KR20180054021A - bidirectional DC-DC converter, and energy storage system including the same - Google Patents

Abstract

Provided are a bidirectional DC-DC converter, and an energy storage system including the same. The bidirectional DC-DC converter has a first node to which a direct current power source is connected, second to fifth nodes, and a ground node. The bidirectional DC-DC converter comprises: a first inductor between the first node and the third node; a first switch and a first diode connected in parallel between the third node and the ground node; a second inductor between the first node and the fourth node; a second switch and a second diode connected in parallel between the fourth node and the ground node; a first capacitor between the second node and the ground node; a third switch between the fourth node and the fifth node; a fourth switch and a third diode connected in parallel between the third node and the fifth node; a fifth switch and a fourth diode connected in parallel between the fifth node and the second node; and a sixth switch and a second capacitor connected in series between the fourth node and the fifth node. According to the present invention, control stability can be secured.

Description

TECHNICAL FIELD [0001] The present invention relates to a bidirectional DC-DC converter, and an energy storage system including the bidirectional DC-DC converter,

The present invention relates to a bi-directional DC-DC converter, and an energy storage system including the same.

Typical bi-directional DC-DC converters operate in unidirectional boost mode with step-up and unidirectional buck-mode with step-down voltage down. Unidirectional bidirectional DC-DC converters are widely used because they have many advantages in terms of the number and size of components compared to isolated bi-directional DC-DC converters. When the non-isolated bidirectional DC-DC converter is operated in the boost mode, if the output voltage is greatly increased with respect to the input voltage, the target output voltage may not be achieved due to the limitation of the boost. Even if the target output voltage is achieved, the duty ratio becomes 0.8 to 0.9 or more, which increases the likelihood of causing unstable control. As an alternative to this, an insulated bidirectional DC-DC converter has appeared, but it requires components such as a transformer, an auxiliary inductor, and a resonant element, which increases the total number of components and low efficiency.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a non-isolated bidirectional DC-DC converter having control stability and an energy storage system including the same.

A bidirectional DC-DC converter according to an aspect of the present invention has a first node to which a DC power source is connected, second to fifth nodes, and a ground node. The bidirectional DC-DC converter includes a first inductor between the first node and the third node, a first switch and a first diode connected in parallel between the third node and the ground node, A second inductor between the fourth node and the ground node, a second switch and a second diode connected in parallel between the fourth node and the ground node, a first capacitor between the second node and the ground node, A fourth switch and a third diode connected in parallel between the third node and the fifth node, a third switch connected in parallel between the fifth node and the second node, A switch and a fourth diode, and a sixth switch and a second capacitor connected in series between the fourth node and the fifth node.

In operation in the boost mode, the first and second switches are interleaved with each other, the third to fifth switches are turned off, and the sixth switch can be turned on. The first and second switches may be turned on at a duty ratio of 50% or more to less than 80%. The second switch may be in a turned-on state when the first switch is turned off, and the first switch may be turned on when the second switch is turned off.

In operation in the buck mode, the third and fourth switches are interleaved with each other, the first, second and sixth switches are turned off, and the fifth switch is turned on. The third and fourth switches may be turned on with a duty ratio of less than 50%. The fourth switch may be in a turn-off state when the third switch is in a turn-on state, and the third switch may be in a turn-off state when the fourth switch is in a turn-on state.

The ratio of the second voltage of the second node to the first voltage of the first node may be at least 6 times and at most 10 times.

The energy storage system according to one aspect of the present invention comprises the bidirectional DC-DC converter, a battery connected between a first node of the bidirectional DC-DC converter and a ground node, a second node of the bidirectional DC- A power converter for converting power between at least one of a DC link, a power generation system, a system, and a load including a first capacitor between nodes and the DC link, and a power converter for controlling the bidirectional DC-DC converter and the power converter And a power conversion system including an integrated controller.

The power conversion apparatus may include a power conversion unit between the power generation system and the DC link unit, and a bi-directional inverter between the system and the load and the DC link unit.

The bidirectional DC-DC converter according to various embodiments of the present invention can ensure control stability because a control signal having a duty ratio of 0.8 or less can be used even when operating in a boost mode with an output voltage 8 times the input voltage . In addition, it can operate in a buck mode that reduces voltage. Thus, an energy storage system comprising a bi-directional DC-DC converter in accordance with various embodiments of the present invention may include a battery having a low voltage.

In addition, the bi-directional DC-DC converter according to various embodiments of the present invention has the advantages of the non-bi-directional bi-directional DC-DC converter and can operate in an interleaved manner to reduce the maximum current in half.

1 shows a circuit diagram of a bidirectional DC-DC converter according to one embodiment.
Fig. 2 shows a control timing diagram when the bi-directional DC-DC converter shown in Fig. 1 operates in the boost mode.
3 to 6 show a bidirectional DC-DC converter operating in the boost mode for each section.
FIG. 7 shows a circuit diagram when the bi-directional DC-DC converter shown in FIG. 1 operates in a buck mode.
8 shows a control timing diagram when the bidirectional DC-DC converter shown in Fig. 7 operates in the buck mode.
9-12 illustrate a bidirectional DC-DC converter operating in the buck mode for each section.
13 schematically illustrates an energy storage system and a peripheral configuration according to one embodiment.
14 is a block diagram illustrating a schematic configuration of an energy storage system according to an embodiment.

