**2. Enhancing Battery Management of Extending Life for RLIB**

Generally, the states of LIB monitored by battery management systems include working temperature, voltage and current, and safety functions to avoid any overcharge/over-discharge. Relative functions of BMS can be categorized into hardware side and software side, as shown in Figure 1. In the hardware side, in case of centralized circuit BMS, cell voltage and temperature are measured by sensors in the external board, MMU (module monitoring unit), as shown in Figure 2a,b. Total data from the slave MMU are collected in the master BCU (battery control unit) for estimating SOC and SOH (state of health) through SPI (serial peripheral interface) protocol, as shown in Figure 2a. The analog-to-digital converter (ADC) measures the working current of the battery. This work is implemented based on Renesas Electronics Corporation ISL78600, as shown in Figure 2b. ISL78600 IC supervises up to 12 series-connected cells in the MMU. For keeping the high-voltage safety of RLIB, one insulation-resistance-measure device is attached on the BCU, as shown in Figure 2a. Besides this, controller area network (CAN) and universal asynchronous receiver transmitter (UART) protocols are also adopted. Through these functions of communication, the online real-time states of the battery, such as working current, SOC, SOH, and temperature, are gathered and transferred to the display or upper-level controller. In the software side, an algorithm embedded in the BCU is developed for estimating SOC and SOH by using basic battery parameters. Cell balancing is conducted in the MMU. A real-time simulator is supported to achieve automatic data acquisition and processing, to further verify the algorithm [22].

In this study, additional enhancing battery management is studied in reusing a large-scale automotive LIB. Functions of life estimation and life extension are highlighted for an RLIB. The schematic hardware of life extension is listed in Figure 2a. One proper ultracapacitor (UC) is parallelly connected with the BMS under the PWM (pulse-width modulation) control, which is used to switch the duty ratio of the IGBT (insulated gate bipolar transistor) in unit time. The application of the ultracapacitor achieves sharing of the RLIB's peak power so as to decrease the depth of discharge (DOD), and hence extends the lifecycle (i.e., SOH) of the RLIB. The duty ratio is a stationary value in every control case. A proper duty ratio can be estimated by calculating from the demand power, sustained time, and maximum power from the battery. The operation board of the BCU is shown in Figure 2c.

**Figure 1.** Basic framework of the battery management system (BMS) [17].

**Figure 2.** In-house battery management system: (**a**) basic diagram; (**b**) board of module monitoring unit (MMU), based on chip ISL78600; (**c**) operation board of BMS.
