In the computerized interlocking system for railway train control, the degree of deterioration of parts can be measured, but the calculation of the lifetime of the system is difficult when the initial value of the parts is unknown. The reason for this is that the range of the initial value of the parts is too wide. In this paper, we propose a new method to appropriately estimate the degree of deterioration of a certain type of part without knowing the initial value by measuring the current value once.

In a vehicle, radiational noise generated by the common-mode current in an inverter system is the cause of electromagnetic issues affecting in-vehicle radio antennas. This paper proposes a new method “Z-matched ACC” for suppressing the common-mode current at the AM band. Using this method, the exciting current of the common-mode transformer, which reduces the common-mode current suppression effect higher than 100kHz in conventional voltage-cancellation ACC, flows into a Z-matched circuit rather than into a motor parasitic capacitor. Therefore, the Z-matched ACC can suppress the common-mode current at the AM band. The suppression effect of the Z-matched ACC is superior to the conventional ACC from 100kHz to 10MHz. In addition, the Z-matched ACC can reduce the size of the common-mode transformer compared to the conventional ACC by reducing the ET product applied to the common-mode transformer.

This paper proposes a method to suppress the capacitor current imbalance between the phase legs of a three-phase inverter circuit. This circuit consists of half-bridge modules and DC-link capacitors closely connected to each module. It can be designed for low stray inductance between power semiconductor devices and DC-link capacitors in each module. However, in the conventional structure, the stray inductance between the phase legs may lead to an imbalance in the capacitor current due to the DC-side resonance phenomenon under a higher switching frequency condition by using a SiC MOSFET. This paper presents the analyses of the equivalent circuit considering the circuit configuration, which suggests that capacitor current imbalance occurs depending on the stray inductance between phase legs. To suppress the capacitor current imbalance, a delta-type bus bar connecting phase legs is proposed. The experiment results at 300V and 4.6A demonstrate the suppression effectiveness of the proposed method.

This paper describes a flux intensifying PM motor with variable leakage magnetic flux. The unique feature of this proposed motor is the ability to passively adjust the magnetic flux linkage into the armature windings in proportion to the armature magnetomotive force and/or armature current phase. The magnetic circuit topology of the flux intensifying PM motor and the passive variable leakage magnetic flux are determined through FE analysis. Then, the driving performance is experimentally elucidated through comparison with that of a reverse salient pole type (flux weakening) PM motor without variable leakage magnetic flux.

Improvement of the light-load regenerative brake control is effective for energy saving in DC-electrified railway systems. Light-load regenerative brake control gain is usually determined by a load shutdown test at a factory. The objective of this study is to develop a method to design light-load regenerative brake control gain though simulation of load shutdown. In this paper, a numerical simulation model of load shutdown test is introduced. Then, light-load regenerative brake control gain is designed by illustrating the behavior of the traction circuit system in the numerical simulation. The proposed method is verified by experimental test with a full scale vehicle traction system.

A bi-directional magnetic-resonant wireless power transfer setup was developed, wherein the secondary circuit was a mirror image of the primary circuit. The setup was a combination of four spiral coils with diameters of 20cm, and inverter units operating at approximately 85kHz of standardization recommended frequencies. Using the setup with two wiring schemes, namely, four-closed circuits and conventional two-closed circuits, maximum efficiencies of 94% and 93%, respectively, were demonstrated successfully with a kW-output at a transfer distance of 10cm. Although the fundamental strength of the leakage magnetic field emitted from the four-closed circuits was almost equal to that from the two-closed circuits, the strengths of the harmonic emissions from the four-closed circuits were from 6 to 9dB less than those from the two-closed circuits because harmonic coil currents of the primary side in the four-closed circuits had directions opposite to each other to cancel out the undesirable harmonic field, whereas, in the two-closed circuits, these coil currents were in the same direction to strengthen up the field twice.

This paper introduces a new three-phase grid-connected inverter for commercial-scale 10-50-kW photovoltaic systems installed on underutilized assets such as rooftops of office buildings. The circuit topology combines an inductorless active bridge with a parallel-connected PWM inverter behaving as an instantaneous reactive power compensator. The active bridge, referred to as 120°-conduction inverter, performs a fundamental-frequency switching and outputs a 120°-block-shaped current, while the instantaneous reactive power compensator suppresses the harmonic current included in the block-shaped current. The main advantage of this strategy is the size reduction of the required ac inductor by a factor of four as well as the reduction in switching device power losses. The theoretical analysis clearly shows that the compensator controls only instantaneous reactive power to synthesize a sinusoidal current, thus eliminating the need for an electrolytic capacitor. A 5-kW experimental setup validates the operating principle and control method of the proposed inverter, and exhibits an inverter efficiency as high as 98.8%.

The possibility of applying fast automated demand response (FastADR) aggregation for office building air-conditioning facilities to the ancillary service participation qualification test of an existing smart grid operator has been studied. Our original time-shifted state space model for the target facility was system-identified through autoregressive modeling using the time-series data of an actual office building. Simulation experiments were carried out to evaluate the ability to track the PJM balancing test signal. The simulation experiments have shown that enlarged FastADR commands are necessary to pass the test as well as to forecast the trade-off room temperature deterioration using such a state space expression model. Our state space model has made it possible for an aggregator to predict the FastADR negawatt transient response along with the room temperature change and decide the appropriate power limitation command values.

In this paper, the driving characteristics of an electromagnet-assisted ferrite magnet motor (EMaFM) are investigated using a 1.5-kW prototype machine. The EMaFM is a new type of synchronous motor, which combines a ferrite magnet motor with an electromagnet motor. Finite element analysis and experimental results show the following. 1) A wide constant power range as well as high torque at low speeds can be achieved by assisting the torque with the built-in electromagnet motor. 2) It is possible to reduce the losses and improve the efficiency by adjusting the field current according to the operating conditions.

In this paper, we investigate the losses caused by circulating currents generated in armature windings of permanent magnet synchronous machines by using electromagnetic field analysis. In the analysis, each parallel connected wire in the windings is modeled by finite elements in order to consider the difference in the electromotive forces and the generation of the circulating currents. The calculated losses are compared with experimental results. It is clarified that the armature copper loss in permanent magnet machines with parallel connected wires considerably increases by the circulating currents.

Conventional two-phase PWM schemes cause harmonic voltages and currents, which are distributed over a wide frequency range however this can be a significant drawback depending on applications. To overcome this problem, the authors propose a novel two-phase PWM scheme with a pulse-voltage injection method for three-phase voltage-fed three-level converters. In this report, the authors present the validity of the proposed PWM scheme based on experimental results.