Brief Description of the Drawings The advantages and features of the present invention, and the manner of achieving them, will be apparent from and elucidated with reference to the embodiments described in conjunction with the accompanying drawings. It is to be understood, however, that the invention is not limited to the embodiments shown herein but may be embodied in many different forms and should not be construed as being limited to the preferred embodiments of the present invention. do. BRIEF DESCRIPTION OF THE DRAWINGS The above and other aspects of the present invention will become more apparent by describing in detail preferred embodiments thereof with reference to the attached drawings. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

The terminology used in this application is used only to describe a specific embodiment and is not intended to limit the invention. The singular expressions include plural expressions unless the context clearly dictates otherwise. In the present application, the terms "comprises" or "having" and the like are used to specify that there is a feature, a number, a step, an operation, an element, a component or a combination thereof described in the specification, But do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, or combinations thereof. The terms first, second, etc. may be used to describe various elements, but the elements should not be limited by the terms. The terms are used only for the purpose of distinguishing one component from another.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. .

1 shows a circuit diagram of a bidirectional DC-DC converter according to one embodiment.

Referring to FIG. 1, a bidirectional DC-DC converter 100 has first to fifth nodes N1 to N5 and a ground node GND.

A DC power supply (C1) is connected between the first node (N1) and the ground node (GND). According to one example, the DC power supply C1 may be a battery. According to another example, the DC power supply C1 may be the output voltage of the rectifying circuit to which the AC voltage is applied. Although not shown in FIG. 1, a capacitor may be connected in parallel with the direct-current power supply C1 between the first node N1 and the ground node GND.

The bidirectional DC-DC converter 100 can operate in a boost mode and a buck mode. When operating in the boost mode, the bi-directional DC-DC converter 100 boosts the voltage of the first node N1 and outputs it to the second node N2. In this case, the first node N1 is the input node and the second node N2 is the output node. When operating in the buck mode, the bi-directional DC-DC converter 100 reduces the voltage of the second node N2 and outputs it to the first node N1. In this case, the second node N2 is the input node, and the first node N1 is the output node. The level of the second voltage V2 of the second node N2 is higher than the level of the first voltage V1 of the first node N1. Although not shown in FIG. 1, a battery may be connected to the first node N1, and a DC link may be connected to the second node N2. The DC link is connected to the input of the inverter so that the inverter can supply the DC link energy to the utility power (Grid) and / or the load.

According to an example, a battery may be connected to the first node N1, and a load or a commercial power may be connected to the second node N2 through a bidirectional inverter. When operating in the boost mode, the battery connected to the first node N1 is discharged, and the discharged power can be supplied to a load or a commercial power source connected to the second node N2. When operating in the buck mode, the battery connected to the first node N1 is charged from a commercial power source connected to the second node N2.

The bidirectional DC-DC converter 100 includes a first inductor L1 between a first node N1 and a third node N3 and a second inductor L1 between a first node N1 and a fourth node N4. (L2). The first current i1 is defined as a current flowing from the first node N1 to the third node N3 through the first inductor L1 and the second current i2 is defined as the current flowing through the first inductor L1 at the first node N1. Is defined as a current flowing through the second inductor (L2) to the fourth node (N4). The first inductor L1 and the second inductor L2 may have the same inductance. However, the present invention is not limited thereto, and the inductances of the first and second inductors L1 and L2 may be different from each other. For ease of understanding of the present invention, it is assumed that the first and second inductors L1 and L2 have the same inductance with each other.

The bidirectional DC-DC converter 100 includes a first switch S1, a first diode D1, and a fourth node N4, which are connected in parallel between a third node N3 and a ground node GND, And a second switch S2 and a second diode D2 connected in parallel between the node GND. The first diode D1 is connected antiparallel to the first switch S1 to allow current to flow from the ground node GND to the third node N3. When the first switch S1 is turned on, a current can also flow from the third node N3 to the ground node GND. The second diode D2 is connected in anti-parallel with the second switch S2 to allow current to flow from the ground node GND to the fourth node N4. When the second switch S2 is turned on, a current can also flow from the fourth node N4 to the ground node GND. The first switch S1 and the first diode D1 may be implemented as a power MOSFET device having a vertical diffused MOS (Vertical Diffused MOS) structure. Also, the second switch S2 and the second diode D2 may also be implemented as power MOSFET devices.

The bidirectional DC-DC converter 100 includes a first capacitor C2 connected between a second node N2 and a ground node GND. According to one example, the first capacitor C2 may constitute a DC link. The first capacitor C2 may stabilize the second voltage V2 of the second node N2. The first capacitor C2 may have a capacitance (capacitance) sufficiently large such that the ripple voltage of the second node N2 is smaller than the level of the second voltage V2.

The bidirectional DC-DC converter 100 includes a third switch S3 between the fourth node N4 and the fifth node N5, and a third switch S3 connected between the third node N3 and the fifth node N5 in parallel A fourth switch S4 and a third diode D3, a fifth switch S5 and a fourth diode D4 connected in parallel between the fifth node N5 and the second node N2, And a sixth switch S6 and a second capacitor C3 connected in series between the node N4 and the fifth node N5.

The third current i3 is defined as the current flowing from the fifth node N5 to the fourth node N4 and the third voltage V3 is defined as the voltage across the second capacitor C3.

The third diode D3 is connected in anti-parallel with the fourth switch S4 to allow current to flow from the third node N3 to the fifth node N5. When the fourth switch S4 is turned on, a current can flow from the fifth node N5 to the third node N3. The fourth switch S4 and the third diode D3 may be implemented as power MOSFET devices.

