METHOD FOR STARTING A ROTOR OF A CLAW POLE MOTOR

Abstract

The invention relates to a method for starting a single-phase claw-pole motor, wherein the claw-pole motor comprises a permanently excited rotor that rotates in one direction during rated operation, an electronically commutated stator, and a Hall effect sensor for determining the relative position of the rotor, the method comprising the following steps: a. generating an impulse to move the rotor in the opposite direction of rotation by applying current to a stator winding by virtue of an inverted Hall effect sensor signal; b. starting the rotor to move in the direction of rotation by applying current to a stator winding by virtue of a Hall effect sensor signal.

Description

METHOD FOR STARTING A ROTOR OF A CLAW POLE MOTOR Field of Invention The invention relates to a method for starting a rotor of a single-phase claw pole motor in accordance with the object of claim 1. Background of the Invention Pumps can be used, for example, in motor vehicles to lift and transport liquids, such as coolants. These pumps are typically operated by an electric drive, which is actively connected to the pump rotor. Single-phase claw-pole motors, which have a permanently excited rotor and an electronically commutated stator, can be used for this purpose. A Hall effect sensor is used to determine the rotor's relative position, which is necessary to switch the current in the stator winding, thus producing the rotor's rotational movement. For example, due to pinwheel effects, the rotor's locking position may be unfavorable, making it difficult for the rotor to overcome the opposing torque during the Ref. 350566 First switching during commissioning. In this case, there is a risk of incorrect pump start-up, meaning the pump starts and the rotor moves in the opposite direction of rotation during nominal operation. There is also a risk of incorrect pump start-up due to insufficient holding torque or excessive friction. Summary of the Invention The object of the invention is to prevent erroneous starting of a pump rotor, especially in the case of a single-phase claw-pole motor. This problem is solved by the method according to claim 1. The method of the invention according to claim 1 is intended for starting the rotor of a single-phase claw-pole motor, wherein the claw-pole motor comprises a permanently excited rotor that, in nominal operation, rotates in one direction, an electronically commutated stator, and a Hall effect sensor for determining the relative position of the rotor. The procedure involves the following steps: a. generating an impulse to move the rotor in the opposite direction by applying current to a stator winding by virtue of an inverted Hall effect sensor signal, and b. Starting the rotor for movement in the direction of rotation by applying current to a stator winding by virtue of a Hall effect sensor signal. The rotor of a pump can be held in any number of positions, preferably eight, when de-energized. The pump's electronics start the pump based on signals from a Hall effect sensor mounted on the stator. The rotor's position before starting is determined by the holding torque (defined by the magnetic circuit), friction, and external torques (e.g., due to hydraulic circuit leakage). When starting from the rest position (holding position), the pump rotor must overcome the motor's brief opposing holding torque during the initial switching in the direction of rotation; that is, sufficient rotational energy must be generated. If this is unsuccessful, a reversal of direction occurs, and thus, a reverse start of the rotor is possible.Furthermore, the switching moment may be offset (for example, due to magnetization of the magnets and the positioning of the Hall effect sensor) and cause the same problem. By means of a brief pulse opposite to the direction of rotation, the rotor has more time and distance (start-up distance) to gain sufficient momentum to overcome the opposing torque. Preferably, it may be foreseen that in the event that during or immediately after the generation of an impulse for the movement of the rotor in the opposite direction of rotation, the start-up is interrupted for a predetermined period of time and a new impulse for the movement of the rotor in the opposite direction of rotation is produced for a predetermined period of time. To prevent false switching, the Hall effect sensor signal can be monitored during and shortly after the generation of a pulse for reverse rotor rotation. If the Hall effect sensor signal detects changes during the monitoring period, the startup process is halted, and after a short delay (e.g., 150 ms), the pulse generation described above is repeated. At the Hall effect sensor's position, the rotor field and the stator's parasitic field overlap. If, before starting, the rotor is displaced from its nominal position to such an extent that the rotor's magnetic field at the Hall effect sensor is very weak, the stator's parasitic field can interfere unacceptably with the rotor's magnetic field. This causes the Hall effect sensor signal to be directly inverted during pulse generation, resulting in erroneous switching. In a preferred embodiment, the rotor starts without generating a pulse if a limited number (e.g., three attempts) of pulse generation repetitions are exceeded. This could be useful, for example, in overcoming a pump blockage, where starting occurs without generating a pulse to move the rotor in the opposite direction of rotation. In an additional mode, a predetermined time period is established based on the supply voltage of the single-phase claw-pole motor. It is possible to change the generation of at least one pulse relative to the predetermined time duration, depending on the supply voltage of the single-phase claw-pole motor. This advantageously decouples the energy input to the winding and effectively prevents or reduces false starts based on the supply voltage. The corresponding predetermined values ​​for the time duration can be calculated or determined experimentally. (Example values ​​are: 1.5 ms at ≤ 11 V; 1.1 ms at 11 V < ≤ 13.5 V; and 0.8 ms at > 13.5 V supply voltage.) Furthermore, the current supply to a stator winding is preferably achieved by switching power electronics. These devices are commonly used components in the prior art, such as MOSFETs or IGBTs. In one mode, the predetermined duration is chosen so that, by moving the rotor in the opposite direction of rotation, it experiences more acceleration than braking during the subsequent start-up to overcome an opposing torque at the initial switching moment, thus ensuring movement in the correct direction. This preferably prevents a false start. To guarantee a correct starting position, at least one pulse may be applied. In the context of the invention, the impulse is a momentary phase switch in the opposite direction of rotation before the actual start, i.e., a current supplied to a stator winding due to an inverted Hall effect sensor signal. In other words, by means of the impulse for the rotor's movement in the opposite direction of rotation, it is ensured that the rotor receives sufficient impulse during the subsequent start in the correct direction of rotation to overcome the opposing torque during the initial phase switch. In one configuration, the Hall effect sensor is mounted on the stator or an electronic circuit board and is offset in the direction of rotation from a central position on a stator pole. This ensures that the rotor starts in the correct direction of rotation. The single-phase claw pole motor is primarily used in electric pumps, especially electric centrifugal pumps. However, other electric liquid pumps are also suitable for this application. Brief Description of the Figures The invention is also explained in more detail below with respect to other features and advantages by means of a description of illustrative embodiments and with reference to the accompanying figures. They show: Figure 1: A flow diagram of a starting process for a single-phase claw-pole motor in accordance with the state of the art, and Figure 2: A flow diagram of a starting of a single-phase claw pole motor according to the present invention. Detailed Description of the Invention Figure 1 shows a flow diagram of a starting process for a single-phase claw-pole motor according to the prior art. For the start-up phase, the motor phases are switched with a 100% duty cycle with respect to the Hall effect sensor frequency, after which a different switching mode can be selected, for example, a 100% duty cycle, a regulated speed, or controlled or regulated motor operation. Depending on the rotor's position (or: locking position, locking state, rest state) before startup, the rotor can start in the correct direction or the opposite direction, which can result in a false start. In other words, the rotor's rest position before startup is too close to the first commutation moment position to generate enough kinetic energy during startup to overcome the opposing torque. The rotor position adopted by the rotor before starting depends on the tolerances or inaccuracies of the following components. • Magnetization of the working magnet • Magnetization of the sensor magnet • Positioning of the Hall effect sensor (delays the switching moment in each case) • Stator geometry / material and manufacturing (influence the interlocking) Therefore, the (weak) acceleration of the rotor during startup from the rest position to the correct direction of movement is converted into braking energy during movement, causing the rotor to slow down and stop. Subsequently, an acceleration on the rotor in the opposite direction of rotation and a braking force in the direction of rotation act so that the rotor moves against the direction of rotation, potentially resulting in a false start. Figure 2 shows a flow diagram of the starting process for a single-phase claw-pole motor according to the present invention. A pulse is generated to move the rotor in the opposite direction of rotation by supplying current to a stator winding due to an inverted Hall effect sensor signal. Specifically, the pulse occurs before the start of the motor. This moves the rotor in the opposite direction for a certain distance. This allows the rotor a longer path to generate sufficient acceleration energy to overcome the opposing torque after the initial commutation. After the initial commutation, a short braking phase and a long acceleration phase occur. The impulse is preferably a momentary phase-switching event (e.g., 1.5 ms) in the opposite direction before starting; that is, a current supplied to a stator winding by virtue of an inverted Hall effect sensor signal. The reverse phase-switching causes the rotor to rotate in the opposite direction and experience more acceleration than braking during subsequent starting, thus preventing starting in the wrong direction. During startup, monitoring is performed using a Hall effect sensor signal. After generating the pulse in the opposite direction of rotation, several switching operations are carried out with a 100% duty cycle, followed by discretionary operation, such as a 100% duty cycle, controlled speed, or controlled or regulated motor operation. It is hereby stated that, as of this date, the best method known to the applicant for putting the aforementioned invention into practice is the one that is clear from the present description of the invention.

