There are two special situations where our method described before is not effective

Document Sample
There are two special situations where our method described before is not effective Powered By Docstoc
					A Universal SOC Model


                Prof. Lei He
  Electric Engineering Department, UCLA
           http://eda.ee.ucla.edu
              LHE@ee.ucla.edu



                 2010. 7
          Outline
    Motivation

    Existing Work

    Proposed Approach

    Experimental Results

    Conclusions



2 of 34
          Motivation
    Demand for Rechargeable Batteries
          Portable Products such as laptops and cell phones
          Electric Vehicles and smart grid
    Battery Management System
          To improve the efficiency of charging and discharging
          To prolong life span
          To satisfy the real-time requirement of power
    Key Models: SOC, SOH, and SOP
          SOC = State of Charge, energy remaining in a battery
          SOH, SOP = State of health, state of power




3 of 34
          Why It is Challenging
  Battery cell is a two-terminal “black box”
  Battery ages (more than NBTI)
  SOC needs to be monitored real-time and life-long
  SOC depends on temperature (like leakage)
  SOC needs to be measured for each cell
  Measurement method should not use complicated
   circuits and systems
  It has to be reliable against rare events
  It needs to be tolerant to abuse to certain degree
  ….




4 of 34
          Outline
    Motivation

    Existing Work

    Proposed Approach

    Experimental Results

    Conclusions



5 of 34
          Existing Work
    Coulomb-Counting Based Estimation
           SoC is an integration function of time.
                                  1 t
            SOCc (t ) = SOCc (0) -  I (t ) dt ,
                                  Q 0
           However, error will be accumulated over time.
    Voltage-Based Estimation
           Bijection between SoC and Open-Circuit Voltage (OCV)
           Then how to obtain OCV from the terminal voltage and
            current?




                                                      Source: P. Moss, G. Au, E. Plichta, and J. P.
                                                      Zheng, “An electrical circuit for modeling the
                                                      dynamic response of li-ion polymer batteries,”
                                                      Journal of The Electrochemical Society, 2008.


6 of 34
          Existing Voltage-based SOC
    A variety of methods
           Weighted Recursive Least Square Regression
           Adaptive Digital Filter
           Extended Kalman Filter
           Radial Basis Function Neural Network
          …
     Simplified circuit models applied to reduced the complexity




7 of 34
                Regression for Existing Models




                            to be                                predetermined
                            decided




 Source: M. Verbrugge, D. Frisch, and B. Koch, “Adaptive Energy Management of Electric and   Source: H. Asai, H. Ashizawa, D. Yumoto, and H. Nakam, “Application of an Adaptive Digital
 Hybrid Electric Vehicles,” Journal of Power Sources, 2005.                                  Filter for Estimation of Internal Battery Conditions,” in SAE World Congress, 2005.




     Parameters need to be tuned for different battery types and individual
     battery cells
8 of 34
          Outline
    Motivation

    Existing Work

    Proposed Approach

    Experimental Results

    Conclusion



9 of 34
           Proposed Approach
    Problem of Existing Work
           Models are developed for specific types of batteries
    Characteristics of Proposed Approach
           Using linear system analysis but without a circuit model
           Low complexity for real-time battery management
    The Only Assumption Used in Proposed Approach
           Within the short observing time window, a battery is
           treated as a time-invariant linear system and the SoC and
           accordingly the OCV is treated as constants.

                            +                                     +
                                             Linear           V
                        V

                            -
                                             System               -


10 of 34
                                             Initial Time Window
                                      Current Load                                                                                                        Impulse Stimulation
                                 0                                                                                                    1
Current (A/m 2)




                                                                                                      Current (A/m 2)
                       -200                                                                                                 0.5

                       -400
                                                                                                                                      0
                                      2      4       6       8   10   12                                                                   0              2             4           6              8    10   12
                                                 T ime (s)                                                                                                                      T ime (s)


                                          Voltage Response                                                                                 x 10
                                                                                                                                                  4                                   Vf
                                                                                                                                      5




                                                                                                             Voltage (V)
                            4.1
         Voltage (V)




