Against this background, Toshiba has succeeded in the world’s first demonstration of wireless monitoring using BLE to realize wireless monitoring of the status of energy storage modules in battery storage systems.
In a storage battery system, 20 or more storage batteries are usually installed in a closed space, surrounded by metal, and wireless communications between each must occur within. Wireless communication requires under the assumption that signals from CMUs to BMUs in each battery will mutually interfere, and that communications are likely to be unstable due to radio wave reflections within the housing. To verify the application of BLE in such a harsh environment, Toshiba designed a system that allows one-time delays and prevents continuous delays, in accordance with the storage battery system’s monitoring cycle. Specifically, the system was designed to stop the charging and discharging of energy storage modules when communication fails over three consecutive cycles, with wireless communication allowing a monitoring cycle of 100 to 200 ms (Fig. 2). Considering that the expected useful lifetime of a typical stationary lithium-ion battery is approximately 10 years, the company set a goal of suppressing errors relative to the monitoring cycle (i.e., communication delay beyond the monitoring cycle), to less than 10-4. Using a storage battery panel with storage modules installed, two BLE modules were installed in each BMU, and 11 CMU-side BLE modules are wirelessly connected for each BMU-side BLE.
Communication delay measurements over four days showed that a monitoring cycle of about 160 ms can reduce communication delays to less than 10-4. For BLE communications, signal interference was modeled with respect to the desired signal and showed that the delay characteristics can be explained through probability calculations (Fig. 3). Such mechanistic analyses enable prediction of delay characteristics and assure reliability when the number of storage batteries increases.
From this demonstration, Toshiba expects to be able to construct storage battery systems using energy storage modules equipped with BLE communication functionality that are operable for long periods of time.