Kyushu University Academic Staff Educational and Research Activities Database
List of Papers
ZHU HONGZHONG Last modified date:2024.06.03

Associate Professor / Renewable Energy Center / Research Institute for Applied Mechanics

1. Ruo Luo, Yingyi Liu, Hongzhong Zhu, Changhong Hu, Numerical and experimental investigation of a floating overhead power transmission system, Ocean Engineering,, 284, 115085, 2023.09, A promising concept of floating offshore overhead power transmission system (FOPTS), in which the power transmission tower is installed on a TLP-type floating foundation, is investigated experimentally and numerically to study its feasibility. A numerical method is proposed in which the potential flow theory is used to evaluate the floating foundation hydrodynamics. The lumped-parameter method with a wake oscillator model is applied to the aerodynamic modelling of the overhead in order to determine the wind-induced motion and the corresponding internal force of the conductors. Multi-body simulations are performed in Simscape® by coupling the floating foundation hydrodynamics and theconductor aerodynamics. Wind-tunnel experiments on a simplified FOPTS model are carried out to study the coupled motion of the TLP tower and the overhead conductor. The proposed numerical method is validated by comparison of the conductor tension and motion to the experiment. Numerical simulations have been performed under realistic offshore environments based on the meteorological data of the Sea of Japan. Wind-wave misalignment effects on the structure of the FOPTS are investigated, and the safety of the conductors, the mooring lines, and the sea navigation are discussed..
2. Hongzhong Zhu, Optimal Semi-Active Control for a Hybrid Wind-Wave Energy System on Motion Reduction, IEEE Transactions on Sustainable Energy, 10.1109/TSTE.2022.3202805, 14, 1, 75-82, 2023.01, [URL], 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..
3. Hongzhong Zhu, Makoto Sueyoshi, Experimental study and attitude control of a floating type shrouded wind turbine, Sustainable Energy Technologies and Assessments, 10.1016/j.seta.2021.101811, 50, 12, 101811, 2022.03, [URL], Thrust force needs to be taken into account in the development of floating-type shrouded wind turbines since it would lead to large tower inclination, and both the power conversion efficiency and the safety margin of the system would be reduced. In this study, a novel spar-type shrouded wind turbine using a hinge to mount the nacelle on the tower, which can maintain the nacelle in the horizontal state even with a large tower inclination, is studied based on a 1:100 model. The characteristics of the wind turbine are studied via wind tunnel experiments and wave basin experiments. In wind tunnel experiments, the wind speed-up performance of the shroud and the self-aligning property of the wind turbine are evaluated. In wave basin experiments, the dynamical response of the wind turbine in idling, operational, and parked modes are studied. A model-based attitude controller for stabilizing the nacelle is also proposed and the control performance is analyzed based on experimental results..
4. Hongzhong Zhu, Changhong Hu, A study on floating overhead power transmission system for offshore energy development: Design and modeling approach, Ocean Engineering, 10.1016/j.oceaneng.2021.1, 236, 15, 109528, 2021.09, [URL], In this paper, a floating overhead power transmission system (FOPTS), which has the potential 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 the conductor on its supportive tower to reduce the coupling effects between the conductor and the towers. Then, a mathematical optimization approach, which can take account of the system’s natural frequencies to avoid first-order wave excitation, is proposed to design the properties of the floating foundation and the conductor. In the modeling, the flexibility of the conductor is taken into account by a lumped parameter method. The aero-hydro-elastic dynamics of the system can be analyzed by the numerical model. 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 wind–wave misalignment. The reliability and issues of the system are discussed based on fully coupled time-domain simulation..
5. Hongzhong Zhu, Changhong Hu, A unified seakeeping and maneuvering analysis of multiple linked towing system with triangular Bodies, Ocean Engineering, 10.1016/j.oceaneng.2021.108577, 222, 108577, 2021.02, [URL], 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..
