Brushless direct current motor, starting method thereof and electric tool

Abstract

The invention discloses a brushless direct current motor, a starting method thereof and an electric tool. The starting method comprises the following steps: injecting voltage pulses in a first preset direction and a second preset direction which are diagonal to each other; acquiring a first current response of the voltage pulse in the first preset direction and a second current response of the voltage pulse in the second preset direction; injecting voltage pulses in a third preset direction and a fourth preset direction which are diagonal to each other; acquiring a third current response and a fourth current response; and determining an initial rotor angle when the brushless direct current motor is started according to the relative magnitudes of the first, second, third and fourth current responses. According to the brushless direct current motor starting method, the initial position of a rotor is determined through pulse voltage injection in multiple pairs of diagonal directions based on the saturated salient pole effect. In addition, in the acceleration process, the commutation position can also be judged through pulse voltage injection in a pair of diagonal directions.

Description

Technical Field

[0001] The present disclosure relates to the field of motors, and in particular to a brushless DC motor and a starting method thereof, and an electric tool equipped with the brushless DC motor. Background Art

[0002] The motor uses the attraction and repulsion of the magnetic poles of permanent magnets and electromagnets to convert electrical energy into rotational kinetic energy. In recent years, brushless DC motors have replaced brushed DC motors and become the mainstream motors used in everyday tools or complex equipment due to their higher efficiency and lower maintenance requirements.

[0003] Brushless DC motors usually use back EMF detection to achieve position recognition. However, since back EMF cannot be detected at low speeds, other methods are needed to achieve position recognition when the motor starts.

[0004] Existing startup is usually achieved by rotor pre-positioning combined with forced commutation or initial position recognition combined with forced commutation. However, the load of the power tool is uncertain, and under heavy load, the reliability of forced commutation is low, which often leads to startup failure.

[0005] Therefore, an improved brushless DC motor starting method is needed. Summary of the invention

[0006] A technical problem to be solved by the present disclosure is to provide an improved brushless DC motor starting method, which is based on the saturated salient pole effect and determines the initial position of the rotor by injecting a pair of or more pairs of pulse voltages in the diagonal direction. In addition, during the acceleration process, the commutation position can also be determined by injecting a pair of pulse voltages in the diagonal direction.

[0007] According to a first aspect of the present disclosure, a method for starting a brushless DC motor is provided, comprising: injecting a voltage pulse in a first preset direction and a second preset direction that are diagonal to each other; obtaining a first current response of the voltage pulse in the first preset direction and a second current response of the voltage pulse in the second preset direction; injecting a voltage pulse in a third preset direction and a fourth preset direction that are diagonal to each other, wherein the first preset direction, the second preset direction, the third preset direction and the fourth preset direction are different from each other; obtaining a third current response of the voltage pulse in the third preset direction and a fourth current response of the voltage pulse in the fourth preset direction; and determining an initial rotor angle of the brushless DC motor when starting according to the relative sizes of the first current response, the second current response, the third current response and the fourth current response.

[0008] Optionally, determining the initial rotor angle when the brushless DC motor is started according to the relative sizes of the first current response, the second current response, the third current response and the fourth current response includes: selecting a semicircle corresponding to a current response with a relatively larger value between the first current response and the second current response as a first range for the initial rotor angle when the brushless DC motor is started; using a semicircle corresponding to a current response with a relatively larger value between the third current response and the fourth current response as a second range for the initial rotor angle when the brushless DC motor is started; and using an overlapping angle range of the first range and the second range as the range for the initial rotor angle.

[0009] Optionally, determining the initial rotor angle of the brushless DC motor when starting according to the relative sizes of the first current response, the second current response, the third current response and the fourth current response includes: selecting the angle range corresponding to the current response with a larger relative value among the first current response, the second current response, the third current response and the fourth current response as the range of the initial rotor angle of the brushless DC motor when starting.

[0010] Optionally, the method also includes: injecting a voltage pulse in a fifth preset direction and a sixth preset direction that are diagonal to each other, wherein the first preset direction, the second preset direction, the third preset direction, the fourth preset direction, the fifth preset direction and the sixth preset direction correspond to six preset directions spaced 60° apart; obtaining a fifth current response of the voltage pulse in the fifth preset direction and a sixth current response of the voltage pulse in the sixth preset direction; and determining the initial rotor angle based on the relative sizes of the fifth current response and the sixth current response.

[0011] Optionally, the method also includes: determining a first acceleration direction to which a rotor acceleration pulse is to be applied based on the range of the initial rotor angle; and selecting a next preset direction of the first acceleration direction as a first detection direction, and selecting a diagonal direction of the first detection direction as a second detection direction; applying a rotor acceleration pulse in the first acceleration direction, and applying a detection voltage pulse in the first detection direction and the second detection direction before or after applying the rotor acceleration pulse; determining whether the rotor angle of the brushless DC motor at the time of starting acceleration reaches a commutation point where the acceleration direction needs to be changed based on the relative sizes of the first detection current response and the second detection current response.

[0012] Optionally, the first acceleration direction, the first detection direction and the second detection direction each correspond to one of the six preset directions, and the first acceleration direction is the closest preset direction perpendicular to the range of the initial rotor angle.

[0013] Optionally, in the direction of rotor rotation, the first detection direction is closer to the rotor angle than the second detection direction, and determining whether the rotor angle of the brushless DC motor reaches a commutation point requiring change of acceleration direction when starting acceleration based on the relative sizes of the first detection current response and the second detection current response includes: when the first detection current response becomes greater than the second detection current response, determining that the rotor angle reaches the commutation point, and using the first detection direction as the second acceleration direction to which a rotor acceleration pulse is to be applied after commutation.

[0014] According to a second aspect of the present disclosure, a method for starting a brushless DC motor is provided, comprising: injecting a voltage pulse in a first preset direction and a second preset direction that are diagonal to each other, and obtaining a first current response of the voltage pulse in the first preset direction and a second current response of the voltage pulse in the second preset direction; injecting a voltage pulse in a third preset direction and a fourth preset direction that are diagonal to each other, and obtaining a third current response of the voltage pulse in the third preset direction and a fourth current response of the voltage pulse in the fourth preset direction; injecting a voltage pulse in a fifth preset direction and a sixth preset direction that are diagonal to each other, and obtaining a fifth current response of the voltage pulse in the fifth preset direction and a sixth current response of the voltage pulse in the sixth preset direction; and determining the range of the initial rotor angle of the brushless DC motor when starting based on the relative sizes of the first current response, the second current response, the third current response, the fourth current response, the fifth current response and the sixth current response.

[0015] Optionally, based on the relative sizes of the first current response, the second current response, the third current response, the fourth current response, the fifth current response and the sixth current response, determining the range of the initial rotor angle when the brushless DC motor is started includes: selecting the semicircle corresponding to the current response with a relatively larger value between the first current response and the second current response as the first range of the initial rotor angle when the brushless DC motor is started; selecting the semicircle corresponding to the current response with a relatively larger value between the third current response and the fourth current response as the second range of the initial rotor angle when the brushless DC motor is started, selecting the semicircle corresponding to the current response with a relatively larger value between the fifth current response and the sixth current response as the third range of the initial rotor angle when the brushless DC motor is started; and taking the overlapping angle range of the first range, the second range and the third range as the sector where the initial rotor angle is located.

[0016] Optionally, based on the relative sizes of the first current response, the second current response, the third current response, the fourth current response, the fifth current response and the sixth current response, determining the range of the initial rotor angle when the brushless DC motor is started includes: selecting the angle range corresponding to the current response with a larger relative value among the first current response, the second current response, the third current response, the fourth current response, the fifth current response and the sixth current response as the sector where the initial rotor angle when the brushless DC motor is started is located.

