DE102020134580A1 - Method for detecting a fault condition in an electronically commutated DC motor - Google Patents

Abstract

The invention relates to a method for detecting a fault condition in an electronically commutated DC motor with a stator, a rotor and a large number of phase windings, and an actuator which includes an electronically commutated DC motor. The method includes operating the electronically commutated DC motor by means of forced commutation, comprising providing forced commutated drive signals for the phase windings, the forced commutated drive signals being commutated at predetermined times independently of a rotor position; determining whether an induced voltage in a de-energized phase winding has a zero crossing while the electronically commutated DC motor is operated by forced commutation; and determining whether a fault condition exists based on whether a zero crossing of the induced voltage in the de-energized phase winding has been detected.

Description

AREA

The invention relates to a method for detecting a fault condition in an electronically commutated DC motor and an actuator that includes an electronically commutated DC motor.

BACKGROUND

Actuators with small electric motors such as brushless direct current motors (BLDC motors) are used, among other things, in the automotive sector and in automation technology, for example as a drive for actuators such as flaps or valves, for example needle valves. For control and monitoring, such actuators can be equipped with sensors such as Hall sensors, in order to determine parameters such as the rotor position, the rotor speed or the position of an actuator coupled to the rotor. For reasons of cost or space, however, the installation of sensors is out of the question for many applications. In these cases, sensorless, brushless DC motors are used, which are particularly suitable for such applications due to their compact design and high efficiency.

However, with BLDC motors, it is not easy to implement sensorless operation, since these motors require commutation of electrical drive signals that is matched to the rotor position. Therefore, methods are required that allow indirect conclusions to be drawn about the rotor position. One such method is based on measuring the voltage induced by rotor motion in a phase winding of the motor in the de-energized state, often referred to as the back electromotive force (BEMF) or BEMF voltage. Depending on the motor geometry, the BEMF voltage has one or more characteristic zero crossings, where a zero crossing occurs when the rotor passes through a certain position. Such a zero crossing can thus be used to determine the point in time at which a moving rotor is in this position. This makes it possible to commutate the drive signals according to the rotor position.

However, this method can only be used above a certain speed, since the induced voltage decreases as the speed decreases. It can therefore ^generally no longer be used below a speed of about 800 ^rpm to 1000 rpm. This is the case when the rotor accelerates from standstill, but also, for example, in the regular operation of low-speed brushless DC motors. In these situations, according to the prior art, the commutation is carried out blindly, ie independently of the rotor position. Furthermore, methods for determining the rotor position are known, in which an inductance variance of the phase windings is measured. However, these methods often cannot be used because, for example, the engine geometry is unsuitable for it.

In contrast to a sensor-controlled commutation or a sensorless commutation based on the BEMF voltage, however, with such a forced commutation it is not readily possible to detect a movement of the rotor. Thus, for example, a blockage of the rotor or of an actuator coupled thereto cannot be detected or can be detected only late. This can result in damage to the rotor and/or other actuator components.

OVERVIEW

It is therefore an object of the invention to specify a method for detecting a fault condition in an electronically commutated direct current motor, with which a blockage can also be detected when the electronically commutated direct current motor is being operated by forced commutation.

This object is achieved according to the invention by a method for detecting a fault condition in an electronically commutated DC motor having the features of claim 1 and an actuator having the features of claim 14. Developments of the invention are specified in the dependent claims.

A method is provided for detecting a fault condition in an electronically commutated DC motor, the electronically commutated DC motor having a stator, a rotor and a plurality of phase windings. The method includes the operation of the electronically commutated DC motor by means of forced commutation, including the provision of forced commutated drive signals for the phase windings, the forced commutated drive signals being commutated at predetermined times independently of a rotor position. While the electronically commutated DC motor is operated by means of forced commutation, it is determined whether an induced voltage in a non-energized phase winding has a zero crossing. Depending on whether a zero crossing of the induced voltage in the de-energized phase winding has been detected, it is determined whether a fault condition exists.

The electronically commutated DC motor can in particular be an electronically commutated DC motor in an actuator, for example in the actuator according to the invention according to one of the embodiments described herein. Correspondingly, the rotor of the electronically commutated DC motor can be mechanically coupled, for example, to a driven wheel and/or to an actuator. The electronically commutated DC motor can be, for example, a brushless DC motor (BLDC motor) or a stepper motor. The method according to the invention is preferably carried out in whole or in part by a control unit of the electronically commutated DC motor or of the actuator.

For the forced commutation, the drive signals can be commutated, for example, with a predetermined frequency, with the frequency being able to be constant or also variable, for example in order to adapt a speed of the rotor. The forced commutation can be used, for example, to accelerate the rotor from standstill and/or to move the rotor at a low speed which, for example, can be too small for reliable sensorless commutation based on the induced voltage in the de-energized phase winding. The drive signals can be provided by the control unit, for example by commutation of a supply voltage using a bridge circuit as described below. The electronically commutated direct current motor is preferably operated throughout the entire process by means of forced commutation.

The induced voltage in the de-energized phase winding can be determined, for example, by means of a voltmeter which is set up to measure the voltage between inputs of the corresponding phase winding. The induced voltage is preferably measured in each phase winding of the electronically commutated DC motor, in particular during the commutation steps in which the respective phase winding is not energized, i.e. at the times when no external voltage is applied to the phase winding. The zero crossing of the induced voltage can be detected, for example, by means of a voltage comparator and/or by means of an analog/digital converter and digital data processing in the control unit. In particular, it can be determined whether the induced voltage of the de-energized phase winding has a zero crossing within a commutation step, i.e. between two successive commutations of the drive signals.

Depending on whether a zero crossing is detected, for example within the last commutation step, it can be determined whether there is a fault condition, for example a blockage of the rotor or an element mechanically coupled to the rotor, or a normal condition in which the rotor rotates unhindered, for example can. For example, the non-occurrence of a zero crossing may indicate that the rotor is locked and unable to move. Conversely, the occurrence of a zero crossing may indicate that the rotor is moving and correspondingly inducing a voltage in the de-energized phase winding.

Even if the speed of the rotor is not high enough, for example, to enable reliable detection of the instant at which a zero crossing of the induced voltage occurs and thus allow sensorless commutation based on the induced voltage, the induced voltage can nevertheless be sufficiently high, to detect whether a zero crossing occurs at all. The occurrence of a zero crossing can already be determined, for example, on the basis of extremes of the induced voltage, which can be large enough for reliable detection even at low ^speeds , for example between 200 ^rpm and 800 rpm. The method according to the invention thus makes it possible to detect a blockage of the rotor even when the electronically commutated DC motor is operated by means of forced commutation and at low speeds.

