Non-inductive brushless motor variable load smooth starting method and system and lifting table

Abstract

The invention provides a non-inductive brushless motor variable load smooth starting method and system and a lifting table, and relates to the technical field of motor control, and the method comprises the steps: obtaining an initial angle of a rotor before the non-inductive brushless motor is started; controlling the non-inductive brushless motor to start according to the initial angle, and then acquiring a first angle and a second angle of a rotor respectively output by a pre-configured high-frequency square wave observer and a pre-configured back electromotive force observer in real time in the starting process, and applying a third angle obtained by performing weighted summation on the first angle and the second angle to smooth starting control of the non-inductive brushless motor. The zero-speed starting control method has the beneficial effects that in the zero-speed starting process of the non-inductive brushless motor, starting control is carried out by adopting the third angle obtained by carrying out weighting processing on the first angle output by the high-frequency square wave observer and the second angle output by the back electromotive force observer, so that continuous torque and stable rotating speed can be obtained in the starting stage; smooth starting can be achieved during variable load starting, shaking is avoided, and the use experience of a user is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of motor control, and in particular to a method and system for smoothly starting a brushless motor with variable load, and a lifting table. Background Art

[0002] As a new type of motor technology, sensorless brushless motors have been widely used in many fields in recent years, especially in smart home devices such as electric lift tables, showing significant advantages. Compared with traditional position sensor motors, sensorless brushless motors not only have a greater cost advantage, but also perform well in reliability and adaptability. These characteristics make sensorless brushless motors increasingly popular in modern office and living environments.

[0003] One of the biggest advantages of brushless motors is their cost-effectiveness. Traditional position sensor solutions require the installation of additional sensors, which not only increases manufacturing costs, but also may increase the complexity of maintenance. Sensor costs, installation and debugging require additional investment, while brushless motors eliminate these links and simplify the design and production process. This cost saving makes brushless motors more competitive in price-sensitive markets, especially in products such as electric lift tables that require mass production, which can effectively reduce the final selling price.

[0004] In addition, traditional motors with position sensors may face the risk of reduced sensitivity or damage under complex environmental conditions. For example, in an environment with a lot of dust or severe electromagnetic interference, the performance of the sensor may be affected, causing unstable operation of the motor or even failure. Sensorless motors avoid this problem because they do not rely on external sensors for position detection, but instead use internal algorithms to control the operating status of the motor. This design allows sensorless brushless motors to maintain high operating reliability under a variety of environmental conditions.

[0005] When the sensorless brushless motor is used in an electric lifting table, the types and weights of items placed on the desktop vary greatly and users can place different load-bearing items at any position and time. For example, adding or removing heavy objects will cause the desktop load to change. Especially when the motor is started at zero speed, the rotor position will be inaccurately positioned and there will be jitter at startup, affecting the user experience. Summary of the invention

[0006] In view of the problems existing in the prior art, the present invention provides a method for smoothly starting a brushless motor with variable load, comprising:

[0007] Step S1, obtaining the initial angle of the rotor of the sensorless brushless motor before starting;

[0008] Step S2, controlling the brushless motor to start according to the initial angle, and then acquiring in real time during the startup process the first angle and the second angle of the rotor respectively output by a pre-configured high-frequency square wave observer and a back electromotive force observer, and applying a third angle obtained by weighted summation of the first angle and the second angle to the smooth startup control of the brushless motor.

[0009] Preferably, the step S1 comprises:

[0010] Step S11, before the sensorless brushless motor is started, the high-frequency square wave observer is used to inject a high-frequency voltage into the D axis of the rotor, and the corresponding high-frequency response envelope signal is analyzed to obtain the observation angle of the rotor;

[0011] Step S12, turning off the high-frequency voltage injection, injecting a pulse signal into the stator winding of the inductive brushless motor, collecting the response current value of each group of two-phase windings of the stator winding, and obtaining the sector position of the rotor according to the response current value of each group of two-phase windings;

[0012] Step S13, performing phase deviation correction on the observation angle according to the sector position to obtain the initial angle.

