Brushless DC motor system, logic control circuit and initial steering judgment method thereof

Abstract

This application discloses a brushless DC motor system, its logic control circuit, and initial direction determination method. The brushless DC motor system includes a power stage, a Hall effect sensor, and a logic control circuit. The logic control circuit includes a comparison circuit, a phase detector, and a logic unit. The logic unit selects forward or reverse start logic based on initial direction information to control the operation of the power stage. This brushless DC motor system, its logic control circuit, and initial direction determination method improve motor starting performance, simplify circuit wiring, and reduce costs.

Description

Technical Field

[0001] The present invention relates to an electronic circuit, and more particularly to a brushless DC motor system, a logic control circuit thereof, and an initial steering determination method. Background Art

[0002] Because they eliminate the need for brushes and commutators, brushless DC motors offer advantages such as low noise, high efficiency, long life, and high reliability. They are widely used in industrial fans, household appliances, pumps, and other fields. During the motor's power-up or startup phase, the rotor typically maintains a certain rotational speed due to environmental interference. To ensure a safe startup, it is necessary to detect the rotor's rotation direction.

[0003] The existing technology uses two Hall sensors to detect the original rotation direction of the rotor. Figure 1 Figure 1 shows the structure of a conventional brushless DC motor system 100. This system uses a first Hall effect sensor H1 and a second Hall effect sensor H2, positioned with a phase difference, to sense the initial rotational direction of the rotor 110 during initial startup. The information sensed by the first and second Hall effect sensors H1 and H2 is transmitted to a logic control circuit 120, which analyzes the phase to determine the initial rotational direction of the rotor. Accordingly, the logic control circuit 120 selects a startup logic (e.g., forward or reverse) to control the operation of the full-bridge circuit in the power stage 130.

[0004] However, two Hall sensors bring complex wiring to the layout and also increase the cost. Summary of the Invention

[0005] Therefore, the purpose of the present invention is to solve the above technical problems in the prior art and to provide an improved brushless DC motor system.

[0006] According to an embodiment of the present invention, a brushless DC motor system is proposed, comprising: a power stage for receiving an input voltage, the power stage having a power switch that is periodically turned on and off to convert the input voltage into energy required by the motor, the motor comprising a rotor and a stator; a Hall sensor for sensing changes in the magnetic field caused by the rotation of the rotor and generating an induction signal; a logic control circuit comprising: a comparison circuit for comparing the magnitude of a feedback voltage representing the reverse electromotive force at both ends of the stator and a reference voltage to generate a comparison signal; a phase detector for detecting the degree of overlap of the in-phase level or complementary level of the induction signal and the comparison signal to generate an initial steering signal; and a logic unit for selecting a forward start logic or a reverse start logic according to the initial steering signal to control the operation of the power stage.

[0007] According to an embodiment of the present invention, a method for determining the initial direction of a brushless DC motor is also proposed. The motor includes a stator and a rotor. The method includes: sensing the magnetic field changes caused by the rotation of the rotor through a Hall sensor to generate an induction signal; comparing the feedback voltage representing the reverse electromotive force at both ends of the stator with the reference voltage to generate a comparison signal; detecting the overlap of the in-phase levels or the complementary levels of the induction signal and the comparison signal to generate an initial direction signal; and selecting the forward start logic or the reverse start logic according to the initial direction signal.

[0008] According to an embodiment of the present invention, a logic control circuit for a brushless DC motor system is also proposed. The brushless DC motor system has a power stage that converts an input voltage into an output voltage, and a Hall sensor that senses changes in a magnetic field to generate an induction signal. The logic control circuit includes: a comparison circuit that compares the feedback voltage representing the reverse electromotive force at both ends of the stator and the reference voltage to generate a comparison signal; a phase detector that detects the overlap of the in-phase level or complementary level of the induction signal and the comparison signal to generate an initial steering signal; and a logic unit that selects forward start logic or reverse start logic according to the initial steering signal to control the operation of the power stage.

