KR102303326B1 - An energy storage system - Google Patents

Abstract

The present invention relates to an energy storage system including an inverter to which a discharge resistor is connected to prevent damage to a relay by inrush current. An energy storage system according to an embodiment of the present invention, in an energy storage system including a grid, an inverter that converts DC power into AC power, is connected to an output terminal of the inverter, and reduces noise of AC power converted by the inverter It includes a filter that supplies the system with a filter, a relay that connects or blocks between the filter and the system, and a discharge resistor that is connected in parallel between the inverter and the filter.

Description

Energy storage system {AN ENERGY STORAGE SYSTEM}

The present invention relates to an energy storage system including an inverter to which a discharge resistor is connected to prevent damage to a relay by inrush current.

An energy storage system is a system that increases energy efficiency by storing produced power in each linked system including a power plant, substation, and transmission line, and then selectively and efficiently using it when power is needed.

The energy storage system can lower the power generation unit cost and reduce the investment and operation cost required for power facility expansion, thereby reducing the electricity rate and saving energy when the overall load factor is improved by leveling the electric load with large fluctuations by time and season. can do.

Such an energy storage system is installed and used in power generation, transmission and distribution, and consumers in the power system. Frequency regulation, stabilization of generator output using new and renewable energy, peak shaving, and load leveling , emergency power supply, etc.

Energy storage systems are largely divided into physical energy storage and chemical energy storage according to storage methods. For physical energy storage, there are methods using pumped water power generation, compressed air storage, flywheels, etc., and for chemical energy storage, there is a method using lithium-ion batteries, lead-acid batteries, and Nas batteries.

Referring to FIG. 1 , an energy storage system including an inverter connected to a conventional grid is shown.

1 is a circuit diagram illustrating an energy storage system including an inverter connected to a conventional grid.

For reference, although not shown in the drawings, a DC input terminal (not shown) of the inverter 100 may be connected to a battery (not shown), and the inverter 100 may receive DC power from the battery.

In addition, the energy storage system of FIG. 1 includes an inverter 100 , a filter 150 , a relay 200 , and a system 300 , a detailed description of each will be omitted.

When the inverter 100 of the energy storage system shown in FIG. 1 receives DC power from a battery, the DC power is provided from the first capacitor C1 provided in the inverter 100 to the DC link DCL.

Also, the DC power provided to the DC link DCL is converted into AC power through the switching operations of the first to fourth switches S1 to S4 and provided to the filter 150 .

The filter 150 reduces the noise of the AC power provided from the inverter 100 and then transmits the AC power to the grid 300 .

However, before driving the inverter 100 as described above, the operation of checking the overall state of the energy storage system is performed, and when it is determined that there is no abnormality in the energy storage system, the relay 200 is turned on to The inverter 100 and the grid 300 are connected.

Specifically, before the inverter 100 is driven, if the energy storage system is in a normal state, there is no particular problem even if the relay 200 is turned on or off, but when the relay 200 is turned on or off When the generated inrush current is large, the relay 200 may be fused due to the inrush current.

In this case, even when the turn-off signal is provided to the relay 200 , as the relay 200 maintains the turned-on state, a problem may occur in the entire energy storage system.

For reference, the magnitude of the inrush current may be determined according to <Equation 1> below.

<Equation 1>

I = C*(dv/dt)

Here, I may be the magnitude of the inrush current, C may be a capacitance of a capacitor in the energy storage system, dv may be a voltage change amount of the capacitor, and dt may be a time change amount.

2 and 3 , a case in which the inrush current becomes the maximum is illustrated.

FIG. 2 is a view for explaining an AC voltage provided in an inverter direction from the AC power in the system of FIG. 1 . 3 is a view for explaining a change in the magnitude of the inrush current according to the turn-on and turn-off of the relay of FIG. 1 .

For reference, in FIG. 2 , the vertical axis indicates AC voltages (+V, -V) applied to the capacitor (eg, any one of the first to fifth capacitors C5 ), and the horizontal axis indicates time (t). can mean

Also, in FIG. 3 , the vertical axis may mean inrush currents (+I, -I) generated when the relay 200 is turned on or off, and the horizontal axis may mean time (t).

