Motor-driven appliance and method for protecting the same

Abstract

A motor-driven device (20) includes a motor (24), a first switch module (25) and a second switch module (21) disposed in a current path from one terminal of a battery (26) to the other terminal of the battery (26), and an MCU (22) connected to the first switch module (25) and the second switch module (21). The first switch module (25) and the second switch module (21) are connected in series with each other, and the first switch module (25) is connected to the motor (24) and adapted to drive the motor (24). The MCU (22) is adapted to control the first switch module (25) and the second switch module (21) respectively. The MCU (22) is further adapted to attempt to control the second switch module (21) to be in a cut-off state after it is powered on, until the MCU (22) determines that the first switch module (25) is normal. The MCU (22) attempts to detect a fault in the switching element in the first switch module (25) before allowing the motor (24) to operate, so the possibility of the motor (24) being damaged by a short circuit in the first switch module (25) is minimized.

Description

Invention Field

[0001] This invention relates to motor-driven appliances, and more particularly to protecting motors from damage caused by malfunctions in the motor drive circuit. Background of the Invention

[0003] Various motor-driven appliances (such as, for example, electric vehicles, power tools, and electric machining machines) are known to include a switching module and a motor, wherein the switching module allows or disables the supply of current to the motor depending on whether the motor's output is required. Some switching modules take the simple form of a user-actuated mechanical switch, while others may take the form of a multiphase motor drive circuit used for brushless motors. Generally, protection for the motor and other components in the circuitry of motor-driven appliances is desirable because the switching module may be damaged or otherwise malfunction, which could lead to accidental motor start-up and injury to the operator, or even damage to the motor or other components in the circuitry due to high currents caused by short circuits.

[0004] Many different protection mechanisms have been developed to provide additional circuitry for motors and other components in case the switching module malfunctions. Examples of such mechanisms include configuring two identical sets of drive circuits for a brushless motor so that the other can be used in place of the first if one fails. Other examples include fault detection circuitry for the switching module in each phase of a multiphase motor. However, conventional protection mechanisms are often very complex in terms of circuitry, leading to additional costs, and are themselves prone to failure. Summary of the Invention

[0005] Accordingly, in one aspect, the present invention is a motor-driven appliance comprising a motor, a first switch module and a second switch module disposed in a current path from one terminal of an energy source to another terminal of the energy source, and a control unit connected to the first switch module and the second switch module. The first switch module and the second switch module are connected in series with each other, and the first switch module is connected to the motor and adapted to drive the motor. The control unit is adapted to control the first switch module and the second switch module respectively. The control unit is further adapted to attempt to control the second switch module to a cut-off state after it is energized, until the control unit determines that the first switch module is functioning normally.

[0006] In some embodiments, the motor is an N-phase brushless motor, and the first switching module includes an arm for each of the N phases. Each arm of the first switching module includes a high-side switching element and a low-side switching element. Each arm is connected to the corresponding phase of the motor's N phases at a point between the high-side and low-side switching elements of the arm.

[0007] In some embodiments, the control unit is adapted to determine that the first switching module is functioning correctly by measuring a single voltage drop within the first switching module.

[0008] In some embodiments, the motor-driven appliance further includes a detector circuit connected to the first switching module. The detector circuit includes a plurality of resistors and is adapted to output the fractional voltage. The control unit is adapted to determine whether any of the high-side and low-side switching elements in the first switching module is short-circuited by comparing the fractional voltage with a fraction of the source voltage fed to the first switching module. The fraction of the source voltage is determined by the plurality of resistors.

[0009] In some embodiments, the control unit is further adapted to determine whether a short circuit has occurred in the disconnecting switching element of the second switching module by comparing the fractional voltage with a fraction of the source voltage.

[0010] In some embodiments, the second switching module further includes a first switching element located in the current path and a second switching element connected to the first switching element. The second switching element is adapted to receive a signal from the control unit to change its switching state, thereby controlling the first switching element to be in the off state or the on state.

[0011] In some embodiments, both the first switching element and the second switching element are transistors. The second switching element is connected to the control terminal of the first switching element.

[0012] In some embodiments, the control unit applies a cut-off signal to the second switching element after it is powered on, so that the first switching element is in the cut-off state, until the control unit determines that the first switching module and the first switching element are both normal.

[0013] In some embodiments, the control unit is further adapted to attempt to control the second switch module to be in a cut-off state after it is powered on, until the control unit determines that both the first switch module and the second switch module are functioning normally.

