CASCADE POSITION CONTROL ARCHITECTURE FOR STEERING SYSTEMS

Abstract

Technical solutions for disturbance feedforward compensation are described to improve the disturbance rejection characteristics of a position control system using a cascaded control structure with an inner speed control loop and an outer position control loop. According to one or more embodiments, a system includes a position controller that receives a rack position input command and a measured rack position and calculates a speed command based on the difference between the rack position input command and the measured rack position. The system further includes a speed controller that receives the speed command and a measured motor speed and calculates an input torque command based on the difference between the speed command and the measured motor speed.The system adjusts the position of a rack by generating a torque amount equivalent to applying the input torque command to a motor.

Description

BACKGROUND

[0001] The present application relates to a system for disturbance feedforward control compensation in a steering system and a method for operating such a system and, in particular, addresses technical problems relating to position control in steering systems using a cascaded position control architecture.

[0002] Steering systems used by vehicles may include a position controller that positions a rack according to a position command. Examples of steering systems with such a position controller include a steer-by-wire (SbW) system incorporating a road wheel actuator (RWA), an electric power steering (EPS) system, and the like. The position controller may receive the position command from a human driver or an autonomous driver, such as an advanced driver assistance system (ADAS).

[0003] US 2015 / 0191200A1 discloses a steering control system in which a motor current command is determined by means of a position control and motor speed control arranged in series, wherein the position control determines a steering angle command based on an actual and target steering angle and the speed control determines a current command based on a speed command ω mand a calculated motor angular velocity ω, wherein the current command is supplied to a motor to adjust a steering angle. US 2020 / 0 108 857 A1 relates to an electric power steering system comprising a serially arranged rotation angle control and speed control for a motor of the steering system. DE 10 2012 105 265 A1 teaches a steering control device in a vehicle that calculates a corrected assist torque in addition to a basic assist rotation element depending on a position of the vehicle's steering rack.US 2017 / 0217479 A1 describes an electric power steering device that determines a motor current command based on an actual and target steering angle, wherein the device particularly includes a position control that determines a target steering angular velocity based on a difference between an actual and target steering angle, and a speed control that determines a current command based on a difference between a target steering angular velocity and a derivative of the actual steering angle. DE 102018112207 A1 discloses a device for controlling a motor of an electric power steering system, which initiates or terminates a motor limiting mode based on a steering angle and information about the electric power steering motor. SUMMARY

[0004] One of the problems underlying the invention is to provide an improved system for disturbance feedforward compensation in a steering system and a corresponding method.

[0005] The problem is solved by the subject matter of the independent claims. Advantageous further developments are the subject matter of the dependent claims.

[0006] Technical solutions for a disturbance feedforward compensation technique are described to improve the disturbance rejection characteristics of a position control system using a cascaded control structure with an inner velocity control loop and an outer position control loop. In accordance with one or more embodiments, a system includes a position controller for a road wheel actuator that receives a rack position input command and a measured rack position and calculates a velocity command based on a difference between the rack position input command and the measured rack position.The system further includes a speed controller for the road wheel actuator, which receives the speed command and a measured motor speed and calculates an input torque command based on the difference between the speed command and the measured motor speed. The system adjusts the position of a rack of the road wheel actuator by generating a torque amount corresponding to the application of the input torque command to a motor. The position controller and the speed controller are further arranged to form a cascaded control loop, each comprising an outer position control loop and an inner speed control loop, with the cascaded control loop providing the tracking of a rack position.

[0007] In accordance with one or more embodiments, a method includes calculating, by a position controller for a road wheel actuator, a speed command based on a difference between a rack position input command and a measured rack position provided as a first feedback term. The method further includes calculating, by a speed controller for the road wheel actuator, an input torque command based on a difference between the speed command and a measured motor speed provided as a second feedback term, wherein the speed controller forms a cascaded control loop with the position controller to provide tracking of a rack position, the cascaded control loop comprising an outer position control loop and an inner speed control loop.The procedure further involves using a motor to adjust the position of a rack of the road wheel actuator by generating a torque amount that corresponds to the input torque command.

[0008] In accordance with one or more embodiments, a steering system comprises a motor, a rack and pinion, and multiple controllers, including a position controller and a speed controller. The controllers perform a method for providing rack and pinion position tracking using a cascaded control loop comprising a speed feedback loop and a position feedback loop. The method involves the position controller for a road wheel actuator calculating a speed command based on the difference between a rack and pinion position input command and a measured rack position, which is provided as the first feedback term.The method further includes the calculation of an input torque command by the speed controller for the road wheel actuator, based on a difference between the speed command and a measured motor speed, which is provided as a second feedback term. The speed controller forms a cascaded control loop with the position controller to provide rack and pinion position tracking, the cascaded control loop comprising an outer position control loop and an inner speed control loop. The method further includes the adjustment of a rack position of the road wheel actuator by a motor by generating a torque value corresponding to the input torque command.

