Linear motor control method, recording medium and system

Abstract

The present invention belongs to the field of motor control technology, and in particular relates to a linear motor control method, which uses sensors to collect the three-phase current of the motor in real time and convert it to a DQ coordinate system to obtain a sampled current; simultaneously obtains the observed value of the same current as the observed current through a self-disturbance rejection observer; calculates the time delay of the sampled current based on the current time series and rotor position relationship obtained after Fourier transform of the observed current and the sampled current, and converts it into multiples of the control period, that is, the number of steps in the control algorithm, and gradually compensates for the predicted current in the model predictive control. This method can accurately identify the total time delay existing in the system, and through iterative optimization, greatly reduces the amount of calculation of the value function and reduces the complexity of the model predictive control, and is suitable for the speed control of linear motors. The present invention also provides a non-transient readable recording medium storing the program of this method and a system containing the medium, which can call the program through the processing circuit to execute the above method.

Description

Technical Field

[0001] This invention belongs to the field of electric motor control technology and discloses a linear motor control method, recording medium, and system. Background Technology

[0002] As the market share of lithography machines, CNC machine tools, and other similar products increases, the application of permanent magnet synchronous linear motors in industrial machinery is becoming more widespread. This places higher demands on the smooth operation and control of these motors. The non-ideal time delay present in permanent magnet synchronous motor drive systems is one of the key issues affecting the control performance of AC drive systems.

[0003] Due to non-ideal factors such as computation delay, sampling delay, system dead zone, and network transmission delay in digital control systems, multiple harmonics are generated in the three-phase sine wave, causing current distortion and affecting the motor's operating performance. This results in increased current pulsation and enhanced vibration during motor operation. The jerking sensation during motor operation severely affects positioning accuracy and the dynamic and static performance of the system, and may even lead to system oscillation or divergence.

[0004] How to obtain the specific value of system delay in real time, and correct the state parameters of motor control by compensating for the deviation of control parameters caused by the delay, so as to offset the negative impact of delay on permanent magnet synchronous motor drive, without consuming too much computing resources and maintaining a low switching frequency, is a problem currently faced by motor control designers. Summary of the Invention

[0005] To address the above problems, this invention provides a linear motor control method, comprising the following steps:

[0006] The three-phase current of the motor is collected in real time by a sensor and transformed to the DQ coordinate system to obtain the sampled current; the observation value of the same current is obtained simultaneously by an active disturbance rejection observer as the observation current.

[0007] Based on the current time series and rotor position relationship obtained from the Fourier transform of the observed current and the sampled current, the time delay of acquiring the sampled current is identified, and then the time delay is converted into a multiple N of the control cycle. N is used as the number of steps in the multi-step model predictive current control algorithm to gradually compensate for the predicted current.

[0008] The progressive compensation predicted current is calculated by using the voltage vector at the current moment to compensate the sampled current at the current moment within the current control cycle. The predicted current obtained through the compensation calculation is substituted into the value function for optimization to obtain the optimized voltage vector after one step of compensation. The calculation and optimization are then performed in the next control cycle until the number of steps is exhausted. By changing the switching state of the inverter during operation, the three-phase pulse corresponding to the optimal voltage vector selected in the last step is applied to the corresponding bridge arm of the inverter to realize the control of the linear induction motor.

[0009] Preferably, the method for obtaining the time delay includes the following steps: performing maximum mode detection on the results of Fourier transform of the sampled current and the observed current respectively, finding the point corresponding to the point with the largest mode in the frequency domain and the phase of the frequency component of that point in the time domain, subtracting the two phases to obtain the phase difference, and the time corresponding to the phase difference is the time delay.

[0010] Preferably, the method for converting the time delay into a multiple N of the control period includes the following steps: dividing the time delay collected multiple times by the value of the control period and performing root mean square calculation, and taking the rounded average of the squared values ​​as the multiple N of the control period.

[0011] Preferably, in each step of the value function optimization, the predicted current corresponding to the three cases with the smallest, second smallest, and second smallest value function values ​​is selected to deduce the optimal, second best, and second best voltage vectors.