1 to 3, before driving of the inverter 100 is started, the relay 200 is turned on at a first point P1, is turned off at a second point P2, and a third point ( It may be turned on again at P3) and may be turned off again at the fourth point P4.

At this time, when the relay 200 is initially turned on at the first point P1 , it can be seen that the inrush current momentarily increases and then decreases again.

However, when the AC voltage provided by the system 300 at the second point P2 at which the relay 200 is turned off is a positive peak voltage PP, a capacitor (eg, the first The first to fifth capacitors C1 to C5 may also be gradually discharged after being charged to the maximum voltage, that is, the positive peak voltage PP.

Here, if the AC voltage provided by the system 300 at the third point P3 at which the relay 200 is turned on again is a negative peak voltage NP, a capacitor (for example, , the first to fifth capacitors C1 to C5) are applied with a voltage VC that is greater than the peak voltage (the magnitude of PP or NP), so that the third point P3 rather than the first point P1 is applied. A larger inrush current may occur in

As such, when a large inrush current is suddenly generated when the relay 200 is turned on and passes through the relay 200 , the relay 200 may be fused. In addition, when the relay 200 is fused, there is a problem that the energy storage system may not operate normally.

The present invention is an energy storage system that can prevent relay fusion by reducing the inrush current generated when the relay is turned on again by reducing the discharge time of the capacitor when the relay is turned off through the discharge resistor connected in parallel to the output terminal of the inverter aims to provide

The objects of the present invention are not limited to the above-mentioned objects, and other objects and advantages of the present invention not mentioned may be understood by the following description, and will be more clearly understood by the examples of the present invention. Moreover, it will be readily apparent that the objects and advantages of the present invention may be realized by the means and combinations thereof indicated in the claims.

In order to achieve the above object, an energy storage system according to an embodiment of the present invention is an energy storage system including a grid, an inverter that converts DC power into AC power, is connected to an output terminal of the inverter, and is converted by the inverter It includes a filter that reduces noise of AC power and supplies it to the grid, a relay that connects or blocks the filter and the grid, and a discharge resistor that is connected in parallel between the inverter and the filter.

It further includes a relay control unit for turning the relay on (turn-on) or turn-off (turn-off).

Capacitors are provided in each of the inverter, the filter, and the system, and when the relay is first turned on by the relay control unit before driving of the inverter is started, capacitors provided in the inverter, the filter, and the system are charged, respectively, and are turned on by the relay control unit When the relay is turned off, the capacitors provided in the inverter, the filter, and the system, respectively, are discharged.

The discharge resistor reduces the discharge time of the capacitor provided in the inverter, the filter, and the system, thereby reducing the inrush current generated when the relay turned off by the relay control unit is turned on again.

The inverter has a first capacitor, first and second switches connected in parallel with the first capacitor, third and fourth switches connected in parallel with the first and second switches, and one end between the first and second switches A first inductor connected to the second inductor, a second inductor having one end connected between the third and fourth switches, a second capacitor having one end connected to the other end of the first inductor and the other end connected to the other end of the second inductor; a third capacitor connected in parallel with the second capacitor, wherein the first and second switches are connected in series with each other, the third and fourth switches are connected with each other in series, and the discharge resistor is connected with the third capacitor in parallel.

The filter includes third and fourth inductors connected in series with the first inductor, fifth and sixth inductors connected in series with the second inductor, and a fourth capacitor connected in parallel with the third capacitor, and a fourth One end of the capacitor is connected between the third and fourth inductors, the other end of the fourth capacitor is connected between the fifth and sixth inductors, and the fourth capacitor is connected in parallel with the discharge resistor.

The system includes an AC power source and a fifth capacitor connected in parallel to the AC power source, and the relay has a first sub relay having one end connected to the fourth inductor and the other end connected to one end of the fifth capacitor, and a sixth end of the relay. and a second sub relay connected to the inductor and the other end connected to the other end of the fifth capacitor.

