Showing papers in "Electrical Engineering in Japan in 2017"

Unified Theory of Electromagnetic Induction and Magnetic Resonant Coupling

Abstract: SUMMARY The difference between electromagnetic induction and magnetic resonant coupling was pointed out in the first proposal of electromagnetic resonant coupling. However, there was no clear technical comparison between the two methods. Therefore, in this study, five circuits are compared by using a phasor diagram, which is a basic and well-known method in electric circuit theory. The transition from typical electromagnetic induction to magnetic resonant coupling is shown. The mechanism of the high efficiency and high-power transfer across a large air gap and displacement is discussed, where the primary- and secondary-side resonant frequencies are the same. From the above discussion, we conclude that when the specific conditions of electromagnetic induction are satisfied, the wireless power transfer can be categorized as electromagnetic resonant coupling. The unified theory of electromagnetic induction and magnetic resonant coupling is verified through experiment.

A Low‐Speed, High‐Torque Motor Drive Using a Modular Multilevel Cascade Converter Based on Triple‐Star Bridge Cells (MMCC‐TSBC)

Abstract: SUMMARY This paper provides an experiment-based discussion on a modular multilevel cascade converter based on triple-star bridge cells (MMCC-TSBC) for a low-speed high-torque motor drive. The TSBC is a direct ac-to-ac power converter capable of achieving bidirectional power flow as well as drawing and feeding three-phase sinusoidal input (supply-side) and output (motor-side) currents with any power factor at both sides. This paper discusses active dc-capacitor-voltage control applied to the low-speed, high-torque motor drive. A specially designed downscaled system combining a 320-V, 38-Hz, 6-pole, 15-kW induction motor with a 400-V, 15-kW TSBC is constructed and tested to confirm the validity of the motor drive. Experimental waveforms obtained from the downscaled system confirm stable operation with the rated load torque across a range from a standstill to the rated speed, including satisfactory start-up performance.

Properties of Space Charge Distributions and Conduction Current in XLPE and LDPE under DC High Electric Field

Abstract: SUMMARY Space charge behavior and conduction current in polyethylene under dc stress were investigated. One of the reasons for the different breakdown property in cross-linked polyethylene (XLPE) from that in low-density polyethylene (LDPE) may be based on the existence of cross-linking by-products in XLPE. Furthermore, a thermal history in cross-linking process for XLPE may also cause of the difference. It is generally accepted that the existence of the cross-linking by-products increase the conduction current in XLPE under dc stress. It is also said that an anneal treatment in air atmosphere may affect to the electrical properties under dc stress. Therefore, we investigated the effect of the cross-linking by-products and the anneal treatment on space charge behavior and conduction current in polyethylene under dc stress. In our research, it is thought that the increasing dissipation power in XLPE is the cause of the breakdown in it under dc stress. Therefore, to calculate the dissipation power in the bulk of test sample, we measured the space charge distribution and the external circuit current simultaneously. Based on the results, we discussed the reason of the difference of the space charge properties in XLPE and LDPE focusing on the cross-linking by-products and the oxidation of the test samples.

Complex Permittivity Spectra of Various Insulating Polymers at Ultrawide‐Band Frequencies

Abstract: SUMMARY Nowadays, trials to use even higher frequencies are pursued to realize high-speed wireless communications. In order to respond to such a trend, dielectric properties of insulating polymers at high frequencies have to be clarified, although the importance of clarifying low-frequency properties is still very high, especially for use as high-voltage insulators. In this regard, complex permittivity spectra from 10 mHz to 4.0 THz were obtained for various insulating polymers. The spectra obtained in the very wide frequency range are important, because they can be a valuable database and they provide various pieces of important information on dielectric characteristics.

