KR101269059B1 - Lithium secondary battery pack for use in solar streetlight - Google Patents

Abstract

Lithium secondary battery pack for solar street light according to the present invention, a plurality of lithium secondary battery cells 112; A printed circuit board 120 connecting the lithium secondary battery cells 112 to each other in series or in parallel and charging and discharging the lithium secondary battery cells 112; A BMS unit 140 connected to the printed circuit board 120 and controlling the lithium secondary battery cell 112 to be charged and discharged stably; And case 150; It includes, the BMS unit 140 is a protection circuit module (PCM) for preventing overcharge, overdischarge, overcurrent, short circuit of the lithium secondary battery cell 121, and the charge of the lithium secondary battery cell 121 is uniformly Characterized in that it comprises a cell balancer (cell balancer) to be made. According to the present invention, since a plurality of lithium secondary batteries are stacked and used, large-capacity charging and discharging is possible. Particularly, when a lithium polymer battery is used, it is very advantageous in terms of capacity and shape. Do. And since the BMS unit and the printed circuit board) is compactly mounted in the case, the overall size can be reduced. At this time, since the BMS is designed to perform not only a PCM function but also a cell balancing function and a reset function, stable charging and discharging can be achieved.

Description

Lithium secondary battery pack for solar street light {Lithium secondary battery pack for use in solar streetlight}

The present invention relates to a lithium secondary battery pack for a solar street light, and in particular, a plurality of lithium secondary batteries are mounted in a case, and together with a battery management system (BMS) for controlling the lithium secondary battery to be stably charged and discharged together. The present invention relates to a lithium secondary battery pack for a solar street light, which enables stable charging and discharging of large capacity.

Since a conventional street light operates by receiving power from the outside without its own power generation equipment, it must be supplied with power through underground or ground power cables from a long distance power supply. Therefore, a long power cable is required, and since a plurality of street lamps must be continuously connected to the power cable, there is a problem in that installation cost and management cost are considerably high. In addition, a safety accident is likely to occur due to a short circuit of the power cable during flooding due to heavy rain.

Therefore, solar streetlights are being gradually increased so that each streetlight includes a solar power generation system so that night lighting is performed according to its own power generation. Such a solar street light must be accompanied by a storage battery (secondary battery) for storing sunlight irradiated at midday as electrical energy.

Lead-acid batteries or Ni / Cd batteries are mostly used for commercially available solar street lights. Lead-acid batteries have the advantages of large capacity, excellent safety, and low cost, but their low energy density not only takes up a lot of installation space, but also shortens the use time, life span, and excessive maintenance costs, as well as lead and sulfuric acid. There is a problem that harmful pollutants are discharged. Ni / Cd batteries, like lead-acid batteries, have a low energy density and occupy a lot of installation space, which causes a problem of emitting highly toxic pollutants such as cadmium (Cd).

Therefore, various methods have been proposed to utilize the installation space efficiently. For example, Japanese Patent Application No. 2001-31548 (a controller for solar street light and solar security lamp and a method for installing a battery) discloses that a large battery is buried in a side ground of a street lamp. However, in this case, there is a high possibility of the occurrence of a short circuit due to the immersion of the battery due to rain water, etc., and also requires a installation work for embedding, there is a problem of low installation efficiency.

In addition, Patent Application No. 2005-28856 (integrated solar LED lighting) discloses that the storage battery is closely attached to the lower portion of the solar cell panel. However, in this case, there is a problem that the high heat of the solar cell panel is transferred to the storage battery as it is, so that the performance of the storage battery is deteriorated.

In addition, Patent Application No. 2006-32922 (Solar Street Light for Easy Installation and Repair) and Patent Application No. 2009-63811 (Control Device for Solar Street Light) are provided such that large-sized batteries protrude outside the props. Is disclosed. In this case, there is a problem that the overall appearance of the street lamp is impaired, and the battery may be easily stolen.

As described above, in the case of a conventional solar street light, a large storage battery may be used, and thus, the storage battery may be embedded in the ground, installed in the lower part of the solar panel, or installed to protrude into a prop. Have

Therefore, there has been proposed a battery-integrated street light that solves the above problems by using a small and large capacity lithium-ion battery embedded in the holding post (see Patent No. 900032). However, since the lithium ion battery uses a liquid electrolyte, there is a possibility of leakage and risk of explosion, as well as a disadvantage that it can be manufactured in a limited size.

