A method for rudder control of a ship's azimuth propeller

Abstract

This invention relates to the field of ship maneuvering and control technology, and proposes a method for controlling the steering of a ship's azimuth propeller. The method includes acquiring the target rudder angle, actual rudder angle, and original ship speed signals; obtaining the effective ship speed through verification and fusion filtering; determining the evaluation ship speed based on the effective ship speed and rate of change; calculating the estimated heeling moment generated by steering in conjunction with the current actual rudder angle; further determining the maximum steering angular velocity using a preset heeling safety threshold, and correcting it according to ship loading information to obtain the final limiting reference value. This value is used to limit the target steering angular velocity, and after acceleration / deceleration planning, it is converted into a pulse frequency signal to drive the steering mechanism to perform maneuvers. This invention effectively ensures the ship's heeling safety and maneuvering stability during steering by dynamically adjusting the steering speed in real time by monitoring ship speed and heeling risk.

Description

Technical Field

[0001] This invention relates to the field of ship maneuvering and control technology, and in particular to a method for controlling the steering of a ship's azimuth propeller. Background Technology

[0002] Existing azimuth propeller-driven rudder control systems typically operate based on fixed rudder angle parameters, failing to adequately consider the differences in heel moment generated by rudder maneuvers under varying speeds, rudder angles, and load conditions. At high speeds, if the pilot issues a large rudder angle command, the rudder mechanism responds rapidly at a preset rate, causing a sharp increase in lateral thrust from the propeller. This can lead to a rapid increase in the ship's heel angle, potentially exceeding the ship's safe stability range and causing instability or even capsizing. Furthermore, existing systems lack the ability to perceive and compensate for real-time ship load conditions, failing to impose additional limits on the rudder rate under full load or low stability conditions. They also lack multi-source verification and fusion mechanisms for ship speed signals, potentially leading to erroneous speed limit judgments when a single sensor malfunctions or data jumps. Therefore, existing rudder control methods suffer from slow response, coarse constraints, and insufficient environmental adaptability in heel safety protection. Summary of the Invention

[0003] To address the aforementioned shortcomings, the present invention aims to propose a rudder control method for a ship's azimuth propeller. This method aims to estimate the heeling moment generated by the rudder turning action and dynamically limit the rudder turning angular velocity accordingly. Combined with adaptive correction based on the ship's load conditions, it achieves safety constraints on the rudder turning process under different speeds and load conditions, thereby preventing the ship from heeling and becoming unstable due to rapid, large-angle rudder turning during high-speed navigation.

[0004] To achieve this objective, the present invention adopts the following technical solution: A method for controlling the steering of a ship's azimuth propeller includes the following steps: S1: Obtain the target rudder angle command, the current actual rudder angle, and the original ship speed signals from several signal sources. Perform validity checks on the original ship speed signals respectively, and obtain the effective ship speed by fusing and filtering the valid ship speed signals. S2: Calculate the rate of change of the effective ship speed, determine the evaluation ship speed based on the effective ship speed and the rate of change of the effective ship speed, and calculate the estimated heeling moment generated by the current rudder turning action based on the evaluation ship speed and the current actual rudder angle. S3: Determine the maximum rudder angle velocity that meets the roll safety condition based on the estimated roll moment and the preset roll safety threshold, and determine the load condition correction coefficient based on the current ship load information. Use the load condition correction coefficient to correct the maximum rudder angle velocity to obtain the corrected maximum rudder angle velocity. S4: Generate a target rudder angle velocity based on the deviation between the target rudder angle command and the current actual rudder angle. Limit the target rudder angle velocity with the corrected maximum rudder angle velocity. Perform acceleration / deceleration planning on the limited target rudder angle velocity, convert it into a pulse frequency signal and output it to drive the rudder mechanism to perform rudder action at the planned speed.

[0005] Preferably, the original ship speed signal includes an absolute ground speed signal based on satellite positioning, a speed signal relative to water based on a log, and an estimated rotational speed signal based on frequency converter feedback; The validity verification of the original ship speed signals includes: Perform physical limit verification on the original ship speed signals: For each original ship speed signal, independently determine whether its rate of change exceeds a preset physical limit threshold. If the rate of change of an original ship speed signal exceeds the physical limit threshold, then mark the original ship speed signal as an invalid signal. Perform a status consistency check on the original ship speed signal: when the numerical deviation of at least two signal sources in the original ship speed signal is greater than the preset logic tolerance, identify and remove the original ship speed signal with faults by comparing the health status bits of each signal source. Processing is performed based on the number of valid signal sources: when only one original ship speed signal is valid, the original ship speed signal corresponding to the valid signal source is taken as the valid ship speed; when there are multiple valid signals, weighted fusion is performed based on the preset confidence weight of each signal source, and first-order inertial filtering and median filtering are performed on the fused signal in sequence to obtain the valid ship speed.

[0006] Preferably, the rate of change of the effective ship speed is obtained by performing a least squares fitting calculation on the effective ship speed; The determination of the evaluation ship speed based on the effective ship speed and the rate of change of the effective ship speed includes: A prediction time window matching the response lag time of the steering action is set, and a linear extrapolation prediction is performed based on the effective ship speed, the rate of change, and the prediction time window to obtain the predicted ship speed. When the rate of change of the effective ship speed is positive and continuously increasing, the predicted ship speed is determined as the evaluated ship speed; when the rate of change of the effective ship speed is negative, the effective ship speed is determined as the evaluated ship speed.

[0007] Preferably, in step S2, the calculation of the estimated tilting moment includes: Establish a pre-estimation relationship for heeling moment related to ship hydrodynamic characteristics; The speed-related heeling moment component, which reflects the intensity of the ship's hydrodynamic action, is determined based on the assessed ship speed, wherein the speed-related heeling moment component is positively correlated with the square of the assessed ship speed. The torque component generated by the deflection of the rudder blade is determined based on the current actual rudder angle, wherein the torque component is positively correlated with the sine value of the current actual rudder angle. The speed-related heel moment component and the applied moment component are nonlinearly weighted and summed, and ship stability characteristic parameters are introduced for correction to dynamically predict the predicted heel moment under the current steering action. The ship stability characteristic parameters include the ship's center of gravity height, displacement, roll moment of inertia, and initial stability height. The estimated heeling moment increases synchronously with the continuous increase of the assessed ship speed or the continuous increase of the current actual rudder angle.

[0008] Preferably, determining the maximum rudder angle velocity that satisfies the roll safety condition based on the estimated roll moment and the preset roll safety threshold includes: The estimated roll moment is compared with a first roll safety threshold and a second roll safety threshold, wherein the first roll safety threshold is less than the second roll safety threshold; When the estimated roll moment is not greater than the first roll safety threshold, the maximum rudder angle velocity of the previous cycle used in the current control cycle is directly used as the maximum rudder angle velocity. When the estimated roll moment is greater than the first roll safety threshold and not greater than the second roll safety threshold, the maximum rudder angle velocity is reduced according to the first decreasing ratio. When the estimated roll moment is greater than the second roll safety threshold, the maximum rudder angle velocity is reduced by a second decreasing ratio, where the second decreasing ratio is greater than the first decreasing ratio. An absolute lower limit is set for the reduced maximum steering angular velocity. The absolute lower limit is calibrated based on the minimum effective steering angular velocity corresponding to the lowest stable operating frequency of the steering mechanism.

[0009] Preferably, a load condition correction coefficient is determined based on the current ship load condition information, and the maximum rudder angle velocity is corrected using the load condition correction coefficient to obtain the corrected maximum rudder angle velocity, including: Obtain current ship status information, including ship draft, cargo loading status, and ballast water status; The current displacement is determined based on the ship's draft and the ship's hydrostatic curve. The longitudinal position of the ship's center of gravity is determined based on the cargo loading status. The ballast water tank level is determined based on the ballast water status, and the weight of the ballast water and its vertical adjustment to the ship's center of gravity are calculated. The current stability height is calculated by combining the current displacement, the longitudinal position of the ship's center of gravity, and the vertical adjustment. The current stability height is compared with the reference stability height specified in the ship's design to obtain the stability height ratio. When the stability height ratio is greater than the preset first stability height threshold, the load condition correction coefficient is determined as the first preset load condition correction coefficient. The first preset load condition correction coefficient is greater than 1. The first stability height threshold is determined based on the ratio of the reference stability height calibrated by the ship design to the minimum allowable stability height under full load conditions. When the stability height ratio is not greater than the first stability ratio threshold and is greater than the preset second stability ratio threshold, the load condition correction coefficient is determined to be 1. The second stability ratio threshold is determined based on the ratio of the reference stability height calibrated by the ship design to the minimum stability height allowed under the ship's ballast conditions. The first stability ratio threshold is greater than the second stability ratio threshold. When the stability height ratio is less than or equal to the second stability ratio threshold, the load condition correction coefficient is determined as the second preset load condition correction coefficient, and the second preset load condition correction coefficient is less than 1. The maximum rudder angle velocity is multiplied by the load condition correction factor to obtain the corrected maximum rudder angle velocity.

