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Emerging Two-Phase Cooling Technologies for Power Electronic Inverters

Description: In order to meet the Department of Energy's (DOE's) FreedomCAR and Vehicle Technologies (FVCT) goals for volume, weight, efficiency, reliability, and cost, the cooling of the power electronic devices, traction motors, and generators is critical. Currently the power electronic devices, traction motors, and generators in a hybrid electric vehicle (HEV) are primarily cooled by water-ethylene glycol (WEG) mixture. The cooling fluid operates as a single-phase coolant as the liquid phase of the WEG does not change to its vapor phase during the cooling process. In these single-phase systems, two cooling loops of WEG produce a low temperature (around 70 C) cooling loop for the power electronics and motor/generator, and higher temperature loop (around 105 C) for the internal combustion engine. There is another coolant option currently available in automobiles. It is possible to use the transmission oil as a coolant. The oil temperature exists at approximately 85 C which can be utilized to cool the power electronic and electrical devices. Because heat flux is proportional to the temperature difference between the device's hot surface and the coolant, a device that can tolerate higher temperatures enables the device to be smaller while dissipating the same amount of heat. Presently, new silicon carbide (SiC) devices and high temperature direct current (dc)-link capacitors, such as Teflon capacitors, are available but at significantly higher costs. Higher junction temperature (175 C) silicon (Si) dies are gradually emerging in the market, which will eventually help to lower hardware costs for cooling. The development of high-temperature devices is not the only way to reduce device size. Two-phase cooling that utilizes the vaporization of the liquid to dissipate heat is expected to be a very effective cooling method. Among two-phase cooling methods, different technologies such as spray, jet impingement, pool boiling and submersion, etc. are being developed. The ...
Date: August 17, 2005
Creator: Hsu, J.S.
Partner: UNT Libraries Government Documents Department

Report on Toyota/Prius Motor Design and Manufacturing Assessment

Description: In today's hybrid vehicle market the Toyota Prius drive system is currently considered the leader in electrical, mechanical, and manufacturing innovations. It is significant that in today's marketplace Toyota is able to manufacture and sell the vehicle for a profit. This project's objective is to analyze and study the Prius drive system to understand the design and manufacturing mechanisms Toyota utilized to achieved their performance and cost goals. During the course of this research effort ORNL has dissected both the 2003 and 2004 Toyota/Prius drive motors. This study is focused primarily on motor design considerations and an assessment of manufacturing issues.
Date: July 28, 2004
Creator: Hsu, J.S.
Partner: UNT Libraries Government Documents Department

Report on Toyota Prius Motor Thermal Management

Description: In the current hybrid vehicle market, the Toyota Prius drive system is considered the leader in electrical, mechanical, and manufacturing innovations. It is a significant accomplishment that Toyota is able to manufacture and sell the vehicle for a profit. The Toyota Prius traction motor design approach for reducing manufacturing costs and the motor s torque capability have been studied and tested. The findings were presented in two previous Oak Ridge National Laboratory (ORNL) reports. The conclusions from this report reveal, through temperature rise tests, that the 2004 Toyota Prius (THSII) motor is applicable only for use in a hybrid automobile. It would be significantly undersized if used in a fuel cell vehicle application. The power rating of the Prius motor is limited by the permissible temperature rise of the motor winding (170 C) and the motor cooling oil (158 C). The continuous ratings at base speed (1200 rpm) with different coolant temperatures are projected from test data at 900 rpm. They are approximately 15 kW with 105 C coolant and 21 kW with 35 C coolant. These continuous ratings are much lower than the 30 kW specified as a technical motor target of the U.S. Department of Energy FreedomCAR Program. All tests were conducted at about 24 C ambient temperature. The load angle of each torque adjustment was monitored to prevent a sudden stop of the motor if the peak torque were exceeded, as indicated by the load angle in the region greater than 90 electrical degrees. For peak power with 400 Nm torque at 1200 rpm, the permissible running time depends upon the initial winding temperature condition. The projected rate of winding temperature rise is approximately 2.1 C/sec. The cooling-oil temperature does not change much during short peak power operation. For light and medium load situations, the efficiency varies ...
Date: February 11, 2005
Creator: Hsu, J.S.
Partner: UNT Libraries Government Documents Department

Report on Toyota/Prius Motor Torque-Capability, Torque-Property, No-Load Back EMF, and Mechanical Losses

