Charging and discharging control apparatus of DC link capacitor in electric power steering relay and method thereof

1. A charging-discharging control apparatus of a DC link capacitor in an electric power steering relay, comprising:

a DC link capacitor configured to turn-on the electric power steering relay by charging an electric charge, a first switching unit configured to control charging of the DC link capacitor by being shorted between the DC link capacitor and a power supply unit; and a second switching unit configured to control discharging of the DC link capacitor by being shorted between the DC link capacitor and a ground,

wherein the first switching unit includes at least one transistor to control the charging of the DC link capacitor using a collector current thereof, and

the second switching unit includes at least one transistor to control the discharging of the DC link capacitor using a collector current thereof,

wherein the first switching unit includes:

a first transistor configured to be connected to the power supply unit through a first resistor; and

a second transistor configured to be connected to the first transistor through a second resistor to control a current flowing in the DC link capacitor from the power supply unit using the first transistor, and

wherein the second switching unit includes:

a third transistor configured to be connected to the DC link capacitor through a third resistor; and

a fourth transistor configured to be connected to the third transistor through a fourth resistor to control a current flowing in the ground from the DC link capacitor using the third transistor.

2. The charging-discharging control apparatus of claim 1 , wherein a collector of the fourth transistor is connected to a base of the third transistor,

when a discharging signal is input to a base of the fourth transistor, the third transistor is turned-on so that the DC link capacitor is shorted with the ground, and

when the discharging signal is not input to the base of the fourth transistor, the third transistor is turned-off so that the DC link capacitor and the ground are opened.

3. The charging-discharging control apparatus of claim 1 , further comprising:

a control unit configured to connect the base of the second transistor to the base of the fourth transistor and control switching of the first transistor and the third transistor using the charging signal and the discharging signal depending on a preset duty.

4. The charging-discharging control apparatus of claim 3 , wherein the duty is preset depending on temperature and a voltage of the power supply unit.

5. The charging-discharging control apparatus of claim 4 , wherein the DC link capacitor is completely discharged by the discharging signal input to the fourth transistor prior to turning-on the relay and is charged by the charging signal input to the second transistor to turn-on the relay.

6. A charging-discharging control apparatus of a DC link capacitor in an electric power steering relay, comprising:

a DC link capacitor configured to turn-on the electric power steering relay by charging an electric charge, a first switching unit configured to control charging of the DC link capacitor by being shorted between the DC link capacitor and a power supply unit; and a second switching unit configured to control discharging of the DC link capacitor by being shorted between the DC link capacitor and a ground,

wherein the first switching unit includes at least one transistor to control the charging of the DC link capacitor using a collector current thereof, and

the second switching unit includes at least one transistor to control the discharging of the DC link capacitor using a collector current thereof,

wherein the first switching unit includes:

a first transistor configured to be connected to the power supply unit through a first resistor; and

a second transistor configured to be connected to the first transistor through a second resistor to control a current flowing in the DC link capacitor from the power supply unit using the first transistor, and

wherein a collector of the second transistor is connected to a base of the first transistor,

when a charging signal is input to a base of the second transistor, the first transistor is turned-on so that the power supply unit is shorted with the DC link capacitor, and

when the charging signal is not input to the base of the second transistor, the first transistor is turned-off so that the power supply unit and the DC link capacitor are opened.

7. A method of a charging-discharging control of a DC link capacitor in an electric power steering relay, comprising:

a first step of measuring a voltage of a power supply unit and an internal temperature;

a second step of determining a discharging duty depending on the measured voltage and the internal temperature;

a third step of discharging the DC link capacitor by a discharging switching unit depending on the discharging duty;

a fourth step of charging the DC link capacitor by a charging switching unit; and

a fifth step of turning-on the electric power steering relay.

8. The method of claim 7 , further comprising:

prior to the first step, setting the duty and storing the set duty in a lookup table so as to discharge the DC link capacitor depending on the voltage of the power supply unit and the internal temperature.

9. The method of claim 7 , wherein in the third step, switching of a switching element which controls discharging of the DC link capacitor is controlled by the switching element using the discharging duty as an input.

10. The method of claim 9 , wherein in the third step, the DC link capacitor is completely discharged.

11. The method of claim 7 , further comprising:

prior to the fourth step, a 4-1-th step of measuring the voltage of a power supply unit and the internal temperature;

a 4-2-th step of setting a duty and storing the set duty in a lookup table so that the DC link capacitor is charged depending on the measured voltage and the internal temperature; and

a 4-3-th step of determining a charging duty depending on the measured voltage and the internal temperature.

12. The method of claim 7 , wherein in the fourth step, switching of a switching element which controls charging of the DC link capacitor is controlled by the switching element using the charging duty as an input.

13. The method of claim 12 , wherein in the fourth step, the DC link capacitor is charged with a preset voltage.