JP5348987B2 - How to detect battery deterioration - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To detect always accurately deterioration of a battery without storing a count value so as to detect a deterioration degree. <P>SOLUTION: In this detection method of the deterioration degree of a battery, the deterioration degree SOH (State of Health) is operated from the first deterioration degree SOH 1 acquired from a change value of a full charge capacity of the battery 1, the second deterioration degree SOH 2 acquired from a discharge internal resistance of the battery 1, and the third deterioration degree SOH 3 from a charge internal resistance of the battery 1. Thus, since the deterioration degree SOH is detected from the full charge capacity, the charge internal resistance, and the discharge internal resistance of the battery, the deterioration degree of the battery is detected accurately from an initial period to an end period without storing a count value such as a current or a temperature. Since the deterioration degree is detected from both internal resistances of the charge internal resistance and the discharge internal resistance in addition to the full charge capacity, a residual capacity in the end period is detected extremely accurately. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a method for detecting the degree of deterioration of a battery, and more particularly to a method for detecting the degree of deterioration of a battery that is optimal for detecting the degree of deterioration of a battery built in a power supply device that drives an electric vehicle.

  The degree of deterioration of the battery is represented by 100% to 0%, the degree of deterioration of the battery that does not deteriorate is 100%, and the degree of deterioration of the battery that has deteriorated and cannot be used is 0%. A battery mounted on an electric vehicle such as a hybrid car deteriorates as time passes or charging / discharging is repeated. A deteriorated battery has low output power. A battery whose output is reduced cannot start the engine of the hybrid car, and the acceleration characteristics are deteriorated. The battery used for this purpose has a degree of deterioration specified from the maximum output power. The battery life can be estimated by detecting the degree of deterioration. For example, it can be estimated that a battery having a degradation degree of 50% after 5 years can be used for the next 5 years using the same charge / discharge characteristics. However, since batteries that deteriorate to 20% after 4 years deteriorate at a rate of 20% per year, it can be estimated that the battery can only be used for about 1 year thereafter until the degree of deterioration reaches 0%. . From this, it is possible to detect the degree of deterioration of the battery, control the charge / discharge power of the battery from the degree of deterioration, and control the life of the battery in a specific period. However, in order to realize this, it is important to accurately detect the deterioration degree of the battery.

  A method for determining the degree of deterioration of the battery from the internal resistance is described in Patent Document 1. However, the method of determining the degree of deterioration of the battery from the internal resistance has a drawback that it cannot be accurately determined except at the end when the internal resistance increases. A method for solving this problem is described in Patent Document 2. The method of Patent Document 2 calculates a current capacity, which is the amount of electric power that can be discharged from a fully charged state to a predetermined discharge voltage value, based on the discharge voltage V and the discharge amount Ah. The degree of deterioration of the battery is calculated as a ratio with the initial capacity that is the amount of electric power that can be discharged from the fully charged state up to the predetermined discharge voltage value.

The method of Patent Document 2 can detect the initial degree of deterioration more accurately than the method using the internal resistance, but it is difficult to accurately detect the final degree of deterioration. Furthermore, in order to eliminate this drawback, the battery deterioration degree SOH is calculated from both the first deterioration degree SOH1 counted from the battery current and temperature and the second deterioration degree SOH2 obtained from the internal resistance of the battery. A method for computing the above has been developed. (See Patent Document 3)
JP-A-8-254573 JP 2000-131404 A JP 2008-122165 A

  The detection method of Patent Document 3 has a feature that it can accurately detect the initial and final deterioration levels of a battery. However, in this method, since the battery current and temperature count values are stored in the non-volatile memory in order to detect the first deterioration degree SOH1, the first deterioration degree SOH1 is accurately determined if the memory fails. There is a drawback that the detection accuracy of the deterioration degree SOH is lowered because the detection becomes impossible. This is because the deterioration degree SOH is calculated from both the deterioration degree SOH1 detected from the battery current and temperature count values and the deterioration degree SOH2 obtained from the internal resistance of the battery.

  The present invention has been developed for the purpose of solving this drawback. An important object of the present invention is to provide a battery deterioration degree detection method that can always accurately detect battery deterioration without storing a count value in order to detect the deterioration degree.

