ELECTRICAL POWER SYSTEM

To provide an electric power system that enables a DCDC converter (DDC) to operate with a predetermined output voltage even when an output voltage indication does not reach the DDC from a host ECU any more.SOLUTION: An electrical power system comprises: a DDC which converts the voltage of a high-voltage battery into a predetermined voltage and outputs it to a low-voltage battery and a low-voltage load; a relay which changes connection states between the high-voltage battery and DDC; and a control unit which is provided to the DDC, and controls the output voltage of the DDC based upon a state of an IG signal and an indication of the host ECU. The control unit is configured to: actuate the DDC based upon transition from an OFF state to an ON state of the IG signal; output a first low voltage from the DDC when the high-voltage battery is connected to the DDC by the relay after the actuation; output an indicated voltage from the DDC when there is an indication for the output voltage from the host ECU after the first low voltage is output; and output a fixed voltage higher than the first low voltage from the DDC when there is not any indication for an output voltage from the host ECU for a first time after the first low voltage is output.SELECTED DRAWING: Figure 1 【課題】ＤＣＤＣコンバーター（ＤＤＣ）に上位ＥＣＵから出力電圧指示が来なくなった場合でも、ＤＤＣを所定の出力電圧にて動作できる電源システムを提供する。【解決手段】高圧バッテリーの電圧を所定の電圧に変換して低圧バッテリー及び低圧負荷へ出力するＤＤＣと、高圧バッテリーとＤＤＣとの接続状態を切り替えるリレーと、ＤＤＣに設けられ、ＩＧ信号の状態及び上位ＥＣＵの指示に基づいてＤＤＣの出力電圧を制御する制御部とを備え、制御部は、ＩＧ信号のオフからオンへの状態遷移に基づいてＤＤＣを起動し、起動後リレーによって高圧バッテリーがＤＤＣに接続されるとＤＤＣから第１低電圧を出力し、第１低電圧を出力した後上位ＥＣＵから出力電圧の指示があれば、ＤＤＣから指示された電圧を出力し、第１低電圧を出力した後第１時間を経過するまでに上位ＥＣＵから出力電圧の指示が無ければ、ＤＤＣから第１低電圧よりも高い固定電圧を出力する。【選択図】図１