KR20170084960A - Changing and discharging apparatus for electric vehicle - Google Patents

Abstract

A charging / discharging device for an electric vehicle is provided. The charge / discharge device for an electric vehicle according to an embodiment of the present invention includes a DC-link stage having two capacitors and a connection point of the capacitors connected to the ground; A three-level DC / DC converter for reducing the voltage of the DC-link terminal to the voltage of the electric vehicle battery or boosting the voltage of the electric vehicle battery to the voltage of the DC-link terminal; A bidirectional three-level DC / AC converter for converting AC power of an AC system to DC power or converting DC power of a DC-link stage to AC power; And a switching controller for controlling the switching of the three-level DC / DC converter and the three-level DC / AC converter, and controlling charging or discharging of the battery in the form of pulsating current identical to that of power on the AC system side.

Description

[0001] The present invention relates to a charging and discharging apparatus for an electric vehicle,

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging / discharging apparatus, and more particularly, to a charging / discharging apparatus for an electric vehicle, which charges a battery mounted in an electric vehicle with electric power of an AC system and discharges surplus electric power of the battery into an AC system.

Generally, an electric vehicle has an on-board battery charger that charges the battery through a system power supply. Such in-vehicle battery chargers are characterized by high efficiency and low weight and volume.

Recently, an electric vehicle with V2G (vehicle-to-grid) function is being developed in cooperation with a smart grid. These V2G electric vehicles use a battery to send surplus power to the grid to sell at peak times with high electricity prices and to charge the battery at low electricity prices.

At this time, the conventional battery charger for an electric vehicle is composed of a two-level DC / DC converter as a bi-directional half-bridge converter and a two-level DC / AC converter as a bi-directional inverter .

Here, a two-level DC / DC converter uses a high-frequency transformer (eg Isolation SRC) for isolation and noise cancellation effects between input and output. The use of such a high frequency transformer not only increases the overall volume and weight due to the transformer, but also causes a price increase.

KR 2011-0037523 A

In order to solve the problems of the related art as described above, one embodiment of the present invention is to provide a charging / discharging apparatus for an electric automation which can improve the power conversion efficiency and miniaturize at the time of charging and discharging the battery.

According to an aspect of the present invention, there is provided a charging / discharging apparatus for an electric vehicle. Wherein the charge / discharge device for an electric vehicle comprises two capacitors, a DC-link terminal having a connection point of the capacitors connected to ground; A three-level DC / DC converter for reducing the voltage of the DC-link stage to a voltage of an electric vehicle battery or boosting a voltage of the battery for the electric vehicle to a voltage of the DC-link stage; A bidirectional three-level DC / AC converter for converting the AC power of the AC system into DC power or converting the DC power of the DC-link stage into AC power; And a switching control unit for controlling the switching of the three-level DC / DC converter and the three-level DC / AC converter so as to charge or discharge the battery in the form of a pulsating current identical to the type of power on the AC system side .

In one embodiment, the three-level DC / DC converter includes a first switch that is turned on to charge the battery by a first capacitor of the DC-link stage; A second switch that is turned on to charge the battery by a second capacitor of the DC-link stage; A third switch that is turned on so that the battery discharges to the second capacitor; And a fourth switch that is turned on to discharge the battery to the first capacitor.

In one embodiment, each of the first to fourth switches may be connected in parallel with a reverse diode.

In one embodiment, the three level DC / AC converter may be an NPC type three level DC / AC converter.

In one embodiment, the NPC type 3-level DC / AC converter is turned on to form a current path for the first capacitor of the DC-link stage and includes a fifth switch and a sixth switch connected in series with each other; A seventh switch and an eighth switch that are turned on to form a current path for the second capacitor of the DC-link stage and are connected in series with each other; A first clamping diode connected between a connection point of the fifth switch and the sixth switch and a connection point of the capacitors; And a second clamping diode connected between a connection point of the seventh switch and the eighth switch and a connection point of the capacitors, and a connection point of the first clamping diode and the second clamping diode may be connected to the connection point of the capacitors have.

In one embodiment, the three level DC / AC converter may be a T type three level DC / AC converter.

In one embodiment, the T-type 3-level DC / AC converter includes a fifth switch that is turned on to form a current path for the first capacitor of the DC-link stage; A sixth switch and a seventh switch that are turned on so that the connection point of the capacitors is connected to the AC system; And an eighth switch that is turned on to form a current path for the second capacitor of the DC-link stage, wherein the sixth switch is connected to the connection point of the capacitors, and the seventh switch is connected to the fifth switch And may be connected to a connection point of the eighth switch.

