publications

Journal Papers

2023

1. 

   Numerical and experimental investigation of a floating overhead power transmission system

   Ruo Luo, Yingyi Liu, Hongzhong Zhu, and 1 more author

   Ocean Engineering, 2023

2022

1. 

   Experimental study and attitude control of a floating type shrouded wind turbine

   Hongzhong Zhu, and Makoto Sueyoshi

   Sustainable Energy Technologies and Assessments, 2022

2. 

   Optimal Semi-Active Control for a Hybrid Wind-Wave Energy System on Motion Reduction

   Hongzhong Zhu

   IEEE Transactions on Sustainable Energy, 2022

   Abs PDF Website

   Integration of wave energy converters and floating wind turbine can potentially reduce the levelized cost of energy. The coupling effects between the wave energy converters and the foundation, however, could amplify the foundation motion so that both the efficiency and the fatigue life of wind turbine would be degraded. In this study, wave energy converters are designed as a controlled suspension system for a novel hybrid wind-wave energy system, and an optimal semi-active control method having predictive ability is proposed for reducing the foundation motion. In the controller design, the physical constraints and the passivity of the wave energy converters are also taken into consideration. A full numerical model taking account of aero-hydro-servo-mooring coupled dynamics is proposed for a comprehensive analysis of the controller under various environmental conditions. Numerical results show that the foundation motion can be reduced by 16% even in very rough sea states with the help of the controller.

2021

1. 

   A unified seakeeping and maneuvering analysis of multiple linked towing system with triangular Bodies

   Hongzhong Zhu, and Changhong Hu

   Ocean Engineering, 2021

   Abs PDF Website

   Three-legged triangular tension leg platforms (TLPs), which are a kind of compliant-type floating structure, are drawing attention from industrial society. To reduce the transportation cost, a multiple linked ship towing system that the platform and anchor are linked and wet towed is studied. A unified seakeeping and maneuvering method which can take account of the hydrodynamic interaction between the bodies and utilize the experimental results for tuning the damping coefficients is proposed to model the towing system. In the method, a low-pass filter is applied to separate the slowly and fast motion components for the maneuvering and seakeeping calculations. The maneuvering and seakeeping problems can thus be solved simultaneously with a same time scale. SimMechanics™, which provides multi-body simulation environment for mechanical systems, is applied to implement the numerical model for studying the fully coupled six degrees-of-freedom (DOFs) motion of the towing system. Besides, experiments are carried out to demonstrate the feasibility of the system and the effectiveness of the numerical model. A circular motion in irregular waves is studied at the end and the issues of the system are discussed accordingly.

2. 

   A study on floating overhead power transmission system for offshore energy development: Design and modeling approach

   Hongzhong Zhu, and Changhong Hu

   Ocean Engineering, 2021

   Abs PDF Website

   In this paper, a floating overhead power transmission system (FOPTS), which has the potentiality to lower the electricity transmission cost for offshore renewable energy, is studied. In the design, a sheave mechanism is applied to mount one end of conductor on its supportive tower so that the coupling effects between the conductor and its supportive towers are reduced. Then, a mathematical optimization approach, which can take account of the placement of system’s natural frequencies to avoid first-order wave excitation, is presented to design the properties of the floating foundation and conductor. In the model-ing, the flexibility of the conductor is handled and both the first-and second-order wave loads are considered. The aero-hydro-elastic dynamics of the system would be analyzed by the numerical model. Finally, a moderate FOPTS in a harsh ocean environment with wind speed of 70 m/s and significant wave height of 14 m is studied with emphasis on the wind-wave misalignment. The feasibility and issues of the system are discussed based on fully coupled time-domain simulation.

2020

1. 

   Integration of a semisubmersible floating wind turbine and wave energy converters: an experimental study on motion reduction

   Hongzhong Zhu, Changhong Hu, Makoto Sueyoshi, and 1 more author

   Journal of Marine Science and Technology, 2020

2. 

   Disturbance observer-based torsional vibration damper for variable-speed wind turbines

   Hongzhong Zhu, and Shigeo Yoshida

   IFAC Journal of Systems and Control, 2020

2019

1. 

