Motor steady state holding control method and system for a steer-by-wire system

Abstract

The application discloses a motor steady-state holding control method and system of a steer-by-wire system, and the method comprises the following steps: collecting rotor position, mechanical angular velocity and target position instruction during the position closed-loop control of the permanent magnet synchronous motor, calculating position error and instruction change rate, calculating position threshold value, speed threshold value and change rate threshold value according to position sensor noise standard deviation and driving speed, and determining that the motor enters a steady state when the three-dimensional conditions simultaneously and continuously meet the set time; locking the integral item output value after entering the steady state, introducing proportional control and virtual damping to calculate the target cross-axis current with the locked value as the baseline, replacing the current output of the position closed-loop control to drive the permanent magnet synchronous motor, and switching to the steady-state holding mode; during the operation of the steady-state holding mode, when the threshold value condition is no longer met or the external load disturbance torque estimated by the linear extended state observer running in parallel exceeds the wake-up threshold value, the steady-state holding mode is exited and the position closed-loop control is restored.

Description

Technical Field

[0001] This invention relates to the field of motor control technology, and specifically to a motor steady-state holding control method and system for a steer-by-wire system. Background Technology

[0002] Steer-by-wire systems are a new type of steering system that eliminates the traditional mechanical connection of the steering column and transmits steering intentions via electronic signals. The permanent magnet synchronous motor, as the core drive component of the steering actuator, directly determines the driver's steering feel and vehicle safety. Position closed-loop control is the fundamental strategy of this system. It calculates the error by comparing the target position with the actual rotor position in real time and uses a proportional-integral controller to generate current commands to drive the motor to track the target position. However, in actual operating conditions, factors such as road resistance, mechanical friction, and sensor noise can cause the motor to generate high-frequency micro-ripples when approaching the target position. Traditional proportional-integral controllers, in steady state, experience unnecessary high-frequency jitter in the quadrature-axis current command due to the continuous accumulation of sensor noise and integral terms. This high-frequency current ripple will cause several adverse consequences: continuous micro-vibrations transmitted to the steering wheel surface cause a tingling sensation in the driver's hands; a significant increase in copper and iron losses in the motor stator windings leads to increased operating temperature and accelerated insulation aging; and the ineffective high-frequency current consumption unnecessarily increases the overall energy consumption of the system.

[0003] To address the aforementioned current jitter issue, existing technologies often employ dead-zone control strategies as an engineering solution. The basic principle is that once the position error reaches a set dead-zone threshold, the controller's current output command is directly set to zero to cut off the electromagnetic torque, avoiding current fluctuations caused by the continuous accumulation of the integral term. However, this direct shutdown strategy has inherent drawbacks: after the current is set to zero, the motor shaft no longer maintains any electromagnetic holding torque, and the system completely loses its ability to resist deviation. In actual driving, lateral disturbances from the road surface continuously act on the steering mechanism through the tires and steering tie rods, causing uncontrolled wheel drift. When the drift exceeds the dead-zone range, the controller reactivates its output for correction, and the current is cut off again after correction. This cycle repeats, forming a typical start-stop limit loop oscillation phenomenon, severely deteriorating the driver's road feel and vehicle stability.

[0004] In summary, existing technologies have the following problems: First, traditional proportional-integral control causes high-frequency current jitter in steady state due to sensor noise and integral accumulation, resulting in a numb steering wheel feel and motor overheating; Second, traditional dead-zone control eliminates jitter by directly shutting off the current output, but at the same time loses the system's position-keeping stiffness in steady state, making it prone to start-stop limit loop oscillations under external disturbances; Third, existing control strategies generally rely on the gradual accumulation of position errors to trigger a response when faced with sudden road impacts, resulting in inherent response lag. Summary of the Invention

[0005] This invention proposes a motor steady-state holding control method and system for a steer-by-wire system, which solves the problem that existing technologies cannot maintain the position holding stiffness of the system while eliminating steady-state current jitter.

[0006] To solve the above-mentioned technical problems, the present invention provides a motor steady-state holding control method for a steer-by-wire system, comprising the following steps: Step S1: During the position closed-loop control of the permanent magnet synchronous motor, which includes an integral term, the rotor position of the permanent magnet synchronous motor is acquired. Mechanical angular velocity and target location instructions Calculate position error and the rate of change of instructions The position threshold is calculated based on the standard deviation of the position sensor noise and the vehicle speed. Speed ​​threshold and rate of change threshold ;when When the set time is continuously met, the permanent magnet synchronous motor is determined to have entered a steady state. Step S2: Lock the current output value of the integral term. Using the locked value as a baseline, introduce proportional control based on the position error and virtual damping based on the mechanical angular velocity, calculate the target quadrature axis current, replace the current output of the position closed-loop control with the target quadrature axis current, drive the permanent magnet synchronous motor, and switch to steady-state holding mode. Step S3: During the operation of the steady-state holding mode, when any of the three threshold conditions in step S1 is no longer met, or when the external load disturbance torque estimated by the parallel-running external disturbance observer exceeds the set disturbance wake-up threshold, the steady-state holding mode is exited and the position closed-loop control is restored.

