Method for starting a rotor of a claw-pole motor

Abstract

A method for starting a rotor of a single-phase claw-pole motor, wherein the claw-pole motor comprises a permanently excited rotor which, during nominal operation, executes a movement in one direction of rotation, an electronically commutated stator and a Hall sensor for determining the relative rotor position, the method comprising the following steps: a. Generation of a pulse by a short-term phase commutation to move the rotor in the opposite direction of rotation by energising a stator winding due to an inverted Hall sensor signal; b. Starting the rotor to move in the direction of rotation by energizing a stator winding based on a Hall sensor signal, wherein in the event that during or immediately after the generation of a pulse to move the rotor in the opposite direction of rotation for a predetermined period of time, the start-up is interrupted and a pulse to move the rotor in the opposite direction of rotation is again generated for a predetermined period of time, wherein the predetermined period of time is determined or ascertained depending on a supply voltage of the single-phase claw-pole motor.

Description

[0001] The invention relates to a method for starting a rotor of a single-phase claw-pole motor according to the subject matter of patent claim 1.

[0002] Pumps can be used, for example, in motor vehicles to pump and transport fluids, such as cooling fluids. Such pumps are typically operated by an electric drive that is operatively connected to the pump rotor. Single-phase claw-pole motors can be used as the electric drive, featuring a permanently excited rotor and an electronically commutated stator. A Hall sensor is used to determine the relative rotor position, which is necessary to commutate the current in the stator winding, resulting in a rotary motion of the rotor.

[0003] Windmilling effects, for example, can cause the rotor's detent position to be unfavorable, making it difficult for the rotor to overcome the counter-torque during the initial commutation. This poses the risk of incorrect pump start-up, meaning that the rotor starts and moves in the opposite direction to its nominal operating direction. Insufficient detent torque or excessive friction also poses a risk of incorrect pump start-up.

[0004] DE 41 22 109 A1 describes a method for controlling the start-up of a two-pole, electronically commutated DC motor (not a claw-pole motor) with a single-phase stator winding and a permanent magnet rotor. According to the method, among other things, the commutation arrangement is blocked for a period of time, the rotor position is determined, and the rotor is rotated by a specific angle in or against the operating direction of rotation. This is intended to ensure reliable start-up of the motor.

[0005] The object of the invention is to prevent incorrect starting of a pump rotor, particularly in a single-phase claw-pole motor. This object is achieved by the method according to patent claim 1.

[0006] The inventive method according to claim 1 is intended for starting a rotor of a single-phase claw-pole motor, wherein the claw-pole motor comprises a permanently excited rotor that moves in one direction during nominal operation, an electronically commutated stator, and a Hall sensor for determining the relative rotor position. The method includes the following steps: a. Generation of an impulse to move the rotor in the opposite direction of rotation by energizing a stator winding based on an inverted Hall sensor signal and b. Starting the rotor to move in the direction of rotation by energizing a stator winding based on a Hall sensor signal, wherein in the event that during or immediately after the generation of a pulse to move the rotor in the opposite direction of rotation for a predetermined period of time, the start-up is interrupted and a pulse to move the rotor in the opposite direction of rotation is again generated for a predetermined period of time, wherein the predetermined period of time is determined or ascertained depending on a supply voltage of the single-phase claw-pole motor.

[0007] The rotor of a pump can lock at any number of points, preferably eight, by detent when deenergized. The pump electronics start the pump based on signals from a Hall sensor attached to the stator. The rotor position before start-up is determined by the detent torque (defined by the magnetic circuit), friction, and external torques (e.g., due to overcurrent in the hydraulic circuit). When starting up from a rest position (detent position), the pump rotor must overcome the brief motor counter-torque during the first commutation in the direction of rotation; in other words, sufficient rotational energy must be generated. If this fails, the direction is reversed, causing the rotor to start incorrectly. Furthermore, the commutation time can be shifted (e.g., due to magnetization of the magnets and the positioning of the Hall sensor), leading to the same problem.By means of a short impulse opposite to the direction of rotation, the rotor is given more time and (start-up) path to gain sufficient momentum and thus overcome the counter-torque.

[0008] To prevent false commutations, it is possible to monitor the Hall sensor signal during and shortly after generating a pulse to move the rotor in the opposite direction. If the Hall sensor signal detects changes during the monitoring period, the start-up is stopped and, after a short time (e.g., 150 ms), the generation of a previously described pulse is repeated.

[0009] At the Hall sensor position, the rotor field and the stator stray field overlap. If the rotor is so far offset from its nominal position before start-up that the rotor magnetic field at the Hall sensor is very weak, the stator stray field can unduly interfere with the rotor magnetic field, causing the Hall sensor signal to be directly inverted during pulse generation, resulting in incorrect commutation.

[0010] The predetermined time period is determined or determined based on the supply voltage of the single-phase claw-pole motor. It is possible to vary the generation of at least one pulse with respect to the predetermined time period depending on the supply voltage of the single-phase claw-pole motor. This advantageously decouples the energy input in the winding and the effective effect on preventing or reducing false starts, depending on the supply voltage. The corresponding predetermined values ​​for the time period can be calculated or determined experimentally. (Example values ​​are: 1.5 msec at <= 11 V; 1.1 msec at 11 V < V <= 13.5 V; and 0.8 msec at > 13.5 V supply voltage)

[0011] In a preferred embodiment, if a limited number of repetitions of such pulse generation is exceeded (for example, three attempts), the rotor starts up without generating a pulse. This could be useful, for example, in the case of overcoming a pump blockage, where the start-up occurs without generating a pulse to move the rotor in the opposite direction.

