Optimal current control methods of a non‐salient pole hybrid field‐synchronous motor for energy‐efficient and wide speed‐range operation

This paper proposes new practical optimal current control methods for a newly emerging class of non‐salient pole synchronous motors with hybrid rotor fields by both permanent magnet and winding. In practical situations with limited voltage, the extensively used permanent magnet synchronous motor hardly achieves an ideal performance that allows simultaneously both low‐speed high‐torque and wide speed‐range operations, due to its constant magnet field. Hybrid field synchronous motors (HFSM) have recently emerged to achieve ideal performance as practical motors with controllable hybrid rotor field. For HFSM, the same torque can be produced by a variety of currents due to nonlinearity between torque and currents. Consequently, appropriate determination of a set of stator and rotor current commands plays a key role in achieving possible energy‐efficient and wide speed‐range operation. Proposed methods determine the current commands corresponding to a given torque command such that total winding copper loss due to stator and rotor currents can be minimized if the exact solution exists; the best approximate torque can be produced if no exact solution exists. The determined current commands are optimal in the sense of energy efficiency or degree of approximation in wide speed‐range operation under voltage limit. New real‐time recursive algorithms searching the optimal current solution are also given. The proposed methods are analytical but practical, and their usefulness is verified through experiments. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 156(1): 70–83, 2006; Published online in Wiley InterScience ( www.interscience. wiley.com ). DOI 10.1002/eej.20156     

A performance analysis of a four‐leg inverter in two AC motor drives with independent vector control

This paper presents a performance analysis of a four‐leg inverter (FLI) in driving two motors with vector control. We show that an expanded two‐arm modulation (ETAM) known as a modulation method of a five‐leg inverter is applicable for the four‐leg inverter and we theoretically analyze a performance analysis of the four‐leg inverter in driving two motors with vector control. © 2006 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Initial rotor position estimation of interior permanent magnet synchronous motor using optimal voltage vector

The initial rotor position estimation is a serious problem affecting sensorless drives of permanent magnet synchronous motors. This paper presents an estimation method of initial rotor position for interior permanent magnet synchronous motors. The principle of the estimation is based on the nonlinear magnetization characteristics of the stator core caused by the magnet of the rotor. The estimation is performed using the variation of the current response caused by the magnetic saturation when the voltage vector is applied to the motor. This method can be performed without motor parameters and any additional hardware. Decision method of the optimal voltage vector applied to the motor is also proposed to accurately implement the estimation. Experimental results show that the initial rotor position can be estimated without rotating the rotor by using the optimal voltage vector. It is found that the average of the estimation error is ±1.34 electrical degrees, and the estimation is completed within 15.2 ms in the test motor. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 156(4): 69–76, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20062     

A calculation method of the total efficiency of wind generators

The spread of wind energy converters is progressing in recent years and its capacity is becoming larger and larger. In order to capture more energy from the wind, it is important to analyze loss characteristics of wind generators for the operating speed which is determined dependent on the wind speed. This paper presents a method to evaluate various losses in a wind generator as a function of wind speed, which is based on steady‐state analysis and thus the calculations can be performed quickly. By using the proposed method, wind turbine power, generator output, various losses, and the total energy efficiency are calculated for three types of wind speed data which are represented by a Weibull function. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 157(3): 52–62, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20426 Copyright © 2006 Wiley Periodicals, Inc.     

Position sensorless driving of BLDCM using neural networks

A sensorless driving method of brushless DC motors (BLDCM) using neural networks has been studied in this paper. Considering the nonlinear characteristics and the parameter error of the modeling, neural networks are introduced to estimate the electromotive force (EMF). The results of simulation and experiment using offline trained neural networks show that the proposed method is useful. In addition, the robustness about the parameters is discussed. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 162(4): 64–71, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20240     

A new separate‐identification method of two stator equivalent core‐loss resistances corresponding to hysteresis and eddy‐current losses for parallel‐type mathematical models of AC motors

