Electric tool and outdoor working vehicle

Abstract

The invention discloses an electric tool which comprises a motor, a power interface, a driving circuit and a plurality of switch elements arranged on a circuit board. A temperature sensing device; a loss estimation unit configured to: determine a power loss of the switching element based on an on-loss of the switching element and a switching loss of the switching element; a control module configured to: determine a temperature of the switching element based at least on an ambient temperature and a power loss of the switching element; based on the temperature of each switch element, the conduction state of each switch element in the driving circuit is adjusted, and the operation of the motor is controlled. According to the technical scheme, reasonable utilization of each switch element in the driving circuit is ensured, and the problems of overuse and accelerated aging of the switch elements caused by overhigh setting of temperature protection points of the circuit board can be solved.

Description

Technical Field

[0001] This application relates to the field of tool and equipment technology, specifically to an electric tool and an outdoor work vehicle. Background Technology

[0002] In related technologies, when outdoor work vehicles perform ramp parking, the rotor position is fixed and the conduction state of each switching element remains unchanged, resulting in an imbalance of three-phase current. The temperature of two or more bridge arm switching elements is significantly higher than that of other bridge arm switches. If the over-temperature protection point is set too high, it will not be conducive to timely execution of over-temperature protection, accelerating device aging, increasing safety risks, and reducing reliability. Conversely, if the over-temperature protection strategy is too conservative, it will waste the output capacity of the power circuit.

[0003] One related technology involves adding temperature sensors at different locations on the control board to improve the effectiveness of over-temperature protection strategies. However, temperature sensors cannot accurately reflect the true temperature status of switching elements at all locations on the control board.

[0004] This section provides background information related to this application, which is not necessarily prior art. Summary of the Invention

[0005] One object of this application is to solve or at least alleviate some or all of the aforementioned problems. Therefore, one object of this application is to provide an electric tool capable of reflecting the true temperature of a switching element and adjusting the operation of a motor based on the true temperature of the switching element.

[0006] To achieve the above objectives, this application adopts the following technical solution: an electric tool, comprising: a motor, including a stator and a rotor; a power interface for connecting to a power supply device to provide electrical energy to the motor; a drive circuit including a plurality of switching elements arranged on a circuit board; a temperature sensing device arranged on the circuit board for sensing the ambient temperature near each switching element; a loss estimation unit configured to: determine the power loss of the switching elements based on the conduction loss and switching loss of the switching elements; and a control module electrically connected to the drive circuit; the control module is configured to: determine the temperature of the switching elements based at least on the ambient temperature and the power loss of the switching elements; and adjust the conduction state of each switching element in the drive circuit based on the temperature of each switching element to control the operation of the motor.

[0007] In some embodiments, the control module is configured to: output a pulse width modulation signal to change the conduction state of each switching element; the loss estimation unit is configured to: estimate the conduction loss of each switching element based at least on the phase current of the motor, the on-state resistance of the switching element and the duty cycle of the pulse width modulation signal; and estimate the switching loss of each switching element based at least on the phase current of the motor and the switching frequency of the switching element.

[0008] In some embodiments, the control module is further configured to update the on-state resistance of the switching element based on a preset relationship curve and the temperature of the switching element.

[0009] In some embodiments, the switching element includes a MOSFET and a diode connected in parallel with the MOSFET; the conduction loss includes the conduction loss of the MOSFET and the conduction loss of the diode; the switching loss includes the switching loss of the MOSFET and the reverse recovery loss of the diode.

[0010] In some embodiments, the control module is specifically configured to calculate the conduction loss of the diode based on the phase current, the duty cycle of the pulse width modulation signal, and the forward voltage drop of the diode.

[0011] In some embodiments, the control module is specifically configured to calculate the reverse recovery loss of the diode based on the number of MOSFETs in parallel, the reverse recovery energy related parameters of the diode, and the switching frequency of the switching element.

[0012] In some embodiments, the temperature of the switching element includes the junction temperature Tj of the switching element; the control module is specifically configured to: calculate the junction temperature Tj of the switching element according to Formula 1; Formula 1 is as follows: Tj=Ploss·Zjb+Tb; where Tb is the ambient temperature of the switching element and Zjb is the first thermal resistance.

[0013] In some embodiments, the temperature sensing device includes a temperature sensor.

