DE102021201859A1 - Method and control unit for switching an electric drive between an operating mode with an active short circuit and a freewheeling operating mode - Google Patents

Abstract

A method for switching, in particular automatic switching, of an electric drive (10) comprising a multi-phase electric machine (18) and a power converter (12) connected upstream of the electric machine (18) is described. There is a switchover between an operating mode with an active short circuit and a freewheeling operating mode depending on at least one signal detected on the electric drive (10).
It is provided that the switching from the operating mode with an active short circuit to the freewheeling operating mode and/or the switching from the freewheeling operating mode to the operating mode with an active short circuit both depend on a signal linked to the speed n of the electrical machine (18). and as a function of a signal linked to an intermediate circuit voltage of an intermediate circuit of the converter (12).
A corresponding computer program product and a corresponding control unit (40) are also described.

Description

The invention relates to a method for switching an electric drive comprising a multi-phase electric machine and a power converter connected upstream of the electric machine between an operating mode with an active short circuit and a freewheeling operating mode as a function of at least one signal detected on the electric drive.

The invention also relates to a corresponding control unit for automatically switching an electric drive comprising a multi-phase electric machine and a power converter connected upstream of the electric machine between an operating mode with an active short circuit and a freewheeling operating mode as a function of at least one signal detected on the electric drive.

An active short-circuit (ACS) is a measure in drive technology that is intended to prevent damage to the electrical machine or the corresponding drive electronics when excessive electrical voltages occur on the one hand and to prevent a high braking torque from occurring on the other hand would set as soon as the rectified voltage of the electrical machine exceeds the applied DC voltage. Targeted AKS is considered a safe mode for electric propulsion. For this purpose, in the case of the electric drive, the connection lines for the mostly multi-phase electric machines are short-circuited by transistors of the power converter.

The document US 2020/0067443 A1 describes an electric drive system with a control unit known as an MCU (MCU: micro control unit) and two subsystems each consisting of a three-phase electrical machine, a power converter connected upstream of this electrical machine and designed as a three-phase inverter. Furthermore, this document describes an operating mode of the respective subsystem with an active short circuit (called 3PS there: three-phase short circuiting) and a freewheeling operating mode of the electric drive (also referred to there as an operating mode with total phase interruption - 6SO: six switches open) as well as a switching of the respective Subsystem between these two modes of operation.

A possible variable, as a function of which switching can take place in a sensible manner, is certainly a speed n of the electrical machine.

If one restricts oneself to a firmly specified voltage range between U _HVmin ≤ U _HV ≤ U _HVmax of a specified operating voltage U _HV (e.g. in the sense of an intermediate circuit voltage of the converter), one can ensure that a manageable map with simply structured boundaries between the two Operating ranges and optionally an intermediate hysteresis results. However, if you want to expand the voltage range, these simple limits are no longer sufficient in many cases.

It is the object of the invention to specify measures that allow the electric drive to be switched between the operating mode with an active short circuit and the freewheeling operating mode in a simple and sensible manner, even in a larger voltage range of the operating voltage (in short: operating voltage range).

The present invention is achieved by a method having the features of claim 1. The object is also achieved by a control unit having the features of claim 7. Preferred embodiments of the invention are described in the dependent claims, in the description and the figures, wherein further features described or shown in the subclaims and/or in the description and/or the figures can represent an object of the invention individually or in any combination, if the opposite is not clearly evident from the context.

The subject matter of the present invention is a method for switching, in particular automatic switching, of an electric drive comprising a multi-phase electric machine and a power converter connected upstream of the electric machine between an operating mode with an active short circuit and a freewheeling operating mode as a function of at least one signal detected on the electric drive. It is provided that switching from the operating mode with an active short circuit to the freewheeling operating mode and/or switching from the freewheeling operating mode to the operating mode with an active short circuit both as a function of a ver with the speed n of the electric machine linked signal and as a function of a signal linked to an intermediate circuit voltage of an intermediate circuit of the converter. With the additional consideration of the intermediate circuit voltage, the operating voltage U _HV is also monitored. If this falls below a value U _HVmin or rises above a value U _HVmax , supplementary or additional operating ranges can be introduced. With a particularly simple definition of the operating voltage, the intermediate circuit voltage can be viewed as this operating voltage itself.