Accordingly, there is a need to use a lithium polymer battery that is smaller than a lithium ion battery and can be manufactured in various shapes and which has a higher capacity than a lithium ion battery. However, even in this case, only one lithium polymer battery is unsuitable for use in solar street lights that require the storage of large amounts of electrical energy.

Therefore, the problem to be solved by the present invention is to use a lithium secondary battery such as a lithium ion battery or a lithium polymer battery as a storage battery, but by stacking a plurality of them to suit a large capacity, and to control the charging and discharging of each lithium secondary battery safely The present invention provides a lithium secondary battery pack for a solar street light that can solve the above-mentioned problems by mounting a battery management system (BMS) in a case that eliminates the possibility of electrolyte leakage and explosion.

Solar secondary battery pack for solar streetlight according to the present invention for achieving the above object,

A plurality of lithium secondary battery cells;

A printed circuit board connecting the lithium secondary battery cells to each other in series or in parallel and charging and discharging the lithium secondary battery cells;

A BMS unit connected to the printed circuit board to control the lithium secondary battery cell to be stably charged and discharged; And

A case accommodating the lithium secondary battery cell, the printed circuit board, and the BMS unit; / RTI >

A cell balancing unit for uniformly charging the lithium secondary battery cell with a protection circuit module (PCM) for preventing the overcharge, overdischarge, overcurrent, and short circuit of the lithium secondary battery cell; cell balancer).

It is preferable that the lithium secondary battery cell is a lithium polymer battery cell.

The plurality of lithium secondary battery cells are preferably formed by laminating individual lithium secondary battery cells having a plate shape in multiple layers.

It is preferable that a plate-shaped thermoelectric element for dissipating heat of the lithium secondary battery cell is interposed between the lithium secondary battery cells so that the lithium secondary battery cell is not overheated, and the thermoelectric element is controlled by the BMS unit.

Preferably, a gap maintaining member is installed in a predetermined region between the lithium secondary battery cells so that the lithium secondary battery cells are spaced a predetermined distance apart.

The printed circuit board and the BMS unit may be installed to be perpendicular to the inside of the case while being positioned on the side of a structure in which the plurality of lithium secondary battery cells are stacked in multiple layers.

The BMS unit monitors the current of the secondary battery cell through a composite IC to turn on / off the charge blocking FET, the discharge blocking FET, and the cell balancing switch to perform excessive charge / discharge prevention and cell balancing functions.

In this case, the BMS unit includes a constant voltage regulator IC, an overcurrent control IC, and a shunt resistor (R _sense ) separately from the complex IC, and the constant voltage regulator IC receives a voltage of a battery pack and makes it a constant voltage to the overcurrent control IC. And the overcurrent control IC divides the voltage across its VSS-VM by the shunt resistor (R _sense ) that is installed between the lithium secondary battery cell and the discharge blocking FET 40 and is connected to the VM stage. If it is detected and the value is above a certain value, it is preferable to recognize the overcurrent and to shut off the discharge FET to perform the overcurrent prevention function.

By providing a reset switch connecting the VSS terminal and the VM terminal of the overcurrent control IC, it is preferable to press the reset switch so that the VSS terminal and the VM terminal are turned on so that the BMS unit performs the original return operation.

According to the present invention, since a plurality of lithium secondary batteries are stacked and used, large-capacity charging and discharging is possible. Particularly, when a lithium polymer battery is used, it is very advantageous in terms of capacity and shape. Do. And since the BMS unit and the printed circuit board) is compactly mounted in the case, the overall size can be reduced. At this time, since the BMS is designed to perform not only a PCM function but also a cell balancing function and a reset function, stable charging and discharging can be achieved.

1 and 2 are views for explaining a lithium secondary battery pack 100 for a solar street light according to the present invention;
3 is a main circuit configuration diagram of the BMS unit 140;
4 is a circuit diagram of a sub-circuit of the BMS unit 140;
5 is a photograph showing a printed circuit board in which a main circuit and a subcircuit of the BMS 140 are actual.