[0007] Preferably, the location threshold is calculated in step S1. Speed ​​threshold and rate of change threshold The formulas are as follows: ; ; ; In the formula, , and These are the dead zone constants for the base position, base velocity, and base rate of change, respectively. The standard deviation of the position sensor noise; Estimate the noise standard deviation for angular velocity; The vehicle speed; The digital quantization resolution for position commands; The standard deviation of the transmission delay of the communication bus; , , , , and These are the corresponding matching gain coefficients.

[0008] Preferably, the determination process of simultaneously and continuously satisfying the set time in step S1 includes: using a state determination timer to accumulate the time; when three threshold conditions are simultaneously satisfied, the state determination timer continues to accumulate; when any threshold condition is no longer satisfied, the accumulation of the state determination timer is paused and a fault-tolerant counter is started; if the count value of the fault-tolerant counter is less than the set fault-tolerant window threshold, the condition loss is determined to be transient noise and the accumulation of the state determination timer is resumed; if the count value of the fault-tolerant counter is not less than the fault-tolerant window threshold, the state determination timer is cleared.

[0009] Preferably, the target quadrature-axis current in step S2 The calculation formula is: ; in, This is the steady-state proportional gain; This is the virtual damping coefficient; This refers to the positional error; It is the mechanical angular velocity; This is a locked value.

[0010] Preferably, the switching to the steady-state maintenance mode in step S2 and the exiting the steady-state maintenance mode in step S3 are both achieved through a transition weighting factor. Achieve smooth transition, output current The expression is: ; in, The current output is for position closed-loop control; The target quadrature-axis current; Transition weighting factor when entering the steady-state maintenance mode The transition weight factor increases linearly from 0 to 1 when exiting the steady-state maintenance mode. It decreases non-linearly from 1 to 0.

[0011] Preferably, the transition weight factor when exiting the steady-state maintenance mode The nonlinear decreasing function is: ; in, This is a local counter that increments according to the control cycle after exit triggering; This represents the number of transition cycles to exit. The number of exit transition cycles is calculated when the process exits because any of the three threshold conditions in step S1 is no longer met. Take the first value; when exiting due to the external load disturbance torque exceeding the disturbance wake-up threshold, the number of exit transition cycles is... Take the second value; the second value is less than the first value.

[0012] Preferably, the external disturbance observer in step S3 is a linear extended state observer, and the discretized state-space equation of the external disturbance observer is: ; ; ; in, This is the observation error; This is an estimate of the angular velocity; This is the current sampled value of the mechanical angular velocity; The sampling period; It is the equivalent moment of inertia; This is an estimated value for electromagnetic torque; and For observer gain; This is the estimated total disturbance. The expression for the external load disturbance torque is: .

[0013] Preferably, the observer gain and Determined using bandwidth parameterization: ; The observer bandwidth Based on the noise standard deviation of the position sensor and the vehicle speed Dynamic adjustment, the calculation formula is: ; in, Maximum observation bandwidth; This is the noise penalty factor; This is the vehicle speed feedforward coefficient; The observer bandwidth A lower limit value is set. When the calculated observer bandwidth Below the lower limit value At that time, the observer bandwidth Limit the amplitude to the lower limit value. .

[0014] The present invention also provides a motor steady-state holding control system for a steer-by-wire system, including a permanent magnet synchronous motor, a position sensor, a current sensor and a controller; The position sensor is used to detect the actual rotor position of the permanent magnet synchronous motor. ; The current sensor is used to detect the armature current of the permanent magnet synchronous motor; The controller is connected to the position sensor, the current sensor, and the vehicle communication bus, respectively, and obtains the target position command through the vehicle communication bus. Based on the vehicle speed, the permanent magnet synchronous motor is subjected to position closed-loop control including an integral term, and is configured as follows: Calculate position error and the rate of change of instructions The position threshold is calculated based on the noise standard deviation of the position sensor and the vehicle speed. Speed ​​threshold and rate of change threshold ,when Simultaneously, the permanent magnet synchronous motor is determined to enter a steady state when the set time is continuously met; Lock the current output value of the integral term, and use this locked value as a baseline to introduce proportional control based on the position error and control based on the actual mechanical angular velocity. The virtual damping is used to calculate the target quadrature axis current, and the target quadrature axis current is used to replace the current output of the position closed-loop control to drive the permanent magnet synchronous motor and enter the steady-state holding mode. During the operation of the steady-state holding mode, when any of the three threshold conditions is no longer met, or when the external load disturbance torque estimated by the parallel-running external disturbance observer based on the armature current exceeds the set disturbance wake-up threshold, the steady-state holding mode is exited and the position closed-loop control is restored.