6. Hongzhong Zhu, Shigeo Yoshida, Disturbance observer-based torsional vibration damper for variable-speed wind turbines, IFAC Journal of Systems and Control, 10.1016/j.ifacsc.2020.100112, 14, 100112, 2020.12, [URL], This paper presents a robust torsional vibration damper for variable-speed wind turbines based on the disturbance observer method. The damper is designed by explicitly taking into account the pole placement of the closed-loop system in the presence of model uncertainties. Unlike the conventional band-pass filter method, it is analyzed that the proposed method not only has good performance on noise attenuation but also can maintain the characteristics of the drivetrain system in the low-frequency region. The performance of other generator speed-based controllers, such as the blade pitch controller, can therefore be preserved without the retuning procedures. An experimental system having high consistency with a 2 MW wind turbine is developed and real-time hardware-in-the-loop experiments are carried out to demonstrate the effectiveness of the damper..
7. Hongzhong Zhu, Changhong Hu, Makoto Sueyoshi, Shigeo Yoshida, Integration of a semisubmersible floating wind turbine and wave energy converters: an experimental study on motion reduction, JOURNAL OF MARINE SCIENCE AND TECHNOLOGY, 10.1007/s00773-019-00671-y, 25, 3, 667-674, 2020.09, The integration of wave energy converters and a floating wind turbine has the potential to reduce the cost of energy, since they can share the mooring system and the infrastructure of the power grid. In this study, oscillating-water-column-type wave energy converters mounted on a semisubmersible-type floating wind turbine are presented. Water tank tests are carried out to illustrate that the wave energy converters can not only capture the wave energy but also help in reducing the motion of the floating platform when active control is applied. This study provides a new perspective on hybrid renewable energy application to widen renewable energy penetration by enhancing system reliability..
8. Hongzhong Zhu, Makoto Sueyoshi, Changhong Hu, Shigeo Yoshida, A study on a floating type shrouded wind turbine: Design, modeling and analysis, Renewable Energy, 10.1016/j.renene.2018.09.028, 134, 1099-1113, 2019.04, 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. (C) 2018 Elsevier Ltd. All rights reserved..
9. Siti Fauziah Toha, Shigeo Yoshida, Hongzhong Zhu, Torsional Vibration Reduction with Augmented Inverse Model-Based Controller in Wind Turbine Drivetrain, 2016 IEEE INTERNATIONAL SYMPOSIUM ON ROBOTICS AND INTELLIGENT SENSORS (IRIS 2016), 10.1016/j.procs.2017.01.211, 105, 203-208, 2017.01, Wind energy has shown promising advantages in reducing the greenhouse effect by minimizing carbon dioxide emissions to improve earth climate. Wind turbine which falls under the umbrella of renewable energy family promises cleaner environment while generating electricity from wind energy with no burnt fossil fuel. However, it portrays challenges in terms of high operating cost due to component failure. Thus this paper discusses on mitigating one of the problems related to wind turbine failure, the torsional vibration reduction in drive train. A generator torque control is investigated together with the particle swarm optimization technique in search for accurate parameters of the controller. This control strategy is a solution to low wind speed areas especially around South East Asian region. An augmented inverse model-based controller and band pass filter is proposed to obtain vibration attenuation at the dominant mode. The modelling endeavor is firstly obtained via particle swarm optimization search capability to obtain an accurate transfer function of the inverse model. A band pass filter (BPF) is then augmented with the inverse model as controller for torsional vibration suppression. Results have shown favorable comparison between the proposed and conventional methods in terms of vibration attenuation level..
10. Hongzhong Zhu, Changhong Hu, Yingyi Liu, Optimum Design of a Passive Suspension System of a Semisubmersible for Pitching Reduction, JOURNAL OF DYNAMIC SYSTEMS MEASUREMENT AND CONTROL-TRANSACTIONS OF THE ASME, 10.1115/1.4033948, 138, 12, 2016.12, With the development of ocean energy exploration, reliable semisubmersible platforms with very small motion are expected to develop. Especially, in a floating offshore wind turbine (FOWT) system, the maximum pitching amplitude is required to be less than a few degrees. To reduce wave-induced pitch motion, a new type semisubmersible 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, first, the conceptual semisubmersible is described. Then, the hydrodynamic loads to the semisubmersible 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-infinity 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 semisubmersible can be remarkably reduced by the designed suspensions..
