An isolated AC/DC converter using a matrix converter (MC), which is a direct AC/AC converter, can be realized with a small size, high efficiency, and long life. Conventional MC control methods require the output frequency to be much lower than the switching frequency. Therefore, these control methods result in large galvanic transformers. This paper proposes an MC control method for the isolated AC/DC converter with the output frequency equal to the switching frequency, which can downsize the transformer. Furthermore, by controlling the instantaneous reactive power, a sinusoidal input current of a unity power factor is realized. Soft switching technology is used to suppress the switching losses. However, it is necessary to reduce the output power factor for soft switching. In this paper, the relationship between soft switching and the output power factor is clarified. The MC achieves the maximum output power factor and soft switching by frequency control using an LC resonant circuit. The effectiveness of the control method was evaluated experimentally.
With the advances in information and communication technology, it has become easier to transmit the onboard equipment data of a train to a ground level so that the data can be analyzed for various purposes. We have focused on train occupancy rate data, which are quantitative data of congestion degree, as the onboard equipment data for use. The objective is to improve convenience for railway companies, as well as for passengers. Our goal is the replacement of the current method for measuring occupancy rates based on visual observation with a method that utilizes occupancy rate data based on the results of pressure detection of air suspensions (AS-based occupancy rates). The present study analyzes the error factors in the calculation of occupancy rates and strives to improve the calculation method to improve the accuracy of the AS-based occupancy rates. As a result, for the improved AS-based occupancy rates, the proportion of errors is less than 10%, which is the difference between the AS-based and passenger-count-based occupancy rates. This accuracy is much better than that of the occupancy rate based on visual observation, whose proportion of errors is more than 20%.
In this paper, the authors propose a circuit simulation model of a single-phase common-mode inductor based on the permeance-capacitance analogy. In the proposed model, the frequency dependency of complex permeability and the leakage inductance are modeled by using electric circuit components. This electromagnetic circuit is realized using gyrators. Furthermore, an electric component, such as a winding stray capacitance, is modeled separately. In the present study, the proposed model is constructed using LTspice. Comparisons between the measurement and simulation results indicate that the proposed model can analyze common-mode inductor impedances with respect to the differential-mode and the common-mode simultaneously.
This paper proposes a technique for reducing the leakage current that flows into a power source as conductive noise. The proposed method eliminates the leakage current between two phases by increasing one phase voltage and decreasing the other phase voltage in a synchronous manner. Through simulation and experiment, it was confirmed that the proposed method reduces the noise by 9dB in the low-frequency band, where the influence of the size of the noise filter is significant.
Recently, research on model predictive control for predicting outputs based on a mathematical model in a microcomputer unit is being conducted to ensure advancements in the field of motor drives moreover, the applications of current control and speed control have been studied. In this study, we examine the method of applying model predictive control to the sensorless control of PMSM, and compare the results obtained when the prediction target is the motor speed and when it is the magnetic position. Furthermore, based on the experimental results, we demonstrate that the proposed method can provide better performance than the conventional PI-control-based method.
In recent years, more than half of the electric power generated in the country is being consumed by motors. Therefore, high performance motors are desired especially for industrial applications. In addition, it is desirable to reduce motor size. Recently, motors called axial gap type have been proposed and researched to achieve both high torque and small size. Axial gap motors are generally suitable for applications requiring flat shape such as a disk. Conventional axial gap motors frequently employ Nd sintered permanent magnets (PMs) to achieve high torque. However, axial gap motors with Nd sintered PMs are not very efficient at high rotational speed due to the eddy current loss arising in the PM. Axial gap motors that use ferrite PMs have also been proposed, but torque density is low. In this paper, an axial gap motor using Nd bonded PMs is proposed to achieve high efficiency in the high-speed and high-torque region. The proposed axial gap motor using Nd bonded PM is compared with other axial gap motors employing Nd sintered PM and ferrite PM through 3D-FEA and experiments. Consequently, it was found that the Nd bonded PM is more effective in enhancing the efficiency of an axial gap motor in the high-speed and high-torque region, compared with Nd sintered PM and ferrite PM.
To meet the increasing demand for high-power isolated converters, interleaved LLC converters are being extensively studied. However, traditional interleaved LLC converters need auxiliary circuits or bulky magnetic components to achieve current balancing among parallel-connected phases, resulting in increased circuit complexity and volume. The automatic current balancing three-phase LLC asymmetric resonant converter was proposed in a previous work. Although phase currents can be balanced automatically by flying capacitors, the conventional asymmetric resonant operation with an asymmetric duty cycle of d ≠ 0.5 has various limitations, such as the increased difficulty in circuit design and analysis, impaired extendibility, and the need of dc blocking capacitors on the transformers' secondary side. This paper proposes a three-phase LLC symmetric resonant converter using flying capacitors. In addition to the automatic current balancing capability, the symmetric resonant operation with d =0.5 simplifies the circuit design and allows the traditional fundamental harmonics approximation to be used for analysis. The experimental verification tests using a 1-kW prototype demonstrated the automatic current balancing performance, regardless of the significant mismatch in the transformers' parameters.
This paper proposes online inductance identification methods, including two identification principles, three identification algorithms, and a compensation signal generation method for the sensorless drive of synchronous reluctance motors. The proposed methods have the following features. (a) The identification object is the “in-phase inductance”, which is only required for the “mirror-phase flux estimation”. (b) The inductance can be identified even in the steady state, where the frequency of the signals in the dq synchronous reference frame is substantially zero, and identifications are the most difficult. (c) The superimposition of a special signal, such as an M-sequence signal, is not required for the identification. (d) A compensation signal is essential for making the identified value converge to the true one. A compensation signal generation method that is applicable in the minimum copper loss control is proposed. (e) The identification can be performed, in principle, in the γδ general reference frame but it is practically performed in the αβ stationary reference frame. (f) Recursive calculations are possible, and the amount of calculations required for the identification is very small. This study also verifies the validity of the proposed identification methods with the aforementioned features through extensive numerical experiments.
SiC merged reverse conductive (MRC) power devices composed of both unipolar devices and bipolar devices have been developed to achieve a smaller chip size, a lower power loss and a higher reliability. SiC MRC power devices such as SiC MRC-MOSFET and SiC MRC-IGBT can achieve this performance, but have the problems of on-voltage degradation and a large snap-back voltage. The former has been solved by the newly developed majority carrier heating-TEDREC (MaCH-TEDREC) method and the latter has been solved by both the newly developed double buffer device structure and novel standard cells with pilot IGBT.
This letter analyzes the current phase lead characteristics of stepper motors in the middle-speed operation range. The phase lead causes instability of the stepper motors controlled by an open-loop position controller, which motivates us to investigate the current phase lead characteristics for control design of the stepper motors. The analysis is verified experimentally.
Our research focuses on the high-frequency converter with the catchphrase "Toward a new information and communication society with an awareness of energy and environmental issues." This document introduces our research topics and laboratory activities.