02-10-2012, 05:50 PM
Flicker-Insensitive Light Dimmer for Incandescent Lamps
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Abstract
This paper presents a new dimmer that does not
amplify light flicker in incandescent lamps. The development of
this new dimmer is motivated by the fact that the incandescent
lamp is very sensitive to voltage fluctuation and the typical
R−C-circuit dimmer for incandescent lamps amplifies the light
flicker considerably. The proposed method utilizes a 16-b microcontroller
to calculate the fluctuation voltage and determine the
appropriate firing angle for a power switch device in the circuit
of the dimmer. The mathematical model and simulation of the
incandescent lamp with the proposed dimmer are also presented.
By dynamically adjusting the firing angle to compensate for the
voltage, the proposed dimmer can substantially diminish the light
flicker. Furthermore, a series of experiments on this dimmer has
been made to test its performance, and the results demonstrate a
remarkable reduction in amplifying effect of light flicker.
INTRODUCTION
VOLTAGE fluctuation is a crucial problem in power quality
issues. The International Electrotechnical Commission
standard states that the magnitude of the voltage fluctuation or
voltage flicker should be within 10% of its rated voltage source
[1]. However, even a relatively minor variation in voltage (e.g.,
0.3% voltage fluctuation) can affect lighting [2]. Voltage flicker
is considered one of the harshest power quality events because
of its harmful effects on most electronic circuits [3]–[5].
Furthermore, the flicker could result in annoyance and health
problems through the eye–brain system [6]. Voltage flicker
can be caused by arc furnaces, welders, and the switching of
heavy loads such as air conditioners, elevators, and pumps.
These loads draw a great current during operation resulting in a
voltage drop due to line impedance [7], [8]. The voltage flicker
could also be produced by two interharmonics [9].
TYPICAL DIMMER
Present day dimmers for incandescent lamps utilize a phasecontrol
circuit to vary the conducting period of each half cycle
of the lamp currents, thus controlling light output. Datta [14]
contributed a study which provides the full-aspect experimental
evaluation of the incandescent lamp with a conventional dimmer
including the measurement of input power factor, harmonic
emission, and the efficiency of dimmers. A common light
dimmer contains a basic phase-control circuit comprised of a
triode for alternating current (TRIAC), adjustable resistor, and
capacitor shown in Fig. 1. The larger the resistance of R1, the
longer it takes for the voltage across the capacitor C1 to rise to
the point where the TRIAC is triggered to its ON-state.
SIMULATION
The purpose of this section is to theoretically prove the
feasibility of the proposed method by deriving the mathematical
model of the incandescent lamp and then simulating the light
intensity when the dynamic-phase-controlled voltage is given.
The heat transfer behavior of an incandescent lamp filament
can be reasonably approximated with the equivalent circuit
shown in [18]. The filament is modeled by the thermal resistance
Rθ (degree Celsius per watt) in parallel with the thermal
capacitor Cθ (watts per degree Celsius).
PROPOSED METHOD
To solve this problem, the dynamic phase controller (DPC)
dimmer is proposed and designed around a light dimming
system [16] by adding a low-cost 16-b microcontroller unit
(MCU) to calculate the fluctuating voltage and then obtain
an appropriate firing angle for each cycle of the line voltage.
Therefore, the firing angle α is dynamic and is updated every
cycle so that the one-cycle rms voltage is controlled to track a
constant target rms voltage by shifting α every cycle. Although
the firing angle could be configured to be updated every halfcycle,
this configuration would create a minor dc bias voltage
due to its potential for asymmetric phase control [16], which is
not allowed according to the IEEE 519 standard [17]. Therefore,
the firing angle is updated every cycle in this paper to
achieve the symmetric phase control.
CONCLUSION
The DPC dimmer, using a low-cost microcontroller, is proposed
in this paper. By dynamically adjusting the firing angle
to compensate for the voltage, the DPC dimmer can reduce
the light flicker. The simulation of the proposed method is
presented, and its result shows the feasibility of the DPC
dimmer. The experimental results show that the D