KR101725348B1 - Dc-dc converter and method for discharging voltage control - Google Patents

Abstract

The relay contact 1 and the relay contactor 2 respectively connected to the voltage terminals of the battery in a simpler and simpler manner, respectively, and the relay contact 1 and the relay contact 2 are switched on or switched off, DC converter for controlling the off-state of the DC-DC converter by using a switching element and a discharging using an inductive resistor.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a DC-DC converter and a discharge voltage control method,

The present invention relates to a DC-DC converter and a discharge voltage control method.

Currently, various batteries for an energy storage system (ESS) are being studied.

Lithium-ion batteries (LiB batteries) have come close to commercialization, yet they have not yet been fully verified in terms of stability and lifetime. Therefore, development of other types of batteries such as a redox flow battery (RFB) is actively under development. The redox flow cell (RFB) is based on the chemical reaction of the redox couple.

Among them, zinc-bromine flow battery (Zn-Br flow battery) is a battery based on chemical reaction in a stack, and has advantages such as output, capacity, and price. However, due to the deposition of zinc metal on the electrode surface of the stack during the reaction or due to the uneven deposition of zinc metal, the opposite separator is damaged . To solve this problem, a process called stripping is performed.

Stripping, on the other hand, is a complete discharge in which the voltage of the stack falls to 0V, which consumes unnecessary power, so the smaller the number of times in terms of system efficiency, the better.

However, as mentioned above, if the stripping function is not performed, it is indispensable that the battery itself is damaged before the efficiency is considered.

The prior art has implemented a stripping function by using a switching element of a DC-DC converter of a zinc-bromine flow cell.

FIG. 1 is a graph showing discharging according to a conventional stripping method. In FIG. 1 (a), S1 corresponds to the discharge voltage of the stack 1, and S2 in FIG. 1 (b) Corresponds to the discharge voltage of the stack (Stack 2).

Referring to FIG. 1, a conventional stripping method includes an insulated gate bipolar transistor (IGBT) or a metal oxide semiconductor field effect transistor (MOSFET), which is a switching element, And the discharge is continued to discharge the stack voltage to 0V.

However, as in the conventional stripping method, the sustained discharge of the low voltage / low current increases the discharging time to increase the power consumption of the BOP (Balance of Plant) such as the pump.

The present invention improves and simplifies the stripping function in a simpler and simpler manner and controls the zinc metal deposition between the stacks uniformly through voltage dispersion control DC converter and a discharge voltage control method capable of reducing the number of stripping operations by reducing the number of stripping operations.

According to an aspect of the present invention, a DC-DC converter is connected to a relay contactor 1 and a relay contactor 2 respectively connected to voltage terminals of the battery, and the relay contact point 1 and the relay contact point 2 Off or switch-off of the switching element, thereby realizing a general discharge using the switching element and a striping using selectively using the inductive resistance.

The relay contactor (1)

And may be connected in series between the positive (+) terminal of the battery and the DC-DC converter.

The relay contact (2)

And may be connected in parallel between the voltage terminal of the battery and the DC-DC converter.

An inductive resistor may be connected to the relay contactor 2.

The relay contact 1 and the relay contactor 2 are connected to each other through a signal cable. The relay contact 1 is switched off and the relay contact 2 is switched on to provide a stripping function using an inductive resistor. The relay contact point 1 is switched on, and the relay contact point 2 is switched off, thereby implementing a stripping function using a switching element.

The stack terminal voltage is monitored for each of a plurality of stacks included in the battery, and the power consumption of each of the plurality of stacks is equally divided to adjust the discharge speed of each stack.

According to another aspect of the present invention, there is provided a discharge voltage control method for controlling a discharge voltage of a DC-DC converter, comprising the steps of: detecting a terminal voltage of a battery to monitor a voltage of each of a plurality of cell stacks; And adjusting the power consumption of each stack if the difference between the stack voltage and the lowest stack voltage exceeds a predefined threshold condition.

Wherein the adjusting comprises:

If the difference exceeds the first threshold condition, increase the power consumption of the stack with the maximum stack voltage and decrease the power consumption of the stack with the lowest stack voltage.

