Brushless DC motor, motor control system, rail train and control method

Abstract

A brushless DC motor of the present invention includes two permanent magnet cylinders arranged coaxially and connected at their ends. A plurality of sets of three-phase armature windings are arranged in a staggered manner along the circumference inside the permanent magnet cylinders. Each permanent magnet cylinder includes a plurality of N poles and a plurality of S poles arranged in a staggered manner along the circumference. The structures of the two permanent magnet cylinders are the same, and each magnetic pole in one permanent magnet cylinder is offset from the corresponding magnetic pole of the same polarity in the other permanent magnet cylinder by a first preset angle. By offsetting the two permanent magnet cylinders by a predetermined angle, the tangential force at the junction of the two poles is dispersed, the torque ripple is reduced, and the running stability is improved. The present invention also discloses a motor control system including the above brushless DC motor and a rail train including the above motor control system. The present invention also discloses a control method for a brushless DC motor.

Description

Technical Field

[0001] The present invention relates to the field of rail transit, and particularly to a brushless DC motor, a motor control system, a rail train, and a control method. Background Art

[0002] A brushless DC motor is a type of synchronous motor and is widely used in various fields. Its main structure includes a stator and a rotor. The rotor is a permanent magnet, and the stator is a three-phase armature winding. Different from ordinary DC motors, a brushless DC motor does not have a commutator. The commutation of the motor is achieved through an inverter frequency conversion technology, where a three-phase alternating current with adjustable frequency is applied to the armature winding of the stator to generate a rotating magnetic field, thereby driving the rotor to rotate. However, in a brushless DC motor, usually, the permanent magnets are arranged side by side, and the N poles and S poles are staggered. The tangential force received at the junction of the N poles and S poles is the largest and decreases towards both sides. Therefore, torque fluctuations will occur in the motor, leading to adverse conditions such as motor resonance.

[0003] In addition, when a brushless DC motor is an essential device for the auxiliary system of a rail train, it is usually connected to a heat dissipation device. Traditional brushless DC motors generally adopt a single-chip control strategy, where control, signal processing, and monitoring protection functions are integrated in the chip, which can meet the use in ordinary static environments. For rail transit vehicles, the use environment is relatively harsh. Therefore, higher requirements are placed on the stability and reliability of the motor. In the operation process of traditional single-chip brushless DC motors, due to various external factors, such as vehicle vibration, voltage and current fluctuations, external interference, etc., the chip may be damaged, resulting in motor failure, and further affecting the normal operation of the vehicle.

[0004] Therefore, how to provide a brushless DC motor and a motor control system that overcome the above problems is a technical problem that those skilled in the art need to solve. Summary of the Invention

[0005] The object of the present invention is to provide a brushless DC motor, a motor control system, and a control method. By staggering two permanent magnet cylinders by a predetermined angle, the tangential force at the junction of the two poles is dispersed, torque fluctuations are reduced, and the running stability is improved. Another object of the present invention is to provide a rail train including the above system.

[0006] To solve the above technical problems, the present invention provides a brushless DC motor, which includes two permanent magnet cylinders arranged coaxially and connected at their ends. Multiple groups of three-phase armature windings are arranged in a staggered manner along the circumference inside the permanent magnet cylinders. Each permanent magnet cylinder includes a plurality of N poles and a plurality of S poles arranged in a staggered manner along the circumference. The structures of the two permanent magnet cylinders are the same, and each magnetic pole in one permanent magnet cylinder is staggered from the corresponding magnetic pole of the same polarity in the other permanent magnet cylinder by a first preset angle.

[0007] Preferably, the first preset angle is one-sixth of the mechanical angle occupied by a single magnetic pole within the permanent magnet cylinder.

[0008] Preferably, each permanent magnet cylinder includes three N poles and three S poles. A single magnetic pole occupies a mechanical angle of 60 degrees, the first preset angle is 10 degrees, and there are three sets of the three-phase armature windings.

