Brushless non-inductive motor control method and electric tool

Abstract

The invention relates to a brushless non-inductive motor control method and an electric tool. According to the technical scheme, the method is based on a control device, the method is used for controlling a motor, and the control method is characterized by comprising the following steps: sequentially applying voltage to three phases of the motor; detecting a voltage value of a suspended phase in the three phases of the motor; when the voltage value of the suspended phase is larger than half of the bus voltage value and smaller than a first voltage threshold value, it is judged that the motor passes through a zero crossing point; therefore, the protection probability of the motor under a large load is effectively reduced, and the customer experience is improved.

Description

Technical Field

[0001] The present application relates to the technical field of electric tools, and in particular to a brushless sensorless motor control method and an electric tool. Background Art

[0002] An electric wrench is an electric tool that uses a motor to quickly tighten or loosen bolts / nuts. It is widely used in engineering fields such as construction, mechanical assembly, and power maintenance.

[0003] In the related art, Chinese patent publication number CN1236338A discloses a portable impact tool driver that is movably connected to the shaft or drive spindle of an existing power tool. The impact tool driver has a driver body, on which a drive shaft is configured so as to be rotationally driven. A hammer element is rotatably engaged with the drive shaft and is rotationally driven thereby. The hammer element is axially movable along the drive shaft. The hammer element has a first impact surface on which at least two impact drivers are provided. An engagement drive mechanism is disposed between the drive shaft and the hammer element and transmits rotation and longitudinal movement to the hammer element. An anvil element has a second impact surface opposite to the first impact surface, on which an impact receiver is provided for periodic impact engagement with the impact driver.

[0004] However, when the current electric wrench is used in a cold weather environment, the controller inside the electric wrench often goes into protection mode, which affects the user experience and needs to be improved. Summary of the Invention

[0005] Based on this, it is necessary to provide a brushless sensorless motor control method and an electric tool to address the problem of frequent protection of the controller.

[0006] In order to solve the above technical problems, this application is implemented as follows: In one embodiment, a brushless sensorless motor control method is provided. The method is based on a control device and is used to control the motor. The control method includes: applying voltage to the three phases of the motor in sequence; detecting a voltage value of a suspended phase among the three phases of the motor; When the voltage value of the suspended phase is greater than half of the bus voltage value and less than a first voltage threshold, it is determined that the motor has passed the zero crossing point.

[0007] In one or other preferred embodiments, when the voltage value of the suspended phase is greater than half of the bus voltage value and less than a first voltage threshold, determining that the motor has passed the zero crossing point includes: When the voltage value of the suspended phase is greater than half of the bus voltage value, and then the voltage value of the suspended phase is greater than half of the bus voltage value and less than the first voltage threshold, it is determined that the motor has passed the zero point.

[0008] In one or other preferred embodiments, when the voltage value of the suspended phase is greater than half of the bus voltage value, and the voltage value of the suspended phase is greater than half of the bus voltage value and less than the first voltage threshold, determining that the motor has passed the zero crossing point includes: After the voltage value of the suspended phase is greater than the bus voltage value, when the voltage value of the suspended phase is greater than half of the bus voltage value and the voltage value of the suspended phase is less than a first voltage threshold, it is determined that the motor has passed the zero point.

[0009] In one or other preferred embodiments, it is characterized in that, after detecting the voltage value of the suspended phase among the three phases of the motor, the method further includes: After the voltage value of the suspended phase is greater than half of the bus voltage value, if the voltage value of the suspended phase has an edge jump, the time value when the voltage value of the suspended phase is equal to half of the bus voltage value during the rising process is recorded, and the commutation period is calculated based on the time value; The motor commutation is controlled based on the commutation period.

[0010] In one or other preferred embodiments, after the voltage value of the suspended phase is greater than half of the bus voltage value, the method further includes: When the first time threshold expires, if the voltage value of the suspended phase does not undergo an edge jump, then when the voltage value of the suspended phase is greater than half of the bus voltage value and less than the first voltage threshold, it is determined that the motor has passed the zero crossing point; The first time threshold is a time value inversely proportional to a time value of a previous cycle, and the inverse proportion is greater than 1 / 2.

[0011] In one or other preferred embodiments, the edge transition includes: The voltage value of the suspended phase is less than half of the bus voltage value; The voltage value of the suspended phase is greater than half of the bus voltage value.

