名取 賢二

This paper proposes a quasi-MPPT (maximum power point tracking) control for integrating multiple energy harvesters of different characteristics. Energy harvesting (EH) technology is a promising technology and is expected to be widely used in various fields. However, the amount of the harvested power is inherently limited and strongly depends on the weather and other conditions. Therefore, multiple energy harvesters are often integrated to increase total harvested energy. In the case of integrating multiple energy harvesters of different characteristics, the control tends to be complicated due to the different characteristics of the energy harvesters. The proposed quasi-MPPT control enables the multiple energy harvesters to work near their MPP voltages by referring to the command voltages derived from preliminary identification of the energy harvesters and measurement of the open-circuit voltages. It achieves harvesting of approximately maximum powers of the multiple energy harvesters by a simple control strategy using a power management circuit. The effectiveness is validated by using an experimental system that consists of photovoltaic (PV) and thermoelectric (TE) energy harvesters.

The voltage drop in GaN HEMTs during reverse conduction is larger than that of Si-MOSFETs, causing an increase in dead-Time loss and a rise in the bootstrap capacitor voltage when a bootstrap circuit is applied. We propose connecting a low-side device in parallel with a Schottky barrier diode as a solution. This allows the bootstrap capacitor to be charged at the appropriate voltage because the voltage drop is lower. This also reduces dead-Time losses but increases the losses due to capacitance across the connected diode terminals. These losses increase with frequency and are not negligible in ultrahigh frequency switching operations such as 1MHz. This study examines the effect of using anti-parallel diodes for GaN devices.

Carrier frequency of N-level flying capacitor converter (FCMLC) is equivalently (N-1) times higher than that of the 2-level converter with the same carrier frequency. In consequence, its control bandwidth is extended. However, updating the command value in that equivalent carrier period causes capacitor voltages to deviate from predetermined voltages. It is caused by mismatches between charging and discharging times of flying capacitors. Imbalanced flying capacitor voltages cause problems such as increase of harmonics in the output current and applied voltages to the devices. In this study, we derive the discrete-time state-space equation of FCMLC considering flying capacitor voltages and analyze stabilities of flying capacitors. Depending on the analysis, a compensation method for capacitor voltages is proposed, and the effectiveness of it is verified by the experiments.

In motion control systems, detailed characteristics of current control systems are usually not considered. However, as the performance of the overall system advances, higher-performance current control systems are required. This paper proposes a novel PI current control method for realizing deadbeat control characteristics. Conventional deadbeat control is complicated because it is necessary to calculate the pulse width for each sampling cycle. On the other hand, proposed method achieves deadbeat characteristics easier than conventional method by simply determining the PI gains. It can also be applied to multi-level inverters. By simulations and experiments, we confirm that the deadbeat characteristic is obtained. The robustness of the system against disturbances and modeling errors is also confirmed.

This paper proposes a control method for a bidirectional isolated three-phase AC/DC Dual Active Bridge (DAB) converter based on matrix converter (MC) that realizes a wide output voltage range. This method achieves the reduction of excessive high frequency link current and soft switching with online calculation by changing two modulation methods according to the input and output voltage ratio. The proposed method realizes higher efficiency in expanded output voltage range with reduced online calculation burden. The feasibility and validity of the proposed method are verified by experimental demonstration.

In this paper, we study a control method that maintains stability regardless of the number of connected power converters in islanded microgrids. It is known that variations in the number of the power converters connected to the islanded microgrids may lead to system instability, since the change of the number of the connected power converters is equivalently considered as variations of the grid impedance. Therefore, we study a control method for the individual power converter that is robust against the grid impedance variations and clarify the stability range, since it is possible to achieve robust stability of the whole microgrid system by configuring it only with the power converters that are robust against the variations of the grid impedance. We present stability analysis, and simulation and experimental verifications of the proposed robust stabilization method.

This paper proposes a sensorless link voltage control method for bidirectional power flow controller for next-generation DC power network. In our previous works, we studied methods to keep the link voltage at a constant value. The methods were implemented based on feedback of the measured link voltage values. It therefore needs additional costs for measuring equipment of the link voltage. In this paper, we propose a link voltage control method that does not use the measured link voltage value, and enables to keep the link voltage certainly higher than the node voltages. The method well simplifies the implementation and reduces the costs. The effectiveness of the proposed method is verified by experimental results.

