Maximum Efficiency Control Strategy of PM Traction Machine Drives in GM Hybrid and Electric Vehicles

This work investigates maximum efficiency control strategies of permanent magnet (PM) traction machine drives that are adopted in General Motors (GM) hybrid and electric vehicles. First, three different current vector control techniques, Maximum Torque Per Ampere (MTPA), Maximum Torque Per Motor Loss (MTPML), and Maximum Torque Per System Loss (MTPSL), are presented to identify the most attractive control strategy for a PM traction machine drive that is being used in a production vehicle. This comparison will show the drive system efficiency and the current vector trajectory for the three different control strategies, providing valuable experimental data to help researchers optimize the operating point efficiency. In addition, a six-step mode of inverter control is evaluated to enhance the drive efficiency and performance under the dc bus voltage constraint in the flux weakening region. Extensive experimental tests on the PM traction machine drive have been performed, aiming to evaluate and identify the most attractive control strategy that can maximize the drive efficiency. The test results presented in this paper confirm that the maximum efficiency operation of the experimental machine drive was achieved by a combination of MTPL control and six-step mode operation. In order to fully comprehend the optimal system efficiency, results of a broader investigation of the drive system losses such as the experimental system loss breakdown and the modeling of inverter losses are also included.