Hereinafter, with reference to the accompanying drawings, preferred embodiments of the present invention will be described in detail. The following embodiments are merely provided to understand the contents of the present invention, and those skilled in the art will be able to make many modifications within the technical scope of the present invention. Therefore, the scope of the present invention should not be construed as being limited to these embodiments.

1 and 2 are views for explaining a lithium secondary battery pack 100 for a solar street light according to the present invention. 1 and 2, the lithium secondary battery cell 110, the printed circuit board 120, and the BMS unit 140 are accommodated together in the case 150, in which case the case 150 is included. Is preferably made of die-cast aluminum so as to have excellent heat dissipation.

The lithium secondary battery cell 110 may be a lithium ion battery or a lithium polymer battery, but it is preferable to use a lithium polymer battery that is compact in size and can be manufactured in various shapes and excellent in capacity compared to a lithium ion battery.

Preferably, the lithium secondary battery cell 110 is stacked in plural layers, and for this purpose, the lithium secondary battery cell 110 may have a plate shape. Even if the lithium secondary battery is suitable for a large capacity and a high output, it is limited to apply to a device that requires the storage of a lot of electrical energy, such as a solar street light, so that a plurality of stacked structures as described above.

Terminals 112 of the plurality of lithium secondary battery cells 110 are connected in series or in parallel with each other through the printed circuit board 120 to be charged and discharged through the external terminal 121. When the lithium secondary battery cell 110 is exposed to high temperature for a long time, a swelling phenomenon may occur and performance may be greatly reduced. Therefore, in order to prevent this by interposing a plate-shaped thermoelectric element 130, for example, a Peltier element between the lithium secondary battery cell 110 to cool it when the lithium secondary battery cell 110 is overheated to a predetermined temperature, for example, 60 ℃ or more. . The thermoelectric element 130 is controlled through the BMS unit 140.

In order to prevent thermal accumulation between the lithium secondary battery cells 110 stacked in a plurality of layers, a gap maintaining member 200 for separating the lithium secondary battery cells 110 by a predetermined interval may be disposed between the lithium secondary battery cells 110. It is interposed. The gap maintaining member 200 is preferably installed only in a predetermined region rather than the entire area of the lithium secondary battery cell 110 so that a predetermined space is formed between the lithium secondary battery cells 110. It is preferable to use a sponge-type double-sided tape as the gap retaining member 200 to fix the adjacent lithium secondary battery cells 110 so as not to separate or slip, and to exhibit a predetermined elastic force when an impact occurs.

The BMS unit 140 is installed to be connected to the printed circuit board 120 to prevent overcharge, overdischarge, overcurrent, and short-circuit of the lithium secondary battery cell 110. In addition to controlling so as to control the charging of each lithium secondary battery 110 is made uniform, and also to be connected to the thermoelectric element 130 is controlled so as not to overheat the lithium secondary battery cell (110).

 In order to minimize the volume of the lithium secondary battery pack 100, the BMS unit 140 and the printed circuit board 120 are positioned on the side of the structure in which the lithium secondary battery cells 110 are stacked in multiple layers, and the case 150. It is preferable to be installed so as to stand vertically in the interior of the.

The BMS unit 140 largely includes a protection circuit module (PCM), a cell balancer, and a heat dissipation control unit. The protection circuit unit is for preventing overcharge, overdischarge, overcurrent, and short circuit of the individual lithium secondary battery cells 110, and the cell balancing unit is for uniformly charging each lithium secondary battery cell 110. The heat dissipation control unit is for preventing the lithium secondary battery cell 110 from overheating.

A lithium secondary battery has a very high risk of overcharging, overdischarging, or overcurrent, which significantly reduces the characteristics of the battery or generates heat or ignition. Therefore, to prevent this is to put the BMS unit 140 inside the case 150.

3 is a diagram illustrating a main circuit of the BMS unit 140. Referring to FIG. 3, the complex IC 50 performs a PCM function and a cell balancing function together. In the conventional BMS unit, a chip for controlling the PCM function and the cell balancing function existed separately, but in the case of the present invention, since a single complex IC 50 is responsible for this, space and cost are reduced. The disadvantage is that there is no detection function for overcurrent, so to compensate for this, an overcurrent IC 10 having an overcurrent control function is separately installed.

