Generally, the insulation breakdown of motors, the main fault associated with motors, is caused by the compound factor of thermal, electrical, mechanical, and environment deterioration. For preventive maintenance for insulation breakdown, the insulation test of a stator coil is performed for motors in the power and industry plant once in several years, periodically.
Insulation failure expensively deteriorates the plant operation. Therefore, for the maintenance of these motors, various tests such as an insulation test and research and development of insulation deterioration diagnosis, on-line PD (partial discharge) monitoring, etc. have been actively carried out. On the other hand, the maintenance of LV (low voltage) motors have stayed in BDM (Break Down Maintenance) because many and many LV motors are running in plant and the maintenance of LV motors should consider cost-effectiveness from HV (High Voltage) motors.
This paper shows that the method of insulation deterioration detection, using analysis of the deference wave of zero-sequence current between the normal condition and the fault condition, can realize life management with an on-line diagnosis system and CBM (condition-based maintenance) for induction motors.

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At present, we are studying active control engine mounts (ACMs) with linear oscillatory actuators (LOAs), mounted on automobiles to reduce frame vibration and noise. The basic construction of our ACM consists of two main parts: a hydraulic mount for passive vibration damping and an LOA for active vibration damping. In this study, we evaluate the active control performance of our improved LOA which has high thrust and good linearity against current, by a dynamic vibration simulation, in which 3-D FEM analysis is coupled with vibration and control analysis. Additionally, we clarify the effect of the control method and the resonance on the performance of the ACM.

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Sliding electric contact technologies play a very important role in the manufacture of various electrical components such as brushes and slip rings of turbine generators, including variable-speed hydraulic turbine generators and wind turbine generators, and elucidating electric wear phenomena of the brush is important for improving the technologies. We classified these phenomena into two modes: bridge rupture and arc discharge evaporation. The modes are based on existent theories in the field of switching the contacts, and they were used to construct an analysis model for elucidating electric brush wear volume. After a theoretical analysis, we examined the accuracy of brush wear prediction on the basis of comparisons between calculated results and experimental results.

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This paper proposes a robust controller for sinusoidal PWM inverters, which can track a sinusoidal reference with zero steady-state error. A closed-loop system for single-phase full-bridge inverters is constructed on the basis of the internal model principle. The appropriate control gains of the constructed closed-loop system are determined using a state-feedback controller design method via linear matrix inequalities. The proposed controller can adapt to the uncertain variations in the load conditions. It is also shown that the pole-placement constraints and control performance indexes based on the H² and H^∞ norms as well as a standard quadric performance index in optimal control can be applied to the proposed robust controller. Digital computer simulation is implemented to confirm the validity of the proposed robust controller with the internal model principle. A prototype experimental model is constructed and tested. Experimental results demonstrate that an excellent and practical robust controller for sinusoidal PWM inverters is realized under uncertain and fluctuating load conditions, including the nonlinear loads such as diode rectifiers.

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Multi-consequent-pole bearingless motors can be used in low-speed rotating and swinging stages (or platforms) under specific conditions. A test machine has been designed and built. In this machine, two axes of freedom are actively controlled in the radial x-y directions. The suspension windings are of a novel toroidal type, in which coils are wound around the stator yoke. The windings realize a short axial length because the coil end-windings are compact. In the design process, the leakage fluxes and magnetic saturation are considered using a three-dimensional finite element analysis. Then, a test machine has been constructed and tested. The rotor was successfully suspended, and its suspension characteristics are presented in this paper.

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An optical disk drive system must realize high-precision control. For this propose, a tracking control system, composed of a high gain servo controller (HGSC) and perfect tracking control (PTC), has been proposed. The conventional tracking control system adequately suppresses the tracking error caused by track eccentricity. However, the conventional system is complicated. The PTC system has a speed-up limitation in the optical disk tracking control system. Hence, this paper proposes a new high-speed and high-precision tracking control system that uses equivalent perfect tracking control (E-PTC). The proposed system realizes simple and quick execution in a digital signal processor for a software servo system. Our experimental results confirm that the proposed system effectively suppresses the tracking error at a DVD+R disk rotation speed of 7200rpm.