[0012] In one or other preferred embodiments, detecting the voltage value of the suspended phase among the three phases of the motor further includes: After the second time threshold expires, detecting a voltage value of a suspended phase among the three phases of the motor; When the voltage value of the suspended phase is less than the bus voltage value, if the voltage value of the suspended phase is greater than or equal to half of the bus voltage value, the current moment value is recorded, and the commutation period is calculated based on the current moment value; controlling the commutation of the motor based on the commutation period; The second time threshold is a time value inversely proportional to a time value of a previous cycle, and the inverse proportion is less than 1 / 2.

[0013] In one or other preferred embodiments, the control method further includes: If after the third time threshold, the voltage value of the suspended phase is always greater than the first voltage threshold, the motor is forcibly controlled to commutate.

[0014] In one or other preferred embodiments, after determining that the motor has passed the zero point, the method further includes: Control the motor to commutate directly; or, Controlling the motor to perform phase commutation after a first time value has passed; The first time value is calculated by using the duration of the previous cycle and the first angle threshold.

[0015] On the other hand, based on the same inventive concept, the present application also discloses an electric tool, comprising: shell; a motor, at least partially housed in the housing; A transmission mechanism, connected to the output shaft of the motor and outputting power to the outside; The control device is housed in the housing and executes the brushless sensorless motor control method described in any one of the above embodiments.

[0016] In the embodiment of the present application, the voltage of the suspended phase is detected for judgment, so that even after the zero point is submerged by the long freewheeling current, the control device can be informed that the zero point has been passed and process it in time, thereby greatly reducing the probability of protection of the control device. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 1 is a flow chart of a brushless sensorless motor control method according to an embodiment of the present application; Figure 2 1 is a flow chart of a brushless sensorless motor control method in another embodiment of the present application; Figure 3 1 is a flow chart of a brushless sensorless motor control method in another embodiment of the present application; Figure 4 The diagram shows a brushless sensorless motor control method and a power tool. DETAILED DESCRIPTION

[0018] To make the above-mentioned objects, features, and advantages of the present application more clearly understood, the specific embodiments of the present application are described in detail below with reference to the accompanying drawings. The following description sets forth many specific details to facilitate a full understanding of the present application. However, the present application can be implemented in many other ways than those described herein, and those skilled in the art can make similar improvements without violating the scope of the present application. Therefore, the present application is not limited to the specific embodiments disclosed below.

[0019] In the description of the present application, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present application.

[0020] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of such features. Throughout the description of this application, "plurality" means at least two, for example, two, three, etc., unless otherwise specifically defined.

[0021] In this application, unless otherwise specified or limited, the terms "installed," "connected," "connect," "fixed," etc. should be understood in a broad sense. For example, they can refer to fixed connection, detachable connection, or integration; mechanical connection or electrical connection; direct connection or indirect connection through an intermediate medium; internal communication between two elements or interaction between two elements, unless otherwise specified. Those skilled in the art will understand the specific meanings of the above terms in this application based on specific circumstances.

[0022] In this application, unless otherwise expressly specified or limited, when a first feature is "above" or "below" a second feature, it may mean that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Furthermore, when a first feature is "above," "above," or "above" a second feature, it may mean that the first feature is directly above or diagonally above the second feature, or simply means that the first feature is at a higher level than the second feature. When a first feature is "below," "below," or "below" a second feature, it may mean that the first feature is directly below or diagonally below the second feature, or simply means that the first feature is at a lower level than the second feature.

[0023] It should be noted that when an element is referred to as being "fixed to" or "disposed on" another element, it may be directly on the other element or there may be an intermediate element. When an element is considered to be "connected to" another element, it may be directly connected to the other element or there may be an intermediate element. The terms "vertical," "horizontal," "upper," "lower," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only implementation methods.

[0024] In an embodiment of the present application, a brushless and sensorless motor control method is disclosed, which is used to solve the problem of frequent protection caused by the motor entering a heavy load after startup. Based on the cause analysis, after the motor is started, if the load on the output shaft of the motor is too large, the current in the motor coil is also correspondingly large. When the motor is commutated, the induced electromotive force generated by electromagnetic induction is also large. The time for the corresponding induced electromotive force to pass through the freewheeling diode will be extended, and it may extend all the way to the zero-crossing point of the motor commutation, causing the zero-crossing point to be submerged in the freewheeling process, resulting in inaccurate motor commutation time, and then causing the current in the motor coil to reach the protection point and trigger protection. The present application focuses on such background research and provides a solution that can solve the above problems. In addition, the execution subject of the method is a control device. In particular, the present application uses an electric tool as an example for explanation, and the control device here is the controller in the electric tool.