[0009] These and other advantages and features will become clearer from the following description when read in conjunction with the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The subject matter considered to be the invention is specifically disclosed and claimed separately in the claims at the end of the description. The foregoing and further features and advantages of the invention will become apparent from the following detailed description when read in conjunction with the accompanying drawings, which: Fig. 1 illustrates an advanced driver assistance system in a vehicle in accordance with one or more embodiments; Fig. 2 is an exemplary embodiment of an electric power steering system; Fig. 3 is an exemplary embodiment of a steer-by-wire system; Fig. 4 illustrates a cascaded position control architecture of a steering system in accordance with one or more embodiments; Fig. 5 represents a cascaded position control architecture of a steering system in accordance with one or more embodiments of the present invention; and Fig. 6 represents a cascaded position control architecture of a steering system for a second order response in accordance with one or more embodiments of the present invention. DETAILED DESCRIPTION

[0011] As used herein, the terms module and submodule refer to one or more processing circuits, such as an application-specific integrated circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group) with memory executing one or more software or firmware programs, a combinational logic circuit, and / or other suitable components that provide the described functionality. As will be appreciated, the submodules described below may be combined and / or further subdivided.

[0012] Fig. Figure 1 represents an advanced driver assistance system in a vehicle according to one or more embodiments. It should be noted that the steering system 40 shown and described can be used in an autonomous or semi-autonomous vehicle or in a more conventional vehicle. In a vehicle 100, an advanced driver assistance system (ADAS) 110 can be coupled with a steering system 40, with one or more road wheels 44 (via one or more control units), and with other control units in the vehicle 100. The ADAS 110 can include one or more processors 112 and one or more memory devices 114.

[0013] The ADAS 110 receives one or more input signals containing data and / or commands from control units such as the controller 16 of the steering system 40. The ADAS 110 can also receive one or more input signals from one or more sensors 116 such as a camera, radar, lidar, or any other sensors. The ADAS 110 can also send signals containing data and / or commands to control units such as a controller 16 of the steering system 40. The ADAS 110 can also receive input from the human driver, such as a destination, one or more preferences, and the like.

[0014] The ADAS 110 can provide notifications to the driver, for example, during an interaction with the driver and / or in response to one or more conditions in the vehicle 100. The notifications can include audio, visual, haptic, torque, and similar notifications. For example, audio / visual notifications can be sent via a driver-vehicle information unit, speakers with which the vehicle 100 is equipped, and the like. Haptic notifications can be provided via a seat, the steering system 40, and the like. The torque notification can be sent via the steering system 40, for example, by generating a torque overlay that can be added to an assist torque to help the driver operate the vehicle 100.

[0015] In one or more examples, the ADAS 110 automatically determines a driving trajectory for the vehicle 100. The sensors 116 are used to provide several ADAS features related to lateral movement of the vehicle 100, such as lane keeping assist, lane centering assist, blind spot assist, etc. These features can help the driver avoid collisions, such as side impacts, frontal impacts, etc. In providing this functionality, the ADAS 110 assesses the driver's intention, such as acceleration, lane changes, etc. ADAS features such as lane keeping assist can rely on sensor-based lane information to detect the vehicle's distance from a lane marking or the likelihood of the vehicle changing lanes based on lateral movement.However, this information is often delayed with regard to driver input. Due to physics, there is a certain delay after the driver applies handwheel torque before the vehicle's movement is affected. For a collision avoidance application, this delay is undesirable, as it could be too late to predict a potential collision and apply the necessary torque.

[0016] The technical solutions described here enable a predicted vehicle trajectory to be determined faster than sensor-based trajectory prediction. To overcome the technical challenges of sensor-based vehicle trajectory prediction, these solutions utilize steering signals, such as torsion bar torque (tbar torque), to predict the vehicle trajectory. The predicted trajectory (or path) can be used to recognize the driver's intentions and, if necessary, to take action to mitigate a potential collision (side, frontal, etc.).

[0017] The technical solutions described here are applicable to both EPS (electric power steering) and SbW (steer-by-wire) systems. With reference to the figures, in which the technical solutions are described with reference to specific embodiments, without limiting them, Fig. 2 an exemplary embodiment of an electric power steering system (EPS system) in a vehicle 100, which is suitable for implementing the disclosed embodiments, and Fig. Figure 3 is an exemplary embodiment of a steering system 40 for implementing the described embodiments. Unless specifically described otherwise, this document refers to a steering system 40, which may be either an EPS, a SbW, or any other type of steering system in which the technical solutions described herein can be used.

