As buildings become taller, faster elevators are needed, and ultra-high-speed elevators need large-capacity power converters. We developed a converter circuit using four parallel-connected IGBTs. This paper explains the technique of balancing the current sharing of the four parallel-connected IGBTs. Especially, this paper reports the bus-bar assembly that reduces the imbalance of inductance between parallel-connected IGBTs. Furthermore, this paper reports the development of a common gate drive circuit and gate-wiring implementation. This balancing technique reduced the current unbalance caused by the assembly by 5%.

Variable speed drive systems with permanent magnet synchronous motors (PMSMs) are widely used for industry applications and electric home appliances. However, structural imperfections in a PMSM and its control system produce torque ripple, which causes mechanical vibration (i.e., frame vibration), rotational speed ripple, acoustic noise, and so on. We previously proposed a control method for suppressing the motor frame vibration of a PMSM by utilizing feedforward compensation control and a method of generating compensation signals for the feedforward control. However, when the operating point of the motor changes during feedforward control, the motor frame vibration sometimes increases. To cope with this problem, we propose a control method for suppressing motor frame vibration that corresponds to the motor torque and load. The experimental results confirmed the effectiveness of the proposed method.

Winding insulation failures are among the most severe electric faults in industrial induction motors. It is believed that these failures start as minor inter-turn faults that eventually lead to serious insulation breakdowns. Therefore, using an online detection technique in early stages could be quite advantageous for avoiding serious failures. In this study, we have focused on the asymmetries in a three-phase circuit, and investigated the negative sequence components of the line current and voltage under various complicated conditions, such as unbalanced supply voltages, different values of the number of shorted turns, and different loads. Based on the experimental results and steady-state equivalent circuit models of an induction motor, we have developed a highly accurate analysis algorithm for the inter-turn stator winding fault, to provide an early warning of impending failures. The proposed algorithm utilizes an off-diagonal term of the sequence component admittance matrix calculated from negative sequence current, voltage and admittance. To improve fault detection performance, the algorithm is exposed to the normal operating range of the motor in the learning stage.

Short-circuiting of element conductors in the AC power cords of household electric appliances or in extension cords is one of the main causes of fire accidents originating from electric equipment. This kind of short circuit is usually observed in cords trampled by something heavy, bent and stretched repeatedly, and so on. 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 a previous paper, the authors pointed out that a short circuit is characterized by a distortion of the voltage waveform from the sinusoidal shape. In this paper, a novel short-circuit detection method is proposed based on the results of further fundamental experiments that can distinguish a short circuit from transient phenomena when household appliances are turned on/off. Furthermore, a prototype wall outlet with short-circuit detector and circuit breaker is proposed. Its performance was evaluated under several operating conditions in the laboratory.

This article presents a technique for improving the flow rate estimation range in an axial-flow water turbine generator, which is used as a substitute for the flow rate control valve in an air conditioning control system. This article also presents a flow rate estimation technique that uses the characteristic function of the axial-flow water turbine generator based on the angular speed, the torque, and the pitch angle of guide vane. The effectiveness of the proposed technique is validated by experiments.

A new type of in-wheel motor, which receives electric power by wireless power transfer using magnetic resonant coupling and control signals by wireless communication, thus eliminating completely the need for power and signal cables, has been developed. This system is called the Wireless In-wheel Motor (W-IWM). The overall efficiency of the W-IWM system has been considerably improved. In particular, burst fire control was applied to the previous generation W-IWM to keep the DC-link voltage stable in wheel side. This control made use of asynchronous rectification, resulting in glitches in the controlled variables when the system commutates between motoring and regeneration, due to wireless signal delay. To achieve more efficient control and smooth energy reversal, this paper proposes a novel control method for W-IWM driving that employs an application of synchronous rectification. The experimental results of the test bench confirm the effectiveness of the proposed method.

The most striking characteristics of linear-motor railway system is that the structure consists of a primary and secondary linear induction motor (LIM). The primary side of the LIM is installed in a rolling stock, and the secondary side of LIM is installed on the track. The magnetic attractive vertical force produced by the LIM increases the running resistance since this force is in the same direction as the gravitational force due to which rolling stocks gain weight virtually from the track side of view. In addition, the efficiency of the LIM has a different characteristics of efficiency compared with the rotary motor. Previous studies have focused on the design method of LIM to improve motor efficiency and decrease energy consumption. However, it is a well-known fact that this kind of approach requires hardware renewal which requests large amount of investments. The purpose of this study is to analyze these characteristics of LIM effects and design the optimal speed profile to minimize the energy consumption as a linear-motor railway system. This smart and economic energy-saving approach is based on the optimization of speed profiles of the linear-motor railway system using dynamic programming.

We describe a method for analyzing the harmonics components of the air-gap magnetic flux density distribution of doubly-fed generators that takes into consideration the influence of the circumference slot arrangement and winding pattern. The proposed method is based on an analytical equation of the permeance and the magnetomotive force (mmf) distributions. This method is applied to analyze quantitatively the harmonic components of the air-gap magnetic flux density distributions of a doubly-fed generator under different driving conditions. The analytical results obtained using the proposed method are in agreement with those of finite element magnetic field analysis (FEA). Thus, this method is shown to be an appropriate and useful method for quantitatively estimating magnetic flux density for doubly-fed generator.

This paper examines a wireless power transfer (WPT) system for a railway, which utilizes an infinitely long primary cable coil without cores and a secondary coil with cores. Both of the primary and secondary circuits in the WPT system have resonant capacitors in series, and the primary circuit utilizes a constant current power source. Because the supply power required for the railway would be larger than that for electric vehicles, it is not easy to supply the required power by utilizing a single secondary coil. Therefore, the railway WPT system should utilize multiple secondary coils. Moreover, the capacity of the secondary coil should be increased in order to decrease the number of secondary coils. Because the area of the secondary coils should be large to increase their capacity, the secondary coils utilize large cores that are manufactured by bonding some small cores. Thus, the characteristics of the secondary coils utilizing bonded cores are studied. On the other hand, magnetic coupling between neighboring secondary coils should be considered to utilize multiple secondary coils. This paper examines these practical problems.

This paper presents review of the first hybrid electric vehicle in the world. The first hybrid electric vehicle was proposed in the USA in 1898, and several prototypes appeared in automobile shows in 1999. In the early 1900s, several types of hybrid system such as series, parallel, range extender or integrated starter generator were developed. In this paper, the technical survey results of articles, patents, and journals are presented.