Greening the Grid (GTG) Program

A Partnership between USAID/India and Government of India

Greening the Grid (GTG) Program

A Partnership between USAID/India and Government of India

Greening the GridGreening the Grid

Knowledge Session on Technical Advancement in RE Interfacing Inverters

Dynasty Hall, WelcomHotel Sheraton, New Delhi

Date: July 30, 2018

Knowledge Session on Technical Advancement in RE Interfacing Inverters

Dynasty Hall, WelcomHotel Sheraton, New Delhi

Date: July 30, 2018

International Experience on Inverter

Technologies

Grid-connected PV-systems differ with the inverter types

…

…

…

…

Central inverter

String inverter

Module (micro)

inverter

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Inverter Types

Example Outdoor Rated Central

Inverter

Example Outdoor Enclosure to

Protect Indoor Rated PV Inverters

Example String Inverter

NREL Failure Rate Data

Slide Credit:

NREL (S. Kurtz)

Spotlight on Inverters –Performance and Reliability Focus

• What should you look for when selecting inverter products?

– Performance

– Resiliency

• How do you compare similar products?

– Datasheet differentiation

– Feature sets

• Project lifecycle and technology evolution

– Will my inverter product be serviceable

– Will suitable products be available when necessary

• Independent testing and evaluations

– Reduce project performance risk

– Improve system operations from onset

PV IN AC Out

Solar Inverters: Basic Functions and Features

• Maximum Power Point Tracking (MPPT) uses a control algorithm to keep the

PV modules operating close to their peak power point, whilst the incoming

solar radiation level and temperature vary.

• Convert DC power from the PV modules into AC power, to connect and

interact with utility grid.

• DC voltage range of inverter compatible with PV array string voltages

• AC output voltage of inverter matched with utility grid voltages

• Disconnect from the grid when necessary, to comply with safety

requirements.

• Provide status reporting and monitoring

Top 10 Inverter Vendors in the United States by

Shipments, 2014 (MWac) (from: GreenTechMedia.com)

Solar Inverters: Standards and Technical Requirements (1)

• US standards are derived from Federal Energy Regulatory Commission (FERC)

Order 661 for Large Generation Interconnection Agreement for renewable

generators above 20 MW.

• US Independent System Operators (ISO) and Balancing Authorities (BA) – PJM,

CAISO, ERCOT, NEISO, NYISO, MISO, SPP have slight distinctions based on local

requirements.

• China’s requirements are covered under GB/T – Z 19963 set of standards.

• Internationally – Germany, Australia – requirements are broadly similar.

• Key aspects used for comparison:

• Power quality (Harmonics, Voltage deviation, Voltage variation)

• Active power control (Regulation range and speed)

• Reactive power control

• Voltage control

• Frequency ride-through protection control

• Voltage ride-through protection control

Solar Inverters: Standards and Technical Requirements (2)

Codes Standards and Requirements

Power Quality

IEEE 519,

IEEE 1547,

NERC VAR-001-4

Harmonics: 5% for general system; 3% for special systems

Voltage deviation: Steady state ±5%, transients 2.5% to 10%

Voltage variation: Specifications by d% and no. of times/hr

Active PowerNERC, FERC, ISO

Standards

Regulation range of active power: 20% - 100%

Speed of regulation of active power: 10%/second

Reactive PowerFERC Order 827,

ISO standards

Power factor 0.95 leading to 0.95 lagging. Grid operator generally mandates

dynamic reactive power regulation

Voltage ControlFERC Order 661,

ISO Standards

Varies by ISO

• May require voltage at POI to be controlled within 95%-105% in AVR mode

• PF range needs to be maintained unless plant is operating <20% rated

capacity

Active Power

Feed-In at

Frequency

Excursion

NERC PRC-024-1

Minimal, varies by ISO

Encouraged to provide over-frequency response.

Solar Inverters: Standards and Technical Requirements (3)

Codes Standards and Requirements

Frequency

ride-throughNERC PRC-024-1,

ISO Standards

Voltage ride-

through

FERC Order 661, ISO

Standards

HVRT Settings:

• >1.2 pu, Trip

• >1.175 pu, 0.2s

• >1.15 pu, 0.5s

• >1.1 pu, 1sec

Minimum required plant response to emergency low voltage

From: NREL

Inverters for Battery Energy Storage Systems (BESS)

• BESS inverters are developed on the

foundation of existing Solar PV inverters

• BESS and Solar PV inverters have 90%

similar hardware. Additional hardware is

required for

o Bi-directional power flow

o Black start capability and off-grid

operation

o Fault protection for internal faults

during islanded operation. DC

short ckt current can be large

o Upgraded thermal management

systems (packaged with battery

modules)

• Software requirements considerably

advanced for BESS inverters

• Full charging and discharging real and

reactive power controls

• Supervisory control decisions

implemented through BESS PCS set-

points.

Advanced Inverters – Rule 21

• California’s smart inverter requirements

(Rule 21) is currently the most

comprehensive set of requirements for

Solar and DG inverters worldwide.

• Mandated by California Public Utilities

Commission (CPUC) to accommodate

and enable wider adoption of PV and

DER. Rule 21 is CAISO interconnection

requirement.

• Phase I went into effect on Sep 9 2017.

• No hardware modifications.

Considerable advances in software and

controls.

• Under previous grid codes, inverter (and

PV plant) would de-energize if frequency

and voltage fall outside set parameters

+

Smart inverters can modulate real and reactive power output to actively support he grid and

continue to operate in wider ranges of frequency and voltage

Rule 21 Phase I inverter functionality

Function Description

Connect/disconnect Physically connects or disconnects from the grid.

Adjust maximum generation

level

Sets maximum generation

Adjust power factor Issues pf angle value

Volt-VAR mode Adjusts reactive power output

Frequency ride-through Sets the frequency parameters for operation

Voltage ride-through Sets the voltage parameters for operation

Event/history logging Request event logs

Status reporting Requests inverter status

• Functionality testing by UL 1741 SA.

• Amendments to IEEE 1547 standards for DER interconnection and 2030.5 for DER

communication is ongoing.

• A recent survey of 6 major inverter supplies of central inverters for the US market

revealed that all six could deliver the requirements.

Rule 21 Phase II and Phase III

• Phase II will establish communication requirements for inverters and require that

inverters can communicate over the internet.

• Effective Mar 1 2018, or 9 months after release of industry-recognized certification

standard.

• Phase III will require remote inverter functions like data monitoring, remote

connection and disconnection.

Benefits• Increased PV and DER penetration

• Improvements in reliability and distribution network visibility

• Better grid management and asset upgrade deferral

Challenges• Ongoing, multi-party engagement

• Standards are slow to keep pace with technology

• Need for new communications infrastructure and protocols

• Lack of compensation mechanism for additional services

Thank you!