[0018] In Fig. 2, the steering mechanism 36 is a rack and pinion system and includes a toothed rack (not shown) within a housing 50 and a pinion gear (also not shown) located beneath a gear housing 52. When the driver input, hereinafter referred to as the handwheel or steering wheel 26, is rotated, the upper steering shaft 29 rotates, and the lower steering shaft 51, connected to the upper steering shaft 29 by a universal joint 34, rotates the pinion gear. Rotation of the pinion gear moves the rack, which moves tie rods 38 (only one shown), which in turn move steering knuckles 39 (only one shown), which turn or turn one or more steerable road wheels 44 or tires (only one shown).Although a rack and pinion system is described here, in other embodiments the EPS can be a steering column assist EPS (CEPS), a pinion assist EPS (PEPS), a dual pinion assist EPS, or any other type of EPS.

[0019] Electric power steering assistance is provided by the control device, generally designated by reference numeral 24, which includes the controller 16 and an electric motor 46, which may be a permanent magnet synchronous motor (PMSM), a permanent magnet direct current motor (PMDC), or any other type of motor, and is hereinafter referred to as the electric motor 46. The controller 16 is supplied with power from the vehicle power supply 10 via a line 12. The controller 16 receives a vehicle speed signal 14, representing the vehicle speed, from a vehicle speed sensor 17. A steering angle is measured by a position sensor 32, which may be an optically coded sensor, a variable resistance sensor, or any other suitable type of position sensor, and which supplies a position signal 20 to the controller 16.The motor speed can be measured with a tachometer or any other device and transmitted to the controller 16 as a motor speed signal 21. One as ω. m The designated motor speed can be measured, calculated, or determined by a combination of these methods. For example, the motor speed ω m as the change in motor position θ, measured by a position sensor 32, over a predetermined time interval. For example, the motor speed ω can be calculated. m as the derivative of the motor position θ from the equation ω m= Δθ / Δt, where Δt is the sampling time and Δθ is the change in position during the sampling interval. Alternatively, the motor speed can be derived from the motor position as the time rate of change of position. It should be noted that there are numerous well-known methods for performing the derivative function.

[0020] When the steering wheel 26 is turned, a torque sensor 28 detects the torque applied to the steering wheel 26 by the driver. The torque sensor 28 can include a torsion bar (not shown) and a variable resistance sensor (also not shown), which outputs a variable torque signal 18 to the controller 16 in proportion to the amount of rotation of the torsion bar. Although this is one type of torque sensor, any other suitable torque sensing device using known signal processing techniques will suffice. In response to the various inputs, the controller sends a command 22 to the electric motor 46, which provides torque assistance to the steering system via a worm gear 47 and a worm wheel 48, thus providing torque assistance for the vehicle steering.

[0021] In the illustrated control device 24, the controller 16 uses the torque, position, speed, and other parameters to calculate one or more commands for delivering the required output power. The controller 16 communicates with the various systems and sensors of the motor control system. The controller 16 receives signals from each of the system sensors, quantifies the received information, and, in response, provides one or more output command signals, in this case, for example, for the electric motor 46. The controller 16 is designed to generate the corresponding voltages from a converter (not shown), which can optionally be integrated into the controller 16 and is referred to here as the controller 16, so that when applied to the electric motor 46, the desired torque or position is generated.In one or more examples, the control device 24 operates in a feedback control mode as a current controller to generate the command 22. Alternatively, in one or more examples, the control device 24 operates in a feedforward control mode to generate the command 22. Since these voltages are related to the position and speed of the electric motor 46 and the desired torque, the position and / or speed of the rotor and the torque applied by a driver are determined. A position encoder is connected to the steering shaft 51 to detect the angular position θ. The encoder can detect the rotational position based on optical detection, a magnetic field fluctuation, or another method. Typical position sensors include potentiometers, resolvers, synchros, encoders, and the like, as well as combinations that include at least one of the aforementioned elements.The position encoder outputs a position signal 20, which indicates the angular position of the steering shaft 51 and thus that of the electric motor 46.

[0022] A desired torque can be determined by one or more torque sensors 28 that transmit torque signals 18 indicating an applied torque. One or more exemplary embodiments include such a torque sensor 28 and its torque signals 18, which can respond to a compliant torsion bar, T-bar, spring, or similar (not shown) device configured to provide a response indicating the applied torque.