In motion control systems, detailed characteristics of power converters are usually not considered. Practically, voltage ripple, harmonics, and electromagnetic interferences (EMI) generated in widely used 2-level inverters become concerns to realize a high-performance control. Compared with 2-level inverters, multi-level (ML) inverters essentially reduce these problems. Furthermore, the equivalent carrier frequency of N-Ievel ML inverters is expected to be N-l times higher than that of the 2-level inverters in case that a carrier phase-shifted modulation is utilized. This paper focuses on the equivalent carrier frequency and studies the performance and stability of current control systems by using ML inverters.

This paper studies a resonance suppression control based on virtual resistance concept for parallel inverters in islanded microgrids. At the inverter systems with LC output filters, resonances often occur due to various reasons. To suppress the resonances, additional resistances are often used to dampen the system (passive damping). However, additional resistance inevitably causes additional losses. On the other hand, many active damping approaches have also been studied. In this paper, we study one of the active damping methods, the resonance suppression control based on virtual resistance concept. In particular, the resonance suppression control implemented at the current-controlled inverter and that implemented at the voltage-controlled inverter in islanded microgrids are comparatively studied. The effectiveness is evaluated by analyses of frequency characteristics, simulation studies, and experimental results in the case of two parallel inverters in islanded microgrids.

This paper studies design of the speed sensorless field oriented control of induction motors considering sudden change of the rotor speed. The controller gains are designed to follow the dynamics of the sudden change of the rotor speed based on an induction motor and current control system model. The primary angular frequency can be estimated properly even when the rotor speed changed suddenly by designing the controller. Also, the time to converge to the command values of the stator current and motor torque is shortened. The effectiveness of the designing method is evaluated by means of simulating slip of the railway vehicle traction.

This paper studies fifth-order filters to realize reduction of filter size for grid-connected inverters. Those filters are expected to achieve better performance with smaller filter size, since they have steeper characteristics than conventional and lower-order ones. The parameters design criteria of those filters are also introduced. The comparative analysis regarding the conventional LCL filter and the proposed fifth-order filters have been presented.

In recent years, AC and DC microgrids have been extensively studied. By constructing microgrids, it is possible to promote installing renewable energy resources. Most of components (renewable energy sources, storage devices, load, and so on) are connected to the microgrids through power converters. Therefore, due to spread of microgrids, the importance and the use of power converters have been increasing. As a practical solution to build microgrids, our group has proposed a concept of 'plug-and-play' converter. The concept means that the plug-and-play converter is flexibly applied to various components with a unified circuit topology in three-phase AC, single-phase AC, and DC microgrids. As one of the essential functions for development of the plug-and-play converter, this paper realizes universal grid interconnection control method. The proposed control method enables to transmit and receive desired active power in three-phase AC, single-phase AC, and DC microgrids, without changing the control system and circuit topology. Simulation studies verify the validity of the universal grid interconnection control method.

SiC-MOSFETs are expected as promising power switching devices from the view point of high-speed switching and lower on-state resistance. In the multilevel inverters, the number of switching devices in the main current path increases. Thus, lower on-state resistance of the SiC-MOSFETs is very useful to reduce conduction loss of the inverter. In addition, to reduce required capacitance of the flying capacitors, higher switching frequency operation is indispensable. From this point of view, the higher switching frequency in high power applications realized by the SiC-MOSFETs is very attractive. In this way, the SiC-MOSFETs can dramatically enhance the advantages of the flying capacitor multilevel inverters. In this paper, as a basis of design consideration for flying capacitor multilevel inverters using SiC-MOSFETs, various experimental investigations employing four different prototypes are carried out. The effect of the number of the output levels and thermal management are demonstrated. In addition, key issues in extension to higher voltage applications are investigated.

This paper studies a novel control approach to multi-terminal power flow controller (MTPFC) for next-generation DC power network. We have proposed and validated bidirectional power flow controller (BPFC) and MTPFC as promising power flow controllers for next-generation DC power networks. In BPFC, total power imbalance possibly causes voltage fluctuation of the inter-stage link capacitor. The fluctuation affects performance of the power flow control. Then, in MTPFC, a compensation node that keeps the inter-stage link capacitor voltage at a predetermined constant value, plays an important role for precise operation of MTPFC. However, the introduction of the compensation node needs additional costs. In this paper, we propose a novel control approach that properly controls power flows even in case that there are fluctuations of the voltage of the inter-stage link capacitor. The control approach is realized by using measured values of the voltages for the control system. The proposed approach is validated by experimental results.

