WO2011082438A1

WO2011082438A1 - Method and means of controlling an electrical load

Info

Publication number: WO2011082438A1
Application number: PCT/ZA2010/000006
Authority: WO
Inventors: Selvanathan Narainsamy; Andrew Gary Wright
Original assignee: Radio Surveillance Technologies (Pty) Ltd
Priority date: 2010-01-04
Filing date: 2010-02-02
Publication date: 2011-07-07

Abstract

The electrical load control system 10 of the invention is illustrated with reference to a controller 10 intended to control an electrical load constituted by a hot water cylinder 12. The controller 10 relies on a public broadcaster to inject switch actuation codes into the normal signal broadcast by the broadcast, either as radio frequency (RF) signals, preferably in the form of RDS (Radio Data System) signals, or as audio frequency, in-band signals, whether in the form of humanly audible tones or as inaudible tones having an audio frequency outside of the normal humanly audible frequency range. The system or controller 10 comprises, at the load 12, a switch 14 connected in circuit with the electrical load 12. The controller 10 includes a RF receiver 20 preset to receive the RF signal of a predetermined public broadcasting service. In the audio-signal embodiment of the invention, the receiver 20 receives the broadcast RF signal and outputs an audio signal through an audio output transducer (not shown) similar to an audio speaker. The controller 10 includes an interface including a control circuit 22 that is interfaced with the switch 14 over a switch interface 24 and with the receiver 20 over a receiver interface 26. The control circuit receiver interface 26 is adapted to monitor the audio output of the receiver transducer for receipt of the publicly broadcast audio control signal. The control circuit 22 includes programmable logic means programmed, on receipt of the publicly broadcast audio control signal, to actuate the control circuit 22 by means of the switch interface 24, to actuate the switch 14, in use to switch the load OFF or ON.

Description

METHOD AND MEANS OF CONTROLLING AN ELECTRICAL LOAD

Technical field

This invention relates to a method and means of controlling electrical power consumption or electrical load.

Background art

In most countries, the cost and availability of electricity is determined to a great extent by peak load. The domestic load (the load on the electricity supply imposed by households) is one of the major contributors to peak load or demand, which has led electrical utilities, for many years, to try and control parts of the domestic load.

It has been shown conclusively that the electricity supply to a number of electrical appliances can be interrupted periodically without causing any real inconvenience. These appliances include under-floor space heating, potable water pumps, swimming pool pumps, area lighting particularly external lighting, air conditioners or any other electrical appliance or installation (domestic or otherwise) that consumes large amounts of electricity and the operation of which can be interrupted periodically without causing real user inconvenience. Hot water cylinders and water heaters for instance, can he interrupted for about an hour or two without inconveniencing the customer because of the thermal capacity of the water in the water heater.

Whilst the electrical load includes more than water heaters, recent research has shown that the controllable electrical load of most households consists mainly of hot water cylinders and water heaters (collectively referred to as the "hot water load") and that this constitutes between 25% and 40% of the total electrical load.

As a result, many suppliers and distributors of electricity try to control these types of appliances of individual customers, the hot water load being one of the simplest to control.

To implement such control, radio frequency (RF) and power line communications (PLC) controllers are sometimes used, as are combination RF/PLC systems. ln the recent past however, the most common hot water load control technology has been ripple control, in which so-called "ripple relays" allow the electricity supplier or utility to disconnect hot water cylinders during high power demand periods, thereby to avoid electricity load shedding, brownouts and blackouts. The most commonly available ripple switches are controlled by the addition of a second frequency that is superimposed on the 50Hz mains frequency. The ripple switches are adapted to detect this superimposed frequency and either switch ON or OFF as directed.

More recently, so-called "smart meters" have been introduced that include on-board programmable logic, by means of which the meter can be programmed to switch the electrical load controlled bythe meter with varying degrees of sophistication.