The fourth diode D4 is connected in anti-parallel with the fifth switch S5 to allow current to flow from the fifth node N5 to the second node N2. When the fifth switch S5 is turned on, a current can also flow from the second node N2 to the fifth node N5. The fifth switch S5 and the fourth diode D4 may be implemented as power MOSFET devices.

The bidirectional DC-DC converter 100 includes a diode connected in reverse parallel to the third switch S3 between the fourth node N4 and the fifth node N5, and a diode connected in anti-parallel connection with the sixth switch S6. Lt; RTI ID = 0.0 > diode. ≪ / RTI >

The second capacitor C3 can stabilize the third voltage V3 between the sixth switch S6 and the fifth node N5. The second capacitor C3 may have a capacitance (capacitance) large enough to generate a small ripple at the third voltage V3. According to another example, the capacity of the second capacitor C3 may be smaller than that of the first capacitor C2.

Fig. 2 shows a control timing diagram when the bi-directional DC-DC converter shown in Fig. 1 operates in the boost mode. 3 to 6 show a bidirectional DC-DC converter operating in the boost mode for each section.

Referring to FIG. 2, when the bidirectional DC-DC converter 100 operates in the boost mode, the first and second switches S1 and S2 are switched interleaved with each other at the switching cycle Ts. The third to fifth switches S3 to S5 are continuously turned off. The sixth switch S6 is continuously turned on and the second capacitor C3 is connected between the fifth node N5 and the fourth node N4. The third voltage V3 is defined as the difference between the potential of the fifth node N5 and the power of the fourth node N4.

During the first period t0-t1 of the switching period Ts, the first and second switches S1 and S2 are all turned on. At time t1, the first switch S1 is turned off, and during the second period t1-t2, the first switch S1 is turned off and the second switch S2 is turned on. At time t2, the first switch S1 is turned on, and during the third period t2-t3, the first and second switches S1 and S2 are both turned on. At a time t3, the second switch S2 is turned off, and during the fourth period t3-t4, the first switch S1 is turned on and the second switch S2 is turned off.

The second section t1-t2 in which the first switch S1 is turned off and the fourth section t3-t4 in which the second switch S2 is turned off may be the same. That is, the duty ratio D = DTs / Ts, which is the ratio of the time DTs during which the first switch S1 is turned on in the switching period Ts, is equal to the duty ratio D of the second switch S2 . However, the present invention is not limited to this, and the duty ratio of the first switch S1 and the duty ratio of the second switch S2 may be different from each other. For ease of understanding of the present invention, it is assumed that the duty ratios of the first and second switches S1 and S2 are equal to each other.

The first switch S1 and the second switch S2 may be turned on at a duty ratio of 50% or more and less than 80%, depending on the step-up ratio of the bi-directional DC-DC converter 100 operating in the boost mode. For example, when the step-up ratio is 4, the first and second switches S1 and S2 can be turned on with a duty ratio D of approximately 50%. When the step-up ratio is 6, the first and second switches S1 and S2 can be turned on with a duty ratio D of approximately 66.7%. When the step-up ratio is 8, the first and second switches S1 and S2 can be turned on with a duty ratio D of approximately 75%. When the step-up ratio is 10, the first and second switches S1 and S2 can be turned on with a duty ratio D of approximately 80%.

As shown in FIG. 2, the first and second switches S1 and S2 may be turned on at a duty ratio D of 50% or more. At this time, the first and second switches S1 and S2 may be turned off interleaved with each other at the switching period Ts. For example, when the first switch S1 is in the turn-off state, the second switch S2 may be in the turn-on state, and when the second switch S2 is in the turn-off state, May be in a turned-on state. That is, there may be no state in which both the first switch S1 and the second switch S2 are turned off.

First, the voltage across the second capacitor C3, that is, the third voltage V3 will be described. The third voltage V3 across the second capacitor C3 can be raised or lowered within the switching period Ts but has an average level after the bi-directional DC-DC converter 100 is stabilized. The second voltage V2 is also a voltage across the first capacitor C2 and has an average level after the bidirectional DC-DC converter 100 is stabilized. The first voltage V1 is constant as the voltage of the DC power supply C1. In the present specification, the average voltage means an average voltage during the switching period Ts after the bidirectional DC-DC converter 100 is stabilized.

Referring to the closed loop formed by the first node N1, the fourth node N4, the fifth node N5 and the third node N3 shown in FIG. 1, the average voltage across the first inductor L1, Since the average voltage across the two inductor L2 is zero, the average third voltage V3 during the switching period Ts is the average voltage across the third diode D3 (i.e., the fifth node N5 and the third And the voltage between the node N3).

The third node N3 and the fourth node N4 are turned on during the first period t0-t1 and the third period t2-t3 during which both of the first and second switches S1 and S2 are turned on Are all connected to the ground node GND, the average third voltage V3 is equal to the average voltage across the third diode D3.

The current flows in the forward direction to the third diode D3 during the second period t1-t2 during which the first switch S1 is turned off and the second switch S2 is turned on. Therefore, both ends of the third diode D3 Is zero.

The third node N3 is connected to the ground node GND and the third diode D3 is connected during the fourth period t3-t4 during which the first switch S1 is turned on and the second switch S2 is turned off, The voltage across the third diode D3 is equal to the second voltage V2.