[0012] Another aspect of the present invention is to provide a non-transient readable recording medium for storing one or more programs containing multiple instructions, which, when executed, cause a processing circuit to perform the aforementioned linear motor control method.

[0013] Another aspect of the present invention provides a linear motor control system, including a processing circuit and a memory electrically coupled thereto, the memory being configured to store at least one program, the program containing multiple instructions, the processing circuit running the program, and capable of executing the aforementioned linear motor control method.

[0014] Compared with existing technologies, the linear motor control method, recording medium, and system provided by this invention have the following advantages:

[0015] This invention studies the unavoidable time delay problem in motor control. Through a time-varying window, it can accurately identify the random and fixed total time delay in the system under both dynamic and steady-state conditions and convert it into the number of iterations in the multi-step model predictive current control algorithm.

[0016] In the process of optimizing motor control parameters using multi-step model prediction current, the vector search method is simplified based on reference current and voltage, which greatly reduces the value functions that need to be involved in the calculation, effectively reduces the complexity of model predictive control, and effectively improves steady-state performance at the same switching frequency. Attached Figure Description

[0017] Figure 1 This is a flowchart of the linear motor control method in an embodiment of the present invention;

[0018] Figure 2 This is a schematic diagram of the linear motor control principle in an embodiment of the present invention;

[0019] Figure 3 This is a flowchart illustrating the calculation of the number of delay periods using a time-varying window model in an embodiment of the present invention.

[0020] Figure 4 This is a comparison chart showing the amount of data required for prediction using the multi-step model of this invention and the conventional multi-step model. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be described below with reference to the accompanying drawings. The described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without innovative effort are within the scope of protection of the present invention.

[0022] An embodiment of the linear motor control method provided by the present invention includes the following steps:

[0023] The three-phase current of the motor is collected in real time by a sensor and transformed to the DQ coordinate system to obtain the sampled current; the observation value of the same current is obtained simultaneously by an active disturbance rejection observer as the observation current.

[0024] Based on the current time series and rotor position relationship obtained from the Fourier transform of the observed current and the sampled current, the time delay of acquiring the sampled current is identified, and then the time delay is converted into a multiple N of the control cycle. N is used as the number of steps in the multi-step model predictive current control algorithm to gradually compensate for the predicted current.

[0025] The progressive compensation predicted current is calculated by using the voltage vector at the current moment to compensate the sampled current at the current moment within the current control cycle. The predicted current obtained through the compensation calculation is substituted into the value function for optimization to obtain the optimized voltage vector after one step of compensation. The calculation and optimization are then performed in the next control cycle until the number of steps is exhausted. By changing the switching state of the inverter during operation, the three-phase pulse corresponding to the optimal voltage vector selected in the last step is applied to the corresponding bridge arm of the inverter to realize the control of the linear induction motor.

[0026] Figure 2 This is a schematic diagram of the linear motor control principle in this embodiment. The control system structure includes a position controller, a speed controller, and a current controller. Both the position controller and the speed controller employ PI control. The position controller receives the position control signal X from the motor's magnetic scale and the reference position X. * Subtraction, followed by PI control to output speed reference value V * After comparison with the feedback speed V, the PI output current reference value i is obtained. * An optimized multi-step model prediction algorithm is used to select the optimal switching state for the corresponding inverter arm. The acquired motor current is transformed and input into a time-varying window integrated model, compared with the observed current, and Fourier analysis is used to extract the variation characteristics between the time series and angles. These characteristics are then used to construct the number of delay compensation cycles N (i.e., the multiple N of the aforementioned delay converted to the control cycle). The parameter N is input into the multi-step model prediction model to compensate for the delay in the system.