A Hybrid DC Circuit Breaker Combining a Multilevel Converter and Mechanical Contactors: Verification of the Principles of Operation by Experiment and Simulation

Abstract: SUMMARY This paper presents a new hybrid dc circuit breaker producing no conducting power loss under normal operating conditions and having the capability to interrupt a large amount of short-circuiting current within several milliseconds. It consists of two reactors for current limiting and current control, two mechanical contactors, and a multilevel converter based on the cascade connection of multiple full-bridge dc/dc converter cells. It is characterized by achieving current commutation from the main mechanical contactor to the multilevel converter with fast current control. This results in eliminating auxiliary power semiconductor switches that produce a nonnegligible conducting power loss under normal operating conditions. This paper discusses both principles of operation and control method of the new hybrid dc circuit breaker. Experimental verification is performed by a downscaled system rated at 300 V and 150 A, along with verification by computer simulation.

Study on Surplus Electricity under Massive Integration of Intermittent Renewable Energy Sources

Abstract: SUMMARY In order to address climate change and energy security issues, intermittent renewable energy sources such as solar photovoltaic (PV) and wind power are gaining considerable attention. However, due to their variability and surplus electricity, the expansion of these renewables is an important challenge for power grid management. Various countermeasures such as rechargeable batteries, suppression, and back-up generators, are considered necessary for the physical integration of intermittent renewables to create an efficient and reliable power generation mix. In this context, we developed a high time-resolution optimal power generation mix model to quantitatively assess the amount of surplus electricity available under the large-scale introduction of PV and wind power in the Hokkaido region of Japan and the potential roles for the countermeasures mentioned above. The main feature of the model is the detailed time resolution at 10 min through a year. This allows us to investigate the impact of variation in various short-cycle renewables on surplus electricity and the deployment of rechargeable batteries. The simulation results suggest that if a proportion of PV and wind power expands more than around 10% and 20% of total demand respectively or if the sum of the proportion of PV and wind power exceeds 20%, the need for suppression grows rapidly. The results also suggest that rechargeable batteries are more economically compatible with PV than wind power is.

Attitude Control of Quadrotor in Consideration of the Effects of a Pole Based on Limited Pole Placement

Abstract: This paper introduces an attitude control technique for a quadrotor aircraft. Considering that the non-linear characteristics of the aircraft makes it difficult to stabilize, a quadrotor controlled with an adaptive algorithm. Accordingly, we proposed a quadrotor application with backstepping based on the Lyapunov function. Furthermore, we designed a separate actuator control to be mounted on the aircraft for the control of the quadrotor. This approach is often used in industrial equipments. In particular, the limited pole placement (LPP) method is applied to design the controller considering the characteristics of the actuator. The representative simulation results are presented and discussed.

Prediction Model on Room Temperature Side Effect due to FastADR Aggregation for a Cluster of Building Air‐Conditioning Facilities

Abstract: SUMMARY In this paper, we have constructed an auto regressive and neural network combined type prediction model for responsive change in the room temperature trend due to the fast automated demand response (FastADR) power limitation of office building air-conditioning facilities. We defined the average of differences between room temperature and set point of each indoor unit for the entire building as a FastADR side effect index for the building. Prediction experiments using an actual office building showed that the root mean square prediction error of our model was 0.23 °C for 5 min after the FastADR. This prediction ability is considered sufficient to estimate the side effect of FastADR power limitation.

Waveform Comparison and Difference Factors in Discharge Currents for Air Discharges from Different ESD Generators

Abstract: SUMMARY Electrostatic discharge (ESD) generators must be calibrated for contact discharges with the current waveform specified in International Electro-technical Commission (IEC)61000-4-2; however, there are no requirements in current waveforms due to their bad reproducibility for air discharges in the IEC standard. Nevertheless, the air discharge immunity testing is under obligation in the present standard. This implies that different ESD generators are likely to provide significantly different test results for air discharge testing. In this study, two types of different ESD generators were used to measure discharge currents both for contact and air discharges with respect to charge voltages from 2 kV to 8 kV under the same conditions of experimental environment. As a result, we confirmed that the measured waveforms were almost identical for contact discharges regardless of charge voltages, while we found that they are quite different for air discharges with the same approaching speed when the charge voltages are increased. The latter result is because the generator has different impedance characteristics deriving from its structure, and because the spark lengths from the generators with the same charge voltage are different. A formula for calculating the discharge current from an ESD generator through an ideal switch in lieu of a spark, which was previously derived by us, was also employed to obtain the current waveform peculiar to the generator, in order to reveal that the formula provides the different upper limit of air discharge current peaks according to the generator.