The disadvantage of these control technologies and ripple controls in particular, lies in the communications infrastructure required to transfer the controlling signals. Compatible communications equipment must be installed on each hot water cylinder to be controlled and the electrical reticulation system requires an extensive network of the signal transmitters that must be installed, in most cases dowi to substation level.

Disclosure of Invention

According to this invention a method of controlling a controllable electrical load comprises the steps of: locating, at the load, a load controller including: a switch adapted for connection in circuit with the load; a receiver previously set to receive and output at least one control signal publicly broadcast by a broadcaster as part of a public radio frequency (RF) broadcasting service; and an interface including a control circuit with programmable logic means, interfaced with the switch and the receiver; programming the load controller receiver interface to monitor the receiver output for receipt of the publicly broadcast control signal; programmingthe load controller control circuit switch interface, on receipt of the publicly broadcast control signal, to actuate the control circuit to actuate the switch, in use to switch the load OFF or ON; and the method including the steps, at the broadcaster, of injecting the control signal into the RF signal to be broadcast, the control signal being inaudible.

The electrical load may be constituted by a load selected from any one or more of a water heater, such as a hotwater cylinder, under-floor space heating, a potable water pump, a swimming pool pump, area lighting, an air conditioner and any electrical installation that consumes large amounts of electricity and the operation of which can be interrupted periodically without causing any real inconvenience.

The control signals can be (but need not be) audio signals. When using audio signals, the signal can be broadcast on an audio frequency outside of the normal humanly audible frequency range or the control system could use audible tones, such as Dual-Tone Multi- Frequency (DTMF) signals, as audio control codes.

In one form of the invention, the method includes the specific step, at the broadcaster, of injecting the control signal into the signal to be broadcast as a Radio Data System (RDS) signal.

The Radio Data System (RDS) or Radio Broadcast Data System (RBDS) as it is known in the United States of America, is a communications protocol for embedding digital data in FM radio broadcasts. The RDS is published as IEC (International Electrotechnical Commission) standard 62106. The RDS protocol standardises several types of information for transmission, including time, station identification and programme information. In addition, the RDS protocol defines a number of features that permit the "packaging" of private (non-public broadcast) data in unused program transmissions.

Alternatively, the control signal could be injected into the audio signal to be broadcast as an audio signal, the control signal being inaudible and broadcast on an audio frequency outside of the normal humanlyaudible frequency range.

A normal, humanlyaudible frequency is a frequency that is audible to the average human, unassisted. The generally accepted normal range of audible frequencies is 20 to 20,000 Hertz, but publicly broadcast F radio typically transmit audio frequencies between 20 Hz and 12 kHz as these frequencies, effectively, are at the lower and upper limits of human hearing.

Broadcasting is conventionally thought of as the distribution of audio and/or video signals which transmit program content to an audience. Where the audience is the general public or a relatively large general audience, the signal can conveniently be referred to as a "publicly broadcast signal". The program content can be referred to as a "broadcast".

In a preferred form of the first embodiment of the invention, the publicly broadcast signal may be constituted by the radio frequency (RF) signal broadcast by a commercial or other radio station, preferably an FM radio station. The switch actuation codes can be inserted as in-band signals into the normal broadcast of the radio station. The publicly broadcast signal could, in the alternative or in addition, be broadcast as part of a television broadcast, by a commercial or other television station, which could include terrestrial television, cable television and satellite television broadcasts. In such an event, the switch actuation code can be inserted as an in-band signal into the normal broadcast ofthe television.

The audio control signal is preferably constituted by a sub- or super-audible tone that is injected onto the audio signal stream bythe broadcaster.

The audio control signal may be injected by means of either or both phase shift keying (PSK) or frequency shift keying (FSK) of a reference signal constituted bythe audio signal stream to be broadcast, to either or both the sub or super-audio band.

In the sub-audio band, the audio control signal frequency may be any one or more frequencies between 10 Hz and 20 Hz.

In the super-audio band, the audio control signal frequency may be any one or more frequencies between 13 kHz and 18 kHz.

The code injection means may be constituted by a coding unit connected in circuit between the broadcaster audio equipment and thebroadcaster RF transmission equipment.

