Residential Battery Storage: The cornerstone of the

Nanogrid and distributed power systems

Antonio GinartSanta Clara, California

1

Power System Centralized vs. Distributed

Wind Farm

Rural

City

Solar Farm

Power plant

Industry

Rural

City

Industry

Distribution

Distributed Paradigm Shift - Renewables

Disadvantages More complex technologiesMore expensive in many casesLess centralized controlPotential for a less reliable gridNeed of new technology and

regulationsPotential for greater power

quality issues

Advantages Potential for better local resource useConsumers have greater

independence Environmentally friendlier Potential for a more robust and

reliable grid (non-single collapse point)CybersecurityNatural disaster

Potential for more economically sound macro-analysis

3

http://www.forbes.com/sites/erikkain/2012/06/27/wildfire-burns-homes-in-colorado-springs/http://www.forbes.com/sites/erikkain/2012/06/27/wildfire-burns-homes-in-colorado-springs/http://www.usatoday.com/story/weather/2013/09/14/boulder-colorado-floods/2813225/http://www.usatoday.com/story/weather/2013/09/14/boulder-colorado-floods/2813225/

Minimum-cost of Electrification Electrification Model (REM)

400,000 non-electrified buildings in the Vaishali district of Bihar, India.

Options

Grid extension (low-voltage lines) Stand alone system (Nanogrid)Microgrid

MIT News (January 2016)4

Nanogrid Operation Mode

Grid-Tied• Frequency

• VoltageBack-upIslanding

Reliability

Independence

Solar Autonomy:

Germany 60%USA 100%

Power PG= Pload

Control Stability

Volt. Freq. Droop

• Load Criticality

• Load sink• Load dumping

Fixed voltage and frequency

TransferSwitch

Fast Low cost

Power

Power

Tariff• Zero export

• Peak demand• Sell/Buy price

Power Quality Flicker

SagSwell

Control Load

Generation5

Power Quality Issues (Back up Mode) Voltage

Clipped current100A peak

Voltage sag

Voltage swell

The standard IEEE 1100• Short term voltage variations (sag ,swell, and transients)• Long term voltage variations (over and under voltages ,

harmonics and noise)

Line voltages under A/C 5 TON system start up

½ cycle8.3ms

1 cycle16.6ms

3600 cycles60 s

>3600 cycles> 60 s

1Transients

2Sag and swell

3 Noise4 Harmonics

5 Under andover Voltages

6

Residential Nanogrid DC-AC

• 12V- 400V • Advantages

• More efficient • Easy control, stable

• Disadvantages• Large investment required• Difficult interruption

(protection, fire)

• Advantages• Required no additional

investment• Easy retrofit

• Disadvantages • Control and stability are

more difficult• Region dependent

• 200-230V 50Hz• 120/240V 60 Hz US

DC Nanogrid AC Nanogrid

7

Basic DC and AC Nanogrids: Solar and Energy Storage

GRID

AC

DC

DC

DC

Bi-directional

Batteries

PV panel Inverter

Bi-directional

GRID

AC

DC

AC

DC

Bi-directional

Batteries

PV panel Inverter

Inverter

DC Nanogrid

DC

AC

AC Nanogrid

AC

8

DC Residential Nanogrid

GRID

AC

DC

Bi-directional

Batteries

PV pannel

Inverter

DC

DC

DC

DC

DC 380VDC

DC

DC

DC

DC

DC

DC

DCBi-directional

DCDC

DC

E or H car

Wind

Generator

DC

DC

DC

AC

Bi-directional

DC 380V9

DC Residential Nanogrid- Control Droop Voltage Control

Bus Voltages

V0V1V2

A B

Current

Source 1

Constant PowerConstant Voltage

PL1 PS1PL1

PL2

State 1

State 2

Overload

DC

DC

DCDC

DC

DC

DC

DCDC

DC

DC

AC

Renewable

Non-Renewable

Co1

Co1

DC BusMPPT

Load

Power

P1

P1

10

Schönberger, J., Duke, R. and Round, S.D., 2006. DC-bus signaling: A distributed control strategy for a hybrid renewable nanogrid. Industrial Electronics, IEEE Transactions on, 53(5), pp.1453-1460.

