WO2009045173A2

WO2009045173A2 - Switching device

Info

Publication number: WO2009045173A2
Application number: PCT/SG2008/000376
Authority: WO
Inventors: Ettanoor Thuppale Mohan Dass
Original assignee: Ettanoor Thuppale Mohan Dass
Priority date: 2007-10-02
Filing date: 2008-10-02
Publication date: 2009-04-09
Also published as: SG151142A1; WO2009045173A3

Abstract

A system for controlling the activation of an electrical load comprising a receiving device for receiving an ambient condition input; a output device, in communication with said receiving device, arranged to output a signal proportional to the ambient condition input; a controller for receiving the signal from said output device and comparing said signal to a reference value; said controller arranged to deactivate a switch in communication with said electrical load on detecting the signal exceeding the reference value and activating the switch when the signal falls below said reference value.

Description

SWITCHING DEVICE

Field of the Invention

The invention relates to electrical systems requiring operation based upon application- specific ambient conditions. For instance, but not limited to, street lighting that is turned off or on depending upon the lumens level.

Background

There are several electrical systems which require operation based upon changes in ambient conditions meeting and exceeding pre-determined threshold levels. Said ambient conditions may include ambient light, water level, temperature, or other such variable condition.

In many instances, the change is based upon time and, as such, an electrical system may be operated and shut down based upon known periods of operation. In the case of ambient light, said known periods may apply to day time or night time operation..

In the case of ambient light, the known periods of day or night time operation vary considerably with time of year, reflected light, imposed shadows etc.. Notionally, street lighting is turned off at dawn and turned on at dusk. Electric or electronic timers are generally used to control electrical loads that need to be operated at some pre-set time. When this pre-set time has to be related to the sunset or sunrise times, it becomes almost impossible to synchronize these two on a daily basis, except by the use of very sophisticated electronic circuitry.

Even when such a sophisticated electronic circuitry can achieve the operation of the load devices synchronized with the sunset and sunrise timings, there need not be any correlation between the ambient light levels at dawn and dusk with the operation of the electrical loads such as streetlights. This may lead to waste of electrical power due to early switching on, or late switching off, of the streetlights

Traditionally this was based upon a time consideration but more recently, switching devices relying upon available sunlight have become more common. In most cases these devices are application-specific and can't satisfy precise operation dictated by ambient light, resulting in wastage of electrical power, additional maintenance cost and compromise on safety considerations. One such arrangement is the use of a photo resistor within said device.

Devices based on photo resistor, sense the drop in resistance of the sensing device due to intensity of direct light to trigger switching operation. However, such devices are susceptible to ambient temperature changes which affect the resistance value of a photo resistor. Hence, for external applications, it is impossible to get precise switch operation related ambient light alone. Further, devices based on photo resistor inherently can handle only small sensing current hence limited scope for sensitivity adjustment. Similarly, such devices based on photo resistors are unable handle large loads in terms of voltage or amperes.

Such an electronic circuitry will also require power to operate it 24 hours a day and 365 days a year and skilled personnel to set the time initially, sometimes in accessible places. Such an electronic circuitry will not take into account the variations in the sunrise and sunset timings within a time zone

Summary of Invention

In a first aspect, the invention provides a system for controlling the activation of an electrical load comprising a receiving device for receiving an ambient condition input; a output device, in communication with said receiving device, arranged to output a signal proportional to the ambient condition input; a controller for receiving the signal from said output device and comparing said signal to a reference value; said controller arranged to deactivate a switch in communication with said electrical load on detecting the signal exceeding the reference value and activating the switch when the signal falls below said reference value.

In a second aspect, the invention provides a method for controlling the activation of an electrical load comprising the steps of: receiving an ambient condition input; outputting a signal proportional to the ambient condition input; comparing said signal to a reference value; deactivating a switch in communication with said electrical load on detecting the signal exceeding the reference value, and; activating the switch when the signal falls below said reference value.