After said reducing,

Determining whether the difference among the stack voltages is less than a second threshold as a result of monitoring the voltages of the plurality of cell stacks, and if the difference is less than the second threshold criterion, And distributing the same value.

After said reducing,

Determining whether the difference among the stack voltages exceeds a third threshold criterion as a result of monitoring respective voltages of the plurality of cell stacks and if the difference exceeds the third threshold criterion, Increasing the power consumption, and reducing the power consumption of the stack with the lowest stack voltage.

After said reducing,

Determining whether the difference among the stack voltages is less than a fourth threshold as a result of monitoring the voltages of the plurality of cell stacks; and if the difference is less than the fourth threshold criterion, And distributing the same value.

After said reducing,

Determining whether the difference among the stack voltages exceeds a fifth threshold criterion as a result of monitoring each voltage of the plurality of cell stacks and if the difference exceeds the fifth threshold criterion, Increasing the power consumption, and reducing the power consumption of the stack with the lowest stack voltage.

According to an embodiment of the present invention, a stripping time of a Zinc-Bromine flow battery is shortened and a discharge rate at which a gap is widened is divided into a voltage of each stack ) Value is monitored in real time to control the discharging speed of each stack so that the discharge end voltage of each stack is made similar or equal at the end of discharge at a certain point of time to shorten the number of stripping can do.

In this way, the stripping time can be reduced and the frequency of use of the switching device can be reduced, so that the life of the MOSFET, which is the main element of the power conversion, can be extended and the temperature can be controlled.

FIG. 1 is a graph showing discharging according to a conventional stripping method.
2 shows a stripping control structure of a zinc-bromine direct current (DC-DC) converter according to an embodiment of the present invention.
FIG. 3 shows current flow in mode 1 in FIG.
FIG. 4 shows the current flow in mode 2 in FIG.
5 is a flowchart illustrating a voltage control method for discharging a zinc-bromine direct current (DC-DC) converter according to an embodiment of the present invention.
6 is a graph illustrating charge / discharge voltage changes of four stacks according to an embodiment of the present invention.
FIG. 7 is a graph showing a voltage change according to voltage control for discharging a zinc-bromine DC-DC converter according to an embodiment of the present invention.
8 is a photograph showing zinc metal deposition before and after voltage control for discharging a zinc-bromine DC-DC converter according to an embodiment of the present invention.
9 is a diagram illustrating an embodiment of a zinc-bromine DC-DC converter according to an embodiment of the present invention.
10 is a graph showing experimental results according to an embodiment of the present invention.
11 shows a comparison result between the discharge using the switching element and the discharge using the inductive resistance according to the embodiment of the present invention.

The invention will be described in more detail in the following examples. However, the following examples are illustrative of the present invention, and the present invention is not limited by the following examples.

2 shows a stripping control structure of a zinc-bromine direct current (DC-DC) converter according to an embodiment of the present invention.

Referring to FIG. 2, it is designed to be switchable to an inductive resistance by using two relay contacts. At this time, the relay contact (relay contact) is controlled by the DC / DC converter.

Here, the DC-DC converter 100 is connected to the battery electrode terminals (+, -). At this time, a relay contact 1 200 is connected between the positive terminal of the battery and the DC-DC converter 100. The relay contact 2 300 is connected in parallel with the battery electrode terminals (+, -).

The DC-DC converter 100 is connected to a relay contact 1 200 and a relay contact 2 300 through a signal cable. The DC-DC converter 100 transmits a switch-on signal or a switch-off signal to the relay contact 1 200 and the relay contact 2 300 through a signal cable, respectively.

A DC-DC converter 100 implemented with a stripping function of a zinc-bromine flow battery and a conventional DC-DC converter for a zinc-bromine (Zn-Br) The stripping function, which is a discharging action of less than 100V, is configured to selectively use the discharging of a switching device and an inductive resistor by using a relay contactor.