[0009] The brushless DC motor system and initial direction determination method according to various aspects of the present invention improve motor starting performance, simplify circuit wiring, and reduce costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 100 is a schematic diagram of a circuit structure of an existing brushless DC motor system;

[0011] Figure 2 A circuit structure diagram 200 of a brushless DC motor system 200 according to an embodiment of the present invention is shown;

[0012] Figure 3 The embodiment of the present invention is shown Figure 2 A schematic diagram of the circuit structure of the phase detector 42 is shown;

[0013] Figure 4 The embodiment of the present invention is shown Figure 2 A schematic diagram of the circuit structure of the phase detector 42-1 is shown;

[0014] Figure 5 Schematic diagram showing the induction signal V when the motor initially rotates in the forward direction according to an embodiment of the present invention H , feedback voltage V FB and a timing diagram of the comparison signal CMP;

[0015] Figure 6 Schematic diagram showing the induction signal V when the motor initially rotates in reverse according to an embodiment of the present inventionH , feedback voltage V FB and a timing diagram of the comparison signal CMP;

[0016] Figure 7 The embodiment of the present invention is shown Figure 2 Schematic diagram of the circuit structure of the phase detector 42-2 shown;

[0017] Figure 8 The schematic diagram shows that when the motor initially rotates forward according to an embodiment of the present invention, due to interference, the induction signal V H , feedback voltage V FB and a timing diagram of the comparison signal CMP;

[0018] Figure 9 The embodiment of the present invention is shown Figure 2 Schematic diagram of the circuit structure of the phase detector 42-3 shown;

[0019] Figure 10 The embodiment of the present invention is shown Figure 2 A schematic diagram of the circuit structure of the phase detector 42-4 is shown;

[0020] Figure 11 The embodiment of the present invention is shown Figure 2 A schematic diagram of the circuit structure of the phase detector 42-5 is shown;

[0021] Figure 12 A flowchart 1200 schematically illustrates a method for determining an initial direction of rotation of a brushless DC motor according to an embodiment of the present invention. DETAILED DESCRIPTION

[0022] Specific embodiments of the present invention will be described in detail below. It should be noted that the embodiments described herein are for illustrative purposes only and are not intended to limit the present invention. In the following description, numerous specific details are set forth to provide a thorough understanding of the present invention. However, it will be apparent to one of ordinary skill in the art that these specific details are not necessarily required to practice the present invention. In other instances, well-known circuits, materials, or methods are not described in detail to avoid obscuring the present invention.

[0023] Throughout this specification, references to "one embodiment," "an embodiment," "an example," or "an example" mean that a particular feature, structure, or characteristic described in connection with that embodiment or example is included in at least one embodiment of the present invention. Therefore, the phrases "in one embodiment," "in an embodiment," "an example," or "an example" that appear in various places throughout this specification do not necessarily refer to the same embodiment or example. Furthermore, particular features, structures, or characteristics may be combined in one or more embodiments or examples in any suitable combinations and / or subcombinations. Furthermore, those skilled in the art will appreciate that the figures provided herein are for illustrative purposes only and are not necessarily drawn to scale. It should be understood that when an element is referred to as being "coupled to" or "connected to" another element, it can be directly coupled or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being "directly coupled to" or "directly connected to" another element, there are no intervening elements. Identical reference numerals indicate identical elements. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0024] Figure 2 FIG. 2 is a schematic diagram of a circuit structure of a brushless DC motor system 200 according to an embodiment of the present invention. Figure 2 In the illustrated embodiment, the brushless DC motor system 200 includes: a power stage 201, which receives an input voltage Vin. The power stage 201 has a power switch that is periodically turned on and off to convert the input voltage Vin into energy required by a motor 202. The motor 202 includes a rotor 21 and a stator 22; a Hall sensor 203, which senses the magnetic field changes caused by the rotation of the rotor 21 and generates an induction signal V H Logic control circuit 204, comprising: a comparison circuit 41, comparing the feedback voltage V representing the reverse electromotive force BEMF at both ends of the stator 22 FB and reference voltage V R The size of the comparison signal CMP is generated; the phase detector 42 detects the sensing signal V H The initial steering signal PJ is generated based on the overlap of the in-phase level or the complementary level of the comparison signal CMP; the logic unit 43 selects the forward start logic or the reverse start logic according to the initial steering signal PJ to control the operation of the power stage 201.

