The non-latch-up IGBT was developed by a Japanese researcher 25 years ago, and thereafter, further modifications have been introduced mainly by Japanese engineers involved in research on power semiconductor devices. The development of non-latch-up IGBT (1984), IEGT (1990), and FS-IGBT (1999) have been the three major milestones that have defined the focus of the research on IGBT development. The 1^st milestone was the development of IGBTs with characteristics better than those of Bipolar junction transistors. The 2^nd milestone was the removal of limitation of blocking voltage without increase of on-state voltage, resulting in achievement of the blocking voltage as high as that of a GTO. The 3^rd milestone resulted in the IGBT becoming the most widely used power semiconductor device. Then, in 2006, a device with electrical characteristics even with those of SiC and GaN devices was reported. This device could be considered the 4^th milestone. In this paper, I attempt to describe the spirit and passion which were shared by the 1^st generation people of the IGBT development.

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This paper proposes a position sensorless control of interior permanent magnet synchronous motors; this method involves the use of an adaptive observer based on direct-type adaptive control for achieving an improvement in responses of speed estimation and control. Although various adaptive observers based on indirect-type adaptive control have been extensively studied so far, improvement in responses of speed estimation and control has not been discussed so much. This paper first shows the response of speed estimation system based on the indirect-type adaptive observer. An adaptive observer based on direct-type adaptive control is then proposed to achieve an improvement in response of speed estimation system. Finally, the effectiveness of the proposed method is proved on some experimental results.

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This paper presents a new method for suppressing circulation currents in a motor simulator system. In conventional system a large transformer at grid frequency has to be used to avoid circulation currents between the motor simulator and a test inverter; further a regenerative converter is required too. In the proposed system, the high frequency components of the circulation current are suppressed by means of a common mode choke, and the low frequency components are suppressed by controlling the zero-phase current. Furthermore, a small medium frequency common mode choke is used instead of both a regenerative converter and the grid frequency transformer. In addition, the proposed system can be used to simulate the transient response of the motor.
The proposed method is validated on the basis of simulation and experimental results. The primary current waveforms with distortions due to voltage errors caused the dead time agree well in the case of the motor simulator and the actual motor. Further, the low frequency component of the circulation current is suppressed to a value less than 1% of the fundamental component in the proposed system.

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This paper proposes a method for error compensation in an indirect matrix converter using zero-voltage switching (ZVS). ZVS helps reduce the junction temperature of switching devices on the inverter-stage by reducing the switching loss of the inverter. However, an input current error is generated by the commutation operation. In this paper, two compensation methods are proposed: one is used for compensating errors in the software commands (command error compensation), and the other is used for compensating errors in the pulse width (pulse width error compensation). The efficiency of the compensation methods have been confirmed by the experimental results. The total harmonic distortion (THD) of the input current using the command compensation and pulse width compensation is 1.5% and 1.4%, respectively. These results prove effectiveness of the proposed compensation methods.

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In this study, we propose a zero-current-switching boost converter that uses coupled inductors in order to improve the efficiency for renewable energy generation systems. The coupled inductors for the converter are analyzed by a finite-elements method software. The inductor currents are controlled by a field-programmable gate array (FPGA) and a 2.5MHz analog- to-digital (A/D) converter. The experimental results show that the efficiency of the proposed converter is higher than that of a conventional converter.

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The use of fuel-cell auxiliary power units (FC-APU) in refrigerator cars employed delivery to for convenience store delivery has been studied. The delivery pattern is assumed to be a typical pattern that includes driving between convenience stores or between a delivery center and a convenience store, unloading, driver's lunch break. The M15 driving mode, which simulates the driving condition in urban areas, is used as the driving mode in the delivery pattern. The FC-APU system includes a proton-exchange membrane fuel cell (PEFC) module, an inverter, and DC/DC converter. Bench tests of the FC-APU are performed to determine the hydrogen fuel consumption rate and the energy efficiency; these values depend on the output power of the PEFC module. The calculated relationship between the output power and fuel consumption rate of a current used system, which consists of an alternator and a secondary battery, are used to estimate the energy efficiency of the current used system. On the basis of the measurement data in this study and the results for the model proposed by Brodric et al. [C. J. Brodrick et al., Trans. Res. D, vol 7, pp. 303 (2002)], the payback period is calculated. The results indicate that the payback period would be 2.1 years when the FC-APU operates at a load of 70%.

