Voltage and Var Control ApplicationsIncluding Smart Inverters, Energy Storage, and Secondary Side Solutions

Dr. Arindam Maitra, EPRIDr. Jason Taylor, EPRI

IEEE PES Meeting, DenverJuly 29th, 2015

1

Uncertainty and Future of the Distribution System

Industry IssueDistribution Planning and Operations are Becoming More Complex

• Traditional methods of managing voltage and reactive power rely on voltage regulators and capacitor banks

• New requirements like peak demand reduction, VVO/CVR for load management are requiring new coordination challenges

• Emerging DER along edge of the n/w

• Autonomous units not well-coordinated with conventional capacitors, voltage regulators and load-tap changers

VVO/CVRProcessor

RTU

End of Line Voltage

Feedback

Standalone

Model-based

Rule-based

Cap banks, Vreg

Cap banks, Vreg, plus Smart inverters

Challenges

Distributed generation• Potential for localized high voltages• Limited visibility of conditions• Fast variations in generation output

Volt/var OptimizationConservation voltage reduction (CVR)

Integration of new distributed voltage controls

Distance from Substation

Volta

ge

• Replace xfmr

• Reconductor

• Line Tap Changer (LTC)

• Cap bank

• Line regulators

Traditional Regulation OptionsBenefits of CVR and VVO:- Lower losses in lines, transformers - Lower losses in end-use devices- Allows more real-power throughput

Volta

ge

Distance from Substation

Upper Threshold

Lower Threshold

Volt/Var Optimization

Grid Impacts of Intermittent Distributed Resources

Source: EPRI

Smart Inverters

Storage

Power Electronic Devices

Potential Benefits– Faster response– Flatter voltage profile– Direct placement for localized problems

Distributed Voltage Regulation

Numerous Potential Performance Objective(s)

Efficiency• Reduced distribution line losses• Improved customer efficiency CVR• Peak Demand reduction

Power Quality

• Flatter voltage profile• Improved harmonics• Voltage flicker• Overvoltage

Asset Utilization

• Reduce LTC tap changes• Reduce line regulator tap changes• Reduce switch cap changes• Deferment of system upgrades

Reliability• Momentary interruption support• Automatic reconfiguration support

Enabling • Increased DER hosting capacity

Smart Inverters

Reactive power dispatch – Output constrained by active power

generation– Multiple control configurations (settings)

Industry Adoption • IEEE standard 1547• California Rule 21 • Manufacturers onboard

0 5 10 15 20 25

1.024

1.026

1.028

1.03

1.032

1.034

1.036

1.038

1.04

1.042

1.044

Hour

Vol

tage

(pu)

---- Voltvar

---- No PV---- PV base

What is the best voltage response?

Depends on the objective

Response using different volt-var settings

Capacitor switching or inverter status change

Control Settings Specification depends upon…

Control Design SensitivitiesTime-series, stochastic assessments• Spatial variation• Temporal variation

performance objective

network characteristics

inverter rating

… as well as Operational Conditions

Formulation of control design practices is needed

Energy Storage Four-quadrant Operation• Voltage regulation using both active

and reactive power

Test Feeder Evaluation• Large voltage variations due to PV

• Storage to provide voltage regulation

• Various deployments considered

PV systems for 57305 feeder

PV Systems for 57307 feeder

Regulator

Substation and meter

Capacitors

PV system

Distance measured from the meter

1.6 miles

1.612 miles

1.579 miles

1.273 miles

1.148 miles

Effect of Energy Storage Location on Voltage

0 0.05 0.1 0.15 0.2

PV Ramp UP

PV Ramp DOWN

Largest Voltage variation (%)

With Energy Storage No Energy Storage

0 0.5 1 1.5 2

PV Ramp UP

PV Ramp DOWN

Largest Voltage variation (%)

With Energy Storage No Energy Storage

0 0.5 1 1.5

PV Ramp UP

PV Ramp DOWN

Largest Voltage variation (%)

With Energy Storage No Energy Storage

0 0.5 1 1.5

PV Ramp UP

PV Ramp DOWN

Largest Voltage variation (%)

With Energy Storage No Energy Storage

The voltage profile improves for each bus. The largest voltage variations at PV buses decrease from 0.014 puto 0.002 pu.

At PV Bus 2

At PV Bus 1

At Feeder End 1

At Substation

210kW/735kWh450kW/1575kWh

2.14MW/7.6MWh

Energy Storage absorbs or generates only active power (Volt/Watt Control)

Effect of Energy Storage Location on Voltage Regulation

00.20.40.60.8

11.21.41.6

Largest voltage variation at PV Bus 2

PV Ramping Up PV Ramping Down

Storage Location

Larg

est v

olta

ge v

aria

tion

(%)

The voltage regulation concerns are demonstrated using PV bus 2

As ES moves away from PV location, the improvement in voltage variation decreases.

PVBus_2

PVBus_1

Energy Storage absorbs or generates only reactive power (Volt-Var Control)

Parameters that Impact ES siting – Voltage Management

Effect on Volt-Watt control Volt-Var Control

Voltage regulation Efficient in regulating voltage Efficient in regulatingvoltage

Losses Depends upon X/R ratio of the feeder

Depends upon X/R ratio of the feeder

Stacked benefits May require oversizing to meet both peak load management

and voltage regulation concerns

Can provide stacked benefits

Life-Cycle cost Decreases due to cycling of battery

Not affected

Smart inverter cost Not required Required to supply vars

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Redu

ctio

n in

Vol

tage

Var

iatio

n (%

)

Storage Location

Active Power Reactive Power

General Study Circuit FindingsImpacts are location and circuit

specific• Distance from PV• System strength• X/R ratio

Active power injection or absorption may better counteract the variations in RES output

Voltage at PV Bus 2

Increasing distance from Substation

Cap BankSubstation

(LTC)

distribution line LVR

0.9

0.92

0.94

0.96

0.98

1

1.02

1.04

#1 #3 #5 #7 #9 #11 #13

volta

ge

highest voltage

lowest voltage

varia

tion

over

tim

e

Limited voltage control

Centralized Control

Distributed Secondary Side Volt-VAR Control

Secondary Side Control

0.9

0.92

0.94

0.96

0.98

1

1.02

1.04

#1 #3 #5 #7 #9 #11 #13

volta

ge

Improved voltage control

Distributed Control

Cap BankSubstation

(LTC)

distribution line LVR

Distributed Secondary Side Volt-VAR Control

Secondary Side Control

Example Secondary Side Voltage Management SolutionsENGO-V10 (Varentec) Shunt connected 240V, 1-phase 0-10 kvar (leading) Voltage and power factor

control 60/50 Hz

IPR-50 (GridCo) In-line Power RegulatorTM

240V, 1-phase 50 kVA Regulation ±10% ±5 kvar 60 Hz

Example European DevicesPCS 100 AVR (ABB) Active Voltage Regulator (AVR) 400 V, 3-phase 400 kVA 50 Hz ± 10% correction Regulation accuracy ± 1 (typical)

LVRSysTM (a-eberie) Low Voltage Regulator System 400 V, 3-phase 55 – 400 kVA 50 Hz ± 6% (± 10% extended range) 9 steps, 1.5% (2.5%)

Continuing EffortsModeling and Simulation• Models of emerging devices• Simulation capabilities for advanced distribution automation• Actual circuit evaluations• Model validation

Planning & Design

• Impact (coordination) with existing (other) voltage regulation components• Coordination/integration with DMS• Determination of control settings practices• Device location and sizing practices