Faculty Profiles - DOKI, Shinji

Papers - DOKI, Shinji

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A Novel Decoupling Control Scheme for Non-Salient Multi-Three-Phase Synchronous Machines Based on Multi-Stator Model Reviewed International journal Open Access

Wang, S; Imai, K; Doki, S

IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS Vol. 59 ( 1 ) page： 886 - 896 2023.1

Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：IEEE Transactions on Industry Applications

As competitive alternatives to conventional three-phase synchronous machines, synchronous multi-three-phase machines (MTPMs) are gaining increasing interests in various fields such as electrified transportation and power generation. The modular configuration is preferred for multi-three-phase drives in specific applications regarding the availability of advanced three-phase power electronics techniques and the superior capability of fault tolerance. The multi-stator (MS) modelling would be an ideal solution for the control of such modular drives as it facilitates power sharing among winding sets in a straightforward way and enables simple post fault strategies compared with the well-known vector space decomposition (VSD) modelling approach. Nevertheless, the strong magnetic coupling existing in MS model has hindered its use due to the instability and the performance deterioration issue. To solve the problem, a new decoupling control scheme directly applied in MS frame is proposed in this paper. The proposed method can deal with non-salient multi-three-phase machines whose three-phase winding sets can be identical or different, under the assumption of the sinusoidal airgap flux. Furthermore, it is shown by analysis the proposed method is characterized by significant simplicity and flexibility compared with the existing decoupling methods. The effectiveness of the proposed method has been verified through experiments including a single-side operation, a power-sharing test, and a post fault tolerant operation on a non-salient dual three-phase permanent magnet synchronous machine with quasi sinusoidal air gap flux.

DOI： 10.1109/TIA.2022.3211827

Active Damping Control Method for Different Dual-Parallel-SPMSM Systems with Single Inverter Reviewed International journal Open Access

Park, C; Doki, S

IEEJ JOURNAL OF INDUSTRY APPLICATIONS Vol. 12 ( 1 ) page： 73 - 83 2023

Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：IEEJ Journal of Industry Applications

This paper presents a stabilization method for different dual parallel surface permanent magnet synchronous motor (SPMSM) systems with a single inverter. When a single inverter drives two synchronous motors, disturbance can cause a torque difference between the two motors. This can cause the motor’s electrical and mechanical resonance. Several damping control methods have been proposed to suppress such resonance. However, such methods consider that the parameters of the two motors are identical. When a single inverter controls two motors with different parameters, the damping control performance deteriorates. Besides, the motor’s resonance sound and current ripple increase. To address these problems, this paper proposes a control method for dual-parallel-SPMSM drive systems with a single inverter.

DOI： 10.1541/ieejjia.22006418

Extended EMF Observer of Dual Three-Phase Permanent Magnet Synchronous Motor Operable in Overmodulation Drive Reviewed International journal Open Access

Imai, K; Doki, S; Kondo, K; Aoki, Y

IEEJ JOURNAL OF INDUSTRY APPLICATIONS Vol. 12 ( 5 ) page： 901 - 913 2023

Language：English Publishing type：Research paper (scientific journal) Publisher：IEEJ Journal of Industry Applications

This paper proposes a novel extended electromotive force (EEMF) observer of a dual three-phase permanent magnet synchronous motor (DTP-PMSM) operable to the position sensorless overmodulation drive. The overmodulation drive occurs in current harmonics, and the estimated EEMF also contains harmonic components, leading to ripple error in the estimated position. Based on the vector space decomposition (VSD) utilized in DTP-PMSM current control, the proposed method can decrease the current harmonics in the overmodulation and the harmonic components in the estimated EEMF, and it can also improve position estimation. The effectiveness of the proposed EEMF observer and the improvement in the position estimation were experimentally verified.

DOI： 10.1541/ieejjia.22005441

Clustering Method of Driving Scenes based on Road Shape by using Road Map Images Reviewed International journal

Hashimoto K., Yanagihara D., Kuniyuki H., Doki K., Funabora Y., Doki S.

4th International Conference on Electrical Communication and Computer Engineering Icecce 2023 2023

Authorship：Last author Language：English Publishing type：Research paper (international conference proceedings) Publisher：4th International Conference on Electrical Communication and Computer Engineering Icecce 2023

Currently, vehicles are equipped with various sensors that can collect a series of driving behavior data while driving. The driving behavior data obtained in this way can be used to analyze the causes of traffic accidents and evaluate driver skills. However, when performing the above analysis, a specific driving scene is defined and driving behavior data for that driving scene is required. On the other hand, the series of driving behavior data obtained during one driving operation is enormous, and it is not easy to pick up desired driving scene data from among them. This research aims to establish a driving scene clustering method for a series of driving behavior data. In this paper, a driving scene is defined as a scene in which road shape and operation are associated, and propose a driving scene clustering method considered road shape. Here, a road map image is acquired from position information obtained from a GPS sensor, and the relationship between the road map image and operation data is clustered based on Coupled-GP-HSMM.