In one embodiment, the three-level DC / AC converter may include a filter that removes harmonics included in a signal input from the AC system or a signal output to the AC system.

The charging and discharging apparatus for an electric vehicle according to an embodiment of the present invention comprises a three-level DC / DC converter and a three-level DC / AC converter. By applying an interleaving switching scheme for alternately switching the switches, Generation can be suppressed, high-efficiency power conversion is possible, and power conversion loss can be reduced.

In addition, the present invention can reduce the heat sink by performing high efficiency power conversion using the 3-level DC / DC converter and the 3-level DC / AC converter and remove the transformer for insulation, And the volume can be alleviated, thus miniaturization can be realized.

Further, the present invention can reduce the manufacturing cost by eliminating the transformer for shrinking and insulating the heat sink, and thus can be manufactured at a low cost, thereby improving the economical efficiency of the charge / discharge device for an electric vehicle.

1 is a schematic configuration diagram of a charge / discharge device for an electric vehicle according to an embodiment of the present invention,
FIG. 2 is a timing chart for explaining a switching method of a charging / discharging apparatus for an electric vehicle according to an embodiment of the present invention,
3 is a circuit diagram of an example of a charge / discharge device for an electric vehicle according to an embodiment of the present invention,
FIGS. 4 to 7 are circuit diagrams showing conduction paths according to switch operation states according to charging and discharging in the 3-level DC / DC converter of FIG. 3,
8 to 10 are circuit diagrams showing a conduction path according to a switch operation state in the 3-level DC / AC converter of FIG. 3,
11 is a circuit diagram of another example of the charge / discharge device for an electric vehicle according to the embodiment of the present invention,
FIGS. 12 to 14 are circuit diagrams showing a conduction path according to a switch operation state in the three-level DC / DC converter of FIG.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings, which will be readily apparent to those skilled in the art to which the present invention pertains. The present invention may be embodied in many different forms and is not limited to the embodiments described herein. In order to clearly illustrate the present invention, parts not related to the description are omitted, and the same or similar components are denoted by the same reference numerals throughout the specification.

1, a charging and discharging apparatus 100 for an electric vehicle according to an embodiment of the present invention includes a three-level DC / DC converter 110, a DC-link stage 120, a three-level DC / AC converter 130 ), And a switching control unit 140.

The three-level DC / DC converter 110 may be connected to the battery side mounted on the electric vehicle. The three-level DC / DC converter 110 may be configured as a bidirectional three-level DC / DC converter. That is, when charging the electric power of the AC system with the battery for the electric vehicle, the three-level DC / DC converter 110 reduces the voltage of the DC-link terminal 120 to the voltage of the electric vehicle battery, The voltage of the battery for the electric vehicle can be boosted to the voltage of the DC-link terminal 120 when the electric power of the battery for the electric vehicle is transmitted to the AC system.

For example, when the voltage (V _dc ) of the DC-link stage 120 is 700 V for charging a battery of 350 V as a battery for an electric vehicle, the 3-level DC / DC converter 110 is connected to the DC- And functions as a step-down converter when discharging the battery for the electric vehicle and transmitting electric power to the DC-link terminal 120. The DC-

The DC-link stage 120 is connected between the three-level DC / DC converter 110 and the three-level DC / AC converter 130 and may be composed of two capacitors C _d1 and C _d2 . At this time, the connection point between the capacitors C _d1 and C _d2 may be connected to the ground.

These DC-link stages 120 may be configured to charge, for example, 360V batteries alternately, for example, 700V, in which case each of the capacitors C _d1 and C _d2 So that the voltages V _dcp and V _dcn are 360V.

The three-level DC / AC converter 130 may be connected to, for example, an AC system of 220V. The three-level DC / AC converter 130 may be configured as a bidirectional three-level DC / AC converter. That is, when the electric power of the AC system is charged by the battery for the electric vehicle, the three-level DC / AC converter 130 converts the AC electric power of the AC electric system into DC electric power, When transmitting, DC power stored in the DC-link stage 120 may be converted to AC power.

The three-level DC / AC converter 130 may be an NPC type 3-level DC / AC converter or a T-type 3-level DC / AC converter as described later.

Here, in the conventional two-level DC / AC converter, one switch is responsible for each voltage of the two capacitors of the DC-link stage. For example, when the total voltage (V _dc ) of the DC-link stage is 700 V, each switch charges a voltage of 700 V.

