BESS - Introduction

In this section, the BESS and its functional operation are discussed.
Figure 1 shows the one-line diagram of a battery energy storage system, which is then connected to a distribution system (see figure 2).
The distribution system, as seen in figure 2, consists of a 100 MVA three-winding transformer that connects a high voltage (154 kV - wye floating) transmission system to a medium (22.9 kV - wye grounded) distribution feeder.
The tertiary winding is 5.7 kV delta. There is a 5 MVAr capacitor bank connected to the MV (medium voltage) winding of the transformer.
A load of 0.5244 MW and 0.1669 MWAr is connected at the middle of the feeder.
The far end of the feeder has the BESS connected to the point of common coupling (PCC).

Figure 1: Battery Energy Storage System

Figure 2: Distribution System Connected with a Battery Energy Storage System

The BESS is operated in two modes: grid forming and grid following.
Grid following inverters do not control their frequency, but follow the grid frequency.
These inverters are currently widely used, but cannot contribute to system stability and safety.
In contrast, grid forming inverter can control the frequency and can be used in islanded/standalone mode or parallel mode.