As described above, when the OFF time of the first switch S1 and the OFF time of the second switch S2 are the same, the average voltage across the third diode D3 is 1/2 of the second voltage V2 . Therefore, the third voltage V3 is equal to 1/2 of the second voltage V2. In the following, it is assumed that the capacitance of the second capacitor C3 is sufficiently large, and the third voltage V3 is constant to 1/2 of the second voltage V2.

Referring to FIGS. 2 and 3, the first switch S1 and the second switch S2 are turned on during the first period t0-t1. 3, the first current i1 flowing through the first inductor L1 flows to the first switch S1 and the second current i2 flowing through the second inductor L2 flows through the first inductor L1, 2 switch S2. The first voltage V1 of the DC power supply C1 is equal to the voltage L1 di1 / dt across the first inductor L1 and the voltage L2 di2 / dt across the second inductor L2. Therefore, the first current i1 increases at a slope of V1 / L1 with respect to time during the first section t0-t1, and the second current i2 also increases with the time during the first section t0-t1 by V2 / L2 < / RTI > At this time, the energy of the DC power source C1 is stored in the first and second inductors L1 and L2. The third current i3 flowing through the second capacitor C3 is zero.

2 and 4, at time t1, the first switch S1 is turned off, the first switch S1 is turned off during the second period t1-t2, and the second switch S2 ) Is turned on. The second current i2 flowing through the second inductor L2 flows to the second switch S2 but the first current i1 flowing through the first inductor L1 flows through the first inductor L1, 3 diode D3, the second capacitor C3, and the second switch S2.

Since the voltage L2 di2 / dt at the both ends of the second inductor L2 is equal to the first voltage V1 of the DC power supply C1, the second current i2 flows through the first section t0- And increases with the slope of V2 / L2 according to time during the second period (t1-t2). The second inductor L2 stores the energy of the DC power supply C1.

The first inductor L1 emits the energy stored during the first period t0-t1. Since the first current i1 flows in the forward direction to the third diode D3, the voltage across the third diode D3 is zero. Since the sum of the voltage (-L1 di1 / dt) between the third node N3 and the first node N1 and the first voltage V1 is equal to the third voltage V3, that is, V2 / 2, 1 current i1 decreases with the slope of - (V2 / 2-V1) / L1 with time. At this time, the third current i3 flowing through the second capacitor C3 is equal to the first current i1.

2 and 5, at time t2, the first switch S1 is turned on again, and during the third period t2-t3, the first switch S1 is turned on in the same manner as the first period t0- The first switch S1 and the second switch S2 are turned on. During the third period t2-t3, the first current i1 increases with the slope of V1 / L1 with time, and the second current i2 also increases with the slope of V2 / L2 with time. At this time, the first and second inductors L1 and L2 store the energy of the DC power supply C1. The third current i3 flowing through the second capacitor C3 is zero.

2 and 6, at time t3, the second switch S2 is turned off. During the fourth period t3-t4, the first switch S1 is turned on and the second switch S2 Is turned off.

The first current i1 flowing through the first inductor L1 flows to the first switch S1 but the second current i2 flowing through the second inductor L2 flows through the first inductor L1, 2 capacitor C3 and the fourth diode D4 to the first capacitor C2.

Since the voltage L1 di1 / dt at both ends of the first inductor L1 is equal to the first voltage V1 of the DC power supply C1, the first current i1 flows at a time during the fourth period t3-t4 It then increases with the slope of V1 / L1. The first inductor L1 stores the energy of the DC power supply C1.

And the second inductor L2 emits the stored energy during the first to third sections tO-t3. The energy emitted from the second inductor L2 is stored in the first capacitor C2. Since the second current i2 flows in the forward direction to the fourth diode D4, the voltage across the fourth diode D4 is zero. The sum of the voltage (-L2 di2 / dt) between the fourth node N4 and the first node N1 and the first voltage V1 is the sum of the second voltage V2 and the third voltage V3, , V2 / 2, the second current i2 decreases with the slope of - (V2 / 2-V1) / L2 with time. At this time, the third current i3 flowing through the second capacitor C3 is equal to the second current i2.

As described above, since the bidirectional DC-DC converter 100 is stabilized, the first current i1 and the second current i2 have the same starting and ending times of the switching cycle Ts. Therefore, referring to the graph of the second current i2 shown in FIG. 2, the second current i2 increases in a slope of V1 / L2 during the first to third periods t0 to t3, the second current i2 decreases at a slope of - (V2 / 2-V1) / L2 during the period t3-t4. Since the magnitude of the second current i2 at the start time and the end time of the switching cycle Ts must be equal to each other, V1 / L2 * (DTs) - (V2 / 2-V1) / L2 * (Ts- Should be zero.

In summary, the step-up ratio (V2 / V1) of the bi-directional DC-DC converter 100 operating in the boost mode is 2 / (1-D).

Therefore, in order to operate at an 8 times boost ratio (V2 / V1), the first and second switches S1 and S2 can be turned on with a duty ratio D of 0.75, i.e. 75%. The second voltage V2 which is the output voltage of the bidirectional DC-DC converter 100 may be 400V when the first voltage V1 as the output voltage of the DC power source C1 is 50V. Even in this case, since the duty ratio D is within 80%, stable control is possible, and the peak current can be reduced to half.

FIG. 7 shows a circuit diagram when the bi-directional DC-DC converter shown in FIG. 1 operates in a buck mode. 8 shows a control timing diagram when the bidirectional DC-DC converter shown in Fig. 7 operates in the buck mode. 9-12 illustrate a bidirectional DC-DC converter operating in the buck mode for each section.

