A load prediction-based energy-saving control system for a three-phase asynchronous motor

Abstract

The present application relates to motor control and industrial energy saving control field, concretely is a kind of three-phase asynchronous motor energy-saving control system based on load prediction, including operation data acquisition prediction module, kinetic energy conversion module, time sequence control module and vector control execution module;Through time series analysis, the predicted overload occurs time and the predicted load torque value are output, combined with equivalent total moment of inertia, basic steady-state mechanical angular velocity, initial excitation current and kinetic energy injection advance time, the pre-acceleration angular velocity increment and excitation current safety climbing rate are calculated;When light load, maintain weak magnetic standby, before heavy load, execute micro-acceleration and build magnetism, when heavy load impact, freeze speed loop integrator and release mechanical kinetic energy, after speed falls back and build magnetism is completed, dynamic unfreezing is carried out;The present application can reduce iron loss and reactive power loss, reduce inverter instantaneous overcurrent risk and improve the torque deficiency phenomenon under heavy load impact.

Description

Technical Field

[0001] This invention relates to the field of motor control and industrial energy-saving control, specifically to an energy-saving control system for a three-phase asynchronous motor based on load prediction. Background Technology

[0002] In the variable load operation environment of three-phase asynchronous motor, the equipment often faces the periodic alternation of light load and heavy load. In order to reduce the no-load active power loss, the direct shaft excitation current is usually reduced to the initial excitation current of the pre-acquired field weakening standby during the light load stage to implement field weakening energy saving.

[0003] To cope with sudden load increases, existing control schemes often rely on feedback adjustment at the moment of heavy load occurrence to significantly increase the command amplitude and improve torque. Although this scheme has basic torque regulation capabilities, due to the inherent electrical response delay of the asynchronous motor rotor, the magnetic flux cannot be established instantaneously, and the inverter hardware has a physical limitation on the maximum safe peak current. When encountering actual heavy load impact, forcibly and rapidly increasing the current can easily lead to instantaneous overcurrent in the inverter. If magnetic flux establishment is limited, the electromagnetic torque in the initial stage of the impact will be less than the actual load torque requirement, causing the motor speed to drop uncontrollably.

[0004] Therefore, how to coordinate the mechanical angular velocity reserve and the electrical flux recovery rate in advance before the arrival of heavy load, and improve the operational stability under sudden load conditions without increasing the peak current output of the inverter, has become an urgent technical problem to be solved. Summary of the Invention

[0005] The purpose of this invention is to provide an energy-saving control system for a three-phase asynchronous motor based on load prediction, addressing the following technical problem: Existing three-phase asynchronous motor variable load control schemes, when dealing with sudden load increases, rely on feedback adjustment at the moment of heavy load occurrence to significantly increase the command amplitude to boost torque. This results in a response lag defect in avoiding instantaneous overcurrent in the inverter and preventing the initial electromagnetic torque from falling below the actual load torque requirement and speed runaway due to limited flux linkage establishment. There is an urgent need for a load-prediction-based energy-saving control system for a three-phase asynchronous motor that can coordinate the mechanical angular velocity reserve and electrical flux linkage recovery rate in advance before the arrival of heavy load, and improve the operational stability under sudden load conditions without increasing the inverter's peak current output. The purpose of this invention can be achieved through the following technical solutions:

[0006] A load prediction-based energy-saving control system for a three-phase asynchronous motor, the system being connected to a three-phase asynchronous motor, an inverter controlling the three-phase asynchronous motor, and sensors for acquiring actual motor speed, actual quadrature-axis current, and actual direct-axis current, comprising:

[0007] The data acquisition and prediction module is used to analyze historical operating cycle data through time series analysis and output the predicted time of heavy load occurrence and the predicted load torque value.

[0008] The kinetic energy conversion module is used to calculate the pre-acceleration angular velocity increment and the excitation current safe ramp-up rate based on the predicted heavy load occurrence time and predicted load torque value, combined with the pre-stored equivalent total rotational inertia of the three-phase asynchronous motor and its connected load, the preset basic steady-state mechanical angular velocity, the pre-acquired initial excitation current during field weakening standby, and the preset kinetic energy injection advance time.

[0009] The timing control module is used to generate a state switching flag and switch the working state based on the difference between the current time and the predicted time of overload occurrence.

[0010] The vector control execution module includes a speed loop proportional-integral controller and a current loop proportional-integral controller. It is used to maintain the pre-acquired initial excitation current during light load under light load conditions based on the state switching flag. After receiving the pre-acceleration angular velocity increment and the excitation current safe ramp-up rate, it performs kinetic energy injection control. When an actual heavy load impact occurs, it sends a speed loop integrator freeze command to the speed loop proportional-integral controller to generate natural slippage in the rotational speed to release mechanical kinetic energy. The vector control execution module is also used to dynamically release the speed loop integrator freeze command by combining the synchronously acquired actual motor speed and actual direct-axis current and comparing the actual motor speed with the preset basic steady-state mechanical angular velocity.

[0011] Optionally, the kinetic energy conversion module calculates the pre-acceleration angular velocity increment in the following manner:

[0012] Obtain the rotor electrical response delay parameters of the three-phase asynchronous motor, the pre-acquired initial excitation current during field weakening standby, the rated excitation current, and the target excitation current required for the corresponding predicted heavy load;

[0013] Based on the target excitation current, the pre-acquired initial excitation current during field weakening standby, the rated excitation current, and the rotor electrical response delay parameters, the equivalent delay time for magnetization, reflecting the lag in flux linkage establishment, is calculated; and the pre-acceleration angular velocity increment is calculated based on the predicted load torque value, the equivalent delay time for magnetization establishment, and the equivalent total moment of inertia.

[0014] Optionally, the kinetic energy conversion module calculates the safe ramp-up rate of the excitation current in the following manner:

[0015] Obtain the maximum safe peak current allowed by the inverter, and calculate the steady-state predicted value of the quadrature axis current required for the corresponding predicted heavy load based on the predicted load torque value.

[0016] Based on the maximum safe peak current and the steady-state predicted value of the quadrature-axis current, the instantaneously permissible maximum direct-axis current is calculated; based on the instantaneously permissible maximum direct-axis current, the pre-acquired initial excitation current during field weakening standby, and the preset kinetic energy injection advance time, the excitation current safe ramp-up rate is calculated and output to limit the rate of change of the excitation current command.

[0017] Optionally, the kinetic energy conversion module performs boundary verification before outputting the pre-acceleration angular velocity increment, specifically including:

[0018] Obtain the pre-stored maximum rotational speed fluctuation threshold;

[0019] The pre-acceleration limit value is determined based on the maximum rotational speed fluctuation threshold and the preset basic steady-state mechanical angular velocity;

[0020] When the calculated pre-acceleration angular velocity increment is greater than the pre-acceleration limit value, the output pre-acceleration angular velocity increment is limited to the pre-acceleration limit value, and a magnetization action is triggered when the pre-acceleration angular velocity increment reaches the pre-acceleration limit value to compensate for the kinetic energy gap corresponding to the excess portion.

