In-vehicle power supply system to detect failure for a bi-directional DC-DC converter's conversion circuit

An in-vehicle power supply system comprising:

• a high-voltage direct-current (DC) power supply;
• a low-voltage storage battery;
• a DC-DC converter including
• an input switch including one terminal and another terminal, the one terminal of the input switch being connected to the high-voltage DC power supply, the input switch being configured to selectively switch between a connected state in which the one terminal of the input switch is connected to the another terminal of the input switch and a disconnected state in which the one terminal of the input switch is disconnected from the another terminal of the input switch,
• a conversion circuit including a high-voltage terminal and a low-voltage terminal, the high-voltage terminal of the conversion circuit being connected to the another terminal of the input switch, the conversion circuit being configured to perform a bidirectional operation of performing a boosting-up operation of obtaining a voltage of the high-voltage terminal by boosting up a voltage of the low-voltage terminal and a stepping-down operation of obtaining a voltage of the low-voltage terminal by stepping down a voltage of the high-voltage terminal, and
• an output switch including one terminal and another terminal, the one terminal of the output switch being connected to the low-voltage terminal of the conversion circuit, the another terminal of the output switch being connected to the low-voltage storage battery, the output switch being configured to selectively switch between a connected state in which the one terminal of the output switch is connected to the another terminal of the output switch and a disconnected state in which the one terminal of the output switch is disconnected from the another terminal of the output switch;
• and
• a controller configured to control the DC-DC converter, wherein
• the controller is configured to, after detecting that a current flowing through the conversion circuit exceeds a predetermined current threshold or that a charge voltage of the low-voltage storage battery exceeds a predetermined voltage threshold, execute a failure determination of the DC-DC converter after instructing the conversion circuit to stop a voltage conversion operation, causing the input switch to switch to the disconnected state, and instructing the output switch to switch to the disconnected state,
• the controller is configured to, in the failure determination:
• execute a first determination operation including (1) an output short-circuit failure determination of detecting a first low voltage value of the low-voltage terminal and determining, based on the first low voltage value, whether or not the output switch has failure due to short-circuit, (2) an output open-circuit failure determination of detecting a second low voltage value of the low-voltage terminal while controlling the output switch to cause the output switch to be in the connected state, and determining, based on the second low voltage value, whether or not the output switch has failure, and (3) an input short-circuit failure determination of detecting a first high voltage value of the high-voltage terminal and determining, based on the first high voltage value, whether or not the input switch has failure due to short-circuit;
• if determining, in the first determination operation, that the output switch does not have failure, execute a second determination operation of detecting a second high voltage value of the high-voltage terminal while instructing the output switch to be in the connected state and instructing the conversion circuit to perform the boosting-up operation, and determining, based on the second high voltage value, whether or not the conversion circuit has failure;
• and
• if determining, in the second determination operation, that the conversion circuit does not have failure, execute a third determination operation including an input open-circuit failure determination of detecting a third high voltage value of the high-voltage terminal while instructing the conversion circuit not to perform the boosting-up operation and while instructing the input switch to be in the connected state, and determining, based on the third high voltage value, whether or not the input switch has failure.