7 and 8, when the bidirectional DC-DC converter 100 operates in the buck mode, the third and fourth switches S3 and S4 are interleaved with each other at the switching cycle Ts. Lt; / RTI > The first, second and sixth switches S1, S2 and S6 are continuously turned off. The fifth switch S5 is continuously turned on.

As described above, when the bidirectional DC-DC converter 100 operates in the buck mode, the second node N2 becomes the input node and the first node N1 becomes the output node. The bidirectional DC-DC converter 100 reduces the second voltage V2 of the second node N2 and outputs the first voltage V1 to the first node N1. Therefore, as shown in FIG. 7, a DC power source VS having the second voltage V2 is connected to the second node N2 between the second node N2 and the ground node GND . The second voltage V2 is higher than the level of the first voltage V1.

The bidirectional DC-DC converter 100 operating in the buck mode can supply the energy of the DC power supply VS to the DC power supply C1 connected to the first node N1, for example, the battery. When the DC power supply C1 is a battery, the battery can be charged when operating in the buck mode. Hereinafter, the DC power source C1 is referred to as a battery C1.

During the first period t0-t1 of the switching period Ts, the third switch S3 is turned off and the fourth switch S4 is turned on. The fourth switch S4 is turned off at the time t1 and the third and fourth switches S3 and S4 are both turned off during the second period t1-t2. At a time t2, the third switch S3 is turned on. During the third period t2-t3, the third switch S3 is turned on and the fourth switch S4 is turned off. The third switch S3 is turned off at time t3 and the third and fourth switches S3 and S4 are all turned off during the fourth period t3-t4.

The first section t0-t1 in which the fourth switch S4 is turned on and the third section t2-t3 in which the third switch S3 is turned on may be the same. That is, the duty ratio (D = DTs / Ts) which is the ratio of the time DTs during which the third switch S3 is turned on in the switching period Ts is equal to the duty ratio D of the fourth switch S4 . However, the present invention is not limited to this, and the duty ratio of the third switch S3 and the duty ratio of the fourth switch S4 may be different from each other. For ease of understanding of the present invention, it is assumed that the duty ratios of the third and fourth switches S3 and S4 are equal to each other.

The first switch S1 and the second switch S2 can be turned on at a duty ratio D of 10% or more and 25% or less, depending on the decompression ratio of the bidirectional DC-DC converter 100 operating in the buck mode have. For example, when the decompression ratio is 1/4, the third and fourth switches S3 and S4 can be turned on with a duty ratio D of approximately 25%. When the decompression ratio is 1/8, the third and fourth switches S3 and S4 can be turned on with a duty ratio D of approximately 12.5%. When the step-up ratio is 1/10, the third and fourth switches S3 and S4 can be turned on with a duty ratio D of approximately 10%.

As shown in FIG. 2, the third and fourth switches S3 and S4 may be turned on with a duty ratio D of 25% or less. At this time, the third and fourth switches S3 and S4 may be turned off interleaved with each other at the switching period Ts. For example, when the third switch S3 is in the turned-on state, the fourth switch S4 may be in the turned-off state, and when the fourth switch S4 is in the turned-on state, Off state. That is, the third and fourth switches S3 and S4 may not be turned on.

8 and 9, the third switch S3 is turned off and the fourth switch S4 is turned on during the first period t0-t1.

The first current i1 flows from the direct current power source VS to the battery C1 via the first inductor L1 between the second node N2 and the first node N1 as shown in Figure 9 . The energy of the DC power supply VS is charged in the first inductor L1 and the battery C1. The difference between the second voltage V2 of the direct current power supply VS and the first voltage V1 of the battery C1 is the difference between the voltage across the first inductor L1 and between the third node N3 and the first node N1 (L1 di1 / dt). The first current i1 increases at a slope of (V2-V1) / L1 with respect to time during the first section t0-t1.

The second current i2 flowing through the second inductor L2 flows to the DC power supply C1 and circulates through the second diode D2. Since the second current i2 flows in the forward direction to the second diode D2, the voltage across the second diode D2 is 0 and the voltage across the second inductor L2, L2 di2 / dt, The sum of the voltage V1 is zero. Therefore, the second current i2 decreases at a slope of -V1 / L2 with time during the first section t0-t1. As will be described in more detail below, the second inductor L2 stores energy during the third period t2-t3 and releases energy to the battery C1 during the first period t0-t1.

8 and 10, at time t1, the fourth switch S4 is turned off, and during the second period t1-t2, the third and fourth switches S3 and S4 are all turned off do.

As shown in FIG. 10, the first current i1 flowing through the first inductor L1 flows to the DC power supply C1 and circulates through the first diode D1. The sum of the voltage (L1 di1 / dt) across the first inductor (L1) and the first voltage (V1) is zero. Therefore, the first current i1 decreases at a slope of -V1 / L1 with time during the second section t1-t2. The first inductor L1 discharges part of the energy stored during the first period t0-t1 to the battery C1 during the second period t1-t2.

The second current i2 flowing through the second inductor L2 flows to the DC power supply C1 and circulates through the second diode D2. The second current i2 decreases to a slope of -V1 / L2 according to time during the second section t1-t2 in the same manner as the first section t0-t1. The second inductor L2 discharges energy to the battery C1 during the second period t1 - t2.

8 and 11, the third switch S3 is turned on at time t2, the third switch S3 is turned on during the third period t2-t3, and the fourth switch S4 Is turned off.