[0017] According to a third aspect of the present disclosure, a method for starting a brushless DC motor is provided, comprising: determining a first acceleration direction to which a rotor acceleration pulse is to be applied based on the range of the initial rotor angle; and selecting a next preset direction of the first acceleration direction as a first detection direction, and selecting a diagonal direction of the first detection direction as a second detection direction; applying a rotor acceleration pulse in the first acceleration direction, and injecting a voltage pulse in the first detection direction and the second detection direction before or after applying the rotor acceleration pulse; and determining whether the rotor angle of the brushless DC motor reaches a commutation point at which the acceleration direction needs to be changed based on the relative sizes of the first detection current response and the second detection current response when starting and accelerating.

[0018] Optionally, in the direction of rotor rotation, the first detection direction is closer to the rotor angle than the second detection direction, and determining whether the rotor angle of the brushless DC motor reaches a commutation point requiring change of acceleration direction when starting acceleration based on the relative sizes of the first detection current response and the second detection current response includes: when the first detection current response becomes greater than the second detection current response, determining that the rotor angle reaches the commutation point, and using the first detection direction as the second acceleration direction to which a rotor acceleration pulse is to be applied after commutation.

[0019] Optionally, when the first detection current response does not become greater than the second detection current response within a predetermined time, the duty cycle of the rotor acceleration pulse applied in the first acceleration direction is increased.

[0020] According to a fourth aspect of the present disclosure, a brushless DC motor is provided, comprising: a motor; a microcontroller; a driver; an inverter; and a bus current acquisition device, wherein a pulse emitted by the microcontroller is converted by the driver into a voltage pulse and acts on the inverter to complete voltage pulse injection in first and second preset directions that are diagonal to each other, and the bus current acquisition device obtains a first current response of the voltage pulse in the first preset direction and a second current response of the voltage pulse in the second preset direction; a pulse emitted by the microcontroller is converted by the driver into a voltage pulse and acts on the inverter to complete voltage pulse injection in third and fourth preset directions that are diagonal to each other, and the bus current acquisition device obtains a third current response of the voltage pulse in the third preset direction and a fourth current response of the voltage pulse in the fourth preset direction; and the microcontroller determines the rotor angle of the brushless DC motor in the starting stage according to the relative sizes of the first current response, the second current response, the third current response, and the fourth current response.

[0021] According to a fifth aspect of the present disclosure, there is provided an electric tool comprising a brushless DC motor started by the method described in the first aspect.

[0022] Therefore, the present disclosure determines the initial position of the rotor by comparing the pulse injection in the diagonal direction and the response current size. The diagonal injection of pulses can reduce the jitter of the motor. In addition, after determining the initial position of the rotor, a pair of short-time pulses can be added on the basis of the normal acceleration pulse width, and the change in the current size generated by the pair of short-time pulses can be used as the basis for the motor commutation. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The above and other objects, features and advantages of the present disclosure will become more apparent through a more detailed description of exemplary embodiments of the present disclosure in conjunction with the accompanying drawings, wherein like reference numerals generally represent like components in the exemplary embodiments of the present disclosure.

[0024] Figure 1 The main structure diagram of the three-phase PWM inverter BLDC load is shown.

[0025] Figure 2 A schematic diagram of six-step commutation is shown.

[0026] Figure 3 The self-inductance variation curve of phase A winding is shown without considering the influence of AC-DC flux linkage.

[0027] Figure 4 The self-inductance variation curve of phase A winding is shown when the influence of AC-DC flux linkage is taken into account.

[0028] Figure 5A schematic diagram of the saturation salient pole effect is shown.

[0029] Figure 6 The self-inductance variation curve of phase A winding is shown when the combined influence of the AC-DC axis flux and the stator winding magnetic potential is considered.

[0030] Figure 7 The distribution diagram of the stator winding magnetic potential is shown.

[0031] Figure 8 A schematic diagram of magnetization and demagnetization in different directions when the rotor is at the position θ=0 is shown.

[0032] Fig.9A -C shows an example of the relative relationship between different initial positions and the stator magnetic potential.

[0033] Fig.10 A schematic flowchart of a brushless DC motor starting method according to an embodiment of the present disclosure is shown.

[0034] Fig.11 A schematic flowchart of a brushless DC motor starting method according to an embodiment of the present disclosure is shown.

[0035] Fig.12 FIG. 1 is a schematic diagram showing a motor acceleration process according to an embodiment of the present disclosure.

[0036] Fig.13 A schematic flowchart of a brushless DC motor starting method according to an embodiment of the present disclosure is shown.

[0037] Fig.14 A schematic flowchart of a brushless DC motor starting method according to an embodiment of the present disclosure is shown.

[0038] Fig.15 A schematic diagram of the composition of a brushless DC motor according to an embodiment of the present disclosure is shown. DETAILED DESCRIPTION

[0039] The preferred embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although the preferred embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments described herein. On the contrary, these embodiments are provided to make the present disclosure more thorough and complete, and to fully convey the scope of the present disclosure to those skilled in the art.

[0040] The motor uses the attraction and repulsion of the magnetic poles of permanent magnets and electromagnets to convert electrical energy into rotational kinetic energy. A brushless DC motor (BLDC) is a motor without brushes and commutators and driven by DC. A brushless motor uses permanent magnets as the rotor and electromagnets as the stator. The stator winding is mostly a three-phase symmetrical star winding and receives a three-phase voltage converted from a DC power supply by a controller. By controlling the magnitude, direction, and timing of the current applied to the three phase windings ABC, the rotor can be made to rotate continuously at the desired speed.

[0041] Figure 1 The main structure diagram of the three-phase PWM inverter BLDC load is shown. Figure 1 The left side of the structure is the inverter, and the right side is the motor. In the BLDC speed control system, in order to apply PWM, an inverter is required to convert DC power into AC power. Figure 1 In the three-phase PWM inverter BLDC load shown in the figure, the power tubes VT1 and VT4 are the upper and lower arm switch tubes of phase A respectively, and D1 and D4 are used as i in the dead time. a The diode for freewheeling; the power tubes VT2 and VT5 are the upper and lower arm switch tubes of phase B respectively, and D2 and D5 are used to switch i during the dead time. b The diode for freewheeling; the power tubes VT3 and VT6 are the upper and lower arm switch tubes of phase C respectively, and D3 and D6 are used to switch i in the dead time. c The figure also shows a single resistor R on the bus for sampling the bus current.

[0042] A classic driving method for brushless DC motors is the three-phase six-step commutation method. Figure 2 The schematic diagram of six-step commutation is shown. Specifically, parts (1)-(6) of the figure show that the three phases ABC complete one rotation of the rotor through six commutations. For simplicity, the permanent magnet rotor is abstractly shown as a structure with a straight line connecting the N pole and the S pole (as shown in the black dotted box in the figure), and the three phases ABC are shown as three circles. The color of the circle indicates the polarity, where a white circle indicates that the corresponding phase is vacant.

[0043] Here, it is assumed that the rotor position shown in part (1) corresponds to θ = 0. At this time, by applying a current of A + C- (i.e., current flows from phase A to phase C, and phase B is idle), a magnetic potential F is generated in the direction indicated by the gray dotted arrow. A+C- , causing the rotor to rotate in the direction indicated by the gray arrow. When the rotor rotates to the position θ = π / 3 as shown in part (2), in order to drive the rotor to rotate further, the applied current can be switched from A+C- to B+C- (i.e., the current flows from phase B to phase C, and phase A is idle), generating a magnetic potential F in the direction indicated by the gray dotted arrow. B+C-, causing the rotor to rotate in the direction indicated by the gray arrow. Similarly, when the rotor subsequently rotates to θ = 2π / 3, π, 4π / 3, and 5π / 3, the current is switched to B+A-, C+A-, C+B-, and A+B- in sequence, eventually causing the rotor to complete one rotation. Subsequently, the switching process in parts (1) to (6) above is repeated continuously, allowing the rotor to continue to rotate.

