Drive circuit for electric motor in roof assembly

Abstract

The invention relates to a drive circuit (12) for a roof assembly comprising a roof panel (2a) movable by a motor (9) between a closed position and an open position, the drive circuit (12) comprising: an H-bridge (13) comprising switching elements (S1-S4) for controlling the speed of the motor (9); an anti-polarity protection switch (14), such as a MOSFET; and at least one measurement circuit (26, 26'). The drive circuit (12) is configured to receive a PWM signal with a duty cycle for operating the H-bridge (13). The at least one measurement circuit (26, 26') is configured to perform a current measurement on at least one of the switching elements (S1-S4, 14), respectively.

Description

Technical Field

[0001] This invention relates to a drive circuit for an electric motor, and more particularly to a drive circuit for an electric motor in a roof assembly. The invention further relates to a current measurement circuit for a roof assembly to facilitate anti-jamming detection, and a method for operating such a drive circuit. Background Technology

[0002] Roof assemblies for vehicles can be equipped with a movable panel that can move between an open position and a closed position. In the closed position, the movable panel covers the roof opening of the roof assembly, while in the open position, the panel leaves the roof opening and exposes the vehicle's interior to the outside. When the movable panel is closed, i.e., when the panel is moved to the closed position, to prevent people and / or objects from becoming trapped between the panel and the edge of the roof opening, the roof assembly can be equipped with sensors or other devices to detect the presence of anything in the path of the movable panel. When such a situation is detected, the drive circuitry that operates the motor used to move the movable panel can activate the motor to stop and / or reverse the movement of the panel. Such an arrangement is commonly referred to as an anti-pinch or anti-jamming system (ATS). Because the response time of detection and activation is critical to the safety level of such an ATS, enhanced detection methods are required. Summary of the Invention

[0003] One object of the present invention is to provide additional input for the anti-jamming detection system (ATS).

[0004] According to the present invention, this objective is achieved by providing a driving circuit according to claim 1 and a method for operating the driving circuit according to claim 5.

[0005] In one aspect, the present invention relates to a drive circuit for a roof assembly including a roof panel movable between a closed position and an open position by a motor, the drive circuit including an H-bridge comprising switching elements for controlling the speed of the motor. The drive circuit further includes a reverse polarity protection switch, such as a MOSFET; and at least one measurement circuit. The drive circuit is configured to receive a PWM signal having a duty cycle for operating the H-bridge. The at least one measurement circuit is configured to perform current measurements on at least one of the switching elements, respectively.

[0006] The disclosed drive circuitry can provide additional signals that can be used as inputs to an anti-jamming algorithm, thereby improving its reliability. The anti-jamming or anti-pinch algorithm is designed to detect whether there is a risk of an object (e.g., a human finger) being caught in the closed roof panel. Therefore, the additional input can be used as an additional alarm and / or as an alert signal indicating the possibility that an object is being jammed.

[0007] The disclosed drive circuit can also provide additional signals that can be used as inputs to a thermal algorithm, thereby improving its reliability. Thermal algorithms are commonly used to detect excessive heating of MOSFETs, particularly components of the H-bridge. The signals can also indicate the self-heating of the MOSFET, for example, when compared to the ambient temperature inside the MOSFET's case. It should be noted that the internal resistance of a MOSFET depends on temperature.

[0008] Monitoring the current flowing through components such as MOSFETs over time can also indicate whether they are functioning properly. For example, a significant deviation of the current from expected values ​​may indicate a MOSFET failure. Such detection allows for improved hardware diagnostic coverage. This can help meet the requirements for higher ASIL (Automotive Safety Integrity Level) ratings.

[0009] It is understandable that the above advantages are achieved with fewer components compared to existing technology solutions, thereby improving the cost-effectiveness of the disclosed drive circuit relative to such existing technology solutions.

[0010] Specific embodiments of the invention are set forth in the dependent claims.