[0009] Preferably, three Hall sensors are sequentially installed along the circumference on the three-phase armature winding. The mechanical angle between two adjacent Hall sensors is 20 degrees. The junction between the outermost Hall sensor and the armature winding is at a second preset angle, and the second preset angle is 20 degrees minus half of the first preset angle.

[0010] The present invention also provides a motor control system, including a main chip, a safety protection chip, a signal processing chip, a switching power supply, a driver, an inverter, and the DC brushless motor described in any one of the above. The main chip is connected to each component and is used to control the operation of the DC brushless motor and monitor the state of the DC brushless motor. The safety protection chip is connected to the driver and the DC brushless motor and is used to turn off the driver or reset the main chip in case of an abnormal state. The signal processing chip is used for signal input and output and communicates with the main chip.

[0011] Preferably, the signal processing chip and the main chip are communicatively isolated through an opto-isolator. The switching power supply includes an isolated-side power supply connected to the signal processing chip and a non-isolated-side power supply connected to the main chip.

[0012] The present invention also provides a rail train, including a heat dissipation device and a motor control system connected to the heat dissipation device. The motor control system is specifically the motor control system described in any one of the above.

[0013] The present invention provides a method for controlling a DC brushless motor, which is used to control the DC brushless motor described in any one of the above, and includes the steps of:

[0014] Based on the positions of the three-phase armature windings obtained by the Hall sensors, determine the three armature windings as the best-force armature winding, the second-best-force armature winding, and the poor-force armature winding;

[0015] Make the best-force armature winding conduct full forward power, the second-best-force armature winding conduct full reverse power, and the poor-force armature winding conduct 0 voltage;

[0016] During the rotation within the same Hall state, the best-force armature winding keeps conducting full forward power, the power of the second-best-force armature winding decreases from full reverse power to 0 voltage, and the power of the poor-force armature winding increases from 0 voltage to full reverse power;

[0017] Rotate to enter the next Hall state. At this time, the previously mentioned best-force armature winding becomes the second-best-force armature winding, the previously mentioned second-best-force armature winding becomes the poor armature winding, and the previously mentioned poor armature winding becomes the best-force armature winding;

[0018] During the rotation process within this Hall state, the best-force armature winding remains energized with reverse full voltage, the second-best-force armature winding is energized from forward full voltage to 0 voltage, and the poor-force armature winding is energized from 0 voltage to forward full voltage;

[0019] Rotate to enter the next lower Hall state and repeat the above-mentioned winding change and power-on process.

[0020] Preferably, it includes six said Hall states, and each said Hall state occupies a mechanical angle of 40 degrees.

[0021] Preferably, the duty ratios of the three-phase armature windings are respectively sin(ang*90 / 40)*duty_x, duty_x, and cos(ang*90 / 40)*duty_x, where ang is the rotation angle of the motor and duty_x is the current duty ratio of the motor.

[0022] The present invention provides a DC brushless motor, which includes two permanent magnet cylinders arranged coaxially and connected at the ends. Multiple sets of three-phase armature windings are arranged in a staggered manner along the circumference inside the permanent magnet cylinders. Each permanent magnet cylinder includes multiple N poles and multiple S poles arranged in a staggered manner along the circumference. The structures of the two permanent magnet cylinders are the same, and the magnetic poles of the same polarity corresponding to each other in one permanent magnet cylinder are staggered by a first preset angle from those in the other permanent magnet cylinder.

[0023] By staggering the two permanent magnet cylinders by a predetermined angle, the tangential force at the junction of the two poles is dispersed, the torque ripple is reduced, and the running stability is improved.

[0024] Furthermore, a three-chip control scheme is adopted. The three chips undertake independent work without interfering with each other and are physically and electrically isolated, which can enhance the stability and reliability of the motor control system and improve the service life of the motor.

[0025] Furthermore, through the above control method and adopting the optimal power-on method, each armature winding can be in a better force point, thereby increasing the motor torque and improving the motor efficiency.

