Permanent magnet brushless motor direct torque control system and method considering maximum torque current ratio

Abstract

The invention discloses a permanent magnet brushless motor direct torque control system and method considering a maximum torque current ratio, and belongs to the technical field of motor control. A current distribution coefficient between a zero-crossing phase winding and a same-direction phase winding required for realizing the maximum torque current ratio is introduced; the distribution coefficient is multiplied by the absolute value of the same-direction phase current to obtain zero-crossing phase current, and the difference between the zero-crossing phase current and the absolute value of the actual zero-crossing phase current is input into a zero-crossing phase current hysteresis controller to obtain a current state signal; and obtaining state signals of six switching tubes of the three-phase bridge type inverter through a switching tube state lookup table by combining a torque state signal obtained by subtracting the reference torque from the actual torque. A 180-degree conduction mode is adopted, on the premise that direct torque control is carried out, current distribution between a zero-crossing phase winding and a same-direction phase winding is controlled to indirectly achieve maximum torque-current ratio control, torque is generated through current in a most efficient mode, and the efficiency and performance of the motor are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of motor control, and in particular to a permanent magnet brushless motor direct torque control system and method taking into account a maximum torque current ratio. Background Art

[0002] A permanent magnet brushless motor is a motor without brushes. It has permanent magnets on its rotor and coils on its stator. The magnitude and direction of the current are controlled by an electronic controller, so that the rotating magnetic field generated by the stator winding interacts with the magnetic field of the rotor permanent magnet, thereby generating torque and driving the rotor to rotate. Since there are no brushes and commutators, permanent magnet brushless motors avoid mechanical friction and wear, and have the advantages of high efficiency, low noise, and long life. According to the classification of driving current waveforms, permanent magnet brushless motors include brushless DC motors and permanent magnet synchronous motors. Among them, brushless DC motors are widely used in many fields such as home appliances, electric vehicles, industrial automation equipment, medical equipment, drones, robots, aerospace, and computer systems due to their simple structure, high power density, and large output torque.

[0003] In the control of permanent magnet brushless motors, direct torque control technology (DTC) is widely used due to its high dynamic response and simple structure. It directly controls the torque and flux of the motor by selecting the appropriate voltage vector, thereby achieving precise control of the motor. DTC does not rely on complex coordinate transformation, but directly analyzes the mathematical model of the motor in the stator coordinate system, and the control method is simpler and faster.

[0004] However, the existing direct torque control methods mainly focus on fast response and simplified control structure. Although direct torque control technology has made some progress in the application of permanent magnet brushless motor control, there are still some defects. First, the existing control method is prone to produce large torque pulsation when running at low speed, which will affect the running stability and system accuracy of the permanent magnet brushless motor. Secondly, the existing direct torque control method does not fully consider the maximum torque current ratio in current distribution, resulting in the inability to achieve the maximum torque output under the same current conditions, thereby affecting the efficiency and performance of the permanent magnet brushless motor. Summary of the invention

[0005] In view of this, the present invention provides a direct torque control system and method for a permanent magnet brushless motor taking into account the maximum torque current ratio. The torque pulsation of the permanent magnet brushless motor is suppressed by combining direct torque control technology with a maximum torque current ratio control method (MTPA), and current is used in the most efficient way to generate torque, thereby improving the efficiency and performance of the permanent magnet brushless motor.

[0006] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0007] In one aspect, the present invention provides a permanent magnet brushless motor direct torque control system considering the maximum torque current ratio, comprising:

[0008] Three-phase bridge inverter for driving permanent magnet brushless motor;

[0009] The zero-crossing phase and the same-direction phase current selection unit, whose input end is respectively connected to the sector judgment unit and the three-phase bridge inverter, and whose output end is respectively connected to the torque calculation unit, is used for the sector information s obtained by the sector judgment unit and the three-phase current i output by the three-phase bridge inverter A 、i B 、i C Determine the zero-crossing phase current i of the permanent magnet brushless motor cross and the same-direction phase current i same ;

[0010] The torque calculation unit has an input end connected to the position sensor, the sector judgment unit and the zero-crossing phase and the same-direction phase current selection unit, and an output end connected to the torque hysteresis controller for the zero-crossing phase current i obtained by the zero-crossing phase and the same-direction phase current selection unit. cross and the same-direction phase current i same The actual torque T is calculated by using the sector information s obtained by the sector judgment unit and the rotor position information θ obtained by the position sensor. e , according to the reference torque T e * and actual torque T e The torque deviation ΔT is obtained by subtracting e , torque deviation ΔT e The torque state signal τ is obtained through the torque hysteresis controller T ;

