Martin Choux

Parameters identification of induction motor dynamic model for offshore applications

The paper presents a technique to identify parameters of the LuGre dynamic friction model applied to represent mechanical losses of an induction motor. This method is based on Artificial Neural Networks (ANNs) system identification which is able to estimate parameters of nonlinear mathematical models. Within the presented approach, the network is first trained to associate model parameters with predicted friction torque, being given the reference motor speed. When this process completes, the inverse operation is performed and the network delivers estimated parameters of the model based on the reference friction torque. These parameters are then integrated with the dynamic model of the induction motor to form a complete virtual simulator of an electrical actuation system. The advantages and practical significance of the proposed technique are illustrated by an example of a scaled version of an induction motor used in an offshore pipe handling machine. It is demonstrated that the model of this system accurately simulates behavior of the experimental motor in the presence of speed and current reference profiles which resemble the ones characterized by offshore conditions. Hence, the model could be successfully applied in simulation based control system design.

Drivetrain design optimization for electrically actuated systems via mixed integer programing

The proposed paper presents a method to optimally select components of a drivetrain for an electrically actuated machine. A simple mathematical model of the machine is established and inequality constraints which determine the choice of drivetrain components are formulated. Elements to be picked (namely, a motor, a gearbox, and a drive) are taken from a discrete set of data provided in the catalogs of industrial motors and drives manufacturers. By solving an optimization problem, a combination of components which both satisfy design requirements and minimize the total drivetrain cost is selected. The operation of the selected drivetrain is verified against the motor loadability curves. In addition, feasibility of other possible drivetrain configurations is checked and benchmarked with the optimal solution. Practical significance of the current work is demonstrated on a winch mechanism which is a popular part of many engineering applications, however, methods presented here could easily be adapted to other machines and industries. The results of the current work allow to reduce conservatism when designing actuation systems, while still satisfying the safety requirements specified by the designer. The system operating conditions are therefore effectively shifted to be closer to the constraints, which results in increasing the overall efficiency of the design and proving its cost-effectiveness.

Robust adaptive backstepping control design for a Nonlinear Hydraulic-Mechanical System

The complex dynamics that characterize hydraulic systems make it difficult for the control design to achieve prescribed goals in an efficient manner. In this paper, we present the design and analysis of a robust nonlinear controller for a Nonlinear Hydraulic-Mechanical (NHM) System. The system consists of an electrohydraulic servo valve and two hydraulic cylinders. Specifically, by considering a part of the dynamics of the NHM system as a norm-bounded uncertainty, two adaptive controllers are developed based on the backstepping technique that ensure the tracking error signals asymptotically converge to zero despite the uncertainties in the system according to the Barbalat lemma. The resulting controllers are able to take into account the interval uncertainties in Coulomb friction parameters and in the internal leakage parameters in the cylinders. Two adaptation laws are obtained by using the Lyapunov functional method and inequality techniques. Simulation results demonstrate the performance and feasibility of the proposed method.

Torque peak reduction and overload monitoring of induction motors in offshore drilling operations

Current drivetrain design procedures for electric actuation systems operating in offshore conditions typically consider two major requirements: to provide sufficient steady-state and maximum motor torques. As a result of this, no information regarding the transient state (e.g. during motor acceleration) is utilized when selecting drivetrain components. This leads to potentially dangerous situations when motors undergo saturation in these regions due to too high dynamic loads. A common reason for this (apart from lack of information about transient state when designing a drivetrain) is applying trapezoidal reference motion profiles that cause discontinuities in system acceleration and infinite values of jerk. To overcome this drawback, the current paper presents an application of a trigonometric scurve trajectory to lower values of torque peaks of motors operating in offshore drilling equipment. In addition, we show a method to monitor time spent by motors in overload regions. These two combined contributions allow to avoid unexpected motors saturation and verify if the components selected for a given electric actuation system will provide for a smooth machine operation. Practical significance of the presented work is demonstrated on a gripper arm mechanism of a full-scale offshore pipe handling machine. The results show not only a serious reduction in motor torque peak values when applying the trigonometric motion profiles (up to two times lower values), but also adaptation of the overall motor torque shapes to avoid too high overloads during the steady-state operation.