[0021] When the calculated pre-acceleration angular velocity increment is less than or equal to the pre-acceleration limit value, the calculated pre-acceleration angular velocity increment is directly output.

[0022] Optionally, the timing control module divides the system operating state into the following four operating stages:

[0023] Field weakening standby phase: When it is detected that the current operating condition is light load, the vector control execution module is instructed to reduce the direct axis excitation current setpoint to the initial excitation current during the pre-acquired field weakening standby phase;

[0024] Pre-acceleration kinetic energy injection stage: When the remaining time before the predicted heavy load occurs reaches the preset kinetic energy injection advance time, the trigger angular velocity setpoint is superimposed and the excitation current setpoint increases linearly.

[0025] Slip compensation stage: When the speed starts to decrease or the actual cross-axis current changes abruptly within the preset time tolerance window corresponding to the predicted heavy load occurrence time, the speed loop integrator freeze command is issued.

[0026] Steady-state recovery phase: After the rotational speed drops back to the preset basic steady-state mechanical angular velocity and the excitation current completes the rated magnetization, the freeze command of the speed loop integrator is dynamically released.

[0027] Optionally, in the vector control execution module:

[0028] The speed loop proportional-integral controller is used to receive a given value formed by the superposition of the preset basic steady-state mechanical angular velocity and the pre-acceleration angular velocity increment, and output a quadrature-axis current command.

[0029] The current loop proportional-integral controller is used to receive the current direct-axis excitation current setpoint and the quadrature-axis current command, and to adjust the current under the limitation of the excitation current safe ramp-up rate.

[0030] The vector control execution module further includes a setpoint smoothing unit, which is used to linearly adjust the setpoint of the direct-axis excitation current according to the safe ramp-up rate of the excitation current, starting from the pre-acquired initial excitation current during the field weakening standby phase, during the kinetic energy injection phase.

[0031] Optionally, the timing control module has a built-in integrator freeze trigger rule, which specifically includes:

[0032] Continuously monitor whether the current time has entered a preset time tolerance window centered on the predicted time of overload occurrence;

[0033] Within the preset time tolerance window, the time derivative of the actual motor speed is calculated in real time; and the pre-stored negative speed drop rate threshold is obtained.

[0034] The configuration is as follows: if the time derivative of the actual motor speed is less than the pre-stored negative speed drop rate threshold, it is determined that the actual heavy load impact has occurred, and the speed loop integrator freeze command is immediately sent to the speed loop proportional integral controller to suspend the accumulation operation of the speed loop integrator and keep the cumulative value of the integral term unchanged at the moment of freezing, so as to limit the sudden increase of electromagnetic torque command.

[0035] Otherwise, maintain the monitoring status and do not issue the speed loop integrator freeze command.

[0036] Optionally, after performing slip compensation, the vector control execution module performs smooth switching and unfreezing according to the following rules:

[0037] The preset basic steady-state mechanical angular velocity is defined as the target value for speed recovery, and 95% of the rated excitation current of the three-phase asynchronous motor is defined as the magnetization completion judgment value. The 95% is an engineering experience setting value, used to characterize that the magnetic flux has been basically established to be sufficient to bear the electromagnetic torque required for stable heavy load, and to avoid waiting for it to fully approach 100%, which would cause the system response to lag.

[0038] Simultaneously collect actual motor speed and actual direct-axis current;

[0039] The configuration is as follows: if the actual motor speed drops back to the basic steady-state mechanical angular velocity, and the actual direct-axis current reaches the magnetic field establishment completion judgment value, then it is determined that the stored mechanical kinetic energy has been released and the electrical magnetic field has been established. The freeze command of the speed loop integrator is dynamically released, the integral gain of the speed loop proportional-integral controller is restored, and the electromagnetic torque smoothly takes over the entire load.

[0040] Otherwise, maintain the freeze command for the velocity loop integrator.

[0041] Optionally, the vector control execution module adopts a light-load and heavy-load partitioned control strategy, specifically:

[0042] In the light-load operating range, the stator flux linkage of the motor is reduced to the flux linkage ratio corresponding to the initial excitation current during the pre-acquired weak-field standby, so as to reduce energy consumption.

[0043] During the transition period before the arrival of heavy load impact, the rising slope of the excitation current is limited by the safe ramp-up rate of the excitation current to avoid the excitation current from rising suddenly and causing the current to exceed the limit.

[0044] Within the heavy-load operating range, the pre-converted mechanical kinetic energy is used to offset the initial impact of the load, and after the kinetic energy is released, the rated magnetic flux smoothly bears the entire load to prevent insufficient motor torque.

[0045] Optionally, the system includes an offline initialization phase and an online adjustment phase:

[0046] Offline initialization phase: The equivalent total rotational inertia of the three-phase asynchronous motor and its connected load is identified through an no-load acceleration test, and the equivalent total rotational inertia is stored in the system storage unit;

[0047] Online adjustment phase: During system operation, the preset kinetic energy injection advance time is dynamically set based on the real-time calculated equivalent delay time of magnetization, and the preset kinetic energy injection advance time is adjusted to a fixed multiple of the equivalent delay time of magnetization to compensate for the time error of the upstream prediction algorithm.

[0048] Compared with the prior art, the present invention has the following beneficial effects:

[0049] 1. This system uses load prediction to pre-control the motor's micro-acceleration to store mechanical kinetic energy and gradually builds up magnetization according to the safe ramp rate. When a heavy load impact occurs, the system generates natural slip by freezing the speed loop integrator, releasing the stored kinetic energy to offset the initial load impact. This scheme effectively avoids the instantaneous overcurrent of the inverter caused by significantly increasing the command amplitude to increase torque, compensates for the insufficient torque caused by the lag in magnetization, and ensures the stable operation of the motor.

[0050] 2. This system adopts a zoned control strategy. In the light load range, it maintains the initial excitation current of the weak magnetic standby mode, which effectively reduces the no-load active power loss. After the heavy load impact, combined with the actual speed and direct shaft current, the integrator freeze command is dynamically released after the speed drops and the magnetic field is established. This ensures that the restored electromagnetic torque can smoothly take over the entire load, realizing a seamless switch between the weak magnetic energy saving and the heavy load impact resistance state. Attached Figure Description

[0051] To more clearly illustrate the technical solutions in the embodiments of this application and the prior art, the accompanying drawings used in the description of the embodiments and the prior art will be briefly introduced below.