On the contrary, the three-level DC / AC converter 130 has a lower loss than the two-level DC / AC converter. That is, the three-level DC / AC converter 130 charges only half the voltage of the entire voltage of the DC-link stage 120 in each switch by a two-level DC / AC converter. As a result, a power semiconductor having a low rated voltage can be used, and the switching loss of the switching element is also reduced, thereby improving the power conversion efficiency. As a result, since the harmonics characteristic of the three-level DC / AC converter 130 is improved, it is possible to reduce the size of the filter for eliminating the harmonics, thereby reducing the manufacturing cost.

For example, since the NPC type 3-level DC / AC converter _charges the entire voltage (V _dc = V _dcp + V _dcn ) of the DC-link stage 120 by dividing the two switches, Lt; RTI ID = 0.0 > 350V. ≪ / RTI > As a result, the NPC type 3-level DC / AC converter can use a power semiconductor having a lower rated voltage than a conventional two-level DC / AC converter.

Also, the T type 3-level DC / AC converter is the same as the NPC type 3 level DC / AC converter 130 in switching manner. In particular, such a T-type 3-level DC / AC converter has the advantage of being smaller in switching loss and conduction loss than the NPC type 3-level DC / AC converter described above.

Further, the three-level DC / AC converter 130 can be controlled by a single power factor control, an independent operation prevention control, and a DC-link (DC bus) voltage control.

Here, the single power factor control is a control method in which the phases of the voltage and the current are the same, and the loss due to the reactive power can be reduced. At this time, the 3-level DC / AC converter 130 is a control technique for supplying a good quality power because it is connected to the AC system.

The stand-alone operation prevention control detects that the device is operated alone and controls the device to stop the operation. Here, the stand-alone operation is to transmit electric power without disconnecting the system and the AC system even if an AC system error occurs. In this case, when single operation is continued, there is a risk of damage or electric shock to the equipment. Therefore, the single operation prevention control method is used to prevent the system from operating alone by sensing AC system power failure.

The DC-link (DC bus) voltage control is to control the overall voltage V _dc (= V _dcp + V _dcn ) of the DC-link stage 120 to be maintained at a constant value (for example, 700 V).

On the other hand, in the case of the three-level DC / AC converter, balanced control of the voltages (V _dcp , V _dcn ) of the two capacitors C _d1 and C _d2 of the _DC- That is, since the capacitors C _d1 and C _d2 of the DC-link stage 120 are alternately charged or discharged, the voltages V _dcp and V _dcn should be theoretically balanced, The voltages of the capacitors C _d1 and C _d2 of the DC-link stage 120 are not balanced because they are not exactly balanced.

Therefore, the three-level DC / DC converter 110 performs the neutral point control to ensure the uniformity of the voltages V _dcp and V _dcn of the capacitors C _d1 and C _d2 of the _DC- do.

In the embodiment of the present invention, the charge / discharge device 100 for an electric vehicle uses the three-level DC / DC converter 110 to control the neutral point of the DC-link terminal 120. That is, the three-level DC / DC converter 110 controls the entire voltage of the DC-link stage 120, and controls the DC-DC converter 120 to control the voltage difference between the first capacitor C _d1 and the second capacitor C _d2 . And performs neutral point control of the link stage 120. [

The switching control unit 140 controls the operation of the three-level DC / DC converter 110 and the three-level DC / AC converter 130. At this time, the switching control unit 140 controls the charging or discharging of the battery for the electric vehicle in the form of the pulsating current which is the same as that of the power of the AC system as shown in FIG.

More specifically, as shown in FIG. 2, in the AC system, when charging or discharging power at a power factor of 1 in which the phases of the voltage (Vgrid) and the current (Igrid) coincide with each other, Power ripple of twice the frequency of the AC system occurs.

At this time, when a constant current / constant voltage control scheme such as a general charge / discharge voltage / current control scheme is used, the capacitors C _d1 and C _d2 of the DC-link stage 120 absorb such power ripple.

As described above, when a conventional constant current / constant voltage method is used, a capacitor having a capacity large enough to absorb power ripple is required, and an electrolytic capacitor is used for this purpose. However, electrolytic capacitors have a short life span as compared with other capacitors and have a disadvantage that they are disadvantageous to the environment of an electric vehicle.

