Photovoltaic Power Conversion Systems - IEEE · PDF filePhotovoltaic Power Conversion Systems Jih-Sheng (Jason) ... • PV industry generates $93B global revenues with ... DC-DC Converter

JSL1

Photovoltaic Power Conversion Systems

Jih-Sheng (Jason) Lai, Ph.D.James S. Tucker Professor

Virginia Polytechnic Institute and State UniversityFuture Energy Electronics Center

106 Plantation RoadBlacksburg, VA 24061

Presentation at

IEEE Virginia Mountain SectionBlacksburg, Virginia

January 31, 2013

JSL2

Outline

1. PV Market Outlook and Cost Targets2. PV Cell Characteristics and Maximum Power

Point Tracking 3. Energy Production Comparison for Different

PV System Architectures4. Commercial PV Power Conversion Circuits

and Efficiency Profiles 5. Future Trends

JSL3

Outline – Part 1

1. PV Market Outlook and Cost Targets2. PV Cell Characteristics and Maximum

Power Point Tracking 3. Energy Production Comparison for Different



JSL4

PV Market Outlook

(GW)• PV market continues growing especially in Asia;

China grew 470% in 2011; US looks to 3GW in 2012• PV industry generates $93B global revenues with

27.4GW installation in 2011 (~$3/W)

20132012

JSL5

Desertec 2050

• MENA desert power can supply around two-thirds of the region’s rising energy demand and 17 percent of EU consumption.

• In 2009, DESERTEC Foundation was founded with financial plan to 2050 • Invest in renewable energy and interconnected grids in EU-MENA• Tunisia started 2-GW CSP in 2011 and scheduled to deliver power in 2016

“Within 6 hours deserts receive more energy from the sun than humankind consumes within a year.”Dr. Gerhard Knies

JSL6

PV System Cost TargetsUS SunShot Initiative (Feb. 2012)

• 75% solar system cost reduction through – Reducing solar technology costs– Reducing grid integration costs – Accelerating solar deployment

• By 2020, cost targets are: – $1/W for utility-scale PV systems – $1.25/W for commercial rooftop PV – $1.50/W for residential rooftop PV

• Inverter cost targets: – $0.10/W for utility-scale systems – $0.11/W for commercial systems – $0.12/W for residential systems

JSL7

Power Electronics Cost Reduction• Solving fundamental power electronics problems at the

component level.• Reducing the cost of advanced components (SiC, GaN). • Addressing reliability failures due to thermal cycling of

materials.• Developing technologies that allow high penetrations of

solar technologies onto grid (VAR control, storage). • Developing PV system technologies that reduce overall

Balance of System costs (high-voltage systems). • Developing technologies that harvest more energy from

sun (MPPT and micro-inverters). • Integrating micro-inverters into modules, reducing

installation effort and achieving further cost reductions through mass production.

JSL8

Outline – Part 2





JSL9

State-of-the-Art Solar PV Technologies

Cell Type *Best Reported Efficiency

Comments

SiliconMono crystalline Poly crystalline

25.0%27.6%

• Conventional technologies • Cost became competitive with Asian manufacturing

Thin FilmsAmorphous SiCadmium Telluride (CdTe)Cadmium Indium gallium diselenide (CIGS)

Nano‐Silicon

12.5%16.7%20.0%

16.7%

• Used in everything, from solar watches to solar shingles to megawatt

• Ink jet printing cost down will challenge Si

Concentrating PV (CPV) 41.6% • Need solar concentrators• Too expensive in near term

Organic and dye sensitized

11.1% Powering portable electronics

* Efficiency data referred to J. Milliken, “Solar Energy Technologies Program Overview,” Apr. 2010, NREL

JSL10

PV Cell V-I Characteristics Representation

Isc +

–D

ID

VVD

+

–

I

ID

V+

–

ID-V curve

V

I-V curveID-V curve

I-V curve

ID

–Isc

I

V V

Derivation of I-V CurveI = Isc – ID

Flip current direction V-I Curve

ID Isc

JSL11

0

10

20

30

40

50

60

70

0 0.1 0.2 0.3 0.4 0.5 0.6

Solar Cell V-I Characteristics as a Function of Temperature

Out

put C

urre

nt (m

A)

Output voltage (V)

Hot

Cold

Maximum power point (MPP)

Isc change +0.04%/°K

Voc change –0.34%/°K

JSL12

Typical Solar Cell V-I Characteristics

0

10

20

30

40

50

60

70

0 0.1 0.2 0.3 0.4 0.5 0.6

Out

put C

urre

nt (m

A)

