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Research Papers

System Modeling and Simulation of In-Stream Hydrokinetic Turbines for Power Management and Control

[+] Author and Article Information
Vasileios Tzelepis

School of Naval Architecture and
Marine Engineering,
University of New Orleans,
2000 Lakeshore Drive,
New Orleans, LA 70148
e-mail: vtzelepi@uno.edu

James H. VanZwieten

Southeast National Marine
Renewable Energy Center,
Florida Atlantic University,
777 Glades Road,
Boca Raton, FL 33067
e-mail: jvanzwi@fau.edu

Nikolaos I. Xiros

School of Naval Architecture and
Marine Engineering,
University of New Orleans,
2000 Lakeshore Drive,
New Orleans, LA 70148
e-mail: nxiros@uno.edu

Cornel Sultan

Mem. ASME
Department of Aerospace and
Ocean Engineering,
Virginia Tech,
215 Randolph Hall,
Blacksburg, VA 24061
e-mail: csultan@vt.edu

1Corresponding author.

Contributed by the Dynamic Systems Division of ASME for publication in the JOURNAL OF DYNAMIC SYSTEMS, MEASUREMENT, AND CONTROL. Manuscript received September 30, 2015; final manuscript received November 7, 2016; published online March 13, 2017. Assoc. Editor: Evangelos Papadopoulos.

J. Dyn. Sys., Meas., Control 139(5), 051005 (Mar 13, 2017) (15 pages) Paper No: DS-15-1472; doi: 10.1115/1.4035235 History: Received September 30, 2015; Revised November 07, 2016

Electricity generation from moving currents without using dams (i.e., in-stream hydrokinetic electricity) has the potential to introduce multiple GW of renewable power to U.S. grids. This study evaluates a control system designed to regulate the generator rotor rate (rpm) to improve power production from in-stream hydrokinetic turbines. The control algorithm is evaluated using numerical models of both a rigidly mounted tidal turbine (TT) and a moored ocean current turbine (OCT) coupled to an induction electric machine model. The moored simulation utilizes an innovative approach for coupling a multiple degrees-of-freedom (DOF) nonlinear hydrodynamic/mechanical turbine model with a nonlinear electromechanical generator model. Based on the turbine torque-speed characteristic, as well as the asynchronous machine features, a proportional–integral (PI) controller is used to generate a correction term for the frequency of the three-phase sinusoidal voltages that are supplied to the asynchronous generator. The speed control of the induction generator through the supply frequency is accomplished by a simplified voltage source inverter (VSI). The simplified VSI consists of control voltage sources (CVSs), while the comparison with a real VSI using diodes and transistors, which are controlled by pulse width modulation (PWM) technique, is also presented. Simulations are used to evaluate the developed algorithms showing that rpm fluctuations are around 0.02 for a tidal turbine operating in a wave field with a 6 m significant wave height and around 0.005 for a moored ocean current turbine operating in a wave field with a 2 m significant wave height.

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References

Figures

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Fig. 1

Artistic rendering of the evaluated experimental turbine design with some of the major components listed. Note that the rotor is not accurately drawn in this rendering.

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Fig. 2

Flow diagram showing the interconnection between the primary numerical simulation components. The dashed line indicates data that are only passed for the moored OCT simulation.

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Fig. 3

Induction machine block of MATLAB/Simulink®

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Fig. 4

Block diagram of the three-phase AC induction generator electrical model

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Fig. 5

The d-q equivalent circuit model of the three-phase symmetrical squirrel single-cage (constant Rr) or wound (variable Rr) induction motor

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Fig. 6

Angles between electric frames (the letters S and R refer to the stator and rotor, respectively, while the indices a, b, and c refer to the three phases)

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Fig. 7

SNMREC’s neutrally buoyant research ocean current turbine design and associated mooring cable are simulated in this paper. Note that the rotor is not accurately drawn and that the cable is not drawn to scale.

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Fig. 8

General form of the PI controller

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Fig. 9

Model in MATLAB/Simulink® referred to the implementation of induction generator simplified scalar control (supply frequency and RMS line-to-line voltage) with the closed-loop feedback from PI controller (MV)

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Fig. 10

Generator load torque (N·m) versus time with an increment step at t = 4 s

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Fig. 11

System frequency versus time for 720 kW IG with a reduction step at t = 7 s

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Fig. 12

Generator electromagnetic torque (N·m) versus time under transient and different steady-state conditions

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Fig. 13

Mechanical rotational speed of generator rotor (rpm) versus time under transient and different steady-state conditions

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Fig. 14

Slip ratio (-) versus time under transient and different steady-state conditions

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Fig. 15

Rotational speed of the OCT rotor (rpm) versus time calculated using the tidal turbine simulation for significant wave height of 0 m

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Fig. 16

Rotational speed of the OCT rotor (rpm) versus time calculated using the tidal turbine simulation for a significant wave height of 6 m

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Fig. 17

Hydrodynamic torque (kN·m) versus time calculated using the TT simulation for a significant wave height of 0 m

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Fig. 18

Hydrodynamic torque (kN·m) versus time calculated using the TT simulation for a significant wave height of 6 m

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Fig. 19

Generator electromagnetic torque (kN·m) versus time calculated using the TT simulation for a significant wave height of 0 m

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Fig. 27

Circuit diagram for a pulse width modulation (PWM) VSI

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Fig. 29

VSI implemented in MATLAB/Simulink® environment

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Fig. 30

Control signal generators for SWPM implemented in MATLAB/Simulink® environment

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Fig. 31

Supply frequency/fundamental frequency versus time. Range from 100% rated frequency (60 Hz) up to 50% rated frequency (30 Hz).

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Fig. 32

Supply line-to-line voltage Vab(s), from two different models (smooth line is the VSI and the non-smooth line is the simplified identical VSI by CVS)

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Fig. 26

Generator electromagnetic torque (kN·m) versus time calculated using the OCT simulation for significant wave height of 4 m

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Fig. 25

Generator electromagnetic torque (kN·m) versus time calculated using the OCT simulation for significant wave height of 2 m

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Fig. 24

Hydrodynamic torque (kN·m) versus time calculated using the OCT simulation for significant wave height of 4 m

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Fig. 23

Hydrodynamic torque (kN·m) versus time calculated using the OCT simulation for significant wave height of 2 m

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Fig. 22

Rotational speed of the OCT rotor (rpm) versus time calculated using the OCT simulation for significant wave height of 4 m

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Fig. 21

Rotational speed of the OCT rotor (rpm) versus time calculated using the OCT simulation for significant wave height of 2 m

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Fig. 20

Generator electromagnetic torque (kN·m) versus time calculated using the TT simulation for a significant wave height of 6 m

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Fig. 28

Control signal generators for SWPM

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