[0013] Preferably, the step S2 further includes acquiring the real-time rotation speed of the sensorless brushless motor during the startup process, and continuously adjusting the weight values ​​of the first angle and the second angle according to the real-time rotation speed.

[0014] Preferably, the calculation formula of the third angle is as follows:

[0015] θ e =(k1+k2)θ eHFI +(1-k1-k2)θ eEMF

[0016] in,

[0017]

[0018] Among them, θ e represents the third angle, θ eHFI represents the first angle, θ eEMF represents the second angle, we represents the real-time speed, w1, w2 and w3 represent the preset first speed threshold, second speed threshold and third speed threshold respectively, Ts represents the current loop discrete time of the brushless motor, i qref (i) represents the expected value of the torque current of the brushless motor, and r is the gain coefficient.

[0019] Preferably, the first speed threshold is 10% of the maximum rated speed of the sensorless brushless motor, the second speed threshold is 28% of the maximum rated speed, and the third speed threshold is 35% of the maximum rated speed.

[0020] The present invention also provides a brushless motor variable load smooth starting system, which applies the brushless motor variable load smooth starting method. The brushless motor variable load smooth starting system is pre-configured with a high-frequency square wave observer and a back electromotive force observer, and includes:

[0021] Angle acquisition module, used to obtain the initial angle of the rotor before the sensorless brushless motor starts;

[0022] An angle adjustment module is respectively connected to the angle acquisition module, the high-frequency square wave observer and the back electromotive force observer, and is used to control the start-up of the brushless motor according to the initial angle, and then obtain the first angle and the second angle of the rotor respectively output by the high-frequency square wave observer and the back electromotive force observer in real time during the startup process, and a third angle obtained by weighted summation of the first angle and the second angle is applied to the smooth startup control of the brushless motor.

[0023] Preferably, the angle adjustment module is also connected to the high-frequency square wave observer, and the angle adjustment module includes:

[0024] A voltage injection unit, used to inject a high-frequency voltage into the D-axis of the rotor using the high-frequency square wave observer before the inductive brushless motor is started, and analyze the corresponding high-frequency response envelope signal to obtain the observation angle of the rotor;

[0025] A sector positioning unit is used to turn off high-frequency voltage injection, inject a pulse signal into the stator winding of the inductive brushless motor, collect the response current value of each group of two-phase windings of the stator winding, and obtain the sector position of the rotor according to the response current value of each group of two-phase windings;

[0026] A phase identification unit is connected to the voltage injection unit and the sector positioning unit respectively, and is used to perform phase deviation correction on the observation angle according to the sector position to obtain the initial angle.

[0027] Preferably, the angle adjustment module includes a weight adjustment unit for acquiring the real-time rotation speed of the sensorless brushless motor during startup, and continuously adjusting the weight values ​​of the first angle and the second angle according to the real-time rotation speed.

[0028] Preferably, the calculation formula of the third angle is as follows:

[0029] θ e=(k1+k2)θ eHFI +(1-k1-k2)θ eEMF

[0030] in,

[0031]

[0032] Among them, θ e represents the third angle, θ eHFI represents the first angle, θ eEMF represents the second angle, we represents the real-time speed, w1, w2 and w3 represent the preset first speed threshold, second speed threshold and third speed threshold respectively, Ts represents the current loop discrete time of the brushless motor, i qref (i) represents the expected value of the torque current of the brushless motor, and r is the gain coefficient.

[0033] The present invention also provides a lifting table, including a brushless motor and a controller connected to the brushless motor, wherein a computer program is stored in the controller, and when the computer program is executed, the above-mentioned brushless motor variable load smooth starting method is implemented to perform lifting starting control.