[0015] Preferably, the external interference observer is a linear extended state observer. The observer gain of the linear extended state observer is determined by the bandwidth parameterization method. The observer bandwidth is dynamically adjusted according to the noise standard deviation of the position sensor and the driving speed, and a lower limit value for the bandwidth is set.

[0016] The advantages of this invention include at least the following: 1. By freezing the integral term and introducing a virtual damping control law after the motor enters steady state, the steady-state high-frequency current ripple caused by the integral amplification of position sensor noise is effectively suppressed, and the heating level and ineffective energy consumption of the motor in the steady-state operating range are significantly reduced. 2. Unlike the traditional dead zone control strategy that directly sets the current output to zero, this embodiment of the invention maintains the closed-loop holding stiffness of the motor shaft with extremely low power consumption by locking the integral term output value and applying a combination of proportional control and virtual damping in steady-state holding mode, thus ensuring the mechanical tightness of the steering wheel of the steer-by-wire system under straight-line holding conditions. 3. By introducing a parallel-running linear extended state observer to estimate the external load disturbance torque in real time, feedforward prediction and rapid wake-up of sudden road impacts are realized, breaking the inherent lag of traditional proportional-integral control, which requires waiting for the position error to gradually accumulate before triggering the response action. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the steady-state holding control system for a permanent magnet synchronous motor according to an embodiment of the present invention. Figure 2 This is a schematic diagram of the method flow according to an embodiment of the present invention. Detailed Implementation

[0018] 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 protection scope of the present invention.

[0019] Example 1 This embodiment provides a method for steady-state control of a motor in a steer-by-wire system, applicable to steer-by-wire systems that use a permanent magnet synchronous motor as the driving element of the steering actuator. For example... Figure 1 As shown, the control system in this embodiment includes a host computer, a multi-dimensional steady-state determination module, a steady-state holding control module, and a linearly extended state observer module. The host computer is responsible for issuing target position commands. The multi-dimensional steady-state determination module determines whether the motor has entered a steady state based on the collected state data. After determining that the motor has entered a steady state, the steady-state holding control module takes over the generation of current commands. The linearly extended state observer module operates in parallel to estimate the external load disturbance torque in real time. The inverter and drive circuit are located between the controller and the permanent magnet synchronous motor. Its input is connected to the controller, and its output is connected to the three-phase windings of the permanent magnet synchronous motor. The inverter and drive circuit receive current commands output by the controller. These current commands include the current output under conventional position closed-loop control and the target quadrature-axis current under steady-state holding mode. Based on the current commands, the inverter generates three-phase drive current to drive the permanent magnet synchronous motor to produce the corresponding electromagnetic torque.

[0020] like Figure 2 As shown, the control method in this embodiment includes the following steps: Step S1: System status data acquisition and multi-dimensional steady-state entry determination.

[0021] Set the controller's sampling period to The actual rotor position of the permanent magnet synchronous motor is acquired in real time through an analog-to-digital converter and a decoder. Actual mechanical angular velocity Armature current and the target location command issued by the host computer. The armature current is among them. This information is used for calculating the electromagnetic torque estimate in the subsequent linear expansion state observer. In this embodiment, the position sensor can be a tunnel magnetoresistive sensor, a Hall sensor, or an inductive sensor. It should be noted that different types of position sensors have different noise floor characteristics under different temperature conditions.

[0022] Based on the collected data, calculate the position error and command change rate. The formula for calculating the position error is: ; in, For target location instructions; This represents the actual rotor position. Command rate of change. It represents the rate of change of the target position command over time, and is used to determine whether the host computer is still continuously issuing position adjustment commands.

[0023] To overcome the impact of different sensor noise characteristics and varying vehicle speeds on the accuracy of steady-state determination, this embodiment employs a dynamic adaptive threshold design. Adaptive thresholds are calculated for the position, speed, and command change rate dimensions, respectively.

[0024] The formula for calculating the location threshold is: ; The formula for calculating the speed threshold is: ; The formula for calculating the rate of change threshold is: ; In the above three threshold calculation formulas, , and These are the basic position dead zone constant, the basic speed dead zone constant, and the basic rate of change dead zone constant. These three basic constants represent the minimum dead zone width required by the system under ideal noise-free and zero-speed conditions. The standard deviation of the position sensor noise represents the statistical dispersion of the random noise superimposed on the position sensor output signal. This parameter can be obtained through offline calibration or online estimation. To estimate the noise standard deviation for angular velocity, since angular velocity is usually obtained from position signal through differential operation, differential operation will amplify noise. Therefore, the noise level contained in the estimated angular velocity value is usually higher than that of the original position signal.

