Auxiliary power supply device and electric power steering system including auxiliary power supply device

摘要

An auxiliary power supply device (40) includes a capacitor (45) that is connected to a main power source (4), and that is able to discharge an electric current to an electric motor (21), the main power source (4) supplying electric power to the electric motor (21); and a booster circuit (43) that boosts a voltage of the main power source (4) and applies the boosted voltage to the auxiliary power source (43). An operation of the auxiliary power supply device (40) is controlled by a control device (30). When supply of the electric power from the main power source (4) to the capacitor (45) is started in a state where a voltage across terminals of the capacitor (45) (capacitor voltage V2) is equal to or higher than a voltage of the main power source (4), the control device (30) increases the voltage (boosted voltage V3) applied to the capacitor (45) by the booster circuit (43) as the capacitor voltage (V2) increases.