Ryozo Nagamune

• PhD
• Professor (Full) at University of British Columbia

Driven by the urgent need to displace fossil fuels for carbon emission reduction and climate change mitigation, offshore wind energy has emerged as a highly promising renewable energy source. By harnessing the power of strong and consistent wind across the vast expanse of the open sea, offshore wind turbines offer extraordinary potential for genera...

Haptic devices are designed to assist humans in operating tasks in a remote or virtual environment. The passivity-based controllers feed back the forces from the environment while maintaining stability. This paper presents the adaptive energy reference time domain passivity approach to overcome the sudden force change inherent in the conventional t...

Floating offshore wind farm control via real-time turbine repositioning has a potential in significantly enhancing the wind farm efficiency. Although the wind farm power capture increase by moving platforms with aerodynamic force has been verified in a recent study, the investigation and mitigation of the fatigue damage caused by such aerodynamic f...

Model error and external disturbance have been separately addressed by optimizing the definite $H_\infty$ performance in standard linear $H_\infty$ control problems. However, the concurrent handling of both introduces uncertainty and nonconvexity into the $H_\infty$ performance, posing a huge challenge for solving nonlinear problems. This art...

Hysteretic nonlinearity behavior ubiquitously occurs in mechanical systems, particularly in high-precision instruments, which severely degrades system output performance. Consequently, it is unavoidable to establish an accurate hysteretic model to describe the hysteretic characteristic of various mechanical systems and to compensate for the system...

This paper proposes a gain-scheduling (GS) control strategy for selective catalytic reduction (SCR) systems in diesel engines, to minimize both nitrogen oxides (NOX) emissions and ammonia (NH3) slip downstream of the SCR catalyst. The proposed GS controller switches among multiple linear time-invariant H∞ controllers based on the engine’s operating...

In this article, a novel control approach with a dynamic parameter and an attitude maneuver planning scheme is proposed for flexible spacecraft to achieve anti‐unwinding attitude maneuver control and vibration suppression. In order to suppress the flexible modal vibration of the flexible spacecraft during the attitude maneuver, an attitude maneuver...

The problem of wind estimation by multirotor drone is suitable for machine learning (ML), because of the unknown drag coefficient changing with orientation. In previous work, we studied this problem experimentally to train a ML model that estimated wind by drone state alone. The primary drawback of this work was a decrease in performance between ra...

We present multiple models for the problem of wind estimation by a multirotor drone in low altitude atmospheric turbulence. Data is collected by test flights with an instrumented drone in proximity to an anemometer for training, validation, and testing. Three machine-learning models are developed: a long-short-term-memory (LSTM) neural-network, a s...

This paper proposes a method to optimize the layout design of floating offshore wind farms (FOWFs), in order to maximize the energy efficiency over a year. It is assumed that each wind turbine be installed on a semi-submersible platform, and that each floating platform be repositioned depending on wind conditions. The platform repositioning is real...

During the past decade, the development of offshore wind energy has transitioned from near shore with shallow water to offshore middle-depth water regions. Consequently, the energy conversion technology has shifted from bottom-fixed wind turbines to floating offshore wind turbines. Floating offshore wind turbines are considered more suitable, but t...

Wind turbines are installed offshore with the assistance of a floating platform to help meet the world’s increasing energy needs. However, the incident wind and extra incident wave disturbances have an impact on the performance and operation of the floating offshore wind turbine (FOWT) in comparison to bottom-fixed wind turbines. In this paper, mod...

To bridge the gap between real-world applications and theoretical achievements, this paper proposes a new synthesis approach of gain-scheduled proportional–integral–derivative (PID) control for linear parameter-varying (LPV) systems. It is recognized that the synthesis problem of PID controllers for LPV systems should be formulated as nonconvex opt...