Determining whether the induced voltage in the de-energized phase winding has a zero crossing may include determining a sign of the induced voltage. For example, a first sign of the induced voltage in the de-energized phase winding can be determined at a first point in time and a second sign of the induced voltage in the de-energized phase winding can be determined at a second point in time after the first point in time. The first and second signs can be compared to determine whether a zero crossing has occurred between the first and second times, i.e. that the first and second signs are different. The sign of the induced voltage can be determined, for example, by means of a voltage comparator. The voltage comparator can be set up, for example, to output a first signal, for example a first voltage or a first digital signal, when the induced voltage is greater than a reference value, for example oV, and to output a second voltage or a second digital signal when the induced voltage is less than the reference value.

In an advantageous development, determining the first sign and determining the second sign each includes comparing the induced voltage with a positive threshold value and/or a negative threshold value, with the respective sign being positive if the induced voltage exceeds the positive threshold value, and is negative when the induced voltage falls below the negative threshold. A voltage comparator with a corresponding hysteresis can be used for this purpose, for example. For example, the voltage comparator can be set up to output the first signal as long as the induced voltage is greater than the negative threshold value and only output the second signal when the induced voltage falls below the negative threshold value, and vice versa. The comparison with the positive and the negative threshold value can, for example, increase the reliability of the zero crossing detection and improve the susceptibility to short-term fluctuations or measurement inaccuracies.

The first and the second point in time, at which the first and the second sign are determined, preferably lie within a commutation step or within two commutation steps that follow one another directly. The first point in time can be, for example, within a first time interval around a first commutation point in time and the second point in time can lie within a second time interval around a second commutation point in time that immediately follows the first commutation point in time. A length of the first time interval and a length of the second time interval can each be less than 25%, preferably less than 10%, of a time difference between the first and second commutation times. In other words, the first and the second point in time can be, for example, just before or just after a commutation. Preferably, the first and the second point in time are shifted by the same time difference in relation to the corresponding commutation point in time, i.e. the first and the second sign are each determined at corresponding points in time in two successive commutation steps. In an advantageous development of the method, the sign is determined as close as possible to the maximum value of the BEMF voltage, for example immediately at the time of commutation before the actual commutation is carried out. The first and second points in time are preferably chosen such that the first point in time is before the first commutation point in time (ti) and the second point in time is before the second commutation point in time (t2).

In an advantageous development of the method, the induced voltage is monitored in several, preferably in all, phase windings of the electronically commutated DC motor in order to detect zero crossings. For example, the induced voltage may be a first induced voltage in a first phase winding while the first phase winding is de-energized. The method may further include determining whether a second induced voltage in a second phase winding crosses zero while the second phase winding is de-energized.

Whether an error condition is present can be determined depending on whether a zero crossing of the first induced voltage was detected and/or whether a zero crossing of the second induced voltage was detected. For example, an error state can be detected if the first induced voltage does not have a zero crossing within a first commutation step and the second induced voltage does not have a zero crossing within a second commutation step immediately following the first commutation step. This can improve the detection of error states. For example, a missing zero crossing within the first or the second commutation step can be caused not only by a blockage of the rotor but also by the rotor running ahead or lagging due to the non-synchronous forced commutation. On the other hand, the absence of a zero crossing both within the first and within the second commutation step can indicate a blockage.

In a further advantageous development, the method can also include determining a direction of the zero crossing of the induced voltage in the de-energized phase winding, for example the first and/or the second induced voltage. Determining whether a fault condition exists may be based on whether a zero crossing of the induced voltage has been detected, for example as described above, and/or whether a direction of the zero crossing corresponds to an expected direction. For example, a fault condition can be detected in addition to or instead of the cases described above if a zero crossing of the first and/or the second induced voltage occurs, but the direction of the zero crossing does not correspond to the direction to be expected. In certain cases, a blocked rotor can lead to a temporary reversal of the direction of rotation of the rotor due to forced commutated drive signals, so that although a voltage is induced in the phase windings, this does not correspond to the expected course.

The method may further include stopping operation of the electronically commutated DC motor, ie interrupting drive signals, and/or reversing a direction of rotation of the electronically commutated DC motor when a fault condition exists. By stopping the operation of the electronically commutated DC motor, damage to the rotor and/or the actuator can be avoided, for example. By reversing the direction of rotation, the rotor can, for example, be moved out of a blockage, for example in order to avoid damage due to forces exerted on the rotor and/or the actuator by the blockage.

In some embodiments, the method may include switching to sensorless commutation when there is no fault condition, wherein in sensorless commutation drive signals for the phase windings are commutated depending on an electrical signal on a phase winding. The electrical signal for the sensorless commutation can be, for example, the induced voltage in a phase winding without current. The drive signals for the phase windings can be commutated, for example, depending on the point in time at which the induced voltage crosses zero. In other embodiments, the electrical signal for the sensorless commutation can also be a current through one or more phase windings. The drive signals for the phase windings can be commutated, for example, depending on the point in time of a characteristic curve point of the current curve and/or when the current reaches a threshold value. The characteristic curve point can be, for example, an extremum or a point of inflection in the course of the current. In other embodiments, there can be no switchover to sensorless commutation and the electronically commutated DC motor can be operated exclusively by means of forced commutation.

In a preferred embodiment, the method further includes receiving a travel distance by which the rotor is to be rotated. An amount of travel is compared to a threshold. Depending on whether the displacement path is smaller or larger than the threshold value, the rotor is rotated by the displacement path in a first or in a second operating mode. The first operating mode and the second operating mode can differ, for example, in a commutation method for the electronically commutated DC motor and/or in a direction of rotation of the rotor.

The travel path can be received, for example, by a control unit of the electronically commutated DC motor or the actuator and can have been transmitted, for example, by a unit external to the actuator, such as an external control device. The travel distance may indicate a change in position of the rotor and/or the actuator, with the amount of travel being indicative of an amount of the change in position. The travel distance can also indicate a direction of the position change, for example a direction of rotation of the rotor, for example by the sign of the travel distance or a direction bit. The travel path can, for example, specify a desired change in the angle of rotation of the rotor or be converted into a corresponding change in the angle of rotation of the rotor. The travel can specify the change in the angle of rotation directly, for example a number of revolutions of the rotor, or indirectly, for example by specifying a parameter for a drive signal of the electric motor, for example a time during which the drive signal is provided, or a number of commutation steps.

The amount of travel is compared to the threshold value, it being possible for the threshold value to be stored in the control unit, for example. The threshold value is preferably a constant value which, for example, has been determined empirically in advance. In some configurations, the threshold may depend on motor parameters, such as a load coupled to the rotor and/or a damping of the rotor. For example, in some embodiments, the threshold is between 20 and 200 commutation steps, in one example between 30 and 100 commutation steps. The threshold value can be selected, for example, so that for travel distances that are greater than the threshold value, the rotor can be braked in a normal operating mode of the electronically commutated DC motor before the travel distance is traversed and the rotor can be stopped at an end position without overrunning.

