Analysis model of leakage current in a long shield power cable in inverter‐fed AC drives

Each time switching occurs, a PWM inverter produces high‐frequency leakage currents flowing through stray capacitors. Since the inverter for a trash conveyance crane is installed far away from the motor, the shield power cables between them become long, and leakage currents pass through the stray capacitances of the shielded cables and flow to the ground. This paper proposes a model circuit for analyzing leakage currents which flow into the shields of the cables. The effectiveness of the proposed model circuit is verified by comparison of simulated leakage currents using the proposed method and measured leakage currents. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 140(2): 65–72, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.2002     

A low‐loss snubber for reducing motor terminal surge voltage

The development of an advanced Insulated Gate Bipolar Transistor (IGBT) has enabled high‐frequency switching operation and has improved the performance of PWM inverters for motor drive. However, the IGBT's high rate of dv/dt has adverse effects on motor insulation stress. In many motor drive applications, the inverter and motor are separated, requiring long motor feeds. The long cable contributes high‐frequency ringing at the motor terminal and results in high surge voltage which stresses the motor insulation. The inverter output filter and RDC snubber are the conventional method for reducing the surge voltage. In this paper, we propose a new low‐loss snubber to reduce the motor terminal surge voltage. The snubber consists of the series connection of chraging/discharging capacitor and the voltage‐clamped capacitor. At IGBT turn‐off, the snubber starts to operate when the IGBT voltage reaches the voltage‐clamped level. Since dv/dt is decreased by snubber operating, the peak level of the surge voltage can be reduced. Also the snubber operates at the IGBT voltage above the voltage‐clamped level, and the snubber loss is largely reduced compared with the RDC snubber. The proposed snubber enables reduction of the motor terminal surge voltage with low loss. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 150(4): 64–72, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10378     

Investigation of VFT surges propagated into transformer and overvoltages applied to winding

Investigations were conducted on the VFT (Very Fast Transient) surges that propagate into a 500‐kV transformer. The disconnector restriking surge and ground fault surged were discussed. It was regarded that a large part of the surge voltage was applied just at the entrance of the transformer winding for the VFT surges. Thus, an equivalent circuit that models the windings was used for the analysis. The overvoltages that appear between the first winding sections at the entrance of the transformer were computed. The following was established. (1) The overvoltage between the first winding sections becomes greater when the magnitude of the voltage change at the transformer terminal is larger. The overvoltage between the first winding sections is not affected by the magnitude of the transformer terminal voltage. (2) For the disconnectors that are not connected directly to the transformer, the voltage change at the transformer terminal is not so large. (3) In the case of a ground fault at the GIS near the transformer, the voltage change at the transformer terminal is the same as that for a disconnector directly connected to the transformer. (4) In actual GIS, the disconnector that is connected directly to the transformer is not usually used. In this situation, the overvoltages that threaten the transformer insulation will not be generated by the restriking of the disconnectors. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 146(2): 20–26, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10225     

Simplified analysis and evaluation of drive characteristics of fully‐pitched winding reluctance motors

Compared to the conventional SRM, fully‐pitched winding reluctance motors have a higher salient ratio for given motor dimensions. In addition, since the generated torque of the motor is determined as the product of the rate of change of mutual inductance with respect to a rotor position and winding current amplitude of the corresponding two phases, the motor is suitable for the bipolar current drives. Accordingly, the conventional general‐purpose inverter drive of the fully‐pitched winding reluctance motor is possible. In this case, the optimum lead angles of voltage play an important role in obtaining the maximum torque and maximum torque/current ratio operations. In this paper, a scheme for determining the optimum angles of voltage without any measurement, and a method for evaluating the drive characteristics in the design stage are proposed by a combination of simple magnetic and electrical analysis. The effectiveness of the proposed analytical scheme is verified by an experiment using a 400‐W prototype fully‐pitched winding reluctance motor. © 2000 Scripta Technica, Electr Eng Jpn 134(1): 45–52, 2001     

Estimation and Reduction of Motor Input Surge Voltage Using Frequency Response Analysis

This paper presents a plain method of calculating the voltage waveform at motor input terminals from the inverter output terminal voltage and also a method of reducing the voltage. The voltage waveform at the motor input terminals is obtained by a frequency domain calculation using the transfer function of the cable and the frequency characteristics of the voltage waveform at the inverter output terminals. The analysis using this method clarifies the mechanism of the rise of the maximum voltage at the motor input terminals, that is, ringing at the motor input terminals, which occurs at specific frequencies at which the transfer gain increases, causing the rise of the maximum voltage. Therefore, to decrease the maximum voltage at the motor input terminals, it is effective to shorten the cable length or cancel the ringing voltage by preswitching. © 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 186(4): 11–19, 2014; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.22482     

