Hybrid system modelling, simulation and visualisation: A crane system

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Hybrid system modelling, simulation and
visualisation A crane system
UNIVERSITY OF CAMBRIDGE
2003 VTB Users and Developers Conference
September 17-18, 2003
Sahan Gamage and Patrick Palmer University of
Cambridge Department of Engineering
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OVERVIEW

• 1. Brief Introduction to the system
• 2. Mathematical Model
• 3. Implementation in VTB/VXE
• 4. Demonstration
• 5. Simulation and Visualisation challenges
• 6. Conclusions

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CNOOC Crane Barge - AMCLYDE Crane

• 5000 tonne lift
• 3 Hooks plus a Whip Hook

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CNOOC(Chinese National Offshore Oil Company)
Crane - Overview

• High Power Demands
• Multiple Large AC Drives
• Power Management System
• Integrated Mechanical and Electrical Systems

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CNOOC
MECHANICAL SYSTEM

• One main hook with 3800T max load
• Two auxiliary hooks with 200T and 800T max
• One whip hook with 50T max
• 51m Boom
• 6 degrees of freedom in the Mechanical System

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CNOOC Crane Barge
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CNOOC
ELECTRICAL SYSTEMS by Ansaldo Hill Graham

• 3 x 5MW Diesel generators
• 2 x 6.6kV 3ph 50Hz buses
• 2 x 3MW Thrusters
• 12 x 1150hp AC Winch Drives
• 3 x 6.6kV input transformers with phase shift
  secondaries
• Paralleled Diode rectifier bridges
• dc bus in three sections
• 9 x 1200 kW AC Drives
• 4 Hoist, 2 Boom, 1 Whip and 6 Swing motors
• 3 Shared braking resistors

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AMCLYDE Crane One Line Diagram
1250A
6600V/3/50Hz
630A
630A
630A
EXTENDED DELTA (PSEUDO 24 PULSE)
3.5MVA
2.5MVA
3.5MVA
-7½º
7½º
DC BUS
BRAKING
BRAKING
BRAKING
MH
MH
BH
MH
BH
MH
7x GE Type GEB AC1150HP, 600V, 6 POLE, 800/1800RPM
6 x 400HP, 600V, 1000/1650RPM
HOISTS
SWING
HILL GRAHAM CONTROLS LTD
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CNOOC
AMCLYDE CRANE CONTROLS - Ansaldo Hill Graham

• Vector Control ac Drives
• Speed reference inputs
• Proportional Integral controllers
• Motor current control with field weakening
• Integrator and Torque limiters
• Main 2 Aux. hooks share the same drive
• 4 motors in the drive
• Selected by clutches
• Controller not aware of the drum selected
• Whip hook has a separate motor and drum
• 2 motor boom hoist system
• 2 sets of 3 motor swing system

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Design issues of the Crane

• Resonance of the swing and boom systems
• Crane Operator Training Pedals, hoist control
  levers and swing
• Controller design for the motor system
• Disc brakes on motor shafts for parking and
  Torque proving.
• 85 efficiency on lifting
• Use of Field weakening in lowering
• Electro-Mechanical Stability of generators and
  the AVR control of bus volts.

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Crane modelling

• Inertial considerations are essential as the
  masses and moments of inertia of the crane
  components are high
• Needs to model the full translational and
  rotational dynamics relative to an inertial
  (non-accelerating) frame of reference
• Electrical drives modeled by their control
  function with an outer loop speed controller.
• Overall system is controlled by the operator

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Crane Mathematical Model
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Crane Mathematical Model(2)

• The rotation of the boom and the swing

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Crane Dynamics Modelling
The basic dynamics of rotation (in Geometric
Algebra)
Use of Geometric Algebra gives ease of derivation
and Implementation in VTB
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Inertial Torque of the Boom
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Dynamics of the Boom
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Crane Mathematical Model - Kinematics
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Dynamics of the Load
(and motor torque demands)
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Modelling the Crane in VTB