Therefore, the charging and discharging apparatus 100 for an electric vehicle according to the present invention eliminates the electric power ripple of the capacitor by charging or discharging the battery with the pulsating current equal to the form of power on the AC system side The DC-link stage 120 can be configured with a low-capacity capacitor. Thus, the DC-link stage 120 can be configured with a low-capacity capacitor without the need to use electrolytic capacitors, thereby improving lifetime and durability.

Hereinafter, a charging / discharging apparatus 100 for an electric vehicle according to an embodiment of the present invention will be described in more detail with reference to FIG. Here, charge / discharge device 100 for an electric vehicle is a case where the three-level DC / AC converter 130 is an NPC type.

The three-level DC / DC converter 110 may be connected to both ends of the battery for the electric vehicle and the ground, and may be configured as a half bridge composed of the first switch S ₁₁ to the fourth switch S ₁₄ .

One end of the first switch S ₁₁ may be connected to the anode B + of the battery for the electric vehicle and the other end thereof may be connected to the anode P of the DC-link terminal 120. The first switch (S ₁₁₎ may be turned on to charge the battery for an electric vehicle by the power of the first capacitors (C _d1) of the DC- link terminal (120).

One end of the second switch S ₁₂ may be connected to the cathode B- of the battery for the electric vehicle and the other end thereof may be connected to the cathode N of the DC- This second switch S ₁₂ may be turned on to charge the battery for the electric vehicle by the electric power of the second capacitor C _d2 of the DC-link terminal 120.

A third switch (S ₁₃₎ may be connected at its one end a first switch (S ₁₁₎ is coupled to the other end the fourth switch (S _14). A fourth switch (S ₁₄₎ may be connected at its one end the third switch (S ₁₃₎ and the other end connected to the second switch (S _12). At this time, the third switch S ₁₃ and the fourth switch S ₁₄ may be connected in series, and the connection point thereof may be connected to the ground.

Here, the first switch (S ₁₁ ) to the fourth switch (S ₁₄ ) may be connected in parallel with reverse diodes, respectively. Each of these reverse diodes is for bidirectional operation by forming a current path when the corresponding switch is turned off.

The three-level DC / DC converter 110 may further include a filter between the battery for the electric vehicle and the battery. Such a filter may consist of inductors L ₁ and L ₂ . Here, the first inductor L ₁ has one end connected to the anode B + of the battery for the electric vehicle, and the other end connected to the first switch S ₁₁ and the third switch S ₁₃ , respectively. One end of the second inductor L ₂ may be connected to the cathode B- of the battery for the electric vehicle and the other end thereof may be respectively connected to the second switch S ₁₂ and the fourth switch S ₁₄ .

4 to 7, the output of the DC / DC converter 110 is determined according to the conduction path according to the switching operation of each of the switches S ₁₁ to S ₁₄ .

First, in the case of charging a battery for an electric vehicle from an AC system, a first switch (S ₁₁₎ is turned on and the second switch (S ₁₂₎ has when the turn-off, as shown in Figure 4, the first switch (S ₁₁ The voltage stored in the first capacitor C _d1 of the DC-link terminal 120 can be used to charge the battery for the electric vehicle. On the other hand, the second capacitor of the second switch (S _12), the first switch (S ₁₁₎ is turned off when, as shown in Figure 5, the second switch DC- link terminal 120 via the (S ₁₂₎ The battery for the electric vehicle can be charged using the voltage stored in the capacitor C _d2 .

Next, the case of transmitting the power of the electric vehicle battery to the AC grid, and the third when the switch (S ₁₃₎ is turned on and the fourth switch (S ₁₄₎ is turned off, as shown in Figure 6, the third switch (C _d2 ) of the DC-link stage 120 through the battery S ₁₃ . In contrast, the fourth is turned on and the switch (S _14), the third switch (S ₁₃₎ is turned off,, as shown in Figure 7, the fourth power of the electric vehicle battery DC via a switch (S ₁₄₎ - the first capacitor (C _d1 ) of the link stage (120).

Thus, the three-level DC / DC converter 110 reduces the current ripple by charging and discharging the first capacitor C _d1 and the second capacitor C _d2 of the DC-link stage 120 at the same duty ratio at half period intervals . As a result, the three-level DC / DC converter 110 can reduce the size of the filter, that is, the size of the inductors (L ₁ , L ₂ ), thereby reducing the size of the entire product.

Meanwhile, in the case of the conventional two-level DC / DC converter, the three-level DC / DC converter 110 according to the embodiment of the present invention may be configured such that one capacitor charges all the output- _{Divides the} total voltage V _dc into a voltage V _dcp corresponding to the first capacitor C _d1 and a voltage V _dcn corresponding to the second capacitor C _d2 .

