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Bypass Removal

Competitiveness & Growth
STATUS | Ongoing
STATUS DATE | 03/09/2008
ACTIVITY CODE |

PAGE CONTENTS

Objectives

The bypass removal after qualification should allow to:

  • Improve the battery reliability as each bypass unit may fail to operate beside a weak module or operate prematurely beside a healthy module or short the module (in case of motion interrupt) when connected in a battery, – Reduce by at least 30 % of the total price of the battery,
  • Reduce significant weight/volume at battery level,
  • Shorten the battery manufacturing lead time:
    • Simplified battery harness
    • Bypass status: 6 months for US by-pass starting from knowledge of satellite application in order to submit export license request to US Department of Defense up to delivery and about the same for European source,
  • Avoid US export licenses if US by-pass is used,
  • Improve battery resistance in nominal mode.

This test program will show that:

  • Concept is valid for all identified cell failure modes,
  • Concept is reliable (robust and stable self-short resistance versus conditions (cycling, time, pulses, etc) and safe versus all types of modules and conditions.

Challenges

  • No ‘safety issue’ during the 50 reversals and similar predictable self-short behaviour show that concept is valuable.
  • Unbalanced currents in cells in parallel lead to adapted battery design and limitations.
  • Self-short applicability depends of spacecraft/battery management constraints possibly interfering with recommended procedure for best conditions (low & stable resistance to limit thermal dissipation)
  • Conducted tests were not covering ‘worst case’ which should have given direct applicability for wide use ahead of model release and predictions. Case by case analysis required consequently.
  • Short characterization performed on modules lead to need of self-short knowledge at cell level.

Plan

The plan has been established in accordance with ESA quality standards.

  • Validation of concept/formulas/model (typical events = f(DOD, N cells)),
  • Evaluation of self-short characteristics,
  • Identification of findings, missing data and further investigation.

Current Status

Bypass removal qualification within this Artès 3 program was successfully completed in May 2005.

  • 1 program shall fly soon without bypass considering possibility to accept ‘constraints’ by typical satellite/battery management.
  • Saft has been granted of new ESA programs (Artès 8, GSTPv3) for identified opened points and further analysis:
    • Get single cell ‘Ri/Rcc, OCV = f(DOD)’ to assess assumptions (localization of dead short for OCV= 0V and maximum Rcc value) and ‘Rcc1 shot = f(I/C)’ to prepare a thermal model.
    • Conduct tests covering ‘worst case’ versus electrical profiles (low rate reversal stopped at Rcc max + high rate eclipse starting from ½ season longest duration; direct high rate reversal; high rate being linked to ‘full unbalanced module status’), temperature, pressure (vacuum) and cell configuration (aged prior short for high internal cell resistance and possibly cycled at low rate after short for frozen high short resistance). Fine thermal mapping will allow to track maximum temperature/self-short location and pressure measurement will allow to determine mechanical margins of safety and classify cell versus MIL STD 1522A regulation. Pass criteria will not be limited to self-shorted cells (see above) but also to healthy neighbours (temperature limitation).