The DC-DC converter 100 forcibly discharges the power of the stack by an inductive resistor in a low-power discharging and stripping state in which the grid power is lost in the embodiment of the present invention, Mode (Stripping mode). That is, the power consumption is adjusted to increase the speed.

At this time, the relay contacts (200, 300) are controlled by the DC / DC converter (100). The control mode is defined as shown in Table 1. Table 1 shows the sequence of relay operation.

division Relay Contactor 1 Relay Contactor 2 Remarks drawing Mode 1 ON OFF (OFF) General discharge (using switching device) 3 Mode 2 OFF (OFF) ON Using inductive resistance 4

Table 1 is a table classified according to the states of the relay contactor 1 200 and the relay contactor 300. Mode 1 corresponds to a general discharge And Mode 2 corresponds to an example in which an inductive resistor is used.

In mode 1, the DC / DC converter 100 outputs a switch-on signal of the relay contactor 1 200 and a switch-off signal of the relay contactor 2 300.

In mode 2, the DC / DC converter 100 outputs a switch-off signal of the relay contactor 1 200 and a switch-on signal of the relay contactor 2 300.

Fig. 3 shows the current flow in mode 1 in Fig. 2, and Fig. 4 shows the current flow in mode 2 in Fig.

Referring to FIG. 3, this corresponds to Mode 1 of Table 1. And corresponds to a general discharge using a switching element of the DC-DC converter 100. A resistor connected to relay contactor 1 (200) is used.

Referring to FIG. 4, this corresponds to Mode 2 of Table 1. A rapid discharge using a stripping resistor 400 and a resistor connected to the relay contactor 2 300 is used.

As described above, the stripping function is improved by selectively performing the discharging using the conventional switching element and the inductive stripping resistance.

Here, an IGBT and a MOSFET device constituting a zinc-bromine DC-DC converter receive a switching signal to step up and down a voltage. At this time, a loss occurs when the input value changes to the output value, and this loss is referred to as a general discharge. Here, the switching element can be considered to be inside the converter.

5 is a flowchart illustrating a method of controlling a discharge voltage of a zinc-bromine direct current (DC-DC) converter according to an embodiment of the present invention.

At this time, although the chemical flow battery was formed into four stack lines (50kWh module standard), it is not limited thereto.

Generally, a Zinc-Bromine battery performs one strip / one cycle or one strip / five cycles.

Referring to FIG. 5, a DC-DC converter 100 detects a terminal voltage of a battery and monitors voltages of a plurality of cell stacks (S101). The monitoring results are shown in Table 2 below.

Stack line 1 161V 5kW discharging Stack line 2 150V 5kW discharging Stack line 3 150V 5kW discharging Stack line 4 140V 5kW discharging

The DC-DC converter 100 determines whether the difference between the maximum voltage and the minimum voltage of the cell stack exceeds a first threshold criterion (S103).

According to Table 2, the maximum voltage (Vmax) of the cell stack becomes the voltage (161V) of the first stack line and the minimum voltage (Vmin) of the cell stack becomes the voltage (140V) of the fourth stack line. And judges whether the difference between the voltage (161 V) of the first stack line and the voltage (140 V) of the fourth stack line exceeds 20 V.

If so, the DC-DC converter 100 adjusts the power value of the corresponding cell stack (S105). That is, as shown in Table 3, the power consumption of the first stack line of the maximum voltage Vmax is increased by two, and the power consumption of the fourth stack line of the minimum voltage Vmin is subtracted by two.

Stack line 1 161V 7kW discharging Stack line 2 150V 5kW discharging Stack line 3 150V 5kW discharging Stack line 4 140V discharging at 3kW

According to Table 3, the power consumption of the first stack line is increased by two to 7 kW, and the power consumption of the fourth stack line is reduced by two to three kW, as compared with Table 2.

The DC-DC converter 100 determines whether the difference between the maximum voltage Vmax and the minimum voltage Vmin of the cell stack is less than the second threshold reference, that is, less than 10 V S107).

