Title: Control and Evaluation of 1000 V Valve Regulated Lead Acid (VRLA) and Lithium-Iron-Phosphate Lithium Ion (LFP-LI) Batteries for High Pulsed Rate Applications*
Authors: Matthew J. Martin, Christopher L. Williams, Kendal D. Mckinzie, David A. Wetz, Clint G. Gnegy-Davidson, Isaac J. Cohen, Caroline S. Westenhover, John M. Heinzel
Title: A pulsed power system’s intermediate energy storage typically requires charge voltages as high as tens to hundreds of kV. While these high charge voltages are easily obtained in the laboratory using utility grid-tied power supplies, they are not so easily generated aboard the future naval ships on which pulsed power systems will be deployed. One possible option being considered involves using high voltage electrochemical energy storage modules (ESMs), whose open circuit potential (OCP) may be as high as 1000VDC, aboard the mobile platform to both power the loads and buffer the onboard generation. A high switching frequency DC/DC converter can be used to transform the ESM’s 1000 VDC voltage up to the charge voltage required of the pulsed power system’s intermediate energy storage. While this seems simple, few have ever really constructed and evaluated a 1000 VDC ESM since there are few, if any, commercial applications that would demand an ESM with these characteristics. In the work presented here, two 1000 VDC electrochemical batteries have been designed, constructed, and evaluated at high pulsed rates. The first is a valve regulated lead acid (VRLA) battery made up of two parallel connected strings of 74 - 12.5 V modules connected in series. The second is a lithium-iron-phosphate lithium-ion (LFP-LI) battery made up of 28 – 38 V modules (10S/1P) connected in series. Since this high OCP is only needed when the pulsed power load is operational, electromechanical relays are used to interconnect the lower voltage modules into a single string of batteries when needed. These relays also double as an operational safety that isolates modules in the event of improper battery operation. Control of these relays in fault isolation conditions is non-trivial and hence is being studied here. The transient nature of battery operation at high C rates has been characterized along with the batteries performance, thermal evolution, and usable capacity at the high rates of interest.