[0025] See Figure 1 FIG1 shows a flow chart of a brushless sensorless motor control method according to an embodiment of the present application. The brushless sensorless motor control method provided by an embodiment of the present application includes the following steps: Step 110: Apply voltage to the three phases of the motor in sequence.

[0026] Specifically, the control device first applies voltage to the three phases of the motor in sequence. This voltage application is accomplished by controlling the power transistors corresponding to the motors to be supplied with voltage, thereby applying the battery pack voltage to the corresponding phases of the motor. The order in which the control device applies voltage to the motors is fixed and can be determined by a pre-stored program in the control device.

[0027] Step 120, detecting the voltage value of the suspended phase among the three phases of the motor; Specifically, when the control device applies voltage to the motor, one phase is inevitably left floating to discharge the voltage. Therefore, detecting the voltage value of the floating phase can serve as the basis for motor commutation. The floating phase here is determined by the control device. When the control device energizes two phases of the motor, the other phase becomes the floating phase. By detecting the voltage of the floating phase among the three phases of the motor, the position of the motor rotor can be determined, facilitating the commutation operation.

[0028] Step 130: When the voltage value of the suspended phase is greater than half of the bus voltage value and less than a first voltage threshold, it is determined that the motor has passed the zero crossing point.

[0029] Specifically, after the control device detects the voltage value of the suspended phase among the three phases of the motor, when the voltage value of the idle phase is greater than half of the bus voltage value and less than the first voltage threshold, it indicates that the rotor of the motor has passed the zero point. Generally speaking, in the control process of the motor, when the power tube is turned on, half of the bus voltage value is defined as the zero point. The reason is that at this time, the suspended phase opposite electromotive force is 0, and the other two opposite electromotive forces cancel each other out. In the absence of a large load, the voltage of the suspended phase will gradually increase from 0 to the bus voltage, and the control device defines the rotor rotation as passing the zero point at half of the bus voltage, and controls the rotor commutation when the suspended phase voltage increases to the bus voltage. Since the motor usually has three phases, it is necessary to control the three corresponding stator poles to change the direction of the magnetic field to drive the movement of the rotor in the stator. Therefore, the control of the motor is repeated with a rotation of 60° as a control cycle.

[0030] In order to control the motor more accurately, in one or other preferred embodiments, step 130 may further include: When the voltage value of the suspended phase is greater than half of the bus voltage value, and then the voltage value of the suspended phase is greater than half of the bus voltage value and less than the first voltage threshold, it is determined that the motor has passed the zero point.

[0031] Specifically, after the control device detects the voltage value of the suspended phase among the three phases of the motor, when the voltage value of the suspended phase is greater than half of the bus voltage value, and the voltage value of the suspended phase is greater than half of the bus voltage value and less than the first voltage threshold, it determines that the motor has passed the zero point. Here, before the control device detects that the voltage value of the suspended phase is greater than half of the bus voltage value and less than the first voltage threshold, it will pre-detect that the voltage of the suspended phase is greater than half of the bus voltage value. The reason is that the suspended phase is the conducting phase before commutation, and the motor is an inductive device. The inductive current cannot change suddenly. Therefore, in the current state, the suspended phase continues to flow. Therefore, before detecting that the voltage value of the suspended phase is greater than half of the bus voltage value and less than the first voltage threshold, the voltage value of the suspended phase will be pulled up by the continuous flow and become greater than half of the bus voltage value.

[0032] In order to control the motor more accurately, in one or other preferred embodiments, the above steps may further include: When the voltage value of the suspended phase is greater than the bus voltage value, and then the voltage value of the suspended phase is greater than half of the bus voltage value and less than the first voltage threshold, it is determined that the motor has passed the zero point.

