Low-precision incremental encoder-based method for ultra-low speed control of servo system

Abstract

Disclosed is a low-precision incremental encoder-based method for ultra-low speed control of a servo system. According to the present invention, a fast speed observer in an ultra-low-speed working state is achieved, only a sampling speed and load torque in an M / T method need to be observed, and position information of an electric motor does not need to be observed, such that the structure of the observer is simplified, and calculation is simple and fast; moreover, the influence of a friction force and cogging torque on a speed change is considered, such that the speed observation precision is further improved. The fast speed observer can reduce hysteresis and measurement dead zones, such that the speed response and the speed control precision in a low-speed working state are greatly improved, the problem in a traditional observer of a large position deviation caused by nonlinear factors such as an external load is avoided, improving the stability and robustness of the system. According to the present invention, the processing of sampling measurement time at a medium-high speed and the processing of switching the observer at a low speed in the M / T method can optimize the speed measurement precision at both the medium-high speed and the ultra-low speed, and can better satisfy the requirements of apparatuses such as a radar on rotating speed control.

Description

An ultra-low speed control method for a servo system based on a low-precision incremental encoder Technical Field

[0001] The present invention belongs to the technical field of servo control systems, and in particular to an ultra-low-speed control method for a servo system based on a low-precision incremental encoder. Background Art

[0002] When detecting high-altitude moving objects, radars, astronomical telescopes, and other equipment often need to operate their servo control systems at ultra-low speeds due to the long distances and slow relative speeds of the targets. Since position feedback in servo control systems is provided by encoders, conventional incremental encoders are often used in applications requiring high-precision speed control. During normal operation of the servo control systems of radar and other equipment, the higher the resolution of the incremental encoder, the higher the system's speed measurement accuracy, and the higher the control accuracy and performance during speed control. Since higher-resolution incremental encoders require greater volume, while radar and other equipment require increasingly smaller volumes, it is necessary to study and analyze the speed control accuracy and performance of servo control systems using relatively low-resolution incremental encoders at medium- to high-speed and ultra-low speeds, in order to achieve better control results and smaller equipment footprints.

[0003] The most commonly used speed measurement method using an incremental encoder is the M / T speed measurement method. This method takes into account the speed measurement accuracy at both low and high speeds. However, when the resolution of the encoder is not high enough, it is impossible to measure many pulses per unit time at high speeds, resulting in limited speed measurement accuracy. At low speeds, the measurement time between two adjacent pulses is too long, resulting in update dead zones and lags where the speed is not updated in multiple control cycles. Friction compensation, cogging torque compensation, and dead zone compensation in conventional low-speed control can effectively improve control performance at low speeds. However, the above methods cannot solve the problems of large update dead zones at low speeds and low speed measurement accuracy at medium and high speeds caused by the low resolution of the encoder.

[0004] In order to solve the problem of decreased control performance caused by low encoder resolution, scholars at home and abroad have conducted a lot of research. The literature (Gao Yang, Yang Ming, Yu Yong, et al. PMSM AC servo system based on disturbance observer [J]. Proceedings of the Chinese Society of Electrical Engineering, 2005, 25 (22): 125-128.) designed a torque disturbance observer to improve the control performance at low speed by observing and compensating for the disturbance, but this method cannot improve the low-speed dead zone and lag caused by the low resolution of the encoder. Xiao-Li Song et al. designed an extended state observer in the literature (Azimuth Control for Large Aperture Telescope Based on Segmented Arc Permanent Magnet Synchronous Motors [J]. Research in Astronomy and Astrophysics, 2021, 21 (7): 163.) to estimate the position information in the system in real time to improve the control accuracy of the system, but the method is complex to calculate, and the position accuracy may be low due to the error of torque current over a long period. The literature (Yin Zhonggang et al. Low-speed creep filter backstepping control method of AC servo system based on disturbance observer [J]. Transactions of China Electrotechnical Society, 2020, 035.0z1: 203-211.) designed a disturbance observer to reduce the influence of interference such as friction during low-speed operation, thereby improving the anti-interference ability of the control system. However, the influence of the low resolution of the encoder was not considered.

