Electric Machines and Drives in HEVs

Abstract

Advances in electric machines, along with progress in power electronics, are the key enablers for electric, hybrid electric, and plug-in hybrid electric vehicles (HEVs). Induction machines, permanent magnet (PM) synchronous machines, PM brushless DC machines, and switched reluctance machines (SRMs) have all been considered in various types of vehicle powertrain applications [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. Brushed DC motors, once popular for traction applications such as in streetcars, are no longer considered a proper choice due to the bulky construction, low efficiency, the need for maintenance of the brush and commutator, high electromagnetic interference (EMI), low reliability, and limited speed range.When using electric motors for powertrain applications, there are a few possible configurations. Today's electric motors, combined with inverters and associated controllers, have a wide speed range for constant torque operations, and an extended speed range for constant power operations, which make the design of the powertrain much easier. Depending on the configuration of the hybrid powertrain, the design and selection of electric motor drives can also be different. For example, for series hybrid vehicles, the powertrain motor needs to be able to provide the required torque and speed for all driving conditions. Hence, the size of the motor will be fairly large, usually rated at 100 kW or more for passenger cars. A PM motor or an induction motor is the preferred choice. For mild and micro hybrids, only a small-size motor of a few kilowatts is required. Therefore the motor can be a claw pole DC motor, or a switched reluctance motor.Traditional automatic transmission or continuous variable transmission (CVT) used in conventional cars are no longer required in electric vehicles (EVs) and many HEVs. However, a fixed gear ratio speed reduction is often necessary. This is due to the fact that a high-speed motor has smaller size and less weight than a low-speed machine. A two-speed automatic transmission may be beneficial in saving vehicle energy consumption.Hybrid Electric Vehicles: Principles and Applications with Practical Perspectives, First Edition.