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Understanding Power Quality: Harmonic Control Devices and Filter Design - Prof. Paul E. Or, Study notes of Electrical and Electronics Engineering

University of Idaho (U of I)Electrical and Electronics Engineering
Prof. Paul E. Ortmann

This lecture from ece 528 covers various harmonic control devices including in-line reactors, zigzag transformers, passive filters, and active filters. The document also provides a filter design example to improve displacement power factor and filter harmonic current.

Typology: Study notes

Pre 2010

Uploaded on 08/18/2009

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Lecture 23
1
ECE 528 – Understanding Power Quality
Paul Ortmann
[email protected]
208-733-7972 (voice)
208-736-3248 (fax)
http://www.ece.uidaho.edu/ee/power/ECE528/
Lecture 23 2
Today…
• Harmonic control devices
–In-line reactors (chokes)
–Zigzag transformers
–Passive filters
–Active filters
–Designing a harmonic filter
pf3
pf4
pf5
pf8
pf9

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Lecture 23

1

ECE 528 – Understanding Power Quality

Paul Ortmann [email protected] 208-733-7972 (voice) 208-736-3248 (fax)

http://www.ece.uidaho.edu/ee/power/ECE528/

Lecture 23 2

Today…

  • Harmonic control devices
    • In-line reactors (chokes)
    • Zigzag transformers
    • Passive filters
    • Active filters
    • Designing a harmonic filter

Lecture 23 3

In-line reactors (chokes)

• Simply a series inductance

  • Presents a series impedance that is directly proportional to frequency
  • Forces DC bus capacitor to charge more slowly
  • Additional benefit:
    • Reduces DC bus overvoltages due to capacitor switching transients – reduced nuisance tripping

Lecture 23 4

In-line reactors (chokes)

• Sizing the in-line reactor

  • Line reactors are typically described as “a 3% reactor”, 3% to 5% are common
  • Size is based on the VA base of the drive
  • Inductance in Henrys is based on XL at the fundamental frequency

XL_5% 0.

(V base)^2

VAbase

:=

Lecture 23 7

Passive filters

  • Shunt passive filters
    • Notch filter is the most popular
    • May employ delta or wye connected capacitors connected to the line or neutral through inductors

Lecture 23 8

Passive filters

  • Series passive filters
    • Provide a high impedance to the target harmonic
    • Must carry full load current
    • Not practical for multiple harmonics
    • Useful in single-phase applications

Lecture 23 9

Low-pass broadband filter

  • Combines shunt and series elements
    • Low impedance for low frequencies
    • Hi impedance for high frequencies
    • (See PSQ p.258)
    • Several basic “building blocks” of the low-pass filter can be placed in series to produce a steeper slope in the frequency response

Lecture 23 10

General approach with passive filters

  • Start at the lowest harmonic of concern
  • Tune filters slightly lower than the target

harmonic

  • Check for resonant points creating high

impedances

  • If system impedance changes, re-evaluate

filter

Lecture 23 13

Filter design procedure

  • Pick tuned frequency
  • Calculate VAR requirements
  • Calculate reactor size
  • Determine filter duty requirements
    • Fundamental
    • Harmonic
    • RMS current and peak voltage
  • Check capacitor ratings
  • Calculate filter frequency response – check for resonance at other harmonics

Lecture 23 14

Filter design example

  • Notch will be at 4.7 th^ harmonic or 282Hz
  • VAR requirement to improve DPF to 96% is 532.23kVAR (Error: top of p. 251)
  • Compute capacitive reactance (wye) of the filter based on VAR need: 0.434 ohm. (eq. 7.21)
  • Capacitive reactance of the filter’s capacitors is higher because inductive reactance will cancel some (eq. 7.22)

Lecture 23 15

Filter design example

  • Capacitive reactance: 0.454 ohms (eq. 7.24)
  • Capacitive reactance and voltage rating determines kVAR rating: 507kVAR at 480V (eq. 7.25) 792kVAR at 600V We’ll use 450kVAR at 480V as a first try.
  • Filter reactor’s fundamental inductive reactance is calculated from capacitor size and harmonic number:

X (eq. 7.26) cap

( 480V) 2 kVARcap

:= =0.512Ω

Lecture 23 16

Filter design example

  • Inductance at fundamental: 0.06148mH (480V capacitors)
  • Duty requirements
    • We compute the fundamental and harmonic voltage and current for the capacitors separately, then add these values to get the total RMS current and peak voltage.
    • Note: eq. 7.34 – Load characteristic is not changed by filter. So we still use 1200kVA to calculate current here.