TW202433845A - Motor soft phase switching method and control circuit thereof - Google Patents

Abstract

A motor is controlled by a PWM signal, and there are two phases according to the direction of the motor current. According to the soft phase switching method of this invention, each phase period includes (1) a soft on period wherein the duty of the PWM signal increases by plural pulses from 0 to a target value; (2) a target conduction period wherein the duty of the PWM signal is maintained at the target value; (3) a soft off period wherein the duty of the PWM signal decreases by plural pulses from the target value to 0; and (4) a fully off period wherein the duty of the PWM signal is maintained at 0. In addition, the method determines how to adjust the time length of the target conduction period by judging whether a hall signal toggles at a time point at which the motor current is zero, and judging whether the soft off period is completed.

Description

Motor phase-commutation soft switching method and control circuit thereof

The present invention relates to a motor phase-changing soft switching method and a control circuit thereof, which can achieve motor phase-changing soft switching in a relatively simple manner, reduce the interference of back electromotive force on motor operation, and do not need to actually detect the back electromotive force.

Please refer to Figures 1A and 1B. Figure 1A shows the motor M and the H-bridge driver circuit that controls the motor M. The H-bridge driver circuit works between the positive and negative power supplies VDD and VSS and includes four switches PA, NA, PB, and NB. Figure 1B shows the equivalent circuit of the motor M, including the resistor R, the inductor L, and the back electromotive force e. The way the H-bridge driver circuit drives the motor M is that the H-bridge driver circuit changes the direction of the current corresponding to the rotor pole of the motor M, which is called "commutation". As shown in the figure, in one phase, switches PA and NB are turned on, switches NA and PB are turned off, and the current path is shown as a solid line; while in the other phase, switches NA and PB are turned on, switches PA and NB are turned off, and the current path is shown as a dotted line.

Please refer to Figure 2. Back EMF will cause resistance. Therefore, in order to achieve better commutation and minimize power consumption, the ideal commutation time is when the back EMF is zero and the current is zero. In order to achieve ideal commutation, the previous technology, such as Taiwan Patent Application No. 107116276, uses the method of detecting the change of back EMF in order to know the best time for commutation. However, the detection of back EMF is more complicated, and back EMF is a signal with a lot of noise. Therefore, controlling the commutation time based on back EMF will make the circuit more complicated and the accuracy is difficult to be ideal.

The present invention is aimed at the above-mentioned problem and proposes a solution to know the best time point for motor switching without detecting back electromotive force. In addition, a soft switching method is proposed.

In one aspect, the present invention provides a motor commutation soft switching method, wherein the motor is controlled by a PWM signal and has two phases according to the direction of the motor current. The method comprises: in each phase control cycle, the motor is controlled according to the following steps: in a soft start phase, the duty ratio of the PWM signal is increased from 0 to a target value by a plurality of PWM pulses; then in a target value conduction phase, the duty ratio of the PWM signal is maintained at the target value; then in a soft shut-down phase, the duty ratio of the PWM signal is maintained at the target value. In the on-stage, a plurality of PWM pulses are used to reduce the duty ratio of the PWM signal from the target value to 0; and then the complete stop stage is entered to maintain the duty ratio of the PWM signal at 0; and the following judgments are made to determine how to adjust the length of the target value conduction stage: judging whether the time point at which a Hall sensing signal changes level overlaps with the time point at which the motor current is zero, wherein the Hall sensing signal is obtained by sensing the operation of the motor with a Hall sensor; and judging whether the soft closing stage is completed.

In one preferred implementation, when the time point of the Hall sensing signal changing level does not overlap with the time point of the motor current being zero and the soft closing phase is not completed, the target value conduction phase time is shortened; when the time point of the Hall sensing signal changing level overlaps with the time point of the motor current being zero and the soft closing phase is completed, the target value conduction phase time is extended.

In one preferred embodiment, the duration of the complete stop phase is variable.

In one preferred embodiment, in the soft start phase, the duty ratio of the PWM signal increases linearly or nonlinearly, and in the soft shut-off phase, the duty ratio of the PWM signal decreases linearly or nonlinearly.

In one preferred embodiment, the step of determining how to adjust the length of the target value conduction phase further includes: referring to the number of magnetic poles of the rotor of the motor.

