A battery-type permanent magnet and forward and reverse excitation methods thereof

Abstract

The present invention discloses a battery-type electric permanent magnet and a forward and reverse excitation method thereof. The electric permanent magnet comprises a battery, a controller and an electric permanent magnet body. The controller comprises an excitation circuit unit connected in parallel with each other and a freewheeling circuit unit connected in series with the excitation circuit unit in a one-to-one correspondence. The excitation circuit unit comprises a first switch and a second switch, and an excitation coil in the electric permanent magnet body is connected between the first switch and the second switch. Both the first switch and the second switch are single-pole double-throw switches, and both ends of the excitation coil are connected to the moving ends of the first switch and the second switch, and the two fixed ends of the first switch and the second switch are respectively connected to the positive pole of the battery and the freewheeling circuit unit, and the freewheeling circuit unit is connected to the negative pole of the battery. The battery-type electric permanent magnet of the present invention has the advantages of large excitation current, large lifting capacity, no need to wait for the freewheeling time, multi-channel fast triggering and simple structure. The forward and reverse excitation method of the electric permanent magnet provided by the present invention has the advantages of simple steps and high safety performance.

Description

Technical Field

[0001] The invention relates to the field of magnetic devices, and in particular to a battery-type electro-permanent magnet and a forward and reverse excitation method thereof. Background Art

[0002] The principle of the battery-type permanent magnet is to use the battery to power the controller, so that the controller outputs a forward or reverse current to excite the excitation coil inside the permanent magnet, so that the reversible magnetic steel surrounding it is activated, and a magnetic field in the same direction or opposite direction as the permanent magnet is generated to absorb or release the target magnetic material. Usually, the excitation coil inside the permanent magnet is a large inductive load, so at the end of the excitation process, the excitation current cannot change suddenly, but requires a certain continuous flow time. The existing large permanent magnets require a large excitation current, while the voltage and current that the battery can provide are limited. Therefore, the charging and demagnetization operations are generally divided into multiple groups and performed in sequence. However, after each group of charging and demagnetization is completed, it is necessary to wait for the continuous flow to complete before the next group of operations can be performed, so the charging and demagnetization time is relatively long. Summary of the invention

[0003] The problem to be solved by the present invention is to provide a battery-type electropermanent magnet with large excitation current, large lifting capacity, no need to wait for freewheeling time, multi-channel rapid triggering and simple structure, in view of the problems existing in the prior art. A method for positive and reverse excitation of the battery-type electropermanent magnet with simple steps and quick operation is also provided accordingly.

[0004] In order to solve the above technical problems, the technical solution proposed by the present invention is:

[0005] A battery-type electro-permanent magnet comprises a battery, a controller and an electro-permanent magnet body, wherein the electro-permanent magnet body comprises an excitation coil, the controller comprises one or more excitation circuit units connected in parallel with each other and a freewheeling circuit unit connected in series with the excitation circuit units in a one-to-one correspondence, the excitation circuit unit comprises a first switch and a second switch, and an excitation coil is connected between the first switch and the second switch; the first switch and the second switch are both single-pole double-throw switches, the two ends of the excitation coil are respectively connected to the moving ends of the first switch and the second switch, and the two fixed ends of the first switch and the second switch are respectively connected to the positive pole of the battery and the freewheeling circuit unit, and the freewheeling circuit unit is connected to the negative pole of the battery.

[0006] As a further improvement of the above technical solution:

[0007] The freewheeling circuit unit includes two unidirectionally conducting first and second transistors connected in parallel, and a third transistor connected between the input ends of the first and second transistors and the negative electrode of the battery; the output ends of the first and second transistors are respectively connected to the two ends of the excitation coil.

[0008] The first transistor and the second transistor are diodes, and the third transistor is a triode.

[0009] The collector of the third transistor is respectively connected to a fixed end of the first switch, a fixed end of the second switch, an input end of the first transistor and an input end of the second transistor, and the emitter of the third transistor is connected to the negative electrode of the battery.

[0010] The third transistor is an IGBT tube.

[0011] The first switch and the second switch are both relays. In the first switch and the second switch, the excitation coil and the freewheeling circuit unit are connected to the normally closed contact.

