WO2023158065A1 - System and method for randomly aligning soc of reusable battery - Google Patents

Abstract

A method for randomly aligning an SOC of a reusable battery according to an embodiment of the invention comprises the steps of: determining initial SOC levels of battery cells; sequencing the battery cells in ascending order of the initial SOC levels of the battery cells; in order to achieve a target SOC level, calculating an optimal total processing time by calculating an operation time of a pack charger and each cell-specific processing time of a cell equalizer; and performing a cell balancing operation in the order of the sequencing during the total processing time.

Description

SOC Random Alignment System and Method for Reusable Batteries

The present invention relates to a system and method for arranging a state of charge (SOC) of a reusable battery, and more particularly, to a system and method for aligning the SOC level of individual cells inside a reusable battery pack to a target SOC level while equalizing the SOC of a reusable battery. It relates to an alignment system and method.

Recently, investment in a battery energy storage system (BESS) has increased significantly. Even after the battery pack of an electric vehicle is discarded, 80% of its usable capacity remains, so it can be reused for other purposes. Therefore, research on an energy storage system (SL-BESS) using a second-life battery is being actively conducted.

Due to differences in characteristics of aged battery cells, battery reuse requires more intensive management during battery maintenance. Therefore, arbitrary arrangement of states of charge (SOC) is essential for the overall reuse process of batteries after use of electric vehicles, such as maintenance of reused batteries and transportation to other places.

In general, in the case of a conventional battery pack charger, since individual cells cannot be selectively charged, the SOC equalization function of individual cells cannot be provided.

On the other hand, conventional methods for equalizing individual cells mostly adopt a so-called minimum cell equalization method using a switch matrix. For example, a battery cell with the lowest SOC level is charged after discharging neighboring cells, and then A cell with the next lower SOC level is selected again and the steps of discharging and charging are repeated. Since the charging pattern continues to change randomly based on the voltage of the battery cells until the difference in SOC level between the battery cells reaches the target value, unnecessary and redundant switching patterns can be used. can't get In addition, there is a problem in that it does not provide a function to reach an arbitrarily selected target SOC level, which does not meet the purpose of SOC arbitrary alignment.

The present invention is to overcome the problems of the prior art described above, and an object of the present invention is to provide a system and method for cooperatively operating a battery pack charger and a cell equalizer in an SOC adjustment process.

A method of randomly arranging the SOC of a reusable battery according to an embodiment of the present invention includes determining initial SOC levels of battery cells, sequencing the battery cells in ascending order of the initial SOC levels of the battery cells, and target SOC levels. Calculating the optimal total processing time by calculating the processing time of each cell of the cell equalizer and the operating time of the pack charger in order to achieve, and performing the cell balancing operation in the order of ranking during the entire processing time. .

An SOC random alignment system for a reusable battery according to an embodiment of the present invention includes a pack charger that simultaneously charges or discharges battery cells included in a battery pack, a cell equalizer that transfers charge to one of the battery cells, and the cell A first switch matrix and a second switch matrix connected between a pair of input terminals of an equalizer and the battery cells, a battery monitoring device (Battery Monitoring IC, BMIC) for monitoring open circuit voltages of the battery cells, and the open circuit from the BMIC and a micro controller unit (MCU) that receives a voltage and calculates an initial SOC level of the battery cells using the open circuit voltage, wherein the MCU ranks the battery cells based on the initial SOC level. do.

According to the SOC random arrangement system and method of the reusable battery according to the present invention configured as described above, the cell balancing time can be minimized and the target SOC can be arbitrarily determined.

1 is a diagram showing an SOC random alignment system of a reusable battery according to an embodiment of the present invention.

2A and 2C are circuit diagrams for explaining the operating principle of the SOC random alignment system for reusable batteries according to an embodiment of the present invention.

3 is a flowchart for explaining a method of operating an SOC random alignment system for a reusable battery according to an embodiment of the present invention.

4 shows an SOC-OCV curve of an operating method of an SOC random alignment system for a reusable battery according to an embodiment of the present invention.

5 to 7 are graphs for explaining a method of calculating a processing time of an operating method of an SOC random alignment system for reusable batteries according to an embodiment of the present invention.

8 is a circuit diagram for explaining a cell balancing operation of a cell equalizer in a method of operating an SOC random alignment system for a reusable battery according to an embodiment of the present invention.

9A and 9B are diagrams for explaining the processing time of the operating method of the SOC random alignment system for reusable batteries according to an embodiment of the present invention.

10A to 10C are diagrams for explaining stability of a battery cell in an operating method of an SOC random alignment system for a reusable battery according to an embodiment of the present invention.

11a to 11c are charts summarizing experimental settings and experimental results for verifying the present invention.