Description: In today's hybrid vehicle market, the Toyota Prius drive system is currently considered the leader in electrical, mechanical, and manufacturing innovations. It is significant that in today's marketplace, Toyota is able to manufacture and sell the vehicle for a profit. This project's objective is to test the torque capability of the 2004 Prius motor and to analyze the torque properties relating to the rotor structure. The tested values of no-load back electromotive force (emf) and mechanical losses are also presented.
Date: September 30, 2004
Creator: Hsu, J.S.
Partner: UNT Libraries Government Documents Department

Corona and Motor Voltage Interim Report

Description: It has been suggested that to meet the FreedomCAR objectives for cost, size, weight, efficiency, and reliability higher buss voltages be utilized in HEV and FC automotive applications. The reasoning is that since electric power is equal to the product of voltage and current for a given power a higher voltage and lower current would result in smaller cable and inverter switching components. Consequently, the system can be lighter and smaller. On the other hand, higher voltages are known to require better and thicker electrical insulation that reduce the available slot area for motor windings. One cause of slow insulation breakdown is corona that gradually erodes the insulation and shortens the life expectancy of the motor. This study reports on the results of a study on corona initiating voltages for mush-wound and bobbin-wound stators. A unique testing method is illustrated.
Date: May 6, 2005
Creator: Hsu, J.S.
Partner: UNT Libraries Government Documents Department

Supply-pollution (SP) loss in induction motor

Description: Power supply in the field is often noticeably polluted with various degrees of harmonics content and unbalanced voltages. In order to assess the energy loss caused by the supply pollution in the widely used induction motors, a method based on the air-gap torque power is discussed.
Date: July 1, 1995
Creator: Hsu, J.S.
Partner: UNT Libraries Government Documents Department

Instantaneous phasor method for obtaining instantaneous balanced fundamental components for power quality control and continuous diagnostics

Description: This paper introduces an instantaneous phasor method that considers three phases simultaneously. This method produces the instantaneous fundamental balanced components of the polluted voltages or currents. A figure shows three-phase voltages that contain 5% of fundamental magnitude for each order of the 3rd, 5th, 7th, 9th and the 11th harmonics, respectively. Additionally, the voltages have 5% unbalance for all voltage components. A 10% fundamental-frequency zero-sequence component, as well as a 10% fundamental-frequency negative-sequence component are also added to the phase voltages. Furthermore, certain high-frequency pulses arbitrarily given at 5% of a 35th order to represent a possible carrier frequency of power electronic circuits are also included.
Date: July 1, 1997
Creator: Hsu, J.S.
Partner: UNT Libraries Government Documents Department

A New Manufacturing Technology for Induction Machine Copper Rotors

Description: The benefits of energy and operational cost savings from using copper rotors are well recognized. The main barrier to die casting copper rotors is short mold life. This paper introduces a new approach for manufacturing copper-bar rotors. Either copper, aluminum, or their alloys can be used for the end rings. Both solid-core and laminated-core rotors were built. High quality joints of aluminum to copper were produced and evaluated. This technology can also be used for manufacturing aluminum bar rotors with aluminum end rings. Further development is needed to study the life time reliability of the joint, to optimize manufacturing fixtures, and to conduct large-rotor tests.
Date: September 4, 2001
Creator: Hsu, J.S.
Partner: UNT Libraries Government Documents Department

Field assessment of induction motor efficiency through air-gap torque

Description: Induction motors are the most popular motors used in industry. This paper further suggests the use of air-gap torque method to evaluate their efficiency and load changes. The fundamental difference between Method E and the air-gap torque method is discussed. Efficiency assessments conducted on induction motors under various conditions show the accuracy and potential of the air-gap torque method.
Date: November 1, 1995
Creator: Hsu, J.S. & Sorenson, P.L.
Partner: UNT Libraries Government Documents Department

Instantaneous reactive power and power factor of instantaneous phasors

Description: The unique property of instantaneous phasors is that at any instant the instantaneous three phase currents and voltages can be represented by a set of balanced phasors. The instantaneous reactive power and the concept of instantaneous power factor can be clearly understood from the instantaneous phasors. This provides a theoretical foundation for power quality monitoring, diagnostics, and compensation methods.
Date: February 1, 1998
Creator: Hsu, J.S.
Partner: UNT Libraries Government Documents Department

