Method and device for non-inductive starting of brushless direct current motor driven by four-switch inverter

Abstract

The invention discloses a non-inductive starting method and equipment for a brushless direct current motor driven by a four-switch inverter, and aims to solve the problems that eight voltage vector amplitudes of the four-switch inverter are unequal and spatial phase distribution is uneven on the basis that the circuit topology of the original four-switch inverter is not changed and the advantages of small size and low cost of the four-switch inverter are reserved. And flux linkage optimization control is carried out based on a principle that volt-second integrals are equal, so that the effect of suppressing the torque ripple of the brushless direct current motor is achieved. And meanwhile, the method is combined with the inductance saturation effect of the brushless direct current motor and is applied to the non-inductive starting of the brushless direct current motor driven by the four-switch inverter, so that the success rate of the non-inductive starting of the brushless direct current motor of the four-switch inverter is improved, and the reliability of low-speed domain operation is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of brushless DC motor control, and particularly relates to a sensorless starting method and device for a brushless DC motor driven by a four-switch inverter. Background Art

[0002] As one of the important development directions of the new generation of drive motors, brushless DC motors have incomparable advantages over DC motors and asynchronous motors in the field of electric drive. Since power electronic devices need to be switched on and off frequently for normal operation, due to the complexity of their control and their own vulnerability, compared with other links of the brushless DC motor drive system, the inverter has become an important link with a relatively high failure rate in the process of implementing various complex control strategies. Therefore, a fault-tolerant four-switch control scheme for three-phase motors is proposed, that is, the midpoint of two capacitors on the DC bus is connected to the faulty-phase winding of the motor, and the other two phases are controlled. Such a control scheme enables the driver to have a more flexible topological structure, and on the basis of saving the system control cost, it can be used as a fault-tolerant control strategy and method to cope with the above-mentioned faults. When a fault occurs, instead of using external equipment, a new control method is relied on to ensure that the motor system can continue to operate within an acceptable range with degraded performance.

[0003] The patent application with the publication number CN114826038A and the name "Control Circuit and Method for Space Voltage Vector of Three-Phase Four-Switch Brushless DC Motor" includes: establishing a permanent magnet synchronous motor system driven by a four-switch inverter; renaming the binary logic function of the switching device; deriving the amplitudes and angles of the corresponding eight voltage vectors; re-dividing the sectors according to the eight voltage vectors; and finally proposing an eight-vector control scheme. This patent application proposes an eight-vector control scheme, which solves the problems of sector division and the selection of corresponding vectors, but does not consider that the eight voltage vectors proposed are asymmetric in angle and unequal in amplitude in space, resulting in excessive torque ripple of the motor.

[0004] In addition, the sensorless starting of existing brushless DC motors is mostly open-loop three-step starting, and all are sensorless starting schemes for six-switch inverters. The patent with the publication number CN114039515B and the name "A Sensorless BLDCM Starting Method Based on Acceleration Curve Fitting" includes: fitting an acceleration curve by using the motor Hall sensor, and at the same time, detecting the initial position of the rotor by using an improved pulse injection positioning method to determine the initial sector and realize static starting. It does not consider the problem of sensorless starting of a four-switch inverter brushless DC motor when one phase of the three-phase inverter fails and turns into a four-switch inverter and the motor stops rotating. Summary of the Invention

[0005] The object of the present invention is to provide a sensorless starting method and device for a brushless DC motor driven by a four-switch inverter, so as to solve the technical problems of torque ripple and low success rate of sensorless starting existing in the four-switch inverter brushless DC motor in the prior art.

[0006] To achieve the above object, the present invention adopts the following technical solutions: A sensorless starting method for a brushless DC motor driven by a four-switch inverter, comprising the following steps; Based on the inductance saturation effect, using the sensorless square-wave pulse voltage method, injecting driving voltage vectors with opposite space phases at adjacent positions into the stator of the brushless DC motor as detection voltage pulses, and obtaining the initial rotor position according to the magnitude of the inductance value of the stator of the brushless DC motor. Adopting the four-switch eight-vector control method, passing eight driving voltage vectors into the stator of the brushless DC motor. First, give the corresponding driving voltage vectors according to the rotation direction of the motor and the sector where the initial rotor position is located, then inject two detection voltage pulses respectively, obtain the sector corresponding to the current rotor position, judge whether sector switching is performed, and then pass the corresponding driving voltage vectors to realize the low-speed starting of the motor in a closed loop. When the number of consecutive sector switches reaches a specified value, switch the brushless DC motor to the sensorless back electromotive force method control. The driving voltage vector is obtained according to the principle of equal volt-second integration of the voltage vectors of the four-switch inverter.

