KR102273767B1 - bidirectional DC-DC converter, and energy storage system including the same - Google Patents

Abstract

A bidirectional DC-DC converter and an energy storage system including the same are provided. The bidirectional DC-DC converter has a first node to which DC power 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, and the first node and the a second inductor between a 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, and the fourth node; a third switch between the fifth node, a fourth switch and a third diode connected in parallel between the third node and the fifth node, and a fifth diode 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.

Description

Bidirectional DC-DC converter, and energy storage system including the same

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

A typical bidirectional DC-DC converter operates in a unidirectional boost mode in which the voltage is stepped up (step-up) and a unidirectional buck mode in which the voltage is stepped down (step-down). Non-isolated bidirectional DC-DC converters are widely used because of their advantages compared to isolated bidirectional DC-DC converters in terms of the number and size of components. When the non-isolated bidirectional DC-DC converter is operated in the boost mode, if the output voltage compared to the input voltage is greatly increased, the target output voltage may not be achieved due to the limit of step-up. Even if the target output voltage is achieved, the duty ratio becomes 0.8 to 0.9 or more, which increases the possibility of causing instability of control. As an alternative to this, an isolated bidirectional DC-DC-converter has appeared, but there are problems such as an increase in the total number of parts and low efficiency because parts such as a transformer, an auxiliary inductor, and a resonant element are required.

An object of the present invention is 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, and the first node and the a second inductor between a 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, and the fourth node; a third switch between the fifth node, a fourth switch and a third diode connected in parallel between the third node and the fifth node, and a fifth diode 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.

When operating in the boost mode, the first and second switches may operate alternately (interleaved), the third to fifth switches may be turned off, and the sixth switch may be turned on. The first and second switches may be turned on with a duty ratio of 50% or more to less than 80%. When the first switch is in a turn-off state, the second switch may be in a turn-on state, and when the second switch is in a turn-off state, the first switch may be in a turn-on state.

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

A ratio of the second voltage of the second node to the first voltage of the first node may be 6 times or more and 10 times or less.

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

The power conversion device may include a power conversion unit between the power generation system and the DC link unit, and a bidirectional inverter between the grid and the load and the DC link unit.

The bidirectional DC-DC converter according to various embodiments of the present invention can secure 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 in which the output voltage is 8 times the input voltage. . In addition, it can operate in a buck mode that lowers the voltage. Accordingly, the energy storage system including the bidirectional DC-DC converter according to various embodiments of the present disclosure 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-isolated bi-directional DC-DC converter, and as it operates in an interleaved manner, the maximum current can be reduced by half.

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

Advantages and features of the present invention and methods of achieving them will become apparent with reference to the detailed description in conjunction with the accompanying drawings. However, the present invention is not limited to the embodiments presented below, it can be implemented in various different forms, and should be understood to include all transformations, equivalents, and substitutes included in the spirit and scope of the present invention. do. The embodiments presented below are provided to complete the disclosure of the present invention, and to fully inform those of ordinary skill in the art to the scope of the present invention. In describing the present invention, if it is determined that a detailed description of a related known technology may obscure the gist of the present invention, the detailed description thereof will be omitted.

The terms used in the present application are only used to describe specific embodiments, and are not intended to limit the present invention. The singular expression includes the plural expression unless the context clearly dictates otherwise. In the present application, terms such as “comprise” or “have” are intended to designate that a feature, number, step, operation, component, part, or combination thereof described in the specification exists, but one or more other features It should be understood that this does not preclude the existence or addition of numbers, steps, operations, components, parts, or combinations thereof. Terms such as first, second, etc. may be used to describe various elements, but the elements should not be limited by the terms. The above terms are used only for the purpose of distinguishing one component from another.

Hereinafter, embodiments according to the present invention will be described in detail with reference to the accompanying drawings, and in the description with reference to the accompanying drawings, the same or corresponding components are given the same reference numerals, and overlapping descriptions thereof are omitted. decide to do

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

Referring to FIG. 1 , the bidirectional DC-DC converter 100 has first to fifth nodes N1-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 an example, the DC power source C1 may be a battery. According to another example, the DC power supply C1 may be an output voltage of a rectifier circuit to which an AC voltage is applied. Although not shown in FIG. 1 , a capacitor may be connected in parallel with the DC power supply C1 between the first node N1 and the ground node GND.