The rotor is then rotated by the travel distance from a start setting or starting position to an end setting or end position. The rotor is preferably initially at a standstill in the starting position. Depending on the amount of travel, different operating modes are selected for moving the rotor, which differ at least in sections in the commutation method used and/or in the direction of rotation of the rotor. In each of the modes of operation, the movement of the rotor can occur in one or more sections or time periods. The sections of movement in an operating mode can be changed, for example, by the used Commutation, the direction of rotation and / or a target speed of the rotor differ from each other. In the first operating mode, the rotor is rotated at least in a section of the movement by means of a different commutation method and/or in a different direction of rotation than in a corresponding section in the second operating mode. The method according to the invention thus enables a suitable adaptation of the corresponding movement parameters to short travel distances in the first operating mode, as a result of which the positioning accuracy can be improved for short travel distances.

In some embodiments, the method of moving the rotor in the first operating mode includes moving the rotor by a minimum amount in a reverse direction of rotation, the reverse direction of rotation being opposite to a target direction of rotation predetermined by the travel path, and moving the rotor by the sum of the minimum amount and the amount of travel in the target direction of rotation. The minimum amount is preferably selected to be sufficiently large to enable timely braking of the rotor after an initial acceleration when starting and to avoid after-rotation of the rotor when the rotor is stopped, for example as described below. For example, the minimum amount may be greater than or equal to the threshold. Such a differential movement of the motor makes it possible to implement even small travel distances that are well below the threshold value without impairing the positioning accuracy. For this purpose, the movement is divided into two movements in different directions, in which the rotor is rotated at least by the minimum amount and the difference between the two movements corresponds to the desired travel path.

In a preferred embodiment, the first operating mode and the second operating mode can differ in addition or preferably as an alternative to the direction of rotation in the commutation method used for the electronically commutated DC motor. The turning of the rotor in the first operating mode can include, for example, moving the rotor by means of forced commutation by the entire amount of the travel path, for example in the desired direction of rotation. Rotating the rotor in the second mode of operation may include moving the rotor by means of sensorless commutation for at least part of the travel.

The turning of the rotor in the second operating mode can include, for example: accelerating the rotor by means of forced commutation in a first period of movement, for example in the desired direction of rotation, and moving the rotor by means of sensorless commutation in a second period of movement after the first period, for example in the desired direction of rotation. In the case of sensorless commutation, drive signals for the phase windings are preferably commutated, as described above, as a function of a zero crossing of an induced voltage in a phase winding which is not supplied with current.

In some embodiments, the above-described determination of the zero crossing of the induced voltage and the determination of whether a fault condition is present can only be carried out in the first operating mode, preferably over the entire travel distance. Alternatively or additionally, the corresponding steps can also be carried out in the second operating mode, for example during acceleration using forced commutation.

In some embodiments, moving the rotor in the first mode of operation includes accelerating the rotor via forced commutation at a first commutation frequency during a first period of motion and moving the rotor via forced commutation at a second commutation frequency during a second period of motion after the first period. The second commutation frequency is preferably lower than the first commutation frequency. The method may further include stopping the rotor at a target position, for example after the end of the second time period.

In the case of forced commutation, the speed of the rotor can be specified, for example, by the commutation frequency, with the speed of the rotor at the end of the second time period preferably being chosen such that the rotor can be brought to a standstill without re-rotating. Due to the lower second commutation frequency, the rotor can be decelerated to a deceleration speed in the second time period before the rotor is stopped at the target position, which is, for example, between 400 min ^-1 and 2000 min ^-1 , preferably between 600 min ^-1 and 1200 min ^{- 1} , in one example between 800 ^rpm and ¹⁰⁰⁰ rpm. At the same time, a higher commutation frequency can be selected for the initial start-up of the rotor, for example to ensure sufficient force to accelerate an actuator from standstill. The speed at the end of the first period can be, for example, between 800 ^rpm and ²⁰⁰⁰ rpm. The second commutation frequency can for example be between 30% and 90%, in one example between 50% and 80% of the first commutation frequency.

Furthermore, an actuator is provided which comprises an electronically commutated direct current motor with a stator, a rotor and at least two phase windings. The actuator further includes an output gear mechanically coupled to the rotor and configured to be mechanically coupled to an actuator. In addition, the actuator includes a control unit that is set up to carry out a method for detecting a fault state in an electronically commutated DC motor according to one of the embodiments described herein.

The electronically commutated DC motor can be a brushless DC motor or a stepper motor, for example. The at least two phase windings can be arranged on or in the stator, in which case the electronically commutated direct current motor can have, for example, between 2 and 16 stator coils formed from the phase windings. The rotor can have one or more magnets, in particular permanent magnets, and can be designed as an external or internal rotor.

The actuator may include a gearbox that mechanically couples the rotor to the output gear. The gear can be a step-up or step-down gear and can comprise, for example, a large number of gear wheels which are coupled to one another and convert a rotary movement of the rotor into a rotary movement of the driven wheel. The driven wheel can, for example, have a driven shaft with a suitable carrier profile or can be connected to such a driven shaft in order to mechanically couple the driven wheel to the actuator.

The control unit can be implemented as hardware and/or software and can include, for example, a processor and a storage medium, the storage medium containing program instructions that can be executed by the processor in order to provide the functionality described here and in particular to carry out the method steps described. Alternatively or additionally, the control unit can include further analog and/or digital electronic circuits. The control unit can be set up to provide suitably commutated drive signals for the electronically commutated DC motor in order to move the rotor. For this purpose, the control unit can have a voltage and/or current source, for example, and/or be set up to control such a source, for example by means of a bridge circuit. In particular, the control unit can be set up to control an amplitude, a pulse width modulation duty cycle, a sign and/or a duration of the drive signals.

The control unit is preferably set up to commutate drive signals for the electronically commutated DC motor. For this purpose, the control unit can be set up, for example, to generate a trigger or switching signal for a bridge circuit that has a number of switches and is set up to commutate an input voltage by means of the switches. The bridge circuit may comprise, for example, a six-switch, six-pulse (B6) bridge circuit for driving a three-phase BLDC motor, or two H-bridges, each with four switches, for driving a bipolar stepper motor. The switches are preferably in the form of semiconductor switches. In some embodiments, the bridge circuit may also include one or more freewheeling diodes, each connected in parallel with one of the switches.

In a preferred embodiment, the actuator has one or more voltage comparators, each set up to compare the voltage across one of the phase windings with a threshold or reference value. For example, the threshold value can be a reference voltage, for example zero volts or a voltage at a star point or a virtual star point of the electronically commutated DC motor. In some configurations, the voltage comparator may have hysteresis with a positive and a negative threshold, for example as described above. In a further embodiment, the comparator can also be replaced or supplemented by an analog-to-digital converter in order to determine the phase voltages directly or indirectly, for example by means of a voltage divider.