[0052] Figure 1 This is a schematic diagram of the energy-saving control system for a three-phase asynchronous motor based on load prediction according to the present invention. Detailed Implementation

[0053] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0054] like Figure 1 As shown, a load prediction-based energy-saving control system for a three-phase asynchronous motor is disclosed. The system is connected to a three-phase asynchronous motor, an inverter controlling the three-phase asynchronous motor, and sensors that collect actual motor speed, actual quadrature-axis current, and actual direct-axis current. The system includes:

[0055] The data acquisition and prediction module is used to analyze historical operating cycle data through time series analysis and output the predicted time of heavy load occurrence and the predicted load torque value.

[0056] The kinetic energy conversion module is used to calculate the pre-acceleration angular velocity increment and the excitation current safe ramp-up rate based on the predicted heavy load occurrence time and predicted load torque value, combined with the pre-stored equivalent total rotational inertia of the three-phase asynchronous motor and its connected load, the preset basic steady-state mechanical angular velocity, the pre-acquired initial excitation current during field weakening standby, and the preset kinetic energy injection advance time.

[0057] The timing control module is used to generate a state switching flag and switch the working state based on the difference between the current time and the predicted time of overload occurrence.

[0058] The vector control execution module includes a speed loop proportional-integral controller and a current loop proportional-integral controller. Based on the state switching flag, it maintains the pre-acquired initial excitation current during light load weak field standby. After receiving the pre-acceleration angular velocity increment and the excitation current safe ramp-up rate, it performs kinetic energy injection control. When an actual heavy load impact occurs, it sends a speed loop integrator freeze command to the speed loop proportional-integral controller, causing the speed to slip naturally to release mechanical kinetic energy. The vector control execution module also combines synchronously acquired actual motor speed and actual direct-axis current, and dynamically releases the speed loop integrator freeze command by comparing the actual motor speed with the preset basic steady-state mechanical angular velocity.

[0059] The kinetic energy conversion module calculates the pre-acceleration angular velocity increment as follows:

[0060] Obtain the rotor electrical response delay parameters of the three-phase asynchronous motor, the initial excitation current and rated excitation current during field weakening standby, and the target excitation current required for the corresponding predicted heavy load;

[0061] Based on the target excitation current, the pre-acquired initial excitation current during field weakening standby, the rated excitation current, and the rotor electrical response delay parameters, the equivalent delay time for magnetization, reflecting the lag in flux linkage establishment, is calculated; and the pre-acceleration angular velocity increment is calculated based on the predicted load torque value, the equivalent delay time for magnetization establishment, and the equivalent total moment of inertia.

[0062] The kinetic energy conversion module calculates the safe ramp-up rate of the excitation current in the following manner:

[0063] Obtain the maximum safe peak current allowed by the inverter, and calculate the steady-state predicted value of the quadrature axis current required for the corresponding predicted heavy load based on the predicted load torque value.

[0064] Based on the maximum safe peak current and the steady-state prediction of the quadrature axis current, the maximum instantaneous allowable direct axis current is calculated; based on the maximum instantaneous allowable direct axis current, the pre-acquired initial excitation current during field weakening standby, and the preset kinetic energy injection advance time, the safe ramp-up rate of the output excitation current is calculated to limit the rate of change of the excitation current command.

[0065] The kinetic energy conversion module performs boundary checks before outputting the pre-acceleration angular velocity increment, specifically including:

[0066] Obtain the pre-stored maximum rotational speed fluctuation threshold;

[0067] The pre-acceleration limit value is determined based on the maximum speed fluctuation rate threshold and the preset basic steady-state mechanical angular velocity;

[0068] When the calculated pre-acceleration angular velocity increment is greater than the pre-acceleration limit value, the output pre-acceleration angular velocity increment is limited to the pre-acceleration limit value, and the magnetization action is triggered when the pre-acceleration angular velocity increment reaches the pre-acceleration limit value to compensate for the kinetic energy gap corresponding to the part exceeding the limit.

[0069] When the calculated pre-acceleration angular velocity increment is less than or equal to the pre-acceleration limit value, the calculated pre-acceleration angular velocity increment is directly output.

[0070] The system is installed in a three-phase asynchronous motor drive device using vector control. The hardware includes at least an inverter, a speed sensor for detecting the actual speed of the motor, a current sensor for detecting the direct-axis current, and a controller for executing the control program. The controller internally implements a data acquisition and prediction module, a kinetic energy conversion module, a timing control module, and a vector control execution module.

[0071] The predicted heavy load occurrence time refers to the expected moment when the load will change from light load to heavy load in the subsequent operating cycle; the predicted load torque value refers to the expected load torque amplitude corresponding to this heavy load; the basic steady-state mechanical angular velocity refers to the reference angular velocity setpoint that the motor maintains for a long time under the current process conditions; the pre-acquired initial excitation current during weak field standby refers to the lower direct-axis current setpoint maintained under light load standby conditions; the kinetic energy injection advance time refers to the length of time that the system starts micro-acceleration and magnetization in advance before the predicted heavy load arrives;

[0072] Within an operating cycle, the operating data acquisition and prediction module first reads historical operating cycle data from the system storage area. The historical operating cycle data can be a sequence of motor speed changes, a sequence of load torque changes, and a cycle marker formed by the production cycle, which are saved according to the control cycle in multiple pre-set historical cycles. Since the load has periodic variation characteristics, the operating data acquisition and prediction module performs time series analysis on the historical sequence and outputs the predicted heavy load occurrence time and the predicted load torque value in the next cycle. The output results are not directly applied to the inverter, but are first sent to the kinetic energy conversion module and the timing control module as a prerequisite for subsequent control actions.

[0073] After receiving the prediction results, the kinetic energy conversion module first reads the equivalent total rotational inertia, the basic steady-state mechanical angular velocity, the pre-acquired initial excitation current during field weakening standby, and the kinetic energy injection advance time from the controller storage unit. The equivalent total rotational inertia represents the total inertia of the motor rotor and connected load after being converted to the motor shaft side. It directly reflects how much mechanical kinetic energy can be stored corresponding to a unit change in angular velocity. Since this system does not rely on the sudden increase in excitation current at the moment of heavy load arrival to directly compensate for the load torque gap, but first converts a part of the electrical energy into mechanical kinetic energy and stores it in the rotating system, this inertia parameter is the basic quantity for converting the pre-acceleration angular velocity increment.

[0074] In the embodiment, the kinetic energy conversion module further reads the rotor electrical response delay parameters of the three-phase asynchronous motor, the initial excitation current during weak field standby, the rated excitation current, and the target excitation current required for the corresponding predicted heavy load. The rotor electrical response delay parameters are used to reflect the inherent electrical hysteresis of the limited flux linkage establishment speed. These parameters can be obtained through the motor no-load step response test or by referring to the parameters on the motor's manufacturer's nameplate.