The bidirectional DC-DC converter 100 may operate in a boost mode and a buck mode. When operating in the boost mode, the bidirectional 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 an input node, and the second node N2 is an output node. When operating in the buck mode, the bidirectional 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 an input node, and the first node N1 is an 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 energy of the DC link to a commercial power supply (Grid) and/or a load.

According to an example, a battery may be connected to the first node N1 , and a load or 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 may be supplied to a load connected to the second node N2 or commercial power. When operating in the buck mode, the battery connected to the first node N1 is charged from the commercial power 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 between the 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 from the first node N1 to the third node N3. 4 is defined as a current flowing through the second inductor L2 to the 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 inductors of the first and second inductors L1 and L2 may be different from each other. For easy understanding of the present invention, it is assumed that the first and second inductors L1 and L2 have the same inductance.

The bidirectional DC-DC converter 100 includes a first switch S1 and a first diode D1 connected in parallel between a third node N3 and a ground node GND, and a fourth node N4 and a ground. It includes a second switch S2 and a second diode D2 connected in parallel between the node GND. The first diode D1 is connected in antiparallel to the first switch S1 to allow a current to flow from the ground node GND to the third node N3 . When the first switch S1 is turned on, a current may also flow from the third node N3 to the ground node GND. The second diode D2 is connected in antiparallel to the second switch S2 to allow a current to flow from the ground node GND to the fourth node N4 . When the second switch S2 is turned on, a current may 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 vertically diffused MOS (MOS) structure. In addition, 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 the second node N2 and the ground node GND. According to an 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 sufficiently large capacitance (capacitance) 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 is connected in parallel between the third switch S3 between the fourth node N4 and the fifth node N5, and the third node N3 and the fifth node N5. The fourth switch S4 and the third diode D3, the fifth switch S5 and the fourth diode D4 connected in parallel between the fifth node N5 and the second node N2, and the fourth 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 a current flowing from the fifth node N5 to the fourth node N4 , and the third voltage V3 is defined as a voltage across the second capacitor C3 .

The third diode D3 is connected in anti-parallel to the fourth switch S4 to allow a current to flow from the third node N3 to the fifth node N5. When the fourth switch S4 is turned on, a current may also 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 to the fifth switch S5 to allow a current to flow from the fifth node N5 to the second node N2. When the fifth switch S5 is turned on, a current may 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 is a diode connected in anti-parallel to the third switch S3 between the fourth node N4 and the fifth node N5, and connected in anti-parallel to the sixth switch S6. A diode may be further included.

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

FIG. 2 shows a control timing diagram when the bidirectional DC-DC converter shown in FIG. 1 operates in a boost mode. 3 to 6 show a bidirectional DC-DC converter operating in a 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 alternately switched with each other at every switching period Ts. The third to fifth switches S3-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 a 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, both the first and second switches S1 and S2 are turned on. At time t1, the first switch S1 is turned off, 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, both the first and second switches S1 and S2 are turned on. At 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 period t1-t2 in which the first switch S1 is turned off and the fourth period t3-t4 in which the second switch S2 is turned off may be the same as each other. 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 during the switching period Ts, is equal to the duty ratio D of the second switch S2. can However, the present invention is not limited thereto, 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 easy 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.

Depending on the step-up ratio of the bidirectional DC-DC converter 100 operating in the boost mode, the first switch S1 and the second switch S2 may be turned on with a duty ratio of 50% or more to less than 80%. For example, when the step-up ratio is 4, the first and second switches S1 and S2 may 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 may 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 may 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 may 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 with a duty ratio D of 50% or more. In this case, the first and second switches S1 and S2 may be alternately turned off at each switching period Ts. For example, when the first switch S1 is turned off, the second switch S2 may be turned on, and when the second switch S2 is turned off, the first switch S1 may be turned on. 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 may be increased or decreased within the switching period Ts, but has a constant level on average after the bidirectional DC-DC converter 100 is stabilized. The second voltage V2 is also a voltage across the first capacitor C2 and has an average constant 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 this specification, the average voltage means an average voltage during the switching period (Ts) after the bidirectional DC-DC converter 100 is stabilized.