Output voltage (V)

Maximum power point

Illumination level (125 mW/cm2)

100 mW/cm2

JSL13

Solar Spectrum: Atmosphere Influence

Air mass definition: AMx = Ax/A1 = 1/cos ()

2

1

hsAM

h

s

AM1 means = 0AM1.5 means = 48.2°

JSL14

Example PV Panel Specifications Kyocera KD180GX-LP

Dimension: 1341mm x 990mm x 36mm (52.8in x 39.0in x 1.4in)Weight: 16.5 kg (36.4 lbs)

48 cells

JSL15

Manufacturer’s Datasheet Kyocera KD180GX-LP

(b) Irradiance effect

0 10 20 30Voltage (V)

9

8

7

6

5

4

3

2

1

0

Cur

rent

(A)

1000W/m2

800W/m2

600W/m2

400W/m2

200W/m2

At 25°C9

8

7

6

5

4

3

2

1

00 10 20 30

Voltage (V)

Cur

rent

(A)

75°C

25°C

50°C

(a) Temperature effect

At 1000W/m2

JSL16

Four-Quadrant Photovoltaic Cell Characteristics

• PV cell may operate in different quadrants: Q1, Q2, Q4.

• Q1 is normal operating zone. Cell is generating power.

• Q2 has reverse cell voltage, may appear in series-connected cells. Cell is dissipating power.

• Q4 has reverse cell current, may appear in parallel-connected cells. Cell is dissipating power.

Isc +

–D

ID

VVD

+

–

I

V

I

Q1Q2

Q4

+

–

+

–

+

–

JSL17

Series String PV Cell Under Shaded Condition

V

I 2 non-shaded cells

1 shaded cell

Io

–Vc Va+VbVBD

Potential hot spot or failure when Vc > VBD

Io

Vo

+

–

Va

Vb

Vc

cbao VVVV

DC-DCConverter

orDC-ACInverter

V

I 2 non-shaded cells

1 shaded cell

Io

Vdiode Va+VbVBD

Io

Vo

+

–

Va

Vb

Vc

DC-DCConverter

orDC-ACInverter

Adding anti-paralleled diode avoids failure

JSL18

Bypass Diodes in a Typical PV Panel

• A PV panel typically consists of 48 to 72 cells with 3 bypass diodes.

• A bypass diode covers 16 to 24 cells.

• For 24 cells case, if each cell voltage is 0.5V, and diode voltage drop is 0.6V, then the worst case shaded cell reverse voltage = 240.5+0.6 = 12.6 V (< breakdown voltage)

Junction box +–

JSL19

Bypass Diode Power Dissipation

Junction box +–

Assume Io = 8A. Diode dissipations:

• Si diode: 0.7V8A = 5.6W • Schottky diode:

0.4V8A = 3.2W • Active diode (synchronous

rectification): (8A)2(5m) = 0.32W

Io

JSL20

Lightning Impact

vDiDilt

MvDiDilt

M

dtdiMv lt

D

ltD iL

kMi

Case a: • Bypass diode

stressed in forward direction

• High forward current (~kA) may destroy diode

Case b: • Bypass diode

stressed in reverse direction

• High induced voltage may exceed diode breakdown voltage VBD and result in over-voltage failure

k: frame reduction factor (0.1-0.5)

M: mutual inductance (20-100 nH)

L: loop inductance of each string (1-3 µH)

JSL21

Lightning Catastrophic Failure Case

–

+

Inverter

• Normally, PVs are protected with metal oxide varistor (MOV), i.e., RGND = 0, VPV = VMOV, but when the ground wire is broken, lightning surge can conduct through parasitic capacitors, i.e., RGND = , VPV = kVsurge, k<1.

• Photos show a catastrophic failure when ground wires were stolen in a MW PV farm installation. All cells were shattered, and diodes were broken.