[0010] Preferably, generating the target rudder angle velocity based on the deviation between the target rudder angle command and the current actual rudder angle includes: Calculate the original rudder angle deviation between the target rudder angle command and the current actual rudder angle, perform shortest path discrimination processing on the original rudder angle deviation, and obtain the corrected rudder angle deviation and direction control signal. The shortest path discrimination processing ensures that the steering mechanism rotates along the shortest arc length direction between the two rudder angles. The absolute value of the corrected rudder angle deviation is compared with a preset first rudder angle dead zone threshold. If the absolute value of the corrected rudder angle deviation is not greater than the first rudder angle dead zone threshold, the target rudder angle velocity is set to zero. If the absolute value of the corrected rudder angle deviation is greater than the first rudder angle dead zone threshold, the corrected rudder angle deviation is mapped to the target rudder angle velocity through a piecewise proportional function. The piecewise proportional function uses a first proportional coefficient when the absolute value of the corrected rudder angle deviation is greater than a preset first deviation threshold, and uses a second proportional coefficient when the absolute value of the corrected rudder angle deviation is not greater than the first deviation threshold but is greater than the first rudder angle dead zone threshold. The first proportional coefficient is greater than the second proportional coefficient.

[0011] Preferably, converting the target steering angular velocity after amplitude limiting into a pulse frequency signal after acceleration / deceleration planning includes: The target rudder angular velocity is compared with the corrected maximum rudder angular velocity, and the smaller of the two values ​​is taken as the target rudder angular velocity after the amplitude is limited. The difference between the limited target rudder angular velocity and the actual output rudder angular velocity command of the previous control cycle is calculated to obtain the angular velocity change. If the absolute value of the angular velocity change exceeds a preset first angular acceleration limit, the limited target rudder angular velocity is increased or decreased according to the first angular acceleration limit to obtain the planned rudder angular velocity command. If the absolute value of the angular velocity change does not exceed the first angular acceleration limit, the limited target rudder angular velocity is directly used as the planned rudder angular velocity command. The planned rudder angle velocity command is converted into a pulse frequency signal, and the pulse frequency signal and the direction control signal are output to the rudder drive unit to drive the rudder mechanism to rotate towards the target rudder angle command at the planned speed.

[0012] One of the above technical solutions has the following advantages or beneficial effects: This invention ensures the reliability of ship speed data by acquiring multi-source ship speed signals and performing validity verification and fusion filtering, avoiding misjudgments of speed limits due to a single sensor malfunction. By calculating the rate of change of effective ship speed and combining it with a prediction time window to determine the assessment ship speed, the heel moment prediction can proactively match the future motion state of the ship, rather than relying solely on a delayed response based on instantaneous ship speed. Using the assessment ship speed and the current actual rudder angle, the predicted heel moment is calculated through a heel moment prediction model, quantifying the hydrodynamic effects of rudder steering into a comparable safety indicator. Finally, the maximum rudder steering angle rate is determined based on the predicted heel moment and a preset safety threshold. The system adaptively adjusts the steering speed limit by introducing a ship load condition correction coefficient, ensuring that the steering speed limit simultaneously reflects the ship's stability margin. Finally, it generates a target steering angular velocity through rudder angle deviation and limits it with a corrected maximum speed limit. This velocity is then converted into a pulse frequency signal to drive the steering mechanism via acceleration / deceleration planning, ensuring that the steering speed is always constrained within the allowable range determined by both heel safety conditions and load conditions. This effectively prevents excessive heeling due to excessive steering speed or changes in load conditions while meeting maneuverability requirements, thus improving the steering safety and adaptability of azimuth propeller ships under different speed and load condition combinations. Attached Figure Description

[0013] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0014] Figure 1 This is a flowchart of the rudder control method for a ship's azimuth propeller provided in an embodiment of the present invention; Figure 2This is a schematic diagram of the structure of the azimuth propeller steering control system provided in an embodiment of the present invention. Detailed Implementation

[0015] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0016] In this invention, the terms "comprising," "including," or any other variations thereof are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0017] This invention is applicable to all types of motor vessels equipped with azimuth propeller propulsion systems, including but not limited to tugboats, engineering vessels, ferries, research vessels, and port operation vessels that require high maneuverability and frequent changes of direction.

[0018] like Figure 2 As shown, the steering control system of this type of vessel can be composed of the following functional modules: The control panel is equipped with an operating handle. The operating handle has a built-in encoder, which is used to collect the steering angle and speed commands given by the driver. The encoder converts the mechanical displacement into digital pulse signals and then transmits them to the PLC control system.

[0019] The PLC control system, as the core computing unit for the overall ship steering control, executes the steering control method for a ship's azimuth propeller described in this invention. The PLC control system is installed in the central control box and receives the target rudder angle command output by the encoder, the current actual rudder angle output by the rudder angle feedback device, the ship speed signal output by the shipborne navigation equipment, and the roll angle signal output by the inertial navigation system. It executes control algorithms such as roll moment prediction, rudder angle velocity limitation, load condition correction, acceleration and deceleration planning, and pulse frequency generation, and issues control commands to the stepper drive system and the variable frequency motor propulsion system respectively.

[0020] The rudder angle feedback device is installed on the slewing shaft end of the rudder mechanism. It uses an absolute or incremental angle encoder to collect the actual pointing angle of the rudder propeller in real time, forming a closed-loop feedback.

[0021] The stepper drive system includes a stepper driver, stepper motors, and a reducer. Two stepper motors are symmetrically arranged on either side of the inverter motor spindle. Each stepper motor is independently driven by its own stepper driver, allowing them to operate synchronously to increase output torque, or to maintain derating operation independently of the other in case of a single motor failure. The reducer converts the high-speed, low-torque output of the stepper motors into low-speed, high-torque steering power, driving the steering mechanism to rotate around the vertical axis.

[0022] The variable frequency motor propulsion system includes a frequency converter and a variable frequency motor. The frequency converter receives speed commands from the PLC control system and adjusts the output power of the variable frequency motor to change the propeller thrust, thereby realizing the linkage control between propulsion power and rudder movement.

[0023] The power distribution box provides branch power supply and power protection for the PLC control system, stepper driver and frequency converter.

[0024] In the above system, the stepper drive system and the variable frequency motor propulsion system are uniformly scheduled by the same PLC control system, and the steering action and propulsion power adjustment are kept synchronized at the control source level.

[0025] A method for controlling the steering of a ship's azimuth propeller, such as... Figure 1 As shown, a preferred embodiment of the present invention includes the following steps: S1: Obtain the target rudder angle command, the current actual rudder angle, and the original ship speed signals from several signal sources. Perform validity checks on the original ship speed signals respectively, and obtain the effective ship speed by fusing and filtering the valid ship speed signals. It should be noted that the target rudder angle command refers to the desired rudder angle position signal input by the driver through the control panel handle. This signal is collected by the encoder built into the handle, converted into a digital quantity, and transmitted to the PLC control system, serving as the input target value for rudder control in step S1. The current actual rudder angle refers to the current actual angle position signal of the rudder mechanism collected in real time by the rudder angle feedback device. This signal reflects the current physical pointing angle of the rudder propeller and is compared with the target rudder angle command to determine the rudder deviation. The raw ship speed signal refers to the ship speed measurement values ​​from different measuring devices, including absolute ground speed signals based on satellite positioning, speed signals based on the log, and estimated rotational speed signals based on frequency converter feedback. These signals reflect the ship's motion state from different physical dimensions. Validity verification refers to the process of checking the rationality of each raw ship speed signal, including physical limit verification and state consistency verification, used to identify and eliminate abnormal or faulty signals. Fusion filtering refers to weighting and fusing multiple valid ship speed signals according to preset weights, and filtering the fusion result to eliminate high-frequency noise, ultimately outputting a smooth and reliable valid ship speed.

