CN110808697A - Method for operating a brushless DC motor - Google Patents

Abstract

The invention relates to a method for operating a brushless DC motor, wherein electrical parameters of the brushless DC motor are known when a speed change of the brushless DC motor is requested and the implementation (35) of the request (30) is delayed ) until the value (I _Mot ) and/or the gradient (dI _Mot ) of the electrical parameter is within a presettable range.

Description

Method for operating a brushless DC motor

technical field

The present invention relates to a method for operating a brushless DC motor. Furthermore, the present invention relates to a computer program implementing each step of the method and a machine-readable storage medium storing the computer program. Finally, the invention also relates to an electronic controller arranged to implement the method.

Background technique

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

A reciprocating piston pump results in a variable load on the motor shaft of a brushless DC motor. Because the motor's supply current is proportional to its required torque, the current curve oscillates with this use of a brushless DC motor.

SUMMARY OF THE INVENTION

In a method for operating a brushless DC motor, electrical parameters of the brushless DC motor are known in the event of a requirement to change the speed of the brushless DC motor. The implementation of this request is delayed until the value and/or the gradient of the electrical variable is within a predefinable range.

The electrical variables are in particular variables proportional to the required torque of the brushless DC motor, for example the supply current, phase current, supply voltage or phase voltage of the brushless DC motor.

The method can be used particularly advantageously when the brushless DC motor is operated with a variable load acting on its motor shaft, for example because it drives a reciprocating piston pump. The variable load causes oscillations in the supply current of the brushless DC motor. If the required speed change is now carried out at a point in time at which the current is close to its local maximum or is already at this local maximum, the current required for the speed increase is also added to the current intensity, which is already high anyway, so that high the peak current. The power supply system for brushless DC motors must be designed to tolerate high peak currents. But the current peak loads not only the electrical components of the brushless DC motor, but also the mechanical components.

The method now enables gentle acceleration of the brushless DC motor in that the speed change is no longer carried out immediately, independent of the current present, but instead is delayed according to the electrical variable, so that high peaks can be prevented. current.

When the brushless DC motor is operating in motorized operation, it is preferred to delay the implementation of this requirement until the value is below a first threshold value, and/or until the gradient is below a second threshold value. Comparing this value with the first threshold value ensures that the already high absolute value of the electrical variable is not further increased by the implementation of this requirement. Comparing this gradient with the second threshold value ensures that during the supply current rise, this requirement is not implemented. For this purpose, in particular a value less than or equal to zero is selected for the second threshold value.

The method can also be used in generator-like operation of brushless DC motors. In this case, too, the method prevents current peaks from occurring, but the sign of the current peaks is reversed relative to the motorized operation. It is therefore preferred here to delay the implementation of the request until the value exceeds the third threshold value and/or the gradient exceeds the fourth threshold value. The fourth threshold value is in particular greater than or equal to zero.

If the occurrence of current peaks is to be avoided particularly reliably, the method is preferably carried out by delaying the request until both the value and the gradient lie within a predeterminable range. For motorized operation, this means that, preferably, the value is below a first threshold value and the gradient is below a second threshold value. Then, in generator-like 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.

A computer program is provided for carrying out each step of the method, especially when the computer program is run on a computer or electronic controller. The computer program enables different embodiments of the method to be carried out in the electronic controller without having to make structural changes here. For this purpose, the computer program is stored on a machine-readable storage medium.

An electronic controller is obtained by running the computer program on a conventional electronic controller, which is provided for operating the brushless DC motor by means of the method.

Description of drawings

FIG. 1 schematically shows a brushless DC motor, which can be operated by means of an embodiment of the method according to the invention.

Figure 2 shows the time profiles of motor speed, torque and supply current for a brushless DC motor operating in a conventional manner.

Figure 3 shows a flowchart of a method according to an embodiment of the invention.

Figure 4 shows a time profile of motor speed, torque and supply current for a brushless DC motor operating by means of a method according to an embodiment of the invention.