As shown in FIG. 11, the first current i1 flowing through the first inductor L1 flows to the DC power supply C1 and circulates through the first diode D1. The first current i1 decreases at a slope of -V1 / L2 with time during the third period t2-t3 as in the second period t1-t2. The first inductor L1 discharges part of the energy stored during the first period t0-t1 to the battery C1 during the third period t2-t3.

The second current i2 flows from the direct current power source VS to the battery C1 via the second inductor L2 between the second node N2 and the first node N1. The energy of the DC power supply VS is charged in the second inductor L2 and the battery C1. The difference between the second voltage V2 of the DC power supply VS and the first voltage V1 of the battery C1 is a voltage across the second inductor L2, that is, a voltage between the third node N3 and the first node N1 (L2 di2 / dt). The second current i2 increases at a slope of (V2-V1) / L2 with time during the third period t2-t3.

8 and 12, at time t3, the third switch S3 is turned off, and during the second period t1-t2, the third and fourth switches S3 and S4 are all turned off do.

As shown in FIG. 12, the first current i1 flowing through the first inductor L1 flows into the DC power supply C1 and circulates through the first diode D1. The first current i1 decreases at a slope of -V1 / L1 according to time during the fourth period t3-t4 as in the second and third periods t1-t3. The first inductor L1 discharges part of the energy stored during the first period t0-t1 to the battery C1 during the fourth period t3-t4.

The second current i2 flowing through the second inductor L2 flows to the DC power supply C1 and circulates through the second diode D2. The second current i2 decreases to a slope of -V1 / L2 according to time during the fourth section t3-t4 as in the first and second sections t0-t2. The second inductor L2 discharges part of the energy stored during the third period t2-t3 to the battery C1 during the fourth period t3-t4.

After the bi-directional DC-DC converter 100 operating in the buck mode is stabilized, the values of the first current i1 and the second current i2 are the same at the start and end points of the switching cycle Ts. Therefore, referring to the graph of the first current i1 shown in Fig. 8, the first current i1 increases at a slope of (V2-V1) / L1 during the first period t0-t1, The first current i1 decreases at a slope of -V1 / L1 during the fourth period t1-t4. Since the magnitude of the first current i1 at the start time and the end time of the switching cycle Ts must be the same,

(V2-V1) / L1 * Ts- -V1 / L1 * (Ts-DTs) = 0.

In summary, the voltage-drop ratio (V1 / V2) of the bi-directional DC-DC converter 100 operating in the buck mode is D.

Therefore, the third and fourth switches S3 and S4 can be turned on at a duty ratio D of 0.125, that is, 12.5%, in order to operate with a 1/8 times reduction ratio (V1 / V2). The bidirectional DC-DC converter 100 is switched to the 1/2-th mode in the buck mode in order to charge the battery C1 having the output voltage of 50V when the second voltage V2 as the DC power source VS or the DC link is 400V. It should operate with a decompression ratio of 8 times. In this case, the duty ratio D is 12.5%, and as the peak current decreases to half, stable control is possible.

13 schematically illustrates an energy storage system and a peripheral configuration according to one embodiment.

Referring to FIG. 13, the energy storage system 1 according to the present embodiment supplies electric power to the load 4 in conjunction with the power generation system 2, the grid system 3, and the like. The energy storage system 1 includes a battery system 20 for storing electric power and a power conversion system (hereinafter referred to as 'PCS') 10. The PCS 10 converts the power provided from the power generation system 2, the system 3 and / or the battery system 20 to a suitable type of power to provide power to the load 4, the battery system 20 and / (3).

The power generation system 2 is a system for generating power from an energy source. The power generation system 2 can supply the power generated by the power generation to the energy storage system 1. [ The power generation system 2 may include at least one of a solar power generation system, a wind power generation system, and a tidal power generation system, for example. For example, the power generation system 2 may include all power generation systems that generate power using renewable energy such as solar heat or geothermal power. The power generation system 2 can configure a large-capacity energy system by arranging a plurality of power generation modules capable of generating power in parallel.

The system 3 may include a power plant, a substation, a transmission line, and the like. When the system 3 is in a steady state, the system 3 supplies power to the load 4 and / or the battery system 20, or supplies power from the battery system 20 and / Can receive. When the system 3 is in an abnormal state, the power transmission between the system 3 and the energy storage system 1 is stopped.

The load 4 may consume the power produced in the power generation system 2, the power stored in the battery system 20, and / or the power supplied from the system 3. Electric devices of the home or factory where the energy storage system 1 is installed may be an example of the load 4. [

The energy storage system 1 can store the power produced by the power generation system 2 in the battery system 20 or supply it to the system 3. [ The energy storage system 1 may supply the power stored in the battery system 20 to the system 3 or may store the power supplied from the system 3 in the battery system 20. The energy storage system 1 also performs an uninterruptible power supply (UPS) function when the system 3 is in an abnormal state, for example, when a power failure occurs, so that the power generated by the power generation system 2 or the battery system 20 Can be supplied to the load (4).

14 is a block diagram illustrating a schematic configuration of an energy storage system according to an embodiment.

14, the energy storage system 1 may include a PCS 10, a battery system 20, a first switch 30, and a second switch 40 for converting power. The battery system 20 may include a battery 21 and a battery management unit 22.