[0044] Since position recognition based on back-EMF detection cannot be performed at low speed, the existing technology usually realizes motor starting by forced commutation. Figure 2 Unlike the commutation when the rotor rotates to the corresponding commutation angle, the so-called "forced commutation" refers to forced commutation when the rotor angle is unknown or has not reached the corresponding phase angle, and the rotor is forced to rotate. Forced commutation has a high success rate when the motor load is not high, but it often leads to startup failure under heavy load. Due to the uncertain motor load, forced commutation is not a reliable and efficient starting method.

[0045] In view of this, the present disclosure proposes a method for starting a brushless DC motor based on initial position detection. The method is based on the saturated salient pole effect, accurately determines the initial position of the rotor by observing the response of the diagonal voltage pulse, and starts the motor based on the detected initial position, thereby avoiding forced commutation.

[0046] In order to deepen the understanding of the principles of the present disclosure, the technical principle of observing the voltage pulse response based on the saturated salient pole effect to determine the initial position of the rotor is first explained.

[0047] The identification of the initial position of the rotor is mainly related to the phase winding inductance. The main factors affecting the phase winding inductance of the salient pole brushless DC motor include two aspects: one is the influence of the AC-DC axis flux, which will change with the position; the other is the magnetic potential generated by the stator winding, which is mainly related to the current passing through the winding. The following analysis takes phase A as an example:

[0048] (a) When the influence of the AC-DC axis flux and the stator winding magnetic potential are ignored, it can be specifically expressed as:

[0049] L aa =L s0 (1)

[0050] Where, L aa Indicates the A-phase winding inductance, L s0 It represents the self-inductance of phase A winding. The quadrature axis is the q axis, and the direct axis is the d axis. The position of the d axis corresponds to the angle of the rotor position θ, and the position of the q axis is 90° ahead of the angle of the rotor position θ. Figure 3The figure shows the change curve of the self-inductance of the A-phase winding without considering the influence of the cross-direct axis flux. As shown in the figure, if the influence of the cross-direct axis flux is not considered, the inductance of the A-phase winding is constant and the magnetic permeability is independent of the rotor position, similar to the surface-mounted motor.

[0051] (b) When only the cross-direct axis flux linkage is affected, because the rotor core has some embedded permanent magnets, the flux linkage caused by the direct and cross-axis air gap magnetic fields will change with the rotor position. At this time, the inductance of the A-phase winding changes with the change of the rotor position. When the rotor position θ = 0 and θ = π, the equivalent air gap through which the A-phase winding flux path passes is the largest (including the permanent magnet air gap), the magnetic resistance is the largest, and the inductance value is the smallest. When θ = π / 2 and θ = 3π / 2, the equivalent air gap through which the A-phase winding flux path passes is the smallest (without the permanent magnet air gap), the magnetic resistance is the smallest, and the inductance value is the largest. During the rotation of the motor, the change period of the air gap length is twice the number of pole pairs, so there is a secondary component. The influence of the cross-direct axis flux linkage can be represented by a second harmonic component, which can be specifically expressed as:

[0052] L aa =L s0 +L s1 cos2θ (2)

[0053] Where, L s1 is the second harmonic amplitude generated by the cross-direct axis flux, L s1 The generation of L is mainly related to the salient pole structure, and L s1 <0. Figure 4 The figure shows the change curve of the self-inductance of the A-phase winding when the influence of the AC-DC flux is considered. At this time, the inductance of the A-phase winding L aa It is no longer a constant, but changes periodically with the change of the rotor position.

[0054] (c) Considering the combined effects of the AC-DC flux linkage and the stator winding magnetic potential, the A-phase winding inductance L aa The changes are more complex. Figure 5 A schematic diagram of the saturation salient pole effect is shown, in which a curve is a BH curve between the magnetic induction intensity B and the magnetic field intensity H, such as Figure 5 As shown in the figure, when the magnetic field strength H gradually increases, the magnetic induction intensity B increases sharply; when H increases further, the increase of B becomes slow again, reaching Figure 5 After the critical saturation point shown in the figure, even if the H value increases further, B hardly increases anymore, that is, it reaches saturation. When designing the motor, the magnetic field H generated by the permanent magnet alone has made the motor operating point close to the critical saturation point of the BH curve. At this time, superimposing any external magnetic field in the same direction will cause the operating point to enter the saturation state. Figure 6 The saturation salient pole effect of the A-phase winding self-inductance under the action of current is shown. a>0 as an example. When θ=0, the winding magnetic potential is in the same direction as the d-axis, the winding magnetic potential plays a magnetizing role, the A-phase magnetic circuit saturation degree is the largest, the inductance value is the smallest, and the motor works on the right side of the critical saturation point; when θ=π / 2 and θ=3π / 2, the winding magnetic potential is perpendicular to the d-axis, the two are orthogonal, and the winding magnetic potential has no effect; when θ=π, the winding magnetic potential and the d-axis are in opposite directions, the winding magnetic potential plays a demagnetizing role, the inductance value is larger than when θ=0, and the motor works on the left side of the critical saturation point. The influence of the stator winding magnetic potential mainly causes the fundamental component to change with the rotor angle. Figure 6 The figure shows the self-inductance variation curve of phase A winding under the combined influence of the AC-DC axis flux and the stator winding magnetic potential. aa It can be specifically expressed as:

[0055] L aa =L s0 +L s1 cos2θ+L s2 cosθ (3)

[0056] Where, L s2 It is the amplitude of the fundamental component generated by the winding magnetic potential.

[0057] It can be seen that the phase winding inductance is determined by the AC-DC axis flux and the winding magnetic potential. When the winding magnetic potential is in the same direction as the d-axis, the inductance is minimum. When the winding magnetic potential is 90° or 270° away from the d-axis, the inductance is maximum.

[0058] Since the BLDC motor is in a stationary state at startup, the θ value is constant (i.e., the d-axis position remains unchanged), the relative position of the rotor position to the voltage application direction can be determined by changing the stator voltage application direction and observing the response.

[0059] Specifically, when voltages of equal amplitude are applied from different directions, different stator winding magnetic potentials will be generated, affecting the saturation degree of the magnetic circuit, and thus affecting the inductance value. At this time, the saturated salient pole effect can be summarized as follows: when the angle between the stator magnetic potential and the d-axis is less than 90°, the inductance decreases; when the angle is greater than 90°, the inductance increases. Changes in the inductance value will affect changes in the response current. Therefore, by applying pulses in different diagonal directions, the position of the d-axis (i.e., the initial θ value) can be determined based on the magnitude of the response current.

[0060] Figure 7 The distribution diagram of the stator winding magnetic potential is shown. A+C- 、F B+C- 、F A-B+ 、F A-C+ 、F B-C+ 、F A+B-They are the stator magnetic potentials formed in the two-way conduction mode of A+C-, B+C-, A-B+, A-C+, B-C+, and A+B-. It should be understood that the stator magnetic potential F A+C- 、F B+C- 、F A-B+ 、F A-C+ 、F B-C+ 、F A+B- and Figure 1 The stator magnetic potential that can be added in the six-step commutation operation shown corresponds to the stator magnetic potential that can be added in the six-step commutation operation shown. Therefore, the "+" sign indicates that current flows out of the phase, and the "-" sign indicates that current flows in. If combined as shown below, the "+" sign indicates that the upper bridge arm is open, and the "-" sign indicates that the lower bridge arm is open.