The control unit may include a microcontroller. The voltage comparator can be integrated into the control unit and in particular into the microcontroller, or can be designed as a unit that is separate from the control unit. The voltage comparator can include an analog and/or digital electronic circuit, in particular a differential amplifier.

character list

• 1: eine Vorrichtung mit einem elektronisch kommutierten Gleichstrommotor gemäß einem Beispiel;
• 2a: einen Stellantrieb mit einem elektronisch kommutierten Gleichstrommotor gemäß einem Beispiel in einer Explosionsdarstellung;
• 2b: den Stellantrieb aus 2a in einer Draufsicht;
• 2c: den Stellantrieb aus 2a in einer perspektivischen Ansicht;
• 3: ein Flussdiagramm eines Verfahrens zum Erkennen eines Fehlerzustands bei einem elektronisch kommutierten Gleichstrommotor gemäß einem Beispiel;
• 4: einen Verlauf der Spannungen an den Phasenwicklungen eines elektronisch kommutierten Gleichstrommotors gemäß einem Beispiel;
• 5: ein Flussdiagramm eines Verfahrens zum Erkennen eines Fehlerzustands bei einem elektronisch kommutierten Gleichstrommotor gemäß einem weiteren Beispiel; und
• 6: ein Flussdiagramm eines Verfahrens zum Erkennen eines Fehlerzustands bei einem elektronisch kommutierten Gleichstrommotor mit zwei Betriebsmodi gemäß einem Beispiel.

The invention is explained in more detail below using exemplary embodiments with reference to the accompanying drawings. The figures show in a schematic representation:

• 1 : a device with an electronically commutated DC motor according to an example;
• 2a 1: an actuator with an electronically commutated DC motor according to an example in an exploded view;
• 2 B : the actuator off 2a in a plan view;
• 2c : the actuator off 2a in a perspective view;
• 3 : a flow chart of a method for detecting a fault condition in an electronically commutated DC motor according to an example;
• 4 : a course of the voltages at the phase windings of an electronically commutated DC motor according to an example;
• 5 1: a flowchart of a method for detecting an error state in an electronically commutated DC motor according to a further example; and
• 6 1 is a flow diagram of a method for detecting a fault condition in an electronically commutated DC motor with two operating modes, according to an example.

DESCRIPTION OF FIGURES

1 12 shows a device 100 according to an example with which the method according to the invention for detecting a fault condition in an electronically commutated DC motor can be implemented, for example the one below with reference to FIG 3 , 5 and 6 described methods 300, 500 and/or 600. The device 100 can, for example, be part of an actuator according to the invention, for example part of the actuator 200 2a-c .

The device 100 includes an electronically commutated DC motor 102, in this example a three-phase brushless DC (BLDC) motor. The electronically commutated DC motor 102 has an outer stator 104 and a movably mounted inner rotor 106 . The rotor 106 includes one or more permanent magnets 108 and may be mechanically coupled to other moving elements (not shown), for example to an actuator such as a valve, for example a valve of an air conditioning unit of a motor vehicle, or a flap, for example a flap of a ventilation device of a motor vehicle. The stator 104 has three phase windings 110 , one end of each of which is connected to the other phase windings 110 via a neutral point 112 . In other configurations of the device 100, the phase windings 110 can also be connected via a delta circuit or be individually controllable.

To control the motor, the device includes a control unit 114, a voltage source 116 and a bridge circuit 118. In the example of FIG 1 these are shown as separate entities. In other configurations, however, the control unit 114, the voltage source 116 and/or the bridge circuit 118 can also be integrated in one unit. The control unit 114 is set up to regulate the currents through the phase windings 110 by means of the voltage source 116 and/or the bridge circuit 118 in such a way that a time-dependent magnetic field is generated which causes the rotor 106 to move. Motor movement can be controlled by controlling the currents. The voltage source can be set up to generate electrical voltage pulses with a variable pulse duty factor as supply voltage for the phase windings 110 by means of pulse width modulation (PWM). In another example, the device 100 can alternatively comprise a controllable DC voltage source which is set up to provide one or more variable DC voltages as supply voltage, and/or the device 100 and in particular the control unit 114 can be set up to use the bridge circuit 118 to carry out pulse width modulation the supply voltage.

Voltage source 116 is connected to phase windings 110 via bridge circuit 118, bridge circuit 118 being set up to commutate the supply voltage provided by voltage source 116, for example on the basis of a trigger or control signal generated by control unit 114. An output of the voltage source 116 is connected to an input 120 of the bridge circuit 118 to apply the supply voltage, for example PWM voltage pulses.

An output 122 of the bridge circuit 118 is connected to a ground contact 124 . The input 120 can be connected via a series of input switches 126 to that end of a phase winding 110 which is not connected to the star point 112 . Likewise, the appropriate end can be coupled to the output 122 by means of a series of output switches 128 . The input and output switches 126, 128 are preferably in the form of semiconductor switches, in particular metal-oxide-semiconductor field effect transistors (MOSFETs). Preferably, the bridge circuit 118 further includes freewheeling diodes (not shown) each connected in parallel with one of the switches 126,128. The freewheeling diodes are set up in direction to block the output 122 and to conduct it in the direction of the input 120.

The control unit 114 is set up to actuate the input switches 126 and the output switches 128 in a suitable manner in order to commutate the supply voltage present at the input 120 . For this purpose, for example, the phase windings 110 can be successively connected in pairs to the input 120 or output 122, so that one phase winding pair is connected in series via the star point 112 between the input 120 and the output 122 and is switched to another phase winding pair with each commutation becomes. For example, voltage curves similar to those in 4 shown curves are generated.

The control unit 114 has an analog/digital converter 130 and a microcontroller 132 for the implementation of the method according to the invention for detecting an error state in an electronically commutated DC motor. The microcontroller 132 includes a processor, for example a central processing unit (CPU), a graphics processing unit (GPU), an application specific integrated circuit (ASIC) and/or a field programmable gate array (FPGA), and a non-volatile storage medium, where the storage medium contains program instructions executable by the processor to provide the functionality described herein. In particular, the microcontroller 132 is set up to one or more of the following with respect to the 3 , 5 and 6 to carry out the methods 300, 500, 600 described in whole or in part.

The analog-to-digital converter 130 is set up to convert one or more analog input signals into corresponding digital signals, for example analog measurement signals from voltage measuring devices 134, a measuring device 138 and/or one or more voltage comparators. For this purpose, the analog/digital converter 130 can have a sample-and-hold circuit, for example. In one example, analog-to-digital converter 130 may have 12-bit resolution. The controller 114 may further include an amplifier circuit (not shown) to amplify the analog input signal prior to conversion. To adjust the high voltages that can occur at the motor phases, the analog-to-digital converter 130 can also include internal or external voltage dividers or equivalent circuits, which are designed to adjust the signals to be measured at the input range of the analog-to-digital converter 130 are.

The voltage measuring devices 134 are each set up to measure the voltage present at one of the phase windings 110 . For this purpose, one input of each voltage measuring device 134 is connected to the star point 112 and another input is connected to the end of the corresponding phase winding 110 that is connected to the bridge circuit 118. In other embodiments, the voltage measuring devices 134 can be set up, for example, to measure the voltage applied to the corresponding phase winding 110 Voltage to measure against a virtual star point (not shown). The control unit 114 can determine, for example, the voltage induced in a phase winding 110 without current by means of the voltage measuring devices 134 .