[0026] The present invention also provides a motor control system including the above-mentioned DC brushless motor, and also provides a rail train including the above-mentioned system. Since the above-mentioned DC brushless motor has the above-mentioned technical effects, the above-mentioned motor control system and rail train also have the same technical effects and will not be introduced in detail here. Description of the Drawings

[0027] Figure 1 A top view schematic diagram of a specific embodiment of the DC brushless motor provided by the present invention;

[0028] Figure 2 A front view schematic diagram of a specific embodiment of the DC brushless motor provided by the present invention;

[0029] Figure 3 A structural block diagram of a specific embodiment of the motor control system provided by the present invention;

[0030] Figure 4 A schematic diagram of an inverter circuit in a specific embodiment of the motor control system provided by the present invention;

[0031] Figure 5 A timing diagram of the bridge arm control signals of the inverter circuit in a specific embodiment of the motor control system provided by the present invention. Specific embodiments

[0032] The core of the present invention is to provide a DC brushless motor, a motor control system and a control method, by staggering two permanent magnet cylinders at a predetermined angle to disperse the tangential force at the junction of the two poles, reduce the torque ripple, and improve the running stability. Another core of the present invention is to provide a rail train including the above system.

[0033] In order to enable those skilled in the art to better understand the solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0034] Please refer to Figure 1 and Figure 2 , Figure 1 A top view schematic diagram of a specific embodiment of the DC brushless motor provided by the present invention; Figure 2 A front view schematic diagram of a specific embodiment of the DC brushless motor provided by the present invention.

[0035] The specific implementation of the present invention provides a DC brushless motor, which includes a rotor and a stator disposed within the rotor. Among them, the stator is a plurality of sets of three-phase armature windings 2 arranged in a circumferential staggered manner, that is, it includes a plurality of sets of U-phase armature windings, V-phase armature windings, and W-phase armature windings. The rotor includes two permanent magnet cylinders 1, and the two permanent magnet cylinders 1 are coaxially arranged and connected at their ends to form a complete sleeve structure. A plurality of sets of three-phase armature windings 2 are disposed as the stator inside the sleeve structure. Each permanent magnet cylinder 1 includes a plurality of N poles and a plurality of S poles, and the N poles and S poles are arranged in a circumferential staggered manner, that is, the arc-shaped plate-like N poles and S poles are staggered around to form a cylindrical structure. At the same time, the sizes of the N poles and S poles are the same to ensure uniform arrangement of the magnetic poles. Further, the structures of the two permanent magnet cylinders 1 are the same, that is, the arc lengths of each magnetic pole are the same, and the two permanent magnet cylinders 1 are arranged in a staggered manner, that is, they are still a complete cylindrical structure in appearance, but the magnetic poles are staggered, rather than the N poles facing the S poles directly. And because the arc lengths of each magnetic pole are the same, when one magnetic pole is staggered, other magnetic poles will also be staggered, so that each magnetic pole in one permanent magnet cylinder 1 is staggered from the corresponding same-polarity magnetic pole in the other permanent magnet cylinder 1 by a first preset angle. According to the attached Figure 2 As can be seen, the N poles of the upper permanent magnet cylinder 1 simultaneously contact the N poles and S poles of the lower permanent magnet cylinder 1, and the S poles of the lower permanent magnet cylinder 1 also simultaneously contact the N poles and S poles of the lower permanent magnet cylinder 1. In Figure 1 the figure, the solid line in the outer circle represents the upper permanent magnet cylinder 1, and the dotted line represents the lower permanent magnet cylinder 1.

[0036] By staggering the two permanent magnet cylinders 1 by a predetermined angle, the tangential force at the junction of the two poles is dispersed, the torque ripple is reduced, and the running smoothness is improved.