This paper proposes a new unified method for identifying equivalent stator core‐loss resistance of AC motors, which can be applied to both induction and synchronous motors. In order to realize AC motors that exhibit high performance such as precise torque generation and/or efficient energy transmission, stator core loss cannot be neglected in designing vector control systems. It is common to model stator core loss in magnetic circuits as loss caused by equivalent resistance in electrical circuit. One of the best mathematical models for controlling AC motors with core loss is a kind of parallel‐type model that succeeds in modeling both eddy‐current and hysteresis losses. The newly proposed method succeeds in identifying separately and simultaneously two kinds of equivalent core‐loss resistances on the model corresponding to eddy‐current and hysteresis losses. The practical usefulness of the method is evaluated and confirmed through experiments using two induction motors of 5.5 and 2.0 kW having relatively high core losses and a permanent magnet synchronous motor of 750 W having relatively low core losses. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 143(4): 50–63, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10152     

Study of drive system for linear induction motor using magnetic energy recovery switch

This paper proposes a power supply suitable for driving linear induction motors. The power supply consists of a voltage source inverter (VSI) and a magnetic energy recovery switch (MERS). Circuit configuration and operation principles of the power supply are described. Power factor correction by MERS can increase the output power. Technical advantages of using MERS compared with increasing the rated voltage of VSI are discussed. Some experiments with a linear induction motor were conducted. The results confirm that MERS can reduce the capacity of the VSI or increase the output with the same VSI capacity. The number of devices and magnitude of losses are evaluated on a large‐scale drive system. A half‐bridge type of MERS is provided and discussed. The half‐bridge MERS mitigates disadvantages of using MERS. © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 169(4): 65–74, 2009; Published online in Wiley InterScience ( www.interscience. wiley.com ). DOI 10.1002/eej.20832     

Optimum control scheme for the maximum efficiency drive of linear synchronous motor used for ropeless elevator

Our research group at Musashi Institute of Technology is currently concentrating on the improvement of the overall efficiency for driving ropeless elevators using a linear synchronous motor (LSM). Since these elevators are ropeless, counterweights cannot be installed in the system. Therefore, the linear motors must develop a higher thrust force. In addition to the improvement of the efficiency of LSM it is also necessary to develop a high‐efficiency drive control method. Our laboratory is involved in studies on efficiency improvement. In order to design an efficient control system, we believe it is necessary to understand changes of efficiency caused by variations of driving conditions, such as load mass, velocity, and required thrust force. The dynamic control method changing the operating point to achieve the maximum power is known as maximum power point tracking (MPPT). This approach is useful and can be applied to the control of LSM for ropeless elevators. The car cage of a ropeless elevator periodically repeats acceleration and deceleration cycles in the process of ascent and descent motions. The optimum‐minimum‐energy consumption is obtained if the system is always operated at the maximum efficiency, even if the drive conditions change. In this paper, we first discuss the basic characteristics of LSM for ropeless elevators. Then, based on these characteristics, we derive the maximum efficiency loci as a unique combination of a current and a power angle for a specific condition. We also provide a design of the MPPT controller of LSM and analyze results of simulation of driving the LSM using MPPT. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 155(3): 70–78, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20061     

Frequency domain analysis of beatless control method for converter‐inverter driving systems applied to AC electric cars

In inverter‐converter driving systems for AC electric cars, the DC input voltage of an inverter contains a ripple component with a frequency that is twice the line voltage frequency, due to the use of a single‐phase converter. The ripple component of the inverter input voltage causes pulsations in the torque and current of driving motors. To decrease the pulsations, a beatless control method, which modifies the slip frequency depending on the ripple component, is applied to the inverter control. In the present paper, the beatless control method is analyzed in the frequency domain. In the first step of the analysis, transfer functions which revealed the relationship among the ripple component of the inverter input voltage, the slip frequency, the motor torque pulsation, and the current pulsation were derived with a synchronous rotating model of induction motors. An analytical model of the beatless control method was then constructed using the transfer functions. The optimal setting of the control method was obtained according to the analytical model. The transfer functions and the analytical model were verified by simulations. © 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 174(4): 51–57, 2011; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21050     

Torque and suspension force in a bearingless switched reluctance motor

Bearingless switched reluctance motors, which can control rotor radial positions with magnetic force, have been proposed. The bearingless switched reluctance motors are characterized by integration of switched reluctance motors and magnetic bearings. These motors have two kinds of stator windings composed of motor main windings and suspension windings in the same stator in order to produce suspension force that can realize rotor shaft suspension without mechanical contacts or lubrication. For successful stable operation, accurate theoretical formulas of instantaneous torque and suspension force are necessary to a rotational speed controller and a rotor radial position controller. This paper derives the theoretical formulas of the instantaneous torque and the suspension force from an assumption of simple permeance distribution. This derivation process makes an assumption that fringing fluxes are distributed on elliptical lines. It is shown with experimental results that the derived theoretical formulas are very accurate in terms of practical application. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 157(2): 72–82, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20157     