[0012] The battery-type electropermanent magnet further includes a single-chip microcomputer connected to the control ends of the first switch and the second switch respectively; the single-chip microcomputer is configured to perform one or both of the following actions:

[0013] When the battery-type permanent magnet is positively excited, the first switch is triggered to operate, and the second switch is not operated;

[0014] When the battery-type electropermanent magnet is reversely excited, the second switch is triggered to act, and the first switch is not acted.

[0015] The battery-type electropermanent magnet also includes a third transistor driving chip for driving the third transistor to conduct. The single-chip microcomputer is also connected to the third transistor driving chip. The third transistor driving chip is connected to the gate of the third transistor. When the single-chip microcomputer triggers the first switch or the second switch, it controls the third transistor driving chip to trigger the third transistor.

[0016] The controller also includes an external unit and a detection unit. The external unit, the detection unit and the single-chip microcomputer are connected by wire or wireless means. The detection unit includes a power detection module. The power detection module detects the power of the battery and sends it to the display module of the external unit to display the power of the battery.

[0017] The external unit also includes a power warning light. When the power detection module detects that the power of the battery is low, the power warning light is controlled to send a warning signal.

[0018] The detection unit also includes an excitation current detection device, which sends a signal to the single-chip microcomputer when the excitation current reaches the maximum allowable value. After receiving the signal, the single-chip microcomputer controls the third transistor driving chip to stop triggering the third transistor.

[0019] The maximum allowable value of the excitation current is the maximum allowable current value of the third transistor or a preset value.

[0020] The detection unit also includes a magnetic flux detection module, and the external unit also includes a lifting indicator light. The magnetic flux detection module sends the measured magnetic flux to the single-chip microcomputer, and the single-chip microcomputer determines whether the preset lifting magnetic flux is reached. The single-chip microcomputer controls the lighting of the lifting indicator light according to the judgment result.

[0021] A forward excitation method for the battery-type permanent magnet, comprising the following steps:

[0022] S1: Relay is forward connected: The microcontroller controls the first switch in an excitation circuit unit to operate, and the second switch does not operate;

[0023] S2: triggering the third transistor: at the same time as step S1, the single chip microcomputer controls the third transistor driving chip so that the third transistor driving chip triggers the gate of the third transistor in the freewheeling circuit unit connected in series with the excitation circuit unit;

[0024] S3: a single excitation coil completes forward excitation: after the excitation current is generated in the excitation coil, the single chip microcomputer controls the third transistor driver chip to stop triggering the gate of the third transistor in the freewheeling circuit unit connected in series with the excitation circuit unit;

[0025] S4: forward excitation completed: the microcontroller starts forward excitation to the next excitation coil, and repeats steps S1 to S3 until all excitation coils are excited.

[0026] A reverse excitation method for the battery-type permanent magnet, comprising the following steps:

[0027] S1: Relay reverse connection: The single chip microcomputer controls the first switch in an excitation circuit unit to not operate, and the second switch to operate;

[0028] S2: triggering the third transistor: at the same time as step S1, the single chip microcomputer controls the third transistor driving chip so that the third transistor driving chip triggers the gate of the third transistor in the freewheeling circuit unit connected in series with the excitation circuit unit;

[0029] S3: a single excitation coil completes reverse excitation: after the excitation current is generated in the excitation coil, the single chip microcomputer controls the third transistor driver chip to stop triggering the gate of the third transistor in the freewheeling circuit unit connected in series with the excitation circuit unit;

[0030] S4: Reverse excitation completed: The microcontroller starts reverse excitation to the next excitation coil, and repeats steps S1 to S3 until all excitation coils are excited.

[0031] Compared with the prior art, the advantages of the present invention are:

[0032] The battery-type permanent magnet of the present invention has an excitation circuit unit and a freewheeling circuit unit connected to the excitation coil in the controller as shown in FIG.Figure 1 As shown in Figure 1, the connection structure is very simple. When forward excitation is performed, Figure 2 As shown, the IGBT is turned on, the first switch is connected to the positive electrode of the battery, and the second switch is connected to the collector of the IGBT. At this time, the current path is as follows Figure 2 As shown by the solid line in the figure; when the positive excitation current is generated in the excitation coil, the IGBT can stop conducting. Due to the large inductance of the excitation coil, the current cannot suddenly change, and the freewheeling current will flow along Figure 2 The dotted line path in the figure automatically continues the current flow, and the continuous current flow path does not pass through the battery and the first switch. Therefore, even if the first switch is suddenly disconnected, it will not bear the reverse pressure generated when the large inductive load is suddenly disconnected, and will not cause arcing or damage to the first switch. When reverse excitation is performed, Figure 3 As shown, the IGBT is turned on, the second switch is connected to the positive electrode of the battery, and the first switch is connected to the collector of the IGBT. The current path and the freewheeling current path are respectively as shown in Figure 3 The solid and dashed paths are shown in .

