KR20140094857A - Battery charger and method of operating the same - Google Patents

Abstract

The present invention relates to a battery charger and an operating method thereof. The battery charger can stably maintain a duty ratio of a switch of a converter and can completely discharge a battery. The battery charger includes: a main converter which is connected to a first power source and a main charging/discharging part; and an auxiliary converter connected to the first power source and an auxiliary charging/discharging part. The auxiliary charging/discharging part is connected to the main charging/discharging part. When the voltage of the main charging/discharging part is greater than a predetermined voltage during a discharging operation of the main charging/discharging part, only the main converter, not the auxiliary converter, is activated. When the voltage of the main charging/discharging part is same or less than a predetermined voltage, both of the main converter and the auxiliary converter are activated.

Description

FIELD OF THE INVENTION [0001] The present invention relates to a battery charger,

The present invention relates to a charger and a driving method thereof.

1 is a view showing a general charger.

1, the charger includes a power source V1, a battery 100, and a converter 102. [

The converter 102 has various types such as an insulated type, a non-interposed type, and a soft type, as shown in Korean Patent Laid-Open Publication No. 2002-0090446, and includes a switch. However, the switch is short-circuited when the duty ratio is generally raised to 0.9 or more.

The feature of such a switch makes it impossible to discharge the battery 100 completely. Specifically, when the voltage of the battery 100 drops below a certain voltage when the battery is discharged, the duty ratio of the switch rises, and thus the switch 100 may be short-circuited, so that the battery 100 can not be discharged below the predetermined voltage.

The present invention provides a charger capable of fully discharging a battery while stably maintaining a duty ratio of a switch of a converter and a driving method thereof.

According to an aspect of the present invention, there is provided a charger including: a main converter connected between a first power source and a main charge / discharge unit; And an auxiliary converter connected between the first power source and the auxiliary charging / discharging unit. When the voltage of the main charging / discharging unit is higher than a predetermined voltage during the discharging operation of the main charging / discharging unit, the auxiliary charging / discharging unit is connected to the main / Only the main converter is activated and both the main converter and the auxiliary converter are activated when the voltage of the main charging / discharging portion is lower than the preset voltage.

A method of driving a charger according to an embodiment of the present invention includes: determining whether a voltage of a battery reaches a preset voltage when a battery is discharged; And adjusting a duty ratio of the first switch or the second switch in the converter that connects the first power source and the battery when the voltage of the battery reaches the preset voltage.

A method of driving a charger according to another embodiment of the present invention includes: outputting a first control signal to a first switch for activating a battery; And outputting a third control signal to a third switch for activating an auxiliary charging / discharging unit connected to the battery when the voltage of the battery reaches a preset voltage upon discharge of the battery.

According to another aspect of the present invention, a method of driving a charger includes discharging a battery; And charging the auxiliary charging / discharging unit connected in series with the battery when the voltage of the battery reaches a predetermined voltage while discharging the battery.

A method of driving a charger according to another embodiment of the present invention includes: forming a first current path through a battery; And forming a second current path via an auxiliary charge / discharge unit connected to the battery. When the voltage of the battery is greater than a preset voltage, only the first current path is activated. When the voltage of the battery is less than the predetermined voltage, The current path is also activated.

The charger and the driving method thereof according to the present invention adjust the duty ratio of the switch in the converter by activating the auxiliary charging / discharging unit when the battery voltage falls below the preset voltage during discharging. As a result, the switch can operate stably, so that a 100% full discharge of the battery is possible.

1 is a view showing a general charger.
2 is a circuit diagram showing a charger according to an embodiment of the present invention.
3 is a circuit diagram of the charger of FIG. 2 according to one embodiment of the present invention.
4 is a flowchart illustrating a driving operation of the charger according to an embodiment of the present invention.
5 to 8 are views showing the operation of a charger according to an embodiment of the present invention.
9 is a diagram showing waveforms of an auxiliary charge / discharge portion according to an embodiment of the present invention.
10 is a diagram showing waveforms of a main charging / discharging portion according to an embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

The present invention proposes a charger capable of fully discharging a voltage of a battery up to 0 V and a driving method thereof. More specifically, the present invention provides a charger that does not increase the duty ratio . This is to forcibly maintain the duty ratio of the switch below the reference value since the duty ratio of the switch can be short-circuited when the duty ratio is raised above the reference value.