[0061] When the stator winding magnetic potential is generated, the corresponding magnetization or demagnetization effect will occur according to the different relative angles between the generated magnetic potential and the rotor position θ. Figure 8 The figure shows the schematic diagram of magnetization and demagnetization in different directions when the rotor is at the position of θ = 0. Figure 1 , Figure 8 The same structure of inner rotor and outer stator is adopted and a more specific motor structure is shown. As shown in the figure, the stator winding includes three-phase windings AX, BY, and CZ. The internal rotor core is embedded with permanent magnets. Figure 8 Parts (1)-(6) in the figure also correspond to the applied stator magnetic potential F A+C- 、F B+C- 、F A-B+ 、F A-C+ 、F B-C+ 、F A+B- (Note that although the position of the ABC phase is Figure 1 The direction of the applied stator magnetic potential is different from that shown in Figure 1, but the direction of the applied stator magnetic potential is determined by the direction of the current flowing through the ABC phases, so the position of the stator magnetic potential is Figure 1 , 6 Same as in 7.)

[0062] exist Figure 8 In parts (1)-(6) of , for ease of understanding, it is assumed that the rotor is at the position θ = 0. Figure 8 It can be regarded as the influence of stator magnetic potential in six directions on inductance when the rotor position is fixed.

[0063] like Figure 8 As shown in part (1), when the stator magnetic potential F is applied A+C- When the stator magnetic potential F is applied, the angle between the stator magnetic potential and the d-axis is less than 90°. According to the previous derivation, the saturation salient polarity will produce a magnetizing effect, the magnetic circuit saturation degree will increase, and the inductance will decrease. The gray part in the figure also shows the stator magnetic potential F applied. A+C- The range in which magnetization effect will be produced.

[0064] like Figure 8 As shown in part (2), when the stator magnetic potential F is applied B+C- When the stator magnetic potential is applied, the angle between the stator magnetic potential and the d-axis is 90°. According to the previous derivation, no magnetization or demagnetization effect will be produced under the action of saturated salient polarity. Similarly, the gray part in the figure shows the effect of applying the stator magnetic potential F. B+C- The range in which magnetization effect will be produced.

[0065] like Figure 8 As shown in part (3), when the stator magnetic potential F is applied A-B+ When the stator magnetic potential F is applied, the angle between the stator magnetic potential and the d-axis is greater than 90°. According to the previous derivation, the demagnetization effect will occur under the action of saturation salient polarity, and the inductance will increase. Similarly, the gray part in the figure shows the A-B+ The range in which magnetization effect will be produced.

[0066] like Figure 8 As shown in part (4), when the stator magnetic potential F is applied A-C+ When the stator magnetic potential F is applied, the angle between the stator magnetic potential and the d-axis is greater than 90°. According to the previous derivation, the demagnetization effect will occur under the action of saturation salient polarity, resulting in an increase in inductance. The gray part in the figure also shows the A-C+ The range in which magnetization effect will be produced.

[0067] like Figure 8 As shown in part (5), when the stator magnetic potential F is applied B-C+ When the stator magnetic potential F is applied, the angle between the stator magnetic potential and the d-axis is less than 90°. According to the previous derivation, the saturation salient polarity will produce a magnetizing effect, the magnetic circuit saturation degree will increase, and the inductance will decrease. Similarly, the gray part in the figure shows the stator magnetic potential F applied. B-C+ The range in which magnetization effect will be produced.

[0068] like Figure 8 As shown in part (6), when the stator magnetic potential F is applied A+B- When the stator magnetic potential is applied, the angle between the stator magnetic potential and the d-axis is 90°. According to the previous derivation, no magnetization or demagnetization effect will be produced under the action of saturated salient polarity. Similarly, the gray part in the figure shows the effect of applying the stator magnetic potential F. A+B- The range in which magnetization effect will be produced.

[0069] Since different inductors can generate different response currents, and according to the above analysis, the inductance L is a function of the angle between the rotor position θ and the stator magnetic potential. Therefore, when the rotor position θ remains unchanged, by applying a fixed-time voltage pulse to different stator windings and observing the response current, the relative angle relationship between the stator magnetic potential and the rotor position θ can be inferred from the magnitude of the response current. Since the angle of the stator magnetic potential is known and the rotor position θ remains unchanged at the initial position, the relative range of the rotor position θ at this time can be derived.

[0070] Further, observe Figure 8 It can be seen that when the rotor is located at any position other than the commutation position (i.e., θ≠0°, 60°, 120°, 180°, 240°, 300°), when a fixed-time voltage pulse is applied to two stator magnetic potential positions on the diagonal line, one position will inevitably produce a magnetizing effect, resulting in a decrease in inductance and an increase in the response current; while the other position will produce a demagnetizing effect, resulting in an increase in inductance and a decrease in the response current. Therefore, by directly comparing the relative magnitudes of the response currents at the two positions, it is possible to determine which semicircle the rotor position is located in. At this time, by applying a fixed-time voltage pulse from another pair of diagonal positions, the rotor position can be further limited according to the relative magnitude of the response current. At this time, there is a half probability of directly determining which sector the rotor position is located in, and the other half probability of determining the two candidate sectors where the rotor position is located. If it is not possible to directly determine which sector the rotor position is located in, a fixed-time voltage pulse is applied from the remaining last pair of diagonal positions, and the sector in which the rotor position is located is finally determined according to the relative magnitude of the response current. Note that in one embodiment, the sector refers to the angular range of the rotor position θ, such as the six angular ranges of 0° to 60°, 60° to 120°, 120° to 180°, 180° to 240°, 240° to 300°, and 300° to 360°. Of course, the present invention is not limited thereto, and other angular ranges may also be used depending on the applied voltage pulse.

[0071] Fig.9A -C shows an example of the relative relationship between different initial positions and stator magnetic potential. Fig.9A -C illustrates how to determine the initial position based on applying a fixed-time voltage pulse at the position.

[0072] Fig.9A The initial position of the middle rotor is θ = 30°. Since the value of θ is actually unknown at this time, we need to determine the sector where θ is located by applying a fixed voltage pulse diagonally and observing its response current. Assume that the order of applying the fixed voltage pulse is AC first, then BC, and finally AB.

[0073] Specifically, first apply AC (i.e. A+C-, the same applies later) direction voltage pulse, then apply CA (i.e. A-C+) direction pulse voltage, the windings generate magnetic potential F A+C- 、F A-C+ , because the rotor N pole is away from F A+C- Therefore, when pulses of the same time and voltage value are applied in the AC and CA directions, the response current in the AC direction is larger than the response current in the CA direction. Therefore, it can be determined that θ falls within the range of -60° to 120°, that is, Figure 8 The range indicated by the gray area in part (1) is not the range indicated by the gray area in part (4). It should be understood that -120° is used here to indicate the range and is actually equivalent to 240°, and the same applies to the following.

[0074] Then, voltage pulses in the BC and CB directions are applied, and the windings generate magnetic potentials F and F respectively. B+C- 、F B-C+ , because the rotor N pole is away from F B+C- Therefore, when pulses of the same time and voltage value are applied in the BC and CB directions, the response current in the BC direction is larger than the response current in the CB direction. Therefore, it can be determined that the range of θ is between 0° and 180°, that is, Figure 8 The range indicated by the gray area in part (2) is as follows. Since θ has been determined to be within the range of -60° to 120° when applying AC and CA diagonal pulse voltages, it can now be determined that θ is within the range of 0° to 120°.