   A study on a floating type shrouded wind turbine: Design, modeling and analysis

   Hongzhong Zhu, Makoto Sueyoshi, Changhong Hu, and 1 more author

   Renewable Energy, 2019

   Abs PDF Website

   This paper addresses a fundamental study of a floating type shrouded wind turbine on the design, mathematical model and motion analysis. Several novel concepts are introduced to the system for cost reduction: a revolute hinge is applied between the tower and the nacelle to maintain the orientation of the nacelle even in a large tower inclination, a swashplate mechanism with cyclic control is employed for blade pitch regulation to improve the system controllability, a novel mooring system with a slewing bearing is utilized to build the passive yawing system, and an advanced spar-type floater is used to obtain high restoring performance with a short spar. Firstly, the design aspects of the main components of the system are given. Then, the numerical model including the structural model, hydrodynamic/aerodynamic model, and the control system is presented. The static and dynamic responses under both the operational situation and survival conditions are finally studied. The paper illustrates the probability of the shrouded wind turbine on floating offshore application, and can provide critical information for the optimization design in next stage.

2017

1. 

   Torsional vibration reduction with augmented inverse model-based controller in wind turbine drivetrain

   Siti Fauziah Toha, Shigeo Yoshida, and Hongzhong Zhu

   Procedia Computer Science, 2017

2016

1. 

   Optimum design of a passive suspension system of a semisubmersible for pitching reduction

   Hongzhong Zhu, Changhong Hu, and Yingyi Liu

   Journal of Dynamic Systems, Measurement, and Control, 2016

   Abs PDF Website

   With the development of ocean energy exploration, reliable semi-submersible platforms with very small motion are expected to develop. Especially, in a floating offshore wind turbine system, the maximum pitching amplitude is required to be less than a few degrees. To reduce wave-induced pitch motion, a new type semi-submersible with suspensions and a design method of the suspension coefficients are presented. In practical case, an add-on wave energy dissipation device mounted on a floating platform, such as the combined wave-wind energy converter system, could be regarded as the suspension system. In this study, firstly, the conceptual semi-submersible is described. Then, the hydrodynamic loads to the semi-submersible are linearized so that the whole system is expressed by a state-space model. The suspension design problem is transformed into solving a constrained H ∞ optimization problem, which after all is the optimal controller design of a feedback system. Finally, numerical examples are performed to verify the effectiveness of the design. The results illustrate that the pitch motion of the semi-submersible can be remarkably reduced by the designed suspensions.

2. 

   A study on control of wave energy converter for motion suppression of semisubmersible

   Hongzhong Zhu, and Changhong Hu

   IFAC-PapersOnLine, 2016

2015

1. 

   Smooth output reconstruction for linear systems with quantized measurements

   Hongzhong Zhu, Toshiharu Sugie, and Hiroshi Fujimoto

   Asian Journal of Control, 2015

   Abs PDF Website

   This paper presents a novel approach to reconstruct the output of linear systems in the case where the measured output is uniformly quantized. By fitting the quantized measurements with polynomials in a moving horizon manner, a smooth signal is reconstructed by solving a convex optimization problem with ℓ1-norm regularization. The quantization feature and the system models are taken into account in the optimization. A numerical example is given to show the excellent reconstruction performance of the proposed method. In addition, the proposed method is implemented in a high-precision linear stage through DSP, and its effectiveness is verified through experiments using a real positioning system.

2014

1. 

   Suppression of Current Quantization Effects for Precise Current Control of SPMSM Using Dithering Techniques and Kalman Filter

   Hongzhong Zhu, and Hiroshi Fujimoto

   Industrial Informatics, IEEE Transactions on, 2014

   Abs PDF Website

   High-precision current control is demanded for many mechatronic systems to improve the static and dynamic performances. However, current measurement error inherent in the measurement system degrade the control accuracy, since the motor currents are not guaranteed to follow the desired references. In this paper, quantization error caused by analog-to-digital converters is studied. The dithering techniques combined with Kalman filter are proposed to suppress the quantization effects. First, two dithered systems, including the subtractively dithered and nonsubtractively dithered systems, are designed to whiten the quantization error. In the design of nonsubtractively dithered system, the probability characteristic of the metering noise is utilized to minimize the measurement noise level. Then, Kalman filter is designed to estimate the real current signals from the dithered current measurements. Since the variance of the total measurement error is theoretically calculable according to the proposed dithering techniques, Kalman gain can be determined analytically. Finally, simulations and experiments are performed to verify the effectiveness of the proposed approaches using a high-precision positioning system.

2. 

