Solectria Smart Inverters, Effective Grounding, and how to work with the Utility

www.solectria.com

Built for the real world Solectria Renewables / Company Confidential © 2014

Being Good Citizens of

the Grid

Claude Colp

Applications Engineer

[email protected]

@ClaudeColp

mailto:[email protected]

www.solectria.com


Introduction

1. Company Overview

2. Relays 27, 59, 81, ect.

3. Effective Grounding

4. Power curtailment

5. Power Factor

6. Reactive power support

7. Solectria’ s work at ESIF

8. Reactive power support

Solectria Renewables

Lawrence, MA

www.solectria.com


Company Overview

www.solectria.com


25 Year Development History

• Inverter power stage technology developed over 25 years of automotive and

military applications

• Proven reliability in harsh conditions

Efficient

Powerful

Reliable

Rugged

Commercial, Utility-Scale, and

Residential PV Inverters

Compact

Low Cost

EV Drives

www.solectria.com


Solectria History

1989 2007 20082005 20092006 2010 2011 2012

Original 10kW

UL Listed

Solectria

Corporation

Founded

Solectria divests

vehicle products to

Azure Dynamics

60/82/95KW

UL Listed

SolrenView Web

Monitoring Introduced

Capacity Expansion

to 200MW

PVI 60/77/90KW

UL Listed

PVI 13-15KW

UL Listed

PVI 3000-5300

Introduced

MSS

Introduced

Capacity Expansion to

800MW

Disconnecting String Combiners

Introduced

SGI 500XT transformerless

600V DC inverter introduced

2013

PVI 14-28TL, 3-phase

transformerless inverters

2014

PVI 3800-7600TL,

1Ph

transformerless

invertersIntroduced SGI 500 Premium Efficiency model

with 97.5% CEC efficiency – highest in the industry

Capacity

Expansion

to 350MW

Introduced the SGI 500XTM & SGI 750XTM

External Transformer

Introduced PVI 50/60/75/85/100KW

& Premium Efficiency Models

• 1989 – Solectria Corporation founded

• 2005 – Solectria Corp. EV division sold to Azure

Dynamics

• 2005 – Solectria Renewables founded

• 2014 – Solectria became wholly owned

subsidiary of Yaskawa Electric

Solectria

Renewables

Founded

SGI Series

UL Listed

New SolrenView GUI

Introduced

Yaskawa Electric Acquires Solectria

Renewables as wholly owned subsidiary

ARCCOM (AFDI String Combiner)

Introduction

www.solectria.com


Yaskawa and Solectria

Yaskawa Electric Corp:

• $3.6 billion Japanese firm focused on motor drives, automation controls and other electrical components

• Company founded in 1915

• 5th largest Japanese inverter supplier, but no U.S. presence

• Global leader in quality

• Manufacturing locations in strategic PV markets

• Track record for technological advancement and leadership

www.solectria.com


Yaskawa and Solectria

So what does this mean for our customers?

Immediately enhanced bankability

Warranty backing by bigger company

Solectria is 100% wholly owned subsidiary

Same team in place as before (sales, marketing, customer

services, executives)

Same manufacturing locations and product offerings

Potential for new market entry in the future

Access to world class quality systems

www.solectria.com


2014 Company Highlights

• Introduction of three-phase string inverters

• Introduction of ARCCOM arc fault detection and rapid

shutdown combiner boxes for 600VDC and 1000VDC central

inverters

• Introduction of SGI 500XTM and SGI 750XTM

• Acquisition of Solectria Renewables by Yaskawa Electric

Corp.

www.solectria.com


Protective Relaying

www.solectria.com


(Digital) Protective Relays

“Microprocessor based devices that that control PV plant

in response to voltage and current measurement”

USED WITH:

… Interconnection Breaker

… Instrument Transformers

Potential Transformers (PTs) … for measuring Voltage

Current Transformers (CTs) … for measuring Current

…Sometimes

Uninterruptible Power Supply (UPS)… for Powering Relay

when grid goes down (not required in all systems)

“I thought inverters had voltage/frequency trip setpoints??!!

They do. Required when utility desires Additional or

Redundant protection

Made by companies like SEL, ABB, Cooper, GE, …

www.solectria.com


ANSI Device Numbers“Standard numbers used by utilities/relay companies to

indicate protective function”

From PVI 50-100 Installation Manual

www.solectria.com


Example One Line

…Showing Protective Relay w/

ANSI Device Numbers

www.solectria.com


Utility ControlWhat is SCADA?

