Ship Dynamic Positioning handle operating mode PID control,

 

    (Automation, Guangdong University of Technology, Guangzhou 510006)

 

Abstract: Ship Dynamic Positioning handle operating modes exhibit multi-variable, strong coupling, nonlinear and time-varying characteristics, proposed an incremental PID decoupling control method. Consider sway yawing angular velocity and the coupling between the problem, using feedforward compensation decoupling method for the dynamic model of the ship decouple; according decoupled dynamic model of the ship, using incremental PID control algorithm, respectively vertical swing speed, sway velocity and yawing angle 3 degrees of freedom to design appropriate controller. Simulation results show that the controller tracking fast, real good robustness to meet the requirements of engineering applications.

 

Keywords: dynamic positioning; dynamic model; handle; decoupling; PID control

 

CLC: TP273 Document identification number: A Article ID :1000 -7024 (2012) 12-4736-05

 

Introduction

 

    Dynamic Positioning (dynamic positioning, DP) with the mooring system is not under its own power through the vessel to maintain the predetermined position, DP system in general by the position measuring system, control system and thrust'' 2 system consists of three parts. . Compared with the traditional way of anchoring, DP system, positioning accuracy, high mobility, easy to operate and is not limited depth. Promote the development of marine development on the growing demand for the DP system and added the DP system research efforts. Currently operating mode DP system rhyme with handle operation mode, heading control, automatic navigation, positioning hold, target tracking and automatic track 2. . Ship Dynamic Positioning handle operating mode is defined by a handle to manipulate the ship, with the manipulation of flexible, simple, fast response and so on. Handle operation mode for the working principle and the ship's dynamics model, proposed the use of incremental PID decoupling control method. Text

 

A kinematic model of the ship

 

    Ship handle control mode refers to the handle on the operation panel to manually control the ship's forward, backward, sliding, stop [f:, steering, navigation and speed ramps. By the ship departing LJ, platform operation is particularly applicable, the operation is flexible, simple and reliable.

 

    Ships in establishing mathematical model, usually using two coordinate systems: one to coordinate OEXE YEZE and onboard coordinates OX YZ, shown in Figure 1. Ground coordinate system in humans, XE pointing north, YE pointing east, ZE point geocentric; in the ship's coordinate system, the coordinate origin 0 is located in the ship's particle, X axis pointing bow, y-axis pointing to the ship's starboard , Z axis pointing to bottom, jealous for the ship's yawing angle.

 

    In the wind, wave and current action, unconstrained movement of the ship has six degrees of freedom motion characteristics, each degree of freedom contains the high and low frequency movements. In general, high-frequency motion does not make ship-generated changes in position, so only consider the dynamic positioning vertical swing, sway and yawing three degrees of freedom in the low-frequency horizontal motion. Ship handle control mode mainly consider vertical swing speed, sway and yawing angle speed motion control, from the ship's kinetic equation (2) can be seen, the ship sway velocity and yawing angular velocity coupling exists, we must first design Decoupler to eliminate the coupling between them, to achieve independent control of each circuit between.

 

2 PID Decoupling Controller Design

 

2.1 Decoupling Control

 

    In the multi-input multi-output control system, when a strong interaction between input and output, it will interfere with the independence of the loop variable control action, or even destroy the normal operation. Therefore, the need to consider the use of decoupling control to eliminate the effects of coupling between the variables. Multivariable coupling system for decoupling, the current use has more: feedforward compensation decoupling method, feedback decoupling method, the diagonal matrix decoupling method and the unit matrix decoupling method 6-8]. Feedforward compensation decoupling method is simple, easy to implement, the effect is significant, widely used in engineering. With feedforward compensator fully decoupled system block diagram shown in Figure 2.