In some specific embodiments, the voltage measuring devices 134 can each be in the form of a voltage comparator which can be set up, for example, to compare the potentials at the two ends of the corresponding phase winding with one another or to compare the voltage present between the two ends with a reference voltage. The comparators can each be set up to output an analog or digital output signal depending on the two input voltages of the corresponding comparator, with the output signal being able to assume a first value, for example, if a first of the input voltages is greater than a second of the input voltages, and a second value , when the first input voltage is less than the second input voltage.

In addition, the device 100 can also have another measuring device 138 which is set up, for example, to measure a current through a shunt resistor 136 which is located between the output 122 of the bridge circuit 118 and the ground contact 124 . The measuring device 138 can be set up, for example, to measure the voltage drop across the shunt resistor 136 . The control unit 114 can use the measuring device 138 to determine, for example, the current flowing through an energized phase winding pair 110 . In other examples, the measuring device 138 can also be set up to measure currents in branches of the bridge circuit and/or in the feed lines between the bridge circuit 118 and the phase windings 110 .

The microcontroller 132 is set up to generate control signals for the voltage source 116 and/or the bridge circuit 118, for example in order to carry out a commutation as described above. The microcontroller 132 is set up, in particular, to carry out forced commutation of the drive signals at predetermined times, independently of a position of the rotor 108 microcontroller 132 can also be set up to carry out sensorless commutation of the drive signals depending on an electrical signal at a phase winding.

The microcontroller 132 can be set up, for example, to carry out the sensorless commutation depending on a zero crossing of an induced voltage measured by the voltage measuring devices 134 in a phase winding without current. For this purpose, the device 100 and in particular the control unit 114 in some embodiments can also have a comparator circuit (not shown) which is set up to detect zero crossings of the voltages measured by the voltage measuring devices 134 . The zero crossings of the voltage induced in an unenergized phase winding 110 can occur at a specific angular position of the rotor 106 and thus allow conclusions to be drawn about the angular position of the rotor 106 and thus a synchronous commutation matched to the rotor position.

Alternatively or additionally, microcontroller 132 can also be set up to carry out the sensorless commutation as a function of a current through phase windings 110 measured by measuring device 138, for example as a function of characteristic curve points such as extremes and/or turning points in the current curve and/or the achievement of a or multiple thresholds through the current.

2a , 2 B and 2c show an exemplary embodiment of an actuator 200 according to the invention. The actuator 200 is in 2a shown in an exploded view, in 2 B in a plan view without the lid 208B and in 1C in a perspective view, with the housing 208 only partially shown as a sectional view.

The actuator 200 comprises a device with an electronically commutated DC motor 102 with a stator 104 and a rotor 106 and a control unit 114 similar to the device 100 1 , where corresponding elements are provided with the same reference numbers. In this example, the electronically commutated DC motor 102 is also designed as a brushless DC motor (BLDC motor), the rotor 106 having a rotor magnet (not shown) designed as a permanent magnet and the stator 104 having three phase windings 110 .

The actuator 200 also includes a gear 202 which mechanically couples the rotor 106 to an output gear 204 . The stator 104 and the rotor 106 are arranged together with the transmission 202 and the output wheel 204 in a housing 208 with a housing shell 208A and a cover 208B. The gear 202 is designed as a reduction gear with a drive wheel 202 - 1 of the rotor 106 and three double gears 202 - 2 , 202 - 3 , 202 - 4 as intermediate wheels and is set up to transmit a rotational movement of the rotor 106 to the driven wheel 204 . The driven wheel 204 is mounted in the housing 208 by means of a guide element 210 so as to be rotatable about an axis of rotation 212 . Furthermore, the output gear 204 is formed in one piece with an output shaft designed as a hollow shaft. The output shaft is set up as a load for connection to an actuator (not shown) via an opening in the housing shell 208A and has a corresponding carrier profile on its inner circumference for this purpose. The actuator 200 can be used, for example, as a valve positioner and set up to move a valve controller such as a valve pin or a valve flap.

Furthermore, a printed circuit board or circuit board 214 with the control unit 114 and a position sensor 216 is arranged above the stator 104 . The control unit 114 is designed similarly to the control unit of the device 100 described above and is set up to control the three-phase BLDC motor 102 and in particular to provide suitably commutated drive signals for the phase windings 110 . The control unit 114 is also set up to carry out the method according to the invention according to one of the embodiments described here, for example the methods 300, 500 and/or 600 described below.

The position sensor 216 is connected to the control unit 114 and is arranged on the circuit board 214 above the driven wheel 204 such that the axis of rotation 212 extends through the position sensor 216 . The position sensor 216 is set up to determine an angular position of the driven wheel 204 about the axis of rotation 212 . For this purpose, a disk-shaped permanent magnet 218, for example an injection-molded or pressed rare-earth magnet such as a plastic-bonded neodymium-iron-boron magnet (NdFeB), is fastened on one end face of the driven wheel 204. The magnet 218 is arranged in a recess in the end face of the output gear 204 so that the axis of rotation 212 extends through the magnet 218 . The position sensor 216 includes a magnetic field sensor, for example a two-dimensional or three-dimensional Hall sensor, which is set up to determine a strength of the magnetic field generated by the magnet 218 along two or three spatial directions. The control unit 114 is set up to use a sensor transmitted by the position sensor 216 sorsignals to determine the angular position of the driven wheel 204, for example by means of a corresponding calibration curve. In some embodiments, actuator 200 may not include position sensor 216 and magnet 218 .

The drive gear 202 - 1 of the rotor 106 is coupled to the intermediate gears 202 - 2 , 202 - 3 , 202 - 4 of the transmission 202 via an opening 214A in the circuit board 214 and to the driven gear 204 thereon. The three intermediate wheels 202 - 2 , 202 - 3 , 202 - 4 are arranged lying on the side of the printed circuit board 214 lying opposite the stator 104 . The intermediate wheel 202-4 meshes with the output wheel 204, which is arranged lying on the same side of the printed circuit board 214 as the stator 104 in the housing 208.

3 FIG. 3 shows a flow diagram of a method 300 for detecting a fault condition in an electronically commutated DC motor according to an exemplary embodiment of the invention. The method 300 can be carried out with the device 100, for example 1 or the actuator 200 off 2a-c are carried out, which are used below to illustrate the method 300 by way of example. In particular, the method 300 can be carried out in whole or in part by the control unit 114 of the device 100 or the actuator 200 . Method 300 is not limited to that defined by the flowchart in 3 indicated sequence limited. As far as technically possible, the steps of method 300 can be carried out in any order and in particular at least partially simultaneously, for example steps 302 and 304.