[0025] In one embodiment of the present invention, the sensing signal V H The overlap of the in-phase level or complementary level of the comparison signal CMP represents the sensed signal V H The phase of the comparison signal CMP is the same as the phase of the sensing signal V HThe comparison signal CMP is high or low at the same time, that is, the two are in phase. The so-called phase in phase means that in one electrical cycle, the induced signal V H The ratio of the in-phase duration of the comparison signal CMP to half an electrical cycle. If the sensing signal V H and the comparison signal CMP are completely in phase, the phase degree is 100%; if the sensing signal V H and the comparison signal CMP are in antiphase, the in-phase degree is 0%; if the sensing signal V H If the comparison signal CMP is interleaved, the phase degree is between 0% and 100%. In one embodiment of the present invention, the electrical cycle represents the sensing signal V generated by the Hall sensor. H The cycle of the induction signal V H The time it takes to change a week.

[0026] In one embodiment of the present invention, when the sensing signal V H When the phase in phase with the comparison signal CMP is large, it means that the initial direction of the motor is forward rotation; when the induction signal V H The phase in phase with the comparison signal CMP is small, indicating that the initial direction of the motor is reverse.

[0027] In one embodiment of the present invention, the initial rotation direction refers to the natural rotation of the rotor caused by environmental factors (such as natural wind or the rotation of a nearby fan) when the motor has not yet started.

[0028] In one embodiment of the present invention, the power stage 201 includes a full-bridge circuit. Specifically, the power stage includes: a first switch S1 and a second switch S2 coupled in series between the input voltage Vin and the reference ground, and a third switch S3 and a fourth switch S4 coupled in series between the input voltage Vin and the reference ground, wherein the motor 202 is coupled between a common coupling node SW1 of the first switch S1 and the second switch S2 and a common coupling node SW2 of the third switch S3 and the fourth switch S4. During normal system operation, when the Hall sensing signal V H When the magnetic field is positive, the first switch S1 and the second switch S2 are turned on in turn, and the fourth switch S4 remains on. H When the magnetic field is negative, the third switch S3 and the fourth switch S4 are turned on in turn, and the second switch S2 remains turned on to generate an output voltage between the nodes SW1 and SW2.

[0029] Figure 3 An embodiment of the present invention is shown Figure 2 FIG. 4 is a schematic diagram of the circuit structure of the phase detector 42. Figure 3 In the embodiment shown, the phase detector 42 includes: a first timer 21, which detects the sensing signal V HThe high level duration in one electrical cycle is counted to generate a first timing signal T1; the second timer 22 generates a first timing signal T2 when the sensing signal V H The high level duration of the comparison signal CMP is timed within the high level duration of the comparison signal CMP to generate a second timing signal T2; the comparison unit 23 compares the first timing signal T1 with the second timing signal T2 to generate the initial turn signal PJ. In another embodiment of the present invention, the first timer 21 can also be used to detect the sensing signal V H The low level duration in one electrical cycle is counted to generate a first timing signal T1; the second timer 22 generates a first timing signal T2 when the sensing signal V H The low level duration of the comparison signal CMP is timed within the low level duration of the comparison signal CMP to generate a second timing signal T2.

[0030] In one embodiment of the present invention, when the motor initially rotates in the forward direction, the sensing signal V H Theoretically, if the installation of the Hall sensor 203 corresponds to the back electromotive force BEMF, the sensing signal V H The duration of the high and low levels in one electrical cycle (i.e., the first timing signal T1) is equal to the duration of the high and low levels of CMP (i.e., the second timing signal T2), i.e., T1 = T2. When the motor initially turns in reverse, the induction signal V H Complementary to the comparison signal CMP, T2=0, at this time T2<T1.

