Historical Evolution of Motor Technology 38 Historical Evolution of Motor Technology

Hiroyuki Mikami, Dr. Eng. OVERVIEW: Driven by a strong desire to produce electric motors using Kazumasa Ide, Dr. Eng. domestic rather than foreign technology, ’s founder, , Yukiaki Shimizu produced three 5-HP electric motors in 1910. Now, a century later, electric motors incorporate a variety of different technologies and have undergone Masaharu Senoo significant changes in their size, performance, and other features. They have Hideaki Seki become a key device that underpins society in a wide range of fields including power generation, industry, transport, and home appliances.

INTRODUCTION fields including power generation, industry, transport, 2010 marked the 100th anniversary of Hitachi’s and home appliances (see Fig. 2). In particular, formation and it is widely known that the company’s in conjunction with advances in microelectronics first product was a 5-HP (horse power) induction motor technology and power semiconductor devices since (see Fig. 1). Although most electric motors in Japan the 1980s, rapid progress has been made in the field at the time were imported from overseas, Hitachi’s of inverters (a form of electrical conversion system) founder, Namihei Odaira, embarked on development and the drive control systems that combine inverters driven by a strong desire to produce electric motors with motors. Along with control functions that have using his team’s own technology developed locally made it possible to supply motors with operating in place of foreign technology. After overcoming characteristics tailored to specific system applications, numerous technical challenges, the result was it also seems likely that this progress was helped along three 5-HP motors produced in 1910. This was the by the desire for greater energy efficiency. Almost all beginning of Hitachi’s activities in the field of electric power generation involves the use of generators and motors as well as its starting point in motor technology electric motors are widely used as power sources in development. factories, railways, and home appliances, and even Now, a century later, the electric motor has become in vehicles and data processing equipment. It is also a key device that underpins society in a wide range of widely known that motors account for approximately

Field Application Output (W) 101 100 1k 10k 100k 1M 10M 100M 1G EPT (main motor) Automotive (HEV) Auxiliary (EPS, pump, etc.) Household AC

Home Refrigerator appliances Washing machine

Vacuum cleaner General purpose (pump, blower, etc.) Elevator Industrial Railroad

Fig. 1—5-HP (horse power) Induction Motor. Steel mill After building up experience and skills through the repair of Power Wind power electrical machinery, Hitachi produced three induction motors systems with an external diameter of approximately 400 mm and a Thermal power weight of approximately 150 kg. The motors were designed EPT: electric power train HEV: hybrid electric vehicle by Naosaburo Takao (who later became Vice-President) and EPS: electric power steering AC: air conditioner manufactured from parts made using a sheet steel processing Fig. 2—Examples of Hitachi Electric Motor Products. machine imported from the UK and a coil winding machine Motors and generators have advanced to become key devices they built themselves. that help underpin society. Hitachi Review Vol. 60 (2011), No. 1 39