DOI： 10.1109/ICECCE61019.2023.10442604

Capacitor Current Reduction in Dual Three-Phase PMSM Drive System by Model Predictive Control Considering Dead Time Reviewed International journal

Sakauchi R., Doki S., Imai K., Kondo K., Aoki Y.

2023 25th European Conference on Power Electronics and Applications EPE 2023 Ecce Europe 2023

Language：English Publishing type：Research paper (international conference proceedings) Publisher：2023 25th European Conference on Power Electronics and Applications EPE 2023 Ecce Europe

This paper proposes a novel capacitor current reduction method in Dual Three-Phase PMSM Drive System. By using Model Predictive Control considering the dead time on the premise of implementation, the method modifies the three-phase voltage command generated by the PI current controller for the current reduction. The effectiveness is verified by simulation and experiment.

DOI： 10.23919/EPE23ECCEEurope58414.2023.10264351

Arm-Mounted Assistive Robot for Measuring Contact Force and Evaluating Wearer Safety Reviewed International journal Open Access

Masaoka, S; Funabora, Y; Doki, S

IEEE ACCESS Vol. 11 page： 114855 - 114863 2023

Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：IEEE Access

We developed a wearable assistive robot that directly measures the contact force acting between the robot and the human body, aiming to enhance the safety of such wearable devices. The force acting on the body is not directly measured, instead, it is estimated by measuring the torque acting on the robot joint in the wearable assistive robot. Despite the risk of failing to recognize dangerous forces due to modeling errors, the forces actually at work have not been examined. Here, we developed an arm-mounted assistive robot that directly measures the contact force as the distribution information to build a system and evaluate safety; in addition, the contact state between the robot and the human body was discussed. Accordingly, two experiments were conducted with 10 subjects. The first verified the contact force measurement performance of the robot, while the second demonstrated the application of contact force information to check the safety of the robot. The proposed robot can accurately measure the contact force, and the robot movement is safe under general control, for example, using the pain tolerance limit as the safety index. This eliminated the risk of not directly monitoring the forces acting on the surface of the human body. Furthermore, our result have implication for evaluating structural problems of the robot by evaluating contact conditions during movements.

DOI： 10.1109/ACCESS.2023.3324417

Application of Finite Control Set-Model Predictive Control for Servo Brake Motion in PMSM Drives Reviewed International coauthorship International journal

Kawai, H; Cordier, J; Kennel, R; Doki, S

IEEE CANADIAN JOURNAL OF ELECTRICAL AND COMPUTER ENGINEERING Vol. 46 ( 2 ) page： 117 - 129 2023

Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：IEEE Canadian Journal of Electrical and Computer Engineering

Finite control set-model predictive control (FCS-MPC) has a simple and intuitive optimization procedure. Therefore, FCS-MPC is increasingly being applied to control strategies for electrical drive systems. This article presents a method for servo brake control of a permanent magnet synchronous motor (PMSM) based on FCS-MPC. Accordingly, we propose a reference trajectory introduced in a cost function for brake motions and an alternating procedure with speed control. Moreover, this article clarifies the problem peculiar to servo-brake control using FCS-MPC, i.e., the reduction in tracking performance near the brake position because of the low resolution of the output voltage. In addition to the conventional method, a finite number of smoothed voltages were applied as candidate voltages for FCS-MPC to improve the tracking performance near the brake position. The smoothed voltages can effectively increase the resolution of the output voltage, which results in fewer steady-state errors in angular position tracking during servo brake motion. The simulation and experimental results obtained using a PMSM drive system reveal that the proposed strategy exhibited high performance in tracking the reference target during the operation of servobrakes and the ability to seamlessly alternate between servo brake and motor operations.

DOI： 10.1109/ICJECE.2022.3233029

Modeling of Novel Dual Three Phase PMSM with Pseudo-Triple Winding Structure and its Current Vector Control Reviewed International journal

Aiba K., Doki S., Kato H., Isogai K.