[0011] The current distribution coefficient calculation unit has an input end connected to the line back electromotive force ratio calculation unit, and an output end connected to the zero-crossing phase current hysteresis controller, which is used to obtain the line back electromotive force ratio k obtained by the line back electromotive force ratio calculation unit. L Calculate the current distribution coefficient m, and according to the current distribution coefficient m and the same-direction phase current i same The absolute value of the zero-crossing phase current i cross The absolute value of the zero-crossing phase current deviation ΔI is obtained by subtracting m , ΔI m The current state signal τ is obtained through the zero-crossing phase current hysteresis controller I ;

[0012] The switch state query table includes the torque state signal τ T and the current state signal τ I, sector information s and the correspondence between the switch tube state signal, wherein the switch tube state information is used to control the on and off of the switch tube in the three-phase bridge inverter to realize direct torque control of the permanent magnet brushless motor considering the maximum torque current ratio.

[0013] Furthermore, the line back electromotive force ratio calculation unit determines the line back electromotive force ratio k based on the rotor position information θ obtained by the position sensor and the sector information s obtained by the sector judgment unit. L .

[0014] Furthermore, the line back electromotive force ratio k in the line back electromotive force ratio calculation unit L for where k ecross (θ), k esame (θ), k eoppo (θ) are the back electromotive force constants of the zero-crossing phase, the same-direction phase, and the reverse-direction phase windings, respectively. cross (θ), e same (θ), e oppo (θ) are the back electromotive force of the zero-crossing phase, same-direction phase, and opposite-direction phase windings respectively.

[0015] Furthermore, the actual torque T calculated by the torque calculation unit is e For: [k ecross (θ)-k eoppo (θ)]i cross +[k esame (θ)-k eoppo (θ)]i same .

[0016] Furthermore, the current distribution coefficient unit determines the permanent magnet brushless motor current distribution coefficient m as

[0017] Furthermore, the torque hysteresis used by the torque hysteresis controller is as follows:

[0018]

[0019] In the formula, τ T (k) is the torque state signal at the current moment, τ T (k+1) is the torque state signal at the next moment, ΔT e is the torque deviation, T th is the threshold value in the torque hysteresis controller.

[0020] Furthermore, the zero-crossing phase current hysteresis controller uses the following zero-crossing phase current hysteresis:

[0021]

[0022] In the formula, τI (k) is the current state signal at the current moment, τ I (k+1) is the current state signal at the next moment, ΔI m is the zero-crossing phase current deviation, I th is the threshold value in the zero-crossing phase current hysteresis controller.

[0023] Furthermore, the switch tube state query table is as follows:

[0024]

[0025] In the table, τ T Represents the torque state signal, τ I Zero-crossing phase current state signal, the six digits represent the switching states of the six switch tubes of the A, B, and C phase bridge arms in the three-phase bridge inverter from left to right, 1 indicates that the switch tube is turned on, and 0 indicates that the switch tube is turned off.

[0026] On the other hand, the present invention further provides a method for direct torque control of a permanent magnet brushless motor considering the maximum torque current ratio, using the above-mentioned direct torque control system of a permanent magnet brushless motor considering the maximum torque current ratio, comprising:

[0027] Determine the rotor position information θ of the permanent magnet brushless motor by using a position sensor connected to the permanent magnet brushless motor;

[0028] The actual speed n of the permanent magnet brushless motor is calculated based on the rotor position information θ;

[0029] Determine the sector information s of the permanent magnet brushless motor at the current moment according to the rotor position information θ;

[0030] According to the sector information s and the three-phase current i output by the three-phase bridge inverter A 、i B 、i C Determine the zero-crossing phase current i of the permanent magnet brushless motor cross and the same-direction phase current i same ;

[0031] By the zero-crossing phase current i cross and the same-direction phase current i same , sector information s and rotor position information θ to calculate the actual torque T e , according to the reference torque T e * and actual torque T e The torque deviation ΔT is obtained by subtracting e , torque deviation ΔT e The torque state signal τ is obtained through the torque hysteresis controller T ;

[0032] The line back electromotive force ratio k LCalculate the current distribution coefficient m, and according to the current distribution coefficient m and the same-direction phase current i same The absolute value of the zero-crossing phase current i cross The absolute value of the zero-crossing phase current deviation ΔI is obtained by subtracting m , ΔI m The current state signal τ is obtained through the zero-crossing phase current hysteresis controller I ;

[0033] Based on the torque state signal τ T , current state signal τ I and sector information s to query the switch tube state query table, the switch tube state query table includes the torque state signal τ T and the current state signal τ I , sector information s and the correspondence between the switch tube state signal, wherein the switch tube state information is used to control the on and off of the switch tube in the three-phase bridge inverter to realize direct torque control of the permanent magnet brushless motor considering the maximum torque current ratio.