[0031] In practical applications, the installation of the Hall sensor 203 is usually staggered with the motor by a certain angle, such as 15 degrees. Therefore, if the initial direction of the motor is forward, the sensing signal V H The direction is the same as the comparison signal CMP, and they are staggered by a certain phase; if the motor is initially reversed, the induction signal V H The comparison signal CMP is in the same direction within the staggered angular phase and in opposite directions at other times. At this time, the first timing signal T1 is usually multiplied by a proportional coefficient k and then compared with the second timing signal T2, such as Figure 4 Phase detector 42-1 is shown.

[0032] Figure 4 The phase detector 42-1 is shown with Figure 3 The phase detector 42 is similar to the Figure 3 The phase detector 42 shown differs in that Figure 4 In the illustrated embodiment, the phase detector 42 - 1 further includes a multiplier 24 that multiplies the first timing signal T1 by a proportional coefficient k and then compares the multiplied signal with the second timing signal T2 at the comparison unit 23 .

[0033] When T2 is greater than the product of T1 and k (i.e. T2>T1*k), it means the motor initially rotates in the forward direction (e.g. Figure 5 On the contrary, when T2 is less than the product of T1 and k (ie, T2 < T1*k), it indicates that the initial direction of the motor is reverse (eg Figure 6 Accordingly, the comparison unit 23 generates a corresponding initial steering signal PJ, which causes the logic unit 43 to select the forward start logic or the reverse start logic, thereby controlling the power stage 201 to operate better.

[0034] Those skilled in the art can select a suitable k value in practical applications. In one embodiment of the present invention, k=0.75.

[0035] The foregoing Figure 3 and Figure 4 The embodiment shown in the figure shows that the sensing signal V H The duration of the level (such as high level or low level) in an electrical cycle is counted, and then the sensing signal V H However, those skilled in the art will appreciate that it is also possible to first time the level duration of the comparison signal CMP and then time the induction signal V H The same phase level duration is counted as follows Figure 7 shown.

[0036] Figure 7 Another embodiment of the present invention is shown Figure 2 The circuit structure diagram of the phase detector 42-2 is shown in FIG. Figure 7 In the embodiment shown, the phase detector 42-2 includes: a first timer 21, a second timer 22 and a comparator 23, wherein the first timer 21 counts the level (such as high level or low level) of the comparison signal CMP within one electrical cycle to obtain a first timing signal T1; the second timer 22 counts the level of the sensing signal V within the duration of the level of the comparison signal CMP H The duration of the in-phase level of the CMOS is used to time the signal and generate a second timing signal T2. Figure 7 The phase detector 42 - 2 may further include a multiplier 24 , which multiplies the first timing signal T1 by a proportional coefficient k and then compares the multiplied first timing signal T1 with the second timing signal T2 at a comparison unit 23 .

[0037] That is, the phase detector includes: a first timer 21, which detects the induction signal V in one electrical cycle. H The second timer 22 counts the sensing signal V within the timing time of the first timer 21. HThe comparison unit 23 compares the first timing signal T1 (or the product of the first timing signal T1 and the proportional coefficient k) with the second timing signal T2 to generate an initial steering signal PJ.

[0038] In practical applications, since the initial speed of the motor is low, the back electromotive force BEMF generated at both ends of the stator 22 is small. H When it becomes high, the feedback voltage V FB Bringing interference / noise, causing the comparison signal CMP to be H Some short pulses appear at the edge transition of Figure 8 shown.

[0039] Therefore, in order to improve the accuracy of detection, the second timing signal T2 can be compared with the first timing signal T1 (or the product of the first timing signal T1 and the proportional coefficient k) for multiple times. For example, the second timing signal T2 can be compared with the first timing signal T1 (or the product of the first timing signal T1 and the proportional coefficient k) in n electrical cycles (such as 2, 3 or more electrical cycles). Within the n electrical cycles, when the number of times the second timing signal T2 is greater than the first timing signal T1 (or the product of the first timing signal T1 and the proportional coefficient k) reaches a set value, it indicates that the initial direction of the motor is forward rotation; when the number of times the second timing signal T2 is greater than the first timing signal T1 (or the product of the first timing signal T1 and the proportional coefficient k) is less than the set value, it indicates that the initial direction of the motor is reverse rotation. Figure 9 Phase detector 42-3 is shown.

