A motor adaptive control method and system for a ball mill

Abstract

This invention relates to the field of electrical automation control technology, and discloses an adaptive control method and system for a ball mill motor. The method includes: acquiring transient voltage and current signals from the stator side of the motor to calculate transient electromagnetic torque, extracting the fundamental wave to calculate the system power factor angle; performing adaptive notch filtering and two-mass elastic inverse dynamic reconstruction on the electromagnetic torque to separate the transient torque pulsation component; calculating the bias amount based on the power factor angle to generate a dynamic target window; calculating the time node of the centroid envelope of the torque pulsation component and converting it into a real-time collision hysteresis angle; comparing the hysteresis angle with the target window to generate a frequency command to adjust the speed. By reconstructing the mechanical transient torque through stator electrical parameters to eliminate signal transmission attenuation, and by adaptively sliding and adjusting the control boundary based on the fundamental wave parameter according to mechanical wear, closed-loop control of the grinding media falling is achieved, stabilizing the long-cycle crushing operation state of the equipment.

Description

Technical Field

[0001] This invention relates to the field of electrical automation control technology, specifically to an adaptive control method and system for the electric motor of a ball mill. Background Technology

[0002] Ball mills are widely used in industries such as mining, building materials, and chemicals. They primarily rely on an electric motor to drive the cylinder to rotate, causing the grinding media and materials inside to rise to a certain height before falling and being crushed through impact and grinding. The actual trajectory of the grinding media and the collision area with the material directly determine the crushing efficiency of the equipment. To maintain high operating efficiency, it is necessary to adjust the speed of the electric motor to ensure that the grinding media fall stably and impact the target area.

[0003] In existing control schemes, acoustic or vibration sensors are typically installed externally on the ball mill to indirectly determine its internal operating status. However, industrial sites are generally characterized by severe dust, high-intensity vibration, and complex environmental noise, making the measurement accuracy of external sensors susceptible to interference and prone to hardware damage. Some methods attempt to directly read conventional electrical signals from the motor side to monitor the operating status, but due to the transmission equipment such as speed reducers between the motor and the ball mill cylinder, the physical flexibility and damping characteristics of the mechanical transmission chain itself attenuate and cause phase lag effects on the high-frequency transient collision signals inside the cylinder, making it difficult for the control system to extract accurate and true grinding and impact characteristics from the stator side.

[0004] Furthermore, during long-term continuous operation, the internal cylinder liner and grinding media of a ball mill undergo continuous wear, resulting in a slow change in the overall mechanical and physical parameters of the system. Current control strategies typically rely on pre-set fixed reference thresholds as the basis for speed adjustment, failing to dynamically adjust based on the actual wear of the mechanical structure. These fixed control thresholds gradually deviate from the actual optimal operating point in the later stages of equipment operation, causing the actual trajectory of the grinding media to deviate from the ideal set area, making it difficult for the equipment to maintain a stable grinding state over a long period. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides an adaptive control method and system for the electric motor of a ball mill. This solves the problems that existing control technologies struggle to accurately obtain the true collision state of the grinding media inside the ball mill under harsh working conditions, and that fixed control thresholds cannot adapt to the long-term wear of the internal mechanical structure, leading to the grinding media's trajectory easily deviating from the set area and the grinding operation being unstable.

[0006] To achieve the above objectives, the present invention provides the following technical solution: an adaptive control method and system for the electric motor of a ball mill, comprising:

[0007] To achieve the above objectives, the first aspect of the present invention provides an adaptive control method for the electric motor of a ball mill, comprising the steps of:

[0008] The three-phase transient voltage signal and three-phase transient current signal of the motor stator side are acquired synchronously, and the transient electromagnetic torque is calculated by coordinate transformation.

[0009] Extract the fundamental waves of the three-phase transient voltage signal and the three-phase transient current signal, and calculate the phase difference between the stator fundamental voltage vector and the stator fundamental current vector as the system fundamental power factor angle;

[0010] The transient electromagnetic torque is subjected to adaptive notch filtering of transmission background noise, and the transient torque pulsation component is separated by reconstruction of the two-mass elastic inverse dynamics transfer function model and bandpass filtering.

[0011] Extract the basic target range and reference power factor angle, calculate the boundary offset of the basic target range based on the system fundamental power factor angle, and generate a dynamic target window;

[0012] Calculate the energy envelope centroid time node of the transient torque pulsation component within the mechanical rotation cycle, obtain the time lag of the energy envelope centroid time node relative to the starting point of the mechanical rotation cycle, and convert it into a mechanical electrical angle as the real-time collision hysteresis angle.

[0013] The real-time collision hysteresis angle is compared with the dynamic target window. Based on the comparison result, a frequency compensation command is generated and superimposed on the inverter's reference operating frequency to adjust the motor speed.

[0014] Furthermore, in the process of calculating the transient electromagnetic torque through coordinate transformation, the three-phase transient voltage and current signals in the three-phase stationary coordinate system are projected onto a two-phase orthogonal rotating coordinate system. The direct-axis components of the stator current, the quadrature-axis components of the stator current, the direct-axis components of the stator voltage, and the quadrature-axis components of the stator voltage are extracted, and the current direct-axis and quadrature-axis components of the stator flux linkage are estimated. Based on the number of pole pairs of the motor, the direct-axis components of the stator flux linkage, the quadrature-axis components of the stator flux linkage, the direct-axis components of the stator current, and the quadrature-axis components of the stator current are calculated. The product of the direct-axis components of the stator flux linkage and the quadrature-axis components of the stator current is subtracted from the product of the quadrature-axis components of the stator flux linkage and the direct-axis components of the stator current. The result is multiplied by three-half of the number of pole pairs of the motor to obtain the transient electromagnetic torque.

[0015] Furthermore, during the extraction of the fundamental frequency and calculation of the phase difference, a digital low-pass filtering algorithm is used to process the acquired voltage and current signals to extract the three-phase fundamental voltage and current signals. Based on these two signals, the stator fundamental voltage vector and stator fundamental current vector are synthesized in a two-phase stationary coordinate system. After calculating the phase angles of both, the phase difference is obtained by subtracting the phase angle of the stator fundamental current vector from the phase angle of the stator fundamental voltage vector. This phase difference is used as the system fundamental power factor angle.

