Constantin C. Stancu

Design and Performance of Electrical Propulsion System of Extended Range Electric Vehicle (EREV) Chevrolet Volt

This paper presents the design and performance details of the Chevrolet Volt electric propulsion system. The propulsion system has two machines: One machine is operating mostly as a motor while the other machine is operating mostly as a generator. Both machines of the Volt electric drive system are permanent-magnet ac synchronous machine types with the magnets buried inside the rotor. The motor has distributed windings. However, as opposed to a conventional stranded winding, the Chevrolet Volt motor has bar-wound construction to improve the motor performance, particularly in the low to medium speed range. At higher speed, the skin and proximity effects in the stator bars lead to increased stator winding losses but are addressed in the design. The bar-wound construction also has excellent thermal performance, in both the steady-state and transient conditions, necessary for full electric vehicle (EV) driving. The generator uses concentrated windings. The concentrated winding construction has good slot fill and short end-turn length. These features resulted in good performance in the intended operational region and were an enabler for machine packaging inside the transmission. Both the machines exhibit excellent efficiency and exceptionally smooth and quiet operation. The machine design and construction details, as well as the measured thermal, electromagnetic, and acoustic noise performances, are presented in this paper.

Separately excited synchronous motor with rotary transformer for hybrid vehicle application

The cost of rare earth (RE) permanent magnet along with the associated supply volatility have intensified the interests for machine topologies which eliminate or reduce the RE magnets usage. This paper presents one such design solution, the separately excited synchronous motor (SESM) which eliminates RE magnets, however, but does not sacrifice the peak torque and power of the motor. The major drawback of such motors is the necessity of brushes to supply the field current. This is especially a challenge for hybrid or electric vehicle applications where the machine is actively cooled with oil inside the transmission. Sealing the brushes from the oil is challenging and would limit the application of such motor inside a transmission. To overcome this problem, a contactless rotary transformer is designed and implemented for the rotor field excitation. The designed motor is built and tested. The test data show that the designed motor outperforms an equivalent interior permanent magnet (IPM) motor, which is optimized for a hybrid application, for both peak torque and power. Better drive system efficiency is measured at high speed compared to the IPM machine, while the later outperforms (for efficiency) the SESM at low and medium speed range.

Design and performance of electrical propulsion system of extended range electric vehicle (EREV) Chevrolet Voltec

This paper presents the design and performance details of the Chevrolet Voltec electric propulsion system. The propulsion system has two machines, one machine is operating mostly as a motor while the other machine is operating mostly as a generator. Both machines of the Voltec electric drive system are permanent magnet AC synchronous machine types with the magnets buried inside the rotor. The motor has distributed windings. However, as opposed to a conventional stranded winding the Chevrolet Volt motor has bar-wound construction to improve the motor performance, especially in the low to medium speed range. At higher speed the skin and proximity effects in the stator bars lead to increased stator winding losses but are addressed in the design. The bar-wound construction also has excellent thermal performance, in both the steady-state and the transient conditions, necessary for full EV driving. The generator uses concentrated windings. The concentrated winding construction has good slot fill and short end-turn length. These features resulted in good performance in the intended operational region and were an enabler for machine packaging inside the transmission. Both the machines exhibit excellent efficiency and exceptionally smooth and quiet operation. Machine design and construction details as well as the measured thermal, electromagnetic and acoustic noise performances are presented in the paper.

Maximum torque-per-ampere control of a saturated surface-mounted permanent magnet motor

The surface-mounted permanent magnet (SMPM) synchronous motor has high torque density and good dynamic response. Consequently, these machines have found applications in electric/hybrid vehicles, where size and volume are at a premium and dynamic response is important for vehicle performance. In these applications, high torque output from the motor is required for short time duration. The high stator current associated with this mode of operation can induce saturation in portions of the motor magnetic circuit and thus introduce saliency into a normally symmetric machine. This phenomenon can be exploited in order to maximize the torque output of the motor for the same stator current. The case of a 75 kW SMPM machine for automotive application is presented. By taking advantage of the saturation induced reluctance torque, up to 4% extra torque output is produced for the same maximum stator current. The improved performance is predicted using FEM calculations and is verified through experimental results.

Control strategies for a high frequency DC-DC converter for electrified vehicles

In this paper, three control strategies for a wide band-gap bidirectional DC-DC converter (BDC) are introduced and combined to improve the vehicle traction system performance. A feed-forward control algorithm is proposed to reduce the voltage ripple of DC-link capacitor located between the BDC and traction inverter. Through voltage control of the BDC, both three-phase short and uncontrolled generator operation may be avoided for an improved fault tolerant response of the interior permanent magnet (IPM) motor drive system. With coordinated control of the converter output voltage, the traction system efficiency can be improved, when compared with constant DC bus voltage operation. The proposed control algorithms are validated through simulation and experiment.