Functional Safety Improvement of Permanent Magnet Synchronous Machines in Traction Drives (ATEM FuSy, Improved Functional Safety in Drive Converters)

Task

Due to variable torque setting and quick control behaviour possible in case of individually driven wheels, electric vehicle drives bear large potential to improve vehicle safety by means of novel driving dynamics control concepts. This however makes highest demands on the functional safety of such drive systems: An incorrect setting of torques generates an undesired yawing torque around the vehicle's vertical axis which is difficult for the driver to control.

Permanent magnet synchronous machines often used in current traction applications pose a special challenge: They are normally also operated in the field weakening range in order to obtain constant power output via a wide speed range without the necessity of a manual transmission. In case of an error occurring within this operating range, the voltage induced by the permanent magnets must be reduced to a reliable extent, which according to the state-of-the-art, generates a non-interruptible braking torque in the drive systems, most likely leading to instable driving coditions.

According to the functional safety standard, titled "Road Vehices - Functional Safety"  (ISO 26262) for automotive electric/electronic systems, manufacturers of drive systems and their components are increasingly confronted with the question, whether the safety levels (Automotive Safety Integrity Level ASIL C/D) can be met and which specific measures have to be taken.

Project Aim and Procedure

The overall goal of this joint project is to improve the functional safety of electric drive systems with permanent magnet synchronous machines by using novel concepts for drive monitoring and error treatment in combination with alternative drive topologies. First, the influences of errors and methods for error detection in machines and converters are investigated. Then appropriate approaches and measures to handle errors are developed which also comprise the investigation of fault-tolerant multi-phase drives. Finally, the measures developed are verified by tests on test benches and in the demonstrator vehicle Frecc0 realised at IFAM.

The combination of model-based and sensor-assisted error detection mechanisms with a fault-tolerant drive topology offers for the first time the opportunity to correct errors in the drive system by means of specific countermeasures which depending on the safety demands are able to reduce and compensate the braking torque, thus being able to guarantee for a safe functioning of the electric vehicle.