40% of all electricity consumption(1). As well as 5-HP (3.7-kW) 4-pole induction motor playing a major role in industrial progress, it is no exaggeration to say that rotating machinery in the form of motors and generators form part of the foundations 1910 1916 1935 1951 1955 1963 1970 1991 1994 1977 2001 Total prod. = 20 M Total prod. = 40 M of modern society. 100 This article reviews the historical evolution of Journal bearing Ball bearing 80 Copper Aluminum the technology used in electric motors together with bar rotor diecast rotor generators, inverter control, and other associated 60 Class E Class A insulation 40 insulation components, describes examples of work being done Steel plate Aluminum Ratio of mass (%) Cast iron frame frame frame on the ongoing development of motors, and looks at 20 New the outlook for the future. JIS 0 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 Year CHANGES IN MOTOR TECHNOLOGY JIS: Japanese Industrial Standards Fig. 3 shows the history of motors and associated technology. This history goes back nearly two Fig. 4—Changing Mass of Hitachi 5-HP Motor. Numerous technical developments have made motors smaller centuries to a series of inventions inspired by Faraday’s and lighter. laws of electromagnetic induction in the first half of the 19th century. Because early motors were powered by batteries, most progress focused on DC (direct Hitachi have changed over time. The adoption of a current) motors. This was followed subsequently by wide range of technologies has reduced motor size the invention of practical induction, synchronous, and to about one-fifth that of the first motor made back other AC (alternating current) motors as AC power in 1910 and advances in production techniques have technology became more advanced. The principles seen cumulative production pass 45 million motors in behind the motors used today were largely worked January 2010. out during the 19th century and they have undergone The following sections describe the changes that steady progress since then by drawing on advances have taken place in the key technologies of design in the three key enabling technologies of design, (analysis), materials, and production techniques that materials, and production techniques. have underpinned the evolution of the electric motor. The 5-HP electric motor described above was also part of this history of progress. Fig. 4 shows a graph Design and Analysis Technologies indicating how the weights of 5-HP motors made by This section takes as an example the use of electromagnetic field analysis in electrical and magnetic design which is considered the most 1830 1900 2000 important design and analysis technology for motors Hitachi 5-HP induction motors and generators.

Motor development at Hitachi Fig. 5 plots the progress in electromagnetic 5-HP motor field analysis alongside the changes in the capacity ▲: Steinmetz ▲: Kron coordinate ▲: 2D magnetic analysis transformation ▲: 3D magnetic of turbine generators which are the largest of all ▲: Concordia theory analysis rotating machines. Because conducting studies on Systematization Design ▲: DC generator / Magneto of motor theory technology full-scale prototypes is impractical when developing ▲: DC generator / ▲: Electrical steel ▲: Rare-earth Dynamo sheet permanent magnet large generators, electromagnetic field analysis ▲: AC generator ▲: SMC has played a role in design investigations since the ▲: Induction motor ▲: Amorphous steel sheet Invention of “motor” Material technology technique was first invented. Quasi two- and three- ▲: Insulation ▲: High-space-factor winding dimensional analyses were first used in the 1960s and Production technology ▲: Segment core three-dimensional analysis using the edge-element- Period of Period of industrial based finite element method is now widely used(2). Period of invention scientific initiatives initiatives Computing speeds have also been improved, not only 2D: two-dimensional 3D: three-dimensional DC: direct current AC: alternating current SMC: soft magnetic composite because of the obvious improvement in the capabilities Fig. 3—History of Motors and Associated Technologies. of the computers themselves, but also through the The electric motor was invented in the 1830s and underwent adoption of a number of computational techniques. scientific and industrial advances during the 20th century. A relationship is evident between this trend and the Historical Evolution of Motor Technology 40

Conventional 4-pole Stator Frame 1,600 1,570 MVA Conventional 2-pole 1,300 MVA Rotor 200 1,200 Air-cooled 2-pole Amn 1,120 MVA 100 800 MVA 800 940 MVA 0 −60 60 Time Harmonic Order 400 250 MVA 0 70 MVA n 60 0 0 m End Max. capacity (MVA) Space Harmonic Order

Hitachi turbine generator Base 3D analysis cover Quasi 3D analysis Electromagnetic field Spectral force resolution Structural vibration 2D analysis

108 Parallel computing Improvements of edge- Cal. by simplified stator model Application of FEA element FEA formulation 106 to electromagnetism 80 Meas. Cal. by complete stator model 70 4 Quasi-3D 10 Robust algorithms 60 formulation for solving non-linear 50 2 problem 10 40 Invention of edge-element FEA 30 Pick up points 1 for noise 1960 1970 1980 1990 2000 2010 20 Relative calculation speed (p. u.)