[0023] In one or more examples, one or more temperature sensors 23 can be arranged on the electric motor 46. The temperature sensor 23 is preferably configured to directly measure the temperature of the sensing section of the electric motor 46. The temperature sensor 23 transmits a temperature signal 25 to the controller 16 to enable the processing and compensation described herein. Typical temperature sensors include thermocouples, thermistors, thermostats, and the like, as well as combinations comprising at least one of the aforementioned sensors, which, when appropriately positioned, provide a calibratable signal proportional to the specific temperature.

[0024] The position signal 20, the motor speed signal 21, and one or more torque signals 18, among others, are applied to the controller 16. The controller 16 processes all input signals to generate values ​​corresponding to each signal, resulting in a rotor position value, a motor speed value, and a torque value available for processing in the algorithms described here. Measurement signals such as those mentioned above are also frequently linearized, compensated, and filtered, as desired, to improve their characteristics or eliminate undesired characteristics of the acquired signal. For example, the signals can be linearized to improve processing speed or to address a large dynamic range of the signal. Furthermore, frequency- or time-based compensation and filtering can be used to eliminate noise or avoid undesired spectral characteristics.

[0025] To perform the described functions and the desired processing, as well as the necessary calculations (e.g., the identification of motor parameters, control algorithms, and the like), the controller 16 can include, without restriction, processors, computers, DSPs, main memory, mass storage, registers, timers, interrupts, communication interfaces, and input / output signal interfaces, and the like, as well as combinations that include at least one of the aforementioned elements. For example, the controller 16 can include input signal processing and filtering to enable accurate sampling and conversion or the acquisition of these signals from communication interfaces. Additional features of the controller 16 and specific processes within it will be discussed in detail later.

[0026] Fig. Figure 3 presents an exemplary SbW system in accordance with one or more embodiments. The steering system 40 includes a handwheel actuator (HWA) 70 and a roadwheel actuator (RWA) 80. The controller 16 is divided into two blocks, namely a microcontroller 16A and a microcontroller 16B, which are assigned to the HWA 70 and the RWA 80, respectively. In other examples, the controller 16 may be distributed in any other way.

[0027] The HWA 70 includes one or more mechanical components, such as the steering wheel 26 (the handwheel), a steering column, and a motor / inverter attached to the steering column either by a gear mechanism or a direct drive system. The HWA 70 also includes the microcontroller 16A, which controls the operation of the mechanical components. The microcontroller 16A receives and / or generates torque through the one or more mechanical components. For example, the microcontroller 16A can send a torque command request to a motor / inverter, which will then generate that torque.

[0028] The RWA 80 includes one or more mechanical components, such as a steering rack, which is coupled to a motor / inverter by an arrangement with a ball nut / ball screw drive or a pinion gear assembly, and the rack is connected to the vehicle's road wheels / tires 44 by tie rods. The RWA 80 includes the microcontroller 16B, which controls the operation of the mechanical components. The microcontroller 16B receives and / or generates torque through the one or more mechanical components. For example, the microcontroller 16B can send a torque command request to a motor / inverter, which will then generate that torque.

[0029] Microcontrollers 16A and 16B are coupled by electrical connections that enable the transmission / reception of signals. As described herein, a controller may include a combination of the HWA controller or microcontroller 16A and the RWA controller or microcontroller 16B, or any of the dedicated microcontrollers.

[0030] In one or more examples, the microcontrollers 16A and 16B of the steering system 40 communicate with each other via a CAN interface (or other similar digital communication protocols). Steering of the vehicle 100, equipped with the steering system 40, is performed using the steering gear. The RWA 80 receives an electronic communication signal indicating a rotation of the steering wheel by the driver. The driver steers the steering wheel to control the direction of the vehicle 100. The angle from the HWA 70 is sent to the RWA 80, which performs position control to regulate a travel distance of the rack and pinion to steer the road wheel. However, due to the lack of a mechanical connection between the steering wheel and the road wheels, the driver is not readily provided with a feel for the road without torque feedback (unlike in the EPS case described above).

[0031] In one or more examples, the HWA 70, coupled to the steering column and steering wheel, simulates the driver's feel for the road. The HWA 70 can apply tactile feedback in the form of torque to the steering wheel. The HWA 70 receives a rack and pinion force signal from the RWA 80 to generate a suitable torque sensation for the driver. Alternatively, the handwheel angle and vehicle speed can also be used to generate a desired torque sensation for the driver.

[0032] As mentioned above, the SbW system and the EPS system described herein are exemplary and the technical solutions described herein are applicable to any type of steering system and therefore a "steering system" herein refers to any type of steering system unless specifically described otherwise.