2023 25th European Conference on Power Electronics and Applications EPE 2023 Ecce Europe 2023

Authorship：Last author Language：English Publishing type：Research paper (international conference proceedings) Publisher：2023 25th European Conference on Power Electronics and Applications EPE 2023 Ecce Europe

In this paper, we propose the control model for a novel dual three-phase PMSM with pseudo-triple winding structure(DTP-PMSM with PTWS) which is one of the new multiple stator winding machines. The proposed control model is represented as the extended form of the conventional dual three-phase winding machine, and the validity is demonstrated by being compared with magnetic field analysis results. Furthermore, the current vector controller for the control model is designed and its performance is confirmed by simulation.

DOI： 10.23919/EPE23ECCEEurope58414.2023.10264324

Performance Evaluation of Position Sensorless Control System with Initial Speed Estimator for Overall Speed Startup Reviewed International journal

Hao R., Doki S., Asahina K., Ide A.

2023 25th European Conference on Power Electronics and Applications EPE 2023 Ecce Europe 2023

Language：English Publishing type：Research paper (international conference proceedings) Publisher：2023 25th European Conference on Power Electronics and Applications EPE 2023 Ecce Europe

Position sensorless control for Permanent-magnet synchronous motors has been investigated in numerous studies, but the issues of flying start at high speed are still a major problem. In our previous research, the issues on conventional position control are presented, and the reasons for these issues are distinguished as the initial response of the speed estimation. Based on this discussion, an initial speed estimation method is proposed as a solution. In this paper, the whole position sensorless control system with the initial speed estimation is presented, which enables the startup from overall speed, and the evaluation experiments are reported.

DOI： 10.23919/EPE23ECCEEurope58414.2023.10264244

Optimal Current Control Methods for Single-Inverter Dual-Parallel-SPMSM with Different Parameters Reviewed International journal Open Access

Park, C; Doki, S

IEEJ JOURNAL OF INDUSTRY APPLICATIONS Vol. 12 ( 5 ) page： 961 - 970 2023

Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：IEEJ Journal of Industry Applications

This paper presents optimal current-control methods for driving two different synchronous motors using a single inverter. When one inverter drives two motors, system efficiency will deteriorate if their loads are not identical. Moreover, even with identical loads, system efficiency will deteriorate if the parameters of the two motors are not identical. To address this issue, this paper proposes optimal current-control methods for systems with two different motors driven by a single inverter.

DOI： 10.1541/ieejjia.22010492

Optimal Current Control Methods for Dual-Parallel-SPMSM with Different Parameters Using a Single Inverter Reviewed International journal

Park C., Doki S.

Icpe 2023 Ecce Asia 11th International Conference on Power Electronics Ecce Asia Green World with Power Electronics page： 211 - 220 2023

Authorship：Last author Language：English Publishing type：Research paper (international conference proceedings) Publisher：Icpe 2023 Ecce Asia 11th International Conference on Power Electronics Ecce Asia Green World with Power Electronics

When one inverter drives both motors, the system efficiency deteriorates if both motors have different loads. Moreover, even if their loads are the same, the system efficiency would also deteriorate if the parameters of both motors are different. To address this issue, this paper proposes optimal current control methods for both different motors using a single inverter.

DOI： 10.23919/ICPE2023-ECCEAsia54778.2023.10213583

Position Sensorless Estimation for Surface Permanent Magnet Synchronous Motors Using Eddy Currents with Loads at a Low speed Reviewed International journal

Miki Y., Tomita M., Hasegawa M., Doki S.

2023 International Future Energy Electronics Conference Ifeec 2023 page： 224 - 229 2023

Language：English Publishing type：Research paper (international conference proceedings) Publisher：2023 International Future Energy Electronics Conference Ifeec 2023

Position sensorless control of surface permanent magnet synchronous motors (SPMSMs) in low-speed regions is challenging because the motor has no magnetic saliency. Several methods using the block commutation drive technique to overcome this problem have been proposed; however, the rotor position is estimated only every 60° owing to the features of the block commutation drive method. Therefore, in this study, we proposed a novel sensorless rotor position estimation method by pasting the conductive nonmagnetic materials on the rotor. When high-frequency voltage is applied, eddy currents flow through the materials and the inductance slightly changes depending on the rotor position. In this study, estimating the continual rotor position from 0° to 360°, in which the sinusoidal vector control commutation is necessary rather than the block commutation drive method, was realized using these inductance changes. Based on the experimental results, we found that the rotor position could be continually estimated from 0 to 360°, which is necessary for sinusoidal vector commutation for an SPMSM with a position estimation error of approximately 6°, although the rotor velocity was low at 1.59 % of the rated velocity and 12 % of the rated load was applied.