Sound pressure level (dBA) 0 2,000 4,000 6,000 8,000 10,000 Year Noise p. u.: per unit FEA: finite element analysis Frequency (Hz)

Fig. 5—Advances in Analysis and Design Techniques Relating Fig. 6—Motor Electromagnetism and Noise Analysis. to Electromagnetic Field Analysis. Motor noise can be estimated quantitatively based on a Large and complex analyses have facilitated the development coupled electromagnetic force, structure, and fluid analysis. of motors, generators, and other machines thanks to advances in the computing environment. analysis, structural analysis, and vibration and noise increase in the capacity of the turbine generators analysis and it has become possible in recent years to made by Hitachi, which has utilized electromagnetic analyze motor noise through coupled electromagnetic field analysis from its very beginnings, and this force, structure, and fluid analysis(5) (see Fig. 6). corroborates the role that analysis techniques have played in increasing capacity. Materials and Production Techniques The ability to use two-dimensional electromagnetic Materials and production techniques have made field analysis to analyze the mechanical movement a major contribution to improvements in motor of the rotating part of the motor (rotor) dates back performance over recent years. In terms of materials, to the latter half of the 1980s. This analysis took a mass production of electrical steel commenced in the considerable length of time in those days meaning 1960s and this material was quickly adopted for use that it could not necessarily simulate all the different in motors. Similarly, rare-earth magnets invented in motor operating conditions and accordingly it was only used in a limited way. To eliminate restrictions 480

) NdFeB magnet like this, Hitachi developed techniques for shortening 3 the calculation time by taking advantage of the various 320 SmCo magnet cyclic aspects of internal motor operation based on 160 AlNiCo magnet

(3) Max. energy

product (kJ/m Ferrite magnet motor theory . These expanded the range of cases that 0 could be analyzed and allowed a complete cycle of the 1910 1950 2000 waveform to be calculated from analysis information Air conditioner compressor motor for a particular region only, including analysis of Stator situations that combined both long-wavelength components and very short-wavelength components Ferrite magnet NdFeB magnet Rotor q-axis as occur in induction motor rotor currents. Based on cut analysis techniques like these, it became possible to Feature Distributed Concentrated Rotor core Thin slot calculate losses caused by short-wavelength/high- winding winding with q-axis cut insulation Performance 3 kNm/m3, 94% 7 kNm/m3, 95% ← , 95.5% ← , 96.0% frequency components that occur due to the motor NdFeB: neodymium iron boron SmCo: samarium cobalt structure and to separate fully the electromagnetic AlNiCo: aluminum nickel cobalt force components associated with each mode and Fig. 7—Advances in Motors Due to Rare-earth Magnets. (4) frequency . Progress has also been made on coupled The invention of the neodymium magnet led to a major step analysis techniques such as electromagnetic field forward in motor performance. Hitachi Review Vol. 60 (2011), No. 1 41