Conventional chargers have been unable to discharge the battery voltage below a predetermined voltage during discharging due to the duty ratio problem of such a switch. However, the charger of the present invention can maintain the duty ratio of the switch below the predetermined value during the battery discharging operation, so that the battery can be fully discharged at 100%. As a result, the lifetime of the battery can be increased. In addition, the converter may be used for battery performance test because the converter can control the voltage of the battery from the maximum voltage to 0V.

Recently, a zinc-bromine flow battery has been used as a large-capacity battery because of its excellent stability and price competitiveness. For example, Zinc Bromflow batteries can be used in Smart Grid's Energy Storage System (ESS), wind power and solar power output compensation devices. However, such a Zinc Bromofluor battery should be subjected to a strip operation which requires a full discharge at a charge / discharge cycle of 6 to 10 times. However, conventional chargers have not been able to fully discharge the battery due to the duty ratio problem, and a new circuit structure capable of discharging the battery completely was needed. The charger of the present invention suggests a drive circuit capable of discharging the battery completely while maintaining the duty ratio of the switch below a preset value.

On the other hand, the driving circuit of the charger of the present invention can be applied to batteries other than the zinc Bromofluor battery.

Hereinafter, various embodiments of the charger of the present invention and the driving method thereof will be described in detail with reference to the accompanying drawings. 2, it is assumed that the voltage Vin of the first power source is an output voltage and the voltage of the charge / discharge units 200 and 204 is an input voltage I will assume.

2 is a circuit diagram showing a charger according to an embodiment of the present invention.

2, the charger of the present embodiment includes a first power source V, a main charging / discharging unit 200, a main converter 202, an auxiliary charging / discharging unit 204 and an auxiliary converter 206 . That is, the charger drive circuit of this embodiment includes a main converter 202, an auxiliary charge / discharge section 204, and a control section (not shown). Here, the main charging / discharging unit 200 means a battery, and the auxiliary charging / discharging unit 204 can be a selectively chargeable capacitor capable of energy activation.

The charger driving circuit drives only the main charging / discharging unit 200 and the auxiliary charging / discharging unit 204 until the voltage of the main charging / discharging unit 200 falls below a preset voltage, And activates not only the main charging / discharging unit 200 but also the auxiliary charging / discharging unit 204 when the voltage of the main charging / discharging unit 200 falls below a preset voltage. For example, the driving circuit deactivates the auxiliary charging / discharging unit 204 until the voltage of the main charging / discharging unit 200 reaches a preset voltage at the time of discharging, and when the voltage reaches the preset voltage, / Discharger 204 can be activated. As a result, the input voltage becomes the voltage Vbat of the main charging / discharging unit 200 until the voltage of the main charging / discharging unit 200 falls below the preset voltage, The input voltage may be a voltage (Vbat + Vcap) corresponding to the sum of the voltage of the main charging / discharging part 200 and the voltage of the auxiliary charging / discharging part 204 when the voltage of the auxiliary charging / discharging part 204 falls below the preset voltage. The control unit determines the logic of the control signals that control the operation of the converters 202 and 206 based on the input voltage. A detailed description thereof will be described later.

The main converter 202 and the auxiliary converter 206 may each be a bi-directional DC / DC converter. Also, various types of converters, such as an insulated type, an non-isolated type, and a soft switching type, can be used as the converters 202 and 206.

According to one embodiment, only the main converter 202 is activated until the voltage of the main charging / discharging unit 200 falls below the preset voltage, and the voltage of the main charging / discharging unit 200 is lower than the preset voltage The auxiliary converter 206 as well as the main converter 202 can be activated. A detailed description thereof will be described later.