[0016] Furthermore, for adaptive notch filtering of transmission background noise, the system calculates the mechanical rotational frequency of the motor rotor based on the motor's current actual operating frequency, number of pole pairs, and transmission ratio of the ball mill reducer. The mechanical rotational frequency is multiplied by the number of teeth on the input stage gear of the reducer to obtain the gear meshing characteristic frequency. This characteristic frequency and its lower harmonic frequencies are set as the stopband center frequency to dynamically adjust the digital adaptive notch filter. The transient electromagnetic torque is input into the digital adaptive notch filter to filter out mechanical transmission background noise, outputting a net torque sequence.

[0017] Furthermore, when reconstructing using the two-mass elastic inverse dynamic transfer function model, the motor rotor is set as the active inertia end, and the ball mill cylinder is set as the driven inertia end. An inverse digital filter is constructed using the motor's rotational inertia, the equivalent stiffness coefficient of the transmission chain, and the mechanical damping coefficient of the transmission chain. The inverse digital filter is then used to perform calculus on the net torque sequence to calculate the true transient mechanical torque that is not attenuated by mechanical damping and is referred to the ball mill cylinder side.

[0018] Furthermore, during the generation of the dynamic target window, the difference between the system fundamental power factor angle and the reference power factor angle is calculated, and the boundary offset is calculated by multiplying the preset phase mapping weighting coefficient with this difference. The lower boundary of the dynamic target window is obtained by adding the boundary offset to the lower boundary of the basic target interval, and the upper boundary of the dynamic target window is obtained by adding the boundary offset to the upper boundary of the basic target interval. The dynamic target window is formed by the lower boundary and the upper boundary of the dynamic target window.

[0019] Furthermore, the steps for calculating the energy envelope centroid time node of the transient torque pulsation component within the mechanical rotation cycle include: extracting the absolute value envelope of the transient torque pulsation component to obtain the envelope signal; performing an integral operation with time variable weighting on the envelope signal to obtain a first integral result; performing an area integral operation without time variable weighting on the envelope signal to obtain a second integral result; and dividing the first integral result by the second integral result to calculate the energy envelope centroid time node of the transient torque pulsation component within the mechanical rotation cycle.

[0020] Furthermore, the steps for obtaining the time lag between the energy envelope center of gravity time node and the starting point of the mechanical rotation cycle, and converting it into a mechanical electrical angle as the real-time collision hysteresis angle, include: subtracting the starting point of the mechanical rotation cycle from the energy envelope center of gravity time node to obtain the time lag; calculating the current mechanical angular velocity of the cylinder using the duration of the mechanical rotation cycle; multiplying the time lag by the mechanical angular velocity to obtain the corresponding mechanical spatial angle; and then multiplying the mechanical spatial angle by the gearbox transmission ratio and the number of pole pairs of the motor to obtain the converted mechanical electrical angle.

[0021] Furthermore, the step of generating frequency compensation instructions based on the comparison results includes: generating a negative frequency compensation instruction when the real-time collision hysteresis angle is less than the lower boundary of the dynamic target window; generating a positive frequency compensation instruction when the real-time collision hysteresis angle is greater than the upper boundary of the dynamic target window; and generating a zero compensation instruction when the real-time collision hysteresis angle is greater than or equal to the lower boundary of the dynamic target window and less than or equal to the upper boundary of the dynamic target window.

[0022] A second aspect of the present invention provides an adaptive control system for the electric motor of a ball mill, for executing the above-described control method, comprising a drive control device, a transmission device, a ball mill body, and electrical sensors.

[0023] The drive control equipment includes a frequency converter, a digital signal processing unit, and a motor. The electrical sensors include a voltage sensor and a current sensor installed on the output side of the frequency converter. The transmission equipment is connected between the motor and the ball mill body.

[0024] Voltage and current sensors are used to synchronously acquire three-phase transient voltage and current signals on the stator side of the motor.

[0025] The digital signal processing unit is used to receive three-phase transient voltage signals and three-phase transient current signals, perform coordinate transformation calculations to solve transient electromagnetic torque, extract the fundamental frequency of the three-phase transient voltage signals and three-phase transient current signals to calculate the fundamental power factor angle of the system, process the transient electromagnetic torque to separate the transient torque pulsation component, generate a dynamic target window and calculate the real-time collision hysteresis angle, compare the real-time collision hysteresis angle with the dynamic target window to generate a frequency compensation command, and superimpose the frequency compensation command into the inverter's reference operating frequency and output it to the inverter.

[0026] The frequency converter is used to adjust the motor speed according to the frequency compensation command, and drive the ball mill body to run through the transmission equipment.

[0027] This invention provides an adaptive control method and system for the electric motor of a ball mill. It has the following beneficial effects:

[0028] 1. This invention calculates transient electromagnetic torque by synchronously acquiring voltage and current signals from the stator side of the motor, and reconstructs and separates the torque signal using a two-mass elastic inverse dynamics transfer function model and bandpass filtering. This method indirectly obtains mechanical collision information inside the ball mill using electrical parameters, avoiding the difficulties of installing external mechanical sensors in dusty and vibrating environments; at the same time, the inverse model offsets the signal attenuation and hysteresis caused by the physical flexibility of the mechanical transmission chain, improving the accuracy of transient torque pulsation component extraction.

[0029] 2. This invention extracts the system's fundamental power factor angle as a reference parameter and calculates the boundary offset of the basic target interval based on its real-time change, thereby generating a dynamic target window. This scheme establishes a mapping relationship between the electrical fundamental parameter and macroscopic physical states such as the wear of the ball mill's internal liner, enabling the target range set by the control system to adaptively slide with the long-term changes of mechanical structure parameters. This avoids control deviations caused by using a fixed threshold and ensures the accuracy of the judgment benchmark under long-term equipment operation.