[0026] Understandably, by acquiring multiple sources of raw ship speed signals and performing validity checks and fusion filtering, redundant acquisition and cross-validation of ship speed information can be achieved. This avoids distortion of ship speed information due to single sensor failure or data jumps, providing reliable basic speed data for subsequent steps and improving the accuracy and robustness of rudder control in sensing ship speed.

[0027] S2: Calculate the rate of change of the effective ship speed, determine the evaluation ship speed based on the effective ship speed and the rate of change of the effective ship speed, and calculate the estimated heeling moment generated by the current rudder turning action based on the evaluation ship speed and the current actual rudder angle. It should be noted that the rate of change of effective ship speed refers to the speed change trend calculated by performing a least-squares fitting method on the effective ship speed, reflecting the ship's current acceleration or deceleration state. The assessed ship speed refers to the reference speed value determined after comprehensively considering the effective ship speed and its changing trend, used for estimating the heel moment. When the ship is accelerating, the predicted ship speed is used to anticipate future increases in the heel moment; when the ship is decelerating, the current effective ship speed is used to avoid overestimation. The heel moment refers to the lateral capsizing moment generated on the ship by the rudder propeller due to hydrodynamic forces during deflection. The magnitude of this moment is positively correlated with the square of the ship speed and the sine of the rudder angle, and is a core indicator for assessing the safety of rudder turns. The estimated heel moment refers to the estimated heel moment generated by the rudder turn, dynamically calculated based on the assessed ship speed and the current actual rudder angle using the heel moment estimation relationship, and is used in subsequent steps to determine the maximum permissible rudder angle rate.

[0028] Understandably, by calculating the rate of change of the effective ship speed and determining the assessment speed based on the effective ship speed and the rate of change, a forward-looking perception of the ship's motion trend can be achieved. Furthermore, by calculating the estimated heeling moment based on the assessment speed and the current actual rudder angle, the hydrodynamic effect of the steering action can be quantified into a comparable safety indicator, thereby enabling steering control to assess heeling risk in advance and provide a basis for subsequent speed limits.

[0029] S3: Determine the maximum rudder angle velocity that meets the roll safety condition based on the estimated roll moment and the preset roll safety threshold, and determine the load condition correction coefficient based on the current ship load information. Use the load condition correction coefficient to correct the maximum rudder angle velocity to obtain the corrected maximum rudder angle velocity. It should be noted that the preset heel safety threshold refers to the heel moment safety boundary value pre-set according to the ship stability design specifications, including the first heel safety threshold and the second heel safety threshold, used to classify different heel risk levels. The maximum rudder turning rate refers to the highest angular velocity allowed for the rudder mechanism to operate under the current heel moment conditions. When the estimated heel moment exceeds the safety threshold, this rate needs to be lowered to limit the increase of the heel moment. Current ship loading information refers to the set of parameters reflecting the ship's current loading status, including the ship's draft, cargo loading status, and ballast water status. The loading status correction factor refers to the multiplication factor determined based on the current ship loading status to correct the maximum rudder turning rate. When the ship is in a high stability state, this factor is greater than 1; when in a low stability state, this factor is less than 1; and when in a normal stability state, this factor is equal to 1.

[0030] Understandably, by comparing the estimated heeling moment with the preset heeling safety threshold to determine the maximum rudder turning rate, the heeling moment is inversely proportional to the angular velocity, thus achieving a constraint. Furthermore, based on the current ship loading information, a loading condition correction coefficient is determined and the maximum rudder turning rate is corrected, so that the angular velocity limit can adapt to the stability changes of the ship under different loading conditions, achieving a dual safety constraint effect where the rudder turning rate limit reflects both the magnitude of the heeling moment and the ship loading condition.

[0031] S4: Generate a target rudder angle velocity based on the deviation between the target rudder angle command and the current actual rudder angle. Limit the target rudder angle velocity with the corrected maximum rudder angle velocity. Perform acceleration / deceleration planning on the limited target rudder angle velocity, convert it into a pulse frequency signal and output it to drive the rudder mechanism to perform rudder action at the planned speed.

[0032] It should be noted that the target steering angle velocity refers to the expected steering angle velocity calculated by the control algorithm based on the deviation between the target steering angle command and the current actual steering angle. This velocity reflects how quickly the steering mechanism approaches the target steering angle. Limiting refers to the process of comparing the target steering angle velocity with the corrected maximum steering angle velocity and taking the smaller value, ensuring that the actual executed steering angle velocity does not exceed the safe upper limit. Acceleration / deceleration planning refers to the process of constraining the limited target steering angle velocity with angular acceleration, limiting the change in angular velocity between adjacent control cycles to avoid mechanical shocks caused by sudden speed changes in the steering mechanism. The pulse frequency signal refers to converting the planned steering angle velocity into the pulse sequence frequency required to drive the steering actuator. This frequency is proportional to the steering angle velocity and is used to precisely control the rotation speed of the steering mechanism.

[0033] Understandably, by generating the target rudder angle velocity based on the rudder angle deviation and limiting it with the corrected maximum rudder angle velocity, the coordination between rudder response requirements and safety constraints is achieved. Furthermore, acceleration and deceleration planning is performed on the limited target rudder angle velocity and converted into a pulse frequency signal output, so that the rudder mechanism rotates towards the target rudder angle according to the smoothly planned speed curve, thereby achieving the effect of both meeting the control response requirements and avoiding mechanical shock and roll risks.

[0034] Preferably, the original ship speed signal includes an absolute ground speed signal based on satellite positioning, a speed signal relative to water based on a log, and an estimated rotational speed signal based on frequency converter feedback; The validity verification of the original ship speed signals includes: Perform physical limit verification on the original ship speed signals: For each original ship speed signal, independently determine whether its rate of change exceeds a preset physical limit threshold. If the rate of change of an original ship speed signal exceeds the physical limit threshold, then mark the original ship speed signal as an invalid signal. Perform a status consistency check on the original ship speed signal: when the numerical deviation of at least two signal sources in the original ship speed signal is greater than the preset logic tolerance, identify and remove the original ship speed signal with faults by comparing the health status bits of each signal source. Processing is performed based on the number of valid signal sources: when only one original ship speed signal is valid, the original ship speed signal corresponding to the valid signal source is taken as the valid ship speed; when there are multiple valid signals, weighted fusion is performed based on the preset confidence weight of each signal source, and first-order inertial filtering and median filtering are performed on the fused signal in sequence to obtain the valid ship speed.

[0035] It should be noted that the absolute ground speed signal refers to the speed signal output by satellite positioning equipment (such as GPS or Beidou receivers) by measuring the rate of change of a ship's position relative to the Earth's surface. This signal reflects the ship's absolute speed in the Earth's coordinate system, is unaffected by water currents, and is suitable for speed reference in open waters. The relative speed signal refers to the signal output by acoustic or electromagnetic speedometers by measuring the ship's speed relative to the surrounding water. This signal directly reflects the relative motion between the ship and the water and is the core input for propeller hydrodynamic calculations. The estimated rotational speed signal refers to the equivalent ship speed signal estimated by the frequency converter based on the propulsion motor speed feedback value, combined with the propeller pitch and slip rate. This signal has a stable correspondence with the ship's actual speed when the propulsion system is operating normally. The physical limit threshold refers to the upper limit value of single-cycle speed change set according to the ship's dynamic performance and kinematic constraints. For example, if a ship's maximum acceleration is approximately 2 knots / second and the control cycle is 100ms, then the maximum speed change per cycle is 0.2 knots, and the physical limit threshold is 0.5 knots. This threshold is used to identify abnormal data jumps caused by sensor malfunctions or communication interference. State consistency verification refers to a verification mechanism that cross-compares multiple signal sources, identifying faulty signal sources by comparing the consistency of their output values. Health status bits refer to the status flags output by each signal source device after self-testing, indicating whether the device is in normal working condition. Reliability weights refer to the fusion weighting coefficients assigned based on the historical accuracy performance of each signal source under different operating conditions; signal sources with higher accuracy are assigned larger weights. First-order inertial filtering refers to a low-pass filtering algorithm that suppresses high-frequency noise by weighted averaging of the current sampled value and the filtered value from the previous cycle. Specifically: ,in, Indicates the first The filtered output value for each control cycle. Indicates the first The original input value for each control cycle. Indicates the first The filtered output value for each control cycle. This represents the filter coefficients, with values ​​ranging from 0 to 1. A larger value indicates a faster response to the current sampled value. Median filtering is a nonlinear filtering algorithm that eliminates impulse interference by taking the median of the neighboring sampled sequences. Logic tolerance is determined based on the statistical analysis of the system errors of each signal source; for example, GPS accuracy is approximately 0.1 units, odometer accuracy is approximately 0.3 units, frequency converter estimation error is approximately 0.5 units, and the overall logic tolerance is taken as 1.0 unit.

