Control of brushless DC motor with static 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 DC motor (BLDC) is used as force feedback actuator. The determination of the position of the BLDC rotor plays a key role in the control algorithm.To obtain a reliable rotor position a classic triple static redundancy (TMR) is implemented. The position signals from the encoder integrated on the motor are computed in three different ways: using a 8-bit microcontroller, a 16-bit microcontroller, and, last, using the software module integrated in a virtual hardware development tool. The virtual hardware platform operates as voter, too. The position is the output of the voting algorithm and it is sent to the 16-bit platform that controls the motor and provides the correct output PWM signals.The communication between virtual hardware and real hardware uses CAN bus. The bus is monitored by a dedicated development tool. Steer-by-wire is a safety critical application and therefore requires time-triggered protocols. In this preliminary architecture a dedicated network has been implemented and therefore the disadvantages of the event-triggered protocol are considerably reduced.Experiments at different baudrates confirm that the voting algorithm produces correct results also in case of failure in one of the modules of the TMR architecture and it is not conditioned by bus loads. This means that the torque control algorithm of the BLDC motor can generate on the steering wheel (directly connected to the motor) a drive feeling like the one produced by a traditional steering system also in this fail-mode.