                              4
                            3.9                                                                                                       0
                            3.8
                            3.7                                                                                                 -5
                                                                                                                                                          2             4           6              8    10   12
                                      2      4       6
                                                 T ime (s)
                                                             8   10   12
                                                                           Convolute with f (t)                                                                                 T ime (s)
     unknown
      region                                                               which satisfies
                                                 = OCV                     f (t )  i(t )   (t )                                                4
                                                                                                                                                                                = OCVf
                                                                                                                                           x 10
         Voltage (V)




                                                                                                                                      5




                                                                                                             Voltage (V)
                            4.2
                                                                           in the window.                                             0
                            4.1                                                                                                 -5
                                      2      4       6       8   10   12                                                                                  2             4           6              8    10   12
                                                 T ime (s)                                                                                                                      T ime (s)
                                                                                                                                                                                                                          v f (t )
                                                                                                                                                                                                                   lim                OCV
                                     + Zero-State Response                                                                                                + Impulse Response                                       t    u f (t )
                                 0
                                                                                                     Voltage (V)
     Voltage (V)




                                                                                                                                      -2
                                                                                                                        10


                         -0.5
                                      2      4       6       8   10   12                                                                        0.1               0.2           0.3          0.4       0.5   0.6
                                                 T ime (s)                                                                                                                       T ime (s)



                                       Unit Step Function                                                                                      x 10
                                                                                                                                                      4                              uf
                                                                                                                                           1
                                                                                                                        Voltage (V)




                                 2
                   Voltage (V)




                                                                                                                                           0
                                 1
                                                                                                                                          -1
                                                                                                                                                              2             4        6             8    10   12
                                 0
                                      2      4       6       8   10   12                                                                                                         T ime (s)
                                                 T ime (s)

                  12 of 34
                                                  Following Windows
                                      Voltage Response                                                                                                           Stimulation
                                                                                                                                                         Current Vf
                             4
                           4.1                                                                                                          1000
                                                                                                                                          0




                                                                                                              VoltageCurrent (A/m 2)
                             4
                           3.9 x 10
                                    -3   History Influence                                    convolution                              -200
                                                                                                                                         500
         Voltage (V)
        Voltage (V)




                                                                                                                      (V)
                            0
                          3.9                                                                                                          -400
                          -10
                          3.8                                                                                                                 00               5               10                15         20     25
                          -20
                          3.8                                                                                                                                                       T ime (s)
                                              5        10               15         20
                           3.7
                           3.7                              T ime (s)                                                                   -500
                                                                                                                                                         Impulse Response
                           3.6                                                                                                         -1000




                                                                                                                     Voltage (V)
                               0
                              12         14 5     16 10        18     15 20       2022   25
                                                                                         24                                                   12              14          16            18             20    22    24
                                                                                                                                           -2
                                                            T ime (s)                                                                   10                                           T ime (s)


                                                                                                                                                   0.1             0.2              0.3           0.4       0.5    0.6
                                                                                                                                                                                     T ime (s)


                                      Current Stimulation                                                                                           Impulse Stimulation
                                                                                                                                        1




                                                                                                            Current (A/m 2)
                                0
Current (A/m 2)




                                                                                                                                       0.5
                       -200
                                                                                                                                                                                                                                v f (t )
                       -400
                           12            14       16           18            20    22    24
                                                                                                                                        0
                                                                                                                                         12              14          16            18             20        22    24     lim                OCV
                                                                                                                                                                                T ime (s)                                t    u f (t )
                                                            T ime (s)




                                      Unit Step Function                                                                                                                                 uf
                                                                                                                                        200
                                                                                                              Voltage (V)




                                2
                  Voltage (V)




                                                                                                                                        100
                                1                                                                                                         0
                                                                                                                                       -100
                                0                                                                                                            12           14             16            18             20     22    24
                                 12      14       16           18            20    22    24
                                                                                                                                                                                    T ime (s)
                                                            T ime (s)




14 of 34
           Special Situations                            lim
                                                                v f (t )
                                                                            OCV
                                                         t    u f (t )
    Case I:
            uf also converges to zero as t approaches infinity.
            I.e., uf(t) = 0 for t > 0.
            Then, the terminal current is constant and the battery becomes
             a pure resistance network.

