Energy management techniques for regenerative active shock absorbers

During any travel, vehicles present movements along their vertical axes due to road roughness, curved trajectory, braking, acceleration and inertial forces. The ordinary task of shock absorbers is to absorb the vertical oscillations, providing comfort to the driver, always maintaining the vehicle stability. In particular, the active ones offer the possibility to change the damping coefficient and the chassis lifting. The present study analyses regenerative hydraulic active shock absorbers, i.e. active shock absorbers able to recover the vibrational energy into electrical one and focuses on the design of a device able to route the recovered energy from the four corners shock absorbers into a battery. Exploiting the reversibility of brushless machines used for the lifting operation in active mode, the suspension movement generates a current, mostly characterized by a frequency component equal to the switching frequency of the brushless machine. This type of current is not suitable for battery charging. Starting from the constraints relative to the battery, and the analysis of the power flow, a DC/DC buck converter (whose output is represented by the port connected to the battery) has been identified as a solution. In order to design a proper current control, the converter has been modelled according to the state space average method. Combing this feedback control with a feedforward one on the converter input voltage, the device is able to smooth enough the current in input to the battery and provide to upper limits the voltages, according to the automotive standard and the battery needs. All simulations have been performed in Simulink environment and a simplified model has been implemented by the usage of a multipurpose power module.