[0033] Furthermore, in order to enhance the magnetic force of the electropermanent magnet, the battery-type electropermanent magnet of the present invention is in a multi-channel form, that is, a plurality of excitation circuit units are connected in parallel, so that one battery can excite a plurality of coils; since the freewheeling path of the freewheeling circuit unit of the present invention does not pass through the battery, when one excitation coil is excited, the next excitation coil can be excited immediately, without waiting for the intermediate freewheeling time, and can be triggered continuously, saving a lot of time; and this multi-channel form can increase the excitation current several times when using batteries of the same voltage, greatly increasing the adsorption capacity of the electropermanent magnet.

[0034] In addition, the forward and reverse excitation method of the battery-type permanent magnet of the present invention also has the above advantages, and the excitation method has simple steps, and the operator only needs to press the indicator button preliminarily, avoiding the occurrence of mistakes during manual operation, and has high safety performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0036] Figure 1 It is a structural schematic diagram of an excitation circuit unit and a freewheeling circuit unit in a battery-type electropermanent magnet of the present invention;

[0037] Figure 2It is a current path diagram of the forward excitation of the battery-type permanent magnet of the present invention;

[0038] Figure 3 It is a current path diagram of reverse excitation of the battery-type permanent magnet of the present invention;

[0039] Figure 4 It is a schematic structural diagram of multiple groups of excitation circuit units in parallel in the battery-type electropermanent magnet of the present invention;

[0040] Figure 5 It is a structural schematic diagram of a control panel in a battery-type electropermanent magnet of the present invention. DETAILED DESCRIPTION

[0041] In order to facilitate the understanding of the present invention, the present invention will be described more comprehensively and meticulously below in conjunction with the accompanying drawings and preferred embodiments of the specification, but the protection scope of the present invention is not limited to the following specific embodiments.

[0042] Example:

[0043] The battery-type electro-permanent magnet of this embodiment includes a battery, a controller and an electro-permanent magnet body, wherein the electro-permanent magnet body includes an excitation coil, a reversible magnetic steel, a permanent magnetic steel and a magnetic pole, and the excitation coil is wound around the periphery of the reversible magnetic steel. During forward excitation, the controller generates a current in the excitation coil and causes the reversible magnetic steel to generate a magnetic field in the same direction as the permanent magnetic steel to adsorb the workpiece; during reverse excitation, the controller generates a current in the excitation coil and causes the reversible magnetic steel to generate a magnetic field in the opposite direction to the permanent magnetic steel, and the two magnetic fields cancel each other out to release the workpiece.

[0044] like Figure 1 As shown, the controller includes one or more excitation circuit units connected in parallel with each other and freewheeling circuit units connected in series with the excitation circuit units in a one-to-one correspondence. The excitation circuit unit includes a first switch K1 and a second switch K2, and an excitation coil is connected between the first switch K1 and the second switch K2; the first switch K1 and the second switch K2 are both single-pole double-throw switches, and the two ends of the excitation coil are respectively connected to the moving ends of the first switch K1 and the second switch K2, and the two fixed ends of the first switch K1 and the second switch K2 are respectively connected to the positive electrode of the battery and the freewheeling circuit unit, and the freewheeling circuit unit is connected to the negative electrode of the battery.

[0045] In this embodiment, the freewheeling circuit unit includes two mutually parallel unidirectional conductive first and second transistors, and a third transistor connected between the input ends of the first and second transistors and the negative electrode of the battery; the output ends of the first and second transistors are respectively connected to the two ends of the excitation coil. The collector of the third transistor is respectively connected to a fixed end of the first switch K1, a fixed end of the second switch K2, and the input end of the first transistor and the input end of the second transistor, and the emitter of the third transistor is connected to the negative electrode of the battery. Among them, the first and second transistors are diodes, and the third transistor is an IGBT tube.