In summary, the charger of the present embodiment selectively activates the auxiliary converter 206 according to the voltage of the main charging / discharging unit 200 during discharging. Specifically, the charger activates the auxiliary converter 206 so that the duty ratio of the switch of the main converter 202 does not rise above a predetermined value when the voltage of the main charging / discharging unit 200 falls below a preset voltage . As a result, the charger can completely discharge the main charging / discharging unit 206 while maintaining the duty ratio of the switch at a predetermined value or lower, that is, discharging to 0V.

3 is a circuit diagram of the charger of FIG. 2 according to one embodiment of the present invention.

3, the main converter 202 includes a first switch G1 and a second switch G2, and the auxiliary converter 206 includes a third switch G3 and a fourth switch G4 can do. The switches G1 to G4 may be N-MOS transistors.

The drain of the first switch G1 may be coupled to the first power source V1 and the source thereof may be coupled to the main charge /

The drain of the second switch G2 may be connected to the first switch G1, and the source may be connected to the ground.

A node between the first switch G1 and the second switch G2 is connected to the main charging / discharging unit 200. [ In addition, an inductor may be additionally formed between the node and the main charging / discharging unit 200.

According to one embodiment, the control section of the drive circuit may transmit the first control signal to the first switch G1 and the second control signal to the second switch G2. The second control signal may be an inverting signal of the first control signal as described later. As a result, if the switches G1 and G2 are the same kind of transistors, the other switches can be turned off when one of the switches G1 and G2 is turned on.

The third switch G3 is connected to one end of the first power supply V1 and one end of the first switch G1, for example, a drain, for example, a drain.

The fourth switch G4 may be connected to the source of the third switch G3 once, for example, the drain thereof.

A node between the third switch G3 and the fourth switch G4 may be connected to the auxiliary charge /

According to one embodiment, the control unit may transmit the third control signal to the third switch G3, and may transmit the fourth control signal to the fourth switch G4. The fourth control signal may be an inverting signal of the third control signal as described later. As a result, if the switches G3 and G4 are the same kind of transistors, the other switch can be turned off when one of the switches G3 and G4 is turned on.

Let's briefly look at the operation of the charger with this structure.

The charger deactivates the third switch G3 until the voltage of the main charging / discharging unit 200 falls below the preset voltage, but when the voltage of the main charging / discharging unit 200 falls below the preset voltage The third switch G3 is activated. This is to prevent the duty ratio of the switch G1 or G2 from rising above a preset value during discharging.

In general, the input voltage and the output voltage are related to the duty ratio of the switch G1 or G2 as expressed in Equation (1) below.

In summary, the duty ratio of the switch G1 or G2 can be expressed by the following equation (2).

Referring to Equation (2), the duty ratio of the switch G1 or G2 can be determined to the input voltage and the output voltage. Assuming that the output voltage is fixed at, for example, 60 V, the duty ratio of the switch G1 or G2 can be lowered by increasing the input voltage. Therefore, the present invention detects the input voltage and switches the corresponding control signal to the switch G1 or G2 so that the duty ratio of the switch G1 or G2 is maintained at a predetermined value, for example 0.9 or less, Can be output.

According to an embodiment of the present invention, when the duty ratio of the switch G1 or G2 is less than a predetermined value, the main charger / discharger 200 and the main charging / discharging unit 202 of the auxiliary charging / When the duty ratio of the switch G1 or G2 is expected to rise above a predetermined value, that is, when the voltage of the main charging / discharging unit 200 reaches the predetermined voltage, the main charging / It is possible to forcibly maintain the duty ratio of the switch G1 or G2 below the predetermined value by activating both the front unit 200 and the auxiliary charging / discharging unit 202. [ As a result, the duty ratio of the switch G1 or G2 can be kept below the predetermined value until the voltage of the main charging / discharging unit 200 is completely discharged. Accordingly, the charger can stably discharge the main / charge discharging unit 200 without error.

In summary, the charger drive circuit of the present invention can adjust the duty ratios of the switches G1 and G2 of the main converter 204 connected to the main charging / discharging unit 200 according to the voltage of the main charging / discharging unit 200 have. Here, the input voltage may be an output voltage due to the characteristics of the bidirectional charger.

