A method for controlling torque of a motor in a stall-tolerant system

Abstract

The application discloses a motor torque control method in a stall hysteresis clamp system, comprising: using a motor position control to replace a torque output method to reduce the influence of a clamp transmission mechanism hysteresis characteristic; in view of the high requirement of a brake system on safety, a redundant design is made on a control system, and meanwhile, the control system load needs to be reduced, and the demand of system control resources is reduced; due to the bumping and impact during vehicle operation, the method of the application reduces the use of force sensors during vehicle operation to avoid the influence of the environment; precise control of the final clamping force is realized through motor position control; a proportional-integral (PI) control algorithm is used to realize motor outer loop design; and motor control is realized by using a magnetic field oriented control (FOC) and a space vector pulse width (SVPWM) modulation method.

Description

Technical Field

[0001] This invention relates to rail transit braking systems, and in particular to a method for controlling motor torque in a stall hysteresis system. Background Technology

[0002] Currently, most rail transit systems use pneumatic valves to control pressure, which drives clamps or treads to achieve wheel friction braking. However, with the development of rail transit braking control systems, motors are increasingly used in non-stalled scenarios under load, where stalling is generally treated as an abnormal state. The traditional method of using pneumatic pressure to drive clamps and generate friction for wheel-rail friction braking is increasingly unable to meet the high requirements of intelligent, green, and lightweight rail transit systems. Therefore, electrification alternatives are increasingly appearing in various applications.

[0003] Furthermore, according to the "Research on Optimization of Hysteresis Characteristics of Electromechanical Brake Cylinder Transmission," electromechanical brake cylinders are similar to pneumatic brake cylinders, with the clamp exhibiting hysteresis characteristics in transmission. When designing the control system, it is necessary to reduce the impact of hysteresis characteristics to achieve precise control of the friction pairs in the braking system. As described in article number DOI: 10.3969 / j.issn.1674-957X.2021.18.004, current electromechanical braking systems require external sensors to be integrated into the motor control system, employing relatively complex control algorithms and placing high demands on chip computational response. Since external pressure sensors are easily affected by the operating environment, especially during train operation where the undercarriage environment is harsh, and the impact is significant when the friction pairs come into contact during braking, causing corresponding impacts and oscillations in the force control closed loop, it is necessary to reduce the control system's reliance on external force sensors. Summary of the Invention

[0004] To address the problems existing in the prior art, this invention provides a clamp stall hysteresis system using motor drive control, which achieves precise control of clamping force with less system resource consumption, while reducing the impact of clamp structure hysteresis characteristics on the application of clamping force. Furthermore, the clamp control components (motor, encoder) are concentrated at the rear end of the clamp, resulting in a more compact structural design, and the brake electronic control unit (EBCU) can meet lightweight design requirements.

[0005] The objective of this invention is achieved through the following technical solutions.

[0006] A motor torque control method in a stall hysteresis system includes: a three-loop PI or PID control loop, consisting of a position loop, a speed loop, and a current loop from the outside to the inside; a rotary transformer or encoder to acquire position signals in real time and feed them back to the control system; and precise control of the direction and magnitude of the motor's magnetic field through magnetic field orientation technology and space vector pulse width modulation to achieve high-performance motor drive and torque output, thereby achieving precise output of motor position, speed, and torque.

[0007] This includes: using position as an important parameter for controlling the application of clamping force, establishing a mathematical model of motor position and clamping force, combining position as an important control parameter with the position information collected in real time by the encoder, calculating the actual clamping force that can be applied at the current position, and making dynamic adjustments in combination with braking and release conditions to achieve precise control of clamping force.

[0008] The current loop processes the current into the FOC controller, which includes processes such as coordinate transformation and current-voltage conversion; then the three-phase voltage is input into the motor to generate torque.

[0009] The magnetic field orientation technology converts the input current into voltage through the forward and inverse transformation of coordinates, which then enters the motor. The feedback current of the motor is then fed back to the upper-level PI controller.

[0010] Based on the current position information obtained from the rotary encoder, and distinguished according to the working conditions, during braking, the relationship between the motor position and the clamping force has a linear segment and a non-linear segment. When the clamping force rises from zero, the relationship between the position and the clamping force transitions from the non-linear segment to the linear segment, and then maintains a linear relationship. When the clamping force rises to more than 40KN, a non-linear change occurs again. During release, the clamping force begins to decrease, and the relationship between the position and the clamping force transitions from a linear relationship to a non-linear relationship, which is the opposite of the braking condition.