The method 300 includes, in step 302, the operation of the electronically commutated DC motor by forced commutation. For this purpose, forced commutated drive signals for the phase windings 110 can be provided by the control unit 114 and the bridge circuit 118 . The forced commutated drive signals are commutated at predetermined times independently of a rotor position, for example with a constant or variable commutation frequency. A respective pair of phase windings 110 can be connected in series between the input 120 and the output 122 of the bridge circuit 118 via the neutral point 112 by means of the switches 126, 128 during each commutation step.

For a three-phase BLDC motor such as in 1 shown, the voltages V _U , V _V , V _W at the three phase windings 110 can have curves 400, 402, 404 as in FIG 4 assume shown schematically. At the times t0, t1, . . . Each of the phase windings 110 is connected to the supply voltage in two successive commutation steps with a first polarity or orientation, is not energized in a third commutation step (i.e. separated from the supply voltage), in two further successive commutation steps with a second polarity opposite to the first polarity connected to the supply voltage and finally not energized again in a sixth commutation step before the corresponding sequence starts again from the beginning.

While the electronically commutated DC motor 102 is operated by forced commutation, it is determined in step 304 whether the induced voltage in a non-energized phase winding has a zero crossing. For example, it can be determined whether the voltage V _U at a first phase winding 110 has a zero crossing during the second commutation step between the commutation times t ₁ and t ₂ . For this purpose, the sign of the voltage V _U can be determined at a first time, for example shortly before or shortly after the commutation time t ₁ , and at a second time, for example shortly before or shortly after the commutation time t ₂ . The sign of the voltage V _U can be determined, for example, using a voltage comparator in the voltage measuring devices 134 or in the control unit 114 . Alternatively or additionally, the sign of the voltage V _U can also be determined by the control unit 114 using the voltage V _U converted into a digital signal by the analog/digital converter 130 by means of computer-aided data processing.

Preferably, the sign of the voltage V _U is determined by comparing the voltage V _U to both a positive threshold V ₊ and a negative threshold V-. The sign of the voltage V _U is determined to be positive when the voltage V _U is greater than the positive threshold V ₊ and negative when the voltage V _U is less than the negative threshold V _- . Between the negative and the positive intermediate value, the sign can be determined, for example, as unchanged, ie corresponding to a previously determined sign, or as undefined, ie that the sign cannot be determined unambiguously.

In step 306 it is then determined whether a fault condition is present depending on whether in step 304 a zero crossing of the voltage V _U in the de-energized phase winding 110 was detected. For example, an error condition can be detected if no zero crossing occurs within the corresponding commutation step, ie between times t ₁ and t ₂ .

In a refinement, method 300 may also include, in step 304, determining whether an induced voltage in one or both of the other phase windings, ie one of voltages V _V and V _W , has a zero crossing in a de-energized state, for example as above described for V _U. Correspondingly, an error state can be detected, for example, if at least one of the voltages V _U , V _V , V _W does not have a zero crossing within a corresponding commutation step. In other cases, an error state can only be detected, for example, if at least two of the voltages V _U , V _V , V _W do not have a zero crossing within two consecutive commutation steps, for example as described below for method 500 from FIG 5 described. The voltages V _U , V _V , V _W are preferably continuously monitored while the electronically commutated DC motor is operated by means of forced commutation.

5 FIG. 5 shows a flowchart of a method 500 for detecting a fault condition in an electronically commutated DC motor according to a further exemplary embodiment of the invention. Method 500 is similar to method 300 3 and can be made with the device 100, for example 1 or the actuator 200 off 2a-c are carried out, which are used below to illustrate the method 500 by way of example. In particular, the method 500 can be carried out in whole or in part by the control unit 114 of the device 100 or the actuator 200 . Method 500 is not limited to that defined by the flowchart in 5 indicated sequence limited. As far as technically possible, the steps of the method 500 can be carried out in any order and in particular at least partially simultaneously. For example, the electronically commutated DC motor may continue to be operated using forced commutation 502 during some or all of the other steps of the method 500 .

The method 500 includes in step 502 the operation of the electronically commutated DC motor by means of forced commutation, for example as in step 302 of the method 300. In step 504, a first induced voltage in a first phase winding 110 in the de-energized state, for example the voltage V _U , to a Zero crossing checked, for example within the commutation step between the commutation times t ₁ and t ₂ . Whether the voltage V _U has a corresponding zero crossing can be determined, for example, as described above for the method 300 .

If the voltage V _U in the first phase winding 110 does not have a zero crossing in the de-energized state, the method 500 proceeds to step 506 . In step 506 it is determined whether a second induced voltage in a second phase winding 110 in the de-energized state has a zero crossing within the later commutation step, for example the voltage Vw within the subsequent commutation step between the commutation times t ₂ and t ₃ . If this is also not the case, it can be determined in step 510 that an error condition, in particular a blockage of the rotor 106 or an element coupled thereto, is present. The operation of the electronically commutated direct current motor 102 can then be interrupted, for example by all phase windings being disconnected from the supply voltage and the rotor 106 possibly being moved back in the opposite direction of rotation. On the other hand, if the voltage Vw crosses zero as expected, this may indicate that the rotor 106 is lagging or leading the magnetic field generated by the phase windings 110 but is not blocked (step 512).

If the voltage V _U in the first phase winding 110 has a zero crossing in the de-energized state, the method 500 proceeds to step 508 . In step 508, a direction of the zero crossing is determined, for example whether the voltage V _U is greater than V ₊ at the first point in time and less than V _- at the second point in time, or vice versa. The direction of the zero crossing is compared with an expected direction, which for example is the case with an idealized curve as in 4 shown would be expected. Depending on this, it is determined whether an error condition is present. If the direction of the zero crossing matches the expected direction, the method goes to step 512, ie no blockage was detected. If, on the other hand, the direction of the zero crossing does not match the expected direction, the method goes to step 510, ie a blockage was detected which, for example, can lead to the rotor swinging back and correspondingly to an induced voltage V _U that deviates from the expected voltage profile. In an analogous manner, after step 506, the direction of the zero crossing of the voltage V _W in the second phase winding 110 can also be checked in order to determine whether a blockage is present.

6 FIG. 6 shows a flow diagram of a method 600 for detecting an error condition an electronically commutated DC motor with two modes of operation according to an exemplary embodiment. The method 600 can be carried out with the device 100, for example 1 or the actuator 200 off 2a-c are carried out, which are used below to illustrate the method 600 by way of example. In particular, the method 600 can be carried out in whole or in part by the control unit 114 of the device 100 or the actuator 200 .

The method 600 includes, in step 602, receiving a travel distance that the rotor 106 is to be rotated. The travel path can be transmitted to control unit 114 by an external control unit, for example, and can indicate a change in the rotational angle of rotor 106, in particular a number of revolutions of rotor 106, and a target direction of rotation for rotor 106. In some configurations, the change in the angle of rotation of the rotor 106 can be specified, for example, by a number of commutation steps to be carried out.