4 is a flowchart illustrating a driving operation of the charger according to an embodiment of the present invention.

Referring to FIG. 4, the control unit of the driving circuit activates the main converter 202 to charge and discharge the main charging / discharging unit 200 (S400). At this time, the auxiliary converter 206 is not activated.

Then, the controller determines whether the number of charging / discharging times of the main charging / discharging unit 200 exceeds a predetermined number of times (S402). For example, when the main charging / discharging unit 200 is a zinc bromide fl ow battery, the control unit can determine whether the number of charge / discharge exceeds six, for example. Here, the preset number of times may vary depending on the manufacturer of the main charging / discharging unit 200.

If the number of charging / discharging times does not exceed the predetermined number, step S400 is performed again.

On the other hand, if the number of charging / discharging exceeds the predetermined number, the controller performs a full discharge operation of the main charging / discharging unit 200. Specifically, the control unit first measures the voltage of the main charging / discharging unit 200 (S404), and outputs the first control signal and the second control signal to the first switch G1 and the second switch G2 of the main converter 202 Respectively, and starts discharging the main charging / discharging unit 200 (S406).

Subsequently, the control unit determines whether the voltage of the main charging / discharging unit 200 reaches a minimum voltage (preset voltage) for forming a duty (S408).

If the voltage of the main charging / discharging unit 200 has not reached the preset voltage, step S406 is performed again.

On the other hand, when the voltage of the main charging / discharging unit 200 reaches the predetermined voltage, the controller transmits the third control signal and the fourth control signal to activate the auxiliary converter 206 (S410). In this case, the main converter 202 remains active. As a result, the input voltage of the charger rises, and therefore the duty ratio of the switch G1 or G2 of the main converter 202 may not rise above a predetermined value.

With the auxiliary converter 206 activated, the control unit controls the switches G1 and G2 of the main converter 202 and the switches G3 and G4 in the auxiliary converter 206 to control the main charge / 200 are completely discharged (S412). That is, the control unit discharges the main charging / discharging unit 200 to 0 V while maintaining the duty ratio of the switch G1 or G2 at a predetermined value or less.

When the main charging / discharging unit 200 is completely discharged, the control unit discharges the auxiliary charging / discharging unit 204 (S414).

Then, the control unit waits for charging / discharging of the main charging / discharging unit 200 (S416).

Hereinafter, the charging and discharging operations of the charger of the present invention will be described on the basis of the charger of Fig.

5 to 8 are views showing the operation of a charger according to an embodiment of the present invention.

(1) Main charge / In the discharge unit 200  Charging operation

5A, the control unit of the driving circuit transmits the first control signal to the first switch G1 to turn on the first switch G1, and the third control signal to the third switch G3 to turn off the third switch G3. As a result, the first current path is formed through the first power source V1, the first switch G1, the main charging / discharging unit 200, and the fifth switch G5, A current flows to the main charging / discharging unit 200 and the main charging / discharging unit 200 is charged. Here, the fifth switch G5 is connected in parallel to the auxiliary charging / discharging unit 204, and can be turned on during the charging operation of the main charging / discharging unit 200. [ As a result, the auxiliary charging / discharging unit 204 is not charged when the main charging / discharging unit 200 is being charged.

Then, the control unit transmits the first control signal to the first switch G1 to turn off the first switch G1. As a result, a second current path is formed through the second switch G2, the main charging / discharging unit 200 and the fifth switch G5, as shown in FIG. 5 (B) (freewheeling).

(2) Main charge / In the discharge unit 200  Discharge operation

6A, the controller transmits a second control signal to the second switch G2 to turn on the second switch G2, and the third control signal to the third switch G3, To keep the third switch G3 in the off state and to transmit the fifth control signal to the fifth switch G5 to turn on the fifth switch G5. Therefore, the third current path is formed through the main charging / discharging part 200, the second switch G2 and the fifth switch G5, and as a result, the charge of the main charging / discharging part 200 is discharged.