[0075] Finally, voltage pulses in the AB and BA directions are applied, and the windings generate magnetic potentials F and F respectively. A+B- 、F A-B+ , rotor N pole from F A+B- Therefore, when pulses of the same time and voltage value are applied in the AB and BA directions, the response current in the AB direction is larger than the response current in the BA direction. Therefore, it can be determined that the range of θ is between -120° and 60°, that is, Figure 7 The range indicated by the gray area in part (6). Since θ has been determined to be within the range of 0° to 120° when applying AC and CA diagonal pulse voltages and BC and CB diagonal voltage pulses, it can be determined that θ is within the range of 0° to 60°, that is, it is located in the first sector.

[0076] exist Fig.9A In the example, after applying three diagonal voltage pulses in different directions, it was determined that the θ range was between 0° and 60°.

[0077] Fig. 9B The initial position of the middle rotor is θ = 165°. At this time, it is still assumed that the order of applying the fixed voltage pulses is AC first, then BC, and finally AB.

[0078] First, apply AC and CA direction pulse voltages, and the windings generate magnetic potential F A+C- 、F A-C+ , because the rotor N pole is away from F A-C+ The response current in the CA direction is larger than that in the AC direction. Therefore, it can be determined that θ falls within the range of 120° to 300°, that is, Figure 8 The range indicated by the grey area in part (4).

[0079] Then, voltage pulses in the BC and CB directions are applied, and the windings generate magnetic potentials F B+C- 、F B-C+ , because the rotor N pole is away from F B+C- is closer, so the response current in the BC direction is larger than the response current in the CB direction. Therefore, it can be determined that the range of θ is between 0° and 180°, that is, Figure 8 The range indicated by the gray area in part (2). Since θ has been determined to be within the range of 120° to 300° when applying the AC and CA diagonal pulse voltages, it can be directly determined that θ is within the range of 120° to 180°, that is, it is located in the third sector.

[0080] exist Fig. 9B In the example, after applying two diagonal voltage pulses in different directions, it can be determined that the range of θ is between 120° and 180°.

[0081] Fig. 9C The initial position of the middle rotor is θ=300°, that is, it is exactly at the commutation position from sector 5 to sector 6. At this time, it is still assumed that the order of applying the fixed voltage pulses is first AC, then BC, and finally AB.

[0082] First, apply AC and CA direction pulse voltages, and the windings generate magnetic potential F A+C- 、F A-C+ , due to the rotor N pole and F A+C and F A-C+ The angles are the same, so the response currents in the AC and CA directions are the same, so it can be determined that θ is 120° or 300°.

[0083] Then, voltage pulses in the BC and CB directions are applied, and the windings generate magnetic potentials F B+C- 、F B-C+ , because the rotor N pole is away from F B-C+ The response current in the CB direction is larger than that in the BC direction. Therefore, it can be determined that the range of θ is between 180° and 360°, that is, Figure 8The range indicated by the gray area in part (5) is shown in Figure 5. Therefore, it can be directly determined that θ is located at 300°, that is, the commutation position from the 5th sector to the 6th sector.

[0084] However, in actual operation, for the consideration of the accuracy of the response current, the voltage pulses in the AB and BA directions can be continuously applied, and since the response current in the AB direction is larger than the response current in the BA direction, it can be determined that the range of θ is between -120° and 60° (i.e., 240° to 360° and 0° to 60°), and thus it is further clarified that the range of θ is between 240° and 360°.

[0085] From the above, it can be seen that when the voltage pulses are injected in the diagonal directions, the rotor angle can be determined according to the magnitude of the corresponding current response, at least to determine whether the rotor angle is Figure 8 Further, the voltage pulse injection in the direction of the object line can reduce the vibration of the rotor.

[0086] By injecting voltage pulses in different diagonal directions, the rotor angle can be reduced to a specific range through the superposition of semicircles.

[0087] Fig.10 A schematic flow chart of a brushless DC motor starting method according to an embodiment of the present disclosure is shown. The method is applicable to the starting phase of a brushless DC motor. More specifically, the method is applicable to determining the initial position of a rotor of a brushless DC motor.

[0088] In step S1010, voltage pulses are injected into a first preset direction and a second preset direction which are diagonal to each other. The preset directions may be two directions which are 180° apart from each other in the six-step commutation, for example, F A+C- and F A-C+ direction.

[0089] Subsequently, in step S1020, a first current response of the voltage pulse in the first preset direction and a second current response of the voltage pulse in the second preset direction are obtained. It should be understood that in order to obtain the first current response and the second current response, respectively, it is necessary to apply voltage pulses successively in the first preset direction and the second preset direction. For the comparability of the current responses, the voltage pulses successively applied in the first preset direction and the second preset direction may be pulses with the same voltage and duration.

[0090] When the initial position is determined, in order to further determine the range of the rotor, voltage pulse injection, current response comparison and rotor angle range determination can be performed at another diagonal position.

[0091] Thus, in step S1030, a voltage pulse may be injected in a third preset direction and a fourth preset direction that are diagonal to each other. The first preset direction, the second preset direction, the third preset direction, and the fourth preset direction are different from each other. Subsequently, in step S1040, a third current response to the voltage pulse in the third preset direction and a fourth current response to the voltage pulse in the fourth preset direction may be acquired.

[0092] Thus, in step S1050, the initial rotor angle of the brushless DC motor when starting can be determined according to the relative magnitudes of the first current response, the second current response, the third current response and the fourth current response.

[0093] In one embodiment, the first preset direction, the second preset direction, the third preset direction and the fourth preset direction may be four directions spaced 90° apart from each other, i.e., corresponding to the four directions in the four-step commutation. In another embodiment, the first preset direction, the second preset direction, the third preset direction and the fourth preset direction may correspond to four of the six directions in the six-step commutation. In other embodiments, there may be four directions with more preset directions. Regardless of the angles spaced apart from each other, the voltage pulse injection and current response comparison of the third preset direction and the fourth preset direction can further narrow the rotor angle range.

[0094] In one embodiment, it can be Fig.9A-C, by comparing the first current response and the second current response and the third current response and the fourth current response respectively, the respective semicircle ranges are determined, and the initial position of the rotor is determined by the overlap of the semicircle ranges. Specifically, when the applied voltage pulse is the same, if the first current response is greater than the second current response, this proves that the first preset direction is closer to the rotor direction, that is, it is in a semicircle centered on the first preset direction. Similarly, when the applied voltage pulse is the same, if the third current response is greater than the fourth current response, this proves that the third preset direction is closer to the rotor direction, that is, it is in a semicircle centered on the third preset direction. At this time, determining the initial rotor angle when the brushless DC motor is started according to the relative sizes of the first current response, the second current response, the third current response and the fourth current response may include: selecting the semicircle corresponding to the current response with a larger relative value between the first current response and the second current response as the first range where the initial rotor angle of the brushless DC motor is located when the brushless DC motor is started; and selecting the semicircle corresponding to the current response with a larger relative value between the third current response and the fourth current response as the second range where the initial rotor angle of the brushless DC motor is located when the brushless DC motor is started. Subsequently, the overlapping angle range of the first range and the second range can be used as the range of the initial rotor angle. In this case, since the first current response and the second current response, as well as the third current response and the fourth current response are compared respectively, it is only necessary that the amplitude and duration of the pulse voltage applied in the first preset direction and the second preset direction are the same, and the amplitude and duration of the pulse voltage applied in the third preset direction and the fourth preset direction are the same, and it is not required that the amplitude and duration of the pulse voltage between the two groups are the same.

