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If the load in question is a resistance heating load, I can see two ways around the problem:
1. Use a circuit much like a triac light dimmer. Make sure the control is smooth enough that the flicker standard is met - no sudden changes in current. Problem here is power line harmonic generation that may violate power line harmonic standards and even radiated emissions standards. 2. Run the load from a switching power supply. Not much of a power supply is needed - rectify the AC, follow with the switching with multiple switch cycles per half-cycle of mains power, no filtering (except for EMC) necessary. Use control similar to that used on harmonic corrected/power factor corrected power supply to minimize harmonic generation. Add sufficient EMC filtering to prevent the switching frequency from showing up on the mains or radiating. Control heater power smoothly to meet the flicker standard. Don Borowski Schweitzer Engineering Labs Pullman, WA jules <[email protected]>@majordomo.ieee.org on 02/18/2003 06:42:47 AM Please respond to jules <[email protected]> Sent by: [email protected] To: [email protected] cc: Subject: flicker results with PWM circuits Dear all, [IMAGE] we have a customer designing and manufacturing Pulse Width Modulation power controllers. These are used in the heating & ventilation industry , within factories and hotels etc. due to the nature of the design switching full power on and off between 2 and 30 times a minute it fails flicker EN61000-3-3. Looking at the std and doing the maths on a 2kw load, it needs to be switching only once a minute to meet flicker requirements. Problem with this is only switching once a minute the control is lost My question is that PWM products obviously cannot meet the flicker std, but what experience do other labs have of this. we found a micro from a co in Sweden which sits in front of the mains input and affectively fools the harmonics tester into, but this is both expensive and not really a solution. What have other labs found, is there a solution, as flicker std only addresses products up to 16A the high power controllers are ok, but they sell many which run at 1.5kVA. Or do manf just 'ignore' the flicker requirements any feedback would be much appreciated. rgds, Jules Julian Jones Hursley EMC Services Brickfield Lane Chandlers Ford, EASTLEIGH Hampshire, SO53 4DP Tel: 023 8027 1111 Fax: 023 8027 1144 [email protected] www.hursley-emc.co.uk (See attached file: image002.gif)Title: Re: flicker results with PWM circuits
If the load in question is a resistance heating load, I can see two ways
around the problem:
1. Use a circuit much like a triac light dimmer. Make sure the control is
smooth enough that the flicker standard is met - no sudden changes in
current. Problem here is power line harmonic generation that may violate
power line harmonic standards and even radiated emissions standards.
2. Run the load from a switching power supply. Not much of a power supply
is needed - rectify the AC, follow with the switching with multiple switch
cycles per half-cycle of mains power, no filtering (except for EMC)
necessary. Use control similar to that used on harmonic corrected/power
factor corrected power supply to minimize harmonic generation. Add
sufficient EMC filtering to prevent the switching frequency from showing up
on the mains or radiating. Control heater power smoothly to meet the
flicker standard.
Don Borowski
Schweitzer Engineering Labs
Pullman, WA
jules <[email protected]>@majordomo.ieee.org on 02/18/2003 06:42:47
AM
Please respond to jules <[email protected]>
Sent by: [email protected]
To: [email protected]
cc:
Subject: flicker results with PWM circuits
Dear all, [IMAGE]
we have a customer designing and manufacturing
Pulse Width Modulation power controllers. These are
used in the heating & ventilation industry , within
factories and hotels etc. due to the nature of the
design switching full power on and off between 2 and
30 times a minute it fails flicker EN61000-3-3.
Looking at the std and doing the maths on a 2kw load,
it needs to be switching only once a minute to meet
flicker requirements. Problem with this is only
switching once a minute the control is lost
My question is that PWM products obviously cannot
meet the flicker std, but what experience do other
labs have of this. we found a micro from a co in
Sweden which sits in front of the mains input and
affectively fools the harmonics tester into, but this
is both expensive and not really a solution.
What have other labs found, is there a solution, as
flicker std only addresses products up to 16A the
high power controllers are ok, but they sell many
which run at 1.5kVA. Or do manf just 'ignore' the
flicker requirements
any feedback would be much appreciated.
rgds,
Jules
Julian Jones
Hursley EMC Services
Brickfield Lane
Chandlers Ford, EASTLEIGH
Hampshire, SO53 4DP
Tel: 023 8027 1111
Fax: 023 8027 1144
[email protected]
www.hursley-emc.co.uk
(See attached file: image002.gif)
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