Means for Solving the Problems and Effects of the Invention

  The battery deterioration degree detection method of the present invention includes a first deterioration degree SOH1 obtained from a change value of the full charge capacity of the battery 1, a second deterioration degree SOH2 obtained from a discharge internal resistance of the battery 1, and a battery. The degree of deterioration SOH is calculated from the third degree of deterioration SOH3 obtained from one charging internal resistance.

  The above detection method detects the degree of deterioration SOH from the full charge capacity of the battery, the charge internal resistance and the discharge internal resistance, so that the count value such as current and temperature is not memorized as in the prior art, from the initial stage to the final stage. There is a feature that can accurately detect the degree of deterioration of the battery. In particular, the above method is characterized in that the degree of deterioration is detected from the internal resistances of both the charge internal resistance and the discharge internal resistance in addition to the full charge capacity, so that the remaining capacity at the end can be detected very accurately.

The battery deterioration degree detection method of the present invention can calculate the deterioration degree SOH of the battery 1 by the following equation.
Deterioration degree SOH = weight 1 × first deterioration degree SOH1
+ Weight 2 × second deterioration degree SOH2
+ Weight 3 x third deterioration degree SOH3
However, weight 1 + weight 2 + weight 3 = 1.
This detection method can accurately determine the degree of degradation SOH by changing the ratio of weight 1, weight 2, and weight 3.

In the method for detecting the degree of deterioration of the battery according to the present invention, the weight 2 and the weight 3 can be increased as the internal resistance of the battery 1 increases.
This detection method can accurately determine the degree of degradation SOH from when the internal resistance is small until it increases.

According to the method for detecting the degree of deterioration of the battery of the present invention, the degree of deterioration SOH of the battery 1 in a state where the output power becomes the minimum output power can be set to 0%.
This detection method can accurately determine the output power from the battery degradation degree SOH.

  Furthermore, the battery deterioration degree detection method of the present invention can set the second deterioration degree SOH2 of the battery 1 when the charging internal resistance of the battery 1 reaches the maximum value to 0%.

  Furthermore, according to the method for detecting the degree of deterioration of the battery of the present invention, the third degree of deterioration SOH3 of the battery 1 when the discharge internal resistance of the battery 1 reaches the maximum value can be set to 0%.

Furthermore, the method for detecting the degree of deterioration of the battery according to the present invention is based on the integrated value of the charging current and discharging current of the battery to be charged / discharged at the first detection timing (t1) and the second detection timing (t2). The capacity change value (δAh) is calculated, and further, the first open circuit voltage (VOCV1) of the battery at the first detection timing (t1) and the second open circuit voltage (VOCV2) of the battery at the second detection timing (t2). ) To determine the first remaining capacity (SOC1 [%]) of the battery from the detected first open-circuit voltage (VOCV1) and the second open-circuit voltage (VOCV2) The remaining capacity (SOC2 [%]) is determined, and the change rate (δS [%]) of the remaining capacity from the difference between the determined first remaining capacity (SOC1 [%]) and the second remaining capacity (SOC2 [%]). ) And the calculated battery capacity change The current full charge capacity ( Ahf ) can be calculated from the value (δAh) and the rate of change of the remaining capacity (δS [%]) to detect the first deterioration degree SOH1.

  Furthermore, in the method for detecting the degree of deterioration of the battery according to the present invention, the degree of deterioration SOH of each unit cell 11 connected in series is detected, and the lowest degree of deterioration SOH is determined as the degree of deterioration SOH of the battery 1. Can do.

  Embodiments of the present invention will be described below with reference to the drawings. However, the examples shown below exemplify battery deterioration level detection methods for embodying the technical idea of the present invention, and the present invention uses battery deterioration level detection methods as follows. Not specified. Further, this specification does not limit the members shown in the claims to the members of the embodiments.

  FIG. 1 is a block diagram of a power supply device used in the method for detecting the degree of battery deterioration according to the present invention. This figure shows a block diagram for determining the degree of deterioration of the battery 1 mounted in the hybrid car. The present invention does not specify the use of the battery for detecting the degree of deterioration, but is most suitable for detecting the degree of deterioration of a battery mounted on a hybrid car, an electric vehicle, or other electric vehicles.