VPV

JSL22

Maximum Power Point of a PV Cell

• Typically, Isc 1.05 to 1.15 IMPP, VMPP 0.8Voc• Defining fill factor (FF)• Typical fill factors are:

– C-Si: 0.75 ~ 0.85– A-Si: 0.5 ~ 0.7

scoc

MPPMPP

scoc

MPP

IVIV

IVPFF

Maximum Power Point (MPP)

JSL23

Multiple Peaks Due to Shading Effect with 3-Bypass Diode Configuration

0

20

40

60

80

100

120

0 4 8 12 16 20 24

012345678

0 4 8 12 16 20 24

partial shaded condition

Pow

er (W

)

Voltage (V)

Cur

rent

(A)

partial shaded condition

full-sun condition

full-sun condition

Shading condition:• Modules a & b: full-sun

condition• Module c: shaded

condition

12-cells in series

a

b

c

V

I

JSL24

Case with Mismatched Panels and Different Irradiation Levels Among Them

Two different types of PV panels in series with different irradiation levels among them can result in multiple MPPs

0 50 100 150 200 250 300 350 4000

200

400

600

800

1000

1200

Voltage(V)

Pow

er(W

)

Voltage--PowerMPP

187.6V 252V 329V

JSL25

Maximum Power Point Tracking (MPPT)

• MPP control is required to harness as much energy as possible.

• Poor MPPT method is equivalent to having additional loss.• Important MPPT design considerations:

– Tracking speed – Control loop stability – Oscillation around MPP including double line frequency oscillation – Global MPP versus local MPP – Which stage performs MPPT, DC-DC stage or DC-AC stage? – Control of VPV or IPV? – Step size? – Digital versus analog

• Almost 20 distinct published methods, ranging from ripple correlation control (a fast method that uses converter ripple to find the MPP) to fuzzy logic controls.

JSL26

Fractional Open-Circuit Voltage• For most PV cell types,

there is a nearly linear relationship between VMPPand VOC, VMPP xVoc

• x depends on PV material, typically 0.74 to 0.8 Voc

• Measure VOC at infrequent intervals, then use the known fraction as the basis for control

• Only an approximation →operation practically never exactly at the MPP

Simple, low cost, fast, and robust

Poor accuracy, lost power during Voc measurement

Cur

rent

(A)

Voltage (V)

10

9

8

00

1

2

3

4

5

7

6

80

20

2

40

4

60

6 1210

Pow

er (W

)

JSL27

Hill-Climbing/Perturb & Observe Methods

• Alter the operating point, by changing a duty ratio slightly.• Check whether the power rises or falls.• Keep changing to get higher power.

Perturbation Change in Power Next PerturbationPositive Positive PositivePositive Negative NegativeNegative Positive NegativeNegative Negative Positive

Key Features• Clear and effective.• Convergence depends on perturbation step size and converter

settling times.• Goes to a local maximum power point.

JSL28

Outline – Part 3


Point Tracking3. Energy Production Comparison for Different



JSL29

Different PCS Architectures

Centralized DC/AC with distributed

series strings

Centralized DC/AC with distributed

series strings+ DC/DC

Centralized DC/AC with

SeriesDC modulesDistributed

series strings+ DC/AC

~MW ~kW DC/DC 100’s W DC/AC ~kW

~100’s W

DistributedAC modules

Centralized DC/AC with Paralleled

DC modules

1 2 3 4 5 6

JSL30

Panel Level Power Electronics Becomes More Popular Choices

DC-AC

(a) String inverter 3‐12kW (e.g. SunnyBoy)

(b) Microinverter 190‐240W (e.g. Enphase)

DC-AC

DC-AC

(c) Series DC‐DC power optimizer (e.g. SolarMagicTM)

DC-AC

(d) Paralleled DC‐DC power optimizer (e.g. VT IntelliSOLARTM)

JSL31

Power Output Comparison with and without Power Optimizer Under Shaded Condition

5s

4A

300V

VPV

IPV

(a) Without SolarMagicTMshaded

DC-AC

4A

5s

300V

VPV

IPV

(b) With SolarMagicTMshaded

DC-AC

DC-DC

Using SolarMagicTM as power optimizer for series connected panelsa) Without SolarMagicTM, the PV inverter output power drops from 1300W to

60W (95% reduction)b) With SolarMagicTM, the PV inverter output power drops from 1450W to

1200W (17% reduction)

JSL32

VT Solar House PCS Configured with SunnyBoy, SolarMagicTM, and Enphase Inverters

AC Grid Configuration

• For each SolarMagic or Enphase, input peak voltage is 40V

• Each PCS branch consists of 26 PV panels with 1.95kW peak power feeding into a “mini micro grid”

• SunnyBoy input peak voltage is 520V

A Mini Micro‐Grid (AC Nano Grid)

https://cosm.com/feeds/16184

JSL33

VT IntelliSOLAR PCS ConfigurationDC Grid Configuration

VT soft‐sw. inverter

(>99% eff.)

VT IBR converter (>97% eff.)