In the preferred form of the invention, the control signal is injected without the intervention ofthe broadcaster, the code injection means being constituted by a coding unit connected in circuit between the broadcaster audio equipment and the broadcaster RF transmission equipment, the coding unit beingunderthe control of a person other than the broadcast, such as a power utility for instance, by means of any one or more of a number communication mechanisms, inducing GSM/GPRS mobile phone communications.

In a further embodiment of the invention, the control method may include the steps of: programming the load controller receiver interface programmable logic means with a unique communications address to render the receiver interface specifically addressable by means of a broadcast control signal including the programmed address; and programming the load controller control circuit switch interface, on receipt of a publicly broadcast control signal including the programmed address of the receiver interface, to actuate the control circuit to actuate the switch, in use to switch the load OFF or ON; the method including the steps of, at the broadcaster, injecting the control signal into the audio signal to be broadcasttogetherwith a code representing the address of the load controller receiver interface address.

The invention includes a control system for a controllable electrical load, the system comprising: at the load, a load controller including: a switch adapted for connection in circuit with the electrical load; a receiver preset to receive and output at least one control signal publicly broadcast by a broadcaster as part of a public radio frequency (RF) broadcasting service; and an interface including a control circuit interfaced with the switch and the receiver; the control circuit receiver interface being adapted to monitor the receiver audio output for receipt of the publicly broadcast audio control signal; and th e control circuit switch interface including programmable logic means programmed, on receipt of the publicly broadcast audio control signal, to actuate the control circuit to actuate the swtch, in use to switch the load OFF or ON; and the control system including means, at the broadcaster, to inject the control signal into the RF signal to be broadcast as an inaudible signal.

The audio control signal may be injected by means of either or both phase shift keying (PSK) or frequency shift keying (FSK) of a reference signal constituted by the audio signal stream to be broadcast, to either or both the sub or super-audio band. In the sub-audio band, the audio control signal frequency may be any one or more frequencies between 10 Hz and 20 Hz and, in the super-audio band, the audio control signal frequency may be any one or more frequencies between 13 kHz and 18 kHz.

In a further embodiment of the invention, the load controller receiver interface programmable logic means may be programmed with a unique communications address to render the receiver interface specifically addressable by means of a broadcast control signal including the programmed address and the load controller control circuit switch interface may be programmed, on receipt of a publicly broadcast control signal including the programmed address of the receiver interface, to actuate the control circuit to actuate the switch, in use to switch the load OFF or ON, the control system including means, at the broadcaster, to inject the control signal into the audio signal to be broadcast together with a code representing the address ofthe load controller receiver interface address.

The code injection means preferably includes means to encrypt the control signals broadcast by the broadcasterand the load controller programmable logic means includes means to decrypt the encrypted control signals broadcast bythe broadcaster.

In this embodiment of the invention, the load controller programmable logic means includes memory means may conveniently be adapted to to store one or more actuation codesin load controller control circuit, the control circuit being programmed to compare an incoming authorisation code to at least one stored code be6re actuating the switch interface.

The audio control codes are sent as in-band signals, in-band signaling being the sending of data and control information in the same band, on the same channel, as is used for the normal transmission - in this case the public broadcasting channel. The two most convenient ways of switching the load OFF and ON is to broadcast swtch actuation codes constituted by SWITCH-ON and SWITCH-OFF codes or to broadcast only actuation codes constituted by SWITCH-OFF codes and switching the load back ON a predetermined time after the switch is switched OFF.

Since the control system of the invention relies on public broadcasting, the actuation codes broadcast are susceptible to recording and replay fraud. To this end, the system is preferably protected against such fraud with the use of one or more data security techniques, including means, programmed into the control circuit, to decrypt encrypted authorisation signals broadcast bythe broadcaster.

Alternatively, the one or more actuation codes (or series of codes) may be stored in memory in the control circuit, the control circuit being programmed to compare an incoming authorisation code to a stored code or a predetermined code before actuating the switch interface, particularly a switch ON command.

