active damper for power electronics based systems · harmony symposium – haofeng bai 14...

H a o f e n g B a i , P h . D s t u d e n tD e p a r t m e n t o f E n e r g y T e c h n o l o g y

h b a @ e t . a a u . d k

Active Damper for Power Electronics Based Systems

H A R M O N Y S Y M P O S I U M – H A O F E N G B A I 2

Outline

Background

Concept: Damping Resistance

Realization of the Active damper

Experimental Results


Background

Background





Background

Power-Electronics Converters

• Grid impedance

• LCL filters of the grid-connected converters

• Limited control bandwidth in high power applications

Harmonic resonance and instability !!![1]. Mollerstedt, E.; Bernhardsson, B., "Out of control because of harmonics-an analysis of the harmonic response of an inverter locomotive," Control Systems, IEEE , vol.20, no.4, pp.70,81, Aug. 2000


Background

Explanation

− Impedance-based Model of Grid Connected Converter

gi

ocY PCCV

LZ

sV*g cli G

gi

PCCV sV*g cli G


Background

Explanation

− Nyquist based stabil i ty analysis

-50

0

103

-90-45

04590

135

(Hz)

YocYL

-1 -0.5 0 0.5 1

-1

-0.5

0

0.5

1Stiff grid

-60

-40

-20

0

103

-90-45

04590

135

(Hz)

YocYL

-1 -0.5 0 0.5 1

-1

-0.5

0

0.5

1

Weak grid


Background

Existing Solutions

− Passive damping• High power loss;• Sensi t ive to parameter changing.

− Active damping• Within the control loop of converter;• Limited by the control bandwidth.

Other possibil i t ies?

Active damper



Background






System with Active Damper

ocY PCCV SVINVi SL SR

1

daR*INV cli G

3 ,max

1sfoc

da

YR

H A R M O N Y S Y M P O S I U M – H A O F E N G B A I 1 0


System with Active Damper

-30

-20

-10

0

103

-90-45

04590

135

Yocm1YL

Frequency (Hz)

Phi (

degr

ee)

Mag

(dB

)

-2 -1 0 1 2

-2

-1

0

1

2

imag

inar

y ax

is



Background






Topology

Fundamental voltage of the grid can be sustained by the series LC filter, which brings the following benefits:

• Low power rating;

• Low dc-link voltage;

• High switching frequency.



Control strategy

11

aa

L s C s

__

ia dcpa dc

KK

s

*ahi

*dcaV

1.5 saT se

Composed of two parts:

• Dc-link voltage control loop

• Harmonic current control loop



Control strategy

11

aa

L s C s

__

ia dcpa dc

KK

s

*ahi

*dcaV

1.5 saT se

DC-link voltage control loop:

• Carried out at q-axis at the fundamental frequency.

• The output of the PI controller are directly fed to the PWM modulation block.



Control strategy

11

aa

L s C s

__

ia dcpa dc

KK

s

*ahi

*dcaV

1.5 saT se

Harmonic current control loop:

• Responsible for mimic the damping resistance;

• Decoupled with the dc-link voltage control loop through a harmonic extraction block.



Impedance model of the active damper

Structurally, the active damper is no different from a grid-tied converter, except with a lower rating and the series LC filter as the controlled plant.

ocaY PCCV

sZ

SVPCCh

clada

V GR vaY

The usual current source in the Norton circuit is replaced by an admittance Yva

1va cla

da

Y GR



A special problem for the active damper

Yva will be non-passive above the bandwidth of the active damper, introducing new possibility for harmonic resonance at higher frequencies with grid capacitance (above the control bandwidth of the active damper).

2ocm va oca oc da oc

grid converteractive damper

Y Y Y Y Y Y

21

L pS S

Y sCL s R

-80-60-40-20

020

()

103

-135-90-45

04590

Yocm2YL2M

ag (d

B)

Phi (

degr

ee)

-1000 -500 0-100

-50

0

50

100


Slightly higher than the upper limit of the non-passive region of the grid converter.


A special problem for the active damper

Solution:A simple first order low-pass filter.

, 2clpf c c

c

G fs

Design of the low-pass filter• The purpose is to avoid deteriorating damping effect

intended for the grid converter over its non-passive range.• Reducing the non-perfection of the current control loop of

the active damper.

1kHzcf



Modified harmonic current control loop

11

aa

L s C s1.5 saT se

*ahi

c

cs

31

ocm lpf cla oca ocda grid converter

active damper

Y G G Y YR

-80-60-40-20

020

103

-90-45

04590

Phi (

degr

ee)

Mag

(dB

)

0

-10 -5 0-0.1

-0.05

0

0.05

0.1



Background






Stabil i ty analysis of the grid converter

Stiff grid

Weak grid


Performance of the active damper

Steady state

Startup process



Effect of the low-pass filter

Without low-pass filter



Effect of the low-pass filter

With low-pass filter


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- P . P ICASSO

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active damper for power electronics based systems · harmony symposium – haofeng bai 14...

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