Abstract
The interest in wave energy converters (WECs) is increasing, the study of grid connection of WEC along with the control system has become inevitable. WEC such as an oscillating water column (OWC) device involves conversions in various physical domains, thus a model describing the conversions at each stage and coupling between them should be accurate yet simple enough to reduce the computation time involved. The already existing models do not include all the components of wave to wire conversion. This paper presents a wave to wire model for control system studies. The model reduction technique is used to create a dynamically equivalent model for any large systems have more interconnecting stages. The dynamics involved in conversion stages are hydrodynamic and aerodynamic coupling at the capture chamber, aerodynamic and thermodynamic coupling inside the capture chamber, aerodynamic and rotor dynamic coupling in air turbine; and rotor dynamics and generator dynamics in the turbine generator coupling. Thus, a wave to wire model is represented to capture all the dynamics involved. It is observed that the model retains its fundamental physics, improves the computation time and reduces the number of unknowns to describe the state-space of OWC system. The accuracy and efficiency of the model is investigated through various static and dynamic analyses and found acceptable for OWC-WEC control system studies.
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Abbreviations
- DFIG:
-
Doubly fed induction generator
- OWC:
-
Oscillating water column
- PTO:
-
Power take-off
- ROM:
-
Reduced-order model
- WEC:
-
Wave energy converter
- a :
-
Wave amplitude
- Vc :
-
Volume of the air chamber
- B :
-
Damping coefficient
- b t :
-
Rotor blade height
- C :
-
Hydrostatic stiffness
- C a :
-
Input power coefficient
- C d :
-
Discharge coefficient
- Cs :
-
Speed of sound
- C t :
-
Torque coefficient
- d :
-
Draft of the OWC
- D t :
-
Diameter of the turbine
- D :
-
System drag
- E ′ dq :
-
Transient voltage
- F a :
-
Added mass force
- F FK :
-
Froude–Krylov force
- F Δpair :
-
Air force on water column
- g :
-
Acceleration due to gravity
- h :
-
Water depth
- H :
-
Wave height
- h a0 :
-
Height of the water column
- i dq :
-
Direct quadrature axis current
- J :
-
Moment of inertia of motor generator set
- k :
-
Wave number
- K :
-
Stiffness coefficient
- K t :
-
Turbine constant
- L :
-
Wavelength
- l r :
-
Chord length of rotor
- M :
-
Water column mass
- R c :
-
Radius of the water column
- R :
-
Resistance
- r t :
-
Mean radius of the turbine
- T i :
-
Time period
- T e :
-
Electromagnetic torque
- T o :
-
Transient open circuit time constant
- T t :
-
Turbine torque
- U r :
-
Circumferential velocity
- v dq :
-
Direct quadrature axis voltage
- v x :
-
Mean axial velocity
- X :
-
Reactance
- X ′ :
-
Transient impedance
- z :
-
Internal free surface elevation
- Z :
-
Impedance
- z t :
-
Number of blades
- γ :
-
Heat capacity ratio of air
- Δp :
-
Pressure drop between the chamber and atmosphere
- ζ:
-
Damping coefficient
- η :
-
Water surface elevation
- θ r :
-
Torsional displacement of the rotor
- ρ a :
-
Density of air
- ρ s :
-
Density of water
- ύ :
-
Water particle velocity
- ϕ :
-
Phase angle of the wave
- ϕ t :
-
Flow coefficient
- ω :
-
Wave angular frequency
- ω r :
-
Rotor angular frequency
- ω s :
-
Generator angular frequency
- m :
-
Mass of air inside the chamber
- M a :
-
Added mass
- N r :
-
Rotor speed
- p :
-
Number of generator poles
- p c :
-
Chamber pressure
- q :
-
Volume flow rate
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Suchithra, R., Samad, A. (2019). Control-Oriented Wave to Wire Model of Oscillating Water Column. In: Murali, K., Sriram, V., Samad, A., Saha, N. (eds) Proceedings of the Fourth International Conference in Ocean Engineering (ICOE2018). Lecture Notes in Civil Engineering , vol 23. Springer, Singapore. https://doi.org/10.1007/978-981-13-3134-3_52
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DOI: https://doi.org/10.1007/978-981-13-3134-3_52
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