In recent years, the demand for high-reliability systems has been on the rise, while DC power distribution systems are widely used in data centers. The authors propose a DC power distribution system that uses a triple active bridge (TAB) DC-DC converter, toward the realization of such higher-reliability systems. The TAB converter is based on an isolated DC-DC converter and can control the DC power flow among the three ports. First, this paper presents a basic power flow control procedure of the TAB converter, using a phase-shift control. Further, two types of higher-reliability DC power distribution systems are proposed using the TAB converter. The experimental design and simulations of a prototype 200-V TAB converter with 500-W power, connected with the single and double loads, are reported. In the experiment, the 200-V TAB converter rated at a power of 500W was constructed from a three-winding transformer and gallium nitride (GaN) power devices. Smooth output waveforms indicate good controllability of the power flow and good functional performance of the proposed DC power distribution system.
This paper presents a meta-parameterized approach for the evaluation of Power Switch Modules (PSMs) in power converters. General models and parameters for the evaluation of power losses and volume of a PSM are presented. Then, meta-parameterization is performed for two semiconductor devices that have been successfully commercialized for low/medium power converters, Si-IGBTs, and SiC-MOSFETs. A comparative analysis based on the efficiency and power density of the considered technologies is presented. A bidirectional non-isolated DC-DC converter topology is considered as application example in order to show how meta-parameters can be used in comparative studies to optimize device selection.
This paper presents a high-speed, low loss, and low noise gate driver for silicon-carbide (SiC) MOSFETs. We propose a gate boost circuit to reduce the switching loss and delay time without increasing the switching noise. The proposed gate driver enables converter-level efficiency improvements or power density enhancements. SiC MOSFETs have attracted significant interest as the next generation power devices. In general, the switching performance of power devices exhibits a trade-off between switching loss and noise. SiC-MOSFETs are expected to switch faster than Silicon IGBTs; however, faster switching might cause switching noise problems such as unwanted electromagnetic interferences (EMI). In this paper, we propose a gate driver topology that improves the switching performance of SiC-MOSFETs, and confirm the reduction in switching loss and delay time through experimental results.
Human sensing and tactile transmission utilizing thermal interface are necessary to support human life or for communicating with people in remote locations. For instance, the devices are used for remote health care, telesurgery, and so on. Many studies have utilized a Peltier device as the thermal interface, and there are many studies on the control and sensing of the device. However, in most of those studies, the heat propagation in the system is not considered, and only the point that is attached to the sensor can be observed and controlled. In particular, this is a problem for health care systems, because it is difficult to obtain information about the inside of the human body where it is hard to attach the sensor. In order to solve this problem, this study considers the heat propagation of materials such as the human body by developing a model based on the thermal diffusion equation. In the case of cooling material, heat propagation changes depending on the material condition, for example, the presence of heat source such as a cancer cell. Based on the thermal characteristics, a method to obtain the heat flow of material using heat propagation is proposed in this paper. It is possible to find a heat source in deep layers of a material by using the proposed method without attaching any sensor inside the material. Some experiments are conducted using aluminum cylinder as a propagation material to verify the validity of the proposed method.
Currently, there is a need for precise motion control of industrial machines. For precise motion, it is important to keep the motion robust against disturbances such as gravity or reaction force from the environment. Industrial machines include flexible components such as gears and couplings, and they are modeled as a resonant system. Models expressing resonant systems are classified into lumped-parameter model and distributed-parameter model. Conventionally, the control theory based on the lumped-parameter model has been widely researched because that model is easy to deal with. However, the position which a disturbance acts on is limited to the generator or the lumped inertia of the load in these methods. Therefore, there is a danger that the disturbance suppression performance may deteriorate in the case that a distributed disturbance acts on the load. Here, the distributed-parameter model considering the position which a disturbance acts on, is proposed based on the wave equation. Wave-based modeling can consider the spatial dynamics of a disturbance. As a result, conventional disturbance suppression control is extended for the spatial dynamics.
This paper proposes a new approach of mechanical power factor analysis for evaluating human active motion. The mechanical power factor is affected by the motion trajectory of an evaluation object. Therefore, in active motion, unified evaluation is difficult using the conventional analysis method. In this study, the power factor evaluation of active motion is realized by applying the perturbation from the evaluation system and using its frequency component for power factor calculation.
Electro-hydrostatic actuators (EHAs) are hydraulic actuators that are flexible and exhibit high backdrivability. Flexible operation and accurate detection of reaction forces are required for robots to be able to perform in environments in which they will be cohabiting with humans. However, nonlinear elements that degrade detection accuracy, such as static friction, backlash, and oil leakage, are present in hydraulic systems. In addition, pressure sensors in hydraulic systems are not very accurate at estimating reaction forces, because they cannot estimate internal forces and viscous friction. In this study, we propose a combination of control algorithms for accurately estimating reaction forces. Static friction is compensated by using feedback modulators. In addition, we use a backlash and oil leakage compensator, which do not require any models, to suppress the relative velocity between the motor-side and load-side. Then, the use of a reaction force observer (RFOB) that exploits both pressure sensors and encoders is proposed. The RFOB can be implemented because disturbances are linearized by the compensators. Experimental results show that reaction forces can be estimated with very high accuracy using the proposed RFOB. In addition, we implemented force control using the RFOB and evaluate the force tracking performances by improving the estimation accuracy.
A novel, very small linear actuator that can realize high force density per cross section without position and force sensors is proposed. This actuator is used in a two-dimensional tactile display, which consists of many small one-dimensional actuators with position and force controllability. The proposed actuator has 3 layer stators, and can achieve a high electro-magnetic force. As a result, a force density of 4mN/mm2 is obtained with a cross section of 4mm × 4mm and a moving stroke of 1mm.
In a DC-electrified railway system, the torque control of traction motors according to the input DC voltage of the traction inverter is generally applied during regeneration. It is effective in increasing the gain of this regenerative brake control for utilization of more regenerative brake power. In this article, the authors investigated the mechanism of increasing regenerative power when the regenerative brake control improved by theoretical analysis and an experimental on-track test.
This paper presents a variable magnetic flux PM motor in which space harmonic power is utilized for the magnetic flux weakening, automatically. The stator has a toroidally-concentrated winding structure, and the torque generation surfaces are composed of three air-gaps, which are single radial-gaps and double axial-gaps. The radial-gap rotor is a consist-magnetized PM rotor, and the axial-gap rotor is a self-excited wound-field rotor. These rotors are coaxially fastened with opposite magnetic pole position. The magnetomotive force of axial-gap rotor can automatically retrieve space harmonic power, which is inevitably generated by a concentrated winding structure. A mechanical design of the prototype is revealed, and the operation principle of the automated-magnetic flux weakening is clarified through the mathematical approach. Then, the operation principle of the electrified reversal magnetic pole is experimentally demonstrated, and the effects of the proposed variable magnetic flux technique are verified using the prototype machine in terms of the adjustable speed drive characteristics and the variable magnetic flux range.
Bearing faults account for a large majority of the faults in a three-phase induction motor. Recently, many research activities were focused on the diagnosis of bearing faults by motor current signature analysis. However, the effective frequency band is not fully understood in terms of the diagnosis of the bearing fault. Moreover, the temporal change in motor stator current spectrum with faulty bearing has not been sufficiently investigated. The purpose of this paper is to clarify the characteristic frequency band and to evaluate the temporal change in the power spectral density of stator current by using powder contaminated bearing before complete halt of the motor. Experiments were performed with normal and powder contaminated bearings in the induction motor. The diagnosis technique for the powder contaminated bearing is discussed based on the experimental results.