[0034] The above technical solution has the following advantages or beneficial effects: during the zero-speed starting process of the brushless motor, the first angle output by the high-frequency square wave observer and the second angle output by the back-electromotive force observer are weighted, and then the third angle obtained by processing is used to control the starting of the brushless motor, so that continuous torque and stable speed can be obtained during the starting phase, and smooth starting can be achieved during variable load starting to avoid jitter, thereby improving the user experience. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 The present invention is a flow chart of a method for smoothly starting a brushless motor with variable load in a preferred embodiment of the present invention;

[0036] Figure 2 A schematic diagram of a sub-process of step S1 in a preferred embodiment of the present invention;

[0037] Figure 3 A circuit diagram of a phase current sampling circuit in a preferred embodiment of the present invention;

[0038] Figure 4 The figure is a schematic structural diagram of a variable load smooth starting system for a brushless motor in a preferred embodiment of the present invention. DETAILED DESCRIPTION

[0039] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. The present invention is not limited to this embodiment, and other embodiments may also fall within the scope of the present invention as long as they conform to the gist of the present invention.

[0040] In a preferred embodiment of the present invention, based on the above problems existing in the prior art, a method for smoothly starting a brushless motor with variable load is provided. Figure 1 As shown, including:

[0041] Step S1, obtaining the initial angle of the rotor of the sensorless brushless motor before starting;

[0042] Step S2, controlling the brushless motor to start according to the initial angle, then obtaining in real time during the startup process the first angle and the second angle of the rotor respectively output by a pre-configured high-frequency square wave observer and a back electromotive force observer, and using a third angle obtained by weighted summation of the first angle and the second angle to apply to the smooth startup control of the brushless motor.

[0043] Specifically, before the system starts, the initial angle of the rotor needs to be obtained, and then the sensorless brushless motor can be controlled to start based on the initial angle. In this embodiment, Figure 2 As shown, the process of obtaining the initial angle in step S1 includes:

[0044] Step S11, before the sensorless brushless motor is started, a high-frequency square wave observer is used to inject a high-frequency voltage into the D axis of the rotor, and a corresponding high-frequency response envelope signal is analyzed to obtain an observation angle of the rotor;

[0045] Step S12, turning off the high-frequency voltage injection, injecting a pulse signal into the stator winding of the brushless motor, collecting the response current values ​​of each group of two-phase windings of the stator winding, and obtaining the sector position of the rotor according to the response current values ​​of each group of two-phase windings;

[0046] Step S13, performing phase deviation correction on the observation angle according to the sector position to obtain an initial angle.

[0047] Specifically, in this embodiment, the high-frequency square wave observer is a software observer, which is preferably installed in the controller of the brushless motor. The brushless motor needs to accurately obtain the rotor position to obtain the maximum torque when starting at zero speed. In this embodiment, it is achieved by injecting a high-frequency pulse square wave into the D axis of the brushless motor in the rotating coordinate system. Here, the high-frequency pulse square wave is preferably 8K-12K high-frequency pulse square wave (not limited to this, related to the PWM carrier frequency), and the injected high-frequency voltage is preferably 5%-30% of the maximum synthetic voltage amplitude of the high-frequency square wave. Then, the following method is used: Figure 3The phase current sampling circuit shown in the figure collects the phase current, and then uses vector change and bandpass and low-pass filtering to obtain the high-frequency response envelope signal, and finally the PLL phase-locked loop deconstructs the observation angle of the rotor. Among them, the above-mentioned process of using vector change and bandpass and low-pass filtering to obtain the high-frequency response envelope signal and deconstructing the observation angle of the rotor by the PLL phase-locked loop is the prior art, which is not the inventive point of the present invention, and the specific process will not be repeated here.

[0048] Further, Figure 3 The circuit includes three branches connected in parallel, namely, a first branch, a second branch and a third branch, wherein each branch includes:

[0049] A first NMOS transistor N1, the gate of the first NMOS transistor N1 is respectively connected to the anode of the first diode D1, one end of the first resistor R1, one end of the second capacitor C2 and one end of the third resistor R3; the cathode of the first diode D1 is respectively connected to the other end of the third resistor R3 and one end of the fourth resistor R4, and the other end of the second capacitor C2 and the other end of the first resistor R1 are connected to the source of the first NMOS transistor N1;

[0050] A second NMOS transistor N2, the gate of the second NMOS transistor N2 is respectively connected to the anode of the second diode D2, one end of the fifth resistor R5, one end of the third capacitor C3 and one end of the sixth resistor R6; the cathode of the second diode D2 is respectively connected to the other end of the sixth resistor R6 and one end of the seventh resistor R7, the other end of the third capacitor C3 and the other end of the fifth resistor R5 are connected to the source of the second NMOS transistor N2; the drain of the second NMOS transistor N2 is connected to the source of the first NMOS transistor N1;

[0051] An eighth resistor R8 , one end of the eighth resistor R8 is connected to the source of the second NMOS transistor N2 , and the other end is grounded.