[0040] Figure 9 The phase detector 42-3 is shown with Figure 4 The phase detector 42-1 is similar to the Figure 4 The difference between the phase detector 42-1 shown is that Figure 9 In the illustrated embodiment, the phase detector 42-3 further includes: a counting circuit 25, which performs counting in response to a comparison result of the second timing signal T2 and the first timing signal T1 (or the product of the first timing signal and the proportional coefficient k); when the count reaches a set value, the initial steering signal PJ is generated.

[0041] The foregoing Figure 3 、 Figure 4 、 Figure 7 、 Figure 9 The phase detector of the embodiment shown compares the sensed signal V H The in-phase level overlap of the comparison signal CMP in one electrical cycle is used to realize the in-phase detection. However, those skilled in the art will appreciate that the induction signal VH The overlap of the complementary level (inverse level) of the comparison signal CMP in one electrical cycle is used to realize the phase detection. Figure 10 Phase detector 42-4 is shown.

[0042] Figure 10 According to another embodiment of the present invention, Figure 2 The circuit structure diagram of the phase detector 42-4 is shown in FIG. Figure 10 In the embodiment shown, the phase detector 42-4 includes: a first timer 21, which detects the sensing signal V in one electrical cycle. H The high level duration or low level duration of one of the comparison signals CMP is counted to generate a first timing signal T1; the second timer 22 counts the sensing signal V within the timing time of the first timer 21. H The first timing signal T1 and the second timing signal T2 are timed to measure the duration of the inverted level (i.e., complementary level) of the other one of the comparison signals CMP to generate a second timing signal T2; the subtraction unit 26 performs a subtraction operation on the first timing signal T1 and the second timing signal T2 to obtain an in-phase duration signal T1-T2; the comparison unit 23 compares the first timing signal T1 with the in-phase duration signal T1-T2 to generate the initial steering signal PJ.

[0043] exist Figure 10 In the illustrated embodiment, the phase detector 42 - 4 may further include a multiplier 24 , which multiplies the first timing signal T1 by the proportional coefficient k and compares the multiplication result with the in-phase duration signal T1 - T2 at the comparison unit 23 to obtain the initial steering signal PJ.

[0044] Figure 10 The embodiment shown compares the in-phase duration signal T1-T2 with the first timing signal T1 (or the product of the first timing signal T1 and the proportional coefficient k) to obtain the initial turn signal. However, those skilled in the art will appreciate that in order to improve the accuracy of detection, the in-phase duration signal T1-T2 and the first timing signal T1 (or the product of the first timing signal T1 and the proportional coefficient k) may be compared multiple times, such as Figure 11 Phase detector 42-5 is shown.

[0045] Figure 11 The phase detector 42-5 is shown with Figure 10 The phase detector 42-4 is similar to Figure 10 The phase detector 42-4 shown is different in that Figure 11In the illustrated embodiment, the phase detector 42-4 further includes: a counting circuit 25, which performs counting in response to a comparison result of the in-phase duration signal T1-T2 and the first timing signal T1 (or the product of the first timing signal and the proportional coefficient k); when the count reaches a set value, the initial steering signal PJ is generated.

[0046] Figure 12 A flowchart 1200 schematically illustrates a method for determining the initial direction of rotation of a brushless DC motor according to an embodiment of the present invention, wherein the motor includes a stator and a rotor. The method includes:

[0047] Step 1201: Using a Hall sensor to sense the magnetic field change caused by the rotation of the rotor, and generate an induction signal;

[0048] Step 1202 , comparing the feedback voltage representing the back electromotive force at both ends of the stator with a reference voltage to generate a comparison signal;

[0049] Step 1203: detecting the overlap of the in-phase levels or the complementary levels of the sensing signal and the comparison signal, and generating an initial turning signal;

[0050] Step 1204: Select forward start logic or reverse start logic according to the initial turn signal.