[0025] In the above formula, This is an estimate of the current vehicle speed. When the vehicle is in motion, high-frequency mechanical vibrations from the road surface are coupled to the steering motor shaft through transmission paths such as the suspension system, steering tie rods, and rack. The higher the vehicle speed, the stronger the coupling interference of road vibrations on the steering system. Therefore, it is necessary to compensate for the threshold using vehicle speed-related terms. The digital quantization resolution of the position command is a parameter that characterizes the minimum resolution step size inherent in the digital encoding of the target position command issued by the host computer. The standard deviation of the transmission delay of the vehicle communication bus is a parameter that reflects the time jitter in the process of transmitting the target position command from the host computer to the steering controller via the communication bus.

[0026] This represents the noise compensation gain coefficient for the position sensor. This represents the coupling gain coefficient between vehicle speed and position threshold. This is the gain coefficient for velocity noise compensation. This is the coupling gain coefficient between vehicle speed and speed threshold. This is the gain coefficient for quantization error compensation. This is the gain coefficient for communication delay jitter compensation.

[0027] For velocity noise compensation gain coefficient This embodiment is based on the 3σ criterion of normal distribution. Under the assumption of normal distribution, the 3σ range can cover 99.73% of noise fluctuation points, therefore... Setting it to around 3 ensures that the speed threshold can correctly filter out false speed fluctuations caused by noise in most cases.

[0028] For quantization error compensation gain coefficient In this embodiment, it is set to a value between 1 and 2. Because single-bit transitions may occur during the transmission of vehicle communication messages, [the following is omitted as it is not explicitly stated]. Setting it to 1.5 means that the system allows the target position command to have tiny fluctuations of 1.5 resolution units at the underlying level without triggering a motor response.

[0029] For the coupling gain coefficient of vehicle speed on speed threshold This embodiment uses a real vehicle chassis bench test for calibration. The specific calibration method is as follows: Under different set vehicle speeds, the vehicle is driven in a straight line, and the amplitude of the high-frequency mechanical vibration transmitted to the steering motor shaft via the steering tie rod and rack is recorded. A scatter plot is drawn with the vehicle speed as the abscissa and the amplitude of the additional angular velocity fluctuation caused by the vibration as the ordinate. Linear regression fitting is then performed using the least squares method, and the slope of the resulting straight line is the [value / slope]. .

[0030] For the digital quantization resolution of position commands In this embodiment, the parameter value is extracted directly from the communication matrix configuration file of the vehicle communication network.

[0031] For the noise standard deviation of angular velocity estimation To obtain the angular velocity data, this embodiment supports both offline calibration and online estimation. The offline calibration method involves collecting tens of thousands of angular velocity sampling data points via a host computer under conditions where the motor is stationary or operating at a constant, very low speed, and calculating the sample standard deviation of these data points as... The calibration value is determined online. The online estimation method involves opening a sliding time window in the microcontroller, for example, the angular velocity sampling values ​​of the most recent 50 control cycles, and calculating the standard deviation of the angular velocity data within this window in real time. In actual operation, the fixed noise standard deviation calibrated offline is used as the reference value during system power-on initialization. During motor operation, when the system determines that it is currently in a low-dynamic condition, the online sliding window is activated to calculate the current noise standard deviation, and the reference value is low-pass filtered to compensate for the noise characteristic drift caused by the long-term degradation of the position sensor.

[0032] When the system simultaneously meets the following three conditions and continues for a set time... At that time, it is determined that the permanent magnet synchronous motor has entered a steady state: Condition 1: The absolute value of the position error is less than the position threshold, that is: ; Condition 2: The absolute value of the actual mechanical angular velocity is less than the velocity threshold, that is: ; Condition 3: The absolute value of the rate of change of the instruction is less than the rate of change threshold, that is: ; If the above three conditions are not met simultaneously, the permanent magnet synchronous motor will continue to execute the conventional position closed-loop control algorithm.

[0033] In determining the duration of the three threshold conditions, this embodiment employs a combination mechanism of a state determination timer and a fault-tolerant counter. When all three threshold conditions are simultaneously met, the state determination timer continuously increments. When any threshold condition is no longer met, the system does not immediately reset the state determination timer; instead, it pauses the increment and starts the fault-tolerant counter. If the counter value is less than the set fault-tolerant window threshold, the condition loss is determined to be a misjudgment caused by transient noise, and the system resumes the state determination timer's increment and continues steady-state determination. If the counter value is not less than the fault-tolerant window threshold, the condition loss is determined to be a genuine state change, and the system resets the state determination timer and restarts the timing. This fault-tolerant mechanism effectively prevents steady-state timing interruptions caused by occasional noise spikes from the position sensor, improving the robustness of steady-state entry determination.