 

2.2 Incremental PID algorithm design

 

    Since entering the field of computer control, digital control and more widely. Control algorithms and logic functions can be implemented by a digital computer to make the control more flexible. He mounted, incremental and Velocity is the ideal PID grate-style three kinds of discrete expression. Using positional PID calculation to the e (k) for accumulating, computing the amount of people '9 -1 "1]. Moreover, the control quantity r (k) corresponds directly to the output of the input actuator, when the computer fault occurs, person executive body will produce amplitude variations, which can cause cell damage and even lead to accidents in production, while the incremental PID control output only increment △ r (k), so the malfunction is little effect. △ r (☆) through A time deviation and the deviation of the first two moments to calculate, A timing control amount f (k) by the △ r (&) and f (kl) by adding together by such a weighting process can reduce the computation time, save memory, and get better control effect. using incremental PID manual / automatic switchover impact of small, easy to implement bumpless rio]. lever operated the ship dynamic positioning mode, the system input signal through the handle and the rotary encoder input , the choice of programmable logic controllers (programrnable logic con-trollcr, PLC) as the main controller, requiring the system output can quickly react incremental PID can meet the control requirements of this mode.

 

     Enter the vertical axis, respectively, swing handle speed, sway velocity and yawing angular velocity limit yawing angle by rotating the encoder input. During the rotation speed of the ship is not too fast, so that the Z axis of the handle to enter the yawing angular velocity limits. External load force of the wind, wave and current through feedforward compensation to the controller output. Figure 3 shows the system frame.

 

    Supply vessels according to the selected model parameters, select the simulation sampling time is 1. 2s, located a vertical swing boat speed "is given as 20m / s, horizontal swing speed" given as lOm / s, yawing angle Ang is given as 50. . Vertical swing speed controller Kci scale factor of 0.3, the integration time constant Tl.r take 47.24, differential time constant TD_r take 0.4724. Sway speed controller proportional coefficient Kcy take 0.29, integration time constant Tly take 23.967. Differential time constant TDy take 0.2397. Yawing angle from the outer loop controller perspective, the inner controller yawing angular velocity. Yawing angle controller scaling factor Kcang 0.1, the integral time constant Tlang take 2.0747, differential time constant TDang take O; yawing angular velocity controller proportional coefficient Kca take 0.029, integration time constant Tla take 6.224, differential time constant TDa take 0.06224. Adjust yawing angle control loop, the first inner parameter tuning, making yawing angular output stable, then set the outer parameters. In still simulation environment, so take the external load force is O, the simulation waveform shown in Figure 4 to Figure 6.

 

    From Figure 4 to Figure 6, the ship's vertical swing speed, sway velocity and yawing angle smooth the transition process, small overshoot, quick response, we design a PID decoupling controller to obtain satisfactory control effect, and can In applications to meet the ship control requirements.

 

    Individually change the sway velocity and yawing angle input, validate the decoupling PID Decoupling Controller situation. Individually change the sway velocity and yawing angle, observe the output waveform changes. Given the ship's sway velocity 30m / s, yawing angle remains 50. , Simulation waveforms shown in Figure 7.

 

    Ship yawing angle to 200. , Sway speed remains lOm / s, simulation waveforms shown in Figure 8.

 

    Figure 5 - Figure 6 and 7 compared to 8 shows that the speed of the input change sway and roll angle will not cause the output of the bow, and the yawing angle of the input changes on the output of sway velocity has no effect, indicating that the text use Decoupler can effectively eliminate the sway speed and yawing angle between the coupling.

 

    Changing parameters of the simulation model ship, ship's parameters by the formula (13) into formula (14), PID decoupling controller parameters remain unchanged. Simulation waveforms shown in Figure 9, we can see that the parameters are changed when the ship after ship vertical swing speed, sway velocity and yawing angle of the output waveform adjustment time increases, the overshoot becomes fire, but still meet the control requirements proved that the controller parameters of the model, have a strong robustness

 

4 Conclusion

 

    According to the working principle of the handle operation mode and the dynamic model of the ship, design a incremental PID decoupling controller, Dynamic Positioning handle operating mode. The first to use feedforward compensation decoupling algorithm effectively eliminates sway velocity and yawing angular coupling between, and then use incremental PID control algorithm respectively vertical swing speed, sway velocity and yawing angle 3 degrees of freedom accordingly The control section. Simulation results demonstrate the effectiveness of decoupling PID controller, small overshoot, fast response, and ship in changing the input parameters of the system can still meet the control requirements. The controller is easy to achieve project has strong robustness.