  The battery 1 is a lithium ion secondary battery or a lithium polymer battery. Lithium ion batteries and lithium polymer batteries have a large voltage change with respect to the remaining capacity, and can accurately detect the full charge capacity and accurately detect the degree of deterioration. However, the detection method of the present invention does not specify a battery for detecting the degree of deterioration as a lithium ion battery or a lithium polymer battery. The battery can be any rechargeable battery such as a nickel metal hydride battery or a nickel cadmium battery. The battery 1 has one or a plurality of rechargeable unit cells 11 connected in series or in parallel. In the battery 1 in which the unit cells 11 are connected in series, the degree of deterioration of each unit cell 11 is detected, and the lowest degree of deterioration is set as the degree of deterioration of the battery 1.

  The battery 1 is discharged by supplying electric power to the motor 6 for running the vehicle, and is charged by the generator 7 so that the remaining capacity is maintained in the vicinity of about 50%. The deterioration level SOH (State of Health) of the battery 1 is detected by the determination circuit 2. The determination circuit 2 includes a current detection circuit 3 that detects a charge / discharge current flowing through the battery 1, a temperature sensor 4 that detects the temperature of the battery 1, and a voltage of the battery 1 in order to detect the deterioration degree SOH of the battery 1. Is connected to a voltage detection circuit 5 for detecting

  The vehicle side includes a bidirectional power converter 8 that supplies electric power supplied from the battery 1 to the motor 6 and supplies electric power from the generator 7 to the battery 1. The bidirectional power converter 8 converts the DC power of the battery 1 into three-phase AC power and supplies it to the motor 6, and converts the AC output from the generator 7 into DC and supplies it to the battery 1. The bidirectional power converter 8 is controlled by the control circuit 9 to control the power supplied from the battery 1 to the motor 6 and the charging power from the generator 7 to the battery 1. The control circuit 9 controls the bidirectional power conversion device 8 in consideration of the deterioration degree SOH of the battery 1 transmitted from the determination circuit 2 on the power supply device side via the communication line 10. When the deterioration degree SOH of the battery 1 is in the expected normal state, the control circuit 9 controls the bidirectional power converter 8 in the normal mode. However, when the degree of deterioration SOH of the battery 1 is smaller than the expected normal state, that is, when the deterioration is severe, the control circuit 9 controls the bidirectional power converter 8 in the limit mode that makes the charge / discharge power smaller than the normal mode. To do. On the other hand, when the deterioration degree SOH of the battery 1 is larger than the expected normal state, that is, when the deterioration is small, the control circuit 9 causes the bidirectional power converter 8 to increase the charge / discharge power more than the normal mode. Or control in normal mode. As described above, the control circuit 9 controls the output of the motor 6 and the generator 7 via the bidirectional power conversion device 8, whereby the life of the battery 1 can be brought close to the target year.

The determination circuit 2 detects the degree of deterioration of the battery 1 and transmits the detected degree of deterioration SOH to the vehicle-side control circuit 9 via the communication line 10. The determination circuit 2 includes a first deterioration degree SOH1 detected from the full charge capacity of the battery 1, a second deterioration degree SOH2 obtained from the discharge internal resistance of the battery 1, and a third deterioration obtained from the charge internal resistance. The deterioration degree SOH is calculated from the degree SOH3. The determination circuit 2 calculates the deterioration degree SOH of the battery 1 using the following equation.
Deterioration degree SOH = weight 1 × first deterioration degree SOH1
+ Weight 2 × second deterioration degree SOH2
+ Weight 3 x third deterioration degree SOH3
However, weight 1 + weight 2 + weight 3 = 1.

  Weight 1, weight 2, and weight 3 are specified by the internal resistance of battery 1, as shown in the graph of FIG. In this figure, the horizontal axis is the relative value of the average value of the discharge internal resistance and the charge internal resistance of the battery, and the weight 1, weight 2 and weight 3 are shown on the vertical axis. However, in this figure, the internal resistance of the battery 1 whose lifetime has been exhausted is set to 100 in a state where the degradation degree SOH of the battery 1 is 0%. As shown in this figure, as the deterioration of the battery 1 progresses and the deterioration degree SOH decreases, the weight 1 is decreased and the weights 2 and 3 are increased. This is because, in the battery 1, the internal resistance accurately specifies the deterioration degree SOH in a state in which the deterioration has progressed due to the increase in the charging internal resistance and the discharging internal resistance. In FIG. 2, the weight 2 and the weight 3 with respect to the average value of the discharge internal resistance and the charge internal resistance are set to the same value, but the weight 2 and the weight 3 are optimal for the discharge internal resistance and the charge internal resistance, respectively. It can be set to any value.