1983 have played a major role in reducing motor size of the coil wound around the mold. Technology was and improving performance. also developed to ensure that the stator core is put Fig. 7 shows the history of permanent magnet together with a high degree of roundness when it is development and advances in permanent magnet separated and reassembled, resulting in small size and motors. Magnet energy product improves progressively low cogging torque. This technology has been used in from ferrite through alnico and samarium-cobalt industrial servo motors since 2000(6). magnets. While the most commonly used magnet in earlier times was the low-cost ferrite magnet, use of INVERTER AND DRIVE CONTROL neodymium magnets (the strongest type of magnet) TECHNOLOGIES grew rapidly after their invention. Looking at the Changes in Variable-speed Systems influence these magnets have had on Hitachi’s air Whereas DC motors had previously been the conditioner compressor motors, initially these motors mainstay for variable-speed motor control, a major used ferrite magnet rotors combined with distributed- shift to AC motors took place in the 1980s. Fig. 9 winding stators. The arrival of the neodymium magnet shows the history of advances in motor drive control. saw the adoption of concentrated windings for the The major factors behind these advances are the stator and, as shown in the figure, smaller coil end performance improvements in microcomputers and size. Although coil ends with concentrated windings the main circuit elements used in inverters. The main are smaller, because they produce large harmonic control method changed progressively to AC motor components in the magnetic flux distribution, the vector control and, in terms of precision, response, and stator and rotor shape become important design speed range, the performance of AC motors came to considerations. Consequently, advances in the surpass that of DC motors. electromagnetic field analysis techniques described above have been complementary with those in magnet Sensorless Control materials and have allowed both axial length to be Fig. 10 shows how vector control of induction roughly halved and efficiency to be improved. motors has evolved. The general-purpose inverter has One example of production technology is a provided the driving force behind induction motor technique for achieving a high space factor (winding control technology. Sensorless vector control was density) through use of a split core. Fig. 8 shows an incorporated in general-purpose inverters in 1989. example of a technique for increasing the density of wires in the winding slots by using a press-forming machine to pressure-mold an aligned pre-wound core. 1960 1970 1980 1990 2000 This achieves a high space factor by molding the wire Motor DCM ACM (IM, SM) into the shape of the slot that is to hold the winding M-G Cycloconverter Power Thyristor Leonard without compromising the insulation performance converter PWM invertor Control Analog-digital circuit Analog hybrid Digital (microprocessor), ASIC Control Sequence control, Vector control High-density wire molding technology algorithm PI control Anti-vibration control Self-bonding wire 1.0 I Precision DCM ACM Clinging (%) 0.05 by energizing 0.25 0.01 60 Response DCM 15 – 20 500 – 1000 (rad/s) 2 ACM

Press die Performance Speed DCM 1:40 1:1000 – 1:200 Winding frame range 1:5 ACM

AC servo motor (2001) DCM: DC motor ACM: AC motor IM: induction motor SM: synchronous motor M-G: motor-generator • Small size PWM: pulse width modulation • High space factor: 75% • Low cogging torque ASIC: application specific integrated circuit PI: proportional/integral • High accuracy • High speed response: roundness: 0.03 mm 500 Hz Fig. 9—History of Advances in Motor Drive Control. State in slot section The performance of variable-speed AC motor systems has improved with advances in control and power conversion Fig. 8—Split Core and Winding with High Space Factor. equipment (Reference: 2001 Annual Conference of Industry Better motor performance was achieved by improving the coil Applications Society, The Institute of Electrical Engineers of space factor and the precision of split core assembly. Japan, S11-1). Historical Evolution of Motor Technology 42

Sensorless vector control Permanent magnet motors were introduced in 5.0 V/F constant • HITACHI • HITACHI • HITACHI Hitachi air conditioners in 1982 and mass-market (Hz) 1.0 HFC-VWA SJ300 SJ700

Minimum 0.0 200% torque frequency at models have used sensorless control since that time. 1970 1980 1990 2000 Since then, permanent magnet motors and sensorless 1989 1999 2006 control have become the industry standard for air Speed sensorless Zero-speed SJ700 vector control sensorless 200% torque at 0.3 Hz, conditioners. PAM (pulse amplitude modulation) vector 150% torque at 0 Hz control which varies the amplitude of voltage pulses 0.3 Hz 200 100 was developed subsequently and technology for 0 300 600 900 1200 −100 −200 driving motors with an ideal sine wave current was Torque (%) -1 HFC-VWA SJ300 Speed (min ) developed in 2002. A form of sensorless control that used neither the position sensor nor current sensor V/F: voltage/frequency originally required when using vector control to drive a Fig. 10—Advances in Vector Control for Induction Motors. motor was developed at the same time, resulting in the Advances in vector control provided improvements in motor ultimate circuit configuration for an ideal drive(7). functionality. Sensorless control without position or current sensors is now being widely adopted in home

6.0 Induction PM motor appliances such as refrigerators, cordless cleaners, and motor • Less & less 4.0 • PAM washing machines as well as in other fields such as in

COP • 120° control 2.0 industry or for auxiliary automotive motors.

