Electric power conversion system for vehicle and control method thereof

An electric power conversion system for a vehicle, the electric power conversion system comprising:

• an AC-DC conversion circuit configured to convert AC charging power into DC power;
• a motor including a plurality of coils each having a first end respectively connected to a neutral point;
• a first switching device configured to selectively allow or block supply of output power from the AC-DC conversion circuit to the neutral point;
• an inverter including:
• a plurality of motor connection terminals respectively connected to second ends of the plurality of coils of the motor,
• DC connection terminals including a positive terminal and a negative terminal, and
• a plurality of switching elements forming electrical connections between the DC connection terminals and the plurality of motor connection terminals;
• a battery connected to the DC connection terminals of the inverter;
• and
• a controller configured to control operations of the AC-DC conversion circuit, the first switching device, and the inverter based on whether or not the battery is charged,
• wherein the AC-DC conversion circuit includes:
• a first bridge circuit including a plurality of switching elements forming a bridge circuit and configured to receive AC charging power from an external AC charging equipment;
• a transformer including:
• a first coil, to which an AC voltage generated by short-circuitry or opening of a switching element in the first bridge circuit is applied, and
• a second coil electromagnetically coupled to the first coil to transform the AC voltage applied to the first coil at a predetermined ratio;
• and
• a second bridge circuit including a plurality of switching elements configured to:
• rectify an output voltage of the second coil or convert an input DC voltage into an AC voltage, and
• apply the converted AC voltage to the second coil,
• wherein the transformer further includes:
• a third coil electromagnetically connected to the first coil or the second coil to output a voltage of the first coil or the second coil by transforming the voltage at a predetermined ratio;
• and
• a low voltage converter controlled by the controller to convert a voltage output from the third coil into a predetermined voltage lower than a voltage of the battery.

A control method of an electric power conversion for a vehicle, the method comprising:

• providing an electric power conversion system having an AC-DC circuit which includes:
• a first bridge circuit including a plurality of switching elements forming a bridge circuit and configured to receive AC charging power from an external AC charging equipment;
• a transformer including a first coil, to which an AC voltage generated by short-circuitry or opening of a switching element in the first bridge circuit is applied, and a second coil electromagnetically coupled to the first coil to transform the AC voltage applied to the first coil at a predetermined ratio;
• and a second bridge circuit including a plurality of switching elements configured to:
• rectify an output voltage of the second coil or convert an input DC voltage into an AC voltage, and apply the converted AC voltage to the second coil, wherein the first bridge circuit includes:
• a first input terminal and a second input terminal, between which a voltage of the AC charging power is applied;
• a first switching element and a second switching element, each having a first terminal respectively connected to the first input terminal;
• a third switching element connected to a second terminal of the first switching element;
• and a fourth switching element connected between a second terminal of the second switching element and a first terminal of the third switching element, and wherein both ends of the first coil of the transformer is connected to the second input terminal and a connection node of the third switching element and the fourth switching element, respectively;
• determining, by a controller, whether the vehicle is in a charging mode in which a battery is charged with AC charging power or in a travel mode in which a motor is actuated;
• when the vehicle is in the charging mode, short-circuiting a first switching device, opening a second switching device, by which causing an output voltage of the AC-DC circuit to be applied to a neutral point, and controlling a plurality of switching elements in an inverter so that a circuit formed by a plurality of switching elements in the inverter and a plurality of coils operates as a boosting converter;
• controlling a low voltage converter to convert the voltage, output from a third coil by electrical coupling between the first coil and the third coil, into a predetermined voltage lower than a voltage of the battery;
• and
• when the vehicle is in the travel mode, opening the first switching device, causing the voltage of the battery to be applied to the second bridge circuit by short-circuiting the second switching device, converting the voltage of the battery by controlling states of the plurality of switching elements in the second bridge circuit so that the converted AC voltage is applied to the second coil, controlling the plurality of switching elements in the inverter so that the circuit formed by the plurality of switching elements and the plurality of coils operates as a boosting inverter, and controlling the low voltage converter to convert the voltage, transformed and output from the third coil by electrical coupling between the second coil and the third coil, into the predetermined voltage lower than the voltage of the battery.