[0011] With reference to the accompanying drawings, further objects, aspects, effects, and details of specific embodiments of the invention will be described in the following detailed description of a number of exemplary embodiments. Attached Figure Description

[0012] By way of example only, embodiments of this disclosure will be described with reference to the accompanying drawings, in which:

[0013] Figure 1A A perspective view showing an example of a roof with an open roof assembly;

[0014] Figure 1B Show Figure 1A Exploded view of the open roof assembly;

[0015] Figure 2 shows the operation. Figure 1A Existing technology examples of drive circuits for roof components;

[0016] Figure 3 Schematic illustration of the operation according to the invention Figure 1AAn example of the drive circuit for the roof assembly;

[0017] Figure 4 Schematic illustration of the operation according to the invention Figure 1A Another example of the drive circuitry for the roof assembly;

[0018] Figure 5 An example of a measurement circuit for a drive circuit according to the present invention is shown schematically;

[0019] Figure 6 Another example of a measurement circuit for a drive circuit according to the present invention is shown schematically;

[0020] Figure 7A An example of a method for operating a drive circuit according to the present invention is shown schematically;

[0021] Figure 7B Another example of a method for operating a drive circuit according to the present invention is illustrated schematically; and

[0022] Figure 8 The graph shows an example of the PWM signal and the blanking signal. Detailed Implementation

[0023] In the following description, terms such as front, side, and rear, or below, above, or forward and backward directions, as well as spatial references for driving movement, are relative to the overall orientation of the vehicle (e.g., a passenger car), and particularly relative to the driver located behind the steering wheel of such a vehicle. Additionally, the X, Y, and Z directions will refer to the directions corresponding to the length, width, and height of the vehicle. In the accompanying drawings, the forward driving movement of the vehicle may be indicated, for example, by arrow D, which points towards the front of the vehicle.

[0024] Figure 1A and 1B The roof is shown, having an open roof assembly 1 disposed therein. The open roof assembly 1 includes a movable panel 2a and a fixed panel 2b. The movable panel 2a is also referred to as a closing member because it is movable over a first roof opening 3a, enabling the opening 3a to be opened and closed. A wind deflector 4 is disposed at the front of the first roof opening 3a.

[0025] In the illustrated embodiment, the movable panel 2a can be in a closed position, where it is positioned above and closes the first roof opening 3a, and is therefore typically positioned within the plane of the roof 1. Further, the movable panel 2a can be in an inclined position, where the rear end RE of the movable panel 2a is raised compared to the closed position, while the front end FE remains in the closed position. Further, the movable panel 2a can be in an open position, where it slides open and the roof opening 3a is partially or completely exposed. In the open position, for example, both the rear end RE and the front end FE can be raised compared to the closed position.

[0026] It should be noted that the roof 1 shown corresponds to a passenger vehicle. However, the invention is not limited to passenger vehicles. Any other type of vehicle that may be equipped with a movable panel is also contemplated.

[0027] Figure 1B As shown Figure 1A The same roof shown has panels 2a and 2b. Specifically, although... Figure 1A The open roof assembly 1 is shown in the open position, but Figure 1B An exploded view of the open roof assembly 1 in the closed position. Further, in Figure 1B The exploded view shows the presence of a second roof opening 3b. The first and second roof openings 3a and 3b are disposed within the frame 5 of the open roof assembly 1. The edge 5a of the frame 5 defines the first roof opening 3a.

[0028] The second roof opening 3b is arranged below the fixed panel 2b to allow light to enter the vehicle interior space through the fixed panel 2b, which is assumed to be a glass panel or a similar transparent panel, for example, made of plastic or any other suitable material. The second roof opening 3b is optional with the transparent or translucent fixed panel 2b, and may be omitted in another embodiment of the open roof assembly 1.

[0029] The wind deflector 4 is typically made of a flexible material, such as a woven or nonwoven fabric with through-holes arranged therein, or a mesh or net. The flexible material is supported by a support structure 4a (e.g., a rod-like or tubular structure), which is directly or indirectly hinged to the frame 5 at a hinge 4b.

[0030] The wind deflector 4 is positioned in front of the first roof opening 3a and adapts to airflow when the movable panel 2a is in the open position. In its raised position, the wind deflector 4 reduces inconvenient noise caused by airflow during driving. When the movable panel 2a is in the closed or tilted position, the wind deflector 4 is held downward below the front end FE of the movable panel 2a.

[0031] Normally, when the movable panel 2a slides to the open position, the wind deflector 4 rises due to spring force, and when the movable panel 2a slides back to its closed position, the wind deflector 4 is pushed downward by the movable panel 2a. Figure 1A In the image, the movable panel 2a is shown in the open position and the wind deflector 4 is shown in the raised position. Figure 1B In the middle, the movable panel 2a is shown in the closed position, and the wind deflector 4 is correspondingly shown in the position in which it is held downward.