When switching the electric drive in the voltage range of the specified operating voltage between the operating mode with an active short circuit and the freewheeling operating mode, a hysteresis advantageously results with regard to the speed n and/or the voltage U _HV . This hysteresis prevents unwanted switching back and forth between the two operating modes and is clearly visible at least in the voltage range of the specified operating voltage.

According to a preferred embodiment of the invention, the signal associated with the speed n of the electrical machine is a voltage curve in the collector voltage Uc of at least one transistor of the power converter. There is a relationship with the speed n of the electrical machine via the collector voltage. The transistors of the power converter are usually bipolar transistors and in particular bipolar transistors with an insulated gate electrode (English insulated-gate bipolar transistor, IGBT for short).

According to a further preferred embodiment of the invention, it is provided that (i) the switching from the operating mode with an active short circuit to the freewheeling operating mode takes place as a function of a fixed speed threshold n1 of the electrical machine and/or a fixed voltage threshold U1 of the intermediate circuit voltage and/or that (ii) switching from the freewheeling operating mode to the operating mode with an active short circuit takes place as a function of a further fixed speed threshold n2 of the electric machine and/or a further fixed voltage threshold U2 of the intermediate circuit voltage. Here, the required functionality is implemented in a particularly simple manner. The speed of the electric machine can be determined from different signals from the electric drive, including the said collector voltage.

As an alternative to switching from the freewheeling operating mode to the operating mode with an active short circuit as a function of another fixed speed threshold n2, the switchover from the freewheeling operating mode to the operating mode with an active short circuit takes place according to a further preferred embodiment of the invention as a function of an electrical feedback device Energy from the electrical machine characteristic voltage curve in the collector voltage Uc of the at least one transistor.

This measure switches over from the freewheeling operating mode (in the document mentioned at the outset US 2020/0067443 A1 also called operating mode with total phase interruption) to the operating mode with active short circuit shortly before the onset of recuperation. The forthcoming start of a corresponding feedback of electrical energy from the electrical machine is detected in the voltage. Since the recuperation current is responsible for a corresponding braking torque, this measure fulfills the required functionality. There is also a connection with the speed of the electrical machine via the collector voltage. The switching limit resulting from this (freewheeling operating mode -> operating mode with active short circuit) corresponds to a speed-dependent rectified no-load voltage.

According to a preferred embodiment of the method according to the invention, it is provided that an operating point suitable for switching over is determined by means of an evaluation circuit for evaluating the voltage profile of the collector voltage Uc of the transistor, which corresponds to the actual collector voltage Uc at least in a currentless phase of a respective half-bridge of the converter, in which this transistor is connected, a low-energy measuring current is superimposed. Such a collector voltage evaluation circuit is already provided in many prior art drivers.

The superimposed measurement current makes it possible to switch reliably from the freewheeling operating mode to the operating mode with an active short circuit before the onset of feedback from the EM to the DC circuit. Without this measuring current, it would only be possible to reliably detect the onset of feedback. The onset of feedback is linked to the occurrence of an unwanted braking torque.

The multi-phase electrical machine is in particular a three-phase electrical machine. Then, the active short-circuit operation mode is a so-called 3PS operation mode (3PS: Three-phase short-circuiting) and the freewheeling operation mode (all-phase-break operation mode) is a so-called 6SO operation mode (6SO: Six Switches Open). Switching from the freewheeling operating mode to the operating mode with an active short circuit is a 6SO -> 3PS switchover, and switching between the operating mode with an active short circuit and the freewheeling operating mode is correspondingly a 3PS -> 6SO switchover.

According to yet another preferred embodiment of the invention, switching over takes place automatically by means of a control unit that monitors the collector voltage of the at least one transistor of the power converter.

The subject matter of the present invention is also a control unit for automatically switching over an electric drive comprising a multi-phase electric machine and a power converter connected upstream of the electric machine between an operating mode with an active short circuit and a freewheeling operating mode as a function of at least one signal detected on the electric drive. It is provided that the control unit is set up to switch the electric drive from the operating mode with an active short circuit to the freewheeling operating mode and/or from the freewheeling operating mode to the operating mode with an active short circuit, both as a function of a signal linked to the speed n of the electrical machine as well as depending on a signal associated with an intermediate circuit voltage of an intermediate circuit of the power converter. It is preferably provided that this control unit is set up to carry out the above-mentioned method.