• Complex Mechanical system with 5 degrees of
  freedom
• Lumped load to remove twisting of the cables
• Light cables so resonance in the cables is not
  possible
• No swing controller implemented
• Brake model implemented, with dynamic losses and
  torsion
• Vector controlled ac drives modeled using dc
  motor equations
• PI controllers on angular velocity of motors
• Driver controller feedback to reference angular
  velocity

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Crane System Implementation in VTB
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Visualisation the Crane in VXE

• Two methods
• classical plots
• 3D plug-ins
• 3D plug-ins can be used in
• flat build-in 3D models
• hierarchy of elementary 3D models
• In hierarchical method a special transform block
  glued to each plug-in before placing in the
  hierarchy
• crane base -gtcrane body-gtcrane arm
• hook (and the load) separate

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Crane in VXE(2)
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Interaction between VTB and VXE

• Bi-directional
• Data input to VXE
• real-time data streams from VTB
• calculated streams
• from file
• generated stream
• Data in VXE can be fed to transform blocks to
• scale/rotate/translate x,y,z (9 DoF) plug-ins
  down the hierarchy
• Data can be fed back to VTB
• keyboard and mouse control in VXE
• any VTB model parameter can be fed

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Crane in VXE
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Crane Demonstration

• Driving using control knobs
• Effects on motor currents of the mechanical
  resonance
• Control strategy on each swing, boom and lift
• Application of break and torque proving

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Discussion of Results

• Resonance of the swing and boom systems can be
  seen in the motor currents
• Damping and other control strategies can be
  observed
• Crane Operator Training Pedals, hoist control
  levers and swing (left/right) through VTB but not
  everything (zero problem).
• Visualisation and driver interaction identifies
  operational issues such as torque proving
  (remember last good motor current).

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VTB Specific Issues

• Flat VTB model hierarchy
• Users need multiple-layer modelling facilities so
  that complex elements may be created from native
  parts.
• e.g. crane from connecting mechanical parts
• Harmonic analysis is important in mixed
  discipline simulation
• e.g. analysis of electrical resonance caused by
  crane dynamics

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Specific VTB Issues(2)

• Lack of stiff solver limits VTB
• e.g. complex dynamical equations in the crane
  system
• Variable time step solver required
• e.g. time step dependant unstability wrt some
  crane parameters
• Manual derivation of RC companion model
  cumbersome for complex systems
• e.g. RC companion model of the crane system is
  the time integration of the linearised system of
  the already complex model

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Simulation and Visualisation Challenges

• Multilevel modelling
• breadth in model levels
• e.g. system boundary
• depth in model levels
• e.g. how complex and closer to reality
• Often inter-related
• e.g. accurate modelling often needs expanding
  boundary

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Simulation and Visualisation Challenges(2)

• Automatic Level Changing
• initial condition handling in level changes
• different time stepping in subsystems
• subsystem synchronisation and co-ordination
• How to make the decision?
• subsystem input activity
• subsystem output demand
• time and space constraints
• user input of some form required

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Visualisation driven Automatic levels

• At a given time observer interacts with
  relatively few details
• focused plot/ 3D visualisation window
• opened feedback controls
• This usually implies the level of detail required
• zoom level -gt depth level
• plots/3D/controls of limited subsystems -gt
  breadth level

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Visualisation driven Automatic levels (2)

• Examples
• if time axis scaling of a rectifier is order of
  magnitude above AC input cycle a simple
  behavioural model may be adequate
• if only the movement of the crane load is
  observed system boundary may be brought to a
  level of simple DC supply for motors
• Combined with subsystem level change strategy,
  this may lead to consistent set of rules
• Complex repeatability requirements since
  dynamical user dependant accuracies
• Sensible manual over-rides required

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Conclusions

• Complex system with electrical and mechanical
  subsystems
• Interdisciplinary issues have to be considered
• dynamics of the crane,
• control of the electrical motors,
• torque proving
• power supply transients
• VTB is capable of handling these issues - but
  only by hand coding mechanical systems.

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The Future?

• Mechanisms made up of an assembly of simple parts
• Multilevel mechanics modelling is required for
  complex systems
• Automatic model change is desirable in complex
  system simulation
• Visualisation cues may be used in simulation