1

Peter Heskes January 2011

The EOS LT project KTI is funded in part by SenterNovem

Minimizing the Impact of Resonances in

Low Voltage Grids

The KTI project

Grid impedance, interaction and resonances

Impedance measurement

Minimizing the impact of resonances

Contents

2

The KTI project

Part 1: Research on new boundary conditions, social importance, consequences and

responsibilities.

(TU/e – EES group, Laborelec)

Part 2: Research on characteristics and

interactions between the grid and

connected appliances and generators

(ECN)

Part 3: Research on and development

of new power electronics to control the

quality of the voltage

(TU/e – EPE group)

Structure of the KTI project

3

Publications

Journal articles

[1] P.J.M. Heskes, J.M.A. Myrzik, W.L. Kling, “Impact of Distribution System’s Non-Linear

Loads with Constant Power on Grid Voltage”, John Wiley ETEP Journal, in-Press.

[2] P.J.M. Heskes, J.M.A. Myrzik, W.L. Kling, “A Harmonic Impedance Measurement System

for Reduction of Harmonics in the Electricity Grid”, International Journal of Distributed

Energy Resources, vol. 5, no. 4, pp. 315-331, Oct./Dec. 2009.

Conference papers

[1] P.J.M. Heskes, J.M.A. Myrzik, W.L. Kling, “Ancillary Services for Minimizing the Impact of

Resonances in Low Voltage Grids by Power Electronics based Distributed Generators”, IEEE

Power Energy Systems General Meeting, Detroit, Michigan, USA, July 24-29, 2011, under review.

[2] P.J.M. Heskes, J.M.A. Myrzik, W.L. Kling, “Harmonic Distortion and Oscillatory Voltages and the

Role of Negative Impedance”, IEEE Power Energy Systems General Meeting, Minneapolis, USA,

July 25-29, 2010.

[3] P.J.M. Heskes, J.M.A. Myrzik, W.L. Kling, “Power Electronic Loads with Negative Differential

Impedance in a Low Voltage Distribution System”, 20th International Conference on Electricity

Distribution, Cired, Prague, 8-11 June 2009.

[5] P.J.M. Heskes, J.M.A. Myrzik, W.L. Kling, “Survey of Harmonic Reduction Techniques

Applicable as Ancillary Service of Dispersed Generators (DG)”, IEEE Young Researchers

Symposium, Technical University of Eindhoven, The Netherlands, February 7-8, 2008.

Grid impedance, interaction and resonances

4

7 31-1-2011

Grid Operator

Point Of Connection

(POC)

Interaction

via

Grid impedance

Customer

Supply voltage

at

POC

Requirements for

quality of voltage

(EN 50160)

Draw current

from

POC

Requirements on

loads for quality of

Current

(IEC 61000-3-2)

Interaction

Example of a LV distribution grid, two PCC and one PoC examples are depicted

Interaction

5

Simplified grid model with a lumped large number of

resistive loads and parallel capacitances

Interaction

The grid loaded with a non-linear load

Interaction

6

Added damping resistance in the distribution grid

Interaction

VPCR = Virtual Parallel Capacitance Reduction

Resonances

VRHD = Virtual Resistive Harmonic Damping

VPCR

active

VPCR + VRHD

active

VRHD

active

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Harmonic impedance measurement

ZgridLine

Neutral

PoC Zload

Controlled

current source

Grid simulator

PC with Matlab

software

A/D

conversion

Sampled

Data

Injection

signal

VI

Current

injection

12V 230V

Injection current for a 50.0Hz grid frequency

The injection current stimulus

The grid voltage is strongly

polluted

Impedance measurement in a laboratory set-up

Harmonic Impedance Measurement

8

Harmonic Impedance Measurement

The system:

• estimates free spots in freq. domain

• inject current on free spots

• collect voltage / current time series

• does domain transformation

• calculates the impedance spectrum

Shift

Measurement

frequencies

Start

Measure Voltage

Magnitude

Spectrum without

Stimulus

Voltage

Magnitude

Spectrum

below limit?