Then, the control unit transmits the second control signal to the second switch G2 to turn off the second switch G2. Therefore, a current path is formed through the main charging / discharging unit 200, the first switch G1, the first power source V1, and the fifth switch G5, and the charge of the main charging / And is discharged through the current path.

(3) Strip operation Current flow (main charge / Discharge part  Above setting frequency Charging and discharging  The main charge / Discharge  Full discharge operation)

In the strip operation, the discharging operation of FIG. 6 continues, and the control unit measures the voltage of the main charging / discharging unit 200.

When the voltage of the main charging / discharging unit 200 reaches a preset voltage, that is, when the duty ratio of the switch G1 or G2 of the main converter 202 is expected to rise above a predetermined value, The third control signal is transmitted to the third switch G3 to turn on the third switch G3 and the fifth control signal is transmitted to the fifth switch G5 as shown in (A) The fifth switch G5 is turned off. Therefore, a current path is formed through the first power source V1, the third switch G3 and the auxiliary charging / discharging unit 204, so that the auxiliary charging / discharging unit 204 is charged. A current path is formed through the main charging / discharging unit 500, the second switch G2 and the auxiliary charging / discharging unit 204 during the charging operation of the auxiliary charging / discharging unit 204, The electric charge of the front part 500 is discharged. Therefore, even if the voltage of the main charging / discharging unit 206 is lowered, the overall input voltage may not be lowered by the voltage of the auxiliary charging / discharging unit 204, for example, 60 V can be maintained. As a result, the duty ratio of the switches G1 and G2 of the main converter 202 may not rise above a predetermined value.

The control unit then transmits the first control signal to the first switch G1 to turn on the first switch G1 and the third control signal to the third switch G3 to turn on the third switch G3, Lt; / RTI > Accordingly, a current path is formed through the main charging / discharging unit 200, the first switch G1, the first power source V1, and the auxiliary charging / discharging unit 204, so that the main charging / discharging unit 200 Is discharged. At this time, a current path is formed through the auxiliary charging / discharging portion 204 and the fourth switch G4, that is, the current is freewheeling through the current path, so that the auxiliary charging / discharging portion 204 is continuously .

The controller discharges the main charging / discharging unit 200 while maintaining the duty ratio of the switches G1 and G2 of the main converter 202 at a predetermined value or less through the above process.

(4) Auxiliary charge / In the discharge part 204  Discharge operation

When the main charging / discharging unit 200 is completely discharged, the control unit performs an operation of discharging the auxiliary charging / discharging unit 204. More specifically, the control unit transmits a first control signal to the first switch G1 to turn off the first switch G1, and transmits the third control signal to the third switch G3, (G3) is turned on. Therefore, as shown in FIG. 8A, a current path is formed through the auxiliary charging / discharging portion 204, the third switch G3 and the first power source V1, and as a result, the auxiliary charging / (204) is discharged.

Then, the control unit transmits the third control signal to the third switch G3 to turn off the third switch G3. Therefore, a current path is formed through the auxiliary charging / discharging portion 204 and the fourth switch G4, so that the charge of the auxiliary charging / discharging portion 204 is discharged.

In summary, the charger of the present invention maintains the duty ratios of the switches G1 and G2 of the main converter 202 below the predetermined value through the above-described processes (1) to (4) 200 can be fully discharged.

Although not described above, let's briefly look at the internal operation of the controller.

The control unit adds the input voltage Edc after passing the current I_bat flowing to the main charging / discharging unit 200 through the PI controller (Proportional-Integral controller), and divides the added voltage by the output voltage to form a duty ratio do. Then, the control unit compares the duty ratio with a switching carrier having a triangular waveform to generate the first control signal and the second control signal. Here, the second control signal may be an inverting signal of the first control signal, and the first control signal and the second control signal may each have a pulse waveform.