Detailed ways

FIG. 1 shows a brushless DC motor 10 with a three-phase current winding, which has a motor shaft 11 . A speed sensor 12 is provided to measure its motor speed. The brushless DC motor 10 is controlled by the electronic controller 20 by means of a bridge circuit 21 in which the supply voltage U _Mot is present and in which the supply current I _Mot flows. The brushless DC motor 10 drives a reciprocating piston diaphragm pump not shown in the transport module of the SCR catalytic system.

With each pump stroke, a variable load M or a variable torque acts on the motor shaft 11 . As shown in FIG. 2, the load M varies with the rotation angle ω of the motor shaft 11, where 2π corresponds to a rotation of 360°, respectively. Pay attention to the oscillation of the load M. The supply current I _Mot oscillates with the time t in synchronization with the current load M. When an acceleration of the hitherto constant motor speed v to a higher value is required at the point in time _t1 , this can only be achieved by abruptly increasing the supply current I _Mot . If the point in time t ₁ lies at a local maximum of the supply current I _Mot , this results in a current peak in the manner shown.

FIG. 3 shows an embodiment of the method according to the invention for the motorized operation of the brushless DC motor 10 . The method begins with a request 30 to increase the speed v of the brushless DC motor 10 at time t ₁ . In the electronic controller 20, the current value I _Mot of the supply current is detected 31. This value is compared with a first threshold value S ₁ in a first comparison 32 . When the value I _Mot is not lower than the first threshold value S ₁ , wait until the condition is met. The gradient dI _Mot of the supply current is then detected 33 . This gradient is compared with a second threshold value S ₂ in a second comparison 34 . When the gradient dI _Mot is not lower than the second threshold value S ₂ , it is also waited until this condition is also satisfied. The implementation 35 of the speed change takes place only when both conditions are met, and the method ends in a final step 36 .

FIG. 4 shows, in a diagram similar to FIG. 2 , the effect of an embodiment of the method according to the invention when the implementation 35 is delayed to the point in time t ₂ at which the value of the supply current I _Mot lies at a local minimum value, and the gradient dI _Mot is therefore zero. Although a sudden increase in the supply current also occurs here, the maximum current strength achieved here is only slightly above the maximum value of the current strength that is always achieved in the oscillating range.

In a further embodiment of the method according to the invention, in which the brushless DC motor 10 is operated as a generator, the method sequence according to FIG. 3 is changed in that, in step 32 , whether the value I _Mot exceeds the third The thresholds are compared and in step 34 it is compared whether the gradient dI _Mot exceeds a fourth threshold. In the same way as in motor operation, the method according to the invention here prevents the occurrence of current peaks, which, however, have a negative sign in generator operation.

Claims (8)

1. A method for operating a brushless DC motor (10), wherein the brushless DC motor (10) is known when the speed (v) of the brushless DC motor (10) is requested (30) to change and delaying ( 35 ) the implementation ( 35 ) of the request ( 30 ) until the value (I _Mot ) and/or the gradient (dI _Mot ) of the electrical parameter is within a predeterminable range. 2. The method according to claim 1, wherein the electrical parameter is a supply current, a phase current, a supply voltage or a phase voltage of the brushless DC motor. 3. The method according to claim 1 or 2, characterized in that the brushless DC motor (10) operates with a variable load (M) acting on its motor shaft (11). 4. The method according to any one of claims 1 to 3, characterized in that in motoring operation of the brushless DC motor (10), the implementation (35) of the request (30) is delayed ) until the value (I _Mot ) is below a first threshold (S ₁ ), and/or the gradient (dI _Mot ) is below a second threshold (S ₂ ). 5 . The method according to claim 1 , wherein the implementation ( 35 of the request ( 30 ) is delayed in the generator-like operation of the brushless DC motor ( 10 ). 6 . ) until the value (I _Mot ) exceeds a third threshold, and/or the gradient (dI _Mot ) exceeds a fourth threshold. 6. A computer program arranged to carry out 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 of claim 6 is stored. 8. An electronic controller (20) arranged to operate a brushless DC motor by means of the method according to any one of claims 1 to 5.

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