[0033] In steering systems, a cascaded control structure with an inner velocity control loop and an outer position control loop can typically be used as an alternative to (full or partial) state feedback with reference to a feedforward control approach. These architectures are used for position control, employing general compensators such as PID controllers for both loops. These compensators do not allow for intuitive and easy tuning and, furthermore, do not always provide robust disturbance rejection capabilities. These technical problems are addressed by the technical solutions described here, which provide a cascaded control structure with dedicated compensators for each of the two loops.With this structure, the resulting transfer function with closed-loop position tracking (under specific conditions) is purely second-order, which makes it easier and more flexible to tune the response compared to typical architectures. Furthermore, the technical solutions described here enable the control system to have improved disturbance rejection. This makes the overall control structure intuitively understandable and easily configurable, providing significant flexibility to modify the command tracking and disturbance rejection characteristics of the overall position control system.

[0034] Fig. Figure 4 shows a block diagram of a cascaded position control system with an inner speed control loop together with an outer position control loop. The figure shows a control system 400, which includes a rack and pinion speed control unit 420 and a rack and pinion position control unit 430, which are controlled by P ω (420) or P θ (430) are shown, while the electrical system 410 of the motor is shown by P e (410) is shown. The electrical and mechanical systems are shown in dotted lines, and the control structures 440 and 450 (which control the operation of the systems) are not typically included in cascaded position control architectures. Since the disturbance feedback (T̃) dSince the effective system, viewed from the perspective of the control signal, remains unchanged before its summation, it is noted that it is not considered in the description presented for selecting the various controller parameters. However, it is understood that for small system inaccuracies (modeling errors), the closed-loop responses effectively remain the same. The transfer functions for the mechanical systems can be represented using the cumulative inertia J and the damping b as follows. Pω=1Js+b Pθ=1s

[0035] Furthermore, the controller (405) for the electromagnetic torque of the motor is controlled by C e modeled. In the preceding discussion, the electrical (control loop) dynamics were ignored, or mathematically it was assumed that C e P e≈ 1, which is a reasonable assumption since the electrical torque control loop is tuned to be considerably faster than the mechanical dynamics. This results in the motor torque command being essentially equal to the actual electromagnetic torque of the motor, as follows. Tc≈Ta

[0036] Furthermore, the rack force estimating device (450) or the disturbance estimating device is provided by at least two transmission functions D t (452) and D ω (454) is shown. The rack force estimate T̃ d It consists of these two transfer functions and can be represented mathematically as follows. T˜d=DtTa+Dωωm

[0037] The transfer functions D t and D ω are used by a state observer to estimate the rack force (T) d), referred to herein as the disturbance. In one or more examples, the rack force estimator 450 includes the disturbance observer, which extends the plant matrix with the disturbance (rack force), modeled as a state with an unknown initial step input. In such a case, the equations of the (extended) plant are as follows. [ω˙T˙d]=[−b / J−1 / J00][ωTd]+[1 / J0][Ta] y=Cx [ω]=

[10] [ωTd]

[0038] The observer equations are obtained using estimates of the asset matrices together with observer gains as follows. x^˙=A^x^+B^u+L(y−y^)=A^x^+B^u+L(Cx−C^x^)=(A^−LC^)x^+B^u+LCx[ω ^˙T^˙d]=[−b^ / J^−L1−1 / J^−L20][ω^T^d]+[1 / J^0][Ta]+[L10L20][ωTd]

[0039] Here, Ĵ and b̂ represent estimated or best known values ​​of cumulative inertia and damping for the system.

[0040] By performing the Laplace transform on this matrix equation, the estimated rack force is obtained as follows. T^d=−L2 / J^s2+(b^ / J^+L1)s−L2 / J^Ta+−L2(s+b^ / J^)s2+(b^ / J^+L1)s−L2 / J^ω

[0041] In these cases, observer gains are adjusted analytically to achieve specific transfer functions, or by using standard techniques such as pole placement or LQE.

[0042] To better explain the one or more embodiments described here with special control loop systems, some derivations with simplifying conditions are described at the beginning. First, the measured speed of the electric motor 46 is obtained as a function of the actual speed and measurement noise as follows. ωm=Fωθm=FωPθω+ωn

[0043] Here ω nIt is understood as the equivalent noise of the speed measurement (estimation), which is a function of the actual noise of the position measurement. The transfer function F ω is essentially designed (as far as possible) to be a derivative of the motor position system P θ compensated, while the noise from the position measurement (θ) m ) is filtered out. The position measurement includes the position of the rack, which is based on the input position command (θ). c ) together with positional noise (θ n ) is based on several factors, which can be introduced. For example, F ω with a derivative and with a low-pass filter with time constant τ ω , be constructed as follows. Fω=sτωs+1

[0044] The velocity responses to various external inputs can be determined as described below, where Tb an input torque based on the input position command is T c a torque command that is based on T b and is based on one or more feedback terms. The feedback terms can include a disturbance estimate T̃. d include, which is calculated by a rack force estimator 450. The feedback terms can further include an ideal derivative (H ω ) which is designed to operate a regulator 440 and is thus an exact reciprocal of the rack and pinion positioning system 430. The following equations further represent as T a This represents a final torque command generated by the electrical system 410 and applied to the mechanical system (420 and 430). The disturbance or rack force T d This influences the final torque command and thus the engine speed and engine position.