Control Example

AC Residential Nanogrid

DieselGas

Stirling

GeneratorsEnergy Storage

MasterController

Solar

DCAC

Wind

Renewable Generators

Transfer switch

@

Control Droop Control Voltages and Frequency

Residential Load

Washer DryerRange Water

HeaterA/CUnit

TVComputer Lighting

Fridge

~Grid

11

Load Handling and Criticality

Residential Load

Range WaterHeater

A/CUnit

Microwave

- Critical Loads +

Washer Dryer Lighting

v

MasterController

@

DumpLoadFridge

TV

Z-Waves

12

13

Droop AC control ( Inverter)

The Bode plots of the output impedance of InvertersL-inverter (with L = 7 mH, R = 0.1Q, and Co = 0 µF)R-inverter (with L = 7 mH, R = 8Q, and Co = 0 µF)C-inverter (with L = 7 mH, R = 0.1Q, and Co = 161 µF).

DC LINK

+

-

FilterInverter

~

Battery / solar

DC

DC

DC/DCConverter

Impedance Inverter

14

Droop AC control

iii QnEE −*~

iii Pn−*~ ωω

QiQ*i

*E

*ω

iP*iP

Assuming δ∼0 and Inductive

δ0

0~Z

EVP0

20

0

0~ZV

ZEVQ −

δ~P EQ ~

Universal Droop Control of Inverters

15

Zhong, Qing-Chang, and Yu Zeng. "Universal Droop Control of Inverters with Different Types of Output Impedance."

Droop controllers for L-, R-, C-, RL-, and RC-inverters.

FundamentalsBack up battery storage

Energy Storage (Why Battery & Capacitor?)

Air CompressorHydraulicsThermal (Molten Salt) Inertia Wheels MagneticsCapacitor (Super)BatteryFlow Batteries

Dynamic Power Compensation (very fast – few milliseconds)Sized according its nanogridAble to regulate the nanogrid Weather prediction via internet

DC LINK

+

-

FilterInverter

Grid

~

Transformer

Battery

DC

DC

DC/DCConverter

Storage Power Conversion @

17

Time responses

18

DC Bus

Battery

AIR

Generators

Intermittent Power Power

Fast Energy Storage

19

Ultra-capacitorElectrolytic capacitor

BatteryElectrolyte

Dielectric

Electroactive material

• 1000M cycles • 95-98% charge efficiency• -40 to 85 oC

• 1M cycles • 99% charge efficiency• -40 to 85 oC

• 10000 cycles • 85-99% charge efficiency• -10 to 60 oC

Batteries: State-of-the-Art • Lead Acid • Nickel–Cadmium• Lithium-ion

• Lithium cobalt oxide LiCoO2 (metal oxide)• Lithium manganese oxide LiMn2O4 (tunneled structure)• Lithium iron-phosphate LiFePO4 (olivine structure)

20

IOXUS super capacitor

21

Batteries

22

• Basic structure• Battery cell• Cell arrangements• Balancing circuits

• Modeling• Life and modeling

• Cycles• Current dependence • Temperature

dependence

• Positive electrode

• Negative electrode (carbon-graphite)

• Electrolyte and separator

Modeling

23

Life Model- Charge capacitace

24

Capacity loss as a function of charge and discharge bandwidth.

Nissan Leaf case https://www.nrel.gov/docs/fy13osti/58550.pdf

http://batteryuniversity.com/learn/article/bu_808b_what_causes_li_ion_to_die

Life model _Impedance Real Part and Aging

25

Battery dimensioning Charge and discharge

Solar –storage relation

27

Peak demand ( other aspect )

Battery Spec TemperatureCharge and Discharge

28

DC LINK

+

-

FilterInverter

Grid

~

Transformer

Battery

DC

DC

DC/DCConverter

Storage Power Conversion @

IN (1C)

Curr

ent p

.u

Temp (oC)

+

-~

DC

AC

DC/AC

-

IACVAC

IDCVDC

Chart1

DisCharge-20-15-10-50510152025303540455011111111111110.80.8Charge-20-15-10-5051015202530354045500.250.250.80.80.80.80.80.80.80.80.25