[0052] Among them, the drain of the first NMOS tube N1 of the first branch is respectively connected to one end of the first capacitor C1 and the 29V power supply end, and the other end of the first capacitor C1 is grounded; the source of the first NMOS tube N1 of the first branch and the drain of the second NMOS tube N2 are connected to the U phase of the inductive brushless motor; the other end of the fourth resistor R4 of the first branch serves as the high-side current sampling end of the U phase, the other end of the seventh resistor R7 of the first branch serves as the low-side current sampling end of the U phase, and one end of the eighth resistor R8 of the first branch serves as the loop current sampling end of the U phase.

[0053] The drain of the first NMOS tube N1 of the second branch is connected to the 29V power supply terminal; the source of the first NMOS tube N1 and the drain of the second NMOS tube N2 of the second branch are connected to the V phase of the inductive brushless motor; the other end of the fourth resistor R4 of the second branch serves as the high-side current sampling end of the V phase, the other end of the seventh resistor R7 of the second branch serves as the low-side current sampling end of the V phase, and one end of the eighth resistor R8 of the second branch serves as the loop current sampling end of the V phase.

[0054] The drain of the first NMOS tube N1 of the third branch is respectively connected to one end of the fourth capacitor C4, one end of the fifth capacitor C5 and the 29V power supply end, and the other ends of the fourth capacitor C4 and the fifth capacitor C5 are grounded; the source of the first NMOS tube N1 of the third branch and the drain of the second NMOS tube N2 are connected to the W phase of the inductive brushless motor; the other end of the fourth resistor R4 of the third branch serves as the high-side current sampling end of the W phase, the other end of the seventh resistor R7 of the third branch serves as the low-side current sampling end of the U phase, and one end of the eighth resistor R8 of the third branch serves as the loop current sampling end of the W phase.

[0055] It is understandable that after the observation angle of the rotor is obtained by injecting a high-frequency square wave, there may be a phase deviation of 180° in the observation angle. For example, if the observation angle is 90°, it may actually be -90°, so further NS polarity identification is required. Since the magnetic circuit saturation of the permanent magnet synchronous motor winding is related to the permanent magnet rotor position and the winding current, it affects the stator inductance; as long as the same voltage pulse size and time are applied, the current response size will only be inversely proportional to the inductance size, and the sector position of the rotor can be determined by detecting the current change amplitude within the same time. Based on this, when performing NS polarity identification, first turn off the high-frequency square wave injection and PWM modulation output. Since the stator coil inductance will change with the rotor pole position, a short level pulse signal is injected into the stator winding to control it. Figure 3 The six NMOS tubes of the three branches are turned on for the same time in pairs and by sampling the bus current of the corresponding branches (the order of short level pulses being turned on in pairs is AB, BA, BC, CB, CA and AC), the corresponding Iab, Iba, Ibc, Icb, Ica and Iac are obtained. By comparing the current amplitudes in pairs, the sector position of the rotor can be located. The specific comparison method is the prior art and is not the inventive point of the present invention. The specific process will not be repeated here.

[0056] The application time of the short level pulse is preferably the shortest time taken for the bus current to gradually increase and become stable.

[0057] After obtaining the sector position of the rotor, the sector position here defines an angle range. The sector position is compared with the observation angle. If the observation angle is within the angle range represented by the sector position, the observation angle is the initial angle. If the deviation between the two is large, that is, the observation angle is not within the angle range represented by the sector position, the observation angle is compensated by 180° to obtain the initial angle.