[0014] Another aspect of the present invention provides a protection method for a motor-driven appliance, the motor-driven appliance including a motor and a control unit. The method includes: energizing the control unit; placing a second switching module in a cut-off state by the control unit; determining by the control unit whether a first switching module adapted to drive the motor is functioning correctly in the current path; and if the control unit detects that the first switching module is functioning correctly, deactivating the cut-off state of the second switching module. The second switching module is located in the current path passing through the motor.

[0015] In some embodiments, the determination performed by the control unit before releasing the cut-off state of the second switch module also includes determining whether the second switch module is functioning correctly.

[0016] Therefore, embodiments of the present invention provide a simple yet highly reliable fault detection circuit system for the switching module of a motor. In an example of a motor drive circuit for a brushless motor comprising six high-side and low-side MOSFETs, the microcontroller unit (MCU) will know whether any of these six MOSFETs, and the MOSFET in the cutoff circuit, is short-circuited and thus faulty. This determination is made when the MCU is powered on and before the MCU sends any drive signals to the motor drive circuit; therefore, the motor will not be harmed by any short circuit because the fault detection process is completed at an early stage. Furthermore, all components in the detector circuit are resistors, which minimizes the possibility of the detector circuit itself failing. The MCU, as described above, can also detect any faults in the cutoff circuit (i.e., the cutoff MOSFET). Therefore, the protection mechanism provided in the embodiments is low-cost and not prone to failure.

[0017] The foregoing summary is not intended to limit the invention of this application as measured by the claims, nor is it intended to limit the scope of the invention in any way. Attached Figure Description

[0018] The foregoing and further features of the invention will become apparent from the following description, taken in conjunction with embodiments provided by way of example only in conjunction with the accompanying drawings, in which:

[0019] Figure 1 This is a schematic diagram showing the circuitry in a motor-driven device according to a first embodiment of the present invention.

[0020] Figure 2 It shows Figure 1 The motor drive circuit and fault protection mechanism in the motor-driven device.

[0021] Figure 3 This shows the MCU determining Figure 1 A flowchart illustrating the process of a fault in the MOSFET of a motor drive circuit in a motor-driven device.

[0022] Figure 4 A motor drive circuit and fault protection mechanism in a motor drive device according to another embodiment of the present invention are shown.

[0023] Figure 5 This shows the MCU determining Figure 4 A flowchart illustrating the process of a fault in the MOSFET of a motor drive circuit in a motor-driven device.

[0024] In the accompanying drawings, similar numbers indicate similar parts in all the embodiments described herein. Detailed Implementation

[0025] In the following claims and preceding description, unless the context requires otherwise due to explicit language or necessary implication, the word "comprising" or its variations such as "comprises" or "comprising" are used in a sense of inclusion, that is, indicating the presence of the described feature but not excluding the presence or addition of other features in different embodiments of the invention.

[0026] As used herein and in the claims, unless otherwise stated, “coupled” or “connected” means electrical coupling or connection, directly or indirectly via one or more electrical devices.

[0027] Now for reference Figure 1 The first embodiment of the present invention is a motor-driven device 20, which can take the form of a portable power tool, household appliance, electric vehicle, etc. It should be noted that the shape factor or final effect of the motor-driven device is irrelevant to the embodiment, as the embodiment concerns the protection of the motor. The motor-driven device 20 includes a battery 26 as an energy source, which can be, for example, a removable battery pack, a built-in fuel cell, a dry cell battery, etc. It should be noted that although the battery 26... Figure 1 The block diagram depicts it as a single component, but it can also contain multiple stacked energy storage devices as illustrated above. The two output terminals BAT+ and BAT- of battery 26 are connected to PCBA 28 (printed circuit board assembly), which includes at least a controller and a switching module for the brushless motor 24 connected to PCBA 28. It should be noted that although PCBA 28 is... Figure 1 While depicted as a single component, in the motor-driven device 20 it can consist of two or more separate PCBAs, on which multiple functional blocks of the device 20's circuitry are distributed. The device 20 may have other components, such as a housing, motor-driven operating elements, user input devices, etc., which are irrelevant to the embodiment and therefore not included in the description. Figure 1 As shown in the image.

