Method, control unit and stepper motor for open / closed loop control of a stepper motor

Abstract

The invention relates to a method for controlling / regulating a stepper motor. The stator winding of the stepper motor is driven by means of a full-bridge circuit having switching elements. The switching elements can be controlled in such a way that a fast decay mode or a slow decay mode can be set. Here, a charge cycle time is stored in one pulse width modulation (PWM) cycle, and the fast decay mode or the slow decay mode of the next PWM cycle is set in dependence on the charge cycle time. The invention also relates to a control unit and to a stepper motor having the full-bridge circuit and the control unit.

Description

Technical Field

[0001] This invention relates to a method for controlling / regulating a stepper motor, wherein the stator windings are driven by a full-bridge circuit with switching elements, wherein the switching elements can be controlled to set a fast decay mode or a slow decay mode. Furthermore, the invention relates to a control unit configured and programmed to perform the method, and a stepper motor having the full-bridge circuit and the control unit. Background Technology

[0002] For example, stepper motors can be used to drive the expansion valve of a heat pump. To drive a stepper motor, a sinusoidal current curve should be applied to the stator windings of the stepper motor.

[0003] One common problem is choosing between different decay modes in the full-bridge circuit used to drive the stator windings of a stepper motor as the target current decreases. While the slow decay mode produces the smallest possible current fluctuation, the current doesn't decrease quickly enough, especially at high gradients and small output amplitudes. The fast decay mode, while causing the current to decay significantly faster, often results in excessive decay. This leads to significantly higher current fluctuations and necessitates recharging the current in the stator windings if necessary. However, current fluctuations around the target current should be minimized to avoid noise and unnecessary losses.

[0004] For example, DE 10 2016 000 847 A1, DE 11 2015 005 791 T5, US 2015 / 0 015 177A1, and US 2010 / 0 157 635 A1 disclose drive circuits and control methods for stepper motors. In the known prior art, a fast and / or slow decay mode is controlled to be employed in a predetermined proportion in the latter half of the descending sine quadrant.

[0005] Furthermore, the mode setting should be achievable with as little prior knowledge as possible, such as information about current amplitude, speed, motor parameters, load, and temperature, as system limitations typically limit the available information and / or intervention possibilities. Intervention possibilities include: setting a current limit for the hardware-based current regulator, under which the charging mode is interrupted; specifying a decay mode for the PWM shutdown cycle; and being able to set the decay mode directly or at the end of the PWM cycle. Available information is the point in the PWM cycle when the current limit is reached and thus the mode switches to the set decay mode.

[0006] Inside the electronic device, current regulation is achieved using a current-limiting circuit, which is programmed to limit the current, i.e., the maximum current. The current itself cannot be detected. However, the timing of the shutdown operation by the current-limiting circuit within the PWM cycle can be determined. Summary of the Invention

[0007] Based on this, the objective of this invention is to provide a further improved technique for controlling / regulating a stepper motor, wherein the stator windings of the stepper motor are driven by a full-bridge circuit with switching elements, and the switching elements can be controlled to enable the setting of a fast decay mode or a slow decay mode.

[0008] This task is solved by an object having the features of an independent claim. The object of a dependent claim is an advantageous implementation.

[0009] A method for controlling / regulating a stepper motor is disclosed. The stator windings of the stepper motor are driven by a full-bridge circuit with switching elements. These switching elements can be controlled to set either a fast decay mode or a slow decay mode. In this method, a charging cycle time is stored within a pulse width modulation (PWM) cycle. This charging cycle time corresponds to the duration of the full-bridge circuit being on (“PWM-An”), allowing current to flow through the stator windings. Then, based on the charging cycle time, i.e., the duration of PWM-An, the fast decay mode or slow decay mode for the next PWM cycle is set. Therefore, it is possible to identify in a simple and robust manner when a fast decay mode is needed for the next PWM cycle, or when a slow decay mode is sufficient.

[0010] The fast or slow decay mode can be set in a software interrupt. This software interrupt is triggered when the current limit is reached during the PWM cycle or when the target current is not reached during the PWM cycle. Therefore, the appropriate decay mode is set for the next PWM cycle.