When the electric drive switches over between the operating mode with an active short circuit and the freewheeling operating mode, there is preferably a hysteresis with regard to the rotational speed n and/or the voltage U _HV .

According to a preferred embodiment of the control unit according to the invention, it is provided that the signal linked to the rotational speed n of the electrical machine is a voltage curve in the collector voltage Uc of at least one transistor of the power converter.

According to a further preferred embodiment of the control unit according to the invention, it is provided that the control unit is set up to switch the electric drive (i) from the operating mode with an active short circuit to the freewheeling operating mode as a function of a fixed speed threshold n1 of the electric machine and/or a fixed voltage threshold U1 of the Switch intermediate circuit voltage and / or (ii) switch from the freewheeling operating mode to the operating mode with an active short circuit depending on another fixed speed threshold n2 of the electric machine and / or another fixed voltage threshold U2 of the intermediate circuit voltage.

As an alternative to switching from the freewheeling operating mode to the operating mode with an active short circuit depending on a further fixed speed threshold n2, the control unit is set up according to another preferred embodiment to switch the electric drive from the freewheeling operating mode to the operating mode with an active short circuit depending on a for switch over a feedback of electrical energy from the electrical machine characteristic voltage curve in the collector voltage Uc of the at least one transistor of the power converter.

In this case, the control unit is preferably set up to determine an operating point that is suitable for switching by means of an evaluation circuit for evaluating the voltage profile of the collector voltage Uc of the transistor, which in turn is set up to calculate the actual collector voltage Uc at least in a currentless phase of a respective half-bridge of the converter in which the transistor is connected to superimpose a low-energy measurement current, this evaluation circuit being formed in particular by a corresponding driver for this transistor.

Furthermore, it is provided in particular that the control unit is set up to monitor the collector voltage Uc of the at least one transistor of the power converter.

• 1 einen Elektroantrieb für ein Kraftfahrzeug mit einem Stromrichter, einer elektrischen Maschine und einer Steuereinheit zum automatischen Umschalten zwischen Betriebsmodi des Elektroantriebs,
• 2 die Ansteuerung eines Transistors des Stromrichters durch eine Steuereinrichtung in schematischer Darstellung,
• 3 ein Spannungs-Drehzahl-Kennfeld des Elektroantriebs mit seinen diversen Bereichen,
• 4 ein Blockdiagramm einer erfindungsgemäßen Realisierung des Umschaltens zwischen Betriebsmodi mit festen Drehzahlwerten,
• 5 ein Spannungs-Drehzahl-Kennfeld des Elektroantriebs mit Grenzen des Umschaltens mit festen Drehzahlwerten,
• 6 ein Spannungs-Drehzahl-Kennfeld des Elektroantriebs mit Grenzen des Umschaltens mit Rekuperationserkennung,
• 7 ein Blockdiagramm einer ersten erfindungsgemäßen Realisierung des Umschaltens mit Rekuperationserkennung und
• 8 eine schematische Darstellung einer zweiten erfindungsgemäßen Realisierung des Umschaltens mit Rekuperationserkennung.

In the following, the invention is shown in drawings using preferred exemplary embodiments and described in more detail below. show:

• 1 an electric drive for a motor vehicle with a power converter, an electric machine and a control unit for automatically switching between operating modes of the electric drive,
• 2 the activation of a transistor of the power converter by a control device in a schematic representation,
• 3 a voltage-speed map of the electric drive with its various areas,
• 4 a block diagram of an implementation according to the invention of switching between operating modes with fixed speed values,
• 5 a voltage-speed map of the electric drive with limits for switching with fixed speed values,
• 6 a voltage-speed map of the electric drive with limits of switching with recuperation detection,
• 7 a block diagram of a first implementation according to the invention of switching with recuperation detection and
• 8th a schematic representation of a second inventive realization of switching with recuperation detection.

the 1 shows an electric drive 10 for a motor vehicle with an electric or hybrid drive system. The electric drive 10 comprises a converter 12 designed as an inverter (inverter). This has a circuit arrangement 14, 16 with a DC part 14 with two DC voltage connections and an AC part 16 with phase connections for three phases to which one in the drive as a traction motor serving electric machine 18 can be connected, or - is connected as shown here. As shown here, this electrical machine 18 can be designed purely as an electric motor or else as a motor generator. A rechargeable battery (an accumulator) or some other type of electrical energy store is usually connected to the DC voltage connections of the DC part 14 .