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In this paper, a new method to calculate reference currents is proposed; this method can be used to achieve fast torque response of interior permanent magnet synchronous motors (IPMSMs). In the conventional method used to calculate the reference currents of IPMSMs, only the steady state condition is considered; the optimal reference currents under the transient condition are not taken into account. By using our proposed method, the torque response of an IPMSM can be enhanced and can be made twice as fast as the response achieved by using the conventional maximum torque per ampere (MTPA) method. Moreover, a method to ensure smooth transition from the transient condition to the steady state condition is also proposed in this paper. The effectiveness of the proposed methods is confirmed by many experimental results.

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A reduction in the power consumed by motors is required for energy saving in the case of electrical appliances and electric vehicles (EV). The motors used for operating these apparatus operate at variable speeds. Further, the motors operate with small load in stationary mode and with large load in start-up mode. A permanent magnet motor can operate at the rated power with a high efficiency. However, the efficiency is lower at small load or high speed because the large constant magnetic force results in substantial core loss. Furthermore, the flux-weakening current that depresses voltage at high speed leads to significant copper loss. Therefore, we have developed a new technique for controlling the magnetic force of permanent magnet on the basis of the load or speed of the motor. In this paper, we propose the novel motor that can vary magnetic flux and we clarify the principle.

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A control scheme for quickly starting a portable X-ray generator used in the livestock industry is proposed in this paper. A portable X-ray generator used to take X-ray images of animals such as horses, sheep and dogs should be capable of starting quickly because it is difficult for veterinarians to take X-ray images of animals at their timing. In order to develop a scheme for starting the X-ray tube quickly, it is necessary to analysis the X-ray tube. However, such an analysis has not been discussed until now. First, the states of an X-ray tube are classified into the temperature-limited state and the space-charge-limited state. Furthermore, existence of “mixed state” that comprises both is newly proposed in this paper. From these analyses, a novel scheme for quickly starting an X-ray generator is proposed; this scheme is considered with the characteristics of the X-ray tube. The proposed X-ray system that is capable of starting quickly is evaluated on the basis of experimental results.

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Thruster controllers of electric propulsion system with fixed pitch propellers are conventionally aimed to control only the shaft speed without utilizing the capabilities of the controllers to apply any other control strategies. In fact, the dynamic operating conditions lead to the fluctuation of motor load. For this reason, utilizing conventional controllers is hard enough due to the critical constraints and limitation of the ship power source. The paper presents study and analysis of efficiency optimization strategy in thruster shaft speed controllers driven by induction motor. The control strategy based on intelligent method called radial basis function neural network (RBFN) is implemented. A set of training data derived from a loss model controller of the induction motor working under indirect field-oriented-control (IFOC) drives is used for training process of RBFN. The loss model controller utilizes schematically the flux generating current as controlling variable. Estimation of the flux generating current through the RBFN process shows significant improvement in motor efficiency especially for low speed and ship transit system.

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This paper focuses on a battery energy storage system that can be installed in a 6.6-kV power distribution system. This system comprises a combination of a modular multilevel cascade converter based on single-star bridge-cells (MMCC-SSBC) and multiple battery modules. Each battery module is connected to the dc side of each bridge-cell, where the battery modules are galvanically isolated from each other. Three-phase multilevel line-to-line voltages with extremely low voltage steps on the ac side of the converter help in solving problems related to line harmonic currents and electromagnetic interference (EMI) issues. This paper proposes a control method that allows each bridge-cell to independently adjust the battery power flowing into or out of each battery module. A three-phase energy storage system using nine nickel-metal-hydride (NiMH) battery modules, each rated at 72V and 5.5Ah, is designed, constructed, and tested to verify the viability and effectiveness of the proposed control method.