[0075] The target excitation current can be determined based on the predicted flux linkage level required for heavy load, preferably set to a value close to the rated excitation current. The kinetic energy conversion module first calculates the difference between the target excitation current and the initial excitation current, then divides this difference by the rated excitation current to obtain a normalized ratio representing the magnetization amplitude. This ratio is multiplied by the rotor electrical response delay parameter to obtain the magnetization equivalent delay time. This magnetization equivalent delay time represents:

[0076] If the system is in a weak magnetic standby state, it needs to go through an inherent electrical setup process to raise the flux linkage level from the current level to the level required to cope with the predicted heavy load. After that, the kinetic energy conversion module divides the product of the predicted load torque value and the equivalent delay time of magnetic setup by the equivalent total moment of inertia to obtain the pre-acceleration angular velocity increment. The pre-acceleration angular velocity increment obtained in this way is used to convert the load torque gap that may occur during the period when magnetic setup is not yet completed into a mechanical angular velocity margin that needs to be reserved in advance.

[0077] The kinetic energy conversion module also needs to calculate the safe ramp-up rate of the excitation current. In practice, the controller first reads the maximum safe peak current allowed by the inverter. This value comes from the inverter's hardware allowable range and is the upper limit that the current setpoint cannot exceed. Based on the predicted load torque value and the motor torque conversion relationship, the controller obtains the steady-state predicted value of the quadrature axis current required to cope with the predicted heavy load. The kinetic energy conversion module calculates the difference between the square of the maximum safe peak current and the square of the steady-state predicted value of the quadrature axis current, and takes the square root of the difference to obtain the maximum instantaneous allowable direct axis current under the expected heavy load conditions.

[0078] Then, the difference between the maximum direct-axis current and the initial excitation current during the field weakening standby is divided by the preset kinetic energy injection advance time to output the excitation current safe ramp-up rate. After this processing, the direct-axis excitation current will not reach the inverter current output limit due to rising too fast during the advance magnetization stage, thus reserving the necessary margin for the quadrature-axis torque current.

[0079] The kinetic energy conversion module performs boundary checks before outputting the pre-acceleration angular velocity increment; specifically, the controller pre-stores a maximum speed fluctuation rate threshold to limit the impact of the micro-acceleration process on the equipment's operating cycle time; this threshold is preferably a proportion of the speed fluctuation allowed by the process, which can usually be selected in the range of 1.5% to 2%;

[0080] The kinetic energy conversion module multiplies the maximum speed fluctuation rate threshold with the basic steady-state mechanical angular velocity to obtain the pre-acceleration limit value. If the pre-acceleration angular velocity increment calculated by the aforementioned formula is greater than the limit value, it indicates that relying solely on speed-up energy storage will cause speed fluctuations to exceed the acceptable range. In this case, the kinetic energy conversion module will limit the final output to the pre-acceleration limit value, and the timing control module will trigger the magnetization action in advance so that the earlier start of the excitation current rise can compensate for the insufficient kinetic energy caused by the limit. If the calculated pre-acceleration angular velocity increment is not greater than the limit value, the calculated value will be output directly. In this way, the system ensures that the energy storage action has sufficient compensation capability while avoiding excessive pre-acceleration from affecting normal operating conditions.

[0081] In a specific configuration example, the preset base steady-state mechanical angular velocity is set to... The equivalent total moment of inertia of the system obtained through offline identification is When the data acquisition and prediction module outputs the predicted load torque value If the equivalent delay time for magnetization is calculated to be... The kinetic energy conversion module calculates and predicts the load torque. Equivalent delay time of magnetization The product of these two factors yields the torque impulse that needs to be pre-stored through mechanical kinetic energy, i.e. ;

[0082] Divide this value by the equivalent total moment of inertia The pre-acceleration angular velocity increment is obtained as Regarding current distribution, it is assumed that the maximum safe peak current allowed by the inverter is... The steady-state prediction value of the quadrature-axis current required to cope with the aforementioned predicted heavy load is... The kinetic energy conversion module calculates the maximum allowable direct-axis current instantaneously through the current vector relationship, that is, for The square of and Taking the square root of the difference of squares yields... ;

[0083] If the initial excitation current during the current pre-acquired field weakening standby is 20A, and the system-set or dynamically adjusted kinetic energy injection advance time is 0.5s, then the calculated excitation current safe ramp-up rate is ( ) / = This quantization calculation example verifies the conversion logic of the algorithm and verifies the distribution relationship between the mechanical angular velocity margin and the electrical flux recovery rate of the system under the inverter hardware constraints.

[0084] After all the above parameters are calculated, the timing control module generates a state switching flag based on the difference between the current time and the predicted heavy load occurrence time. During the light load phase, the timing control module outputs a field weakening standby flag, and the vector control execution module maintains the direct-axis excitation current setpoint at the initial excitation current and keeps the speed loop setpoint at the basic steady-state mechanical angular velocity. As the operation progresses, when the remaining time reaches the kinetic energy injection advance time, the timing control module switches to the kinetic energy injection state and issues a new state flag to the vector control execution module.

[0085] When triggered by this flag, the vector control execution module adds the pre-acceleration angular velocity increment to the basic steady-state mechanical angular velocity to form an updated speed loop setpoint. At the same time, it smoothly increases the direct-axis excitation current setpoint according to the aforementioned excitation current safe ramp-up rate. In this way, the motor undergoes controlled small-amplitude acceleration, converting additional electrical energy into mechanical kinetic energy and storing it in the rotor and load inertia. On the other hand, the flux linkage level begins to gradually recover, creating conditions for subsequent heavy-load takeover.

[0086] When the actual heavy load impact begins to occur, the system does not increase the torque by continuously accumulating the integral term of the speed loop to significantly increase the command amplitude. Instead, it uses the timing control module to issue a speed loop integrator freeze command. After freezing, the speed loop proportional-integral controller keeps the current integral accumulation value unchanged and only allows a limited proportional action to participate in the output, thereby avoiding excessive quadrature-axis current commands before the magnetic flux is fully established.

[0087] At this point, the motor speed will drop from the level after slight acceleration back to the basic steady-state mechanical angular velocity. The mechanical kinetic energy released during the drop is used to fill the energy demand in the initial stage of the load surge. After the actual motor speed continuously collected by the sensor drops back to the basic steady-state mechanical angular velocity, and the actual quadrature-axis current indicates that the magnetization has been basically completed, the vector control execution module releases the speed loop integrator freeze command and restores the speed loop integral function, so that the electromagnetic torque can smoothly bear the entire load. This achieves the sequential coordination between light load low flux energy saving, slow magnetization before heavy load, release of mechanical kinetic energy in the initial stage of impact, and smooth takeover of the electromagnetic torque in the subsequent stage.

[0088] Using the above implementation method, under light load conditions, the motor is in the initial excitation current state, and iron loss and reactive power loss are reduced accordingly. Before predicting heavy load, the system prepares in advance through limited micro-acceleration and limited excitation current ramp-up. Therefore, when heavy load arrives, the risk of instantaneous overcurrent of the inverter can be reduced, and the torque deficiency caused by the lag in flux establishment can be reduced.

