Dynamic Minimum Voltage Tracking in Electrochemical Batteries for Power Capability Estimation in Microgrids

Abstract

This paper proposes a new algorithm to dynamically calculate the minimum battery voltage at which the peak power of a battery is drawn. This voltage limit is applied to calculate the corresponding discharging current in order to obtain the maximum instantaneous power from the battery. When the discharging current magnitude is greater than the aforementioned current, the discharging process becomes inefficient and the battery enters into what is referred to in this paper as a wasted energy process. This working condition can only be reached if the required application voltage is smaller than the calculated dynamic voltage for peak power. This situation can occur in a stationary application like a microgrid. In this case, unlike traditional methods, maximum power can be obtained at a lower current rate in a more efficient discharge process. The proposed power capability estimation algorithm in discharge processes is based on the partnership for new generation vehicles (PNGVs) specifications, but making use of the calculated dynamic minimum voltage. This algorithm was validated on an 11 Ah 210 Ni-Cd battery stack and compared with the classical PNGV algorithm. Results show that the wasted energy process can be avoided with the proposed algorithm and that around 3% more energy can be extracted at a higher power rate.