[0028] from Figure 1As can be seen, battery 26 outputs direct current (DC) power to PCBA 28, which means that a current path is established from one terminal (i.e., BAT+) of battery 26 to the other terminal (i.e., BAT-) of battery 26. The brushless motor 24 and any other electrical components of device 20 are located in this current path, but the motor drive circuit on PCBA 28 is required to convert the DC power from battery 26 into a frequency-controlled three-phase output (represented by U, V, and W) for motor 24. The motor drive circuit and its protection mechanisms will be described in more detail below.

[0029] Turn now Figure 2 The figure shows a schematic diagram of PCBA 28, including control circuitry and protection mechanisms for the brushless motor 24. MCU 22 acts as the control unit of the motor drive device 20, connected to the motor drive circuit 25, the cut-off circuit 21, and the detector circuit 23. MCU 22 is adapted to control the motor drive circuit 25 and the cut-off circuit 21, respectively. In this embodiment, the motor drive circuit 25 is a first switching module, and the cut-off circuit 21 is a second switching module. MCU 22, the cut-off circuit 21, and the detector circuit 23 together form the protection mechanism for the motor 24. MCU 22 is powered by battery 26 through a power supply circuit (not shown) separate from the motor drive circuit 25.

[0030] As those skilled in the art will understand, the motor drive circuit 25 adopts a conventional configuration of six MOSFETs Q5-Q10. The three arms of the motor drive circuit 25 correspond to the three phases U, V, and W of the motor 24, respectively. Each arm has a pair of high-side MOSFETs (Q6, Q7, or Q5) and low-side MOSFETs (Q9, Q8, or Q10). At the points between the high-side MOSFETs (e.g., Q5) and low-side MOSFETs (e.g., Q10) in the arm, there are wires connecting to the corresponding phases of the motor 24. The N-channel MOSFETs Q5-Q10 are switching elements in the motor drive circuit 25, and their gates are connected to the MCU 22, as described by... Figure 2 The markings UHSD, ULSD, VHSD, VLSD, WHSD, and WLSD indicate this. The drains of the high-side MOSFETs Q5-Q7 are connected to the battery terminal BAT+, and their sources are connected to the low-side MOSFETs Q8-Q10. As understood by those skilled in the art, the rotation of motor 24 is controlled by MCU 22 using a six-step commutation technique (sometimes referred to as 60-degree or 120-degree control). The six-step technique creates a voltage system with six vectors on an electronic rotation, using a Hall sensor (not shown) to determine the real-time position of the rotor.

[0031] Connected to the motor drive circuit 25 is a detector circuit 23, which extracts a single voltage division B for the MCU 22 to determine potential faults in any of the MOSFETs Q5-Q10 and MOSFET Q12 in the cutoff circuit 21. The detector circuit 23 contains two outputs connected to the MCU 22 via a suitable voltage sensing device (not shown): the battery voltage A (which serves as the source voltage at the input of the motor drive circuit 25) and the voltage division B. The voltage division B is named so because it is generated by a voltage divider circuit in the detector circuit 23, which consists of multiple resistors R3, R6, R8, R13, and R15. Voltage division B is the only voltage to be measured, and if all seven MOSFETs Q5-Q10 and Q12 are functioning correctly, B should be a fixed fraction of the battery voltage A. However, if one or more of the MOSFETs are short-circuited, one or more of the aforementioned resistors will be bypassed due to the short circuit, depending on the location of the faulty MOSFET(s), so the actual measured voltage B will differ from the fixed fractional value. Figure 2 In this embodiment, the four resistors R3, R6, R15, and R13 have the same resistance value. A capacitor C2 is connected in parallel with resistor R15 between R8 and ground. Capacitor C2 serves as a voltage filter for voltage division B.