Sheet1

Units 5000/year (30 amps)USAEuro largeEuro

Power in KW7.26.93.63680

Price w/$$0.114$0.119$0.201

Inductor inverter$70$60

Inductor DCDC10070

Silicon Inverter6060

silicon DCDC6060

heatsink inverter3030

heatsink DC/DC3030

enclosure and fan150120

PC ( driver , voltage sensor)5050

PC microcontroller7070

ATS and connection5050

current sensors 3030

web connection4040

connectors4025

filters and high volatge protection4030

$820$725

Battery Specs TemperatureCharge and Discharge Energy storage

29

+

-~

DC

AC

DC/AC

IAC VACIDCVDC

IDC_ CHARGE = 0.8 P.UIDC_ DISCHARGE=1.0 P.U

+

-~

DC

AC IACVAC

IDCVDC

ACRMSRMSDCDCDC PVIVIP =⋅== .. ηη η

IDC_ DISCHARGEηIDC_ CHARGE = η >0.8

Energy and Power Arrangement

30

3 ampere-hours, 3.2 V 14x16

+

-~

DC

AC

DC/AC

IAC VACIDCVDC

Power= kW

η

Energy = kW/h

Battery system in a nanogrid go from 4kw/h to 16 kW/h

Inverters Fundamentals

Solar Inverter Evolution

* Kouro, S. Leon, J.I. ; Vinnikov, D. ; Franquelo, L.G. “Grid-Connected Photovoltaic Systems: An Overview of Recent Research and Emerging PV Converter Technology” Industrial Electronics Magazine, IEEE Volume:9 , Issue: 1 P:47 - 61 March 2015

LF- Transformer HF-Transformer Transformerless

Safety Parasitic current

32

Bi-directional Inverter ( Voltages based)

33

• Inverter Topology Type (Basic topologies and their advantages and disadvantages)

• Inverter Connection Type• Low-frequency transformer:

• The basic structure consists of one or more H-bridges Single H-bridge, high PWM • Center tap• Multiple H-bridges with interleaving

• The course contains some design examples.• High-frequency transformer

• The isolation is accomplished by high-frequency switching on the DC side using a high-frequency core, traditionally ferrite. Recent developments in low-cost and low-loss materials are challenging ferrite use.

• Topology and Design examples, including inverter and magnetic parts • Use of new semiconductors GaN and SIC

• TransformerlessEliminating the transformer reduces cost and significantly improves efficiency. This course analyzes the topologies that can achieve transformerless operation

Voltages Based Bi-directional inverter

Voltage Based Inverter

LF- Transformer (UPS)

HF-Transformer

Transformerless

Low Frequency Bi-directional inverter

Voltage Inverter

NAfBVRMS .44.4 max=

)()( tdt

Ntv ωΦ∂−=

Φ

Low Frequency Bi-directional inverterinterleaving

V

20kHz

HF Inverter _Hard Switch

High frequency ZCS

Vicor solution

Xiaoyan Yu and Paul Yeaman, “A new high efficiency isolated bidirectional DC-DC converter for DC-bus and battery bank interface

Transformerless Design _Motivation

• Cost reduction with additional weight and size reduction

• Efficiency increase and low cost

Average Parameter Comparisonsfor PV Inverters up to 6.5kW

Transformerless LF-Transformer

HF-Transformer

Avg. Efficiency (%) 95.7 94.5 94.1Avg. Power per Weight (kW/kg) 0.213 0.0753 0.168

Avg. Power per Volume (kW/m3) 115.2 84.7 80.2

EXAMPLE OF TRANSFORMERLESSINVERTER

GRID

500uH

20uf

V

+

_

V

+

_

DC-LinkBattery

11 12 13 14

DC-DC Split phase Inverter

BidirectionalControl 15

INVERTER DEVICE, ENERGY STORAGE SYSTEM AND METHOD OF CONTROLLING AN INVERTER DEVICEPublication number: 20170077836

https://patents.justia.com/patent/20170077836

With interleaving7KW 2- Split phase system 240/120V

2000uf

GRID

500uH

20uf

V

+

_

V

+

_

PRINCIPLE OF OPERATION 3-LEVEL

V2

V2

+

+

-

-

Positive Buck

SW

Negative Buck

on

PWM1

2

3

4

1

3

4

2

V2

+

-

V2

+

-

Positive Buck

Negative Buck

SW

NCP NCP2

Reverse energy transfer

on

PWM1

2

3

4~

+

-

Short circuit the inductor

VL

OFF

PWM1

2

3

4~

+

-

Regenerating Stage Charging the capacitor

VL

DC/DC basic operation

1

2

V

+

-

Discharge Charge

PWM1

2

V

+

-

PWMONOFF

OFF OFF

1

2

V

+

-

PWM

ON

OFF

1

2

V

+

-

PWMOFF

OFF

TRANSFORMERLESS OPERATION

DC LINK

+

-

Filter

Inverter

Grid

~

Transformer

Battery

DC

DC

DC/DCConverter

+

-

L

Para

sitic

cap

acita

nces

L

DC LINK

+

-

FilterInverter

Grid

~

Transformer

Battery DC/DC

Converter

LPa

rasi

tic

capa

cita

nces

(a)

(b)

dA

QVC

AdQdzEV o

o

d εε

==⇒== ∫.