A DC Micro‐Grid 400V DC Bus


• Paralleled power optimizers for individual panels • High overall system efficiency (>96%) with VT

integrated boost resonant (IBR) converter and soft‐switching inverter

• No aluminum electrolytic capacitors; no cooling fans • DC micro‐grid architecture with arc detection and

protection at local PV panels• Potentially low cost with more integration


Front view of PV panels

Other DC sources

Back view of PV panels

3kW PV source

2kW other DC sources

Weather tight connections

DC link cable

VT FEEC building

5kW inverter240VAC

Idc iac

JSL34

PCS Power Outputs and Irradiance LevelUn-shaded Case – March 17, 2011

0400800120016002000

0 2 4 6 8 10 12 14 16 18 20 22 24

Microinverter

0400800120016002000

0 2 4 6 8 10 12 14 16 18 20 22 24

Centralized inverter

02004006008001000

0 2 4 6 8 10 12 14 16 18 20 22 24

Irradiance

11.78kWh

11.77kWh

Hour

W/m

2P

o(W

)P

o(W

)

March 17, 2011

Late start

• PCS outputs well associate with the irradiance level• Without much shading, centralized inverter may produce more

energy than microinverter does even with late start in the morning

JSL35

Comparison of Energy Production under Un-Shaded Condition for a Two-Month Period

0

50

100

150

200

250

300

350

400

450

500

0 10 20 30 40 50 60 day

Energy produ

ction (kWh)

Enphase: 482 kWh

Sunnyboy: 481 kWh

SolarMagic: 469 kWh

4/1/2011 – 5/31/2011

• With the same 95.5% CEC efficiency, string inverter produces almost the same amount of energy as microinverter does over a two‐month period.

• Adding SolarMagicTM power optimizer does not improve the energy output because the solar house is in a wide open area.

JSL36

PCS Power Outputs and Irradiance LevelManually Shaded Case – June 21, 2011

040080012001600

0 2 4 6 8 10 12 14 16 18 20 22 24

Microinverter

040080012001600

0 2 4 6 8 10 12 14 16 18 20 22 24

Centralized inverter

02004006008001000

0 2 4 6 8 10 12 14 16 18 20 22 24

Irradiance

Hour

8.95 kWh / 11 kWh (19.2% reduction)

9.73kWh / 11 kWh (11.5% reduction)

3 out of 26 panels were covered

• Significant power/energy output reduction on centralized inverter case.

JSL37

Comparison of Energy Production under Partial Shaded Condition for a Two-Month Period

0

50

100

150

200

250

300

350

400

450

500

0 10 20 30 40 50 60

Energy produ

ction (kWh)

Enphase: 514 kWhSolarMagic: 470 kWh Sunnyboy: 449 kWh

day

6/1/2011 – 7/31/2011

• Cumulated energy production over a two‐month period further verifies the partial shading impact to the centralized inverter

JSL38

Outline – Part 4





JSL39

Inverter Efficiency Standards• California Energy Commission (CEC)

– All inverters must meet the requirements in Emerging RenewablesProgram, Final Guidebook, Eighth Edition, Section C Inverters.

– There are no set minimum requirements, but the conversion efficiency must be tested and reported to CEC –as defined here.

• IEC 61683:1999, First Edition, 1999-11, Photovoltaic systems –Power conditioners – Procedures for measuring efficiency. – This standard describes guidelines for measuring the efficiency of

power conditioners used in standalone and utility interactive photovoltaic systems, where the output of the power conditioner is a stable ac voltage of constant frequency or a stable dc voltage. The efficiency is calculated from a direct measurement of input ad output power in the factory. An isolation transformer is included where it is applicable.

• China: GB/T 20514-2006 Photovoltaic systems – Power conditioners – Procedure for measuring efficiency. – Based on IEC 61683:1999.

JSL40

CEC and IEC Weighted Efficiency Measurement

CEC IEC

5% 0 0.03

10% 0.04 0.06

20% 0.05 0.13

30% 0.12 0.10

50% 0.21 0.48

75% 0.53 0

100% 0.05 0.20

JSL41

CEC Efficiency Evaluation for a 200-W PV Inverter Sample #5Sample #4Sample #3Sample #2Sample #1Specified

Eff.Input voltage

Output powerEff.Input

voltageOutput powerEff.Input



voltageOutput power

Input voltage

Output power

95.71349.16620195.70649.16120195.7349.15920195.70249.16220195.68949.166200.95100%

95.9149.253157.695.90349.251157.695.91449.248157.695.89549.247157.695.9149.247157.675%