[0034] Furthermore, the method further comprises: obtaining a speed deviation Δn by subtracting a given speed n* from an actual speed n of the permanent magnet brushless motor, and obtaining a reference torque T by passing the speed deviation Δn through a speed controller ASR. e *.

[0035] The above technical solution has the following advantages:

[0036] (1) The present invention proposes a direct torque control method for a permanent magnet brushless motor taking into account the maximum torque-current ratio. Compared with the direct torque control technology alone, the maximum torque-current ratio control strategy is added to operate the permanent magnet brushless motor, so that the maximum torque output can be obtained under a given current. By maximizing the torque per ampere rather than simply increasing the current, the minimum copper loss operation is achieved, thereby reducing the energy loss in the permanent magnet brushless motor.

[0037] (2) The present invention proposes a direct torque control method for a permanent magnet brushless motor taking into account the maximum torque current ratio. By applying the maximum torque current ratio control strategy, it can ensure that the current distribution of the permanent magnet brushless motor during operation is optimized, reducing the energy loss caused by the current, thereby reducing the heat loss of the permanent magnet brushless motor, which helps to extend the service life of the permanent magnet brushless motor. Especially in applications such as electric vehicles, the use of the maximum torque current ratio control strategy can maximize the use of battery energy, increase cruising range, and reduce carbon emissions. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] 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 labor.

[0039] Figure 1 It is a structural block diagram of a permanent magnet brushless motor direct torque control method system considering the maximum torque current ratio in an embodiment of the present invention;

[0040] Figure 2 is the torque hysteresis used by the torque hysteresis controller of the control system in the embodiment of the present invention;

[0041] Figure 3 is the zero-crossing phase current hysteresis loop used by the zero-crossing phase current hysteresis loop controller in the embodiment of the present invention;

[0042] Figure 4 It is a schematic diagram of sector division in an embodiment of the present invention. DETAILED DESCRIPTION

[0043] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0044] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0045] like Figure 1As shown, in an embodiment of the present invention, a permanent magnet brushless motor direct torque control system considering the maximum torque current ratio includes: a brushless DC motor (BLDCM), a three-phase bridge inverter, a position sensor, a speed calculation unit, a sector judgment unit, a zero-crossing phase and a same-direction phase current selection unit, a torque calculation unit, a line back electromotive force ratio calculation unit, a current distribution coefficient calculation unit, a torque hysteresis controller, a zero-crossing phase current hysteresis controller and a switch tube state query table; wherein:

[0046] The BLDCM is connected to a three-phase bridge inverter, and the three-phase bridge inverter outputs three-phase current to the BLDCM, and drives the BLDCM in a three-phase conduction mode.

[0047] The position sensor is connected to the BLDCM and is used to determine the BLDCM rotor position θ.

[0048] The input end of the speed calculation unit is connected to the position sensor, and the output end is connected to the speed controller ASR, which is used to calculate the actual speed n of BLDCM from the rotor position information θ obtained by the position sensor; the speed deviation Δn is obtained by subtracting the given speed n* from the actual speed n, and the speed deviation Δn is passed through the speed controller ASR to obtain the reference torque Te*.

[0049] The input end of the sector judgment unit is connected to the position sensor, and the output end thereof is respectively connected to the zero-crossing phase and the same-direction phase current selection unit, the torque calculation unit, and the line back electromotive force ratio calculation unit, so as to determine the sector information s where the BLDCM is located at the current moment according to the rotor position information θ obtained by the position sensor.

[0050] like Figure 4 As shown, the zero-crossing phase current i in each sector cross , same-direction phase current i same The relationship between the three-phase current is shown in Table 1.

[0051] Table 1

[0052]

[0053] The zero-crossing phase winding, the same-direction phase winding, and the opposite-direction phase winding in each sector are shown in Table 2.