[0011] The compensation method for hysteresis systems under stall conditions is as follows: When the target clamping force decreases, the torque decreases synchronously, resulting in clamp hysteresis. Torque compensation is used to address the hysteresis problem in the clamping system. When hysteresis occurs, reducing the torque output will result in a smaller final decrease in clamping force. Therefore, real-time compensation is required based on the magnitude of the clamping force decrease. It is necessary to identify the current state of a step-down clamping force, and then determine the amount of compensation for this clamping force decrease based on the step magnitude, the step slope, and the current step slope. Compensation is performed without considering the hysteresis phenomenon, by additionally reducing the torque output, i.e., additionally lowering the target position. The greater the decrease, the smaller the compensation amount; the greater the slope, the smaller the compensation amount.

[0012] When the braking force increases, the clamping force and torque increase proportionally. When the braking force decreases, the ratio of clamping force to torque changes, increasing compared to the rising side. Combining this with the characteristics of the hysteresis system, position control is used for position compensation as described above. During the release condition, the system normally releases to the release position, at which point the clamping force drops to zero. Upon re-braking, position control is applied to increase the output torque.

[0013] An external pressure sensor is used to determine the initial position of the motor clamp, and a force sensor is used to monitor the clamping force.

[0014] The clamping force is controlled by the combined action of a position loop, a speed loop, and a current loop. The braking process is formed by the combination of the current loop, the position loop, and the speed loop; the release process is formed by the combination of the speed loop and the current loop.

[0015] Compared to existing technologies, the advantages of this invention are as follows: Based on the "Research on Optimization of Hysteresis Characteristics of Electromechanical Brake Cylinder Transmission," this invention addresses the hysteresis characteristic of the transmission mechanism that occurs during release. When the input torque is applied, the motor output force does not change linearly, exhibiting hysteresis. This invention's analysis reveals that due to the characteristics of the transmission mechanism, under the same input torque, the motor output force in the release state is greater than that in the braking state. This invention changes the method of input torque by using an input position method to achieve position closed-loop control, thereby reducing the hysteresis characteristic of the transmission mechanism.

[0016] This invention does not employ algorithms requiring more computation, but instead uses the classic PID+FOC motor control method. Since the system is designed to control two motors simultaneously using a single MCU (DSP), the amount of data exchanged is relatively large. Therefore, a simple algorithm is used to fulfill the control requirements while still meeting the overall control specifications.

[0017] The sensor of this invention is only used to locate the zero position of the clamp after the vehicle is powered on. Once the zero position is determined, the sensor is only used for fault monitoring and does not participate in clamping force control. This avoids the value fluctuations of the sensor that occur when the clamp friction pair collides with the wheel during vehicle movement, which would affect the control effect.

[0018] This invention eliminates the use of sensors in the clamping force control process, transforming the clamping force closed-loop control into a motor position closed-loop control. This invention identifies a relationship between the clamping force and the motor position, using position and current control for both braking and releasing processes. It avoids the use of external force sensors for force closed-loop control, reducing the impact of force sensor instability on the overall system control performance. By transforming the clamping force closed-loop relationship into a motor position closed-loop relationship, this invention fixes the closed-loop control to the motor itself. Attached Figure Description

[0019] Figure 1 This is a flowchart of the overall control system.

[0020] Figure 2 Schematic diagram of Field Direction Control (FOC);

[0021] Figure 3 This is a schematic diagram of the motor position and clamping force control model;

[0022] Figure 4 This is a schematic diagram of the hysteresis characteristics of the clamp;

[0023] Figure 5 This is a schematic diagram illustrating how the control method of the present invention reduces the impact of hysteresis characteristics. Detailed Implementation

[0024] The technical solutions of 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.

[0025] This invention provides a torque control method for an electromechanical clamp stall hysteresis system, which achieves precise clamping force control, high response, and saves system resources while reducing the impact of clamping force caused by clamp hysteresis.

[0026] A motor torque control method in a stall hysteresis system includes: a three-loop PI control circuit, consisting of a position loop, a speed loop, and a current loop from the outside to the inside; a rotary transformer (encoder) that collects position signals in real time and feeds them back to the control system; and field orientation technology (FOC) that achieves high-performance motor drive and torque output by precisely controlling the direction and magnitude of the motor's magnetic field, thereby achieving precise output of motor position, speed, and torque.