[0036] Understandably, by introducing multi-source heterogeneous ship speed signals (satellite positioning ground speed, log speed to water, and frequency converter estimated rotational speed) and performing independent validity checks, redundant acquisition and cross-validation of ship speed information can be achieved. When multiple signals are valid, they are weighted and fused based on preset confidence weights, and first-order inertial filtering and median filtering are performed sequentially to effectively eliminate random errors and sudden interference from a single sensor. This improves the reliability, robustness, and smoothness of the effective ship speed data, providing an accurate speed basis for subsequent steps.

[0037] For example, the PLC control system reads three raw boat speed signals in a certain control cycle: GPS ground speed is 12.5 knots, speed measured by the log is 12.2 knots, and the speed estimated by the frequency converter corresponds to a boat speed of 12.8 knots. After physical limit verification, the single-cycle changes of the three signals are 0.3 knots, 0.2 knots, and 0.4 knots, respectively, all of which do not exceed the preset physical limit threshold of 0.5 knots. Therefore, all three signals pass the physical limit verification. Entering the state consistency verification stage, the maximum deviation between the three signals is 0.6 knots between the GPS ground speed and the speed measured by the log. This deviation is less than the preset logic tolerance of 1.0 knot, so there is no need to query the health status bit, and all three signals are determined to be valid. Since multiple valid signals exist, the PLC control system performs weighted fusion according to preset confidence weights (GPS ground speed weight: 0.4, speed log weight: 0.35, inverter estimated speed weight: 0.25), obtaining a fused ship speed of 12.5×0.4 + 12.2×0.35 + 12.8×0.25 = 12.47 knots. Then, a first-order inertial filter with a filtering coefficient of 0.3 is applied to the fused ship speed, resulting in a filtered ship speed of 12.43 knots. Finally, the median of the filtered sequences from the most recent five control cycles is taken, and the final output effective ship speed is 12.4 knots.

[0038] Preferably, the rate of change of the effective ship speed is obtained by performing a least squares fitting calculation on the effective ship speed; The determination of the evaluation ship speed based on the effective ship speed and the rate of change of the effective ship speed includes: A prediction time window matching the response lag time of the steering action is set, and a linear extrapolation prediction is performed based on the effective ship speed, the rate of change, and the prediction time window to obtain the predicted ship speed. When the rate of change of the effective ship speed is positive and continuously increasing, the predicted ship speed is determined as the evaluated ship speed; when the rate of change of the effective ship speed is negative, the effective ship speed is determined as the evaluated ship speed.

[0039] It should be noted that least squares fitting refers to a mathematical method that determines the parameters of the best-fitting straight line for a data sequence by minimizing the sum of squared errors. In step S3, it is used to extract the speed change trend from the historical sequence of effective ship speeds. The prediction time window refers to the time span set according to the physical lag time between the receiving of the command and the actual generation of the heeling moment by the steering mechanism. This window is used to extrapolate the current speed trend to future moments so that the heeling moment prediction can match the actual response timing of the steering action. Linear extrapolation prediction refers to a prediction method that extends the speed trend to the end of the prediction time window based on the current speed and rate of change obtained by least squares fitting, according to the assumption of uniform speed change. Specifically: ,in, Indicates the predicted ship speed. Indicates the current effective ship speed. This represents the rate of change of the effective ship speed. This indicates the prediction time window. A continuously increasing state refers to a trend where the rate of change of effective ship speed remains positive over multiple consecutive control cycles, used to determine whether the ship is in a stable acceleration process.

[0040] Understandably, by performing least squares fitting on the effective ship speed to obtain the rate of change of the effective ship speed, and setting a prediction time window that matches the lag of the steering response for linear extrapolation, the assessed ship speed can reflect the expected speed state of the ship at future moments. When the ship is accelerating, the predicted ship speed is used to respond in advance to the future increase in heeling moment, and when the ship is decelerating, the current effective ship speed is used to avoid over-prediction, so as to make the heeling moment prediction forward-looking and adapt to the time lag characteristics of the steering action.

[0041] For example, the effective ship speed history buffer maintained by the PLC control system contains data from the most recent 10 control cycles (each cycle is 100ms). The rate of change of the effective ship speed is found to be 0.8 knots / second using least squares fitting, and the current effective ship speed is 12.4 knots. Based on the response lag time of the steering mechanism, a prediction time window of 2 seconds is set. After linear extrapolation, the predicted ship speed is 12.4 + 0.8 × 2 = 14.0 knots. Since the rate of change is positive and has remained positive for the most recent 5 cycles, the ship is determined to be in a stable acceleration state, and therefore the assessed ship speed is determined to be 14.0 knots. This assessed ship speed will be used for the heel moment prediction in step S2, ensuring that the prediction result matches the heel risk when the ship reaches a higher speed in 2 seconds.

[0042] Preferably, in step S2, the calculation of the estimated tilting moment includes: Establish a pre-estimation relationship for heeling moment related to ship hydrodynamic characteristics; The speed-related heeling moment component, which reflects the intensity of the ship's hydrodynamic action, is determined based on the assessed ship speed, wherein the speed-related heeling moment component is positively correlated with the square of the assessed ship speed. The torque component generated by the deflection of the rudder blade is determined based on the current actual rudder angle, wherein the torque component is positively correlated with the sine value of the current actual rudder angle. The speed-related heel moment component and the applied moment component are nonlinearly weighted and summed, and ship stability characteristic parameters are introduced for correction to dynamically predict the predicted heel moment under the current steering action. The ship stability characteristic parameters include the ship's center of gravity height, displacement, roll moment of inertia, and initial stability height. The estimated heeling moment increases synchronously with the continuous increase of the assessed ship speed or the continuous increase of the current actual rudder angle.

[0043] It should be noted that the estimated heeling moment relationship refers to a mathematical model based on ship hydrodynamics theory. This model describes the functional relationship between the heeling moment generated by the rudder propeller under different combinations of ship speed and rudder angle and related physical quantities. The speed-dependent heeling moment component refers to the heeling moment component that reflects the influence of the incoming current pressure on the intensity of the hydrodynamic action of the rudder propeller. This component is proportional to the square of the evaluated ship speed and is determined by the formula for the incoming current pressure, which satisfies the following relationship: ,in, Indicates the incoming flow pressure. This indicates the density of water. This represents the assessed ship speed in SI units (m / s) after unit conversion. The speed-related heeling moment components satisfy the following relationship: ,in, This represents the velocity-dependent tilting moment component, in N·m. The velocity component coupling coefficient is a dimensionless value, verifiable by CFD simulation; a value of 0.85 is used. The unit is Pascal (Pa), which is... , This refers to the side projection area of ​​the rudder propeller, in square meters. This is a dimensionless coefficient of thermal drag. The lateral force arm, measured in meters (m), extends from the rudder blade's lateral pressure center to the ship's center of gravity. This arm converts the lateral water pressure of the rudder propeller into a heeling moment about the ship's longitudinal axis. The action moment component reflects the heeling moment's effect on lateral thrust caused by the rudder blade's deflection angle. This component is proportional to the sine of the rudder angle and is determined by the rudder's lift theory. It is approximately linear at small rudder angles but exhibits unsaturated characteristics at large rudder angles. The action moment components satisfy the following relationship: ,in, Indicates the torque component, The rudder effect pressure coefficient, determined through open-water rudder propeller tests, reflects the lift characteristics of the rudder blade at a specific angle of attack. Its unit is Pa, and it is set to 1000. For rudder height. Nonlinear weighted summation refers to the calculation process of nonlinearly combining the velocity-related roll moment component and the applied moment component. It uses a multiplicative coupling method to reflect the interactive enhancement effect between the two components, where the original roll moment satisfies the following relationship: ,in, Indicates the original tilting moment. The nonlinear coupling index, determined through fitting of actual ship test data, reflects the degree of synergistic enhancement between the speed and rudder angle components. An index greater than 1 indicates a synergistic enhancement effect between the two components. Ship stability characteristic parameters refer to inherent parameters reflecting a ship's resistance to heeling, including the ship's center of gravity height (vertical distance from the center of gravity to the baseline), displacement (mass of water displaced by the ship), roll moment of inertia (measure of the ship's inertia about its longitudinal axis), and initial metacentric height (vertical distance from the initial metacentric center to the center of gravity). These parameters are used to correct the estimated relationship to adapt to specific ship types; therefore, the corrected estimated heeling moment satisfies the following relationship: ,in, This indicates the estimated tilting moment, in units of... , The unit is , The reference stability height is expressed in meters (m). This is the current stable height, in meters (m). This is the baseline displacement, expressed in tons (t). Given the current discharge volume, in tons (t), then The dimensionless scale correction factor, obtained by fitting a series of ship type test data, reflects the nonlinear effect of displacement changes on the heel moment transmission characteristics. This correction makes the estimated heel moment adaptable to the current stability state and loading condition of the ship.