Therefore, since the switches S ₁₁ to S _{14 of the} three-level DC / DC converter 110 bear only half the voltage of the conventional two-level DC / DC converter, the losses caused by the parasitic capacitors and the reverse recovery The reverse recovery loss is reduced. Therefore, the three-level DC / DC converter 110 can improve the power conversion efficiency by reducing the loss as described above.

Moreover, the three-level DC / DC converter 110 can reduce the current ripple in half by switching the switch interleaved, thereby further reducing the overall filter size.

As a result, the three-level DC / DC converter 110 reduces the power conversion loss due to the reduction of the switching loss and the improvement of the harmonics, thus enabling high-efficiency power conversion. Moreover, the three-level DC / DC converter 110 can reduce manufacturing costs due to the reduction of heat sinks, transformers, and filter sizes compared to conventional two-level DC / DC converters.

This three-level DC / DC converter 110 controls the charging / discharging voltage / current of the battery for the electric vehicle and the neutral point of the DC-link terminal 120. Here, this neutral point control can be achieved by controlling the switching of each of the switches S ₁₁ to S ₁₄ by the switching control unit 140.

The DC-link stage 120 may be composed of two capacitors C _d1 and C _d2 . Here, the first capacitor C _d1 has one end connected to the switch S ₁₁ of the three-level DC / DC converter 110 and the fifth switch S ₂₁ of the NPC type three-level DC / AC converter 130 ' And the other end thereof may be connected to the second capacitor C _d2 . The second capacitor C _d2 has one end connected to the first capacitor C _d1 and the other end connected to the fourth switch S ₁₄ of the three level DC / DC converter 110 and the NPC type three level DC / AC Respectively, to the eighth switch S ₂₄ of the converter 130 '.

Thus, the first capacitor C _d1 and the second capacitor C _d2 are connected in series, and the connection point thereof is connected to the ground to form the neutral point (0). Here, DC- link terminal 120, the neutral point (O) is the third switch (S ₁₃₎ of the three-level DC / DC converter 110 and the fourth switch (S ₁₄₎ of a connection point type and the NPC three level DC / AC of Can be connected to the connection point of the first clamping diode D ₁ and the second clamping diode D ₂ of the converter 130 '.

Referring again to FIG. 3, the NPC type 3-level DC / AC converter 130 'may be connected to the anode P, the cathode N and the neutral point O of the DC-link stage 120.

The NPC type 3 level DC / AC converter 130 'includes a fifth switch S ₂₁ to an eighth switch S ₂₄ and two clamping diodes D ₁ and D ₂ to perform switching for power conversion. .

Here, the fifth switch (S ₂₁₎ may be connected at its one end is connected to the positive electrode (P) of the DC- link terminal 120 and its other end a sixth switch (S _22). In addition, a sixth switch (S ₂₂₎ may be connected at one end to the fifth switch (S ₂₁₎ is coupled to the other end thereof a seventh switch (S _23). The fifth switch S ₂₁ and the sixth switch S ₂₂ connected in series form a current path to the first capacitor C _d1 of the DC-link terminal 120 to be transmitted to the AC system, (C _d1 ). In addition, a sixth switch (S ₂₂₎ may be turned on if the output of the neutral point (O) to the AC grid.

One end of the seventh switch S ₂₃ may be connected to the sixth switch S ₂₂ and the other end thereof may be connected to the eighth switch S ₂₄ . Further, the eighth switch (S ₂₄₎ may be connected to the negative (N) in its one end is connected to a seventh switch (S _23), the other end thereof is DC- link terminal (120). The seventh switch S ₂₃ and the eighth switch S ₂₄ connected in series form a current path for the second capacitor C _d2 of the DC-link terminal 120 to be transmitted to the AC system, (C _d2 ). Also, the seventh switch (S ₂₃₎ may be turned on if the output of the neutral point (O) to the AC grid.

Here, the fifth switch (S ₂₁₎ through the eighth switch (S ₂₄₎ has a reverse diode can be connected in parallel, respectively. Each of these reverse diodes is for bidirectional operation by forming a reverse current path according to the ON operation of the corresponding switch.