[0089] In this embodiment, the timing control module divides the system's operating state into the following four operating stages:

[0090] Field weakening standby phase: When it is detected that the current operating condition is light load, the vector control execution module is instructed to reduce the direct axis excitation current setpoint to the pre-acquired initial excitation current during field weakening standby.

[0091] Pre-acceleration kinetic energy injection stage: When the remaining time before the predicted heavy load occurs reaches the preset kinetic energy injection advance time, the trigger angular velocity setpoint is superimposed and the excitation current setpoint increases linearly.

[0092] Slip compensation phase: When the speed starts to decrease or the actual cross-axis current suddenly changes within the preset time tolerance window corresponding to the predicted heavy load occurrence time, a speed loop integrator freeze command is issued.

[0093] Steady-state recovery phase: After the speed drops back to the preset basic steady-state mechanical angular velocity and the excitation current completes the rated magnetization, the freeze command of the speed loop integrator is dynamically released.

[0094] In the vector control execution module:

[0095] The speed loop proportional-integral controller is used to receive a setpoint formed by the superposition of the preset base steady-state mechanical angular velocity and the pre-acceleration angular velocity increment, and output the quadrature-axis current command;

[0096] The current loop proportional-integral controller is used to receive the current direct-axis excitation current setpoint and quadrature-axis current command, and to regulate the current under the limit of the excitation current safe ramp-up rate.

[0097] The vector control execution module also includes a setpoint smoothing unit, which is used to linearly adjust the setpoint of the direct-axis excitation current according to the safe ramp-up rate of the excitation current, starting from the initial excitation current during the field weakening standby, during the kinetic energy injection phase.

[0098] The timing control module has built-in integrator freeze trigger rules, which specifically include:

[0099] Continuously monitor whether the current time has entered the preset time tolerance window centered on the predicted time of heavy load occurrence;

[0100] Within a preset time tolerance window, the time derivative of the actual motor speed is calculated in real time; and the pre-stored negative speed drop rate threshold is obtained.

[0101] The configuration is as follows: if the time derivative of the actual motor speed is less than the pre-stored negative speed drop rate threshold, it is determined that the actual heavy load impact has occurred, and a speed loop integrator freeze command is immediately sent to the speed loop proportional integral controller to suspend the accumulation operation of the speed loop integrator and keep the cumulative value of the integral term unchanged at the moment of freeze, so as to limit the sudden increase of electromagnetic torque command.

[0102] Otherwise, maintain the monitoring status and do not issue a speed loop integrator freeze command.

[0103] After performing slip compensation, the vector control execution module performs smooth switching and unfreezing according to the following rules:

[0104] The preset basic steady-state mechanical angular velocity is defined as the target value for speed recovery, and 95% of the rated excitation current of the three-phase asynchronous motor is defined as the judgment value for magnetization completion. 95% is an engineering experience setting value, used to characterize that the magnetic flux has been basically established to be sufficient to bear the electromagnetic torque required for stable heavy load, and to avoid waiting for it to fully approach 100%, which would cause the system response to lag.

[0105] Simultaneously collect actual motor speed and actual direct-axis current;

[0106] The configuration is as follows: if the actual motor speed drops back to the basic steady-state mechanical angular velocity and the actual direct shaft current reaches the magnetic field establishment completion judgment value, then it is determined that the stored mechanical kinetic energy has been released and the electrical magnetic field has been established. The speed loop integrator freeze command is dynamically released, the integral gain of the speed loop proportional-integral controller is restored, and the electromagnetic torque smoothly takes over the entire load.

[0107] Otherwise, maintain the speed loop integrator freeze command.

[0108] This implementation further explains the system's operating sequence and the changes in signals within the controller. The timing control module divides a complete operating cycle into four stages: the field weakening standby stage, the pre-acceleration kinetic energy injection stage, the slip compensation stage, and the steady-state recovery stage. In the field weakening standby stage, the prerequisite is that the operating data acquisition and prediction module has not yet given a heavy load warning, or although a prediction result has been given, the current time before the predicted heavy load occurrence time is still greater than the kinetic energy injection advance time, and the operating condition is still in the light load range. At this time, the timing control module outputs a field weakening standby flag, and the setpoint smoothing unit in the vector control execution module gradually reduces the direct-axis excitation current setpoint to the initial excitation current, eventually maintaining it near that value.

[0109] Simultaneously, the speed loop proportional-integral controller maintains the basic steady-state mechanical angular velocity at the setpoint, while the current loop proportional-integral controller outputs a normal quadrature-axis current command according to the current speed error and controls the direct-axis current at the field-weak standby level. Since the flux linkage is low at this time, the motor mainly maintains light-load operation with basic iron loss and basic reactive power consumption.

[0110] When the timing control module determines that the remaining time has reached the kinetic energy injection advance time based on the difference between the current time and the predicted heavy load occurrence time, the system enters the pre-acceleration kinetic energy injection phase; reaching means that within the control cycle, the remaining time changes from being greater than the advance time to being no greater than the advance time.

[0111] Once the judgment is valid, the timing control module switches the status flag and simultaneously activates two types of actions: First, the angular velocity setpoint is superimposed, that is, the basic steady-state mechanical angular velocity is added to the pre-acceleration angular velocity increment output by the aforementioned kinetic energy conversion module to form a new velocity loop setpoint; Second, the excitation current setpoint is linearly increased, that is, the setpoint smoothing unit increases the direct-axis excitation current setpoint in cycles according to the excitation current safe ramp-up rate, starting from the initial excitation current.

[0112] During this phase, after receiving the new angular velocity setpoint, the speed loop proportional-integral controller calculates the quadrature-axis current command based on the speed error. Since the setpoint is higher than the basic steady-state mechanical angular velocity, the motor will produce a limited acceleration process, and the actual angular velocities of the rotor and the connected load will increase accordingly, thereby increasing the kinetic energy stored in the mechanical system.

[0113] Synchronously, the current loop proportional-integral controller receives the direct-axis excitation current setpoint and the quadrature-axis current command, and adjusts the inverter output under the limit of the excitation current safe ramp-up rate, so that the direct-axis current gradually increases and the quadrature-axis current is distributed according to the speed loop requirements. Since the growth rate of the direct-axis current is limited, even if the quadrature-axis current increases to achieve micro-acceleration, the total inverter current can still be kept within the allowable range.

[0114] During the slip compensation phase, the system no longer simply determines that a heavy load has arrived based on the predicted time point, but instead combines the time tolerance window and the actual measured quantity to make the judgment. The time tolerance window is a range of allowable errors set around the predicted time of heavy load occurrence, used to absorb the deviation between the prediction result and the actual arrival of heavy load. Within this window, the timing control module continuously monitors the changes in the actual motor speed and the quadrature axis component of the stator current. If the speed starts to decrease, or the quadrature axis component shows a sudden change that exceeds the set current fluctuation threshold, it indicates that the sudden increase in load has begun to act on the motor shaft system. At this time, it is necessary to avoid the speed loop integral term from continuing to accumulate and driving the quadrature axis current command to rise rapidly.

