On the static accuracy of charge-discharge units of one class intended for electrical tests of high capacity Li-ion batteries

Rechargeable energy storages are one of the basic components of spacecraft power systems. Characteristics of such energy storages significantly effect on the duration of the spacecraft life cycle in the orbit. In recent years, designers of spacecraft power systems frequently use Li-ion batteries as rechargeable energy storage. This is due to the fact that the inherent energy characteristics of Li-ion batteries are distinctly higher than that of other types of batteries with a similar cycle life. To verify whether a battery satisfies the stated requirements, battery manufacturer performs a series of qualification tests, in particular, the specially designed cyclic tests, which allow estimating the battery cycle life. These tests can take several months (the exact duration depends on the battery model), which negatively affects the overall spacecraft production duration and cost. Performing of the cycle testing according to the principles of Dynamic Stress Test can significantly reduce the overall time of development and production of batteries, which in turn allows reducing the cost of designing and testing of the spacecraft power systems. Dynamic Stress Test is a type of loading testing that allows verifying whether the battery can deliver the specified power to the consumer under all anticipated operating conditions. Basic principles of Dynamic Stress Test are charging and discharging of the battery by currents of large magnitude, and discharging of the battery at constant power, according to special program. Performing of Dynamic Stress Test requires special charge-discharge units that allow performing a full cycle of electrical tests of batteries, including cyclic testing. Providing the required accuracy of measurement and stabilization of certain attributes of Li-ion battery operating modes is one of the problems that arise during the development of such charge-discharge units. The following attributes are of particular interest: charge and discharge currents, discharge powers, battery voltages. The analysis of the charge-discharge unit as a control system allows evaluating the steady-state stabilization error of the required attributes of the developed device. Moreover, using a digital integrator in the control system of the charge-discharge unit allows providing specified values of steady-state stabilization error of required attributes in different test modes.