DC microgrid has been drawing much attention in recent years. In DC microgrid, introduction of renewable energies to demand sides possibly causes power imbalance and reverse power flows on feeders. These problems cause increase of distribution losses and voltage rises in feeders. To overcome these problems, a power flow control method among multiple DC feeders (nodes) is required. We have studied bidirectional power flow controller (BPFC) based on a bidirectional buck-boost converter. It realizes power flow control by intentionally generating voltage difference between two terminals. Furthermore, BPFC has been extended to multi-terminal power flow controller (MTPFC) that realizes power flow control among multiple DC nodes. However, output voltages of BPFC and MTPFC are excessively higher than minimally required voltages for realizing the power flow control. That leads to unnecessary increase of conversion capacity of the circuit, and therefore seriously deteriorates the efficiency. Then, we studied a novel circuit structure, floating bidirectional power flow controller (F-BPFC). F-BPFC outputs the voltage just equal to the minimally required voltage for realizing the power flow control. Therefore, it is able to be implemented with low conversion capacity, and significantly improves the efficiency. In this paper, to realize highefficiency power flow control among multiple DC nodes, we extend F-BPFC to multi-terminal cases. We call it, floating multi-terminal power flow controller (F-MTPFC). We study the power flow control by using F-MTPFC with introduction of a novel control method. The effectiveness, feasibility, and efficiency of F-MTPFC are validated by experimental studies.

It is expected that electric railways realize further energy-saving performance. In electric railways, the energy consumption depends on the train scheduling. Therefore, some researches have addressed energy saving by studying train scheduling. One of the researches optimized energy consumption by changing train scheduling based on mathematical models. However, it did not consider uncertainties of operation conditions. Since there inevitably exist uncertainties like adhesion coefficient and vehicle load, those possibly affect the optimality. In this paper, we explicitly consider vehicle load variation. The energy consumption is modeled taking the vehicle load variation into account. Then, we study optimization of energy saving based on the derived energy consumption model. The effectiveness of the optimization approach is validated by simulation studies.

This paper studies efficiency improvement of DC power network by using multi-terminal power flow controller (MTPFC). We have proposed MTPFC for flexible and precise power flow control in DC power networks. The circuit topology and the control method have been investigated and it has been clarified that MTPFC is effective for power flow control in DC power networks. In this paper, we address efficiency improvement by reducing the loss in distribution line of power network by using MTPFC. A case study is conducted and the effectiveness for efficiency improvement is discussed.

DC power networks with introduction of distributed generation (DG) and energy storage (ES) systems have been drawing much attention in recent years. To control power flows in DC power networks, voltage of each terminal is usually an only controllable variable. Therefore, implementation of control method is generally simple, but it lacks flexibility particularly when the structure of the power network is complicated. To overcome the problem, a more flexible power flow control method that includes a power flow controller implemented on the distributed line has been proposed. The controller makes additional voltage differences on the distribution line and realizes bidirectional and flexible power flow control. In this paper, we consider DC power networks with complicated connections of DG and ES systems. For implementing simple and intuitive power flow control, we propose a multi-terminal power flow control method that consists of a multi-terminal power flow controller (MTPFC) and a compensation node for MTPFC. The control method makes the DC power network simpler and enables to realize flexible and robust power flow control. The effectiveness and the feasibility of the proposed control method are validated by experimental studies.

In motion control systems, detailed characteristics of power converters and motors are usually not considered. Practically, voltage ripple, harmonics, and electromagnetic interferences (EMI) generated in widely used 2-level converters become concerns to realize a high-performance control. Those possibly degrade the control performance especially in sensitive applications such as the case of small motors, high-speed and high-precision systems, and haptic systems. In this paper, performance improvement of motion control systems by applying multi-level converters is studied experimentally in a force control system of a DC motor. Some experimental results clarify that force control gain and cutoff frequency of DOB (disturbance observer) are able to be larger in the case of multi-level converters compared with the case of 2-level converters. It is confirmed that the multi-level converter improves the force control performance compared with the case of 2-level converter even when an identical control system is used.