[0033] Specifically, after the control device detects the voltage value of the suspended phase in the three phases of the motor, when the voltage value of the suspended phase is greater than half of the bus voltage value, and when the voltage value of the suspended phase is greater than half of the bus voltage value and less than the first voltage threshold, it determines that the motor has passed the zero point. Here, before the control device detects that the voltage value of the suspended phase is greater than half of the bus voltage value and less than the first voltage threshold, it will pre-detect that the voltage of the suspended phase is greater than the bus voltage value. The reason is that the basis for the generation of freewheeling is that the inductance formed by the coil in the suspended phase of the motor generates an induced electromotive force due to Lenz's law. This induced electromotive force needs to be discharged through the freewheeling diode connected in parallel on the two poles of the power tube, so at this time, the voltage of the suspended phase minus the voltage drop of the freewheeling diode is equal to the bus voltage value, so the voltage of the suspended phase at this time must be greater than the bus voltage value. When the voltage value of the suspended phase is greater than the bus voltage value, it means that the suspended phase has entered the freewheeling state.

[0034] In particular, the first voltage threshold can be any value between half the bus voltage value and the bus voltage value. In the embodiment of the present application, the first voltage threshold is 7 / 8 of the bus voltage value, or the bus voltage value can be directly selected as the first voltage threshold. By superimposing the conditions, it is determined that the current moment has passed the zero crossing point, thereby improving the accuracy of the motor commutation and reducing the probability of the motor protection occurring.

[0035] In order to perform real-time control on the motor during the motor control process, in one or other preferred embodiments, step 130 further includes: Step 140: Control the motor to directly perform commutation; or, Controlling the motor to perform phase commutation after a first time value has passed; The first time value is calculated by using the duration of the previous cycle and the first angle threshold.

[0036] Specifically, after determining that the motor has passed the zero point, the control device can control the motor to directly perform phase change. When the motor directly performs phase change, it means that the current cycle has ended, and another phase will stop being energized and enter the suspended phase. At this time, the above-mentioned phase change detection operation is repeated. At the same time, the current cycle is also used as a criterion for the control device to make judgments in the next cycle. In order to improve the torque of the motor, the control device often chooses to directly perform phase change after determining that the rotor of the motor has passed the zero point. In addition, the control device can also control the motor to perform phase change after a first time value after determining that the motor has passed the zero point; the first time value here can be calculated by the length of the previous cycle and the first angle threshold. The rotor speed can be calculated by the length of the previous cycle. Since the two adjacent cycles are close, the speed of the current cycle can refer to the speed of the previous cycle. The first angle threshold can be determined based on the lead angle or the lag angle, and is preferably 15 degrees in the embodiment of the present application. It can also be directly obtained by multiplying the ratio of the first angle threshold to 60 degrees by the cycle length of the previous cycle. For example, if the previous cycle length is 2ms and the first angle threshold is 15 degrees, the first time value can be calculated to be 0.5ms.

[0037] See Figure 2 FIG2 shows a partial flow chart of a brushless sensorless motor control method in another embodiment of the present application. In order to obtain a more accurate control period value during the motor control process, in one or other preferred embodiments, the following steps may be further included after step 120 (the following method is defined as an edge method): Step 210: After the voltage value of the suspended phase is greater than half of the bus voltage value, if the voltage value of the suspended phase has an edge jump, the time value when the voltage value of the suspended phase becomes equal to half of the bus voltage value during the rising process is recorded, and the commutation period is calculated based on the time value; Specifically, after detecting the voltage value of the suspended phase among the three phases of the motor, the control device makes a judgment based on the voltage value of the suspended phase. Since the coil of the motor inevitably acts as an inductor, a continuous current situation will inevitably occur, so the voltage of the suspended phase will first appear to be greater than half of the bus voltage value. After the voltage value of the suspended phase is greater than half of the bus voltage value, when the voltage has an edge jump, it means that the rotor of the motor has experienced a zero-crossing process, and the control device can determine the commutation cycle based on this. After detecting the occurrence of an edge jump, the control device records the moment when the voltage value of the suspended phase is equal to half of the bus voltage value during the rising process, and calculates the commutation cycle based on the moment value, thereby obtaining a relatively accurate commutation cycle and improving the accuracy of the motor's rotor commutation.

[0038] Preferably, in one or other preferred embodiments, the edge transition includes: The voltage value of the suspended phase is less than half of the bus voltage value; The voltage value of the suspended phase is greater than half of the bus voltage value.

[0039] Specifically, the control device is defined as follows: when the voltage of the suspended phase is less than half of the bus voltage value, it is defined as 0; when the voltage value of the suspended phase is greater than half of the bus voltage value, it is defined as 1. Therefore, when the voltage value of the suspended phase gradually rises, the voltage value of the suspended phase will go from 0 to 1, so an edge jump process occurs.