DOI： 10.1109/IFEEC58486.2023.10458604

Turning a Functional Cloth Into an Actuator by Combining Thread-Like Thin Artificial Muscles and Embroidery Techniques Reviewed International journal

Nakagawa, K; Sakai, Y; Funabora, Y; Doki, S

IEEE ROBOTICS AND AUTOMATION LETTERS Vol. 7 ( 3 ) page： 5827 - 5833 2022.7

Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：IEEE Robotics and Automation Letters

In this letter, we propose to turn various existing cloths, especially functional cloths, into actuators by combined embroidery technology and thin McKibben artificial muscles. Most of the textile sensors so far are made by weaving active yarns into each other or into other base cloths. These devices have a limited choice of cloths that can be actuated. We create a prototypical actuator that can be deformed in three dimensions using thin artificial muscles and embroidery techniques on a functional cloth used for hook-and-loop fasteners and textiles that can observe pressure. Our experimental results indicate that the force of the artificial muscles can be transmitted to the cloth using fixation by embroidery and that the actuator can be variously deformed in three dimensions. We show that functional cloths can be made into actuators while maintaining their own functions using the proposed method.

DOI： 10.1109/LRA.2022.3157401

Basic Verification of Contact Force-Based Control with Full Body-Worn Assistive Robot Reviewed International journal

Masaoka S., Funabora Y., Doki S.

2022 IEEE/SICE International Symposium on System Integration, SII 2022 page： 144 - 149 2022.1

Language：English Publishing type：Research paper (international conference proceedings) Publisher：2022 IEEE/SICE International Symposium on System Integration, SII 2022

This paper evaluates the performance of contact force-based control with developed wearable assistive robots enabling the contact force measurement between the wearer and the robot. Almost all the conventional assistive robots are controlled with their joint torque measured via torque sensors. These robots have risks exerting excessive force on the wearer because torque sensors cannot detect contact force exerting the wearer. Our research group developed the contact force-based control and evaluated its performance only on the simulation. Also, we developed a prototype of a wearable robot enabling to measure and detect the contact force. In this paper, tracking performance to the wearer's movements, one of the basic performances of wearable robots, is confirmed via the experience. As a result, contact force-based control can operate in full accordance with the command of zero contact force.

DOI： 10.1109/SII52469.2022.9708851

Current Control System with High-Frequency Signal Injection for Dual Three-Phase Permanent Magnet Synchronous Motor Reviewed International journal Open Access

Imai, K; Doki, S; Kondo, K; Aoki, Y

IEEJ JOURNAL OF INDUSTRY APPLICATIONS Vol. 11 ( 1 ) page： 27 - 40 2022

Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：IEEJ Journal of Industry Applications

Dual three-phase permanent magnet synchronous motors have the characteristics of multi-phase and permanent magnet synchronous motors, whose double- and decoupled-winding models based on the vector space decomposition have been reported. High-frequency signal injection methods enable position sensorless control, parameter identification, and the search for maximum torque per ampere operating points. However, the current control system with high-frequency signal injection for a dual three-phase permanent magnet synchronous motor has not yet been sufficiently discussed. This study compares the double- and decoupled-winding models for the current control system with the high-frequency signal injection and proposes a current control system with high-frequency signal injection. Furthermore, this study proposes a position sensorless control method at low speed based on the high-frequency voltage injection as an application of the proposed current control system with the high-frequency signal injection. Experiments verify the effectiveness of the proposed current control system with the high-frequency signal injection and the proposed position sensorless control method.

DOI： 10.1541/ieejjia.20012955

AR Image Presentation based on Gaze Information for Operator support in teleoperation Reviewed International journal

Doki K., Funabora Y., Doki S., Yano Y.

Sami 2022 IEEE 20th Jubilee World Symposium on Applied Machine Intelligence and Informatics Proceedings page： 395 - 400 2022

Language：English Publishing type：Research paper (international conference proceedings) Publisher：Sami 2022 IEEE 20th Jubilee World Symposium on Applied Machine Intelligence and Informatics Proceedings

The authors have been tackling a new teleoperation system with a head-mounted display (HMD) and an omnidirectional camera to reduce the workload of an operator. Some experimental results verified that presentation of AR images based on sensor information could reduce the workload and prevent the deterioration of the task quality due to the transmission delay of images. However, the range of the field of view (FOV) of an HMD is narrower than that of a human. This difference might cause accidents by overlooking hazards that are outside the FOV of the HMD. To solve this problem, the authors propose a new method of AR image presentation based on gaze information not to overlook hazards. Some experimental results using a driving simulator verified the usefulness of the proposed method.