To lessen the recovery load during SWITCH-ON (if a number of hot water cylinders are switched ON in an area for instance) the programmable logic means is preferably provided with means to switch ON different loads in an area in sequence or at random, but not simultaneously. This is conveniently achieved by providing each control system with a timer adapted to switch its controlled load ON a predetermined time after the predetermined SWITCH-ON time (whether determined bythe time elapsed since SWITCH- OFF or by means of a SWITCH-ON code). The time could be predetermined to be random.

Brief description of the drawings

The invention will be further described with reference to the accompanying drawing which is a block diagram of an electrical load control system, installed at an electrical load constituted by a hot water cylinder.

Best Modes for Carrying Out the Invention

This invention provides a relatively inexpensive, easy to install system to control the electrical loads constituted by electrical appliances and installations, whether domestic, commercial or industrial, which consume large amounts of electricity, but which can be switched off periodically without causing any real inconvenience. Examples of such loads include water heaters, such as hot water hot water cylinders (domestic or otherwise), under-floor space heating, water pumps, swimming pool pumps, air conditioners and even area lighting.

The description that follows describes a hot water cylinder controller as an example of one implementation of this invention, but it will be appreciated that this is done purely for illustrative purposes. It is not htended therebyto limit the invention.

The electrical load control system 10 of the invention is illustrated with reference to the example of a hot water cylinder controller 10 which is intended to control a controllable electrical load constituted bya hot water hot water cylinder 12.

Instead of the complex control technologies for ripple control in particular and the additional communications infrastructure required to communicate within these systems, this invention proposes the use of one or more existing communication systems with wide coverage as a communication channel. An example of such a communication channel is FM radio, but any public broadcasting network will suffice, including AM radio networks, television networks and even telecommunications networks.

The examples used in this specification rely on a commercial or other broadcaster, such as an FM radio station, inserting or injecting audio frequency switch actuation codes as in- band signals into the normal audio signal broadcast bythe radio station.

The audio control signals may be injected or seeded into the broadcast audio signal as humanly audible tones (as in the alternative example described above) or as inaudible signals or tones having an audio frequency outside of the normal humanly audible frequency range.

The system or controller 10 comprises, at the load 12, a switch 14 connected in circuit with the electrical load 12. The controller 10 is installed on the electrical distribution board 16 serving the hot water cylinder 12, with the switch 14 in series with the hot water cylinder circuit breaker 18.

The controller 10 includes a radio frequency (RF) receiver 20 preset to receive the radio frequency (RF) signal of a predetermined publicly broadcast radio frequency (RF) broadcasting service. Like any radio receiver, the receiver 20 receives the broadcast RF signal and outputs an audio signal through an audio outputtransducer(not shown) similar to an audio speaker.

The controller 10 includes an interface including a control circuit 22 that is interfaced with the switch 14 over a switch interface 24 and with the receiver 20 over a receiver interface 26.

The control circuit receiver interface 26 is adapted to monitor the audio output of the receiver transducer for receipt of the publicly broadcast audio control signal.

The control circuit 22 includes programmable logic means programmed, on receipt of the publicly broadcast audio control signal, to actuate the control circuit 22 by means of the switch interface 24, to actuate the swtch 14, in use to switch the load OFF or ON.

The audio control signal is preferably constituted by a digital code constituted by a sub- or super-audible tone that is injected onto the audiosignal stream by the broadcaster. The most convenient digital modulation techniques for transmission of such a digitally represented code include Amplitude-shift keying (ASK), Frequency-shift keying (FSK) and Phase-shift keying (PSK).

The audio control signal may be injected into the reference wave or signal constituted by the audio signal stream to be broadcast, in either or both the sub- or super- audio frequency band. In the sub-audio band, the audio control signal frequency may be anyone or more frequencies between 10 Hz and 20 Hz. In the super-audio band, the audio control signal frequency may be any one or more frequencies between 13 kHz and 18 kHz.