[0014] Secondly, this application provides an electric tool, comprising: a motor, including a stator and a rotor; a power interface for connecting to a power supply device to supply electrical energy to the motor; a drive circuit including a plurality of switching elements arranged on a circuit board; a control module electrically connected to the drive circuit, the control module being configured to output a pulse width modulation signal to change the conduction state of each switching element in the drive module; further comprising: a temperature estimation unit for estimating the junction temperature of each switching element; the control module being further configured to: acquire the junction temperature of each switching element; and adjust the pulse width modulation signal according to the junction temperature of each switching element when the junction temperature of at least one switching element exceeds a temperature threshold.

[0015] In some embodiments, the temperature estimation unit includes a temperature sensing device and a loss estimation unit; the temperature sensing device is disposed on a circuit board and is used to sense the ambient temperature near each switching element; the loss estimation unit is used to determine the power loss of the switching element based on the conduction loss and the switching loss of the switching element.

[0016] In some embodiments, the pulse width modulation signal includes a first electrical signal; the first electrical signal is used to drive the rotor to rotate.

[0017] In some embodiments, the pulse width modulation signal includes a second electrical signal; the second electrical signal is used to lock the position of the rotor.

[0018] In some embodiments, the power tool is an outdoor work vehicle.

[0019] In some embodiments, the temperature threshold T 预 The range is: T 预 ≤175℃.

[0020] The advantages of this application are as follows: The drive circuit includes multiple switching elements arranged on a circuit board, and a temperature sensing device is arranged on the circuit board, enabling the temperature sensing device to sense the ambient temperature surrounding each switching element. The power tool includes a loss estimation unit, which determines the power loss of the switching elements based on their conduction loss and switching loss. The control module is configured to determine the temperature of the switching elements based at least on the ambient temperature and the power loss of the switching elements. Then, based on the temperature of each switching element, the conduction state of each switching element in the drive circuit is adjusted to control the operation of the motor. The technical solution of this application makes the determined temperature of the switching elements more accurate, improves the accuracy of temperature protection, and prevents the circuit board temperature protection point from being set too high, leading to overuse of the switching elements and accelerated aging, thus reducing reliability. At the same time, it can prevent the output capacity of the switching elements from being underutilized or the design redundancy of the switching elements from being too conservatively set, thereby improving the performance of the power tool. Attached Figure Description

[0021] Figure 1 A physical diagram of a ride-on lawnmower provided for an embodiment of this application;

[0022] Figure 2 A schematic diagram of the circuit system of a power tool provided in an embodiment of this application;

[0023] Figure 3 A flowchart for determining temperature information of a switching element is provided as an embodiment of this application;

[0024] Figure 4 A flowchart for adjusting a pulse width modulation signal is provided as an embodiment of this application;

[0025] Figure 5 A waveform diagram showing the three-phase current amplitude and rotor position angle during normal operation of a motor, provided as an embodiment of this application;

[0026] Figure 6 This diagram illustrates the effect of using the control method of this application to control the junction temperature of each switching element in the drive circuit. Detailed Implementation

[0027] Before explaining any implementation of this application in detail, it should be understood that this application is not limited to its application to the structural details and component arrangements set forth in the following description or shown in the above drawings.

[0028] In this application, the terms "comprising," "including," "having," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element.

[0029] In this application, the term "and / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent three cases: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this application generally indicates that the preceding and following related objects have an "and / or" relationship.

[0030] In this application, the terms "connection," "combination," "coupling," and "installation" can refer to direct connection, combination, coupling, or installation, or indirect connection, combination, coupling, or installation. For example, a direct connection refers to two parts or components being connected together without the need for an intermediary, while an indirect connection refers to two parts or components each being connected to at least one intermediary, with the connection achieved through the intermediary. Furthermore, "connection" and "coupling" are not limited to physical or mechanical connections or couplings, but can also include electrical connections or couplings.

[0031] In this application, those skilled in the art will understand that relative terms (e.g., “about,” “approximately,” “basically,” etc.) used in conjunction with quantities or conditions are to include the values ​​and have the meaning indicated by the context. For example, such relative terms include at least the degree of error associated with the measurement of a particular value, tolerances associated with the particular value due to manufacturing, assembly, use, etc. Such terms should also be considered as disclosing a range defined by the absolute values ​​of the two endpoints. Relative terms may refer to a certain percentage (e.g., 1%, 5%, 10% or more) of the indicated value. Numerical values ​​not using relative terms should also be disclosed as specific values ​​with tolerances. Furthermore, “basically” when expressing relative angular relationships (e.g., substantially parallel, substantially perpendicular) may refer to a certain degree (e.g., 1 degree, 5 degrees, 10 degrees or more) added to or subtracted from the indicated angle.