This paper introduces a dynamic parametric wind farm model that is capable of simulating floating wind turbine platform motion coupled with wake transport under time-varying wind conditions. The simulator is named FOWFSim-Dyn as it is a dynamic extension of the previously developed steady-state Floating Offshore Wind Farm Simulator (FOWFSim). One-d...

This paper proposes a discrete-time preview-feedback controller capable of reducing nitrogen oxide (NOx) emissions with affordably low ammonia (NH3) slip downstream of a catalyst for selective catalytic reduction (SCR) systems. Because of the high NOx reduction rate, SCR systems are increasingly adopted in diesel engines. However, slow dynamics of...

This letter presents linear parameter-varying (LPV) controller design for the urea-based selective catalytic reduction (SCR) system in diesel engines to reduce nitrogen oxides (NO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">X</sub> ) and ammonia (NH <sub xmlns:mml="http://www.w3.org/1998/Math/MathM...

This paper implements a recently developed social hierarchy-based distributed economic model predictive control (DEMPC) algorithm in floating offshore wind farms for the purpose of power maximization. The controller achieves this objective using the concept of yaw and induction-based turbine repositioning (YITuR), which minimizes the overlap areas...

This paper introduces a novel concept for addressing non-convexity in the cost functions of distributed economic model predictive control (DEMPC) systems. Specifically, the proposed algorithm enables agents to self-organize into a hierarchy which determines the order in which control decisions are made. This concept is based on the formation of soc...

This paper introduces a dynamic parametric wind farm model that is capable of simulating floating wind turbine platform motion coupled with wake transport under time-varying wind conditions. Partial differential equations are used to model dynamic propagation of wake centerline locations and average velocities, while momentum recovery is approximat...

Gastrointestinal (GI) cancers are among some of most significant public health issues worldwide. Early cancer diagnosis will increase GI cancer patients’ survival rate, however, developing endoscopes for early cancer detection is a challenge as it is difficult to design a high-resolution optical scanner. In this paper, we report a new 3D optical sc...

This paper validates a robust $H_\infty$ controller design method, experimentally, on miniaturized prototypes of the magnetically-actuated lens-tilting optical image stabilizers (OISs) with product variabilities. Five small-scale OIS prototypes with product variations are constructed by 3D printing. For the prototypes, the model parameters are iden...

This work examines the steady-state potential and feasibility of Yaw and Induction-based Turbine Repositioning (YITuR), which is a wind farm control concept that passively repositions floating offshore wind turbines using existing turbine control degrees of freedom. To this end, the Floating Offshore Wind Farm Simulator (FOWFSim) is developed to mo...

This paper proposes H∞ controller design for platform position transfer and regulation of floating offshore wind turbines. The platform movability of floating wind turbines can be utilized in mitigating the wake effect in the wind farm, thereby maximizing the wind farm’s total power capture and efficiency. The controller is designed so that aerodyn...

This paper develops an online parameter estimation and control method for both rigid and flexible feed drive systems with unmeasurable parameter variations. The perturbations of the state-space model caused by the parameter variations are formulated, thereby making it possible to obtain the parameter variations in real-time by estimating the pertur...

This paper proposes a hybrid Gaussian process (GP) approach to robust economic model predictive control under unknown future disturbances in order to reduce the conservatism of the controller. The proposed hybrid GP is a combination of two well-known methods, namely, kernel composition and nonlinear auto-regressive. A switching mechanism is employe...

This paper proposes a hybrid Gaussian process (GP) approach to robust economic model predictive control under unknown future disturbances in order to reduce the conservatism of the controller. The proposed hybrid GP is a combination of two well-known methods, namely, kernel composition and nonlinear auto-regressive. A switching mechanism is employe...

This paper proposes an almost disturbance decoupling (ADD) control strategy for solving the force control problem of an electro-hydraulic load simulator containing mechanical backlash. This method can enhance the force tracking performance of the load simulator by decoupling position disturbance and mitigating the backlash effect. Based on a propos...