[0044] Understandably, by establishing a pre-estimation relationship for the heel moment, the speed-related heel moment component (positively correlated with the quadratic of the assessed ship speed) and the action moment component (positively correlated with the sine of the rudder angle) are nonlinearly weighted and summed, and ship stability characteristic parameters are introduced for correction. This allows for the dynamic prediction of the heel moment under the current rudder turning action, thereby quantifying the hydrodynamic effect of rudder turning into a comparable safety indicator. This enables subsequent steps to implement rudder turning angular velocity limits based on the prediction results.

[0045] Preferably, determining the maximum rudder angle velocity that satisfies the roll safety condition based on the estimated roll moment and the preset roll safety threshold includes: The estimated roll moment is compared with a first roll safety threshold and a second roll safety threshold, wherein the first roll safety threshold is less than the second roll safety threshold; When the estimated roll moment is not greater than the first roll safety threshold, the maximum rudder angle velocity of the previous cycle used in the current control cycle is directly used as the maximum rudder angle velocity. When the estimated roll moment is greater than the first roll safety threshold and not greater than the second roll safety threshold, the maximum rudder angle velocity is reduced according to the first decreasing ratio. When the estimated roll moment is greater than the second roll safety threshold, the maximum rudder angle velocity is reduced by a second decreasing ratio, where the second decreasing ratio is greater than the first decreasing ratio. An absolute lower limit is set for the reduced maximum steering angular velocity. The absolute lower limit is calibrated based on the minimum effective steering angular velocity corresponding to the lowest stable operating frequency of the steering mechanism.

[0046] It should be noted that the first heel safety threshold refers to a lower-level heel risk boundary value set according to the ship's stability design specifications. When the estimated heel moment does not exceed this threshold, the current steering action is considered to be within a safe range, and no angular velocity limit is required. The second heel safety threshold refers to a higher-level heel risk boundary value set according to a certain proportion of the ship's stability vanishing angle. This threshold is greater than the first heel safety threshold. When the estimated heel moment exceeds this threshold, the heel risk is considered high, and the steering angular velocity needs to be significantly reduced. The first reduction ratio refers to the smaller reduction ratio used when the estimated heel moment is between the two thresholds, used to achieve gradual speed limiting. The second reduction ratio refers to the larger reduction ratio used when the estimated heel moment exceeds the second heel safety threshold, used to achieve rapid speed limiting. The absolute lower limit value refers to the minimum value that cannot be exceeded after the maximum steering angular velocity has been reduced. This value is calculated based on the minimum stable operating frequency of the steering drive unit, ensuring that the steering mechanism maintains basic responsiveness after speed limiting and does not completely stop.

[0047] Understandably, by comparing the estimated roll moment with the first and second roll safety thresholds in three levels, the maximum steering angular velocity is reduced by a differentiated decreasing ratio under different roll risk levels, and an absolute lower limit is set to prevent excessive speed limiting. This achieves an inverse proportional constraint between the roll moment and the angular velocity, thus achieving the effect of adaptively adjusting the steering rate according to the roll risk level and maintaining the basic response capability of the steering mechanism while ensuring roll safety.

[0048] Specifically, the PLC control system executes the following logic in each control cycle: It compares the estimated roll moment obtained in step S2 with a preset first roll safety threshold and a second roll safety threshold. If the estimated roll moment is not greater than the first roll safety threshold, it indicates that the current roll risk is low, and the maximum steering angle velocity of the previous control cycle is directly used as the maximum steering angle velocity of the current cycle, i.e., no adjustment is made to the angle velocity. If the estimated roll moment is greater than the first roll safety threshold but not greater than the second roll safety threshold, it indicates that the roll risk is at a moderate level, and the maximum steering angle velocity is reduced according to the first decreasing ratio. The reduced maximum steering angle velocity satisfies the following relationship: ,in, Indicates the first Maximum rudder angle speed per control cycle Indicates the first Maximum rudder angle speed per control cycle Indicates the first decreasing percentage. This represents the relative position of the roll moment between the two threshold levels, used to achieve progressive speed limiting. If the estimated roll moment exceeds the second roll safety threshold, it indicates a higher roll risk. The maximum rudder angle rate is then reduced according to the second decreasing ratio. The reduced maximum rudder angle rate satisfies the following relationship: ,in, Indicates the second decreasing ratio. This is the reciprocal of the excess value, used to achieve rapid speed limiting. Each adjustment requires verification: if the adjusted maximum steering angular velocity is less than the absolute lower limit, it is forcibly set to the absolute lower limit, which is calculated based on the lowest stable operating frequency of the steering drive unit.

[0049] For example, assuming the maximum rudder angular velocity of the previous control cycle is 10 degrees / second, the first roll safety threshold is 30000 N·m, the second roll safety threshold is 50000 N·m, the first reduction ratio is 0.2, the second reduction ratio is 0.5, and the absolute lower limit is 2 degrees / second. The PLC control system compares the estimated roll moment of 41520 N·m with the two thresholds. Since the estimated roll moment is between the first and second roll safety thresholds, it is reduced according to the first reduction ratio: the maximum rudder angular velocity of the current cycle is 10×(1-0.2×(41520-30000) / (50000-30000))=10×(1-0.2×11520 / 20000)=10×(1-0.1152)=10×0.8848=8.848 degrees / second. The adjusted 8.848 degrees / second is greater than the absolute lower limit of 2 degrees / second, so the maximum rudder angular velocity for the current cycle is determined to be 8.848 degrees / second.

[0050] Preferably, a load condition correction coefficient is determined based on the current ship load condition information, and the maximum rudder angle velocity is corrected using the load condition correction coefficient to obtain the corrected maximum rudder angle velocity, including: Obtain current ship status information, including ship draft, cargo loading status, and ballast water status; The current displacement is determined based on the ship's draft and the ship's hydrostatic curve. The longitudinal position of the ship's center of gravity is determined based on the cargo loading status. The ballast water tank level is determined based on the ballast water status, and the weight of the ballast water and its vertical adjustment to the ship's center of gravity are calculated. The current stability height is calculated by combining the current displacement, the longitudinal position of the ship's center of gravity, and the vertical adjustment. The current stability height is compared with the reference stability height specified in the ship's design to obtain the stability height ratio. When the stability height ratio is greater than the preset first stability height threshold, the load condition correction coefficient is determined as the first preset load condition correction coefficient. The first preset load condition correction coefficient is greater than 1. The first stability height threshold is determined based on the ratio of the reference stability height calibrated by the ship design to the minimum allowable stability height under full load conditions. When the stability height ratio is not greater than the first stability ratio threshold and is greater than the preset second stability ratio threshold, the load condition correction coefficient is determined to be 1. The second stability ratio threshold is determined based on the ratio of the reference stability height calibrated by the ship design to the minimum stability height allowed under the ship's ballast conditions. The first stability ratio threshold is greater than the second stability ratio threshold. When the stability height ratio is less than or equal to the second stability ratio threshold, the load condition correction coefficient is determined as the second preset load condition correction coefficient, and the second preset load condition correction coefficient is less than 1. The maximum rudder angle velocity is multiplied by the load condition correction factor to obtain the corrected maximum rudder angle velocity.

