KR20160080439A - Dc-dc converter in secondary cell system and methof for - Google Patents

Abstract

Disclosed are a DC-DC converter of a secondary cell system and a control method thereof. The converter of the present invention includes: four arms connected to a load resistor in parallel individually; and upper and lower switching devices connected to each of the arms, thereby lowering rating specifications and reducing a size of an inner inductor. Therefore, a current ripple can be minimized when a secondary cell is charged.

Description

Technical Field [0001] The present invention relates to a DC-DC converter of a secondary battery system,

The present invention relates to a DC-DC converter of a secondary battery system and a control method thereof.

The success or failure of renewable energy generation systems represented by solar power or wind power is in fact determined by efficiency and stability. Compared to conventional fossil fuel power generation that produces a constant output, renewable energy is irregular due to the surrounding environment and weather. This inability to control is a major obstacle to commercialization.

The technology that is desperately needed to solve the problem is the large capacity secondary battery. A large capacity secondary battery can maintain a constant output by storing surplus power when the power generation efficiency is good and adding the power when the power efficiency is low.

Accordingly, the development of such a secondary battery is accelerating, one of which is a redox flow cell. The redox flow battery has advantages such that it can be easily mass-produced and can be used for a long time, and active research is being conducted.

In such a plurality of secondary battery systems, an unidirectional bidirectional DC-DC converter is used, the operation of which is a discharging operation for boosting a low voltage battery side voltage to a high voltage inverter DC link voltage and, conversely, .

Such charging or discharging is realized by switching the power semiconductor in the DC-DC converter, and the electrical rated specifications of the power semiconductor are determined from the voltage and current specifications of the secondary battery.

FIG. 1 is a diagram for explaining a configuration of a DC-DC converter of a conventional secondary battery system, and it can be confirmed that power semiconductor elements S1 and S2 are used.

The conventional DC-DC converter operates in a buck mode (charge) and a boost mode (discharge) for charging or discharging a secondary battery.

FIG. 2A shows an operation state when the DC-DC converter of FIG. 1 is in a buck mode, and FIG. 2B shows an operation state when the DC-DC converter of FIG. 1 is in a boost mode.

That is, in the buck mode, the second switch S2 operates as a diode, and in the boost mode, the first switch S1 operates as a diode, thereby controlling charging or discharging.

However, recently, in the large-capacity secondary battery system such as the redox flow battery, the specification of the voltage and the current is increasing, and as a result, the rated specifications of the power semiconductor elements S1 and S2 used in the conventional DC- There is a problem that it becomes difficult to retrofit a device suitable for the specification.

In addition, as the voltage and current specifications of the secondary battery system increase, the reactance of the inductor L used in the DC-DC converter must also increase in size. This increases the overall size of the converter, the conventional DC-DC converter constituted of the arm has a problem that there is a limitation in reducing the switching current ripple at the time of charging which directly affects the life of the secondary battery.

Therefore, with such a conventional DC-CD converter, there is a problem that the energy storage system (ESS) can not efficiently cope with the trend toward compactness.

SUMMARY OF THE INVENTION The present invention is directed to a DC-DC converter and a control method therefor of a secondary battery system that minimizes current ripple during charging of a secondary battery while lowering the rated specification of the power semiconductor device and reducing the size of the internal inductor .

According to an aspect of the present invention, there is provided a converter of a first aspect of the present invention for boosting or down-converting a voltage applied from a battery to a load resistor, the converter being connected in parallel to the load resistor, An upper switching element and a first lower switching element; A second upper switching element and a second lower switching element connected in parallel to the load resistor to constitute a second arm; A third upper switching element and a third lower switching element connected in parallel to the load resistor to constitute a third arm; A fourth upper switching element and a fourth lower switching element connected in parallel to the load resistor to constitute a fourth arm; A first inductor coupled between a first node between the first upper switching element and the first lower switching element and an input node of the battery; A second inductor connected to the second node and the input node between the second upper switching element and the second lower switching element; A third inductor connected to the third node and the input node between the third upper switching element and the third lower switching element; And a fourth node between the fourth upper switching element and the fourth lower switching element and a fourth inductor connected to the input node.