The control unit subtracts the sum of the voltage V_cap of the auxiliary charging / discharging unit 204 from the reference voltage V_cap ref for the auxiliary charging / discharging unit 204 and the voltage V_bat of the main charging / discharging unit 200 After passing through the PI controller, subtracting the current (I_cap) flowing from the current passing through the PI controller to the auxiliary charging / discharging part 204, and passing it through the PI controller. Then, the control unit divides the output from the PI controller by the voltage V_cap of the auxiliary charging / discharging unit 204 and divides the voltage by the input voltage Edc to form a duty ratio. The duty ratio and the triangular waveform And compares the switching carriers to generate a third control signal and a fourth control signal. Here, the fourth control signal may be an inverting signal of the third control signal, and the third control signal and the fourth control signal may each have a pulse waveform.

FIG. 9 is a view showing waveforms of an auxiliary charging / discharging part according to an embodiment of the present invention, and FIG. 10 is a view showing waveforms of a main charging / discharging part according to an embodiment of the present invention. However, in the experiment, the preset voltage which is a reference for the activation of the auxiliary converter is set to 60V.

Referring to FIGS. 9 and 10, in the T1 period, the battery voltage is equal to or higher than 60 V (preset voltage), so that the auxiliary converter 206 is not activated. As a result, the voltage of the auxiliary charging / discharging unit 204 is 0 V.

Subsequently, the auxiliary converter 206 is activated at the time when the T1 period ends and the T2 period starts. As a result, as shown in the first graph of FIG. 9, the total input voltage maintains the 60V voltage in the T2 period, The main charging / discharging unit 200 is fully discharged as shown in the second graph of FIG. In this case, as can be seen from the last graph of FIG. 10, the duty ratio of the switches G1 and G2 of the main converter 202 does not exceed 0.9. When the duty ratio of the switches G1 and G2 exceeds 0.9, the switches G1 and G2 may be short-circuited.

Subsequently, in the period T3, the charge of the auxiliary charging / discharging unit 204 is discharged, and the main charging / discharging unit 200 can be recharged again in the period T4.

Meanwhile, as can be seen from the third graph in FIG. 9 and the third graph in FIG. 10, the controller can control the currents of the charge / discharge units 200 and 204 with a small current of less than 1A.

It will be apparent to those skilled in the art that various modifications, additions and substitutions are possible, without departing from the spirit and scope of the invention as defined by the appended claims. Should be regarded as belonging to the following claims.

200: main charge / discharge unit 202: main converter
204: Auxiliary charge / discharge unit 206: Auxiliary converter

Claims (26)

