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DE-102019204134-B4 - Phase current determination using the on-resistance and junction temperature of a field-effect transistor

DE102019204134B4DE 102019204134 B4DE102019204134 B4DE 102019204134B4DE-102019204134-B4

Abstract

Method for determining a phase current of an inductive load connected to a half-bridge (160), the method comprising the steps: - 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 switching-on phase of the first switching element (110) and a switching-on phase of the second switching element (120) and/or between the switching-on phase of the second switching element (120) and the switching-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), 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 in the passive freewheeling phase the phase current flows through one of the two freewheeling diodes (111, 121); - Detection (S2) of 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 (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); - Determining (S4) the phase current through the switched-on switching element (110, 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; - Detection (S6) of a second voltage applied to the freewheeling diode (111, 121) through which the phase current flows; - Determining (S7) a second temperature of the phase current-carrying freewheeling diode (111, 121) based on the detected second voltage, the phase current and a predetermined second temperature characteristic of the phase current-carrying freewheeling diode (111, 121); 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); wherein the procedure is continued in a cyclic sequence of steps after execution of the eighth step (S8) with the first step (S1).

Inventors

  • Michael Eckl
  • Matthias Maser
  • Edgar Jerichow
  • Andreas Plange
  • Andreas Schnell

Assignees

  • Schaeffler Technologies AG & Co. KG

Dates

Publication Date
20260513
Application Date
20190326

Claims (10)

  1. 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, whereby 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, whereby in the switch-on phase of the first switching element (110) the phase current flows through the first switching element (110), whereby in the switch-on phase of the second switching element (120) the phase current flows through the second Switching element (120) flows, where 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 where, during 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 switched-on element (110, 120) based on the determined on-resistance and the first voltage; Determine (S5) the direction of the phase current during the passive freewheeling phase and identify the freewheeling diode (111, 121) through which the phase current flows; Detect (S6) a second voltage applied to the freewheeling diode (111, 121) through which the phase current flows; Determine (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); wherein the procedure is continued in a cyclic sequence of steps after execution of the eighth step (S8) with the first step (S1).
  2. Procedure according to Claim 1 , where the phase current in the passive freewheeling phase is a freewheeling current of the inductive load (160).
  3. Procedure according to one of the 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.
  4. 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.
  5. 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.
  6. 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.
  7. 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.
  8. 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); the first switching element (110) and the second switching element (120) forming part of a half-bridge for driving the inductive load (160); a voltage measuring device (130) configured 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 whereby 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).
  9. Pre-assembly unit (200) for determining the phase current of an electric motor, wherein the pre-assembly unit (200) comprises three devices (100) according to Claim 8 comprising, wherein the inductive load (160) is a winding of the electric motor, wherein the ballast (200) is designed to operate an electric motor with three-phase alternating current, and wherein the ballast (200) is designed to distribute the phase current of three phases of the electric motor with the devices (100) according to Claim 8 to determine.
  10. computer program which, when executed on a processor, a device (100) according Claim 8 initiates proceedings according to one of the Claims 1 until 7 to be carried out, whereby the execution of the procedural steps is carried out according to one of the Claims 1 until 7 is assigned to either an ASIC or a microcontroller, wherein the process 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, detecting (S6) a second voltage applied to the freewheeling diode (111, 121) through which the phase current flows, 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 The execution of the process by the microcontroller is assigned to the phase current-carrying freewheeling diode (111, 121), and the process 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 of 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).

Description

Technical field 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 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. 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 to the diode in the forward direction. Taking the diode's characteristic curves into account, the diode's temperature can be determined by measuring 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 precise temperature determination. During normal operation of the FET, the body diode is reverse-biased. 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. DE 10 2012 109 745 A1 discloses a circuit arrangement comprising 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, resulting from a predefined current flowing through the field-effect transistor. DE 10 2017 210 457 A1 Disclosing a semiconductor control device with two adjacent FETs whose source terminals 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 across a body diode of the FET. DE 10 2008 055 696 A1 Disclosing 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 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. 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. 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. 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. 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 free