Power source system

1 . A power source system comprising a first battery string, a second battery string, and a third battery string, wherein:

each of the first to third battery strings includes a plurality of batteries capable of outputting direct-current power;

the first to third battery strings are Y-connected so as to output three-phase alternating-current power to three-phase output terminals as well as connected to a neutral line;

on the neutral line, a neutral line capacitor for blocking a direct current, a neutral line switch disposed in series to the neutral line capacitor, and an electric resistance element disposed in parallel to the neutral line switch are provided;

a first phase relay, a second phase relay, and a third phase relay are provided bet twee the first battery string, the second battery string, and the third battery string, respectively, on one side and the three-phase output terminals on the other side;

the power source system further comprises a control device that controls the neutral line switch, the first phase relay, the second phase relay, and the third phase relay; and

the control device is configured to execute the following:

executing pre-charging of the neutral line capacitor by outputting three-phase alternating-current power from the first to third battery strings to the three-phase output terminals when each of the first phase relay, the second phase relay, and the third phase relay is in a conducting state while the neutral line switch is in an interrupted state; and

putting the neutral line switch in a conducting state after the pre-charging of the neutral line capacitor is completed.

2 . The power source system according to claim 1 , wherein the control device controls the first to third battery strings so as to bring current values of the three-phase output terminals close to zero during the execution of the pre-charging of the neutral line capacitor.

3 . The power source system according to claim 1 , wherein:

the power source system further comprises a detection circuit that separately detects string voltages respectively output from the first to third battery strings;

each of the first to third battery strings includes a plurality of battery circuits;

each of the plurality of battery circuits includes a battery, a direct-current output terminal, and a switch circuit that switches between connection and disconnection between the battery and the direct-current output terminal; and

the control device is configured to output three-phase alternating-current power from the first to third battery strings to the three-phase output terminals by controlling the switch circuits respectively included in the first to third battery strings based on the string voltages of the respective first to third battery strings detected by the detection circuit.

4 . The power source system according to claim 3 , wherein:

the detection circuit includes a first filter circuit, a second filter circuit, and a third filter circuit;

each of the first filter circuit, the second filter circuit, and the third filter circuit includes a capacitor and an inductor; and

the first filter circuit, the second filter circuit, and the third filter circuit are disposed between the first battery string, the second battery string, and the third battery string, respectively, on one side and the first phase relay, the second phase relay, and the third phase relay, respectively, on the other side.