A main converter connected between the first power source and the main charge / discharge unit; And
And an auxiliary converter connected between the first power source and the auxiliary charging / discharging unit,
Wherein the auxiliary charging / discharging unit is connected to the main / charging discharging unit, and when the voltage of the main charging / discharging unit is greater than a predetermined voltage during the discharging operation of the main charging / discharging unit, Only the main converter is activated and both the main converter and the auxiliary converter are activated when the voltage of the main charging / discharging part is lower than the predetermined voltage. The charger of claim 1, wherein the main charging / discharging unit is a zinc-bromine flow battery. The method according to claim 1,
Further comprising a control unit for controlling the converters to perform a strip operation for discharging the main charging / discharging unit when the charging / discharging operation of the main charging / discharging unit is performed a preset number of times. The method of claim 1, wherein the converters are bi-directional DC-DC converters, the main converter includes a first switch and a second switch, the auxiliary converter includes a third switch and a fourth switch,
Wherein the first switch is connected to the first power source and the node between the first switch and the second switch is connected to the main charging / discharging part, and the third switch is connected to the first power source and the first switch And a node between the third switch and the fourth switch is connected to the auxiliary charging / discharging unit,
The third switch is in the off state until the voltage of the main charging / discharging portion reaches the predetermined voltage upon the discharge of the main charging / discharging portion, and when the voltage of the main charging / discharging portion reaches the preset voltage, - the charger being turned on. 5. The method of claim 4,
And a fifth switch connected in parallel to the auxiliary charging / discharging unit,
And the fifth switch is turned off when the third switch is turned on. 5. The charger of claim 4, wherein the duty ratio of the first switch or the second switch is maintained at 0.9 or lower while the voltage of the main charging / discharging portion is discharged to 0V. The method of claim 4, wherein the first switch to the fourth switch are all NMOS transistors, and the second control signal input to the second switch is an inverting signal of the first control signal input to the first switch And the fourth control signal input to the fourth switch is an inverting signal of the third control signal input to the third switch. The charger of claim 1, wherein the auxiliary charging / discharging unit is discharged after the main charging / discharging unit is discharged to 0V. Determining whether a voltage of the battery reaches a predetermined voltage when the battery is discharged; And
And adjusting a duty ratio of a first switch or a second switch in a converter that connects the first power source and the battery when the voltage of the battery reaches the preset voltage. The apparatus of claim 9, wherein the duty ratio of the first switch or the second switch is adjusted by activating an auxiliary charging / discharging unit connected in series with the battery when the voltage of the battery reaches the predetermined voltage. The charger driving method. 11. The method of claim 10, wherein when the voltage of the battery reaches the predetermined voltage, the third switch connected between the first power source and the auxiliary charging / discharging unit is turned on. 10. The method of claim 9,
Determining whether the number of charging / discharging times of the battery is equal to or greater than a predetermined number;
Discharging the battery to 0V when the number of charging / discharging times of the battery is equal to or greater than the preset number of times. 13. The method of claim 12,
Discharging the auxiliary charging / discharging unit connected in series with the battery after discharging the battery to 0V. 13. The method of claim 12, wherein the duty ratio of the first switch or the second switch is maintained at 0.9 or lower while the voltage of the battery is discharged to 0V. Outputting a first control signal to a first switch for activating the battery; And
And outputting a third control signal to a third switch for activating an auxiliary charging / discharging unit connected to the battery when the voltage of the battery reaches a preset voltage upon discharging of the battery. Way. 16. The method of claim 15, wherein the duty ratio of the third switch is determined by the voltage of the battery and the voltage of the auxiliary charging / discharging unit. 16. The method of claim 15, wherein the duty ratio of the first switch is determined according to the voltage of the battery. 16. The method of claim 15,
Outputting a second control signal to a second switch connected to the first switch;
Outputting a fourth control signal to a fourth switch connected to the third switch; And
And outputting a fifth control signal to a fifth switch connected in parallel with the auxiliary charging / discharging unit,
Wherein the second control signal is an inverting signal of the first control signal and the fourth control signal is an inverting signal of the third control signal. The method as claimed in claim 18, wherein the third control signal and the fourth switch are turned on so that the third switch or the fourth switch is turned on until the battery is fully discharged from when the voltage of the battery reaches the predetermined voltage. 4 < / RTI > control signal. The method of claim 18, further comprising: when the voltage of the battery is greater than the predetermined voltage, turning on the fifth switch and when the voltage is lower than the predetermined voltage, outputting the fifth control signal to turn off the fifth switch And the charging device is driven. Discharging the battery; And
And charging the auxiliary charging / discharging unit connected in series with the battery when the voltage of the battery reaches a preset voltage while discharging the battery. The method of claim 21, further comprising: forming a current path through the battery, the main converter connected between the first power source and the battery, and the auxiliary charging / discharging unit when the voltage of the battery is equal to or lower than the predetermined voltage, And a current path is formed through the auxiliary converter connected between the first power source and the auxiliary charging / discharging unit and the auxiliary charging / discharging unit. 23. The method of claim 22, wherein when the voltage of the battery is completely discharged, a current path is formed through the auxiliary charging / discharging unit, the auxiliary converter, and the first power source. Forming a first current path through the battery; And
And forming a second current path via an auxiliary charge / discharge unit connected to the battery,
Wherein when the voltage of the battery is greater than a preset voltage, only the first current path is activated, and when the voltage of the battery is equal to or lower than the predetermined voltage, Is activated. 25. The method of claim 24, wherein the first current path is a current path for discharging the battery, and the second current path is a current path for charging the auxiliary charging / discharging unit. 25. The method of claim 24,
And forming a third current path via the auxiliary charge / discharge unit when the battery is completely discharged,
Wherein the third current path is a current path for discharging the auxiliary charging / discharging portion, and the first current path is not activated when the third current path is formed.

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