[0005] Summary of the Invention

[0006] The purpose of the present invention is to provide a servo system ultra-low speed control method to address the problems of low-speed dead zone and lag caused by low-resolution encoders under the small volume requirements of the above-mentioned radar and other equipment, which can improve the speed measurement accuracy and control performance at ultra-low speeds.

[0007] The technical solution to achieve the purpose of the present invention is: a servo system ultra-low speed control method based on a low-precision incremental encoder, the method comprising the following steps:

[0008] Step 1: Obtain the current position information of the servo system through the incremental encoder to obtain the current mechanical angle θ;

[0009] Step 2: Sample the three-phase current i a 、i b , calculate i by current reconstruction c , then the excitation current i is obtained by combining the current mechanical angle θ with the rotation transformation of the vector control d With torque current i q ;

[0010] Step 3: Set a timer to measure the time difference between the moment when the control system obtains the position in the current control cycle and the moment when the control system obtains the position in the next control cycle to obtain the precise time T of the position measurement. mea , and use the M / T method to measure speed and use the speed measurement result as the speed feedback output ω, establish speed and current controller, and form a dual closed-loop vector control system of current and speed;

[0011] Step 4: Offline identify the friction curve of the Stribeck model, the cogging torque waveform and the motor parameters, and obtain the relevant motor parameters and feedforward compensation values; the feedforward compensation values ​​include the friction feedforward compensation value i friction * The feedforward compensation value i of the cogging torque CT * ;

[0012] Step 5: For the low speed stage of T method speed measurement in M / T method, a fast speed observer is established, using the torque current feedback value i q , combined with the motor parameters and the feedforward compensation value i of friction and cogging torque friction * 、i CT * , calculate the observed value of the velocity At low speeds, it participates in speed closed-loop control as speed feedback.

[0013] Furthermore, in step 2, the following servo system mathematical model needs to be established:

[0014] Where θ is the mechanical angle of the motor; ω is the mechanical angular velocity of the motor; ψ f is the permanent magnet flux of the motor; p is the number of pole pairs of the motor; R s is the stator resistance of the motor; i d 、i q are the excitation current and torque current of the motor respectively; u d 、u q are the dq axis voltages of the motor respectively; L is the motor inductance; J is the inertia of the motor; T e 、T L 、T f 、T CT They are the motor electromagnetic torque, load torque, friction torque and cogging torque respectively; is the differential operator.

[0015] Furthermore, in step 3, the M / T method speed measurement specifically includes the following steps:

[0016] Step 3.1: According to the timer module designed by the chip, the corresponding timer interrupt is turned on at the position acquisition moment of each control cycle, and the precise time T of the position measurement is obtained by calculation. mea ;

[0017] Step 3.2, calculate the speed feedback value ω(n) of the current detection cycle:

[0018] Among them, M n 、M n-1 They are respectively the encoder pulse numbers in the current detection cycle n and the next detection cycle n-1 generated by the orthogonal pulse counting module designed according to the chip, and t m is the encoder's most recent pulse time interval, and N is the resolution of the incremental encoder.

[0019] Furthermore, the t m The maximum value is set to 100ms.

[0020] Furthermore, the friction force feedforward compensation value i in step 4 is friction * is the function value of the real-time speed, the feedforward compensation value of the cogging torque i CT * is the function value of the real-time position.

