 110 before its commissioning.
[0041] It should also be noted that "comprehensive" does not exclude any other elements or steps, and "a" or "an" does not exclude a plurality. Furthermore, it should be noted that features or steps described with reference to one of the above embodiments may also be used in combination with other features or steps from other embodiments described above. Reference numerals in the claims are not to be considered as limitations. Reference symbol list 100 Device 110 first switching element 111 first freewheeling diode 112 first source 113 first drain 114 first gate 115 first conducting channel 120 second switching element 121 second freewheeling diode 122 second source 123 second drain 124 second gate 125 second conducting channel 130 first voltage measuring device 140 second voltage measuring device 150 Control device 160 Inductive load 170 Star point 180 DC voltage source 190 knots 200 ballast unit
Claims
Method for determining a phase current of an inductive load (160) connected to a half-bridge, the method comprising the steps of: - Generating (S1) the phase current through the inductive load (160) connected to the half-bridge by means of pulse width modulation, wherein a first switching element (110) and a second switching element (120) of the half-bridge are alternately switched on, wherein a passive freewheeling phase is provided between a switch-on phase of the first switching element (110) and a switch-on phase of the second switching element (120) and / or between the switch-on phase of the second switching element (120) and the switch-on phase of the first switching element (110), in which both switching elements (110, 120) are switched off, wherein in the switch-on phase of the first switching element (110) the phase current flows through the first switching element (110), wherein in the switch-on phase of the second switching element (120) the phase current flows through the second switching element (120) flows,wherein the first switching element (110) has a first integrated freewheeling diode (111) and the second switching element (120) has a second integrated freewheeling diode (121), and wherein in the passive freewheeling phase the phase current flows through one of the two freewheeling diodes (111, 121); - Detect (S2) a first voltage applied to one of the two switching elements (110, 120) during the turn-on phase of the corresponding turned-on switching element (110, 120); - Determine (S3) a turn-on resistance of the turned-on switching element (110, 120) based on a first temperature of the turned-on switching element (110, 120) and a predetermined first temperature characteristic of the turned-on switching element (110, 120); - Determine (S4) the phase current through the turned-on switching element (110, 120).120) based on the determined on-resistance and the first voltage;- Determining (S5) a direction of the phase current during the passive freewheeling phase and determining the freewheeling diode (111, 121) through which the phase current flows;- Detecting (S6) a second voltage applied to the freewheeling diode (111, 121) through which the phase current flows;- Determining (S7) a second temperature of the freewheeling diode (111, 121) through which the phase current flows based on the detected second voltage, the phase current and a predetermined second temperature characteristic of the freewheeling diode (111, 121) through which the phase current flows; and- Equating (S8) the first temperature of the switching element (110, 120) with the second temperature of the freewheeling diode (111, 121) integrated into the corresponding switching element (110, 120); the procedure continues in a cyclical sequence of steps after the execution of the eighth step (S8) with the first step (S1). Method according to claim 1, wherein the phase current in the passive freewheeling phase is a freewheeling current of the inductive load (160). Method according to one of claims 1 or 2, wherein the first and second switching element (110, 120) are each a field-effect transistor with a source (112, 122), a gate (114, 124) and a drain (113, 123) in which a channel (115, 125) is switched, wherein the source (112, 122) is internally connected to a substrate of the field-effect transistor, and wherein the freewheeling diode (111, 121) is a body diode of the field-effect transistor. Method according to one of the preceding claims, wherein the on-resistance of the switching elements (110, 120) and the freewheeling diodes (111, 121) depends on the temperature. Method according to one of the preceding claims, wherein the direction of the phase current during the passive freewheeling phase is determined by reference to a voltage level at a node between the two switching elements (110, 120) of the half-bridge. Method according to one of the preceding claims, wherein the switching elements (110, 120) are a high-side switching element and a low-side switching element of the half-bridge, respectively. Method according to one of the preceding claims, wherein the magnitude of the phase current through the inductive load (160) during a cycle, represented by the switch-on phase of the first switching element (110), passive freewheeling phase and switch-on phase of the second switching element (120), is predicted according to a model. Device (100) for determining the phase current of an inductive load (160), the device comprising: a first switching element (110) with an integrated first freewheeling diode (111); a second switching element (120) with an integrated second freewheeling diode (121); wherein the first switching element (110) and the second switching element (120) are part of a half-bridge for controlling the inductive load (160); a voltage measuring device (130) designed to detect voltages applied to the switching elements (110, 120);a control device (150) configured to switch the switching elements (110, 120), to determine the temperature of at least one freewheeling diode (111, 121), to determine the temperature of at least one switching element (110, 120) based thereon, to determine the on-resistance of the at least one switching element (110, 120) based thereon and on a predetermined first temperature characteristic, and to determine the phase current of the inductive load (160) through the at least one switching element (110, 120) based thereon, wherein the phase current in a passive freewheeling phase is a freewheeling current of the inductive load (160);and wherein the control device (150) is configured to determine the temperature of the freewheeling diode (111, 121) based on a measured voltage, a predetermined second temperature characteristic, and the freewheeling current of the inductive load (160), and wherein the control device is configured to update the determined temperature of the freewheeling diode (111, 121). A pre-connection unit (200) for determining the phase current of an electric motor, wherein the pre-connection unit (200) comprises three devices (100) according to claim 8, wherein the inductive load (160) is a winding of the electric motor, wherein the pre-connection unit (200) is designed to operate an electric motor with a three-phase alternating current, and wherein the pre-connection unit (200) is designed to determine the phase current of three phases of the electric motor with the devices (100) according to claim 8. A computer program which, when executed on a processor, causes a device (100) according to claim 8 to perform a method according to any one of claims 1 to 7, wherein the execution of the method steps according to any one of claims 1 to 7 is assigned to either an ASIC or a microcontroller, wherein the method steps of detecting (S2) a first voltage applied to one of the two switching elements (110, 120) during the switch-on phase of the corresponding switched-on switching element (110, 120), determining (S4) the phase current through the switched-on switching element (110, 120) based on the determined switch-on resistance and the first voltage, determining (S5) a direction of the phase current during the passive freewheeling phase and determining the freewheeling diode (111, 121) through which the phase current flows, and detecting (S6) a freewheeling diode (111, 121) through which the phase current flows.121) applied second voltage and determining (S7) a second temperature of the freewheeling diode (111, 121) through which the phase current flows, based on the detected second voltage, the phase current and a predetermined second temperature characteristic of the freewheeling diode (111, 121) through which the phase current flows, are assigned to execution by the ASIC, and wherein the procedure steps of determining (S3) an on-resistance of the switched-on switching element (110, 120) based on a first temperature of the switched-on switching element (110, 120) and a predetermined first temperature characteristic of the switched-on switching element (110, 120) and equating (S8) the first temperature of the switching element (110, 120) with the second temperature of the freewheeling diode (111, 121) integrated into the corresponding switching element (110, 120) are assigned to execution by the microcontroller.