Hydrodynamic Coefficients and Wave Loads for a WEC Device in Heaving Mode

International audienceThis paper deals with the hydrodynamic parameter computation of a Wave Energy Converter (WEC) that consists of a cylindrical buoy sliding along a partially submerged platform made up of a plate and a column. The computed parameters are particularly needed for the development of a simple hydrodynamic time-dependant model based on the Cummins formulation. This model is intended to be used for WEC control purposes. A semi-analytical approach is therefore proposed for the computation of the hydrodynamic coefficients and the excitation forces. The boundary value problem is solved using variable separation and matched eigenfunction expansion methods. Analytical expressions for the velocity potential are then obtained for each subdomain. Using afterwards these expressions enables the hydrodynamic coefficients and the excitation force to be computed. Numerical results are given for different radiuses of the buoy, column and plate and are compared with previously published models

On the Generator Constraint Design of a Wave Energy Converter at a Pre-Sizing Stage

International audienceThis paper deals with the constraint pre-design of the energy conversion chain for a wave energy converter application. At the first step, and because the control input is the torque (or the linear force) delivered by the generator, we start by limiting mechanically the nominal velocity. For that purpose, we introduce a new quantity based on short-term wave analysis, namely the maximum expected relative velocity. It may be evaluated when both the wave energy converter is controlled or not. Using long-term wave analysis, based on a known local wave climate, we can constraint the maximum relative velocity that the system have to handle. It appears that because of the constraint applied on the torque, it has to be chosen when no loading is applied. Once it have been chosen, we can then determine the generator nominal power rating based on a time-domain analysis. In this context we use two simple criteria (i) one based on the maximisation of the produced electrical energy, (ii) the second on the maximisation of the annual profit. From numerical investigation, it appears that it exists a point which make a compromise between these two antinomic criteria

Optimal control for a self-reacting point absorber: A one-body equivalent model approach

International audienceThis paper deals with the optimal control of a self-reacting Wave Energy Converter (WEC) where the reaction force is obtained using a damping-plate. Model Predictive Control (MPC) is applied for unconstrained and constrained input control cases. Objective function attempting to optimise the power generation is directly formulated as an absorbed power maximisation problem and thus no optimal references, such as buoy and/or spar velocity, is required. Moreover, rather than using the full WEC model in the optimisation problem which can be time-consuming, and because of linear assumptions, we propose the use of a phenomenologically one-body equivalent model derived using the Thévenin 's theorem. Index Terms—wave energy converter, phenomenologically one-body equivalent model, optimal control, model predictive control

Modelling and Preliminary Studies for a Self-Reacting Point Absorber WEC

International audienceThis paper deals with the special case modelling, in both frequency and time domain, of a self-reacting wave energy converter where the reaction force is obtained using a damping plate. In order to take into account the viscous damping that arises on the plate due to the flow separation at the sharp corners, an additional non-linear term have to be introduce. The influence of this non-linearity is then evaluate in a qualitative manner and obviously it is found that we can not neglect it

Hydrodynamic Coefficient Computation for a Partially Submerged Wave Energy Converter

International audienceThis paper deals with the hydrodynamic parameter computation of a wave energy converter that consists of a cylindrical buoy sliding along a partially submerged platform made up of a plate and a column. The computed parameters are especially needed for the development of a simple hydrodynamic time-dependant model, based on the Cummins' formulation. This model is intended for WEC control purposes. A semi-analytical approach is proposed for the computation of the hydrodynamic coefficients and the excitation forces. The boundary value problem is solved by using variable separation and matched eigenfunction expansion methods. Analytical expressions for the velocity potential are then obtained for each sub-domain. The hydrodynamic coefficients and the excitation force can then be computed by using these expressions. Numerical results are given for different buoy, column, and plate radiuses and clearly the bearing surface of the plate has a significant influence on the wave excitation force applied to the submerged platform

Robustness analysis of Passivity-based Controllers for Complementarity Lagrangian Systems

In this paper we study the robustness of tracking controllers for Lagrangian systems subject to frictionless unilateral constraints. The stability analysis incorporates the hybrid and nonsmooth dynamical features of the overall system. This work provides details on the robustness of such controllers with respect to the modelling errors of the dynamic, the uncertainty on the constraint position, and with respect to the measurement noise

Tracking Control of Complementarity Lagrangian Systems

In this paper we study the tracking control of Lagrangian systems subject to frictionless unilateral constraints. The stability analysis incorporates the hybrid and nonsmooth dynamical feature of the overall system. The difference between tracking control for unconstrained systems and unilaterally constrained ones, is explained in terms of closed-loop desired trajectories and control signals. This work provides details on the conditions of existence of controllers which guarantee stability. It is shown that the design of a suitable transition phase desired trajectory, is a crucial step. Some simulation results provide information on the convergence of such controller. Finally the extension towards the case of multiple impacts, is considered

Virtual-Sensor-Based Maximum-Likelihood Voting Approach for Fault-Tolerant Control of Electric Vehicle Powertrains

International audienceThis paper describes a sensor fault-tolerant control (FTC) for electric-vehicle (EV) powertrains. The proposed strategy deals with speed sensor failure detection and isolation within a reconfigurable induction-motor direct torque control (DTC) scheme. To increase the vehicle powertrain reliability regarding speed sensor failures, a maximum-likelihood voting (MLV) algorithm is adopted. It uses two virtual sensors [extended Kalman filter (EKF) and a Luenberger observer (LO)] and a speed sensor. Experiments on an induction-motor drive and simulations on an EV are carried out using a European urban and extraurban driving cycle to show that the proposed sensor FTC approach is effective and provides a simple configuration with high performance in terms of speed and torque responses

A Fuzzy-Based Strategy to Improve Control Reconfiguration Performance of a Sensor Fault-Tolerant Induction Motor Propulsion

International audienceThis short paper deals with the transition performance improvement of a sensor fault-tolerant controller devoted to automotive applications. Indeed, improvements are brought over a previously developed technique that exhibit abrupt changes in the torque if a sensor fault is detected and after a transition from a control technique to another one [1]. The Fault-Tolerant Control (FTC) system firstly concerns the sliding mode control technique since better performances are obtained with an encoder to get the speed information. In the event of unavailability of the speed sensor, a sensorless fuzzy control technique is applied. In the proposed active fault-tolerant control approach a short and a smooth transition are achieved from the encoder-based control technique to the sensorless one using an appropriate fuzzy logic decision approach

An Improved Fault-Tolerant Control Scheme for PWM Inverter-Fed Induction Motor-Based EVs

International audienceThis paper proposes an improved fault-tolerant control scheme for PWM inverter-fed induction motor-based electric vehicles. The proposed strategy deals with power switch (IGBTs) failures mitigation within a reconfigurable induction motor control. To increase the vehicle powertrain reliability regarding IGBT open-circuit failures, 4-wire and 4-leg PWM inverter topologies are investigated and their performances discussed in a vehicle context. The proposed fault-tolerant topologies require only minimum hardware modifications to the conventional off-the-shelf six-switch three-phase drive, mitigating the IGBTs failures by specific inverter control. Indeed, the two topologies exploit the induction motor neutral accessibility for fault-tolerant purposes. The 4-wire topology uses then classical hysteresis controllers to account for the IGBT failures. The 4-leg topology, meanwhile, uses a specific 3D space vector PWM to handle vehicle requirements in terms of size (DC bus capacitors) and cost (IGBTs number). Experiments on an induction motor drive and simulations on an electric vehicle are carried-out using a European urban driving cycle to show that the proposed fault-tolerant control approach is effective and provides a simple configuration with high performance in terms of speed and torque responses