[0051] It should be noted that the ship's hydrostatic curve refers to the design curve describing the variation of hydrostatic performance parameters (such as displacement, center of buoyancy, waterplane area coefficient, etc.) of the ship at different drafts. This curve is provided by the ship designer and pre-stored in the PLC control system, used to retrieve parameters such as the current displacement based on the measured draft. Cargo loading status refers to the current loading distribution of the ship's cargo holds, including the weight and center of gravity position of the cargo in each hold. This status is obtained through the ship's loading instrument or loading manual and is used to determine the longitudinal position of the ship's center of gravity. Ballast water status refers to the liquid level and distribution within the ship's ballast tanks, monitored in real time by level sensors, used to calculate the weight of the ballast water and its vertical adjustment effect on the ship's center of gravity. Vertical adjustment refers to the vertical displacement of the ship's overall center of gravity caused by the weight of the ballast water acting on the center of gravity position of the ballast tanks; this displacement changes the ship's stability height. The stability height ratio refers to the ratio of the current stability height to the reference stability height. This ratio reflects the stability margin level of the current load condition relative to the design reference, where the current stability height satisfies the following relationship: ,in Indicates the current level of stability. The height of the center of buoyancy (obtained from the hydrostatic curve). Let the initial steady center radius be , Let this be the center of gravity height. The current stability height is compared to the reference stability height to obtain the stability height ratio. The stability height ratio satisfies the following relationship: ,in Indicates the ratio of stability height. Indicates the current level of stability. This represents the reference stability height. The first stability ratio threshold refers to the boundary value for determining whether the ship is in a high stability state. It is calibrated based on the ratio of the reference stability height to the minimum allowable stability height under full load conditions. For example, if the reference stability height is 1.0m and the minimum allowable stability height under full load is 0.83m, the ratio is approximately 1.2, so it is taken as 1.2. The second stability ratio threshold refers to the boundary value for determining whether the ship is in a low stability state. It is calibrated based on the ratio of the reference stability height to the minimum allowable stability height under ballast conditions. For example, if the reference stability height is 1.0m and the minimum allowable stability height under ballast is 1.25m, the ratio is approximately 0.8, so it is taken as 0.8. The first preset load condition correction factor refers to a correction factor greater than 1 used in high stability conditions to appropriately relax the maximum turning rate. For example, if, after maneuverability assessment, a 15% increase in turning rate is allowed in high stability conditions, it is taken as 1.15. The second preset load condition correction factor refers to a correction factor less than 1 used under low stability conditions to further tighten the maximum steering angular velocity. If, after stability and safety assessment, the steering rate needs to be reduced by 15% under low stability conditions, then 0.85 is chosen. The corrected maximum steering angular velocity satisfies the following relationship: ,in This indicates the corrected maximum rudder angular velocity. Indicates the maximum rudder angular velocity. This represents the load condition correction factor.

[0052] Understandably, the displacement is determined by the hydrostatic curve associated with the ship's draft, the longitudinal position of the center of gravity is determined by the cargo loading status, and the vertical adjustment is calculated based on the ballast water status. The current stability height is then calculated comprehensively. The ratio of the current stability height to the reference stability height is compared with the two-level stability ratio threshold to determine the corresponding load condition correction coefficient. Finally, this coefficient is used to correct the maximum turning angular velocity, so that the angular velocity limit can adapt to the stability changes of the ship under different loading conditions. This achieves the dual safety constraint effect of the turning rate limit reflecting both the magnitude of the heel moment and the ship's load condition.

[0053] For example, the PLC control system obtains the current average draft as 6.5 meters using a draft sensor, and finds the corresponding displacement of 5500 tons in the hydrostatic curve. After obtaining the cargo loading status using a loading instrument, the longitudinal position of the ship's center of gravity is calculated to be at the forward 5% of the ship's length. Ballast tank level sensors obtain the liquid level data for each tank, calculating the total weight of ballast water to be 800 tons. The ballast water center of gravity is 2.0 meters above the baseline, resulting in a vertical adjustment of 0.15 meters to the overall ship's center of gravity. Combining these parameters, the current stability height is calculated to be 0.85 meters, and the baseline stability height is 1.0 meter, resulting in a stability height ratio of 0.85. The first stability ratio threshold is 1.2, and the second stability ratio threshold is 0.8. Since 0.8 < 0.85 < 1.2, the ship is determined to be in a normal stability state, and the loading condition correction factor is set to 1. Assuming the maximum rudder angle velocity obtained in step S3 is 8.848 degrees / second, the corrected maximum rudder angle velocity is 8.848 × 1 = 8.848 degrees / second. If the ship is under full load, the stability height ratio drops to 0.75 (less than 0.8), then the load condition correction factor is determined to be 0.85, and the corrected maximum rudder angle velocity becomes 8.848 × 0.85 = 7.52 degrees / second, achieving further speed limiting under low stability conditions.

[0054] Preferably, generating the target rudder angle velocity based on the deviation between the target rudder angle command and the current actual rudder angle includes: Calculate the original rudder angle deviation between the target rudder angle command and the current actual rudder angle, perform shortest path discrimination processing on the original rudder angle deviation, and obtain the corrected rudder angle deviation and direction control signal. The shortest path discrimination processing ensures that the steering mechanism rotates along the shortest arc length direction between the two rudder angles. The absolute value of the corrected rudder angle deviation is compared with a preset first rudder angle dead zone threshold. If the absolute value of the corrected rudder angle deviation is not greater than the first rudder angle dead zone threshold, the target rudder angle velocity is set to zero. If the absolute value of the corrected rudder angle deviation is greater than the first rudder angle dead zone threshold, the corrected rudder angle deviation is mapped to the target rudder angle velocity through a piecewise proportional function. The piecewise proportional function uses a first proportional coefficient when the absolute value of the corrected rudder angle deviation is greater than a preset first deviation threshold, and uses a second proportional coefficient when the absolute value of the corrected rudder angle deviation is not greater than the first deviation threshold but is greater than the first rudder angle dead zone threshold. The first proportional coefficient is greater than the second proportional coefficient.

[0055] It should be noted that the original rudder angle deviation refers to the algebraic difference between the target rudder angle command and the current actual rudder angle, which directly reflects the angular interval between the two rudder angles. The shortest path discrimination processing refers to the calculation process of correcting the original rudder angle deviation for a 360-degree rotation range of a full-aperture propeller: when the absolute value of the original rudder angle deviation is greater than 180 degrees, 360 degrees are subtracted from the deviation (or 360 degrees are added) to ensure that the steering mechanism always rotates along the shortest arc length direction, avoiding taking a longer path for rudder turning. The corrected rudder angle deviation refers to the actual angle deviation value used for control obtained after the shortest path discrimination processing. The direction control signal refers to the steering direction command determined according to the sign of the corrected rudder angle deviation, used to control the rotation direction of the steering drive unit. The first rudder angle dead zone threshold refers to the minimum effective deviation value set to avoid repeated jittering of the steering mechanism near the target rudder angle; when the absolute value of the deviation is less than this threshold, the steering action stops. The piecewise proportional function refers to a mapping function that uses different gain coefficients based on the magnitude of the deviation. A larger proportional coefficient is used for large deviations to achieve rapid convergence, while a smaller proportional coefficient is used for small deviations to achieve fine alignment. The first deviation threshold is the boundary value dividing the large deviation interval into the small deviation interval. When the absolute value of the corrected rudder angle deviation exceeds this threshold, it is determined to be a large deviation state requiring rapid convergence. The first proportional coefficient refers to the proportional gain value used within the large deviation interval. This coefficient is used to convert the corrected rudder angle deviation into the target rudder angle velocity, and a larger value is used for rapid response. The second proportional coefficient refers to the proportional gain value used within the small deviation interval. This coefficient is smaller than the first proportional coefficient and is used to convert the corrected rudder angle deviation into the target rudder angle velocity. A smaller value is used for fine alignment and to suppress terminal oscillations.

