1A Reviewof

ACTIVE POWER FILTERS

Prepared byPARK KI-WON

R&D Center , POSCON

2001. 02. 09

21. Issues on Harmonics

Nature of Harmonics Generalized power theory Measurement / Metering

Impacts of Harmonics Parallel / Series Resonance, RMS / Peak Value Increase

Source of Harmonics Voltage source vs.Current source Static vs. Dynamic

Standards on Harmonics: Harmonic Limits Utility companies / Customers / Manufacturers IEC / IEEE

Harmonics Reduction/Elimination

32. Source of Harmonics

Non-linear magnetization of a transformer Very small compared to rated current

Power electronics based equipment UPS, PC, Welder, Printer Rectifier, Variable Speed Drive Due to discontinuous current flows

[ ]Wb

[ ]Ai [sec]t

( )t ( )ti

4( )tiline

CLoadLoadLoadLoadACACACACSupplySupplySupplySupply

Voltage Source Type Harmonic Diode rectifiers with capacitive filtering

5Current Source Type Harmonic Thyristor converters with inductive filtering

( )tilineL

LoadLoadLoadLoadACACACACSupplySupplySupplySupply

63. Standards/Guides on Harmonic Limits

IEC 1000-3-2( International Electrotechnical Commission ) Harmonic current emission limits for individual equipments Small equipments < 16A European standard (CELENEC)

IEC 1000-3-4 Harmonic current limits of overall installation Medium to large installations >16A Related to line stiffness (SCC)

IEEE 519-1992 Limits at PCC (Interfacing) Harmonic voltage limits for utility company Harmonic current limit for customers(

74. How Harmonic Reduction/Elimination?

Line-Friendly Load Multi-pulsed system : Series and/or parallel Active current shaping( PFC converter )

Passive Filters Simple, low cost, robust Sensitive to environments: line impedance, load change, ageing of component Subject to parallel/series resonance Easily overloadable : switch off or be damaged, plant modification Over Compensation at which have already a good power factor

Active Filters

8Series vs. Shunt

Shunt Tuned Filter High voltage: 50 < Q < 150 Low voltage: 10 < Q < 50

LC1

C

L

R

CL

RQ 1=

C1

L

R

FZ

)(FZ

5. Passive Filters

9LC1

C

L

R

FZ

C1

L

R

)(FZ

bR

bR

CRb1

Damped High-Pass Filter (2nd order)

10

Non-linear load

Power system

I5 I7 I11 Ih IS I1

IL

5th tuned filter

7th tuned filter

11th tuned filter

High-pass filter

Typical Passive Filter System

11

6. Parallel Resonance

Due to load current harmonic Voltage distortion will be very high Overvoltage

ACACACACSupplySupplySupplySupply

L

C

parallelZ

hihi

)1(11

12

2 ==

+= LCwhen

LCLj

CjLj

CjLj

Z parallel

12

Parallel Resonance with Passive Filter

FZ

SZ

LhI

ShI LhI

FhI

FSSF ZZZ ||=

LC1

R

C1

L

)||( LLS

SL

1 (0dB)

CLS

1 CLLS )||(

1

Lh

ShII

SFZ

LLL

S +

CLS21

Parallel resonance Tuned frequency

CLLS )(1+

CLLSp

)(1+

CLL

RRQ S

Sp

+

+

1

13

Possible Cause of Parallel Resonance Detuning Filter : shift of resonance frequency Capacitance change due to fuse blow C and L may be damaged Temperature Line structure change

Typical Design Practice Tuned to slightly lower harmonic frequency (3~10%)

Effect of Ls (SCC) High Ls : good for avoiding parallel resonance Higher Ls : Higher Q for parallel resonance

14

7. Series Resonance

hv

DistortedDistortedDistortedDistortedSupplySupplySupplySupply

L

C

seriesZ

hi

hv

)1(011C

LwhenC

LjCj

LjZseries

=

=+=

Due to line voltage harmonics Excessive harmonic current flow Overload, Breakdown

15

Series Resonance Due to Neighborhood Harmonic Source

1TRZPCCPCCPCCPCC

hi

............

Plant #1Plant #1Plant #1Plant #1

2TRZ

Plant #2Plant #2Plant #2Plant #2

ACACACACSupplySupplySupplySupply

Fi lterFi lterFi lterFi lter

16

Equivalent Circuits Transforms

hI

2TRZ

LIFZ1TRZ

ShV LIFZ

1TRZ 2TRZ

SZ

1TRhSh ZIV =

PCC

Series Resonance

will be occurred

17

8. Troubles due to Harmonic Pollutions

Heating of the electrical equipment Trip of circuit breaker Fuse blown Capacitor damage kWh fault Loss of motor winding and iron Perturbing torques on the motor shaft Damage of Sensitive electronic equipment Malfunction of PLL circuit Communication interference

Parallel and Series Resonance will occured Increase of RMS and Peak Value Excessive Neutral Currents

18

9. Motivations for taking action against Harmonics

Harmonics lead to premature ageing of the electrical Installation

Excessive amount of harmonics must eliminatefor economic reasons

The utility company impose penalties on users

Harmonic pollution may disturb equipment in other plants THD limitation of voltage / current present at PCC IEC 1000-3-6 : Assessment of emission limits for disturbing loads

in MV and HV power systems

19

10. Function of APFs

Main function Compensate current and voltage harmonic.

Additional functions Current-related compensation

Reactive power, current unbalance, neutral current Using shunt-APF for the most part

Voltage-related compensation Voltage unbalance, flicker, spikes, regulation Using series-APF for the most part

22

Shunt APF stand-alone

Eliminate current harmonics

Reactive power compensation

Balancing unbalanced current

NonlinearLoad

Shunt Active FilteriF

NonlinearLoad

Seies Active Filter

vF

13. Topology based classification

Series APF stand-alone

Eliminate voltage harmonics

Regulate and balance the terminal voltage

Damp out harmonic propagation