  In the above method, the weight 1, the weight 2, and the weight 3 are specified from the internal resistance of the battery 1. However, the detection method of the present invention specifies weight 1 to weight 3 from the second deterioration degree SOH2 and the third deterioration degree SOH3 specified from the discharge internal resistance and the charge internal resistance of the battery 1, or the first It is also possible to specify weight 1 to weight 3 from the degree of deterioration SOH determined from the third degree of deterioration. Also in this case, the degree of deterioration SOH decreases, in other words, as the end of life is approached, the weight 1 is decreased and the weights 2 and 3 are increased.

Furthermore, the determination circuit 2 determines the first deterioration degree SOH1 by the following equation.
First degradation degree SOH1 (%) =
100 × [current full charge capacity (Ahf) −term full charge capacity (Ahe)] /
[Initial full charge capacity (Ahs)-final full charge capacity (Ahe)]

For example, when the initial full charge capacity (Ahs) is 5 [Ah] and the final full charge capacity (Ahe) is 2.5 [Ah], the current full charge capacity (Ahf) of the battery is 3.75 [Ah]. If it is, the deterioration degree SOH is calculated as 50% by the following equation from the above equation.
Deterioration degree SOH = 100 × [5-3.75] / [5-2.5] = 50%

The determination circuit 2 detects the current full charge capacity (Ahf) of the battery 1 by the following method.
As shown in FIG. 3, between the first detection timing (t ₁ ) and the second detection timing (t ₂ ), the battery capacity change from the integrated value of the charging current and discharging current of the charged / discharged battery. The value (δAh) is calculated. Further, the first open circuit voltage (V _OCV1 ) of the battery at the first detection timing (t ₁ ) and the second open circuit voltage (V _OCV2 ) of the battery at the second detection timing (t ₂ ) are detected, The first remaining capacity (SOC ₁ [%]) of the battery is determined from the detected first open circuit voltage (V _OCV1 ), and the second remaining capacity ( _{B OCV2} ) of the battery is determined from the second open circuit voltage (V _OCV2 ). SOC ₂ [%]) is determined. The remaining capacity (SOC) with respect to the open circuit voltage (V _OCV ) is measured and stored in advance. The rate of change of the remaining capacity (δS [%]) is calculated from the difference between the determined first remaining capacity (SOC ₁ [%]) and the second remaining capacity (SOC ₂ [%]). From the remaining capacity change rate (δS [%]) and the capacity change value (δAh) detected as described above, the current full charge capacity (Ahf) of the battery can be calculated by the following equation.
Full charge capacity (Ahf) = δAh / (δS / 100)

The method of detecting the full charge capacity (Ahf) of the battery by the above method is, for example, the first detection timing (t ₁ ) at a predetermined timing for turning on the ignition switch that is the main switch of the vehicle. And the second detection timing (t ₂ ) is after the ignition switch is turned off. Further, a constant time is set between the first detection timing (t ₁ ) and the second detection timing (t ₂ ), or, after the first detection timing (t ₁ ), the capacitance change value (δAh). By setting the timing when becomes a predetermined value as the second detection timing (t ₂ ), the current full charge capacity (Ahf) can be detected more accurately.

  Furthermore, the determination circuit 2 detects the discharge internal resistance and the charge internal resistance of the battery 1, and determines the second deterioration degree SOH2 from the discharge internal resistance and the third deterioration degree SOH3 from the charge internal resistance. An equivalent circuit of the battery 1 having the internal resistance (R) is shown in FIG. When the battery 1 of this equivalent circuit is charged and discharged and the current I and the output voltage VL are detected, the result is as shown in FIGS. In FIG. 5, the discharge internal resistance (Rd) is calculated from the slope of the line A indicating the current-voltage characteristics of the battery. In FIG. 6, the charge internal resistance (Rc) is calculated from the slope of the line B indicating the current-voltage characteristics of the battery. Is calculated.

