Method and system for compensating lithium battery capacity of a hybrid vehicle

Abstract

The application provides a compensation method and system for lithium battery capacity of a hybrid vehicle, and the method comprises the following steps: S1, acquiring the current system capacity of the lithium battery of the hybrid vehicle, and judging whether the current system capacity is within a preset compensation limit range; if yes, executing step S2, and if no, ending the compensation; S2, acquiring the discharge capacity and the charging capacity of the hybrid vehicle within a preset time, and judging whether the vehicle needs capacity compensation based on the discharge capacity and the charging capacity; if yes, executing step S3, and if no, ending the compensation; S3, calculating a capacity compensation value based on the discharge capacity and the charging capacity of the hybrid vehicle within the preset time, and performing capacity compensation on the lithium battery of the vehicle based on the capacity compensation value. The compensation method and system are based on capacity changes, can calculate a correction compensation amount in real time, avoid long-time active compensation, reduce unnecessary charging capacity, reduce lithium battery heating and reduce lithium battery throughput, and are efficient and energy-saving.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium battery capacity, and more particularly relates to a compensation method and system for lithium battery capacity of a hybrid vehicle. BACKGROUND

[0002] Lithium batteries are batteries that use non-aqueous electrolyte solutions with lithium metal or lithium alloy as the positive or negative electrode material. Lithium batteries can be roughly divided into two categories: lithium metal batteries and lithium ion batteries. With the wide application of new energy in many industries and fields, lithium batteries have developed unprecedentedly and have been widely used in various fields such as public transportation, road transportation, and mining machinery, especially in the automotive industry. Lithium batteries play a role in energy storage and power control performance in hybrid vehicles. The drive system of a hybrid vehicle is composed of two or more single drive systems that can operate simultaneously. The driving power of the vehicle is provided by the single drive system alone or jointly according to the actual driving state of the vehicle. Due to the differences in components, arrangement and control strategy, various classification forms are formed. The energy-saving and low-emission characteristics of hybrid vehicles have attracted great attention in the automotive industry and have become a focus of automotive research and development.

[0003] Hybrid vehicles include, but are not limited to, oil-electric hybrid, extended-range, and hydrogen fuel vehicles. Lithium batteries in oil-electric hybrid vehicles fully utilize the energy storage and power performance of lithium batteries, and there are many ways to control them. Ultimately, dynamic balance of electric power is achieved, which enables lithium battery performance to be fully utilized. Battery capacity is one of the important performance indicators for measuring battery performance. Therefore, during the operation of a hybrid vehicle, the battery system needs to control the capacity of the lithium battery. If the capacity of the battery cannot be well controlled, the lithium battery as an energy storage system is likely to cause capacity loss, which can cause irreversible damage to the lithium battery system. These conditions not only affect the performance of the lithium battery and shorten its service life, but also affect the safety of the battery and even the safety of the vehicle, thereby posing a safety hazard. Therefore, it is necessary to propose a battery capacity compensation method that can keep the battery capacity of the vehicle in dynamic balance without causing electric power loss. SUMMARY

[0004] Based on the above-mentioned shortcomings and deficiencies in the prior art, one of the purposes of the present application is to at least solve one or more of the above-mentioned problems in the prior art. In other words, one of the purposes of the present application is to provide a compensation method and system for lithium battery capacity of a hybrid vehicle that meets one or more of the aforementioned needs.

[0005] In order to achieve the above-mentioned purposes of the application, the following technical solutions are adopted in the present application:

[0006] In a first aspect, the present application provides a method for compensating the capacity of a lithium battery of a hybrid vehicle, comprising the steps of:

[0007] S1, obtaining the current system capacity of the lithium battery of the hybrid vehicle, and determining whether the current system capacity is within a preset compensation boundary range, if yes, executing step S2, if not, ending the compensation;

[0008] S2, obtaining the discharge capacity and the charge capacity of the hybrid vehicle within a preset time, and determining whether the vehicle needs capacity compensation based on the discharge capacity and the charge capacity, if yes, executing step S3, if not, ending the compensation;

[0009] S3, calculating the capacity compensation value based on the discharge capacity and the charge capacity of the hybrid vehicle within a preset time, and compensating the capacity of the lithium battery of the vehicle based on the capacity compensation value.