Looking at the closed circuit 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 and the 2 Since the average voltage across the inductor L2 is 0, the average third voltage V3 during the switching period Ts is the average voltage across the third diode D3 (ie, the fifth node N5 and the third voltage between nodes N3).

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

During the second period t1-t2 in which the first switch S1 is turned off and the second switch S2 is turned on, current flows in the forward direction through the third diode D3, so that both ends of the third diode D3 voltage is zero.

During a fourth period t3-t4 in which the first switch S1 is turned on and the second switch S2 is turned off, the third node N3 is connected to the ground node GND and the third diode D3 ), since a current flows in the forward direction, the voltage across the third diode D3 is the same as 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. same as Accordingly, the third voltage V3 is equal to 1/2 of the second voltage V2. Hereinafter, it is assumed that the capacitance of the second capacitor C3 is sufficiently large, so that the third voltage V3 is constant at 1/2 of the second voltage V2.

2 and 3 , during the first period t0 - t1 , the first switch S1 and the second switch S2 are turned on. 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 is 2 flows to the 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. Accordingly, the first current i1 increases with a slope of V1/L1 with time during the first period t0-t1, and the second current i2 also increases with time V2 during the first period t0-t1. It increases with the slope of /L2. At this time, the energy of the DC power supply 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 , the first switch S1 is turned off at time t1, 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 is 3 flows through the diode D3, the second capacitor C3 and the second switch S2.

Since the voltage L2 di2/dt across the second inductor L2 is the same as the first voltage V1 of the DC power source C1, the second current i2 is the second current i2 following the first section t0-t1. It increases with the slope of V2/L2 according to time during 2 sections (t1-t2). The second inductor L2 stores energy of the DC power supply C1.

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

2 and 5 , the first switch S1 is turned on again at time t2, and during the third period t2-t3, the first switch S1 is the same as the first period t0-t1. (S1) and the second switch (S2) are turned on. During the third period t2-t3, the first current i1 increases with a slope of V1/L1 with time, and the second current i2 also increases with a slope of V2/L2 with time. At this time, the first and second inductors L1 and L2 store energy of the DC power supply C1. The third current i3 flowing through the second capacitor C3 is zero.

2 and 6 , the second switch S2 is turned off at time t3, the first switch S1 is turned on during the fourth period t3-t4, 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 is It flows to the first capacitor C2 through the second capacitor C3 and the fourth diode D4.

Since the voltage L1 di1/dt across the first inductor L1 is the same as the first voltage V1 of the DC power source C1, the first current i1 is Accordingly, it increases with the slope of V1/L1. The first inductor L1 stores energy of the DC power supply C1.

The second inductor L2 emits stored energy during the first to third periods t0-t3. Energy emitted from the second inductor L2 is stored in the first capacitor C2. Since the second current i2 flows in the forward direction through the fourth diode D4, the voltage across the fourth diode D4 is zero. The sum of the voltage (-L2 di2/dt) and the first voltage V1 between the fourth node N4 and the first node N1 is the sum of the second voltage V2 and the third voltage V3, that is, , and V2/2, the second current i2 decreases with a slope of -(V2/2-V1)/L2 with time. In this case, the third current i3 flowing through the second capacitor C3 is the same as 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 value at the start time and end time of the switching period Ts. Accordingly, referring to the graph of the second current i2 shown in FIG. 2 , the second current i2 increases with a slope of V1/L2 during the first to third periods t0-t3, and the fourth period During (t3-t4), the second current i2 decreases with a slope of -(V2/2-V1)/L2. Since the magnitude of the second current i2 at the start and end time of the switching period Ts should be the same, V1/L2*(DTs)- (V2/2-V1)/L2*(Ts-DTs) = It should be 0.