[0045] The control system 400 further shows the position controller 470, which controls a motor speed (ω c ) based on a positional error (θ c ) determined. The determined motor speed can be the speed at which the electric motor 46 is to be moved. The position error is defined as the difference between the input position command (θ) c ) and the measured position of the rack (θ m ) is calculated. In one or more examples, a speed error (ω e ) based on a difference between the calculated engine speed (ω c ) and a measured motor speed (ω m ) is calculated. The motor speed error is used to calculate the input torque command T b by a speed controller 460. The speed responses to various external inputs can be determined as described below: ω=Pω(Ta−Ta)=(1+PωPeCe(Cω−Hω)FωPθ)−1(PωPeCeCωωc +PωPeCe(Hw−Cω)Fωθn−PωTd)=Mωcωc+Mωnθn+MωdTd

[0046] Here is M ωc a transfer function for tracking the calculated motor speed ω c ; M ωn is a transfer function for tracking the rack position noise θ n ; and M ωd is a transfer function for fault rejection (fault = rack force T) d ).

[0047] The transfer function M ωc The following code can be used to track the velocity response. Mωc=(1+PωPeCe(Cω−Hw)FωPθ)−1PωPeCeCωωc≈(1+Pω(Cω−Hω)FωPθ)−1PωCωωc

[0048] Here, it is assumed that the dynamics of the electrical control are ideal, i.e., P e C e≈ 1, since the electrical torque control is typically tuned to be much faster than the mechanical dynamics. Furthermore, it is assumed that F ω is an ideal derivative and thus an ideal reciprocal of the motor position system P θ This implies that F ω P θ ≈ 1. The transfer function M ωc To track the speed response, proceed as follows. Mωc=(1+Pω(Cω−Hω))−1PωCω=(Pω−1−Hω+Cω)−1Cω

[0049] Assuming that the term Pω−1−Hω the inverse of an “effective investment” P ωe is, i.e. Pωe=(Pω−1−Hω)−1, then the transfer function of the closed control loop can be written as follows. Mωc=(1+PωeCω)−1PωeCω

[0050] It should be noted that this is a transfer function where the effective system replaces the actual system. Consequently, if the state feedback is chosen to have a gain of -b v is, where b v The effective system, referred to as "virtual damping", becomes the following. Pωe=1Js+b+bv

[0051] Furthermore, to obtain an ideal response from a first-order velocity control loop, a proportional-integral controller (PI controller) is used as controller C. ω used. The PL controller or speed controller 460 is designed with gains as functions of the system parameters and the term of virtual damping. Cω=Kω(J˜+b˜+bv)

[0052] Using the PI controller or speed controller 460, assuming accurate parameter estimates, leads to the following response from the speed control loop. Mωc=Kωs+Kω

[0053] Here, the value of the virtual damping helps to maintain the first-order characteristic curve even in the face of modeling uncertainties, which can be understood by examining the transfer function of the effective system. If b v is chosen so that it is high enough, the effective Investment≈1bv and the compensator becomes Kωbvs The system and controller parameters do not strongly influence the response of the control loop, as they become negligible compared to the term of virtual damping. The transfer function for disturbance rejection can be obtained similarly (assuming accurate parameter estimation) as follows. Mωd=(Pω−1−Hω+Cω)−1≈1Js+b+bv+Kω

[0054] Accordingly, virtual damping, in addition to high bandwidth, provides additional flexibility in tuning the disturbance rejection characteristics of the closed-loop control system 400. The inclusion of the integrator in the velocity control loop results in stepwise tracking of the control loop as well as disturbance rejection of the control loop (plant input).