[0030] 3. This invention calculates the time node of the centroid of the energy envelope of the transient torque pulsation component, converts it into a real-time collision hysteresis angle characterizing the concentrated impact direction of the grinding media, and compares this angle with a dynamic target window to adjust the inverter output frequency. This mechanism directly generates frequency compensation commands based on the actual trajectory spatial characteristics of the grinding media, realizing dynamic closed-loop fine-tuning of the motor speed. This ensures that the grinding media inside the ball mill always converge and remain within the set target area, stabilizing the crushing work state of the system. Attached Figure Description

[0031] Figure 1 This is an architecture diagram of an adaptive control system for a ball mill motor according to an embodiment of the present invention;

[0032] Figure 2 This is a flowchart of an adaptive control method for the electric motor of a ball mill according to an embodiment of the present invention;

[0033] Figure 3 This is a comparison diagram of collision hysteresis angle tracking in an embodiment of the present invention;

[0034] Figure 4 This is a comparison chart of the product fineness qualification rate in an embodiment of the present invention. Detailed Implementation

[0035] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] See attached document Figure 1 The present invention provides an adaptive control system for the electric motor of a ball mill, including a drive control device, a transmission device, a ball mill body, and electrical sensors.

[0037] The drive control equipment includes a frequency converter, a digital signal processing unit, and a motor. Electrical sensors, including voltage and current sensors, are located on the output side of the frequency converter. The transmission device connects the motor to the ball mill body.

[0038] See attached document Figure 2 This invention provides an adaptive control method for the electric motor of a ball mill, comprising the following steps:

[0039] S10 synchronously acquires the three-phase transient voltage signal and three-phase transient current signal on the stator side of the motor, performs coordinate transformation calculation based on the three-phase transient voltage signal and three-phase transient current signal, and calculates the transient electromagnetic torque of the motor.

[0040] S20 extracts the fundamental frequency of the three-phase transient voltage signal and the three-phase transient current signal, calculates the phase difference between the stator fundamental voltage vector and the stator fundamental current vector, and uses the phase difference as the system fundamental power factor angle.

[0041] S30 performs adaptive notch filtering on the transmission background noise of transient electromagnetic torque, reconstructs the signal through a two-mass elastic inverse dynamics transfer function model, and uses a bandpass filter for frequency band filtering to separate the transient torque pulsation component.

[0042] S40, extract the basic target interval and reference power factor angle, and calculate the offset of the boundary of the basic target interval based on the system fundamental power factor angle to generate a dynamic target window;

[0043] S50, calculate the energy envelope of the transient torque pulsation component within the mechanical rotation cycle, obtain the time lag of the center of gravity time node relative to the starting point of the mechanical rotation cycle, and convert the time lag into a mechanical electric angle as the real-time collision hysteresis angle.

[0044] S60 compares the real-time collision hysteresis angle with the dynamic target window interval boundary, generates a frequency compensation command based on the comparison result, and superimposes the frequency compensation command into the inverter's reference operating frequency to adjust the motor speed.

[0045] Step S10, which involves synchronously acquiring the three-phase transient voltage and current signals from the stator side of the motor and calculating the transient electromagnetic torque, specifically includes the following sub-steps:

[0046] S101, synchronously acquire the electrical characteristic signals of the motor stator side. The system uses voltage and current sensors configured between the inverter output and the motor to acquire physical signals. While the motor acts as a drive source, its stator electrical characteristics are also direct physical parameters reflecting the fluctuations in the mechanical load inside the ball mill. When the grinding media inside the ball mill impacts the material, the mechanical impact force acts in the opposite direction along the transmission chain to the motor rotor, thus causing minute high-frequency fluctuations in the stator-side electrical signals.

[0047] The current sensor employs a Hall effect current sensor, and the voltage sensor uses a resistor divider voltage detection circuit. The inverter's internal digital signal processing unit performs analog-to-digital conversion on the analog signals output by the sensors at a set sampling frequency, acquiring discrete three-phase transient voltage and current signals. To accurately capture high-frequency transient components containing mechanical impact characteristics, the sampling frequency is configured to be no less than twice the inverter's pulse width modulation switching frequency. Under normal conditions, the sampling frequency is set within the range of 10kHz to 20kHz to avoid frequency aliasing during the analog-to-digital conversion process.

[0048] S102, Perform coordinate transformation operations. The digital signal processing unit projects the three-phase transient voltage and current signals in the three-phase stationary coordinate system to a two-phase orthogonal rotating coordinate system. For the transformation operations from the three-phase stationary coordinate system to the two-phase stationary coordinate system and the two-phase orthogonal rotating coordinate system, those skilled in the art can use conventional Clark transform and Park transform. The matrix derivation and operation processing are well-known techniques in the field and will not be elaborated here.

[0049] The orientation angle parameters required to perform the above-mentioned rotational coordinate transformation can be directly measured by an encoder installed on the motor rotor shaft, or estimated by a sensorless flux linkage observer inside the frequency converter. After the above coordinate transformation calculation, the digital signal processing unit extracts the direct-axis component of the stator current, the quadrature-axis component of the stator current, the direct-axis component of the stator voltage, and the quadrature-axis component of the stator voltage.

[0050] S103 calculates the transient electromagnetic torque of the motor. The digital signal processing unit calculates the electromagnetic torque at the rotor shaft end of the motor based on the direct-axis component and quadrature-axis component of the stator current and the corresponding flux linkage state. In the dynamic transmission model, the electromagnetic torque directly reflects the power output by the motor to overcome instantaneous load disturbances at the mechanical ends. The digital signal processing unit estimates the current direct-axis and quadrature-axis components of the stator flux linkage using a voltage-current integral model or a flux linkage observer. The number of pole pairs of the motor is determined based on the inherent nameplate parameters of the motor. The system calculates the transient electromagnetic torque based on the number of pole pairs, the direct-axis component of the stator flux linkage, the quadrature-axis component of the stator flux linkage, the direct-axis component of the stator current, and the quadrature-axis component of the stator current. The calculation formula is as follows:

[0051] ;

[0052] In the above formula: Indicates transient electromagnetic torque; Indicates the number of pole pairs of the electric motor; Represents the direct-axis component of the stator flux linkage; Indicates the cross-axis component of the stator flux linkage; Represents the direct-axis component of the stator current; This represents the quadrature-axis component of the stator current. The digital signal processing unit continuously executes the above calculation process based on the sampling period, outputting a discrete data sequence of transient electromagnetic torque that varies with time, which serves as the basic data input for subsequent extraction of mechanical transmission dynamics features.