[0010] As a preferred scheme, the discharge capacity calculation formula of the hybrid vehicle within a preset time in step S2 is:

[0011]

[0012] wherein S1 represents the discharge capacity of the hybrid vehicle within a preset time, a represents the starting point of the time for calculating the discharge capacity, b represents the ending point of the time for calculating the discharge capacity, I 1 represents the instantaneous discharge current of the hybrid vehicle.

[0013] As a preferred scheme, the charge capacity calculation formula of the hybrid vehicle within a preset time in step S2 is:

[0014]

[0015] wherein S2 represents the charge capacity of the hybrid vehicle within a preset time, a represents the starting point of the time for calculating the charge capacity, b represents the ending point of the time for calculating the charge capacity, I 2 represents the instantaneous charge current of the hybrid vehicle.

[0016] As a preferred scheme, before executing step S3, it is also necessary to calculate a correction judgment value based on the discharge capacity and the charge capacity, and to determine whether the correction judgment value is within a preset correction range, if yes, executing step S3, if not, executing step S4, wherein step S4 is: calculating the capacity compensation value based on the discharge capacity and the charge capacity of the hybrid vehicle within a preset time and a preset correction coefficient, and compensating the capacity of the lithium battery of the vehicle based on the capacity compensation value.

[0017] As a preferred solution, the calculation formula of the modified judgment value is:

[0018]

[0019] wherein K' represents the modified judgment value, S 1 represents the discharge capacity of the hybrid vehicle within a preset time, S 2 represents the charge capacity of the hybrid vehicle within a preset time.

[0020] As a preferred solution, the calculation formula of the capacity compensation value in step S3 is:

[0021]

[0022] wherein Ah represents the capacity compensation value, S 1 represents the discharge capacity of the hybrid vehicle within a preset time, S 2 represents the charge capacity of the hybrid vehicle within a preset time.

[0023] As a preferred solution, the calculation formula of the capacity compensation value in step S4 is:

[0024]

[0025] wherein Ah represents the capacity compensation value, S 1 represents the discharge capacity of the hybrid vehicle within a preset time, K represents a correction coefficient, S 2 represents the charge capacity of the hybrid vehicle within a preset time.

[0026] As a preferred solution, before the capacity compensation of the vehicle lithium battery based on the capacity compensation value, it is further needed to judge whether the capacity compensation value is less than a preset minimum capacity compensation value, if yes, the capacity compensation of the vehicle lithium battery is performed, if not, the compensation is ended.

[0027] In a second aspect, the present application further provides a compensation system for the capacity of a lithium battery of a hybrid vehicle, based on the compensation method for the capacity of a lithium battery of a hybrid vehicle in any of the above solutions, comprising a capacity acquisition module, a judgment module, a calculation module and a compensation module connected in sequence, wherein the calculation module is further connected with the capacity acquisition module.

[0028] The capacity obtaining module is configured to obtain a current system capacity of the lithium battery of the hybrid vehicle, and is further configured to obtain a discharge capacity and a charge capacity of the hybrid vehicle within a preset time;

[0029] The judging module is configured to judge whether the current system capacity is within a preset compensation range, and is further configured to judge whether the vehicle needs capacity compensation based on the discharge capacity and the charge capacity;

[0030] The calculating module is configured to calculate a capacity compensation value based on the discharge capacity and the charge capacity of the hybrid vehicle within the preset time.

[0031] The compensating module is configured to compensate the capacity of the lithium battery of the vehicle based on the capacity compensation value.

[0032] As a preferred scheme, the calculating module is further configured to calculate a correction judgment value, and is configured to calculate the capacity compensation value based on the discharge capacity and the charge capacity of the hybrid vehicle within the preset time and a preset correction coefficient.

[0033] The judging module is further configured to judge whether the correction judgment value is within a preset correction range, and is configured to judge whether the capacity compensation value is less than a preset minimum capacity compensation value.

[0034] The present application has the following advantages over the prior art:

[0035] The compensation method and system of the present application take the capacity change of the lithium battery as a reference, and correct the compensation amount according to real-time calculation results to avoid long-term active compensation, thereby reducing unnecessary charging capacity, reducing lithium battery heating and reducing lithium battery throughput, thereby prolonging the service life of the lithium battery, and reducing the energy consumption of the hybrid vehicle, achieving high efficiency and energy saving.