An iterative learning (IL) approach to disturbance prediction for economic model predictive control (EMPC) is proposed and applied to an integrated solar thermal system (ISTS). The disturbance in the system, which is the user hot water demand, is predicted iteratively by taking advantage of the repetitive nature of hot water consumption and utilize...

In this paper, an optimal control strategy is developed for managing a heat pump in an integrated solar thermal system. Solar thermal systems usually operate with both feedback and feedforward controllers. The focus of many existing studies in solar thermal system applications has been on the feedback part, while less effort has been made to improv...

This paper presents platform position control of utility-scale floating offshore wind turbines in surge and sway directions using aerodynamic thrust force. The position control will be useful in mitigating the wake effect, and thus maximizing the total power capture, of an offshore wind farm. A linear-quadratic-integrator (LQI) controller is design...

This paper aims to determine the optimal strategy to operate the pump in a sanitary pump station (SPS) to minimize its energy consumption over a specified time window. An SPS collects sanitary waste from nearby neighbourhoods in a city and then pumps the waste to a treatment plant for processing. Sustained operation of SPSs, even during power outag...

This article presents a review of control strategies for maximizing power production within wind farms. Discussions focus on three notable concepts; power de-rating, yaw-based wake redirection, and turbine repositioning. Existing works that have examined the potential of these concepts via optimization studies, numerical simulation, experimentation...

This paper presents uncertainty modeling and robust controller design for 3 degrees-of-freedom miniaturized optical image stabilizers (OISs) against product variabilities. To develop a mathematical model of OISs with product variations, both model and uncertainty structures are determined by finite element analysis. The model parameters are identif...

This paper presents the design of multiple parameter-dependent robust controllers for mass-produced miniaturized optical image stabilizers (OIS’s), which are used to minimize the image blur in mobile devices caused by hand-induced camera shake. The dynamics of batch-fabricated OIS’s with inevitable product variations is represented by a set of line...

This paper presents a novel approach to designing switching linear parameter‐varying (SLPV) controllers with improved local performance and an algorithm for optimizing switching surfaces to further improve the performance of the SLPV controllers. The design approach utilizes the weighted average of the local L2‐gain bounds (representing the local p...

This paper proposes an application of the switching gain-scheduled (S-GS) proportional-integral-derivative (PID) control technique to the electronic throttle control (ETC) problem in automotive engines. For the S-GS PID controller design, a published linear parameter-varying (LPV) model of the electronic throttle valve (ETV) is adopted whose dynami...

3D printing and moulding (3DPM) method is applied to the fabrication of a miniature magnetic actuator for optical image stabilization (OIS) applications. Polydimethylsiloxane (PDMS) and strontium ferrite (SrFe) nano powder are used as the main structural materials. Young’s modulus and the magnetization of the material with SrFe-doping ratios rangin...

This paper formulates and solves the problem of optimizing switching surfaces (SSs) in switching LPV (SLPV) controller design to further enhance the control performance. The conditions for the SLPV controller synthesis under fixed SSs are first presented, which involves a finite number of linear matrix inequalities. The SS design problem is then fo...

This paper presents a physics-based control-oriented model for general floating offshore wind turbines that contains as many as six platform degrees of freedom (DOFs) and two drivetrain DOFs. The model is derived from the first principles, and therefore, can be manipulated by its real physical parameters while maintaining accuracy across the highly...

This paper addresses the problem of designing output-feedback switching linear parameter-varying (LPV) controllers under inexact measurement of scheduling parameters. The switching LPV controllers are robustly designed so that the stability and -gain performance of the switched closed-loop system can be guaranteed even under controller switching de...

This paper proposes a method to design a multi-input multi-output (MIMO) linear parameter-varying (LPV) feedback controller for contour error minimization in two-and three-axis computer-numerical-control (CNC) machines. The design method generates a controller of a special and novel structure, that is, a series connection of a coordinate transforma...