12A to 12C are diagrams illustrating operation waveforms of a minimum cell equalization method, which is a conventional method.

13a to 13c are diagrams showing operating waveforms of an operating method of an SOC random alignment system for a reusable battery according to the present invention.

Since the present invention may have various modifications and various embodiments, specific embodiments are illustrated in the drawings and described in more detail in the detailed description. In describing the present invention, if it is determined that a detailed description of related known technologies may obscure the gist of the present invention, the detailed description will be omitted.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a diagram showing an SOC random alignment system of a reusable battery according to an embodiment of the present invention.

Referring to FIG. 1 , the battery pack PACK may include a plurality of battery cells B1 to Bn connected in series. Here, n is a natural number greater than 1. For example, an electric vehicle may include a plurality of battery packs. After using the electric vehicle, the voltage of one cell of the battery may be 3.6V or about 4V, and the voltage of one battery pack may be about 80V.

The SOC random alignment system 100 of a reused battery includes a pack charger 110, a cell equalizer 120, a battery monitoring device (Battery Monitoring IC, BMIC; 130), an arithmetic unit (micro controller unit, MCU; 140), and A first switch matrix S _M and a second switch matrix S _R may be included.

The pack charger 110 may be a bidirectional DC converter that charges or discharges the battery pack PACK from an external power source. The pack charger 110 may simultaneously charge or discharge the plurality of battery cells B1 to Bn included in the battery pack PACK. Accordingly, the speed of the SOC alignment process may be increased, and the SOC level of the battery cell may be readjusted to a target SOC level. The pack charger 110 may charge or discharge the battery pack PACK with a constant current according to the operation of the cell equalizer 120 . In this case, the charge current is defined as a positive current and the discharge current as a negative current.

The cell equalizer 120 may be a unidirectional DC-DC converter that transfers charge from the battery pack PACK to one of the battery cells B1 to Bn. For example, the cell equalizer 120 may be a constant current type charger capable of charging only one battery cell with a constant current, and the battery cells B1 to Bn may be equalized by the cell equalizer 120 . A pair of output terminals of the cell equalizer 120 may be connected to the battery pack PACK, and a pair of input terminals of the cell equalizer 120 may be connected to the first switch matrix S _M1 to S _M(n+1) and the second switch. It may be connected to one of the battery cells B1 to Bn through the matrices S _R1 to S _R4 .

The BMIC 130 may always monitor open circuit voltages Vbat of individual battery cells B1 to Bn. The BMIC 130 may output open circuit voltages Vbat of the battery cells B1 to Bn.

The MCU 140 may transmit a command CMD to output the open circuit voltage Vbat of the individual battery cells B1 to Bn to the BMIC 130 . The MCU 140 may receive open circuit voltages Vbat of the battery cells B1 to Bn from the BMIC 130 . The MCU 140 may analyze the SOC level corresponding to the battery charge amount for each of the battery cells B1 to Bn using the open circuit voltage Vbat of the battery cells B1 to Bn. The MCU 140 may generate and output selection signals SEL1 and SEL2 based on the analysis result.

The first switch matrix S _M and the second switch matrix S _R may be connected between the input terminal pair 121 of the cell equalizer 120 and the battery cells B1 to Bn. The first switch matrix S _M and the second switch matrix S _R select one battery cell from among the battery cells B1 to Bn, and use the selected battery cell as a pair of output terminals 122 of the cell equalizer 120. can be connected to The first switch matrix S _M may include a plurality of first switches S _M1 to S _M(n+1) , and the second switch matrix S _R may include a plurality of second switches S _R1 ~ S _R4 ) may be included. For example, when the number of battery cells B1 to Bn is n, the number of first switches may be n+1 and the number of second switches may be four. The configuration of the first switch matrix S _M and the second switch matrix S _R has an effect of reducing the number of switches in the SOC random arrangement system of the reusable battery.

The first selection signal SEL1 may determine the switching pattern of the first switch matrix S _M , and the second selection signal SEL2 may determine the switching pattern of the second switch matrix S _R . The first switch matrix S _M may select one of the battery cells B1 to Bn in response to the first selection signal SEL1, and the second switch matrix S _R may select one battery cell from among the battery cells B1 to Bn in response to the first selection signal SEL1. In response to SEL2), the direction of the selected battery cell may be determined. For example, in order to connect the first battery cell B1 to the output terminal pair 122 of the cell equalizer 120, some of the first switches S _M1 and S _M2 in response to the first selection signal SEL1 may be turned on, and some of the second switches S _R1 and S _R4 may be turned on in response to the second selection signal SEL2.