EKF-based estimation and control of electric drivetrain in offshore pipe racking machine

A typical challenge for electric drivetrains is to reduce the number of sensors required for control action or system monitoring. This is particularly important for electric motors operating in offshore conditions, since they work in hostile environment which often damages data acquisition systems. Therefore, this paper deals with verification and validation of the extended Kalman filter (EKF) for sensorless indirect field-oriented control (IFOC) of an induction motor operating in offshore conditions. The EKF is employed to identify the speed of the induction motor based on the measured stator currents and voltages. The estimated speed is used in the motor speed control mode instead of a physical encoder signal. In addition, we utilize a stationary frame model of the induction machine to assess the fidelity level of the EKF-based estimation of rotor fluxes. The experimental setup is used to validate accuracy of the EKF-based state estimation and motor speed control. The importance of the current work is demonstrated on an example of a full-scale offshore drilling equipment. Real-world speed and load profiles sustained by the gripper arm of the vertical pipe racking machine are scaled down and reproduced by the experimental setup. The proposed EKF algorithm accurately estimates both speed and electromagnetic torque experienced by the reference full-scale electric drivetrain, creating a potential to reduce the number of data acquisition devices in similar type of equipment.

Leakage-detection in blade pitch control systems for wind turbines

The main contribution of the work is a systematic study evaluating the performance of different filters for leakage detection in pitch control systems. The effectiveness of the proposed methods is examined in a Matlab/Simulink real-time environment. The test bed consists of the following elements: hydraulic power unit, servo valve, two leakage bypasses, hydraulic cylinder, payload and xPC-based control system. The filters are tested with the state-augmentation and the hypothesis testing approaches. To our knowledge, the comparison of these different approaches has not been done previously for this type of application. The paper concludes on the accuracy and sensitivity of the leakage detection as well as the computational complexity and the real-time performance.

Load Torque Estimation Method to Design Electric Drivetrains for Offshore Pipe Handling Equipment

One of the main design objectives for electric drivetrains operating in offshore drilling equipment is to keep them as small, yet as effective, as possible, to minimize space they occupy on drill floor and maximize their performance. However, practical experience shows that typically choices made by design engineers are too conservative due to the lack of enough data characterizing load conditions. This results in too costly and too heavy selected components. Therefore, in the current paper we present a method to estimate required full-scale motor torque using a scaled down experimental setup and its computational model. A gripper arm of an offshore vertical pipe handling machine is selected as a case study for which the practical significance of the current work is demonstrated. The presented method has a potential to aid design of electrically actuated offshore drilling equipment and help design engineers choose correctly dimensioned drivetrain components.

Extended friction model of a hydraulic actuated system

The main contribution of this paper is an experimental validation and comparison of three different friction models for an electro-hydraulic servo system. The first is the well-kn own LuGre model which incorporates dynamic friction effects. The second model is based on a relatively recent publication by Yanada in 2008 [6], which incorporates liquid film thickness in the servo valve. The third model is a new contribution presented in this paper, where valve underlap and mass acceleration are combined with the LuGre model. The experimental results show that for hydraulic systems, the film thickness model is an improvement over the LuGre model, while the new model presented in this paper is an improvement over both the LuGre and the film thickness models. An accurate friction model is an important tool for reliability engineers when distinguishing maintenance related degradation from dynamic effects.

Mitigation of Fatigue Damage and Vibration Severity of Electric Drivetrains by Systematic Selection of Motion Profiles

The offshore drilling industry is among the most demanding markets for electrical equipment. Heave motion, irregular cyclic loads, harsh weather conditions, and vibrations are causing accelerated deterioration of drilling equipment. One of the most common solutions to these problems is to design actuation systems of such machinery overly conservative to gain additional safety, which results in too high initial investment and maintenance costs. To mitigate the fatigue damage and vibration severity of rotating elements of electric drivetrains operating offshore, this paper presents a comparative analysis of four popular input functions used in motion control of industrial systems. We evaluate them not only by using well-known performance indicators, such as maximum load or velocity, but also by assessing their influence on fatigue life and vibration severity of electric drivetrains. The rainflow counting algorithm is used to assign amplitudes and mean values of distinguished cycles from random loading history. Then, the Palmgren-Miner rule together with S-N curves are applied to determine the total damage for cycles with varying amplitudes. In addition, we quantify the cumulative effect of vibrations and jerk on machine damage by using the metric based on the jerk energy. The importance of this study is illustrated on a full-scale offshore pipe handling machine by benchmarking simulation results with the field data. The outcomes demonstrate not only a serious decrease in damage caused by vibrations for smooth motion profiles, but also provide a basis to formulate rules of thumb for selection of the most suitable motion profile for certain applications.

Fault diagnosis for nonlinear hydraulic-mechanical drilling pipe handling system

Leakage and increased friction are common faults in hydraulic cylinders that can have serious consequences if they are not detected at early stage. In this paper, the design of a fault detector for a nonlinear hydraulic mechanical system is presented. By considering the system in steady state, two residual signals are generated and analysed with a composite hypothesis test which accommodates for unknown parameters. The resulting detector is able to detect abrupt changes in leakage or friction given the noisy pressure and position measurements. Test rig measurements validate the properties of residuals and high fidelity simulation and experimental results demonstrate the performance and feasibility of the proposed method.