Study of Lightning Risk Evaluation of Distribution Systems

Abstract: SUMMARY Recently, concept of the lightning risk management has been proposed for the minimization of damages caused by lightning. In distribution systems (power distribution lines, low-voltage distribution lines, telecommunication lines, and customer appliances), lightning protection measures based on the lightning risk management are effective since the number of facilities is enormous. In this paper, for the establishment of lightning risk management method of distribution systems, we expressed the lightning risk assessment method of distribution systems and examined the influence of arrangement of customer house on the lightning risk values of power distribution lines and customer appliances.

Investigation of Degradation and Voltage Response of Lithium‐Ion Battery Based on Impedance and Electromotive Force Measurement

Abstract: SUMMARY Detailed information on degradation process of lithium-ion batteries is essential to manage the batteries throughout their lifetime because degradation of the batteries associated with long-term usage is inevitable. To evaluate degradation degree of the batteries in detail, it is necessary to separately make clear the decrease in output power due to the increase in AC impedance and the decrease in battery capacity caused by the decrease in electromotive force. In this study, therefore, the authors at first propose a new evaluation method of detailed degradation process of lithium-ion batteries through measurements of AC impedance and electromotive force of degraded batteries. It is made clear that this proposed evaluation method can provide simple but detailed diagnosis of battery degradation degree, indicating usefulness of the proposed method. Next, as a first step for performance simulation of degraded lithium-ion batteries, the authors make clear that the already developed simulation method of battery transient voltage response, validity of which has been confirmed only for new batteries, is also applicable to degraded batteries.

Discharge Pattern Discrimination for Composite Insulation System in Vacuum

Abstract: SUMMARY In order to develop higher-voltage vacuum circuit breakers (VCBs), the investigation of discharge phenomenon in vacuum is necessary. In vacuum interrupters (VIs) with composite insulation systems, the discharge has complex and various patterns at the internal insulation failures. In this paper, based on the discharge development characteristics, we propose a discrimination method for the discharge pattern in vacuum. We measured the applied voltage, anode current, and shield potential waveforms, respectively. From the feature of the measured waveforms, we classified the discharge patterns. Furthermore, based on the relation between discharge development time and discharge path length, we estimated the discharge patterns and discharge path lengths. In addition, we conducted a verification experiment of the discrimination method using a VI model. Experimental results revealed that the estimated discharge patterns and discharge path lengths were consistent with the observed discharge ones and the effectiveness of the discrimination method was confirmed.

Development of Magnetic Levitation System for Science and Technology Education: Magnetic Levitation Control by Using a Hall Element Displacement Sensor with Neural Network

Abstract: SUMMARY In this study, we developed a magnetic levitation system using a Hall element displacement sensor with neural network for science and technology education. The sensor configured with three Hall elements was devised in order to measure displacement from an electromagnet to a levitated object with a permanent magnet. Use of the Hall element displacement sensor achieves a lower cost magnetic levitation system. Furthermore, three-layered feedforward neural network was utilized in order to improve the precision of the Hall element displacement sensor. Finally, operation verification of the developed magnetic levitation system was conducted by designing state feedback regulator with observer.

Manufacturing and Control of a Variable Magnetic Flux Motor Prototype with a Mechanical Adjustment Method

Abstract: SUMMARY A new structure and control method for a variable magnetic flux motor (VMFM) is proposed to achieve a high-efficiency electric vehicle (EV) motor drive under a wide range of conditions. A VFMF prototype that was designed by considering the loss was manufactured and evaluated in an experiment. The prototype demonstrated low iron loss and sufficient max torque. Thus, the prototype can provide a high-efficiency drive with low output, which is frequently the case for EVs. Map control enables a wide phase angle for the vector-control drive of the VMFM under a changing magnetic flux. Thus, the VMFM provides a high-efficiency drive under a wide range of conditions.