[0051] In one embodiment of the present invention, the detecting of the overlap of the in-phase levels or the complementary levels of the sensing signal and the comparison signal includes: timing the high-level duration or the low-level duration of one of the sensing signal and the comparison signal within one electrical cycle to generate a first timing signal; timing the in-phase level duration of the other of the sensing signal and the comparison signal within the time for timing one of the sensing signal and the comparison signal to generate a second timing signal; and comparing the first timing signal and the second timing signal or comparing the product of the first timing signal and the proportional coefficient with the second timing signal to generate the initial steering signal.

[0052] In one embodiment of the present invention, the detection of the overlap of the same-phase levels or the complementary levels of the sensing signal and the comparison signal further includes: comparing the sizes of the first timing signal (or the product of the first timing signal and the proportional coefficient) and the second timing signal multiple times: when the number of times the second timing signal is greater than the first timing signal (or the product of the first timing signal and the proportional coefficient) reaches a set value, it indicates that the initial direction of the motor is forward rotation; when the number of times the second timing signal is greater than the first timing signal (or the product of the first timing signal and the proportional coefficient) is less than the set value, it indicates that the initial direction of the motor is reverse rotation.

[0053] In another embodiment of the present invention, the detection of the overlap of the in-phase levels or the complementary levels of the sensing signal and the comparison signal includes: timing the high-level duration or the low-level duration of one of the sensing signal and the comparison signal within one electrical cycle to generate a first timing signal; timing the inverted-phase level duration of the other one during the timing of one of the sensing signal and the comparison signal to generate a second timing signal; subtracting the first timing signal from the second timing signal to generate an in-phase duration signal; and comparing the first timing signal with the in-phase duration signal or comparing the product of the first timing signal and the proportional coefficient with the in-phase duration signal to generate the initial steering signal.

[0054] In one embodiment of the present invention, the detection of the overlap of the in-phase levels or the complementary levels of the sensing signal and the comparison signal further includes: multiple comparisons of the first timing signal (or the product of the first timing signal and the proportional coefficient) and the in-phase duration signal: when the number of times the in-phase duration signal is greater than the first timing signal (or the product of the first timing signal and the proportional coefficient) reaches a set value, it indicates that the initial direction of the motor is forward rotation; when the number of times the in-phase duration signal is greater than the first timing signal (or the product of the first timing signal and the proportional coefficient) is less than the set value, it indicates that the initial direction of the motor is reverse rotation.

[0055] The brushless DC motor systems and methods according to the aforementioned embodiments of the present invention determine the initial direction of the motor by utilizing the back electromotive force generated by the motor stator in combination with the sensing signal of the Hall sensor, thereby improving the motor starting performance, simplifying circuit wiring, and reducing costs.

[0056] While the present invention has been described with reference to several exemplary embodiments, it should be understood that the terms used are descriptive and illustrative, rather than restrictive. Since the present invention can be embodied in many forms without departing from the spirit or essence of the invention, it should be understood that the above-described embodiments are not limited to any of the foregoing details, but should be interpreted broadly within the spirit and scope of the appended claims. All changes and modifications that fall within the scope of the claims or their equivalents are intended to be covered by the appended claims.

Claims

1. A brushless DC motor system comprising: a power stage receiving an input voltage, wherein the power stage has a power switch that is periodically turned on and off to convert the input voltage into energy required by the motor, wherein the motor includes a rotor and a stator; The Hall sensor senses the change in magnetic field caused by the rotation of the rotor and generates an induction signal; Logic control circuit, including: A comparison circuit compares the feedback voltage representing the back electromotive force at both ends of the stator with the reference voltage to generate a comparison signal; A phase detector detects the overlap of the in-phase level or complementary level of the sensing signal and the comparison signal to generate an initial steering signal; A logic unit selects forward start logic or reverse start logic according to the initial steering signal to control the operation of the power stage; wherein the phase detector includes: a first timer for timing a high level or a low level of one of the sensing signal and the comparison signal within one electrical cycle to obtain a first timing signal; a second timer, for timing a duration of a same-phase level of the other of the sensing signal and the comparison signal within a timing time of the first timer, to obtain a second timing signal; The comparison unit compares the first timing signal with the second timing signal, or compares the product of the first timing signal and the proportional coefficient with the second timing signal to generate an initial turning signal.