[0055] The position control loop for position tracking is determined next by continuing the derivative from the previous derivative. ω=Mωcωc+Mωnθn+MωdTd Pθ−1θ=MωcCθ(θc−θm)+Mωnθn+MωdTd→θ=Mθcθc+MθdTd+Mθnθn

[0056] Based on the transfer function for position tracking, a proportional controller (P-controller) is used as the position controller C. θ 470 is used and designed to provide reinforcement K θexhibits. Accordingly, the transfer function of the control loop is as follows (given the above response of the speed control loop). Mθc=KωKθs2+Kωs+KωKθ

[0057] Consequently, the control loop for position tracking exhibits an ideal second-order response. The control signal is calculated for all external outputs as follows, following the same approach described above. Ta=(1+PeCe((Cω−Hω)Fω+CωCθ)PθPω)−1(PeCeCωCθθc−PeCe((Cω−Hω)Fω+CωCθ)PθPωTd+PeCe((Cω−Hω)Fω+CωCθ)θn) Ta=Ucθc+UdTd+Unθn

[0058] Fig. Figure 5 shows a block diagram of a cascaded position control system in accordance with one or more embodiments. For simplification, the electrical system P is shown in the block diagram. e 410 and the corresponding controller C e405, which are considered ideal inverses of each other (described here), are not shown. Furthermore, the speed controller 460 is a PI controller in the speed control loop, and the position controller 470 is a P controller in the position control loop using the transfer functions described here.

[0059] In one or more examples, a desired natural frequency ω is selected. f and a desired damping ratio ζ the gains of the position controller 470 and the speed controller 460 are configured as follows. Kω=2ςωf Kθ=ωf2ς

[0060] The input position command (θ c The position control loop (505) is modified. The modification is based on the measured rack position. The modified position command is used by the position controller 470 to generate a speed command.

[0061] The speed command is adjusted (515) using the measured motor speed, which is fed back into the speed control loop. In one or more examples, the measured speed is determined as a derivative of the measured rack position. The modified speed command is used by the speed controller 460 to determine the input torque command T b to generate, which is to be applied to the mechanical and electrical system.

[0062] The input torque command is modified in the disturbance feedback loop using a disturbance estimate. In one or more examples, the disturbance estimate T̃ is used. d scaled using a 510 disturbance controller, which uses a gain parameter K dis configured. The output of the disturbance controller 510 is added to the input torque command (535) to create an adjusted torque command T. c to generate. In one or more examples, the input torque command is further modified using the controller 440 for virtual damping, which is used for the virtual damping term b. v is configured. The output T n The virtual damping controller's value is added to the input torque command (525) to form a torque command T. x to generate. In one or more examples, the torque command T x as described above, modified by the disturbance estimate.

[0063] Fig.Figure 6 presents a block diagram of an architecture with a cascaded position control system in accordance with one or more embodiments. The selection of gains described herein is illustrated. With the control architecture shown, the control loop can be tuned intuitively and easily, achieving the objectives of tracking step commands and rejecting step disturbances. It also offers the additional flexibility of improving disturbance rejection characteristics independently of command tracking. For example, by adjusting the parameters of the position controller 470, the velocity controller 460, the disturbance controller 510, and the virtual damping controller 440, the control system 400 can be tuned to track the input position command in an improved manner.

[0064] Test results using the control architecture described here were recorded to examine the responses of the position output and torque signal to various external inputs (including the position command, rack force disturbance, and position sensor noise) for varying natural frequencies and damping ratios. In the sample test results, the system bandwidth increased with increasing natural frequencies for a critically damped system. Simultaneously, disturbance rejection improved, and the response to noise decreased. With varying damping ratios, the system exhibited the expected responses, and it was observed that the system evolved from an insufficiently damped system to a critically damped system and finally to an overdamped system.The test results also confirmed that the structure provided by the technical solutions described here allows the manipulation of the system's fault rejection properties independently of the command response.

[0065] The technical solutions described here address technical problems with steering systems such as steer-by-wire (SbW) systems, which include a road radar actuator (RWA) with a position controller. Position control is implemented using feedback control architectures such as PID, which employ position feedback. Tuning the calibrations for such a control system is usually not very intuitive and requires significant adjustments in the vehicle. Furthermore, it is difficult to explicitly tune PID for robustness against system parameter fluctuations. The technical solutions described here address these problems by using a special cascaded control structure that is intuitive and easy to tune because the bandwidth is built into the control parameters.Furthermore, the architecture provided by the technical solutions ensures robust position tracking despite parameter fluctuations.

[0066] The control structure with cascaded control loops uses position and velocity feedback for position tracking. Furthermore, in one or more examples, a virtual damping term is added to the tracking command to improve robustness. Additionally, the control loop structure allows for easy determination of control calibrations using system parameters (inertia, damping).

[0067] The technical solutions presented here can be a system, a process, and / or a computer program product at any possible level of integration of technical details. The computer program product can include one or more computer-readable storage media containing computer-readable program instructions to cause a processor to execute aspects of the technical solutions presented here.

[0068] Aspects of the present technical solutions are described here with reference to flowchart illustrations and / or block diagrams of processes, devices (systems), and computer program products in accordance with embodiments of the technical solutions. It is understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer-readable program instructions.