[0054] Table 2

[0055]

[0056] The input end of the zero-crossing phase and the same-phase current selection unit is connected to the sector judgment unit and the three-phase bridge inverter respectively, and the output end thereof is connected to the torque calculation unit respectively, for calculating the torque of the three-phase current i according to the sector information s and the three-phase current i A 、i B 、i C Determine the BLDCM zero-crossing phase current icross and the same-direction phase current i same .

[0057] The input end of the torque calculation unit is connected to the position sensor, the sector judgment unit and the zero-crossing phase and the same-direction phase current selection unit respectively, and the output end is connected to the torque hysteresis controller for calculating the torque of the zero-crossing phase current i cross , same-direction phase current i same , sector information s and rotor position information θ to calculate the actual torque T e , according to the reference torque T e * and actual torque T e The torque deviation ΔT is obtained by subtracting e , torque deviation ΔT e The torque state signal τ is obtained through the torque hysteresis controller T ;

[0058] Among them, Figure 2 As shown in Figure 2, the torque hysteresis used by the torque hysteresis controller is as follows:

[0059]

[0060] In the formula, τ T (k) is the torque state signal at the current moment, τ T (k+1) is the torque state signal at the next moment, ΔT e is the torque deviation, T th is the threshold value in the torque hysteresis controller.

[0061] Among them, the actual electromagnetic torque T e for [k ecross (θ)-k eoppo (θ)]i cross +[k esame (θ)-k eoppo (θ)]i same , where k ecross (θ), k esame (θ), k eoppo (θ) are the back electromotive force constants of the zero-crossing phase, same-direction phase, and opposite-direction phase windings respectively.

[0062] The input end of the line back electromotive force ratio calculation unit is connected to the position sensor and the sector judgment unit respectively, and the output end is connected to the current distribution coefficient calculation unit, which is used to determine the line back electromotive force ratio k according to the rotor position information θ and the sector information s. L ;

[0063] Specifically, the back EMF comparison coefficient k L for where k ecross (θ), k esame(θ), k eoppo (θ) are the back electromotive force constants of the zero-crossing phase, the same-direction phase, and the reverse-direction phase windings, respectively. cross (θ), e same (θ), e oppo (θ) are the back electromotive force of the zero-crossing phase, same-direction phase, and opposite-direction phase windings respectively.

[0064] The input end of the current distribution coefficient calculation unit is connected to the line back electromotive force ratio calculation unit, and the output end is connected to the zero-crossing phase current hysteresis controller to calculate the line back electromotive force ratio k. L Calculate the current distribution coefficient m, and according to the current distribution coefficient m and the same-direction phase current i same The absolute value of the zero-crossing phase current i cross The absolute value of the zero-crossing phase current deviation ΔI is obtained by subtracting m , ΔI m The current state signal τ is obtained through the zero-crossing phase current hysteresis controller I ;

[0065] Among them, the current distribution coefficient m is

[0066] Among them, Figure 3 As shown, the zero-crossing current hysteresis controller uses the following zero-crossing current hysteresis:

[0067]

[0068] In the formula, τ I (k) is the current state signal at the current moment, τ I (k+1) is the current state signal at the next moment, ΔI m is the zero-crossing phase current deviation, I th is the threshold value in the zero-crossing phase current hysteresis controller.

[0069] The switch state query table includes the torque state signal τ T and the current state signal τ I , sector information s and the correspondence between the switch tube status signal, and the switch tube status information is used to control the on and off of the switch tube in the three-phase bridge inverter to realize BLDCM direct torque control considering the maximum torque current ratio.

[0070] The switch tube status query table is shown in Table 3.

[0071] Table 3

[0072]

[0073] In the table, τ T Represents the torque state signal, τ IZero-crossing phase current state signal, the six digits represent the switching states of the six switch tubes of the A, B, and C phase bridge arms in the three-phase bridge inverter from left to right, 1 indicates that the switch tube is turned on, and 0 indicates that the switch tube is turned off.

[0074] It should also be noted that the present invention is not only applicable to BLDCM, but also to permanent magnet synchronous motors.