2. The brushless DC motor system of claim 1 , wherein the phase detector further comprises: The counting circuit counts in response to the comparison result of the second timing signal and the first timing signal, or in response to the comparison result of the second timing signal and the product of the first timing signal and the proportional coefficient; when the count reaches a set value, the initial turning signal is generated.

3. A brushless DC motor system comprising: a power stage receiving an input voltage, wherein the power stage has a power switch that is periodically turned on and off to convert the input voltage into energy required by the motor, wherein the motor includes a rotor and a stator; The Hall sensor senses the change in magnetic field caused by the rotation of the rotor and generates an induction signal; Logic control circuit, including: A comparison circuit compares the feedback voltage representing the back electromotive force at both ends of the stator with the reference voltage to generate a comparison signal; A phase detector detects the overlap of the in-phase level or complementary level of the sensing signal and the comparison signal to generate an initial steering signal; A logic unit selects forward start logic or reverse start logic according to the initial steering signal to control the operation of the power stage; wherein the phase detector includes: a first timer for timing a high-level duration or a low-level duration of one of the sensing signal and the comparison signal within one electrical cycle to generate a first timing signal; a second timer, for timing a duration of a complementary level of the other of the sensing signal and the comparison signal within a timing time of the first timer, and generating a second timing signal; a subtraction unit, performing a subtraction operation on the first timing signal and the second timing signal to obtain an in-phase duration signal; The comparison unit compares the first timing signal with the in-phase duration signal, or compares the product of the first timing signal and the proportional coefficient with the in-phase duration signal to generate the initial turning signal.

4. The brushless DC motor system of claim 3 , wherein the phase detector further comprises: The counting circuit counts in response to the comparison result of the in-phase duration signal and the first timing signal, or in response to the comparison result of the in-phase duration signal and the product of the first timing signal and the proportional coefficient; when the count reaches a set value, the initial turning signal is generated.

5. A method for determining the initial direction of rotation of a brushless DC motor, the motor comprising a stator and a rotor, the method comprising: The Hall sensor senses the magnetic field changes caused by the rotation of the rotor and generates an induction signal; Comparing the feedback voltage representing the back electromotive force at both ends of the stator with the reference voltage to generate a comparison signal; detecting the overlap of the in-phase level or the complementary level of the sensing signal and the comparison signal to generate an initial turning signal; Select forward start logic or reverse start logic according to the initial turn signal; The detection of the overlap of the in-phase level or the complementary level of the sensing signal and the comparison signal comprises: Within one electrical cycle, timing a high-level duration or a low-level duration of one of the sensing signal and the comparison signal to generate a first timing signal; During the time of timing one of the sensing signal and the comparison signal, the duration of the in-phase level of the other signal is timed to generate a second timing signal; The initial steering signal is generated by comparing the first timing signal with the second timing signal or by comparing the product of the first timing signal and the proportional coefficient with the second timing signal.

6. The method of claim 5, further comprising: The first timing signal or the product of the first timing signal and the proportional coefficient is compared with the second timing signal multiple times; wherein: When the second timing signal is greater than the first timing signal or greater than the product of the first timing signal and the proportional coefficient for a number of times reaching a set value, it indicates that the initial direction of the motor is forward rotation; When the second timing signal is greater than the first timing signal or greater than the product of the first timing signal and the proportional coefficient for a number of times less than a set value, it indicates that the initial direction of the motor is reverse.