[0011] Specifically, during the software interruption, a rapid decay mode can be set when the charging cycle time is less than a first threshold. A time below the first threshold means that the current in the stator windings is already within the current-limiting region (or even above that region). By setting the rapid decay mode, a faster current decrease can be achieved, especially in the second quadrant of the sinusoidal oscillation. Therefore, the sinusoidal shape of the current can be formed more accurately.

[0012] Advantageously, the fast decay mode can only be set when the charging cycle time is less than a first threshold a predetermined number of times. The predetermined number of times can be set to, for example, 3 or a greater value. When the time falls below this number, the decay mode of the previous PWM cycle can be maintained. In this way, it is ensured that the fast decay mode is not immediately set when the time first falls below the first threshold.

[0013] Furthermore, in the software interrupt, a slow decay mode can be set when the charging cycle time exceeds a second threshold. Exceeding the second threshold means that rapid decay is no longer needed because the current must be rebuilt. By setting the slow decay mode, it is then ensured that rapid discharge does not occur during the duration of the low PWM level (“PWM-Aus”) in the PWM cycle.

[0014] The second threshold can be greater than the first threshold. Therefore, adjustment hysteresis is achieved, and the system does not continuously switch back and forth between decay modes.

[0015] Preferably, when the charging cycle time exceeds the second threshold, the counter used to detect the predetermined number of times, or the debouncing counter, can be reset. Therefore, the counter is reinitialized, allowing for proper switching to the fast decay mode when the current limit is reached again.

[0016] Furthermore, during the software interrupt, when the charging cycle time is greater than or equal to a first threshold and less than or equal to a second threshold, the decay mode of the previous PWM cycle can be maintained. As previously mentioned, this avoids unnecessary switching between decay modes.

[0017] A control unit is also disclosed, which is configured and programmed to perform the method according to the above aspects. For this purpose, the control unit can receive or determine the charging cycle time and drive the switching elements of the full-bridge circuit according to a set attenuation mode.

[0018] Furthermore, a stepper motor is disclosed, having a stator winding for driving the stepper motor and a full-bridge circuit with switching elements. The switching elements can be controlled to allow setting a fast decay mode or a slow decay mode. The stepper motor has a control unit according to the above aspects.

[0019] The method, the control unit, and the stepper motor can be used to drive the expansion valve of the heat pump. The heat pump is preferably applicable to vehicles. Attached Figure Description

[0020] The present invention will now be described in detail with reference to the accompanying drawings. The drawings show: Figure 1 shows a flowchart for generating PWM drive signals to control / regulate a stepper motor; and Figure 2 shows the flowchart of the software interrupt, in which the decay mode is set for the next PWM cycle. Detailed Implementation

[0021] The present invention will now be described with reference to the accompanying drawings and preferred embodiments. However, the description of these embodiments should not be considered exhaustive.

[0022] This method is used to control or adjust a stepper motor. For this purpose, the stator windings of the stepper motor are driven by a full-bridge circuit with switching elements. These switching elements can be controlled to allow setting a fast decay mode or a slow decay mode. Such devices are known in the prior art.

[0023] Figure 1 shows a flowchart for generating a PWM drive signal to control / regulate a stepper motor. After starting, initialization is performed in slow decay mode in step S1. In the subsequent step S2, a PWM cycle is started, and the charging cycle time is set to zero. In step S3, it is checked whether the current limit, i.e., the maximum current, has been reached.

[0024] If the current limit is not reached in step S3, step S4 is executed, in which the charging cycle time is increased. Therefore, as long as the current limit is not exceeded, the full bridge is in the "PWM-An" state. In this way, the current in the stator windings of the stepper motor is established towards the saturation value.

[0025] In the subsequent step S5, it is checked whether the PWM cycle has ended. If the PWM cycle has not ended, return to step S3, where it is checked whether the current limit has been reached.

[0026] If the PWM cycle ends, proceed to step S100, where the charging cycle time is stored and a software interrupt is triggered. The software interrupt in step S100 will be described in detail below. After step S100, the method returns to step S2 and starts a new PWM cycle.

[0027] If the current limit is reached in step S3, step S100 is executed, in which the charging cycle time is stored and a software interrupt is triggered. As previously mentioned, the software interrupt in S100 will be described in detail below. When the current limit is exceeded, the full-bridge circuit switches to "PWM-Aus", and the current in the stator winding decays according to the set decay mode.