[0040] Step 220: Control the motor commutation based on the commutation period.

[0041] Specifically, after calculating the commutation period based on the time value, the control device controls the motor commutation based on the commutation period, specifically performing commutation at the expiration of the commutation period. This improves the accuracy of the rotor commutation control. Furthermore, after commutation is completed, the detection of the current cycle is declared complete, and the next cycle can begin. This method is defined as the edge method.

[0042] In order to facilitate the control device to clearly distinguish the phase switching moment, in one or other preferred embodiments, after the voltage value of the suspended phase is greater than half of the bus voltage value in step 210, the following steps are further included: When the first time threshold expires, if the voltage value of the suspended phase does not undergo an edge transition, the process proceeds to step 130 .

[0043] Specifically, after the voltage value of the suspended phase of the motor is greater than half of the bus voltage value, if the voltage value of the suspended phase does not undergo an edge jump after the first time expires, it can be considered that the freewheeling time is too long and the zero crossing point is submerged in the freewheeling process. Therefore, the control device switches to executing step 130 to determine whether the rotor has passed the zero crossing point.

[0044] The first time threshold is a time value inversely proportional to the time value of the previous cycle, and the inverse ratio is greater than 1 / 2. Preferably, in the embodiment of the present application, the inverse ratio is 5 / 8, that is, after 5 / 8 of the previous cycle, if no edge jump occurs, the control device switches to executing step 130.

[0045] See Figure 3 FIG3 shows a partial flow chart of a brushless sensorless motor control method in another embodiment of the present application. In order to obtain a more accurate control period value during the motor control process, in one or other preferred embodiments, step 120 may further include the following steps (the following method is defined as a level method): Step 310 , detecting a voltage value of a suspended phase among the three phases of the motor after the second time threshold expires; Specifically, the control device detects the voltage value of the suspended phase among the three phases of the motor from the expiration of the second time threshold; the second time threshold here is a time value inversely proportional to the time value of the previous cycle, and the inverse proportion is less than 1 / 2. In particular, the inverse proportion can be infinitely close to 1 / 2, and the value of the inverse proportion depends on the sampling frequency of the voltage value of the suspended phase. Preferably, the embodiment of the present application is preferably 3 / 8. In this process, the control device starts to detect the voltage value of the suspended phase among the three phases of the motor after the second time threshold expires.

[0046] Step 320: When the voltage value of the suspended phase is less than the bus voltage value, if the voltage value of the suspended phase is greater than or equal to half of the bus voltage value, record the current time value and calculate the commutation period based on the current time value.

[0047] Specifically, after the control device detects the voltage value of the suspended phase among the three phases of the motor, when the voltage value of the suspended phase is less than the bus voltage value, if the voltage value of the suspended phase is greater than or equal to half of the bus voltage value, the current moment value is recorded, and the commutation period is calculated based on the current moment value. Here, the suspended phase voltage value is less than the bus voltage value, which effectively distinguishes the suspended phase voltage value from the continuous current exceeding the zero crossing point. The suspended phase voltage value is greater than or equal to the bus voltage value, indicating that the rotor of the motor has passed the zero crossing point. In the case of a short continuous current, when the voltage value of the suspended phase just appears to be greater than or equal to half of the bus voltage value and less than the bus voltage value, it is the moment of the zero crossing point. Therefore, this moment is recorded, and the commutation period is calculated based on this moment.

[0048] Step 330: Control the motor commutation based on the commutation period.

[0049] Specifically, after calculating the commutation period, the control device controls the motor commutation based on the commutation period. This means that commutation is performed at the expiration of the commutation period, thereby improving the accuracy of rotor commutation control. Furthermore, after commutation is completed, the detection of the current cycle is declared complete, and the next cycle can now begin.

[0050] Reference Figure 1 In order to avoid the entire cycle being flooded by the freewheeling current due to the freewheeling current being too long and the control device being unable to make a judgment, in one or other preferred embodiments, the control method further includes: Step 150: If after the third time threshold, the voltage value of the suspended phase is always greater than the first voltage threshold, the motor is forced to commutate.