[0058] By obtaining an accurate initial angle, reliable electromagnetic torque can be obtained, thereby realizing the start of the brushless motor with heavy load at zero speed. When the brushless motor starts, it runs at a relatively low speed. Considering that high-frequency square wave injection is suitable for salient pole motors, the equivalent condition of its voltage equation is established under low speed conditions. Therefore, at low speed (preferably 10% of the maximum rated speed of the brushless motor), the first angle output by the high-frequency square wave observer is used to smoothly start the brushless motor. At this time, the high-frequency square wave injection is simplified to a simple RL circuit, and the corresponding D-axis injection voltage calculation formula is equivalent to the following:

[0059]

[0060] Among them, u din represents the D-axis injection voltage, L d Indicates the D-axis inductance, di din represents the D-axis injection response current.

[0061] In permanent magnet synchronous motors, the magnetic circuit of salient pole motors is asymmetric (L q >L d ), the magnitude of the back electromotive force EMF is not only related to the speed of the motor, but also to the change of the stator current di q / dt(current i q Differential) related, the specific calculation formula is as follows:

[0062]

[0063] Among them, E α 、E β It represents the extended electromotive force EMF in the α and β coordinate systems, L d , L q are the stator inductances of the d-axis and q-axis respectively, i d 、i q are the d-axis and q-axis currents, respectively. is the permanent magnet flux, θ e is the electrical angle, ω e is the electrical angular velocity, pi q It represents the time derivative of the q-axis current.

[0064] It can be seen from the above formula that the load state of the brushless motor during the startup process will affect the magnitude of the extended back electromotive force. When the motor starts running under variable load and heavy load, the stator i q The current has a large change, resulting in extended back electromotive force distortion. Therefore, when the speed is higher than 35% of the maximum rated speed of the sensorless brushless motor, the second angle output by the back electromotive force observer is used to smoothly start the sensorless brushless motor.

[0065] When the real-time speed of the brushless motor is between 10% and 35% of the maximum rated speed of the brushless motor, the output angles of the high-frequency square wave observer and the back-electromotive force observer need to be comprehensively considered. In this embodiment, smooth starting control of the brushless motor is achieved by weighted processing of the first angle of the rotor output by the high-frequency square wave observer and the second angle of the back-electromotive force observer, so as to eliminate the jitter caused by variable load.

[0066] In a preferred embodiment of the present invention, step S2 also includes obtaining the real-time rotation speed of the sensorless brushless motor during the startup process, and continuously adjusting the weight values ​​of the first angle and the second angle according to the real-time rotation speed.

[0067] In a preferred embodiment of the present invention, the calculation formula of the third angle is as follows:

[0068] θ e =(k1+k2)θ eHFI +(1-k1-k2)θ eEMF

[0069] in,

[0070]

[0071] Among them, θ e represents the third angle, θ eHFI represents the first angle, θ eEMF represents the second angle, we represents the real-time speed, w1, w2 and w3 represent the preset first speed threshold, second speed threshold and third speed threshold respectively, Ts represents the current loop discrete time of the brushless motor, i qref (i) represents the expected value of the torque current of the brushless motor, that is, the reference current output by the speed loop in the startup phase. If a segmented linearization is added to the front link of the current loop, each segment can use i qref (i)-i qref (i-1) represents, r is the gain coefficient.

[0072] In this embodiment, when the real-time speed is between the first speed threshold and the second speed threshold, considering the disturbance introduced by the rapid step change of the torque current under the variable load condition, the q-axis response current (i qref (i) qref (i-1)) is added to the conversion calculation weight value.

[0073] In a preferred embodiment of the present invention, the first speed threshold is 10% of the maximum rated speed of the sensorless brushless motor, the second speed threshold is 28% of the maximum rated speed, and the third speed threshold is 35% of the maximum rated speed.