PWM变频器供电对异步电机绝缘的影响

本文介绍了电机在PWM变频器供电时影响其定子绝缘的因素、解决方案,以及有待进一步研究的问题。     

Power factor improvement of single‐phase diode rectifier circuit by field‐weakening of inverter‐driven IPM motor

This paper proposes a novel inverter drive system to improve the input power factor of single‐phase diode rectifier. Conventional rectifiers need a high‐frequency switching device and a reactor to improve the input power factor. However, the proposed power converter does not need the switching device, electrolytic capacitor, or reactor. By making many ripples across the DC‐bus voltage, the input power factor can be improved. The proposed system consists of only a single‐phase diode rectifier, small film capacitor, three‐phase inverter, and motor. The proposed system adopts an interior permanent magnet (IPM) synchronous motor. The IPM motor is well known as a high‐efficiency motor and can realize field weakening. The basic ideas of the inverter control method are based on the following operations: the inverter's controlled synchronous with the DC‐bus ripple voltage by field‐weakening method, and direct active power feeding from the source side to the motor without smoothing the DC‐bus voltage. This paper describes that the proposed method can obtain an input power factor of 97.3% by experimental tests, and realizes the goals of small size and long life of the system. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 152(2): 66–73, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20047     

A new method of characteristic analysis for three‐phase induction motors

Generally speaking, the characteristics of induction motors (IM) are analyzed by means of the equivalent circuit with d–q transformation. Although this method is simple, the magnetic flux distributions in the stator and rotor are defined as sinusoidal waves. Therefore, the equivalent circuits become relatively complex for the high‐frequency components and transient states. For detailed analysis, the finite element method (FEM) is used. The FEM can take account of the influence of skewed rotor bars and slots, and of the skin coefficient. However, the calculation time is very long for high‐frequency components and transient analysis. We therefore propose a new method of characteristic analysis for IM. The proposed method analyzes the magnetic flux simply based on the construction of the IM. It can analyze transient and steady states and high‐frequency components regardless of the type of source. The influence of skewed rotor bars and slots can also be treated simply. This paper describes the method of analysis, presents the results of the proposed method and compares them with experimental results, and describes the d–q transition. © 2001 Scripta Technica, Electr Eng Jpn, 135(4): 64–75, 2001     

High‐efficiency and low‐acoustic‐noise drive system using an open‐winding AC motor and two space vector modulated inverters

The combining of the outputs of two inverters using interphase reactors is a widely used method for supplying large AC drives rated at more than several thousand kilowatts. Certain drawbacks are associated with this method, such as high acoustic noise and high losses due to the interphase reactors. To overcome this problem, in this paper a new low‐acoustic‐noise and high‐efficiency drive system using an open‐winding AC motor and two space vector modulated inverters is proposed. This configuration consists of a three‐level inverter with switching once per cycle and a two‐level inverter of about 1 kHz switching frequency, connected to the opposite terminals of the open‐winding motor. With the proposed configuration, good current waveforms and high efficiency can be obtained. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 144(3): 46–57, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10157     

Parameter identification of simplified common‐mode equivalent circuit for inverter‐fed motor drive systems by applying computer‐aided optimization software

This paper deals with common‐mode (CM) electromagnetic interference (EMI) in an inverter‐fed motor drive system. A simplified CM equivalent circuit including π‐type equivalent circuit for the motor winding is proposed by using the waveform of the common‐mode current flowing in the ground conductor. Moreover, a parameter identification method applying the computer‐aided software modeFRONTIER is proposed to decide objectively the circuit parameters of the proposed simplified equivalent circuit. Validity and effectiveness of the proposed equivalent circuit are confirmed by comparing the measured impedance characteristics with the calculated ones. Finally, the possibility of a nonlinear phenomenon is discussed in this system. It is shown that the accuracy of simulation result can be improved by introducing the nonlinear element. © 2015 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Theoretical and experimental analysis of a simple PWM‐1 controlled interrupted electric circuit

In this paper, we analyze a simple PWM‐1 controlled interrupted electric circuit in order to essentially understand the circuit fundamental characteristics. First, we explain the circuit dynamics, and then we define the return map by using the exact solution. Next, we focus on the existence region of the solution (invariant interval) and bifurcation phenomena in the circuit. In particular, we find the circuit has three types of the invariant interval depending on the parameter. We also clarify that the period‐doubling bifurcation and the border‐collision bifurcation effect in the existence region of the periodic solution in a wide parameter plane. Finally, the mathematical results are verified by the laboratory experiment. Copyright © 2012 John Wiley & Sons, Ltd.     