Summarizing the above equation, the step-up ratio (V2/V1) of the bidirectional DC-DC converter 100 operating in the boost mode becomes 2/(1-D).

Accordingly, in order to operate at a step-up ratio V2/V1 of 8 times, the first and second switches S1 and S2 may be turned on with a duty ratio D of 0.75, that is, 75%. When the first voltage V1 that is the output voltage of the DC power C1 is 50V, the second voltage V2 that is the output voltage of the bidirectional DC-DC converter 100 may be 400V. Even in this case, since the duty ratio D is within 80%, stable control is possible, and the peak current can be reduced by half.

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

Referring to FIGS. 7 and 8 , when the bidirectional DC-DC converter 100 operates in the buck mode, the third and fourth switches S3 and S4 are alternated with each other at every switching period Ts. is switched 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 an input node and the first node N1 becomes an 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 a second voltage V2 is connected to the second node N2 between the second node N2 and the ground node GND. can 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 may supply energy of the DC power supply VS to the DC power supply C1 connected to the first node N1, for example, a battery. When the DC power source C1 is a battery, the battery may 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. At time t1, the fourth switch S4 is turned off, and during the second period t1-t2, both the third and fourth switches S3 and S4 are turned off. At 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. At time t3, the third switch S3 is turned off, and during the fourth period t3-t4, both the third and fourth switches S3 and S4 are turned off.

The first period t0-t1 in which the fourth switch S4 is turned on and the third period t2-t3 in which the third switch S3 is turned on may be the same as each other. That is, the duty ratio (D = DTs/Ts), which is the ratio of the turn-on time DTs of the third switch S3 in the switching period Ts, may be the same as the duty ratio D of the fourth switch S4. can However, the present invention is not limited thereto, 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 easy 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.

Depending on the step-down ratio of the bidirectional DC-DC converter 100 operating in the buck mode, the first switch S1 and the second switch S2 may be turned on with a duty ratio D of 10% or more and 25% or less. have. For example, when the pressure reduction ratio is 1/4, the third and fourth switches S3 and S4 may be turned on with a duty ratio D of approximately 25%. When the pressure reduction ratio is 1/8, the third and fourth switches S3 and S4 may 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 may 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. In this case, the third and fourth switches S3 and S4 may be alternately turned off at each switching period Ts. For example, when the third switch S3 is turned on, the fourth switch S4 may be turned off. When the fourth switch S4 is turned on, the third switch S3 is turned on. may be in a turned off state. That is, there may not be a state in which all of the third and fourth switches S3 and S4 are turned on.

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

As shown in FIG. 9 , a first current i1 flows from the DC power source VS to the battery C1 through the first inductor L1 between the second node N2 and the first node N1 . . 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 DC power source VS and the first voltage V1 of the battery C1 is the voltage across the first inductor L1, that is, the third node N3 and the first node N1. ) equal to the voltage (L1 di1/dt) between The first current i1 increases with a slope of (V2-V1)/L1 according to time during the first period 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 through the second diode D2, the voltage across the second diode D2 is 0, and the voltage L2 di2/dt across the second inductor L2 and the first The sum of the voltages V1 is zero. Accordingly, the second current i2 decreases with a slope of -V1/L2 according to time during the first period 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.

Referring to FIGS. 8 and 10 , the fourth switch S4 is turned off at time t1 , so that all of the third and fourth switches S3 and S4 are turned off during the second period t1 - t2 . 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. Accordingly, the first current i1 decreases with a slope of -V1/L1 according to time during the second period t1-t2. The first inductor L1 discharges a portion 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 with a slope of -V1/L2 according to time during the second period t1-t2, like the first period t0-t1. The second inductor L2 emits 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 on. ) is turned off.

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 with a slope of -V1/L2 according to time during the third period t2-t3 as in the second period t1-t2. The first inductor L1 discharges a portion of the energy stored during the first period t0 - t1 to the battery C1 during the third period t2-t3.

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

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

As shown in FIG. 12 , 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 with 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 a portion 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 with a slope of -V1/L2 according to time during the fourth period t3-t4, like the first and second periods t0-t2. The second inductor L2 discharges a portion of the energy stored during the third period t2-t3 to the battery C1 during the fourth period t3-t4.

