This paper proposes a new observer that estimates the rotor flux of induction motors for sensorless vector control. The proposed observer has the following attractive features. Observer gains can be designed easily and clearly based on the analyses of the observer's characteristic equation. The observer can estimate the rotor flux stably in both motoring and regenerating operations for all speed ranges. Extensive experimental investigations verify that the proposed observer can operate properly in both torque and speed control modes for all speed ranges including zero-crossing frequency.

In interleaved DC-DC converters, current control is required to solve the problem of unbalanced inductor current. Generally, the same number of current sensors as the number of phases are required for inductor current control, and it increases the cost and circuit volume. In previous work, inductor current control of three-phase interleaved bidirectional boost converters was achieved by high-side DC-link current detection using a current sensor. This paper proposes an inductor current estimation method for three-phase interleaved bidirectional buck-boost converters using a current sensor on a DC bus. In addition, the effectiveness of the proposed method is verified by experimental results. As a result, this paper shows that each inductor current can be estimated with our proposed method in bidirectional buck-boost operation. Experimental results showed that the proposed method could estimate the inductor current with an error rate of 0.146% or less.

At present, many types of induction motors (IMs) are used as the power sources of industrial machines. Generally, middle and small size IMs have skewed slots in the rotor bar, which is made of aluminum die cast, to reduce abnormal starting torques and electromagnetic vibration and noise. The rotor iron and rotor bars are shorted, and an electrical potential difference is generated between the rotor bars by skewing, so that the current, which is called inter-bar current, flows in the direction of rotation. However, many unclear issues exist with regard to the inter-bar current. Therefore, we have experimentally studied the effect of the inter-bar current on the characteristics of an IM. In a previous paper, a trial rotor was investigated by using the finite element method (FEM). In this paper, the effects of the inter-bar current on the characteristics of an IM are demonstrated through experiments with many test motors, which include some trial rotors that follow the previous results. In particular, it is shown that the stray load torque in the reverse rotational test is remarkably reduced when the rotor is heated to about 500°C (abbr. post-heating), and that its influence extends the improvement of the starting torque and running performance. Furthermore, the resistance between the rotor bars are measured using ultra-low resistance meter.

This paper proposes a design method of installed fuel cell (FC) power and lithium-ion battery (LiB) capacity for fuel cell hybrid railway vehicles. To reduce the cost of such vehicles, reduction of the FC power and LiB capacity is needed. To achieve this, this paper discusses a reasonable design method of FC power and LiB capacity based on energy strategy and a FC output pattern considering load conditions such as running patterns and gradient. The proposed design method can be used to develop environment-friendly railway traction systems for nonelectrified lines.

A high-precision positioning stage is an important apparatus for high-precision industries. Generally, the stages have 6-degrees of freedom (6 DOF: x, y, z, θ_x, θ_y, and θ_z) to control. However, coupling forces between the axes deteriorate the control performance. To address this problem, this paper proposes a decoupling method that utilizes a high-precision positioning stage with additional actuators. According to a model that considers the misalignment among the Center of Gravity (CoG), the Center of Rotation (CoR), the actuation point, and the measurement point, the coupling characteristics from the translational force to the angle can be changed by varying the height of the actuation point. The model indicates that a “CoR-driven method” can suppress the coupling in the low-frequency range and a “CoG-driven method” can suppress the coupling in the high-frequency range. This paper proposes a “CoR and CoG hybrid-driven method” using complementary filters to place the actuation point at the CoR and CoG in the low and high-frequency ranges, respectively. The effectiveness of the proposed method is verified by experiments using a 6 DOF high-precision positioning stage.

In order to increasing the efficiency of axial gap motors, a motor was designed to achieve an efficiency of 98% based on the IE 5-11kW motor (motor efficiency of 96%). Based on the design, we created a prototype with ceramic housings, thinned coil conductors, and nanocrystalline materials for the stator core as real items to reduce losses. We verified its effect by evaluating the motor characteristics. As a result, it was confirmed that the prototype can achieve a motor efficiency of 98.3% at 3,000min-1 and 11kW rated driving. Moreover, in the temperature rise test, it was demonstrated that class B type (130°C) could be achieved.

This paper proposes countermeasures to reduce radiated AM radio frequency noise caused by the VVVF (variable-voltage/variable-frequency) inverter system incorporated with an electric railway car. First, the common-mode current flowing through a cooling fin earth line is studied, and the connection change of the line shows good attenuation of the 1.26MHz resonance component. Second, the common-mode current flowing though the motor earth line with a capacitor is focused upon, and the modified connections of the line to the outside of the input common-mode core achieves fine noise reduction in the range from 500kHz to 1.5MHz. In such cases, the existing input common-mode core is utilized to establish the impedance, which is efficient in both the noise reduction and the countermeasure cost reduction. Finally, a current simulation model which is paid attention to the AM radio frequency range is examined with the measured impedance data of the VVVF inverter system. The currents flowing thorough the cooling fin earth line and the motor earth line is simulated, and these simulated currents show good agreement with the measured one.

This paper describes the carrier electromagnetic noise caused by PWM pulse modifying technique of DC bus current detection. It is cleared from theoretical analysis that the influence factors of carrier harmonics are DC voltage, self-inductance and pulse modifying width. As estimated the carrier electromagnetic noise, we propose the new evaluation index of radiation area electromagnetic force to multiply the radial electromagnetic force and gap surface area. The proposed evaluation index can be estimated the increase of carrier electromagnetic noise within 1.5dB error by experiment. Also, the one phase pulse modifying method to reduce the carrier electromagnetic noise is proposed. The effect of this method was demonstrated in the experiment.

This paper investigates the influence of hysteretic property on motor performance in magnetic field analyses of interior permanent magnet (IPM) motors with concentrated winding or distributed winding. As a result, it is clarified that the influence of hysteretic property as well as eddy current may be large in IPM motors with concentrated winding due to the change of magnetic paths in the core back depending on the degree of magnetic saturation.

The authors developed a physics-based equivalent circuit model of a lithium-ion battery (LIB) whose parameters are continually updated, reflecting the theoretical calculation results of the Butler-Volmer equation, diffusion equations of the lithium-ion and lithium, and Nernst equations of the liquid and solid phases. The developed model was applied to the charge/discharge simulations of a LIB, and the experimental and simulated results of constant current discharges and pulsed-charge/discharge were found to be in excellent agreement. In particular, using the developed model, analyzing transient responses of the LIB derived from the transition of the electric double layer charging to the electrode reaction is possible. These results demonstrate that the electrochemical performance of a LIB can be calculated on a circuit simulator using the developed model.