[0032] In this application, those skilled in the art will understand that the function performed by a component can be performed by one component, multiple components, one part, or multiple parts. Similarly, the function performed by a part can also be performed by one part, one component, or a combination of multiple parts.

[0033] In this application, the directional terms "upper," "lower," "left," "right," "front," and "rear" are used to describe the orientation and positional relationships shown in the accompanying drawings and should not be construed as limiting the embodiments of this application. Furthermore, in the context, it should be understood that when an element is mentioned as being connected "upper" or "lower" to another element, it can be directly connected to the other element "upper" or "lower," or indirectly connected through an intermediate element. It should also be understood that directional terms such as upper side, lower side, left side, right side, front side, and rear side not only represent positive orientation but can also be understood as lateral orientation. For example, "below" can include directly below, lower left, lower right, lower front, and lower rear.

[0034] In this application, the terms "control module," "processor," "central processing unit," "CPU," and "MCU" are used interchangeably. When using the unit "control module," "processor," "central processing unit," "CPU," or "MCU" to perform a specific function, unless otherwise stated, these functions can be performed by a single or multiple of the aforementioned units.

[0035] In this application, the terms "device," "module," or "unit" are used to describe devices that can be implemented in hardware or software to perform a specific function.

[0036] In this application, the terms “calculation,” “judgment,” “control,” “determine,” “identify,” etc., refer to the operation and process of a computer system or similar electronic computing device (e.g., control module, processor, etc.).

[0037] The power tools provided in this application may include, but are not limited to, outdoor work vehicles, such as farm vehicles, ride-on lawnmowers, and stand-up lawnmowers; these tools may also be used for other purposes, such as mixers. Any power tool that incorporates the substantive content of the technical solutions disclosed below will fall within the protection scope of this invention.

[0038] The power tool described in this embodiment is a ride-on lawnmower as an example. Figure 1 This is a physical diagram of a ride-on lawnmower provided in an embodiment of this application. Figure 2 This is a schematic diagram of the circuit system of a power tool provided in an embodiment of this application. (Reference) Figure 1 and Figure 2As shown, in this embodiment, the directions front, back, left, right, up, and down are described as follows: Figure 1 The directions shown are as follows. Specifically, when a user is carried on a manned lawnmower 100 located on the ground, the direction the user is facing is defined as forward, the direction behind is defined as rear, the direction to the left is defined as left, the direction to the right is defined as right, the direction closer to the ground is defined as downward, and the direction further away from the ground is defined as upward.

[0039] like Figure 1 As shown, the manned lawnmower 100 provided in this embodiment includes: a frame 91, a walking assembly 93, a mowing assembly 10, an operating assembly 50, a power supply 96, a support 92, and a steering operating device 56. The walking assembly 93 includes walking wheels for moving the manned lawnmower on the ground and a walking motor for driving the walking wheels. The mowing assembly 10 includes mowing elements and a drive motor for driving the mowing elements. The operating assembly 50 is configured for user operation to control the manned lawnmower 100. The manned lawnmower also includes a power interface for connecting to the power supply 96, which includes at least one battery pack. The support 92 is configured to support the user. The steering operating device 56 is used to control the steering of the manned lawnmower 100.

[0040] In this embodiment, the support 92 may include a seat. In some embodiments, the support may also be a platform for a user to stand on. The walking assembly 93 supports other components of the manned lawnmower 100. The manned lawnmower 100 is powered by a power supply 96 to the mowing assembly 10 and the walking assembly 93, thereby enabling the manned lawnmower 100 to be used as an electric tool. In some embodiments, the manned lawnmower 100 includes a grass collection device. The grass collection device is used to collect grass clippings cut by the mowing assembly 10. The grass collection device includes a grass basket assembly, which is detachably mounted at the rear of the support 92.

[0041] The mowing assembly 10 can also be detached from the manned lawnmower 100. In some embodiments, the manned lawnmower 100 can be connected to other working attachments, such as a snowplow assembly. In this case, strictly speaking, the manned lawnmower 100 is no longer just a riding lawnmower, but a riding snowplow, capable of performing different tasks depending on the connected working attachments.