[0034] Step S2: Steady-state hold mode control.

[0035] When step S1 determines that the permanent magnet synchronous motor has entered a steady state, the controller does not cut off the motor's current output, but instead switches from conventional position closed-loop control to steady-state holding mode. At the moment of switching to steady-state holding mode, the system first locks the current output value of the integral term in the conventional position closed-loop control, and records this locked value as... It should be noted that the locking time is... The timing begins at the moment when the system officially enters a steady state after the timing ends, not after three conditions are met. At that moment, from the moment the steady-state hold mode is entered until the closed-loop control at the recovery position is completed, the integral term remains locked and does not update. During the smooth transition, the integral term also stops updating because the output current has been taken over by the transition weight factor. If integral calculations continue to be performed, integral saturation will be introduced, which may lead to violent oscillations when the closed-loop control is restored.

[0036] In steady-state holding mode, the system introduces a virtual damping control law to calculate the target quadrature-axis current. The calculation formula is as follows: ; in, This is the steady-state proportional gain; The virtual damping coefficient is set. This refers to the positional error; This refers to the actual mechanical angular velocity; This is the locked value. In the above control law, the proportional term... Multiply by position error It provides basic position restoring force, enabling the system to pull the motor rotor back to the target position even when subjected to minor external disturbances. Virtual damping term. Multiply by mechanical angular velocity A speed-dependent damping force is provided for the motor's movement to suppress potential oscillations. Lock-in value As a fixed bias term, it compensates for the static load faced by the system when entering steady state, ensuring that the current baseline in steady-state holding mode is consistent with the closed-loop output before entering steady state.

[0037] It should be noted that the steady-state proportional gain Not equal to the proportional gain in conventional position closed-loop control This embodiment eliminates the torque step that may be caused by the difference between the two proportional gains and the introduction of virtual damping by introducing a smooth transition weighting factor.

[0038] To prevent abnormal noises or jerking in the steering system caused by sudden changes in commands during mode switching, this embodiment introduces a smooth transition weighting factor. The final output current command is: ; in, The current output is for conventional position closed-loop control; The target quadrature-axis current is the current in steady-state holding mode.

[0039] When entering steady-state maintenance mode, the transition weight factor according to The value increases linearly from 0 to 1, achieving a gradual switch from conventional closed-loop control to steady-state holding mode. This is a local counter that increments according to the control cycle after being triggered. Number of transition cycles; transition time , This is the controller sampling period.

[0040] When exiting steady-state maintenance mode, the transition weight factor The transition weight factor decreases non-linearly from 1 to 0. The non-linear decreasing function for the exit transition weight factor is: ; in, This is a local counter that increments according to the control cycle after exit triggering; This represents the number of exit transition cycles. This quadratic function form allows the weight to decrease rapidly in the initial stage of exiting the transition, quickly restoring the dominant position of closed-loop control, while the decreasing rate slows down in the later stage, avoiding abrupt changes at the end of the transition.

[0041] This embodiment sets different exit transition cycle numbers for different exit trigger reasons. When the system exits due to any of the three threshold conditions in step S1 no longer being met, it determines that the driver intends to follow or make minor position adjustments. In this case, the transition weight factor should undergo a relatively gentle decay process, and the number of transition cycles should be reduced. The first value is chosen; this first value is a relatively large one to ensure a smooth transition. When the system exits due to external load disturbance torque exceeding the disturbance wake-up threshold, it must restore the full-range closed-loop stiffness as quickly as possible to counteract the external impact, and the number of exit transition cycles is [number missing]. Take a second value, which is less than the first value, so that the transition weight factor undergoes an extremely steep decay to achieve rapid wake-up.

[0042] Step S3: Rapid exit based on interference observation.

[0043] During steady-state operation, the system runs an external disturbance observer in parallel to estimate the external load disturbance torque applied to the motor shaft in real time. The exit condition for the steady-state mode includes two parallel decision paths: first, exiting when any of the three threshold conditions in step S1 is no longer met; second, exiting when the absolute value of the external load disturbance torque estimated by the external disturbance observer exceeds the set disturbance wake-up threshold. The two exit conditions are parallel; triggering either condition will exit the steady-state holding mode and resume normal position closed-loop control.

