Control of brushless motor with hybrid redundancy for force feedback in steer-by-wire applications

In this paper we propose a hardware-in-the-loop (HIL) approach to implement a preliminary architecture for force-feedback control in steer-by-wire (SBW) applications. A brushless motor is used as force feedback actuator. The determination of the position of the rotor plays a key role in the control algorithm. To obtain a reliable rotor position a hybrid redundancy has been implemented. The position signals of the encoder integrated on the motor are computed in three different ways: using a 8-bit microcontroller, a 16-bit microcontroller, and, last, using a FPGA. A virtual hardware platform operates as voter. The position estimated by the voter is used by the 16-bit platform to generate the PWM signals needed to control the motor. The voter executes a simple self diagnostic process, too and in case of failure in more than one module performs a reconfigurations of the system and the position estimated by a fourth back-up module is used by the 16-bit microcontroller to implement the motor control algorithm. In particular, the results of hardware-in-the-loop experiments show as using a redundant architecture like the one proposed in this paper, it is possible to control the motor in order to recreate on a steering wheel (directly connected to the motor) a drive feeling like the one produced by a traditional steering system also in case of failure in one, or more than one module, of the system.