[0042] The operating component 50 may include a control panel 52 and a pedal assembly. The pedal assembly includes an accelerator assembly 591 and a brake assembly 592. The steering operating component 56 may include a steering wheel, which can be operated by a user to control the direction of travel of the manned lawnmower 100.

[0043] In this embodiment, motor 12 will be used to replace the travel motor. Motor 12 includes stator windings and a rotor that rotates around the stator windings. In some embodiments, motor 12 is a three-phase brushless motor, including a rotor with permanent magnets and electronically commutated three-phase stator windings U, V, and W. In some embodiments, the three-phase stator windings U, V, and W are connected in a star configuration, and in other embodiments, they are connected in a delta configuration. However, it must be understood that other types of brushless motors are also within the scope of this disclosure. Brushless motors may have fewer or more than three phases.

[0044] Based on the above power tools, refer to Figure 2 As shown, the system also includes a drive circuit 171 and a control module 17. The drive circuit 171 is electrically connected to the stator windings U, V, and W of the motor 12, and is used to transfer current from the power supply to the stator windings U, V, and W to drive the motor to rotate. In one embodiment, the drive circuit 171 includes multiple switching elements Q1, Q2, Q3, Q4, Q5, and Q6 arranged on a circuit board. The switching elements Q1-Q6 can be field-effect transistors, IGBT transistors, etc. The switching elements Q1, Q2, Q3, Q4, Q5, and Q6 form a three-phase bridge. Among them, Q1, Q3, and Q5 are upper bridge switches, and Q2, Q4, and Q6 are lower bridge switches. The upper and lower bridge switches of each phase bridge circuit are connected to the same winding. The gate terminal of each switching element is electrically connected to the control module, and is used to receive control signals from the control module 17 to change their respective conduction states, thereby changing the current and / or voltage applied by the power supply to the stator windings U, V, and W of the motor, and driving the motor 12 to operate. In one optional embodiment, the control signal for the control module 17 is a pulse width modulation (PWM) signal, and the control module 17 is configured to output the PWM signal to change the conduction state of each switching element. In some embodiments, the PWM signal can be understood as a vector pulse width signal in field-oriented control (FOC) or a drive signal for a pulse width modulation (PWM) signal in brushless motor position loop control (BLDC). In some embodiments, the PWM signal can also be a parking signal or a braking signal, etc.

[0045] The power tool also includes a temperature sensing device 181, which is also disposed on the circuit board for sensing the ambient temperature near each switching element. In an optional embodiment, the temperature sensing device 181 includes a temperature sensor, thereby enabling the temperature sensing device 181 to sense the ambient temperature near each switching element. Exemplarily, the temperature sensor may specifically be a negative temperature coefficient thermistor, thereby improving the sensitivity and operating temperature range of the temperature sensor and reducing its size.

[0046] In an optional embodiment, the control module can be configured to adjust the conduction state of each switching element in the drive circuit based on the ambient temperature obtained by the temperature sensing device, so as to control the operation of the motor.

[0047] The power tool also includes a loss estimation unit 182, which is configured to determine the power loss of the switching element based on the conduction loss and the switching loss of the switching element.

[0048] The conduction loss of a switching element can be understood as the loss of the switching element when it is in the conducting state. Conduction loss occurs when the switching element is in the conducting state after the driving and switching waveforms have stabilized. Switching loss can be understood as the loss during the transition process of the driving and switching waveforms when the switching element is driven from one operating state to another.

[0049] The power loss of a switching element can be understood as the power consumption lost during the input-output conversion process. The power loss of a switching element is mainly formed by its conduction loss and switching loss. Therefore, other losses of the switching element can be ignored, and the power loss of the switching element is determined based on its conduction loss and switching loss. In an optional embodiment, the power loss of the switching element is determined based on its conduction loss, switching loss, and conduction frequency.

[0050] In an optional embodiment, the loss estimation unit 182 is configured to: estimate the conduction loss of each switching element based at least on the phase current of the motor, the on-state resistance of the switching element, and the duty cycle of the pulse width modulation signal; and estimate the switching loss of each switching element based at least on the phase current of the motor and the switching frequency of the pulse width modulation signal.

