Charging system

A charging system that charges a battery by using an external power source with an output voltage lower than an output voltage of the battery, the charging system comprising:

• a motor that includes stator coils;
• a first inverter connected to first ends of the stator coils;
• a second inverter connected to second ends of the stator coils;
• a neutral point switching element that connects the second ends of the stator coils to a neutral point;
• a power receiving terminal that includes a connection positive electrode end and a connection negative electrode end to which the external power source is able to be connected, and in which the connection negative electrode end is connected to a battery negative electrode end of the battery;
• a circuit selector that switches a connection relationship between the first inverter, the second inverter, the neutral point, and the power receiving terminal;
• and
• a controller, wherein
• the first inverter includes
• a first ground end, and
• first series connectors to which a first upper switching element and a first lower switching element are connected in series, the first series connectors being connected in parallel between a battery positive electrode end of the battery and a first ground end,
• the first end of each of the stator coils is connected to a center point of each of the first series connectors,
• the second inverter includes
• a second ground end, and
• second series connectors to which a second upper switching element and a second lower switching element are connected in series, the second series connectors being connected in parallel between the battery positive electrode end of the battery and a second ground end,
• the second end of each of the stator coils is connected to a center point of each of the second series connectors,
• any one of following modes is selectable in the circuit selector:
• a motor driving mode that connects the first ground end and the second ground end to the battery negative electrode end;
• a first charging mode that connects the first ground end to the battery negative electrode end and connects the second ground end to the connection positive electrode end by disconnecting from the battery negative electrode end;
• a second charging mode that connects the second ground end to the battery negative electrode end and connects the first ground end to the connection positive electrode end by disconnecting from the battery negative electrode end;
• and
• a neutral point charging mode that connects the neutral point to the connection positive electrode end and connects the first ground end to the battery negative electrode end, and
• in a case where the motor is driven by the first inverter and the second inverter, the controller sets the circuit selector to the motor driving mode and holds the neutral point switching element to OFF,
• in response to the external power source being connected to the power receiving terminal, the controller compares a first accumulated stress of the first lower switching element, a second accumulated stress of the second lower switching element, and a third accumulated stress of the neutral point switching element,
• in a case where the second accumulated stress is smallest, the controller holds the neutral point switching element to OFF, sets the circuit selector to the first charging mode, and charges the battery by turning the first lower switching element ON and OFF,
• in a case where the first accumulated stress is smallest, the controller holds the neutral point switching element to OFF, sets the circuit selector to the second charging mode, and charges the battery by turning the second lower switching element ON and OFF, and
• in a case where the third accumulated stress is the smallest, the controller holds the neutral point switching element to ON, sets the circuit selector to the neutral point charging mode, and charges the battery by turning the first lower switching element ON and OFF.