In step 604, an amount of the travel path received in step 602 is compared with a threshold value, which can be stored in a memory of control unit 114, for example. The threshold may be a constant value or may depend on a load coupled to the rotor 106 and/or damping of the rotor 106, for example. If the amount of travel is less than the threshold, the method continues with step 606 and the rotor 106 is rotated by the travel in a first mode of operation. If the amount of travel is greater than or equal to the threshold, method 600 proceeds to step 614 and rotate rotor 106 by travel in a second mode of operation.

In the first operating mode for smaller travel distances, the rotor 106 is rotated in step 606 by means of forced commutation in the desired direction of rotation, with the electronically commutated DC motor 102 being operated over the entire travel distance by means of forced commutation. For this purpose, in some embodiments, a constant commutation frequency can be used throughout the travel.

In other configurations, the rotor 106 can first be accelerated in a first section or period of time by forced commutation with a first or starting commutation frequency from standstill into the desired direction of rotation. The number of commutations with the start-up commutation frequency, the amplitude and/or the pulse duty factor of the supply voltage provided by the voltage source 116 and the start-up commutation frequency itself can be selected, for example, so that the rotor 106 reaches a first speed which, for example, is between 800 min ^-1 and 2000 min ^-1 . The rotor 106 can then be moved further in the desired direction of rotation in a second section or time period following the first time period by means of forced commutation at a second commutation frequency that differs from the first commutation frequency. The second commutation frequency is preferably lower than the first commutation frequency and can be selected, for example, in such a way that the rotor 106 is braked to a deceleration speed. Alternatively or additionally, a different amplitude and/or a different pulse duty factor for the supply voltage provided by the voltage source 116 can also be used in order to decelerate the rotor 106 . The deceleration speed is preferably chosen such that the deceleration speed is sufficiently low so that the rotor 106 can be stopped without re-rotating. The deceleration speed can be less than or equal to the first speed, for example, and can be between 600 ^rpm and ¹²⁰⁰ rpm, for example.

While the rotor 106 is moved in step 606 by means of forced commutation, it can be checked in step 608 whether an error condition, for example a blockage, is present, for example using method 300 or 500. If there is a blockage, the operation of the electronically commutated DC motor can be stopped 102 can be stopped in step 610, for example by interrupting the drive signals.

If no blockage is detected, the movement of the rotor 106 can be continued in step 606 until either a blockage is detected in step 608 or the rotor 106 has been rotated the entire amount of travel. If the latter is the case, the rotor 106 is stopped at a target position in step 612 once the rotor 106 has been rotated by the amount of travel. For this purpose, the control unit 114 can, for example, determine the speed of the rotor 106 and/or the number of commutation steps carried out in step 606 in order to determine a position of the rotor 106 and to compare it with a starting position of the rotor 106 . In order to stop the rotor 106 in the target position, the control unit 114 can energize a pair of the phase windings 110 with a constant holding current by means of the bridge circuit 118 . The rotor 106 is preferably stopped based on the deceleration speed to which the rotor 106 was decelerated in step 606 . The deceleration speed is preferably chosen so that the rotor 106 in the by the Bestro tion of the phase windings 110 predetermined equilibrium position comes to a standstill without going through another complete revolution.

In the second operating mode for larger travel distances, the rotor 106 is initially accelerated in a first section or time period in step 614 by means of forced commutation in the desired direction of rotation, preferably from a standstill. The number of commutation steps in step 614, the amplitude and/or the duty cycle of the supply voltage provided by voltage source 116, and the commutation frequency are selected such that rotor 106 reaches a first speed in step 614, which is between 800 ^rpm and 2000 rpm, for example can be min ^-1 . The first speed is preferably sufficiently high so that, for example, the times at which zero crossings of the voltage induced by rotor 106 in the respective de-energized phase winding 110 occur can be reliably detected by control unit 114 in order to carry out sensorless commutation coordinated with the rotor position to be able to carry out. In one example, the forced commutation in step 606 includes between 2 and 10 commutation steps.

In some embodiments, during this forced commutation in step 608, as described above, it can be checked whether an error condition is present, for example using method 300 or 500, and, if necessary, the operation of the electronically commutated DC motor 102 can be stopped in step 610 if an error condition is present.

If no error state occurs during the acceleration of the rotor 106 in step 614, it is possible to switch to a sensorless commutation in step 616, by means of which the rotor 106 is moved further in the desired direction of rotation in a second section or time period. In this case, the drive signals for the phase windings 110 are commutated by the control unit 114 by means of the bridge circuit 118 depending on an electrical signal at the phase windings 110 . In particular, as described above, the electrical signal can be the induced voltage in the respectively unenergized phase winding 110 and the drive signals for the phase windings 110 can be commutated depending on the times of the zero crossings of the induced voltage. In step 616, in some embodiments, the rotor 106 may be further accelerated, for example to a second speed, which may be, for example, between 1000 ^rpm and ⁵⁰⁰⁰ rpm.

In step 618, the rotor 106 is then decelerated to a deceleration speed using sensorless commutation. The deceleration speed is preferably selected such that a sensorless commutation can just about be carried out reliably, for example based on the zero crossings of the induced voltage at the deceleration speed, but the deceleration speed is sufficiently low so that the rotor 106 can be stopped without re-rotating. The deceleration speed can be less than or equal to the first speed, for example, and can be between 600 ^rpm and ¹²⁰⁰ rpm, for example. The deceleration rate in step 618 may correspond to the deceleration rate from step 606 .

Once the rotor 106 has rotated the predetermined amount of travel, the rotor 106 is stopped at the corresponding target position in step 618, for example similar to step 612. To adjust the travel of the rotor 106, for example, the length of the time period in which the rotor is moved in step 616 by means of sensorless commutation can be suitably adjusted. The acceleration of the rotor 106 in step 614 and the deceleration of the rotor to the deceleration speed in step 618 can, however, always take place in the same way in some embodiments, regardless of the amount of travel, i.e., for example, the same number of commutation steps regardless of the amount of travel and/or have the same duration.

The described embodiments according to the invention and the figures are only intended to serve as purely exemplary illustrations. The invention can vary in its form without changing the underlying functional principle. The scope of protection of the method according to the invention and the device according to the invention results solely from the following claims.

