Power tool and outdoor work vehicle

Abstract

A power tool and a temperature estimation method for a plurality of switching elements. The power tool comprises: a motor; a power interface configured to be connected to a power supply device so as to provide electrical energy to the motor; a drive circuit comprising a plurality of switching elements arranged on a circuit board; a temperature sensing device arranged on the circuit board and configured to sense the ambient temperature near the plurality of switching elements; a control module electrically connected to the drive circuit, the control module being configured to output a pulse width modulation signal so as to change the on-state of the plurality of switching elements; and a loss estimation unit configured to estimate the power loss of the switching elements on the basis of the turn-on loss and the switching loss of the plurality of switching elements, wherein the control module is configured to estimate the temperature of the switching elements on the basis of the ambient temperature and the power loss of the switching elements, and adjust the on-state of the switching elements on the basis of the temperature of the switching elements so as to control the operation of the motor.

Description

Power tools and outdoor work vehicles

[0001] This application claims priority to Chinese Patent Application No. 202411037007.0, filed on July 30, 2024, and Chinese Patent Application No. 202510935231X, filed on July 7, 2025, the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of tool and equipment technology, such as an outdoor work vehicle and power tools. Background Technology

[0003] 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.

[0004] 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.

[0005] This section provides background information related to this application, which is not necessarily related to the technology. Summary of the Invention

[0006] One objective of this application is to solve or at least mitigate some or all of the aforementioned problems. To this end, this application provides an outdoor work equipment and power tool, as well as a control method thereof, that can improve operational stability.

[0007] One embodiment provides an electric tool, including: a motor, including a stator and a rotor; a power interface configured to connect 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 configured to sense the ambient temperature near the plurality of switching elements; a control module electrically connected to the drive circuit, configured to output a pulse width modulation signal to change the conduction state of the plurality of switching elements; a loss estimation unit configured to estimate the power loss of the switching elements based on the conduction loss and switching loss of the plurality of switching elements; and the control module configured to estimate the temperature of the switching elements based on the ambient temperature and the power loss of the switching elements, and adjust the conduction state of the switching elements based on the temperature of the switching elements to control the operation of the motor.

[0008] In some embodiments, 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.

[0009] In some embodiments, the loss estimation unit is configured to estimate the switching losses of the switching elements based at least on the phase current of the motor and the switching frequency of the switching elements.

[0010] In some embodiments, the control module is configured to update the on-state resistance of the switching element based on a preset relationship curve and the temperature of the switching element.

[0011] 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.

[0012] In some embodiments, the control module is configured to estimate 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.

[0013] In some embodiments, the control module is configured to estimate 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.

[0014] In some embodiments, the control module is configured to acquire the junction temperature of each switching element and adjust the pulse width modulation signal when the junction temperature of at least one switching element exceeds a preset temperature.

[0015] In some embodiments, the preset temperature range is greater than or equal to 65°C and less than or equal to 85°C.

[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 temperature sensing device includes a temperature sensor.

[0019] In some embodiments, power tools include outdoor work vehicles.

[0020] In some embodiments, the motor is a brushless motor.

[0021] One embodiment provides a method for estimating the temperature of multiple switching elements in a drive circuit of a power tool. The power tool includes a motor and a control module. The control module is configured to output a pulse width modulation signal to change the conduction state of the multiple switching elements. The temperature estimation method includes: sensing the ambient temperature of the multiple switching elements based on a temperature sensing device; estimating the conduction loss of the multiple switching elements based on the phase current of the motor, the on-state resistance of the multiple switching elements, and the duty cycle of the pulse width modulation signal; estimating the switching loss of the multiple switching elements based on the phase current of the motor and the switching frequency of the pulse width modulation signal; and the control module estimating the temperature of the multiple switching elements based on the ambient temperature, the conduction loss of the multiple switching elements, and the switching loss of the multiple switching elements.

[0022] In some embodiments, the control module updates the on-state resistance of the switching element based on a preset relationship curve and the temperature of the switching element.