The filter is an Electro Magnetic Compatibility (EMC) filter.

As described above, according to the present invention, by reducing the discharge time of the capacitor when the relay is turned off through the discharge resistor connected in parallel to the output terminal of the inverter, the inrush current generated when the relay is turned on again is reduced to prevent relay fusion can do. In addition, it is possible to prevent accidents that may occur in inverters, etc. due to relay fusion.

1 is a circuit diagram illustrating an energy storage system including an inverter connected to a conventional grid.
FIG. 2 is a view for explaining an AC voltage provided in an inverter direction from the AC power in the system of FIG. 1 .
3 is a view for explaining a change in the magnitude of the inrush current according to the turn-on and turn-off of the relay of FIG. 1 .
4 is a circuit diagram illustrating an energy storage system according to an embodiment of the present invention.
FIG. 5 is a view for explaining an AC voltage provided in the direction of an inverter from the AC power in the grid of FIG. 4 .
6 is a view for explaining a change in the magnitude of the inrush current according to the turn-on and turn-off of the relay of FIG. 4 .

The above-described objects, features and advantages will be described below in detail with reference to the accompanying drawings, and accordingly, those of ordinary skill in the art to which the present invention pertains will be able to easily implement the technical idea of the present invention. In describing the present invention, if it is determined that a detailed description of a known technology related to the present invention may unnecessarily obscure the gist of the present invention, the detailed description will be omitted. Hereinafter, preferred embodiments according to the present invention will be described in detail with reference to the accompanying drawings. In the drawings, the same reference numerals are used to indicate the same or similar components.

Hereinafter, an energy storage system 1 according to an embodiment of the present invention will be described with reference to FIGS. 4 to 6 .

4 is a circuit diagram illustrating an energy storage system according to an embodiment of the present invention. FIG. 5 is a view for explaining an AC voltage provided in the direction of an inverter from the AC power in the system of FIG. 4 . 6 is a view for explaining a change in the magnitude of the inrush current according to the turn-on and turn-off of the relay of FIG. 4 .

Referring to FIG. 4 , the energy storage system 1 according to an embodiment of the present invention includes an inverter 100 , a filter 150 , a relay 200 , a relay control unit 250 , a system 300 , a discharge resistor ( DR) may be included.

For reference, although not shown in the drawings, the energy storage system 1 includes a distributed power system, a power conversion system (PCS), a battery, a load, a battery management system (BMS), a power management system (PMS), and an energy management system (EMS). System) may be further included.

Specifically, the distributed power system may generate power by using one or more of fossil fuel, nuclear fuel, and renewable energy. For example, the distributed power system may be a renewable power generation system using new and renewable energy, such as a solar power generation system, a wind power generation system, and a tidal power generation system.

The PCS may store power generated in the distributed power system in a battery or transmit it to the system 300 and a load. In addition, the PCS can deliver the power stored in the battery to the grid or load. The PCS can also store power supplied from the grid in a battery.

In addition, the PCS may control charging and discharging of the battery based on the state of charge (hereinafter referred to as “SOC level”) of the battery.

In addition, the PCS may generate a schedule for the operation of the energy storage system 1 based on the power price of the power market, the power generation plan of the distributed power system, the amount of power generation and the power demand of the system.

For reference, the inverter 100 may be provided inside the PCS. Of course, the inverter 100 may be provided outside the PCS, or when provided outside, it may be connected to the PCS to receive power from the PCS.

The battery may receive and store at least one of the power of the distributed power system and the system 300 , and may supply the stored power to at least one of the system 300 and the load.

Such a battery may include at least one battery cell, and each battery cell may include a plurality of bare cells.

Also, although not shown in the drawings, the battery may be connected to the inverter 100 (ie, a DC input terminal (not shown) of the inverter) to provide DC power to the inverter 100 .

The load receives power from one or more of a distributed power system, a battery, and a grid, and consumes the supplied power.

Loads may also include, for example, homes, large buildings, factories, and the like.

