Braking method and braking device for a direct current brushless motor

Abstract

This invention provides a braking method and braking device for a brushless DC motor. The brushless DC motor includes multiple bridge arms, each bridge arm having an upper bridge arm switch and a lower bridge arm switch connected in series. The bridge arms are connected to a stator coil of the brushless DC motor through a node between the upper and lower bridge arm switches. The method includes: receiving a braking signal for braking the brushless DC motor; generating a first control signal in response to the braking signal to control all upper bridge arm switches to open or control all lower bridge arm switches to open; and generating a second control signal in response to the braking signal to control all lower bridge arm switches or all upper bridge arm switches not controlled by the first control signal to be turned on in a predetermined manner to generate a gradually increasing current in all bridge arms and all stator coils to brake the brushless DC motor.

Description

Technical Field

[0001] This invention relates to the field of electric motors, and in particular, to a braking method and braking device for a brushless DC motor. Background Technology

[0002] Brushless DC motors (BLDC) are widely used in various electric devices, such as electric vehicles, electric circular saws, and electric chainsaws.

[0003] During the use of the aforementioned electric equipment, to ensure user safety, when the equipment receives a braking signal from the user (e.g., detecting that the user has pressed a safety switch or emergency stop button, or detecting that the user has released a relevant switch button), it is usually necessary to stop the DC brushless motor of the equipment within a short period of time. That is, to rapidly brake the DC brushless motor so that the related mechanical motion caused by the DC brushless motor stops quickly. However, during the braking process of the DC brushless motor, the instantaneous current generated at the moment of braking is usually large. This large current may damage the relevant power components. In addition, the braking process can easily cause a jerking sensation in the electric equipment, resulting in a poor user experience.

[0004] Therefore, a method is needed to smoothly brake the brushless DC motor. Summary of the Invention

[0005] According to one aspect of an exemplary embodiment of the present invention, a braking method for a brushless DC motor (BLDC) is provided, the brushless DC motor including a plurality of bridge arms, each bridge arm having an upper bridge arm switch and a lower bridge arm switch connected in series, the bridge arm being connected to a stator coil of the brushless DC motor through a node between the upper bridge arm switch and the lower bridge arm switch, the method comprising: receiving a braking signal for braking the brushless DC motor; generating a first control signal in response to the braking signal to control all upper bridge arm switches to open or control all lower bridge arm switches to open; and generating a second control signal in response to the braking signal to control all lower bridge arm switches or all upper bridge arm switches not controlled by the first control signal to be turned on in a predetermined manner to generate a gradually increasing current in all bridge arms and all stator coils to brake the brushless DC motor.

[0006] According to another exemplary embodiment of the present invention, a braking device for a brushless DC motor is provided, the brushless DC motor including a plurality of bridge arms, each bridge arm having an upper bridge arm switch and a lower bridge arm switch connected in series, the bridge arm being connected to a stator coil of the brushless DC motor through a node between the upper bridge arm switches and the lower bridge arm switches, the device comprising: a first unit configured to receive a braking signal for braking the brushless DC motor; a second unit configured to generate a first control signal in response to the braking signal to control all upper bridge arm switches to disconnect or control all lower bridge arm switches to disconnect; and a third unit configured to generate a second control signal in response to the braking signal to control all lower bridge arm switches or all upper bridge arm switches not controlled by the first control signal to be turned on in a predetermined manner to generate a gradually increasing current in all bridge arms and all stator coils to brake the brushless DC motor.

[0007] According to another aspect of an exemplary embodiment of the present invention, a computer-readable medium storing instructions that, when executed by a processor, cause the processor to perform the braking method for a brushless DC motor described above according to embodiments of the present disclosure.

[0008] According to an exemplary embodiment of the present invention, a braking method and braking device for a brushless DC motor can short-circuit each stator coil of the brushless DC motor by controlling the upper bridge arm switch and the lower bridge arm switch, and generate a gradually increasing current in the short-circuit circuit to brake the brushless DC motor. This enables the brushless DC motor to brake smoothly without jerking, improving device safety and user experience during the braking process of the brushless DC motor. Attached Figure Description

[0009] The invention can be better understood from the following description of specific embodiments of the invention in conjunction with the accompanying drawings, wherein:

[0010] Figure 1 A schematic diagram of braking a brushless DC motor (BLDC) according to an exemplary embodiment is shown.