[0095] In another embodiment, the four current responses obtained can be directly compared simultaneously. At this time, determining the initial rotor angle when the brushless DC motor is started according to the relative sizes of the first current response, the second current response, the third current response, and the fourth current response can include: selecting the angle range corresponding to the current response with a larger relative value among the first current response, the second current response, the third current response, and the fourth current response as the range of the initial rotor angle when the brushless DC motor is started. At this time, it is preferred that the pulse voltages applied in the first preset direction, the second preset direction, the third preset direction, and the fourth preset direction all have the same amplitude and duration.

[0096] Furthermore, in the use scenario of a six-step commutation motor, the starting method may also include voltage pulse injection, current response comparison, and determination of the rotor angle range at the third diagonal position. At this time, voltage pulses may be injected in the fifth preset direction and the sixth preset direction which are diagonal to each other, wherein the first preset direction, the second preset direction, the third preset direction, the fourth preset direction, the fifth preset direction, and the sixth preset direction correspond to six preset directions spaced 60° apart. Subsequently, the fifth current response of the voltage pulse in the fifth preset direction and the sixth current response of the voltage pulse in the sixth preset direction are obtained. And the initial rotor angle may be determined based on the relative size of the fifth current response and the sixth current response.

[0097] At this time, the present disclosure can be implemented as a method for starting a brushless DC motor for a motor usage scenario with six-step commutation. Fig.11 A schematic flowchart of a brushless DC motor starting method according to an embodiment of the present disclosure is shown.

[0098] In step S1110, a voltage pulse is injected in a first preset direction and a second preset direction which are diagonal lines to each other, and a first current response of the voltage pulse in the first preset direction and a second current response of the voltage pulse in the second preset direction are acquired.

[0099] In step S1120, a voltage pulse is injected in a third preset direction and a fourth preset direction which are diagonal to each other, and a third current response of the voltage pulse in the third preset direction and a fourth current response of the voltage pulse in the fourth preset direction are obtained;

[0100] In step S1130, a voltage pulse is injected in a fifth preset direction and a sixth preset direction which are diagonal to each other, and a fifth current response of the voltage pulse in the fifth preset direction and a sixth current response of the voltage pulse in the sixth preset direction are obtained.

[0101] In step S1140, based on the relative sizes of the first current response, the second current response, the third current response, the fourth current response, the fifth current response and the sixth current response, the range of the initial rotor angle when the brushless DC motor is started is determined.

[0102] Similarly, one can Fig.9A-C, the respective semicircle ranges are determined by comparing the current responses pair by pair, and the initial position of the rotor is determined by the overlap of the semicircle ranges. At this time, based on the relative sizes of the first current response, the second current response, the third current response, the fourth current response, the fifth current response and the sixth current response, determining the range of the initial rotor angle when the brushless DC motor is started includes: selecting the semicircle corresponding to the current response with a larger relative value between the first current response and the second current response as the first range of the initial rotor angle when the brushless DC motor is started; selecting the semicircle corresponding to the current response with a larger relative value between the third current response and the fourth current response as the second range of the initial rotor angle when the brushless DC motor is started, selecting the semicircle corresponding to the current response with a larger relative value between the fifth current response and the sixth current response as the third range of the initial rotor angle when the brushless DC motor is started; and taking the overlap angle range of the first range, the second range and the third range as the sector of the initial rotor angle (for example, which 60° angle range).

[0103] Similarly, the six current responses obtained may also be directly compared simultaneously. At this time, based on the relative magnitudes of the first current response, the second current response, the third current response, the fourth current response, the fifth current response, and the sixth current response, determining the range of the initial rotor angle when the brushless DC motor is started includes: selecting the angle range corresponding to the current response with a larger relative value among the first current response, the second current response, the third current response, the fourth current response, the fifth current response, and the sixth current response as the sector (for example, which 60° angle range) where the initial rotor angle when the brushless DC motor is started is located.

[0104] After the initial position of the rotor is determined, closed-loop acceleration can be performed. However, as the speed increases, the difficulty of pulse insertion gradually increases, the control complexity increases, and the inserted pulses are likely to cause multiple reverse forces, thus affecting the control of the motor. In order to reduce the impact on the motor, two detection pulses can be inserted before the acceleration pulse during the acceleration phase to determine the rotor position.

[0105] For the convenience of explanation, Fig.9A The acceleration scheme disclosed herein is described by taking the initial rotor position of as an example. Assume that the initial position detection has been completed by, for example, the aforementioned method or other methods, and it is determined that the initial rotor position is within the range of 0° to 60° (i.e., located in the first sector). At this time, the rotor needs to be accelerated.

[0106] Since the direction perpendicular to the rotor position vector is the best control direction, the direction located in the rotor rotation direction (assuming that the rotor rotates counterclockwise as shown in the figure) and closest to the initial rotor position range is selected as the acceleration direction. That is, the direction perpendicular to the lower limit of the initial rotor position range (that is, 0° in this example) and located in the rotor rotation direction (that is, the 90° direction in this example) is selected as the acceleration direction. That is, the first acceleration vector is F B+C- .

[0107] The acceleration vector F B+C- Add F before or after A-B+ and F A+B- The vector direction is short-time pulse, and the rotor gradually approaches F from the A phase axis. B+C- Direction, F A-B+ The response current generated by the vector is less than F A+B- When the rotor is at about 60°, the inductance values ​​generated by the two pulse voltages are close to equal, and the response currents are basically the same. When the rotor is greater than 60°, F A-B+ The response current generated by the vector is greater than F A+B- The current at this moment can be used as the phase change mark point, and the vector is perpendicular to the next moment, which is the best phase change point. A-C+ and F A+C- , the normal acceleration pulse is F A-B+ Repeat the above steps to gradually accelerate the motor to the specified speed.

[0108] Fig.12 FIG. 1 is a schematic diagram showing a motor acceleration process according to an embodiment of the present disclosure. When determining that the initial rotor position is located in the first sector, the F B+C- Before the acceleration pulse in the direction, add F A-B+ and F A+B - A short pulse in the vector direction is used to detect whether the rotor rotates to the commutation point. As shown in the figure, the duration of the short pulse is Ts, and it is a detection pulse used to detect the commutation point.

[0109] As shown in the figure, before the first acceleration, i A-B+ <i A+B- , indicating that the rotor has not reached 60°, and the F B+C -direction, the duration of the display pulse is obviously longer than the duration of the detection pulse. Before the second acceleration, i A-B+ =i A+B- , indicating that the rotor is close to or at the 60° position, and it is still possible to B+C - direction. Before the third acceleration, i A-B+ >i A+B-, indicating that the rotor is already at a position greater than 60°, and it is still possible to B+C- The acceleration pulse is applied in the direction of F (in other embodiments, it can also be changed to F at this time A-B+ Then, the commutation is determined and during the fourth acceleration, F is added instead. A-C+ and F A+C- A short pulse in the vector direction is used to detect whether the rotor rotates to the commutation point, and then the F A-B+ Apply acceleration pulse in the direction.

[0110] at this time, Fig.10 or Fig.11 The method shown may also include: determining a first acceleration direction (eg, Fig.12 F B+C- direction); and selecting a first detection direction and a second detection direction (eg, Fig.12 F A-B+ and F A+B- direction); applying a rotor acceleration pulse in a first acceleration direction, and applying a detection voltage pulse in the first detection direction and the second detection direction before or after applying the rotor acceleration pulse; determining whether the rotor angle of the brushless DC motor when starting to accelerate reaches a commutation point where the acceleration direction needs to be changed according to the relative sizes of the first detection current response and the second detection current response.

[0111] Specifically, the first acceleration direction, the first detection direction and the second detection direction may each correspond to one of the six preset directions, and the first acceleration direction is a direction closest to the range of the initial rotor angle in the rotor rotation direction.