[0074] The present invention also provides a brushless motor variable load smooth starting system, which uses the brushless motor variable load smooth starting method, such as Figure 4 As shown, the variable load smooth starting system of the brushless motor is pre-configured with a high-frequency square wave observer 1 and a back electromotive force observer 2, including:

[0075] Angle acquisition module 3, used to obtain the initial angle of the rotor before the sensorless brushless motor starts;

[0076] The angle adjustment module 4 is respectively connected to the angle acquisition module 3, the high-frequency square wave observer 1 and the back electromotive force observer 2, and is used to control the start-up of the brushless motor according to the initial angle, and then obtain the first angle and the second angle of the rotor respectively output by the high-frequency square wave observer 1 and the back electromotive force observer 2 in real time during the startup process, and use the third angle obtained by weighted summation of the first angle and the second angle to apply to the smooth startup control of the brushless motor.

[0077] In a preferred embodiment of the present invention, the angle adjustment module 4 is also connected to the high-frequency square wave observer 1, and the angle adjustment module 4 includes:

[0078] The voltage injection unit 41 is used to inject a high-frequency voltage into the D axis of the rotor using a high-frequency square wave observer before the sensorless brushless motor is started, and analyze the corresponding high-frequency response envelope signal to obtain the observation angle of the rotor;

[0079] The sector positioning unit 42 is used to turn off the high-frequency voltage injection, inject a pulse signal into the stator winding of the brushless motor, collect the response current value of each group of two-phase windings of the stator winding, and process the response current value of each group of two-phase windings to obtain the sector position of the rotor;

[0080] The phase identification unit 43 is connected to the voltage injection unit 41 and the sector positioning unit 42 respectively, and is used to correct the phase deviation of the observation angle according to the sector position to obtain the initial angle.

[0081] In a preferred embodiment of the present invention, the angle adjustment module 4 includes a weight adjustment unit 44 for obtaining the real-time speed of the sensorless brushless motor during startup and continuously adjusting the weight values ​​of the first angle and the second angle according to the real-time speed.

[0082] In a preferred embodiment of the present invention, the calculation formula of the third angle is as follows:

[0083] θ e =(k1+k2)θ eHFI +(1-k1-k2)θ eEMF

[0084] in,

[0085]

[0086] Among them, θ e represents the third angle, θ eHFI represents the first angle, θ eEMF represents the second angle, we represents the real-time speed, w1, w2 and w3 represent the preset first speed threshold, second speed threshold and third speed threshold respectively, Ts represents the current loop discrete time of the brushless motor, i qref (i) represents the expected value of the torque current of the brushless motor, and r is the gain coefficient.

[0087] The present invention also provides a lifting table, including a brushless motor and a controller connected to the brushless motor, wherein a computer program is stored in the controller, and when the computer program is executed, the above-mentioned brushless motor variable load smooth starting method is implemented to perform lifting start control.

[0088] The above description is only a preferred embodiment of the present invention, and does not limit the implementation mode and protection scope of the present invention. For those skilled in the art, it should be aware that all solutions obtained by equivalent substitutions and obvious changes made using the contents of this specification and illustrations should be included in the protection scope of the present invention.

Claims

1. A method for smoothly starting a brushless motor with variable load, characterized in that: include: Step S1, obtaining the initial angle of the rotor of the sensorless brushless motor before starting; Step S2, controlling the brushless motor to start according to the initial angle, and then acquiring in real time during the startup process the first angle and the second angle of the rotor respectively output by a pre-configured high-frequency square wave observer and a back electromotive force observer, and applying a third angle obtained by weighted summation of the first angle and the second angle to the smooth startup control of the brushless motor.

2. The variable load smooth starting method of the brushless motor according to claim 1 is characterized in that: The step S1 comprises: Step S11, before the sensorless brushless motor is started, the high-frequency square wave observer is used to inject a high-frequency voltage into the D axis of the rotor, and the corresponding high-frequency response envelope signal is analyzed to obtain the observation angle of the rotor; Step S12, turning off the high-frequency voltage injection, injecting a pulse signal into the stator winding of the inductive brushless motor, collecting the response current value of each group of two-phase windings of the stator winding, and obtaining the sector position of the rotor according to the response current value of each group of two-phase windings; Step S13, performing phase deviation correction on the observation angle according to the sector position to obtain the initial angle.