[0032] Figure 1B A drive assembly is further shown, comprising a first guide assembly 6a, a second guide assembly 6b, a first drive cable 7, a second drive cable 8, and a drive motor 9. The first and second guide assemblies 6a and 6b are arranged on corresponding side ends SE of the movable panel 2a and each may include a guide and a mechanism. The guide is coupled to the frame 5, while the mechanism includes movable parts and is slidably movable within the guide. The first and second drive cables 7 and 8 are disposed between the mechanism of the respective guide assembly 6a and 6b and the drive motor 9.

[0033] Drive cables 7 and 8 connect drive motor 9 to the mechanisms of the corresponding guide components 6a and 6b, so that the mechanisms begin to move when drive motor 9 is operated. Specifically, the drive motor 9 moves the core of drive cables 7 and 8 to push or pull the mechanisms of the corresponding guide components 6a and 6b. Such drive components are well known in the art and therefore will not be described further herein. However, any other suitable drive components may be used without departing from the scope of the invention.

[0034] In the illustrated embodiment, guide components 6a, 6b can be initiated by raising the rear end RE of the movable panel 2a, thereby placing the movable panel 2a in an inclined position. Then, from the inclined position, guide components 6a, 6b can begin to slide to place the movable panel 2a in an open position. However, the invention is not limited to such embodiments. For example, in another embodiment, the movable panel 2a can be moved to the inclined position by raising the rear end RE, and the open position can be achieved by first lowering the rear end RE and then sliding the movable panel 2a under a fixed panel 2b or under any other structure or element disposed behind the rear end RE of the movable panel 2a. In another exemplary embodiment, the movable panel 2a may be movable only between a closed position and an inclined position, or between a closed position and an open position.

[0035] In the illustrated embodiment, the drive motor 9 is mounted at the recess 10 near or below the front end FE of the movable panel 2a in the closed position. In another embodiment, the drive motor 9 can be positioned at any other suitable location or orientation. For example, the drive motor 9 can be arranged near or below the rear end RE of the movable panel 2a in the closed position or below the fixed panel 2b.

[0036] Control unit 11 is schematically shown and operatively coupled to drive motor 9. Control unit 11 can be any kind of processing unit well known to those skilled in the art: a software-controlled processing unit or a dedicated processing unit, such as an ASIC. Control unit 11 can be a standalone control unit, or it can be operatively connected to another control unit, such as a multi-purpose vehicle control unit. In yet another embodiment, control unit 11 can be embedded in or be part of such a multi-purpose vehicle control unit. Essentially, control unit 11 can be implemented by any control unit suitable for, capable of, and configured to perform operations on drive motor 9 and thus the movable roof assembly 1. An anti-jamming system can be implemented by control unit 11, for example, by executing an algorithm for that purpose.

[0037] Referring to Figure 2, a prior art example of a drive circuit 12 is schematically shown. The drive circuit 12 includes an H-bridge 13, which consists of four switches S1-S4 for operating a motor, such as... Figure 1BThe example drive motor 9. The H-bridge has a pair of input terminals 18, 19 and a pair of output terminals 20, 21. Output terminals 20, 21 are connected to motor 9. The drive circuit 12 further includes a switch 14 for reverse polarity protection. In this example, the switch is a MOSFET, such as a PMOS, NMOS, or IGBT MOSFET. At least when a MOSFET is used for reverse polarity protection, the drive circuit further includes a charge pump 15 to ensure that the switch 14 for reverse polarity protection can be placed in the on mode during operation of the drive circuit 12. The drive circuit 12 is powered by a DC voltage battery or other suitable power source 16, which is connected to a pair of input terminals 22, 23 (one positive input terminal and one negative input terminal) of the drive circuit 12. The reverse polarity protection MOSFET 14 is connected in series between the positive input terminal 22 of the drive circuit 12 and the positive input terminal 18 of the H-bridge 13 via its source and drain. The operation of the reverse polarity protection MOSFET 14 is controlled by a charge pump 15 located in a circuit branch connected between the gate of the MOSFET 14 and the negative input terminal 23. The voltage supplied by the charge pump determines whether and how the MOSFET is turned on. If the power supply terminals are connected incorrectly (i.e., ground and positive are swapped), the reverse polarity MOSFET prevents a short circuit in the H-bridge.