[0037] Further, the staggering angle between the upper and lower permanent magnet cylinders 1 should not be too large, because the transverse magnetic field generated between the same layers is the magnetic field that actually does work in the motor, while the longitudinal magnetic field generated between the upper and lower layers cannot do work on the armature. As the staggering angle increases, the longitudinal magnetic field will increase, resulting in a decrease in the motor torque. According to experience, the preset staggering angle α is preferably 1 / 6 of the mechanical angle occupied by a single magnetic pole. Taking a three-pole-pair motor as an example, each permanent magnet cylinder 1 includes three N poles and three S poles, and a single magnetic pole occupies a 60-degree mechanical angle. The first preset angle is 10 degrees, and it also includes three sets of three-phase armature windings 2. The larger the staggering angle, the smaller the torque ripple, but the greater the torque loss. Correspondingly, the smaller the staggering angle, the greater the torque ripple, but the smaller the torque loss.

[0038] Based on the DC brushless motor provided in the above specific embodiments, the tangential forces received by the armature winding at different positions are different. To obtain a greater torque, the accurate position of the armature winding needs to be known. Therefore, three Hall sensors 3 are sequentially installed along the circumference on the three-phase armature winding 2. The mechanical angle between two adjacent Hall sensors 3 is 20 degrees. The distance between the outermost Hall sensor 3 and the junction of the armature winding is the second preset angle β, and the second preset angle β is 20 degrees minus half of the first preset angle α, that is, β = 20 – α / 2. Through the above arrangement method, the torque loss can be reduced, and a greater output torque and higher efficiency can be achieved.

[0039] Please refer to Figure 3 , Figure 3 which is the structural block diagram of a specific embodiment of the motor control system provided by the present invention.

[0040] The specific embodiment of the present invention also provides a motor control system, including a main chip, a safety protection chip, a signal processing chip, a switching power supply, a driver, an inverter, a three-phase EMI, a bridge rectifier circuit, and the DC brushless motor provided in the above specific embodiment. The main chip is connected to each component and is used to control the operation of the DC brushless motor and monitor the state of the DC brushless motor. The safety protection chip is connected to the driver and the DC brushless motor and is used to turn off the driver or reset the main chip in case of abnormal conditions. The signal processing chip is used for signal input and output and communicates with the main chip. Further, the signal processing chip and the main chip are communicatively isolated through an optocoupler isolator. The switching power supply includes an isolated-side power supply connected to the signal processing chip and a non-isolated-side power supply connected to the main chip.

[0041] Specifically, the three-phase EMI is arranged at the input end of the motor three-phase power supply. The three-phase 380V / 50Hz alternating current is provided by the vehicle auxiliary system and is connected to the bridge rectifier circuit, which serves to suppress the electromagnetic interference of the three-phase input power supply and improve the power consumption quality. The bridge rectifier circuit full-wave rectifies the three-phase alternating current processed by the three-phase EMI into an intermediate DC voltage, which is supplied to the switching power supply and the inverter. The inverter circuit in the inverter inversely converts the intermediate DC voltage into an AC square wave voltage, which is supplied to the three-phase armature winding 2 of the motor. The Hall sensor 3 uses a magnetosensitive position sensor to convert the collected rotor position signal into an electrical signal and transmit it to the control circuit. The control circuit and the control algorithm determine the conduction sequence and on-off time of each phase of the armature winding, and then control the power module.

[0042] The signal processing chip is responsible for collecting the input digital / analog signals, including but not limited to 485 bus signals, 4 - 20mA current signals, 0 - 10V voltage signals, and controlling the output digital / analog signals, including but not limited to fault reporting signals and operating status signals. The signal processing chip and the related peripheral circuits are isolated from the main circuit through isolators, using separate isolated power supplies and isolated grounds, and the communication with the main chip is also isolated through optocoupler isolators. All input and output signals are processed by the signal processing chip, and then transmitted to the main chip through dual - machine communication after being isolated by the isolator. This can effectively prevent external input / output from interfering with the main chip and improve the system stability. The main chip is responsible for the control of the DC brushless motor, providing drive signals, and real - time monitoring of the motor's operating status to ensure the normal operation of the motor. The safety protection chip is responsible for monitoring the operating status of the motor. Once an abnormality is detected, it can turn off the driver or reset the main chip to prevent abnormal motor operation caused by the failure of the main chip. Further, the driver, according to the 6 - channel PWM signals output by the main chip, controls the conduction and disconnection of the upper and lower two power transistors in the same bridge arm of the PWM - driven enhanced drive inverter circuit. At the same time, the driver integrates an over - current detection and protection module. Once an over - current fault occurs in the system, the driver outputs to cut off the motor, thus playing the role of protecting the circuit. The switching power supply takes power from the intermediate DC circuit and converts it into two low - voltage power supplies through a high - frequency transformer. One is the isolated - side power supply for powering the signal input module, and the other is the non - isolated - side power supply for powering the motor control circuit.

