Method for operating a brushless direct current motor

Abstract

The invention relates to a method for operating a brushless DC motor, wherein upon a request to change the speed of the brushless DC motor, an electrical quantity of the brushless DC motor is ascertained, and the implementation (35) of the request (30) is delayed until the value (I Mot ) and / or the gradient (dI Mot ) of the electrical quantity lies within a predefinable range.

Description

TECHNICAL FIELD

[0001] The invention relates to a method for operating a brushless DC motor. Furthermore, the invention relates to a computer program which implements each step of the method and to a machine-readable storage medium which stores the computer program. Finally, the invention also relates to an electronic controller which is set up to implement the method. BACKGROUND

[0002] Brushless DC motors (BLDC) are used, for example, in the automotive sector in order to drive reciprocating piston pumps which are used as pumps in transport modules for SCR catalytic systems (Selective Catalytic Reduction) or as fuel pumps. Like a three-phase current synchronous motor, a brushless DC motor is constructed with an excitation by permanent magnets. The three-phase current windings are actuated by a suitable circuit, as a result of which the three-phase current windings generate a rotating magnetic field which synchronously moves (mitzieht) the permanently excited rotor. The sub-coils are usually energized here by means of a bridge circuit.

[0003] A reciprocating piston pump causes a variable load on the motor shaft of the brushless DC motor. Since the supply current of the motor is proportional to the required torque, the current profile oscillates in the case of this use of the brushless DC motor. SUMMARY

[0004] In the method for operating a brushless DC motor, an electrical variable of the brushless DC motor is ascertained in the event of a request to change the speed of the brushless DC motor. The implementation of the request is delayed until the value and / or the gradient of the electrical variable lies within a predefinable range.

[0005] The electrical variable is in particular a variable which is proportional to the required torque of the brushless DC motor, for example the supply current, the phase current, the supply voltage or the phase voltage of the brushless DC motor.

[0006] The method can be used particularly advantageously when the brushless DC motor is operated with a variable load on its motor shaft, for example because it drives a reciprocating piston pump. The variable load causes an oscillation of the supply current of the brushless DC motor. If the required speed change is now implemented at a point in time at which the current is close to or already at its local maximum, the required current for the speed increase is added to the current intensity which is already high in any case, so that a high peak current occurs. The power supply system of the brushless DC motor must be designed to tolerate high peak currents. The current peaks not only load the electrical components of the brushless DC motor, but also the mechanical components.

[0007] Now, the method enables a gentle acceleration of the brushless DC motor, in that the speed change is no longer implemented immediately independently of the current prevailing current, but rather, in contrast, is delayed in dependence on the electrical variable, so that it is possible to prevent high peak currents from occurring.

[0008] When the brushless DC motor is operated in motoring operation, the implementation of the requirement is preferably delayed until the value is below a first threshold value, and / or until the gradient is below a second threshold value. By comparing the value with the first threshold value, it is ensured that an already high absolute value of the electrical variable is not further increased by the implementation of the requirement. By comparing the gradient with the second threshold value, it is ensured that the requirement is not implemented during a rise in the supply current. For this purpose, a value less than or equal to zero is selected in particular for the second threshold value.

[0009] The method can also be used in the generator operation of the brushless DC motor. Here, the method also prevents current peaks from occurring, the sign of which is exchanged relative to the motoring operation. It is therefore preferred here that the implementation of the requirement is delayed until the value exceeds a third threshold value and / or the gradient exceeds a fourth threshold value. The fourth threshold value is in particular greater than or equal to zero.

[0010] When it is particularly important that current peaks should be avoided, the method is preferably executed in such a way that the requirement is delayed until both the value and the gradient lie within a predefinable range. For the motoring operation, this means that, preferably, the value is below the first threshold value and the gradient is below the second threshold value. In the generator operation of the brushless DC motor, it is therefore preferred that the value exceeds the third threshold value and the gradient exceeds the fourth threshold value.

[0011] A computer program is provided for carrying out each step of the method, in particular when the computer program is executed on a computer or an electronic controller. The computer program can enable the implementation of different embodiments of the method in an electronic controller without having to make structural changes here. For this purpose, the computer program is stored on a machine-readable storage medium.

[0012] An electronic controller is obtained by running the computer program on a conventional electronic controller, which is provided for operating a brushless DC motor by means of the method. BRIEF DESCRIPTION OF DRAWINGS

[0013] Figure 1 A brushless DC motor is shown schematically, which can be operated by means of an embodiment of the method according to the application.

[0014] Figure 2 Time curves of the motor speed, the torque and the supply current of a brushless DC motor are shown, which is operated in a conventional manner.

[0015] Figure 3 A flow chart of a method according to an embodiment of the application is shown.