[0023] One embodiment provides an outdoor work vehicle, including: a set of wheels for supporting the vehicle to move on the ground; a motor for driving the set of wheels or work attachments; a power interface for connecting to a power supply device to provide power to the motor; a drive circuit including multiple switching elements arranged on a circuit board; a control module electrically connected to the drive circuit, configured to output a pulse width modulation signal to change the conduction state of each switching element in the drive module; a temperature estimation unit for estimating the junction temperature of each switching element; the control module is also 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.

[0024] 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.

[0025] 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.

[0026] 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. Attached Figure Description

[0027] Figure 1 is a physical diagram of a ride-on lawnmower provided in an embodiment of this application;

[0028] Figure 2 is a schematic diagram of the circuit system of an electric tool provided in an embodiment of this application;

[0029] Figure 3 is a flowchart of determining the temperature information of a switching element according to an embodiment of this application;

[0030] Figure 4 is a flowchart of adjusting a pulse width modulation signal according to an embodiment of this application;

[0031] Figure 5 is a waveform diagram of the three-phase current amplitude and rotor position angle when a motor is operating normally, according to an embodiment of this application.

[0032] Figure 6 shows the effect of controlling the junction temperature of each switching element in the drive circuit using the control method of this application. Detailed Implementation

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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.).

[0043] 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.

[0044] This embodiment uses a ride-on lawnmower as an example to illustrate the power tool. Figure 1 is a physical diagram of a ride-on lawnmower provided in this embodiment, and Figure 2 is a schematic diagram of the circuit system of a power tool provided in this embodiment. Referring to Figures 1 and 2, in this embodiment, the directions of front, back, left, right, up, and down are described as those shown in Figure 1. In some embodiments, when a user is carried on a manned lawnmower 100 located on the ground, the direction the user is facing is defined as front, the direction behind is defined as back, 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 down, and the direction farther from the ground is defined as up.

[0045] As shown in Figure 1, the manned lawnmower 100 provided in this embodiment includes: a frame 91, a set of wheels 93, a mowing assembly 10, an operating assembly 50, a power supply 96, a support 92, and a steering operating device 56. The mowing assembly 10 can be understood as an accessory for the manned lawnmower 100. The set of wheels 93 includes wheels that drive the manned lawnmower on the ground and a motor for driving the wheels. The mowing assembly 10 includes a mowing element and a drive motor for driving the mowing element. 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.

[0046] 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 wheel set 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 wheel set 93, thus enabling it to be used as an electric tool. In some embodiments, the manned lawnmower 100 includes a grass collection device. The grass collection device collects grass clippings cut by the mowing assembly 10. The grass collection device includes a grass basket assembly detachably mounted at the rear of the support 92.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] Based on the power tool described above, referring to Figure 2, it further 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 transmit 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 selected from 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 of each switching element is electrically connected to the control module 17 to receive control signals from the control module 17, thereby changing its respective conduction state and thus altering the current and / or voltage applied to the stator windings U, V, and W of the motor by the power supply device, driving the motor 12 to operate. In an optional embodiment, the control signal of the control module 17 is a pulse width modulation (PWM) signal, and the control module 17 is configured to output a PWM signal to change the conduction state of each switching element. In some embodiments, the PWM signal can be understood as the vector pulse width signal in field-oriented control (FOC) or the drive signal of the 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 brake signal, etc.

[0051] 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. For example, the temperature sensor may be a negative temperature coefficient thermistor, thereby improving the sensitivity and operating temperature range of the temperature sensor and reducing its size.

[0052] In an optional embodiment, the control module may 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.

[0053] 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 switching loss of the switching element.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] In one alternative embodiment, the switching element includes a MOSFET and a diode connected in parallel with the MOSFET.

[0059] 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.

[0060] 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.

[0061] 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 through relevant technical means or pre-stored in the storage device in the power tool.

[0062] 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.