From another perspective, the present invention provides a control circuit for executing a motor phase-commutation soft switching method, for generating a PWM signal to drive a motor, wherein the motor has two phases according to the direction of the motor current, and the rotation of the motor is sensed by a Hall sensor to generate a Hall sensing signal, the control circuit comprises: a pulse generating circuit, for generating the PWM signal to drive the motor; a judgment circuit, for providing an indicator to the processor, a processor, according to a speed control command transmitted from the outside to control the pulse generating circuit to generate the PWM signal, and adjust the control of the pulse generating circuit according to the indicator; and wherein, in the control cycle of each phase, The method comprises the following stages: in a soft start stage, the duty ratio of the PWM signal is increased from 0 to a target value by using a plurality of PWM pulses; then in a target value conduction stage, the duty ratio of the PWM signal is maintained at the target value; then in a soft shut-down stage, the duty ratio of the PWM signal is decreased from the target value to 0 by using a plurality of PWM pulses; and then entering a complete stop stage, maintaining the duty ratio of the PWM signal at 0; and wherein the judgment circuit judges whether the time point of the Hall sensing signal switching level overlaps with the time point of the motor current being zero, and judges whether the soft shut-down stage is completed, so as to provide an indicator corresponding to the judgment result to the processor.

The following detailed description is based on specific embodiments to make it easier to understand the purpose, technical content, features and effects of the present invention.

The drawings in the present invention are schematic diagrams, which are mainly intended to show the relationship between various circuit components or signal waveforms, and the shapes and sizes are not drawn according to scale.

Please refer to Figure 3, which illustrates that the motor commutation soft switching method of the present invention is based on the output of the Hall sensor, rather than on the detection of the back electromotive force. Since the back electromotive force corresponds to the change of the motor rotor magnetic pole, that is, the peak and valley of the magnetic flux, the output of the Hall sensor (i.e., the Hall sensing signal) can be used to obtain relevant information about the time point of the back electromotive force change. However, since the Hall sensor generates an output with a time delay (as shown by Td in the figure), the commutation time point obtained from the Hall sensor output will lag slightly behind the time point when the actual back electromotive force is zero, but this lag value is fixed, and from the perspective of the motor speed control requirement, this lag value is negligible. In contrast, in the prior art that determines the switching time based on back EMF detection, the noise brought by the back EMF has various sources and is not necessarily a fixed value or inertial. Therefore, it is difficult to accurately maintain it within a fixed tolerance range.

Please refer to FIG. 4, which shows an embodiment of the control circuit for executing the motor phase-changing soft switching method of the present invention. As shown in the figure, the motor module 20 includes a control circuit 21, a drive circuit 23, a motor M, and a Hall sensor 25; the control circuit 21 includes a processor 211, a judgment circuit 212, and a pulse generating circuit 213. When a speed control command is transmitted from the outside, the processor 211 controls the pulse generating circuit 213 to generate a PWM signal according to the speed control command, and controls the motor M through the drive circuit 23 to rotate at the speed indicated by the speed control command. The drive circuit 23 can be, for example but not limited to, an H-bridge drive circuit. The rotation of the motor M is sensed by the Hall sensor 25 and fed back to the control circuit 21 for feedback control. In the present invention, the judgment circuit 212 generates an on-time adjustment index according to the relevant signal to adjust the on-time length of the PWM signal generated by the pulse generating circuit 213, thereby controlling the optimal time point of the switching. The details of the judgment circuit 212 will be described in detail later.

Please refer to Figures 5 and 6 for further explanation of the motor phase-changing soft switching method embodiment of the present invention. According to the present invention, in each phase control cycle, there are four stages T1~T4, which have the following meanings: T1: soft start stage T2: target value conduction stage T3: soft shutdown stage T4: complete stop stage