[0028] Then, step S6 is executed, in which the attenuation mode is queried and set in the full-bridge circuit. In step S7, it is checked whether the PWM cycle has ended.

[0029] If the PWM cycle has not ended in step S7, return to step S6. If the PWM cycle has ended in S7, return to step S2 and start a new PWM cycle.

[0030] The software interrupt in S100 will be described below with reference to the flowchart shown in FIG2. As mentioned earlier, the charging cycle time of the current PWM cycle is stored before the software interrupt is triggered. In the triggered software interrupt, the decay mode is now selected based on the charging cycle time and a counter (hereinafter referred to as the debouncing counter). The reason is that a short charging cycle time means that the current cannot be decayed sufficiently, while a long charging cycle time means that the current decays quickly enough.

[0031] In step S101, the charging cycle time is first compared with a first threshold. If the charging cycle time is lower than the first threshold, the de-jitter counter is incremented by one in step S102. In step S103, the de-jitter counter is compared with a predetermined number of times. If the de-jitter counter exceeds the predetermined number of times, a software interrupt is initiated, proceeding to step S104, and the attenuation mode is set to fast attenuation mode. The software interrupt then ends, and the process returns to the flowchart in Figure 1.

[0032] If the de-jitter counter is less than a predetermined number of times in step S103, the current attenuation mode is maintained according to step S106. Then the software interrupt ends and returns to the flowchart in Figure 1.

[0033] If, in step S101, it is determined that the charging cycle time is greater than or equal to the first threshold, then in step S105, it is checked whether the charging cycle time is greater than the second threshold. If the charging cycle time is less than or equal to the second threshold, the software interrupt proceeds to step S106, and the current attenuation mode is maintained. The software interrupt then ends, and the process returns to the flowchart in Figure 1.

[0034] If the charging cycle time exceeds the second threshold in step S105, a software interrupt is initiated, proceeding to step S107, where a slow decay mode is set. Furthermore, the debouncing counter is reset in step S107. After step S107 is completed, the software interrupt ends, and the process returns to the method shown in Figure 1.

[0035] The above method allows for the appropriate setting of the attenuation mode, thereby maintaining a sinusoidal shape, especially in the second (and fourth) sinusoidal quadrants.

Claims

1. A method for controlling / regulating a stepper motor, wherein the stator winding is driven by a full-bridge circuit with switching elements, wherein, The switching element can be controlled to allow for the setting of a fast decay mode or a slow decay mode. Its features are, One charging cycle time is stored in one pulse width modulation (PWM) cycle, and The fast decay mode or the slow decay mode of the next PWM cycle is set according to the charging cycle time.

2. The method according to claim 1, characterized in that, The fast decay mode or the slow decay mode is set in a software interrupt, which is triggered when the current limit is reached during the PWM cycle or when the target current is not reached during the PWM cycle.

3. The method according to claim 2, characterized in that, In the software interrupt, when the charging cycle time is less than a first threshold, the rapid decay mode is set.

4. The method according to claim 3, characterized in that, The fast decay mode is set only when the charging cycle time is less than the first threshold a predetermined number of times; otherwise, the decay mode of the previous PWM cycle is maintained.

5. The method according to any one of claims 2 to 4, characterized in that, In the software interrupt, when the charging cycle time is greater than the second threshold, the slow decay mode is set.

6. The method according to claim 3 or 4 and claim 5, characterized in that, The second threshold is greater than the first threshold.

7. The method according to claim 6, characterized in that, When the charging cycle time is greater than the second threshold, the counter used to detect the predetermined number of times is reset.

8. The method according to claim 6 or 7, characterized in that, In the software interrupt, when the charging cycle time is greater than or equal to the first threshold and less than or equal to the second threshold, the decay mode of the previous PWM cycle is maintained.

9. A control unit configured and programmed to perform the method of any one of claims 1 to 8.

10. A stepper motor having a full-bridge circuit, the full-bridge circuit driving the stator windings of the stepper motor and having switching elements, wherein, The switching element can be controlled to enable the setting of a fast decay mode or a slow decay mode, characterized in that it has a control unit according to claim 9.

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