The BMS may monitor the state of the battery and control charging and discharging operations of the battery. In addition, the BMS can monitor the state of the battery including the SOC level, which is the state of charge of the battery, and the monitored battery state (eg, voltage, current, temperature, remaining wattage, lifespan, charge state, etc.) information is sent to the PCS. can provide

In addition, the BMS may perform a protection operation to protect the battery. For example, the BMS may perform one or more of an overcharge protection function, an overdischarge protection function, an overcurrent protection function, an overvoltage protection function, an overheat protection function, and a cell balancing function for the battery.

The BMS can also adjust the SOC level of the battery.

Specifically, the BMS may receive a control signal from the PCS and adjust the SOC level of the battery based on the received signal.

The PMS may control the PCS based on battery-related data provided from the BMS.

Specifically, the PMS may monitor the state of the battery and monitor the state of the PCS. That is, the PMS can control the PCS according to its efficiency based on the battery-related data received from the BMS.

In addition, the PMS can provide the battery-related data collected by monitoring the state of the battery through the BMS to the EMS.

The EMS may generate battery maintenance and repair information based on the battery data received from the PMS, and may provide the generated battery maintenance and repair information to the BMS through the PMS.

As described above, the energy storage system 1 according to an embodiment of the present invention may further include a distributed power supply system, PCS, battery, load, BMS, PMS, and EMS, but for convenience of description, energy storage It will be described as an example that the system 1 includes only the inverter 100 , the filter 150 , the relay 200 , the relay control unit 250 , the system 300 , and the discharge resistor DR.

The inverter 100 may convert DC power into AC power.

Specifically, the inverter 100 connects the first to third capacitors C1, C2, and C3, the first to fourth switches S1, S2, S3, and S4, and the first and second inductors L1 and L2. may include

The first and second switches S1 and S2 may be connected in parallel with the first capacitor C1, and the third and fourth switches S3 and S4 may be connected in parallel with the first and second switches S1 and S2. have.

Here, the first and second switches S1 and S2 may be connected to each other in series, and the third and fourth switches S3 and S4 may be connected to each other in series.

In addition, a first gate signal S1_G and a first source signal S1_S may be provided to the first switch S1 , and a second gate signal S2_G and a second source signal S2_S may be provided to the second switch S2 . ) may be provided, a third gate signal S3_G and a third source signal S3_S may be provided to the third switch S3 , and a fourth gate signal S4_G and A fourth source signal S4_S may be provided.

For reference, the first to fourth switches S1 , S2 , S3 , and S4 may include, for example, an insulated gate bipolar mode transistor (IGBT), but is not limited thereto.

In the case of the first inductor L1 , one end may be connected between the first switch S1 and the second switch S2 , and the other end may be connected to one end of the second capacitor C2 .

In the case of the second inductor L2 , one end may be connected between the third switch S3 and the fourth switch S4 , and the other end may be connected to the other end of the second capacitor C2 .

In the case of the second capacitor C2 , one end may be connected to the other end of the first inductor L1 , and the other end may be connected to the other end of the second inductor L2 .

The third capacitor C3 may be connected in parallel with the second capacitor C2 . Also, the third capacitor C3 may be connected in parallel with the discharge resistor DR.

The filter 150 may be connected to the output terminal of the inverter 100 , and may reduce noise of the AC power converted by the inverter 100 and supply it to the system 300 .

Here, the output terminal of the inverter 100 may refer to the vicinity of the third capacitor C3.

Specifically, the filter 150 may include third to sixth inverters L3, L4, L5, and L6 and a fourth capacitor C4.

The third and fourth inductors L3 and L4 may be connected in series with the first inductor L1 , and the fifth and sixth inductors L5 and L6 may be connected in series with the second inductor L2 .

The fourth capacitor C4 may be connected in parallel with the third capacitor C3 . Also, in the case of the fourth capacitor C4 , one end may be connected between the third and fourth inductors L3 and L4 , and the other end may be connected between the fifth and sixth inductors L5 and L6 .

Also, the fourth capacitor C4 may be connected in parallel with the discharge resistor DR.

For reference, the filter 150 may be, for example, an Electro Magnetic Compatibility (EMC) filter, but is not limited thereto.