Claims

1. A method for starting a rotor of a single-phase claw-pole motor, wherein the claw-pole motor comprises a permanently excited rotor that, during nominal operation, moves in one direction of rotation, an electronically commutated stator, and a Hall effect sensor for determining the relative position of the rotor, characterized in that it comprises the following steps: a. generating an impulse to move the rotor in the opposite direction by applying current to a stator winding by virtue of an inverted Hall effect sensor signal, b. starting the rotor for movement in the direction of rotation by applying current to a stator winding by virtue of a Hall effect sensor signal.

2. Method according to claim 1, characterized in that, in the event that during, or immediately after, the generation of an impulse for the movement of the rotor in the opposite direction of rotation, the starting is interrupted for a predetermined period of time and an impulse is again made for the movement of the rotor in the opposite direction of rotation for a predetermined period of time.

3. Method in accordance with any of claims 1 or 2, characterized in that if a limited number of repetitions in such impulse generation are exceeded, a rotor start-up occurs without the generation of an impulse for movement in the direction of rotation.

4. Method in accordance with any of the preceding claims, characterized in that the predetermined time period dependent on a supply voltage of the single-phase claw pole motor is checked or determined.

5. Method in accordance with any of the preceding claims, characterized in that the supply of current to a stator winding is effected by switching the power electronics.

6. A method in accordance with any of the preceding claims, characterized in that the predetermined time period is chosen such that, when moving the rotor in the opposite direction of rotation, it experiences more acceleration than braking on subsequent start-up to overcome a counter-rotating torque at an initial switching moment, to ensure movement in the direction of rotation.

7. Method in accordance with any of the preceding claims, characterized in that the Hall effect sensor is mounted on the stator or on an electronic circuit board and is arranged offset in the direction of rotation with respect to a central position of a pole of the stator.

8. Method in accordance with any of the preceding claims, characterized in that the single-phase claw pole motor is used in electric pumps, in particular in electric centrifugal pumps.

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