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Smart PV Inverters

Technology today and tomorrow André Lüthi Leader of Technical Sales Support Sputnik Engineering AG Biel/Bienne

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Agenda

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Sputnik Engineering AG

Why do we need smart inverters?

A look back

Todays technology

Challenges/Outlook

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André Lüthi IEA PVPS Task 14 – Utility Workshop

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Sputnik Engineering AG

Our knowhow is based on grid connected inverters

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Why do we need intelligent inverters?

PV Market development [MW]

Source: EPIA Global Market Outlook 2013

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Situation Europe


Quelle: EPIA Global Market Outlook 2013

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Possible problems in distribution networks

Local voltage increases

Increased exposure of the network resources (lines, transformers, etc.)

Possible problems in the transmission network

Balance production / consumption

Avoid excessive energy fluxes over large distances

Frequency 50Hz

Load variations and deviations from forecast

Use of energy and control energy

Power plant outage

Production Load

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A look back

In the near past the applicable grid codes did not allow PV inverters to behave

“smart"

A few examples:

Immediate disconnection from the network if f > 50.2 Hz

Immediate disconnection from the network in case of over/undervoltages

Only injection of pure active power allowed

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A look back

In particular, the 50.2 Hz criteria has already led to some serious problems:

The primary control reserve in the ENTSO-E network is around 3 GW; the power of

the PV systems, which behave "wrong", exceed this value significantly

As a consequence, around 400,000 PV systems in Germany are currently being

retrofitted or re-parameterized

…this potential problem does not only exist in Germany!

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Todays technology

The currently available "smart" features in our

inverters can be roughly divided into three

categories:

Generation management

Static voltage support (reactive power)

Dynamic grid support (fault-ride-through)

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Todays technology

Setpoint specification for active and reactive power

Active power: limitation in % steps

Reactive power: specification of power factor or Q-values in the range + / - 0.8

Also possible via remote interface

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Todays technology

Active power / frequency curve (P(f) function)

Autonomous reduction of active power at elevated grid frequency

Various P(f) functions for different countries or grid codes

Source: BDEW «Erzeugungsanlagen am MS-Netz 2008» (Germany)

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Todays technology

Active power / mains voltage characteristic (P(UAC) function)

Autonomous reduction of active power at elevated grid voltage

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Todays technology

Power gradient function

"Soft-Start" function for a soft (re)start behavior of the inverter

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Todays technology

Reactive power functions

By using the reactive power functions of the inverter the local grid voltage can be

“controlled” >> the capacity of the existing networks is increased!

There are several functions available:

Fixed setpoints for cosphi / Q

Cosphi (PAC) characteristic

Q (UAC) characteristic

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Todays technology

Example: distribution grid - only consumption

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Todays technology

Example: distribution grid - consumption & supply

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Todays technology

Example: distribution grid - consumption & supply incl. reactive power

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Todays technology

Success Story

23 kW PV system in the deepest Emmental

The pure active power feed did regularly led to local violations of the 110% voltage

criteria

After consultation with the local distribution grid operator, a Q(UAC) curve was

activated in the inverter

>> Result: Problem solved - without grid expansion or other expensive measures!

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Todays technology

Increased immunity against grid voltage disturbances

In the event of a short circuit in the local distribution grid, the inverter with FRT

function doesn’t disconnect from the grid, but “rides through" the voltage drop and

can thus help to prevent large-scale blackouts

If required, the inverter can also support the grid within milliseconds injecting a

defined reactive current

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Dynamic grid support (fault-ride-through)

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Todays technology

Solar Park Controller (SPC)

Opportunity to build up an expanded control loop with the aim to monitor network

parameters at the connection point of the PV system

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Todays technology

Solar Park Controller (SPC)

To date, only a few (10-20) large plants (> 1 MW) are using a SPC function,

primarily in Germany

The requirements for this function are still not very well defined and there is a lack

of standardization

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Todays technology

Modern PV inverters already offer a variety of "smart" functions

However, most of todays’ smart functions operate autonomously, i.e. without active

influence from the outside

In a real "Smart Grid" the ability to actively influence the functionalities is of great

importance

Conclusion

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«Network Code for Requirements for

Grid Connection Applicable to all

Generators» (NC RfG)

Central “framework" document, which

defines the essential minimum

requirements for all types of generators

> 800 W

Will be legally binding after entry into

force

Challenges/Outlook

Activities at the ENTSO-E level

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Challenges/Outlook

Implementation of the requirements at the normative level (CENELEC) is in

progress (EN 50438:2013, TS / EN 50549-1/-2 etc.)

The availability of sophisticated standards (including both the technical

requirements as well as compliance criteria, i.e. tests and pass/fail criteria) is

absolutely critical to a timely and comprehensive implementation of the required

functions in PV inverters and other types of generators

Activities at the level of ENTSO-E - NC RFG

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Challenges/Outlook

(Bi-directional) communication interface between the generator and the control

center: the IEC 61850 approach is used sporadically in case of large systems,

however a use case of a "suitable" interface for the masses, is currently not visible

(which can also be used for small plants)

This problem has also been identified during the "EU PV Grid" project

Storage: what conditions need to be fulfilled to justify the integration of a local

storage?

This question is influenced by the market model (price indicator) and in the long

term possibly also by technical necessities (regulations)

Extends the capabilities of PV in terms of system services (SDL)

Some other topics/challenges

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The ball is in your corner now…

…any questions?

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