[0011] Figure 2 A schematic diagram of control signals and currents for a brushless DC motor according to an exemplary embodiment is shown.

[0012] Figure 3 A flowchart of a braking method for a brushless DC motor according to an exemplary embodiment of the present invention is shown.

[0013] Figure 4 A schematic diagram of the control signals and currents of a brushless DC motor according to an exemplary embodiment of the present invention is shown.

[0014] Figure 5 A schematic diagram of the control signals and currents of a brushless DC motor according to another exemplary embodiment of the present invention is shown.

[0015] Figure 6 A block diagram of a braking device for a brushless DC motor according to an exemplary embodiment of the present invention is shown. Detailed Implementation

[0016] The features and exemplary embodiments of various aspects of the present invention will now be described in detail. Numerous specific details are set forth in the following detailed description to provide a thorough understanding of the invention. However, it will be apparent to those skilled in the art that the invention may be practiced without requiring some of these specific details. The following description of embodiments is merely intended to provide a better understanding of the invention by illustrating examples of the invention. The invention is by no means limited to any specific configurations and algorithms presented below, but covers any modifications, substitutions, and improvements to elements, components, and algorithms without departing from the spirit of the invention. Well-known structures and techniques are not shown in the drawings and the following description in order to avoid unnecessarily obscuring the invention.

[0017] Figure 1 A schematic diagram of braking a brushless DC motor (BLDC) according to an exemplary embodiment is shown.

[0018] like Figure 1 As shown, the brushless DC motor 100 includes three bridge arms H1, H2, and H3. An upper bridge arm switch U+ and a lower bridge arm switch U- are connected in series on bridge arm H1; an upper bridge arm switch V+ and a lower bridge arm switch V- are connected in series on bridge arm H2; and an upper bridge arm switch W+ and a lower bridge arm switch W- are connected in series on bridge arm H3. Each upper bridge arm switch U+, V+, and W+ is shown as being in the open state, and each lower bridge arm switch U-, V-, and W- is shown as being in the closed state.

[0019] Bridge arm H1 is connected to the stator coil U of the brushless DC motor 100 via node N1 between the upper bridge arm switch U+ and the lower bridge arm switch U-. Bridge arm H2 is connected to the stator coil V of the brushless DC motor 100 via node N2 between the upper bridge arm switch V+ and the lower bridge arm switch V-. Bridge arm H3 is connected to the stator coil W of the brushless DC motor 100 via node N3 between the upper bridge arm switch W+ and the lower bridge arm switch W-. Figure 1 In this system, each stator coil is indicated by U, V, and W on the connection lines between the stator coil and the corresponding node.

[0020] The rotor of the DC brushless motor 100 is a permanent magnet. Figure 1(Not shown) When braking a brushless DC motor, the stator coils are typically short-circuited, causing a current to flow through the rotating rotor in the short-circuit circuit. This converts the rotor's mechanical energy (kinetic energy) into heat energy in the circuit, reducing the rotor's rotational speed until it stops, thus braking the brushless DC motor. This braking process is commonly used in scenarios requiring rapid braking, such as stopping the brushless DC motor within 1 to 2 seconds or less. In some cases, this braking process is referred to as electronic braking.

[0021] Figure 1 Taking the example of the upper bridge arm switches U+, V+, and W+ all being open and the lower bridge arm switches U-, V-, and W- all being closed, the braking of a brushless DC motor 100 is illustrated. In this case, each stator coil in the brushless DC motor 100 is short-circuited, and the current flow in the short-circuit circuit is as follows: Figure 1 As shown by the dashed arrow in the image.