Inject a Current

signal to the grid

No

Calculate

Impedance

Spectrum

Measure Voltage

(and Current)

time series

Transformation to

frequency domain

Ancillary services for harmonic reduction

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VPCR and VHRD

VPCR = Virtual Parallel Capacitance Reduction

VRHD = Virtual Resistive Harmonic Damping

The inverter’s basic block diagram with focus on the grid interfacing part

Time domain lab experiments

Laboratory set-up

Experimental result of vgrid polluted with

10% of the 11th harmonic

10

inverter currents

VPCR = off

VRHD = off

Time domain lab experiments

1 1.02 1.04 1.06 1.08 1.1 -2

-1

0

1

2

i in

v (t)

1 1.02 1.04 1.06 1.08 1.1 -2

-1

0

1

2

I gri

d (

t)

time (seconds)

Experimental result of iinv and igrid without activated ancillary services

DC

Power

supply

model

Inverter model

iinv

vgrid

Output filter

model

H-Bridge

driver model

Controller

model

Lout

Cout

+

-

Lgrid Rgrid

Grid model

voltage

source

fundamental with 10%

of 11th harmonic

H-bridge

model

igrid

inverter currents

VPCR = on

VRHD = off

DC

Power

supply

model

Inverter model

iinv

vgrid

Output filter

model

H-Bridge

driver model

Controller

model

Lout

Cout

+

-

Lgrid Rgrid

Grid model

voltage

source

fundamental with 10%

of 11th harmonic

H-bridge

model

igrid

1 1.02 1.04 1.06 1.08 1.1 -2

-1

0

1

2

1 1.02 1.04 1.06 1.08 1.1 -2

-1

0

1

2

time (seconds)

i in

v (t)

I g

rid (

t)

Experimental result of iinv and igrid with activated VPCR

Time domain lab experiments

11

inverter currents

VPCR = on

VRHD = on

DC

Power

supply

model

Inverter model

iinv

vgrid

Output filter

model

H-Bridge

driver model

Controller

model

Lout

Cout

+

-

Lgrid Rgrid

Grid model

voltage

source

fundamental with 10%

of 11th harmonic

H-bridge

model

igrid

1 1.02 1.04 1.06 1.08 1.1 -2

-1

0

1

2

1 1.02 1.04 1.06 1.08 1.1 -2

-1

0

1

2

time (seconds)

I gri

d (

t)

i in

v (t)

Experimental result of iinv and igrid with activated VPCR and VRHD

Time domain lab experiments

Large scale model

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Large scale computer simulations with the validated inverter model

Goal: estimate the total grid impedance at the LV Busbar

Cable 50 Al

customer 11 customer 12 customer 19 customer 20

10m 10m 10m

customer 21 customer 22 customer 29 customer 30

10m 10m

customer 31 customer 32 customer 39 customer 40

10m 10m

customer 41 customer 42 customer 49 customer 50

10m 10m

Cable 50 Al

customer 1 customer 2 customer 9 customer 10

10m 10m10m

10m

10m

10m

Cable 50 Al

Cable 50 Al

Cable 50 Al

5 streets with 10 inverters each on line 1

A

A

Single Home connection Inverter

Cap. load

Zhome

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Inverter’s controller block with resonators on the fundamental

(50Hz) and the 3th, 5th, 7th, 9th and 11th harmonic.

The ancillary service inverter controls the (50Hz) and the 3th, 5th,

7th, 9th and 11th harmonic.

3 5 7 9 11

100 inverters + 100 capacitive

loads connected

Harmonic impedance measured at the substation busbar with

100 inverters as well as 100 capacitive loads connected.

5 7

3

9

11

Large scale computer simulations

no ancillary services active

14

100 inverters + 100 capacitive

loads connected

5 7

3

9

11

Large scale computer simulations

limited VPCR active

Harmonic impedance measured at the substation busbar with

100 inverters as well as 100 capacitive loads connected.

100 inverters + 100 capacitive

loads connected

full VPCR active

Large scale computer simulations

Harmonic impedance measured at the substation busbar with

100 inverters as well as 100 capacitive loads connected.

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100 inverters + 100 capacitive

loads connected

both VPCR and VRHD active

Large scale computer simulations

Harmonic impedance measured at the substation busbar with

100 inverters as well as 100 capacitive loads connected.

Author Name-Country-SessionX-

BlockY-Paper ID

30 P.J.M. Heskes Netherlands Session 2 Paper ID 0549

Conclusions

Based on study, simulations and laboratory measurements:

• VPCR virtually reduces capacitances that can bring resonances,

• VPCR + VRHD virtually reduces capacitances and damp resonances.

These two ancillary services can be implemented in power electronics

based inverters for DG. The actual working range depends on the

performance of the control system.

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Thank you for your kind

attention