[0075] In another embodiment, the present invention further provides a method for performing direct torque control of a motor using the motor direct torque control system considering the maximum torque current ratio of the above embodiment, which specifically includes the following steps:

[0076] S1, using a position sensor connected to the motor to determine the motor rotor position information θ;

[0077] S2, calculating the actual speed n of the permanent magnet brushless motor based on the rotor position information θ;

[0078] S3, determining the sector information s of the permanent magnet brushless motor at the current moment according to the rotor position information θ;

[0079] S4, according to the sector information s and the three-phase current i output by the three-phase bridge inverter A 、i B 、i C Determine the zero-crossing phase current i of the permanent magnet brushless motor cross and the same-direction phase current i same ;

[0080] S5, by the zero-crossing phase current i cross and the same-direction phase current i same , sector information s and rotor position information θ to calculate the actual torque T e , according to the reference torque T e * and actual torque T e The torque deviation ΔT is obtained by subtracting e , torque deviation ΔT e The torque state signal τ is obtained through the torque hysteresis controller T ;

[0081] S6, by line back electromotive force ratio k L Calculate the current distribution coefficient m, and according to the current distribution coefficient m and the same-direction phase current i same The absolute value of the zero-crossing phase current i cross The absolute value of the zero-crossing phase current deviation ΔI is obtained by subtracting m , ΔI m The current state signal τ is obtained through the zero-crossing phase current hysteresis controller I ;

[0082] S7, based on torque state signal τ T, current state signal τ I and sector information s to query the switch tube state query table, the switch tube state query table includes the torque state signal τ T and the current state signal τ I , sector information s and the correspondence between the switch tube state signal, wherein the switch tube state information is used to control the on and off of the switch tube in the three-phase bridge inverter to realize direct torque control of the permanent magnet brushless motor considering the maximum torque current ratio.

[0083] Compared with the direct torque control technology alone, the scheme in the above embodiment adds the maximum torque current ratio control strategy to operate the permanent magnet brushless motor, which can obtain the maximum torque output under a given current. By maximizing the torque per ampere rather than simply increasing the current, the minimum copper loss operation is achieved, thereby reducing the energy loss in the permanent magnet brushless motor.

[0084] The scheme in the above-mentioned embodiment, by applying the maximum torque current ratio control strategy, can ensure that the current distribution of the permanent magnet brushless motor during operation is optimized, reduce the energy loss caused by the current, and thus reduce the heat loss of the permanent magnet brushless motor, which helps to extend the service life of the permanent magnet brushless motor. Especially in applications such as electric vehicles, the use of the maximum torque current ratio control strategy can maximize the use of battery energy, increase cruising range, and reduce carbon emissions.

[0085] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A permanent magnet brushless motor direct torque control system considering the maximum torque current ratio, characterized in that: include: Three-phase bridge inverter for driving permanent magnet brushless motor; The zero-crossing phase and the same-direction phase current selection unit, whose input end is respectively connected to the sector judgment unit and the three-phase bridge inverter, and whose output end is respectively connected to the torque calculation unit, is used for the sector information s obtained by the sector judgment unit and the three-phase current i output by the three-phase bridge inverter A 、i B 、i C Determine the zero-crossing phase current i of a permanent magnet brushless motor cross and the same-direction phase current i same ; The torque calculation unit has an input end connected to the position sensor, the sector judgment unit and the zero-crossing phase and the same-direction phase current selection unit, and an output end connected to the torque hysteresis controller for the zero-crossing phase current i obtained by the zero-crossing phase and the same-direction phase current selection unit. cross and the same-direction phase current i same The actual torque T is calculated by using the sector information s obtained by the sector judgment unit and the rotor position information θ obtained by the position sensor. e , according to the reference torque T e * and actual torque T e The torque deviation ΔT is obtained by subtracting e , torque deviation ΔT e The torque state signal τ is obtained through the torque hysteresis controller T ; The current distribution coefficient calculation unit has an input end connected to the line back electromotive force ratio calculation unit, and an output end connected to the zero-crossing phase current hysteresis controller, which is used to obtain the line back electromotive force ratio k obtained by the line back electromotive force ratio calculation unit. L Calculate the current distribution coefficient m, and according to the current distribution coefficient m and the same-direction phase current i same The absolute value of the zero-crossing phase current i cross The absolute value of the zero-crossing phase current deviation ΔI is obtained by subtracting m , ΔI m The current state signal τ is obtained through the zero-crossing phase current hysteresis controller I ; The switch state query table includes the torque state signal τ T and the current state signal τ I , sector information s and the correspondence between the switch tube state signal, wherein the switch tube state information is used to control the on and off of the switch tube in the three-phase bridge inverter to realize direct torque control of the permanent magnet brushless motor considering the maximum torque current ratio.

2. A permanent magnet brushless motor direct torque control system considering the maximum torque current ratio according to claim 1, characterized in that: The line back electromotive force ratio calculation unit determines the line back electromotive force ratio k based on the rotor position information θ obtained by the position sensor and the sector information s obtained by the sector judgment unit. L .