[0069] The flowcharts and block diagrams in the figures illustrate the architecture, functionality, and operation of possible implementations of systems, procedures, and computer program products in accordance with various embodiments of the presented technical solutions. In this regard, each block in the flowcharts or block diagrams can represent a module, segment, or section of instructions, comprising one or more executable instructions for implementing the described logical functions. In some alternative implementations, the functions described in the blocks may occur out of the order shown in the figures. For example, two consecutively shown blocks may actually be executed essentially simultaneously, or the blocks may sometimes be executed in reverse order, depending on the functionality involved.

[0070] It should also be noted that each block of the block diagrams and / or flowchart illustrations and combinations of blocks in the block diagrams and / or flowchart illustrations may be implemented by specialized hardware-based systems that perform the described functions or acts or that perform combinations of specialized hardware and computer processing.

[0071] Furthermore, it should be noted that all modules, units, components, servers, computers, terminals, or devices described herein as examples and executing instructions include or can otherwise access computer-readable media such as mass storage media, computer mass storage media, or data mass storage devices (removable and / or non-removable), such as magnetic disks, optical disks, or tapes. Computer storage media can include volatile and non-volatile, removable and non-removable media implemented by any method or technology for storing information, such as computer-readable instructions, data structures, program modules, or other data. These computer storage media can be part of the device or accessible to or connectable to it.All applications or modules described herein can be implemented using computer-readable / executable instructions stored on these computer-readable media or otherwise maintained.

[0072] Although the technical solutions have been described in detail in connection with only a limited number of embodiments, it is easy to understand that the technical solutions are not limited to these disclosed embodiments. Instead, the technical solutions can be modified to include any number of variations, changes, substitutions, or equivalent arrangements not described above, but which are consistent with the concept and scope of the technical solutions. Furthermore, although various embodiments of the technical solutions have been described, it is understood that aspects of the technical solutions may only include some of the described embodiments. Therefore, the technical solutions should not be interpreted as being limited to the foregoing description.

Claims

[1] System that includes: a position controller (470) for a road wheel actuator configured to: receive a rack position input command and a measured rack position; and calculate a speed command based on a difference between the rack position input command and the measured rack position; a speed controller (460) for the road wheel actuator, which is designed to: to receive the speed command and a measured motor speed; and calculate an input torque command based on a difference between the speed command and the measured motor speed; and wherein the system adjusts a position of a rack of the road wheel actuator by generating a torque amount corresponding to the application of the input torque command to an electric motor (46), wherein the position controller (470) and the speed controller (460) are arranged to form a cascaded control loop each comprising an outer position control loop and an inner speed control loop, the cascaded control loop providing tracking of a rack position. [2] The system of claim 1, further comprising a damping controller configured to: calculate a first torque command by scaling the measured motor speed using a damping term; and modify the input torque command by adding the first torque command to the input torque command to track the rack position. [3] The system of claim 1, further comprising a fault controller (510) configured to: to estimate a rack force acting on the rack; and modify the input torque command using the estimated rack force. [4] The system of claim 3, wherein the rack force being estimated is scaled using a configurable parameter. [5] The system of claim 1, wherein the velocity command is calculated based on a configurable parameter of the position controller (470). [6] The system of claim 5, wherein the position controller (470) is a proportional controller. [7] The system of claim 1, wherein the input torque command is calculated based on a configurable parameter of the speed controller (460). [8] The system of claim 7, wherein the speed controller (460) is a proportional-integral controller. [9] Procedure which includes: a position controller (470) for a road wheel actuator calculates a speed command based on a difference between a rack position input command and a measured rack position provided as a first feedback term; a speed controller (460) for the road wheel actuator calculates an input torque command based on a difference between the speed command and a measured motor speed provided as a second feedback term, the speed controller (460) forming a cascaded control loop with the position controller (470) to provide tracking of a rack position, the cascaded control loop comprising an outer position control loop and an inner speed control loop; and an electric motor (46) adjusts a position of a rack of the road wheel actuator by generating a torque amount corresponding to the input torque command. [10] The method of claim 9, further comprising: a first torque command is calculated by a damping controller by scaling the measured motor speed using a damping term; and the input torque command is modified by adding the first torque command to the input torque command to track the rack position. [11] The method of claim 9, wherein the velocity command is calculated based on a configurable parameter of the position controller (470). [12] The method of claim 9, wherein the position controller (470) is a proportional controller. [13] The method of claim 9, wherein the input torque command is calculated based on a configurable parameter of the speed controller (460). [14] The method of claim 9, wherein the speed controller (460) is a proportional-integral controller.

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