[0007] Further, there are six detection voltage pulses, and zero-vector voltage pulses are passed between the driving voltage vector and the detection voltage pulses and between adjacent detection voltage pulses.

[0008] Further, the voltage vectors of the four-switch inverter are obtained through a binary logic function with the four-switch inverter as a unit.

[0009] Further, the magnitude of the inductance value of the stator of the brushless DC motor is obtained through the non-conducting phase terminal voltage, and the initial rotor position is obtained according to the corresponding relationship between the three-phase inductance of the brushless DC motor and the rotor position and the amplitude of the bus current response.

[0010] Further, the sectors are divided into 12. The sectors with the same effective voltage vectors are combined, and then sector V and sector VI, as well as sector XI and sector XII are combined to obtain 6 sectors.

[0011] Further, the judgment condition for sector switching is whether the current rotor position passes through the commutation point.

[0012] Further, the commutation point is divided according to the magnitude order of the three-phase inductances corresponding to the two adjacent sectors, and the three-phase inductances are obtained based on the non-conducting phase terminal voltage of the current sector.

[0013] In a second aspect, a sensorless starting system for a brushless DC motor driven by a four-switch inverter is provided, including a detection module, a starting module, and a switching module, where: Detection module: Based on the inductance saturation effect, using the sensorless square-wave pulse voltage method, inject drive voltage vectors with opposite space phases at adjacent positions into the stator of the brushless DC motor as detection voltage pulses, and obtain the initial rotor position according to the magnitude of the inductance value of the stator of the brushless DC motor; Starting module: Used to adopt the four-switch eight-vector control method to apply eight drive voltage vectors to the stator of the brushless DC motor. First, give the corresponding drive voltage vectors according to the rotation direction of the motor and the sector where the initial rotor position is located, then inject two detection voltage pulses respectively to obtain the sector corresponding to the current rotor position, judge whether sector switching is performed, and then apply the corresponding drive voltage vectors to achieve the low-speed starting of the motor in a closed loop; Switching module, used to switch the brushless DC motor to sensorless back electromotive force method control when the number of consecutive sector switches reaches a specified value; The drive voltage vector is obtained according to the principle of equal volt-second integration of the voltage vectors of the four-switch inverter.

[0014] In a third aspect, a terminal device includes a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, the steps of the above method are implemented.

[0015] In a fourth aspect, a computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, the steps of the above method are implemented.

[0016] Compared with the prior art, the present invention has the following beneficial technical effects: A sensorless starting method for a brushless DC motor driven by a four-switch inverter according to the present invention, without changing the original four-switch inverter circuit topology and retaining the advantages of small size and low cost of the four-switch inverter, aims at the problems of unequal magnitudes and uneven spatial phase distributions of the eight voltage vectors of the four-switch inverter, and performs flux linkage optimization control based on the principle of equal volt-second integration to achieve the effect of suppressing torque ripple of the brushless DC motor. At the same time, it is combined with the inductance saturation effect of the brushless DC motor and applied to the sensorless starting of the brushless DC motor driven by the four-switch inverter, improving the success rate of sensorless starting of the four-switch inverter brushless DC motor and increasing the reliability of operation in the low-speed range.

[0017] The present invention adopts a switching strategy that determines the switching time based on the number of sector switches, which can effectively improve the success rate of sensorless starting.

[0018] Preferably, a zero-vector voltage pulse is applied between the driving voltage vector and the detected voltage pulse and between adjacent detected voltage pulses. The length of the zero-vector voltage pulse is greater than or equal to the time when the bus current response basically drops to zero, ensuring that the bus current basically drops to zero.

[0019] Preferably, the judgment condition for sector switching is whether the current rotor position passes through the commutation point, the corresponding relationship between the driving voltage vector and the detected voltage pulse, and the voltage at the non-conducting phase terminal. Thus, the commutation point can be obtained to achieve closed-loop low-speed starting. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a flowchart of a sensorless starting method for a brushless DC motor driven by a four-switch inverter according to an embodiment of the present invention; Figure 2 It is a space voltage vector diagram of a four-switch inverter brushless DC motor; Figure 3 It is a control process diagram for suppressing torque ripple of a brushless DC motor; Figure 4 It is a schematic diagram of flux linkage control based on equal volt-second integration; Figure 5 It is a schematic diagram of finally synthesizing the stator flux linkage of a brushless DC motor; Figure 6 It is a schematic diagram of inductance saturation effect; Figure 7 It is an equivalent circuit diagram of the motor in the four-switch inverter (1001) stage; Figure 8 It is a vector injection sequence diagram for the rotor external synchronous acceleration stage; Figure 9 It is a diagram of the relationship between the rotor spatial position and the voltage vector; Figure 10 It is a flowchart of the synchronous switching program; Figure 11 It is a diagram of the dynamic speed regulation process of a brushless DC motor; Figure 12 It is a dynamic torque diagram of a brushless DC motor. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0021] In order to enable those skilled in the art to better understand the solution of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0022] It should be noted that like reference numerals and letters refer to like items in the following figures, and thus, once an item is defined in one figure, it need not be further defined and explained in subsequent figures.