“Supervisory Control and Data Acquisition”

= Control and Monitoring

What would utility want to control? On/Off (Remote shut down)

Ramp rate

Real Power/Reactive Power/PF

How is this implemented? Control of Interconnection Breaker

24V Remote Shutdown

Shunt Trip

Modbus RTU, Modbus TCP, DNP3

Utility usually interfaces with inverters

through RTU’s, Protective Relays, Plant Controller

www.solectria.com


Example One Line

…Showing the piecesIN

VE

RT

ER

SIN

VE

RT

ER

SIN

VE

RT

ER

S

I

www.solectria.com


Effective Grounding

of PV inverters

www.solectria.com


Distribution Feeder

Load

Vb = Vc = 173%

CLOSEDOPEN

CB

SLGFault

Sync. Gen.

Consider an islanded operation where the grid is disconnected and a single line to ground fault is applied to the island.

Generator neutral shift generates the over-voltages on unfaulted phases.

Va = Vb = Vc = 100%

Single phase loads can be damaged from the overvoltage.

Non-Grounded Synchronous DG

http://www.google.com/url?sa=i&rct=j&q=&esrc=s&frm=1&source=images&cd=&cad=rja&docid=HCtNlTBsuUrZmM&tbnid=KP08xAVfsB2geM:&ved=0CAUQjRw&url=http://www.iwcommunitylearning.ac.uk/mod/page/view.php?id=2655&ei=vxqNUZXOBMrJ0AHU_IDIDw&bvm=bv.46340616,d.dmQ&psig=AFQjCNHwlV6nKQpyAgPHjvXlJtzl2BFDGg&ust=1368287821251674


www.solectria.com


Distribution Feeder

Load

CLOSEDOPEN

CB

SLGFault

Sync. Gen.Vb = Vc = 100%

Effective Grounding allows 125% over-voltage and impedance grounding(for protection relay coordination)

𝑋0𝑋1

< 3,𝑅0𝑋1

< 1

Grounding the generator neutral prevents over-voltages on unfaulted phases.

Va = Vb = Vc = 100%

Ref: IEEE Std. 142, IEEE Std. C62.92 series

Solidly Grounding Synchronous DG



www.solectria.com


Distribution Feeder

Load

CLOSEDOPEN

CB

SLGFault

PV InverterVb = Vc = 100%

In contrast to the synchronous generator, a PV Inverter is a current source and

no overvoltage will be generated due to the neutral shifting.

Even without the inverter neutral grounding (3-wire connection), over-voltage

will not be generated if the load is predominantly wye-connected.

Does same happen with PV inverters?

Va = Vb = Vc = 100%

“… When the inverter-based DG is isolated from the utility voltage source, there is no derived neutral shift.”

- Dr. Michael Ropp, 39th Annual Western Protective Relay Conference, Oct. 2012.



http://www.google.com/url?sa=i&rct=j&q=&esrc=s&frm=1&source=images&cd=&cad=rja&docid=HBI9uUvzMC9bdM&tbnid=JDnaKBmP6_ANbM:&ved=0CAUQjRw&url=http://www.solren.com/wp-content/uploads/2012/01/&ei=PlqNUYTJCrLC0AGBmoHgCQ&bvm=bv.46340616,d.dmQ&psig=AFQjCNHVppBiSGkCtsaHRUC4zBepLL4E-Q&ust=1368304571409643


www.solectria.com


Distribution Feeder

Load

Vb = Vc = 173%

CLOSEDOPEN

CB

SLGFault

Solectria’s simulation results showed a negligible voltage rise in unfaulted phases with 50% delta load and 50% wye grounded loads. With 80% delta-connected load, phase voltages went up to 120%, which is still less than the maximum over-voltage with the effective grounding. (125%)

Va = Vb = Vc = 100% PV Inverter

In practical cases, most of the loads will be wye grounded in 3-phase 4-wire system.

PV inverter with pure delta loads





www.solectria.com


Several utilities require effective grounding by meeting X0/X1 ratio

1.5 < X0/X1 < 2.5

NGRID, HECO, XCEL, PEPCO, BGE, Indianapolis…

Some utilities use separate guidelines for inverter based distribution generation(DG) which makes more sense as the inverter characteristics is quite different from the rotating machine type generators

XDG0 = 0.6*Zbase +/- 10%

GMP, Hydro One…

Effective Grounding

www.solectria.com


Minimal hardware and installation cost

Need to coordinate with the main circuit breaker

Can be used with any medium voltage transformer configuration

Suggested Design PracticeCase 1. PV plant effective grounding with one or multiple inverters (universal solution)

GroundingBank

51G

www.solectria.com


Effective Grounding

PVI 3ɸ-String Inverters Require grounding transformer for

effective grounding, Zig-Zag or Yg-Δ

www.solectria.com


Grounding bank (transformer)

A grounding bank is a small special transformer configured in Zig-Zag or Delta-Wye.