[0051] The on-state resistance of a switching element can be understood as the resistance value of the switching element when it is turned on under forward voltage. It is understood that different temperatures will affect the resistance value. In an optional embodiment, the on-state resistance of the switching element at the current temperature can be determined based on a junction temperature-on-state resistance lookup table and the current temperature information of the switching element.

[0052] In one alternative embodiment, the switching element includes a MOSFET and a diode connected in parallel with the MOSFET.

[0053] The conduction losses of switching elements include the conduction losses of MOSFETs and diodes. In this embodiment, the conduction loss of the MOSFET can be calculated based on the phase current, the on-state resistance of the switching element, the duty cycle of the pulse width modulation signal, and the number of MOSFETs connected in parallel. The conduction loss of the diode can be calculated based on the phase current, the duty cycle of the pulse width modulation signal, and the forward voltage drop of the diode.

[0054] The switching losses of switching elements include the switching losses of MOSFETs and the reverse recovery losses of diodes. In this embodiment, the switching losses of MOSFETs can be calculated based on the phase current, bus voltage, number of MOSFETs connected in parallel, relevant parameters of MOSFET switching loss energy, and the switching frequency of the switching element. The reverse recovery losses of diodes can be calculated based on the number of MOSFETs connected in parallel, relevant parameters of diode reverse recovery energy, and the switching frequency of the switching element.

[0055] It should be noted that the parameters mentioned in this embodiment, such as the phase current of the motor, the duty cycle of the pulse width modulation signal, the switching frequency of the switching element, the forward voltage drop of the diode, the number of parallel MOSFETs, the reverse recovery energy of the diode, and the preset relationship curve, can all be obtained by existing technical means or pre-stored in the storage device in the power tool. The specific acquisition method will not be described in this embodiment.

[0056] In this embodiment, the control module 17 of the power tool is configured to: determine the temperature of the switching element based at least on the ambient temperature and the power loss of the switching element; and adjust the conduction state of each switching element in the drive circuit based on the temperature of each switching element to control the operation of the motor.

[0057] The temperature of the switching element can include the junction temperature Tj of the switching element. In some embodiments, the power tool further includes a temperature estimation unit 18 for estimating the junction temperature of each switching element based on the ambient temperature and the power loss of the switching element. Determining the temperature of the switching element based at least on the ambient temperature and the power loss of the switching element specifically includes: calculating the junction temperature of the switching element according to Formula 1. This eliminates the need for additional hardware and utilizes existing solutions for driving circuits using MOSFETs, where only a temperature sensing device is placed on the circuit board. This simplifies the structure of the driving circuit and facilitates its miniaturization.

[0058] In this embodiment, Formula 1 is: Tj = Ploss·Zjb + Tb. Where Ploss is the power loss of the switching element, Tb is the ambient temperature of the switching element, and Zjb is the first thermal resistance.

[0059] The first thermal resistance may include the thermal resistance from the switching element to the temperature sensing device. In an alternative embodiment, the first thermal resistance can be determined by determining the thermal model from the inside of the switching element to the temperature sensing device in the drive circuit based on the hardware topology and characteristics of the circuit board.

[0060] In some embodiments, the temperature estimation unit 18 includes a temperature sensing device 181 and a loss estimation unit 182. The temperature sensing device 181 is disposed on a circuit board and is used to sense the ambient temperature near each switching element. The loss estimation unit 182 is used to determine the power loss of the switching element based on the conduction loss and switching loss of the switching element.

[0061] Figure 3 This is a flowchart illustrating how to determine the temperature information of a switching element, as provided in an embodiment of this application. Specifically, refer to... Figure 3 As shown, firstly, the on-state resistance of the switching element at the current junction temperature is determined using the junction temperature-on-resistance lookup table. Then, based on the phase current, the on-state resistance of the switching element, the duty cycle of the pulse width modulation signal, and the number of MOSFETs in parallel, the conduction loss of the MOSFETs is calculated. Based on the phase current, the duty cycle of the pulse width modulation signal, and the forward voltage drop of the diode, the conduction loss of the diode is calculated. Based on the phase current, the bus voltage, the number of MOSFETs in parallel, the relevant parameters of MOSFET switching loss energy, and the switching frequency of the switching element, the switching loss of the MOSFETs is calculated. Finally, based on the number of MOSFETs in parallel, the relevant parameters of diode reverse recovery energy, and the switching frequency of the switching element, the reverse recovery loss of the diode is calculated. Then, based on the sum of the MOSFET conduction loss, the MOSFET switching loss, the diode conduction loss, and the diode reverse recovery loss, the power loss of the switching element is determined. Finally, based on the temperature of the switching element, the power loss of the switching element, and the first thermal resistance, the junction temperature of the switching element is calculated. It should be noted that the junction temperature of the switching element calculated in the last step is used as the junction temperature corresponding to the on-state resistance at the next moment, thus making the on-state resistance based on it more accurate.