[0112] In the direction of rotor rotation, the first detection direction is closer to the rotor angle than the second detection direction, and determining whether the rotor angle of the brushless DC motor reaches a commutation point at which the acceleration direction needs to be changed when the brushless DC motor starts to accelerate according to the relative magnitude of the first detection current response and the second detection current response includes: when the first detection current response becomes greater than the second detection current response, determining that the rotor angle reaches the commutation point, and using the first detection direction as the second acceleration direction to which the rotor acceleration pulse is applied after commutation (for example Fig.12 F A-B+ direction).

[0113] At this point, the present disclosure may be implemented as a brushless motor starting method including an initial position determination and acceleration scheme of the above diagonal short-duration pulse injection. Fig.13FIG. 1 is a schematic flow chart of a method for starting a brushless DC motor according to an embodiment of the present disclosure. The method can be regarded as, for example, Fig.15 The motor shown is executed under the operation scheme of the microcontroller.

[0114] First, send the motor start command and start the initialization operation of position recognition. Then, the six directions can be divided into three groups according to the diagonal line, and the pulse voltage is applied one by one to obtain the magnitude of the response current. According to the magnitude of the response current, the initial position of the rotor (for example, which sector it is located in) is determined, and then the acceleration processing stage is carried out. If it is not possible to accelerate to the specified position within the expected time, the acceleration can be gradually increased. Fig.12 The duty cycle of the acceleration pulse is shown, thereby increasing the load capacity. If the specified speed is reached without overcurrent, the startup process is completed. If overcurrent occurs, an overload alarm can be issued.

[0115] In the implementation of the present disclosure, as described above for Fig.12 The described acceleration method based on detection pulses can also be independent of the initial angle determination method based on diagonal pulse application as disclosed above. In this case, Fig.10 The methods S1010 to S1030 shown can be regarded as an acceleration scheme. To this end, the starting method may also include: before injecting voltage pulses in the first preset direction and the second preset direction, determining the range of the initial rotor angle when the brushless DC motor is started, and determining the first acceleration direction to apply the rotor acceleration pulse according to the range; selecting a direction perpendicular to the first acceleration direction as the first preset direction and the second preset direction; after injecting voltage pulses in the first preset direction and the second preset direction, applying the rotor acceleration pulse in the first acceleration direction, and determining the rotor angle of the brushless DC motor in the starting stage according to the relative size of the first current response and the second current response includes: determining whether the rotor angle of the brushless DC motor reaches the commutation point when starting and accelerating according to the relative size of the first current response and the second current response.

[0116] Fig.14 A schematic flow chart of a brushless DC motor starting method according to an embodiment of the present disclosure is shown. The starting method at this time is a starting acceleration method performed after determining the range of the initial rotor angle.

[0117] In step S1410, a first acceleration direction in which a rotor acceleration pulse is to be applied is determined according to the range of the initial rotor angle.

[0118] In step S1420, a preset direction next to the first acceleration direction is selected as a first detection direction, and a diagonal direction of the first detection direction is selected as a second detection direction.

[0119] In step S1430, a rotor acceleration pulse is applied in a first acceleration direction, and a voltage pulse is injected in the first detection direction and the second detection direction before or after the application of the rotor acceleration pulse.

[0120] In step S1440, it is determined whether the rotor angle of the brushless DC motor when starting acceleration reaches a commutation point where the acceleration direction needs to be changed according to the relative magnitudes of the first detection current response and the second detection current response.

[0121] In one embodiment, the first acceleration direction, the first detection direction, and the second detection direction may each correspond to one of the six preset directions as described above, and the first acceleration direction is the closest preset direction perpendicular to the range of the initial rotor angle. For example, the preset direction closest to the direction perpendicular to the starting angle of the range of the initial rotor angle may be selected as the first acceleration direction. For example, when it is determined that the initial rotor angle is within the range of 0° to 60°, the preset direction closest to the direction perpendicular to the starting angle 0° (i.e., 90°) is selected, i.e., F B+C- direction as the first acceleration direction. In the example of the present invention, since the motor rotates counterclockwise, the selected first acceleration direction can be the nearest preset direction that is located in the direction of motor rotation and perpendicular to the range of the initial rotor angle. In other words, when the starting angle is 0°, the selected vertical direction is 90°, not 270°. For another example, in other embodiments, it can be further determined whether the position of the initial rotor angle in the range of 0° to 60° is closer to 0° or 60°. If the initial rotor angle is closer to 0°, the preset direction closest to the direction perpendicular to the initial rotor angle can be selected (at this time, the "vertical direction" is between the 90° preset direction and the 150° preset direction and is closer to the 90° preset direction), so 90° is selected, that is, F B+C- direction as the first acceleration direction.

[0122] In the direction of rotor rotation, the first detection direction is closer to the rotor angle than the second detection direction, and determining whether the rotor angle of the brushless DC motor reaches a commutation point where the acceleration direction needs to be changed when starting acceleration based on the relative sizes of the first detection current response and the second detection current response includes: when the first detection current response becomes greater than the second detection current response, determining that the rotor angle reaches the commutation point, and using the first detection direction as the second acceleration direction to which a rotor acceleration pulse is to be applied after commutation.

[0123] When the first detection current response does not become greater than the second detection current response within a predetermined time, the duty ratio of the rotor accelerating pulse applied in the first accelerating direction is increased.

[0124] In addition, the present disclosure may also be implemented as a brushless DC motor. Fig.15 A schematic diagram of the composition of a brushless DC motor according to an embodiment of the present disclosure is shown. As shown in the figure, in addition to the motor part, the brushless DC motor also includes a voltage, a microcontroller (MCU), a driver, an inverter and a bus current acquisition device. Specifically, the pulse emitted by the microcontroller is converted by the driver into a voltage pulse to act on the inverter to complete the injection of voltage pulses in the first preset direction and the second preset direction that are diagonal to each other. The bus current acquisition device obtains a first current response of the voltage pulse in the first preset direction and a second current response of the voltage pulse in the second preset direction. The microcontroller determines the rotor angle of the brushless DC motor in the startup phase according to the relative size of the first current response and the second current response.

[0125] Combination Fig.13 It can be seen that in one embodiment, the MCU can first send six short pulses, which act on the motor through the driver and the inverter to collect the bus current of the six pulses respectively (for example, through Figure 1 The resistor R shown in the figure is used to determine the initial position by the current. Then the acceleration start is performed. On the basis of the normal acceleration pulse width, a pair of short-time pulses is added. The change in the current generated by the pair of short-time pulses is used as the basis for the motor commutation.

[0126] The present disclosure may also be implemented as an electric tool, including a brushless DC motor started by the method described above.

[0127] The brushless motor starting method of the present invention can determine the initial position of the rotor by comparing the pulse injection in the diagonal direction and the response current size. The diagonal injection of the pulse can reduce the jitter of the motor. In addition, after determining the initial position of the rotor, a pair of short-time pulses can be added on the basis of the normal acceleration pulse width, and the change in the current size generated by the pair of short-time pulses can be used as the basis for the motor commutation.

[0128] The embodiments of the present disclosure have been described above, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and changes will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The selection of terms used herein is intended to best explain the principles of the embodiments, practical applications, or improvements to the technology in the market, or to enable other persons of ordinary skill in the art to understand the embodiments disclosed herein.