95.79849.278114.495.77849.275114.495.78849.283114.495.80249.278114.495.79349.28114.450%

95.52649.24667.3195.46449.23467.2695.46749.23767.2695.52549.23867.395.51749.2467.30530%

95.21649.12243.7295.21549.1143.7295.16749.10843.795.22249.13143.7395.20649.11743.72320%

94.41649.32120.394.40549.30920.2994.41949.3120.394.46649.29920.3194.08349.33520.226Vmax10%

95.43640.208200.995.43840.212200.995.44940.20120195.46140.21820195.42840.214200.93100%

95.8540.326148.595.8440.321148.595.82640.32148.595.81940.327148.595.84740.324148.575%

95.90340.347114.195.91240.348114.195.88340.347114.195.89540.347114.195.89140.348114.0650%

95.55540.14766.7295.5440.14566.7195.56840.14466.7395.54740.14166.7195.60240.14466.75130%

95.25940.31545.0895.26940.31645.0895.30340.29745.195.26740.30345.0895.26740.31345.08820%

94.17540.151994.16140.1561994.17340.1181994.18640.151994.18240.14219.004Vnom10%

94.80231.263202.694.82831.273202.694.79131.269202.594.83331.275202.694.83131.275202.65100%

95.49231.118148.495.50431.118148.495.47431.114148.495.49731.117148.495.49331.116148.4175%

95.79131.13310595.76331.138104.995.78831.13710595.79531.14510595.78631.151104.9550%

95.46331.12866.5195.44331.12766.595.44231.12466.4995.47431.12966.5295.43531.1366.4930%

95.30931.29144.2195.30831.2744.2195.31431.28144.2195.26231.28744.1995.30831.27344.21420%

94.00831.29219.294.02131.2419.294.02231.29219.294.00631.26819.294.02731.26319.201Vmin10%

(%)(Vdc)(W)(%)(Vdc)(W)(%)(Vdc)(W)(%)(Vdc)(W)(%)(Vdc)(W)(Vdc)(% of rated)

JSL42

CEC Efficiency Evaluation Report for a 200-W Microinverter

CEC Efficiency

Vmin: 95.4% Vnom: 95.7% Vmax: 95.7%

Average: 95.6%9192939495969798

0% 20% 40% 60% 80% 100%Percent output power

Effi

cien

cy (%

)

Vnom = 40.5 V

Vmin = 31 V

Vmax = 50 V

• Minimum 5 samples are needed for efficiency evaluation. • Efficiencies need to be measured at different input voltages and

different load conditions. The final reported CEC efficiency is the average of CEC efficiencies at three voltages.

JSL43

A Grid-Tie Solar Power Conversion System

AC/DCVPV

+

–

HFPWM

DC/AC

HFXformer HF

SPWMDC/AC

VacVdc

VPV

IPV

DC-AC inverter with AC filtering (Low frequency)

PV source

Utility grid

DC-DC converter with isolation (Low to High voltage DC)

JSL44

Isolated Single- v.s. Two-Stage Configurations

(a) Single PWM stage type, no high voltage energy storage

(b) Two‐PWM stage type, with high voltage DC bus and energy storage

AC/DCRectifier

HFSPWMDC/AC

Vac

Vdc

Vin

+

–

HFPWMDC/AC

HighFreq.

Xformer

AC/DCRectifier

Vin

+

–

HFPWMDC/AC

HighFreq.

Xformer LFunfolding

DC/AC

Vac

• Single PWM stage is generally more efficient, but requires largestorage capacitor at the input to stabilize MPPT

• Two PWM stages mean more costly components and higher switching loss, but the system allows high voltage DC bus to absorb 120Hz ripple and thus eliminating electrolytic capacitor

JSL45

Switching with Hybrid Line and PWM Frequencies

S1

S2

S3

S4

S4

S1

S2

S3

vo

Features:• Line frequency switching for bottom or top switches (IGBT as the

switching device) • PWM switching for top switching (MOSFET as the switching

device)• Ultra fast reverse recovery diodes can be used for freewheeling • Potential high efficiency • Less shoot-through concerns• Ground loop leakage current is an issue with unipolar PWM

JSL46

Ground Loop Leakage Current Issues• With thin-film PV getting more popular, the parasitic

capacitance between PV and ground also draws more attention due to the increase of the ground loop leakage current.

• Different inverter modulation methods may produce the same output load current, but they may see different output common mode voltage against the neutral and ground, and thus producing different ground loop leakage current.