电力电缆绝缘击穿点定位的新方法

探讨了电阻法对高压击穿点定位的原理,寻求一种简便可行的电缆定位技术,并找出一种可用于电力电缆绝缘击穿点定位的新方法,结果表明该方法精度高,且简便易行,其定位结果的精度不受击穿点电阻和测试导线电阻以及接触电阻的影响。     

一种电力电缆绝缘击穿点定位的新方法

本文介绍了一种电力电缆绝缘击穿点定位的新方法。该方法简便易行,其定位结果的精度不受击穿点电阻和测试用连接导线的电阻及其接触电阻的影响。     

A novel PWM technique with switching‐loss reduction for independent drive of two 3‐phase AC motors fed by a five‐leg inverter

This paper presents a novel pulse width modulation (PWM) technique with switching‐loss reduction for a five‐leg inverter (FLI). The PWM technique, in which the available maximum voltage for two motors adds up to DC bus voltage, has been proposed as the strategy for the FLI. Therefore, the DC bus voltage is fully available as the PWM strategy. However, the conventional PWM technique requires the frequency, phase, and amplitude of the phase voltage commands of a motor to produce zero‐sequence voltages (ZSVs). The novel PWM strategy has some efficient features. These features are discussed in this paper. The validity of the novel PWM technique will be shown by experimental results. © 2011 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

基于绕线式高压电动机转子绝缘性能的研究

为解决高压电动机波绕转子端部绕组断路故障问题,经理论研究和试验分析后,采用提高绝缘强度、固化粘接转子绕组和铁心,用绝缘材料填充转子绕组间的间隙的措施提高转子绕组绝缘性能。模拟和现场试验证明了该法有效,可用于实际工程。     

Optimum design approach for low‐speed,high‐torque permanent magnet motors

This paper presents an optimum design approach for low‐speed, high‐torque permanent magnet motors. The approach is divided into two steps: the first consists of the rough estimation of torque by linear analysis, and the second the optimization of the motor configuration by nonlinear FEM analysis. Under restricted dimensional specifications and electrical requirements, a 16‐pole, 18‐coil permanent magnet motor with a rating of 600 Nm and 300 rpm was designed and constructed. © 2001 Scripta Technica, Electr Eng Jpn, 135(4): 52–63, 2001     

数字式雷电/操作冲击计数器的研制

介绍了一种数字式冲击计数器。它能准确地识别电站遭受雷害和操作冲击的情况,并能自动地分别记录扣存贮雷电与操作冲击的次数,其统计结果对于电力系统防雷和过电压防护具有重要意义。     

A sensorless drive system for brushless DC motors using a digital phase‐locked loop

This paper proposes a sensorless drive system for Brushless DC (BLDC) motors using a Digital Phase‐Locked Loop (DPLL). The Back Electromotive Force (BEMF) voltage is measured from the motor winding to determine the permanent magnet rotor position using the DPLL, and Pulse Width Modulation (PWM) limits the motor current to control the speed of BLDC motors. The proposed method can drive BLDC motors using an open‐loop control without stepping out. Also, the proposed method is compared experimentally with a control method that uses Hall sensors. Experimental results for the BLDC motor show the effectiveness of the proposed method. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 142(1): 57–66, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10074     

高压电动机定子线圈匝间绝缘问题的探讨

在实践经验的基础上，分析了我国匝间绝缘短路的主要原因，提出在匝间绝缘的设计，制造工艺及耐压试验等工序采取合理措施，以提高匝间绝缘的可靠性。     

Stator‐core structure and winding technology for EPS motors

Electric power steering (EPS) motors must have the performance characteristics of precision machines. They should be compact and produce high power. Moreover, the loss torque and the change of loss torque should be as low as possible. In this study, dividing the stator core into small blocks and winding the coils densely on the blocks are shown to be effective techniques for achieving compact high‐power motors. We examined whether I‐shaped divided cores or T‐shaped divided cores were more suitable for EPS motors in terms of motor performance and production cost. We built two experimental motors, one with I‐shaped divided cores and the other with T‐shaped divided cores, and measured three important characteristics of EPS motors: output torque, loss torque, and loss torque change. The T‐type motor proved to have better performance for all three characteristics. Moreover, the productivity of the T‐type motor was shown to be higher than that of the I‐type motor, indicating that overall, T‐shaped divided cores are advantageous for the stators of EPS motors. Next, we considered a new winding method for the continuous winding of two T‐shaped cores in order to achieve a compact terminal connection board. The extending lines made by the new winding method do not extend beyond the coil end. Therefore, this method will contribute to reduction of the axial dimension of EPS motors. © 2011 Wiley Periodicals, Inc. Electr Eng Jpn, 175(1): 35–42, 2011; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21085