The relay 200 may connect or block the filter 150 and the system 300 .

Specifically, the relay 200 may include a first sub relay SR1 and a second sub relay SR2.

In the case of the first sub relay SR1 , one end may be connected to the fourth inductor L4 , and the other end may be connected to one end of the fifth capacitor C5 .

In the case of the second sub relay SR2 , one end may be connected to the sixth inductor L6 , and the other end may be connected to the other end of the fifth capacitor C5 .

The relay control unit 250 may turn the relay 200 on or off.

For reference, the relay control unit 250 may be controlled by a device such as the aforementioned PCS, PMS, EMS, or the like, or may be controlled by an external device.

The system 300 may include an AC power source AP and a fifth capacitor C5 connected in parallel to the AC power source AP.

In the case of the fifth capacitor C5 , one end may be connected to the other end of the first sub relay SR1 , and the other end may be connected to the other end of the second sub relay SR2 .

The discharge resistor DR may be connected in parallel between the inverter 100 and the filter 150 .

Specifically, the discharge resistor DR reduces the discharge time of the capacitors (that is, the first to fifth capacitors C1 to C5) provided in the inverter 100, the filter 150, and the system 300, respectively, Inrush current generated when the relay 200 turned off by the relay controller 250 is turned on again can be reduced. Specific details on this will be described later.

In the energy storage system 1 configured as described above, before the inverter 100 is driven, an operation of checking the overall state of the energy storage system 1 is performed, and it is determined that there is no abnormality in the energy storage system 1 . In this case, the relay 200 may be turned on by the relay controller 250 to connect the inverter 100 and the grid 300 .

That is, before the inverter 100 is driven, when the energy storage system 1 is in a normal state, there is no particular problem even if the relay 200 is turned on or off, but the relay 200 is turned on or If the inrush current generated during turn-off is large, the relay 200 may be fused due to the inrush current.

Here, before driving of the inverter 100 is started, the charging or discharging operation of the capacitors C1 to C5 according to the turn-on or turn-off of the relay 200 will be described as follows.

First, when the relay 200 is turned on for the first time by the relay control unit 250 before the drive of the inverter 100 is started, the capacitors (that is, the inverter 100 ), the filter 150 , and the system 300 are respectively provided. , the first to fifth capacitors C1 to C5) may be charged.

After that, when the relay 200 turned on by the relay control unit 250 is turned off, the capacitors (that is, the first to fifth capacitors (that is, the first to fifth capacitors) C1~C5)) may be discharged.

Specifically, with reference to FIGS. 4 to 6 , the change in inrush current according to the turn-on or turn-off of the relay 200 before the driving of the inverter 100 is started will be described as follows.

For reference, in FIG. 5 , the vertical axis indicates AC voltages (+V, -V) applied to the capacitor (eg, any one of the first to fifth capacitors C5 ), and the horizontal axis indicates time (t). can mean

In addition, in FIG. 6 , the vertical axis may mean inrush currents (+I, -I) generated when the relay 200 is turned on or off, and the horizontal axis may mean time (t).

4 to 6, before the drive of the inverter 100 is started, the relay 200 is turned on at a first point P1, is turned off at a second point P2, and a third point ( It may be turned on again at P3 ) and may be turned off again at the fourth point P4 .

Here, when the relay 200 is first turned on at the first point P1, it can be seen that the inrush current increases momentarily and then decreases again.

In addition, when the AC voltage provided by the system 300 at the second point P2 at which the relay 200 is turned off is a positive peak voltage PP, a capacitor (eg, For example, the first to fifth capacitors C1 to C5 may also be discharged after being charged to the maximum voltage, that is, the positive peak voltage PP.

However, due to the existence of the discharge resistor DR, the voltage charged in the first to fifth capacitors C1 to C5 may be rapidly discharged.

Specifically, as shown in FIG. 2 , it can be confirmed that the discharge slope DS′ when there is a discharge resistance is steeper than the discharge slope DS when there is no discharge resistance as shown in FIG. 5 .