[0036] Specifically, on the one hand, the compensation method and system of the present application first calculate the system capacity of the lithium battery to preliminarily judge whether capacity compensation is needed, and then calculate the discharge capacity and the charge capacity within a preset time to further judge whether capacity compensation is needed. The deviation of the preliminary judgment can be corrected through the further judgment, and the two-step judgment can accurately analyze whether the battery system truly needs capacity compensation, thereby reducing unnecessary active capacity compensation, reducing unnecessary charging capacity and charging operation, and significantly improving the economy.

[0037] Specifically, in another aspect, the compensation method and system of the present application judge whether the compensation value needs to be corrected by calculating a correction judgment value based on the discharge capacity and the charge capacity of the lithium battery within a preset time and comparing the correction judgment value with a preset correction range, and correct the compensation value, which can effectively avoid the compensation value being too small or too large due to errors. If the compensation value is too small and is not corrected, the compensated battery capacity does not meet the demand of the lithium battery, so that the number of compensation of the lithium battery increases, thereby increasing the start frequency of the compensation system, which increases the workload of the compensation system, so that the working efficiency of the compensation system is not high, and the economy is also reduced. If the compensation value is too large and is not corrected, the compensated battery capacity exceeds the demand of the lithium battery, and the braking of the hybrid vehicle itself can generate part of the recoverable energy, and if the capacity of one compensation is too large, energy waste can be caused, thereby significantly reducing the economy. Therefore, correcting the compensation value can effectively improve the working efficiency of the compensation system, improve the compensation effect, make the lithium battery system in dynamic balance, and ensure the working performance of the lithium battery.

[0038] Further or more detailed beneficial effects will be described in the specific embodiments in combination with specific examples. BRIEF DESCRIPTION OF DRAWINGS

[0039] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0040] Figure 1 is a flow chart of the compensation method for the lithium battery capacity of the hybrid vehicle according to the present application.

[0041] Figure 2 is a schematic diagram of the compensation system for the lithium battery capacity of the hybrid vehicle according to the present application. DETAILED DESCRIPTION

[0042] The technical solutions in the embodiments of the present application will be described clearly and completely in combination with the drawings in the embodiments of the present application.

[0043] In the following description, a plurality of embodiments of the present application are provided, and different embodiments can be replaced or combined, so that the present application can also be considered to include all possible combinations of the same and / or different embodiments described. Therefore, if one embodiment includes features A, B and C, and another embodiment includes features B and D, the present application should also be considered to include one or more embodiments containing all other possible combinations of A, B, C and D, although the embodiment may not be explicitly described in the following content.

[0044] The following description provides examples, and is not intended to limit the scope, applicability or example set forth in the claims. Alterations and further modifications of the described elements are possible without departing from the scope of the application. Various examples can omit, substitute, or add various procedures or components as appropriate. For instance, the methods described can be performed in an order different than described, and various steps can be added, omitted, or combined. Also, features described with respect to some examples can be combined in other examples.

[0045] In order to better understand the embodiments of the present application, before the specific embodiments of the present application are explained in detail, the application scenarios thereof are described.

[0046] Embodiment one:

[0047] As shown in the figure, the embodiment provides a compensation method for lithium battery capacity of a hybrid vehicle, comprising the steps of: Figure 1 S1, acquiring the current system capacity of the lithium battery of the hybrid vehicle, and determining whether the current system capacity is within a preset compensation boundary range, if yes, executing step S2, if not, ending the compensation;

[0048] S2, acquiring the discharge capacity and charge capacity of the hybrid vehicle within a preset time, and determining whether the vehicle needs capacity compensation based on the discharge capacity and charge capacity, if yes, executing step S3, if not, ending the compensation;

[0049] S3, calculating a capacity compensation value based on the discharge capacity and charge capacity of the hybrid vehicle within a preset time, and performing capacity compensation on the lithium battery of the vehicle based on the capacity compensation value.

