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Irina Green, Senior Advisor, Regional Transmission,California ISO
WECC Modeling and Validation Subcommittee Workshop September 18, 2020
DER Representation in Composite Load Model
ISO Public
DER Types (NERC Reliability Guideline) Utility-Scale Distributed Energy Resources (U-DER):
directly connected to the distribution bus or through a dedicated, non-load serving feeder. They are three-phase and can range in capacity, for example, from 0.5 to 20 MW
Retail-Scale Distributed Energy Resources (R-DER): offset customer load. Include residential, commercial, and industrial customers. Typically, the residential units are single-phase while the commercial and industrial units can be single- or three-phase facilities.
Distributed Energy Resources may include: Distributed Generation – in front or behind the meter Energy Efficiency – load modifier embedded in load forecast Demand Response – demand or supply side, can be used as
mitigation Energy Storage – can be modeled as aggregated, supply or
demand side•
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DER in Composite Load Model in Power Flow Behind the Meter (BTM) DER are modeled in power flow as a
part of load
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Aggregated amounts of BTM-PV modeled at each bus by specifying the P and Q values of the PV as separate entries in the power flow load data, including the following values: Pdg - MW output of distributed generation Qdg - MVAr of distributed generation (sign convention
same as generators) Stdg - DG status DGmax – Installed capacity of distributed generation
Interface bus Load = Gross load (Load before PV)
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Behind the Meter DER in Composite Load Model in Power Flow, GE PSLF
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11114 BUS 11114Net Load shown
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DER in Composite Load Model in Dynamic Stability Studies
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Utility scale DER
Retail scale DER
Currently, DER models in dynamic stability exist only for solar PV. Other types of DER are modeled as generators, or as load modifiers
ISO Public
Modeling Behind the Meter (BTM) Distributed Generation DER_A model is available in all major software platforms: GE
PSLF, PSS/E, PowerWorld as stand alone or part of composite load
California ISO uses GE PSLF BTM DER are modeled in power flow as a part of load BTM DER are modeled in dynamic stability as part of the
composite load model CMPLDWG (individual bus model) or _CMPLDW (modular model for climate zones and types of feeders)
DER parameters are modeled in dynamic stability with the _CMP_DER_A model
DER_A model that is used for the utility scale DER is identical to the _CMP_DER_A model that is used for the retail scale DER
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Modeling BTM Distributed Generation in Dynamic Stability
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Load on the bus 375 MWDER on the bus 311 MWDER capacity 384 MW
Before initialization
After initialization
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Modeling Retail Scale DER in Dynamic Stability as Part of Load
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Composite Load When voltage is below specified values, the model trips
fractions of each motor, electronic and static load The fractions of load that are tripped and voltages, at which
they are tripped, are specified by the userDER as part of Composite Load Model
Distributed generation assumed having unity power factor DER also have settings at which voltages and frequencies
they may be tripped or reconnected DER solar PV models are simplified compared to the models
of large solar PV plants
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DER_A Dynamic Model
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Active Power-Frequency Control
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Bypassed if low voltage
To freq. relay model
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Reactive Power-Voltage Control
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Active and Reactive Current Priority Logic
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Fractional Tripping• Represents fractions of DER tripping and recovering for abnormal
voltage or frequency• Use engineering judgement, specific data not available• DER_A model represents aggregate behavior• Vtripflag – voltage tripping, Ftripflag – frequency tripping• Vl – voltage trip thresholds, tvl – tripping timing• Vrfrac – fraction of DER that recovers when voltage recovers• No partial tripping on frequency• Tv- time delay on partial voltage tripping• Can approximately model momentary cessation
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Voltage Source Representation
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NERC SPIDER (System Planning Impact from DER) WG – DER_A Modeling Guideline
NERC SPIDERWG developed guideline on use of the DER_A model, and its parameter values
The Guideline is approved by NERC Provides detailed understanding of the
model Provides recommendations for
developing parameters for the model and values of DER_A parameters to use