One end of the first clamping diode D ₁ may be connected to the connection point of the fifth switch S ₂₁ and the sixth switch S ₂₂ and the other end thereof may be connected to the second clamping diode D ₂ . In addition, the second clamping diode (D ₂₎ is that once the first is connected to the first clamping diode (D _1), has its other end can be connected to a connection point of the seventh switch (S ₂₃₎ and the eighth switch (S ₂₄₎ . Here, the connection point of the first clamping diode D ₁ and the second clamping diode D ₂ may be connected to the neutral point O of the DC-link terminal 120.

At this time, the first clamping diode D ₁ forms a current path connecting the neutral point O to the AC system when the output current has a positive value, and the second clamping diode D ₂ has a negative Value, it is possible to form a current path connecting the neutral point O to the AC system.

The NPC type 3 level DC / AC converter 130 'may further include a filter connected to a connection point between the sixth switch S ₂₂ and the seventh switch S ₂₃ . Such a filter removes harmonics included in a signal input from an AC system or a signal output to an AC system, and may be a low-pass filter composed of an inductor L ₃ and a capacitor C _g .

The NPC type 3-level DC / AC converter 130 'configured as described above outputs 3 levels when DC power of the DC-link terminal 120 is converted into AC power. For example, when the fifth switch S ₂₁ and the sixth switch S ₂₂ are turned on and the seventh switch S ₂₃ and the eighth switch S ₂₄ are turned off, The anode P of the first capacitor C _d1 is connected to the AC system so that the NPC type 3 level DC / AC converter 130 'outputs "V _dc / 2", that is, the voltage "V _dcp " On the contrary, when the seventh switch S ₂₃ and the eighth switch S ₂₄ are turned on and the fifth switch S ₂₁ and the sixth switch S ₂₂ are turned off, N is connected to the AC system so that the NPC type 3 level DC / AC converter 130 'outputs "-V _dc / 2", that is, the voltage "V _dcn " of the second capacitor C _d2 . When the sixth switch S ₂₂ and the seventh switch S ₂₃ are turned on and the fifth switch S ₂₁ and the eighth switch S ₂₄ are turned off, the neutral point of the DC- (O) is connected to the AC system so that the NPC type 3 level DC / AC converter 130 'outputs "0V".

8 to 10, the output of the NPC type 3-level DC / AC converter 130 'is determined according to the conduction path according to the switching operation of each of the switches S ₂₁ to S ₂₄ .

That is, when the output current of the NPC type 3 level DC / AC converter 130 'has a positive value, as shown in FIG. 8, the fifth switch S ₂₁ and the sixth switch S ₂₂ are turned on A current path can be formed in the first capacitor C _d1 , the fifth switch S ₂₁ , the sixth switch S ₂₂ and the AC system.

9, when the sixth switch S ₂₂ and the seventh switch S ₂₃ are turned on, the neutral point O of the DC-link stage 120, the first clamping diode D ₁ , , The seventh switch (S ₂₃ ), and the AC system.

Further, as shown in FIG. 10, a current path can be formed in the AC system and a diode connected in reverse parallel to the second capacitor C _d2 , the seventh switch S ₂₃ and the eighth switch S ₂₄ , have.

On the other hand, the output current is the case with a negative value, in Figure 8, AC lines, a fifth switch (S ₂₁₎ and the sixth switch (S ₂₂₎ and a diode, and a first capacitor (C _d1) connected respectively to the opposite parallel A current path can be formed. 9, a current path can be formed at the neutral point O of the AC system, the seventh switch S ₂₃ , the second clamping diode D ₂ , and the DC-link stage 120. 10, a current path may be formed in the AC system, the seventh switch S ₂₃ , the eighth switch S ₂₄ , and the second capacitor C _d2 .

Although not shown in FIG. 3, the first to fourth switches S ₁₁ to S ₁₄ of the three-level DC / DC converter 110 and the fifth switch of the NPC type 3-level DC / AC converter 130 ' The gates of the eighth switch S ₂₁ to the eighth switch S ₂₄ may be connected to the switching controller 140. In other words, the switching control unit 140 controls the switching of the first switch (S ₁₁₎ through the eighth switch (S _24).

At this time, the switching controller 140 receives the current and / or voltage for the input and output of the NPC type 3-level DC / AC converter 130 ', and outputs the 3-level DC / DC converter 110 and the NPC type 3 level DC / AC < / RTI > converter 130 '.

For example, although not shown in the drawing, the switching control unit 140 may be configured so that each of the capacitors C _d1 and C _{d2 of} the DC-link stage 120 corresponding to the input of the NPC type 3 level DC / AC converter 130 ' And receives the current or voltage from the output of the NPC type 3-level DC / AC converter 130 'through the sensor.