[0032] Turning to the cut-off circuit 21, it can be seen that this circuit is connected in series with the motor drive circuit 25 in the current path from BAT+ to BAT-. Cut-off circuit 21 is designed to cut off the current path when necessary, preventing power supply to the motor 24 even if the motor drive circuit 25 experiences a short circuit or other fault, thus preventing damage to the motor 24. Cut-off circuit 21 includes a trigger input connected to a trigger (not shown) of the motor drive device 20, wherein the trigger input is connected to the gate of the cut-off switching element (MOSFET Q12) via a resistor R1. When the user does not press the trigger (not shown) of the motor drive device 20, the trigger input will always turn off Q12, as the trigger supplies gate drive current to Q12 to turn it on when closed. On the other hand, before Q12, the trigger input is also connected to another MOSFET Q1, which is controlled by the MCU 22 via a force_cut-off pin connected to the control terminal (which is the gate) of Q1. Q1 is connected to common ground on the other side (via its source). During normal operation of the motor-driven device, MCU 22 does not provide a force_cut-off signal to the force_cut-off pin, so Q1 is not turned on, and any gate drive signal to Q12 will drive Q12 into its on state due to the user pressing the trigger. However, if MCU 22 outputs a force_cut-off signal to the force_cut-off pin connected to the gate of Q1, the current flowing through R1 bypasses the gate of Q12 and flows to ground through R2 and Q1. Accordingly, Q12 is turned off (not turned on), regardless of whether the tool trigger is activated.

[0033] Now we turn to the operation of the aforementioned fault detection and motor protection mechanisms. Figure 3This diagram illustrates how MCU 22 determines potential faults in MOSFETs Q5-Q10 of the motor drive circuit 25 and Q12 of the cutoff circuit 21 before allowing motor 24 to operate. The method begins at step 30, where the user presses a trigger on the motor drive device 20 to turn it on. Once the trigger is pressed, in step 31, MCU 22 is powered on and operational via its power supply circuit connected to battery 26. However, MCU 22 does not immediately turn on motor 24 upon power-up, and specifically, it does not send drive signals to Q5-Q10 in the motor drive circuit 25 at this stage. Instead, MCU 22 first applies a force_cut-off signal to Q1 in the cutoff circuit 21. With the force_cut-off signal in place, Q1 becomes on when the user simultaneously presses the trigger, so the gate drive current from the trigger is not delivered to Q12, causing Q12 to de-conduct. In this way, besides the lack of a drive signal provided to Q5-Q10, there is also no current flowing from BAT+ to BAT-, so motor 24 will not start under any circumstances.

[0034] After applying a force_cut-off signal to Q1, MCU 22 then attempts to determine any potential faults in Q5 through Q10 and Q12. In step 34, MCU 22 first reads the battery voltage at BAT+, which is the source voltage A. As mentioned above, the source voltage A is not directly coupled to MCU 22 because its amplitude might be too large for MCU 22. Instead, the source voltage A (and the same applies to the divided voltage B) is reduced to an acceptable range for MCU 22 via a voltage sensing device. Then, in step 35, MCU 22 checks the amplitude of the divided voltage B. In step 36, MCU 22 determines whether B = 0. If so, the method proceeds to step 43, where MCU 22 determines that Q12 is shorted, and then the method ends at step 44 because at least one of the critical MOSFETs is faulty, and the motor drive unit 20 cannot start until the user replaces the faulty component.

[0035] If the MCU 22 finds that the voltage division B is not equal to zero in step 36, the method proceeds to step 37, where the MCU 22 determines whether B = 0.03A. If so, in step 40, the MCU 22 determines that all critical MOSFETs Q5-Q10 and Q12 are normal, so the motor drive device 20 can be started. Therefore, a fraction of 0.03A is the aforementioned fixed fraction value indicating that the motor drive circuit 25 is in a normal state. If B is found to be not equal to 0.03A in step 37, the method proceeds to step 38, where the MCU 22 determines whether B = 0.045A. If so, this means that at least one of the high-side MOSFETs is shorted, or at least one of the low-side MOSFETs is shorted, but not both the high-side and low-side MOSFETs are shorted simultaneously, and in step 41, the MCU 22 sequentially determines a fault on only one of the high-side and low-side MOSFETs. On the other hand, if both the high-side MOSFET and the low-side MOSFET are shorted simultaneously, B will not be equal to 0.045A (and the method proceeds to step 39), but will be equal to 0.09A, and in step 42, the MCU 22 will sequentially determine the fault on both the high-side and low-side. Regardless of whether the fault occurs on one or both of the high-side and low-side, the method will proceed from steps 41 and 42 to the aforementioned step 44.

[0036] In general, for Figure 3 The method in the article, MCU 22 is based on Figure 2 The resistor values ​​shown are used to calculate the expected value of B (i.e., a fixed fractional value) using the following formula, which states that B should equal 0.03A if everything is normal. However, if any of Q5, Q6, and Q7 are shorted, the effective value of R3 in the formula becomes zero. Similarly, if any of Q8, Q9, and Q10 are shorted, the effective value of R6 in the formula becomes zero. If Q12 in circuit 21 is shorted, the effective value of R13 in the formula becomes zero. All of the above will result in an actual value of B that differs from 0.03A, such as the fractions 0.045A and 0.09A shown in steps 38 and 39. The MCU 22 then compares the actual magnitude of the divided voltage B with the different fractions to determine the location of the fault in the circuit.