[0022] For example, the upper and lower bridge arm switches used in brushless DC motors are typically power devices, such as power transistors, e.g., NMOS or PMOS transistors. In this case, the switching on and off of each power transistor can be controlled by a control signal applied to the gate of each power transistor.

[0023] Figure 2 A schematic diagram of control signals and currents for a brushless DC motor according to an exemplary embodiment is shown.

[0024] exist Figure 2 In the middle, control signal G U- G V- and G W- respectively applied to Figure 1 The control signals of each lower bridge arm switch U-, V- and W-, and each control signal G U- G V- and G W- They are identical. Current i U The current in the stator coil U is, i.e. Figure 2 The current in the short-circuit circuit during the braking process of a brushless DC motor is illustrated using stator coil U as an example (it should be understood that the current in other stator coils is similar). The bottom horizontal axis represents the time axis t.

[0025] At time t0, the brushless DC motor 100 receives a braking signal. At this time, the upper and lower bridge arm switches can be controlled as follows: Figure 1The on and off states are shown. For example, when each bridge arm switch is an NMOS transistor, a low-level signal can be applied to the gates of each upper bridge arm switch U+, V+, and W+, and a low-level signal can be applied to the gates of each lower bridge arm switch U-, V-, and W-. Figure 2 The high-level signal G shown U- G V- and G W- This allows each upper and lower bridge arm switch to have the following characteristics: Figure 1 The on and off states are shown.

[0026] At this time, the rotation of the rotor of the brushless DC motor 100 will generate an induced electromotive force voltage V in the stator coil U. U As shown in the following equation (1):

[0027] V U =k e ×RPM×sinθ (1)

[0028] In equation (1), V U The induced electromotive force voltage of the stator coil U is k. e RPM is the induced electromotive force constant of the brushless DC motor 100, θ is the rotor speed, and θ is the rotor angle (relative to the predetermined angle origin).

[0029] The induced electromotive force voltage V generated above U This results in a current i being generated in the stator coil U. U According to the volt-second law, the current i U The following equation (2) must be satisfied:

[0030] L×i U =V U ×t (2)

[0031] In equation (2), i U Let U be the current in the stator coil U, L be the inductance of the stator coil, and t be the braking time of the DC brushless motor.

[0032] Transforming equation (2), we obtain the following equation (3):

[0033] i U =V U ×t / L (3)

[0034] Substituting equation (1) into equation (3), we obtain the following equation (4):

[0035] i U =k e ×RPM×sinθ×t / L (4)

[0036] During the braking process of a brushless DC motor, the rotor speed (RPM) changes with time, and the rotor angle (θ) also changes with time. e Since L is a constant, equation (4) can be transformed into an integral over time t, as shown in equation (5) below:

[0037] i U =(k e / L)×∫(RPM×sinθ)dt (5)

[0038] Therefore, at the instant of braking the brushless DC motor, i.e., near time t0, the current i U It has an instantaneous maximum value, after which the current i U The current value gradually decreases, such as Figure 2 As shown.

[0039] As described above, the instantaneous high current can cause a large current surge to the power devices of a brushless DC motor (e.g., the switched-on lower bridge arm switches U-, V-, and W-), thereby reducing the lifespan of the power devices or even damaging them.

[0040] Furthermore, this large instantaneous current causes the rotor's rotational kinetic energy to be rapidly converted into heat energy in the short-circuit circuit, resulting in a rapid decrease in the rotor's speed. This generates a large braking impact force on the relevant mechanical shafts and gears of the brushless DC motor, leading to wear on these components and a jerky feeling, resulting in a poor user experience.

[0041] To at least partially overcome the above-mentioned drawbacks, an exemplary embodiment of this application provides a braking method for a brushless DC motor.

[0042] Figure 3 A flowchart of a braking method for a brushless DC motor according to an exemplary embodiment of the present invention is shown.