[0044] It should be noted that when a continuous, slow drift force is applied externally, the integral term is frozen in steady-state mode, and the system relies solely on the proportional term. Multiply by position error To counteract this, as external forces continue to act, the positional error... It will gradually accumulate and increase. When the accumulated position error exceeds the adaptive position threshold... When the steady-state error condition in step S1 is no longer met, the system automatically exits the steady-state holding mode and resumes normal position closed-loop control, reusing the integral term to eliminate the steady-state error. This mechanism ensures that the system will not produce unrecoverable position deviations when facing slow drift.

[0045] In this embodiment, the external disturbance observer is a linear extended state observer. The linear extended state observer models the external load disturbance torque as an extended dimension of the system state and tracks this extended state in real time through an error feedback mechanism, thereby achieving online estimation of external disturbances. Its discretized state-space equation is as follows.

[0046] ; ; ; In the above system of equations, The observation error is defined as the difference between the estimated angular velocity and the actual sampled angular velocity. This is the estimated angular velocity output by the linearly extended state observer. This is the current sampled value of the actual mechanical angular velocity, obtained through differential calculation and acquired by the position sensor. This is the sampling period of the controller. The equivalent rotational inertia of the steering system on the motor shaft includes the rotational inertia of the motor rotor itself and the load-side inertia converted by the gear ratio. Based on the current quadrature axis current The estimated electromagnetic torque value is obtained by calculating the motor torque constant. and This is the error feedback gain of the linearly extended state observer, which is applied to the angular velocity estimation channel and the disturbance estimation channel, respectively. The total disturbance estimate, including the external load disturbance torque, is estimated for the linearly extended state observer.

[0047] External load disturbance torque It is derived from the total disturbance estimate and its expression is: ; Error feedback gain of linear extended state observer and This directly determines the observer's tracking speed to external disturbances and the amplification degree of high-frequency noise from the position sensor. This embodiment uses the bandwidth parameterization method to tune the error feedback gain. Through pole placement, the gain parameter is related to the observer bandwidth. The following parsing relationship exists between them: ; Observer bandwidth This is a crucial tuning parameter. A larger bandwidth results in a smaller estimation delay for external disturbances by the observer, allowing the system to respond almost instantaneously upon receiving an impact. However, a higher bandwidth setting amplifies the noise from the position sensor quadratically, causing drastic fluctuations in the estimated disturbance signal. To resolve the inherent conflict between tracking speed and noise suppression in bandwidth selection, this embodiment sets the observer bandwidth... With position sensor noise standard deviation and driving speed Together, the observer's gain is dynamically tuned. The formula for calculating the observer bandwidth is: ; in, The maximum observation bandwidth allowed by the controller hardware sampling capability. This is the observer noise penalty coefficient; the larger the coefficient, the stronger the attenuation effect of noise on bandwidth. This is the observer speed feedforward coefficient, used to automatically increase the observer bandwidth under high vehicle speed conditions to enhance interference immunity.

[0048] Through the aforementioned dynamic variable bandwidth design, when the vehicle is stationary or in a low-speed steady state and the position sensor has a high noise floor, the system automatically reduces the observer bandwidth. This improves the smoothness of disturbance estimation and prevents false triggering due to noise amplification. When vehicle speed is high and the risk of high-frequency mechanical impact from the road surface increases, the system automatically increases the observer bandwidth. To ensure the external load disturbance torque It can be captured quickly without delay, thus achieving the optimal balance between filtering robustness and dynamic disturbance rejection in the system.

[0049] Furthermore, this embodiment addresses the observer bandwidth. A lower limit is also set. and upper limit value Specifically, the candidate bandwidth is first calculated using the dynamic bandwidth formula described above, and then upper and lower limit limiting is applied to obtain the actual observer bandwidth, i.e. When the position sensor noise standard deviation When the value approaches zero or the vehicle speed feedforward term is large, the candidate bandwidth may exceed the maximum observation bandwidth allowed by the controller hardware sampling capability. At this point, limit its amplitude to This ensures that the actual observer bandwidth does not exceed the maximum bandwidth allowed by the hardware; under extremely high noise conditions, the noise penalty term in the formula may cause excessive attenuation of the candidate bandwidth when it falls below the lower limit. Limit it to This ensures that the observer maintains a minimum level of external disturbance detection capability under any operating conditions.

[0050] Under extreme operating conditions characterized by high speed and high noise, the noise penalty term and the vehicle speed feedforward term in the bandwidth calculation formula may exhibit contradictory adjustment directions. The noise penalty term tends to reduce bandwidth to suppress noise amplification, while the vehicle speed feedforward term tends to increase bandwidth to enhance disturbance rejection response. Proper calibration is crucial to address this. and By adjusting the weighting ratio, this embodiment makes the system prioritize noise suppression to ensure system stability under such extreme conditions, while also utilizing a lower limit value. The bandwidth limiting function prevents excessive bandwidth attenuation that could lead to a complete loss of anti-interference capability.