[0037]

[0038] As can be seen from the above, the method in the embodiment provides a robust mechanism for detecting faults in critical MOSFETs and protects the motor by not providing a drive signal to the motor and not releasing the cutoff at Q12 until all critical MOSFETs are found to be functioning correctly. If one of these MOSFETs malfunctions, the motor drive device cannot start, and the user needs to replace the defective component. In subsequent trials, the above method will be repeated to ensure all MOSFETs are in good condition. It should also be noted that, although not shown in the flowchart, a fault in MOSFET Q1 (if any) will also be detected through... Figure 3 The method implicitly captures this because if Q1 is shorted, Q1 will always be on regardless of any force_cut-off signal from MCU 22 (i.e., when MCU 22 “attempts” to put the cut-off circuit 21 into the off state), thus maintaining the off state of Q12 and protecting the motor 24.

[0039] Turn Figures 4 to 5 In another embodiment of the present invention, a schematic diagram of the PCBA and the operation method of the fault detection and motor protection mechanism will be described. For the sake of brevity, only the following sections will describe... Figures 4 to 5 The embodiments and Figures 2 to 3 The differences compared to the embodiments in the text. Figure 4 The circuit also includes a motor drive circuit 125, an MCU (not shown), a cut-off circuit 121, and a detector circuit 123, whose interconnections are... Figure 2 The interconnections are similar. However, the circuitry within the cutoff circuit 121 and the detector circuit 123 is similar to that in... Figure 2 There are slight differences compared to the corresponding parts in the circuit. In the cutoff circuit 121, a diode D13 and a resistor 26 are connected in parallel between the trigger input and Q12, which helps protect the Q12 current from reverse current. Furthermore, there are now additional resistors R33 and R32 in the cutoff circuit 121 connected to the gate and source of another MOSFET Q20. In the detector circuit 123, with... Figure 2 The main difference between the detector circuit in the original is that it lacks a capacitor for filtering the divided voltage B.

[0040] Figure 5 It shows the use of Figure 4 The operation method of circuit fault detection and motor protection mechanism. Figure 5 All steps 130 to 136 and their in Figure 3 The corresponding parts are basically the same, and will not be described again in this article. Differences begin from step 137, where... Figure 5In this method, different fractions of the source voltage A are used as the basis for detecting MOSFET faults. In step 137, the MCU first determines whether B is equal to or greater than 1 / 22*A. If so, in step 140, the MCU determines that at least one of Q5-Q10 is shorted. The method ends at step 144 because at least one of the critical MOSFETs is faulty, and the motor-driven device cannot start until the user replaces the faulty component.

[0041] If the MCU detects in step 137 that the voltage B is below 1 / 22*A, the method proceeds to step 138, where the MCU determines whether B is between zero and 1 / 33*A. If so, this means that at least one of MOSFETs Q5-Q10 is shorted, and the MCU sequentially identifies this fault in step 141. Then, the method proceeds to step 144. On the other hand, if all MOSFETs Q5-Q10 and Q12 are normal, the check result in step 138 will be true, and the method proceeds to step 139, where the MCU determines that the situation is normal, so the motor drive device can be started in step 142.

[0042] Therefore, exemplary embodiments have been fully described. While specific embodiments are mentioned in the description, it will be apparent to those skilled in the art that these specific details can be altered to practice the invention. Therefore, the invention should not be construed as being limited to the embodiments set forth herein.

[0043] Although embodiments have been shown and described in detail in the accompanying drawings and the foregoing description, they should be considered illustrative rather than restrictive in nature. It should be understood that exemplary embodiments are shown and described only and do not limit the scope of the invention in any way. It is understood that any feature described herein can be used with any embodiment. Illustrative embodiments are not mutually exclusive, nor do they exclude other embodiments not listed herein. Accordingly, the invention also provides embodiments that include combinations of one or more of the illustrative embodiments described above. Modifications and changes can be made to the invention as set forth herein without departing from the spirit and scope of the invention; therefore, only the limitations specified in the appended claims should apply.