[0043] like Figure 3 The braking method shown is applicable to, for example... Figure 1 The brushless DC motor 100 shown includes multiple bridge arms. Figure 1 The diagram shows three bridge arms (but this application is not limited to this), and each bridge arm has an upper bridge arm switch connected in series (e.g., ...). Figure 1 The upper arm switch (U+, V+, or W+) and the lower arm switch (e.g., Figure 1 The lower bridge arm switch (U-, V-, or W-) is connected to each bridge arm via a node between its upper and lower bridge arm switches (e.g., Figure 1 Nodes N1, N2, or N3 in the diagram are connected to a stator coil of a brushless DC motor (e.g., Figure 1 (Stator coils U, V, or W in the middle).

[0044] like Figure 3 As shown, in step S110, a braking signal for braking the brushless DC motor is received.

[0045] For example, the braking signal could be generated when the user presses the safety switch button or emergency stop switch button, or when the user releases the relevant switch button.

[0046] In step S120, a first control signal is generated in response to the braking signal to control all upper arm switches to open or control all lower arm switches to open.

[0047] In one embodiment, the first control signal is a signal with a constant level.

[0048] For example, it can be similar to... Figure 1 and Figure 2 As shown, a first control signal is used to control all upper bridge arm switches to disconnect. When the upper bridge arm switches are all power transistors, such as NMOS transistors, the first control signal can be a constant low-level signal.

[0049] In step S130, a second control signal is generated in response to the braking signal to control all lower bridge arm switches or all upper bridge arm switches not controlled by the first control signal to be turned on in a predetermined manner to generate a gradually increasing current in all bridge arms and all stator coils to brake the brushless DC motor.

[0050] It should be understood that Figure 1 Steps S120 and S130 can be executed simultaneously.

[0051] For example, while the first control signal controls all upper bridge arm switches to be disconnected, the second control signal can be used to control all lower bridge arm switches to be connected in the predetermined manner, so as to generate a gradually increasing current in the short-circuit loop formed by each bridge arm and each stator coil, so as to brake the brushless DC motor.

[0052] The braking method for a brushless DC motor according to an exemplary embodiment of the present invention can short-circuit each stator coil of the brushless DC motor by controlling the upper bridge arm switch and the lower bridge arm switch, and generate a gradually increasing current in the short-circuit circuit to brake the brushless DC motor. This enables the brushless DC motor to brake smoothly without jerking, improving device safety and user experience during the braking process of the brushless DC motor.

[0053] In one embodiment, the second control signal generated in step S130 can be a pulse width modulation (PWM) signal.

[0054] In order to generate a gradually increasing current in the short-circuit loop by controlling the pulse width modulation signal, in one embodiment, the frequency of the pulse width modulation signal may be greater than a predetermined threshold. This predetermined threshold can be set according to the duration of the braking time required for the brushless DC motor to complete braking.

[0055] For example, if the braking time of a brushless DC motor is required to be 100 milliseconds, the predetermined threshold can be set to the frequency value corresponding to a period of 100 microseconds. In other words, the period corresponding to the frequency of the predetermined threshold can be approximately two orders of magnitude smaller than the duration of the braking time.

[0056] It should be understood that the above braking time period and the size of the predetermined threshold are just examples, and the braking time period and the predetermined threshold can be set to any other value according to actual needs.

[0057] In addition, to ensure user safety, braking is required immediately upon receiving the braking signal. Therefore, in one embodiment, the start time (t0) of the braking time period can be the time when the braking signal is received, and the end time (t2) of the braking time period can be determined based on the duration and start time of the braking time period.

[0058] In this case, in order to obtain the above-mentioned gradually increasing current, in one embodiment, the duty cycle of the pulse width modulation signal can be gradually increased during the first time period from the start time (t0) to the first time (t1) within the braking time period, so that the turn-on time of all lower bridge arm switches or all upper bridge arm switches controlled by the second control signal is gradually increased, so as to generate a gradually increasing current in all bridge arms and all stator coils.

[0059] For example, within the first time period, the duty cycle of the pulse width modulation signal can be adjusted cycle by cycle, or the duty cycle of the pulse width modulation signal can be adjusted at predetermined intervals.