For example, assuming that the PWM (pulse width modulation) duty ratio target value of the switch (any switch on the current path is acceptable, in this embodiment, switch PA is used as an example, see Figure 1A or 1B) is 50% according to the speed requirement, then in the soft start phase T1, the PWM duty ratio increases from 0 to 50% with a plurality of PWM pulses, for example, it can increase linearly or nonlinearly. Correspondingly, the motor current also rises slowly to the corresponding current target value, corresponding to the speed indicated by the speed control command. Then enter the target value conduction phase T2, in which the switch operates according to the duty ratio target value (50% in this embodiment), and the motor current is also maintained at the corresponding current target value. Then, the soft-off phase T3 is entered. In this phase, the PWM duty ratio decreases from 50% to 0 with a plurality of PWM pulses, for example, it can decrease linearly or nonlinearly, wherein the time length of the soft-start phase T1 and the soft-off phase T3, or the number of PWM pulses used, can be the same or different (the same in this embodiment). Then, the full stop phase T4 is entered. In this phase, the PWM duty ratio is 0. In the above phases, the length of the target value conduction phase T2 is variable to adjust the switching time point to be exactly or as close as possible to the time point when zero current occurs. Furthermore, in another embodiment, in addition to the length of the target value conduction phase T2 being variable, the length of the complete stop phase T4 is also variable.

Please refer to FIG. 7, which shows an embodiment of the judgment circuit of the present invention. In this embodiment, the judgment circuit 212 generates the on-time adjustment indicator through logical operation according to the zero current indicator and the soft closing indicator; in addition, if the same circuit may be applied to different types of motor rotors, the judgment circuit 212 can also receive information about the number of magnetic poles and make judgments based on this number.

In detail, the zero current indicator indicates whether the time point of the Hall sensing signal switching level overlaps with the time point of zero current; the information of zero current can be obtained from the sensing current, and the method of sensing current is common knowledge in the analog circuit industry, so it will not be elaborated here. The soft closing indicator indicates whether the aforementioned soft closing stage T3 is completed. When the time point of the Hall sensing signal level change does not overlap with the time point of zero current, and the soft closing phase T3 is not completed, it means that the time of the target value conduction phase T2 should be shortened to give enough time for the soft closing phase T3 and make the time point of the Hall sensing signal level change overlap with the time point of zero current. Therefore, the conduction time adjustment indicator indicates that the time of the target value conduction phase T2 should be shortened. When the time point of the Hall sensing signal switching level overlaps with the time point of zero current and the soft closing phase T3 has been completed, it means that the soft closing phase T3 can be delayed, that is, it means that the time of the target value conduction phase T2 should be extended so that the time point of the Hall sensing signal switching level overlaps with the time point of zero current. Therefore, the on-time adjustment indicator indicates that the time of the target value conduction phase T2 should be extended.

According to the above operation, the control circuit 21 can be adjusted to the best possible switching time point in an adaptive manner, and reduce the negative effect of back electromotive force on the operation through soft start and soft shutdown.

The present invention has been described above with respect to the preferred embodiments. However, the above description is only for those familiar with the art to easily understand the content of the present invention, and is not used to limit the maximum scope of the present invention. Under the same spirit of the present invention, those familiar with the art can think of various equivalent changes. For example, the present invention can be applied not only to single-phase four-pole motors, but also to other types of motors; or, more than two circuits shown in the figure can be combined to form a single circuit; or, a circuit shown in the figure can be disassembled to form more than two circuits; in addition, in the circuit of the embodiment shown, other circuits can be added to provide other functions, such as but not limited to early or delayed conduction of the motor rotor control switch (not shown), etc. The scope of the present invention should cover the above and all other equivalent changes.

20: Motor module 21: Control circuit 211: Processor 212: Judgment circuit 213: Pulse generation circuit 23: Drive circuit 25: Hall sensor M: Motor NA, NB: Switch PA, PB: Switch T1: Soft start phase T2: Target value conduction phase T3: Soft shutdown phase T4: Complete stop phase Td: Time delay VDD: Positive power supply VSS: Negative power supply

FIG. 1A shows a motor M and an H-bridge drive circuit for controlling the motor M. FIG. 1B shows an equivalent circuit of the motor M. FIG. 2 shows that the optimal switching time corresponds to the time point when the back electromotive force is zero. FIG. 3 illustrates that the motor switching soft switching method of the present invention is based on the output of the Hall sensor rather than on the detection of the back electromotive force. FIG. 4 shows an embodiment of the control circuit for executing the motor switching soft switching method of the present invention. FIG. 5-6 further illustrate an embodiment of the motor switching soft switching method of the present invention. FIG. 7 shows an embodiment of the judgment circuit of the present invention.

