Patent Application
20140035480
The present invention relates to the control of luminance of gas-discharge lamps and the use of apparatus for such application.
The role of lamps is to illuminate a certain location, be it an indoor space or an outdoors environment, so as to make objects discernible to the observers. Ambient light however is subject to changes over time, sometimes quite rapidly and typically following a diurnal cycle of natural light intensity change. Artificial light is intended to compensate for the lack of natural light during dark hours of the day, in dark places, or for many other local reasons. For implementing control over the Illumination, it is required to increase or decrease the amount of illuminating elements, e.g. lamps, or change the luminance of existing ones, or both.
Gas discharge lamps are light sources that are often used for general purpose lighting, both indoor, such as in homes, houses, industrial spaces, as well as outdoors e.g. street lighting. In such devices, the illumination is produced as the free electrons accelerated by the electric field inside the lamp collide with gas atoms and other atoms inside the lamp. The collision causes electrons in orbit to jump to a higher energy state. When such electrons revert to their original state, energy is released in the form of light. Typically noble gasses are used for such lighting, xenon, neon, helium and argon are mostly used or some combination thereof. When the electrons are accelerated in an electric field through the gas ions, some electrons are raised to a high level of energy and when they return to their basic level of energy, the surplus energy is discharged in the form of photons, sensed by the eyes as light.
The gas discharge lamps are also referred to as electric discharge lamps, vapor lamps, and more rarely just as discharge lamps. In addition to the noble gas, metals or metal salts may be added to the container in which the gas is disposed. Typically, gas discharge lamps operate more efficaciously at higher frequency AC input. In order to prevent self-destruction, gas discharge lamps employ a ballast, referred to also as choke, which contains a coil, usually wound over iron core. The ballast may be integral with the lamp or it physically placed outside of the lamp and connected electrically to the lamp.
A system for the control of luminance of a gas-discharge lamp, which includes a variable frequency drive (VFD) accepting AC voltage supply. The VFD is has a constant ratio of frequency to AC voltage ratio of the output. Raising the frequency of the output of the VSD would result in an equivalent rise in the voltage. Typically, a ballast on the input AC of the lamp is required and the power factor correction capacitor usually associated with the lamp is to be removed.
The invention may be understood upon reading of the following detailed description of non-limiting exemplary embodiments thereof, with reference to the following drawings, in which:
The following detailed description of the invention refers to the accompanying drawings referred to above. Dimensions of components and features shown in the figures are chosen for convenience or clarity of presentation and are not necessarily shown to scale. Wherever possible, the same reference numbers will be used throughout the drawings and the following description to refer to the same and like parts.
In accordance with the present invention, the luminance of a gas discharge lamp is controlled by a device otherwise used for driving AC electric motors. The concept of control of luminance used hereinafter means the change, reduction or increase of luminous intensity. The term driving is used hereinafter, as known in the art, to define the ability to control the rotational speed of an AC electric motor. More specifically, the device used in accordance with the present invention is a variable frequency drive (VFD), also known as variable voltage variable frequency drive. In VFD the ratio between the output voltage and output frequency that feeds the motor is kept constant. As can be seen in
One prevalent variant of the VFD is the pulse width modulation (PWM) technique for voltage output control. PWM drives are well known in the art for applying control over the speed and frequency of power tolls, as can be seen in U.S. Pat. No. 6,696,814, the contents of which are incorporated herein by reference. In this method, the DC/AC converter uses switching to form a quasi-alternating current. The switches are in implemented as thyristors, bipolar transistor devices or transistorized devices or as IGBTs, for more details see for example U.S. Pat. No. 6,462,974, the contents of which are incorporated herein by reference. The control over the output voltage is not a closed loop circuit, and a change of the output voltage level, negative or positive, is approximated by the switching only. As a schematic description of the above discussed matter, as can be seen in
In VFD, the output voltage, and the waveform in general can be controlled by pre-programming or on-line for several AC voltage output rates and programs, such as gradual increase or decrease of amplitude. As mentioned above the modern PWM circuits employing IGBT lend themselves to easy and accurate control over voltage supply by the PWM circuit. As such, the PWM circuitry does not offer a full feedback controlled voltage supply loop. However, for the sake of keeping track of required illumination levels, a light sensor can be added to complete the loop. To help explain the implementation of the service programming in the framework of the command module, reference is first made to
The term service control in the context of the present invention relates to illumination specific applications associated with luminance control. A pre-supplied set of programs that are intended to offer alternative illumination features, such as for different lamp types or different lighting regimes is the PSSP and SSP. Typically the producer of the VFD provides also a human/programmed command module that facilitates manual or automated control of the electro-mechanical load by the VFD. In the context of the present invention, additional services are provided to accommodate the VFD to its usage in the control application over the luminance driven by the VFD. An example of usage of such automated control, is the application of different lighting regimes employing respective different voltage output levels, set for different hours of the day. For example, a sensor connected to the processor running an SP senses that natural luminance is low, and that the lamp or lamps such a s street lamps are to be turned on. The SP would wait for, say 15 minutes, getting clock pulses, to preclude the influence induced by a passing cloud, after which, if darkness prevails, the VFD would start turning on the associated lamp at a gradual controlled rate until full programmed luminance is obtained. Lights can be turned on at a fixed hour, such as four in the morning. Another example is a working room in which lights are to be turned on at a fraction luminance during the day and luminance is raised during night hours. User intervention may be applied as long as the program permits. Yet another example is an infrared motion sensor, that detects the presence of a person entering a room, in such an example, the entrance invokes the SP to start a cascade of events that leads to automatic illumination of a room, or hallway. The examples portrayed above demonstrate an important aspect of the implementation of a system of the invention. The carefully planned reduction or increase in luminous intensity is conducive to energy saving strategy of power usage.
Since gas discharge lamps are inherently different than electromechanical loads, some limitations may be inserted into the service programs in order to prevent damages to the lamps/ballast and other electronic components of the illumination hardware. In case the original program parameters of the producer of the VFD may be found to be unacceptable with respect to current parameters supplied to the lamp, or else be found too limiting, change may be require. In order to adapt the VFD to the control/drive of the gas discharge lamp, some experimentation may be required in order study the security and or efficiency aspects of the current parameters and possible limitations bestowed by the VFD.
In another aspect of the invention a communications interface is installed. As can be seen in
An arrangement in accordance with the present invention is applicable for three phase AC line and a single phase line voltage. The AC line used dictates the architecture of the rectifier circuit. For each phase two solid state rectifiers are required, and for the output switching, for each phase an equal set of switches is required. An advantage of the system of the invention stems from the fact that any AC or DC source that can feed the DC bus (see
The system of the invention can also be used for emergency lighting energy supply. To such an end, for example, a battery is connected to DC bus 22 using a relay, such that when the mains AC supply fails, the relay connects the battery to DC bus 22 to feed converter 24.
In another aspect of the present invention, it has been shown experimentally that using the system of the invention can shorten the time the illuminations starts. In gas discharge lamps, typically a period of time passes since turning on the switch and the actual illumination begins. The implementation of a VFD in accordance with the invention can shorten the time to full illumination considerably.
