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Module Embedded Micro-inverter Smart Grid Ready Residential Solar Electric System

This material is based upon work supported by the Department of Energy- under Award DE-EE0005344.

$3/W total installed price vs. GE base residential system @ $4/W;

$0.13/kWh LCOE (< average EIA 2015 retail electricity price)

Simplified module integration

Safety, MPPT and grid support functions including Volt/VAR support

Module Embedded Micro-inverter Develop and demonstrate power electronics technologies that address:

Objective 1—An Innovative microinverter topology that reduces the cost from the best in class microinverter and provides high efficiency (>96%

CEC - California Energy Commission), and 25+ year warranty, as well as reactive power support.

Objective 2—Integration of microinverter and PV module to reduce system price by at least $0.25/W through a) accentuating dual use of

the module metal frame as a large area heat spreader reducing operating temperature, and b) eliminating redundant wiring and

connectors.

Objective 3—Centralization of a subset of microinverter smart grid and safety functions into an intelligent back-feed capable circuit breaker

that can protect the dedicated PV circuit and simplify such functionality for individual microinverters for lower total system cost.

Technology Summary Program Summary

Key Milestones & Deliverables

Year 1 • Lab demonstrations of micro-inverter breadboard

designed for thin film module with 96% CEC

efficiency and Volt/VAR support and intelligent circuit

breaker

• System cost projection

Year 2 • Micro-inverter prototype and reliability test

• Micro-inverter cost data

• AC PV module design

Year 3 • 2.5KW pilot system demonstration

Integrated micro-inverter with plug and play interconnections

Safety and protection at the feeder circuit level through intelligent breaker

Technical Impact SEGIS-AC program

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Optimization of the Electrical System: GE vision

• System performance optimization • Wider voltage input • Volt/Var support • Mechanical integration

• Total system cost reduction

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Differentiations

Gen 1 micro-inverter Module embedded micro-inverter

Not reactive power capable Volt/VAR

CEC 96% CEC 96%

Electrolytic Cap Opto-coupler

High reliability No electrolytic cap, no opto-

coupler

Micro-inverter optimization Focused on electrical system optimization

4.0$/W system cost Reduced system cost 3$/W

Rack mounted Mechanical integration AC-PV module (no-junction box)

PLC Zigbee communication

Si-module Si-module, HV GaAs-module, Thin film

Unsubsidized target installed price of $<3.00/W is competitive with retail electricity

• Topology generates output with high frequency ripple, which reduces the size of the output filter needed to fulfill the grid requirements.

• Special control t keep the circuit efficiency high under a wider operating region.

• Adequate behavior for transformer-less operation with respect to the common-mode noise.

• Topology and control algorithms modify the output characteristics of the PV panel(s).

• This yields higher converter efficiency when connected to a higher PV voltage source.

• Simple integration with added safety

Key design features

Topology

• Input stage is a partial power processing LLC resonant converter and the

output stage consists of two interleaved full bridge inverters.

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Interleaved DC/AC inverter stage Input partial power processing

LLC resonant DC/DC stage

Topology

• Topology generates an output with high frequency ripple, which reduces the

size of the output filter needed to fulfill the grid requirements.

• Special control under light load, keeping the circuit efficiency high under a

wider operating region.

• Adequate behavior for transformer-less operation with respect to the

common-mode noise.

• This yields higher converter efficiency when connected to a higher PV

voltage source.

• The topology and operation have been verified for both high voltage thin film

panels as well as for mc-Si panels with minor modifications to the input

stage.

• A 96% efficiency was achieved for the high voltage version and preliminary

measurements show an efficiency of 95.5% was achieved for the low

voltage version

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Grid Support Functions

1.00

1.01

1.02

1.03

1.04

1.05

7:00 AM 11:00 AM 3:00 PM 7:00 PMHour

Feeder

Voltage (

pu)

XV

QR

V

PV

X

V

QR

V

PV

Voltage variation is caused by the interaction of power output with system resistance

Proposed Solution for Voltage Variation Leveraged from Large Scale PV System

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Grid Support Functions Var support based on

power level (1-10sec) Active Anti-islanding (10 - 100ms)

Var support based on

voltage level (1-10 ms)

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Experimental Results

50% UV Waveforms at 100% load OF Waveforms at 100% load, pf = 1

Soft start Low output current THD

UF Waveforms at 100% load, pf = 1

Anti-islanding shutdown

Mechanical Integration

• Simple panel integration with module with no dc cables

• No Junction box

• Cheaper installation cost (labor/material)

• Simpler AC harness with half the cable length requirement of regular AC

cabling

• Grounding through AC ground line

• Enhanced connection/disconnection safety

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DC and AC Connectors Micro-inverter

+

Ongoing and Future Work

• Testing the integrated ACPV and preliminary verification of

compliance with UL 1741/UL1703.

• Setting up and running ACPV based system in 2 demo sites (rated 2.5kW each).

• Demonstrate system level communication and control and response to grid commands

• ACPV module certification.

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