[0046] The battery-type permanent magnet of this embodiment, when performing forward excitation, Figure 2 As shown, the IGBT is turned on, the first switch K1 is connected to the positive electrode of the battery, and the second switch K2 is connected to the collector of the IGBT. At this time, the current path is as follows Figure 2 As shown by the solid line in the figure; when the positive excitation current is generated in the excitation coil, the IGBT can stop conducting. Due to the large inductance of the excitation coil, the current cannot suddenly change, and the freewheeling current will flow along Figure 2 The dotted line path in the figure automatically continues the current flow, and the continuous current flow path does not pass through the battery and the first switch K1. Therefore, even if the first switch K1 is suddenly disconnected, it will not bear the reverse pressure generated when the large inductive load is suddenly disconnected, and will not cause arcing or damage to the first switch K1. When reverse excitation is performed, Figure 3 As shown, the IGBT is turned on, the second switch K2 is connected to the positive electrode of the battery, and the first switch K1 is connected to the collector of the IGBT. The current path and the freewheeling current path are respectively as shown in Figure 3 The solid and dashed paths are shown in .

[0047] Of course, according to the above method, it is also feasible to set the freewheeling circuit unit before the positive electrode of the battery and the excitation circuit unit, but this implementation should still be regarded as a simple transformation of the present implementation and should still fall within the protection scope of the present invention.

[0048] In this embodiment, the first switch K1 and the second switch K2 are both relays. In the first switch K1 and the second switch K2, the excitation coil and the freewheeling circuit unit are connected to the normally closed contact. In this embodiment, the battery-type electro-permanent magnet also includes a single-chip microcomputer connected to the control ends of the first switch K1 and the second switch K2 respectively; the single-chip microcomputer is configured to perform the following actions: when the battery-type electro-permanent magnet is positively excited, the first switch K1 is triggered to act, and the second switch K2 is not acted; when the battery-type electro-permanent magnet is reversely excited, the second switch K2 is triggered to act, and the first switch K1 is not acted. The excitation action of the battery is controlled by the single-chip microcomputer, which can effectively avoid manual misoperation and has high safety performance.

[0049] In this embodiment, the battery-type electropermanent magnet also includes a third transistor driver chip for driving the third transistor to conduct, the single-chip microcomputer is also connected to the third transistor driver chip, the third transistor driver chip is connected to the gate of the third transistor, and the single-chip microcomputer triggers the first switch K1 or the second switch K2 while controlling the third transistor driver chip to trigger the third transistor.

[0050] Furthermore, in order to enhance the magnetic force of the electro-permanent magnet, the battery-type electro-permanent magnet of this embodiment is in a multi-channel form, such as Figure 4 As shown, multiple excitation circuit units are connected in parallel, so that one battery can excite multiple coils; since the freewheeling path of the freewheeling circuit unit of this embodiment does not pass through the battery, when one excitation coil is excited, the next excitation coil can be excited immediately without waiting for the intermediate freewheeling time, and can be triggered continuously, with an extremely fast response speed, saving a lot of time; and this multi-channel form can increase the excitation current many times when using batteries of the same voltage, greatly increasing the adsorption capacity of the electropermanent magnet.

[0051] In this embodiment, the controller also includes an external unit and a detection unit. The external unit, the detection unit and the single-chip computer are connected by wired or wireless means. The detection unit includes a power detection module. The power detection module detects the power of the battery and sends it to the display module of the external unit to display the power of the battery, so that the operator can observe and charge the battery in time, avoiding the situation where the battery is low when the electromagnet is needed, resulting in work delays.

[0052] The external unit also includes a power warning light. When the power detection module detects that the battery power is low, the power warning light is controlled to send a warning signal. After the operator observes the warning signal, the magnetization operation is prohibited to prevent unsafe operation caused by low magnetic force; in this case, the demagnetization operation can still be performed.

[0053] In this embodiment, the detection unit further includes an excitation current detection device, which sends a signal to the single-chip microcomputer when the excitation current reaches the maximum allowable value. After receiving the signal, the single-chip microcomputer controls the third transistor driver chip to stop triggering the third transistor to prevent a short circuit accident. The maximum allowable value of the excitation current can be preset to the maximum allowable value of the current of the third transistor or preset according to specific working conditions.