[0053] Step S20, which involves extracting the fundamental frequency of the three-phase transient voltage and current signals and calculating the system's fundamental power factor angle, specifically includes the following sub-steps:

[0054] S201 performs the fundamental component extraction operation. The digital signal processing unit uses a digital low-pass filter algorithm or a fast Fourier transform algorithm to filter the acquired three-phase transient voltage and current signals. The broadband signal on the stator side of the motor contains high-frequency switching harmonics generated by the inverter's pulse width modulation, transient impact fluctuations during mechanical transmission, and low-frequency fundamental components characterizing the overall working state of the motor.

[0055] To accurately extract the fundamental frequency without introducing excessive phase delay, the cutoff frequency of the digital low-pass filter algorithm is set slightly higher than the actual operating fundamental frequency of the motor. In practice, the cutoff frequency of the digital low-pass filter algorithm is set to 1.2 to 1.5 times the actual operating fundamental frequency of the motor. Through this digital low-pass filter algorithm, the system filters out high-frequency components from the three-phase transient voltage and current signals, extracting the three-phase fundamental voltage and current signals.

[0056] S202, Construct the fundamental space vector and calculate the phase difference. The digital signal processing unit synthesizes the stator fundamental voltage vector and stator fundamental current vector in a two-phase stationary coordinate system based on the three-phase fundamental voltage signal and the three-phase fundamental current signal. The matrix operation rules for synthesizing the three-phase signal space vector can be calculated using conventional stationary coordinate transformations, which are well-known techniques in the field and will not be elaborated upon here.

[0057] After synthesizing the vectors, the system calculates the phase angles of the stator fundamental voltage vector and the stator fundamental current vector respectively. The specific phase angle calculation process utilizes the orthogonal components of the vectors in the two-phase stationary coordinate systems, obtained through arctangent function calculation, or extracted using a digital phase-locked loop algorithm. The digital signal processing unit subtracts the phase angle of the stator fundamental current vector from the phase angle of the stator fundamental voltage vector to obtain the phase difference between the two. The system uses this phase difference as the system fundamental power factor angle. The formula for calculating the system fundamental power factor angle is as follows:

[0058] ;

[0059] In the above formula: Indicates the fundamental power factor angle of the system; The phase angle represents the stator fundamental voltage vector; The phase angle represents the stator fundamental current vector.

[0060] S203 establishes a physical mapping relationship between electrical parameters and the slowly changing macroscopic mechanical state. During long-term operation, the ball mill's internal cylinder liner will experience physical wear due to continuous friction between the grinding media and materials, resulting in an increase in the effective inner diameter of the cylinder. Consequently, the overall rotational inertia and mass distribution of the system will change slowly.

[0061] This change in mechanical structural parameters alters the load reverse torque characteristics at the motor drive end. The long-period drift of the mass distribution at the mechanical load end changes the work ratio of reactive to active power on the stator side, ultimately manifesting as a slow drift in the system's fundamental power factor angle. Therefore, the system uses the calculated system fundamental power factor angle as a fundamental parameter for evaluating the macroscopic physical wear state inside the ball mill, providing a static reference benchmark for subsequent micro-dynamic control calibration.

[0062] Step S30, which involves adaptive notch filtering of the transient electromagnetic torque to reduce transmission background noise, signal reconstruction using a two-mass elastic inverse dynamics transfer function model, and separation of the transient torque pulsation component, specifically includes the following sub-steps:

[0063] S301 performs adaptive notch filtering for transmission background noise. In the ball mill transmission system, the gearbox gears generate fixed and periodic mechanical vibrations during meshing. This vibration acts as background noise, superimposed on the transient electromagnetic torque of the motor, masking the actual material collision signals inside the ball mill cylinder. The digital signal processing unit calculates the current mechanical rotational frequency of the motor rotor based on the motor's current operating frequency, the number of pole pairs, and the gearbox transmission ratio. The system calculates the current gear meshing characteristic frequency based on the mechanical rotational frequency and the number of teeth on the input stage gear of the gearbox, using the following formula:

[0064] ;

[0065] In the above formula: Indicates the characteristic frequency of gear meshing; This indicates the mechanical rotation frequency of the motor rotor; This indicates the number of teeth on the input stage gear of the speed reducer.

[0066] The number of teeth on the input stage gear of the reducer is obtained based on the inherent hardware parameters of the reducer. The mechanical rotational frequency of the motor rotor is calculated by dividing the actual operating electrical frequency output by the frequency converter by the number of pole pairs of the motor. The system uses the calculated gear meshing characteristic frequency and its lower harmonic frequencies as the stopband center frequency and dynamically configures the digital adaptive notch filter. The digital signal processing unit inputs the transient electromagnetic torque obtained in step S10 into the digital adaptive notch filter to filter out the deterministic periodic mechanical transmission background noise and output the purified net torque sequence.

[0067] S302 uses a two-mass elastic inverse dynamics transfer function model for signal reconstruction. The ball mill drive system has a large moment of inertia, and the coupling and drive shaft possess physical flexibility. The entire mechanical transmission chain is equivalent to a low-pass filter, causing the high-frequency impact signal generated by the collision of grinding media inside the mill cylinder to attenuate in amplitude and lag in phase when transmitted to the stator of the motor. To compensate for the attenuation effect of the physical transmission chain on the high-frequency mechanical signal, the system constructs a two-mass elastic inverse dynamics transfer function model at the digital algorithm layer. The system uses the motor rotor as the active inertia end and the ball mill cylinder as the driven inertia end. The digital signal processing unit calls pre-configured motor moment of inertia, transmission chain equivalent stiffness coefficient, and transmission chain mechanical damping coefficient to construct an inverse digital filter.

[0068] The aforementioned physical parameters of the transmission chain can be extracted from the factory specifications of the transmission equipment, or estimated using conventional offline motor parameter identification algorithms under system no-load conditions. The system utilizes this inverse digital filter to perform calculus on the purified net torque sequence, applying high-frequency amplitude gain and phase lead compensation to the signal at a mathematical level. This inverse reconstruction operation counteracts the low-pass attenuation effect caused by the flexibility of the mechanical transmission, calculating the true transient mechanical torque, undamped by mechanical damping, referred to the ball mill cylinder side.