[0051] This embodiment provides a motor steady-state holding control system for a steer-by-wire system, used to implement the motor steady-state holding control method described in Embodiment 1. The control system of this embodiment includes a position sensor and a controller.

[0052] A position sensor is installed at the rotor end of the permanent magnet synchronous motor to detect the actual position of the motor rotor in real time. In this embodiment, the position sensor can be a tunnel magnetoresistive sensor, a Hall sensor, or an inductive sensor.

[0053] The controller connects to the position sensor, receives the actual rotor position signal output by the position sensor, and receives the target position command from the host computer. The controller performs position closed-loop control including an integral term on the permanent magnet synchronous motor and is configured to: calculate the position error and command change rate based on the actual rotor position, actual mechanical angular velocity, and target position command; calculate the position threshold, speed threshold, and change rate threshold based on the noise standard deviation of the position sensor and the vehicle speed; determine that the permanent magnet synchronous motor has entered steady state when the absolute value of the position error is less than the position threshold, the absolute value of the mechanical angular velocity is less than the speed threshold, and the absolute value of the command change rate is less than the change rate threshold, and all of these conditions are met for a set time; lock the current output value of the integral term, introduce proportional control based on the position error and virtual damping based on the mechanical angular velocity using the locked value as a baseline, calculate the target quadrature-axis current, and switch to steady-state holding mode; during steady-state holding mode operation, when any of the three threshold conditions is no longer met, or when the external load disturbance torque estimated by the parallel-running external disturbance observer exceeds the set disturbance wake-up threshold, exit the steady-state holding mode and resume position closed-loop control.

[0054] In this embodiment, the external disturbance observer integrated within the controller is a linear extended state observer, whose gain is determined using a bandwidth parameterization method. The observer bandwidth is dynamically adjusted based on the noise standard deviation of the position sensor and the vehicle speed, and a lower bandwidth limit is set to ensure that the observer maintains a minimum external disturbance sensing capability under any operating condition. The specific structure, parameter tuning method, and working principle of the linear extended state observer are consistent with those described in Embodiment 1, and will not be repeated here.

[0055] The technical features of the above embodiments can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described; only preferred embodiments of the present invention are illustrated. The descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the present invention. As long as the combination of these technical features does not contradict each other, it should be considered within the scope of this specification.

[0056] It should be noted that those skilled in the art can make various modifications and improvements without departing from the inventive concept, and these all fall within the scope of protection of this invention. Therefore, the scope of protection of this invention should be determined by the appended claims.

Claims

1. A method for steady-state motor holding control in a steer-by-wire system, characterized in that, Includes the following steps: Step S1: During the position closed-loop control of the permanent magnet synchronous motor, which includes an integral term, the rotor position of the permanent magnet synchronous motor is acquired. Mechanical angular velocity and target location instructions Calculate position error and the rate of change of instructions The position threshold is calculated based on the standard deviation of the position sensor noise and the vehicle speed. Speed ​​threshold and rate of change threshold ;when When the set time is continuously met, the permanent magnet synchronous motor is determined to have entered a steady state. Step S2: Lock the current output value of the integral term. Using the locked value as a baseline, introduce proportional control based on the position error and virtual damping based on the mechanical angular velocity, calculate the target quadrature axis current, replace the current output of the position closed-loop control with the target quadrature axis current, drive the permanent magnet synchronous motor, and switch to steady-state holding mode. Step S3: During the operation of the steady-state holding mode, when any of the three threshold conditions in step S1 is no longer met, or when the external load disturbance torque estimated by the parallel-running external disturbance observer exceeds the set disturbance wake-up threshold, the steady-state holding mode is exited and the position closed-loop control is restored.

2. The motor steady-state holding control method for a steer-by-wire system according to claim 1, characterized in that: In step S1, the position threshold is calculated. Speed ​​threshold and rate of change threshold The formulas are as follows: ； ； ； In the formula, , and These are the dead zone constants for the base position, base velocity, and base rate of change, respectively. The standard deviation of the position sensor noise; Estimate the noise standard deviation for angular velocity; The vehicle speed; The digital quantization resolution for position commands; The standard deviation of the transmission delay of the communication bus; , , , , and These are the corresponding matching gain coefficients.

3. The motor steady-state holding control method for a steer-by-wire system according to claim 1, characterized in that: The determination process for simultaneously and continuously satisfying the set time in step S1 includes: using a state determination timer to accumulate the time; when three threshold conditions are simultaneously satisfied, the state determination timer continues to accumulate; when any threshold condition is no longer satisfied, the accumulation of the state determination timer is paused and a fault-tolerant counter is started; if the count value of the fault-tolerant counter is less than the set fault-tolerant window threshold, the condition loss is determined to be transient noise and the accumulation of the state determination timer is resumed; if the count value of the fault-tolerant counter is not less than the fault-tolerant window threshold, the state determination timer is cleared to zero.