Reference List

100

contraption

102

electronically commutated DC motor

104

stator

106

rotor

108

rotor magnet

110

phase windings

112

star point

114

control unit

116

voltage source

118

bridge circuit

120

input of the bridge circuit

122

output of the bridge circuit

124

grounding

126

input switch

128

exit switch

130

Analog to digital converter

132

microcontroller

134

tension gauges

136

shunt resistance

138

gauge

200

actuator

202

transmission

202-1, 202-2, 202-3, 202-4

gear wheels

204

output gear

208

Housing

208A

- housing shell

208B

- Case cover

210

guide element

212

axis of rotation

214

circuit board

214A

- Opening in the board

216

position sensor

218

magnet

300

Method for detecting a fault condition in an electronically commutated DC motor

302

Operating the electronically commutated DC motor using forced commutation

304

Determining if voltage in dead phase winding has a zero crossing

306

Determining whether an error condition exists

400

Voltage curve of the voltage V _U in a first phase winding

402

Voltage curve of the voltage V _V in a second phase winding

404

Voltage curve of the voltage V _W in a third phase winding

500

Method for detecting a fault condition in an electronically commutated DC motor

502

Operating the electronically commutated DC motor using forced commutation

504

Determining whether voltage in the first dead phase winding has a zero crossing

506

Determining whether voltage in second dead phase winding has a zero crossing

508

Verify direction of zero crossing is in expected direction

510

Determining that there is a blockage

512

Determining that there is no blockage

600

Method for detecting a fault condition in an electronically commutated DC motor

602

Receiving the travel distance

604

Compare travel distance to threshold

606

Moving the rotor using forced commutation in the first operating mode

608

Check for blockage

610

Stopping the operation of the electronically commutated DC motor

612

Stopping the rotor after rotating by the travel distance

614

Accelerating the rotor using forced commutation in the second operating mode

616

Moving the rotor using sensorless commutation

618

Deceleration of the rotors from deceleration speed

620

Stopping the rotor after rotating by the travel distance

Claims (16)

Method (300, 500, 600) for detecting a fault condition in an electronically commutated DC motor (102) having a stator (104), a rotor (106) and a plurality of phase windings (110), the method (300, 500, 600 ) comprises: operating the electronically commutated DC motor (102) by forced commutation, comprising providing forced commutated drive signals for the phase windings (110), the forced commutated drive signals being commutated at predetermined times independently of a rotor position; determining whether an induced voltage (V _U , V _V , V _W ) in a de-energized phase winding (110) crosses zero while the electronically commutated DC motor (102) is forced commutation; and determining whether a fault condition exists based on whether a zero crossing of the induced voltage (V _U , V _V , V _W ) in the de-energized phase winding (110) has been detected. Method (300, 500, 600) according to claim 1 , wherein determining whether the induced voltage (V _U , V _V , V _W ) in the de-energized phase winding (110) has a zero crossing comprises: determining a first sign of the induced voltage (V _U , V _V , V _W ) in the de-energized phase winding (110) at a first time; determining a second sign of the induced voltage (V _U , V _V , V _W ) in the dead phase winding (110) at a second time after the first time; and comparing the first and second signs. Method (300, 500, 600) according to claim 2 , wherein determining the first sign and determining the second sign each comprises: comparing the induced voltage (V _U , V _V , V _W ) to a positive threshold (V ₊ ), the respective sign being positive when the induced voltage (V _U , V _V , V _W ) exceeds the positive threshold (V ₊ ); and comparing the induced voltage (V _U , V _V , V _W ) with a negative threshold (V _- ), with the respective sign being negative if the induced voltage (V _U , V _V , V _W ) exceeds the negative threshold (V _- ) below. Method (300, 500, 600) according to claim 2 or 3 , wherein the first time is within a first time interval around a first commutation time (t ₁ ), the second time is within a second time interval around a second commutation time (t ₂ ) immediately following the first commutation time, and a length of the first time interval and a length of the second time interval are in each case less than 25%, preferably less than 10% of a time difference between the first and the second commutation instant (t ₁ , t ₂ ). procedure after claim 4 , wherein the first time before the first commutation time (t ₁ ) and the second time before the second commutation time (t ₂ ). The method (300, 500, 600) of any preceding claim, wherein: the induced voltage is a first induced voltage (V _U ) in a first phase winding (110) while the first phase winding (110) is de-energized; the method (500, 600) further comprising: determining whether a second induced voltage (V _V , V _W ) in a second phase winding (110) is a zero having continuity while the second phase winding (110) is de-energized; and determining whether a fault condition exists based on whether a zero crossing of the first induced voltage (V _U ) has been detected and whether a zero crossing of the second induced voltage (V _V , V _W ) has been detected. Method (300, 500, 600) according to claim 6 , a fault condition being detected if the first induced voltage (V _U ) does not have a zero crossing within a first commutation step and the second induced voltage (V _W ) does not have a zero crossing within a second commutation step immediately following the first commutation step. The method (300, 500, 600) of any preceding claim, wherein: the method further comprises determining a direction of zero crossing of the induced voltage (V _U , V _V , V _W ) in the unenergized phase winding (100); and determining whether a fault condition exists based on whether a zero crossing of the induced voltage (V _U , V _V , V _W ) has been detected and whether a direction of the zero crossing corresponds to an expected direction. Method (300, 500, 600) according to claim 8 , where an error condition is detected when the direction of the zero crossing is not in the expected direction. A method (300, 500, 600) according to any one of the preceding claims, the method comprising reversing a direction of rotation of the electronically commutated DC motor (102) when a fault condition exists. Method (300, 500, 600) according to one of the preceding claims, wherein the method comprises switching to sensorless commutation when there is no fault condition, wherein in the sensorless commutation drive signals for the phase windings (110) depend on an electrical signal (V _U , V _V , V _W ) are commutated on a phase winding (110). The method (600) of any preceding claim, further comprising: receiving a travel distance by which the rotor (102) is to be rotated; comparing an amount of travel to a threshold; and rotating the rotor (106) by the travel distance, wherein the rotor (106) is rotated in a first mode of operation when the amount of travel is less than the threshold and rotated in a second mode of operation when the amount of travel is greater than the threshold is wherein: rotating the rotor (106) in the first mode of operation comprises moving the rotor (106) the full amount of travel via forced commutation; and rotating the rotor (106) in the second mode of operation comprises: accelerating the rotor (106) using forced commutation in a first period of motion and moving the rotor (106) using sensorless commutation in a second period of motion after the first period, wherein in sensorless commutation, drive signals for the phase windings (110) are commutated as a function of a zero crossing of an induced voltage (V _U , V _V , V _W ) in a phase winding (110) without current. Method (600) according to claim 12 wherein rotating the rotor (106) in the first mode of operation comprises: accelerating the rotor (106) by forced commutation at a first commutation frequency during a first period of movement; and forcing the rotor (106) to move at a second commutation frequency for a second period of movement after the first period, the second commutation frequency being less than the first commutation frequency. An actuator (200) comprising: an electronically commutated DC motor (102) having a stator (104), a rotor (106) and a plurality of phase windings (110); an output gear (204) mechanically coupled to the rotor (106) and adapted to be mechanically coupled to an actuator; and a control unit (114) which is set up to carry out a method (300, 500, 600) according to one of the preceding claims. Actuator (200) after Claim 14 , wherein the actuator (200) comprises a voltage comparator which is adapted to compare the voltage (V _U , V _V , V _W ) across one of the phase windings (100) with a threshold value. Actuator (200) after claim 15 , wherein the control unit (114) comprises a microcontroller (132) and the voltage comparator is integrated into the control unit (114).

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