[0069] S303 utilizes a bandpass filter for frequency band filtering to separate transient torque pulsation components. The process of the grinding media detaching from the mill wall and impacting the material bed after impact is characterized by a series of broadband, random, high-frequency physical impacts. The system uses a digital bandpass filter to selectively extract the frequency bands of the reconstructed true mechanical transient torque. In practice, due to differences in the grinding media size and mill diameter among different ball mill specifications, the concentrated characteristic frequency distribution region of the impact varies.

[0070] The lower passband cutoff frequency of a digital bandpass filter is typically set to 30Hz, and the upper passband cutoff frequency is set to 150Hz. The digital signal processing unit inputs the actual mechanical transient torque into this digital bandpass filter, filtering out residual low-frequency steady-state load torque components and ultra-high-frequency electrical switching noise components, separating the high-frequency transient torque pulsation component generated solely by the physical behavior of the grinding body collision. This transient torque pulsation component serves as the direct data source for subsequent extraction of microscopic dynamic state features.

[0071] Step S40 involves extracting the basic target interval and reference power factor angle, and generating a dynamic target window by offsetting the boundary of the basic target interval based on the system fundamental power factor angle. This process specifically includes the following sub-steps:

[0072] S401, extract the basic target range and reference power factor angle under the baseline operating condition. When the ball mill is running under new liner installation or calibration conditions, the system regards the current mechanical state as the baseline physical state. In practice, technicians obtain the calibration angle range at which the grinding media achieves optimal grinding efficiency under this baseline physical state through offline external acoustic array calibration or quantitative material grinding efficiency comparison experiments. The system sets the lower limit of this calibration angle range as the lower boundary of the basic target range and the upper limit as the upper boundary of the basic target range. The lower and upper boundaries of the basic target range together constitute the basic target range.

[0073] The system extracts and records the fundamental power factor angle calculated under the reference physical state, using it as the reference power factor angle. The digital signal processing unit stores the lower boundary of the basic target interval, the upper boundary of the basic target interval, and the reference power factor angle in its internal memory as static comparison benchmarks for subsequent calculations.

[0074] S402, calculate the boundary offset for dynamic adjustment. The digital signal processing unit calculates the difference between the system fundamental power factor angle and the reference power factor angle, which were acquired in real time in step S20. The system multiplies this difference using pre-configured phase mapping weighting coefficients to calculate the boundary offset for adjusting the target range. The calculation formula is as follows:

[0075] ;

[0076] In the above formula: This represents the boundary offset obtained from the solution; Indicates the phase mapping weighting coefficients; Indicates the fundamental power factor angle of the system; This represents the reference power factor angle. The phase mapping weighting coefficient is used to characterize the proportional mapping relationship between the system fundamental power factor angle offset caused by liner wear and the offset of the optimal drop angle of the grinding media.

[0077] In practice, the specific value of this coefficient is determined by the fitting function of the internal geometric dimension measurement data of the ball mill under no-load conditions and the corresponding electrical phase angle, and the conventional value range is set between 0.5 and 1.5.

[0078] S403 generates a dynamic target window that is linked to the mechanical state. The digital signal processing unit superimposes the calculated boundary offsets onto the lower and upper boundaries of the basic target interval to generate the dynamic target window. The system adds the boundary offsets to the lower boundary of the basic target interval to calculate the lower boundary of the dynamic target window. The system adds the boundary offsets to the upper boundary of the basic target interval to calculate the upper boundary of the dynamic target window.

[0079] As the liner wears continuously, leading to an increase in the effective inner diameter of the cylinder, the force model and trajectory of the grinding media during rotation change. Through the aforementioned bias calculations, the system enables the boundary conditions for control decisions to adaptively slide and offset in response to the mechanical wear state. This dynamic mapping mechanism ensures that the target range set by the control system adapts to changes in actual mechanical structural parameters during long-term operation of the ball mill, thereby guaranteeing the accuracy of subsequent control commands.

[0080] Step S50, which involves calculating the energy envelope of the transient torque pulsation component within the mechanical rotation cycle at the center of gravity time node, obtaining the time lag of the center of gravity time node relative to the start point of the mechanical rotation cycle, and converting the time lag into a mechanical electrical angle as the real-time collision hysteresis angle, specifically includes the following sub-steps:

[0081] S501, Determine the mechanical rotation cycle and starting point. The digital signal processing unit calculates the duration of a single mechanical rotation cycle of the ball mill cylinder based on the current actual operating frequency of the motor, the number of pole pairs of the motor, and the gearbox transmission ratio. Specifically, the digital signal processing unit obtains the mechanical rotation frequency of the motor rotor in real time by measuring the encoder installed on the motor rotor shaft, or by dividing the current actual operating frequency of the motor by the number of pole pairs of the motor and combining this with slip compensation. The digital signal processing unit divides the mechanical rotation frequency of the motor rotor by the gearbox transmission ratio to obtain the mechanical rotation frequency of the ball mill cylinder, and takes the reciprocal of this mechanical rotation frequency as the duration of a single mechanical rotation cycle.

[0082] The system utilizes a position sensor mounted on the motor rotor shaft or transmission shaft to acquire zero-position pulse signals, using the trigger moment of these zero-position pulse signals as the starting point of the mechanical rotation cycle. This starting point corresponds to a fixed geometric reference position inside the ball mill cylinder, providing a reference zero point for subsequent time and space conversions. The specific circuitry and triggering mechanism for the position sensor to acquire the zero-position pulse signals can be implemented using conventional incremental encoders or proximity switches, which are well-known technologies in the field and will not be elaborated upon here.

[0083] S502, Calculate the time node of the energy envelope centroid. Within a single mechanical rotation cycle, the grinding media inside the ball mill are lifted to a specific height as the mill rotates and then fall, releasing mechanical energy by impacting the material. The digital signal processing unit extracts the absolute value envelope of the transient torque pulsation component separated in step S30 to obtain an envelope signal characterizing the high-frequency collision intensity. The system performs a time-weighted integral operation on this envelope signal and divides it by the unweighted pure area integral result of the envelope signal to calculate the time node of the energy envelope centroid of the transient torque pulsation component within the mechanical rotation cycle. The calculation formula is as follows:

[0084] ;

[0085] In the above formula: Indicates the time point of the energy envelope centroid; Indicates the starting point of the mechanical rotation cycle; Indicates the duration of a single mechanical rotation cycle; Indicates the transient torque ripple component; This represents the time variable. In the digital signal processing unit, the above continuous-time integration operation is implemented by summing and accumulating discrete data sequences within the corresponding sampling period. This time node represents the equivalent moment when energy release is concentrated during the impact of the grinding media.

