Residential Battery Storage: The cornerstone of the Nanogrid and distributed power systems

Antonio Ginart Santa Clara, California

1 Power System Centralized vs. Distributed

Nuclear plant

Nanogrid <100 kW Power coal plant Hydro plant Residential <25 kW High Voltages

Power plant City P Power plant Distributed o Distribution <69kV Rural Power plant

w Microgrid e r Industry

Industry Solar Farm Centralized Distributed V V Wind Farm City Rural Rural City 2 Distributed Paradigm Shift - Renewables

Disadvantages Advantages More complex technologies Potential for better local resource use More expensive in many cases Consumers have greater independence Less centralized control Environmentally friendlier Potential for a less reliable grid Potential for a more robust and Need of new technology and reliable grid (non-single collapse point) regulations Cybersecurity Potential for greater power Natural disaster quality issues Potential for more economically sound macro-analysis

3 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

4 MIT News (January 2016) Nanogrid Operation Mode

Tariff • Zero export • Peak demand Power Grid-Tied • Sell/Buy price Quality Flicker Transfer Back-up • Frequency Sag Switch • Voltage Islanding Swell Reliability Fast P P Low o o cost Power PG= Pload w Independence w • Load e Control e Criticality r Stability r Load sink Solar • Volt. Freq. Load Autonomy: • Droop Germany 60% dumping USA 100% Control Load Fixed voltage and frequency Generation 5 Power Quality Issues (Back up Mode)

Voltage Voltage swell

Voltage sag ½ cycle 1 cycle 3600 cycles >3600 cycles 8.3ms 16.6ms 60 s > 60 s Transients 1 Sag and swell 2 Clipped current 3 Noise 100A peak 4 Harmonics 5 Under and over Voltages

The standard IEEE 1100 Line voltages under A/C 5 TON system start up • Short term voltage variations (sag ,swell, and transients) • Long term voltage variations (over and under voltages , harmonics and noise)

6 Residential Nanogrid DC-AC DC Nanogrid AC Nanogrid • 12V- 400V • Advantages • Advantages • Required no additional investment • More efficient • Easy retrofit • Easy control, stable Disadvantages • Disadvantages • • Control and stability are • Large investment required more difficult • Difficult interruption • Region dependent (protection, fire) • 200-230V 50Hz • 120/240V 60 Hz US

7 Basic DC and AC Nanogrids: Solar and Energy Storage

DC Nanogrid AC Nanogrid

Bi-directional AC DC AC G DC AC DC G R AC Inverter R PV panel I PV panel Inverter Bi-directional I D Bi-directional D AC

DC DC

DC Batteries Inverter Batteries

8 DC Residential Nanogrid

Bi-directional

AC

DC G

DC 380V DC Wind DC R Inverter I DC D DC PV pannel Bi-directional Generator

DCDC DC 380V DC DCDC DC Batteries DCDCAC Bi-directional

DCDC DC E or H car

9 DC Residential Nanogrid- Control

Droop Voltage Control

MPPT DC Bus

DC P1 P o DC Co1 w Renewable e P1 r DCDCDCDC

DCDCAC Non-Renewable Co1 Load Source 1 A B V0 State 1 V1 State 2 V Control Example 2 Overload Bus VoltagesBus PL1 Schönberger, J., Duke, R. and Round, S.D., 2006. DC-bus signaling: A distributed control strategy for a hybrid PS PL2 1 renewable nanogrid. Industrial Electronics, IEEE Transactions on, 53(5), pp.1453-1460. PL1

Constant Voltage Constant Power

Current 10 AC Residential Nanogrid

Energy Renewable Generators Generators Storage @ Grid Solar Wind Diesel Master ~ Control Gas Controller  Droop Control Stirling  Voltages and Frequency

Transfer DC AC switch

Dryer Washer TV Computer Range Water A/C Lighting Fridge Heater Unit Residential Load 11 Load Handling and Criticality

- Critical Loads + @ Z-Waves

Master Controller

v

Dump Dryer Washer TV Range Microwave Water A/C Lighting Load Heater Fridge Unit

Residential Load

12 Droop AC control ( Inverter)

Inverter Impedance

DC/DC Battery / solar Converter DC LINK Filter Inverter + DC

- DC ~ The Bode plots of the output impedance of Inverters = L-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).

13 Droop AC control

Assuming δ∼0 and Inductive ω* * ω ω − 2 i ~ ni Pi EV0 EV V P ~ δ Q ~ 0 − 0 Z0 Z0 Z0 Pi * Pi E* P ~ δ Q ~ E * Ei ~ E − niQi

Q*i Qi

14 Universal Droop Control of Inverters Droop controllers for L-, R-, C-, RL-, and RC-inverters.

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

15 Fundamentals Back up battery storage Energy Storage (Why Battery & Capacitor?) Storage Power Conversion DC/DC @ Converter DC LINK Air Compressor Battery Inverter Transformer + DC Filter Hydraulics Grid

Thermal (Molten Salt) - DC ~ Inertia Wheels Magnetics Dynamic Power Compensation Capacitor (Super) (very fast – few milliseconds) Battery Sized according its nanogrid Flow Batteries Able to regulate the nanogrid Weather prediction via internet

17 Time responses Power Power Intermittent

DC Bus Battery AIR

Generators

18 Fast Energy Storage

Ultra-capacitor Electrolytic Battery Electrolyte capacitor Dielectric

Electroactive material • 1000M cycles • 1M cycles • 10000 cycles • 95-98% charge efficiency • 99% charge efficiency • 85-99% charge efficiency • -40 to 85 oC • -40 to 85 oC • -10 to 60 oC

19 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 • Positive electrode • Negative electrode (carbon-graphite) • Electrolyte and separator • Basic structure • Battery cell • Cell arrangements • Balancing circuits • Modeling • Life and modeling • Cycles • Current dependence • Temperature dependence 22 Modeling

23 Life Model- Charge capacitace

Capacity loss as a function of charge and discharge bandwidth.