The SOC arbitrary alignment system 100 of the reusable battery may further include an activation switch Sen. The activation switch Sen may be a switch for blocking current input to the cell equalizer 120 in an emergency situation. The activation switch Sen may be controlled in response to an activation signal EN output from the MCU 140 .

According to an embodiment of the present invention, the MCU 140 may sort the battery cells B1 to Bn based on the initial SOC levels of the battery cells B1 to Bn. For example, the MCU 140 may arrange the battery cells B1 to Bn in ascending order of initial SOC levels of the battery cells B1 to Bn. Since the lower the initial SOC level, the greater the amount of charge to be charged in the corresponding battery cell, the MCU 140 generates a selection signal so that the connection time of the battery cell to the cell equalizer 120 increases as the initial SOC level of the battery cell decreases. SEL1 and SEL2 may be generated. The MCU 140 adjusts the turn-on time of the switches included in the first switch matrix S _M and the second switch matrix S _R based on the initial SOC levels of the battery cells B1 to Bn, thereby controlling the battery life. The time during which cells are connected to the cell equalizer 120 can be adjusted.

2A and 2C are circuit diagrams for explaining the operating principle of the SOC random alignment system for reusable batteries according to an embodiment of the present invention.

First, FIG. 2A describes an operation when the pack charger 110 operates and the cell equalizer 120 does not operate. At this time, the pack charger is activated by the control signal CTRL, while the first selection signal ( All switches included in the first switch matrix S _M and the second switch matrix S _R are turned off by the SEL1) and the second selection signal SEL1. Referring to FIGS. 1 and 2A together, the pack charger 110 can directly charge or discharge the entire battery pack PACK with the pack charger current Ic, which is a constant current. The pack charger current Ic is used to simultaneously supply energy to the battery cells B1 to Bn included in the battery pack PACK or simultaneously release energy from the battery cells B1 to Bn included in the battery pack PACK. It may be a current for Accordingly, the pack charger 110 may adjust the SOC level of the entire battery pack PACK.

The control signal CTRL may be an activation signal for activating the pack charger 110 during the pack charger processing time. Also, in response to the control signal CTRL, the pack charger 110 may change the direction of the pack charger current Ic. In other words, the pack charger 110 may supply energy to the entire battery pack PACK or discharge energy from the entire battery pack PACK in response to the control signal CTRL.

The MCU 140 may determine the available capacity of the entire battery pack PACK and calculate the capacity required to charge or discharge the entire battery pack PACK. The MCU 140 may generate and output a control signal CTRL based on the calculation result.

Next, FIG. 2B describes an operation when the cell equalizer 120 operates and the pack charger 110 does not operate. At this time, the switches included in the first switch matrix S _M and the second switch matrix S _R are turned on in the above-described pattern by the first selection signal SEL1 and the second selection signal SEL2 to form one A cell of is selected, and the pack charger is deactivated by the control signal CTRL. Referring to FIGS. 1 and 2B together, energy is transferred from a battery pack connected to the input terminal pair 121 of the cell equalizer 120, and a predetermined cell balancing current Ibal is generated through the output terminal pair 122. can be printed out. At this time, if the battery pack discharge current flowing into the input terminal pair of the cell equalizer 120 is defined as Ip, the current flowing in the selected cell becomes Ibal-Ip by Kirchoff's Current Law (KCL) and the selected The current flowing in the remaining cells becomes (-Ip). Accordingly, the SOC level of the battery cells selected through the first switch matrix S _M and the second switch matrix S _R can be adjusted through the cell balancing current Ibal. Accordingly, SOC differences between the battery cells B1 to Bn may be equalized. In other words, the cell equalizer 120 may distribute the energy of the entire battery pack PACK to individual battery cells.

Meanwhile, FIG. 2C describes an operation principle in a more general case in which both the cell equalizer 120 and the pack charger 110 are operating. At this time, by the first selection signal SEL1 and the second selection signal SEL1 The switches included in the first switch matrix S _M and the second switch matrix S _R are turned on in the above-described pattern to select one cell, and the pack charger 110 operates by the control signal CTRL. become activated. Referring to FIGS. 1 and 2C together, a predetermined cell balancing current ( Ibal) can be output. In addition, the pack charger 110 also supplies a predetermined current, the pack charger current Ic, to the battery pack. As described above, since the battery pack discharge current flowing into the input terminal pair 121 of the cell equalizer is defined as Ip, the current flowing in the selected cell is Ibal by Kirchoff's Current Law (KCL) -Ip+Ic and the current flowing to the remaining unselected cells becomes -Ip+Ic. Accordingly, the SOC level of the battery cells selected through the first switch matrix S _M and the second switch matrix S _R can be adjusted through the pack charger current Ic and the cell balancing current Ibal. Accordingly, SOC differences between the battery cells B1 to Bn may be equalized. In other words, the pack charger 110 and the cell equalizer 120 may distribute the energy of the entire battery pack PACK to individual battery cells through cooperative control.