[0060] In addition, in order to ensure the duration requirement of the above braking time period and improve braking efficiency, in one embodiment, the duty cycle of the pulse width modulation signal can be 1 during the second time period from the first time (t1) to the cutoff time (t2) within the braking time period, so that the current generated on all bridge arms and all stator coils during the second time period has the maximum current value during the braking time period.

[0061] In other words, during the second time period, a constant-level control signal can be applied to each of the corresponding lower bridge arm switches (or upper bridge arm switches) to keep each lower bridge arm switch in the ON state, thereby improving the braking efficiency of the brushless DC motor. For example, the first time period can be set to a time period that allows the current in the short-circuit circuit to gradually increase to near the maximum current value, thereby ensuring the stability and efficiency of braking.

[0062] Figure 4 A schematic diagram of the control signals and currents of a brushless DC motor according to an exemplary embodiment of the present invention is shown.

[0063] and Figure 2 Similarly, Figure 4 Let's take stator coil U as an example for explanation. It should be understood that other stator coils are similar.

[0064] Figure 4 The second control signal G U- G V- and G W- (wherein, control signal G) U- G V- and G W- (The signals are identical to each other) are pulse width modulation signals, whose duty cycle gradually increases during the first time interval from time t0 to time t1, causing the current i U The current gradually increases. During the second time interval from time t1 to time t2, the duty cycle of the second control signal is 1. Near time t1, the current reaches its maximum value, then gradually decreases until the braking of the brushless DC motor ends at time t2. It should be understood that, for simplicity and ease of understanding, Figure 4 (and Figure 2 The control signal of the lower bridge arm switch and the change in current of the stator coil U are shown only schematically, and the entire process of current change is not shown.

[0065] Reference Figure 3 and Figure 4 In one embodiment, to shorten the actual braking time, the ratio of the first time period to the second time period can be made less than a predetermined value. For example, the predetermined threshold can be 1 / 10 or any other value less than 1.

[0066] Furthermore, in one embodiment, the first time t1 and the initial duty cycle can be set according to the rotational speed of the brushless DC motor and the duration of the braking period. For example, the initial duty cycle can be set to any value between 0% and 10%.

[0067] It should be understood that the above settings for the first time and initial duty cycle are just examples, and the first time and initial duty cycle can be set to any other value according to actual needs.

[0068] By using the above methods, the braking of the brushless DC motor can have a smaller instantaneous current, reducing the current surge on the power devices of the brushless DC motor and increasing the service life of the power devices.

[0069] Furthermore, as the duty cycle of the second control signal gradually increases during the first time period, the heat generated in the stator coil gradually increases, as shown in the following equation (6):

[0070] P = (V U ×Duty)×(V U ×Duty) / r (6)

[0071] In equation (6), Duty represents the duty cycle, P can represent the heat energy (braking power) generated in the stator coil U during the short-circuit time period corresponding to the duty cycle, and r represents the equivalent resistance of the short-circuit circuit.

[0072] The gradual increase in heat energy in the short-circuit circuit indicates that the kinetic energy of the DC brushless motor rotor is gradually decreasing. Therefore, the braking process of the DC brushless motor can be performed smoothly, which improves the stability of the DC brushless motor braking, reduces the jerking sensation, and improves the user experience.

[0073] Figure 4 The illustration shows an embodiment where each upper bridge arm switch is off and each lower bridge arm switch is on. This application is also applicable to embodiments where each upper bridge arm switch is on and each lower bridge arm switch is off.

[0074] Figure 5 A schematic diagram of the control signals and currents of a brushless DC motor according to another exemplary embodiment of the present invention is shown.

[0075] and Figure 2 and Figure 4 Similarly, Figure 5 Let's take stator coil U as an example for explanation. It should be understood that other stator coils are similar.

[0076] Figure 5 The second control signal is the control signal G used to control the connection of each upper bridge arm. U+ G V+ and G W+ Among them, the control signal G U+ G V+ and G W+ They are the same. Figure 5 In the illustrated embodiment, with Figure 4 Similarly, as shown, the current i in the stator coil U can also be made... U Gradually increase, thereby achieving the same Figure 4 The same braking effect is shown.