After the bidirectional DC-DC converter 100 operating in the buck mode is stabilized, the first current i1 and the second current i2 have the same value at the start time and end time of the switching period Ts. Accordingly, referring to the graph of the first current i1 shown in FIG. 8 , during the first period t0-t1, the first current i1 increases with a slope of (V2-V1)/L1, and the second During to the fourth period t1 to t4, the first current i1 decreases with a slope of -V1/L1. Since the magnitude of the first current i1 at the start and end time of the switching period Ts should be the same,

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

Summarizing the above equation, the step-down ratio (V1/V2) of the bidirectional DC-DC converter 100 operating in the buck mode becomes D.

Accordingly, in order to operate at a reduced pressure ratio V1/V2 of 1/8 times, the third and fourth switches S3 and S4 may be turned on with a duty ratio D of 0.125, that is, 12.5%. When the second voltage (V2), which is the voltage of the DC power supply (VS) or the DC link, is 400V, in order to charge the battery C1 having an output voltage of 50V, the bidirectional DC-DC converter 100 is 1/ It should be operated with a decompression ratio of 8 times. In this case, the duty ratio (D) is 12.5%, and as the peak current is reduced by half, stable control is possible.

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

Referring to FIG. 13 , the energy storage system 1 according to the present embodiment supplies power to the load 4 in connection with the power generation system 2 and the grid system 3 . The energy storage system 1 includes a battery system 20 for storing power and a power conversion system (hereinafter referred to as 'PCS') 10 . The PCS 10 converts power provided from the power generation system 2 , the grid 3 , and/or the battery system 20 into an appropriate form of power to the load 4 , the battery system 20 and/or the grid. (3) can be supplied.

The power generation system 2 is a system that produces electric power from an energy source. The power generation system 2 may supply power generated by power generation to the energy storage system 1 . The power generation system 2 may include, for example, at least one of a solar power generation system, a wind power generation system and a tidal power generation system. 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 heat. The power generation system 2 may configure a large-capacity energy system by arranging a plurality of power generation modules capable of generating power in parallel.

The grid 3 may include a power plant, a substation, a transmission line, and the like. When the grid 3 is in a steady state, the grid 3 supplies power to the load 4 and/or the battery system 20 , or supplies power from the battery system 20 and/or the power generation system 2 . can receive When the grid 3 is in an abnormal state, power transmission between the grid 3 and the energy storage system 1 is stopped.

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

The energy storage system 1 may store the power generated by the power generation system 2 in the battery system 20 or may supply it to the system 3 . The energy storage system 1 may supply the electric power stored in the battery system 20 to the system 3 , or store the electric power supplied from the system 3 in the battery system 20 . In addition, the energy storage system 1 performs a UPS (Uninterruptible Power Supply) function when the system 3 is in an abnormal state, for example, when a power outage occurs, and the power produced by the power generation system 2 or the battery system 20 ) stored in the load (4) can be supplied.

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

Referring to FIG. 14 , the energy storage system 1 may include a PCS 10 that converts power, a battery system 20 , a first switch 30 , and a second switch 40 . The battery system 20 may include a battery 21 and a battery manager 22 .

The PCS 10 converts power provided from the power generation system 2 , the grid 3 , and/or the battery system 20 into an appropriate form of power to the load 4 , the battery system 20 and/or the grid. (3) can be supplied. 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 may convert the power generated by the power generation system 2 into a DC link voltage and transmit it to the DC link 12 . The power converter 11 may include, for example, 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 generates DC power, the power converter 11 may include a DC-DC converter circuit for converting the DC power generated by the power generation system 2 into another DC power. When the power generation system 2 generates AC power, the power converter 11 may include a rectifying circuit for converting AC power generated by the power generation system 2 into DC power.