[0027] Figure 3 This is a flowchart illustrating the calculation of the number of delay periods using the time-varying window model in this embodiment. The sampled current and observed current are simultaneously input into the time-varying window model, and the Fourier transform method is used to extract the variation characteristics between the time series and angles. Under complex operating conditions, when the current waveform has many harmonics, the output value may have many abrupt outliers, sometimes not integers or unable to accurately represent the delay present in the actual experiment. Therefore, it is necessary to filter and separate the outlier sequences. Outlier detection uses a majority voting rule to dynamically adjust the calculated number of delay periods, ensuring that the adjusted number is as close as possible to an integer multiple of the period. Then, root mean square calculation is performed to obtain the final identification result. This method can monitor and identify the delay in the motor control system within a time window that changes with the motor current, automatically adjusting the output value of the time window according to changes in the current signal, achieving an accuracy rate of up to 98% in determining the number of delay periods.

[0028] Traditional model predictive current control algorithms only select the optimal voltage vector within a single control cycle, neglecting motor performance under multiple control cycle delays and ignoring the impact of the selected voltage vector on the future state of the motor system, thus leading to local optima. To address this issue, this invention studies an optimized multi-step model predictive control algorithm to compensate for time delays. To reduce computational load, this invention designs a new method for selecting vectors, specifically as follows: First, initialize parameters. Through the aforementioned calculations, the number of time delay compensation cycles N = 5. Define the order and location for storing the current prediction values ​​after each prediction step. Similar to the traditional single-step model prediction principle, traverse all voltage vectors (the switching of the three-phase switches controlled by the inverter will constitute 7 types of voltage vectors) and substitute them into the value function calculation. Select the sequence value (including voltage vector and predicted current) corresponding to the minimum value function value and store it as outputNr. Simultaneously, save the sequence values ​​(3 voltage vectors and 3 predicted currents) corresponding to the minimum, second minimum, and third minimum value function values ​​in K1_array. Second, determine the output... If the prediction step number N is equal to 1, then substitute the voltage vector corresponding to outputNr into the motor control system to obtain the switching state value of the next control cycle. If not, then substitute the values ​​in K1_array into the value function after the prediction in step 2 to calculate the value function value. Select the sequence corresponding to the minimum value function value and replace it with outputNr. At the same time, store the three sequences corresponding to the minimum, second minimum, and second second minimum values ​​into K2_array. Then determine if the prediction step number N is equal to 2. If so, then substitute the voltage vector corresponding to outputNr into the motor control system to obtain the switching state value of the next control cycle. If not, continue to substitute and calculate until the prediction step number 5 is reached.

[0029] Figure 4 This invention compares the multi-step model predictive optimization control principle with the computational data volume of conventional multi-step models. As is known in traditional multi-step model predictive control, to calculate, select, and optimize the switching states across multiple control cycles, the predicted value at time (k+1)T is obtained from the state variables sampled at the current time kT. Based on this, the predicted value at time (k+2)T is obtained, and so on, until the predicted value at time (k+N+1)T is obtained, where N is the number of prediction steps. The optimal control vector is selected through value function calculation, and the process continues in the next control cycle. When the number of prediction steps N is 2, the value function needs to calculate 7+7... 2 =56 times. When the number of prediction steps N is 3, the value function needs to be calculated 7+7 times. 2 +7 3=399 times, the amount of computation is too large, which not only wastes computing power and data resources, but may also create new time delays. The relevant process in this application simplifies the complex value function optimization process of multi-step prediction, filters out voltage vectors with large errors, and selects only the three cases with the smallest value function value, namely the optimal, second optimal and second-second optimal voltage vectors. This improves the steady-state performance of the current and reduces the complexity of the algorithm.

[0030] According to the mathematical model of a permanent magnet synchronous linear motor, the voltage and current formulas are as follows:

[0031]

[0032] ψ d =ψ f +L d i d +L dq i q

[0033] ψ q =L q i q +L dq i d

[0034] Among them, u d u q i d i q These are the steady-state voltage and current components, respectively.

[0035] R s ψ is the resistance of the mover winding; V is the mover speed of the motor; d , ψ q For permanent magnet magnetic flux linkage ψ f Components along the dq axis; τ is the motor pole pitch, t is time, L d L q Inductances L and L are respectively the direct-axis and quadrature-axis inductances. dq For mutual induction.