0

A: total area of the plateD: distance between the platesεo: permittivity constant

8.8541× 10−12 F/m

Ground current for 1uF total parasitic capacitance

0

0.2

0.4

0.6

0.8

1

0 0.002 0.004 0.006 0.008 0.01 0.012

Tota

l Par

asitc

Cap

acia

tanc

e (u

F)

Distance beetween the plates d ( mm)

Total Parasitic Capacitance for 100 m2

C P=1uf , F DC= 10kHz F INV=16kHz

1A>0.47A

Evaluation Ground Current UL 1741

DC LINK

+

-

FilterInverter

Grid

~

Transformer

Battery DC/DC

Converter

L

Para

sitic

ca

paci

tanc

es

1mH

C P=10uf , F DC= 10kHz F INV=16kHz

1A

C P=1uf , F DC= 10kHz F INV=16kHz

1A>0.47A

Current Based Bi-directional inverter

DC AC DC AC DC AC

AC-link and bidirectional switches

SOFT SWITCHED HIGH FREQUENCY AC-LINK CONVERTER

ANAND KUMAR BALAKRISHNAN

Inverter tied-grid control

Generalized d,q control

Decoupling

Battery DC BUS Current Control PWM

Modulator Transformation

BAT + PI PI

Lω

Lω

Id

abc

dq

abc

dq

abc

dq

abcαβ

PI0

Grid

ACFilter

BAT

PLL

+ ++Error

+

Id

VDC

+

++++

+--

Inverter

+ +- ++ +

Iq

Vd

Vq

-

Iqref

+

POWER RELATION BETWEEN A BATTERY SYSTEMAND A SINGLE PHASE AC SYSTEM(

DC LINK

+

-

Filter

Inverter

Grid

~

Battery

DC

DC

DC/DCConverter

V DC

IDC(t)

I(t)AC

V(t)AC

200

100%

122%

(%)

(a)

(b)

Inverter Control

Power ACVrms ACIrms AC

I(t)AC Ref

V(t)AC

VDC(t)Battery

P(t)AC

VDC(t)Link

IDC(t)Battery

Power ACVrms ACIrms AC

I(t)AC Ref

VBattery

P(t)AC

VDCLink

Ibatt_ref

V(t)AC-

+

I(t)ACPIPWM

+

PI

PWMIBattery

-(b)(a)

Stand Alone

GUI

GUI and Weather Prediction

Energy Storage Prices • 10,000 cycles and/or 10 years, 80% charge

DC Battery PackAC System

http://eupd-research.com/59

Nanogrid-Energy Storage: Why Now?

Renewables Intermittence (generate “the need”)Price (large price reduction)Regulation (zero export to the grid)Tariffs (peak demand) Weather Prediction via Internet Power grid reliability and safety Smart Grid

Technology Conversion

To Availability and Affordability

60

Thanks! Questions?

61

Residential Battery Storage: �The cornerstone of the Nanogrid and distributed power systemsPower System Centralized vs. Distributed Distributed Paradigm Shift - RenewablesMinimum-cost of Electrification �Electrification Model (REM) �Nanogrid Operation Mode Power Quality Issues (Back up Mode) Residential Nanogrid �DC-AC Basic DC and AC Nanogrids: �Solar and Energy StorageDC Residential Nanogrid DC Residential Nanogrid- Control AC Residential NanogridLoad Handling and Criticality Droop AC control ( Inverter) Droop AC control Universal Droop Control of InvertersFundamentals�Back up battery storageEnergy Storage (Why Battery & Capacitor?)Time responses Fast Energy Storage Batteries: State-of-the-Art IOXUS super capacitor BatteriesModelingLife Model- Charge capacitace Life model _Impedance �Real Part and AgingBattery dimensioning �Charge and discharge Solar –storage relation Battery Spec Temperature�Charge and DischargeBattery Specs Temperature�Charge and Discharge Energy storageEnergy and Power Arrangement Inverters Fundamentals Solar Inverter EvolutionBi-directional Inverter ( Voltages based) Voltages Based Bi-directional inverter Low Frequency Bi-directional inverter Low Frequency Bi-directional inverter�interleavingHF Inverter _Hard Switch High frequency ZCSVicor solutionTransformerless Design _Motivation Average Parameter Comparisons� for PV Inverters up to 6.5kW�Example of Transformerless�Inverter With interleavingPrinciple of Operation 3-LevelReverse energy transfer �DC/DC basic operation Transformerless Operation Ground current for 1uF total parasitic capacitance Evaluation Ground Current UL 1741 Current Based Bi-directional inverter AC-link and bidirectional switchesInverter tied-grid controlGeneralized d,q controlPower relation between a battery system and a single phase AC system�Inverter ControlStand AloneGUIGUI and Weather Prediction Energy Storage Prices Nanogrid-Energy Storage: Why Now?Thanks! Questions?