3. The variable load smooth starting method of the brushless motor according to claim 1, characterized in that: The step S2 also includes obtaining the real-time rotation speed of the sensorless brushless motor during the startup process, and continuously adjusting the weight values ​​of the first angle and the second angle according to the real-time rotation speed.

4. The variable load smooth starting method of the brushless motor according to claim 3 is characterized in that: The calculation formula of the third angle is as follows: i e =(k1+k2)θ eHFI +(1-k1-k2)θ eEMF in, Among them, θ e represents the third angle, θ eHFI represents the first angle, θ eEMF represents the second angle, we represents the real-time speed, w1, w2 and w3 represent the preset first speed threshold, second speed threshold and third speed threshold respectively, Ts represents the current loop discrete time of the brushless motor, i qref (i) represents the expected value of the torque current of the brushless motor, and r is the gain coefficient.

5. The variable load smooth starting method of the brushless motor according to claim 4 is characterized in that: The first speed threshold is 10% of the maximum rated speed of the sensorless brushless motor, the second speed threshold is 28% of the maximum rated speed, and the third speed threshold is 35% of the maximum rated speed.

6. A brushless motor variable load smooth starting system, characterized in that: The method for smoothly starting a brushless motor with variable load as claimed in any one of claims 1 to 5 is applied, wherein the brushless motor with variable load smooth starting system is pre-configured with a high-frequency square wave observer and a back electromotive force observer, including: Angle acquisition module, used to obtain the initial angle of the rotor before the sensorless brushless motor starts; An angle adjustment module is respectively connected to the angle acquisition module, the high-frequency square wave observer and the back electromotive force observer, and is used to control the start-up of the brushless motor according to the initial angle, and then obtain the first angle and the second angle of the rotor respectively output by the high-frequency square wave observer and the back electromotive force observer in real time during the startup process, and a third angle obtained by weighted summation of the first angle and the second angle is applied to the smooth startup control of the brushless motor.

7. The variable load smooth starting system of the brushless motor according to claim 6 is characterized in that: The angle adjustment module is also connected to the high-frequency square wave observer, and the angle adjustment module includes: A voltage injection unit, used to inject a high-frequency voltage into the D-axis of the rotor using the high-frequency square wave observer before the inductive brushless motor is started, and analyze the corresponding high-frequency response envelope signal to obtain the observation angle of the rotor; A sector positioning unit is used to turn off high-frequency voltage injection, inject a pulse signal into the stator winding of the inductive brushless motor, collect the response current value of each group of two-phase windings of the stator winding, and obtain the sector position of the rotor according to the response current value of each group of two-phase windings; A phase identification unit is connected to the voltage injection unit and the sector positioning unit respectively, and is used to perform phase deviation correction on the observation angle according to the sector position to obtain the initial angle.

8. The variable load smooth starting system of the brushless motor according to claim 6 is characterized in that: The angle adjustment module includes a weight adjustment unit, which is used to obtain the real-time rotation speed of the sensorless brushless motor during the startup process, and continuously adjust the weight values ​​of the first angle and the second angle according to the real-time rotation speed.

9. The variable load smooth starting system of the brushless motor according to claim 8, characterized in that: The calculation formula of the third angle is as follows: i e =(k1+k2)θ eHFI +(1-k1-k2)θ eEMF in, Among them, θ e represents the third angle, θ eHFI represents the first angle, θ eEMF represents the second angle, we represents the real-time speed, w1, w2 and w3 represent the preset first speed threshold, second speed threshold and third speed threshold respectively, Ts represents the current loop discrete time of the brushless motor, i qref (i) represents the expected value of the torque current of the brushless motor, and r is the gain coefficient.

10. A lifting table, characterized in that: It includes a brushless motor and a controller connected to the brushless motor, wherein a computer program is stored in the controller, and when the computer program is executed, the brushless motor variable load smooth starting method as described in any one of claims 1 to 5 is implemented to perform lifting and lowering starting control.

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