At the broadcaster, the control signal is injected by means of a coding unit (not shown) connected in circuit between the broadcaster audio equipment and the broadcaster RF transmission equipment. Signal control of the coding unit is not in the hands of the broadcaster. Instead, signal control of the coding unit left up to the person wishing to control the controller 10 (and similar controllers located within the broadcast footprint of the broadcaster), such as a power utilityfor instance. There are a number of way in which the utility can controls the coding unit remotely, such as a GSM/GPRS mobile phone link communications. The control circuit 22 is preferably programmed with a unique address code (illustrated by block 23). The unique address code 23 may be any unique number or code, but is preferably constituted by the serial number of the hot water cylinder controller 10.

FM receivers are mass produced and therefore cost effective devices to use for the purposes of this invention. In the example given, the receiver 20 is constituted by an FM receiver which means that the broadcastermust of necessity be an FM radio station. The FM receiver 20 is pre-tuned to the broadcast frequency of the broadcaster.

The audio output of the FM receiver 20 is fed to an appropriate receiver interface 26, whether in audio or other format and this input to the receiver interface 26 is fed to the control circuit 22 to permit the control circuit 22 to monitorthe FM receiver 20 output for any switch actuation codes that might be broadcast bythe broadcaster.

Instead of relying on an audio control signal, it is also feasible to make use of the RDS, on its own or in addition to the use of audio signals, to broadcast the control signals required by the system 10 of the invention. The Radio Data System (RDS) or Radio Broadcast Data System (RBDS) as it is known in the United States of America (published as IEC (International Electrotechnical Commission) standard 62106), is a communications protocol for embedding digital data signals in FMradio broadcasts.

Throughout a supply period, the utility, using the coding unit under its control, will periodically seed the broadcaster's public broadcast with the switch actuation codes appropriate to the various sub-regions in which the hot water cylinders 12 are to be controlled.

In installing a plurality of controllers 10 in the broadcaster's broadcast area, the utility will allocate similar switch actuation codes to all the controllers 10 in a number of sub-regions in the region and ensure that all the controllers 10 in each such sub-region are programmed with the switch actuation codes appropriate to that subregion.

Having control of the coding unit, there is no need for the utility to supply the broadcaster with switch actuation codes or to advise the broadcaster when it wishes to have such switch actuation codes broadcast. The utility can run its own programme and seed the public broadcast with switch actuation codes either on a predetermined schedule (say all the hot water cylinders 12 in several non-adjacent sub-regions throughout the region) or on an ad-hoc basis to cope with any overload on the electricity supply system.

Each controller 10 in the broadcast region receives each switch actuation code so broadcast byway of its FM receiver 20, the output of which is fed to the control circuit 22 receiver interface 26. The control circuit 22 is programmed to monitor the receiver interface 26 and to compare the received switch actuation codes to the switch actuation codes or tones programmed into its control circuit 22.

If the comparison is positive, the control circuit 22 outputs a control signal to the switch interface 24 to actuate opening and closing of the switch 14. On actuation of the switch 14, the hot water cylinder 12 is switched OFF or ON, depending on the configuration of the controller 10.

One way of controlling the switch 14 and the hot water cylinder 12 is to broadcast switch actuation codes constituted bySWITCH-ON and SWITCH-OFF codes.

The alternative is to broadcast only an actuation code constituted by a SWITCH-OFF code and switching the load back ON a predetermined time afer the switch is switched OFF.

In the first alternative, a switch actuation code constituted by a SWITCH-OFF code is broadcast and received by all the controllers 10 in broadcast region. The controllers 10 intended to be controlled (having the broadcast code programmed into their control circuits 22), each actuates and opens the switch 14 by means of the switch interface 24 to switch the hot water cylinder 12 connected to that controller 10 OFF. The hot water cylinder 12 will now remain OFF until the broadcaster broadcasts the appropriate SWITCH-ON code for that area. When this happens, the affected controllers 10 actuate and each one opens the switch 14 by means of the switch interface 24 to switch the hot water cylinder 12 connected to that controller 10 back ON. The hot water cylinder 12 will now remain ON until the broadcaster again broadcasts the appropriate SWITCH-OFF code for that area.