[0086] S503, Physical conversion of time characteristics to spatial angle. The digital signal processing unit subtracts the starting point of the mechanical rotation cycle from the calculated energy envelope centroid time node, obtaining the time difference between the two. The system uses this time difference as the time lag of the centroid time node relative to the starting point of the mechanical rotation cycle. This time lag reflects the time span required for the grinding media to travel from the reference zero position to the energy concentration collision point. The digital signal processing unit calculates the current mechanical angular velocity of the ball mill cylinder using the duration of a single mechanical rotation cycle. The system multiplies the calculated time lag by the current mechanical angular velocity to obtain the corresponding mechanical spatial angle of the ball mill cylinder.

[0087] To align with the electrical control variables of the drive control equipment, the digital signal processing unit (DSP) converts the mechanical spatial angle into a corresponding electrical reference angle, i.e., the mechanical electrical angle, based on the number of motor pole pairs and the gearbox transmission ratio. In practice, the DSP multiplies the calculated mechanical spatial angle by the gearbox transmission ratio, and then by the number of motor pole pairs to obtain the mechanical electrical angle that matches the electrical control. The system uses this mechanical electrical angle as the real-time collision hysteresis angle, which characterizes the spatial orientation of the concentrated impact of the grinding media within the cylinder.

[0088] Step S60, which involves performing closed-loop control of inverter command fine-tuning based on the spatial comparison results, specifically includes the following sub-steps:

[0089] S601, perform real-time comparison of spatial boundary conditions. The digital signal processing unit acquires the real-time collision hysteresis angle calculated in step S50, as well as the lower and upper boundaries of the dynamic target window generated in step S40. The system numerically compares the real-time collision hysteresis angle with the lower and upper boundaries of the dynamic target window, respectively. The physical significance of this comparison process is to determine whether the actual impact position of the grinding media inside the ball mill deviates from the optimal operating area adaptively adjusted by the mechanical wear state.

[0090] S602 triggers the determination and generates a frequency compensation command. The digital signal processing unit determines the direction and value of the inverter frequency adjustment based on the numerical comparison results. When the real-time collision hysteresis angle is less than the lower boundary of the dynamic target window, it indicates that the actual collision position of the grinding body group has advanced, and the system triggers and generates a negative frequency compensation command; when the real-time collision hysteresis angle is greater than the upper boundary of the dynamic target window, it indicates that the actual collision position of the grinding body group has lagged, and the system triggers and generates a positive frequency compensation command; when the real-time collision hysteresis angle is greater than or equal to the lower boundary of the dynamic target window and less than or equal to the upper boundary of the dynamic target window, it indicates that the current drop trajectory is within the optimal operating range, and the system triggers and generates a zero compensation command.

[0091] In practical implementation, for the calculation of frequency compensation values ​​in positive and negative frequency compensation commands, the system uses a proportional-integral (PI) control algorithm, taking the difference between the real-time collision hysteresis angle and the target window over-limit boundary as input. To prevent the closed-loop system from outputting excessive adjustment amounts under strong external interference, which could lead to motor loss of synchronism or overload, the digital signal processing unit performs safety limiting processing on the frequency compensation values ​​output by the PI control algorithm. In conventional applications, this limiting range is usually set within ±5% of the inverter's reference operating frequency. The specific operational structure of the PI control algorithm can be implemented by those skilled in the art using conventional closed-loop controller design; its parameter tuning is well-known in the field and will not be elaborated upon here.

[0092] S603 executes inverter output adjustment to change the drop trajectory. The digital signal processing unit superimposes the generated frequency compensation value onto the inverter's reference operating frequency to obtain the target operating frequency. The inverter's reference operating frequency is obtained based on the process setpoint of the upper control system or the preset rated operating parameters of the local controller. Its calculation formula is as follows:

[0093] ;

[0094] In the above formula: Indicates the target operating frequency; Indicates the reference operating frequency of the frequency converter; This indicates the frequency compensation value. The system uses this target operating frequency as the input command for the inverter's pulse width modulation module, adjusting the fundamental frequency of the three-phase AC power output on the inverter's output side, thereby adjusting the actual output speed of the motor. The change in motor speed is transmitted to the ball mill cylinder through the mechanical transmission chain, altering the cylinder's mechanical rotational angular velocity.

[0095] The change in the rotational angular velocity of the cylinder alters the magnitude of the centrifugal force during the lifting of the grinding media by the cylinder wall, forcing a change in the starting point of the grinding media's detachment from the cylinder wall, and thus changing the trajectory of the grinding media inside the cylinder. By continuously looping the above closed-loop control logic, the system ensures that the real-time collision hysteresis angle decreases and dynamically converges within the dynamic target window, maintaining the grinding operation state of the ball mill system.

[0096] Combined with appendix Figure 3 and attached Figure 4 The following is a specific application embodiment to further illustrate the implementation process and technical effects of the present invention.

[0097] Application scenarios and device parameter configuration:

[0098] This embodiment applies the adaptive control system for a ball mill motor provided by the present invention to an MQG3.2×4.5 grid-type ball mill. The system drive control device uses a frequency converter, the rated power of the motor is 1200kW, the frequency converter's reference operating frequency is set to 50Hz, and the number of pole pairs of the motor is set to 4. The transmission ratio of the reducer is set to 5.8, and the number of teeth on the input stage gear of the reducer is set to 24. The sampling frequency of the digital signal processing unit inside the frequency converter is configured to 15kHz, and the experimental comparison period is set to 180 days.

[0099] Extraction of basic parameters under calibration conditions:

[0100] During the initial operation phase after replacing the new liners and completing the break-in process of the ball mill (see attached document) Figure 3 (With a running time of 0 days), the system considers the current mechanical state as the baseline physical state. Through external calibration testing, the calibration angle range of the grinding media drop under this baseline physical state is obtained as [210°, 225°]. The system sets the lower boundary of the basic target interval to 210° and the upper boundary of the basic target interval to 225°.