The PCS 10 converts the power provided from the power generation system 2, the system 3 and / or the battery system 20 to a suitable type of power to provide power to the load 4, the battery system 20 and / (3). The PCS 10 may include a power converter 11, a DC link 12, a bidirectional inverter 13, a bidirectional DC-DC converter 100, and an integrated controller 15.

The power converter 11 may be a power converter connected between the power generation system 2 and the DC link 12. The power converter 11 can convert the power produced in the power generation system 2 into a DC link voltage and transmit it to the DC link 12. The power converter 11 may include a power conversion circuit such as a converter circuit, a rectifier circuit or the like depending on the type of the power generation system 2. [ When the power generation system 2 produces direct current power, the power converter 11 may include a DC-DC converter circuit for converting the direct current power generated in the power generation system 2 to another direct current power. When the power generation system 2 produces AC power, the power converter 11 may include a rectification circuit for converting the AC power generated in the power generation system 2 to DC power.

When the power generation system 2 is a photovoltaic power generation system, the power converter 11 generates a maximum power point (maximum power point) so as to maximize the power produced by the power generation system 2, Tracking control of the MPPT converter circuit. When there is no power generated in the power generation system 2, the operation of the power converter 11 is stopped and the power consumed in the power converter 11 can be minimized or reduced.

The level of the DC link voltage may become unstable due to a problem such as an instantaneous voltage drop in the power generation system 2 or the system 3 or a peak load generation in the load 4. [ However, the DC link voltage needs to be stabilized for the normal operation of the bi-directional DC-DC converter 100 and the bi-directional inverter 13. The DC link 12 may be connected between the power converter 11, the bidirectional inverter 13 and the bidirectional DC-DC converter 100 to maintain the dc link voltage constant or substantially constant. The DC link 12 may comprise, for example, a large capacitance capacitor. DC link 12 may include a first capacitor Cl coupled to a second node N2 of bi-directional DC-DC converter 100 of FIG. According to another example, the DC link 12 may be connected between the second node N2 of the bi-directional DC-DC converter 100 of FIG. 1 and the ground node GND. The DC link voltage may be, for example, 400V.

The bidirectional inverter 13 may be a power conversion device connected between the DC link 12 and the first switch 30. The bidirectional inverter 13 can convert the DC link voltage provided from at least one of the power generation system 2 and the battery system 20 into an AC voltage of the system 3 and output it. The bidirectional inverter 13 converts the AC voltage supplied from the system 3 to a DC link voltage and outputs it to the DC link 12 in order to store the power of the system 3 in the charging mode in the battery system 20 .

The bidirectional inverter 13 may include a filter for removing harmonics from the AC voltage output to the system 3. [ The bidirectional inverter 13 includes a phase locked loop (PLL) for synchronizing the phase of the AC voltage output from the bidirectional inverter 13 with the phase of the AC voltage of the system 3 to suppress or limit the generation of the reactive power, Circuit. The bidirectional inverter 13 may also perform functions such as limiting the voltage range, improving the power factor, removing direct current components, protecting or reducing transient phenomena, and the like.

The bidirectional DC-DC converter 100 may be connected between the DC link 12 and the battery system 20. The bidirectional DC-DC converter 100 can DC-DC convert the power stored in the battery system 20 into the DC link voltage in the discharge mode and output it to the DC link 12. The bidirectional DC-DC converter 100 also includes a DC-to-DC converter (not shown) for converting the DC link voltage of the DC link 12 into a DC voltage at an appropriate voltage level And output it to the battery system 20. When the charging or discharging of the battery system 20 is not performed, the operation of the bidirectional DC-DC converter 100 is interrupted, so that the power consumption may be minimized or reduced.

The integrated controller 15 may monitor the status of the power generation system 2, the system 3, the battery system 20, and the load 4. For example, the integrated controller 15 determines whether a power failure has occurred in the system 3, whether power is generated in the power generation system 2, the amount of power produced in the power generation system 2, the charge state of the battery system 20, The amount of power consumption and time of the load 4 can be monitored.

The integrated controller 15 controls the operation of the power converter 11, the bidirectional inverter 13, the bidirectional DC-DC converter 100, the battery system 20, the first switch 30, 2 switch 40 can be controlled.

The integrated controller 15 can control the first to sixth switches S1 to S6 of the bi-directional DC-DC converter 100 shown in Fig. For example, the integrated controller 15 turns off the first and second switches S1 and S2 so that the bi-directional DC-DC converter 100 operates in the boost mode, 5 switches S3-S5 may be turned off, and the sixth switch S6 may be turned on. The integrated controller 15 controls the third and fourth switches S3 and S4 to interleave and turn on the first, second, and third switches so that the bidirectional DC-DC converter 100 operates in the buck mode, And the sixth switches S1, S2, and S6 and turn on the fifth switch S5.

When a power failure occurs in the system 3, the integrated controller 15 can control the power stored in the battery system 20 or the power generated in the power generation system 2 to be supplied to the load 4. In addition, the integrated controller 15 may prioritize the electrical devices of the load 4, and may preferentially prioritize electrical devices of higher priority, if sufficient power can not be supplied to the load 4 The load 4 may be controlled. In addition, the integrated controller 15 can control the charging and discharging of the battery system 20.