[0021] Furthermore, step 5 specifically includes:

[0022] Step 5.1, according to the motor rotation equation:

[0023] The feedforward compensation value i combining friction and cogging torque friction * 、i CT * ,get:

[0024] Step 5.2: Since speed observation is only performed at low speed, the formula for calculating the speed is:

[0025] Among them, t m The encoder's most recent pulse time interval;

[0026] Step 5.3, construct the state equation of the speed observer according to formula (4) and formula (5):

[0027] Where, C = [1 0]; y = ω; u = i q -i friction * -i CT* ;in is the derivative of the model state observation value in the current control cycle, is the derivative of the model state observation value in the next control cycle, is the derivative of the model output observation value of the current control cycle, y(k) is the model output observation value of the current control cycle, u(k) is the system input variable value of the current control cycle, L is the feedback gain matrix of the observer, A, B, C are the corresponding variable coefficient matrices, T s is the control period of the control system; is the observed value of the load torque; l1 and l2 are feedback gain coefficients;

[0028] Step 5.4, take the expected bandwidth ω n and the damping ratio ξ, the feedback matrix L can be obtained according to the characteristic matrix of the observer:

[0029] Step 5.5, substitute formula (7) into formula (6) to calculate the observed value of the available velocity

[0030] Furthermore, the desired bandwidth ω in step 5.4 n Get the cutoff bandwidth of the speed closed loop.

[0031] Compared with the prior art, the present invention has the following significant advantages:

[0032] 1) This invention implements a fast speed observer for a servo control system operating at ultra-low speeds. The observer only needs to observe the M / T method sampled speed and load torque, eliminating the need to observe the motor's position information. This simplifies the observer structure and makes calculations relatively simple and fast. It also considers the effects of friction and cogging torque on speed variations, further improving the accuracy of speed observation. This fast observer can reduce hysteresis and measurement dead zones caused by low encoder accuracy, significantly improving speed response and speed control accuracy at low speeds. It also avoids the large position deviations often associated with traditional observers due to nonlinear factors such as external loads, thereby enhancing system stability and robustness.

[0033] 2) The present invention organically combines the M / T method speed measurement with a low-speed fast speed observer. By processing the high-speed sampling measurement time of the M / T method and processing the low-speed switching observer, it can optimize the speed measurement accuracy at medium and high speeds while optimizing the speed measurement accuracy at ultra-low speeds, and can better meet the speed control requirements of equipment such as radar.

[0034] The present invention is further described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] FIG1 is a block diagram of the system control principle of the present invention.

[0036] FIG2( a ) is a schematic diagram showing the timing expansion of encoder signal measurement of the M method in the M / T method speed measurement proposed in the present invention.

[0037] FIG2( b ) is a schematic diagram showing the timing expansion of the encoder signal measurement of the T method in the M / T method speed measurement proposed in the present invention.

[0038] FIG3 is a block diagram showing the principle of the fast speed observation considering friction and cogging torque mentioned in FIG1 .

[0039] FIG4 is a flowchart of the main interrupt software implementation of the servo system used in the present invention to implement vector control.

[0040] FIG5( a ) is a comparison diagram of the speed waveform of the present invention under ultra-low speed working state and the speed waveform of the traditional M / T method speed measurement.

[0041] FIG5( b ) is an enlarged waveform diagram of FIG5( a ). DETAILED DESCRIPTION

[0042] In order to make the purpose, technical solutions and advantages of this application more clear, the following further describes this application in detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0043] It should be noted that if the embodiments of the present invention involve directional indications (such as up, down, left, right, front, back, etc.), the directional indications are only used to explain the relative position relationship, movement status, etc. between the various components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indications will also change accordingly.

[0044] In addition, if there are descriptions involving "first", "second", etc. in the embodiments of the present invention, the descriptions of "first", "second", etc. are only for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features specified as "first" and "second" may explicitly or implicitly include at least one of such features. In addition, the technical solutions between the various embodiments can be combined with each other, but this must be based on the fact that ordinary technicians in this field can implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0045] In one embodiment, the present invention provides an ultra-low-speed control method for a servo system based on a low-precision incremental encoder. The control principle is shown in FIG1 , including a speed closed loop, a q-axis current closed loop, and a d-axis current closed loop.