The cell equalizer 120 may include an analog controller 123 inside the cell equalizer 120 to make the cell balancing current Ibal, which is the current of the output terminal pair 122, constant. For example, the cell equalizer 120 may make the cell balancing current Ibal constant through duty ratio control or frequency control. The analog controller 123 may exist outside the cell equalizer 120 .

According to an embodiment of the present invention, the target SOC level can be achieved by cooperatively operating the pack charger 110 and the cell equalizer 120 in the SOC adjustment process. Accordingly, capacities of the battery cells B1 to Bn may be equalized. The battery cells B1 to Bn may simultaneously receive current from the pack charger 110 and the cell equalizer 120 . Whether during charging or discharging, the sum of the two currents can be maintained within the battery's tolerance.

Also, the pack charger 110 and the cell equalizer 120 may operate according to a coordinated operating algorithm. In other words, battery cell balancing and charging or discharging of the battery pack may be simultaneously performed. Therefore, the cell balancing time can be optimized.

3 is a flowchart for explaining an operating method of an SOC random alignment system for a reusable battery according to an embodiment of the present invention, and FIG. It is a mapping curve (SOC-OCV curve) between the cell SOC level and the cell open circuit voltage (OCV), which is the basis for calculating the SOC level of .

First, referring to FIGS. 1 and 3 together, the operating method of the SOC random alignment system of the reusable battery may include a charging strategy establishment operation (S110 to S170) and a cell balancing operation (S180).

The BMIC 130 may initially measure the open circuit voltages (Vbat) of the battery cells (S110).

The MCU 140 may receive open circuit voltages Vbat of battery cells from the BMIC 130 . The MCU 140 determines the initial SOC level corresponding to the open circuit voltage (Vbat) of the battery cells using a mapping curve (SOC-OCV curve) between the preset cell SOC level and the open cell voltage of the battery (see FIG. 4). It can (S120).

The MCU 140 may order and index the battery cells B1 to Bn in ascending order of initial SOC levels of the battery cells B1 to Bn (S130). Also, the MCU 140 may calculate an average value of all SOC levels (S130). In a cell balancing operation after the charging strategy establishment operation, the cell balancing operation may be performed on the battery cells B1 to Bn in the sorting order.

The MCU 140 may calculate the total processing time of the cell balancing operation (S140). The total processing time is the processing time (tc) of the pack charger and the processing time (ti) of the cell equalizer for each of the battery cells (B1 to Bn) (where i is a sequence number and has an integer from 1 to n). Here, 1 represents a cell with the highest sequence, and n represents a cell with the lowest sequence as the number of cells connected in series.) (S140). In the cell balancing operation after the charging strategy establishment operation, the battery cells B1 to Bn may be connected one by one to the output terminal pair 122 of the cell equalizer 120 in the above sequential order, and the output terminal pair of the cell equalizer 120 The battery cell connected to 122 may be charged during the processing time of the cell equalizer 120 for the corresponding battery cell.

In other words, the switching patterns of the first switch matrix S _M and the second switch matrix S _R may be determined based on the charging strategy. In addition, as the charging time of the battery cell increases, the amount of charge charged in the battery cell increases. Accordingly, the MCU 140 may set a relatively long processing time of the cell equalizer for a battery cell having a relatively low SOC level and a relatively short processing time of the cell equalizer for a battery cell having a relatively high SOC level. there is.

5 to 7 are graphs for explaining a method of calculating a processing time according to an embodiment of the present invention.

Referring to FIG. 5 , the x-axis represents the battery cell number indicating the physical cell connection order of the currently aligned battery cells B1 to Bn, and the y-axis represents the SOC level (%) of the corresponding battery cells B1 to Bn. ). The SOC level may mean an initial SOC level corresponding to the open circuit voltage Vbat of the battery cells B1 to Bn.

Referring to FIG. 6 , the x-axis represents the sequence numbers of battery cells B1 to Bn, which are sequenced in ascending order of SOC level, and the y-axis represents the SOC level (%) of the corresponding battery cells B1 to Bn. The battery cells B1 to Bn may be ordered and indexed in order of SOC levels from low to high. Here, it is emphasized that the battery cell number and sequence number may be different depending on the state of the initial SOC level of each cell.

Referring to FIG. 7 , the x-axis represents the sequence numbers of battery cells (B1 to Bn) sequenced in ascending order of SOC level, and the y-axis represents the cell equalizer processing time (ti) of the corresponding battery cells. As shown in FIG. 7 , a charging time of a battery cell having a relatively low SOC level may be set relatively long, and a charging time of a battery cell having a relatively high SOC level may be set relatively short.

