An optimal operating point control of lithium-ion battery in a power compensator for DC railway system

An optimal operating point control method of lithium-ion battery for a power compensator of a DC railway system is developed in this paper. The compensator consists of a DC/DC converter and a lithium-ion battery bank. The regenerative energy is stored to the battery, and the energy is released to powering trains. The charging and discharging currents are determined according to the feeding-line voltage. The stored energy is maximized by controlling the maximum discharging current according to the state-of-charge (SOC) and the internal resistance of the battery. The maximum charging current of the DC/DC converter is identical to the maximum current of the battery, for improving the efficiency of the train system. Numerical simulations are carried out to confirm the proposed maximum power point tracking (MPPT) method. An experiment is also carried out to prove the effectiveness of the proposed method. Both results show that the proposed method improves the stored energy by 20% compared with that of a conventional system.