[0101] The system calculates and records the fundamental power factor angle under this operating condition, using it as the reference power factor angle, and measures... =35°. The pre-configured phase mapping weighting coefficients within the system are: =1.2.

[0102] Adaptive bias and closed-loop control process under long-cycle operation:

[0103] See attached document Figure 3 As operating time increases, the cylinder liner undergoes physical wear. Taking the control process when the system has been running continuously for 120 days as an example, the following steps are performed:

[0104] The system fundamental power factor angle, calculated in real time by the digital signal processing unit, has slowly drifted to =38°. The system calculates the boundary offset used to adjust the target interval based on the formula:

[0105] ;

[0106] Right now: =1.2×(38°−35°)=3.6°;

[0107] The digital signal processing unit superimposes the boundary offset onto the lower boundary of the basic target interval, calculating the lower boundary of the dynamic target window to be 213.6° (corresponding to the attached figure). Figure 3 (Data from the black dotted line on day 120); By overlaying the boundary offset onto the upper boundary of the base target interval, the upper boundary of the dynamic target window is calculated to be 228.6° (corresponding to the attached data). Figure 3 (The black dashed line data for the 120th day).

[0108] At this operating node, if frequency closed-loop regulation is not implemented (corresponding to the attached...) Figure 3 (In traditional constant frequency control), due to the wear of the liner, the trajectory of the grinding media changes, and the calculated real-time collision hysteresis angle will drop to about 208.7°, which is less than the lower boundary of the dynamic target window of 213.6°.

[0109] When the control system of this invention is used, if it is determined that the real-time collision hysteresis angle has an out-of-limit tendency to be less than the lower boundary of the dynamic target window, the digital signal processing unit triggers and generates a negative frequency compensation command. Within the adjustment period of this embodiment, the frequency compensation value is calculated by the proportional-integral control algorithm. =−0.4Hz. The digital signal processing unit calculates the target operating frequency according to the formula:

[0110] ;

[0111] Right now: =50+(−0.4)=49.6Hz;

[0112] The system uses the target operating frequency as an input command to adjust the fundamental frequency of the three-phase AC power on the inverter output side. The reduction in inverter output frequency lowers the motor speed, which in turn reduces the mechanical rotational angular velocity of the cylinder. This decrease in cylinder rotational angular velocity alters the centrifugal force of the grinding media, forcing a delay in the initial point of the grinding media's detachment from the cylinder wall, thus causing a lag in the actual collision location.

[0113] Through continuous looping of this closed-loop control logic, the collision hysteresis angle decreases in real time and dynamically converges within the dynamic target window. (See attached...) Figure 3As shown, on day 120, the adaptive control of the present invention adjusts and maintains the real-time collision hysteresis angle at a position of approximately 221°, which is between the lower boundary and the upper boundary of the dynamic target window.

[0114] Experimental verification and effect comparison:

[0115] See attached document Figure 4 Experiments were conducted to verify and compare the control method of this invention with the traditional constant frequency control method. The traditional constant frequency control method operates at a constant frequency of 50Hz and does not perform inverter output regulation.

[0116] As operating time increases, the real-time collision hysteresis angle of the traditional constant frequency control method gradually deviates from the optimal operating range (e.g., Figure 3 As shown in the figure, this led to a deterioration in the crushing operation. The product fineness qualification rate continued to decline from about 85.3% in the early stage of operation to about 77.8% by the 180th day.

[0117] In contrast, the control method of this invention maintains the real-time collision hysteresis angle within the dynamic target window by adaptively adjusting the dynamic target window and regulating the motor speed in a closed loop. (Appendix) Figure 4 Experimental results show that the product fineness qualification rate using the control method of this invention remains stably within the range of 84% to 86% over a 180-day operating period. Furthermore, the experimental group using the control method of this invention maintains a power consumption per ton of ore between 18.4 kWh / t and 18.7 kWh / t over 180 days, demonstrating stable system energy-saving performance compared to the traditional constant-frequency control group.

Claims

1. An adaptive control method for the electric motor of a ball mill, characterized in that, Includes the following steps: The three-phase transient voltage signal and three-phase transient current signal of the motor stator side are acquired synchronously, and the transient electromagnetic torque is calculated by coordinate transformation. Extract the fundamental waves of the three-phase transient voltage signal and the three-phase transient current signal, and calculate the phase difference between the stator fundamental voltage vector and the stator fundamental current vector as the system fundamental power factor angle; The transient electromagnetic torque is subjected to adaptive notch filtering of transmission background noise, and after reconstruction by the two-mass elastic inverse dynamics transfer function model and bandpass filtering, the transient torque pulsation component is separated. Extract the basic target interval and reference power factor angle, calculate the boundary offset of the basic target interval based on the fundamental power factor angle of the system, and generate a dynamic target window; Calculate the energy envelope centroid time node of the transient torque pulsation component within the mechanical rotation cycle, obtain the time lag of the energy envelope centroid time node relative to the starting point of the mechanical rotation cycle, and convert it into a mechanical electrical angle as the real-time collision hysteresis angle. The real-time collision hysteresis angle is compared with the dynamic target window, and a frequency compensation command is generated based on the comparison result and superimposed on the inverter's reference operating frequency to adjust the motor speed.

2. The adaptive control method for the electric motor of a ball mill according to claim 1, characterized in that, The steps for calculating the transient electromagnetic torque through coordinate transformation include: The three-phase transient voltage signal and the three-phase transient current signal in the three-phase stationary coordinate system are projected onto a two-phase orthogonal rotating coordinate system to extract the stator current direct-axis component, stator current quadrature-axis component, stator voltage direct-axis component, and stator voltage quadrature-axis component. Estimate the current direct-axis component and quadrature-axis component of the stator flux linkage; The transient electromagnetic torque is calculated based on the number of pole pairs of the motor, the direct-axis component of the stator flux linkage, the quadrature-axis component of the stator flux linkage, the direct-axis component of the stator current, and the quadrature-axis component of the stator current. The transient electromagnetic torque is obtained by subtracting the product of the direct-axis component of the stator flux linkage and the quadrature-axis component of the stator current from the product of the direct-axis component of the stator flux linkage and the direct-axis component of the stator current, and multiplying the result by three-half of the number of pole pairs of the motor.