[0027] This invention uses position as a crucial parameter for controlling clamping force, differing from methods that use current (torque) to control clamping force. It replaces the torque output method similar to pneumatic drive systems, decoupling torque output from clamping force to reduce hysteresis inherent in the clamping structure. A mathematical model of motor position and clamping force is established, using position as a key control parameter combined with real-time encoder-collected position information to calculate the actual clamping force that can be applied at the current position. Dynamic adjustments are made based on braking and release conditions to achieve precise control of the clamping force. As described in the paper "Optimization Research on Hysteresis Characteristics of Electromechanical Brake Cylinder Transmission," clamps exhibit the characteristic that the actual clamping force differs when the clamping force increases and decreases under the same torque output, and also shows inconsistent clamping force for the same torque output. This invention does not employ torque control but instead uses position control, linking the clamping force to the motor's rotation angle, i.e., position. The rise and fall of the target clamping force are identified, and different correlation methods are used for rise and fall, providing corresponding compensation for the control of the decreasing clamping force.

[0028] See Figure 1 The overall structure of the control system includes: an outer control loop, consisting of a position loop, a speed loop, and a current loop from the outside in; the current loop processes the current before it enters the FOC controller, which includes coordinate transformation and current / voltage conversion processes; then the three-phase voltage is input to the motor to generate torque. For example, given a target position, the target current is input to the FOC controller after three-loop control; after processing by the FOC controller, the processed real-time voltage is input to the three phases (UVW) of the motor; then, through the motor and hardware acquisition circuitry, the current and position signals are fed back to the outer current and position loops; thus, the system control loop forms a closed loop, completing one cycle of control. The entire system follows this process of cyclical control, ultimately achieving closed-loop control of the clamping force torque.

[0029] See Figure 2 The embodiments of the present invention utilize field-oriented control (FOC) technology, such as... Figure 2 As shown in the flow diagram, the classic FOC controller converts the input current into voltage through the forward and reverse transformation of the coordinates, which then enters the motor. The feedback current of the motor is then fed back to the upper-level PI controller.

[0030] See Figure 3 This invention discloses a method for controlling clamping force and motor position.

[0031] Based on the current position information obtained from the rotary encoder, and distinguished according to the working conditions, during braking, the relationship between the motor position and clamping force has a linear segment and a non-linear segment. When the clamping force increases from zero, the relationship between position and clamping force transitions from the non-linear segment to the linear segment, and then maintains a linear relationship until the clamping force increases to greater than 40 kN, at which point a non-linear change occurs again. During release, the clamping force begins to decrease, and the relationship between position and clamping force transitions from a linear relationship to a non-linear relationship, which is the opposite of the braking condition.

[0032] See Figure 4 This is a schematic diagram of the hysteresis characteristics of an existing clamping system. Regardless of whether the torque is generated by air pressure, hydraulic pressure or electric motor, there is no hysteresis when the clamping force increases, but there is hysteresis when the clamping force decreases. That is, the input torque decreases, but the clamping force does not decrease synchronously with the decrease of the torque.

[0033] See Figure 5 This invention addresses the handling and compensation method for hysteresis systems under stall conditions. When the target clamping force decreases, the torque decreases simultaneously, causing clamp hysteresis. This invention employs a torque compensation method to handle the hysteresis problem in the clamping system. When hysteresis occurs, reducing the torque output results in a smaller final decrease in clamping force; therefore, real-time compensation is required based on the magnitude of the clamping force decrease. It is necessary to identify the current state of a step-down clamping force decrease, and then determine the amount of compensation for this clamping force decrease based on the magnitude of the decrease, the slope of the decrease, and so on. Compensation is performed without considering hysteresis, additionally reducing the torque output, i.e., additionally lowering the target position. The greater the decrease, the smaller the compensation; the greater the slope of the decrease, the smaller the compensation.

[0034] When the braking force increases, the clamping force and torque increase proportionally. When the braking force decreases, the ratio of clamping force to torque changes, increasing compared to the rising side. This invention, combining the characteristics of a hysteresis system, uses position control for the position compensation described above. In the release condition, the system normally releases to the release position, at which point the clamping force drops to zero. During re-braking, position control is performed to increase the output torque.