Referring again to FIGS. 1 and 3 , the MCU 140 may compare the target SOC and the average SOC, and determine the direction of the pack charger current output from the pack charger 110 according to the comparison result.

Specifically, the MCU 140 may compare the target SOC and the average SOC (S150). If the target SOC is lower than the average SOC (YES in S150 ), all energies of the battery cells B1 to Bn included in the battery pack PACK should be discharged. Accordingly, the MCU 140 may generate a control signal CTRL to set the direction of the pack charger current Ic to the first direction (eg, negative direction) (S160). In a cell balancing operation after the charging strategy establishment operation, the pack charger 110 may simultaneously discharge energy of the battery cells B1 to Bn included in the battery pack PACK in response to the control signal CTRL.

If the target SOC is higher than the average SOC (NO in S150 ), energy must be supplied to all of the battery cells B1 to Bn included in the battery pack PACK. Therefore, the MCU 140 may generate the control signal CTRL to set the direction of the pack charger current Ic to the second direction (eg, positive direction) of the pack charger 100 (S170). In a cell balancing operation after the charging strategy establishment operation, the pack charger 100 may simultaneously supply energy to the battery cells B1 to Bn included in the battery pack PACK in response to the control signal CTRL.

When the direction setting of the pack charger current Ic is completed, a cell balancing operation may be performed (S180). Cell balancing operations may be performed in the above sorted order during the entire processing time. During the entire processing time, the battery cells (B1 to Bn) may be connected to the output terminal pair 122 of the cell equalizer 120 one by one in the sorted order, and the operation of the pack charger is performed by the pack charger placed at the end of the entire processing time. It can be done during processing time. Depending on the selection of the algorithm, the cell equalizer processing time of the last battery cell may be 0 seconds. Therefore, considering substantially (n-1) cell balancing operation steps (t1 to t(n-1)) and one pack charger operation step (tc), a total of n steps are required to rearrange the SOC of the battery. required, where n means the total number of battery cells included in the battery pack PACK.

When the cell balancing operation is finished, the operation of the SOC random alignment system of the reusable battery is finished.

Hereinafter, a process of calculating the processing time (tc) of the pack charger and the processing time (ti, i = 1 to n) of the cell equalizer for the i-th battery cell of SEQ ID NO will be described.

Assuming that all battery cells have the same nominal capacity, the available capacity (Q(t)) of the battery cell may be defined as Equation 1 below.

Here, Qnom may mean the nominal capacity of each battery cell.

Since the SOC of a battery cell means the ratio of available capacity to nominal capacity, it can be expressed as [Equation 2] as follows through [Equation 1] above.

At each step of the SOC randomization process, the cell equalizer 120 may provide a constant current to individual battery cells to increase the capacity of the battery cells. Due to this, it is possible to maintain a balance of SOC levels between battery cells.

8 is a circuit diagram for explaining a cell balancing operation of the cell equalizer 120 according to an embodiment of the present invention. Assuming that the cell balancing current Ibal, which is the output current of the cell equalizer 120, is unipolar and maintained constant as shown in FIG. 8, the current Ip flowing through the input terminal pair 121 of the cell equalizer 120 Can be determined as in [Equation 3] below.

Here, vi denotes the voltage of the i-th battery cell of sequence number, Vpack denotes the voltage of the battery pack, and η denotes the power conversion efficiency of the cell equalizer 120 .

Assuming that the pack charger current Ic is constant, the actual current Ii flowing through the i-th battery cell of SEQ ID NO is given by Equation 4 below. This has been illustrated schematically in Figure 2c.

At this time, the current flowing through the remaining battery cells may be calculated as in [Equation 5] below. This is also illustrated schematically in Figure 2c.

For battery safety, the actual current flowing through the battery cell must be less than the maximum allowable current level in the data sheet.

The remaining capacity of each battery cell can be expressed as in [Equation 6] below.

Here, Qnom means the nominal capacity of each battery cell, and SOCi means the individual SOC level of the i-th battery cell of SEQ ID NO.

As shown in [Equation 7], the initial SOC level of the i-th battery cell of SEQ ID NO: may be estimated using OCVi information. where f represents the mapping function by the SOC-OCV curve.

After time ti, the SOC level of the i-th battery cell of SEQ ID NO is given by Equation 8 below.

Here, under an ideal condition in which energy loss in the battery itself does not occur, the SOC level after cell balancing is an average of initial SOC levels. The average (SOCinit_avg) of the initial SOC levels of the battery cells is given by Equation 9 below.