This paper proposes an uncertainty modeling and robust controller design method for miniaturized 3 degrees-of-freedom OISs to deal with its product variabilities. A mathematical model of OISs with product variabilities is developed based on finite element analysis of uncertainties specific for this device. μ-synthesis technique is applied to the un...

In this paper, we deal with the problem of simultaneous design of state-feedback switching linear parameter-varying (LPV) controllers and switching surfaces for LPV plants to further improve the performance of the switching LPV controllers. The LPV plants that we consider have polynomially parameter-dependent state-space matrices. Using slack varia...

This paper proposes a general control-oriented non-linear model for floating offshore wind turbine systems. It contains as many as six platform degrees of freedom as well as the rotor degree of freedom, and can account for full field wind and wave disturbances. Additionally, it accepts individual blade pitch, generator torque and yaw control inputs...

This paper presents robust control of large-scale prototypes for miniaturized optical image stabilizers (OIS's) with product variations. Based on the conceptual design of a miniaturized lens-tilting OIS for mobile applications, large-scale 3-DOF prototypes are fabricated as a proof of concept. Variations in geometrical parameter of the lens platfor...

Extended Abstract: This paper proposes a method to design a MIMO Linear Parameter Varying (LPV) feedback controller for countering tracking of two and three axes CNC machine. Depends on the direction of the trajectory velocity, contouring error changes. To minimize the tracking error in the normal direction, we design a varying controller to minimi...

This paper presents an application of gain-scheduling (GS) control techniques to a floating offshore wind turbine on a barge platform for above rated wind speed cases. Special emphasis is placed on the dynamics variation of the wind turbine system caused by plant nonlinearity with respect to wind speed. The turbine system with the dynamics variatio...

This paper presents modeling and control methods for an integrated thermal hydronic system (ITHS) consisting of a solar thermal collector, a thermal storage unit and a thermal booster. Control inputs are: valves activation time, pitch angle, solar pump rate and compressor rate, measurements are: temperatures at critical points, and disturbances are...

Abstract: In the Computer Numerical Control (CNC) machine tool system, the machine tool dynamics change during the operation. For example, in the Parallel Kinematic Machine (PKM), the inertia, stiffness and damping coefficients vary due to the variation of the tool tip position on the work volume. In the Serial Kinematic Machine (SKM), dynamic vari...

This paper investigates a potential advantage of utilizing blade pitch control over the conventional fixed blade pitch strategy in low wind speed for horizontal-axis offshore floating wind turbines mounted on a barge platform. To examine the advantage, simulation studies with a 5MW wind turbine model in the software FAST are conducted. The generate...

This paper proposes an algorithm to design switching surfaces for the switching linear parameter-varying (LPV) controller with hysteresis switching. The switching surfaces are sought for to optimize the bound of the closed-loop L2-gain performance. An optimization problem is formulated with respect to parameters characterizing Lyapunov matrix varia...

This paper presents a method to design a smooth switching gain-scheduled linear parameter varying (LPV) controller for LPV systems. The moving region of the gain-scheduling variables is divided into a specified number of local subregions as well as subregions for the smooth controller switching, and one gain-scheduled LPV controller is assigned to...

This paper presents a new method for controlling the height of a mineral processing dry‐surge ore pile between specified upper and lower levels by manipulating the outlet ore flow. The upper level should not be exceeded for safety, while the height should always be higher than the lowest allowable level to maintain a reserve for continuous operatio...

This paper presents a concept of optical image stabilization for miniature digital cameras using magnetic actuators. The proposed device has a 3 degrees-of-freedom flexible lens platform, which is actuated by four magnetic actuators. The device uses position feedback control to counter-rotate the lens to compensate for vibration disturbance introdu...

This paper proposes a parallel structure of a feedback controller for the ball--screw drive systems which have significant dynamic variations during operations. The controller consists of two controllers with two different objectives. One controller aims at moving the workpiece table so that its position tracks reference trajectories with high spee...