[0062] In an optional embodiment, the control module is further configured to: acquire the junction temperature of each switching element; and adjust the pulse width modulation signal according to the junction temperature of each switching element when the junction temperature of at least one switching element exceeds a temperature threshold.

[0063] The temperature threshold can be set according to the performance of the switching element and the actual application requirements. In one optional embodiment, the temperature threshold is less than or equal to the upper limit of the normal operating temperature of the switching element. In another optional embodiment, the temperature threshold T... 预 The range of values ​​for is T 预 ≤175℃. In some embodiments, the temperature threshold is 165℃. In some embodiments, the temperature threshold is 170℃. In some embodiments, the temperature threshold is 175℃. In some embodiments, the temperature threshold is 150℃.

[0064] The statement that at least one switching element's junction temperature exceeds a temperature threshold can be understood as either the junction temperature of one switching element exceeding the temperature threshold, or the junction temperatures of multiple switching elements exceeding the temperature threshold. It should be noted that each switching element can be set with its own corresponding temperature threshold; that is, each switching element can correspond to a temperature threshold, and the temperature thresholds of each switching element can be the same or different. To simplify the information processing, this embodiment is described with the assumption that all switching elements have the same temperature threshold, but this does not imply any limitation on the temperature thresholds of each switching element.

[0065] In some embodiments, adjusting the pulse width modulation signal according to the junction temperature of each switching element may specifically include adjusting the pulse width modulation signal to fine-tune the rotor position to a bridge arm switch whose junction temperature does not exceed a temperature threshold, thereby transferring heat.

[0066] In some embodiments, the pulse width modulation signal includes a first electrical signal, which is used to drive the rotor to rotate.

[0067] In some embodiments, the pulse width modulation signal includes a second electrical signal; the second electrical signal is used to lock the position of the rotor.

[0068] Figure 4 A flowchart illustrating the adjustment of a pulse width modulation signal is provided for embodiments of this application. In some embodiments, reference is made to... Figure 4 As shown, the junction temperature of each switching element is obtained. When the junction temperature of one or more switching elements exceeds the temperature threshold, the junction temperatures of the upper and lower bridge switches of each phase are compared to determine the lower bridge arm among the switching elements of each phase as the first bridge arm, and the relatively lower bridge arm among the higher bridge arms among the switching elements of each phase as the second bridge arm. Then, by adjusting the pulse width modulation signal, the rotor position is finely adjusted to the conduction range of each first bridge arm. If each first bridge arm is an upper bridge arm or a lower bridge arm, the second bridge arm replaces the bridge arm of the same phase as the second bridge arm to conduct, thereby transferring the heat to the relatively lower bridge arm of each phase, thus avoiding the accelerated aging of the device caused by concentrated heat.

[0069] Figure 5 This is a waveform diagram showing the three-phase current amplitude and rotor position angle during normal operation of a motor, provided as an embodiment of this application. In an exemplary embodiment, reference is made to... Figure 5As shown, if the junction temperature of the upper bridge component of phase C is greater than the temperature threshold when the rotor position angle is 210°, the rotor position can be adjusted to a position between 330° and 450° by adjusting the pulse width modulation signal, so that the lower bridge component of phase C is turned on. Due to the fine adjustment of the rotor position, the position of the riding lawnmower will hardly change. However, this method makes the junction temperature of each switching component more even, increases the temperature rise time of the circuit board, that is, increases the electronic parking time, thereby avoiding the over-temperature protection triggered by the excessive temperature of some bridge arm switching components, and thus avoiding premature triggering of temperature protection and causing the vehicle to roll backward. This is beneficial to improving the safety performance and reliability of power tools.