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This paper proposes a method to derive the frequency response of an actuator with a solid iron core. This actuator is designed for a thrust magnet bearing of a high-speed motor. The actuator is treated as a distributed system with eddy currents in the solid iron core. Theoretical formulation of the frequency response is derived by using Maxwell's equations and by using a simple magnetic circuit model. The finite element analysis results and the experimental results are also obtained. A method for obtaining the rational expression of the frequency response is derived. Although the method is essentially based on a least-square method, it is modified to some extent in order to obtain a rational expression. By using this rational expression, we show that the controller for the magnetic bearings can be designed with usable accuracy, before manufacturing the actual actuator.

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This paper proposes a technique for reducing the leakage current that flows into a power source as conductive noise. Output voltages of an inverter system consist of a d-axis voltage that generates a flux current, a q-axis voltage that generates a torque current, and a zero-sequence voltage. The zero-sequence voltage does not affect the driving characteristics of the load. The proposed method applies a zero-sequence voltage to the output voltage references in a circuit containing grounding capacitors. As a result, the fundamental frequency component of the zero-sequence voltage produced by the inverter decreases and the leakage current reduces. This allows a decrease in the size of the common-mode chokes. The leakage current can be reduced further by increasing the additional zero-sequence voltage reference. The experimental results show that the proposed method can reduce the leakage current when the zero-sequence voltage is applied.

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In a head-positioning control system of a hard disk drive, the head-positioning accuracy is worsened because of the airflow-induced vibration of disks (called “disk flutter”). Therefore, the control system must compensate for the disk-flutter-induced positioning error. In this paper, we propose a new framework of the head-positioning control system using a resonant filter to suppress the disk-flutter-induced positioning error. The control system uses resonant filters with variable gains that depend on the cylinder number of the head position and the modal shape of the flow-induced vibration of disks. The resonant filter can obtain a circular vector locus that recedes from the unstable point on the Nyquist diagram and can decrease the sensitivity function's gain at a specific frequency. The variable gains are optimized depending on the cylinder number of the head position. As a result, the resonant filter is able to improve the transient response after track-seeking control. The result of track-seeking simulations showed that the proposed method was effective in decreasing the positioning error caused by the disk-flutter-induced vibration and improving the seek time of the hard disk drive.

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A STATCOM is expected to be suitable for use as voltage control equipment for a distribution system that needs to be controlled to suppress the voltage deviation caused by an increase in the number of photovoltaic energy sources. A Y-connection MMC is a promising alternative for the STATCOM circuit topology. However, it has been known that the Y-connection MMC cannot achieve capacitor voltage balance between phases with unbalance current output for compensating system voltage unbalance. To solve this problem, we propose a novel method to control the capacitor voltage in the case of an unbalance current output.
The proposed control involves feedforward and feedback zero sequence voltage control. The feedforward control prevents capacitor voltage unbalance between phases, which is caused by the unbalance current that the Y-connection MMC outputs. The feedback control cancels the remaining control error of the feedforward control.
We verified the performance of the control through transient simulation. The Y-connection MMC with the proposed control can achieve capacitor voltage balance between phases even when the Y-connection MMC outputs an unbalance current.
Additionally, we determined the maximum unbalance current output produced by the Y-connection MMC in relation to the rated capacitor voltage.

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A three-phase buck rectifier using single-switch legs with a snubber energy recovery feature is studied. To verify the effectiveness of the rectifier, a prototype employing three insulated-gate bipolar transistors as the active power devices is implemented. The experimental results under pulsewidth modulation (PWM) confirm that the rectifier contributes to the improvement in efficiency and to the sinusoidal input current with a near-unity power factor.

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A single-phase two-stage boost sinusoidal rectifier using a capacitor for the pumping action is proposed. To realize a sinusoidal input current independent of the load, an asymmetrical half-bridge is introduced. The capacitor of an asymmetrical half-bridge is discharged to the supply for current wave-shaping and to the capacitor for the pumping action. The experimental results confirm that higher values of the output voltage can be easily obtained with a near-unity power factor sinusoidal input current.

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Transcutaneous energy transmission is the most promising non-invasive method for supplying driving energy to a totally implantable artificial heart. Studies have been conducted on a transcutaneous energy and information transmission system that can simultaneously transmit energy and information by using a single transcutaneous transformer. In this paper, we report the information transmission characteristics from the inside to the outside of the human body by using the transcutaneous transformer with misalignment between the external and internal coils.

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This report introduces the research activities in Tokyo Tech Power Electronics Laboratory. This laboratory focuses on new power electronics technologies and their applications to industries, electric power transmission and/or distribution systems for smart grid concepts, electric power generations using renewable energy resources, and so on. All members in this Lab. are studying hard to bring a sustainable society in coming days.

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