[0063] 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 includes: calculating the junction temperature of the switching element according to Formula 1. This eliminates the need for additional hardware and allows for estimation of the junction temperature of the switching element using a solution that only requires a temperature sensing device on the circuit board for driving circuits using MOSFETs. This simplifies the structure of the driving circuit and facilitates miniaturization of the driving circuit.

[0064] 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.

[0065] 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.

[0066] 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.

[0067] Figure 3 is a flowchart illustrating a method for determining the temperature information of a switching element according to an embodiment of this application. In some embodiments, referring to Figure 3, the on-state resistance of the switching element at the current junction temperature is first determined using a junction temperature-on-state resistance lookup table. Then, the conduction loss of the MOSFET is 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 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 switching loss of the MOSFET is calculated based on the phase current, the bus voltage, the number of MOSFETs connected in parallel, the switching loss energy parameters of the MOSFET, and the switching frequency of the switching element. The reverse recovery loss of the diode is calculated based on the number of MOSFETs connected in parallel, the reverse recovery energy parameters of the diode, and the switching frequency of the switching element. The power loss of the switching element is then determined based on the sum of the conduction loss of the MOSFET, the switching loss of the MOSFET, the conduction loss of the diode, and the reverse recovery loss of the diode. Finally, the junction temperature of the switching element is calculated based on the temperature of the switching element, the power loss of the switching element, and the first thermal resistance. 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.

[0068] 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.

[0069] 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℃.

[0070] 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.

[0071] In some embodiments, adjusting the pulse width modulation signal according to the junction temperature of each switching element may 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.

[0072] In some embodiments, the pulse width modulation signal includes a first electrical signal, which is used to drive the rotor to rotate.

[0073] 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.

[0074] Figure 4 is a flowchart of adjusting a pulse width modulation signal according to an embodiment of this application. In some embodiments, referring to Figure 4, the junction temperature of each switching element is obtained. When the junction temperature of one or more switching elements exceeds a temperature threshold, the junction temperatures of the upper and lower bridge switches of each phase are compared to determine the lower-temperature bridge arm among the switching elements of each phase as the first bridge arm, and the relatively lower-temperature bridge arm among the higher-temperature 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 heat to the relatively lower-temperature bridge arm of each phase, thus avoiding the accelerated aging of the device caused by concentrated heat.

[0075] Figure 5 is a waveform diagram of the three-phase current amplitude and rotor position angle when the motor is operating normally according to an embodiment of this application. In an exemplary embodiment, referring to Figure 5, if the junction temperature of the upper bridge element 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 element of phase C is turned on. Due to the fine adjustment of the rotor position, the position of the riding lawnmower hardly changes. However, this method makes the junction temperature of each switching element more uniform, 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 elements, and thus avoiding premature triggering of temperature protection and causing the vehicle to roll backward, which is beneficial to improving the safety performance and reliability of power tools.

[0076] Figure 6 illustrates the junction temperature effect of each switching element in the drive circuit controlled by the control method of this application. As shown in Figure 6, the temperature of the lower C-phase transistor rises to the threshold of 75°C before 62 seconds. 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 transistor and the upper B-phase transistor replace the lower C-phase transistor in bearing the load, causing their temperatures to rise, thus lowering the temperature of the lower C-phase transistor. Before 62 seconds, the upper A-phase transistor, the upper B-phase transistor, and the lower C-phase transistor are conducting. Due to the different current magnitudes and thermal resistances, the temperature rise of phase C is more significant. After adjusting the rotor position for 62 seconds, the lower A-phase transistor, the upper B-phase transistor, and the upper C-phase transistor are conducting.