Air conditioner 1970 1980 1990 2000

1982 2002 EXAMPLE INITIATIVES FOR FUTURE Conventional Less & less PM Concerns in recent years about how to prevent Position Current sensor Sensorless Sensorless sensor Soft global warming are driving demands to reduce motor MPU based Controller sensor energy consumption by making motors even smaller PMSM Sin-wave Development of position- current and more efficient. To achieve both smaller size and sensorless control with 120° Ideal sine wave current drive commutation,use of PM introduced in consumer appliances higher efficiency, it is necessary to minimize as far as motors in air conditioners. using “less & less” technology. possible the various types of energy loss that occur COP: coefficient of performance PM: permanent magnet inside motors while simultaneously dealing with the PAM: pulse amplitude modulation MPU: microprocessor unit reduction in heat dissipation performance that results Fig. 11—Advances in Sensorless Control of Permanent Magnet when motors are made smaller. Motors. Against this background and on the occasion of Advances in control techniques for permanent magnet motors the 100th anniversary of the company’s founding, that do not use position and current sensors and which were developed for use in air conditioners. Hitachi, Ltd. in collaboration with Hitachi Industrial Equipment Systems Co., Ltd. produced a prototype concept motor in 2010 with the intention of achieving Compared to V/F (voltage/frequency) control used even smaller motor sizes in future. The prototype previously which kept the flux swing constant, vector involved the development of technology to improve control achieves a significant improvement in low-speed heat dissipation, a coupled magnetic field and thermal torque by controlling the torque components. Zero- analysis technique that simultaneously analyzes the hertz sensorless technology was first commercialized magnetic flux and heat flow in the motor, and design in 1999 and succeeded in performing vector control at optimization techniques that are based on this analysis 0 Hz, something that was not previously possible. technology. It is this analysis technology that makes Fig. 11 shows the history of sensorless control the greatest contribution to the design of motors for techniques for permanent magnet motors. Development small size and the following sections describe the of permanent magnet motor control was undertaken technology itself together with the prototype motor primarily for air conditioning appliances. The size and that was investigated with its aid(8). efficiency of permanent magnet motors underwent a sudden improvement with the invention of rare-earth Coupled Magnetic Field and Thermal Analysis magnets, but because they cannot be started without an and Shape Optimization Techniques inverter, the applications for these motors have grown Because the objective was to make a smaller motor, with the help of control technology. a permanent magnet configuration was chosen for the Hitachi Review Vol. 60 (2011), No. 1 43 prototype. The technologies required for permanent Stator core magnet motor design can be broadly divided into x6 electrical design, cooling design, and demagnetization x analysis (demagnetization: the loss by a magnet of its 8 Coil magnetism). Conventionally, the most common design approach has been to treat electrical design, cooling x7 x design, and demagnetization analysis separately and x5 9 x base the design on individual analyses that dealt 2 x4 x with losses, temperature, or other parameters. Also, Rotor core 1 x design conditions such as the variation in material 3 x characteristics or dimensional tolerances often have 10 specific ranges. Accordingly, it was essential to Permanent magnet run analyses based on severe conditions to ensure (a) Optimized variables in magnetic field analysis model performance could be achieved even under worst-case Objective function conditions. This design methodology meant that excess Variable x margins were built into the motor’s structural design and performance, in which case a series of prototypes (1) Calculation of material History of constants temperature rise would be produced after the design stage to adjust the extent of these structural design and performance (2) Generation of finite element mesh margins. Read previous Typically, the structural design of a motor is (3) 2D-magnetic field analysis values. determined by the required torque performance and Optimization permitted temperature rise. Problems that arise when engine (4) Calculation of motor losses a motor is made smaller while keeping the same (5) Calculation of thermal History of output and efficiency include that losses remain the resistances core length same despite the smaller chassis and the excessive (6) Steady-state thermal rise in temperature due to the reduction in surface network analysis area for dissipating heat. The problems associated (7) Calculation of motor with higher temperature include loss of magnetism characteristics in permanent magnets and an increase in winding Set newvalues. resistance, resulting in a deterioration in motor torque Objective function F(x) characteristics. In other words, there is a trade-off (b) Flow of proposed method between motor size and temperature. Accordingly, Fig. 12—Newly Developed Coupled Magnetic Field and striking a good balance between temperature rise and Thermal Analysis and Shape Optimization Techniques. torque performance is a key point when designing Linked analysis of heat and magnetic fields together with shape motors for small size and it is considered essential that optimization achieved both a shorter design time and a smaller the temperature in the actual environment where the motor. motor is to be used be considered in the analysis if a design that achieves this balance is to be obtained. In response, Hitachi has developed analysis set in the objective function and the calculation is technologies that can be used to design smaller repeated until the objective function criterion (which permanent magnet motors by linking magnetic field in this case is the minimum motor size) is satisfied, analysis using the two-dimensional finite element with the optimization engine used each time to set the method with thermal analysis using the equivalent variables for the next iteration subject to the specified thermal network method and combining these with restrictions. shape optimization using mathematical programming methods. Fig. 12 shows a flow chart of this analysis Prototype Results technique. The analysis starts by setting assorted A prototype 5-HP permanent magnet motor motor variables which are used as the basis of a two- produced using the above techniques achieved a dimensional magnetic field analysis which is followed volume only one-fifteenth that of Hitachi’s original by a thermal analysis. The results of the analysis are 5-HP induction motor from 1910 (and only one-third Historical Evolution of Motor Technology 44