[0056] Understandably, by performing shortest path discrimination processing on the original rudder angle deviation, the steering mechanism is ensured to rotate along the shortest arc length direction to shorten the response time; by setting the first rudder angle dead zone threshold, the rudder mechanism is prevented from oscillating due to repeated adjustments of small deviations near the target position; by mapping the corrected rudder angle deviation to the target steering angle velocity through a piecewise proportional function, the target rudder angle is quickly approached when there is a large deviation, and the alignment is precise when there is a small deviation, thus achieving the effect of balancing steering response speed and end-point positioning accuracy.

[0057] Specifically, the PLC control system calculates the original rudder angle deviation, which satisfies the following relationship: ,in represents the original rudder angle deviation, For target rudder angle command, This is the current actual rudder angle. The original rudder angle deviation is processed using the shortest path judgment: if the original rudder angle deviation is greater than 180°, the corrected rudder angle deviation is the original rudder angle deviation minus 360°; if the original rudder angle deviation is less than -180°, the corrected rudder angle deviation is the original rudder angle deviation plus 360°; otherwise, the corrected rudder angle deviation equals the original rudder angle deviation. The direction control signal determines the clockwise or counterclockwise rudder direction based on the sign of the corrected rudder angle deviation. The absolute value of the corrected rudder angle deviation is compared with the first rudder angle dead zone threshold (0.5° in this embodiment): if the absolute value of the corrected rudder angle deviation is not greater than the first rudder angle dead zone threshold, the target rudder angle velocity is set to zero, and rudder turning is stopped to avoid jitter. If the absolute value of the corrected rudder angle deviation is greater than the first rudder angle dead zone threshold, a piecewise proportional function mapping is used: a first deviation threshold is set (15° in this embodiment), and when the absolute value of the corrected rudder angle deviation is greater than the first deviation threshold, a first proportional coefficient (0.6 in this embodiment) is used, and the target rudder angle velocity satisfies the following relationship: ,in Indicates the target's rudder angle velocity. This represents the first proportionality coefficient. This represents the absolute value of the corrected rudder angle deviation. When the absolute value of the corrected rudder angle deviation is not greater than the first deviation threshold and is greater than the first rudder angle dead zone threshold, the second proportional coefficient (0.3 in this embodiment) is used, and the target rudder angle velocity satisfies the following relationship: ,in, This represents the second proportionality coefficient. The first proportionality coefficient is greater than the second proportionality coefficient, resulting in a higher angular velocity gain over the large deviation range.

[0058] Preferably, converting the target steering angular velocity after amplitude limiting into a pulse frequency signal after acceleration / deceleration planning includes: The target rudder angular velocity is compared with the corrected maximum rudder angular velocity, and the smaller of the two values ​​is taken as the target rudder angular velocity after the amplitude is limited. The difference between the limited target rudder angular velocity and the actual output rudder angular velocity command of the previous control cycle is calculated to obtain the angular velocity change. If the absolute value of the angular velocity change exceeds a preset first angular acceleration limit, the limited target rudder angular velocity is increased or decreased according to the first angular acceleration limit to obtain the planned rudder angular velocity command. If the absolute value of the angular velocity change does not exceed the first angular acceleration limit, the limited target rudder angular velocity is directly used as the planned rudder angular velocity command. The planned rudder angle velocity command is converted into a pulse frequency signal, and the pulse frequency signal and the direction control signal are output to the rudder drive unit to drive the rudder mechanism to rotate towards the target rudder angle command at the planned speed.

[0059] It should be noted that the target steering angular velocity after limiting refers to the smaller value obtained by comparing the target steering angular velocity with the corrected maximum steering angular velocity obtained in step S3. This value reflects both the steering response requirements and is subject to safety constraints. The actual output steering angular velocity command of the previous control cycle refers to the angular velocity value finally output to the steering drive unit after acceleration / deceleration planning in the previous cycle, serving as the benchmark reference for acceleration limits in the current cycle. The angular velocity change refers to the difference between the target steering angular velocity after limiting in the current cycle and the actual output angular velocity command of the previous cycle. The sign of this change reflects the acceleration or deceleration trend, and the absolute value reflects the severity of the speed change. The first angular acceleration limit refers to the preset upper limit of the steering angular velocity change rate, in degrees / second², used to constrain the acceleration of the steering mechanism to avoid mechanical shock. The planned steering angular velocity command refers to the final determined angular velocity output value after acceleration / deceleration planning. This value adds acceleration constraints to the target steering angular velocity after limiting, making speed changes smoother. The pulse frequency signal refers to the frequency value of the planned rudder angular velocity command converted into a drive pulse sequence according to the transmission parameters of the rudder mechanism. This frequency value is proportional to the angular velocity and is the direct control input of the rudder drive unit.

[0060] Understandably, a safe speed limit is achieved by comparing the target steering angular velocity with the corrected maximum steering angular velocity and taking the smaller value. Furthermore, the difference between the limited target steering angular velocity and the actual output of the previous cycle is calculated. If the change in angular velocity exceeds the first angular acceleration limit, the limit is increased or decreased, thus constraining the rate of change of steering speed. Finally, the planned steering angular velocity command is converted into a pulse frequency signal and output along with the direction control signal, driving the steering mechanism to rotate towards the target steering angle according to the smoothly planned speed curve. This achieves the effect of satisfying steering response requirements while avoiding mechanical shock caused by sudden speed changes.

[0061] Specifically, the PLC control system compares the target rudder angular velocity with the corrected maximum rudder angular velocity obtained in step S3, and takes the smaller value as the target rudder angular velocity after limiting. The target rudder angular velocity after limiting satisfies the following relationship: ,in, This indicates the target's rudder angle velocity after amplitude limiting. Indicates the target's rudder angle velocity. This represents the corrected maximum rudder angular velocity. The difference between the target rudder angular velocity after limiting and the actual output rudder angular velocity command from the previous control cycle is calculated to obtain the change in angular velocity. The change in angular velocity satisfies the following relationship: ,in, Indicates the change in angular velocity. Indicates the first The actual output steering angle velocity command for each control cycle. The absolute value of the change in angular velocity is compared with a preset first angular acceleration limit: if the absolute value of the change in angular velocity is greater than the first angular acceleration limit, the adjustment is made according to the first angular acceleration limit. The planned steering angle velocity command satisfies the following relationship: ,in, Indicates the first After planning each control cycle, the rudder angle speed command is executed. The sign function representing the change in angular velocity. Indicates the first angular acceleration limit. This formula represents the control period. It converts the angular acceleration limit multiplied by the control period into the maximum allowable angular velocity increment within a single period, ensuring that the angular velocity and angular acceleration dimensions are matched. If the absolute value of the angular velocity change does not exceed the first angular acceleration limit, the target steering angular velocity after the limit is directly used as the planned steering angular velocity command. Finally, the planned steering angular velocity command is converted into a pulse frequency signal, which satisfies the following relationship: ,in, Indicates pulse frequency signal, Indicates the reduction ratio of the speed reducer. Indicates the microstepping value of the stepper driver. This indicates the single-step rotation angle of the motor. This pulse frequency signal, along with the direction control signal, is output to the steering drive unit, driving the steering mechanism to perform steering actions at the planned speed.

[0062] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0063] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. A method for controlling the steering of a ship's azimuth propeller, characterized in that, Includes the following steps: S1: Obtain the target rudder angle command, the current actual rudder angle, and the original ship speed signals from several signal sources. Perform validity checks on the original ship speed signals respectively, and obtain the effective ship speed by fusing and filtering the valid ship speed signals. S2: Calculate the rate of change of the effective ship speed, determine the evaluation ship speed based on the effective ship speed and the rate of change of the effective ship speed, and calculate the estimated heeling moment generated by the current rudder turning action based on the evaluation ship speed and the current actual rudder angle. S3: Determine the maximum rudder angle velocity that meets the roll safety condition based on the estimated roll moment and the preset roll safety threshold, and determine the load condition correction coefficient based on the current ship load information. Use the load condition correction coefficient to correct the maximum rudder angle velocity to obtain the corrected maximum rudder angle velocity. S4: Generate a target rudder angle velocity based on the deviation between the target rudder angle command and the current actual rudder angle. Limit the target rudder angle velocity with the corrected maximum rudder angle velocity. Perform acceleration / deceleration planning on the limited target rudder angle velocity, convert it into a pulse frequency signal and output it to drive the rudder mechanism to perform rudder action at the planned speed.