In the second alternative, a switch actuation code constituted by a SWITCH-OFF code is broadcast and received by all the controllers 10 in broadcast region. The controllers 10 intended to be controlled (having the broadcast code programmed into their control circuits 22), each actuates and opens the switch 14 by means of the switch interface 24 to switch the hot water cylinder 12 connected to that controller 10 OFF. The control circuit 22 is provided with a timer and is programmed to keep the hot water cylinder 12 switched OFF for a predetermined time (say 2 hours). On expiry of the programmed time, the controller 10 actuates and opens the switch 14 by means of the switch interface 24 to switch the hot water cylinder 12 connected to that controller 10 back ON. The hot water cylinder 12 will now remain ON until the broadcaster again broadcasts the appropriate SWITCH-OFF code for that area.

If a number of hot water cylinders 12 are simultaneously switched ON in an area, the resultant drain on supply (of a number of hot water cylinders heating the water contained therein back up to the set temperature) in that area will cause a sudden and high recovery load which is undesirable. To this end, the control circuit 22 is programmed to ensure that the hot water cylinders, even though the controllers 10 receive the switch actuation codes simultaneously, are not switched ON simultaneously. For this purpose, the control circuit

22 is provided with a timer and programmed to switch its associated hot water cylinder 12 ON at a predetermined time after receipt of the switch actuation code. If each controller 10 in the area is programmed with a different time, the hot water cylinders 12 in the area will switch ON in sequence. More preferably however, the predetermined time is simply a random random delay that is applied before switching ON, so that the hot water cylinders 12 in the area switch ON at random.

With individually addressable controllers 10, it becomes possible to control individual hot water cylinders 12 or other electrical loads in an area.

This makes it possible to implement alternative means of avoiding sudden recovery loads, for instance by using a pre-programmed switching schedule by means of which the coding unit is used to switch the loads in an area ON or by programming different switch ON delays into individual controllers 10 in an area.

In addition, the utility can implement proper exception management. It becomes possible, for example, for a resident of an area to apply for a special dispensation. Since the controller 10 is individually addressable, the resident may make application to the utility to keep her hot water cylinder 12 switched on in a particular load shedding period. The utility, if it accepts the resident's application, can now seed the broadcast with the address code

23 of the resident's controller 10 followed by one or more special codes, such as a skip code that is adapted to instruct the controller 10 to skip the next one or more SWITCH OFF codes relevant to the resident's area. Depending on the skip code sent, the controller 10

Claims

control circuit program is reprogrammed to disregard the next one or more SWITCH OFF codes notwithstanding that the SWITCH OFF code is relevant to the resident's area. Once the programmed numberof SWITCH OFF codes has been broadcast, the control circuit 22 program is reset to normal.

Industrial applicability

This invention proposes the use of existing installed communication networks for electrical load control

Claims . A method of controlling a controllable electrical load comprisng the steps of: locating, at the load, a load controller including: a switch adapted for connection in circuit with the load; a receiver previously set to receive and output at least one control signal publicly broadcast by a broadcasteras part of a public radio frequency (RF) broadcasting service; and an interface including a control circuit with programmable logic means, interfaced with the switch and the receiver; programming the load controller receiver interface to monitor the receiver output for receipt of the publicly broadcast control signal; programming the load controller control circuit switch interface, on receipt of the publicly broadcast control signal, to actuate the control circuit to actuate the switch, in use to switch the load OFF or ON; and the method including the steps, at the broadcaster, of injecting the control signal into the RF signal to be broadcast, the control signal being inaudible.

2. A method of controlling a controllable electrical load according to claim 1 in which the electrical load is constituted by a load selected from any one or more of a water heater, such as a hot water cylinder, under-floor space heating, a potable water pump, a swimming pool pump, area lighting, an air conditioner and any electrical installation that consumes large amounts of electricity and the operation of which can be interrupted periodicallywithout causing anyreal inconvenience.