[0038] To drive the motor, pulse width modulation (PWM) signals are used to operate switches S1-S4. This allows for soft start and / or soft stop via the duty cycle of the PWM signals. The duty cycle determines the duration of the switches being open and closed, thereby controlling the voltage supplied to the motor and thus the motor speed. To drive the motor in a first rotational direction, switches S1 and S4 are simultaneously and repeatedly opened and closed. To drive the motor in a second rotational direction opposite to the first, switches S3 and S2 are simultaneously and repeatedly opened and closed. Therefore, the duty cycle of the PWM signals determines the motor's rotational speed, and the selection of the switch pairs determines the motor's direction. Depending on the motor's connection method, the first direction can be either a forward / closed direction or a reverse / open direction.

[0039] To detect clamping of an object, changes in the current drawn by the motor can be monitored. For this purpose, a shunt resistor 17 is placed between the common negative side of the H-bridge 13 (in this example, it could be located at input terminal 19 of the H-bridge) and the ground wire 24. The ground wire 24 is also connected to the negative terminal 23 of the drive circuit 12. A drop in voltage across the shunt resistor 17 can be monitored, indicating a change in the current drawn by the motor 9. For this purpose, a measuring circuit 25 is connected in parallel to the shunt resistor 17. The voltage signal thus measured indicates the current drawn by the motor and can be used for clamping detection.

[0040] refer to Figure 3 The diagram schematically illustrates a first example of a drive circuit according to the invention. Here, the same reference numerals are used for the same parts and elements as in FIG2. In this example, there is no shunt resistor, and the common negative side of the H-bridge 13 (which may be located on input terminal 19) is in direct contact with the ground wire 24.

[0041] In this example, to obtain a voltage signal that can be used for pinch detection, measurement circuit 26 is configured to measure the voltage across MOSFET switch S4. The measurement circuit has input terminals 27, 28 to be connected to different sides of switch S4. To ensure that the voltage is measured when the MOSFET is on, the measurement signal needs to be sampled synchronously with the PWM signal operating switch S4. Since this switch is only operated and therefore turned on when the motor rotates in the first direction, a second measurement circuit 26' can be configured to measure the voltage across MOSFET switch S2, which is turned on when the motor is operated to rotate in the second direction. This allows for bidirectional monitoring of the voltage for pinch detection.

[0042] For each MOSFET, the resistance between the drain and source when it is turned on (i.e., Rds) on This is known in advance. And as the inventors discovered, in the event of pinching, the increase in current leads to an increase in the voltage drop across the internal resistance of the MOSFET. Therefore, microcontrollers (such as...) Figure 1B (Part of the control unit 11) can be based on the measured voltage signal and the known Rds on The current drawn is calculated. This current can then be used as the input to the pinch detection system.

[0043] refer to Figure 4 This schematically illustrates another example of a drive circuit according to the present invention. Here, for... Figure 3 The same parts and components are used with the same reference numerals. In this example, there is also no shunt resistor, and the common negative side of H-bridge 13 (which may be located on input terminal 19) is in direct contact with ground wire 24.

[0044] In this example, to obtain a voltage signal that can be used for pinch detection, measurement circuit 26 is configured to measure the voltage on reverse polarity protection MOSFET 14. One terminal 27 is connected to a node located at or near the source side of the MOSFET, while another terminal 28 is connected to a node located at or near the drain side of the MOSFET.

[0045] The inventors have discovered that changes in the current drawn by the motor can also be reflected in the voltage across the reverse-polarity MOSFET. In the event of pinch-in, the increase in current causes a rise in the voltage drop across the internal resistance of the reverse-polarity MOSFET. Therefore, monitoring this voltage signal can indicate the current drawn by the motor.

[0046] When performing current measurements on the MOSFETs of an H-bridge, the properties of the PWM signal driving the circuit can affect the measurement. Specifically, the duty cycle of the PWM signal determines the time window in which the measurement can be performed. For example, with a carrier frequency of 20 kHz and a duty cycle of 20%, the time window is approximately 0.02 ms. Upon startup, the current will rise initially and needs to stabilize for the remainder of the conduction phase. Therefore, when the duty cycle is low, aliasing may occur, and the measurement results may be prone to deviation. This effect is absent or less pronounced when measuring a reverse-polarity MOSFET, as this MOSFET is not operated by a PWM signal.