3. A permanent magnet brushless motor direct torque control system considering the maximum torque current ratio according to claim 2, characterized in that: The line back electromotive force ratio k in the line back electromotive force ratio calculation unit L for where k ecross (θ), k esame (θ), k eoppo (θ) are the back electromotive force constants of the zero-crossing phase, the same-direction phase, and the reverse-direction phase windings, respectively. cross (θ), e same (θ), e oppo (θ) are the back electromotive force of the zero-crossing phase, the same-direction phase, and the opposite-direction phase windings respectively.

4. A permanent magnet brushless motor direct torque control system considering the maximum torque current ratio according to claim 3, characterized in that: The actual torque T calculated by the torque calculation unit e For: [k ecross (θ)-k eoppo (θ)]i cross +[k esame (θ)-k eoppo (θ)]i same .

5. A permanent magnet brushless motor direct torque control system considering the maximum torque current ratio according to claim 1, characterized in that: The current distribution coefficient unit determines the permanent magnet brushless motor current distribution coefficient m as follows:

6. A permanent magnet brushless motor direct torque control system considering the maximum torque current ratio according to claim 1, characterized in that: The torque hysteresis used by the torque hysteresis controller is as follows: In the formula, τ T (k) is the torque state signal at the current moment, τ T (k+1) is the torque state signal at the next moment, ΔT e is the torque deviation, T th is the threshold value in the torque hysteresis controller.

7. A permanent magnet brushless motor direct torque control system considering the maximum torque current ratio according to claim 1, characterized in that: The zero-crossing current hysteresis loop used by the zero-crossing current hysteresis loop controller is as follows: In the formula, τ I (k) is the current state signal at the current moment, τ I (k+1) is the current state signal at the next moment, ΔI m is the zero-crossing phase current deviation, I th is the threshold value in the zero-crossing phase current hysteresis controller.

8. A permanent magnet brushless motor direct torque control system considering the maximum torque current ratio according to claim 1, characterized in that: The switch tube state query table is as follows: In the table, τ T Represents the torque state signal, τ I Zero-crossing phase current state signal, the six digits represent the switching states of the six switch tubes of the A, B, and C phase bridge arms in the three-phase bridge inverter from left to right, 1 indicates that the switch tube is turned on, and 0 indicates that the switch tube is turned off.

9. A method for direct torque control of a permanent magnet brushless motor considering the maximum torque current ratio, characterized in that: A permanent magnet brushless motor direct torque control system considering the maximum torque current ratio as claimed in any one of claims 1 to 8, comprising: Determine the rotor position information θ of the permanent magnet brushless motor by using a position sensor connected to the permanent magnet brushless motor; The actual speed n of the permanent magnet brushless motor is calculated based on the rotor position information θ; Determine the sector information s of the permanent magnet brushless motor at the current moment according to the rotor position information θ; According to the sector information s and the three-phase current i output by the three-phase bridge inverter A 、i B 、i C Determine the zero-crossing phase current i of the permanent magnet brushless motor cross and the same-direction phase current i same ; By the zero-crossing phase current i cross and the same-direction phase current i same , sector information s and rotor position information θ to calculate the actual torque T e , according to the reference torque T e * and actual torque T e The torque deviation ΔT is obtained by subtracting e , torque deviation ΔT e The torque state signal τ is obtained through the torque hysteresis controller T ; The line back electromotive force ratio k L Calculate the current distribution coefficient m, and according to the current distribution coefficient m and the same-direction phase current i same The absolute value of the zero-crossing phase current i cross The absolute value of the zero-crossing phase current deviation ΔI is obtained by subtracting m , ΔI m The current state signal τ is obtained through the zero-crossing phase current hysteresis controller I ; Based on the torque state signal τ T , current state signal τ I and sector information s to query the switch tube state query table, the switch tube state query table includes the torque state signal τ T and the current state signal τ I , sector information s and the correspondence between the switch tube state signal, wherein the switch tube state information is used to control the on and off of the switch tube in the three-phase bridge inverter to realize direct torque control of the permanent magnet brushless motor considering the maximum torque current ratio.

10. A method for direct torque control of a permanent magnet brushless motor considering the maximum torque current ratio according to claim 9, characterized in that: Also includes: The speed deviation Δn is obtained by subtracting the given speed n* of the permanent magnet brushless motor from the actual speed n. The speed deviation Δn is passed through the speed controller ASR to obtain the reference torque T e *.

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