At this time, if it is less than 10V, the power consumption is distributed equally to the plurality of cell stacks (S109). If it is less than 10 V, it corresponds to the case where there is no change in the maximum voltage Vmax and the minimum voltage Vmin. For example, the first stack line is 148V, the second stack line is 145V, the third stack line is 145V, and the fourth stack line is 139V.

The DC-DC converter 100 determines whether the difference between the maximum voltage Vmax and the minimum voltage Vmin of the cell stack exceeds a third threshold value as a result of monitoring the next voltage (S111). For example, exceeds the third threshold criterion, i.e., 30 V.

If so, the DC-DC converter 100 adjusts the power value of the corresponding cell stack (S113). That is, as shown in Table 4, the power consumption of the first stack line of the maximum voltage Vmax is increased by 3, and the power consumption of the fourth stack line of the minimum voltage Vmin is decreased by 3.

Stack line 1 During discharge of 133V 10kW Stack line 2 141V 5kW discharging Stack line 3 132V 5kW discharging Stack line 4 During discharge of 133V 0kW

The DC-DC converter 100 determines whether the difference between the maximum voltage Vmax and the minimum voltage Vmin of the cell stack is equal to or less than a fourth threshold value, for example, less than 15 V (S115).

At this time, if satisfied, the power consumption is distributed equally to the plurality of cell stacks (S117).

The DC-DC converter 100 determines whether the difference between the maximum voltage Vmax and the minimum voltage Vmin of the cell stack exceeds a fifth threshold value, for example, 40 V as a result of the next voltage monitoring (S119).

If so, the DC-DC converter 100 multiplies the stack line representing the maximum voltage by 3 and makes the stack line representing the lowest voltage zero (S121).

As described above, it is possible to reduce the number of stripping by uniformly bringing zinc metal deposition between the stacks through the voltage dispersion control. The discharge rate at which the gap is widened is monitored in real time on the voltage value of each stack to control the discharge rate of each stack so that the discharge end voltage of each stack Voltage) are made similar or equal to eliminate the imbalance of the zinc deposition between the stacks.

6 is a graph illustrating charge / discharge voltage changes of four stacks according to an embodiment of the present invention.

Referring to FIG. 6, four stack lines (S1, S2, S3, S4) are formed on the basis of a 50 kWh module. Here, the discharge curves of the four stack lines (S1, S2, S3, and S4) show that the drop rates of the voltage during the discharge are different from each other.

This is because the balance can not be controlled by giving the same command value to the four converters. As the time passes, the gap becomes wider and the voltage of each stack is unbalanced at a certain end. This means that the SOC (State Of Charge) is different and the deposition of the zinc metal is unbalanced.

FIG. 7 is a graph showing a voltage change according to voltage control for discharging a zinc-bromine direct current (DC-DC) converter according to an embodiment of the present invention.

Referring to FIG. 7, the discharging rate of each stack is controlled by monitoring the voltage value of each stack in real time. Then, as shown in FIG. 6, at the end of the discharge at a certain point of time, the discharge end voltage of each stack is made similar / equal to eliminate the unbalance of the zinc deposition between the stacks. This results in a reduction in the number of times of stripping, and the zinc metal deposition state of each stack is uniformly changed as shown in FIG.

8 is a photograph showing zinc metal deposition before and after voltage control for discharging a zinc-bromine DC-DC converter according to an embodiment of the present invention.

Referring to FIG. 8A, it can be seen that before the voltage balance control, the zinc metal deposition is in an unbalanced state.

On the other hand, referring to FIG. 8 (b), it can be seen that the zinc metal deposition is balanced by controlling the voltage balance as described above.

Experimental results of the above-described contents will be described with reference to FIGS. 10 and 11. FIG.

FIG. 9 is a diagram illustrating an embodiment of a zinc-bromine DC-DC converter according to an embodiment of the present invention. FIG. 10 is a graph showing an experimental result according to an embodiment of the present invention. to be.

9, a DC-DC converter 100 for a zinc-bromine flow cell, to which a stripping resistor 400 controlled by relay contacts 200 and 300 is added, is connected to a charge / discharge unit .

Stripping operation was implemented by setting 4Kw output based on input voltage 200V and output voltage 360V.

