Energy Storage Controls Modeling for

Distribution Planning Roger C. Dugan, FIEEE

EPRI, Knoxville, TN

14TD0671

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Distribution Planning and Storage

• What do distribution planners need to include storage?

• EPRI has been doing research since 2009

• Many findings are encapsulate in OpenDSS storage models

• As US states and Canadian provinces push for more storage, there will be more advances in the near future

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“Storage” Element Model in OpenDSS

% Eff. Charge/Discharge Idle | Discharge | Charge

Idling Losses

kW, kvar

kWh

STORED

Other Key

Properties

% Reserve

kWhRated

kWhStored

%Stored

kWRated

etc.

A Generic Storage Model with Key Planning Characteristics

“StorageController” Element in OpenDSS

Discharge Mode

Charge Mode

kW Target

Discharge Time

Total Fleet kW Capacity

Total Fleet kWh

et. al.

Storage “Fleet” Substation

V, I Comm Link

Time + Discharge rate

Peak Shaving

Load Following

Loadshape

Controls One or More Storage Elements from a Remote or Local Location

Control Modes in OpenDSS

• Static:

• Time:

• Peak Shave:

• Load Following:

• Loadshape:

• Dynamics:

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We have found the following modes to be useful in

modeling Storage in Distribution System Analysis

Sequential Power Flow

Electromechanical Transients

Control Modes

• Static: A solution of one power flow state with storage discharging or charging at specified rates or idling. This provides a partial picture of the situation by simulating limiting conditions but does not reveal issues that might be exposed through time-series simulation.

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Control Modes

• Time: Trigger ON at a specified time at a specified constant discharge or charge level.

• Peak Shave: Discharges when load exceeds a specified value and attempts to limit the load current or power to the value. Charges at a scheduled time.

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Control Modes

• Load Following: Triggers ON at a specified time and attempts to limit the load to the value at that time by following the load.

• Loadshape: Storage charge and discharge cycle is determined by a predefined shape.

• Dynamics: For modeling fast-changing phenomena such as frequency control on microgrids.

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SOME EXAMPLES …

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Load Shapes With and Without Storage

Mode=Peak Shave, Target=8000 kW, Storage=75 kWh

Charge=2:00 @ 30%

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

0 50 100 150 200 250 300

Hours

kW

0

10

20

30

40

50

60

70

80

Base kW

Net kW

kWh Stored

Simple Peak Shave Example with 3-Hour Storage

From EPRI

Smart Grid Demo - AEP

Community Energy Storage

Load Shapes With and Without Storage

Mode=Peak Shave, Target=8000 kW, Storage=25 kWh

Charge=2:00 @ 30%

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

0 50 100 150 200 250 300

Hours

kW

0

5

10

15

20

25

30

Base kW

Net kW

kWh Stored

“Ran Out of Gas”

Simple Peak Shave Example With 1-Hour Storage

Detail on Peak Shaving Application

12

0

5

10

15

20

25

30

0

2000

4000

6000

8000

10000

170 180 190 200 210 220 230

kW

h

kW

Hours into Simulation

Load Following with Storage, 25 kWh Storage UnitsDischarge Trigger @ 1300, 30% charge rate @ 0200

No Storage

Storage

kWh Stored

Using Storage to Extend Solar PV

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-500

0

500

1000

1500

2000

0

1000

2000

3000

4000

5000

6000

7000

8000

1 1441

Demand_wPV+Storage

Demand_wPV

Storage Ouput

PV Output

De

man

d (k

W)

PV

an

d S

otr

age

Ou

tpu

t (k

W)

Minutes

Charging

Discharging

Source: EPRI, 2012, Analysis of Distribution System Effects of Energy Storage Through Simulation and

Modeling, Palo Alto, CA, US. 1024285

Using Storage for Smoothing PV

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Power Output for the Smoothing Operation

15

-1500

-1000

-500

0

500

1000

1500

0 1440 2880 4320 5760 7200 8640

ES O

utp

ut

(kW

)

Minutes

Dynamics Modeling of VSC-Based DESS Device for Frequency Control

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Signal provided by

external controller

Inverter: Intelligent Volt-Var Control

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Sunderman, Dugan, Smith, “Open Source Modeling of Advanced Inverter Functions for Solar Photovoltaic

Installations “, Paper No. 14TD0479

Conclusions

• Static power flows provide a partial picture by simulating limiting conditions

• Does not reveal issues that might be exposed through time-series simulation.

– Storage is a “disruptive” technology that alters the loadshape

• Dynamics simulation capability needed for frequency control of microgrids, etc.

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Questions?

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