To realize massive integration of distributed renewable energy resources in future power system, the development of efficient measures for their integration is required. Using DC grid is more efficient and more compatible for the integration of renewable energy resources and energy storage devices. In the next-generation DC power network, many kinds of nodes which consist of generators, loads, energy storage devices, and so on and links (distribution lines) are connected. Thus, the grid structure is complex, and flexible power flow controls are essential. In a DC distribution network, the only controllable parameter is voltage of nodes, thus it is difficult to control the power flow of each link independently. In this paper, we study a power flow control on the links named link voltage control based on a bidirectional buck-boost converter implemented on the link. In addition to the voltage difference between the nodes, the link voltage controller generates additional voltage difference on the link intentionally. Thus, it is possible to control power flow of a specific link independently without affecting power flow of other links. In this way, flexible controls of power flows in a multi-terminal DC power network become possible. The effectiveness of the power flow control is demonstrated by experiments. The high controllability of the link voltage controller will contribute to the realization of future DC power grid.

This paper studies analysis of bilateral control system with time delay based on mechanical power factor (MPF) concept. MPF is an interesting and useful performance index for evaluation of motion control systems. In this paper, first, effect of time delay and the effectiveness of a time-delay compensation method by using communication disturbance observer (CDOB) in bilateral control systems are analyzed based on MPF. Then, effects of the controller gains on the performance are studied also based on MPF. The obtained analysis results will be useful guidelines for design of bilateral control systems with time delay.

In the field of motion control systems, voltage ripple, harmonics, and electromagnetic interferences (EMI) in an output of converters negatively affect the control performance. However, so far, there has been practically few works that explicitly consider the power converters in motion control systems. Currently, general 2-level converters are widely used. However, it is concerned that the 2-level converter becomes one of the obstacles to realize high-performance control because the output voltage has high harmonics and EMI. Those possibly degrade the position or force control performance. As the solution to this problem, linear amplifiers may be useful because they outputs continuous voltage without pulsed waveform. However, low efficiency of the linear amplifiers becomes critical issue as the power converter. In this paper, performance improvement of the motion control systems by applying multilevel converters is investigated as a solution to realize both high control performance and high efficiency at a higher level. From the results of some experiments, it is seen that current waveform is distorted in the case of using the 2-level converter due to the output voltage ripple of the converter. In addition, the operation of disturbance observer (DOB) causes current ripple with lower frequency. On the other hand, it is confirmed that 9-level converter reduces the ripples of the current effectively. Moreover, EMI which is major concern in high-performance control system such as extremely small motor applications for high-precision control, can be improved by using the multi-level converter even without any filters.

Performance indices are useful as design guidelines of control systems. One of useful performance indices for bilateral teleoperation systems is transparency. It evaluates bilateral teleoperation systems based on a definition of the ideal state of bilateral control. Since the concept is intuitive, it has been widely used in many applications. The evaluation or analysis based on transparency is usually done in frequency domain by using frequency characteristics of the subject control systems. However, in some applications, online performance evaluation methods or performance indices by using experimental or simulation data are more desirable and useful. In this paper, a concept of mechanical power factor (MPF) is studied as an eligible performance index for online performance evaluation of bilateral teleoperation systems. Some fundamental studies on impedance transmission verify the validity of MPF. Moreover, the verification is extended to cases with time delays. The results clarify that MPF is valid as a performance index of bilateral teleoperation systems in the cases with/without time delays. © 2014 IEEE.

In this paper, we study disturbance-attenuation characteristic of a structure of time-delay system with communication disturbance observer (CDOB). A time-delay compensation method based on network disturbance (ND) concept and CDOB has been proposed and used in various kinds of time-delay systems and the effectiveness has been verified theoretically and experimentally. The advantage is that it works even when a time-delay value is unknown or a time-delay model is unavailable, since it does not need a time-delay model. However, it has been pointed out that the system-model error seriously affects the steady-state characteristics and causes steady-state error. Then, some approaches to handle such a problem have been proposed so far. It has turned out that one of those proposed approaches overcomes such a problem and achieves zero steady-state error in case that there are system-model errors. However, the robustness against disturbance, or the disturbance-attenuation characteristic has not been studied. Therefore, in this paper, the disturbance-attenuation characteristic of the structure is studied. The characteristic is studied compared with that of the conventional structure. © 2013 IEEE.