            OCV = V (t )  I (t ) Reff
     Case II:
            The first sample of terminal current in the window is close to 0.
            Then move the window to the next sample as the starting point.
            The extreme case is that the sampled current is keeps 0
            battery in open-circuit state.

            OCV = V (t )
15 of 34
           Outline
    Motivation

    Existing Works

    Proposed Approach

    Experimental Results

    Conclusion



16 of 34
           Experimental Settings
    Verified via dualfoil5, a popular battery simulator
           Simulation input: current waveform, load or power.
           Battery materials: a library containing common materials.
           Simulation output: SOC, OCV, terminal voltage and current.
    Implementation Environment
           MATLAB 7.01 running on a dual-core Pentium 4 CPU at a
           1.73GHz clock frequency.




17 of 34
           Accuracy
    The extracted SoC fits well with the simulated data
     (labeled as simulated) for different current profiles.
                    100                                               Simulated              100                                               Simulated
                                                                      Ours                                                                     Ours
                     80                                                                       80




                                                                                     SOC %
            SOC %




                     60                                                                       60




                                                                                                       Current (A/m2)
                              Current (A/m2)




                                                 0                                                                      -24

                     40                        -20                                            40                        -26
                                               -40
                     20                         1000       1010     1020
                                                                                              20                        -28
                                                                                                                              0     1000     2000
                                                         Time (s)                                                                 Time (s)
                      0                                                                        0
                          0                     500        1000       1500    2000                 0                     500        1000      1500     2000
                                                         Time (s)                                                                 Time (s)
                                               (a) Periodical Discharge                                                   (b) Constant Power


                    100                                               Simulated              100                                               Simulated
                                                                      Ours                                                                     Ours
                     80                                                                       80
                                                                                     SOC %
            SOC %




                     60                                                                       60       Current (A/m2)
                              Current (A/m2)




                                               -18                                                                        0

                     40                                                                       40                        -20
                                               -20
                                                                                                                        -40
                     20                        -22
                                                     0     1000     2000
                                                                                              20                              0     1000     2000
                                                         Time (s)                                                                 Time (s)
                      0                                                                        0
                          0                     500        1000       1500    2000                 0                     500        1000      1500     2000
                                                         Time (s)                                                                 Time (s)
                                                  (c) Constant Load                                                     (d) Piecewise Discharge

18 of 34
           Universality
    Error within 4% for different materials for active positive
     material / electrolyte / negative positive material of
     batteries (Labeled).
    For each type of battery
           Only a discharge from fully-charged to empty-charged is
           conducted to build up the bijection between OCV and SoC.
           No other tuning is needed.
                             10%
                                         Graphite/LiPF 6/CoO2
                             8%
                                         Tungsten oxide/Perchlorate/CoO2
                             6%          Graphite/30% KOH in H2O/V2O5
                 SOC error




                             4%

                             2%

                             0%
                               0   500           1000           1500       2000
                                                 Time (s)
19 of 34
                   Robustness
        The algorithm converges quickly to the correct SoC
         despite an upset on SoC.

              100%
  SOC error




                  50%

                  0%
                        0.1   0.2       0.3    0.4   0.5
                                    Time (s)
                  20%
      OCV error




                  10%

                  0%
                        0.1   0.2       0.3    0.4   0.5
                                    Time (s)

20 of 34
           Conclusions
    A Universal State-of-Charge Algorithm for Batteries
           A simple yet accurate algorithm to calculate open-circuit
           voltage (OCV) based on terminal voltage and current of
           the battery.
           Only linear system analysis used without any circuit
           model and hence universality to discharge current profile
           and any battery types without modification.
           Experiments showing less than 4% SoC error compared
           to detailed battery simulation.
    Future work
           Fixed point and FPGA implementation
           Hardware in loop testing


21 of 34

				
DOCUMENT INFO
Shared By:
Categories:
Tags:
Stats:
views:2
posted:9/12/2012
language:Unknown
pages:19