State estimation of a novel brake-by-wire system based on cascade observer

Pressure regulation is the primary function of the brake-by-wire (BBW) system, and its prerequisite is the precise pressure acquisition. In autonomous vehicles(AVs), a higher fail-safe level is required that a backup pressure source is available when the main pressure source fails. So the use of pressure sensors, like the existing method, for pressure regulation will increase the cost of BBW systems in AVs. To meet the requirement of brake redundancy and the cost limit, a novel BBW system with a redundant pressure supply unit is designed and its electro-mechanical-hydraulic model is analyzed in this research. A time-domain observer (TDO) of motor speed is designed based on the periodic characteristics of motor current to get more system information. Next, the robust observer of pressure is proposed based on the existing current sensor and the derived motor speed. Its computational burden is reduced by calculating the matrices offline. The estimator developed in this paper is verified in typical pressure regulation conditions. Experimental results show that the estimation error of the motor speed is within 3% and has the potential to be improved, and the error of pressure is within 0.1 MPa, and the observer exhibits enough robustness under different initial condition perturbations.