When the power generation system 2 is a photovoltaic power generation system, the power converter 11 tracks the maximum power point so as to obtain the maximum power generated by the power generation system 2 according to fluctuations in insolation, temperature, etc. (Maximum Power Point) Tracking) may include an MPPT converter circuit that performs control. When there is no power generated by the power generation system 2 , the operation of the power converter 11 is stopped, so that the power consumed by the power converter 11 can be minimized or reduced.

Due to problems such as an instantaneous voltage drop in the power generation system 2 or grid 3, or a peak load generation in the load 4, the level of the DC link voltage may become unstable. However, the DC link voltage needs to be stabilized for normal operation of the bidirectional DC-DC converter 100 and the bidirectional 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 keep the DC link voltage constant or substantially constant. DC link 12 may include, for example, a large capacitor. The DC link 12 may include a first capacitor C1 connected to the second node N2 of the bidirectional DC-DC converter 100 of FIG. 1 . According to another example, the DC link 12 may be connected between the second node N2 and the ground node GND of the bidirectional DC-DC converter 100 of FIG. 1 . 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 may convert a 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 grid 3 and output it. The bidirectional inverter 13 converts the AC voltage provided from the grid 3 into a DC link voltage and outputs it to the DC link 12 in order to store the power of the grid 3 in the battery system 20 in the charging mode. can

The bidirectional inverter 13 may include a filter for removing harmonics from the AC voltage output to the grid 3 . In addition, the bidirectional inverter 13 is a phase locked loop (PLL) for synchronizing the phase of the AC voltage output from the bidirectional inverter 13 and the phase of the AC voltage of the grid 3 in order to suppress or limit the generation of reactive power. circuit may be included. In addition, the bidirectional inverter 13 may perform functions such as limiting a voltage fluctuation range, improving a power factor, removing a DC component, protecting or reducing transient phenomena, and the like.

The bidirectional DC-DC converter 100 may be coupled between the DC link 12 and the battery system 20 . The bidirectional DC-DC converter 100 may DC-DC convert power stored in the battery system 20 into a DC link voltage in a discharging mode and output it to the DC link 12 . In addition, the bidirectional DC-DC converter 100 DC-DC converts the DC link voltage of the DC link 12 into a DC voltage of an appropriate voltage level (eg, a charging voltage level required by the battery system 20) in the charging mode. and output to the battery system 20 . When charging or discharging of the battery system 20 is not performed, the operation of the bidirectional DC-DC converter 100 is stopped, thereby minimizing or reducing power consumption.

The integrated controller 15 may monitor the status of the power generation system 2 , the grid 3 , the battery system 20 , and the load 4 . For example, the integrated controller 15 determines whether a power outage has occurred in the system 3, whether power is produced in the power generation system 2, the amount of power produced in the power generation system 2, the state of charge of the battery system 20, It is possible to monitor the power consumption and time of the load 4 .

The integrated controller 15 includes the power converter 11, the bi-directional inverter 13, the bi-directional DC-DC converter 100, the battery system 20, the first switch 30, and the second according to the monitoring result and a predetermined algorithm. 2 It is possible to control the operation of the switch (40).

The integrated controller 15 may control the first to sixth switches S1 to S6 of the bidirectional DC-DC converter 100 illustrated in FIG. 1 . For example, the integrated controller 15 turns off the first and second switches S1 and S2 alternately (interleaved) with each other so that the bidirectional DC-DC converter 100 operates in the boost mode, and the third to third The fifth switches S3-S5 may be turned off, and the sixth switch S6 may be turned on. The integrated controller 15 is configured such that the bidirectional DC-DC converter 100 operates in the buck mode, the third and fourth switches S3 and S4 are turned on alternately (interleaved) with each other, and the first, second, and the sixth switches S1 , S2 , and S6 may be turned off, and the fifth switch S5 may be turned on.