Motor module

21: Control circuit

211: Processor

212: Judgment circuit

213: Pulse generating circuit

23: Driving circuit

25: Hall sensor

M: Motor

Claims (10)

A motor commutation soft switching method, wherein the motor is controlled by a PWM signal and has two phases according to the direction of the motor current, the method comprising: In each phase control cycle, the motor is controlled according to the following steps: In the soft start phase, the duty ratio of the PWM signal is increased from 0 to a target value with a plurality of PWM pulses; Then in the target value on phase, the duty ratio of the PWM signal is maintained at the target value; Then in the soft off phase, the duty ratio of the PWM signal is decreased from the target value to 0 with a plurality of PWM pulses; and Then entering the full stop phase, maintaining the duty ratio of the PWM signal at 0; and Making the following judgment to determine how to adjust the length of the target value on phase: Determine whether the time point at which a Hall sensing signal changes level overlaps with the time point at which the motor current is zero, wherein the Hall sensing signal is obtained by sensing the operation of the motor with a Hall sensor; and Determine whether the soft closing stage is completed. A motor phase-changing soft switching method as described in claim 1, wherein when the time point of the Hall sensing signal changing level does not overlap with the time point of the motor current being zero and the soft closing phase is not completed, the target value on-phase time is shortened; when the time point of the Hall sensing signal changing level overlaps with the time point of the motor current being zero and the soft closing phase is completed, the target value on-phase time is extended. A motor commutation soft switching method as described in claim 1, wherein the duration of the complete stop phase is variable. A motor commutation soft switching method as described in claim 1, wherein in the soft start phase, the duty ratio of the PWM signal increases linearly or nonlinearly, and in the soft shutdown phase, the duty ratio of the PWM signal decreases linearly or nonlinearly. The motor commutation soft switching method as described in claim 1, wherein the step of determining how to adjust the length of the target value conduction phase further includes: referring to the number of magnetic poles of the rotor of the motor. A control circuit for executing a motor phase-changing soft switching method is used to generate a PWM signal to drive a motor, wherein the motor has two phases according to the direction of the motor current, and the rotation of the motor is sensed by a Hall sensor to generate a Hall sensing signal, the control circuit comprises: A pulse generating circuit, used to generate the PWM signal to drive the motor; A judgment circuit, used to provide an indicator to the processor, A processor, according to a speed control command transmitted from the outside to control the pulse generating circuit to generate the PWM signal, and adjust the control of the pulse generating circuit according to the indicator; and In each phase control cycle, the following stages are included: In the soft start phase, the duty ratio of the PWM signal is increased from 0 to a target value by using a plurality of PWM pulses; Then, in the target value conduction phase, the duty ratio of the PWM signal is maintained at the target value; Then, in the soft shutdown phase, the duty ratio of the PWM signal is decreased from the target value to 0 by using a plurality of PWM pulses; and Then, the full stop phase is entered, and the duty ratio of the PWM signal is maintained at 0; And wherein, the judgment circuit judges whether the time point of the Hall sensing signal switching level overlaps with the time point of the motor current being zero, and judges whether the soft shutdown phase is completed, so as to provide an indicator corresponding to the judgment result to the processor. A control circuit for executing a motor phase-changing soft switching method as described in claim 6, wherein, when the time point of the Hall sensing signal changing level does not overlap with the time point of the motor current being zero and the soft closing phase is not completed, the indicator indicates that the target value on-phase time should be shortened; when the time point of the Hall sensing signal changing level overlaps with the time point of the motor current being zero and the soft closing phase is completed, the indicator indicates that the target value on-phase time should be extended. A control circuit for executing a motor commutation soft switching method as described in claim 6, wherein the duration of the complete stop phase is variable. A control circuit for executing a motor commutation soft switching method as described in claim 6, wherein in a soft start phase, the duty ratio of the PWM signal increases linearly or nonlinearly, and in a soft shutdown phase, the duty ratio of the PWM signal decreases linearly or nonlinearly. A control circuit for executing a motor phase-changing soft switching method as described in claim 6, wherein the judgment circuit further judges and generates the indicator based on the number of magnetic poles of the motor's rotor.

Images