[0077] 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 tool, comprising: Electric motor; A power interface is configured to connect to a power supply device to provide electrical energy to the motor; The driving circuit includes multiple switching elements arranged on a circuit board; A temperature sensing device disposed on the circuit board is configured to sense the ambient temperature near the plurality of switching elements; A control module, electrically connected to the drive circuit, is configured to output a pulse width modulation signal to change the conduction state of the plurality of switching elements; The loss estimation unit is configured to estimate the power loss of the switching elements based on the conduction loss and switching loss of the multiple switching elements. The control module is configured to estimate the temperature of the switching element based on the ambient temperature and the power loss of the switching element, and adjust the conduction state of the switching element based on the temperature of the switching element to control the operation of the motor.

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

3. The power tool according to claim 2, wherein, The loss estimation unit is configured to estimate the switching loss of the switching element based at least on the phase current of the motor and the switching frequency of the switching element.

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

5. The power tool according to claim 3, wherein, 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.

6. The power tool according to claim 5, wherein, The control module is configured to estimate 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.

7. The power tool according to claim 5, wherein, The control module is configured to estimate the reverse recovery loss of the diode based on the number of MOSFETs in parallel, the reverse recovery energy parameters of the diode, and the switching frequency of the switching element.

8. The power tool according to claim 1, wherein, The control module is configured to acquire the junction temperature of each of the switching elements and adjust the pulse width modulation signal when the junction temperature of at least one of the switching elements exceeds a preset temperature.

9. The power tool according to claim 8, wherein, The preset temperature range is greater than or equal to 65°C and less than or equal to 85°C.

10. The power tool according to claim 1, wherein, The motor includes a stator and a rotor; the pulse width modulation signal includes a first electrical signal; the first electrical signal is used to drive the rotor to rotate.

11. The power tool according to claim 10, wherein, The pulse width modulation signal includes a second electrical signal; the second electrical signal is used to lock the position of the rotor.

12. The power tool according to claim 1, wherein, The temperature sensing device includes a temperature sensor.

13. The power tool according to claim 1, wherein, The power tools include outdoor work vehicles.

14. The power tool according to claim 1, wherein, The motor is a brushless motor.

15. A method for estimating the temperature of multiple switching elements in a drive circuit of an electric tool, the electric tool including a motor and a control module, the control module being configured to output a pulse width modulation signal to change the conduction state of the multiple switching elements; The temperature estimation method includes: The ambient temperature of the multiple switching elements is sensed using a temperature sensing device; The conduction losses of the multiple switching elements are estimated based on the phase current of the motor, the on-state resistance of the multiple switching elements, and the duty cycle of the pulse width modulation signal. The switching losses of multiple switching elements are estimated based on the phase current of the motor and the switching frequency of the pulse width modulation signal. The control module estimates the temperature of the multiple switching elements based on the ambient temperature, the conduction loss of the multiple switching elements, and the switching loss of the multiple switching elements.

16. The temperature estimation method according to claim 15, wherein, The control module updates the on-state resistance of the switching element based on a preset relationship curve and the temperature of the switching element.

17. An outdoor work vehicle, comprising: The walking wheel set supports the outdoor work vehicle to move on the ground; The motor is used to drive the walking wheel set or working attachments. A power interface is provided for connecting a power supply device to enable the power supply device to provide electrical energy to the motor. The driving circuit includes multiple switching elements arranged on a circuit board; A control module is electrically connected to the drive circuit. The control module is configured to output a pulse width modulation signal to change the conduction state of each of the switching elements in the drive module. This also includes: A temperature estimation unit is used to estimate the junction temperature of each of the aforementioned switching elements; The control module is also configured to acquire the junction temperature of each of the switching elements, and 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.

18. The outdoor work vehicle according to claim 17, wherein, The temperature estimation unit includes a temperature sensing device and a loss estimation unit; the temperature sensing device is arranged on the circuit board and is used to sense the ambient temperature near each of the switching elements. 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.

19. The outdoor work vehicle according to claim 17, wherein, The pulse width modulation signal includes a first electrical signal; the first electrical signal is used to drive the rotor to rotate.

20. The outdoor work vehicle according to claim 17, wherein, The pulse width modulation signal includes a second electrical signal; the second electrical signal is used to lock the position of the rotor.

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