7. A method for determining the initial direction of rotation of a brushless DC motor, the motor comprising a stator and a rotor, the method comprising: The Hall sensor senses the magnetic field changes caused by the rotation of the rotor and generates an induction signal; Comparing the feedback voltage representing the back electromotive force at both ends of the stator with the reference voltage to generate a comparison signal; detecting the overlap of the in-phase level or the complementary level of the sensing signal and the comparison signal to generate an initial turning signal; Select forward start logic or reverse start logic according to the initial turn signal; The detection of the overlap of the in-phase level or the complementary level of the sensing signal and the comparison signal comprises: Within one electrical cycle, timing a high-level duration or a low-level duration of one of the sensing signal and the comparison signal to generate a first timing signal; During the time of timing one of the sensing signal and the comparison signal, the duration of the inverted level of the other signal is timed to generate a second timing signal; Performing a subtraction operation on the first timing signal and the second timing signal to generate an in-phase duration signal; The initial turning signal is generated by comparing the first timing signal with the in-phase duration signal or by comparing the product of the first timing signal and the proportional coefficient with the in-phase duration signal.

8. The method of claim 7, further comprising: The first timing signal or the product of the first timing signal and the proportional coefficient is compared with the in-phase duration signal for multiple times; wherein: When the in-phase duration signal is greater than the first timing signal or greater than the product of the first timing signal and the proportional coefficient for a number of times reaching a set value, it indicates that the initial direction of the motor is forward rotation; When the in-phase duration signal is greater than the first timing signal or greater than the product of the first timing signal and the proportional coefficient for a number of times less than a set value, it indicates that the initial direction of the motor is reverse.

9. A logic control circuit for a brushless DC motor system, the brushless DC motor system having a power stage for converting an input voltage into an output voltage and a Hall effect sensor for sensing a change in a magnetic field and generating an induction signal, the logic control circuit comprising: A comparison circuit compares the feedback voltage representing the back electromotive force at both ends of the stator with the reference voltage to generate a comparison signal; A phase detector detects the overlap of the in-phase level or complementary level of the sensing signal and the comparison signal to generate an initial steering signal; A logic unit selects forward start logic or reverse start logic according to the initial steering signal to control the operation of the power stage; wherein the phase detector includes: a first timer for timing a high level or a low level of one of the sensing signal and the comparison signal within one electrical cycle to obtain a first timing signal; a second timer, for timing a duration of a same-phase level of the other of the sensing signal and the comparison signal within a timing time of the first timer, to obtain a second timing signal; The comparison unit compares the first timing signal with the second timing signal, or compares the product of the first timing signal and the proportional coefficient with the second timing signal to generate an initial turning signal.

10. The logic control circuit of claim 9, wherein the phase detector further comprises: The counting circuit counts in response to the comparison result of the second timing signal and the first timing signal, or in response to the comparison result of the second timing signal and the product of the first timing signal and the proportional coefficient; when the count reaches a set value, the initial turning signal is generated.

11. A logic control circuit for a brushless DC motor system, the brushless DC motor system having a power stage for converting an input voltage into an output voltage and a Hall effect sensor for sensing a change in a magnetic field and generating an induction signal, the logic control circuit comprising: A comparison circuit compares the feedback voltage representing the back electromotive force at both ends of the stator with the reference voltage to generate a comparison signal; A phase detector detects the overlap of the in-phase level or complementary level of the sensing signal and the comparison signal to generate an initial steering signal; The logic unit selects the forward start logic or the reverse start logic according to the initial turn signal to control the operation of the power stage; The phase detector comprises: a first timer for timing a high-level duration or a low-level duration of one of the sensing signal and the comparison signal within one electrical cycle to generate a first timing signal; a second timer, for timing a duration of a complementary level of the other of the sensing signal and the comparison signal within a timing time of the first timer, and generating a second timing signal; a subtraction unit, performing a subtraction operation on the first timing signal and the second timing signal to obtain an in-phase duration signal; The comparison unit compares the first timing signal with the in-phase duration signal, or compares the product of the first timing signal and the proportional coefficient with the in-phase duration signal to generate the initial turning signal.

12. The logic control circuit of claim 11 , wherein the phase detector further comprises: The counting circuit counts in response to the comparison result of the in-phase duration signal and the first timing signal, or in response to the comparison result of the in-phase duration signal and the product of the first timing signal and the proportional coefficient; when the count reaches a set value, the initial turning signal is generated.

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