This paper studies a design method of time-delay systems with communication disturbance observer (CDOB). A time-delay compensation method based on network disturbance (ND) concept and CDOB has been proposed and applied to various control systems. It compensates time-delay effect without using time-delay model and the effectiveness is equivalent to that of Smith predictor. Furthermore, it works even when time-delay value is unknown, since it does not need time-delay models. In past works, some design methods of time-delay systems with CDOB have been studied basically by using Nyquist diagram. However, detailed design methods of the transient characteristics have not been researched well due to the characteristics of Nyquist diagrams. In other words, we have not addressed design methods based on detailed pole placements studies in order to arbitrarily design the transient characteristics. In this paper, we study a design method of time-delay systems with CDOB based on pole placements by using Pade approximation. The detailed design of the transient characteristics is accomplished by the analytical results. The adequacy of the presented design method is validated by simulation studies. © 2012 IEEE.

This paper proposes a reduction method of steady-state errors in time-delay systems with communication disturbance observer (CDOB). A time-delay compensation method based on network disturbance (ND) concept and CDOB has been proposed and applied to various time-delay systems. The validity has been verified by experimental results. On the other hand, a defect of the method on steady-state characteristics has also been pointed out. System model errors lead to serious steady-state errors in the method. Therefore, some approaches to address such a problem have been studied so far. In this paper, a novel and simple approach to handle the steady-state error problem is proposed. The proposed method reduces steady-state errors by designing system models appropriately. Design procedures of the method are also studied. Finally, it is validated by simulation studies. © 2011 IEEE.

This paper presents a modified structure for robustness enhancement of time-delay systems with communication disturbance observer (CDOB). A time-delay compensation method based on network disturbance (ND) concept and CDOB has been proposed and applied to various time-delay systems. The effectiveness is the same as Smith predictor. In addition, it works even when the value of time delay is unknown, since the method compensates time-delay effects without time-delay models. However, it has a problem of the robustness on system model errors. In case there are model errors of the system, serious steady-state error occurs. In this paper, a modified structure that enhances the robustness of time-delay systems with CDOB is proposed. The structure enhances the robustness and achieves zero steady-state error. The effectiveness of the proposed structure is presented by a case study of a time-delayed motor control system. In addition, this paper addresses stability and transient characteristics of the proposed structure. ©2009 IEEE.

In this paper, the impedance perceived by an operator of a robot in multilateral control system under constant communication time delay is considered. The multilateral control system is one of the methods which transmit tactile sense to many remote places. Time delay possibly makes the performance of the multilateral control system worse. For example, time delay makes an operator feels large operational force. The operational force means that the operator feels the force except the reaction force from the environment. Moreover, time delay makes the operator feels that the environment is softer than the real stiffness. In this paper, the multilateral control system with three robots is considered. By frequency characteristics of the impedance perceived by the operator, the effect of time delay on the impedance perceived by the operator is verified. The results obtained in the analysis are verified by experimental results.

This paper discusses the problem of time delayed control system with communication disturbance observer (CDOB) when the system suffers large external force. This method is based on the concept of network disturbance that consider the effect of time delay as a disturbance in acceleration dimension. CDOB estimate the effect of time delay to the system and using the estimation result compensate it. In practical application, disturbance observer (DOB) is used simultaneously with CDOB to compensate disturbances other than network disturbance, such as external force, friction, gravitation effect, etc. When such disturbance forces are quite large, the accuracy of network disturbance estimation is degraded. A method using shadow system is proposed to decompose the disturbances thus accurate time delay compensation can be achieved.

Bilateral control robots are one of the master-slave teleoperation robots. The Bilateral control robot achieves communication of force sensation between master system and slave system. As one of the bilateral control systems, a three-channel bilateral control system was proposed. The three-channel bilateral control system has only three communication channels and the position information is transmitted only from master system to slave system. Moreover, there are micro-macro bilateral control systems that are one of the applications of bilateral control system. The micro-macro bilateral control system consists of master and slave system, the sizes of that systems are different. Therefore the system contains scaling factors of information. This paper proposes a three-channel micro-macro bilateral control system with scaling of control gains. The proposed method is designed based on reproducibility and operationality that are one of evaluation indices of bilateral control systems. The validity of the proposed method is confirmed by analysis and experiment.

This paper proposes a novel structure of time delayed control systems with communication disturbance observer (CDOB). Time delay problem is one of difficult issues in control engineering and the effects seriously induces performance deterioration and destabilization. Therefore, many kinds of time delay compensation methods or stabilization methods have been proposed so far. As one of those methods, a time delay compensation method based on the concept of network disturbance (ND) and CDOB has been proposed. The method sufficiently compensates time delay without using delay time model. The stability of the method also has been studied in detail and it has been verified that the stability depends on the value of a cutoff frequency of a low-pass filter (LPF) in CDOB. Since the value always has constraint caused by some limitations of devices, the dependency is not desirable. In this paper, a novel structure of the time delayed control systems with CDOB, the stability of which does not depend on the value of cutoff frequency, is proposed. The method eliminates the time delay element from the characteristic polynomial. Therefore the system is not destabilized by time delay anymore. Furthermore, the system can be designed easily by stability criteria for rational characteristic polynomials. The validity is verified by stability analysis (Nyquist diagram) and simulation results. Finally, we make some remarks on the design of time delayed control systems with CDOB.