[0023] It should be noted that the terms "first", "second", etc. in the description, claims and above-mentioned figures of the present invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged under appropriate circumstances 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 "comprising" and "having" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device that comprises a series of steps or units need not be limited to those steps or units clearly listed, but may include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0024] The present invention will be further described in detail below with reference to the accompanying drawings: As Figure 1 shown, a sensorless starting method for a brushless DC motor driven by a four-switch inverter includes the following steps: Step 1, based on the inductance saturation effect, using the sensorless square-wave pulse voltage method, injecting drive voltage vectors with opposite space phases at adjacent positions into the stator of the brushless DC motor as detection voltage pulses, and obtaining the initial rotor position according to the magnitude of the inductance value of the stator of the brushless DC motor. Specifically, in the rotor pre-positioning stage, based on the inductance saturation effect, the sensorless square-wave pulse voltage method is adopted, and the initial rotor position identification is realized by judging the magnitude of the stator inductance value. In order to prevent the rotor position from shifting due to the detection voltage pulse during the process of detecting the initial position, the detection voltage pulses are injected in the order of k1u1 - k5u5 - k2u2 - k6u6 - k3u3 - k7u7 - k4u4 - k8u8, that is, two drive voltage vectors with opposite phases in space are injected to cancel the rotor position displacement caused by the previous vector. Based on the inductance saturation effect, the inductance value is judged by using the non-conducting phase terminal voltage. Due to the four-switch topology, the ABC three-phase windings of the vectors u2 and u6 are all in the conducting state. Therefore, the vectors u2 and u6 can be not considered as detection voltage pulses in the rotor pre-positioning stage, that is, the detection voltage pulses are 6.

[0025] The magnitude of the inductance value of the stator of the brushless DC motor is obtained through the non-conducting phase terminal voltage, and the initial rotor position is obtained according to the correspondence between the three-phase inductance of the brushless DC motor and the rotor position and the amplitude of the bus current response.

[0026] The driving voltage vector is obtained according to the principle of equal volt-second integration of the voltage vectors of the four-switch inverter. The voltage vectors of the four-switch inverter are obtained through a binary logic function with the four-switch inverter as the unit. When

[0027] In the formula: k = 1, 2, 3, 4. The four switching devices form two arms of the three-phase four-switch inverter. According to the characteristics of the voltage source inverter, the two switching devices in each arm cannot conduct simultaneously. A total of 8 effective space voltage vectors u 1 to u 8 and one zero vector u 0 can be obtained, and its amplitude is , and the spatial mutual difference is , U d is the DC bus voltage. The amplitudes and distributions of the voltage vectors are shown in Table 1: Table 1 Amplitudes and Distributions of Voltage Vectors

[0028] The torque ripple suppression strategy is based on the minimum spatial phase difference angle, that is, taking The rotor one week is divided into 12 sectors. The time is allocated according to the principle of equal flux linkage in each sector to ensure equal final flux linkage. According to the physical relationship between the stator voltage and the flux linkage:

[0029] Where Ψ s ( t ) is the magnitude of the stator flux linkage at t time; Ψ s ( t 0) is the magnitude of the stator flux linkage at t 0 time; u s is the stator voltage vector. The change law of the flux linkage of the brushless DC motor depends on the volt-second integration of the stator voltage. The electromagnetic torque of the brushless DC motor can be obtained from the vector product of the stator winding current and the rotor flux linkage:

[0030] Where K is a constant related to the type of motor; T e is the electromagnetic torque; Ψ f is the rotor permanent magnet flux linkage; δ is the load angle. By applying different voltage vectors u s , the stator flux linkage can be realizedΨ s The magnitude and direction of the electromagnetic torque change. To reduce the electromagnetic torque pulsation, the stator flux trajectory should be controlled to be as circular as possible. That is, the volt-second integral of each stator voltage vector should be controlled to be equal. The equality of the volt-second integrals of each stator voltage vector is achieved by:

[0031] in k i is the voltage vector u s The action time adjustment coefficient; i The voltage vector number can be 1, 2, 3, ... 8; C is a constant related to the motor speed. u 1. u 2. u 4 respectively into the above formula to obtain:

[0032] The voltage vector is finally obtained by combining u 1~ u 8 Relationship between the flux trajectory adjustment coefficients corresponding to the amplitude