This paper proposes an application of the switching gain-scheduled control technique to the flexible ball-screw drive servo system with a wide range of operating conditions. The wide operating range is caused by the change of the table position and the workpiece mass during the machining operation, and leads to plant dynamics variations. To achieve...

The ball-screw stiffness variations and the workpiece mass removals can lead to significant changes in feed drive dynamics during cutting processes. This paper proposes a controller design method to track a desired trajectory and suppress the structural vibration with consideration of dynamics variations. To take into account the dynamics variation...

Machine tool chatter is detrimental to productivity and the overall quality of manufactured parts. Analytical stability models are used to predict the occurrence of chatter for a given set of machining conditions and improve productivity. Conventional chatter models typically assume that parameters are constant, which can lead to an unsuitable stab...

The three way catalytic converter (TWC) is a critical component for the mitigation of tailpipe emissions of modern spark ignition internal combustion (IC) engines. Because the TWC operates effectively only when the air-fuel ratio is very close to stoichiometric, accurate control of the air-fuel ratio is required. This paper uses a switching linear...

In this paper a method is presented to design a robust servo controller for flexible ball screw drive systems with dynamics variation. Two sources of dynamics variations, which are the stiffness variation and the workpiece inertia variation, inherent to the ball screw systems, are considered. For the ball screw system with a large range of dynamics...

Most machine tools rely on precision ball screw drives to accurately position the workpiece relative to the tool. The quality of the machining outcome depends significantly on the tracking performance of the workpiece position over a desired trajectory. This paper addresses the minimization of the tracking error in a ball screw drive system in the...

In this paper, a problem of designing a switched dynamic outputfeedback controller for a plant with time-invariant parametric uncertainties is considered. The controller is designed so that the switched closed-loop system satisfies the robust finite-time tracking property, i.e., the time-domain state trajectories with plant perturbations stay in a...

This paper presents a new technique to design switching gain-scheduling controllers for plants with measurable time-varying parameters. By dividing the parameter set into a sufficient number of subsets, and by designing a robust controller to each subset, the designed switching gain-scheduling controllers achieve a desired L2-gain performance for e...

This paper addresses double-loop robust tracking controller design of the miniaturized linear motor drive precision stage with mass and damping ratio uncertainties. As an inner-loop, a disturbance observer (DOB) is employed to suppress exogenous low frequency disturbances such as friction and cutting force. To further eliminate the residual disturb...

The positioning performance of high-speed, high-accuracy light-weight motion control systems is usually restricted by the structure flexibility and model parameter-varying caused by load mass variation. It needs to develop novel motion control algorithm to eliminate the residual vibration in the end-effectors, as well as to be robust over the load...

This brief proposes a new design procedure for track-following control systems in hard disk drives. The procedure is automated, in the sense that, for given experimental frequency response data of the suspension arm dynamics and a model structure, it automatically derives a transfer function set with uncorrelated parametric uncertainties. Subsequen...

An event-based sampled discrete-time linear system representing a port-fuel-injection process based on wall-wetting dynamics is obtained and formulated as a linear parameter varying (LPV) system. The system parameters used in the engine fuel system model are engine speed, temperature, and load. These system parameters can be measured in real-time t...

This paper proposes a technique to model uncertainties associated with linear time-invariant systems. It is assumed that the uncertainties are only due to parametric variations caused by independent uncertain variables. By assuming that a set of a finite number of rational transfer functions of a fixed order is given, as well as the number of indep...

Precise low speed motion control is important for the industrial applications of both micro-milling machine tool feed drives and electro-optical tracking servo systems. It calls for precise position and instantaneous velocity measurement and disturbance, which involves direct drive motor force ripple, guide way friction and cutting force etc., esti...

This paper presents a novel technique for designing robust track-following output-feedback controllers in hard disk drives (HDDs). In this paper, the manufacturing variations of HDDs are modeled as polytopic parametric uncertainties in linear time-invariant discrete-time systems. For this model, the robust track-following control problem is formula...