This paper discusses the effects of controller parameters on transparency of time delayed bilateral teleoperation systems with communication disturbance observer (CDOB). A time delay compensation method based on the concept of network disturbance (ND) and CDOB is a novel and efficient for time delay compensation of time delayed bilateral teleoperation systems. Besides, transparency is one of useful performance evaluation indices of bilateral systems. In this paper, the effects of controller parameters on a specific definition of transparency for time delayed cases are discussed. At first, the effects of controller parameters on the transparency are analyzed. Then the validity of the analytical results is verified by simulation results.

Time delay in bilateral teleoperation systems seriously deteriorates the performance and possibly affects the stability. A novel time delay compensation method based on the concept of network disturbance (ND) and communication disturbance observer (CDOB) has been proposed and the validity has been verified by simulation and experimental results so far. However the validity of the time delay compensation method on performance has not been analyzed. This paper presents analysis of the validity of the time delay compensation method on performance. The analysis is discussed based on performance index of bilateral teleoperation systems, transparency. The analytical results are verified by simulation results.

This paper presents stability analysis and a novel design method of time delayed control systems. The time delayed control systems are constructed based on a time delay compensation method using the concept of network disturbance and communication disturbance observer. At first, the effect of time delay in control systems is described briefly and the effectiveness of the time delay compensation method is presented. Then analysis about the effects of parameters in control systems on stability of the time delayed control systems is analyzed. The main part of this paper is proposal of a novel design method of time delayed control systems according to the analytical results. Simulation results verify the validity of analytical results and proposed design method. The results also demonstrate the effectiveness of the time delay compensation method using the concept of network disturbance and communication disturbance observer.

A time delay compensation method based on the concept of network disturbance and communication disturbance observer has been proposed so far. The method has the same effectiveness as that of Smith predictor and the validity has been experimentally verified. Furthermore, the advantage of the method is that it works without delay time model. However, whereas the method has been practically applied in several situations, the robustness has never been studied so far. In this paper, we present robustness of the time delayed control systems with the lime delay compensation method. Some problems caused by model uncertainty and constraint on cutoff frequency are firstly discussed. Then a time delayed control system with communication disturbance observer based on two-degree-of-freedom control structure is designed. The control system makes it possible to achieve zero steady-state error. Moreover, the transient response is designed easily by parameters of controllers. Here, the transient characteristic and the attenuation performance of model uncertainty can he designed separately. Simulation results verify the validity of the control system.

In a research area of bilateral teleoperation systems, time delay generated in communication line is one of very serious problems. Time delay in control systems induces severe phase delay. Then the phase delay possibly destabilizes the system and deteriorates performance of the system. Therefore many studies about time delay in bilateral teleoperation systems have been conducted so far. Some researches have accomplished stabilization method or compensation method of constant time delay. However compensation of time-varying or fluctuant time delay has not been completed. This paper introduces a novel compensation method of time delay. The method is based on the concept of network disturbance (ND) and communication disturbance observer (CDOB). CDOB estimates ND and estimated value is utilized for the compensation of time delay. In addition, because it does not need delay time model, it can be applied to systems with time-varying or fluctuant time delay. Furthermore the method is very simple and it is very easy to implement. The effectiveness of the proposed method is verified by simulation and experimental results.

In any physical systems, there inevitably exists time delay. Since it has very characteristic and distinctive properties, control of time delayed systems is even now a very difficult and unresolved problem. Therefore a lot of researches about time delay have been studied so far. A distinguished time delay compensation method is Smith predictor. It can equivalently eliminates time delay from closed control loop and stabilize time delayed systems. However precise delay time model is needed for implementation of the method. It is therefore necessary to measure accurate delay time. In these circumstances, authors have proposed a novel time delay compensation method based on the concept of network disturbance (ND) and communication disturbance observer (CDOB). In this method, delay time model is not needed. It is therefore not necessary to measure delay time. Hence it can be flexibly applied to many kinds of time delayed systems. In this paper, a design method of time delayed control system based on the concept of ND and CDOB is proposed. Dynamic property of ND leads to derivation of two design conditions of CDOB. Then actual design procedure of CDOB based on derived design conditions is presented. The validity of proposed design method is verified by experimental results.