A grounding bank is external to PV inverters and provides effective grounding, so that it does not impact the inverters transformer life.

A single grounding bank can provide effective grounding for a large PV plant, which minimizes the installation cost.

For a SGI 500kW inverter installed at 480V distribution feeder, grounding bank cost

can be several $K.

PV Inverter

Groundingbank

51G



www.solectria.com


Can be used with a wye-delta medium voltage transformer only

Can be effectively grounded with a grounding bank also

Minimal hardware and installation cost

Suggested Design PracticeCase 2. PV plant effective grounding with grounding inductor and a dedicated wye-delta MV Transformer

Groundinginductor

51G

www.solectria.com


Effective Grounding Summary

Most 3-phase 4-wire systems support single phase loads, which puts the effective grounding requirement for PV inverters in question.

Many utilities request effective grounding with a controlled impedance for relay protection coordination.

Solectria provides impedance tables for all commercial and utility scale PV inverters to help customers design an effectively grounded PV system.

Effective grounding using Zig-Zag transformer is a universal solution for ungrounded DG.

Many Solectria inverters have an internal wye-delta isolation transformer with a neutral connection which can be used to provide effective grounding. When used, neutral over-current protection is strongly recommended.

www.solectria.com


Power Curtailment

www.solectria.com


Power Curtailment

30

40

50

60

70

80

90

50 60 70 80 90 100

Po

we

r in

KW

percentage

Pcmd

Pout

80kW 50kW 80kW

www.solectria.com


Advantages of Power Curtailment

• 100kW interconnection Limit

PLC

700k

W

750k

W

~50k

W

Monday through Friday

www.solectria.com


Advantages of Power Curtailment

PLC

170k

W

70kW

~100kW

Saturday and Sunday

23% limit

• 100kW interconnection Limit

www.solectria.com


Case Study – Xcel Energy

Product: 504, PVI 82KW – SCADA controlled, VAR supports

Modules Amonix

Installer Amonix, Cogentrix

Location Alamosa, CO

System Size 30 MW

www.solectria.com


Reactive Power

www.solectria.com


Inverter Capacity for VARs

• Inverter and AC interconnection have to be sized to carry both real and reactive current

Example: 500kVA @ 0.95 PF

475 kW

15

6 k

VA

r

www.solectria.com


Inverter Capacity for VARs



475 kW

475 kW

15

6 k

VA

r

www.solectria.com


Inverter Capacity Allocation for VARs



475 kW475 kW

156 kVAr

www.solectria.com


Power factor control = +/- 0.8 (+/- 0.95 prefered)

Maximum reactive power control = 60%

May require power curtailment for reactive power control

May conflict with the islanding detection

Inverter Capacity Allocation for VARs

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

0 0.2 0.4 0.6 0.8 1Q

Re

acti

ve p

.u.

P Active p.u.

www.solectria.com


• PPA owned (“in front of the fence”)

o UL1741 enforces a PF > 0.95

VAR support

(remote utility option)

-1000

-800

-600

-400

-200

0

200

400

600

800

1000

-720 -630 -540 -450 -360 -270 -180 -90 0 90 180 270 360 450 540 630 720

voltage current power (rms) real power (rms)

www.solectria.com


Reactive Power Control

The waveform shows instantaneous transient response of the inverter

output current (red) from full inductive to full capacitive.

www.solectria.com


DNP3 Compliant Smart Grid Inverters

www.solectria.com


High Penetration Scenario Example:

• 1.7 MW site in Cedarville NJ• 4.7 miles from substation 12kV feeder, 6MW mid-day load• Concerns of local overvoltage• Utility has closed circuit for more PV

0.5 MW

1.7 MW

www.solectria.com


Overvoltage Concerns

3.0% of points exceed +5% limit

www.solectria.com


The effect of reactive power on

distribution lines

PCC voltage is being pulled down.

VAR Absorption

PCC voltage is being pushed up.