Here, considering the power conversion efficiency η of the cell equalizer 120 representing the circuit loss generated by the cell equalizer 120, the average SOC level after cell balancing is finished becomes lower than the average of the initial SOC. If the difference is defined as an equivalent SOC loss (SOC _L ), the equivalent SOC loss is estimated as shown in Equation 10 below.

Here, t _total means the sum of processing times of each cell required in the cell equalizing step as shown in [Equation 11] below.

At this time, since the pack charger additionally compensates for the SOC loss and realigns the SOC level to the target SOC level, SOCtarg, the processing time tc of the pack charger is expressed as in [Equation 12] below.

Here, if the processing time (tc) has a positive value, the pack charger current should operate as a charging current (positive direction), and if the processing time (tc) has a negative value, the polarity of the pack charger current (Ic) is reversed. have to make it work.

At every hour step, only one battery cell can be charged by the current of [Equation 4], and the other battery cells can be discharged by the negative value of the current of [Equation 5]. That is, the pack charger current Ic can simultaneously adjust the overall SOC level of the battery cells. Therefore, the change in capacity from the initial SOC level to the target SOC level for the battery cell having the first sequence number (ie, the smallest SOC level in the case of ascending sequencing) after the entire processing time is calculated as shown in [Equation 13] below do.

Similarly, in general, the change in capacity of the battery cell having the i-th sequence number is given by Equation 14 below.

In this step, the following method may be applied to obtain an optimal processing time ti of each step for each battery cell and pack charger.

That is, when the processing time ti of each step in [Equation 14] is greater than or equal to 0, the capacity of the battery cell having the i-th sequence number through [Equation 11] and [Equation 12] The change can be expressed as in [Equation 15] below.

Here, the sum of the processing times (t _total ) of the cell equalizer operation steps is already defined in [Equation 11]. Therefore, the processing time ti of each step can be rearranged as in [Equation 16].

Since the initial SOC levels of the battery cells have already been sequenced and processed in order, the processing time of each stage is t1≥t2≥... ≥tn. This is because, in the case of sequencing in ascending order of initial SOC, the cell with the lowest initial SOC level, which is SEQ ID NO: 1, must be balanced for the longest time.

9A and 9B are diagrams for explaining processing time calculated according to an embodiment of the present invention.

Referring to FIG. 9A , it is physically impossible for the processing time (t16 to t20) to have a negative value from the 16th step, and instead, the cell balancing current of the corresponding cell equalizer 120 should be inverted.

According to an embodiment of the present invention, since the cell equalizer 120 that provides only one-way current does not provide such current inversion (negative balancing current), a time offset may be introduced to solve the problem of negative processing time. . In other words, by adding the processing time of each step to the same value and setting the time tn required for the last step to 0, the time required for all other steps can always be corrected to be greater than 0.

Figure 9b shows the step-by-step processing time adjusted by sealing the time offset. Referring to FIG. 9B, if tn is set to 0, the processing time of each step (ti, i = 1, 2, ..., n) is not a negative value. In other words, the processing time tn of the battery cell having the n-th sequence number can be calculated as shown in Equation 17 below.

Here, when tn = 0 is set, the total processing time (t _total ) can be expressed as in [Equation 18] below.

Therefore, if the time offset is introduced, from [Equation 1], [Equation 16], and [Equation 18], the processing time ti of the i-th battery cell of SEQ ID NO is finally 19].

Here, SOCmax(t0) means the maximum initial SOC of the battery cell. Therefore, the sequential charging of each battery cell in n stages can achieve SOC adjustment to the target SOC level according to [Equation 19] above.

The target SOC level may include the first to third SOC levels. As an example, the SOC random alignment system of reusable batteries may lower the SOC level of each battery cell to a first SOC level (eg, typically 25% or less) for safe transportation to another location. The SOC random alignment system of a reusable battery may equalize all cells at a second SOC level (eg, 45%) for the purpose of battery maintenance. The SOC arbitrary alignment system of the reusable battery may adjust the SOC level of each battery cell to a third SOC level (eg, 60%) for almost complete charging of the battery pack. According to one embodiment of the present invention, the SOC random alignment system of the reusable battery has the effect of having a degree of freedom of the target SOC.

Conventional methods for equalizing individual cells in the prior art mostly adopt a so-called minimum cell equalization method using a switch matrix. Select the cell in again and repeat the same steps. Since the charging pattern continues to change randomly based on the voltage of the battery cells until the SOC level difference between the battery cells reaches a target value, unnecessary and redundant switching patterns may be used, and optimal operation time may not be obtained. In addition, there is a problem in that it does not provide a function to reach an arbitrarily selected target SOC level, which does not meet the purpose of SOC arbitrary alignment.