[0115] More specifically, the integrator freeze triggering rule in the embodiment can be implemented by the controller according to discrete control cycles. In each cycle, the controller reads the current speed sample value and the speed sample value of the previous cycle. To avoid the high-frequency sampling noise being amplified by differential calculation within a very short control cycle, which could lead to incorrect system state switching, the controller performs first-order low-pass filtering or moving average smoothing on the speed sampling sequence in actual operation. The difference between the smoothed current and previous cycle speed sample values ​​is divided by the control cycle to obtain the time derivative of the actual motor speed that accurately reflects the true mechanical dynamics of the system. When the time derivative is less than the pre-stored negative speed drop rate threshold, it indicates that the speed drop has reached a level that can be judged as a heavy load impact.

[0116] The negative speed drop rate threshold is a negative value, which can be set by combining the inertia of the driven equipment and the allowable speed fluctuation test, as long as it can distinguish between the noise disturbance of the conventional system and the impact of the actual load. Once this condition is met, the timing control module immediately sends a speed loop integrator freeze command to the speed loop proportional-integral controller, setting the integral term gain to zero and keeping the cumulative value of the integral term unchanged at the moment of freeze. In this way, the speed loop output no longer rises continuously due to the continuous accumulation of speed error, and the quadrature-axis current command is limited to a range that does not exceed the preset safety limit. If the above conditions are not met, the timing control module continues to maintain the monitoring state without triggering the freeze.

[0117] After entering the frozen state, the motor is allowed to exhibit natural slip under heavy load, meaning that the actual speed drops from the level increased during the injection phase back to the basic steady-state mechanical angular velocity. This drop process is actively controlled by the system to release mechanical kinetic energy. Because the mechanical system has already stored additional kinetic energy through micro-acceleration before this, this kinetic energy can be converted into the mechanical output required by the load during the speed drop, bearing part of the impact load before magnetization is completed. Simultaneously, the direct-axis excitation current continues to rise according to the predetermined safe creep rate, and the motor flux linkage gradually recovers to near the rated value.

[0118] During the steady-state recovery phase, the vector control execution module performs smooth switching and unfreezing according to the rules of the implementation example. Specifically, the controller uses the basic steady-state mechanical angular velocity as the target value for speed recovery, and 95% of the rated excitation current as the magnetization completion judgment value. This percentage is used to indicate that the flux linkage is close to the rated state and is sufficient to bear the electromagnetic torque required for stable heavy load. The controller synchronously collects the actual motor speed and the actual quadrature shaft current in each control cycle. When it is detected that the actual motor speed has fallen back to the basic steady-state mechanical angular velocity and the actual quadrature shaft current has reached the aforementioned magnetization completion judgment value, it indicates that the previously stored mechanical kinetic energy has been basically released and the electrical magnetization process has been basically completed.

[0119] At this time, the vector control execution module dynamically releases the freeze command of the speed loop integrator, restores the integral gain of the speed loop proportional-integral controller, and allows the integral term to participate in the regulation again. Since the release action occurs after the flux linkage has been restored and the speed has returned to the reference value, the electromagnetic torque can smoothly take over the entire load without sudden torque changes before and after the freeze. If the above two conditions are not met at the same time, the freeze state remains unchanged.

[0120] In this embodiment, the setpoint smoothing unit performs linear reconstruction of the direct-axis excitation current setpoint during the kinetic energy injection stage without changing the current loop structure, so that the change from the initial excitation current to the target excitation current proceeds gradually along the restricted slope; this can avoid the total current impact caused by step-up raising of the excitation current setpoint, and also facilitates the timing control module to arrange pre-acceleration and magnetization in the same advance interval.

[0121] After adopting the above four-stage operation mode, the sequence of actions of the system within one operating cycle is clear: first, it enters the weak magnetic standby state, then it slightly increases the speed to store energy and simultaneously builds magnetism slowly; when a heavy load actually occurs, the speed loop integral term is frozen and the speed is allowed to drop to release kinetic energy; after the magnetism is built up, the normal speed loop regulation is restored; the state transition between each stage is triggered by both actual physical quantities and predicted quantities, so it can improve the operating stability under sudden load conditions without increasing the inverter peak current;

[0122] In this embodiment, the vector control execution module adopts a light-load and heavy-load partitioned control strategy, specifically as follows:

[0123] In the light-load operating range, the stator flux linkage of the motor is reduced to the flux linkage ratio corresponding to the initial excitation current during the weak field standby, in order to reduce the no-load active power loss on the stator side.

[0124] During the transition range before the arrival of heavy load impact, the rising slope of the excitation current is limited by the safe ramp-up rate of the excitation current to avoid the excitation current from rising suddenly and causing the current to exceed the limit.

[0125] Within the heavy-load operating range, the pre-converted mechanical kinetic energy is used to offset the initial impact of the load, and after the kinetic energy is released, the rated magnetic flux smoothly bears the entire load to prevent insufficient motor torque.

[0126] The system includes an offline initialization phase and an online adjustment phase:

[0127] Offline initialization phase: The equivalent total rotational inertia of the three-phase asynchronous motor and its connected load is identified through no-load acceleration test, and the equivalent total rotational inertia is stored in the system storage unit;

[0128] Online adjustment phase: During system operation, the preset kinetic energy injection advance time is dynamically set based on the real-time calculated equivalent delay time of magnetization, and the preset kinetic energy injection advance time is adjusted to a fixed multiple of the equivalent delay time of magnetization to compensate for the time error of the upstream prediction algorithm.

[0129] This implementation describes the light-load and heavy-load zone control strategy, as well as the setting method of equivalent total rotational inertia and kinetic energy injection advance time. The zone control strategy does not simply divide the working conditions into two states: light-load and heavy-load. Instead, it dynamically adjusts the control target according to the changes in the working conditions, so that the motor adopts different flux linkages and energy distribution methods in different load ranges.

[0130] Within the light-load operating range, the prerequisite is that the load prediction results indicate that there is no heavy load requiring immediate response in the short term, and the actual operating state meets the light-load judgment. At this time, the vector control execution module lowers the motor stator flux linkage to the flux linkage ratio corresponding to the initial excitation current during the field weakening standby. Since the excitation current of the asynchronous motor is directly related to the stator flux linkage, after the direct-axis excitation current drops to the preset initial excitation current setpoint, the stator flux linkage decreases synchronously, and iron loss and reactive power loss also decrease accordingly. Here, the flux linkage ratio can be determined according to the minimum requirement of the equipment for transient torque reserve. It is preferable to use the operating point of the preset lower limit ratio of the rated flux linkage to ensure the ability to quickly recover the required torque response while reducing losses.