Accordingly, the invention may be embodied by a device that continuously measures the total ambient light level and compares it to a fϊeld-settable threshold to switch "On" or switch "Off an electrical load. The ambient light measurement is by photovoltaic module / panel and the switching of the electrical load is through the activation of conventional switchgears like contactors and circuit breakers. Measuring total ambient light rather than direct sunlight yields more realistic, reliable and flexible method of decision making to switch "On" or switch "Off an electrical load without any reference to sunrise and sunset timings under all weather conditions and in all seasons. The threshold can be field-set to meet the operational or statuary or safety requirements of the electrical loads

In a preferred embodiment, the invention measures the ambient light levels (that may include reflected and scattered natural, or artificial, light) in real time using photovoltaic energy generation and compares it with a pre-set (field adjustable) value to perform Solid-state switching of conventional high capacity electrical switch gear like, contactors and breakers.

In this embodiment, total ambient light may be measured in real time without reference to a clock and without the need for any external power source for its operation. The device may be field-set, such that its unattended operation follows the measured ambient light level. This may overcome the drawbacks of the current concepts or systems, and so may be applicable to a wide range of applications. This arrangement provides many benefits, including the ability to control an electrical load in kilowatts with a system operating on milliwatts. That is, the magnitude of the electrical load controlled is not limited by this device.

Further, unlike an arrangement using a photo resistor, a system according to the present invention may not require an external power source like battery, and so avoiding some maintenance issues.

In a preferred embodiment, the system may not require field calibration or field maintenance.

Li a preferred embodiment, the reference voltage may be adjusted so as be applicable for artificial light sensed operation, such as for security applications.

In a preferred embodiment, the system may be employed as a remote load switching device by simulating photovoltaic input.

Applications of the invention may include, but are not limited to :

• Street lighting in urban and rural areas, including highways; Space lighting in public buildings both inside and outside; Common lighting in public housing; • Public utility area (parks & recreation grounds) lighting;

• Short fly-over road lighting with or without provision for natural light ingress Security lighting based on intruder detection or on demand or ambient light (airport perimeter road);

• Automated animal feed systems in mechanized and remote farms;

• Various applications in intelligent building systems;

• As power switching component of a sensing circuit regardless of the variable sensed.

Brief Description of Drawings

It will be convenient to further describe the present invention with respect to the accompanying drawings that illustrate possible arrangements of the invention. Other arrangements of the invention are possible and consequently, the particularity of the accompanying drawings is not to be understood as superceding the generality of the preceding description of the invention.

Figure 1 is a schematic view of the system according to one embodiment of the present invention;

Figure 2 is a flow chart of the method according to a further embodiment of the present invention;

Figure 3 is an electrical diagram of the system according to a further embodiment of the present invention, and;

Figure 4 is an electrical diagram of the system according to a still further embodiment of the present invention.

Description of Preferred Embodiment The system 5 has shown in Figure 1 comprises a photovoltaic panel 15 in communication with a self contained control unit 10 in which is located a controller (not shown). The controller receives input from terminals 20 marked "S+" and "S-" providing the ambient light level inputs from the panel 15 and compares this to a predetermined reference voltage. The reference voltage is supplied by an AC supply input 30 so that the reference may be adjusted based upon certain parameters relating to the installation, which for this embodiment may be set at 12V.

In one embodiment it is envisaged that the device will be used for street lighting and so configured to turn on at dusk and switched off at dawn. The ambient light is received by the photovoltaic panel 15 and acted upon by the controller within the unitary unit 10. The system 5 measures the ambient light in terms of output from a photovoltaic panel 15, conditions it and compares it with the reference value to fire a set of Thyresistors, which in turn handle the power device contactor's coil energizing load.

An advantage of this embodiment is that each street light may be configured to its location by adjusting output from the panel 15 to which is compared the reference value. Thus in highly exposed areas, the reference voltage may be somewhat higher as compared to a shaded area which may require the street lighting to be switched on earlier than that of the exposed area.

Further the combination of panel and unitary unit 10 may be arranged to service an array of street lighting such that the electrical load for which the invention is applied is applicable to a number of lights having similar configurations with regard to reference voltage.

The reference value supplied to the comparator circuit acts as a threshold corresponding to the desired ambient light level. By observing the Lux levels of the ambient light with a hand-held "Lux-meter" at site, the potentiometer 55 in the sensing circuit can be set to fire Thyresistors and in turn the power device contactor.

