330VDC Variable voltage controller for light lamp regulation

[valeriogiampa]

I'm using an halogen lamp power controller based on a Zero Voltage Crossing Circuit, Triac and microcontroller. The experimental result of this solution is not soddisfacent.
I would change this lamp controller solution with a DC/DC variable voltage controller that is able to adjust the output voltage from 48vdc to 330vdc from a DC input bus of 330vdc.
Can anyone suggest a circuit or an evaluation kit that I can use to evaluate the performance of this circuit?
Best Regards

 

[FvM]

I wonder which of your specifications can't be achieved with standard phase angle control?

 

[valeriogiampa]

Hi,
I have to drive a resistive load. It is necessary to control the output power. The best way is to drive the output voltage of a DC/DC converter based on an IGBT. The Triac can be used with ZVC, but It is not ideal for the load.
I think a solution based on an AC/DC (based on a 4 diode), Capacitive filter and an DC/DC converter based on IGBT.
The outut voltage can be regulated from 50 to 330VDC.
The max current can be 12A.

 

[schmitt trigger]

You are talking about driving an incandescent lamp, correct?
As FvM asked, what is wrong with using AC phase control?

edit: for a lamp load you really want to control light output. A closed loop employing photocell feedback and phase control can achieve the tight regulation you require.

 

[D.A.(Tony)Stewart]

The problem with Halogen light control ( and all tungsten filaments) is that although mostly resistive ( with some wound inductance), it is very nonlinear with temp. or current with hot/cold resistance ratio of 10. (This implies a 12A load takes 120A peaks on worst case startup. This also implies a minimum duty cycle as 15A triacs rated for 120A peaks must drop after so many cycles, so you cannot sustain a 1% d.f. unless you choose a much bigger Triac )

This leads to hysteresis with late phase angle control on startup due to "non-soddisfacente" or inadequate trigger thresholds for cold vs hot. gate current on most household dimmer Triacs. (but not all)

If used in a closed loop with time response being slower for off to low levels it can lead to instability if using a closed loop control but not impossible with light feedback as SchmitTrigger suggested and care on PID loop gain.

However if using a pulse gate drive with sufficient current to overcome trigger-current required for cold resistance loads, you can get precise phase control much better than an RC filter pot to control the trigger voltage.

I would suggest a pulse transformer or DIAC to drive the Triac with sufficient pulse current for 1/10th the hot load resistance on the tungsten bulb. ( ie. not a ZCS with missing pulses)

If there is any annoying acoustic resonance of a filament at low duty cycles at 50Hz, then PWM DC would be better or essentially a buck-boost SMPS.

 

[FvM]

I just remembered that a lighting controller for more than 1000 W lamp power also undergoes the EN61000 power quality regulations. Phase angle control without harmonic filters most likely won't keep the harmonic current requirements, neither a rectifier without PFC. State-of-the-art solution for high power lighthing control (e.g. for theatres) are high frequent pwm sine dimmers or good old Variacs.

 

[D.A.(Tony)Stewart]

reading thru the harmonic and flicker test criteria and getting it qualified can be enough to dampen the drive to recreate the wheel, except for the hardy. **broken link removed**

 

[valeriogiampa]

With the stardard solution based on a triac and ZVC circuit I have verified same problems: Triac damage and electronic control circuit damage after triac damage, very short duration time for the halogen lamp, imperfect light intensity control for the final application of the system. This lamp is not used for litghing application, but for cooking application.
A DC/DC high power voltage regulator can be easy to control with a correct current and voltage feedback signals.
In the first case (the circuit based on a triac) an EMI filter is used. In this second topology of circuit that I would test, I think that I use an EMI Filter and a PFC controller after the AC/DC full wave rectifier.
I am interested at evaluation board, OEM module o simple schematic circuit that I can use to test this second circuit topology in laboratory and to analyze the vantages and disvantages versus the classic solution (based on a triac).
The suggested aspect related at the triac based circuit or at the emi regulations are more important, but I have to evaluate after the comparasion between the two solutions.