In one embodiment of the present invention, the first and second inductors constitute a first coupling inductor, and the third and fourth inductors constitute a second coupling inductor.

In an embodiment of the present invention, the phase difference between the first upper switching element and the first lower switching element, the phase difference between the second upper switching element and the second lower switching element, the phase difference between the third upper switching element and the third lower switching element And the phase difference between the fourth upper switching element and the fourth lower switching element may be substantially 180 degrees.

According to another aspect of the present invention, there is provided a method of controlling a converter, the method including controlling a phase difference between the first upper switching element and a second upper switching element, And the phase difference between the third upper switching element and the fourth upper switching element are respectively substantially 90 degrees.

In an embodiment of the present invention, the phase difference between the first lower switching element and the second lower switching element, the phase difference between the second lower switching element and the third lower switching element, and the phase difference between the third lower switching element and the fourth lower switching element It is possible to control the phase difference of the elements to be substantially 90 degrees.

The present invention as described above can realize a compact secondary battery system, reduce current ripple, and maximize efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram illustrating a configuration of a conventional DC-DC converter of a secondary battery system. FIG.
FIG. 2A shows an operation state when the DC-DC converter of FIG. 1 is in a buck mode.
FIG. 2B shows an operation state when the DC-DC converter of FIG. 1 is in a boost mode.
3 is a circuit diagram illustrating a DC-DC converter according to an embodiment of the present invention.
4 is an exemplary diagram for explaining a switching operation of a switching element of the DC-DC converter of the present invention.

While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that the invention is not intended to be limited to the particular embodiments, but includes all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.

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

3 is a circuit diagram illustrating a DC-DC converter according to an embodiment of the present invention.

As shown in the figure, four arms (A1 to A4) connected in parallel to the load resistance R for outputting a voltage Vo to be applied to the load resistance R by reducing or boosting the battery voltage Vbat of the present invention , Each of the arms A1 to A4 may be connected to an upper switching element and a lower switching element which are power semiconductors.

That is, the first upper switching element Su1 and the first lower switching element Sd1 may be connected to the first arm A1, and the second upper switching element Su2 and the second lower switching element Sd2 may be connected to the second arm A2. And the third upper switching element Su3 and the third lower switching element Sd3 may be connected to the third arm A3 and the fourth upper switching element Su4 and the fourth lower switching element Sd4 may be connected to the fourth arm A4. have.

At this time, the phase difference between the upper switching element and the lower switching element can be arranged to be substantially 180 degrees. That is, the phase difference between the first upper switching element Su1 and the first lower switching element Sd1 is substantially 180 degrees, the phase difference between the second upper switching element Su2 and the second lower switching element Sd2 is substantially 180 degrees, The phase difference between the element Su3 and the third lower switching element Sd3 is substantially 180 degrees and the phase difference between the fourth upper switching element Su4 and the fourth lower switching element Sd4 is substantially 180 degrees.

Also, the phase difference between the first upper switching element Su1 and the second upper switching element Su2 is substantially 90 degrees, the phase difference between the second upper switching element Su2 and the third upper switching element Su3 is substantially 90 degrees, The phase difference between the element Su3 and the fourth lower switching element Sd4 can be controlled to be substantially 90 degrees.

Similarly, the phase difference between the first lower switching element Sd1 and the second lower switching element Sd2 is substantially 90 degrees, the phase difference between the second lower switching element Sd2 and the third lower switching element Sd3 is substantially 90 degrees, The phase difference between the element Sd3 and the fourth lower switching element Sd4 can be controlled to be substantially 90 degrees.

This is shown in FIG.

4 is an exemplary diagram for explaining a switching operation of a switching element of the DC-DC converter of the present invention. In Fig. 4, the switching element of the first arm A1 is denoted by S1, the switching element of the second arm A2 is denoted by S2, the switching element of the third arm A3 is denoted by S3, Although the switching device is shown as S4, it can be applied to both the upper and lower switching devices, and thus is shown for the sake of simplicity.

As shown in the figure, the first switching device S1, the second switching device S2, the third switching device S3, and the fourth switching device S4 can be controlled to have a phase difference of 90 degrees, respectively.