[0033] k 1 is the control variable for realizing the speed regulation of BLDCM and satisfies the basic regulation coefficient of the 12-time voltage vector action time of the six modes in Table 3-4. Substituting the above relationship into the rotation period T of the entire brushless DC motor, the following formula can be obtained:

[0034] Finally, we get:

[0035] The final synthetic brushless DC motor stator flux diagram is Figure 5 Shown The sensorless starting method of the brushless DC motor driven by the four-switch inverter includes three stages: rotor pre-positioning stage, rotor external synchronous acceleration stage, and synchronous switching stage: Step 2: Using the four-switch eight-vector control method, eight driving voltage vectors are introduced into the stator of the brushless DC motor. First, the corresponding driving voltage vector is given according to the direction of motor rotation and the sector where the rotor is initially located. Then, two detection voltage pulses are injected respectively to obtain the sector corresponding to the current rotor position, determine whether to perform sector switching, and then introduce the corresponding driving voltage vector to achieve low-speed start of the motor closed loop. Among them, the sector corresponding to the current position of the rotor is obtained by collecting the terminal voltage of the non-conducting phase and the amplitude of the bus current response.

[0036] Step 3: When the continuous sector switching times reach the specified value, switch the brushless DC motor to the control method of back electromotive force without sensors; The judgment condition for sector switching is whether the current rotor position passes through the commutation point. The commutation point is divided according to the magnitude order of the three-phase inductances corresponding to the two adjacent sectors, that is, the magnitude order of the three-phase inductances corresponding to the two adjacent sectors is different, and the three-phase inductances are obtained based on the terminal voltage of the non-conducting phase of the current sector.

[0037] In an embodiment provided by the present invention, a method for sensorless starting of a brushless DC motor driven by a four-switch inverter is provided. The present invention will be further described in detail below with reference to the accompanying drawings: Eight voltage vectors are composed of Figure 2 As shown, an αβ coordinate system is established, and there are a total of 8 space voltage vectors u 1~ u 8, and their amplitudes are , and the spatial mutual difference is , and the eight voltage vectors can be obtained through a binary logic function with switching devices as units. When

[0038] In the formula: k =1, 2, 3, 4. Four switching devices form two arms of a three-phase four-switch inverter. According to the characteristics of a voltage source inverter, the two switching devices in each arm cannot be turned on simultaneously and are switched in a complementary manner. The amplitudes and distributions of the voltage vectors are shown in Table 2: Table 2 Amplitudes and Distributions of Voltage Vectors

[0039] To suppress the torque ripple control of the brushless DC motor, one revolution of the rotor is divided into 12 sectors, and the working time of the voltage vector in each sector is T / 12. According to the BLDCM control principle, when the angle between the control voltage vector and the rotor magnetic pole direction is 90°, the generated electromagnetic torque is the largest.

[0040] In sector I, the rotor position is between 11π / 6 and 0, and voltage vector u 3 is selected, corresponding to the switching signal (0010), and the voltage vector amplitude is / 4 U d .

[0041] In sector II, the rotor position is between 0 and π / 6, and voltage vector u 3 is selected, corresponding to the switching signal (0010), and the voltage vector amplitude is / 4 U d 。

[0042] Sector Ⅲ, with the rotor position between π / 6 and 2π / 6, select the voltage vector u 4, corresponding to the switching signal (0110), and the voltage vector amplitude is / 2 U d 。

[0043] Sector Ⅳ, with the rotor position between 2π / 6 and π / 2, select the voltage vector u 4, corresponding to the switching signal (0110), and the voltage vector amplitude is / 2 U d 。

[0044] Sector Ⅴ, with the rotor position between π / 2 and 4π / 6, select the voltage vector u 5, corresponding to the switching signal (0100), and the voltage vector amplitude is / 4 U d 。

[0045] Sector Ⅵ, with the rotor position between 4π / 6 and 5π / 6, select the voltage vector u 6, corresponding to the switching signal (0101), and the voltage vector amplitude is / 6 U d 。

[0046] Sector Ⅶ, with the rotor position between 5π / 6 and π, select the voltage vector u 7, corresponding to the switching signal (0001), and the voltage vector amplitude is / 4 U d 。

[0047] Sector Ⅷ, with the rotor position between π and 7π / 6, select the voltage vector u 7, corresponding to the switching signal (1001), and the voltage vector amplitude is / 4 U d 。

[0048] Sector Ⅸ, with the rotor position between 7π / 6 and 8π / 6, select the voltage vector u 8, corresponding to the switching signal (0010), and the voltage vector amplitude is / 2 U d 。