[0046] The method comprises:

[0047] Step 1: Obtain the current position information of the servo system through the incremental encoder to obtain the current mechanical angle θ;

[0048] Step 2: Check the three-phase current i of the servo system. a 、i b The sampling is performed by current reconstruction to calculate i c , and then combine the current mechanical angle θ to obtain the excitation current i through vector control rotation transformation d With torque current i q , respectively as the closed-loop current feedback of the d and q axes to participate in the current closed-loop control. The following servo system mathematical model can be established:

[0049] Where θ is the mechanical angle of the motor; ω is the mechanical angular velocity of the motor; ψ f is the permanent magnet flux of the motor; p is the number of pole pairs of the motor; R s is the stator resistance of the motor; i d 、i q are the excitation current and torque current of the motor respectively; u d 、u q are the dq axis voltages of the motor respectively; L is the motor inductance; J is the inertia of the motor; T e 、T L 、T f 、T CT They are the motor electromagnetic torque, load torque, friction torque and cogging torque respectively; is the differential operator.

[0050] Step 3: Set a timer to measure the time difference between the moment when the control system obtains the position in the current control cycle and the moment when the control system obtains the position in the next control cycle to obtain the precise time T of the position measurement. mea , and the M / T method is used to measure the speed and the speed measurement result is used as the speed feedback output ω, a speed and current controller is established to form a dual closed-loop vector control system of current and speed.

[0051] Here, the timing expansion diagram of the encoder signal measurement of the proposed M / T method for speed measurement is shown in Figure 2(a) and Figure 2(b), in which the timer module of the FPGA chip is designed to measure the time difference between the moment when the control system obtains the position in the current control cycle and the moment when the next control cycle is obtained, so as to obtain the precise time T of the position measurement. mea, which can improve the speed measurement accuracy at high speeds. By designing the orthogonal pulse technology module of the FPGA chip, the M / T method speed measurement is completed. This method is used to measure speed and the speed measurement results are used as the preliminary speed feedback output ω. The speed and current PI controllers are established to form a dual closed-loop vector control system of current and speed.

[0052] The M / T method speed measurement specifically includes the following steps:

[0053] Step 3.1: According to the chip design, the timer module starts the corresponding timer interrupt at the position acquisition time of each control cycle, and obtains the precise time T of the measured position measurement by calculation. mea ;

[0054] Step 3.2, calculate the speed feedback value ω(n) of the current detection cycle;

[0055] Among them, M n 、M n-1 They are respectively the encoder pulse numbers in the current detection cycle n and the next detection cycle n-1 generated by the orthogonal pulse counting module designed according to the chip, and t m is the encoder's most recent pulse time interval, and N is the resolution of the incremental encoder.

[0056] Step 4: Offline identification of motor parameters is established in the current loop. As shown in Figure 1, the friction (stribeck model) and cogging torque offline identification and feedforward compensation methods and dead zone compensation methods established in the speed loop are the same as other traditional methods. The motor parameters include the number of pole pairs P of the motor, the stator resistance R of the motor, and the stator resistance R of the motor. s , the motor's inductance L=L d =L q , the permanent magnet flux of the motor ψ m , motor inertia J, friction feedforward compensation value i friction * is the function value of the real-time speed, the feedforward compensation value of the cogging torque i CT * is the function value of the real-time position. The specific methods are all traditional methods and will not be described in detail. However, using these two compensation values ​​as inputs to participate in the speed estimation of the proposed fast speed observer will eliminate the influence of friction and cogging torque on the torque current and improve the accuracy of speed observation.

[0057] Step 5: For the low speed stage of T method speed measurement in M / T method, a fast speed observer is established, using the torque current feedback value i q , combined with the motor parameters and the feedforward compensation value i of friction and cogging torque friction * 、i CT *, calculate the observed value of the velocity At low speeds, it participates in speed closed-loop control as speed feedback.