VAR Generation

www.solectria.com


Example: PF control

• Feeder could be reopened for PV after PF adjustment to 0.97• “Flicker” Mitigation (cloud induced voltage transients)

< 0.1% of points exceed 5% limit

www.solectria.com


Baseline – No PV

Benefit to Utility

Example: Volt-VAR control

Inverter Volt-Var Control

• Reduced wear out of electromechanical voltage regulators• Flatter voltage profile overall

20% PV Penetration

Possible additional Voltage Regulator

action

www.solectria.com


Matthew Rylander

Increasing Hosting Capacity with Smart

InvertersWithout Volt/var Control Volt/var Control

5000 cases shown

Each point = highest primary voltage

ANSI voltage limit

ANSI voltage limit

160% increase in

hosting capacity

60% increase in

hosting capacity

Increasing penetration (kW)M

axim

um

Fe

ed

er

Vo

lta

ge

(p

u)

Ma

xim

um

Fe

ed

er

Vo

lta

ge

s (

pu

)

Increasing penetration (kW)

No observable violations regardless of size/location

Possible violations based upon size/location

Observable violations occur regardless of size/location

PV Hosting Capacity (kW)

Without Volt/var With Volt/var

Primary Voltage

Deviation

1st violation 938 >2500

50% scenarios with violation 1323 >2500

All scenarios with violation 1673 >2500

Primary

Over Voltage

1st violation 540 880

50% scenarios with violation 871 1464

All scenarios with violation 1173 2418

Slide courtesy of Matthew Rylander, EPRI

http://www.google.com/url?sa=i&rct=j&q=&esrc=s&frm=1&source=images&cd=&cad=rja&docid=8sdzBfNNPWVO6M&tbnid=hdsXYVBMtDl3zM:&ved=0CAUQjRw&url=http://smartgridcc.org/news-events/member-spotlight-electric-power-research-institute-epri&ei=8z4TUajrNMux0AGMkIGAAQ&bvm=bv.42080656,d.dmQ&psig=AFQjCNHUmrTBjuUIU5A8kD2fRMQLBLnf3g&ust=1360302191218604


www.solectria.com


Solectria’s Work in this Field



www.solectria.com


o Smart Grid Ready Inverter Development

Implement and test grid support functions on existing

commercial and utility scale inverters.

Add DNP3 communication capability on to the existing inverters

Hardware reliability enhancement and efficiency increase

Cost Reduction

o Plant Master Controller Development

Support smart grid inverters with the latest DNP3 protocol

Plant level supervisory controller with customizable system

integration capability

Secondary protection and preventive maintenance

www.solectria.com


Product Testing

• The Energy System

Integration Facility

(ESIF) at NREL was

chosen to test the SGI

500 features due to its

advanced capabilities

• The EPRI facility in

Knoxville, TN was

chosen to test the PVI

100KW for their

expertise in inverter

testing.

NREL Test Setup Size

PV simulator 1MW

Grid Simulator 1.2MW

Output Power 400kW

Reactive Power + 300kvar

www.solectria.com


Volt-var testing at ESIF

Test # EUT Terminal Voltage EUT Reactive Power Output Ramp

Time

(s)

Time

Window

(s)

Reversio

n

Time (s)

PASS

/FAIL

Volt % kvar % Max available var

Test 2 432 90 300 100 5 60 Never

time

out

p

475.2 99 0 100

484.8 101 0 100

518.4 108 -309 100

www.solectria.com


Balanced LVRT/HVRT at ESIF

10% Balanced sag for 120 cycles,

passive LVRT

Balanced voltage swell of 118%;

active ride through trip test

condition

www.solectria.com


Unbalanced LVRT (IEEE P1668) at ESIF

ZVRT for 120 cycles

Single phase sagBalanced Sag

• 89% of Faults are unbalanced faults

www.solectria.com


Frequency/Watt at ESIF

www.solectria.com


Watts, Hz and Volts

• Utilities like their “Volts” and “Hz” to stay within boundaries.

• When generation is High (+Watts) system wide frequency rises

(+Hz)

Functions that control “Watts” depending on “Hz”, such as

Frequency-Watt, are essential for being a good citizen on the grid.

• An increase in generation (+Watts) results in a local increase in

Voltage (+Volts)

Functions that control “Watts” depending on ”Volts”, such as Volt-

Watt, can be useful to regulate local voltage when the vars are

exhausted.

www.solectria.com


Questions?

www.solectria.com


One size doesn’t fit all,

But one company does

Thank You!

Date post:	11-Jul-2015
Category:	Engineering
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Solectria Smart Inverters, Effective Grounding, and how to work with the Utility

Engineering