• The ground loop leakage current may be alleviated by providing circuit isolation, modulation methods, or different circuit topologies.

JSL47

Non-isolated H5TM Inverter – Avoid Leakage Current with Unipolar Switching (SMA 8000TL)

Basic Operation:• S3 and S5 operates in SPWM on negative cycle• S4 and S5 operates in SPWM on positive cycle• Complementary PWM at the input No

leakage current • IGBT’s S1 and S2 serve as low frequency

selection network• S6 is for over-voltage protection

208 VAC output8 kWPower

98.0 %CEC efficiency98.3 %Max. efficiency345 VNominal voltage

300–480VPV voltage range

JSL48

Full-Bridge Inverter with Low-Frequency Transformer Isolation (SMA 5000US)

• Inverter uses a full-bridge IGBT module • Transformer contains leakage

inductance to serve as differential mode inductance

• Reasonable efficiency • Very bulky and heavy (150 lbs for a 5-

kW inverter)

PV array

Transformer with leakage inductance

30’s

240 VAC output5 kWPower

95.5%CEC efficiency96.4%Max. efficiency310 VNominal voltage

250–480VPV voltage range

JSL49

A Microinverter with Two-stage Power Conversion

Push-pull DC-DC

Features:• Two power stages, two PWM stages • Push-pull stage converts the input voltage

to around 230V (26 kHz)• Inverter uses fast reverse recovery diodes

and IGBTs (30 kHz) • Low THD• Relatively low efficiency

VPV

vac

120 VAC output voltage212 WPower

94.5 %CEC efficiency95.3 %Max. efficiency50 VNominal voltage

36–55 VPV voltage range

Full-bridge DC-AC

Exeltech

JSL50

Active-Snubber Flyback Microinverter

Q3

D2

D1

Sx2 S2

S1Sx1

Q1

Q2 Q4Q5

Basic Operation:• Interleaved flyback converters serve as single-stage power conversion. Sx1 and

Sx2 are auxiliary switches for active snubber. • Q1, Q2, Q3, and Q4 thyristors serve as polarity selection switches. • Q5 helps commutate thyristors under low dc bus voltage condition.Key Design Features:• Single-stage power conversion, good overall efficiency• Good waveform fidelity, low THD • Burst mode operation at load below 30% of rated power• Concern on the life span of electrolytic capacitors

190 WPower

95 %CEC efficiency95.4 %Max. efficiency32.5 VNominal voltage

22–40 VPV voltage range

Enphase

JSL51

Highly Efficient and Reliable Concept (Heric) Inverter

Vdc

LoRo

S1

S2 S4S5

S6

IoIS1

IS3

S3

IS2

IS4

a b

• Unipolar operation to reduce current ripple. • Main switches (S1 ~ S4) operate in switching frequencies• Auxiliary switches (S5 and S6) with fast reverse recovery diodes operate

in low-frequency to serve as the freewheeling path to avoid reverse recovery problem of slow body diode of the main switch, which are CoolMOS with very low conduction drop.

S5

S1,S4

S2,S3

S6

Vo

Fraunhofer Society

JSL52

Outline – Future Trend




and Efficiency Profiles5. Future Trends

JSL53

Future Trend in Cost Reduction

• Cost Target – with 10¢/W as cost target, pressure is high to further reduce the cost of power electronics

• More Power Electronics Integration – with 50/60-Hz low-frequency component, cost and size reduction on inverter side is difficult, but DC-DC will have chance for more integration

• More Use of Wide Bandgap Devices – By pushing frequency to MHz range, GaN and SiC devices will be adopted for significant size and cost reduction

• Plug-and-Play – Ease of installation is a way to reduce labor cost. We may see more integration with PV panels and power electronics

JSL54

Future Trend in Efficiency Figures Historical figures: Enphase inverter was 95.5% in Gen-1 and 96% in Gen-2 SMA inverter was 95.5% with isolated version and 98% with

non-isolated version Efficiency will continue moving up. Future

development needs to target: Micro-inverter – 97% String/centralized inverter – 99%

Key factors driving up efficiency Wide bandgap and super-junction devices More efficient converter/inverter circuit

• with reduced circulating current for conduction loss reduction • With soft switching for switching loss elimination

JSL55

Documents

Photovoltaic Power Conversion Systems - IEEE · PDF filePhotovoltaic Power Conversion Systems Jih-Sheng (Jason) ... • PV industry generates $93B global revenues with ... DC-DC Converter