[0058] The principle block diagram of the fast speed observation considering friction and cogging torque is shown in FIG3 . The fast speed observer is implemented according to the following steps:

[0059] Step 5.1, according to the motor rotation equation:

[0060] The feedforward compensation value i combining friction and cogging torque friction * 、i CT * ,get:

[0061] Step 5.2: Since speed observation is only performed at low speed, the formula for calculating the speed is:

[0062] Among them, t m The encoder's most recent pulse time interval;

[0063] Step 5.3, according to formula (11) and formula (12), the state equation of the speed observer is constructed as follows:

[0064] Where, C = [1 0]; y = ω; u = i q -i friction * -i CT * ;in is the derivative of the model state observation value in the current control cycle, is the derivative of the model state observation value in the next control cycle, is the derivative of the model output observation value of the current control cycle, y(k) is the model output observation value of the current control cycle, u(k) is the system input variable value of the current control cycle, L is the feedback gain matrix of the observer, A, B, C are the corresponding variable coefficient matrices, T s is the control period of the control system; is the observed value of the load torque; l1 and l2 are feedback gain coefficients;

[0065] Step 5.4, take the expected bandwidth ω n and the damping ratio ξ, the feedback matrix L can be obtained according to the characteristic matrix of the observer:

[0066] Step 5.5, substitute formula (14) into formula (13) to calculate the observed value of the available velocity

[0067] Here preferably, generally according to engineering experience, the expected bandwidth ω n Get the cutoff bandwidth of the speed closed loop.

[0068] The system control solution used in the experimental platform of this embodiment is a dual-chip architecture of ARM and FPGA. The ARM is responsible for the main motor control, the calculation of the three-loop control, and other important functions. The FPGA, as the main peripheral, realizes information exchange with the ARM and information exchange with external sensors, and participates in the signal processing of some functions. Among them, the M / T method speed measurement is designed and implemented in the FPGA, and the fast speed observer is implemented in the speed loop of the vector control designed in the ARM. The main interrupt software implementation flow chart of the servo system for vector control is shown in Figure 4. The speed waveform obtained in the ultra-low speed working state and the speed waveform of the M / T method speed measurement are compared in Figures 5(a) and 5(b). The experimental motor uses a 2500-line incremental encoder. It can be seen that at ultra-low speeds (such as 0.1rpm), the proposed control method reduces the update dead zone and lag of the speed measurement, improving the speed control accuracy and performance of the system.

[0069] In one embodiment, a servo system ultra-low speed control system based on a low-precision incremental encoder is provided, the system comprising:

[0070] The first module is used to obtain the current position information of the servo system through the incremental encoder to obtain the current mechanical angle θ;

[0071] The second module is used to implement: sampling three-phase current i a 、i b , calculate i by current reconstruction c , then the excitation current i is obtained by combining the current mechanical angle θ with the rotation transformation of the vector control d With torque current i q ;

[0072] The third module is used to achieve: by setting a timer to measure the time difference between the moment when the control system obtains the position in the current control cycle and the moment when the next control cycle is obtained, so as to obtain the precise time T of the position measurement mea , and use the M / T method to measure speed and use the speed measurement result as the speed feedback output ω, establish speed and current controller, and form a dual closed-loop vector control system of current and speed;

[0073] The fourth module is used to realize: offline identification of the friction curve and cogging torque waveform of the Stribeck model and motor parameters, and obtain relevant motor parameters and feedforward compensation values; the feedforward compensation value includes the friction feedforward compensation value ifriction * The feedforward compensation value i of the cogging torque CT * ;

[0074] The fifth module is used to achieve: for the low speed stage of T method speed measurement in M / T method, a fast speed observer is established, using the torque current feedback value i q , combined with the motor parameters and the feedforward compensation value i of friction and cogging torque friction * 、i CT * , calculate the observed value of the velocity At low speeds, it participates in speed closed-loop control as speed feedback.

[0075] The specific limitations of the servo system ultra-low-speed control system based on a low-precision incremental encoder can be found in the limitations of the servo system ultra-low-speed control method based on a low-precision incremental encoder described above, and will not be repeated here. Each module in the aforementioned servo system ultra-low-speed control system based on a low-precision incremental encoder can be implemented in whole or in part through software, hardware, or a combination thereof. Each of the aforementioned modules can be embedded in or independent of a processor in a computer device in hardware form, or can be stored in a memory in the computer device in software form, so that the processor can call and execute the corresponding operations of each of the aforementioned modules.