According to an embodiment of the present invention, the battery cells are aligned based on the initial SOC level, and the cell equalizer 120 and the pack charger 110 cooperate to equalize and adjust the SOC level of the battery cells to a target SOC level. there is. At this time, only one switching pattern is assigned to each cell, and the entire process is completed with a total of n steps. In other words, by providing an optimal switching pattern, the power loss of the circuit can be reduced and the overall processing time can be shortened. In addition, [Equation 19] is a simple formula that does not require repetitive calculation, so it can be easily implemented with a low-cost MCU.

10A to 10C are diagrams for explaining stability of a battery cell according to an embodiment of the present invention.

The total processing time of the cell equalizer 120 may be from 0 seconds to t _total (=t1+t2+...+tn) seconds. In order to minimize the total processing time, the operation time of the pack charger overlaps with the operation of the cell equalizer 120 and is organized in the first time period tc1, which is the first part, or the second time period after the first time period tc1, which is the middle part. It can be organized in the time section tc2 or in the third time section tc3 after the second time section tc2. For example, the start point of the first time interval tc1 may be 0 seconds, and the end point of the third time interval tc3 may be t _total seconds.

10A shows a case in which the operation of the pack charger is performed in a first time period tc1, FIG. 10B shows a case in which the operation of the pack charger is performed in a second time period tc2, and FIG. This indicates a case in which the operation is performed in the third time interval tc3.

As shown in FIGS. 10A and 10B , when the operation of the pack charger is organized in the front part or the middle part, the SOC level of some battery cells may fall below a safety limitation. In other words, when the operation of the pack charger is executed at the beginning or in the middle of the entire processing time, the stability of the battery cell may be damaged. Therefore, in order to ensure stability and performance of the battery cell, the current of the pack charger needs to be designed to be less than a certain value, and the operation of the pack charger is preferably executed at the end of the entire processing time.

11A shows parameter setting values for comparing and verifying the present invention and the existing method. Under similar initial SOC level conditions, the first SOC level (25%) and the second SOC level (45%) in the two methods, respectively. A test was conducted to achieve three target SOC levels of the second SOC level (60%). The subject formed a battery pack by connecting 20 18650 type cylindrical 3.6 V/2.9Ah lithium ion batteries, and the pack charger current (Ic) was set to 0.53A and the cell equalizer current (Ibal) was set to 1.3A.

11B to 11C are charts summarizing initial voltage and initial SOC, end voltage and end SOC applied with the conventional method, and end voltage and end SOC applied with the method of the present invention for each of the 20 cells.

12A is an experimental waveform for achieving a target SOC level of the first SOC level (25%) by applying a conventional method. 12B is a test waveform for achieving a target SOC level of the second SOC level (45%) by applying a conventional method. 12C is a test waveform for achieving a target SOC level of a third SOC level (60%) by applying a conventional method. Each graph shows waveforms of 20 cell voltages, and the initial voltage and voltage waveforms after achieving the target SOC are enlarged and added to the left and right sides, respectively. It shows that it takes about 8 hours or more while repeating charging and inverting irregularly for each cell voltage.

13a is an experimental waveform for achieving a target SOC level of the first SOC level (25%) by applying the present invention. 13B is a test waveform for achieving a target SOC level of the second SOC level (45%) by applying a conventional method. 13C is a test waveform for achieving a target SOC level of a third SOC level (60%) by applying a conventional method. Each graph shows waveforms of 20 cell voltages, and the initial voltage and voltage waveforms after achieving the target SOC are enlarged and added to the left and right sides, respectively. Each cell voltage is sequentially charged only once, and the processing time is reduced to about 6 hours and 30 minutes.

The embodiments of the present invention described in this specification and the configurations shown in the drawings relate to the most preferred embodiments of the present invention, and do not cover all the technical ideas of the present invention, so various equivalents that can replace them at the time of filing It should be understood that there may be water and variations. Therefore, the present invention is not limited to the above-described embodiments, and various modifications can be made by anyone having ordinary knowledge in the art to which the present invention belongs without departing from the gist of the present invention claimed in the claims. , such changes are within the scope of the recitation of the claims.