The DC part of the power converter 12 has a voltage side 20 and a zero-potential side 22, between which a capacitor 24 and three half-bridges 26, 28, 30 (one for each of the phases) with two switching devices 32, 34 per half-bridge 26, 28, 30 are arranged is. The circuit arrangement generally contains current and voltage measuring units (not shown here) for measuring various currents and voltages in the circuit arrangement. Each of the switching devices 32, 34 of the example shown here consists of a transistor 36 and a diode 38 connected in parallel with the transistor 36. The transistors 36 are in the example in the form of IGBTs (IGBT: insulated-gate bipolar transistor—bipolar transistor with insulated gate electrode). .

the 2 shows in a greatly simplified schematic representation the control of the transistor 36 or the transistors 36 by a control device 40. The control device 40 receives data (from current and voltage measuring units only indicated by arrows), from which it calculates the operating point or the operating points of the transistor 36 or the transistors 36 are determined. The control device 40 controls the transistor(s) 36 via a driver 42 (in the sense of a device driver for the transistor(s) 36). For this purpose, the control device 40 outputs corresponding signals to the driver 42, which then converts them into corresponding hardware-related control signals for the corresponding transistor 36. In addition, signals from the transistor 36 also go back to the corresponding driver 42 . Among other things, a signal that corresponds to the collector voltage of at least one transistor 36 of the power converter 12. Controller 40 and driver 42 are implemented within a computer-based controller.

The control unit 40 is provided, among other things, for automatically switching the electric drive 10 between an operating mode with an active short circuit (AKS) and a freewheeling operating mode as a function of at least one signal detected on the electric drive 10 . The switching can be divided into two sections: (a) switching from the operating mode with an active short circuit to the freewheeling operating mode and (b) switching from the freewheeling operating mode to the operating mode with an active short circuit. In the case of the three-phase AC part 16 shown here or the three-phase electrical machine shown here, the operating mode with active short-circuit is also referred to as 3PS (3PS: three-phase short-circuiting) and the freewheeling operating mode is also referred to as 6SO operating mode (6SO: six switch open) referred to.

the 3 shows a voltage-speed characteristic diagram of the electric drive 10 with its areas. The switching of the electric drive 10 between the operating mode with active short circuit (AKS) and the freewheeling operating mode is described below on the basis of this voltage/speed characteristic diagram will. Both the normal operating voltage range is considered here, i.e. the map ranges in the voltage range U _HVmin ≤ U _HV ≤ U _HVmax of a specified “normal” operating voltage U _HV , as well as an operating range with an operating voltage U _HV ≤ U _{HVmin below} . The corresponding map areas are: a freewheeling area (6SO area) 44, an active short-circuit area (AKS area or 3PS area) 46 and a hysteresis area 48 lying between these two areas 44, 46. In the normal operating voltage area the freewheeling range 44 from the speed n = 0 to a first limit 50 at a constant speed n = n1 of the electric machine 18. The active short-circuit range 16 is located above a second limit 52, which is characterized by a further constant speed n = n2 is given. In between there is a speed-limited sub-range 48' of the hysteresis range 48. In the operating range below the normal operating voltage range, the freewheeling range 44 extends from the voltage U _HV = 0V to the first limit 50 at a fixed voltage threshold U1 of the intermediate circuit voltage. The active short-circuit area 46 is located above the second limit 52, which is given by a further fixed voltage threshold U2 of the intermediate circuit voltage just below the voltage U _HVmin . U1 < U2 < U _{HVmin applies} .