   Mechanical deformation analysis and high-precision control for ball-screw-driven stages

   Hongzhong Zhu, and Hiroshi Fujimoto

   IEEE/ASME transactions on mechatronics, 2014

   Abs PDF Website

   Ball-screw-driven stages are widely used in industry for long-range and high-precision fabrication. One of the main difficulties in dealing with high-precision motion control is the nonlinear friction, which originates at elastic deformation of the mechanical components. In this paper, first, a novel mechanical model of a ball-screw-driven stage is proposed to analyze the elastic deformation dynamics under various motion conditions. It is achieved that the mechanical deformation characteristic of fast motions differs from the case of slow motions in the zero-speed region, and therefore, performing friction compensation should take the motion conditions into account. Then, based on this observation, a sinc-function-based friction compensation method for slow motions including both reverse motions and nonreverse motions and a Sigmoid-function-based friction compensation method for fast reverse motions are proposed to improve the control performance. Thanks to the very few parameters, the proposed methods can save much trouble in design and maintenance and are particularly suitable for control purposes. Finally, the advantages of the proposed methods are evaluated by experiments.

2013

1. 

   Velocity estimation of motion systems based on low-resolution encoders

   Hongzhong Zhu, and Toshiharu Sugie

   Journal of Dynamic Systems, Measurement, and Control, 2013

   Abs PDF Website

   This paper proposes a new approach to estimate the velocity of mechanical system in the case where the optical incremental encoder is used as the position sensor. First, the actual angular position is reconstructed via moving horizon polynomial fitting method by taking account of quantization feature and the plant dynamics. Then, the reconstruction signal is applied to a classical observer to obtain the velocity estimation. Its robustness against the position sensor resolution and the degree of the polynomial is discussed by some numerical examples. Experiments with very low-resolution encoder in low speed range also confirm its effectiveness.

2. 

   Proposal of position reconstruction with polynomial fitting approach for precise motion control

   Hongzhong Zhu, Hiroshi Fujimoto, and Toshiharu Sugie

   IFAC Proceedings Volumes, 2013

   Abs PDF Website

   Optical encoders are extensively used for position measurements in motion controlsystems. The inherent quantization feature of encoders limits the control performance in manyapplications. This paper shows a way to reconstruct the smooth position signal from thequantized measurements. The method uses a polynomial fitting approach where the degreeof polynomial is automatically selected via a convex optimization method. In addition, theinformation of the plant is exploited by combining an observer. The effectiveness of the proposedmethod is verified by simulations and experiments using a high-precision linear stage.

3. 

   Overcoming current quantization effects for precise current control using dithering techniques

   Hongzhong Zhu, and Hiroshi Fujimoto

   IEEJ Journal of Industry Applications, 2013

2011

1. 

   Reconstruction of Plant Output from Quantized Measurement—A Moving Horizon Polynomial Fitting Approach

   Hongzhong Zhu, and Toshiharu Sugie

   IFAC Proceedings Volumes, 2011

   Abs Website

   This paper presents a new approach to reconstruct the plant output of linear time-invariant systems in the case where the available output measurement is quantized. By fitting the quantized measurement data with polynomials in a moving horizon manner, a smooth approximation of plant output is obtained via solving a convex optimization problem. Applying the signal to an observer, the plant output is reconstructed by taking account of the plant dynamics. It is guaranteed that the error between the true and the reconstructed output is bounded. Experimental validation is given by using a DC motor positioning system. It turns out that the proposed approach achieves small reconstruction error and accurate tracking control. In addition, the approach yields a smooth reconstruction signal so that the plant input is well behaved (or smooth) even if PID controller is employed for the plant subject to quantized output measurement.

International Conference Papers

2022

1. A Numerical Investigation of an Offshore Overhead Power Transmission System

   Ruo Luo, Hongzhong Zhu, and Changhong Hu

   2022

2018

1. Release of a reliable open-source package for performance evaluation of ocean renewable energy devices

   Yingyi Liu, Shigeo Yoshida, Hiroshi Yamamoto, and 4 more authors

   2018
2. A Study on Integration of Wave Energy Converter and Semi-Submersible Floating Wind Turbine: A Water Tank Test

   H. Zhu, C. Hu, M. Sueyoshi, and 1 more author

   In 4th Asian Wave and Tidal Energy Conference (AWTEC), 2018

2017

1. A study on torsional vibration reduction for variable-speed variable-pitch wind turbines

   Hongzhong Zhu, Shigeo Yoshida, Hiroyuki Kajiwara, and 3 more authors

   In 2017 IEEE International Conference on Mechatronics (ICM), 2017
2. Modelling and attitude control of a shrouded floating offshore wind turbine with hinged structure in extreme conditions

   Hongzhong Zhu, Makoto Sueyoshi, Changhong Hu, and 1 more author

   In 2017 IEEE 6th International Conference on Renewable Energy Research and Applications (ICRERA), 2017

2016

1. Control of a Combined Floating Platform with Wave Energy Converter for Pitching Reduction

   Hongzhong Zhu, and Changhong Hu

   In Conference Proceedings The Japan Society of Naval Architects and Ocean Engineers 22, 2016
2. Suspension design of a semi-submersible platform