[0051] Specifically, after detecting the voltage value of the suspended phase, if the third time threshold expires and the voltage value of the suspended phase remains greater than the first voltage threshold, where the third time threshold is the duration of the previous cycle, this indicates that the rotor has remained in the freewheeling state for the duration of the previous cycle. At this point, it is impossible to determine whether the rotor has passed through the zero crossing point. In this case, the control device forcibly controls the motor commutation, forcibly ending the current cycle and entering the next one, and uses the duration of the previous cycle as the basis for determining the duration of the next cycle.

[0052] See Figure 4 , Figure 4 shows a voltage waveform of one phase of a motor in another embodiment of the present application; in the figure, the upper part shows a voltage waveform of short freewheeling, and the lower part shows a comparison diagram of the voltage waveform of long freewheeling. The following two methods are used to sort out the complete process of motor control. In the process of motor control, the control device plays the most core role. The control device transmits control instructions to each power tube, and controls the power supply of any two phases of the three phases of the motor and the suspension of another phase by controlling the on and off of the power tube. When the control device receives the start instruction, the control device controls the power tube to be turned on and off in sequence with a predetermined duty cycle in advance, that is, the voltage is applied to the three phases of the motor in sequence, and the motor is gradually controlled to start. It is worth mentioning that when the motor starts, the control device does not start at full load. Therefore, the duty cycle of the instructions issued by the control device gradually increases. Therefore, even if the load applied to the output shaft of the motor is large, it is not easy to have excessive freewheeling.

[0053] After the predetermined period, the duty cycle output by the control device reaches full load, or 100%. At this point, if the load on the motor's output shaft is light, the current in the motor coil is low, resulting in a shorter freewheeling current in the suspended phase, which is reflected in a narrower portion of the waveform. At this point, if the edge method is used, the control device determines that a zero crossing has occurred when the suspended phase voltage experiences an edge transition, that is, a transition from 0 to 1. The zero crossing is then determined as the moment when the suspended phase voltage equals half the bus voltage, and the commutation cycle is calculated for commutation.

[0054] If the level method is used for control, the voltage value in the suspended phase will be detected only after the second time threshold expires. As long as the voltage value of the suspended phase is greater than or equal to half of the bus voltage value and less than the bus voltage value, the moment when it is greater than or equal to half of the bus voltage value is determined as the zero crossing point and the commutation cycle is calculated for commutation.

[0055] When the load on the output shaft of the motor is large, the current in the motor coil is large, which will cause the freewheeling in the suspended phase to be longer, that is, the part reflected in the waveform is wider. At this time, if the edge method is used, when the freewheeling time exceeds the zero crossing point, the control device cannot detect the situation where the voltage value of the suspended phase is less than half of the bus voltage value, that is, the process from 0 to 1 cannot occur, and the edge jump cannot be detected. At this time, if the technical solution of the present application is not adopted, the rotor of the motor will not be commutated. Such a situation will cause the current in the motor coil to surge and trigger overcurrent protection. The technical solution of the present application, by the control device not detecting the edge jump after the first time expires, the control device selects the control device to determine that the rotor has passed the zero crossing point when the voltage value of the suspended phase is greater than half of the bus voltage value and less than the first voltage threshold. The rotor is considered to have passed the zero crossing point at this time. The control device then determines that the rotor has passed the zero crossing point and subsequently performs direct commutation or waits for the first time value to commutate, thereby reducing the probability of overcurrent protection caused by the rotor not commutating.

[0056] When the level method is used for control, if the freewheeling time is longer than the zero-crossing point, if the control logic of recording the current moment value and calculating the commutation period based on the current moment value is still used when the freewheeling time is greater than or equal to half of the bus voltage value and less than the bus voltage value, the control period will be lengthened due to the freewheeling. If multiple commutation periods are superimposed on this basis, the commutation lag will be serious and the commutation disorder will be caused, thereby triggering protection. However, when the technical solution of the present application is used, if the voltage of the suspended phase is greater than the bus voltage value after the second time threshold expires, the logic of determining that the motor has passed the zero-crossing point is switched to when the voltage value of the suspended phase is greater than half of the bus voltage value and the voltage value of the suspended phase is less than the first voltage threshold. Although the commutation time point is slightly advanced, the early commutation can provide greater torque, which can easily help the motor overcome the current large load dilemma and switch to a smaller current situation, thereby overcoming the problem of long freewheeling and entering the normal control logic of the motor.