[Overcharge prevention]

When the lithium ion battery is continuously charged even in a fully charged state, the battery voltage continues to increase, and when the battery is overcharged to 4.2V or more, the electrolyte breaks down at the positive electrode, thereby increasing the internal pressure of the battery. During overcharging, dendritic lithium metal is precipitated at the negative electrode, which causes internal short-circuit to ignite or explode, causing fire.

Therefore, in general, charging is constant current-constant voltage charging, and the voltage during constant voltage charging should be controlled so as not to exceed the battery rating. However, if the charger breaks down or you accidentally charge it with another charger, there is a risk of exceeding the battery's maximum rating. In this case, the charging current is cut off so as not to exceed the battery's maximum rating. This function is called overcharge protection.

To make the best use of the battery's capacity, the charger is designed to charge up to the battery's maximum rated capacity. For this reason, the overcharge detection voltage should be very high in accuracy, and each voltage should be detected when the batteries are connected in series. Commercially available overcharge protection circuits have an accuracy of ± 25 mV. Even after overcharging is detected and the protection circuit is activated, the discharge to the load occurs through the parasitic diode of the charge-blocking FET. In addition, the overcharge detection operation requires a delay time in order to cope with pulse charging or to prevent malfunction due to noise.

In FIG. 3, the overcharge blocking for the individual lithium secondary batteries BAT1 to BAT4 is performed through the charge blocking FET 30. That is, the battery voltage is continuously sensed, and when the battery voltage becomes higher than the reference value, the circuit is cut off by giving an off (0ff) signal to the gate terminal of the charge blocking FET 30.

[Overdischarge prevention]

Generally, a lithium ion battery is charged to 4.1-4.3V, and discharge completes at 2.7-3.0V. In a lithium ion battery, lithium contained in a graphite crystal structure as a negative electrode active material is inserted into a positive electrode through an electrolyte during discharge. If the battery is over discharged due to any cause, the discharge continues even after lithium in the negative electrode is depleted. At this time, since the electrons can no longer be supplied from the cathode, electrons are supplied from the Cu foil, which is the current collector, and at the same time, the Cu foil is dissolved. Even in this case, the battery may be ignited due to internal short circuit and lose its function as a battery. Therefore, when the battery voltage is below a certain value, the discharge current is cut off and this function is called an over discharge protection function.

In the overdischarge state, the battery capacity is extremely low, so the current consumption of the protection IC must be very small, and the current consumption of the overdischarge protection circuit on the market is also a few μA. When the charger is connected after the over-discharge protection circuit operates, charging is performed through the parasitic diode of the discharge blocking FET. In addition, in order to cope with pulsed discharge, a delay time is also required for overdischarge detection.

In FIG. 3, the overdischarge blocking of the individual lithium secondary batteries BAT1 to BAT4 is performed through the discharge blocking FET 40. That is, the battery voltage is continuously sensed, and when the battery voltage is lower than the reference value, the circuit is cut off by giving an off (0ff) signal to the gate terminal of the discharge blocking FET 40.

[Overcurrent protection]

If the battery is short-circuited between the external terminals of the battery by a metal during storage or use, or short circuit due to the failure of the connected equipment, there is a possibility of ignition even when a large current flows and heat or flammable material is in contact. In addition, a lithium ion battery using an organic solvent as an electrolyte has a high temperature during overcurrent, and in the worst case, reaches a melting point (180 ° C.) of lithium and becomes extremely dangerous. Therefore, when the current flows above a certain value, the discharge current is cut off and this function is called overcurrent protection.

Overcurrent protection features cutoff current and delay time. For example, when the external terminal 121 of the battery pack 100 is short-circuited and the discharge current exceeds 10A, the discharge is momentarily stopped (hundreds of μs), and when an abnormal current (5A or more) flows due to a malfunction of the device. After the non-response time (about 10 ms), the discharge is stopped. The overcurrent protection function is operated in the same state as the overdischarge protection function, but in the case of the overcurrent protection, the external terminal 121 of the battery pack 100 is opened to return to a usable state.

In FIG. 3, the complex IC 50 has to be monitored for current at all times, and thus does not function properly when entering the overcharge or overdischarge region. In order to compensate for this disadvantage, an overcurrent control IC 10 having an overcurrent control function is installed separately.

