New methodology to on-site estimate the state of health of batteries for elevator applications

This paper presents a new method to determine the state of health or SOH of one or more batteries supplying an elevator. The proposed method permits an accurate estimation of the state of health or SOH of at least one single battery, without the need of extra elements in the regular architecture of an elevator, because some existing elements are used for this purpose. In order to achieve this objective, a partial discharge of the energy storage system is forced through the braking resistor of the elevator if the SOH of the battery has to be estimated, with a duty cycle less than a 100%, because the braking resistor is limited in its working temperature and it is not designed for continuous discharging. In the aforementioned discharging process the battery voltage, the current delivered by the battery to the braking resistor and the number of pulses done during the test are measured. Taking into account these measurements during the pulsed discharge an approximation of the available capacity within the battery is obtained. A previous characterization of the energy storage system in the laboratory permits to know the amount of pulses that the energy storage system under test has to supply in order to be considered suitable to continue operating the elevator. Thus, evaluating the amount of pulses given by the battery in situ in the real application and comparing it with the required minimum value obtained in the characterization in the laboratory, the SOH value of the energy storage system is estimated. This paper presents the whole methodology followed to reach this estimation.