[0049] Sector Ⅹ, with the rotor position between 8π / 6 and 9π / 6, select the voltage vector u8, corresponding to the switching signal (0010), the amplitude of the voltage vector is / 2 U d 。

[0050] In sector Ⅺ, the rotor position is between 9π / 6 and 10π / 6, and the voltage vector u 1 is selected, corresponding to the switching signal (1000), and the amplitude of the voltage vector is / 4 U d 。

[0051] In sector Ⅻ, the rotor position is between 10π / 6 and 11π / 6, and the voltage vector u 2 is selected, corresponding to the switching signal (1010), and the amplitude of the voltage vector is / 6 U d 。

[0052] The control diagram for suppressing the torque ripple of the brushless DC motor is as Figure 3 shown. Finally, the twelve sectors are re - combined into six sectors. First, the sectors with the same - acting voltage vectors are combined, and then sector Ⅴ and sector Ⅵ, as well as sector Ⅺ and sector Ⅻ are combined, that is, sector Ⅰ and sector Ⅱ are combined, sector Ⅲ and sector Ⅳ are combined, sector Ⅴ and sector Ⅵ are combined, sector Ⅶ and sector Ⅷ are combined, sector Ⅸ and sector Ⅹ are combined, and sector Ⅺ and sector Ⅻ are combined.

[0053] Time allocation is carried out on the principle that the flux in each sector is equal to ensure that the final flux is equal. According to the physical relationship between the stator voltage and the flux:

[0054] where Ψ s ( t ) is the magnitude of the stator flux at time t ; Ψ s ( t 0) is the magnitude of the stator flux at time t 0; u s is the stator voltage vector. The flux change law of the brushless DC motor depends on the volt - second integral of the stator voltage. The electromagnetic torque of the brushless DC motor can be obtained from the vector product of the stator winding current and the rotor flux:

[0055] where K is a constant related to the type of motor; T e is the electromagnetic torque; Ψ f is the rotor permanent - magnet flux; δis the load angle. By applying different voltage vectors u s , the stator flux can be controlled Ψ s The magnitude and direction of the electromagnetic torque change, and thus the magnitude of the electromagnetic torque. To reduce the electromagnetic torque pulsation, the stator flux trajectory should be controlled to be as circular as possible. That is, the volt-second integral of each stator voltage vector should be controlled to be equal.

[0056] The volt-second integral of each stator voltage vector is equal to Figure 4 As shown. It is implemented by the following formula:

[0057] in k i is the voltage vector u s The action time adjustment coefficient; i The voltage vector number can be 1, 2, 3, ... 8; C is a constant related to the motor speed. u 1. u 2. u 4 respectively into the above formula to obtain:

[0058] The voltage vector is finally obtained by combining u 1~ u 8 Relationship between the flux trajectory adjustment coefficients corresponding to the amplitude

[0059] k 1 is the control variable for realizing the speed regulation of BLDCM and satisfies the basic regulation coefficient of the 12-time voltage vector action time of the six modes in Table 3-4. Substituting the above relationship into the rotation period T of the entire brushless DC motor, the following formula can be obtained:

[0060] Finally, we get:

[0061] The final synthetic brushless DC motor stator flux diagram is Figure 5 shown.

[0062] The sensorless starting method of the brushless DC motor driven by the four-switch inverter includes three stages: rotor pre-positioning stage, rotor external synchronous acceleration stage, and synchronous switching stage: The inductor saturation effect is caused by Figure 6 Based on the inductor saturation effect, the non-inductive square wave pulse voltage method is used to identify the initial position of the rotor by judging the size of the inductance value; During the rotor pre-positioning stage, based on the inductance saturation effect, the non-sensing square-wave pulse voltage method is adopted, and the initial rotor position is identified by judging the magnitude of the inductance value. To prevent the rotor position from shifting due to the detection voltage pulse during the initial position detection process, the detection voltage pulses are injected in the order of k 1 u 1- k 5 u 5- k 2 u 2- k 6 u 6- k 3 u 3- k 7 u 7- k 4 u 4- k 8 u 8, that is, two vectors with opposite phases in space are injected to cancel the rotor position displacement caused by the previous vector. Based on the inductance saturation effect, the inductance value is judged by the non-conducting phase terminal voltage, and for vectors u 2 and u 6, due to the four-switch topology, all three-phase windings of ABC are in the conducting state, so vectors u 2 and u 6 can be not considered as the detection voltage pulses during the rotor pre-positioning stage.