3. The adaptive control method for the electric motor of a ball mill according to claim 1, characterized in that, The steps of extracting the fundamental frequencies of the three-phase transient voltage signal and the three-phase transient current signal, and calculating the phase difference between the stator fundamental voltage vector and the stator fundamental current vector, include: The three-phase transient voltage signal and the three-phase transient current signal are filtered using a digital low-pass filter algorithm to extract the three-phase fundamental voltage signal and the three-phase fundamental current signal. The stator fundamental voltage vector and the stator fundamental current vector are synthesized in a two-phase stationary coordinate system based on the three-phase fundamental voltage signal and the three-phase fundamental current signal; Calculate the phase angle of the stator fundamental voltage vector and the phase angle of the stator fundamental current vector respectively, and subtract the phase angle of the stator fundamental current vector from the phase angle of the stator fundamental voltage vector to obtain the phase difference between the stator fundamental voltage vector and the stator fundamental current vector.

4. The adaptive control method for the electric motor of a ball mill according to claim 1, characterized in that, The steps for adaptive notch filtering of the transmission background noise for the transient electromagnetic torque include: The mechanical rotation frequency of the motor rotor is calculated based on the current actual operating frequency of the motor, the number of pole pairs of the motor, and the transmission ratio of the reducer of the ball mill. The gear meshing characteristic frequency is obtained by multiplying the mechanical rotation frequency of the motor rotor by the number of teeth of the input stage gear of the reducer. The gear meshing characteristic frequency and the lower harmonic frequency of the gear meshing characteristic frequency are set as the stopband center frequency, and the digital adaptive notch filter is dynamically adjusted. The transient electromagnetic torque is input into the digital adaptive notch filter to filter out mechanical transmission background noise and output a net torque sequence.

5. The adaptive control method for the electric motor of a ball mill according to claim 4, characterized in that, The steps for reconstructing the inverse dynamic transfer function model of a two-mass elastic system include: The motor rotor is set as the active inertia end and the ball mill cylinder is set as the driven inertia end; The inverse digital filter is constructed by calling the preset moment of inertia of the motor, the equivalent stiffness coefficient of the transmission chain, and the mechanical damping coefficient of the transmission chain. The net torque sequence is subjected to calculus and integration using the inverse digital filter to calculate the true transient mechanical torque that is not attenuated by mechanical damping and is referred to the cylinder side of the ball mill.

6. The adaptive control method for the electric motor of a ball mill according to claim 1, characterized in that, The steps of calculating the boundary offset of the fundamental target interval based on the fundamental power factor angle of the system and generating the dynamic target window include: Calculate the difference between the fundamental power factor angle of the system and the reference power factor angle; The boundary offset is calculated by multiplying the pre-set phase mapping weighting coefficient with the difference. The lower boundary of the dynamic target window is calculated by adding the boundary offset to the lower boundary of the basic target interval. The upper boundary of the dynamic target window is calculated by adding the boundary offset to the upper boundary of the basic target interval. The dynamic target window is formed by the lower boundary of the dynamic target window and the upper boundary of the dynamic target window.

7. The adaptive control method for the electric motor of a ball mill according to claim 1, characterized in that, The steps for calculating the energy envelope centroid time node of the transient torque pulsation component within the mechanical rotation cycle include: The absolute value envelope of the transient torque pulsation component is extracted to obtain the envelope signal; The first integral result is obtained by performing an integral operation with time variable weighting on the envelope signal; The second integral result is obtained by performing an area integral operation on the envelope signal without time-variable weighting. Dividing the first integral result by the second integral result yields the energy envelope centroid time node of the transient torque pulsation component within the mechanical rotation cycle.

8. The adaptive control method for the electric motor of a ball mill according to claim 1, characterized in that, The step of obtaining the time lag of the energy envelope centroid time node relative to the start point of the mechanical rotation cycle, and converting it into a mechanical electrical angle as the real-time collision hysteresis angle, includes: Subtract the mechanical rotation cycle start point from the energy envelope centroid time node to obtain the time lag; The current mechanical angular velocity of the ball mill cylinder is calculated using the duration of the mechanical rotation cycle. Multiplying the time lag by the current mechanical angular velocity yields the mechanical spatial angle corresponding to the cylinder of the ball mill; The mechanical spatial angle is multiplied by the transmission ratio of the reducer and then by the number of pole pairs of the motor to obtain the converted mechanical electrical angle.

9. The adaptive control method for the electric motor of a ball mill according to claim 1, characterized in that, The step of generating the frequency compensation command based on the comparison result includes: When the real-time collision hysteresis angle is less than the lower boundary of the dynamic target window, a negative frequency compensation command is generated. When the real-time collision hysteresis angle is greater than the upper boundary of the dynamic target window, a positive frequency compensation command is generated. When the real-time collision hysteresis angle is greater than or equal to the lower boundary of the dynamic target window and less than or equal to the upper boundary of the dynamic target window, a zero compensation command is generated.

10. An adaptive control system for a ball mill motor, used to execute the adaptive control method for a ball mill motor according to any one of claims 1 to 9, characterized in that, This includes drive control equipment, transmission equipment, the ball mill body, and electrical sensors; The drive control device includes a frequency converter, a digital signal processing unit, and a motor. The electrical sensors include a voltage sensor and a current sensor disposed on the output side of the frequency converter. The transmission device is connected between the motor and the ball mill body. The voltage sensor and the current sensor are used to synchronously acquire the three-phase transient voltage signal and the three-phase transient current signal on the stator side of the motor; The digital signal processing unit is used to receive the three-phase transient voltage signal and the three-phase transient current signal, perform coordinate transformation calculations to solve the transient electromagnetic torque, extract the fundamental power factor angle of the three-phase transient voltage signal and the three-phase transient current signal, process the transient electromagnetic torque to separate the transient torque pulsation component, generate a dynamic target window and calculate the real-time collision hysteresis angle, compare the real-time collision hysteresis angle with the dynamic target window to generate a frequency compensation command, and superimpose the frequency compensation command into the inverter's reference operating frequency and output it to the inverter. The frequency converter is used to adjust the speed of the motor according to the frequency compensation command, and drive the ball mill body to run through the transmission device.

Images