CAISO uses parameters from this guideline: 30% as of IEEE Std 1547-2003 and 70% as of IEEE Std 1547-2018, Category II
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DER_A Default Parameters (SPIDER Guideline)Active Power-Frequency Control
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DER_A Default Parameters (SPIDER Guideline)Reactive Power-Voltage Control
• Kqv=0, no voltage control• With dynamic voltage control, SPIDER Guideline recommended• Kqv=5, Dbd1= -0.12, Dbd2=0.1
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DER_A Default Parameters (SPIDER Guideline)Active-Reactive Current Priority Logic
• If DER is a generator (Ipmin = 0), storage (Ipmin=-Ipmax)
• Pqflag = 0 – Q priority, =1- P priority• Inverters prior to IEEE 1547-2018
Standard not required to have voltage control – P priority
• After the approval of IEEE 1547-2018 -voltage control, Q priority
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Why do we need to model DER?Growth of DER, as Modeled in the CAISO Cases
(BTM)
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PG&E Example Daily Load
Existing DER as of 2019 – 8,661 MW (all)
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Behind the Meter DER Sensitivity Studies
In addition to the studies of the Transmission Planning Process, CAISO performed numerous sensitivity studies of the BTM DER parameters
The latest studies included : Voltage regulation from DER Impact of the DER on frequency regulation DER parameters as Category II compared with Category
III according to the IEEE Standard 1547-2018 Also performed studies with DER netted with load The studies concluded that modeling DER makes significant
difference in the study results DER parameters have large impact on the system
performance and the simulation results.
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Study Example: Hypothetical Summer Peak, Behind the Meter DER dispatched at 80% installed capacity
Behind the meter DER installed capacity at CAISO 18,600 MW, dispatched 14,880 MW
PG&E (Northern California) Load 31,654 MW gross, 24,240 MW net Behind the meter DER installed capacity 9,270 MW Behind the meter DER dispatched 7,416 MW
Fresno zone, Load MW 2,846 MW gross,1,634 MW net Behind the meter DER installed capacity 1,515 MW Behind the meter DER dispatched 1,212 MW
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Contingency Studied, power flow case with 80% Behind-the-Meter DER dispatched
Fresno area, Gates- Midway 230 kV line outage
Why 230 kV? Larger difference in DER performance
3- fault on the sending end with normal clearance (6 cycles, 0.1 s)
DER cases studied: Category II, No voltage control, Category III, No voltage control Category II, Voltage control, Category III, Voltage control DER netted with load
Cases with voltage control, kqv=5, dead-band +0.1/-0.12
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Behind the Meter DER Parameters in this Study
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Assumed hot summer day, DER dispatched at 80% of installed capacity The peak case has high load, thus stalling of single-phase air-conditioners with faultsDER_A parameters as recommended by SPIDER Modeling Guideline for inverters according to IEEE 1547-2018
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Results Summary for the Cases Studied No criteria violations with this contingency
Loss of Composite Load and DER with Contingency
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Comparison of the five cases. Voltage at feeder end
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Higher recovery voltage with Cat III and voltage control
Lowest voltage with Cat II and no voltage control
With netted DER higher transient voltage because of lower induction motor load due to netting
Significantly better performance with Cat III settings
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Comparison of load and DER on a 70 kV bus close to fault
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NET LOAD DER OUTPUT
This DER tripped, except for Cat. III with voltage control
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Load and DER on another bus
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DER recovered for Cat. III with or without voltage control, but did not recover for Cat II
Net load: blue –no DER, red and brown Cat II, green and purple Cat III
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Conclusions from the IEEE 1547 Std setting studies DER ride-through capability and adequate trip settings lead to a
significant reduction of DER trip There is less load reduction if DER have Category III requirements
and settings, than with Category II If DER have Category III requirements and settings, system
performance is significantly better than with Category II. Some DER trip for low voltage with faults and don’t recover when
voltage recovers. There are fewer DER that trip and don’t recover with Category III.
In addition, voltage regulation on the Behind the Meter DER can provide some additional help with faults ride through and may allow the induction motors not to stall. There is less load reduction if DER have voltage control If DER have voltage control, their active power output during
transient period will be lower because of the reactive current priority
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