VEHICLE POWER SUPPLY SYSTEM AND CONTROL METHOD OF VEHICLE POWER SUPPLY SYSTEM

A vehicle power supply system includes a power source control device (88) that executes a process of switching a connection state of a driving circuit (61a) to the main power source (45) and an auxiliary power source (81) including; a process of switching the connection state so as to transition to a backup state as a voltage decrease of the main power source (45) occurs, and a process of switching the connection state so as to transition to a normal state as the voltage decrease of the main power source (45) is resolved. After a voltage decrease of the main power source (45) occurs, a turning-side control device (60) of a steering control unit (1) sets an output-limited state for a turning-side motor (32). The output-limited state is canceled upon the power source control device (88) completing switching of the connection state so as to transition.