Despite having such a high degree of miniaturization, the motor achieved a very high Hitachi’s first motor (IM) efficiency of approximately 94% in continuous operation tests. Current model (IM) Prototype FUTURE OUTLOOK (PM) The evolution of the electric motor has been underpinned by design, production, and material technologies. In recent years in particular, motor performance has received a major boost from a variety of simulation techniques and other advances such as in materials technology, particularly in the field of permanent magnet motors. Prompted by concerns Fig. 13—Comparison of Original 5-HP Motor, Current about reducing the burden on the environment, it is Production Model, and New Prototype. anticipated that, in addition to the expected further The body of the prototype motor is only one-fifteenth the size of improvements in efficiency, the future will also Hitachi’s original motor. see further research into motor structure aimed at reducing material usage through smaller motor sizes and making available materials that do not include scarce resources(9). With use of electric motors Prototype 5-HP motor and inverters becoming standard practice, it is also designed by anticipated that motors, inverters, and motor control Design will become integrated in both a structural and design Division sense. In terms of control, vector control has entered widespread use starting with 120° commutation control, and it seems likely that control techniques that take account of motor non-linearity caused by magnetic saturation will enter practical use in order to combine controllability with small size and light weight(10). In the field of design technology, meanwhile, it is anticipated that integrated design Fig. 14—Prototype Motor on Show at Hitachi uVALUE methods will be adopted using techniques based on Convention 2010 held in Japan. overall optimization instead of designing the inverter, The prototype motor was included in the 100th Anniversary motor, and control separately as in the past and then Exhibit and was made using a design prepared by Hitachi’s Design Division. having to tune their combined operation.