[0054] In this embodiment, the detection unit also includes a magnetic flux detection module, and the external unit also includes a lifting indicator light. The magnetic flux detection module sends the measured magnetic flux to the single-chip microcomputer, and the single-chip microcomputer determines whether the preset lifting magnetic flux is reached. The single-chip microcomputer controls the lighting of the lifting indicator light according to the judgment result. The operator can perform operations according to the prompts of the lifting indicator light, thereby further improving the safety performance.

[0055] The external unit of the battery-type permanent magnet of this embodiment also includes a control panel. The above-mentioned lifting indicator light, power warning light and display module are all arranged on the control panel for easy viewing by the operator. The control panel is as shown in FIG. Figure 5 As shown, in addition, the control panel is also equipped with landing detection, magnetization button, demagnetization button, lock button and magnetic penetration depth adjustment knob. The operator only needs to press the indicator button initially, avoiding mistakes in complex manual operation.

[0056] This embodiment also specifically provides a forward excitation method for the battery-type permanent magnet, the steps of which include:

[0057] S1: Relay is forward connected: The single chip microcomputer controls the first switch K1 in an excitation circuit unit to operate, and the second switch K2 does not operate;

[0058] S2: triggering the third transistor: at the same time as step S1, the single chip microcomputer controls the third transistor driving chip so that the third transistor driving chip triggers the gate of the third transistor in the freewheeling circuit unit connected in series with the excitation circuit unit;

[0059] S3: a single excitation coil completes forward excitation: after the excitation current is generated in the excitation coil, the single chip microcomputer controls the third transistor driver chip to stop triggering the gate of the third transistor in the freewheeling circuit unit connected in series with the excitation circuit unit;

[0060] S4: forward excitation completed: the microcontroller starts forward excitation to the next excitation coil, and repeats steps S1 to S3 until all excitation coils are excited.

[0061] This embodiment also specifically provides a reverse excitation method for the battery-type permanent magnet, the steps of which include:

[0062] S1: Relay reverse connection: The single chip microcomputer controls the first switch K1 in an excitation circuit unit to not operate, and the second switch K2 to operate;

[0063] S2: triggering the third transistor: at the same time as step S1, the single chip microcomputer controls the third transistor driving chip so that the third transistor driving chip triggers the gate of the third transistor in the freewheeling circuit unit connected in series with the excitation circuit unit;

[0064] S3: a single excitation coil completes reverse excitation: after the excitation current is generated in the excitation coil, the single chip microcomputer controls the third transistor driver chip to stop triggering the gate of the third transistor in the freewheeling circuit unit connected in series with the excitation circuit unit;

[0065] S4: Reverse excitation completed: The microcontroller starts reverse excitation to the next excitation coil, and repeats steps S1 to S3 until all excitation coils are excited.

[0066] The above is only a preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above embodiments. For those skilled in the art, improvements and changes obtained without departing from the technical concept of the present invention should also be regarded as the protection scope of the present invention.

Claims

1. A battery-type permanent magnet, comprising a battery, a controller and an permanent magnet body, wherein the permanent magnet body comprises an excitation coil, characterized in that: The controller comprises one or more excitation circuit units connected in parallel with each other and freewheeling circuit units connected in series with the excitation circuit units in a one-to-one correspondence, wherein the excitation circuit units comprise a first switch (K1) and a second switch (K2), and an excitation coil is connected between the first switch (K1) and the second switch (K2); The first switch (K1) and the second switch (K2) are both single-pole double-throw switches, one end of the excitation coil is connected to the moving end of the first switch (K1), the other end of the excitation coil is connected to the moving end of the second switch (K2), the two fixed ends of the first switch (K1) are respectively connected to the positive pole of the battery and the freewheeling circuit unit, the two fixed ends of the second switch (K2) are respectively connected to the positive pole of the battery and the freewheeling circuit unit, and the freewheeling circuit unit is connected to the negative pole of the battery; The freewheeling circuit unit comprises two mutually parallel unidirectional conductive first and second transistors, and a third transistor connected between the input ends of the first and second transistors and the negative electrode of the battery; the output ends of the first and second transistors are respectively connected to the two ends of the excitation coil; The first transistor and the second transistor are diodes, and the third transistor is a triode; The collector of the third transistor is respectively connected to a fixed end of the first switch (K1), a fixed end of the second switch (K2), an input end of the first transistor and an input end of the second transistor, and the emitter of the third transistor is connected to the negative electrode of the battery; the battery-type electro-permanent magnet also includes a third transistor driving chip for driving the third transistor to conduct, and the third transistor driving chip is connected to the base of the third transistor.