In the example, switching from the operating mode with an active short circuit to the freewheeling operating mode (3PS -> 6SO) takes place at the fixed speed value n1 or the fixed voltage threshold U1, i.e. at the first limit 50. The speed n and when the fixed speed value n1 is reached determined by monitoring the collector voltage of at least one transistor 36 of the power converter 12. The operating voltage U _HV and when the fixed voltage threshold U1 is reached is determined via the intermediate circuit voltage (dropping across the capacitor 24) between the voltage side 20 and the zero-potential side 22 of the DC part. This corresponds to the operating voltage U _HV . Switching from the freewheeling operating mode to the operating mode with an active short circuit (6SO -> 3PS) takes place at the fixed speed value n2 or the further fixed voltage threshold U2, i.e. at the second limit 52. The speed n and when the fixed speed value n2 is reached are monitored the collector voltage of at least one transistor 36 of the power converter 12 is determined. The operating voltage U _HV and the attainment of the further fixed voltage threshold U2 is determined via the intermediate circuit voltage (dropping across the capacitor 24) between the voltage side 20 and the zero potential side 22 of the DC part. Additionally is in 3 the rectified no-load voltage is also drawn in, which--as will be mentioned later--can be used as an alternative second limit 52'. In the case of this alternative procedure, switching from the freewheeling operating mode to the operating mode with an active short circuit (6SO -> 3PS) takes place in the area of the alternative second limit 52' as a function of an electrical energy feedback from the electrical machine 18 (via the AC Part 16 in the DC part 14) characteristic voltage curve in the collector voltage of at least one transistor 36 of the power converter 12. This results in a (switching) hysteresis with the resulting hysteresis range 48.

Overvoltages in the operating voltage, i.e. operating voltages above U _HVmax , can still occur, particularly in the low speed range, i.e. where the freewheeling range 44 is in the normal operating voltage range (with U _HVmin ≤ U _HV ≤ U _HVmax ). located. Above the voltage U _Hvmax there is another fixed voltage threshold Umax, above which the operating mode with an active short circuit always prevails or is selected. This is also done by means of the control unit 40.

the 4 shows an embodiment of switching with fixed speed values n1, n2 and fixed voltage thresholds U1, U2, U _max (with U _max >U _HVmax ). Input signals are the collector voltage Uc, the operating or intermediate circuit voltage U _HV . There is a module 54 for monitoring the operating voltage by comparing it with the voltage thresholds U1 and U2, a module 55 for monitoring the operating voltage by comparing it with the voltage threshold Umax and a module 56 for monitoring the speed by comparing it with the speed values n1, n2 and downstream logic gates (AND gate 58 and OR gate 60), which combine the output signals with one another.

the 5 shows the resulting operating states via operating voltage and speed (or collector voltage) of the circuit 4 . Freewheeling range 44, active short-circuit range 46 and hysteresis range 48 as well as switching limits 50, 52 result from fixed speed values n1, n2 and voltage thresholds U1, U2, U _max (=U _{OV_max} ). The hysteresis 48 for low speeds n extends into a range between U _{HV_max} and U _{OV_max} .

the 6 shows the operating states that result from the aforementioned recuperation detection. Freewheeling range 44, active short-circuit range 46 and hysteresis range 48 also result here, as well as the limits 50, 52' of switching from the fixed speed value n1, the rectified th no-load voltage (which marks the start of recuperation) and the voltage thresholds U1, U2, Umax (= U _{OV_max} ). Here, too, the hysteresis 48 for low speeds n extends into a range between U _{HV_max} and U _{OV_max} .

If, by switching from the freewheeling operating mode to the operating mode with an active short circuit (6SO -> 3PS) in the area of the alternative second limit 52', depending on a voltage curve in the collector voltage of at least one transistor 36 of the If a recuperation detection can be implemented in the power converter 12, which also works outside the operating voltage range, the system encounters a fundamental problem, which in 6 is recognizable.

In the triangular area 62, the distance between switching 3PS -> 6SO and 6SO -> 3PS also decreases with UHV. This would lead to unstable operating points. In the delta region 64, the circuit is in a dilemma between 3PS and 6SO. However, this can also be resolved as a function of speed by the fact that 6SO is dominant.

Another problem arises because the switchover logic and the 3PS drivers have to work in the event of a fault in the control unit, i.e. even if the KL30 voltage is lost. Therefore, these must be supplied from the voltage UHV.

As a result of a loss of the KL30 voltage of the primary control electronics, the battery contactors can open at the same time. If 3PS is now set due to the speed, the voltage UHV drops so that the supply of switching logic and driver is no longer guaranteed.

Out of 6 the link logic between voltage and speed-dependent switchover can be derived. Two implementation options are presented below:

7 Figure 12 shows a block diagram of the first implementation of switching. The module 56 for monitoring the speed off 4 is replaced here by a module 56' with recuperation detection from the collector voltage Uc, which will be discussed below.