Nissan Leaf case https://www.nrel.gov/docs/fy13osti/58550.pdf 24 Life model _Impedance Real Part and Aging

25 Battery dimensioning Charge and discharge Solar –storage relation

Peak demand ( other aspect )

27 Battery Spec Temperature Charge and Discharge

I (1C) N Storage Power Conversion DC/DC DC LINK @ Battery Converter Inverter Transformer p.u + DC Filter Grid Current - DC ~

Temp (oC) DC/AC

+ AC IDC IAC VDC - ~ VAC - DC

28 Battery Specs Temperature Charge and Discharge Energy storage

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

DC/AC

+ AC + AC I I IAC IDC AC V DC VDC V DC AC ~ VAC ~ - - DC DC η η

PDC = I DC .VDC =η ⋅ I RMS .VRMS = PAC

I = η I DC_ CHARGE DC_ DISCHARGE η >0.8

29 Energy and Power Arrangement

3 ampere-hours, 3.2 V 14x16

Energy = kW/h

Power= kW

DC/AC

+ AC I I V DC AC DC ~ VAC - DC η

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

30 Inverters Fundamentals Solar Inverter Evolution

 LF- Transformer  HF-Transformer  Transformerless  Safety  Parasitic current

* 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 32 Bi-directional Inverter ( Voltages based)

• 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 • Transformerless Eliminating the transformer reduces cost and significantly improves efficiency. This course analyzes the topologies that can achieve transformerless operation 33 Voltages Based Bi-directional inverter

Voltage Based Inverter

 LF- Transformer (UPS)

 HF-Transformer

 Transformerless Low Frequency Bi-directional inverter

Φ Voltage Inverter

∂ v(t) = −N Φ(ωt) dt

VRMS = 4.44 fBmax A.N Low Frequency Bi-directional inverter interleaving

20kHz

V 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 Comparisons for PV Inverters up to 6.5kW

Transformerless LF- HF- Transformer Transformer Avg. Efficiency (%) 95.7 94.5 94.1 Avg. 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 TRANSFORMERLESS INVERTER

Battery DC-DC DC-Link Split phase Inverter

1 2 31 1 1 41

500uH + G V R _ I + D V _ 20uf

Bidirectional 5 Control 1 INVERTER DEVICE, ENERGY STORAGE SYSTEM AND METHOD OF CONTROLLING AN INVERTER DEVICE Publication number: 20170077836 With interleaving

7KW 2- Split phase system 240/120V

2000uf

500uH + G V R _ I + D V _ 20uf PRINCIPLE OF OPERATION 3-LEVEL

Positive Buck Positive Buck 1 + 1 + PWM V V 2 2 3 - - 4

SW SW 3 + + on 4 V V 2 2 2 2 - Negative Buck - Negative Buck

NCP NCP2 Reverse energy transfer

1 1 PWM PWM

Short circuit Regenerating Stage the inductor Charging the capacitor

3 VL 3 VL

on + + 4 OFF 4

2 ~ 2 ~ - - DC/DC basic operation

Charge Discharge

1 1OFF 1 1OFF PWM ON PWM PWM PWM OFF

+ + + +

V V V V ON OFF OFF OFF - - - - 2 2 2 2 TRANSFORMERLESS OPERATION

d Q.d V ε A V = Edz = ⇒ C = = o ∫0 ε o A Q d

Battery DC/DC DC LINK L Converter Inverter

+ DC Transformer Filter A: total area of the plate Grid - D: distance between the plates + εo: permittivity constant

8.8541× 10−12 F/m capacitances Parasitic DC ~ - L

(a) Converter Inverter Filter Transformer DC/DC DC LINK Grid Battery L

+

Parasitic Parasitic ~ - capacitances capacitances

(b) Ground current for 1uF total parasitic capacitance

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

Total Parasitic Capacitance for 100 m2 1

0.8 1A>0.47A

0.6

0.4

0.2

0 0 0.002 0.004 0.006 0.008 0.01 0.012

Total Parasitc Capaciatance (uF) Capaciatance Parasitc Total Distance beetween the plates d ( mm) Evaluation Ground Current UL 1741

Inverter 1mH Converter Filter Transformer DC/DC DC LINK Grid Battery L

+ ~ Parasitic

capacitances capacitances -

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

1A 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

PWM Current Control Transformation Battery DC BUS Modulator BAT

V αβ DC abc + BAT - PI + + PI + + + ++ abc Error + - - Inverter Id Lω dq Decoupling Id dq Lω Iq + abc AC I 0 + PI + + qref + - + + PLL Filter +V d dq

Vq abc Grid POWER RELATION BETWEEN A BATTERY SYSTEM AND A SINGLE( PHASE AC SYSTEM

Battery DC/DC DC LINK IDC(t) Converter Inverter DC + Filter Grid I(t)AC

- V DC V(t)AC DC ~

(a) 200

122%

(%) 100%

(b) Inverter Control

V(t)AC

Power AC Vrms IDC(t)Battery AC I(t)AC Ref P(t)AC

Irms AC I(t)AC VBattery - PWM VDCLink PWM PI I V(t)AC Battery PI +

V (t) V (t) Power AC DC Battery DC Link - + (a) Vrms AC Ibatt_ref (b) P(t)AC I(t)AC Ref Irms AC Stand Alone GUI GUI and Weather Prediction Energy Storage Prices

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

AC System DC Battery Pack

59 http://eupd-research.com/ Nanogrid-Energy Storage: Why Now?

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

60 Thanks! Questions?

61