   Hongzhong Zhu, Changhong Hu, Yingyi Liu, and 1 more author

   In International Conference on Offshore Mechanics and Arctic Engineering, 2016

2014

1. Suppression of Current Quantization Effects for Precise Current Control of SPMSM Using Dithering Techniques and Kalman Filter

   Hongzhong Zhu, and Hiroshi Fujimoto

   Industrial Informatics, IEEE Transactions on, 2014
2. Proposal of fast and high-precision control for ball-screw-driven stage by explicitly considering elastic deformation

   Hongzhong Zhu, and Hiroshi Fujimoto

   In 2014 IEEE 13th International Workshop on Advanced Motion Control (AMC), 2014

2013

1. Proposal of nonlinear friction compensation approach for a ball-screw-driven stage in zero-speed region including non-velocity-reversal motion

   Hongzhong Zhu, and Hiroshi Fujimoto

   In IECON 2013-39th Annual Conference of the IEEE Industrial Electronics Society, 2013

2012

1. Overcoming current quantization effects for precise current control by combining dithering techniques and Kalman filter

   Hongzhong Zhu, and Hiroshi Fujimoto

   In IECON 2012-38th Annual Conference on IEEE Industrial Electronics Society, 2012

Other Papers

2021

1. A Study on Electrical Wire and Floating Tower Interaction for an Offshore Overhead Power Transmission System

   Ruo Luo, Hongzhong Zhu, and Changhong Hu

   2021

2020

1. An Experimental Study on Tower-Wire Interaction for Offshore Overhead Power Transmission Concept

   Hongzhong Zhu, Luo Ruo, Changhong Hu, and 1 more author

   In The autumn meeting of The Japan Society of Naval Architects and Ocean Engineers (JASNAOE), 2020
2. Numerical Study on a Multi-Body Ship Towing System for a Floating Offshore Tower

   Hongzhong Zhu, Changhong Hu, Makoto Sueyoshi, and 1 more author

   In Conference Proceedings The Japan Society of Naval Architects and Ocean Engineers 30, 2020

2019

1. Design and Modeling of a Hybrid Wind-Wave Energy Concept

   Hongzhong Zhu, Changhong Hu, and Makoto Sueyoshi

   In Conference Proceedings The Japan Society of Naval Architects and Ocean Engineers 28, 2019

2016

1. 2016S-GS6-15 Control of a Combined Floating Platform with Wave Energy Converter for Pitching Reduction

   Hongzhong Zhu, and Changhong Hu

   In Conference Proceedings The Japan Society of Naval Architects and Ocean Engineers 22, 2016

2015

1. LQG ならびにスライディングモード制御によるドライブトレインダンパの基礎検討

   梶原宏之,  吉田茂雄,  朱洪忠, and 3 more authors

   風力エネルギー利用シンポジウム, 2015
2. 出力平滑化とドライブトレイン制振を両立する制御手法の基礎検討

   小川靖之,  中田成幸,  小野純二, and 3 more authors

   風力エネルギー利用シンポジウム, 2015

2014

1. High-Precision Control for Ball-Screw-Driven Stage in Zero-Speed Region by Explicitly Considering Elastic Deformation

   Hongzhong Zhu, and Hiroshi Fujimoto

   MEC, 2014

2013

1. Angular Acceleration detection Method by Ultra-high Resolution Encoder with Hybrid Sampling Time for Automotive Motor application

   Masato Kanematsu, Hongzhong Zhu, Takayuki Miyajima, and 4 more authors

   In Proc. IEE of Japan Technical Meeting Record, RM-13-72, LD-13-82, HCA-13-048, 2013

2012

1. Servo Performance Enhancement of Motion System using Quantized Output Reconstruction Approach

   Hongzhong Zhu, Hiroshi Fujimoto, and Toshiharu Sugie

   電気学会研究会資料. IIC/電気学会産業計測制御研究会 [編], 2012
2. Optimal Analog-to-Digital Converter Resolution on Current Control for Precise Positioning Control

   Hongzhong Zhu, and Hiroshi Fujimoto

   電気学会研究会資料. IIC/電気学会産業計測制御研究会 [編], 2012

Patents

2022

1. Floating type hybrid wind-wave energy conversion system

   Hongzhong Zhu

   2022

   JP Patent 2022-134370

2016

1. Controller and control method

   Hiroshi Fujimoto, Hongzhong Zhu, Koji Yamamoto, and 1 more author

   2016

   US Patent 9,417,622