The block 66 (Frequ Mon) resets the output if the determined speed n falls below n1. As soon as the output is reset (/6SO), the Frequ Mon is set to a high frequency value independently of the Uc input and maintained at this value as long as /6SO remains set. This ensures that, although no frequency can be measured in the /6SO state, /6SO is not immediately requested again immediately after the return to the 3PS state, which would result in the circuit chattering.

Block 68 (Rekup Mon) sets the output of the circuit as soon as current flow through the monitored transistor 36 or its parallel diode 38 is detected, or as soon as the voltage across the transistor 36 under consideration drops to such an extent that a current flow occurs if the speed is to be expected soon.

The block 70 (Lock 6SO) together with the two downstream logic gates (inverter 72 and AND element 74) is intended to prevent a downstream flip-flop 76 from being set in the 3PS state. That wouldn't be too bad, but the switch-off delay of block 70 (lock 6SO) causes flip-flop 76 to set again immediately after switching to state 6SO, Rekup Mon. This prevents bouncing and, above all, prevents the decaying AKS current (lu, Iv, Iw - builds up in the 3PS state) from triggering the recuperation detection. The monitoring module 54 (in a slight modification as modules 54, 54') and the logic gates 58, 60 are then analog 4 connected, the logic gates 58, 60 being connected downstream of the RS flip-flop 76.

• - Die höchste Priorität bekommt U_HV > U_{OV_max}. Der Ausgang dieses Blocks überschreibt, wenn er 1 ist, die drehzahlabhängigen Blöcke. (OR)
• - Die nächste Priorität soll n < n1 erhalten. Erst wenn n > n1 ist, werden die Umschaltungen aktiv. (AND)
• - Die beiden Umschaltungen werden verknüpft (OR)
• - In den beiden Dreiecksbereichen 62, 64 unterhalb von U2 soll die spannungsabhängige Umschaltung gegenüber der drehzahlabhängigen dominieren, um nicht in einen instabilen Bereich zu gelangen, wo nichtmehr ausreichend Abstand zwischen n1 und n2 herrscht. (AND)

This results in the following link after the output of the RS flip-flop 76:

• - U _HV > U _{OV_max} gets the highest priority. The output of this block, when 1, overwrites the speed dependent blocks. (OR)
• - The next priority should be n < n1. The switchovers only become active when n > n1. (AND)
• - The two switches are linked (OR)
• - In the two triangular areas 62, 64 below U2, the voltage-dependent switching should dominate over the speed-dependent switching in order not to get into an unstable area where there is no longer a sufficient distance between n1 and n2. (AND)

The following relationship results: $$3\text{hp}/6\text{SO}=\text{u}>\text{Umax OR}\left(\text{n}>\text{<figure-callout id="1" label="n" filenames="DE102021201859A1\_0010.png,DE102021201859A1\_0012.png" state="{{state}}">n</figure-callout>}1\text{AND}\left\{3\text{hp}/6\text{SO}\left(\text{u}\right)\text{OR}\left[\text{u}>\text{u}2\text{AND}3PS/6\text{SO}\left(\text{n}\right)\right]\right\}\right)$$

$$\begin{array}{l}3PS/6SO=U>Umax\text{ OR }(n>n1\text{ AND }\{\left[3PS/6SO\left(U\right)\right]\text{ OR }[U>U2\text{ AND }3PS\\ /6SO\left(n\right)]\})\end{array}$$

This relationship can also be represented as a truth table (Table 1): Table 1: Truth table implementation 1 of Fig. 7 U > Umax n > n1 U > U2 3PS /6SO (U) voltage depend. 3PS /6SO (U) speed depend. Output 3PS/6S0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 1 0 0 0 0 0 1 1 0 0 0 1 0 0 0 0 0 1 0 1 0 0 0 1 1 0 0 0 0 1 1 1 0 0 1 0 0 0 0 0 1 0 0 1 0 0 1 0 1 0 1 0 1 0 1 1 1 0 1 1 0 0 X 0 1 1 0 1 x->1 0 1 1 1 0 0 0 1 1 1 1 1 $$\begin{array}{l}3PS/6SO=u>umax\text{OR}(\left[n>\mathrm{<figure-callout\; id="1"\; label="n"\; filenames="DE102021201859A1\_0010.png,DE102021201859A1\_0012.png"\; state="\{\{state\}\}">n</figure-callout>}1\text{AND}u<u2\text{AND}3PS/6SO\left(u\right)\right]\\ \text{OR}\left[n>\mathrm{<figure-callout\; id="1"\; label="n"\; filenames="DE102021201859A1\_0010.png,DE102021201859A1\_0012.png"\; state="\{\{state\}\}">n</figure-callout>}1\text{AND}u>u2\text{AND}3PS/6SO\left(n\right)\right]\end{array}$$