Claims

1. A method for starting a brushless DC motor, comprising: injecting a voltage pulse in a first preset direction and a second preset direction which are diagonal to each other; Acquire a first current response to the voltage pulse in the first preset direction and a second current response to the voltage pulse in the second preset direction; injecting a voltage pulse in a third preset direction and a fourth preset direction which are diagonal to each other, wherein the first preset direction, the second preset direction, the third preset direction and the fourth preset direction are different from each other; Acquire a third current response to the voltage pulse in the third preset direction and a fourth current response to the voltage pulse in the fourth preset direction; and An initial rotor angle of the brushless DC motor when starting is determined according to relative magnitudes of the first current response, the second current response, the third current response, and the fourth current response.

2. The method of claim 1, wherein: Determining the initial rotor angle of the brushless DC motor when starting according to the relative magnitudes of the first current response, the second current response, the third current response, and the fourth current response comprises: Selecting a semicircle corresponding to a current response with a larger relative value between the first current response and the second current response as a first range of an initial rotor angle when the brushless DC motor is started; using a semicircle corresponding to a current response with a larger relative value between the third current response and the fourth current response as a second range of an initial rotor angle when the brushless DC motor is started; and The overlapping angle range of the first range and the second range is used as the range of the initial rotor angle.

3. The method of claim 1, wherein: Determining the initial rotor angle of the brushless DC motor when starting according to the relative magnitudes of the first current response, the second current response, the third current response, and the fourth current response comprises: An angle range corresponding to a current response with a larger relative value among the first current response, the second current response, the third current response and the fourth current response is selected as a range of an initial rotor angle when the brushless DC motor is started.

4. The method of claim 1, further comprising: injecting a voltage pulse in a fifth preset direction and a sixth preset direction which are diagonal to each other, wherein the first preset direction, the second preset direction, the third preset direction, the fourth preset direction, the fifth preset direction and the sixth preset direction correspond to six preset directions spaced 60° apart; Acquire a fifth current response to the voltage pulse in the fifth preset direction and a sixth current response to the voltage pulse in the sixth preset direction; and The initial rotor angle is determined based on relative magnitudes of the fifth current response and the sixth current response.

5. The method of claim 4, further comprising: Determining a first acceleration direction in which a rotor acceleration pulse is to be applied according to the range of the initial rotor angle; Selecting a preset direction next to the first acceleration direction as a first detection direction, and selecting a diagonal direction of the first detection direction as a second detection direction; Applying a rotor acceleration pulse in a first acceleration direction, and applying a detection voltage pulse in the first detection direction and the second detection direction before or after applying the rotor acceleration pulse; as well as Whether the rotor angle of the brushless DC motor reaches a commutation point where the acceleration direction needs to be changed when starting acceleration is determined according to the relative magnitudes of the first detection current response and the second detection current response.

6. The method of claim 5, wherein: The first acceleration direction, the first detection direction, and the second detection direction each correspond to one of the six preset directions, and The first acceleration direction is a nearest preset direction perpendicular to the range of the initial rotor angle.

7. The method of claim 6, wherein: In the rotor rotation direction, the first detection direction is closer to the rotor angle than the second detection direction, and determining whether the rotor angle of the brushless DC motor reaches a commutation point at which the acceleration direction needs to be changed when starting acceleration according to the relative magnitude of the first detection current response and the second detection current response includes: When the first detection current response becomes greater than the second detection current response, it is determined that the rotor angle reaches the commutation point, and the first detection direction is used as a second acceleration direction to which a rotor acceleration pulse is applied after commutation.

8. A method for starting a brushless DC motor, comprising: Injecting a voltage pulse in a first preset direction and a second preset direction which are diagonal lines to each other, and acquiring a first current response to the voltage pulse in the first preset direction and a second current response to the voltage pulse in the second preset direction; Injecting a voltage pulse in a third preset direction and a fourth preset direction which are diagonal lines to each other, and acquiring a third current response of the voltage pulse in the third preset direction and a fourth current response of the voltage pulse in the fourth preset direction; Injecting a voltage pulse in a fifth preset direction and a sixth preset direction which are diagonal lines to each other, and acquiring a fifth current response of the voltage pulse in the fifth preset direction and a sixth current response of the voltage pulse in the sixth preset direction; as well as Based on the relative magnitudes of the first current response, the second current response, the third current response, the fourth current response, the fifth current response and the sixth current response, a range of an initial rotor angle when the brushless DC motor is started is determined.

9. The method of claim 8, wherein: Determining the range of the initial rotor angle of the brushless DC motor when it is started based on the relative magnitudes of the first current response, the second current response, the third current response, the fourth current response, the fifth current response, and the sixth current response includes: Selecting a semicircle corresponding to a current response with a larger relative value between the first current response and the second current response as a first range of an initial rotor angle when the brushless DC motor is started; The semicircle corresponding to the current response with a larger relative value between the third current response and the fourth current response is selected as the second range of the initial rotor angle when the brushless DC motor is started. selecting a semicircle corresponding to a current response with a larger relative value between the fifth current response and the sixth current response as a third range of an initial rotor angle when the brushless DC motor is started; and The overlapping angle range of the first range, the second range and the third range is taken as the sector where the initial rotor angle is located.

10. The method of claim 8, wherein: Determining the range of the initial rotor angle of the brushless DC motor when it is started based on the relative magnitudes of the first current response, the second current response, the third current response, the fourth current response, the fifth current response, and the sixth current response includes: The angle range corresponding to the current response with a larger relative value among the first current response, the second current response, the third current response, the fourth current response, the fifth current response and the sixth current response is selected as the sector in which the initial rotor angle of the brushless DC motor is located when starting.

11. A method for starting a brushless DC motor, comprising: Determining a first acceleration direction in which a rotor acceleration pulse is to be applied according to the range of the initial rotor angle; as well as Selecting a preset direction next to the first acceleration direction as a first detection direction, and selecting a diagonal direction of the first detection direction as a second detection direction; Applying a rotor acceleration pulse in a first acceleration direction, and injecting a voltage pulse in the first detection direction and the second detection direction before or after applying the rotor acceleration pulse; Whether the rotor angle of the brushless DC motor reaches a commutation point where the acceleration direction needs to be changed when starting acceleration is determined according to the relative magnitudes of the first detection current response and the second detection current response.

12. The method of claim 11, wherein: In the rotor rotation direction, the first detection direction is closer to the rotor angle than the second detection direction, and determining whether the rotor angle of the brushless DC motor reaches a commutation point at which the acceleration direction needs to be changed when starting acceleration according to the relative magnitude of the first detection current response and the second detection current response includes: When the first detection current response becomes greater than the second detection current response, it is determined that the rotor angle reaches the commutation point, and the first detection direction is used as the second acceleration direction to which the rotor acceleration pulse is applied after commutation.

13. The method of claim 11, wherein: When the first detection current response does not become greater than the second detection current response within a predetermined time, the duty ratio of the rotor accelerating pulse applied in the first accelerating direction is increased.

14. A brushless DC motor, comprising: Motor; Microcontroller; Driver; Inverter; and Bus current acquisition device, The pulses sent by the microcontroller are converted by the driver into voltage pulses to act on the inverter to complete the voltage pulse injection in the first preset direction and the second preset direction which are diagonal to each other. The bus current acquisition device acquires a first current response to the voltage pulse in the first preset direction and a second current response to the voltage pulse in the second preset direction; The pulses sent by the microcontroller are converted by the driver into voltage pulses acting on the inverter to complete the voltage pulse injection in the third preset direction and the fourth preset direction which are diagonal to each other. The bus current acquisition device acquires a third current response to the voltage pulse in the third preset direction and a fourth current response to the voltage pulse in the fourth preset direction; and The microcontroller determines the rotor angle of the brushless DC motor during a startup phase according to relative magnitudes of the first current response, the second current response, the third current response, and the fourth current response.

15. An electric tool comprising a brushless DC motor started by the method according to any one of claims 1 to 13.

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