[0063] The equivalent circuit diagram of the motor in the four-switch inverter (1001) stage is shown in Figure 7 . By combining two-by-two conduction and single-tube conduction and using non-complementary pulses, six detection pulses are applied to the brushless DC motor to achieve voltage vector volt-second balance. Finally, the terminal voltage of the non-conducting phase is collected to judge the magnitudes of the three inductances. The specific analysis is as follows:

[0064] U d is the DC bus voltage; R is the resistance of the brushless DC motor; L is the inductance of the brushless DC motor; e is the back electromotive force of the brushless DC motor. During the pre-positioning stage, since the motor does not rotate, the back electromotive force e= is 0, and because the internal resistance R of the motor is very small and can be ignored, so after ignoring the resistance and back electromotive force, there is:

[0065] In the state of the four-switch inverter (1001), there is: , Then there is:

[0066] Non-conducting terminal voltage is:

[0067] In the state of the four-switch inverter (0110), there are:

[0068] From the above two equations, when the inverter is in the states of (1001) and (0110), the non-conducting phase terminal voltage can be used to calculate and the magnitudes; for single-switch conduction, its DC bus voltage is half of the original, and still satisfies the above relationship: In the state of the four-switch inverter (1000), there are: , then there is:

[0069] Non-conducting phase terminal voltage is:

[0070] In the state of the four-switch inverter (0001), there are:

[0071] After obtaining , , the magnitudes, according to the two cases corresponding to the three-phase inductance and the rotor position: the sector corresponding to the N pole position and the sector corresponding to the S pole position. Then, the magnitude of the bus current response can be used. The detection pulse with the largest bus current response amplitude is the N pole, and finally the pre-positioning of the rotor position is realized.

[0072] After injecting the corresponding detection voltage pulse, the zero vector is needed, that is, all the switching tubes are turned off, with a certain time interval from the next voltage pulse. The length of the zero vector voltage pulse needs to be greater than or equal to the time when the bus current response basically drops to zero. During the period when the switching tube is turned on, due to the small equivalent resistance of the loop, the bus current approximately rises linearly. During the period when the switching tube is turned off, due to the inductive nature of the loop, the current in the winding cannot change suddenly, so it flows back to the power supply through the diode anti-parallel to the switching tube, and the bus power supply quickly reverses. After the falling time and the tailing time, the bus current basically drops to zero.

[0073] The vector injection sequence diagram in the rotor external synchronous acceleration stage is shown in Figure 8As shown. The external synchronous acceleration stage of the rotor is also based on the inductance saturation effect. During the acceleration process, two detection voltage vectors are applied to detect the rotor position, thereby realizing closed-loop control. After obtaining the initial rotor position, under the four-switch eight-vector control method, eight drive voltage vectors can be applied. First, the corresponding drive voltage vector is given according to the rotation direction of the motor, and then two detection voltage pulses are respectively injected. By collecting the terminal voltage of the non-conducting phase and the amplitude of the bus current response, the sector corresponding to the current rotor position can be obtained, and then the corresponding drive voltage vector is applied to realize the closed-loop low-speed start.

[0074] The relationship diagram between the rotor spatial position and the voltage vector is as Figure 9 shown. Define the three phases of the motor as ABC. When the rotor position detection is within the corresponding 60° sector range, the drive voltage vector does not change at all; if the rotor position detection is in the next 60° sector, the drive voltage vector needs to be adjusted. After obtaining the accurate rotor position, in order to obtain the maximum starting torque, a drive voltage vector with a 90° angle to the rotor position needs to be applied. Specifically as follows: Assume that during the rotor pre-positioning stage, the detected rotor position is between 330° and 30°, that is, within the 110 sector, then the corresponding injected drive voltage vector is u 3, and the conduction state of the four-switch inverter is (0010), that is ; when the rotor reaches 30°, the sector switches to 010, and the drive voltage vector that should be injected is u 4, and the conduction state of the four-switch inverter is (0110), that is ; so the 30° position is the commutation point of the motor. The relationship between the inductances of the sectors 30° before and after the 30° position of the commutation point is: In the range from 0° to 30°:

[0075] In the range from 30° to 60°:

[0076] So only need to judge and to judge the position where the rotor is located. Therefore, the detection pulses are and , and then sample the terminal voltage of the non-conducting phase to obtain the commutation point. The inductance magnitude relationships corresponding to all commutation points are shown in Table 3: Table 3 Inductance magnitude relationships corresponding to all commutation points

[0077] The drive voltages corresponding to all commutation points are shown in Table 4: Table 4 Drive voltages corresponding to all commutation points

[0078] From the above two tables, the corresponding relationship between the driving voltage vector and the detected voltage pulse during the external synchronous acceleration stage of the rotor can be obtained. Thus, the commutation point can be acquired to achieve closed-loop low-speed startup.