[0043] During operation, the signal processing chip is responsible for input and output control. First, it collects the externally input speed and torque signals, converts them into digital signals, and sends them to the main chip through the isolator. Then, it receives the feedback signals sent back by the main chip and outputs them through the output circuit. The main chip is responsible for the drive and management of the motor. First, it receives the speed and torque signals from the signal processing chip through the isolator, and then collects the motor's status information, including voltage, current, temperature, Hall, etc. When the motor is in normal condition, that is, no over - current, over - voltage, or over - temperature occurs, the controller sets the duty ratio output according to the speed setting and sets the output phase sequence according to the position of Hall sensor 3. Once an abnormality occurs, the driver is turned off until it is normal.

[0044] Adopting a three - chip control scheme, the three chips each undertake independent work, do not interfere with each other, and are isolated physically and electrically, which can enhance the stability and reliability of the motor control system and improve the service life of the motor.

[0045] Please refer to Figure 4 and Figure 5 , Figure 4 which is a schematic diagram of the inverter circuit in a specific embodiment of the motor control system provided by the present invention; Figure 5This is the timing diagram of the bridge arm control signals of the inverter circuit in a specific implementation of the motor control system provided by the present invention.

[0046] The specific implementation of the present invention also provides a DC brushless motor control method for controlling the DC brushless motor provided by the above specific implementation, including the steps:

[0047] According to the positions of the three-phase armature windings 2 obtained by the Hall sensor 3, determine the three armature windings as the best-force armature winding, the sub-optimal force armature winding, and the poor-force armature winding;

[0048] Apply full positive voltage to the best-force armature winding, full negative voltage to the sub-optimal force armature winding, and 0 voltage to the poor-force armature winding;

[0049] During the rotation within the same Hall state, the best-force armature winding maintains full positive voltage, the voltage of the sub-optimal force armature winding decreases from full negative voltage to 0 voltage, and the voltage of the poor-force armature winding increases from 0 voltage to full negative voltage;

[0050] Rotate into the next Hall state. At this time, the previous best-force armature winding becomes the sub-optimal force armature winding, the previous sub-optimal force armature winding becomes the poor armature winding, and the previous poor armature winding becomes the best-force armature winding;

[0051] During the rotation within this Hall state, the best-force armature winding maintains full negative voltage, the voltage of the sub-optimal force armature winding decreases from full positive voltage to 0 voltage, and the voltage of the poor-force armature winding increases from 0 voltage to full positive voltage;

[0052] Rotate into the next lower Hall state and repeat the above winding changes and power-on processes.

[0053] Specifically, it includes six Hall states, and each Hall state occupies 40 degrees of mechanical angle. Further, the duty ratios of the three-phase armature windings 2 are sin(ang*90 / 40)*duty_x, duty_x, and cos(ang*90 / 40)*duty_x respectively, where ang is the motor rotation angle and duty_x is the current duty ratio of the motor.

[0054] According to Figure 4 It can be known that the inverter circuit has three bridge arms, which respectively control the UVW three-phase armature windings. Each bridge arm consists of upper and lower parts, namely H1, L1, H2, L2, H3, L3. By controlling the on-off conditions of the upper and lower bridge arms, the voltage of the corresponding armature winding can be controlled. The motor windings are generally star-connected. The existing control methods cannot exert the maximum torque of the motor. In addition, since the motor does not always select the optimal armature to be powered on, there is also a loss in the motor efficiency.