2. The battery-type electropermanent magnet according to claim 1, characterized in that: The first switch (K1) and the second switch (K2) are both relays, and in the first switch (K1) and the second switch (K2), the excitation coil and the freewheeling circuit unit are connected to a normally closed contact.

3. The battery-type electropermanent magnet according to claim 2, characterized in that: The battery-type electro-permanent magnet further comprises a single-chip microcomputer connected to the control ends of the first switch (K1) and the second switch (K2), respectively; the single-chip microcomputer is configured to perform one or two of the following actions: When the battery-type permanent magnet is positively excited, the first switch (K1) is triggered to operate, and the second switch (K2) is not operated; When the battery-type electropermanent magnet is reversely excited, the second switch (K2) is triggered to operate, and the first switch (K1) is not operated.

4. The battery-type electropermanent magnet according to claim 3, characterized in that: The single chip microcomputer is also connected to a third transistor driving chip. When the single chip microcomputer triggers the first switch (K1) or the second switch (K2), it controls the third transistor driving chip to trigger the third transistor.

5. The battery-type electropermanent magnet according to claim 4, characterized in that: The controller also includes an external unit and a detection unit. The external unit, the detection unit and the single-chip microcomputer are connected by wire or wireless means. The detection unit includes a power detection module. The power detection module detects the power of the battery and sends it to the display module of the external unit to display the power of the battery.

6. The battery-type electropermanent magnet according to claim 5, characterized in that: The external unit also includes a power warning light. When the power detection module detects that the power of the battery is low, the power warning light is controlled to send a warning signal.

7. The battery-type electropermanent magnet according to claim 5, characterized in that: The detection unit also includes an excitation current detection device, which sends a signal to the single-chip microcomputer when the excitation current reaches the maximum allowable value. After receiving the signal, the single-chip microcomputer controls the third transistor driving chip to stop triggering the third transistor.

8. The battery-type electropermanent magnet according to claim 7, characterized in that: The maximum allowable value of the excitation current is the maximum allowable current value of the third transistor or a preset value.

9. The battery-type electropermanent magnet according to claim 5, characterized in that: The detection unit also includes a magnetic flux detection module, and the external unit also includes a lifting indicator light. The magnetic flux detection module sends the measured magnetic flux to the single-chip microcomputer, and the single-chip microcomputer determines whether the preset lifting magnetic flux is reached. The single-chip microcomputer controls the lighting of the lifting indicator light according to the judgment result.

10. A forward excitation method for a battery-type electropermanent magnet according to any one of claims 1 to 9, comprising the steps of: S1: Relay forward connection: The single chip microcomputer controls the first switch (K1) in an excitation circuit unit to operate, and the second switch (K2) does not operate; S2: triggering the third transistor: at the same time as step S1, the single chip microcomputer controls the third transistor driving chip so that the third transistor driving chip triggers the base of the third transistor in the freewheeling circuit unit connected in series with the excitation circuit unit; S3: a single excitation coil completes forward excitation: after the excitation current is generated in the excitation coil, the single chip microcomputer controls the third transistor driver chip to stop triggering the base of the third transistor in the freewheeling circuit unit connected in series with the excitation circuit unit; S4: forward excitation completed: the microcontroller starts forward excitation to the next excitation coil, and repeats steps S1 to S3 until all excitation coils are excited.

11. A reverse excitation method for a battery-type electropermanent magnet according to any one of claims 1 to 9, comprising the steps of: S1: Relay reverse connection: The single chip microcomputer controls the first switch (K1) in an excitation circuit unit to not operate, and the second switch (K2) to operate; S2: triggering the third transistor: at the same time as step S1, the single chip microcomputer controls the third transistor driving chip so that the third transistor driving chip triggers the base of the third transistor in the freewheeling circuit unit connected in series with the excitation circuit unit; S3: a single excitation coil completes reverse excitation: after the excitation current is generated in the excitation coil, the single chip microcomputer controls the third transistor driver chip to stop triggering the base of the third transistor in the freewheeling circuit unit connected in series with the excitation circuit unit; S4: Reverse excitation completed: The microcontroller starts reverse excitation to the next excitation coil, and repeats steps S1 to S3 until all excitation coils are excited.

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