[0076] In one embodiment, a computer device is provided, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein when the processor executes the computer program, the following is achieved:

[0077] Step 1: Obtain the current position information of the servo system through the incremental encoder to obtain the current mechanical angle θ;

[0078] Step 2: Sample the three-phase current i a 、i b , calculate i by current reconstruction c , then the excitation current i is obtained by combining the current mechanical angle θ with the rotation transformation of the vector control d With torque current i q ;

[0079] Step 3: Set a timer to measure the time difference between the moment when the control system obtains the position in the current control cycle and the moment when the control system obtains the position in the next control cycle to obtain the precise time T of the position measurement. mea , and use the M / T method to measure speed and use the speed measurement result as the speed feedback output ω, establish speed and current controller, and form a dual closed-loop vector control system of current and speed;

[0080] Step 4: Offline identify the friction curve of the Stribeck model, the cogging torque waveform and the motor parameters, and obtain the relevant motor parameters and feedforward compensation values; the feedforward compensation values ​​include the friction feedforward compensation value i friction * The feedforward compensation value i of the cogging torque CT * ;

[0081] Step 5: For the low speed stage of T method speed measurement in M / T method, a fast speed observer is established, using the torque current feedback value i q , combined with the motor parameters and the feedforward compensation value i of friction and cogging torque friction * 、i CT * , calculate the observed value of the velocity At low speeds, it participates in speed closed-loop control as speed feedback.

[0082] For the specific limitations of each step, please refer to the limitations of the ultra-low-speed control method for a servo system based on a low-precision incremental encoder mentioned above, which will not be repeated here.

[0083] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are only illustrative of the principles of the present invention. Without departing from the spirit and scope of the present invention, any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention shall be included in the scope of protection of the present invention.

Claims

1. A servo system ultra-low speed control method based on a low-precision incremental encoder, characterized in that: The method comprises the following steps: Step 1, obtain the current position information of the servo system through the incremental encoder to obtain the current mechanical angle θ; Step 2: Sample the three-phase current i a 、i b , calculate i by current reconstruction c Then, the excitation current i is obtained by combining the current mechanical angle θ with the rotation transformation of the vector control. d With torque current i q ; Step 3: Set a timer to measure the time difference between the moment when the control system obtains the position in the current control cycle and the moment when the next control cycle is reached to obtain the precise time T of the position measurement. mea , and use the M / T method to measure the speed and use the speed measurement result as the speed feedback output ω, establish the speed and current controller, and form a dual closed-loop vector control system of current and speed; Step 4, offline identification of the friction curve of the Stribeck model, the cogging torque waveform and the motor parameters, and acquisition of relevant motor parameters and feedforward compensation values; the feedforward compensation value includes the friction feedforward compensation value i friction * The feedforward compensation value i of the cogging torque CT * ; Step 5: For the low speed stage of the T method speed measurement in the M / T method, a fast speed observer is established, using the torque current feedback value i q , combined with the motor parameters and the feedforward compensation value i of friction and cogging torque friction * 、i CT * , calculate the observed value of the velocity At low speeds, it participates in speed closed-loop control as speed feedback.

2. The ultra-low speed control method for a servo system based on a low-precision incremental encoder according to claim 1, characterized in that: In step 2, the following servo system mathematical model needs to be established: Where θ is the mechanical angle of the motor; ω is the mechanical angular velocity of the motor; ψ f is the permanent magnet flux of the motor; p is the number of pole pairs of the motor; R s is the stator resistance of the motor; i d 、i q are the excitation current and torque current of the motor respectively; u d 、u q are the dq axis voltage of the motor respectively; L is the motor inductance; J is the inertia of the motor; T e 、T L 、T f 、T CT They are the motor electromagnetic torque, load torque, friction torque and cogging torque respectively; is the differential operator.