11. Hongzhong Zhu, Changhong Hu, A Study on Control of Wave Energy Converter for Motion Suppression of Semisubmersible, IFAC-PapersOnLine, 10.1016/j.ifacol.2016.10.434, 49, 23, 380-385, 2016.01, With the development of ocean energy exploration, reliable floating platforms with very small motion are expected to develop. For instance, the maximum pitching amplitude of a floater for floating offshore wind turbine is required to be less than a few degrees. On the other hand, ocean waves contain abundance of untapped renewable energy with very high power density. Integration of floating platform with wave energy converters while reducing the structure interaction becomes significant for offshore development. In this paper, control of wave energy converters on reducing the pitch motion of a floating platform is studied. Firstly, a mathematical model of the whole system is proposed. The control of wave energy converters leads to solve a constrained optimization problem. Secondly, hybrid model predictive control is presented to synthesize the controller. Finally, numerical examples are given to verify the effectiveness of the proposed controller. It is shown that the reduction of pitch motion of the platform and the wave energy extraction are compatible..
12. Hongzhong Zhu, Toshiharu Sugie, Hiroshi Fujimoto, Smooth Output Reconstruction for Linear Systems with Quantized Measurements, Asian Journal of Control, 10.1002/asjc.950, 17, 3, 1039-1049, 2015.05, 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 (1)-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..
13. Hongzhong Zhu, Hiroshi Fujimoto, Mechanical Deformation Analysis and High-Precision Control for Ball-Screw-Driven Stages, IEEE-ASME TRANSACTIONS ON MECHATRONICS, 10.1109/TMECH.2014.2337933, 20, 2, 956-966, 2015.04, 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..
14. Hongzhong Zhu, Hiroshi Fujimoto, Suppression of Current Quantization Effects for Precise Current Control of SPMSM Using Dithering Techniques and Kalman Filter, IEEE TRANSACTIONS ON INDUSTRIAL INFORMATICS, 10.1109/TII.2014.2307195, 10, 2, 1361-1371, 2014.05, 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..
15. Hongzhong Zhu, Hiroshi Fujimoto, Toshiharu Sugie, Proposal of position reconstruction with polynomial fitting approach for precise motion control, IFAC-PapersOnline, 10.3182/20130410-3-CN-2034.00058, 46, 5, 231-236, 2013.09, Optical encoders are extensively used for position measurements in motion control systems. The inherent quantization feature of encoders limits the control performance in many applications. This paper shows a way to reconstruct the smooth position signal from the quantized measurements. The method uses a polynomial fitting approach where the degree of polynomial is automatically selected via a convex optimization method. In addition, the information of the plant is exploited by combining an observer. The effectiveness of the proposed method is verified by simulations and experiments using a high-precision linear stage..
16. Hongzhong Zhu, Toshiharu Sugie, Velocity Estimation of Motion Systems Based on Low-Resolution Encoders, JOURNAL OF DYNAMIC SYSTEMS MEASUREMENT AND CONTROL-TRANSACTIONS OF THE ASME, 10.1115/1.4007065, 135, 1, 2013.01, 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..
17. Hongzhong Zhu, Hiroshi Fujimoto, Overcoming Current Quantization Effects for Precise Current Control using Dithering Techniques, IEEJ Journal of Industry Applications, 10.1541/ieejjia.2.14, 2, 1, 14-21, 2012.08, Accurate current signals are required for precise current control of AC motor drives. However, current measurement errors that involve metering error and quantization error are unavoidable because of the inaccuracy of current sensors and the quantizing feature of analog-to-digital converters in all digital motion control systems. The quantization error contains harmonic components that can induce torque ripple, thus deteriorating the control performance. Therefore, it is necessary to suppress the quantization effects. In this paper, two dithered systems, namely, the subtractively dithered system and nonsubtractively dithered system, are presented in order to remove the quantization-based harmonic components of the measured current signals by whitening the quantization error. Moreover, for ease of practical implementation, the design of dither signals is analyzed for nonsubtractively dithered system, considering cases where the metering error is uniform noise or Gaussian noise. It is shown that by applying the dither having a suitably chosen probability density function, the total measurement error can be rendered spectrally white. The effectiveness of the proposed methods is verified through simulations and experiments using a high-precision linear stage..