This paper presents technical justification for implementing the capability to change automatically the effective number of turns in the stator of propulsion motors while they run, adapting to changes in speed and load of the vehicle. Our simulation studies show significant potential benefits on efficiency and battery size in a typical electrically propelled vehicle when the stator of its IPM motor is modified to be able to switch between its standard and twice the number of turns, as it operates.Along eight different standard driving cycles, the reference vehicle with a motor modified to switch between 9 and 18 stator-turns showed better utilization of the available voltage, lower stator currents, better efficiency in the motor, power electronics, battery, and cabling as well as higher overall vehicle system efficiency, than an identical vehicle with an unmodified motor having 9 fixed stator turns. In addition, the size and cost of the battery with the switching-capable motor can potentially be reduced and the need for voltage boosting to meet the power demand in some of the driving cycles can potentially be eliminated.For a fully electric EV configuration, the vehicle with the reconfigurable turn motor consumed between 4% and 27% less energy and required between 5% and 20% less peak power than the vehicle with the conventional 9-turn motor, depending on the driving cycle.For a hybrid, HEY configuration, the vehicle with the reconfigurable turn motor consumed between 13% and 23% less electrical energy and required between 16% and 39% less electric power than the vehicle with the conventional 9-turn motor, depending on the driving cycle.

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.

Significant research at the Oak Ridge National Laboratory (ORNL) Power Electronics and Electric Machinery Research Center (PEEMRC) is being conducted to develop ways to increase (1) torque, (2) speed range, and (3) efficiency of traction electric motors for hybrid electric vehicles (HEV) within existing current and voltage bounds. Current is limited by the inverter semiconductor devices' capability and voltage is limited by the stator wire insulation's ability to withstand the maximum back-electromotive force (emf), which occurs at the upper end of the speed range. One research track has been to explore ways to control the path and magnitude of magnetic flux while the motor is operating. The phrase, real time flux control (RTFC), refers to this mode of operation in which system parameters are changed while the motor is operating to improve its performance and speed range. RTFC has potential to meet an increased torque demand by introducing additional flux through the main air gap from an external source. It can augment the speed range by diverting flux away from the main air gap to reduce back-emf at high speeds. Conventional RTFC technology is known as vector control [1]. Vector control decomposes the stator current into two components; one that produces torque and a second that opposes (weakens) the magnetic field generated by the rotor, thereby requiring more overall stator current and reducing the efficiency. Efficiency can be improved by selecting a RTFC method that reduces the back-emf without increasing the average current. This favors methods that use pulse currents or very low currents to achieve field weakening. Foremost in ORNL's effort to develop flux control is the work of J. S. Hsu. Early research [2,3] introduced direct control of air-gap flux in permanent magnet (PM) machines and demonstrated it with a flux-controlled generator. The configuration eliminates the problem of demagnetization because it diverts all the flux from the magnets instead of trying to oppose it. It is robust and could be particularly useful for PM generators and electric vehicle drives. Recent efforts have introduced a brushless machine that transfers a magneto-motive force (MMF) generated by a stationary excitation coil to the rotor [4]. Although a conventional PM machine may be field weakened using vector control, the air-gap flux density cannot be effectively enhanced. In Hsu's new machine, the magnetic field generated by the rotor's PM may be augmented by the field from the stationery excitation coil and channeled with flux guides to its desired destination to enhance the air-gap flux that produces torque. The magnetic field can also be weakened by reversing the current in the stationary excitation winding. A patent for advanced technology in this area is pending. Several additional RTFC methods have been discussed in open literature. These include methods of changing the number of poles by magnetizing and demagnetizing the magnets poles with pulses of current corresponding to direct-axis (d-axis) current of vector control [5,6], changing the number of stator coils [7], and controlling the air gap [8]. Test experience has shown that the magnet strengths may vary and weaken naturally as rotor temperature increases suggesting that careful control of the rotor temperature, which is no easy task, could yield another method of RTFC. The purpose of this report is to (1) examine the interaction of rotor and stator flux with regard to RTFC, (2) review and summarize the status of RTFC technology, and (3) compare and evaluate methods for RTFC with respect to maturity, advantages and limitations, deployment difficulty and relative complexity.

The purpose of this report is to document the results of a study designed to enhance the performance of future military generator sets (gen-sets) in the medium power range. The study includes a market survey of the state of the art in several key component areas and recommendations comprising a design philosophy for future military gen-sets. The market survey revealed that the commercial market is in a state of flux, but it is currently or will soon be capable of providing the technologies recommended here in a cost-effective manner. The recommendations, if implemented, should result in future power generation systems that are much more functional than today's gen-sets. The number of differing units necessary (both family sizes and frequency modes) to cover the medium power range would be decreased significantly, while the weight and volume of each unit would decrease, improving the transportability of the power source. Improved fuel economy and overall performance would result from more effective utilization of the prime mover in the generator. The units would allow for more flexibility and control, improved reliability, and more effective power management in the field.

Limited testing provides evidence that a particular energy efficient motor (EEM) appears to have a unique susceptibility to reduced negative sequence impedance. The effect of the reduction in negative sequence impedance is to allow a higher negative sequence current now under conditions of voltage unbalance or negative sequence harmonic distortion in the bus voltage. This higher current flow results in additional heating of the rotor and 120 Hz vibration, and may combine with other conditions to cause premature failure. In addition, energy efficient motors operate at slightly higher speeds, and may sometimes cause the driven loads to require more horsepower from the motor causing further overheating. Existing industry guidance for the application of three phase motors in poor power quality environments may be inadequate because this guidance does not consider the combined effect of such conditions as voltage unbalance, harmonic distortion and over voltage. A specific application of an EEM is studied in this paper; the motor may be failing due to a combination of over voltage, voltage unbalance, harmonic distortion and loading the motor to full rated load, while the motor has a Service Factor of 1.0.

Efficiency evaluation of in-service motors is a challenge to industry. Without a dynamometer or torque cell attached, determining the output power is difficult. The purpose of this CRADA was to develop an on-line motor monitoring device that will determine the condition and performance of a motor without removing the motor from operation.

Unlike testing motor efficiency in a laboratory, certain methods given in the IEEE-Std 112 cannot be used for motor efficiency evaluations 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. This paper separates and compares the 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

The majority of electric motor applications are pumps, fans, blowers, and certain compressors that follow the load torque pattern described in this paper. It has long been known that simply replacing the old motor with a high-efficiency motor might not produce the expected efficiency gain. This paper suggests calculations for the effective efficiency and temperature rise of high-efficiency motors. The reliability in terms of temperature rise, downsizing, power factor, harmonics, mechanical structure, etc., are discussed