[0047] Therefore, the disclosed example of the drive circuit provides an output signal via its corresponding measurement circuit, which can be used as an input to an anti-jamming algorithm to improve its reliability. Such an anti-jamming algorithm can be executed by a control unit (e.g., control unit 11). The additional signal can also be used as a further input to a thermal algorithm to improve its reliability. Thermal algorithms are commonly used to detect excessive heating of components such as MOSFETs, particularly components of an H-bridge. For example, since two MOSFETs are typically provided in a single package, and each MOSFET is connected to a different branch of the H-bridge, a temperature sensor placed between the two MOSFETs in the same package can provide an indication of (excessive) heating. Upon detection of a temperature rise, a current signal can help identify which of the two MOSFETs is heating up. The signal can also provide an indication of the MOSFET's self-heating, for example, when compared to the ambient temperature of the components within the package. It should be noted that the internal resistance of the MOSFET depends on temperature, therefore the current-temperature profile can be known, and deviations can be detected.

[0048] Figure 5An example of measurement circuits 26, 26' is shown. Measurement circuits 26, 26' provide an amplification stage. Terminal 28, connected to the node at the drain side of the MOSFET, is connected to the negative input of operational amplifier OP1 via a network of transfer resistors R2, R3, R4. Terminal 27, connected to the node at the source side of the MOSFET, is connected to the positive input of operational amplifier OP1 and ground 29 via a network of voltage divider resistors R5, R6. The amplifier reference ground 29 outputs a voltage signal that indicates the motor current. This signal can also be referred to as a current sensing signal. This voltage signal or current sensing signal can also be used to determine whether the MOSFET is turned on.

[0049] Figure 6 Another example of measurement circuits 26, 26' is shown. In this example, measurement circuits 26, 26' add a filter stage section 32 before the amplification stage, the filter stage section 32 being connected to terminal 27. More specifically, Figure 5 The voltage divider resistor network is replaced by filter stage 32. Filter stage 32 contains an RC filter consisting of resistor R51 and filter capacitor C1. The output of the RC network R51 and C1 can be located at node 33. The filter stage further includes two diodes connected in parallel between node 33 and ground 29 with opposite conduction directions. A positive voltage source 31 (approximately +5 V in this example) is connected to node 33 via resistor R61. Terminal 30 for receiving the blanking signal is connected to node 33 via another resistor R62. Node 33 is further connected to the positive input terminal of operational amplifier OP1 via resistor R52.

[0050] Terminal 30, used to receive the blanking signal, allows for improved measurement results because it discharges capacitor C1, meaning no charge is stored after the blanking signal is provided. This blanking signal is then transmitted via a microcontroller (i.e., a control unit, such as...) Figure 1B The control unit 11 is provided and will be synchronized in opposite phase with the PWM signal. Preferably, the duration of the microcontroller activating the blanking signal is exactly longer than the start time of the conduction phase of the MOSFET on which the measurement is performed. This ensures that the measurement is performed when the MOSFET is fully turned on, rather than at the start or beginning of the conduction phase.

[0051] like Figure 4As shown, when measurements are performed on the MOSFETs of the H-bridge, the blanking signal provides improvement by eliminating ripple or interference generated by the partially charged capacitor C1. Furthermore, the potential aliasing effect can be reduced when the blanking signal is set to partially overlap with the effective portion of the PWM signal's duty cycle, because the initial discharge of the capacitor holding the RC filter stage will cause the current measurement to start at the appropriate time, i.e., when the MOSFET is in full-on mode. Reference Figure 8 The diagram shows an example of a PWM signal and such a partially overlapping blanking signal. In this example, the duty cycle is set to 40%. The blanking signal is out of phase and overlaps with it before the rising edge of the PWM signal reaches its maximum amplitude.

[0052] refer to Figure 7A , showing the operation Figure 3 and / or Figure 4 An example of a method for driving a circuit. The method can be implemented using a microcontroller (e.g., Figure 1B The control unit 11) executes the procedure. With the drive circuit 12 provided, the method begins by activating 701 the power supply 16 for the drive circuit 12. This is followed by activating 702 the charge pump 15 to control the conduction of the reverse polarity protection switch 14. When the motor is started for operating the roof panel, the method continues by providing 703 a PWM signal with a predetermined duty cycle to the H-bridge of the drive circuit for controlling the motor speed. The motor speed is directly related to the selected predetermined duty cycle. During operation of the roof panel, 706 current measurements are performed on one or more switching elements S1-S4 14 respectively.

[0053] refer to Figure 7B , showing the operation Figure 3 and / or Figure 4 Another example of the method of driving the circuit. With Figure 7A Similar operations in the examples have the same reference numerals. Except... Figure 7A A 704 blanking signal, which is inverted compared to the PWM signal, is provided to the measurement circuits 26 and 26'. A 705 blanking signal is maintained until the switching element whose current is to be measured is in the on state. For this purpose, the blanking signal partially overlaps with the initial portion of the effective duty cycle of the PWM signal to ensure that the MOSFET has been properly turned on and is at least close to full conduction. In this way, the influence of the filter stage of the measurement circuit on the signal to be measured can be prevented.