New Simple High-Quality Torque Control for Permanent-Magnet Synchronous Motors: Compensating for Torque Ripple Caused by Nonsinusoidal Back EMF

Abstract: SUMMARY This paper proposes a new and simple torque-sensorless torque control method for permanent-magnet synchronous motors (PMSMs) with nonsinusoidal back EMF. The method suppresses the sixth and/or 12th harmonic torque ripples caused by the back EMF in a feedforward manner even at high speeds; it consists of two subordinate methods for compensation command generation and command-tracking current control. The first subordinate method generates compensation current commands to cancel the torque ripples based on a mathematical model of PMSMs. The second method controls the stator current to track a current command containing both fundamental and compensatory components. In conjunction with the current control, a dedicated disturbance observer that employs a digital speed-varying band-pass filter as a disturbance filter is also proposed. The effectiveness and usefulness of the proposed method were verified through extensive experiments.

Isolated Ac/Dc Converter Using Soft Switching Technique

Abstract: SUMMARY This paper presents a high-frequency isolated ac/dc converter using the soft switching technique. The ac/dc converter consists of a matrix converter for transforming three-phase ac voltage to high-frequency ac voltage, a high-frequency transformer, and an ac/dc rectifier. In order to reduce the switching loss, soft switching at every commutation of the matrix converter and ac/dc converter is achieved. The effectiveness of the proposed converter and the control scheme was verified by experiments.

Short-Term Wind Power Prediction for Wind Turbine via Kalman Filter Based on JIT Modeling

Abstract: SUMMARY This paper addresses wind power prediction, which is known to be a key technology in energy management systems. In this paper, a 24-h-ahead power prediction method using a filter theory is proposed for wind power generation. The prediction method is a simple algorithm. The procedure of prediction consists of two steps: the data processing and the calculation of the predicted values. In data processing, in order to obtain the correlative data from the database, we employ just-in-time modeling. In the calculation of the predicted values, we propose a regression model for wind speed and wind power, and the unknown parameters are estimated using a constrained Kalman filter. Moreover, in the procedure used to estimate the unknown parameters, reduction and convergence of the variables are also guaranteed. Finally, the advantages of the proposed method over the conventional method are shown through actual prediction evaluations.

Trajectory Design of Galvano Scanner Considering Voltage Constraint of Current Amplifier

Abstract: SUMMARY This paper proposes a new method for designing feedforward inputs for Galvano scanners in laser drilling machines. The heat generated by current amplifiers becomes a problem as the positioning speed of the Galvano scanner is increased. The proposed method involves the use of a final-state control that considers the voltage constraint of a current amplifier. By constraining the applied voltage to the motor, the power supply voltage of the current amplifier is reduced. Therefore, the electricity consumed and the heat generated by the current amplifier can be reduced. The effectiveness of the proposed method is shown through simulation and experimental results.

Preparation of Exoergic Insulating Composite Material Using Electrostatic Adsorption Model

Abstract: SUMMARY To understand the properties of composite insulating materials, dc breakdown testing and the thermal conductivity measurement of polymethylmethacrylate (PMMA)/aluminum oxide (alumina) composite material created using the electrostatic adsorption method were performed. In the PMMA/alumina sample, which has an alumina as a main particle and a PMMA as an adsorption particle, the dc breakdown strength decreased as the alumina content was increased. It is thought that the increase of the interface between an alumina particle and a PMMA particle leads to a lower dc breakdown strength. The thermal conductivity in PMMA/alumina composite material increased with an increase in the alumina content. From these results, it is suggested that the electrostatic adsorption method can produce the various structures in the material and the insulating materials with various properties such as a higher thermal conductivity and greater tolerable breakdown strength by using a combination of the particle size of the main particle and the adsorption particles.