This is because the discharge resistor DR reduces the discharge time by rapidly discharging the voltage charged in the first to fifth capacitors C1 to C5.

Accordingly, assuming that the AC voltage provided by the system 300 at the third point P3 at which the relay 200 is turned on again is the negative peak voltage NP, the capacitor provided in the energy storage system 1 (For example, a voltage VC′ smaller than that of the conventional one (ie, when there is no discharge resistor as shown in FIG. 1 ) may be applied to the first to fifth capacitors C1 to C5 .

That is, the amount of voltage change of the capacitor (eg, the second capacitor C2) when there is no discharging resistance as shown in FIG. )), the voltage change amount is smaller.

In addition, since the amount of voltage change when the relay 200 is turned on at the third point P3 is reduced compared to the prior art, the magnitude of the inrush current according to the above-mentioned <Equation 1> is also smaller than that of the prior art.

As described above, in the energy storage system 1 according to an embodiment of the present invention, the capacitor C1 when the relay 200 is turned off through the discharge resistor DR connected in parallel to the output terminal of the inverter 100 . By reducing the discharge time of ~ C5), it is possible to reduce the inrush current generated when the relay 200 is turned on again, thereby preventing the relay 200 from fusion. In addition, it is possible to prevent an accident that may occur in the inverter 100 or the like due to the fusion of the relay 200 in advance.

For those of ordinary skill in the art to which the present invention pertains, various substitutions, modifications and changes are possible within the scope of the present invention without departing from the technical spirit of the present invention, so the above-described embodiments and the accompanying drawings is not limited by

100: inverter 150: filter
200: relay 250: relay control unit
300: strain

Claims (8)

An energy storage system comprising a system, comprising:
an inverter that converts DC power into AC power;
a filter connected to the output terminal of the inverter, reducing noise of AC power converted by the inverter and supplying it to the system;
a relay connecting or blocking the filter and the system;
a discharge resistor connected in parallel between the inverter and the filter; and
And a relay control unit for turning the relay on (turn-on) or turn-off (turn-off),
Each of the inverter, the filter and the system includes a capacitor,
When the relay is turned on for the first time by the relay control unit before driving of the inverter is started, capacitors respectively provided in the inverter, the filter, and the system are charged,
When the turned-on relay is turned off by the relay control unit, the inverter, the filter, and the capacitors provided in the system are discharged.
energy storage system.
delete delete According to claim 1,
The discharge resistance is
By reducing the discharge time of the capacitor provided in each of the inverter, the filter, and the system, the inrush current generated when the relay turned off by the relay control unit is turned on again
energy storage system.
According to claim 1,
The inverter is
a first capacitor;
first and second switches connected in parallel with the first capacitor;
Third and fourth switches connected in parallel with the first and second switches;
a first inductor having one end connected between the first and second switches;
a second inductor having one end connected between the third and fourth switches;
a second capacitor having one end connected to the other end of the first inductor and the other end connected to the other end of the second inductor;
A third capacitor connected in parallel with the second capacitor,
The first and second switches are connected in series with each other,
The third and fourth switches are connected in series with each other,
The discharge resistor is connected in parallel with the third capacitor
energy storage system.
6. The method of claim 5,
The filter is
third and fourth inductors connected in series with the first inductor;
fifth and sixth inductors connected in series with the second inductor;
a fourth capacitor connected in parallel with the third capacitor;
One end of the fourth capacitor is connected between the third and fourth inductors, and the other end of the fourth capacitor is connected between the fifth and sixth inductors,
The fourth capacitor is connected in parallel with the discharge resistor.
energy storage system.
7. The method of claim 6,
The system is
Comprising an AC power source and a fifth capacitor connected in parallel to the AC power source,
The relay is
A first sub relay having one end connected to the fourth inductor, the other end connected to one end of the fifth capacitor, and a second sub relay having one end connected to the sixth inductor and the other end connected to the other end of the fifth capacitor. with relay
energy storage system.
According to claim 1,
The filter is an EMC (Electro Magnetic Compatibility) filter.
energy storage system.

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