$$\begin{array}{l}3PS/6SO=u>umax\text{OR}(n>\mathrm{<figure-callout\; id="1"\; label="n"\; filenames="DE102021201859A1\_0010.png,DE102021201859A1\_0012.png"\; state="\{\{state\}\}">n</figure-callout>}1\text{AND}\{\left[3PS/6SO\left(u\right)\right]\text{OR}[u>u2\text{AND}3PS\\ /6SO\left(n\right)]\})\end{array}$$

The crossed-out section in the above formula represents an optional condition. The crossed-out entries in Tables 1 and 2 are theoretical in nature, presented for completeness only, and do not occur because they contradict at least one of the stated conditions. The entry "x->1" in Table 1 corresponds to the content of the condition "[n>n1 AND U>U2 AND 3PS/6SO(n)]" of the above formula and is in particular a change (based on this condition) to the output signal to interpret "1". The character "X" in Table 1 should preferably be interpreted as "not defined".

8th shows a block diagram of the second implementation of the switching analogous to the first implementation, but with a link via the AND gate 58 before the inputs of the RS flip-flop 76.

$$\begin{array}{l}\text{R}=\text{U}<\text{Umax AND }3\text{PS}/6\text{SO OR U}<\text{U}1\\ 3\text{PS}/6\text{SO}=\text{Q}\end{array}$$

The following applies: $$\text{S}=\text{u}>\text{Umax OR Rekup AND U}>\text{u}2$$

$$\begin{array}{l}\text{R}=\text{u}<\text{Umax AND}3\text{hp}/6\text{SO OR U}<\text{<figure-callout id="1" label="u" filenames="DE102021201859A1\_0010.png,DE102021201859A1\_0012.png" state="{{state}}">u</figure-callout>}1\\ 3\text{hp}/6\text{SO}=\text{Q}\end{array}$$

$$\text{R}=3\text{PS}/6\text{SO}\left(\text{n}\right)\text{ OR U}<\text{U}1$$

$$3\text{PS}/6\text{SO}=\text{ Q OR U}>\text{Umax}$$

Advantageously, the monitoring U>Umax can also be pushed behind the flip-flop: $$\text{S}=3\text{hp}/6\text{SO}\left(\text{n}\right)\text{AND U}>\text{u}2$$

$$\text{R}=3\text{hp}/6\text{SO}\left(\text{n}\right)\text{OR U}<\text{<figure-callout id="1" label="u" filenames="DE102021201859A1\_0010.png,DE102021201859A1\_0012.png" state="{{state}}">u</figure-callout>}1$$

$$3\text{hp}/6\text{SO}=\text{Q OR U}>\text{max}$$

This relationship can also be represented as a truth table (Table 2): Table 2: Truth table implementation 1 of Fig. 8 U > Umax n < n1 U < U1 U > U2 recovery S R 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 10 0 0 0 0 0 0 1 1 1 0 0 0 1 0 0 0 1 0 0 1 0 1 0 1 0 0 1 1 0 0 1 0 0 1 1 1 0 1 0 1 0 0 0 0 1 0 1 0 0 1 0 1 0 1 0 1 0 0 1 0 1 0 1 1 0 1 0 1 1 0 0 0 1 0 1 1 0 1 0 1 0 1 1 1 0 0 1 0 1 1 1 1 0 1

Reference List

10

electric drive

12

power converter

14

DC part

16

AC part

18

electric machine

20

voltage side

22

zero potential side

24

capacitor

26, 28, 30

half bridges

32

switching device (voltage side)

34

Switching device (zero potential side)

36

transistor

38

diode

40

control device

42

driver

44

freewheel area

44', 44"

