This paper describes the relationship between the shaft voltage and the bearing grease in a brushless DC motor driven by a PWM inverter. The motor has an insulated rotor to reduce the shaft voltage. At first, we establish a method that determines the bearing capacitance by using the proposed bridge-type equivalent circuit and calculates the shaft voltage from the equivalent circuit. Next, we establish a method calculating the dielectric breakdown voltage of a bearing from the oil film thickness of the bearing grease. Finally, we compare the calculated dielectric breakdown voltage with the shaft voltage of the motor. In addition, we confirm the validity of the insulated rotor in the motor by clarifying the fact that in the motor the shaft voltage is less than or equal to the dielectric breakdown voltage of the bearing grease over the practical operating speed range.
When distributed generators (DGs) such as photovoltaic (PV) systems are widely employed in distribution systems, it is important to quickly prevent the islanding operation caused by a power system fault to ensure electrical safety. So, we propose a novel islanding detection method by harmonic injection synchronized with the exciting current harmonics of the pole transformer. We have developed the prototype inverters that apply the proposed method and carried out an experimental study with a resonant circuit having a quality factor ranging from 0.5 to 3.0. We were able to show the feasibility of detecting the islanding operation quickly and reliably, even if the islanding state is in the nondetection zone. According to the experimental results, it was demonstrated that mutual interference does not occur owing to the synchronous state between the active signals, and it was also shown that the proposed method is applicable to the islanding detection system under clustered installation of PV systems.
This paper proposes a new feedback-type dead-time compensation method. The proposed method compensates the output voltage by employing two operations. First, the normal compensation matches the width of the output pulse to that of the input pulse with reduced delay time from the input pulse to the output pulse compared with the conventional method. Second, the short pulse compensation generates an output pulse after a few pulses are input so that the average value of the output signal equals that of the input signal. The voltage utilization factor of the proposed method is almost 100%, because there is no limit to the compensation and the decrease in the fundamental output caused by dead time is eliminated. The experimental results using a 100-kHz input signal show that there is no discrepancy between the output pulse width and the input pulse width. Furthermore, the THD of the compensated output current, when the output frequency is 50Hz, is eliminated, compared with that of the output current without compensation. These results show that the proposed method has low distortion and high voltage utilization factor characteristics.
This paper proposes a new current source converter using a coupled inductor, which is derived from the circuit of the matrix converter with an additional inductor. The proposed circuit has the bidirectional power conversion ability, providing step-up and step-down operation in each direction, and can switch the direction of the power flow in a few microseconds. This paper describes the principle of operation, the simulation results and the experimental results of the proposed circuit.
This paper describes some characteristics of a compound magnetomotive forces (CMMF) motor employing a dual winding (DW) method. The CMMF motor can utilize three kinds of characteristics because of a special magnet arrangement. A 4-12 pole CMMF motor with changeable electric and magnetic characteristics had already been proposed in the previous study. The CMMF motor, however, has a problem in its driving range because of voltage interference. In this study, the DW method is proposed to solve this problem by utilizing magnet pole combinations and the winding distribution. This paper shows that the proposed motor can achieve multiple high-efficiency points by utilizing the parameter distribution for two kinds of magnet characteristics.
A hybrid electric vehicle (HEV) is one of the solutions to improve the efficiency of a drive and to reduce CO2 emissions. It is desirable to decrease the motor size and to increase the maximum torque to minimize the size of the driving units. For these purposes, motors employing permanent magnet have been commonly used recently. Depending on the electrical output up-rating of an HEV motor, parallel circuit will be employed in the armature circuit. However, this could possibly cause noise and vibration in the motor because the motor driving systems of HEVs or electric vehicles (EVs) must operate over large variable speed ranges of up to 1: 5. The authors analyzed the features of the noise patterns and identified the main cause. Mock-up tests were conducted to confirm the main cause, and the countermeasures including a winding scheme change, were determined. This paper describes the mechanism of sub-harmonics frequency noise and vibrations arising from rotor eccentric motion and currents in parallel circuits and a method to decrease them.
Hybrid Vehicles (HEVs) and Electric Vehicles (EVs) improve the efficiency of a drive and reduce CO2 emissions by regenerative braking and operating the engine under optimum conditions. It is desirable to decrease the motor size and increase the maximum torque to minimize the driving units. For these purposes, motors employing permanent magnets have been commonly used recently. The motor driving systems of HEVs and EVs must operate over variable speed ranges of up to 1: 5. Over this large range, smooth, silent operations are desirable and important. The skew method is often adopted to ensure a smooth start and stop and silent operation by reducing the torque ripple. However, this method possibly causes noise and motor vibration. This paper describes the mechanism of torsional resonance noise and vibrations arising from the skew method and a countermeasure to decrease them by optimizing the skew phase distribution in the rotating axis.
In recent years, remarkable advancement of new power semiconductor devices, such as SiC and GaN, enables the increase of switching frequency of power converters, and hence the volume of passive components, such as AC filters and transformers, can be reduced. However, temperature rise caused by the inductor loss is increasing, and hence iron loss evaluation of the inductor is one of the most important issues to realize high power density converters. Conventionally, an improved generalized Steinmetz equation (iGSE) has proposed in order to calculate the iron loss under a pulse voltage magnetizing condition. However, accurate iron loss calculation of the AC filter inductor used in a PWM inverters cannot be realized. The authors have proposed two methods of iron loss evaluation of AC filter inductors. The first one is a loss map method which can calculate the iron loss without using a real PWM inverter. Another one is an ILA (Inductor Loss Analyzer) which can measure the iron loss in every switching period in a real PWM inverter. In this paper, comparisons of the iron loss between the ILA and the loss map method on both the single-phase and three-phase inverters are studied. It is found that iron loss of the AC filter inductor in the three-phase PWM inverter which is calculated by the loss map method cause a large error on a specific condition. In order to prevent the calculation error, the authors proposed a revised loss map method and proved the effectiveness of the method.
This paper describes the resonance characteristics of two types of commonly used electric power steering motors: the 8-pole-12-slot and the 10-pole-12-slot motors. The relationship between the excitation modes and the characteristic vibrational modes is clarified by conducting a coupled magnetic field-structural analysis and carrying out a modal analysis on a prototype. Finally, the 8-pole-12-slot and 10-pole-12-slot motors are compared in terms of their generated noise.
This paper presents a modular push-pull PWM converter (MPC) for a battery energy storage system, which is intended for grid connections to medium-voltage or high-voltage power systems. The converter per phase consists of a center-tapped transformer and two arms consisting of a cascade connection of multiple bidirectional PWM chopper-cells with floating dc capacitors. This paper discusses the operating performance and control method of the MPC, focusing on voltage balancing of all the floating capacitors. Moreover, a comparison is made between the MPC and a modular multilevel cascade converter (MMCC-DSCC), both of which are used as the same battery energy storage system. The validity of the operating performance and control method is confirmed by both computer simulation using the “PSCAD/EMTDC” software package and experiment using a three-phase, 200-V, and 5-kW downscaled model.
Our laboratory focuses on new power electronics technologies and their applications for industrial and consumer use, especially IH, wireless power transfer system, x-ray generator, nano-satellite and power conversion system with high-frequency multi-winding transformer.