[0050] Specifically, the preset compensation boundary range in step S1 provided by the embodiment has two limiting factors, one is the system capacity setting of the lithium battery of the hybrid vehicle, and the other is the working road condition of the hybrid vehicle. The preset compensation boundary range can generally be set to 50% of the system capacity, and the value can also be adjusted according to the actual working condition. The preset compensation boundary range in the embodiment is set to 50%. Selecting the middle section of the system capacity as the compensation boundary range can make the capacity of the lithium battery after compensation be in balance within a more appropriate range, which is conducive to improving the service life of the lithium battery system.

[0051] Specifically, one preferred embodiment of step S2 provided by the embodiment has a discharge capacity calculation formula for the hybrid vehicle within a preset time:

[0052]

[0053] ​

[0054] wherein S1 represents the discharge capacity of the hybrid vehicle within a preset time, a represents the time starting point for calculating the discharge capacity, b represents the time ending point for calculating the discharge capacity, I 1 represents the instantaneous discharge current of the hybrid vehicle.

[0055] Specifically, the step S2 provided in the embodiment has a preferred embodiment, and the formula for calculating the charge capacity of the hybrid vehicle within a preset time is:

[0056]

[0057] wherein S2 represents the charge capacity of the hybrid vehicle within a preset time, a represents the time starting point for calculating the charge capacity, b represents the time ending point for calculating the charge capacity, I 2 represents the instantaneous charge current of the hybrid vehicle.

[0058] More specifically, the instantaneous discharge current and the instantaneous charge current of the hybrid vehicle in the above two preferred embodiments are obtained through the following steps: first, the current sensor is used to detect the digital signal or CAN signal within the time period of a-b, and the detected digital signal or CAN signal is transmitted to the battery management system for processing; then the battery management system calculates the instantaneous discharge capacity and the instantaneous charge capacity through integration, and stores the instantaneous discharge capacity and the instantaneous charge capacity on the storage chip of the battery management system; finally, all the instantaneous discharge capacities and the instantaneous charge capacities are respectively accumulated to obtain the discharge capacity and the charge capacity of the lithium battery of the hybrid vehicle within the time period of a-b. In order to improve the calculation accuracy, the accumulation of current and time in the above steps is calculated in millisecond units. The formula for the integration calculation of the instantaneous discharge capacity is: I 1* t wherein S1' represents the instantaneous discharge capacity, I 1 represents the instantaneous discharge current of the hybrid vehicle, t represents the instantaneous time for calculating the instantaneous discharge capacity. The formula for the integration calculation of the instantaneous charge capacity is: I 2* t wherein S2' represents the instantaneous charge capacity, I 2 represents the instantaneous charge current of the hybrid vehicle, t represents the instantaneous time for calculating the instantaneous charge capacity.

[0059] Specifically, after step S2, the embodiment provides a preferred embodiment, before step S3 is performed, it is also necessary to calculate a correction judgment value based on the discharge capacity and the charge capacity, and judge whether the correction judgment value is in a preset correction range, if yes, step S3 is performed, if not, step S4 is performed, the step S4 is: based on the discharge capacity and the charge capacity of the hybrid vehicle within a preset time and a preset correction coefficient, a capacity compensation value is calculated, and the vehicle lithium battery is compensated based on the capacity compensation value.

[0060] More specifically, there are two limiting factors of the preset correction range, one is the nominal capacity of the lithium battery system, and the other is the preset compensation range. In the embodiment, the preset correction range is set to 0.9-1.1, and if the range of the preset correction range is set too large or too small, it will affect the correction judgment and thus affect the compensation value. If the range of the preset correction range is set too large, it is more likely that no correction is needed when the correction judgment is made, and the compensation effect will be affected if the capacity compensation is directly performed without correction when the correction is needed. If the range of the preset correction range is set too small, it is more likely that correction is needed when the correction judgment is made, and the final compensation value will be wrong if the correction is made when no correction is needed, thus affecting the compensation effect.

[0061] Specifically, the embodiment provides a preferred embodiment, and the calculation formula of the correction judgment value is:

[0062]

[0063] Wherein K' represents the correction judgment value, S 1 represents the discharge capacity of the hybrid vehicle within a preset time, S 2 represents the charge capacity of the hybrid vehicle within a preset time.