Active power components of instantaneous phasors

Description: The instantaneous phasor method originated by the author to solve power quality and efficiency of three-phase systems with unbalanced and distorted voltages and currents has a unique symmetrical property. The phasors of one phase can be used to represent three phases. The power quality of a three-phase system can be indicated by the roundness of the trajectories of the voltage and current phasors. The fundamental-frequency, positive-sequence components of the immediate past cycle can be obtained to guide the compensation of the present values. This approach for power quality improvement is different from the recent development of the instantaneous reactive power. The active power components of instantaneous phasors are studied in this paper.
Date: August 1, 1998
Creator: Hsu, J.S.
Partner: UNT Libraries Government Documents Department

Instantaneous phasor method under severely unbalanced situations

Description: The new instantaneous phasor method originated by the author for obtaining instantaneous balanced fundamental components is further studied under severely unbalanced situations. Selection of the initial and synchronization phasors becomes important. An example is presented. This technique may substitute for the fast Fourier transformation (FFT) plus symmetrical component method for active power quality control and for continuous diagnostics. The influence of high magnitudes of harmonics will be discussed in a separate paper.
Date: December 1, 1997
Creator: Hsu, J.S.
Partner: UNT Libraries Government Documents Department

Induction-motor field efficiency evaluation using instantaneous phasor method

Description: Induction motors are the most commonly used motors in industry. They are important components in the chains of drive systems. Motor efficiency is the ratio of shaft output power to motor input power. IEEE Std 112 presents many methods for induction-motor efficiency tests that may not all be suitable for field efficiency evaluations. The new instantaneous phasor method originated by the author is applied for the evaluation of efficiency of induction motors installed in the field.
Date: August 1, 1998
Creator: Hsu, J.S.
Partner: UNT Libraries Government Documents Department

Barriers to the Application of High-Temperature Coolants in Hybrid Electric Vehicles

Description: This study was performed by the Oak Ridge National Laboratory (ORNL) to identify practical approaches, technical barriers, and cost impacts to achieving high-temperature coolant operation for certain traction drive subassemblies and components of hybrid electric vehicles (HEV). HEVs are unique in their need for the cooling of certain dedicated-traction drive subassemblies/components that include the electric motor(s), generators(s), inverter, dc converter (where applicable), and dc-link capacitors. The new coolant system under study would abandon the dedicated 65 C coolant loop, such as used in the Prius, and instead rely on the 105 C engine cooling loop. This assessment is important because automotive manufacturers are interested in utilizing the existing water/glycol engine cooling loop to cool the HEV subassemblies in order to eliminate an additional coolant loop with its associated reliability, space, and cost requirements. In addition, the cooling of power electronic devices, traction motors, and generators is critical in meeting the U.S. Department of Energy (DOE) FreedomCAR and Vehicle Technology (FCVT) goals for power rating, volume, weight, efficiency, reliability, and cost. All of these have been addressed in this study. Because there is high interest by the original equipment manufacturers (OEMs) in reducing manufacturing cost to enhance their competitive standing, the approach taken in this analysis was designed to be a positive 'can-do' approach that would be most successful in demonstrating the potential or opportunity of relying entirely on a high-temperature coolant system. Nevertheless, it proved to be clearly evident that a few formidable technical and cost barriers exist and no effective approach for mitigating the barriers was evident in the near term. Based on comprehensive thermal tests of the Prius reported by ORNL in 2005 [1], the continuous ratings at base speed (1200 rpm) with different coolant temperatures were projected from test data at 900 rpm. They are approximately 15 ...
Date: September 30, 2006
Creator: Hsu, J.S.; Staunton, M.R. & Starke, M.R.
Partner: UNT Libraries Government Documents Department

Power electronics and electric machinery challenges and opportunities in electric and hybrid vehicles

Description: The development of power electronics and electric machinery presents significant challenges to the advancement of electric and hybrid vehicles. Electronic components and systems development for vehicle applications have progressed from the replacement of mechanical systems to the availability of features that can only be realized through interacting electronic controls and devices. Near-term applications of power electronics in vehicles will enable integrated powertrain controls, integrated chassis system controls, and navigation and communications systems. Future applications of optimized electric machinery will enable highly efficient and lightweight systems. This paper will explore the areas where research and development is required to ensure the continued development of power electronics and electric machines to meet the rigorous demands of automotive applications. Additionally, recent advances in automotive related power electronics and electric machinery at Oak Ridge National Laboratory will be explained. 3 refs., 5 figs.
Date: June 1, 1997
Creator: Adams, D.J.; Hsu, J.S.; Young, R.W. & Peng, F.Z.
Partner: UNT Libraries Government Documents Department