When charging the battery for an electric vehicle from the AC system, the charge / discharge device 100 for an electric vehicle configured as described above first converts the power of the AC system to DC power by the NPC type 3 level DC / AC converter 130 ' Level stage DC-DC converter 110. The three-level DC / DC converter 110 reduces the power stored in the capacitors C _d1 and C _d2 of the DC-link stage 120 to charge the battery. At this time, the bidirectional three-level DC / DC converter 110 switches the first switch S ₁₁ and the second switch S ₁₂ to reduce the voltage of the DC-link terminal 120 to the battery voltage to charge the battery .

In addition, when the electric power of the battery for the electric vehicle is transmitted to the AC system, the three-level DC / DC converter 110 boosts the voltage of the battery to the voltage of the DC- Can be stored in the capacitors C _d1 and C _d2 . At this time, the three-level DC / DC converter 110 switches the third switch S ₁₃ and the fourth switch S ₁₄ to boost the voltage of the battery to the voltage of the DC- (120). At this time, the 3-level DC / AC converter 130 'can convert the DC voltage stored in the DC-link stage 120 to AC and output it to the AC system.

11 shows a case where the three-level DC / AC converter 130 is a T type.

T-type three-level DC / AC converter (130 ") may comprise a fifth switch (S ₃₁₎ through the eighth switch (S ₃₄₎ to perform switching for power conversion.

This T-type three-level DC / AC converter 130 "can be connected to the anode P, the cathode N and the neutral point O of the DC-

Here, the fifth switch (S ₃₁₎ may be connected at its one end is connected to the positive electrode (P) of the DC- link terminal 120 and its other end an eighth switch (S _34). This fifth switch S ₃₁ may be turned on to form a current path to the first capacitor C _d1 of the DC-link stage 120 to transmit to the AC system or to charge the first capacitor C _d1 .

A sixth switch (S ₃₂₎ may be connected at its one end is connected to the neutral point (O) of the DC- link stage 120 and the other end is the seventh switch (S _33). A seventh switch (S ₃₃₎ may be connected each at its one end a sixth switch, the fifth switch is connected to (S ₃₂₎ and the other end (S ₃₁₎ and the eighth switch (S _34). That is, the sixth switch (S ₃₂₎ and the seventh switch (S ₃₃₎ is series-connected neutral point (O) and a fifth switch (S ₃₁₎ and the eighth switch (S ₃₄₎ of the link terminal DC- 120 As shown in FIG. This, the sixth switch (S ₃₂₎ and the seventh switch (S ₃₃₎ may be turned on so that the neutral point (0) of the DC- link terminal 120 is connected to the AC grid.

The eighth switch _S34 may have one end connected to the fifth switch _S31 and the other end connected to the negative electrode N of the DC-link terminal 120. [ The eighth switch (S ₃₄₎ may be turned on and sent to the AC grid to form a current path for the second capacitor (C _d2) of the link terminal DC- 120, or to charge the second capacitor (C _d2) .

Here, the fifth switch (S ₃₁₎ through the eighth switch (S ₃₄₎ has a reverse diode can be connected in parallel, respectively. Each of these reverse diodes is for bidirectional operation by forming a current path according to the ON / OFF operation of the corresponding switch.

The T-type three-level DC / AC converter (130 ") may further comprise a filter that is connected to the connection point of the fifth switch (S _31), the eighth switch (S _34). The filter input from the AC grid Pass filter composed of an inductor L ₃ and a capacitor C _g , and removes harmonics contained in a signal or a signal output to the AC system.

In the T type 3-level DC / AC converter 130 ", the fifth switch S ₃₁ and the seventh switch S ₃₃ operate in a complementary manner, and the sixth switch S ₃₂ and the eighth switch S ₃₄ complementarily operate to generate a three level voltage having three voltage levels (+ V _dc / 2, 0, -V _dc / 2). Here, complementary operation occurs when one switch is turned on And the other one switch is turned off. The three-level voltage generated by the switching operation is output to the AC system through the LC filter.

When more specifically described with reference to Figures 12 to 14, T-type three-level DC / AC converter (130 "), the output is determined in accordance with the conduction path of the switching operations of the switches (S ₃₁ ~ S ₃₄₎ .

That is, when the output current of the T type 3-level DC / AC converter 130 "has a positive value, as shown in FIG. 12, when the fifth switch S ₃₁ is turned on, the first capacitor C _d1 ), The fifth switch ( _S31 ), and the AC system.