4. The motor steady-state holding control method for a steer-by-wire system according to claim 1, characterized in that: The target quadrature-axis current in step S2 The calculation formula is: ； in, This is the steady-state proportional gain; This is the virtual damping coefficient; This refers to the positional error; It is the mechanical angular velocity; This is a locked value.

5. The motor steady-state holding control method for a steer-by-wire system according to claim 1, characterized in that: Switching to the steady-state maintenance mode in step S2 and exiting the steady-state maintenance mode in step S3 are both achieved through a transition weighting factor. Achieve smooth transition, output current The expression is: ； in, The current output is for position closed-loop control; The target quadrature-axis current; Transition weighting factor when entering the steady-state maintenance mode The transition weight factor increases linearly from 0 to 1 when exiting the steady-state maintenance mode. It decreases non-linearly from 1 to 0.

6. The motor steady-state holding control method for a steer-by-wire system according to claim 5, characterized in that: The transition weighting factor when exiting the steady-state maintenance mode The nonlinear decreasing function is: ； in, This is a local counter that increments according to the control cycle after exit triggering; This represents the number of transition cycles to exit. The number of exit transition cycles is calculated when the process exits because any of the three threshold conditions in step S1 is no longer met. Take the first value; when exiting due to the external load disturbance torque exceeding the disturbance wake-up threshold, the number of exit transition cycles is... Take the second value; the second value is less than the first value.

7. The motor steady-state holding control method for a steer-by-wire system according to claim 1, characterized in that: The external disturbance observer mentioned in step S3 is a linear extended state observer, and the discretized state-space equation of the external disturbance observer is: ； ； ； in, This is the observation error; This is an estimate of the angular velocity; This is the current sampled value of the mechanical angular velocity; The sampling period; It is the equivalent moment of inertia; This is an estimated value for electromagnetic torque; and For observer gain; This is the estimated total disturbance. The expression for the external load disturbance torque is: 。 8. The motor steady-state holding control method for a steer-by-wire system according to claim 7, characterized in that: The observer gain and Determined using bandwidth parameterization: ； The observer bandwidth Based on the noise standard deviation of the position sensor and the vehicle speed Dynamic adjustment, the calculation formula is: ； in, Maximum observation bandwidth; This is the noise penalty factor; This is the vehicle speed feedforward coefficient; The observer bandwidth A lower limit value is set. and upper limit value When the calculated observer bandwidth Below the lower limit value At that time, the observer bandwidth Limit the amplitude to the lower limit value. When the calculated observer bandwidth Higher than the upper limit value At that time, the observer bandwidth Limit to the upper limit value .

9. A motor steady-state holding control system for a steer-by-wire system, characterized in that, Includes permanent magnet synchronous motors, position sensors, current sensors, and controllers; The position sensor is used to detect the actual rotor position of the permanent magnet synchronous motor. ; The current sensor is used to detect the armature current of the permanent magnet synchronous motor; The controller is connected to the position sensor, the current sensor, and the vehicle communication bus, respectively, and obtains the target position command through the vehicle communication bus. Based on the vehicle speed, the permanent magnet synchronous motor is subjected to position closed-loop control including an integral term, and is configured as follows: Calculate position error and the rate of change of instructions The position threshold is calculated based on the noise standard deviation of the position sensor and the vehicle speed. Speed ​​threshold and rate of change threshold ,when Simultaneously, the permanent magnet synchronous motor is determined to enter a steady state when the set time is continuously met; Lock the current output value of the integral term, and use this locked value as a baseline to introduce proportional control based on the position error and control based on the actual mechanical angular velocity. The virtual damping is used to calculate the target quadrature axis current, and the target quadrature axis current is used to replace the current output of the position closed-loop control to drive the permanent magnet synchronous motor and enter the steady-state holding mode. During the operation of the steady-state holding mode, when any of the three threshold conditions is no longer met, or when the external load disturbance torque estimated by the parallel-running external disturbance observer based on the armature current exceeds the set disturbance wake-up threshold, the steady-state holding mode is exited and the position closed-loop control is restored.

10. The motor steady-state holding control system for a steer-by-wire system according to claim 9, characterized in that: The external interference observer is a linear extended state observer. The observer gain of the linear extended state observer is determined by the bandwidth parameterization method. The observer bandwidth is dynamically adjusted according to the noise standard deviation of the position sensor and the driving speed, and a lower limit value for the bandwidth is set.

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