IEEE Electrification Magazine - September 2015 - 50

Vt

Pref and Qref Can Be
Connected to the REPC_A
or REPC_B Plant
Controller Models

reec_c
regc_a
Iqcmd'

Q Control

Qref

Current
Limit
Logic

Ipcmd'

P Control

Pref

Iqcmd

Ipcmd

Pqflag
= 1 (P priority)
= 0 (Q priority)

Iq
Generator/
Converter
Model
Ip

Pgen

Figure 5. A block diagram of the BESS model, excluding the plant controller.

With the aforementioned background in mind, the BESS
model concept is shown in Figure 5. The existing renewable
energy generator/converter (REGC_A) model, without any
modifications, is used to represent the power converter interface between the batteries and the grid. Then, the existing
renewable energy electrical control (REEC) model is augmented to add to it a feature to allow for both charging and discharging with a simple representation of the battery storage.
This simple representation of the charge/discharge mechanism is shown in Figure 6.
The new renewable energy electrical controller type C
(REEC_C) incorporates this simple charging/discharging
model. This new module, when incorporated with the
REGC_A model, can then represent a BESS unit. Furthermore, the plant controller modules can be used with these
models to allow one to emulate various functionalities
such as frequency regulation.
The added new feature shown in Figure 6 has the following key features:
xx
A representation of the initial state of charge (SOC) of
the battery-this is a user input to the model, which
tells the model how much charge the battery currently
has prior to the simulation being initiated.

SOCmax
Power
Generated

1
T.s

-

SOC
+

Initial SOC

xx
A representation of the maximum and minimum

allowable SOC (shown as SOCmax and SOCmin)-most
battery manufacturers will recommend that the battery
not be left in a state of full charge or full discharge to
preserve the battery's longevity and performance. Thus,
the model can simulate this by specifying the maximum and minimum recommended SOC during operation, which is something the actual controls would also
respect and enforce. Many vendors recommend operating the batteries within a range of 20-80% SOC.
xx
The simple integrator block, with the time constant T,
which represents the process of charging and discharging, can be understood by considering the fact that the
level of charge in the battery is proportional to stored
energy. Energy is the time integral of power since
power is specified in units of watts = joules (energy) per
second. Thus, by integrating the power coming out of
(or going into when charging) the BESS, we get a representation of the SOC.
xx
The logic block at the end of the model represents the
action of collapsing the output of the converter (i.e.,
forcing its active current output) to zero once the
maximum or minimum SOC has been reached.

If SOC ≥ SOCmax
Ipmin = 0
elseif SOC ≤ SOCmin
Ipmax = 0

SOCmin

Figure 6. A block diagram of the charging and discharging mechanism of the BESS model.

50

I E E E E l e c t r i f i cati o n M agaz ine / SEPTEMBER 2015

Maximum Active
Current Limit (Ipmax)
Minimum Active
Current Limit (Ipmin)



Table of Contents for the Digital Edition of IEEE Electrification Magazine - September 2015

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IEEE Electrification Magazine - September 2015 - Cover3
IEEE Electrification Magazine - September 2015 - Cover4
http://www.nxtbook.com/nxtbooks/pes/electrification_december2019
http://www.nxtbook.com/nxtbooks/pes/electrification_september2019
http://www.nxtbook.com/nxtbooks/pes/electrification_june2019
http://www.nxtbook.com/nxtbooks/pes/electrification_march2019
http://www.nxtbook.com/nxtbooks/pes/electrification_december2018
http://www.nxtbook.com/nxtbooks/pes/electrification_september2018
http://www.nxtbook.com/nxtbooks/pes/electrification_june2018
http://www.nxtbook.com/nxtbooks/pes/electrification_december2017
http://www.nxtbook.com/nxtbooks/pes/electrification_september2017
http://www.nxtbook.com/nxtbooks/pes/electrification_march2018
http://www.nxtbook.com/nxtbooks/pes/electrification_june2017
http://www.nxtbook.com/nxtbooks/pes/electrification_march2017
http://www.nxtbook.com/nxtbooks/pes/electrification_june2016
http://www.nxtbook.com/nxtbooks/pes/electrification_december2016
http://www.nxtbook.com/nxtbooks/pes/electrification_september2016
http://www.nxtbook.com/nxtbooks/pes/electrification_december2015
http://www.nxtbook.com/nxtbooks/pes/electrification_march2016
http://www.nxtbook.com/nxtbooks/pes/electrification_march2015
http://www.nxtbook.com/nxtbooks/pes/electrification_june2015
http://www.nxtbook.com/nxtbooks/pes/electrification_september2015
http://www.nxtbook.com/nxtbooks/pes/electrification_march2014
http://www.nxtbook.com/nxtbooks/pes/electrification_june2014
http://www.nxtbook.com/nxtbooks/pes/electrification_september2014
http://www.nxtbook.com/nxtbooks/pes/electrification_december2014
http://www.nxtbook.com/nxtbooks/pes/electrification_december2013
http://www.nxtbook.com/nxtbooks/pes/electrification_september2013
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