Electric power conversion systems – Current conversion – Including an a.c.-d.c.-a.c. converter
Reexamination Certificate
1999-09-23
2001-08-28
Nguyen, Matthew (Department: 2838)
Electric power conversion systems
Current conversion
Including an a.c.-d.c.-a.c. converter
C315S307000
Reexamination Certificate
active
06282105
ABSTRACT:
FIELD OF THE INVENTION
The sent invention concerns a device and method for powering discharge lamps of a public lighting network.
BACKGROUND OF THE INVENTION
The technical sector of the invention concerns the field of power supply methods and devices for powering public lighting networks.
The discharge lamps used for public lighting are conventionally powered by an electrical distribution network through inductive resistors called ballasts. The illumination and power of these lamps are strongly affected by the voltage of the electrical distribution network. Moreover, an unsatisfactory correlation is noted between the needs for high-degree illumination in the evenings when traffic is at its busiest and when energy consumption is at its peak. The network voltage is therefore at its lowest point and the lighting level is at its lowest.
At night during the “low-consumption hours”, the network voltage regains its high limit and thus corresponds with the conventional devices used for public lighting at a maximum lighting level when the traffic, the satisfactory lighting of local residents and energy saving involve a reduced lighting level. This results in a significant waste of electric energy.
On the other hand, it is now admitted that the frequency (50 or 60 hertz) of the electric distribution network is too low to ensure maintaining ionization of the electric arc of lamps and which is therefore interrupted and reignited twice per period, namely 100 (or 120) times per second. Reignition is obtained by a voltage peak which provokes ageing of the lamps when the lighting oscillations generate a stroboscopic effect, that is a source of visual fatigue. By feeding the electric arc with a frequency current greater than 5 kilohertz, these drawbacks are eliminated and the lifetime of the lamp is significantly lengthened.
The patent application FR 2,542,152 describes a method and device for powering discharge lamps with frequencies of about 800 hertz to 150 kilohertz by a pseudo-square, trapezoid or square signal delivered by a generator which can be fed with DC by a mounting shown on
FIGS. 6 and 7
of this document. Said mounting comprises:
a diode bridge connected to the network supply,
a self-inductive resistor connected to this single polar source by a reversing switch controlled by a control circuit fixing the period of the sequence cycle and the conduction time. The energy stored in the self-inductive resistor is discharged into the output capacitors by passing through a diode. Control of the switching transistor is carried out by a mounting comprising an oscillator, a single vibrator and control transistors. A transistor connected to a circuit equipped with Zenner diodes acts on the conduction time of the switch according to the output voltage and regulates the output voltage so as to compensate the fluctuations of variations of the charge of the network supply voltage.
This type of AC-DC converter, which is equipped with automatic control regulating the output voltage, has various drawbacks, and in particular owing to the complexity of the automatic control circuits for obtaining a steady, precise and reliable operation and linked with the difficulty to satisfy the standardizing constraints seeking to limit the radiated electromagnetic waves or feeders.
The U.S. Pat. No. 4,630,005 describes an AC-DC converter feeding several AC-DC converters (forming a type of electronic ballast) which each feed one or several discharge lamps. The AC-DC converter consists of a simple mounting of diodes adapted for a three-phase input voltage and to output delivery an AC voltage on three wires.
The U.S. Pat. No. 4,277,728 describes (
FIGS. 1 and 2
a
) a supply system similar to the one described in the Patent FR 2,542,152. The embodiment of the AC-DC converter shown on
FIG. 2
b
of this document uses a transformer whose primary is connected in series to a switching transistor, at the output of a diode bridge equipped with a filter. The output voltage is regulated by changing either the cyclic ratio or the switching frequency. The output voltage, filtered from the harmonic 2 of the network frequency, is used to modify the frequency of the control circuit of the switch so as to keep a constant output voltage. The devices described in this document are adapted to feed a single lamp requiring a weak power, namely several tens of watts.
SUMMARY OF THE INVENTION
The object of the present invention concerns a method and device for feeding a group of several discharge lamps which are improved, as well as a public lighting network implementing this method and device.
One object of the invention is to provide a simple reliable inexpensive device able to feed a distribution network with a D.C. current from an alternative network for public lighting and an improved method for feeding a public lighting network.
One object of the invention is to put right the drawbacks of systems generally used for feeding discharge lamps used in public lighting.
According to a first characteristic, the invention consists of providing a system for feeding a group of discharge lamps of a lighting network which comprises:
a device (called “central unit”) situated at the connection point of the alternative energy network taking from a network a sinusoidal and in phase current feeding the feed line of the group of lamps by a continuous voltage source galvanically isolated from the network and supplying (injecting) the group of lamps with a fixed power able to be adjusted according to several reference variables, and
devices (called “generators”) situated close to each lamp and providing the lamps with a current of medium frequency, that is a frequency of generally between 5 kilohertz and 100 kilohertz and in particular between 15 and 20 kilohertz.
In other words, the invention consists of feeding a group of lamps situated downstream from a connection point at the energy network by a central unit which galvanically isolates it from the network and transmits a DC voltage to the generators associated with the lamps independent of fluctuations of the network and able to vary according to a power reference variable. The central unit takes from the network a sinusoidal current in phase with a low harmonic rate. The generators provide the lamps with a “hypersonic” frequency periodic electric signal which significantly increases the lifetime of the lamps.
According to another characteristic, the invention consists of providing a DC feeding device from an AC source in intended, in particular for feeding a large number of discharge lamps of a public lighting system, with a power of several hundreds or thousands of watts and comprising:
a diode bridge
at least one rectified voltage—DC voltage converter fed by the diode bridge which is a transformer converter, whose output is galvanically isolated from the input and which does not have an automatic control for the output voltage.
The invention is based on the combination of:
the use of a transformer converter (generally known as “fly-back” converter), and
an automatic control of the delivered (or “injected”) power to the primary of the transformer, excluding any output automatic control, and
a galvanic isolation between the input and output of the converter.
The use of a “fly-back” converter for powers generally less than or equal to 1 kilowatt runs counter to a presumption generally admitted according to which this type of converter is only to be used for applications requiring only some tens of kilowatts owing to the fact that when the power increases, the stray inductance of the transformer limits its use or because the output of this type of converter is affected by this stray.
The absence of adjustment of the output D.C. voltage of the converter shall also go against a generally admitted prejudgment according to which it is necessary to adjust this voltage for avoiding energy waste caused by variations of the network voltage. However, users of the system carrying out voltage adjustments have had experience in modifying the group-points of the regulator from time to time so as to compensat
Boudan Jacques Emile
Froidefond Jacques
Dubno Herbert
Nguyen Matthew
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