Instantaneous power factor determined by instantaneous phasors

Description: The instantaneous power factor can be clearly understood from the instantaneous phasors. The unique property of instantaneous phasors is that at any instant the instantaneous three-phase currents and voltages can be represented by a set of balanced phasors. The instantaneous power factor resembles the familiar format of power factor derived from the conventional phasors. This new concept can be used for power quality monitoring, diagnostics, and compensations.
Date: March 1998
Creator: Hsu, J. S.
Partner: UNT Libraries Government Documents Department

A Machine Approach for Field Weakening of Permanent-Magnet Motors

Description: The commonly known technology of field weakening for permanent-magnet (PM) motors is achieved by controlling the direct-axis current component through an inverter, without using mechanical variation of the air gap, a new machine approach for field weakening of PM machines by direct control of air-gap fluxes is introduced. The demagnetization situation due to field weakening is not an issue with this new method. In fact, the PMs are strengthened at field weakening. The field-weakening ratio can reach 1O:1 or higher. This technology is particularly useful for the PM generators and electric vehicle drives.
Date: April 2, 2000
Creator: Hsu, J.S.
Partner: UNT Libraries Government Documents Department

Study of the Advantages of Internal Permanent Magnet Drive Motor with Selectable Windings for Hybrid-Electric Vehicles

Description: This report describes research performed on the viability of changing the effectively active number of turns in the stator windings of an internal permanent magnet (IPM) electric motor to strengthen or weaken the magnetic fields in order to optimize the motor's performance at specific operating speeds and loads. Analytical and simulation studies have been complemented with research on switching mechanisms to accomplish the task. The simulation studies conducted examine the power and energy demands on a vehicle following a series of standard driving cycles and the impact on the efficiency and battery size of an electrically propelled vehicle when it uses an IPM motor with turn-switching capabilities. Both full driving cycle electric propulsion and propulsion limited starting from zero to a set speed have been investigated.
Date: November 30, 2007
Creator: Otaduy, P.J.; Hsu, J.S. & Adams, D.J.
Partner: UNT Libraries Government Documents Department

Report on the feasibility study for improving electric motor service centers in Ghana

Description: On March 3 and 4, 1998, a visit was made to Oak Ridge National Laboratory (ORNL) by two officials from Ghana: Mr. I.K. Mintah, Acting Executive Director, Technical Wing, Ministry of Mines and Energy (MOME) and Dr. A.K. Ofosu-Ahenkorah, Coordinator, Energy Efficiency and Conservation Program, MOME. As a result of this visit, Dr. John S. Hsu of ORNL was invited by MOME to visit the Republic of Ghana in order to study the feasibility of improving electric motor service centers in Ghana.
Date: December 10, 1999
Creator: Hsu, J.S.; Jallouk, P.A. & Staunton, R.H.
Partner: UNT Libraries Government Documents Department

Comparison of induction motor field efficiency evaluation methods

Description: Unlike testing motor efficiency in a laboratory, certain methods given in the IEEE-Std 112 cannot be used for motor efficiency in the field. For example, it is difficult to load a motor in the field with a dynamometer when the motor is already coupled to driven equipment. The motor efficiency field evaluation faces a different environment from that for which the IEEE-Std 112 is chiefly written. A field evaluation method consists of one or several basic methods according to their physical natures. Their intrusivenesses and accuracies are also discussed. This study is useful for field engineers to select or to establish a proper efficiency evaluation method by understanding the theories and error sources of the methods.
Date: October 1, 1996
Creator: Hsu, J.S.; Kueck, J.D.; Olszewski, M.; Casada, D.A.; Otaduy, P.J. & Tolbert, L.M.
Partner: UNT Libraries Government Documents Department

Nature and measurements of torque ripple of permanent-magnet adjustable-speed motors

Description: Torque ripple of permanent-magnet motors can be classified into four types depending on the nature of their origin. The four types are pulsating torque, fluctuating torque, reluctance cogging torque, and inertia and mechanical system torque. Pulsating torques are inherently produced by the trapezoidal back-emf`s and trapezoidal currents used in certain permanent-magnet adjustable-speed motors. The torque ripples caused by pulsating torques may be reduced by purposely produced fluctuating counter torques. Air-gap torque measurements are conducted on a sample motor. Experimental results agree with theoretical expectations.
Date: August 1, 1995
Creator: Hsu, J.S.; Scoggins, B.P.; Scudiere, M.B.; Marlino, L.D.; Adams, D.J. & Pillay, P.
Partner: UNT Libraries Government Documents Department

