Using Field-Oriented Control for Electric Drives in Vehicles

May 29, 2014 // By Michael Seidl, Texas Instruments
Field-oriented control (FOC) differs from ordinary control approaches for electric motors by providing precise control capabilities based on torque and speed. These features are also relevant for electric motors used in motor vehicles, electric vehicles and e-bikes. Conventional FOC solutions need a position sensor, which results in additional costs and limited options for designers. However, there are alternatives.

Texas Instruments' InstaSPIN-FOC solution, combined with the company's FAST software sensor algorithm, is an ideal solution for this dilemma. Enabling a straightforward entry into the world of sensor less field-oriented control, it can be used for robust, highly reliable and energy-efficient motor designs in the e-mobility segment.

Electric motors are indispensable parts of today’s vehicles. A medium-class car currently has an average of ten pumps and compressors and around 40 electric motors in total. Depending on equipment specifications, this number can rise to more than 100 in premium-class cars. Apart from water and fuel pumps, electric drives are used for adaptive suspension controls, blowers, compressors, power steering, windshield wipers and window lifts.

Approximately 40 electric motors can be found in medium-class cars, including drives for pumps, compressors and power steering. Premium-class cars frequently include more than 100.

The e-mobility sector is another promising application for electric drives. This field includes hybrid vehicles powered by a conventional combustion engine in addition to the electric drive as well as purely electric vehicles. Current examples of electric passenger cars include the BMW i3, the VW E-up and the Opel Ampera. In the commercial segment, electric motors can be used for electric busses operated by local transport authorities.

Requirements for Electric Motors Used in Vehicles

Electric motors used in vehicles must provide the following features:

  • High efficiency
  • Small size and low weight
  • High robustness
  • Reliable operation and low maintenance requirements
  • Minimum noise
  • Low manufacturing costs

These requirements apply to traction motors in vehicles (e. g. wheel hub motors) as well as motors driving pumps, ventilators, window lifts or power steering.

FOC Increases the Efficiency of Electric Motors

FOC is an established method to increase the efficiency of any electric motor, including traction motors, as well as the auxiliary drives required in an electric car. The FOC approach offers several advantages:

  • Motors can be operated at their optimum torque and speed at any time
  • FOC
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