A direct battery-driven LED lighting technology using
constant-power control is proposed for LED luminaire in
the present study. A system dynamics model of LED luminaire
was derived and used in the design of the feedback
control system. The PI algorithm was adopted in the controller.
The test result of the control system has shown that
the power of 18 W and 100 W LED luminaires can be controlled
accurately with error 2–5% at battery voltage
change 12–22.5%.
A real solar LED street lighting system using the constant-
power control technique was then designed and built
for long-term field test in a remote area.
The design of the solar LED street lighting system has
three unique features: (1) using the near-maximumpower-
point operation (nMPPO) concept in the design of
photovoltaic power generation system (Huang et al.,
2006) to avoid the maximum-power-point- tracking controller
(MPPT); (2) to charge the battery after the overcharge
point using PWM control technique; (3) to drive
LED for lighting directly from the battery using constant-
power control technique developed in the present
study.
A microprocessor(PIC)-based solar charging/discharging
controller was designed and built for LED lighting control
according to the constant-power control technique, for
battery charging control according to the 3-phase charge
control technique (Huang et al., 2010b), and for LED dimming
control according to a desirable schedule using the
time-variant constant-power setting values (Pset) in the
controller.
The dimming schedule of LED was designed with four
modes from 18 W in full load at beginning to 4.5 W before
sunrise. It was shown that the constant-power control performs
satisfactory in tracking the dimming schedule. The
total energy consumption of LED lighting was 125 Wh
per night.
The field test data shows that one clear-day charging can
provide LED lighting for at least three consequent nights.
The long-term performance for battery charging at daytime
and discharging (LED lighting) at night was found satisfactory
and no any failure since the installation. This verifies
the technical feasibility of constant-power control for
LED lighting and its application in solar lighting system.