This paper proposes a new multi-port converter with interleaved magnetic coupling technologies for integrating complex dc power systems. With the focus on the impedance behavior of coupled magnetic components and the operate parameters, this multi-port converter integrate one isolated dc-dc converter and two multi-phase boost converters and controls these topologies independently. From this integration, the proposed converter is able to connect four dc applications or sources in one circuit, which signifacantly reduces the cost and reduce the total power consumption of systems such as electric vehicles or grid-connected industries. In this paper, the basic circuit behavior is clarified, and the theoretical considerations are verified by experiments. An application example of the proposed circuit as a multifunctional system is demonstrated with simulation results. Such an approach may open up various application fields for the future dc electric power system.
This paper presents a protection circuit for a fault under load (FUL). The protection circuit is characterized by the reverse transfer capacitance characteristic of IGBTs. The reverse transfer capacitance depends on the collector-emitter voltage and has a significant influence on the switching behavior under short-circuit conditions and normal conditions. An FUL is detected by monitoring a gate current because the current flows through the reverse transfer capacitance of IGBTs from the collector terminal to the gate terminal under FUL conditions. A physics-based IGBT model shows high accuracy for both static and dynamic characteristics, making it useful for developing a protection circuit for IGBTs subjected to short-circuit conditions. Simulated results using the physics-based IGBT model and experimental results verify the validity of the proposed protection circuit.
Although motors that use rare-earth permanent magnets typically exhibit high performance, high costs and concerns about the stability of raw material supplies are leading to their decreased production. In this research, the magnet shape, the number of magnet layers and the number of poles are investigated to obtain target rated torque under the same external diameter and stack length. Next, the characteristics of an IPMSM with bonded rare-earth magnets and an IPMSM with sintered rare-earth magnets are compared under the same current. Moreover, the efficiency of the models are compared under the constant output power.
Malfunction and failure of electronic equipment can result from the occurrence of electrostatic discharges. Such problems increase as the use of low-voltage electronic devices increases. There are relevant test methods available for electronic devices, such as the human body model (HBM) and the field-induced charge device model (FICDM). In contrast, there are no test methods available for electronic equipment when a charged human body passes in front of a metal box that encases electronics. The authors measured the induced voltage generated in a metal box encasing electronic equipment when a charged body passes in front of the metal box. We have previously observed the occurrence of positive and negative induced voltages that are generated by the movement of a charged object. In this study, we focus on the induced voltage generated when a charged object moves away from a metal box. This situation represents that of a charged human body moving away from the metal box encasing electronic equipment. The measured results show that the value of the induced voltage is -300% greater than the voltage of a moving charged body under these experimental conditions. The results are compared with those calculated on the basis of capacitances and electric charges. These results show that the voltages induced in an ungrounded metal box, when a charged body moves away from the metal box, become large enough to cause malfunctions and failure of electronic equipment.
This study investigates a suitable rotor structure of permanent-magnet-assisted synchronous reluctance motor (PMASynRM) with ferrite magnets for torque ripple reduction. In order to reduce noise and vibration, the torque ripple should be small. The effects of shifting the flux barriers of rotor on torque performance are examined, and a suitable rotor structure is proposed for reducing the torque ripple. The performance of the proposed PMASynRM is evaluated based on FEM and experiments, and it is confirmed that the torque ripple can be reduced without any reduction in average torque.
Short-circuiting in element conductors in the AC power cord is one of the main causes of fire accidents originating from electric equipment. It is not easy to detect this type of short-circuit fault with a conventional circuit breaker, because the duration of a short circuit is rather short, and the magnitude of the short-circuit current is smaller than the threshold for operation. In this paper, voltage and current waveforms are analyzed in detail when element conductors for a 100-V AC power cord are artificially short-circuited. The authors focus on a feature that characterizes the short-circuit phenomenon, namely, the distortion of the voltage waveform from the sinusoidal shape between arc generation and the extinction of the conductor elements. Two possible diagnosis methods are discussed for short-circuit detection: one is based on the duration of specified voltage range, and the other is based on the area formed between the measured and reference voltage waveforms.
This paper presents a theoretical discussion on triangular-carrier frequencies of a modular multilevel cascade converter based on double-star chopper cells (MMCC-DSCC, hereafter referred to as the DSCC) with phase-shifted PWM. The DSCC consists of multiple cascaded chopper cells and a center-tapped inductor per leg. Low voltage steps bring significant reductions in harmonic voltage and current to BTB (back-to-back) or HVDC (high-voltage direct-current) systems using two DSCCs. When the DSCC adopts the 6-kV GCTs (gate-commutated thyristors) that are commercially available in the market, the switching frequency should be less than 200Hz to improve conversion efficiency. Theoretical analysis developed in this paper reveals that the most suitable triangular-carrier frequency is 125Hz or 175Hz. Simulated waveforms obtained from a three-phase 66-kV, 200-MW DSCC are included to verify this analysis. The analytical and simulated results agree well with each other.
In this study, a novel approach to realizing low-voltage distortion with a new multilevel inverter is presented. The inverter targets systems with rechargeable batteries. The advantage of the proposed single-phase 7-level inverter is that the line-line voltage of seven steps can be outputted and the voltage distortion can be reduced. This paper presents the control method. The experimental results show that the voltage THD of the proposed 7-level inverter becomes 18.2% when the voltage reference is the same as the DC-link voltage, and is smaller than that of the conventional 2-level and 3-level inverters. Furthermore, at the same voltage reference, the simulation results show that (i) the difference between each electric charge supplied by each cell battery in the asymmetrical DC voltage sources is less than 20% and (ii) the switching loss of the U-phase switching devices in the proposed inverter is only 1/10 that of the 2-level inverter and 1/3 that of the 3-level inverter.
When we touch a soft, yielding object such as the human body, we feel a sensation of softness. In virtual training systems for medical procedures such as palpation, the display of softness at multiple fingertips is critical and essential. This paper proposes a softness-display device using a flexible sheet, and we present the concept of softness display at multiple fingers by combining the developed softness-display device and our previously developed side-faced-type multifingered haptic interface. Further, we carried out several experiments to investigate the validity of the proposed system.
In a railway train forward looking system, it is necessary to capture a clear image of the rails in the distance using a cab-mounted camera. Therefore, we developed an improved railway train forward looking system. The current system has certain function in term of camera view control. However, since the rail extraction result of the system is discontinuous in time, the system cannot operate the camera view control smoothly. Therefore, we improved the system using rail extraction algorithm to obtain a favorable zoomed camera image. In this paper, we report on the algorithm and test results.
Our research focuses on the power conversion system and the electrical machinery system based on the powerelectronics technology. Our research group consists of three laboratories. Three faculty members, 38 students are with the research group.