[0054] Detailed embodiments of the invention have been disclosed herein; however, it should be understood that the disclosed embodiments are merely examples of the invention, which can be embodied in various forms. Therefore, the specific structural and functional details disclosed herein should not be construed as limiting, but merely as the basis of the claims and as a representative basis for teaching those skilled in the art to utilize the invention in various ways with any suitable specific structure contemplated. In particular, features set forth and described in the individual dependent claims may be applied in combination, and thus any advantageous combination of such claims is disclosed.

[0055] Furthermore, it is anticipated that structural elements can be generated by applying three-dimensional (3D) printing technology. Therefore, any reference to structural elements is intended to cover any computer-executable instructions that instruct a computer to generate such a structural element using 3D printing technology or similar computer-controlled manufacturing techniques. Additionally, any such reference to structural elements is also intended to cover a computer-readable medium carrying such computer-executable instructions.

[0056] Furthermore, the terms and phrases used herein are not limiting but rather provide an understandable description of the invention. As used herein, the term "a" is defined as one or more. As used herein, the term "a plurality" is defined as two or more. As used herein, the term "another" is defined as at least a second or more. As used herein, the terms "comprising" and / or "having" are defined as including (i.e., open-ended language). As used herein, the term "link" is defined as a connection, but not necessarily a direct connection.

[0057] Although the invention has been described above with reference to specific embodiments, the invention is not limited to the specific forms set forth herein. Rather, the invention is limited only by the appended claims, and other embodiments besides the specific embodiments described above are also possible within the scope of these appended claims.

[0058] Furthermore, although exemplary embodiments have been described above with some exemplary combinations of components and / or functions, it should be understood that alternative embodiments may be provided by different combinations of components and / or functions without departing from the scope of this disclosure. Additionally, it is particularly contemplated that specific features described separately or as part of an embodiment may be combined with other separately described features or parts of other embodiments.

Claims

1. A drive circuit (12) for a roof assembly, the roof assembly including a roof panel (2a) movable between a closed position and an open position by a motor (9), the drive circuit (12) comprising: H-bridge (13), the H-bridge (13) includes switching elements (S1-S4) for controlling the speed of the motor (9). Reverse polarity protection switch (14), such as MOSFET; as well as At least one measurement circuit (26, 26'); The drive circuit (12) is configured to receive a PWM signal with a duty cycle for operating the H-bridge (13). The at least one measurement circuit (26, 26') is configured to perform current measurement on at least one of the switching elements (S1-S4, 14), respectively.

2. The driving circuit according to claim 1, wherein, The measurement circuit (26, 26') is arranged to transmit a voltage indicating the current signal as input to the anti-trapping algorithm.

3. The driving circuit according to claim 1 or 2, wherein, The measurement circuit (26, 26') includes a filter stage (32) with a filter capacitor (C1); and The measurement circuit (26, 26') is configured to receive a blanking signal for discharging the filter capacitor (C1).

4. The driving circuit according to any one of claims 1-3, further comprising: A charge pump (15) is configured to control the conduction of the reverse polarity protection switch (14).

5. A method for operating a drive circuit (12) according to any one of the preceding claims, the method comprising: Activate (701) the power supply (16) for the drive circuit (12); A PWM signal with a predetermined duty cycle is provided to the H-bridge (13) (703); (706) Current measurement is performed on one or more switching elements (S1-S4, 14) respectively.

6. The method for operating the drive circuit (12) according to claim 4 according to claim 5, the method further comprising: Activate (702) the charge pump (15) to put the reverse polarity protection switch (14) in the on state.

7. The method according to claim 5 or 6, further comprising: A blanking signal (704) is provided to the measurement circuit (26, 26'); The blanking signal is inversely related to the PWM signal.

8. The method of claim 7, further comprising: The blanking signal (705) is maintained until the switching element (S1-S4, 14) whose current is to be measured is in the on state.

9. A control unit for a roof assembly of a vehicle, the control unit being configured to perform the method according to any one of claims 5-8.

10. A roof assembly for a vehicle, comprising: The roof panel (2a) is movable between a closed position and an open position by a motor (9); And the control unit according to claim 9.

11. A vehicle comprising: The roof assembly according to claim 10.

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