[0064] Specifically, the embodiment provides a preferred embodiment of step S3, and the calculation formula of the capacity compensation value in step S3 is:

[0065]

[0066] Wherein Ah represents the capacity compensation value, S 1 represents the discharge capacity of the hybrid vehicle within a preset time, S 2 represents the charge capacity of the hybrid vehicle within a preset time.

[0067] Specifically, the embodiment provides a preferred implementation, and the calculation formula of the capacity compensation value in step S4 is:

[0068]

[0069] wherein Ah represents the capacity compensation value, S 1 represents the discharge capacity of the hybrid vehicle within a preset time, K represents a correction coefficient, S 2 represents the charge capacity of the hybrid vehicle within a preset time.

[0070] More specifically, the correction coefficient has two limiting factors, one is the lithium battery system capacity, and the other is the working road condition of the hybrid vehicle. In the embodiment, the correction coefficient is in the range of 0.9-1.1, and the value is selected according to the actual situation.

[0071] Specifically, the embodiment provides a preferred implementation, and before the capacity compensation of the vehicle lithium battery based on the capacity compensation value, it is also necessary to judge whether the capacity compensation value is less than a preset minimum capacity compensation value. If yes, the capacity compensation of the vehicle lithium battery is performed, and if no, the compensation is ended.

[0072] More specifically, the minimum capacity compensation value is related to the system calibration capacity of the lithium battery, and in the embodiment, the minimum capacity compensation value is selected as 10% of the system calibration capacity of the lithium battery.

[0073] Embodiment two:

[0074] As shown in Figure 2 The embodiment provides a compensation system for the capacity of a lithium battery of a hybrid vehicle, which is based on the compensation method in any of the above schemes and comprises a capacity acquisition module, a judgment module, a calculation module and a compensation module connected in sequence, and the calculation module is further connected with the capacity acquisition module. The capacity acquisition module is used to acquire the current system capacity of the lithium battery of the hybrid vehicle and is also used to acquire the discharge capacity and the charge capacity of the hybrid vehicle within a preset time. The judgment module is used to judge whether the current system capacity is within a preset compensation range and is also used to judge whether the vehicle needs capacity compensation based on the discharge capacity and the charge capacity. The calculation module is used to calculate a capacity compensation value based on the discharge capacity and the charge capacity of the hybrid vehicle within a preset time. The compensation module is used to perform capacity compensation on the vehicle lithium battery based on the capacity compensation value.

[0075] Specifically, this embodiment provides a preferred implementation method, wherein the calculation module is further used to calculate a correction judgment value, and to calculate a capacity replenishment value based on the discharge capacity and charging capacity of the hybrid vehicle within a preset time and a preset correction coefficient; the judgment module is further used to determine whether the correction judgment value is within a preset correction range, and to determine whether the capacity compensation value is less than a preset minimum capacity compensation value.

[0076] It should be noted that for the aforementioned method embodiments, for the sake of simplicity, they are all expressed as a series of action combinations, but those skilled in the art should be aware that this application is not limited by the order of the actions described, because according to this application, certain steps can be performed in other orders or simultaneously. Secondly, those skilled in the art should also be aware that the embodiments described in the specification are all preferred embodiments, and the actions and modules involved are not necessarily required by this application.

[0077] In the above embodiments, the description of each embodiment has its own focus. For parts that are not described in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0078] The above is only an exemplary embodiment of the present disclosure and cannot be used to limit the scope of the present disclosure. That is, any equivalent changes and modifications made according to the teachings of the present disclosure are still within the scope of the present disclosure. After considering the specification and practicing the disclosure herein, those skilled in the art will easily think of the implementation scheme of the present disclosure. This application is intended to cover any variation, use or adaptation of the present disclosure, which follows the general principles of the present disclosure and includes common knowledge or customary technical means in the art that are not recorded in the present disclosure. The description and examples are to be regarded as exemplary only, and the scope and spirit of the present disclosure are defined by the claims.