Optimization of multiobjective system reliability design using FLC controlled GA

A practical optimal reliability design of a system requiring high system reliability could be formulated as an appropriate mathematical programming model; however, in the real world, we should be concerned with some kinds of decision criteria. In particular, system reliability and construction cost are basically in conflict with each other, so that when taking both of them into consideration, the system reliability design model can be formulated as a bi‐objective mathematical programming model. In this research, we consider a bi‐criteria redundant system reliability design problem which is optimized by selecting and assigning system components among different valuable candidates for constructing a series‐parallel redundant system. Such a problem is formulated as a bi‐criteria nonlinear integer programming (bi‐nIP) model. In the past decade, several researchers have developed many heuristic algorithms including genetic algorithms (GAs) for solving multi‐criteria system reliability optimization problems and obtained acceptable and satisfactory results. Unfortunately, the Pareto solutions obtained by solving a multi‐objective optimization problem using a GA cannot guarantee its quality, and the number of Pareto solutions obtained is sometimes small. In order to overcome such problems, we propose a hybrid genetic algorithm combined with a Fuzzy Logic Controller (FLC) and a local search technique to obtain as many Pareto solutions and as good as possible. The efficiency of the proposed method is demonstrated through comparative numerical experiments. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 158(3): 72–80, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20319     

Novel straight and circular road driving control of electric power assisted wheelchair based on fuzzy algorithm

This paper describes a novel straight and circular road driving control scheme for electric power‐assisted wheelchairs. “Electric power‐assisted wheelchair” which assists the driving force by electric motors is expected to be widely used as a mobility support system for elderly people and disabled people, however, the performance of straight and circular road driving must be further improved because the two wheels drive independently. This paper proposes a novel driving control scheme based on fuzzy algorithm to realize stable and reliable driving on straight and circular roads. The suitable assisted torque of the right and left wheels is determined by fuzzy algorithm based on the posture angular velocity of the wheelchair and the human input torque proportion of the right and left wheels. Some experiments on the practical roads show the effectiveness of the proposed control system. © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 170(1): 36–44, 2010; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20846     

Echo canceler algorithm for adaptive Volterra filters in double talk states

In an acoustic echo canceler, it is necessary to consider the nonlinearity of an echo path in order to attenuate an echo signal conventionally, and various methods using adaptive Volterra filters have been proposed. Many of those methods have not resulted in a decisive solution about the double talk states in a nonlinear acoustic echo canceler. In this paper, we propose an echo canceler algorithm for adaptive Volterra filters using the idea of the OECLMS (Orthogonal Expanded Correlation Least Mean Squares) algorithm in consideration of the double talk problem. The convergence speed of the proposed method is improved by using Gram‐Schmidt orthogonalization for the input signal. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 161(2): 42– 51, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20369     

Carrier‐envelope phase‐stabilized chirped‐pulse amplification system

We demonstrated a carrier‐envelope phase (CEP) stabilized chirped‐pulse amplifier system. This amplifier system is composed of grating based pulse‐stretcher and compressor, a regenerative amplifier and a multi‐pass amplifier. We employed a new pulse‐pick‐up method to select CEP stabilized seed pulses. This pulse selection method is different from established practice which is based on pulse train timing, but is based on CEP of seed pulse. We measured amplitude‐to‐phase noise conversion coefficient of microstructure fiber and evaluated the additional out‐of‐loop error of carrier‐envelope offset (CEO) control. We also investigated the effect of beam pointing of the measured fringe shift in self‐referencing spectral interference method. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 157(3): 35–42, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20334 Copyright © 2006 Wiley Periodicals, Inc.     