10 (a) shows that the stripping time is long and the power consumption is large. FIG. 10 (b) shows that the discharge time is short because the slope is abruptly inclined due to the discharge of the inductive resistance. Therefore, FIG. 10 (b) means that the power consumption is small.

11 shows a comparison result between the discharge using the switching element and the discharge using the inductive resistance according to the embodiment of the present invention.

Referring to FIG. 11, it can be seen that not only the discharge using the general discharge contrast inductive resistance using the switching element is shortened in time, but also the power consumption is reduced by half.

Claims (12)

Is connected in series with a relay contact 1 connected to the positive terminal of a zinc-bromine flow battery (Zn-Br flow battery)
A relay contact 2 connected to the positive and negative terminals of the zinc-bromine flow cell and connected in parallel to the inductive resistor,
And is connected to the relay contactor 1 and the relay contactor 2 through a signal cable,
A first stripping function using an inductive resistor by switching off the relay contact point 1 and switching on the relay contact point 2, a first stripping function using an inductive resistor to switch on the relay contact point 1, DC converter for selectively implementing two striping functions. delete delete delete delete The method according to claim 1,
The DC-DC converter monitors the stack terminal voltage for each of a plurality of stacks included in the battery, and distributes power equally to the plurality of stacks to adjust a discharging speed of each stack. A method for controlling a discharge voltage of a DC-DC converter,
Monitoring terminal voltages of a zinc-bromine flow battery (Zn-Br flow battery) and monitoring respective voltages for a plurality of cell stacks, and
Adjusting the power consumption of each stack if the difference between the maximum stack voltage and the lowest stack voltage in each stack voltage exceeds a predefined first threshold voltage,
The DC-DC converter includes:
A relay contact 1 connected in series with a relay contact 1 connected to a positive terminal of the zinc-bromine flow cell and connected to a positive terminal and a negative terminal of the zinc-bromine flow cell, And is connected to the relay contactor 1 and the relay contactor 2 through a signal cable,
A first stripping function using an inductive resistor by switching off the relay contact point 1 and switching on the relay contact point 2, a first stripping function using an inductive resistor to switch on the relay contact point 1, 2 < / RTI > stripping function. 8. The method of claim 7,
Wherein the adjusting comprises:
Increasing the power consumption of the stack having the maximum stack voltage and decreasing the power consumption of the stack having the lowest stack voltage if the difference exceeds the first threshold voltage
/ RTI > 9. The method of claim 8,
After said reducing,
Determining whether a difference between a maximum stack voltage and a minimum stack voltage of each stack voltage is less than a second threshold voltage as a result of monitoring the voltages of the plurality of cell stacks,
Distributing power to the plurality of cell stacks with the same value if the second threshold voltage is less than the second threshold voltage
Further comprising the steps of: 10. The method of claim 9,
After said reducing,
Determining whether a difference between a maximum stack voltage and a minimum stack voltage of each of the stack voltages exceeds a third threshold voltage as a result of monitoring respective voltages for the plurality of cell stacks,
Increasing the power consumption of the stack having the maximum stack voltage and decreasing the power consumption of the stack having the lowest stack voltage when the third threshold voltage is exceeded
Further comprising the steps of: 10. The method of claim 9,
After said reducing,
Determining whether a difference between a maximum stack voltage and a minimum stack voltage of each stack voltage is less than a fourth threshold voltage as a result of monitoring the voltages of the plurality of cell stacks,
Dividing the power consumption into the same value in the plurality of cell stacks if the fourth threshold voltage is less than the fourth threshold voltage
Further comprising the steps of: 10. The method of claim 9,
After said reducing,
Determining whether a difference between a maximum stack voltage and a minimum stack voltage of each of the stack voltages exceeds a fifth threshold voltage as a result of monitoring respective voltages for the plurality of cell stacks,
Increasing the power consumption of the stack having the maximum stack voltage and decreasing the power consumption of the stack having the lowest stack voltage when the fifth threshold voltage is exceeded
Further comprising the steps of:

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