名取 賢二

Filters are inevitable for grid-connected inverters to attenuate the current harmonics caused by the pulse width modulation which is usually used in power conversion systems. High-order filters have attracted much attention because they attenuate the current harmonics effectively. Nevertheless, the high-order filters have some resonances which cause instability of the system. In addition, the resonance frequencies shift to high as the inductors and capacitors are smaller. It implies that the resonance frequencies may be beyond the Nyquist frequency in downsizing the filter. This complicates the stability and performance analyses of the system. This paper investigates rigorous input-output stability and analyses a robust performance based on the sampled-data control theory regardless of whether the resonance frequencies are beyond the Nyquist frequency or not. Our analysis contributes to downsizing the filter synthesis while the stability and the robustness are guaranteed even if the resonance frequencies are beyond the Nyquist frequency. The effectiveness of the proposed method is verified through simulations and experiments.

In recent years, SiC switching devices have attracted attention because they can increase traction motor current and improve the motor performance compared with traction inverters using Si switching devices. Regenerative power is increased by improving motor performance, and there are examples that demonstrate the energy saving of railway vehicles has been achieved. However, the characteristics of the current and the loss of inverters applying both devices assuming specific applications, such as commuter trains, are unclear. Therefore, the trade-off relationship between motor performance improvement due to inverter current increase and inverter loss is unclear. In this study, the characteristics of the current and loss of the inverter are clarified, assuming the application of SiC switching devices.

To realize flexible power flow control for DC power networks, we have proposed a bidirectional power flow controller (BPFC) based on a bidirectional buck-boost converter. It is possible to control the power flow by intentionally introducing additional voltage difference between two terminals. However, we have not investigated the efficiency of BPFC for power flow control in detail so far (in previous papers). Because many power converters are expected to be installed in future DC power networks, efficiency investigation is vital. In this paper, we first reveal the energy efficiency of BPFC and study ways to improve the efficiency. Then, we propose a novel structure of the BPFC, which drastically improves its efficiency. We call the proposed structure floating bidirectional power flow controller (F- BPFC). The efficiency and characteristics of the F- BPFC are experimentally compared with those of the BPFC and its superiority is clarified in this paper.

This paper presents the effectiveness of a time-delay compensation method based on the concept of network disturbance and communication disturbance observer for bilateral tele-operation systems under time-varying delay. The most efficient feature of the compensation method is that it works without time-delay models (model-based time-delay compensation approaches like Smith predictor usually need time-delay models). Therefore, the method is expected to be widely applied to network-based control systems, in which time delay is usually unknown and time varying. In this paper, the validity of the time-delay compensation method in the cases of both constant delay and time-varying delay is verified by experimental results compared with Smith predictor.

In bilateral teleoperation, the human operator manipulates the master robot while watching video images that are sent from the slave side. Live video streaming causes a significant communication delay to the system. However, a conventional definition of transparency for bilateral control does not consider this delay. In this paper, a novel definition of transparency is proposed. If perfect transparency is achieved, the visual sense and tactile sense synchronize. This transparency is nearly achieved by applying a compliance control to the slave controller. By using this structure, the slave robot contacts the environment safely even if there exist communication delay between the master side and the slave side. In addition, the visual sense and tactile sense synchronize. The validity of the proposed method is shown by numerical and experimental results.

In a research field of network-based control systems (NBCSs), the time delay problem is one of the most significant issues. Efficient stabilization methods of time delayed control systems enable NBCSs to be flexibly applied to many kinds of situations. A novel time delay compensation method based on the concept of network disturbance (ND) and communication disturbance observer (CDOB) has been proposed. The compensation method has the same effectiveness as that of the Smith predictor. In addition, since the method is simple and does not need time delay model or time delay measurement, it can be easily implemented to various applications. However;, the design method has not been concerned so far. This paper therefore presents stability analysis and studies a practical design procedure of the time delayed control systems with CDOB. At first, the concept of ND is introduced and the validity of the time delay compensation method is described. Then an analysis about the effects of parameters in control systems on stability is conducted. Characteristics of the effects of parameters on stability come out. Then we study a practical design procedure of the time delayed control systems. The validity of the design procedure is validated by experimental results. In the experiment, we also verify the performance of the system in the case of time-varying delay. Finally, comparative study of the method to the Smith predictor is presented.

This paper presents a design method of time-delayed control systems. Because of the tremendous spread of computer networks, control strategies for time-delayed control systems are needed for network-based control systems (NBCSs) and other network applications. Although model-based or predictive control methods (like a Smith predictor) are often used for time-delay compensation, the performance often deteriorates when the value of time delay is uncertain. In these circumstances, a novel time-delay-compensation method based on the concept of network disturbance (ND) and communication disturbance observer (CDOB) has been proposed. The method has the same effectiveness for time-delay compensation as that of the Smith predictor. Furthermore, because the method works without delay-time model, it can be flexibly applied to many kinds of time-delayed control systems. In this paper, a design method of CDOB, considering the dynamic property of ND, is proposed in the situation or constant time delay. The dynamic property of ND leads to two design conditions of CDOB. Those design conditions are derived considering relationships between poles of CDOB and ND dynamics. Then, the actual design procedure of CDOB based on derived design conditions is presented in two different delay cases. The stability of the designed control systems is clarified by stability analysis. The validity of the proposed design method is verified by experimental results. Finally, we present experimental results in the case of random delay as an example of practical application of the time-delay compensation method to actual NBCSs.

This paper presents an expression of system connection considering transmission delay. In a research field of decentralized system or information system, expression method of the system connection is very important issue. Therefore some expression methods of system connection have been proposed so far. However those expressions are mainly based on binary operation and can not consider the transmission delay on connection paths although the concept of time is efficient for expression of system connection.<br>In this paper, expression methods of system connection considering transmission delays on the paths are proposed. Those expressions are based on exponential-type expression and can express both connections and transmission delays. Furthermore the expression that can express connections, transmission delays and past subsystems is also proposed. As one example of the application of proposed expressions, application for path selection of the design of network-based control system is described.

Bilateral control is one of the control methods of teleoperation systems. Human operators can feel reaction force from remote environment by means of this control scheme. This paper presents a novel control architecture for bilateral teleoperation with/without time delay. The proposed bilateral control system has three communication channels between master and slave robots. In concrete terms, this system has two transmission channels of position and force information from the master side to the slave side and one transmission channel of force information from the slave side to the master side. The master controller of the proposed three-channel teleoperation system does not include a position controller, i.e. only force control is implemented in the master side, in order to improve operationality in the master side. The three-channel controller with time delay as well as without time delay gives better performance (higher transparency) than other conventional controllers such as four-channel controllers and so on. In the proposed controller, models of a slave robot and communication time delay are not required differently from conventional methods, and robust acceleration control is achieved by using the disturbance observer (DOB). Hybrid matrices are utilized to analyze four-channel and three-channel control systems. Transmission characteristics of force and position information between master and slave robots are clarified in the analysis. The validity of the proposed method is confirmed by experimental results. © 2007 The Institute of Electrical Engineers of Japan.