[0012] Furthermore, the stator winding is preferably energized by commutation of power electronics. These components are commonly used in the state of the art, such as MOSFETs or IGBTs.

[0013] In one embodiment, the predetermined time period is selected such that, due to the movement of the rotor in the opposite direction of rotation, it experiences more acceleration than deceleration during subsequent start-up in order to overcome a counter-torque at a first commutation instant and ensure movement in the direction of rotation. This preferably prevents false start-up. To ensure a correct start-up position, at least one pulse can be applied.

[0014] In the context of the invention, the pulse is a brief phase commutation in the opposite direction of rotation before the actual start-up, i.e., a current flowing through a stator winding due to an inverted Hall sensor signal. In other words, the pulse for moving the rotor in the opposite direction of rotation ensures that the rotor receives sufficient momentum during the subsequent start-up in the correct direction of rotation to overcome the counter-torque during the initial commutation.

[0015] According to one design, the Hall sensor is mounted on the stator or on an electronic circuit board and is offset in the direction of rotation with respect to the center position of a stator pole. This ensures that the rotor starts in the correct direction of rotation.

[0016] The single-phase claw-pole motor is preferably used in electric pumps, especially electric centrifugal pumps. However, other electric liquid pumps are also conceivable for this application.

[0017] The invention will be explained in more detail below with regard to further features and advantages based on the description of exemplary embodiments and with reference to the accompanying drawings. Fig. 1 a process flow diagram of a start-up of a single-phase claw-pole motor according to the prior art and Fig. 2 is a process flow diagram of a start-up of a single-phase claw-pole motor according to the present invention.

[0018] Fig. Figure 1 shows a process flow diagram for the start-up of a single-phase claw-pole motor according to the prior art. At the start of the start-up phase, the motor phases are commutated with a 100% duty cycle relative to the Hall sensor frequency. Afterward, a different commutation mode can be selected, for example, a continued 100% duty cycle or a controlled speed, or open-loop or closed-loop motor operation.

[0019] Depending on the rotor position (or detent position, rest position, or idle position) before start-up, the rotor can start in the correct or opposite direction of rotation, which can result in a so-called false start-up. In other words, the rotor's rest position before start-up is too close to the position of the first commutation instant to generate enough kinetic energy during start-up to overcome the counter-torque.

[0020] The rotor position assumed by the rotor before start-up depends on the tolerances or inaccuracies of the following components: • Magnetization of the working magnet • Magnetization of the sensor magnet • Hall sensor positioning (shifts the commutation time) • Stator geometry / material and processing (affect the locking)

[0021] The (weak) acceleration of the rotor when starting from a rest position into the correct direction of movement is converted into braking energy during the movement, causing the rotor to decelerate and stop. As a result, the rotor is accelerated in the opposite direction of rotation and decelerated in the same direction, causing the rotor to move in the opposite direction of rotation, which can result in a false start.

[0022] Fig.Figure 2 shows a process flow diagram for starting 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 energizing a stator winding based on an inverted Hall sensor signal. In particular, the pulse is generated before the start of start-up. This essentially moves the rotor back a certain distance in the opposite direction. This allows the rotor an increased distance to generate sufficient acceleration energy to overcome the counter-torque after the first commutation time. After the first commutation time, a short braking phase and a long acceleration phase occur. The pulse is preferably a short-term (e.g., 1.5 msec) phase commutation in the opposite direction before start-up, i.e., energizing a stator winding based on an inverted Hall sensor signal.The reverse phase commutation causes the rotor to shift in the opposite direction of rotation and to experience more acceleration than deceleration during subsequent start-up, which prevents start-up in the wrong direction.

[0023] During start-up, monitoring is performed using a Hall sensor signal. After generating the pulse in the opposite direction, several commutations occur with a 100% duty cycle, followed by any desired operation, for example, continued 100% duty cycle or a controlled speed, or open-loop or closed-loop motor operation.

Claims

[1] Method for starting a rotor of a single-phase claw-pole motor, the claw-pole motor comprising a permanently excited rotor which, during nominal operation, executes a movement in one direction of rotation, an electronically commutated stator and a Hall sensor for determining the relative rotor position, the method comprising the following steps: a. Generation of a pulse by a short-term phase commutation to move the rotor in the opposite direction of rotation by energising a stator winding due to an inverted Hall sensor signal; b. Starting the rotor to move in the direction of rotation by energizing a stator winding based on a Hall sensor signal, wherein in the event that during or immediately after the generation of a pulse to move the rotor in the opposite direction of rotation for a predetermined period of time, the start-up is interrupted and a pulse to move the rotor in the opposite direction of rotation is again generated for a predetermined period of time, wherein the predetermined period of time is determined or ascertained depending on a supply voltage of the single-phase claw-pole motor. [2] Method according to claim 1, wherein when a limited number of repetitions of such generation of pulses is exceeded, the rotor starts up without generating a pulse for movement in the direction of travel. [3] Method according to one of the preceding claims, wherein the current supply to a stator winding is effected by commutation of power electronics. [4] Method according to one of the preceding claims, wherein the predetermined time period is selected such that the movement of the rotor in the opposite direction of rotation causes it to experience more acceleration than braking during the subsequent start-up in order to overcome a counter-torque at a first commutation time in order to ensure a movement in the direction of rotation. [5] Method according to one of the preceding claims, wherein the Hall 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 stator pole. [6] Method according to one of the preceding claims, wherein the single-phase claw-pole motor is used in electric pumps, in particular in electric centrifugal pumps.

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