© 2021 by XOLTA
21
Figure 4.3:
Grid voltage varia-
tions and XOLTA
outdoor BESS active
power output
operating in the grid
voltage support mode
4.1.4 Load following
Load following is an operational mode used to support a microgrid. The XOLTA system tracks the
microgrid consumption in real time and provides power when needed.
4.2 Site controller state machine
The XOLTA Energy Storage System (ESS) Site Controller (SC) is a finite-state machine with three distinct states;
• SLEEP (idle)
• RUN (active)
• ERROR
Transitions from one state to the other occur through intermediate sequential procedures. The SC state
diagram can be found in Figure 4.5 and a short description of the states and transitional procedures is
provided in sections 4.2.1 and 4.2.2.
4.2.1 SC States
4.2.1.1 Sleep state
The system is idling; it is only monitoring and transmitting battery vitals and waiting for a request
to activate. In this state the DC contactor of the battery is open. The inverter is inactive (IGBTs off)
with both the AC and DC contactors open. For a period of system inactivity of more than 30 mins,
the BMS is disabled and turned off in order to further reduce energy losses. Upon a state change
request, the system is able to be active and ready to receive and inject power within a few seconds.
The detailed state diagram of the XOLTA outdoor BESS is presented in Figure 4.5.
Power
[kW
]
40
224
226
228
230
232
20
0
–20
–40
234
236
238
5.0
5.2
5.4
5.6
5.8
6.0
6.2
6.4
Voltage
[V
]
Time [day]
Average voltage
Inverter active power