The terminals 30 marked "N" and "L" are the AC inputs for reference voltage generation and to provide AC power to drive external contactors (switchgear) via terminals A2, one for each contactor. The device may further benefit from adjusting the sensitivity of a particular unit to a degree greater than is provided by the AC supply 30. To this end, a sensitivity adjustment 55 may be applied such that an operator making a local inspection may make an adjustment to a particular unit according to local observations.

The unit 10 may further provide LED signals to indicate that a signal from the panel 15 has registered 45 and further that the switch has been activated so as to provide a visual indication of the contact made 50.

Accordingly, on switching the electrical load, contactors 25 are activated or deactivated according to the signal received from the panel 15. Figure 2 shows a process according to the present invention. The first step involves adjustment of the threshold, including making any fine resolution adjustments 65 based on local conditions in which the unit 10 is located.

The controller then commences sampling 70 the output from the photovoltaic panel 15. The system is operated by the output signal whose output potential can range from 2V to 20V when exposed to ambient light. The system generates it own fixed regulated DC power supply (fixed reference) derived from the AC input, in this case, 12V.

If necessary, the output signal is conditioned 75, before a comparison 85 is made with the reference voltage. If greater, then the switch is activated 100. Otherwise, the sampling recommences.

A further embodiment includes a decision branch when the switch is activated. This allows for the circumventing the process if the previous cycle/iteration was less than the reference voltage 80. If so, then the process continues to the switch activation step 95.

In a further embodiment, a further decision branch 90 includes testing whether the output signal is considerably (abnormally) higher than the reference voltage, such as a spike in the system caused by a lighting flash. In this case, the system progresses to deactivating 100 the switch. With reference to Figure 3, the system according to the present invention is embodied in a circuit diagram 105. The circuit 105 includes five basic functional¹ elements or circuits.

Firstly, a reference voltage generator circuit 110 produces the DC reference voltage of 12V. Next is provided an input signal conditioning and threshold setting circuit 115 for receiving the ambient condition input and conditioning this to produce a signal. In this embodiment, the threshold setting is adjustable using a potentiometer.

Also, there is provided an error signal generating and zero cross over switching circuit 120. This provides, inter alia, for the power switching to occur at a phase angle of 0 or 180 degrees so as to switch at near zero voltage, prolonging the life of the power of the power switching components. Lastly, there is a power switching output, generating opto-coupler and triac circuit 125 to effectively isolate the control circuit from the power circuit.

The solar photovoltaic module output is compared with the fixed reference to generate an error signal by a logic comparator. This error signal is used to switch the AC power "On" or "Off. Below the set threshold value, for all values of solar photovoltaic module out put the error signal remains constant. This error signal is built with a hysterics to prevent switch chattering effect when the ambient light hovers around the threshold value The AC switching pre-driver is in-built with "Zero" cross detection network. This

"Zero" cross network will allow the AC switching component to switch the AC, only when the sinusoidal wave crosses the zero point (0° or 180°- Phase Angle)

The AC switching pre-driver is an "Opto-Isolator" built with an LED and a "Triac". The error signal potential is applied to the "Opto-Isolator". The LED in the "Opto-Isolator" turns on and switches the built in "Triac".

When the "Opto-Isolator"/"Triac" switches at zero cross over point in turn switch on AC load switching switchgear like contactors or breakers. The mains switching components can be either a "Triac" or SCR.

