Literature Survey on Power Quality Issues Due Lighting Loads. Standards for Power Quality of Lighting Loads is presented. Power Factor and THDi impact of Fluorescent Lamps, CFL, and LED lights is presented. Diode Rectifiers, Passive LC Filters and Valley Fill Circuits, Active Filters using Power Factor Control PFC Boost Regulator are compared. Simulated Impact of Lighting Load on the Power System is presented

1. Power Quality Due To Lighting
Loads
Nereus Fernandes

2. Agenda

Standards for Lighting Loads :
− IEC 61000-3-2
− IEEE519
− NEMA ANSI C82.77 - 2002

Lighting Loads Considered are :
− Fluorescent Tubes, CFL

Magnetic & Electronic Ballasts
− LED Lamp Drivers
− Mixed Loads

Power Quality Parameters :
− Power Factor
− THDi

Study of effect of Diversity & Combined load on Power System

4. IEC 61000-3-2 Application Guidelines

5. `
IEC 61000-3-2 Standard
Low Power but significant numbers!
Costs kept low in residential lighting so quality standards
relaxed, resulting in devices with high THD with low PF
– most papers use these devices for study / impact analysis

6. Lower the PF =>
Lower the permitted 3rd
Harmonic
IEC 61000-3-2 THDi limits

7. IEEE519
 Isc = short circuit current at PCC
 IL = fundamental component of
load current
 TDD = Total Demand Distortion
=Harmonic distortion current
Max Demand load current
 Specified at the PCC
IEEE Draft for harmonics in single
phase equipment 2001
 For combinations of non-linear
loads like PCs, CFL, EV battery
chargers – Harmonic current
limits for the load combination is
as per the table

8. NEMA ANSI C82.77-2002

Harmonic Emission Limits – Related Power Quality Requirements for
Lighting Equipment

Supersedes PF & THD of ANSI C82.11

PCC THD should be consistent with ANSI/IEEE519
Low Power but significant numbers!
Costs kept low in residential lighting
so quality standards relaxed, resulting
in devices with high THD with low PF
– most papers use these devices for
study / impact analysis

9. NEMA ANSI C82.77-2002
Tighter requirements
for commercial

10. NEMA ANSI C82.77-2002

Industrial limits are similar to commercial limits

11. Fluorescent Lamp Basics

Ac Mains Voltage applied is not sufficient to ionize vapor and strike arc between
electrodes ( needed >320Vrms with heated electrodes, >1KV with cold electrodes )

Glow discharge initiated in glow starter caused bimetallic contact to bend and close

Electrode filaments are pre-heated

Starter contacts cool and open – sharp reduction in inductor current causes large
voltage across the ballast, with suitable timing this adds to the AC supply voltage to
produce high voltage sufficient to ionize the vapor and strike an arc between the
electrodes

Once arc is struck vapor exhibits negative resistance – increasing current, heats the
vapor, increases ionization, decreasing resistance and further increasing current. The
Ballast limits the current through the fluorescent tube
arc

12. Fluorescent Lamp Basics

Arc is re-struck in the next half-cycle at a lower voltage – as vapor is already ionized

Arc Extinguish Time is 1ms

Operation at higher frequency results in non extinguishing of the arc – resulting in
around 7-10% improvement in illumination and elimination of 50Hz flicker
- Advantages of Hi Frequency operation are available in electronic ballasts

Operation with DC will result in mercury accumulation at the cathode and early failure

13. Magnetic Ballast

Non-linearity in Current is due to the arc in
series with the ballast
− THD typically ~15 – 20%
− 3rd
Harmonic dominant

Lagging power factor due to inductive ballast
− PF is corrected by capacitor

Uncompensated (NPF Ballast )
− Total Power = 38W
− VA = 61.4 Power factor =
0.62

Compensated (HPF Ballast )
− Total Power = 38W
− VA = 38.9 Power factor =
0.97

14. Electronic Ballasts for Fluorescent
Tubes & CFL

Electronic Ballasts similar for Fluorescent Tubes and CFL

Life Expectancy of Electronic Ballasts
− Fluorescent Tube Ballast 1,00,000 hrs (10 yrs)

Typically include Active Power Factor Correction Circuits
− CFL Ballast 15,000 hrs = life of tube

Ballast is part of the assembly and thrown away along with the tube
at the end of tube life (waste!)

Tendency to go for the cheapest circuit resulting in Power Quality
Issues

Typically do not include Power Factor Correction Circuits on the
basis that they are small loads ( but huge number of installations –
20 % of generated power – will cause issues! )

15. Harmonic Line Current Reduction Techniques
− Passive Components ( L & C ) introduce high impedance to harmonics thus
smoothing input current to equipment.