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This paper presents a modular multilevel cascade converter based on double-star chopper-cells (MMCC-DSCC), which is intended for grid connection to medium-voltage power systems without the use of line-frequency transformers. The converter is characterized by a modular arm structure consisting of cascade connection of multiple bidirectional PWM chopper-cells with floating dc capacitors. It is necessary to achieve voltage-balancing control of all the dc capacitors. However, the voltage control achieved by averaging control and individual-balancing control imposes certain limitations on the operating conditions. This paper proposes arm-balancing control to achieve voltage balancing under all the operating conditions. The validity of the arm-balancing control as well as the theory developed in this paper is shown by performing a computer simulation and experiment.

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This paper presents a novel 2-degrees-of-freedom (2-DOF) controller design for the robust vibration suppression positioning of mechatronic systems against the frequency perturbation in mechanical vibration modes. The authors have already proposed an linear matrix inequality (LMI)-based feedforward (FF) compensator design method to provide the robust properties in positioning against the perturbation, while the feedback (FB) controller has been independently designed to ensure the robust stability on the basis of the 2-DOF controller design concept. However, a problem still remains in the conventional design that the FB characteristic causes the deterioration of the FF control performance because the undesired response in the FB system due to the perturbation affects the ideal response by the FF compensation. The proposed controller design in this paper, therefore, includes the FB control system with the perturbation in the FF design model to solve the problem in the conventional design. In addition, the FB controller is optimally designed to improve the positioning performance as a cooperated design between FB and FF controllers. The effectiveness of the proposed approach has been verified by numerical simulations and experiments using a prototype.

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In this paper, an approach that can be adopted to analyze to compensate for driving acoustic noises during the fast positioning control of a table system is presented. In order to appropriately compensate for the acoustic noises, the noise characteristics were experimentally analyzed by measuring the machine stand vibration, and background noises were eliminated by spectral subtraction. Further, A-weighted analyses were introduced to consider the human auditory characteristics. A vibration suppression technique based on the noise analyses was applied to a prototype of a linear-motor-driven table system, and the effectiveness of the approach was verified by conducting a series of experiments.

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A power electronic system generally has multiple domains, and the rate of change of variables varies across the domains. Such systems are called multirate systems and they can be efficiently simulated by adopting numerical integration process according to the multirate characteristic. Two methods for performing the multirate analysis have been proposed. The first method is the circuit partitioning method in which a system is divided with large energy-storage elements into subcircuits which have their own optimum time step sizes for numerical integration. For example, a system in which converters and inverters are connected in cascade with large capacitors is divided into subcircuits and analyzed efficiently. The other method is the envelope-following (EF) method; in this method only selected voltage and current ripples are computed so that the envelopes corresponding to these ripples can be accurately determined. The number of skipped switch cycles can be adjusted optimally according to the variation rates of the envelopes. A new multirate method is proposed in this study. It is a combination of the two abovementioned methods, and therefore, it has the advantages of both the methods. First, the computational flow of the proposed method is described briefly. Then, precise numerical processes, for example, the selection of the step sizes of the fast and slow domains and the iteration correction taking into consideration the interactions between the domains, are described. Finally, a simulated motor drive system is investigated to verify the effectiveness of the proposed method.

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A method for motor surge voltage suppression is proposed in this paper. The proposed method has following advantages: (1) an LC filter is not required for suppressing the surge voltage at the motor terminal, (2) the energy stored in the main power cable, which cause the motor surge voltage, is regenerated to the inverter dc bus line, and (3) effective surge suppression is achieved stably regardless of the power cable length and power rating of the system. Consequently, the proposed method has advantage in volume and efficiency compared to conventional surge suppression methods. In this paper, the circuit configuration of the system is shown and the operation principle of the proposed method is explained. Effectiveness of this method is confirmed through the experimental results.

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This paper describes the design considerations and experimental verification of an LIM rail brake armature. In order to generate power and maximize the braking force density despite the limited area between the armature and the rail and the limited space available for installation, we studied a design method that is suitable for designing an LIM rail brake armature; we considered adoption of a ring winding structure. To examine the validity of the proposed design method, we developed a prototype ring winding armature for the rail brakes and examined its electromagnetic characteristics in a dynamic test system with roller rigs. By repeating various tests, we confirmed that unnecessary magnetic field components, which were expected to be present under high speed running condition or when a ring winding armature was used, were not present. Further, the necessary magnetic field component and braking force attained the desired values. These studies have helped us to develop a basic design method that is suitable for designing the LIM rail brake armatures.

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