Evaluation of 2004 Toyota Prius Hybrid Electic Drive System Interim Report - Revised

Description: The 2004 Toyota Prius is a hybrid automobile equipped with a gasoline engine and a battery-powered electric motor. Both of these motive power sources are capable of providing mechanical drive power for the vehicle. The engine can deliver a peak power output of 57 kilowatts (kW) at 5000 revolutions per minute (rpm) while the motor can deliver a peak power output of 50 kW at 1300 rpm. Together, this engine-motor combination has a specified peak power output of 82 kW at a vehicle speed of 85 kilometers per hour (km/h). In operation, the 2004 Prius exhibits superior fuel economy compared to conventionally powered automobiles. Laboratory tests were conducted to evaluate the electrical and mechanical performance of the 2004 Toyota Prius and its hybrid electric drive system. As a hybrid vehicle, the 2004 Prius uses both a gasoline-powered internal combustion engine and a battery-powered electric motor as motive power sources. Innovative algorithms for combining these two power sources results in improved fuel efficiency and reduced emissions compared to traditional automobiles. Initial objectives of the laboratory tests were to measure motor and generator back-electromotive force (emf) voltages and determine gearbox-related power losses over a specified range of shaft speeds and lubricating oil temperatures. Follow-on work will involve additional performance testing of the motor, generator, and inverter. Information contained in this interim report summarizes the test results obtained to date, describes preliminary conclusions and findings, and identifies additional areas for further study.
Date: July 31, 2007
Creator: Ayers, C.W.; Hsu, J.S.; Marlino, L.D.; Miller, C.W.; Ott, G.W., Jr.; Oland, C.B. et al.
Partner: UNT Libraries Government Documents Department

Report on Toyota/Prius Motor Torque Capability, Torque Property, No-Load Back EMF, and Mechanical Losses, Revised May 2007

Description: In today's hybrid vehicle market, the Toyota/Prius drive system is currently considered the leader in electrical, mechanical, and manufacturing innovations. It is significant that in today's marketplace, Toyota is able to manufacture and sell the vehicle for a profit. This project's objective is to test the torque capability of the 2004 Prius motor and to analyze the torque properties relating to the rotor structure. The tested values of no-load back electromotive force (emf) and mechanical losses are also presented.
Date: May 31, 2007
Creator: Hsu, J.S.; Ayers, C.W.; Coomer, C.L.; Wiles, R.H.; Burress, T.A.; Campbell, S.L. et al.
Partner: UNT Libraries Government Documents Department

16,000-rpm Interior Permanent Magnet Reluctance Machine with Brushless Field Excitation

Description: The reluctance interior permanent magnet (RIPM) motor is currently used by many leading auto manufacturers for hybrid vehicles. The power density for this type of motor is high compared with that of induction motors and switched reluctance motors. The primary drawback of the RIPM motor is the permanent magnet (PM) because during high-speed operation, the fixed PM produces a huge back electromotive force (emf) that must be reduced before the current will pass through the stator windings. This reduction in back-emf is accomplished with a significant direct-axis (d-axis) demagnetization current, which opposes the PM's flux to reduce the flux seen by the stator wires. This may lower the power factor and efficiency of the motor and raise the requirement on the alternate current (ac) power supply; consequently, bigger inverter switching components, thicker motor winding conductors, and heavier cables are required. The direct current (dc) link capacitor is also affected when it must accommodate heavier harmonic currents. It is commonly agreed that, for synchronous machines, the power factor can be optimized by varying the field excitation to minimize the current. The field produced by the PM is fixed and cannot be adjusted. What can be adjusted is reactive current to the d-axis of the stator winding, which consumes reactive power but does not always help to improve the power factor. The objective of this project is to avoid the primary drawbacks of the RIPM motor by introducing brushless field excitation (BFE). This offers both high torque per ampere (A) per core length at low speed by using flux, which is enhanced by increasing current to a fixed excitation coil, and flux, which is weakened at high speed by reducing current to the excitation coil. If field weakening is used, the dc/dc boost converter used in a conventional RIPM motor may be ...
Date: October 31, 2007
Creator: Hsu, J. S.; Burress, T. A.; Lee, S. T.; Wiles, R. H.; Coomer, C. L.; McKeever, J.W. et al.
Partner: UNT Libraries Government Documents Department