[0131] During the transition period before the arrival of heavy load impact, the prerequisite is that the timing control module has determined that the kinetic energy injection advance interval has been entered. The technical issues that need to be balanced in this stage are: if the excitation current rises too quickly, the total inverter current may approach the upper limit after the superposition of the direct axis component and the quadrature axis component; if the excitation current rises too slowly, the flux linkage recovery will be insufficient when the actual heavy load arrives. Therefore, the vector control execution module uses the safe ramp-up rate of the excitation current to limit the rise slope of the excitation current.

[0132] In each control cycle, the controller calculates the new direct-axis excitation current setpoint for the current cycle based on the direct-axis excitation current setpoint of the previous cycle and the current allowable slope, and sends it to the current loop proportional-integral controller. After this processing, the excitation current rises linearly or approximately linearly throughout the entire transition range, rather than experiencing a sudden increase, thereby avoiding current over-limit.

[0133] If an actual heavy load impact has occurred within the heavy load operating range, the system first uses the pre-converted mechanical kinetic energy to offset the initial impact of the load. The pre-converted mechanical kinetic energy refers to the additional kinetic energy stored in the rotating component in the previous stage by increasing the speed loop by a pre-acceleration angular velocity increment.

[0134] When a heavy load is first applied, this mechanical kinetic energy is released to reduce the motor's dependence on instantaneous electromagnetic torque. After the speed drops, the kinetic energy release ends, and the magnetization reaches near the rated value, the vector control execution module then smoothly undertakes the entire load with the rated flux linkage. In this way, the motor will not experience a significant torque gap due to insufficient flux linkage at the moment the heavy load begins, nor will the inverter current be overloaded due to the rapid rise of the excitation current.

[0135] Regarding the offline initialization phase of the embodiment, the controller obtains the equivalent total moment of inertia during the initial system tuning in conjunction with an no-load acceleration test. The specific implementation steps are as follows: the motor is run under near-no-load conditions in a predetermined acceleration mode, the speed change is collected by the speed sensor, and the moment of inertia is calculated in combination with the known driving torque conditions. Here, near-no-load conditions refer to the motor being physically connected to the on-site mechanical transmission components and working mechanism, such as a conveyor belt without processed materials or an idle mixing device, but the equipment body is not in a state of heavy load resistance with materials.

[0136] Under these conditions, the controller outputs a specified test drive torque command, accelerating the motor and all idling mechanical transmission components as a whole, and extracts the ratio between the electromagnetic torque increment and the rate of change of angular velocity collected at this time. Since the identified object includes not only the motor rotor body, but also the transmission components connected to the motor shaft and the load-converted inertia, the final result is the equivalent total moment of inertia. After identification, this value is written to the system storage unit for direct use by the kinetic energy conversion module in subsequent operation. Inertia identification does not need to be repeated during online control, thereby reducing the control calculation burden and ensuring that the calculation of the pre-acceleration angular velocity increment has a fixed basis.

[0137] During the online adjustment phase, the system does not set the kinetic energy injection advance time to a fixed value, but dynamically sets it based on the magnetic equivalent delay time calculated in real time. Specifically, the kinetic energy conversion module calculates the magnetic equivalent delay time according to the aforementioned rules each time it receives new prediction overload information.

[0138] The controller adjusts the kinetic energy injection advance time to a fixed multiple of the magnetization equivalent delay time; this fixed multiple is used to provide a margin for prediction error compensation, preferably a ratio greater than 1; in this way, if there is a time error in the upstream prediction result, the system can still ensure that the excitation current rises and the micro-acceleration energy storage action starts earlier by using an appropriately amplified advance time, thereby reducing the impact of the upstream prediction algorithm time error on the system's heavy load impact suppression performance.

[0139] In a typical operating cycle, the offline initialization phase provides the basic parameter of equivalent total rotational inertia; the online adjustment phase then recalculates the equivalent delay time of magnetization based on each predicted load condition and generates the corresponding kinetic energy injection advance time; the light load and heavy load zone control strategies take effect in sequence: under light load, the flux linkage is reduced to save energy; in the transition interval, excitation is restored at a safe slope and a slight speed increase is performed; when the heavy load arrives, the previously stored mechanical kinetic energy is released, and the restored rated flux linkage bears the entire load;

[0140] Therefore, the system can integrate the requirements for light-load steady-state control and heavy-load shock resistance within the same control framework, and always limit the processing objects to objective physical quantities such as motor speed, load torque, current and flux linkage.

[0141] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. An energy-saving control system for a three-phase asynchronous motor based on load prediction, characterized in that, The system is connected to a three-phase asynchronous motor, an inverter that controls the three-phase asynchronous motor, and sensors that collect actual motor speed, actual quadrature-axis current, and actual direct-axis current, and includes: The data acquisition and prediction module is used to analyze historical operating cycle data through time series analysis and output the predicted time of heavy load occurrence and the predicted load torque value. The kinetic energy conversion module is used to calculate the pre-acceleration angular velocity increment and the excitation current safe ramp-up rate based on the predicted heavy load occurrence time and predicted load torque value, combined with the pre-stored equivalent total rotational inertia of the three-phase asynchronous motor and its connected load, the preset basic steady-state mechanical angular velocity, the pre-acquired initial excitation current during field weakening standby, and the preset kinetic energy injection advance time. The timing control module is used to generate a state switching flag and switch the working state based on the difference between the current time and the predicted time of overload occurrence. The vector control execution module includes a speed loop proportional-integral controller and a current loop proportional-integral controller. It is used to maintain the pre-acquired initial excitation current during light load under light load conditions based on the state switching flag. After receiving the pre-acceleration angular velocity increment and the excitation current safe ramp-up rate, it performs kinetic energy injection control. When an actual heavy load impact occurs, it sends a speed loop integrator freeze command to the speed loop proportional-integral controller to generate natural slippage in the rotational speed to release mechanical kinetic energy. The vector control execution module is also used to dynamically release the speed loop integrator freeze command by combining the synchronously acquired actual motor speed and actual direct-axis current and comparing the actual motor speed with the preset basic steady-state mechanical angular velocity.

2. The energy-saving control system for a three-phase asynchronous motor based on load prediction according to claim 1, characterized in that, The kinetic energy conversion module calculates the pre-acceleration angular velocity increment in the following manner: Obtain the rotor electrical response delay parameters of the three-phase asynchronous motor, the pre-acquired initial excitation current during field weakening standby, the rated excitation current, and the target excitation current required for the corresponding predicted heavy load; Based on the target excitation current, the pre-acquired initial excitation current during field weakening standby, the rated excitation current, and the rotor electrical response delay parameters, the equivalent delay time for magnetization, reflecting the lag in flux linkage establishment, is calculated; and the pre-acceleration angular velocity increment is calculated based on the predicted load torque value, the equivalent delay time for magnetization establishment, and the equivalent total moment of inertia.

