influence of harmonic grid resonance on the operation of grid-connected...

09-17-2014

Felix Fuchs Institute for Drive Systems

and Power Electronics

Influence of Harmonic Grid Resonance on the Operation of Grid-Connected Converters

Institut für Antriebssysteme

und Leistungselektronik

Institute for Drive Systems


Influence of Harmonic Grid Resonance on the

Operation of Grid-Connected Converters

F. Fuchs; A. Mertens

Institute for Drive Systems and Power Electronics

Leibniz Universität Hannover, Germany

09-17-2014

Presentation at ECCE 2014 in Pittsburgh, PA, USA

09-17-2014




1

Overview on Presentation

Introduction

Emulation of a Variable Grid Resonance

Wind Turbine and Laboratory System

Transfer Function Based Analysis

Experimental Validation

09-17-2014




2

Introduction

Converter Topologies

Current Control methods

Power Control methods

Grid Layout

PFCC

Cable Capacitances

HVDC?

Notch Filters

With/without communication

Droop control

Two, Three or Multilevel converters

Voltage Level

Voltage Level

with/without PWM

Switching Frequ.

In the following: Examples of Resonance Analysis in Hannover

Research field Resonances in grids

with renewables

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3

Laboratory setup for grid-connected converters in Hannover

• Resonances in cower control

Two level converters: several test benches ready to use

Microgrid control // Power control methods // high switching frequencies (8-16 kHz)

Introduction

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4

Introduction

Hexverter as multilevel converter option for high power wind turbines

Laboratory setup for grid-connected converters in Hannover

• Slow switching (825 Hz) grid-connected NPC converter with LCL filter

Doctoral thesis in Hannover in 2014 on LVRT control and LCL filter design

• Multilevel research group: promising concept ‚Hexverter‘ (patented)

Complexer control in combination with resonances in wind park

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5

Introduction

High Power Test Bench (scale 1:10)

• GeCoLab in Hannover going in operation at the

end of 2014: 1.2 MW converter generator test

bench including a 690 V grid emulator

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6


Introduction

Variable Grid Resonance: Emulation




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7

Grid impedance seen by the converter is time varying and not only inductive

[1] :


0 50 100 150 200 250 300 350 400 450 5003

3.5

4

4.5

5

5.5

6

6.5

7

7.5

8

frequency [Hz]

Impedance [

Ohm

]

[1]

Papath

anass

iou, S.A

; Papadopoulo

s, M

.P.,

"Harm

onic

analy

sis

in a

pow

er

syst

em

with w

ind g

ener-

ation,"

Pow

er

Deliv

ery

, IE

EE T

ransa

ctio

ns

on ,

vol.21, no.4

, pp.2

006, 2016,

Oct

. 2006

Frequency [Hz]

Impedance

[O

hm

]

0 500 0

8

09-17-2014




8


[2] :

[2] Schlabbach, Jürgen, Dirk Blume, and Thomas Stephanblome, eds. Voltage quality in electrical power systems. No. 36. IET,

2001.

-> sudden change of resonance frequency due to switchable capacitance possible


09-17-2014




9


[3] :

[3] Das, J.C. Power system analysis: short-circuit load flow and harmonics.CRC press, 2002.

Large Industrial Distribution system

Case 1: all loads, sources and PFCC are operating an nominal value

Case 2: Some loads, sources and PFFC are are not operating

Case 3: Additional 30 MVA and 18 MW converter load connected by long cable


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10

Is there a general possible range for grid impedance seen by the converter ?


Example: Parallel resonance

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11


Is there a general possible range for grid impedance seen by the converter ?

• Simple approach to emulate a series and parallel resonance:

All Impedances are transformed to the low voltage level

Low voltage side of turbine transformer

Leakage inductance transformer

Medium voltage grid - Standard short circuit powers

Power factor correction capacitance (PFC)

Distance parameter for PFC

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12

PFCC location MV grid short circuit power

PFCC rating MV grid X/R ratio

Influence factors on grid impedance emulation


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13


Introduction





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14


Fully Sized 2 MW wind turbine

All data is provided within the paper

Design of grid filter according to the grid codes :

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15


Filter design according to grid codes

Complies with Harmonic limits!

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16


Introduction





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17


Standard grid voltage oriented dq current control is analysed

• With grid voltage feedforward (GVFF) (b) and without GVFF (c)

𝐺𝑝𝑙𝑎𝑛𝑡 𝐺0

With G

VFF

Without

GVFF

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18


Results for the proposed grid impedance with resonance

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19


Simulation results for critical

resonance combination

• Predicted stability/instability for con-

trol with/without GVFF is validated

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20


Introduction





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21


Laboratory Setup (p.u. transformed parameters)

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22


Results

• Predicted Instability not

Observable, due to higher

Resistances in laboratory

• Including higher resistances

in predictions, instability with

increased controller (285%)

gain is predictable

• Control with GVFF allows

Higher bandwidth than with-

out GVFF concerning

resonance

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23

Conclusion

Grids with Renewables and Resonances is interdisciplinary research field

Grid impedance seen by converter depends on several factors

Here: Approach for grid impedance with series and parallel resonance

dq Current Control with GVFF allows higher bandwidth than without GVFF

09-17-2014




Institut für Antriebssysteme

und Leistungselektronik

Institute for Drive Systems


Thank you for your attention!

F. Fuchs; A. Mertens

Institute for Drive Systems and Power Electronics

Leibniz Universität Hannover

Germany

The Lower Saxony Research Association ’Smart Nord’ acknowledges the support of

the Lower Saxony Ministry of Science and Culture through the ”Nieders¨achsisches

Vorab” grant programme (grant ZN 2764).

09-17-2014




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