[0055] For the control method provided in the specific implementation manner of the present invention, first, the positions of the armature windings of each phase are obtained according to the Hall sensor 3, so as to deduce that the three armature windings are the optimal force - receiving armature winding, the sub - optimal force - receiving armature winding, and the poor force - receiving armature winding. The inverter can control the armature windings to be in three states: getting positive electricity, getting negative electricity, and being suspended. The optimal force - receiving armature winding is fully energized, which can be fully energized in the positive direction or in the negative direction. The other two armature windings are energized in the reverse direction. That is, if the optimal force - receiving armature winding is energized in the positive direction, the other two armature windings are energized in the negative direction; if the optimal force - receiving armature winding is energized in the negative direction, the other two armature windings are energized in the positive direction. Being fully energized is relative to the current state of the motor. For example, if the current duty cycle is 50%, then 50% is considered the full - electricity state, and the other two windings can be allocated corresponding duty cycles according to the current force trend. Combining with the following table, the following table is the logic table of the Hall state and the phase sequence relationship. Positive represents the upper - bridge arm conducting and getting positive electricity; negative represents the lower - bridge arm conducting and getting negative electricity; "↑" represents the trend strengthening, increasing from 0 to the set duty cycle; "↓" represents the trend weakening, decreasing from the set duty cycle to 0. The positive and negative voltages loaded on the windings shown in the following table are related to the Hall placement position and the winding direction. This embodiment only elaborates on the control algorithm and does not list all combinations.

[0056]

[0057] When the Hall state is 000, the V - phase is the optimal force - receiving armature winding, conducting the positive full - voltage, the W - phase is the sub - optimal force - receiving armature winding, conducting the negative full - voltage, and the U - phase is the poor force - receiving armature winding, conducting 0 voltage. During the rotation process in the 000 state, the V - phase remains conducting the positive full - electricity, the electricity of the W - phase decreases from the reverse full - voltage to 0 voltage, and the electricity of the U - phase increases from 0 voltage to the reverse full - voltage.

[0058] At this time, it enters the downward - shifted Hall state, the 100 state. The U - phase becomes the optimal force - receiving armature winding, the V - phase becomes the sub - optimal force - receiving armature winding, and the W - phase becomes the poor force - receiving armature winding. In fact, when the rotation in the 000 state passes half, the voltage of the U - phase starts to be higher than that of the W - phase. The U - phase is upgraded to the sub - optimal force - receiving armature winding, and the voltage of the W - phase becomes the poor force - receiving armature winding until the voltage change is completed and it enters the 100 state. The U - phase becomes the optimal force - receiving armature winding, and the V - phase becomes the sub - optimal force - receiving armature winding.

[0059] During the rotation process in the 100 state, the U - phase remains conducting the negative full - electricity, the electricity of the V - phase decreases from the positive full - voltage to 0 voltage, and the electricity of the W - phase increases from 0 voltage to the positive full - voltage. It can be seen that after entering the 110 state, the W - phase becomes the optimal force - receiving armature winding, the U - phase becomes the sub - optimal force - receiving armature winding, and the V - phase becomes the poor force - receiving armature winding. According to the above table, the above steps are cycled to achieve the optimal power - on. Through the above - mentioned control method, by adopting the optimal power - on method, each armature winding can be at a better force - receiving point, thereby increasing the motor torque and improving the motor efficiency.

[0060] The changes of the sub-optimal force-bearing armature winding and the differential force-bearing armature winding follow a sine relationship. Based on the current rotational speed and the current time, the angle rotated currently can be obtained. For each state mechanical angle (0 - 40°), it is first linearized to (0 - 90°), then the sine / cosine of it is taken, and then multiplied by the current duty cycle to obtain the final duty cycle. Assume that in the 000 state, the motor has rotated by ang°, and the current duty cycle of the motor is duty_x. Then the duty cycles of the control signals for the bridge arms corresponding to the U / V / W phase armature windings (the upper bridge arm of V, the lower bridge arms of U and W) are sin(ang * 90 / 40) * duty_x, duty_x, and cos(ang * 90 / 40) * duty_x respectively.