The first switch 30 and the second switch 40 are connected in series between the bidirectional inverter 13 and the system 3 and perform a short circuit and an open operation under the control of the integrated controller 15, 2) and the system (3). The short circuit and the open state of the first switch 30 and the second switch 40 can be determined depending on the states of the power generation system 2, the system 3, and the battery system 20. [ Specifically, when the power from at least one of the power generation system 2 and the battery system 20 is supplied to the load 4 or the power from the system 3 is supplied to the battery system 20, (30) is short-circuited. When supplying power from at least one of the power generation system 2 and the battery system 20 to the system 3 or supplying power from the system 3 to at least one of the load 4 and the battery system 20 The second switch 40 is short-circuited.

When a power failure occurs in the system 3, the second switch 40 is opened and the first switch 30 is short-circuited. That is, power from at least one of the power generation system 2 and the battery system 20 is supplied to the load 4, and power supplied to the load 4 is prevented from leaking to the system 3. [ In this way, by operating the energy storage system 1 as a stand alone system, the worker working on the power line of the system 3 can be operated by the power transmitted from the power generation system 2 or the battery system 20 It is possible to prevent accidents caused by electric shock.

The battery system 20 can supply and store power from at least one of the power generation system 2 and the system 3 and supply the stored power to at least one of the load 4 and the system 3. [ The battery system 20 may be connected to the first node N1 of the bi-directional DC-DC converter 100 of FIG. The output voltage of the battery system 20 may be, for example, 50V.

The battery system 20 may include a battery 21 that includes at least one battery cell for storing power, and a battery management unit 22 that controls and protects the battery 21. The battery management unit 22 is connected to the battery 21 and can control the overall operation of the battery system 20 according to a control command from the integrated controller 15 or an internal algorithm. For example, the battery management unit 22 may perform an overcharge protection function, an over discharge protection function, an over current protection function, an over voltage protection function, an overheat protection function, a cell balancing function, and the like.

The battery management unit 22 can obtain voltage, current, temperature, remaining power, life, state of charge (SOC), and the like of the battery 21. For example, the battery management unit 22 may measure the cell voltage, current, and temperature of the battery 21 using sensors. The battery management unit 22 can calculate the residual power amount, life span, charging state, etc. of the battery 21 based on the measured cell voltage, current, and temperature. The battery management unit 22 can manage the battery 21 based on the measurement result and the calculation result and can transmit the measurement result and the calculation result to the integrated controller 15. [ The battery management unit 22 can control charging and discharging operations of the battery 21 in accordance with the charging and discharging control commands received from the integrated controller 15. [

The bidirectional DC-DC converter 100 can convert the voltage between the battery system 20 having an output voltage of, for example, 50 V and the DC link 12 having a DC link voltage of 400 V, for example. Although the step-up ratio of the bidirectional DC-DC converter 100 is approximately 8 times, according to the embodiments of the present invention, the control stability can be ensured because the control signal having the duty ratio of 80% or less can be used, It is possible to stabilize the power conversion. In addition, bidirectional DC-DC converter 100 can operate in a buck mode that reduces voltage. Therefore, since the output voltage of the battery system 20 can be lowered, when a small capacity is required, a battery 21 including a small number of battery cells can be used.

It is to be understood that the scope of the present invention is not limited to the above-described embodiments, and all ranges equivalent to or equivalent to the claims of the present invention are included in the scope of the present invention I will say.

Claims (10)

A bi-directional DC-DC converter having a first node, a second to fifth nodes, and a ground node to which a DC power source is connected,
A first inductor between the first node and the third node;
A first switch and a first diode connected in parallel between the third node and the ground node;
A second inductor between the first node and the fourth node;
A second switch and a second diode connected in parallel between the fourth node and the ground node;
A first capacitor between the second node and the ground node;
A third switch between the fourth node and the fifth node;
A fourth switch and a third diode connected in parallel between the third node and the fifth node;
A fifth switch and a fourth diode connected in parallel between the fifth node and the second node; And
And a sixth switch and a second capacitor connected in series between the fourth node and the fifth node. The method according to claim 1,
Characterized in that, in operation in the boost mode, the first and second switches are interleaved with each other, the third to fifth switches are turned off, and the sixth switch is turned on. -DC converter. 3. The method of claim 2,
Wherein the first and second switches are turned on at a duty ratio of greater than or equal to 50% and less than 80%. 3. The method of claim 2,
Wherein the second switch is in a turned-on state when the first switch is in a turn-off state and the first switch is in a turn-on state when the second switch is in a turn-off state. The method according to claim 1,
In operation in the buck mode, the third and fourth switches are interleaved with each other, the first, second and sixth switches are turned off, and the fifth switch is turned on A bidirectional DC-DC converter. 6. The method of claim 5,
And the third and fourth switches are turned on with a duty ratio of less than 50%. 6. The method of claim 5,
Wherein the fourth switch is in a turn-off state when the third switch is in a turn-on state, and the third switch is in a turn-off state when the fourth switch is in a turn-on state. The method according to claim 1,
Wherein the ratio of the second voltage of the second node to the first voltage of the first node is 6 times or more and 10 times or less. 9. A bidirectional DC-DC converter according to any one of claims 1 to 8,
A battery connected between a first node of the bidirectional DC-DC converter and a ground node;
A DC link including a first capacitor between a second node of the bi-directional DC-DC converter and the ground node;
A power converter for converting power between at least one of the power generation system, the grid, and the load and the DC link; And
And a power conversion system including the bidirectional DC-DC converter and an integrated controller for controlling the power conversion device. 10. The method of claim 9,
Wherein the power conversion apparatus includes a power conversion unit between the power generation system and the DC link unit, and a bi-directional inverter between the system and the load and the DC link unit.

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