When a power failure occurs in the system 3 , the integrated controller 15 may 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, when sufficient power cannot be supplied to the load 4, the integrated controller 15 prioritizes the electrical devices of the load 4, and preferentially applies power to the high-priority electrical devices. It is also possible to control the load 4 to supply. In addition, the integrated controller 15 may control 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 grid 3, and perform short-circuit and open operations under the control of the integrated controller 15 to generate a power generation system ( Controls the flow of current between 2) and the grid (3). The short-circuit and open states of the first switch 30 and the second switch 40 may be determined according to the states of the power generation system 2 , the system 3 , and the battery system 20 . Specifically, when power from at least one of the power generation system 2 and the battery system 20 is supplied to the load 4 or power from the grid 3 is supplied to the battery system 20 , the first switch (30) becomes a short circuit state. When power from at least one of the power generation system 2 and the battery system 20 is supplied to the grid 3 or power from the grid 3 is supplied to at least one of the load 4 and the battery system 20 , the second switch 40 is in a short-circuited state.

When a power outage occurs in the system 3 , the second switch 40 is in an open state and the first switch 30 is in a short-circuited state. That is, while supplying power from at least one of the power generation system 2 and the battery system 20 to the load 4 , the 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, a worker who works on the power line of the system 3 can use the power transmitted from the power generation system 2 or the battery system 20 . To prevent electric shock accidents.

The battery system 20 may receive 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 bidirectional DC-DC converter 100 of FIG. 1 . The output voltage of the battery system 20 may be, for example, 50V.

The battery system 20 may include a battery 21 including at least one battery cell to store power, and a battery manager 22 to control and protect the battery 21 . The battery manager 22 is connected to the battery 21 and may 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 manager 22 may perform an overcharge protection function, an overdischarge protection function, an overcurrent protection function, an overvoltage protection function, an overheat protection function, a cell balancing function, and the like.

The battery manager 22 may obtain the voltage, current, temperature, remaining power, lifespan, and state of charge (SOC) of the battery 21 . For example, the battery manager 22 may measure the cell voltage, current, and temperature of the battery 21 using sensors. The battery manager 22 may calculate the amount of power remaining, the lifespan, and the state of charge of the battery 21 based on the measured cell voltage, current, and temperature. The battery manager 22 may manage the battery 21 based on the measurement result and the calculation result, and transmit the measurement result and the calculation result to the integrated controller 15 . The battery manager 22 may control charging and discharging operations of the battery 21 according to a charging and discharging control command received from the integrated controller 15 .

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

The spirit of the present invention should not be limited to the above-described embodiments, and not only the claims described below, but also all scopes equivalent to or changed from these claims are within the scope of the spirit of the present invention. will do it

Claims (10)

A bidirectional DC-DC converter having a first node to which a DC power source is connected, second to fifth nodes, and a ground node, comprising:
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 bidirectional DC-DC converter comprising a sixth switch and a second capacitor connected in series between the fourth node and the fifth node. According to claim 1,
Bidirectional DC, characterized in that when operating in the boost mode, the first and second switches operate alternately 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,
Bidirectional DC-DC converter, characterized in that the first and second switches are turned on with a duty ratio of 50% or more to less than 80%. 3. The method of claim 2,
The bidirectional DC-DC converter, characterized in that when the first switch is in a turn-off state, the second switch is in a turn-on state, and when the second switch is in a turn-off state, the first switch is in a turn-on state. According to claim 1,
When operating in the buck mode, the third and fourth switches operate alternately (interleaved) with each other, the first, second and sixth switches are turned off, and the fifth switch is turned on. bidirectional DC-DC converter. 6. The method of claim 5,
wherein the third and fourth switches are turned on with a duty ratio of less than 50%. 6. The method of claim 5,
The bidirectional DC-DC converter, characterized in that when the third switch is turned on, the fourth switch is turned off, and when the fourth switch is turned on, the third switch is turned off. According to claim 1,
Bidirectional DC-DC converter, characterized in that 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. The bidirectional DC-DC converter of 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 comprising a first capacitor between a second node of the bidirectional DC-DC converter and the ground node;
a power conversion device for converting power between the DC link and at least one of a power generation system, a grid, and a load; and
and a power conversion system including an integrated controller for controlling the bidirectional DC-DC converter and the power conversion device. 10. The method of claim 9,
The power conversion device comprises a power conversion unit between the power generation system and the DC link unit, and a bidirectional inverter between the grid and the load and the DC link unit.

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