Since communication time delay is a serious problem for bilateral control systems, a great number of researches about delay compensation in bilateral teleoperation with time delay have been studied so far. Some of delay compensators are designed to eliminate phase lag of feedback control and applicable to 4ch-controllers. However, the desired results are not always obtained, even though those compensators are applied to the conventional bilateral 4ch-controller with time delay. This is because these compensators do not take force controllers into account. This paper presents a bilateral 4ch-controller that delay compensators are applied to by considering the force controllers. The proposed controller is designed to control both position and force of a master robot and a slave robot by using only 2 degrees of freedom (DOF). One DOF is utilized for position control, and the other is utilized for force control. Therefore, the position controller and the force controller are shared by the master and slave robots. If delay compensators are applied to the proposed bilateral controller, position and force responses of the master robot correspond with those values of the slave robot, respectively. The validity of the proposed method is verified by simulation and experimental results.

Time delay in bilateral teleoperation systems is inevitable and very serious problem. It possibly destabilize systems and deteriorates the performance of systems. Many researches about time delay in bilateral teleoperation systems have been proposed so far. In such a situation, authors have proposed a time delay compensation method based on the concept of network disturbance (ND) and communication disturbance observer (CDOB). It can stabilize time delayed bilateral systems. Furthermore since the method does not need delay time model, it is applicable to the case with time-varing or fluctuant time delay like that of Internet. In this paper, a new design method (or condition) of cutoff frequency of low pass filter (LPF) in CDOB considering approximated poles of ND is proposed. The validity of proposed design method (or condition) is verified by simulation results.

Bilateral control is an effective method for reproduction of tactile sense. Therefore many researches have been conducted so far. That is about not only stability but also performance. In this paper, one of evaluation indices of bilateral systems, "Transparency" is applied to the case with time delay. Both master and slave site of the system used in this research come with acceleration control system by disturbance observer. Therefore the system is very robust to disturbance and parameter variation. The relation of force and position information of both master and slave is formulated using hybrid matrix. Then frequency responses of the elements of hybrid matrix are analyzed taking band-width of disturbance observer and reaction force observer, time delay into account. From those frequency responses, it is found out that there exists unfamiliar phenomenon (an infinite number of resonances) induced by the dimensionless characteristic of time delay. Therefore the relation of time delay and the phenomenon is discussed and clarified using Pade approximation. Then using the result, new stabilization method is proposed. It is based on phase-lead compensation. © 2005 IEEE.

Because of the distinctive characteristics, time delay is even now a difficult and unresolved problem in control engineering. Therefore many compensation methods of it have been proposed so far. The most famous one of them all is Smith predictor. It is a kind of prediction method and equivalently eliminates time delay from closed control loop. State predictive control is briefly an extension of Smith predictor in state space. However it should be noted that the performances of these methods deteriorate in case that time delay is fluctuant and unpredictable. In this paper, a new approach to design of feedback systems with time delay is proposed. It is based on innovative time delay compensation method by disturbance observer and the concept of network disturbance. Because this method does not need delay time model, it is applicable to the system with fluctuant and unpredictable time delay. Furthermore it also considers suppression technique of disturbance. Then new controller that can be designed regarding transient and steady-state response separately is proposed. The validity of proposed method is verified by simulation and experimental results. © 2005 IEEE.

Smith Predictor is a well-known method for compensating time delay in control systems. Therefore, it has been applied to many systems with time delay so far. However, delay time should be estimated precisely in this method. So, if time delay is fluctuant and unpredictable, like the communication delay over the Internet, performance of Smith Predictor deteriorates. This paper proposes "Communication Disturbance Observer". It regards the error caused by time delay as disturbance torque (or acceleration), then it can observe and compensate the error. Furthermore, it doesn't need to estimate the value of delay time; therefore it can be applied to control systems with fluctuant and unpredictable time delay. It can be said that control system with "Communication Disturbance Observer" is robust to time delay and fluctuation of that. Effectiveness and robustness of proposed method is shown by result of simulation and experiment. In experiment, master-slave manipulator was used over the Internet. We were able to get the sense of touch from the environment of remote site.