To switch an inductive load two "Triacs" are employed connected back to back. AC potential is available at the output to drive contactors to switch on the connected load/s

Device Terminals

In this embodiment, the device has three pairs of terminals for connections

1. A pair of reverse polarity protected solar photovoltaic module sensing input terminal ("S+" & "S-"). Accidental reverse connection of solar photovoltaic module will not harm the device / Invention and will make it inoperative

2. A pair of AC potential input terminals, Line ("L") and Neutral ("N"). Interchanging the polarity will have no impact on the device / Invention

3. An AC potential output terminal marked "A2" for each switchgear device. Invention's output polarity and potential must be matched with that of the switchgear device to be connected if its polarity is a concern

Applications & Merits

1. The device can be used for switching (On/Off) of any kind of electrical load by ambient light, for example the streetlights based on Lux levels on the road surface, farm animal feeding systems based on the twilight level, etc., automatically;

2. The device can be used to switch "On & Off' the public lighting (parks, corridors of public buildings, etc.,) based on the Lux levels of the "Darkest" spot in the area being illuminated;

3. The device can be employed to respond to artificial light rather than to natural light on an "As and When Needed" basis. A simple remotely operated light bulb can switch "On" or "Off a much higher power load. For example remote operation of security perimeter lights of a large area as and when needed;

4. The device can be employed as a "Detector" to respond to artificial light to switch "On" much higher load - Intruder alert in security systems;

5. More frequently or manually or mechanically switched (On and Off) operations of electrical loads can be fitted with this device as a static switch to minimize or eliminate the wear and tear problem and increase reliability;

6. Switch (On / Off) single phase and three phase electrical loads;

7. Once the ambient light threshold is set the system will operate without further adjustment or human intervention and follows the seasonal variations in weather, hence ideal for inaccessible locations.

8. As a power switching component of a sensing circuit regardless of the variable monitored or sensed

Figure 4 shows an alternative circuit 130 according to the present invention. A reference voltage generator circuit 145 is adopted which is similar to that of Figure 3 with some components removed to limit complexity. The solar photovoltaic module 140 which comprises an input signal conditioning and threshold setting circuit 143 is also incorporated. The circuit according to Figure 4 differs from that of Figure 3 by the incorporation of a proprietary integrated circuit 150 and the addition of a trim pot 155 for the setting of the threshold value which simplifies the circuit as compared to Figure 3. The error signal generating circuit 132 and output power switching circuit 135 are substantially the same as the equivalent circuits in Figure 3. Further differences include the use of a Triac 136 in the place of an opto-isolator using a similar integrated circuit 157. Comparator circuit feedback resistors have been selected to achieve a better characteristic response to prevent a switch chattering effect when the ambient light hovers around the threshold value. The main power output switching circuit 135 is the same as that of Figure 3 except for the use of a SCR accepting signal from the integrated circuit 157 instead of from an opto-isolator used in Figure 3.

Claims

1. A system for controlling the activation of an electrical load comprising a receiving device for receiving an ambient condition input; an output device, in communication with said receiving device, arranged to output a signal proportional to the ambient condition input; a controller for receiving the signal from said output device and comparing said signal to a reference value; said controller arranged to deactivate a switch in communication with said electrical load on detecting the signal exceeding the reference value and activating the switch when the signal falls below said reference value.

2. The system according to claim 1 wherein said ambient condition input includes any one of: light, water level indication from a water containment apparatus, heat and change in temperature.

3. The system according to claim 2 wherein light includes direct, reflected and scattered natural light.

4. The system according to claim 2 wherein light includes artificial light.

5. The system according to any one of the preceding claims wherein the electrical load includes a device for detecting the 0 or 180° phase angle of said electrical load.

6. The system according to claim 4 wherein the detection device and controller are in communication such that the controller is arranged to activate or deactivate the switch at the 0 or 180° degrees phase angle of said electrical load.

7. The system according to any one of the preceding claims wherein the controller is further adapted to deactivate the switch on a detection of a discontinuous increase in the output above said reference.

8. The system according to any one of the preceding claims wherein the output device further includes a conditioner for conditioning the output so as to produce the signal based on a desired threshold.

9. The system according to claim 8 wherein the desired threshold is dependent upon lumen levels of an area in which the system is located..

10. The system according to claim 8 or 9 wherein the conditioning device is further arranged to process the output such that it follows a hysteretic path between the dusk and dawn event.

11. A method for controlling the activation of an electrical load comprising the steps of: receiving an ambient condition input; outputting a signal proportional to the ambient condition input; comparing said signal to a reference value; deactivating a switch in communication with said electrical load on detecting the signal exceeding the reference value, and; activating the switch when the signal falls below said reference value.