A permanent magnet‐assisted synchronous reluctance motor

Permanent magnet motors have attracted a lot of attention recently for their potential for saving energy. However, they are only used for certain applications because the magnets are expensive. This paper discusses the optimum design of the low‐cost, highly efficient magnet‐ assisted reluctance motors with a minimum amount of magnets. The motor considered in this study is a multi‐flux barrier reluctance motor. The configuration by which permanent magnets are embedded to the innermost side of the rotor to obtain maximum output with the minimum amount of magnets was evaluated through simulation and experiments with a prototype motor. As a result, we established a method for designing motors capable of realizing the same efficiency as permanent magnet motors with only one‐fourth the amount of magnets. In our experiments, we achieved a high efficiency of 94.5% with a 750‐W motor. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 142(4): 66–74, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10123     

A force‐reflecting friction‐free bilateral system based on a twin drive control system with torsional vibration suppression

This paper proposes a new friction‐free bilateral system based on twin drive control system considering resonant frequency for bilateral systems. The twin drive system consists of two motors which are coupled by the differential gear. The output torque becomes a different torque of both motors. The nonlinear friction torque of the twin drive system can be easily compensated. However, the resonant frequency and the antiresonant frequency caused by the tensional vibration exist. This paper proposes a new two‐mass model of twin drive system that supresses torsional vibration by state feedback. The proposed control method is applied to the bilateral robot, and the effectiveness of the control method is confirmed by the experimental results. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 159(1): 72–79, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20355     

Hopping height control for hopping robots

In recent years, legged robots have progressed and are able to walk just like human beings. Hopping offers a possibility of moving faster and avoiding larger obstacles than walking. Thus, hopping becomes more significant. Copyright © 2004 Wiley Periodicals, Inc. In this paper, to take account of torque limits of motors, we propose the method of controlling the hopping height by changing the leg length at bottom. Considering an actual environment, the environment will change as the robot moves around. Therefore, we describe a way to estimate the actual thrust force. Using the estimated thrust force, command value of leg length in the landing phase is determined. The effectiveness of the proposed method is confirmed by simulation and experimental results. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 155(1): 64–71, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20172     

High‐efficiency UV LEDs using quaternary InAlGaN

High‐efficiency ultraviolet (UV) light sources are very attractive for application to the medical field, white lighting, high‐density memories, and so on. We have demonstrated that 300‐ to 370‐nm UV emission is considerably enhanced by the introduction of several percent of In into AlGaN due to an In‐segregation effect. We fabricated 310‐nm‐band UV LEDs with quaternary InAlGaN emitting layers on a sapphire substrate and obtained submilliwatt output power. We also fabricated 350‐nm‐band InAlGaN‐based quantum‐well LEDs on GaN substrates in order to eliminate the effects of threading dislocations. The maximum UV output power obtained was as high as 7.4 mW under room‐temperature CW operation. The maximum external quantum efficiency (EQE) was 1.1% with an injection current of 50 mA, which is the highest EQE ever obtained for 350‐nm‐band UV LEDs with top‐emission geometry. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 157(3): 43–51, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20287 Copyright © 2006 Wiley Periodicals, Inc.     

A new current control method for energy‐efficient/wide‐speed‐range drive of permanent magnet synchronous motor

This paper proposes a new current control method for energy‐efficient and/or wide‐speed‐range drive of salient‐pole permanent magnet synchronous motors. The proposed method is distinguished from conventional ones by the following features. (1) The original command is a signed current norm. (2) The exact d‐axis and q‐axis current commands that perform energy‐efficient and/or wide‐speed‐range drive are analytically and simply determined from the singed current norm command. (3) For speed control mode, the system turns out to be nonlinear, but its stability can be guaranteed based on Popov's stability theorem. (4) It can be applied for a mode similar to torque control. (5) Current limitation can be carried out accurately but very simply. Concrete analytical d‐axis and q‐axis current commands are presented, which satisfy exactly one of three optimum current control codes such as maximum torque, maximum power factor, and voltage limitation. A design method for PI speed controller that guarantees system stability is also presented. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 161(3): 66–77, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20305     

Development of diode‐pumped solid‐state laser HALNA for fusion reactor driver

The diode‐pumped slab laser for inertial fusion energy driver has been demonstrated, which produces the 1053‐nm output energy of 10 J at 10 Hz. The glass slab laser amplifier has been pumped by quasi‐CW 290‐kW AlGaAs laser‐diode arrays at 803 nm. The optical system can compensate for thermal effects by use of zigzag optical propagation, image‐relayed telescope, and 45^° Faraday rotator. The output energy of 10.6 J at 1 Hz with the optical‐to‐optical conversion efficiency of 19.9% has been successfully obtained. Also, the 10‐Hz operation has been performed with an output energy of 5.1 J. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 155(2): 27–35, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20288