 

[D.A.(Tony)Stewart]

Triac with ZVC and hysteretic controller for temp, is just as easy to control.

But you may face the same challenges with EMI, heat dissipating and blown drivers from cold resistance unless you learn to solve the problems you have now.

First understand why it failed from evaluating theory for peak current during turn on and peak voltage for turn off with the coil & wiring inductance or ask the right questions after you try. There are NTC discs called Inrush Current limiters (ICL) that are very inexpensive, that may help.

 

[FvM]

What's the cold resistance of your heater? I don't think that an inrush current limiter is acceptable for a heater controller due to involved losses.

Instead of a regular PFC AC/DC converter and succeeding buck converter, I would consider a bridge rectifier and chopping the full-wave rectified voltage. Filters only used as far as required for EMI reduction.

 

[chuckey]

If inrush current is a big problem, and remember this is for a heater, why not ramp up your current slowly if the filament is cold then switch to the actual temperature stabilising mode.
Frank

 

[schmitt trigger]

I fully understand your problem now.

I would start with a PFC controller, which will provide a regulated DC voltage, and then just chop the output voltage to suit your requirements. TI has plenty of eval boards.

This is an eval board for a circuit that is fairly simple to use:

https://www.ti.com/tool/ucc28180evm-573

 

[D.A.(Tony)Stewart]

This is an example of a 15A ICL

The cold to hot resistance of this metal oxide part from 25 to 220'C at rated current is 10 Ohm : 0.048 Ohm = 200:1 since tungsten is 1:10 ratio for cold to hot, so it regulates very well. Loss at 15A is 15*15*0.048= 10W or 10/3300W =0.3% loss. To Eliminate even this heat, a delayed bypass relay could be used. Since the tungsten is mainly resistive, no PFC is needed, and inrush protection will extend the life of the heater significantly.

 

[schmitt trigger]

The reason I suggested a PFC is because:
1) The original poster want a regulated DC output.
2) Because of the power level involved, he must harmonic requirements for the EU.
3) An evaluation board is available.


There are many ways to skin a cat, this is one of them.

 

[D.A.(Tony)Stewart]

THanks Schmitt T,, no worries. I knew that.

Just adding emphasis that if he chooses not to use PWM, that PFC is not required (because there is no rectifier capacitance loading effects) and the tungsten is a pure non-linear resistor ( with a tiny bit of inductance that comes into play when switching )

The ICL is a "cheap and dirty" yet effective solution, although, the disc does need ventilation away from any other electronics as it is normal to run very hot and overall is very efficient for power loss.

The Polyfuse(TM) metal oxide resistor has the (opposite) positive temperature coefficient (PTC) and can be used as short circuit resettable fuse protection. It is designed to regulate the resistance above normal operating current by regulating the temperature to 85'C. Like a fuse trip time depends on I^2 value over rating but comes in ALL ranges of current from mA to hundreds of Amps and may be strung in parallel.

 

[FvM]

Since the tungsten is mainly resistive, no PFC is needed, and inrush protection will extend the life of the heater significantly.

It's not clear to me which control method you are suggesting. Phase angle is banned for heating applications by power quality regulations (and for high power lighting too). Full wave switching is possible as long it doesn't collide with flicker avoidance requirements and can be tolerated by the load. The question is if the peak current at lowest output power (and respective low filament temperature) will be acceptable. In any case, the RMS current with low duty cycle full wave switching will be unwanted high.

I imagine that a buck PFC with unfiltered output (fullwave rectified waveform) could be the most effective solution.

 

[D.A.(Tony)Stewart]

I am not sure even how to avoid flicker with a DC-DC with a manually changing target and constantly cycling temperature and load. The flicker specs are quite severe. But they should be much better than my concept of an ICL regulated hysteretic half cycle dropping Triac controller.

I was thinking the ICLs would not produce any rectangular currents, but that's not good enough.



How does one prevent >4% change in line voltage if the line impedance is 0.4Ohms per IEC. Or even smaller changes in one minute.

Tony "sunnysky" Stewart