[0079] During the synchronous switching stage, when the speed of the brushless DC motor reaches a certain value, its back electromotive force can stably reach the minimum value required for zero-crossing detection. At this time, the control method can be changed and switched to the zero-crossing detection control of the back electromotive force in the medium and high-speed state. The switching strategy that determines the switching time based on the number of sector switches can effectively improve the success rate of sensorless startup.

[0080] The flow chart of the synchronous switching program is shown by Figure 10 As shown. When using this switching strategy for control, if the sector switching is continuously successful, it indicates that the sector judgment is accurate. When the specified number of switches is reached, it is switched to the sensorless back electromotive force method control. The number of switches is related to the synchronous switching time. The smaller the number of switches, the shorter the synchronous switching time and the faster the startup time; the larger the number of switches, the longer the synchronous switching time and the higher the startup success rate. Therefore, the number of switches should be combined with the actual situation, taking into account both the startup time and ensuring the startup success rate.

[0081] The speed curve of a sensorless startup method for a brushless DC motor driven by a four-switch inverter is shown as Figure 11 As shown. Using a sensorless startup method for a brushless DC motor driven by a four-switch inverter can enable the speed of the brushless DC motor to quickly reach the given value of 500 r / min in 0.01 s, and can quickly reach the given value of 1000 r / min at 0.3 s, with a relatively fast response speed. After using the sensorless startup method for a brushless DC motor driven by a four-switch inverter, the speed fluctuation of the motor is small under no-load conditions before 0.5 s, basically a straight line. Under the load condition after suddenly applying 1 N·m at 0.5 s, the speed fluctuation also basically remains unchanged. It can be seen that using the control method of eight voltage vectors can improve the steady-state operation characteristics of the motor and effectively suppress the speed fluctuation of the motor.

[0082] The torque waveform of a sensorless startup method for a brushless DC motor driven by a four-switch inverter is shown as Figure 12As shown in the figure. A sensorless starting method for a brushless DC motor driven by a four-switch inverter has good dynamic performance. When the motor starts, it can start with the maximum torque. When the speed reaches the given 500 r / min, due to the no-load state, the torque basically drops to 0. When the speed further increases, it also reaches the speed regulation given 1000 r / min with the maximum torque. After stabilization, the torque drops to 0. Until a load torque of 1 N*m is suddenly applied at 0.5 s, the torque stabilizes at 1 N*m. After adopting the sensorless starting method for a brushless DC motor driven by a four-switch inverter, the maximum torque ripple of the BLDCM is only 1.4 N*m. It can be seen that a sensorless starting method for a brushless DC motor driven by a four-switch inverter can effectively suppress the torque ripple of the motor.

[0083] The present invention also provides a sensorless starting system for a brushless DC motor driven by a four-switch inverter, including a detection module, a starting module, and a switching module, where: Detection module: Based on the inductance saturation effect, using the sensorless square-wave pulse voltage method, injecting drive voltage vectors with opposite space phases at adjacent positions into the stator of the brushless DC motor as detection voltage pulses, and obtaining the initial rotor position according to the magnitude of the inductance value of the stator of the brushless DC motor. Starting module: Used to adopt the four-switch eight-vector control method to apply eight drive voltage vectors to the stator of the brushless DC motor. First, give the corresponding drive voltage vectors according to the rotation direction of the motor and the sector where the initial rotor position is located, then inject two detection voltage pulses respectively to obtain the sector corresponding to the current rotor position, judge whether to perform sector switching, and then apply the corresponding drive voltage vectors to achieve the low-speed starting of the motor in a closed loop. Switching module, used to switch the brushless DC motor to the sensorless back electromotive force method control when the number of consecutive sector switches reaches a specified value.

[0084] Those skilled in the art should understand that the embodiments of the present invention can be provided as a method, a system, or a computer program product. Therefore, the present invention can be implemented in the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present invention can be implemented in the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0085] The present invention is described with reference to the flowcharts and / or block diagrams of methods, apparatuses (systems), and computer program products according to embodiments of the present invention. It should be understood that each flow and / or block in the flowchart and / or block diagram, and the combination of flows and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to the processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing devices to generate a machine, such that the instructions executed by the processor of the computer or other programmable data processing devices produce means for implementing the functions specified in one or more flows and / or blocks Figure 1 in one or more flows and / or blocks Figure 1 or in one or more blocks.

[0086] These computer program instructions can also be stored in a computer-readable memory that can direct a computer or other programmable data processing device to work in a specific manner, such that the instructions stored in the computer-readable memory produce a manufactured article including instruction means that implement the functions specified in one or more flows and / or blocks Figure 1 in one or more flows and / or blocks Figure 1 or in one or more blocks.

