*5.2. Experimental Results*

To verify the proposed control strategy of the MMC-BESS, a downscaled prototype was built in the laboratory [24]. The configuration of the prototype is shown in Figure 16. The main parameters are listed in Table 2. The controller structure of the prototype was designed with a single digital-signal processor (DSP) as the main controller and three field-programmable gate arrays (FPGAs) as the auxiliary controllers in each phase. The battery module in individual SMs is composed of three 12 V/24 Ah lead-acid battery cells due to the consideration of cost reduction compared with other type of batteries [25]. Note that the switching frequency of battery side DC/DC converters is different from MMC side converters. Given that the power rate of individual batteries is usually lower than the MMC side, semiconductor devices and switching frequency can be selected separately at the battery side DC/DC converter [26]. With the development of wide bandgap devices, the conversion efficiency between batteries and MMC can be enhanced at high-power levels [27].



**Figure 16.** Configuration of the three-phase MMC-BESS prototype. (**a**) Picture. (**b**) Circuit.