CONCLUSIONS the volume of current 5-HP induction motors) (see Motors and generators are examples of products Fig. 13). The motor development also drew on the that utilize magnetism in their operation. This article leading-edge materials of the Hitachi Group including has reviewed the historical evolution and future the use of neodymium magnets from Hitachi Metals, outlook for these machines along with the inverter- Ltd. in the rotor, enameled wire from , based control systems used to drive them. Ltd., and organic chemical materials from Hitachi As with the relationship between motors and Chemical Co., Ltd. control and motors and inverters, it is anticipated that An example of the prototype motor produced electric drive will continue to make rapid advances using a design from Hitachi’s Design Division was in the future through the ability to produce designs unveiled to the public at the “Hitachi uVALUE that are even better at balancing reliability, structural Convention 2010” held in July 2010 in Japan where it design, and value by designing motors and inverters was included in an exhibit celebrating the company’s as a single unit. 100th anniversary (see Fig. 14). Hitachi Review Vol. 60 (2011), No. 1 45 REFERENCES (6) Y. Enomoto, “Factor Analysis on Cogging Torques in (1) “Energy Efficiency in Motor Driven Systems 2007 Segment Core Motors,” The Transactions of the Institute Conference Reports,” The Japan Electrical Manufacturers’ of Electrical Engineers of Japan 124-D, No. 1, p. 85 (Jan. Association, Electrical Manufacture 14 (Oct. 2007). 2004). (2) S. Wakui, “3D Magnetic Field Analysis of a Turbine (7) Y. Kawabata, “Study of Control for Position Sensorless and Generator Stator Core-end Region,” The Transactions of Motor Current Sensorless Permanent Magnet Synchronous the Institute of Electrical Engineers of Japan 124-D, No. 1, Motors Drives,” Proceedings of the 2002 Japan Industry pp. 77–84 (2004). Applications Society Conference 1, No. 171 (2002). (3) H. Mikami, “Analysis of Higher Harmonic Components in (8) N. Iwasaki, “Miniaturization Design and Performance Magnetic Fields on Three Phase Squirrel-Cage Induction Evaluation of Prototype Permanent Magnet Synchronous Motors Considering Higher Harmonics in the Secondary Motor Optimally Designed with Thermo-Magnetic Field Current,” The Transactions of the Institute of Electrical Coupling Analysis,” The Papers of Technical Meeting on Engineers of Japan 116-D, 158–116 (Jan. 1996). Rotating Machinery, IEE Japan, RM-10-66 (May 2010). (4) K. Ide, “Analysis of the Harmonics of the Void Magnetic Flux (9) H. Amano, “Examination of Applying Amorphous Rolled Waves of the Synchronous Machine Considering Positive- Core to Permanent Magnet Synchronous Motors,” The phase/negative-phase Separation,” The 1992 National Papers of Technical Meeting on Rotating Machinery, IEE Convention Record I.E.E.Japan, No. 708 (1992). Japan, RM-08-122 (Nov. 2008). (5) K. Siohata, “A Method for Analyzing Electromagnetic-Force- (10) H. Nagura, “New Vector Controller for PM Motors Which Induced Vibration and Noise Analysis,” The Transactions of Modeled the Cross-Coupling Magnetic Flux Saturation,” the Institute of Electrical Engineers of Japan 118-D, No. 11, Proceedings of the 2009 Japan Industry Applications Society p. 1301 (Nov. 1998). Conference, No. 1-151 (2009).

ABOUT THE AUTHORS

Hiroyuki Mikami, Dr. Eng. Kazumasa Ide, Dr. Eng. Joined Hitachi, Ltd. in 1990, and now works at the Joined Hitachi, Ltd. in 1988, and now works at Department of Motor Systems Research, Hitachi the Department of Power Electronics Systems Research Laboratory. He is currently engaged in Research, Hitachi Research Laboratory. He is research and development of motors, generators, currently engaged in research and development of and drive systems. Dr. Mikami is a member of The power electronics equipment including motors. Dr. Institute of Electrical Engineers of Japan and The Ide is a senior member of The Institute of Electrical Institute of Electrical and Electronics Engineers, Inc. Engineers of Japan and IEEE. (IEEE).

Yukiaki Shimizu Masaharu Senoo Joined Hitachi, Ltd. in 1972, and now works at Joined Hitachi, Ltd. in 1975, and now works at the the Motor Power Systems Division. He is currently Motor Power Systems Division. He is currently engaged in a project to strengthen motor and inverter engaged in a project to strengthen motor and inverter development. development. Mr. Senoo is a member of The Institute of Electrical Engineers of Japan.

Hideaki Seki Joined Hitachi, Ltd. in 1979, and now works at the Motor Power Systems Division. He is currently engaged in a project to strengthen motor and inverter development.