[0087] These computer program instructions can also be loaded onto a computer or other programmable data processing device, such that a series of operation steps are executed on the computer or other programmable device to generate a computer-implemented process, so that the instructions executed on the computer or other programmable device provide steps for implementing the functions specified in one or more flows and / or blocks Figure 1 in one or more flows and / or blocks Figure 1 or in one or more blocks.

[0088] 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 the scope of its protection. Although the present invention has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: after reading the present invention, those skilled in the art can still make various changes, modifications, or equivalent replacements to the specific implementation manners of the invention, but these changes, modifications, or equivalent replacements are all within the scope of the claims of the invention pending approval.

Claims

1. A sensorless starting method for a brushless DC motor driven by a four-switch inverter, characterized in that, It includes the following steps: Based on the inductance saturation effect, the non-sensing square-wave pulse voltage method is adopted to inject drive voltage vectors with opposite space phases at adjacent positions into the stator of the brushless DC motor as detection voltage pulses, and the initial rotor position is obtained according to the magnitude of the inductance value of the stator of the brushless DC motor; The four-switch eight-vector control method is adopted to apply eight drive voltage vectors to the stator of the brushless DC motor. First, the corresponding drive voltage vectors are given according to the rotation direction of the motor and the sector where the initial rotor position is located. Then, two detection voltage pulses are respectively injected to obtain the sector corresponding to the current rotor position, determine whether sector switching is performed, and then apply the corresponding drive voltage vectors to achieve the low-speed start of the motor in a closed loop; When the continuous sector switching times reach the specified value, switch the brushless DC motor to the non-sensing back electromotive force method control; The drive voltage vector is obtained according to the principle of equal volt-second integration of the voltage vector of the four-switch inverter.

2. A sensorless starting method for a brushless DC motor driven by a four-switch inverter according to claim 1, characterized in that, There are six detection voltage pulses, and zero-vector voltage pulses are applied between the drive voltage vector and the detection voltage pulses and between adjacent detection voltage pulses.

3. A sensorless starting method for a brushless DC motor driven by a four-switch inverter according to claim 1, characterized in that The voltage vector of the four-switch inverter is obtained through a binary logic function with the four-switch inverter as the unit.

4. A sensorless starting method for a brushless DC motor driven by a four-switch inverter according to claim 1, characterized in that The magnitude of the inductance value of the stator of the brushless DC motor is obtained through the voltage at the non-conducting phase terminal, and the initial rotor position is obtained according to the corresponding relationship between the three-phase inductance of the brushless DC motor and the rotor position and the amplitude of the bus current response.

5. A sensorless starting method for a brushless DC motor driven by a four-switch inverter according to claim 1, characterized in that, The sectors are divided into 12. The sectors with the same effective voltage vectors are combined, and then sector V and sector VI as well as sector XI and sector XII are combined to obtain 6 sectors.

6. A sensorless starting method for a brushless DC motor driven by a four-switch inverter according to claim 1, characterized in that The judgment condition for sector switching is whether the current rotor position passes through the commutation point.

7. A sensorless starting method for a brushless DC motor driven by a four-switch inverter according to claim 6, characterized in that, The commutation point is divided according to the magnitude order of the three-phase inductances corresponding to the two adjacent sectors, and the three-phase inductances are obtained based on the voltage at the non-conducting phase terminal of the current sector.

8. A sensorless starting system for a brushless DC motor driven by a four-switch inverter, characterized in that, It includes a detection module, a start module and a switching module, where: Detection module: Based on the inductance saturation effect, the non-sensing square-wave pulse voltage method is adopted to inject drive voltage vectors with opposite space phases at adjacent positions into the stator of the brushless DC motor as detection voltage pulses, and the initial rotor position is obtained according to the magnitude of the inductance value of the stator of the brushless DC motor; Start module: It is used to adopt the four-switch eight-vector control method to apply eight drive voltage vectors to the stator of the brushless DC motor. First, the corresponding drive voltage vectors are given according to the rotation direction of the motor and the sector where the initial rotor position is located. Then, two detection voltage pulses are respectively injected to obtain the sector corresponding to the current rotor position, determine whether sector switching is performed, and then apply the corresponding drive voltage vectors to achieve the low-speed start of the motor in a closed loop; Switching module, which is used to switch the brushless DC motor to the non-sensing back electromotive force method control when the continuous sector switching times reach the specified value; The drive voltage vector is obtained according to the principle of equal volt-second integration of the voltage vector of the four-switch inverter.

9. A terminal device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the processor executes the computer program, it realizes the steps of the method described in any one of claims 1-7.

10. A computer-readable storage medium storing a computer program, characterized in that, When the computer program is executed by the processor, it realizes the steps of the method described in any one of claims 1-7.

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