[0077] Figure 6 A block diagram of a braking device 600 for a brushless DC motor according to an exemplary embodiment of the present invention is shown.

[0078] like Figure 6 As shown, the braking device 600 for a brushless DC motor according to an embodiment of the present disclosure includes a first unit 610, a second unit 620 and a third unit 630.

[0079] The first unit 610 is configured to receive a braking signal for braking a brushless DC motor.

[0080] The second unit 620 is configured to generate a first control signal in response to a braking signal to control all upper arm switches to open or control all lower arm switches to open.

[0081] In one embodiment, the first control signal can be a signal with a constant level.

[0082] The third unit 630 is configured to generate a second control signal in response to a braking signal to control all lower arm switches or all upper arm switches not controlled by the first control signal to be turned on in a predetermined manner to generate a gradually increasing current in all arms and all stator coils to brake the brushless DC motor.

[0083] In one embodiment, the second control signal may be a pulse width modulation signal.

[0084] In one embodiment, the frequency of the pulse width modulation signal can be greater than a predetermined threshold. The predetermined threshold can be set according to the duration of the braking time required for the brushless DC motor to complete braking.

[0085] In one embodiment, the frequency of the pulse width modulation signal can be a fixed frequency or a frequency that varies with time.

[0086] In one embodiment, the start time of the braking period can be the time when the braking signal is received, and the end time of the braking period can be determined based on the duration and the start time.

[0087] In one embodiment, during the first time period from the start time to the first time during the braking time period, the duty cycle of the pulse width modulation signal can be gradually increased so that the on-time of all lower bridge arm switches or all upper bridge arm switches controlled by the second control signal gradually increases, thereby generating a gradually increasing current in all bridge arms and all stator coils.

[0088] Furthermore, in one embodiment, during the second time period from the first time to the cutoff time within the braking time period, the duty cycle of the pulse width modulation signal can be 1, such that the current generated on all bridge arms and all stator coils during the second time period has the maximum current value during the braking time period.

[0089] In one embodiment, the ratio of the first time period to the second time period may be less than a predetermined value.

[0090] In one embodiment, the first time and the initial duty cycle can be set according to the speed of the brushless DC motor and the duration.

[0091] The above has been referred to Figures 3 to 5 The first control signal, the second control signal, and specific examples of the braking process have been described in detail and will not be repeated here. In other words, the braking device for a brushless DC motor according to embodiments of this disclosure can perform the actions described above. Figures 3 to 5 The braking method for a brushless DC motor.

[0092] According to an exemplary embodiment of the present invention, a braking device for a brushless DC motor can short-circuit each stator coil of the brushless DC motor by controlling the upper bridge arm switch and the lower bridge arm switch, and generate a gradually increasing current in the short-circuit circuit to brake the brushless DC motor. This enables the brushless DC motor to brake smoothly without jerking, improving device safety and user experience during the braking process of the brushless DC motor.

[0093] According to embodiments of the present disclosure, a computer-readable medium storing instructions that, when executed by a processor, cause the processor to perform the braking method for a brushless DC motor described above according to embodiments of the present disclosure.

[0094] It should be understood that this disclosure is not limited to the specific configurations and processes described above and shown in the figures. For the sake of brevity, detailed descriptions of known methods are omitted here. In the above embodiments, several specific steps are described and shown as examples. However, the method process of the present invention is not limited to the specific steps described and shown, and those skilled in the art can make various changes, modifications, and additions, or change the order of steps, after understanding the spirit of the present invention.

[0095] The functional blocks shown in the above-described structural diagram can be implemented as hardware, software, firmware, or a combination thereof. When implemented in hardware, they can be, for example, electronic circuits, application-specific integrated circuits (ASICs), appropriate firmware, plug-ins, function cards, etc. When implemented in software, the elements of this invention are programs or code segments used to perform the required tasks. The programs or code segments can be stored on a machine-readable medium or transmitted over a transmission medium or communication link via data signals carried in a carrier wave. "Machine-readable medium" can include any medium capable of storing or transmitting information. Examples of machine-readable media include electronic circuits, semiconductor memory devices, ROM, flash memory, erasable ROM (EROM), floppy disks, CD-ROMs, optical disks, hard disks, fiber optic media, radio frequency (RF) links, etc. Code segments can be downloaded via computer networks such as the Internet, intranets, etc.