In addition, as shown in Figure 13, the sixth switch (S ₃₂₎ and the seventh switch (S ₃₃₎ is, the neutral point (O), a sixth switch (S ₃₂₎ of the DC- link terminal (120) when turned on, A diode connected in parallel to the third switch S ₁₃ in reverse direction, and an AC system.

In addition, as shown in Figure 14, the eighth switch may be a current path formed by the diode and the AC system (S ₃₄₎ and a reverse parallel-connected.

Conversely, when the output current of the T type 3-level DC / AC converter 130 "has a negative value, in FIG. 12, the AC system, the diode connected in reverse parallel to the fifth switch _S31 , may be a current path formed of the (C _d1). in addition, in FIG 13, AC lines, the seventh switch (S _33), the sixth switch (S ₃₂₎ and a reverse connection diode is connected, and the DC- link terminal (120 The current path can be formed at the neutral point O of the AC system, the eighth switch S ₃₄ , and the second capacitor C _{d2 in} Fig.

The T-type three-level DC / AC converter (130 ") is applied to the full voltage (V _dc) at the time of switching operation, the fifth switch (S ₃₁₎ and the eighth switch (S _34), the DC- link terminal (120) However, the sixth switch (S ₃₂₎ and the seventh switch (S ₃₃₎ is so applied with half the voltage of the DC- link terminal 120, it is possible to improve the overall efficiency by reducing the switching loss. At this time, the output It is possible to reduce the size of the filter.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

100: charge / discharge device for electric vehicle 110: three-level DC / DC converter
120: DC-link stage 130: Three level DC / AC converter
140: switching control unit S ₁₁ to S ₁₄ : first to fourth switches
_{S 21 ~ S 24, S 31} ~ S 34: the fifth switch to eighth switch
D ₁ , D ₂ : Clamping diode L ₃ , C _g : LC filter

Claims (8)

A DC-link stage consisting of two capacitors, the connection point of which is connected to ground;
A three-level DC / DC converter for reducing the voltage of the DC-link stage to a voltage of an electric vehicle battery or boosting a voltage of the battery for the electric vehicle to a voltage of the DC-link stage;
A bidirectional three-level DC / AC converter for converting the AC power of the AC system into DC power or converting the DC power of the DC-link stage into AC power; And
And a switching control unit for controlling the switching of the three-level DC / DC converter and the three-level DC / AC converter so as to charge or discharge the battery in the form of pulsating current identical to the form of power on the AC system side. Charging and discharging devices for automobiles. The method according to claim 1,
The three-level DC / DC converter includes:
A first switch that is turned on to charge the battery by a first capacitor of the DC-link stage;
A second switch that is turned on to charge the battery by a second capacitor of the DC-link stage;
A third switch that is turned on so that the battery discharges to the second capacitor; And
And a fourth switch that is turned on so that the battery discharges to the first capacitor. 3. The method of claim 2,
Wherein each of the first to fourth switches is connected in parallel with a reverse diode. The method according to claim 1,
Wherein the three-level DC / AC converter is an NPC type three-level DC / AC converter. 5. The method of claim 4,
The NPC type 3-level DC / AC converter includes:
A fifth switch and a sixth switch that are turned on to form a current path for the first capacitor of the DC-link stage and are connected in series with each other;
A seventh switch and an eighth switch that are turned on to form a current path for the second capacitor of the DC-link stage and are connected in series with each other;
A first clamping diode connected between a connection point of the fifth switch and the sixth switch and a connection point of the capacitors; And
And a second clamping diode connected between a connection point of the seventh switch and the eighth switch and the connection point of the capacitors,
And the connection point of the first clamping diode and the second clamping diode is connected to the connection point of the capacitors. The method according to claim 1,
The three-level DC / AC converter is a T-type three-level DC / AC converter. The method according to claim 6,
The T-type 3-level DC / AC converter includes:
A fifth switch that is turned on to form a current path for the first capacitor of the DC-link stage;
A sixth switch and a seventh switch that are turned on so that the connection point of the capacitors is connected to the AC system; And
And an eighth switch that is turned on to form a current path for the second capacitor of the DC-link stage,
Wherein the sixth switch is connected to the connection point of the capacitors, and the seventh switch is connected to the connection point of the fifth switch and the eighth switch. The method according to claim 1,
Wherein the three-level DC / AC converter includes a filter for removing harmonics included in a signal input from the AC system or a signal output to the AC system.

Images