3. The energy-saving control system for a three-phase asynchronous motor based on load prediction according to claim 1, characterized in that, The kinetic energy conversion module calculates the safe ramp-up rate of the excitation current in the following manner: Obtain the maximum safe peak current allowed by the inverter, and calculate the steady-state predicted value of the quadrature axis current required for the corresponding predicted heavy load based on the predicted load torque value. Based on the maximum safe peak current and the steady-state predicted value of the quadrature-axis current, the instantaneously permissible maximum direct-axis current is calculated; based on the instantaneously permissible maximum direct-axis current, the pre-acquired initial excitation current during field weakening standby, and the preset kinetic energy injection advance time, the excitation current safe ramp-up rate is calculated and output to limit the rate of change of the excitation current command.

4. The energy-saving control system for a three-phase asynchronous motor based on load prediction according to claim 2, characterized in that, The kinetic energy conversion module performs boundary checks before outputting the pre-acceleration angular velocity increment, specifically including: Obtain the pre-stored maximum rotational speed fluctuation threshold; The pre-acceleration limit value is determined based on the maximum rotational speed fluctuation threshold and the preset basic steady-state mechanical angular velocity; When the calculated pre-acceleration angular velocity increment is greater than the pre-acceleration limit value, the output pre-acceleration angular velocity increment is limited to the pre-acceleration limit value, and a magnetization action is triggered when the pre-acceleration angular velocity increment reaches the pre-acceleration limit value to compensate for the kinetic energy gap corresponding to the excess portion. When the calculated pre-acceleration angular velocity increment is less than or equal to the pre-acceleration limit value, the calculated pre-acceleration angular velocity increment is directly output.

5. The energy-saving control system for a three-phase asynchronous motor based on load prediction according to claim 1, characterized in that, The timing control module divides the system's operating state into the following four operating stages: Field weakening standby phase: When it is detected that the current operating condition is light load, the vector control execution module is instructed to reduce the direct axis excitation current setpoint to the initial excitation current during the pre-acquired field weakening standby phase; Pre-acceleration kinetic energy injection stage: When the remaining time before the predicted heavy load occurs reaches the preset kinetic energy injection advance time, the trigger angular velocity setpoint is superimposed and the excitation current setpoint increases linearly. Slip compensation stage: When the speed starts to decrease or the actual cross-axis current changes abruptly within the preset time tolerance window corresponding to the predicted heavy load occurrence time, the speed loop integrator freeze command is issued. Steady-state recovery phase: After the rotational speed drops back to the preset basic steady-state mechanical angular velocity and the excitation current completes the rated magnetization, the freeze command of the speed loop integrator is dynamically released.

6. The energy-saving control system for a three-phase asynchronous motor based on load prediction according to claim 1, characterized in that, In the vector control execution module: The speed loop proportional-integral controller is used to receive a given value formed by the superposition of the preset basic steady-state mechanical angular velocity and the pre-acceleration angular velocity increment, and output a quadrature-axis current command. The current loop proportional-integral controller is used to receive the current direct-axis excitation current setpoint and the quadrature-axis current command, and to adjust the current under the limitation of the excitation current safe ramp-up rate. The vector control execution module further includes a setpoint smoothing unit, which is used to linearly adjust the setpoint of the direct-axis excitation current according to the safe ramp-up rate of the excitation current, starting from the pre-acquired initial excitation current during the field weakening standby phase, during the kinetic energy injection phase.

7. The energy-saving control system for a three-phase asynchronous motor based on load prediction according to claim 5, characterized in that, The timing control module has a built-in integrator freeze trigger rule, which specifically includes: Continuously monitor whether the current time has entered a preset time tolerance window centered on the predicted time of overload occurrence; Within the preset time tolerance window, the time derivative of the actual motor speed is calculated in real time; and the pre-stored negative speed drop rate threshold is obtained. The configuration is as follows: if the time derivative of the actual motor speed is less than the pre-stored negative speed drop rate threshold, it is determined that the actual heavy load impact has occurred, and the speed loop integrator freeze command is immediately sent to the speed loop proportional integral controller to suspend the accumulation operation of the speed loop integrator and keep the cumulative value of the integral term unchanged at the moment of freezing, so as to limit the sudden increase of electromagnetic torque command. Otherwise, maintain the monitoring status and do not issue the speed loop integrator freeze command.

8. The energy-saving control system for a three-phase asynchronous motor based on load prediction according to claim 7, characterized in that, After performing slip compensation, the vector control execution module performs smooth switching and unfreezing according to the following rules: The preset basic steady-state mechanical angular velocity is defined as the target value for speed recovery, and 95% of the rated excitation current of the three-phase asynchronous motor is defined as the magnetization completion judgment value. The 95% is an engineering experience setting value, used to characterize that the magnetic flux has been basically established to be sufficient to bear the electromagnetic torque required for stable heavy load, and to avoid waiting for it to fully approach 100%, which would cause the system response to lag. Simultaneously collect actual motor speed and actual direct-axis current; The configuration is as follows: if the actual motor speed drops back to the basic steady-state mechanical angular velocity, and the actual direct-axis current reaches the magnetic field establishment completion judgment value, then it is determined that the stored mechanical kinetic energy has been released and the electrical magnetic field has been established. The freeze command of the speed loop integrator is dynamically released, the integral gain of the speed loop proportional-integral controller is restored, and the electromagnetic torque smoothly takes over the entire load. Otherwise, maintain the freeze command for the velocity loop integrator.

9. The energy-saving control system for a three-phase asynchronous motor based on load prediction according to claim 1, characterized in that, The vector control execution module adopts a light-load and heavy-load partitioned control strategy, specifically: In the light-load operating range, the stator flux linkage of the motor is reduced to the flux linkage ratio corresponding to the initial excitation current during the pre-acquired weak-field standby, so as to reduce energy consumption. During the transition period before the arrival of heavy load impact, the rising slope of the excitation current is limited by the safe ramp-up rate of the excitation current to avoid the excitation current from rising suddenly and causing the current to exceed the limit. Within the heavy-load operating range, the pre-converted mechanical kinetic energy is used to offset the initial impact of the load, and after the kinetic energy is released, the rated magnetic flux smoothly bears the entire load to prevent insufficient motor torque.

10. A three-phase asynchronous motor energy-saving control system based on load prediction according to claim 2, characterized in that, The system includes an offline initialization phase and an online adjustment phase: Offline initialization phase: The equivalent total rotational inertia of the three-phase asynchronous motor and its connected load is identified through an no-load acceleration test, and the equivalent total rotational inertia is stored in the system storage unit; Online adjustment phase: During system operation, the preset kinetic energy injection advance time is dynamically set based on the real-time calculated equivalent delay time of magnetization, and the preset kinetic energy injection advance time is adjusted to a fixed multiple of the equivalent delay time of magnetization to compensate for the time error of the upstream prediction algorithm.

Images