3. The ultra-low speed control method of a servo system based on a low-precision incremental encoder according to claim 1, characterized in that: In step 3, the M / T method speed measurement includes the following steps: Step 3.1: According to the timer module designed by the chip, the corresponding timer interrupt is turned on at the position acquisition time of each control cycle, and the precise time T of the position measurement is obtained by calculation. mea ; Step 3.2, calculate the speed feedback value ω(n) of the current detection cycle: Among them, M n 、M n-1 They are respectively the encoder pulse numbers in the current detection cycle n and the next detection cycle n-1 generated by the orthogonal pulse counting module designed according to the chip, and t m is the encoder's most recent pulse time interval, and N is the resolution of the incremental encoder.

4. The ultra-low speed control method for a servo system based on a low-precision incremental encoder according to claim 3, characterized in that: The m The maximum value is set to 100ms.

5. The ultra-low speed control method of a servo system based on a low-precision incremental encoder according to claim 1, characterized in that: The friction feedforward compensation value i in step 4 friction * is the function value of the real-time speed, the feedforward compensation value of the cogging torque i CT * is the function value of the real-time position.

6. The ultra-low speed control method of a servo system based on a low-precision incremental encoder according to claim 2, characterized in that: Step 5 specifically includes: Step 5.1, according to the motor rotation equation: The feedforward compensation value i combining friction force and cogging torque friction * 、i CT * ,get: Step 5.2, since speed observation is only performed at low speed, the formula for calculating the speed is: Among them, t m It is the encoder's most recent pulse time interval; Step 5.3, according to formula (4) and formula (5), the state equation of the speed observer is constructed as follows: In the formula, C=[1 0];y=ω;u=i q -and friction * -and CT * ; among them is the derivative of the model state observation value of the current control cycle, is the derivative of the model state observation value in the next control cycle, is the derivative of the model output observation value of the current control cycle, y(k) is the model output observation value of the current control cycle, u(k) is the system input variable value of the current control cycle, L is the feedback gain matrix of the observer, A, B, C are the corresponding variable coefficient matrices, T s is the control period of the control system; is the observed value of the load torque; l1 and l2 are feedback gain coefficients; Step 5.4, take the expected bandwidth ω n and the damping ratio ξ, the feedback matrix L can be obtained according to the characteristic matrix of the observer: Step 5.5, substitute formula (7) into formula (6) to calculate the observed value of the available velocity:

7. The ultra-low speed control method for a servo system based on a low-precision incremental encoder according to claim 6, characterized in that: The desired bandwidth ω described in step 5.4 n Get the cut-off bandwidth of the speed closed loop.

8. A servo system ultra-low speed control system based on a low-precision incremental encoder according to the method of any one of claims 1 to 7, characterized in that: The system comprises: The first module is used to achieve: obtaining the current position information of the servo system through an incremental encoder to obtain the current mechanical angle θ; The second module is used to implement: sampling the three-phase current i a 、i b , calculate i by current reconstruction c Then, the excitation current i is obtained by combining the current mechanical angle θ with the rotation transformation of the vector control. d With torque current i q ; The third module is used to achieve: by setting a timer to measure the time difference between the moment when the control system obtains the position in the current control cycle and the moment when the next control cycle is obtained, so as to obtain the precise time T of the position measurement mea , and use the M / T method to measure the speed and use the speed measurement result as the speed feedback output ω, establish the speed and current controller, and form a dual closed-loop vector control system of current and speed; The fourth module is used to achieve: offline identification of the friction curve of the Stribeck model, the cogging torque waveform and the motor parameters, and acquisition of relevant motor parameters and feedforward compensation values; the feedforward compensation value includes the friction feedforward compensation value i friction * The feedforward compensation value i of the cogging torque CT * ; The fifth module is used to achieve: for the low-speed stage of T method speed measurement in M / T method, a fast speed observer is established, using the torque current feedback value i q , combined with the motor parameters and the feedforward compensation value i of friction and cogging torque friction * 、i CT * , calculate the observed value of the velocity At low speeds, it participates in speed closed-loop control as speed feedback.

9. A computer 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, the method according to any one of claims 1 to 7 is implemented.

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