IEEE Power & Energy Magazine - Grid Edge 2023 - 82

battery-based IBPS launched by the Imperial Irrigation District
in California uses 30 1.25-MVA inverters and can black
start motor loads and energize high-voltage transformers. This
control concept can be scaled by simply adding more inverters.
Increasing the number of inverters or accepting degraded
performance, such as deeper voltage sags during motor starts,
can help to overcome the high-current rating requirements.
In general, most existing megawatt-size GFM applications
have technology of interest for bulk power systems. However,
depending on the exact requirements, the costs can be high
compared to the same-sized GFL IBPSs. The primary cost
drivers are the energy buffer, oversized equipment, and the
need for different control strategies based on user specifications.
Table 1 shows some functional requirements for GFM IBPSs
and IBPS aspects affected by these requirements, compared to
table 1. Examples of functional requirements
for GFM IBPSs and affected product aspects
compared to GFL IBPSs.
Affected Product Aspects of GFM BPSs
Compared to GFL IBPSs
Examples of
Functional
Requirements
for GFM IBPSs
Fast active
power
variations
Response to
the grid voltage
vector shift
Inrush currents
Fault current
contributions
Yes
Yes
Yes
Yes
No
No
Yes
Yes
Yes
Is a Higher
Current
Capability
Required?
(Hardware)
Potentially
Is an
Energy
Buffer
Needed?
(Hardware)
Yes
Are Control
Algorithm
Changes
Needed?
(Software)
Yes
GFL technology. Additional information regarding the functional
requirement examples listed in the table is provided later
in this section.
The behavior as a voltage source can demand fast power
output variations from a GFM IBPS during system transients,
which are caused by generation tripping, a grid voltage
vector shift (see Figure 2), or a system split. These variations
in ac power output will likely demand an additional
source of energy in PV and wind IBPSs. The magnitude and
duration of these power surges are important design considerations
that will lead to additional costs.
Battery-based IBPSs do not require an additional source
of energy as long as the battery's response speed allows the
GFM to maintain its designed characteristics. To withstand
all transients, particularly grid voltage vector shifts,
supercapacitors may be needed, which results in additional
cost implications.
Furthermore,
the inrush currents needed to energize
transformers can significantly increase the current capability
requirements. The ratings and characteristics of equipment
energized solely by the GFM IBPSs are important
design considerations.
Current contributions during faults in excess of the
IBPS rated current are commonly not required in present GFL
IBPSs. An increased fault current contribution needed from
GFM IBPSs is an important design consideration that will lead
to additional costs.
Design considerations for GFM IBPSs are affected by the
grid characteristics associated with active and reactive power
changes caused by voltage angle and magnitude changes,
respectively, at the point of interconnection of the IBPS.
Understanding the expected range of these variations will
reduce the likelihood of undesirable interactions.
In today's setting, where expectations for the functionality and
I
Z
VInverter
VGrid
I
VGrid
VInverter
Change in
I·Z
the Grid Voltage
I
VGrid new
performance of GFM IBPSs are nonuniform across different
interconnections, manufacturers lack incentives and guidance
to develop GFM capability.
Nonuniform requirements will
drive up the development cost for
manufacturers and, consequently,
for the IBPS project developers.
Commonly agreed upon requirements
for active and reactive power
performance, the response to small
and large disturbances, and control
modes are necessary to allow manufacturers
to develop and maintain one
set of products and reduce the complexity
for product applications.
Ancillary services or other marketVInverter
VGrid
old
I·Z
figure 2. The vector shift and response expected from a GFM IBPS. The GFM inverters
will keep the voltage and frequency reference constant or stable, as long they
do not exceed their current limit. In the case of a vector shift of the grid side, the
inverter voltage (VInverter) is identical before and after the change in grid voltage. Thus,
the voltage drop (I·Z) and inverter current (I) have to change.
82
ieee power & energy magazine
based approaches should be developed
to assign value to the system
benefits from GFM technology, similarly
to frequency support and black
start services. In this case, the market
november/december 2019

IEEE Power & Energy Magazine - Grid Edge 2023

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