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„Grid control for inverter dominated power systems“

RESEARCH PROJECT VERBUNDNETZSTABIL

Soenke Rogalla

Fraunhofer Institute for Solar Energy Systems ISE

IRED Side Event Workshop

Vienna, 17.10.2018

www.ise.fraunhofer.de

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AGENDA

The Project “VerbundnetzStabil”

Motivation and Fundamentals

Definitions

First Findings and Results

Inverter Control und First Test Results

Currently Open Research Questions

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The Project “VerbundnetzStabil” Key Facts

Project goals:

Stability of interconnected systems with a high share of power electronics based generation

Development, simulation, analysis, implementation and testing of new approaches for the control of grid connected converters

Partners

Fraunhofer ISE

Kaco new energy

TransnetBW

University Stuttgart IFK

Duration

8/2017 – 7/2020

Funding:

Federal Ministry for Economic Affairs and Energy (BMWi)

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The Project “VerbundnetzStabil” Scope

Requirements for a stable inverter-dominated interconnected system • Review of today‘s and future the stability aspects • Specification of future inverter requirements

Inverter control development • Development of new control strategies • Implementation on an inverter platform

Modelling, simulation and validation • Components modelling • System Simulation • Validation by Microgrid testing

Utilization of results • Publications • Contribution to standardization work

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Motivation Share of Renewables / Share of Synchronous Generators

Net installed conventional generation capacity in Germany

Electricity production in Germany in week 18 2018

Wind & PV: ~90% of load

Today: Always still a high share of spinning generators grid connected!

Future: Times with (very) low share of spinning generators expected!

Source: www.energy-charts.de (15.10.2018)

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Fundamentals Power-Frequency-Behavior of the UTCE Grid

Inertia

Self-regulating effect

Primary control

Secondary control

Power-Frequency-Behavior

(TA = 12s, PGridLoad = 300 GW, ΔP = 3 GW) intrinsic

controlled

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Categorization of Control Strategies for Grid-Connected Inverters

Stromeinprägend

(Current-Controlled Inverter)

Netzspeisend

(Grid-Feeding)

Application: Basic grid-feeding

Netzstützend

(Grid-Supporting)

Application: Grid-feeding with

advanced functions (ancillary services)

Spannungseinprägend (Voltage-Controlled Inverter)

Netzbildend

(Grid-Forming)

Application: Single generator in small island grids

Netzerhaltend

(Grid-Sustaining)

Application: parallel operation in interconnected

systems or Microgrids

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Categories of Inverter Control Principle of Operation

Grid-Feeding

Grid-Supporting

Grid- Forming

Grid- Sustaining

Behavior Ideal Current Source

Ideal Current Source

Ideal Voltage Source

Real Voltage Source

Control PQ - Controller

PQ – Controller + System Services (LVRT, Q(U), …)

const. Frequency/ Voltage (isochronous)

Droop-Control (Static Control)

Source Impedance

Z = ∞ Z = ∞ Z = 0 finite, ≠ 0

Output Frequency

Synchronous to the Grid Freq.

Synchronous to the Grid Freq.

Fixed Frequency Defined by Droop

Scope of Application

On-Grid On-Grid Off-Grid On-Grid and Off-Grid

Inertia No No Infinite finite, ≠ 0

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First Findings Analysis of Today‘s and Future Stability Aspects

Figure: Kundur, P., et.al., “Definition and Classification of Power System Stability”, IEEE Transactions on Power Systems , Vol 19, No. 2, S. 1387-1401. (May 2004)

Affected by loss of inertia

Affected by higher power gradients / higher RoCoF

Affected by increased power transits

Focus of the project: Instantaneous behavior / transient stability

Definitions for grid stability should be extended for inverter-based grids!

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First Findings Behavior of current-controlled inverters after disturbances

Current-controlled inverters can significantly influence voltage and frequency stability of the power system

Research question

Influence of the Phase-Locked-Loop (PLL) on inverter infeed behavior after grid voltage phase angle jumps?

Phase angle needed by the inverter control an estimated by a PLL

Simulative investigations Inverter feed-in behavior strongly influenced by the PLL parametrization

Additional reactive power infeed after phase angle jumps

Synthetic scenario Severe disturbances in the transmission grid cause large phase angle jumps

PLL parametrization significantly influences power system stability

Inverter feed-in after a phase angle jump of 30° PLL-parametrizations: fast and slow PLL

Source: University of Stuttgart - Institute of Combustion and Power Plant Technology - Department Power Generation and Automatic Control - Christian Schöll

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Synchronization and inertia emulation by P- and Q-droops

Virtual impedance supports stable on-grid operation

Supply of harmonic currents by high dynamic voltage controller

Over-load handling by alternating current limiter

Inverter Control Grid-Sustaining Control with Droop Approach

Source: R. Singer, M. Bader, C. Siedle, „Results for a MV-Hybrid-Microgrid Test Campaign in the MW-Range”, 3rd INTERNATIONAL HYBRID POWER SYSTEMS WORKSHOP, Tenerife, May 2018

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Microgrid Testing of Grid-Sustaining Inverters Laboratory Setup

Inverter1 (1000 kVA)

Grid-Supporting or Grid-Sustaining

Inverter 2 (725 kVA)

Grid-Supporting or Grid-Sustaining

Diesel Genset (275 kV)

cosPhi / P Control or Voltage control

Load Bank (2280 kVA)

Ohmic 1820 kW Inductive 1370 kVar

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Measurement Results Single Inverter: On-Grid Behavior

Set point Change Active Power Set point Change Reactive Power

Vo

ltag

e C

urr

ent

Act

ive

, Rea

ctiv

e,

Ap

par

ent

Pow

er

Vo

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ent

Act

ive

, Rea

ctiv

e,

Ap

par

ent

Pow

er

100 kW 700 kW 100 kVar ind. 100 kVar cap.

100 ms 110 ms

Set point: Set point:

Source: R. Singer, M. Bader, C. Siedle, „Results for a MV-Hybrid-Microgrid Test Campaign in the MW-Range”, 3rd INTERNATIONAL HYBRID POWER SYSTEMS WORKSHOP, Tenerife, May 2018

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Measurement Results Falling into Island - MV

Mai

ns

Vo

ltag

e Is

lan

d V

olt

age

Mai

ns

Cu

rren

t

Loss of Mains

200 kW

0 kW

220 kW

500 kW

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Measurement Results Falling to Island - LV

Loss

of

Mai

ns

Vo

ltag

e C

urr

ent

Vo

ltag

e C

urr

ent

Vo

ltag

e C

urr

ent

Vo

ltag

e C

urr

ent

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Current Research Questions Which kind of current-limitation is suitable in over-load situations?

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Current Research Questions Further open questions

How to define the inertia from inverters?

Required power vs. required energy?

One system level / on plant level?

Which kind of inverters should deliver future inertial?

Wind-/PV-generators? Battery storage?

Contribution of small decentralized units?

What‘s the difference for „normal operation“ and „alert operation“?

Transition from transient to stationary behavior?

Desired transient (instantaneous) behavior: Voltage source with emulated inertia

Desired stationary behavior: Power source

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Thank you for your attention

Fraunhofer Institute for Solar Energy Systems ISE

Sönke Rogalla

www.ise.fraunhofer.de, www.testlab-pe.de

Soenke.rogalla@ise.fraunhofer.de