If the open voltage of the battery 1 is Vo and the voltage is VL at the discharge current Id,
VL = Vo−Rd × Id
From this equation, the discharge internal resistance (Rd) is calculated as Rd = (Vo−VL) / Id.

Also, if the open voltage of the battery 1 is Vo and the voltage is VL at the charging current Ic,
VL = Vo + Rc × Ic
From this equation, the charging internal resistance (Rc) is calculated by Rc = (VL−Vo) / Ic.

  The second deterioration degree SOH2 and the third deterioration degree SOH3 of the battery with respect to the discharge internal resistance and the charge internal resistance of the battery 1 are measured in advance and stored in the LUT of the determination circuit 2, or the determination circuit 2 And the second deterioration degree SOH2 and the third deterioration degree SOH3 with respect to the charging internal resistance are stored as functions. The second deterioration degree SOH2 and the third deterioration degree SOH3 with respect to the discharge internal resistance and the charge internal resistance, which are stored in the LUT or stored as a function, are values shown in FIG. From this figure, for example, when the discharge internal resistance and the charge internal resistance of the battery are 300 mΩ, the second deterioration degree SOH2 and the third deterioration degree SOH3 are set to 60%. Further, the second deterioration degree SOH and the third deterioration degree SOH3 when the discharge internal resistance and the charge internal resistance of the battery 1 reach the maximum values are set to 0%. In FIG. 7, for the sake of simplicity, the second deterioration degree SOH2 and the third deterioration degree SOH3 with respect to the discharge internal resistance and the charge internal resistance are set to the same value. The deterioration degree SOH2 and the third deterioration degree SOH3 can be set to optimum values by measuring a battery actually used.

  The determination circuit 2 calculates the first deterioration degree SOH1, the second deterioration degree SOH2, and the third deterioration degree SOH3 by the above method, and calculates the calculated first deterioration degree SOH1 and second deterioration degree SOH2. The weight 1, weight 2, and weight 3 are specified from the third deterioration degree SOH3, and the battery deterioration degree SOH is determined. FIG. 8 shows a flowchart in which the determination circuit 2 calculates the deterioration degree SOH.

[Step of n = 1]
In this step, the determination circuit 2 detects the current full charge capacity (Ahf) of the battery, and determines the first deterioration level SOH1 from the detected full charge capacity (Ahf). The first deterioration degree SOH1 is detected by the following equation.
First degradation degree SOH1 (%) =
100 × [current full charge capacity (Ahf) −term full charge capacity (Ahe)] /
[Initial full charge capacity (Ahs)-final full charge capacity (Ahe)]
In the above formula, the initial full charge capacity (Ahs) and the final full charge capacity (Ahe) are specified in advance.

[Step of n = 2]
In this step, the determination circuit 2 calculates the discharge internal resistance from the current and voltage of the battery being discharged, and calculates the discharge internal resistance from the current and voltage of the battery being charged. At this time, filtering by temperature is performed to increase measurement accuracy. This is because the discharge internal resistance and the charge internal resistance change with temperature. The filtering by temperature detects the battery temperature when detecting the discharge internal resistance and the charge internal resistance of the battery, and converts the detected temperature into an internal resistance at a set temperature as a function. The determination circuit 2 that filters the internal resistance stores the change of the internal resistance with respect to the temperature as a function or in the LUT. From this stored value, the internal resistance is filtered and corrected to the internal resistance at the set temperature.
[Step n = 3]
Further, the determination circuit 2 calculates the second deterioration degree SOH2 from the discharge internal resistance and the third deterioration degree SOH3 from the charge internal resistance based on the stored LUT and function.
[Step n = 4]
In this step, the determination circuit 2 specifies weight 1, weight 2, and weight 3. Weight 1, weight 2, and weight 3 are specified from FIG.
[Step n = 5]
The determination circuit 2 calculates the deterioration degree SOH of the battery 1 from the weight 1 and the first deterioration degree SOH1, the weight 2 and the second deterioration degree SOH2, and the weight 3 and the third deterioration degree SOH3. The determination circuit 2 calculates the deterioration degree SOH using the following equation.
Deterioration degree SOH = weight 1 × first deterioration degree SOH1
+ Weight 2 × second deterioration degree SOH2
+ Weight 3 x third deterioration degree SOH3

  The determination circuit 2 determines the deterioration degree SOH of the battery 1 as described above, and transmits the determined deterioration degree SOH to the vehicle-side control circuit 9 via the communication line 10.