With this configuration, it can be seen that the switching frequency of the DC-DC converter of the present invention can be increased four times. For example, if the switching frequency of the DC-DC converter of the embodiment of the present invention in Fig. 3 is 10 kHz, the operation of the DC-DC converter according to one embodiment of the present invention is that the DC- Operation. With such a high switching frequency, in the DC-DC converter of the present invention, current ripple can be reduced during charging or discharging of the secondary battery, so that the life and utilization of the secondary battery can be improved.

In addition, since the DC-DC converter of the present invention is composed of four arms, the current applied to each arm is reduced to 1/4 of the rated current, so that the rating of the switching device, This is particularly advantageous in the supply and demand of a switching element, which is a power semiconductor, in a large-capacity ESS system or in the construction of a converter.

As the electrical rating of each arm is reduced to 1/4, the current in the inductor connected to each arm may correspondingly decrease. Basically, the size of the inductor is due to the thickness of the coil depending on the current capacity, so it can be reduced by reducing the coil thickness of the inductor.

3, according to the topology of the DC-DC converter of the present invention, the node N1 between the first upper switching element Su1 and the first lower switching element Sd1 and the inductor L1 are connected to the battery input node B, The node N2 between the second upper switching element Su2 and the second lower switching element Sd2 and the inductor L2 may be connected to the battery input node B. [ In addition, the inductor L3 is connected to the node N3 between the third upper switching element Su3 and the third lower switching element Sd3 and the battery input node B, and the node N4 between the fourth upper switching element Su4 and the fourth lower switching element Sd4 And the battery input node B may be connected to the inductor L4.

In this case, the inductors L1 and L2 constitute a first coupling inductor, and the inductors L3 and L4 constitute a second coupling inductor. That is, by using two coupling inductors for four arms, the overall size of the converter can be reduced.

In the description of the present invention, an example constituted by four arms will be described, but the present invention is not limited thereto. That is, it may be constituted in various ways in consideration of the rating of the secondary battery system, the rating of the power semiconductor, etc., such as 8 arms or 16 arms.

According to the DC-DC converter topology of the secondary battery system according to the present invention, the secondary battery system can be made compact, the current ripple can be reduced, and the efficiency can be maximized.

While the invention has been shown and described with reference to certain preferred embodiments thereof, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined by the appended claims. Accordingly, the true scope of the present invention should be determined by the following claims.

Claims (5)

A converter for boosting or stepping down a voltage applied from a battery and providing the voltage to a load resistor,
A first upper switching element and a first lower switching element connected in parallel to the load resistor to constitute a first arm;
A second upper switching element and a second lower switching element connected in parallel to the load resistor to constitute a second arm;
A third upper switching element and a third lower switching element connected in parallel to the load resistor to constitute a third arm;
A fourth upper switching element and a fourth lower switching element connected in parallel to the load resistor to constitute a fourth arm;
A first inductor coupled between a first node between the first upper switching element and the first lower switching element and an input node of the battery;
A second inductor connected to the second node and the input node between the second upper switching element and the second lower switching element;
A third inductor connected to the third node and the input node between the third upper switching element and the third lower switching element; And
A fourth inductor between the fourth upper switching element and a fourth lower switching element and a fourth inductor coupled to the input node.
The converter according to claim 1, wherein the first and second inductors constitute a first coupling inductor, and the third and fourth inductors constitute a second coupling inductor.
The method of claim 1, wherein the phase difference between the first upper switching element and the first lower switching element, the phase difference between the second upper switching element and the second lower switching element, the phase difference between the third upper switching element and the third lower switching element, And the phase difference between the fourth upper switching element and the fourth lower switching element is substantially 180 degrees.
A method for controlling a converter according to any one of claims 1 to 3,
The phase difference between the first upper switching element and the second upper switching element, the phase difference between the second upper switching element and the third upper switching element, and the phase difference between the third upper switching element and the fourth upper switching element are substantially 90 The control method comprising:
5. The method of claim 4,
The phase difference between the first lower switching element and the second lower switching element, the phase difference between the second lower switching element and the third lower switching element, and the phase difference between the third lower switching element and the fourth lower switching element are substantially 90 The control method comprising:

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