100; SOC Random Alignment System for Reusable Batteries

110; pack charger 120; cell equalizer

121: cell equalizer input terminal pair

122: cell equalizer output terminal pair

123: analog controller 130; BMIC

140; MCU

Claims (13)

1. determining initial SOC levels of battery cells included in a battery pack;

   sequencing the battery cells in ascending order of the initial SOC levels of the battery cells;

   Calculating an optimal total processing time by calculating a processing time for each cell of a cell equalizer and an operating time of a pack charger to achieve a target SOC level; and

   A method of randomly arranging the SOC of a reusable battery, characterized in that it comprises the step of performing a cell balancing operation in the order of ranking during the entire processing time.
2. The method of claim 1, wherein the performing of the cell balancing operation comprises:

   connecting the battery cells to a pair of output terminals of a cell equalizer one by one in the order of ranking;

   charging a battery cell connected to the pair of output terminals by the cell equalizer;

   A method of randomly arranging SOC of a reusable battery comprising the step of simultaneously discharging energy from the battery cells or simultaneously supplying energy to the battery cells by a pack charger.
3. According to claim 2,

   The total processing time is the sum of processing times of the cell equalizer for each of the battery cells,

   The SOC random arrangement method of a reusable battery, characterized in that the total processing time includes a part of the operating time of the pack charger.
4. According to claim 3,

   In calculating the total processing time, the processing time of the cell equalizer for each of the battery cells is calculated by [Equation 1],

   The operating time of the pack charger includes calculating by [Equation 2],

   [Equation 1]

   

   [Equation 2]

   

   In Equation 1, t _i is the processing time for each of the battery cells, SOC _{init_avg} is the average of the initial SOC levels of the battery cells, SOC _i is the individual SOC level of the ith battery cell of SEQ ID NO, and SOC _L is Equivalent SOC loss, Qnom is the nominal capacity of the battery cells, Ip is the discharge current of the battery pack, t _total means the sum of processing times of each cell required in the cell equalizing step,

   In Equation 2, SOC _targ is the target SOC level, and Ic is the current of the pack charger.
5. According to claim 3,

   In calculating the total processing time, the last processing step is omitted by applying the time offset calculated by [Equation 3] to the processing time of the cell equalizer for each of the battery cells,

   Including calculating the operating time of the pack charger by [Equation 4],

   [Equation 3]

   

   [Equation 4]

   

   In Equation 3, t _i is the processing time for each of the battery cells, SOC _{init_avg} is the average of the initial SOC levels of the battery cells, SOC _i is the individual SOC level of the ith battery cell of SEQ ID NO, and Qnom is the It is the nominal capacity of the battery cells, SOCmax means the maximum initial SOC of the battery cell, Vt means the voltage of the i-th battery cell of SEQ ID NO, Vpack means the voltage of the battery pack, and Ibal means the predetermined cell means balancing current,

   In Equation 4, SOC _targ is the target SOC level, and Ic is the current of the pack charger.
6. According to claim 3,

   In calculating the operating time of the pack charger by [Equation 5], the current direction of the pack charger is changed according to the sign of the result,

   [Equation 5]

   

   In Equation 5, tc is the processing time of the pack charger, SOC _targ is the target SOC level, SOC _{init_avg} is the average of the _initial SOC levels of the battery cells, SOC _L is the equivalent SOC _loss , and Qnom is the SOC random arrangement method of a reusable battery, characterized in that the nominal capacity of the battery cells, and Ic is the current of the pack charger.
7. According to claim 3,

   The operation of the pack charger is performed during the processing time of the pack charger at the end of the total processing time.
8. According to claim 3,

   comparing the average value of the initial SOC levels of the battery cells with a target SOC level, and determining a direction of a pack charger current output from the pack charger according to a result of the comparison; Random sorting method.
9. a pack charger that simultaneously charges or discharges battery cells included in the battery pack;

   a cell equalizer transferring charge to one of the battery cells;

   a first switch matrix and a second switch matrix connected between the pair of input terminals of the cell equalizer and the battery cells;

   a battery monitoring device (Battery Monitoring IC, BMIC) for monitoring open circuit voltages of the battery cells; and

   A micro controller unit (MCU) receiving the open circuit voltage from the BMIC and calculating initial SOC levels of the battery cells using the open circuit voltage;

   The SOC random sorting system of a reusable battery, characterized in that the MCU ranks the battery cells based on the initial SOC level.
10. According to claim 9,

    The SOC random sorting system of a reusable battery, characterized in that the MCU ranks the battery cells in ascending order of the initial SOC level.
11. According to claim 9,

    The SOC random sorting system of a reusable battery, characterized in that the battery cells are connected one by one to the output terminal pair of the cell equalizer in the sequence order.
12. According to claim 9,

    The MCU adjusts the time each battery cell is connected to the cell equalizer by adjusting the turn-on time of the switches included in the first switch matrix and the second switch matrix based on the initial SOC level. Characterized in that SOC random alignment system for reusable batteries.
13. According to claim 9,

    Wherein the MCU compares the average value of the initial SOC levels of the battery cells with a target SOC level, and determines a direction of a pack charger current output from the pack charger according to a result of the comparison. system.

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