[0061] In addition to the above motor control system, the specific implementation of the present invention also provides a rail train including the above motor control system. For the structures of other parts of the rail train, reference can be made to the prior art and will not be elaborated herein.

[0062] The DC brushless motor, motor control system, rail train and control method provided by the present invention have been introduced in detail above. Specific examples are used herein to elaborate on the principle and implementation manner of the present invention. The description of the above embodiments is only used to help understand the method and its core idea of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and modifications can still be made to the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. A method for controlling a direct current brushless motor, characterized in that, For controlling a DC brushless motor, the DC brushless motor includes two permanent magnet cylinders (1) arranged coaxially and connected at their ends. A plurality of three-phase armature windings (2) are arranged in a staggered manner along the circumference inside the permanent magnet cylinders (1). Each permanent magnet cylinder (1) includes a plurality of N poles and a plurality of S poles arranged in a staggered manner along the circumference. The structures of the two permanent magnet cylinders (1) are the same, and the magnetic poles of the same polarity corresponding to each other in one permanent magnet cylinder (1) are offset by a first preset angle from the magnetic poles of the same polarity in the other permanent magnet cylinder (1). Three Hall sensors (3) are sequentially installed along the circumference on the three-phase armature winding (2). The mechanical angle between two adjacent Hall sensors (3) is 20 degrees. The distance between the outermost Hall sensor (3) and the junction of the armature winding is a second preset angle, and the second preset angle is 20 degrees minus half of the first preset angle. The method for controlling the DC brushless motor includes the steps of: Judging the three armature windings as the best-force armature winding, the sub-best-force armature winding, and the poor-force armature winding according to the positions of the three-phase armature windings (2) obtained by the Hall sensors (3); Applying full positive voltage to the best-force armature winding, applying full negative voltage to the sub-best-force armature winding, and applying 0 voltage to the poor-force armature winding; During the rotation within the same Hall state, the best-force armature winding keeps applying full positive voltage, the voltage applied to the sub-best-force armature winding decreases from full negative voltage to 0 voltage, and the voltage applied to the poor-force armature winding increases from 0 voltage to full negative voltage; When the motor rotor rotates into the next Hall state, the previous best-force armature winding becomes the sub-best-force armature winding, the previous sub-best-force armature winding becomes the poor-force armature winding, and the previous poor-force armature winding becomes the best-force armature winding; During the rotation of the motor rotor within this Hall state, the best-force armature winding keeps applying full negative voltage, the voltage applied to the sub-best-force armature winding decreases from full positive voltage to 0 voltage, and the voltage applied to the poor-force armature winding increases from 0 voltage to full positive voltage; When the motor rotor rotates into the next Hall state again, repeat the above winding change and power-on process.

2. The method for controlling a direct current brushless motor according to claim 1, characterized in that, It includes six Hall states, and each Hall state occupies a mechanical angle of 40 degrees.

3. The method for controlling a direct current brushless motor according to claim 2, characterized in that, The duty ratios of the three-phase armature windings (2) are respectively sin(ang*90 / 40)*duty_x, duty_x, and cos(ang*90 / 40)*duty_x, where ang is the rotation angle of the motor rotor and duty_x is the current duty ratio of the motor.

4. The method for controlling a direct current brushless motor according to claim 1, characterized in that, The first preset angle is one-sixth of the mechanical angle occupied by a single magnetic pole inside the permanent magnet cylinder (1).

5. The method for controlling a direct current brushless motor according to claim 1, characterized in that, Each permanent magnet cylinder (1) includes three N poles and three S poles. A single magnetic pole occupies a mechanical angle of 60 degrees. The first preset angle is 10 degrees, and three groups of three-phase armature windings (2) are arranged inside the permanent magnet cylinder (1).

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