Claims

1. A method for compensating the capacity of a lithium battery of a hybrid vehicle, characterized in that: Including steps: S1. Obtaining the current system capacity of the hybrid vehicle lithium battery and determining whether the current system capacity is within a preset compensation limit range, if so, executing step S2; otherwise, terminating compensation; S2. Obtaining the discharge capacity and charge capacity of the hybrid vehicle within a preset time, and determining whether the vehicle needs capacity compensation based on the discharge capacity and charge capacity, and if so, executing step S3; otherwise, terminating the compensation; S3. calculating a capacity compensation value based on the discharge capacity and the charge capacity of the hybrid vehicle within a preset time, and performing capacity compensation on the vehicle lithium battery based on the capacity compensation value; Before executing step S3, it is necessary to calculate a correction judgment value based on the discharge capacity and the charge capacity, and determine whether the correction judgment value is within a preset correction range. If so, step S3 is executed; otherwise, step S4 is executed. Step S4 is: calculating a capacity replenishment value based on the discharge capacity and the charge capacity of the hybrid vehicle within a preset time and a preset correction coefficient, and performing capacity compensation on the vehicle lithium battery based on the capacity compensation value; The calculation formula of the modified judgment value is: Wherein K' represents the modified judgment value, S1 represents the discharge capacity of the hybrid vehicle within a preset time, and S2 represents the charge capacity of the hybrid vehicle within a preset time; The calculation formula of the capacity compensation value in step S4 is: Ah=S1*K-|S2| Wherein, Ah represents the capacity compensation value, S1 represents the discharge capacity of the hybrid vehicle within a preset time, K represents the correction coefficient, and S2 represents the charge capacity of the hybrid vehicle within a preset time.

2. The method for compensating the capacity of a hybrid vehicle lithium battery according to claim 1, characterized in that: The calculation formula for the discharge capacity of the hybrid vehicle within the preset time in step S2 is: Wherein, S1 represents the discharge capacity of the hybrid vehicle within a preset time, a represents the starting point of calculating the discharge capacity, b represents the ending point of calculating the discharge capacity, and I1 represents the instantaneous discharge current of the hybrid vehicle.

3. The method for compensating the capacity of a hybrid vehicle lithium battery according to claim 2, characterized in that: The calculation formula for the charging capacity of the hybrid vehicle within the preset time in step S2 is: Wherein, S2 represents the charging capacity of the hybrid vehicle within a preset time, a represents the starting point of calculating the charging capacity, b represents the ending point of calculating the charging capacity, and I2 represents the instantaneous charging current of the hybrid vehicle.

4. The method for compensating the capacity of a hybrid vehicle lithium battery according to claim 1, characterized in that: The calculation formula of the capacity compensation value in step S3 is: Ah=S1-|S2| Wherein, Ah represents the capacity compensation value, S1 represents the discharge capacity of the hybrid vehicle within a preset time, and S2 represents the charge capacity of the hybrid vehicle within a preset time.

5. A method for compensating the capacity of a hybrid vehicle lithium battery according to claim 1 or 4, characterized in that: Before performing capacity compensation on the vehicle lithium battery based on the capacity compensation value, it is also necessary to determine whether the capacity compensation value is less than a preset minimum capacity compensation value. If so, capacity compensation is performed on the vehicle lithium battery; otherwise, compensation is terminated.

6. A hybrid vehicle lithium battery capacity compensation system, based on the hybrid vehicle lithium battery capacity compensation method according to claim 1, characterized in that: It includes a capacity acquisition module, a judgment module, a calculation module, and a compensation module connected in sequence, wherein the calculation module is also connected to the capacity acquisition module; The capacity acquisition module is used to obtain the current system capacity of the hybrid vehicle's lithium battery and is also used to obtain the discharge capacity and charge capacity of the hybrid vehicle within a preset time; The judgment module is configured to judge whether the current system capacity is within a preset compensation limit range, and further configured to judge whether the vehicle needs capacity compensation based on the discharge capacity and the charge capacity; The calculation module is configured to calculate a capacity compensation value based on a discharge capacity and a charge capacity of the hybrid vehicle within a preset time; The compensation module is used to perform capacity compensation on the vehicle lithium battery based on the capacity compensation value.

7. A hybrid vehicle lithium battery capacity compensation system according to claim 6, characterized in that: The calculation module is further configured to calculate a correction judgment value, and to calculate a capacity replenishment value based on the discharge capacity and charge capacity of the hybrid vehicle within a preset time and a preset correction coefficient; The judgment module is further configured to judge whether the correction judgment value is within a preset correction range, and to judge whether the capacity compensation value is less than a preset minimum capacity compensation value.

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