Sub-areas (freewheel area)

46

AKS area

48

hysteresis range

50

first border

52

second border

52'

second border (alternative)

54 - 60

module

62

triangle area

64

triangle area

66 - 76

module

n

rotational speed

Uc

collector voltage

UHV

operating or intermediate circuit voltage

t

time

QUOTES INCLUDED IN DESCRIPTION

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Patent Literature Cited

• US 2020/0067443 A1 [0004, 0014]

Claims (10)

Method for switching, in particular automatic switching, of an electric drive (10) comprising a multi-phase electrical machine (18) and a power converter (12) connected upstream of the electrical machine (18) between an operating mode with an active short circuit and a freewheeling operating mode depending on at least one signal detected on the electric drive (10), characterized in that switching from the operating mode with an active short circuit to the freewheeling operating mode and/or switching from the freewheeling operating mode to the operating mode with an active short circuit depends both on a speed n of the electrical machine (18) linked signal as well as depending on a with an intermediate circuit voltage of an intermediate circuit of the power converter (12) linked signal. procedure after claim 1 , characterized in that the with the speed n of the electrical machine (18) linked signal is a voltage profile in the collector voltage Uc of at least one transistor (36) of the converter (12). procedure after claim 1 or 2 , characterized in that the switchover from the operating mode with an active short circuit to the freewheeling operating mode takes place as a function of a fixed speed threshold n1 of the electrical machine (18) and/or a fixed voltage threshold U1 of the intermediate circuit voltage and/or that the switchover from the freewheeling Operating mode takes place in the operating mode with an active short circuit depending on a further fixed speed threshold n2 of the electric machine (18) and/or a further fixed voltage threshold U2 of the intermediate circuit voltage. procedure after claim 2 or 3 , characterized in that the switchover from the freewheeling operating mode to the operating mode with an active short circuit takes place as a function of a voltage curve in the collector voltage Uc of the at least one transistor (36) that is characteristic of a feedback of electrical energy from the electrical machine (18). procedure after claim 4 , characterized in that an operating point suitable for switching over is determined by means of an evaluation circuit for evaluating the voltage profile of the collector voltage Uc of the transistor (36), which corresponds to the actual collector voltage Uc at least in a currentless phase of a respective half-bridge (26, 28, 30) of the Converter (12), in which this transistor (36) is connected, superimposed a low-energy measuring current. Procedure according to one of claims 2 until 5 , characterized in that the switching takes place automatically by means of a control unit (40) which monitors the collector voltage Uc of the at least one transistor (36) of the converter (12). Control unit (40) for automatically switching over an electric drive (10) comprising a multi-phase electrical machine (18) and a power converter (12) connected upstream of the electrical machine (18) in a voltage range of a predetermined operating voltage between an operating mode with active short circuit and a freewheeling operating mode depending on at least one signal detected on the electric drive (10), characterized in that the control unit (40) is set up to switch the electric drive (10) from the operating mode with an active short circuit to the freewheeling operating mode and/or from the freewheeling operating mode to to switch over the operating mode with an active short circuit both as a function of a signal linked to the speed n of the electrical machine (18) and as a function of a signal linked to an intermediate circuit voltage of an intermediate circuit of the converter (12). control unit after claim 7 , characterized in that the with the speed n of the electrical machine (18) linked signal is a voltage profile in the collector voltage Uc of at least one transistor (36) of the converter (12). control unit after claim 7 or 8th , characterized in that the control unit (40) is set up to switch the electric drive (10) - from the operating mode with an active short circuit to the freewheeling operating mode as a function of a fixed speed threshold n1 of the electric machine (18) and/or a fixed voltage threshold U1 of the Switch intermediate circuit voltage and / or - from the freewheeling operating mode in the operating mode with an active short circuit depending on a white other fixed speed threshold n2 of the electrical machine (18) and/or a further fixed voltage threshold U2 of the intermediate circuit voltage. control unit after claim 8 or 9 , characterized in that the control unit (40) is set up to switch the electric drive (10) from the freewheeling operating mode to the operating mode with an active short-circuit as a function of a voltage curve in the collector voltage Uc that is characteristic of a feedback of electrical energy from the electrical machine (18). of the at least one transistor (36) of the power converter (12).

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