[0016] Figure 4 A time curve of the motor speed, torque and supply current of a brushless DC motor is shown, which is operated by means of a method according to an embodiment of the application. DETAILED DESCRIPTION

[0017] Figure 1 A brushless DC motor 10 with a three-strand three-phase current winding is shown, which has a motor shaft 11. A speed sensor 12 is provided for measuring its motor speed. The brushless DC motor 10 is controlled by means of a bridge circuit 21 by an electronic controller 20, in which there is a supply voltage U Mot and a supply current I Mot flows in the bridge circuit. The brushless DC motor 10 drives a reciprocating piston membrane pump, which is not shown in the transport module of an SCR catalytic system.

[0018] By individual pump strokes, a variable load M or a variable torque acts on the motor shaft 11. As is shown, Figure 2 the load M changes with the angle of rotation ω of the motor shaft 11, where 2π corresponds to a rotation of 360°, respectively. The oscillation of the load M is to be noted. The supply current I Mot oscillates in synchronism with the current load M over time t. When at a point in time tl it is required to accelerate the hitherto constant motor speed v to a higher value, this can only be achieved by a sudden increase in the supply current I Mot . If the point in time tl lies at a local maximum of the supply current I Mot , this leads to a current peak in the shown manner.

[0019] Figure 3 An embodiment of the method according to the application for the motor operation of the brushless DC motor 10 is shown. The method starts when at a point in time tl it is required to increase the speed v of the brushless DC motor 10 by 30. In the electronic controller 20, the current value I Mot of the supply current is detected 31. This value is compared in a first comparison 32 with a first threshold value S1. When the value I Mot is not below the first threshold value S1, then it is waited until this condition is met. Subsequently, the gradient dI Mot of the supply current is detected 33. This gradient is compared in a second comparison 34 with a second threshold value S2. When the gradient dI Mot is not below the second threshold value S2, again it is waited until this condition is also met. Only when both conditions are met, an implementation 35 of a speed change is carried out, and the method ends in a last step 36.

[0020] Figure 4 With Figure 2 A similar illustration shows the effect of an embodiment of the method according to the invention when implementation 35 is delayed to time point t2, at which time the value of the supply current I... Mot It lies at a local minimum, and its gradient dI Mot Therefore, it is zero. Although a sudden increase in supply current also occurs here, the maximum current intensity achieved here is only slightly above the maximum value of the current intensity achieved within the oscillation range.

[0021] In another embodiment of the method according to the invention, the brushless DC motor 10 operates in a generator-like manner, according to... Figure 3 The method flow has been changed as follows: in step 32, the value I... Mot Whether it exceeds the third threshold is compared, and the gradient dI is evaluated in step 34. Mot Whether it exceeds the fourth threshold is compared. In the same manner as in motor-type operation, the method according to the invention prevents current peaks from occurring here, however, where the current peaks have a negative sign in generator-type operation.

Claims

1. A method for operating a brushless DC motor (10), wherein the brushless DC motor (10) operates with a variable load (M) acting on its motor shaft (11), wherein the value of an electrical parameter (I) of the brushless DC motor (10) is known when a change in the speed (v) of the brushless DC motor (10) is required (30). Mot And determine the value of the electrical parameter (I) Mot Whether it is within a preset range, wherein when the value of the electrical parameter (I) is within a preset range. Mot When the electrical parameter is within the preset range, the gradient of the electrical parameter is detected and it is determined whether the gradient of the electrical parameter is within the preset range. The speed change is only implemented when the gradient of the electrical parameter is also within the preset range.

2. The method according to claim 1, characterized in that, The electrical parameter is the supply current or supply voltage of the brushless DC motor.

3. The method according to claim 2, characterized in that, The electrical parameters are the phase current or phase voltage of the brushless DC motor.

4. The method according to any one of claims 1 to 3, characterized in that, During the motor operation of the brushless DC motor (10), the implementation of the requirement (30) is delayed (35) until the value of the electrical parameter (I) is reached. Mot If the gradient is below the first threshold (S1), and / or the gradient (dI) is below the first threshold (S1), and / or the gradient ...). Mot It is below the second threshold (S2).

5. The method according to any one of claims 1 to 3, characterized in that, In the generator-type operation of the brushless DC motor (10), the implementation of the requirement (30) is delayed (35) until the value of the electrical parameter (I) is reached. Mot If the gradient exceeds the third threshold, and / or the gradient (dI) Mot It exceeds the fourth threshold.

6. A computer program product comprising a computer program configured to perform each step of the method according to any one of claims 1 to 5.

7. A machine-readable storage medium on which the computer program according to claim 6 is stored.

8. An electronic controller (20) configured to operate a brushless DC motor by means of any one of claims 1 to 5.

Images