Adv : Simple, robust, cheaper

Disadv : large heavy low freq magnetics, not applicable to wide input voltage
range or higher power, no sinusoidal input current
− Active electronic circuitry shape the input current to make it sinusoidal and in
phase with the line voltage

These circuits are called PFC ( power factor correction ) circuits ~ now
synonymous with harmonic line current reduction
− Adv : extensive elimination of harmonics, pf near 1, wide input voltage
range, higher power, light weight
− Disadv : increased complexity, part count , cost

16. Electronic Ballasts – Front Ends :

Basic Input System
− No Filtering, No PF improvement
− R1 used to limit peak current value

Input System with Passive
Filtering
− Easy Implementation, Low Cost
− Power Loss in Passive Components
− Bulky 50Hz inductor

17. Electronic Ballasts – without Filter

18. CFL Harmonic Analysis - Measured CFL Harmonic Analysis - Simulated
All Odd Harmonics present without Filter
Arc represented by
equivalent resistance
Simple Bridge Rectifier
with Capacitor

19. Electronic Ballasts – Front End : Traditional Valley Fill

20. 
Developed Valley Fill Harmonic Filtering
− Addition of Resistor Rvf
− Charging Current spikes reduced at voltage peak.
Charging for Vs > Vp/2. Both CVF1 and CVF2
charged to Vp/2
− When Rectified voltage falls below Vp/2, CVF1 and
CVF2 are effectively in parallel and clamp DC bus
to Vp/2
− Cheap
− Reduces Current Harmonics
− PF > 0.9, THD < 30%
− DC Bus Ripple is 50%
Electronic Ballast

21. 
Developed Valley Fill Filtering ( contd )
− Crest Factor Control Circuit

Voltage rise is sensed by the controller and inverter frequency is controlled near the
peak to ensure reduced Lamp Current.
− Yellow => DC Bus Voltage
− Green => Lamp Current
− Blue => Lamp Voltage
Electronic Ballast – Front End : Developed Valley Fill

22. Electronic Ballast – Front End : Boost Converter

24. Normal Power Factor
High Power Factor

25. LED lighting Driver Circuits - Commonly used Converter Types

AC to DC Converters – front-ends are similar to those in electronic ballasts

Isolated converters are used in case of large exposed heat-sinks
1. Basic converter: A very simple passive circuit. This also includes so called AC LEDs which
consist of back to back LEDs with some passive current limiting element.
2. Buck converter: A simple switching regulator which does not provide electrical isolation. This is
suitable only in in applications where the LEDs not accessible.
3. Flyback converter: A slightly more complicated single stage switching regulator which provides
electrical isolation. The LEDs can be accessible without posing any risk of electric shock.
4. Multistage converter: Consists of a Boost regulator front end which provides a high power
factor and a back end to provide isolation and current regulation. This could be a Flyback or
resonant stage.

26. LED Driver - Basic Converter

Basic Converter – AC LED
− Series connection of low-power LEDs
and current limiting element connected
directly to the AC line
− Voltage drop across the LEDs means
that the line current flows only during
the peak of the AC cycle
− Triac dimmers do not work
− High Current & efficient LEDs cannot be
used
− Low cost products but they are not
green as they have very poor power
factors

27. LED Driver – Buck Converter
 Buck converter suitable when
isolation not required
 Power Factor Correction
using Valley Fill
 Simple and low cost

28. LED Driver – Flyback Converter

Flyback Converter is used when
isolation is required

Valley PFC can be used
OR
Direct operation from the full wave
rectified bus without smoothing
capacitor
− Very few components needed
− Higher input current ripple,
discontinuous; leads to high
THD

Suitable for low power levels ~
50W

29. THD not specified for direct flyback converter ! - typically used when THD compliance not needed

30. LED Driver – Multistage with PFC Boost Reg.
Front End

Boost Regulator in the front
end draws continuous
current due to the input
inductor

Back-end can be any
configuration that preferably
draws continuous current

In this example, the back-
end is LLC resonant half
bridge
− Pf > 0.95
− THD <10%

31. PFC stage
LLC Stage
LED Driver – Multistage with PFC Boost Reg.
Front End

32. Harmonics in Low Wattage LED Lamps

33. 
Phillips LED bulbs
use Valley Fill
Technique

Osram 4W & 6W LED
bulbs have no
harmonic filters.
8W LED bulb uses
active filtering

34. LED Lamp Current Harmonics
Valley
Fill
Active PFC
No PFC
No PFC

35.  Each household is represented by
Norton Equivalent with harmonics
injected by the household
− 3KW linear load
− Injected harmonics – (value not
specified in the paper ! )
 These are combined for each level to
present a Norton equivalent to the
next upper level
 Effect of 28,800 consumers modeled
(15x4x10x8x6)
 Two distribution systems modeled
− Underground
− Overhead
 THDv calculated at different levels in
the Distribution Network
 Simulation Software not specified in
paper

37. Grid Household

38. Impact on Ripple Control Systems operating at 1050 Hz

0.3% Distortion is the limit specified by Ripple Control Systems

0.08% Distortion considering safety margins selected as limit

Increased THD due to huge installations of average and poor quality CFLs can significantly
degrade the Power System Quality to below standard limits causing malfunction of equipment
-especially at light overall loads – thereby requiring system upgrade that could be avoidable
Grid Household
21th
Harmonic = 1050Hz
used for control in old
Networks
Poor CFLs generate
21st
voltage harmonic
that is more than limits

39. 
Diversity Factor = Vector Sum of harmonic (measured)
Arithmetic Sum of Harmonic (calculated )

When using a combination of different Lamps the resultant
vector harmonic may be reduced if the phases are different /
opposite

Lamps with Power <25W have less stringent THD limits

40. 
When using a combination of different
Lamps the resultant vector harmonic may
be reduced if the phases are different /
opposite

Hence some reduction in net harmonics is
observed when combination of LEDs and
CFLs is used

41. 4 CFL + 2 LED 28 CFL + 2 LED → CFL
Harmonic levels
converge towards
CFL
Conclusion

Due to load diversity - reduction in higher order harmonics and THD observed

As all lighting moves towards CFL or LED, stricter harmonic limits needed at device level

42. Thank You