[0070] Figure 6 This demonstrates the effect of the control method of this application on controlling the junction temperature of each switching element in the drive circuit, from... Figure 6 As can be seen, before 62 seconds, the temperature of the lower C-phase tube rises to the threshold of 75℃. Around 62 seconds later, the control module changes the pulse width modulation signal to fine-tune the rotor position. After 62 seconds, the lower A-phase tube and the upper B-phase tube replace the lower C-phase tube in bearing the load, causing their temperatures to rise, thus lowering the temperature of the lower C-phase tube. Before 62 seconds, the upper A-phase tube, the upper B-phase tube, and the lower C-phase tube are conducting. Due to the different current magnitudes and thermal resistances they bear, the temperature rise of phase C is more significant. After adjusting the rotor position for 62 seconds, the lower A-phase tube, the upper B-phase tube, and the upper C-phase tube are conducting.

[0071] The foregoing has shown and described the basic principles, main features, and advantages of this application. Those skilled in the art should understand that the above embodiments do not limit this application in any way, and all technical solutions obtained by equivalent substitution or equivalent transformation fall within the protection scope of this application.

Claims

1. An electric power tool, comprising: a motor including a stator and a rotor; a power supply interface configured to access a power supply device to cause the power supply device to supply electric power to the motor; a drive circuit including a plurality of switching elements arranged on a circuit board; a temperature sensing device arranged on the circuit board, the temperature sensing device configured to sense an ambient temperature in a vicinity of each of the switching elements; a control module electrically connected to the drive circuit; characterized in that the electric power tool further comprises: a loss estimation unit configured to determine a power loss of each of the switching elements based on a conduction loss and a switching loss of each of the switching elements; and the control module is configured to determine a temperature of each of the switching elements based on the ambient temperature and the power loss of each of the switching elements, and to adjust a conduction state of each of the switching elements based on the temperature of each of the switching elements to control an operation of the motor.

2. The power tool of claim 1, wherein, the control module is configured to output a pulse width modulation signal to change the conduction state of each of the switching elements; the loss estimation unit is configured to estimate the conduction loss of each of the switching elements based on at least a phase current of the motor, an on-state resistance of each of the switching elements, and a duty cycle of the pulse width modulation signal; and to estimate the switching loss of each of the switching elements based on at least the phase current of the motor and a switching frequency of each of the switching elements.

3. The power tool of claim 2, wherein, the control module is further configured to update the on-state resistance of each of the switching elements according to the temperature of each of the switching elements based on a preset relationship curve.

4. The power tool of claim 2, wherein, each of the switching elements includes a MOS transistor and a diode connected in parallel with the MOS transistor; the conduction loss includes a conduction loss of the MOS transistor and a conduction loss of the diode; and the switching loss includes a switching loss of the MOS transistor and a reverse recovery loss of the diode.

5. The power tool of claim 4, wherein, the control module is specifically configured to calculate the conduction loss of the diode according to the phase current, the duty cycle of the pulse width modulation signal, and a conduction voltage drop of the diode.

6. The power tool of claim 4, wherein, the control module is specifically configured to calculate the reverse recovery loss of the diode according to a number of the MOS transistors connected in parallel, a reverse recovery energy related parameter of the diode, and the switching frequency of each of the switching elements.

7. The power tool of claim 1, wherein, the temperature sensing device includes a temperature sensor. 8.An outdoor work vehicle, comprising: a motor including a stator and a rotor; a power supply interface configured to access a power supply device to cause the power supply device to supply electric power to the motor; a drive circuit including a plurality of switching elements arranged on a circuit board; a control module electrically connected to the drive circuit, the control module being configured to output a pulse width modulation signal to change a conduction state of each of the switching elements in the drive module; characterized in that the outdoor work vehicle further comprises: a temperature estimation unit configured to estimate a junction temperature of each of the switching elements; the control module is further configured to obtain the junction temperature of each of the switching elements, and to adjust the pulse width modulation signal according to the junction temperature of each of the switching elements when the junction temperature of at least one of the switching elements exceeds a temperature threshold.

9. The outdoor work vehicle of claim 8, characterized in that The temperature estimation unit comprises a temperature sensing device and a loss estimation unit; the temperature sensing device is arranged on the circuit board and is used for sensing the ambient temperature near each switching element; The loss estimation unit is used for determining the power loss of the switching element based on the conduction loss of the switching element and the switching loss of the switching element.

10. The utility vehicle of claim 8, characterized in that, The pulse width modulation signal comprises a first electric signal; the first electric signal is used for driving the rotation of the rotor.

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