[0096] This invention can be implemented in other specific forms without departing from its spirit and essential characteristics. For example, the algorithm described in a particular embodiment can be modified without departing from the basic spirit of the invention. Therefore, the present embodiments are to be regarded as exemplary rather than limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description, and all changes falling within the meaning and scope of the claims and their equivalents are thus included within the scope of the invention.

Claims

1. A braking method for a brushless DC motor, the brushless DC motor comprising a plurality of bridge arms, each bridge arm having an upper bridge arm switch and a lower bridge arm switch connected in series, the bridge arm being connected to a stator coil of the brushless DC motor through a node between the upper bridge arm switch and the lower bridge arm switch, the method comprising: Receive a braking signal for braking the brushless DC motor; In response to the braking signal, a first control signal is generated to control all upper arm switches to open or control all lower arm switches to open. as well as In response to the braking signal, a second control signal is generated to control all lower arm switches or all upper arm switches not controlled by the first control signal to be turned on in a predetermined manner, so as to generate a gradually increasing current in all arms and all stator coils to brake the brushless DC motor. The second control signal is a pulse width modulation signal, the frequency of which is greater than a predetermined threshold, and the duration of the period corresponding to the frequency of the predetermined threshold is two orders of magnitude smaller than the duration of the braking time required for the brushless DC motor to complete braking.

2. The braking method according to claim 1, wherein, The start time of the braking period is the time when the braking signal is received, and the end time of the braking period is determined based on the duration and the start time.

3. The braking method according to claim 2, wherein, During the braking period, from the start time to the first time, the duty cycle of the pulse width modulation signal gradually increases, so that the turn-on time of all lower bridge arm switches or all upper bridge arm switches controlled by the second control signal gradually increases, so as to generate a gradually increasing current in all bridge arms and all stator coils.

4. The braking method according to claim 3, wherein, During the second time period from the first time to the cutoff time within the braking time period, the duty cycle of the pulse width modulation signal is 1, such that the current generated on all bridge arms and all stator coils during the second time period has the maximum current value during the braking time period.

5. The braking method according to claim 4, wherein, The ratio of the first time period to the second time period is less than a predetermined value.

6. The braking method according to any one of claims 3-5, wherein, The first time and the initial duty cycle are set according to the rotational speed of the brushless DC motor and the duration.

7. The braking method according to any one of claims 2-5, wherein, The frequency of the pulse width modulation signal is a fixed frequency or a frequency that varies with time.

8. The braking method according to any one of claims 1-5, wherein, The first control signal is a signal with a constant level.

9. A braking device for a brushless DC motor, the brushless DC motor comprising a plurality of bridge arms, each bridge arm having an upper bridge arm switch and a lower bridge arm switch connected in series, the bridge arm being connected to a stator coil of the brushless DC motor through a node between the upper bridge arm switch and the lower bridge arm switch, the device comprising: The first unit is configured to receive a braking signal for braking the brushless DC motor. The second unit is configured to generate a first control signal in response to the braking signal to control all upper arm switches to disconnect or control all lower arm switches to disconnect. as well as The third unit is configured to generate a second control signal in response to the braking signal, to control all lower arm switches or all upper arm switches not controlled by the first control signal to be turned on in a predetermined manner, so as to generate a gradually increasing current in all arms and all stator coils to brake the brushless DC motor. The second control signal is a pulse width modulation signal, the frequency of which is greater than a predetermined threshold, and the duration of the period corresponding to the frequency of the predetermined threshold is two orders of magnitude smaller than the duration of the braking time required for the brushless DC motor to complete braking.

10. A computer-readable medium storing instructions that, when executed by a processor, cause the processor to perform the braking method according to any one of claims 1-8.

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