First, the voltage of the battery pack 100 is input from the constant voltage regulator IC 20, and a constant voltage of 3.7 V is generated, which is then sent to the overcurrent control IC 10. The overcurrent control IC 10 monitors the terminal current. A current value obtained by dividing the voltage across the (VSS-VM) by the shunt resistor 60 (R _sense ) is detected through the overcurrent control IC 10. If this value is greater than or equal to a predetermined value, the discharge control FET 40 is shut off by recognizing it as an overcurrent. The shunt resistor 60 is installed between the discharge blocking FET 40 and the lithium secondary batteries BAT1 to BAT4, and is also connected to the VM terminal of the overcurrent control IC 10.

[Cell Balancing Function]

Cell balancing is very important when several cells are connected in parallel. Lithium ion batteries cannot be chemically overcharged without damaging the active material. The electrolyte decomposition voltage is close to the full charge termination voltage of 4.1 to 4.3 V / cell. Therefore, monitoring and control are necessary to avoid damage due to overcharging. In the case of a single cell, the battery voltage is adjusted so as not to exceed a specified value, but the lithium secondary battery connected in series has a complicated problem.

Although the voltage of the battery pack 100 appears to be within an acceptable limit, one of the battery cells BAT1 to BAT4 connected in series may be damaged due to unbalance between the batteries. This imbalance is most often due to a change in internal impedance or a decrease in battery capacity due to aging. In any case, if any of the battery cells BAT1 to BAT4 in the battery pack 100 causes variation in battery characteristics, the battery cells are continuously overcharged during charging. Battery cells with reduced capacity or high impedance (BAT1 to BAT4) exhibit large voltages when charged and discharged. Cell balancing is to obtain the maximum effective capacity from the battery pack 100, and to extend the charge and discharge life. During charging, the unbalanced battery cells BAT1 to BAT4 first reach the end-of-charge voltage and the charger starts to shut down.

Cell balancing is to control the battery cells of high voltage until the remaining remaining battery cells (BAT1 ~ BAT4), so that all the battery cells reach the charging end voltage. Cell balancing is typically applied during and at the end of charging. This is because the cycle is generally used after the charging is completed.

In FIG. 3, the battery pack 100 is illustrated when four battery cells BAT1 to BAT4 are connected in series. As the service life of the battery pack 100 increases, an unbalance in capacity between the battery cells BAT1 to BAT4 occurs, thereby causing a voltage deviation between individual battery cells. When the voltage imbalance occurs, the efficiency of the battery decreases and the battery balancing circuit in the complex IC 50 discharges the battery cell having a high voltage through the balancing resistor R _VDD 70 connected in parallel with the battery cell. By doing so, balance is achieved.

When charging, a battery cell having a voltage lower than the charge upper limit voltage is charged with a normal current, but when an arbitrary battery cell reaches the charge upper limit voltage 4.20V first, the cell balancing on / off switch is controlled through the control of the composite IC 50. ) Is turned on to begin charging at low current through the balancing resistor R _VDD 70 in parallel with the cell. At the same time, the battery cell lower than the charge upper limit voltage continues charging with the normal current. Therefore, the battery cells are charged with a gradient of the voltage rise in nature. If all of the battery cells BAT1 to BAT4 reach the charge cutoff voltage of 4.25V, the charging is terminated.

[Reset function]

When the battery pack is manufactured or connected to the customer, a transient component current (Inrush Current) may be generated due to the capacitive load of the load stage, so that the BMS unit 140 blocks the overcurrent or the short-circuit current detection. Will perform. In this case, in order to solve the blocking state, there was a need to connect a charger to form a charging current.

The reset function was added as a way of simply returning the BMS unit 140 from the unintentional blocking state. When the battery pack 100 is turned on, the discharge terminal and the resistance are connected and a voltage is applied to Vm and is always kept shut.

When the reset switch connecting between the VM terminal and the VSS terminal of the overcurrent control IC 10 is pressed, the VM terminal and the VSS terminal are instantaneously turned on so that the BMS unit 140 has a cutoff state (overcurrent or overdischarge). It is canceled to perform the original return operation.

4 is a diagram illustrating a subcircuit of the BMS unit 140. This is to secondaryly perform the protection operation when the protection operation for charging fails in the main circuit of FIG. 3. In the present invention, the secondary protection IC 80 is used for such secondary protection. In other applications, the fuse is blown to prevent the battery pack from being permanently used, but in the present invention, the charge control FET 30 is controlled through the secondary protection IC 80 to lower the battery cell voltage. When it was possible to return.