[0036] After simplification, we get:

[0037]

[0038] in, P n B is the number of pole pairs of the motor; F is the coefficient of friction; L It is the thrust of the motor.

[0039] Discretizing it yields:

[0040]

[0041] In the Kth control cycle, when the number of prediction steps is N,

[0042]

[0043] The value function is:

[0044] J = ||i * k+1 -i k+2 || 2+ ||i * k+2 -i k+3 || 2 +……+||i * k+N -i k+N+1 || 2 The superscript * represents a given reference value.

[0045] The optimized multi-step MPCC strategy has smaller current ripple compared to the traditional multi-step MPCC strategy, and does not improve steady-state performance at the expense of significantly increasing the switching frequency.

[0046] Assembling the above methods and steps into a program and storing it on a hard disk or other non-transitory storage medium constitutes an embodiment of the "non-transitory readable recording medium" of the present invention; while electrically connecting the storage medium to a computer processor and enabling control of the linear motor through data processing constitutes an embodiment of the "linear motor control system" of the present invention.

[0047] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention can take the form of a computer program product embodied on one or more computers or available storage media (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0048] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowcharts and / or block diagrams, as well as combinations of processes and / or blocks in the flowcharts and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowcharts and / or block diagrams. Figure 1 a process or multiple processes and / or boxes Figure 1A device that provides the functions specified in one or more boxes.

[0049] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 a process or multiple processes and / or boxes Figure 1 The function specified in one or more boxes.

[0050] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operational steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing the instructions executed on the computer or other programmable device for implementing the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

[0051] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A linear motor control method, characterized in that, Includes the following steps: The three-phase current of the motor is collected in real time by a sensor and transformed to the DQ coordinate system to obtain the sampled current; the observation value of the same current is obtained simultaneously by an active disturbance rejection observer as the observation current. Based on the current time series and rotor position relationship obtained from the Fourier transform of the observed current and the sampled current, the time delay of acquiring the sampled current is identified, and then the time delay is converted into a multiple N of the control cycle. N is used as the number of steps in the multi-step model predictive current control algorithm to gradually compensate for the predicted current. The progressive compensation predicted current is calculated by using the voltage vector at the current moment to compensate the sampled current at the current moment within the current control cycle. The predicted current obtained through the compensation calculation is substituted into the value function for optimization to obtain the optimized voltage vector after one step of compensation. The calculation and optimization are then performed in the next control cycle until the number of steps is exhausted. By changing the switching state of the inverter during operation, the three-phase pulse corresponding to the optimal voltage vector selected in the last step is applied to the corresponding bridge arm of the inverter to realize the control of the linear induction motor. The method for obtaining the time delay includes the following steps: performing maximum mode detection on the results of Fourier transform of the sampled current and the observed current respectively, finding the point corresponding to the point with the largest mode in the frequency domain and the phase of the frequency component of that point in the time domain, subtracting the two phases to obtain the phase difference, and the time corresponding to the phase difference is the time delay. The root mean square (RMS) of the time delays collected from multiple data acquisitions is calculated by dividing each data acquisition by the control period. The resulting squared average is then rounded down and used as a multiple N of the control period.

2. The linear motor control method according to claim 1, characterized in that, Each step of the value function optimization involves selecting the predicted current corresponding to the three cases with the smallest, second smallest, and second smallest value function values ​​to deduce the optimal, second best, and second best voltage vectors.

3. A non-transitory readable recording medium for storing one or more programs containing multiple instructions, characterized in that, When the instruction is executed, the processing circuit will perform a linear motor control method according to any one of claims 1-2.

4. A linear motor control system, comprising a processing circuit and a memory electrically coupled thereto, characterized in that, The memory is configured to store at least one program, the program containing multiple instructions, and the processing circuit runs the program to execute a linear motor control method according to any one of claims 1-2.

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