[0057] This application also discloses a power tool comprising a housing, a motor, a transmission mechanism, and a control device. The motor is at least partially housed in the housing, and the transmission mechanism is connected to an output shaft of the motor to output power. The control device is also housed in the housing and executes the brushless, sensorless motor control method described in any of the aforementioned embodiments.

[0058] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0059] The above-described embodiments merely represent several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that a person of ordinary skill in the art may make various modifications and improvements without departing from the spirit of the present application, and these modifications and improvements fall within the scope of protection of the present application. Therefore, the scope of protection of the present patent application shall be determined by the appended claims.

Claims

1. A brushless sensorless motor control method, the method is based on a control device, the method is used to control the motor, characterized in that: The control method includes: applying voltage to the three phases of the motor in sequence; detecting a voltage value of a suspended phase among the three phases of the motor; When the voltage value of the suspended phase is greater than half of the bus voltage value and less than a first voltage threshold, it is determined that the motor has passed the zero crossing point.

2. The brushless sensorless motor control method according to claim 1, characterized in that: When the voltage value of the suspended phase is greater than half of the bus voltage value and less than a first voltage threshold, determining that the motor has passed the zero crossing point includes: When the voltage value of the suspended phase is greater than half of the bus voltage value, and then the voltage value of the suspended phase is greater than half of the bus voltage value and less than the first voltage threshold, it is determined that the motor has passed the zero point.

3. The brushless sensorless motor control method according to claim 2, wherein: When the voltage value of the suspended phase is greater than half of the bus voltage value, and the voltage value of the suspended phase is greater than half of the bus voltage value and less than the first voltage threshold, determining that the motor has passed the zero crossing point includes: After the voltage value of the suspended phase is greater than the bus voltage value, when the voltage value of the suspended phase is greater than half of the bus voltage value and the voltage value of the suspended phase is less than a first voltage threshold, it is determined that the motor has passed the zero point.

4. The brushless sensorless motor control method according to claim 1, characterized in that: After detecting the voltage value of the suspended phase among the three phases of the motor, the method further includes: After the voltage value of the suspended phase is greater than half of the bus voltage value, if the voltage value of the suspended phase has an edge jump, the time value when the voltage value of the suspended phase is equal to half of the bus voltage value during the rising process is recorded, and the commutation period is calculated based on the time value; The motor commutation is controlled based on the commutation period.

5. The brushless sensorless motor control method according to claim 4, characterized in that: When the voltage value of the suspended phase is greater than half of the bus voltage value, the method further includes: When the first time threshold expires, if the voltage value of the suspended phase does not undergo an edge jump, then when the voltage value of the suspended phase is greater than half of the bus voltage value and less than the first voltage threshold, it is determined that the motor has passed the zero crossing point; The first time threshold is a time value inversely proportional to a time value of a previous cycle, and the inverse proportion is greater than 1 / 2.

6. The brushless sensorless motor control method according to claim 4, characterized in that: The edge transition includes: The voltage value of the suspended phase is less than half of the bus voltage value; The voltage value of the suspended phase is greater than half of the bus voltage value.

7. The brushless sensorless motor control method according to claim 1, characterized in that: The detecting of the voltage value of the suspended phase among the three phases of the motor further includes: After the second time threshold expires, detecting a voltage value of a suspended phase among the three phases of the motor; When the voltage value of the suspended phase is less than the bus voltage value, if the voltage value of the suspended phase is greater than or equal to half of the bus voltage value, the current moment value is recorded, and the commutation period is calculated based on the current moment value; controlling the commutation of the motor based on the commutation period; The second time threshold is a time value inversely proportional to a time value of a previous cycle, and the inverse proportion is less than 1 / 2.

8. The brushless sensorless motor control method according to claim 1, characterized in that: The control method further includes: If after the third time threshold, the voltage value of the suspended phase is always greater than the first voltage threshold, the motor is forcibly controlled to commutate.

9. The brushless sensorless motor control method according to claim 1, characterized in that: After determining that the motor has passed the zero point, the method further includes: Control the motor to commutate directly; or, Controlling the motor to perform phase commutation after a first time value has passed; The first time value is calculated by using the duration of the previous cycle and the first angle threshold.

10. An electric tool, characterized in that: include: shell; a motor, at least partially housed in the housing; A transmission mechanism, connected to the output shaft of the motor and outputting power to the outside; A control device is housed in the housing and executes the brushless sensorless motor control method according to any one of claims 1 to 9.

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