[0035] This invention uses a rotating motor to drive a lead screw to lift the clamp, generating and maintaining clamping force. The motor body employs field-oriented control (FOC), and voltage modulation uses space vector pulse width modulation (SVPWM) to achieve precise torque output. Position control is performed using a torque motor in a stalled state. The motor control employs a multi-loop PI (proportional-integral) or PID (proportional-integral-derivative) control system, consisting of a position loop, a speed loop, and a current loop from the outside in. This three-loop, step-by-step control system design ensures continuous, high-efficiency, and high-response motor torque output. To ensure the accuracy of the position loop control, this invention uses a rotary transformer (encoder) as a position signal acquisition tool, collecting position information in real time at a certain frequency. Compared to traditional pneumatic clamping systems, this invention's electromechanical stall hysteresis control system eliminates the need for pneumatic piping on the brake caliper, replacing pneumatic valve control with motor control, reducing system weight, saving undercarriage space, and facilitating overall structural replacement and maintenance.

Claims

1. A method for controlling motor torque in a stalled hysteresis system, characterized in that... include: The three outer loop PI or PID control loops, from the outside in, are the position loop, speed loop, and current loop; the rotary transformer or encoder collects the position signal in real time and feeds it back to the control system; the direction and magnitude of the motor's magnetic field are precisely controlled through magnetic field orientation technology and space vector pulse width modulation method to achieve high-performance motor drive and torque output, and to achieve precise output of motor position, speed and torque.

2. The motor torque control method in a stalled hysteresis system according to claim 1, characterized in that... include: Using position as a crucial parameter for controlling the application of clamping force, a mathematical model of motor position and clamping force is established. By combining position as an important control parameter with the position information collected in real time by the encoder, the clamping force that can be actually applied at the current position is calculated. Dynamic adjustments are then made in conjunction with braking and release conditions to achieve precise control of the clamping force.

3. The motor torque control method in a stalled hysteresis system according to claim 1, characterized in that... The current loop processes the current into the FOC controller, which includes processes such as coordinate transformation and current-voltage conversion; then the three-phase voltage is input into the motor to generate torque.

4. The motor torque control method in a stalled hysteresis system according to claim 1, characterized in that... The magnetic field orientation technology converts the input current into voltage through the forward and inverse transformation of coordinates, which then enters the motor. The feedback current of the motor is then fed back to the upper-level PI controller.

5. The motor torque control method in a stalled hysteresis system according to claim 1, characterized in that... Based on the current position information obtained from the rotary encoder, and distinguished according to the working conditions, during braking, the relationship between the motor position and the clamping force has a linear segment and a non-linear segment. When the clamping force rises from zero, the relationship between the position and the clamping force transitions from the non-linear segment to the linear segment, and then maintains a linear relationship. When the clamping force rises to more than 40KN, a non-linear change occurs again. During release, the clamping force begins to decrease, and the relationship between the position and the clamping force transitions from a linear relationship to a non-linear relationship, which is the opposite of the braking condition.

6. The motor torque control method in a stalled hysteresis system according to claim 1, characterized in that... The compensation method for hysteresis systems under stall conditions is as follows: When the target clamping force decreases, the torque decreases synchronously, resulting in clamp hysteresis. Torque compensation is used to address the hysteresis problem in the clamping system. When hysteresis occurs, reducing the torque output will result in a smaller final decrease in clamping force. Therefore, real-time compensation is required based on the magnitude of the clamping force decrease. It is necessary to identify the current state of a step-down clamping force, and then determine the amount of compensation for this clamping force decrease based on the step magnitude, the step slope, and the current step slope. Compensation is performed without considering the hysteresis phenomenon, by additionally reducing the torque output, i.e., additionally lowering the target position. The greater the decrease, the smaller the compensation amount; the greater the slope, the smaller the compensation amount. When the braking force increases, the clamping force and torque increase proportionally. When the braking force decreases, the ratio of clamping force to torque changes, increasing compared to the rising side. Combining this with the characteristics of the hysteresis system, position control is used for position compensation as described above. During the release condition, the system normally releases to the release position, at which point the clamping force drops to zero. Upon re-braking, position control is applied to increase the output torque.

7. A motor torque control method in a stalled hysteresis system according to claim 1, characterized in that... An external pressure sensor is used to determine the initial position of the motor clamp, and a force sensor is used to monitor the clamping force.

8. A motor torque control method in a stalled hysteresis system according to claim 1, characterized in that... The clamping force is controlled by the combined action of a position loop, a speed loop, and a current loop. The braking process is formed by the combination of the current loop, the position loop, and the speed loop; the release process is formed by the combination of the speed loop and the current loop.

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