DOI： 10.1109/SAMI54271.2022.9780732

Stability Improvement Method of Position Sensor less Control for Single Inverter Dual Parallel IPMSMs Drive System by Using Signal Injection Reviewed International journal

Park C., Doki S.

2022 International Power Electronics Conference IPEC Himeji 2022 Ecce Asia page： 583 - 588 2022

Authorship：Last author Language：English Publishing type：Research paper (international conference proceedings) Publisher：2022 International Power Electronics Conference IPEC Himeji 2022 Ecce Asia

This paper proposes a method to drive a single-inverter dual interior permanent magnet synchronous motor (IPMSM) system by using signal injection. Considerable research has been performed to decrease the size and cost of dual motor drive systems by driving two synchronous motors with one inverter. In general, the control is implemented considering one of the two motors. Such systems may become unstable because of the mechanical/electrical resonance occurring in the uncontrolled motor. Therefore, methods to suppress this resonance have been established. Notably, resonance control is challenging to implement at low speeds because the phase of the rotor with sensorless control cannot be easily estimated. To address this problem, signal injection and signal processing methods for such systems was established in this study.

DOI： 10.23919/IPEC-Himeji2022-ECCE53331.2022.9806970

Performance Evaluation of Startup and Driving Strategy at Overall Speed with Extended ElectroMotive Force for Position Sensorless Permanent Magnet Synchronous Motor Reviewed International journal

Hao R., Kozakura T., Doki S.

2022 International Power Electronics Conference IPEC Himeji 2022 Ecce Asia page： 362 - 367 2022

Authorship：Last author Language：English Publishing type：Research paper (international conference proceedings) Publisher：2022 International Power Electronics Conference IPEC Himeji 2022 Ecce Asia

Extended electro-motive force (EEMF) estimation method is a fast position estimation method used for overall speed. In our previous research, we have reported the startup and drive method with EEMF from standstill. However, starting a free-running PMSM, which is known as the flying start, is rarely taken into consideration in the most position sensorless research. Under such condition, the rotor speed is unobservable before the startup. In this paper, a startup and driving strategy at overall speed with EEMF by speed and signal injection is proposed, and the evaluation experiments are reported.

DOI： 10.23919/IPEC-Himeji2022-ECCE53331.2022.9806847

Operator Assistance for Remote Driving with Augmented Image based on Gaze Information Reviewed International journal

Dokil K., Suzuki K., Funabora Y., Doki S., Yano Y.

IEEE International Symposium on Industrial Electronics Vol. 2022-June page： 1094 - 1099 2022

Language：English Publishing type：Research paper (international conference proceedings) Publisher：IEEE International Symposium on Industrial Electronics

The authors have been aiming to realize a remote driving system with an HMD(Head Mounted Display) and a 360-degree camera to decrease the task load of the operator. Therefore, we have been tackling an operator assistance method of remote driving applying Augmented Reality(AR). In the previously proposed methods, AR video presented to the operator is generated based on sensing information of 3D LiDAR to deal with the communication delay. In this paper, a new generation method of AR image is proposed, in which Gaze information of the operator is used to create a 3D object to draw his attention to a hazard that might cause a traffic accident. The usefulness of the proposed method has been evaluated based on the results of the experiments using a driving simulator which has a scenario of a person jumping out from a park.

DOI： 10.1109/ISIE51582.2022.9831663

Motor Drive Method that Enlarges the Applied Voltage without Causing High Harmonics under the Voltage Supply Unbalance in Three Phase Dual Winding Permanent Magnet Motor Reviewed International journal Open Access

Suzuki Takashi, Doki Shinji

IEEJ JOURNAL OF INDUSTRY APPLICATIONS Vol. 11 ( 3 ) page： 506 - 513 2022

Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：IEEJ Journal of Industry Applications

To realize automated drive of a vehicle, more reliability to the motor drive system is required. The three phase dual winding permanent magnet motor drive using two inverters with corresponding voltage supplies is one of the potential candidates for the reliable motor drive system. With the respective voltage supply and winding connected to the inverter, the two motor drive systems are electrically independent. Thus, even if when a failure occurs in one of the systems, the other system can continue the motor drive. However, there is an issue: a voltage drop in one of the voltage supplies reduces the sinusoidal wave region of the drive system as the rotor of the motor is common in the two windings and the back electromotive voltage in the two windings are the same. The motor drive method that enlarges the applied voltage without causing high harmonics under the voltage supply unbalance in the three phase dual winding permanent magnet motor is proposed in this paper.

DOI： 10.1541/ieejjia.21009935

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