  The determination circuit 2 sets the degree of deterioration SOH of the battery 1 to 0% when the output power is the minimum output power. By detecting such a deterioration degree SOH, the life of the battery 1 can be known. Further, various parameters in each deterioration degree SOH, for example, the relationship between the voltage and the battery capacity (SOC) in the deterioration degree SOH, the full charge capacity (Ahf) in the deterioration degree SOH, etc. are stored in advance, and Such stored parameters can be used according to the detected degree of degradation SOH at that time.

  In the electric vehicle, a large number of unit cells 11 are connected in series to increase the output voltage of the battery 1. The degree of deterioration of the battery 1 is determined by detecting the degree of deterioration of each unit cell 11 and setting the degree of deterioration of the unit cell 11 having the lowest degree of deterioration as the degree of deterioration of the battery 1.

It is a block diagram of the power supply device used for the detection method of the deterioration degree of the battery concerning one Example of this invention. It is a graph which shows the weight 1, the weight 2, and the weight 3 with respect to the relative value of internal resistance. It is a figure which shows the principle which detects the present full charge capacity (Ahf) of a battery. It is a figure which shows the equivalent circuit of the battery which has internal resistance. It is a graph which shows the current-voltage characteristic at the time of discharge of a battery. It is a graph which shows the current-voltage characteristic at the time of charge of a battery. It is a graph which shows deterioration degree SOH2 and SOH3 with respect to internal resistance. It is a flowchart in which the determination circuit calculates the deterioration degree SOH.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Battery 2 ... Determination circuit 3 ... Current detection circuit 4 ... Temperature sensor 5 ... Voltage detection circuit 6 ... Motor 7 ... Generator 8 ... Bidirectional power converter 9 ... Control circuit 10 ... Communication line 11 ... Unit cell

Claims (7)

A first deterioration degree SOH1 obtained from the change value of the full charge capacity of the battery, a second deterioration degree SOH2 obtained from the discharge internal resistance of the battery, and a third deterioration degree SOH3 obtained from the charge internal resistance of the battery, A method for detecting the degree of deterioration of a battery that calculates the degree of deterioration SOH from
The battery deterioration degree detection method according to claim 1, wherein the battery deterioration degree SOH is calculated by the following equation.
Deterioration degree SOH = weight 1 × first deterioration degree SOH1
+ Weight 2 × second deterioration degree SOH2
+ Weight 3 x third deterioration degree SOH3
However, weight 1 + weight 2 + weight 3 = 1. According to the internal resistance increases, the detection method of the deterioration degree of the battery as described in claim 1 to increase the weight 2 and the weight 3.   The battery deterioration degree detection method according to claim 1, wherein the battery deterioration degree SOH in a state where the output power becomes the minimum output power is set to 0%.   The battery deterioration degree detection method according to claim 1, wherein the second deterioration degree SOH2 of the battery when the charging internal resistance of the battery reaches a maximum value is 0%.   The battery deterioration degree detection method according to claim 1, wherein the third deterioration degree SOH3 of the battery when the discharge internal resistance of the battery reaches a maximum value is 0%. In the first detection timing and the second detection timing, the battery capacity change value (Ah) is calculated from the integrated value of the charging current and discharging current of the battery to be charged / discharged,
Further, the first open voltage of the battery at the first detection timing and the second open voltage of the battery at the second detection timing are detected, and the first remaining capacity of the battery is detected from the detected first open voltage. (%) And the second remaining capacity (%) of the battery from the second open circuit voltage, and the difference between the determined first remaining capacity (%) and second remaining capacity (%) Shows the rate of change in remaining capacity (%)
Calculate
2. The battery according to claim 1, wherein the first deterioration degree SOH <b> 1 is detected by calculating a current full charge capacity (Ah) from the calculated battery capacity change value (Ah) and remaining capacity change rate (%) . Degradation detection method. The battery deterioration degree detection method according to claim 1, wherein the deterioration degree SOH of each unit cell connected in series with each other is detected, and the lowest deterioration degree SOH is determined as the battery deterioration degree SOH.

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