5 is a photograph showing a printed circuit board on which a main circuit and a subcircuit of the BMS 140 are mounted together.

As described above, according to the present invention, since a plurality of lithium secondary batteries are stacked and used, large-capacity charging and discharging is possible. Particularly, when a lithium polymer battery is used, it is very advantageous in terms of capacity and shape. It is preferable to install. In addition, since the BMS unit 140 and the printed circuit board 120 are compactly mounted in the case 150, the overall size thereof may be reduced. At this time, since the BMS 140 is designed to perform not only a simple PCM function but also a cell balancing function and a reset function, stable charging and discharging may be achieved.

10: Overcurrent Control IC
20: constant voltage regulator IC
30: charge blocking IC
40: discharge blocking IC
50: composite IC
60: shunt resistance
70: balancing resistance
71: cell balancing on / off switch
100: lithium secondary battery pack
110: lithium secondary battery cell
120: printed circuit board
121: external terminal
130: thermoelectric element
140: BMS part
150: Case

Claims (9)

A plurality of lithium secondary battery cells;
A plate-shaped thermoelectric element interposed between the plurality of lithium secondary battery cells to dissipate heat of the lithium secondary battery cell so that the lithium secondary battery cell is not overheated;
A printed circuit board connecting the lithium secondary battery cells to each other in series or in parallel and charging and discharging the lithium secondary battery cells;
A battery management system (BMS) connected to the printed circuit board to control the lithium secondary battery cell to be charged and discharged stably and to control the thermoelectric element so as not to overheat the lithium secondary battery cell connected to the thermoelectric element. ; And
A case accommodating the lithium secondary battery cell, the printed circuit board, and the BMS unit; Including;
A cell balancing unit for uniformly charging the lithium secondary battery cell with a protection circuit module (PCM) for preventing the overcharge, overdischarge, overcurrent, and short circuit of the lithium secondary battery cell; Lithium secondary battery pack for solar street light comprising a cell balancer). The lithium secondary battery pack for solar street light of claim 1, wherein the lithium secondary battery cell is a lithium polymer battery cell. The lithium secondary battery pack for solar street light of claim 1, wherein the plurality of lithium secondary battery cells are formed by stacking individual lithium secondary battery cells having a plate shape in multiple layers. delete According to claim 1, Lithium secondary battery pack for solar street light, characterized in that the gap maintaining member is provided in a predetermined region between the lithium secondary battery cells so that the lithium secondary battery cells are spaced a predetermined interval. The solar cell apparatus of claim 3, wherein the printed circuit board and the BMS unit are installed on the side surface of the structure in which the plurality of lithium secondary battery cells are stacked in a plurality of layers, and installed vertically in the case. Lithium secondary battery pack for light street light. The method of claim 1, wherein the BMS unit monitors the current of the secondary battery cell through a composite IC to turn on / off the charge blocking FET, the discharge blocking FET, and the cell balancing switch to perform excessive charge / discharge prevention and cell balancing functions. Secondary battery pack for solar street light, characterized in that. 10. The method of claim 7, wherein the BMS unit comprises a constant voltage regulator IC, an overcurrent control IC having a VSS terminal and a VM terminal, and a shunt resistor (R _sense ) separately from the complex IC, wherein the constant voltage regulator IC measures a voltage of a battery pack. It receives an input and makes it a constant voltage and sends it to the overcurrent control IC, and the shunt resistor (R _sense ) is installed between the lithium secondary battery cell and the discharge blocking FET to be connected to the VM terminal, and the overcurrent control IC is the VSS terminal. And a voltage obtained by dividing the voltage applied between the terminal and the VM terminal by the shunt resistor (R _sense ). If the value is equal to or greater than a predetermined value, the current is recognized as an overcurrent and the discharge blocking FET is cut off to perform an overcurrent prevention function. Lithium secondary battery pack for solar street light. 9. The reset switch according to claim 8, wherein a reset switch is provided to connect between the VSS terminal and the VM terminal of the overcurrent control IC, and when the reset switch is pressed, the VMS terminal and the VM terminal are connected so that the BMS unit performs a return operation. Lithium secondary battery pack for solar street light, characterized in that to be.

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