2. The rudder control method for a ship's azimuth propeller according to claim 1, characterized in that, The original ship speed signal includes an absolute ground speed signal based on satellite positioning, a speed signal relative to water based on a log, and an estimated rotational speed signal based on feedback from a frequency converter. The validity verification of the original ship speed signals includes: Perform physical limit verification on the original ship speed signals: For each original ship speed signal, independently determine whether its rate of change exceeds a preset physical limit threshold. If the rate of change of an original ship speed signal exceeds the physical limit threshold, then mark the original ship speed signal as an invalid signal. Perform a status consistency check on the original ship speed signal: when the numerical deviation of at least two signal sources in the original ship speed signal is greater than the preset logic tolerance, identify and remove the original ship speed signal with faults by comparing the health status bits of each signal source. Processing is performed based on the number of valid signal sources: when only one original ship speed signal is valid, the original ship speed signal corresponding to the valid signal source is taken as the valid ship speed; when there are multiple valid signals, weighted fusion is performed based on the preset confidence weight of each signal source, and first-order inertial filtering and median filtering are performed on the fused signal in sequence to obtain the valid ship speed.

3. The rudder control method for a ship's azimuth propeller according to claim 2, characterized in that, The rate of change of the effective ship speed is obtained by performing a least squares fitting calculation on the effective ship speed. The determination of the evaluation ship speed based on the effective ship speed and the rate of change of the effective ship speed includes: A prediction time window matching the response lag time of the steering action is set, and a linear extrapolation prediction is performed based on the effective ship speed, the rate of change, and the prediction time window to obtain the predicted ship speed. When the rate of change of the effective ship speed is positive and continuously increasing, the predicted ship speed is determined as the evaluated ship speed; when the rate of change of the effective ship speed is negative, the effective ship speed is determined as the evaluated ship speed.

4. The rudder control method for a ship's azimuth propeller according to claim 1, characterized in that, In step S2, the calculation of the estimated tilting moment includes: Establish a pre-estimation relationship for heeling moment related to ship hydrodynamic characteristics; The speed-related heeling moment component, which reflects the intensity of the ship's hydrodynamic action, is determined based on the assessed ship speed, wherein the speed-related heeling moment component is positively correlated with the square of the assessed ship speed. The torque component generated by the deflection of the rudder blade is determined based on the current actual rudder angle, wherein the torque component is positively correlated with the sine value of the current actual rudder angle. The speed-related heel moment component and the applied moment component are nonlinearly weighted and summed, and ship stability characteristic parameters are introduced for correction to dynamically predict the predicted heel moment under the current steering action. The ship stability characteristic parameters include the ship's center of gravity height, displacement, roll moment of inertia, and initial stability height. The estimated heeling moment increases synchronously with the continuous increase of the assessed ship speed or the continuous increase of the current actual rudder angle.

5. The rudder control method for a ship's azimuth propeller according to claim 1, characterized in that, Determining the maximum rudder angle velocity that satisfies the roll safety condition based on the estimated roll moment and the preset roll safety threshold includes: The estimated roll moment is compared with a first roll safety threshold and a second roll safety threshold, wherein the first roll safety threshold is less than the second roll safety threshold; When the estimated roll moment is not greater than the first roll safety threshold, the maximum rudder angle velocity of the previous cycle used in the current control cycle is directly used as the maximum rudder angle velocity. When the estimated roll moment is greater than the first roll safety threshold and not greater than the second roll safety threshold, the maximum rudder angle velocity is reduced according to the first decreasing ratio. When the estimated roll moment is greater than the second roll safety threshold, the maximum rudder angle velocity is reduced by a second decreasing ratio, where the second decreasing ratio is greater than the first decreasing ratio. An absolute lower limit is set for the reduced maximum steering angular velocity. The absolute lower limit is calibrated based on the minimum effective steering angular velocity corresponding to the lowest stable operating frequency of the steering mechanism.

6. The rudder control method for a ship's azimuth propeller according to claim 5, characterized in that, Based on the current ship loading information, a loading correction factor is determined. This loading correction factor is then used to correct the maximum rudder angle velocity, resulting in the corrected maximum rudder angle velocity, which includes: Obtain current ship status information, including ship draft, cargo loading status, and ballast water status; The current displacement is determined based on the ship's draft and the ship's hydrostatic curve. The longitudinal position of the ship's center of gravity is determined based on the cargo loading status. The ballast water tank level is determined based on the ballast water status, and the weight of the ballast water and its vertical adjustment to the ship's center of gravity are calculated. The current stability height is calculated by combining the current displacement, the longitudinal position of the ship's center of gravity, and the vertical adjustment. The current stability height is compared with the reference stability height specified in the ship's design to obtain the stability height ratio. When the stability height ratio is greater than the preset first stability height threshold, the load condition correction coefficient is determined as the first preset load condition correction coefficient. The first preset load condition correction coefficient is greater than 1. The first stability height threshold is determined based on the ratio of the reference stability height calibrated by the ship design to the minimum allowable stability height under full load conditions. When the stability height ratio is not greater than the first stability ratio threshold and is greater than the preset second stability ratio threshold, the load condition correction coefficient is determined to be 1. The second stability ratio threshold is determined based on the ratio of the reference stability height calibrated by the ship design to the minimum stability height allowed under the ship's ballast conditions. The first stability ratio threshold is greater than the second stability ratio threshold. When the stability height ratio is less than or equal to the second stability ratio threshold, the load condition correction coefficient is determined as the second preset load condition correction coefficient, and the second preset load condition correction coefficient is less than 1. The maximum rudder angle velocity is multiplied by the load condition correction factor to obtain the corrected maximum rudder angle velocity.

7. The rudder control method for a ship's azimuth propeller according to claim 1, characterized in that, The target rudder angle velocity is generated based on the deviation between the target rudder angle command and the current actual rudder angle, including: Calculate the original rudder angle deviation between the target rudder angle command and the current actual rudder angle, perform shortest path discrimination processing on the original rudder angle deviation, and obtain the corrected rudder angle deviation and direction control signal. The shortest path discrimination processing ensures that the steering mechanism rotates along the shortest arc length direction between the two rudder angles. The absolute value of the corrected rudder angle deviation is compared with a preset first rudder angle dead zone threshold. If the absolute value of the corrected rudder angle deviation is not greater than the first rudder angle dead zone threshold, the target rudder angle velocity is set to zero. If the absolute value of the corrected rudder angle deviation is greater than the first rudder angle dead zone threshold, the corrected rudder angle deviation is mapped to the target rudder angle velocity through a piecewise proportional function. The piecewise proportional function uses a first proportional coefficient when the absolute value of the corrected rudder angle deviation is greater than a preset first deviation threshold, and uses a second proportional coefficient when the absolute value of the corrected rudder angle deviation is not greater than the first deviation threshold but is greater than the first rudder angle dead zone threshold. The first proportional coefficient is greater than the second proportional coefficient.

8. The rudder control method for a ship's azimuth propeller according to claim 7, characterized in that, After performing acceleration / deceleration planning on the target steering angular velocity after amplitude limiting, the signal is converted into a pulse frequency signal, including: The target rudder angular velocity is compared with the corrected maximum rudder angular velocity, and the smaller of the two values ​​is taken as the target rudder angular velocity after the amplitude is limited. The difference between the limited target rudder angular velocity and the actual output rudder angular velocity command of the previous control cycle is calculated to obtain the angular velocity change. If the absolute value of the angular velocity change exceeds a preset first angular acceleration limit, the limited target rudder angular velocity is increased or decreased according to the first angular acceleration limit to obtain the planned rudder angular velocity command. If the absolute value of the angular velocity change does not exceed the first angular acceleration limit, the limited target rudder angular velocity is directly used as the planned rudder angular velocity command. The planned rudder angle velocity command is converted into a pulse frequency signal, and the pulse frequency signal and the direction control signal are output to the rudder drive unit to drive the rudder mechanism to rotate towards the target rudder angle command at the planned speed.

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