[0044] It should be understood that if this document references any prior art publication, such reference does not constitute an endorsement that the publication constitutes part of common general knowledge in the art in Australia or any other country.

[0045] For example, in Figure 1In the embodiments described, the battery is shown as the energy source for the motor-driven device; however, those skilled in the art will recognize that other types of energy sources, such as mains power, generators, solar panels, etc., can also be used. Similarly, although a brushless motor is shown in the above embodiments, the protection mechanisms of the present invention can also be applied to other types of motors, such as AC motors or DC brushed motors. The number of phases of the brushless motor does not necessarily have to be three, as it can be generalized to N phases, where N is greater than 1.

[0046] It should be noted that, Figure 2 and Figure 4 The circuit structures of the detector circuit and the cut-off circuit shown are not intended to be limiting, as other types of circuit systems can also be used for the same purpose, as long as the overall circuit is designed to achieve the purpose of the invention, that is, to initially apply the cut-off state to the motor current path until all switching elements are found to be functioning properly.

[0047] Various embodiments of the present invention can protect motors and any other electrical components in the main circuit path from damage caused by large currents resulting from a short circuit in one or more switching elements. Specifically, for example, other electrical components besides the motor include other types of energy-consuming components (i.e., loads), such as lighting equipment, sound equipment, and displays. Embodiments of the present invention can also protect power supply devices such as batteries and power converters from damage.

Claims

1. A motor-driven appliance, comprising: a) Electric motor; b) A first switch module and a second switch module, which are disposed in series with each other in a current path from one terminal of the energy source to the other terminal of the energy source; the first switch module is connected to the motor and adapted to drive the motor; c) A control unit connected to the first switch module and the second switch module; the control unit is adapted to control the first switch module and the second switch module respectively; The control unit is further adapted to attempt to control the second switch module to be in the off state after it is powered on, until the control unit determines that both the first switch module and the second switch module are normal. The control unit is further adapted to determine whether the first switch module and the second switch module are functioning properly based on the source voltage and the branch voltage.

2. The motor-driven appliance according to claim 1, wherein, The motor is an N-phase brushless motor, and the first switching module includes an arm for each of the N phases; Each arm of the first switching module includes a high-side switching element and a low-side switching element; each arm is connected to the corresponding phase of the N phases of the motor at a point between the high-side switching element and the low-side switching element of the arm.

3. The motor-driven appliance according to claim 2, wherein, The control unit is adapted to determine the normality of the first switching module by measuring a single voltage drop within the first switching module.

4. The motor-driven appliance according to claim 3, further comprising a detector circuit connected to the first switching module; the detector circuit comprising a plurality of resistors and adapted to output the divided voltage; wherein, The control unit is adapted to determine whether any of the high-side and low-side switching elements in the first switching module is short-circuited by comparing the fractional voltage with a fraction of the source voltage fed to the first switching module, wherein the fraction of the source voltage is determined by the plurality of resistors.

5. The motor-driven appliance according to claim 4, wherein, The control unit is further adapted to determine whether a short circuit has occurred in the disconnecting switching element in the second switching module by comparing the fractional voltage with a fraction of the source voltage.

6. The motor-driven appliance according to claim 1, wherein, The second switching module further includes a first switching element located in the current path and a second switching element connected to the first switching element; the second switching element is adapted to receive a signal from the control unit to change its switching state, thereby controlling the first switching element to be in the off state or the on state.

7. The motor-driven appliance according to claim 6, wherein, Both the first switching element and the second switching element are transistors, and the second switching element is connected to the control terminal of the first switching element.

8. The motor-driven appliance according to claim 7, wherein, After being powered on, the control unit applies a cut-off signal to the second switching element to put the first switching element in the cut-off state until the control unit determines that the first switching module and the first switching element are both normal.

9. A method for protecting a motor-driven appliance according to any one of claims 1 to 8, the method comprising: a) Power on the control unit using a power source; b) The control unit places the second switch module in the off state; The second switch module is located on the current path passing through the motor; c) The control unit determines whether the first switching module, which is adapted to drive the motor on the current path, is functioning properly; d) If the control unit detects that the first and second switch modules are functioning normally, it releases the off state of the second switch module; and e) Determine whether the first and second switching modules are functioning correctly based on the source voltage and the branch voltage.

10. The protection method according to claim 9, wherein, Step c) further includes determining whether the second switch module is functioning correctly.

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