Load power reduction control and supply system

Details Load power reduction control and supply system Load power reduction control and supply system

2000-01-13

2001-02-20

Berhane, Adolf Deneke (Department: 2838)

Electricity: power supply or regulation systems

Output level responsive

Using a three or more terminal semiconductive device as the...

C315S360000

Reexamination Certificate

active

06191568

ABSTRACT:

This invention is a combined load power consumption reduction system, voltage stabilizing control system, and power supply system, particularly for controlling the power supplied to street-lighting loads (luminaires) and especially for high-intensity discharge (HID) and fluorescent luminaires.
BACKGROUND OF THE INVENTION
Street lighting systems may be operated by manually operated switches, but more frequently they are operated under the control of a photoelectric cell or timer or a programmed combination of both a timer and a photoelectric cell. In conventional such systems, steady-state power is applied to the load at full rated voltage.
Experience shows that street lights may operate at power levels substantially below rated power levels without causing a perceptible decline in the illumination provided. While during peak night-time traffic hours it may be desirable to operate the street lamps at full rated voltage, nevertheless in the middle night-time hours when traffic intensity is low and many people are asleep, municipalities for economic reasons may choose to operate street lamps at reduced power levels. Satisfactory control circuits to permit reduced power level operation (sufficient to provide satisfactory off-peak illumination) to occur automatically, subject to various overrides to deal with particular circumstances, are not readily available.
SUMMARY OF THE INVENTION
The invention is a load voltage and power control and supply system for the supply of power to a load for which, over particular periods of time, usually on a daily basis, it is desired to reduce power. The invention has particular application to street lighting systems and similar systems in which, for a period of several hours during the night (when traffic is minimal and many people are asleep), the lighting system can operate at reduced power. The system according to the invention is able to act as a voltage stabilizer as well as a controlled power reduction system.
The power control system according to the invention may operate the load from a single control location, even if the load is spatially dispersed, as in the case of a multiplicity of luminaires. Experience shows that moderately reduced power (say a 30% reduction in power) supplied to such luminaires does not appreciably diminish the adequacy of the illumination at such reduced power levels as compared with full-power illumination.
Further, the power control system is able to reduce power in stepwise decrements each of which reduces power by a small amount insufficient to diminish noticeably the ambient illumination.
In one aspect, the invention provides a power control unit for connection between a source of power and a load, and for control of power supplied to the load, comprising the combination of the following components:
1) a power supply circuit connectable to the power source for providing an output current at controllably variable output voltage levels over a range of voltage values (thereby to be able to effect a stepwise reduction in output voltage from the high end to the low end of the range);
2) a driver circuit (which may be integral with the power supply circuit) for driving the power supply circuit so as to set the output voltage level at which the output current is for the time being supplied to the load; and
3) a controller (preferably a microcontroller) for controlling the driver circuit to drive the power supply circuit to provide output power at a voltage set by the driver circuit in response to the controller. At the high end of the voltage range, the controller provides a signal to the driver circuit that compels the driver circuit to set a high output voltage level for the power supply circuit output so as to supply power at a set high-power setting. This high-power setting persists for a period of time T
Hi
starting upon the occurrence of a high-power start condition, and ending upon the occurrence of a high-power end condition. At the low end of the voltage range, the controller provides a signal to the driver circuit that compels the driver circuit to set a low output voltage level for the power supply circuit output so as to supply power to the load at a set low power for a later period of time T
Lo
starting upon the occurrence of a low-power start condition and ending upon the occurrence of a low-power end condition.
The controller in operation may transmit a sequence of control signals to the driver circuit to cause the driver circuit to (i) set the high output voltage level so as to supply power at the set high power setting for the period of time T
Hi
, (ii) set the low output voltage level so as to supply power to the load at the set low power for the period of time T
Lo
, and (iii) set a series of diminishing voltage levels during a transition period between time periods T
Hi
and T
Lo
. The time periods T
Hi
and T
Lo
may be recurrent, for example diurnally recurrent in the case of street lighting systems.
During the transition period following time period T
Hi
and preceding time period T
Lo
, the controller controls the driver circuit to set a series of output voltage levels for the power supply circuit diminishing controllably from the set high output voltage level to the set low output voltage level in accordance with selected characteristics of the load. Preferably the voltage is stepwise decremented from rated load voltage to a target reduced voltage level. In the case of a load constituting a bank of luminaires, the aforementioned selected characteristics may be, for example, (i) the maximum voltage drop that a luminaire may tolerate before snuffing out (which value may vary with the type of luminaire and the voltage prevailing when the voltage reduction occurs) and (ii) the maximum voltage reduction that can be effected without causing a noticeable reduction in illumination by the luminaires. This latter will be especially important in street lighting situations, because a noticeable reduction in illumination may impair vision or cause alarm to motorists passing by the luminaires. Accordingly, each sequential voltage reduction, proceeding from full rated voltage to target reduced voltage, will generally be selected to be less than the lesser of values (i) and (ii) above. The stepwise reductions may be selected to be some specified percentage of the previously prevailing voltage level.
The power control unit may advantageously including a sensor of supply current to the load, to which current the controller is responsive. During the transition period and after the supply current to the load has stabilized, the controller provides the next succeeding stepped output voltage level reduction.
The power control unit may include an autotransformer whose output is supplied to the load and whose output voltage level is variable in response to the driver circuit.
The power supply circuit may include a compensating transformer whose secondary winding is connected in series with the load and whose primary winding is connected between the center tap of the autotransformer and a variable tap on the autotransformer winding. The autotransformer is connected so that the secondary winding voltage is added to the output voltage of the autotransformer to constitute the output voltage level for supply to the load.
The driver circuit may include a servomotor connected to the variable tap on the autotransformer winding and responsive to the controller. In this case, the voltage applied to the primary winding of the compensating transformer is taken from the variable tap, whose position on the autotransformer winding is controlled by the servomotor in response to the controller.
The power supply circuit may in an alternative embodiment include an autotransformer whose winding is tapped at a first output tap that provides the high output voltage and also tapped at a second output tap that provides the low output voltage. Preferably one input terminal of the autotransformer is located at a tap positioned between the said output taps, and the other input terminal of the autotransformer is connected to the zero volt

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