3. A method of controlling a controllable electrical load according to claim2 including the specific step, at the broadcaster, of injecting the control signal into the signal to be broadcast as a Radio Data System (RDS) signal.

4. A method of controlling a controllable electrical load accordingto claim 3 including the specific step, at the broadcasterand priorto RF transmission of the broadcast, of injecting the control signal into the audio signal to be broadcast as an audio signal, the control signal being inaudible and broadcast on an audio frequency outside of the normal humanly audible frequency range.

5. A method of controlling a controllable electrical load according to claim 4 in which the publicly broadcast signal is constituted by the radio frequency (RF) signal publicly broadcast by a public F radio station and which includes the specific steps of inserting the switch actuation codes as in-band audio signals into the normal audio broadcast of the radio station.

6. A method of controlling a controllable electrical load according to claim 4 in which the publicly broadcast signal is constituted by the publicly broadcast television signal publicly broadcast by a public television station and which includes the specific steps of inserting the switch actuation codes as an in-band audio signal into the audio portion of the normal broadcast of the television station.

7. A method of controlling a controllable electrical load according to anyone of claims 4 to 6 in which the audio control signal is injected by means of either or both phase shift keying (PSK) or frequency shift keying (FSK) of a reference signal constituted by the audio signal stream to be broadcast, to either or both the sub- or super-audio band.

8. A method of controlling a controllable electrical load according to claim 7 in which, in the sub-audio band, the audio control signal frequency is any one or more frequencies between 10 Hz and 20 Hz and, in the super-audio band, the audio control signal frequency is any one or more frequencies between 13 kHz and 18 kHz.

9. A method of controlling a controllable electrical load according to any one of the preceding claims in which the control signal is injected without the intervention of the broadcaster, the code injection means being constituted by a coding unit connected in circuit between the broadcaster audio equipment and the broadcaster RF transmission equipment, the coding unit being under the control of a person other than the broadcaster, by means of suitable communication means. 0. A method of controlling a controllable electrical load according to any one of the preceding claims including the steps of programming the load controller receiver interface programmable logic means with a unique communications address to render the receiver interface specifically addressable by means of a broadcast control signal including the programmed address; and programming the load controller control circuit switch interface, on receipt of a publicly broadcast control signal including the programmed address of the receiver interface, to actuate the control circuit to actuate the switch, in use to switch the load OFF or ON; the method including the steps of, at the broadcaster, injecting the control signal into the audio signal to be broadcast together with a code representing the address of the load controller receiver interface address.

11. A control system for a controllable electrical load, the system comprising: at the load, a load controller including: a switch adapted for connection in circuit with the electrical load; a receiver preset to receive and output at least one control signal publicly broadcast by a broadcaster as part of a public radio frequency (RF) broadcasting service; and an interface including a control circuit interfaced with the switch and the receiver; the control circuit receiver interface being adapted to monitor the receiver audio output for receipt of the publicly broadcast audio control signal; and the control circuit switch interface including programmable logic means programmed, on receipt of the publicly broadcast audio control signal, to actuate the control circuit to actuate the switch, in use to switch the load OFF or ON; and the control system including means, at the broadcaster, to inject the control signal into the RF signal to be broadcast as an inaudible signal.

12. A control system for a controllable electrical load according to claim 11 in which the electrical load is constituted by a load selected from any one or more of a water heater, such as a hot water cylinder, under-floor space heating, a potable water pump, a swimming pool pump, area lighting, an air conditioner and any electrical installation that consumes large amounts of electricity and the operation of which can be interrupted periodicallywithout causing anyreal inconvenience. 3. A control system for a controllable electrical load according to either of claims 11 or 12 in which the control signal injecting means is adapted to inject the control signal into the signal to be broadcast as a Radio Data System (RDS) signal. 4. A control system for a controllable electrical load according to claim 3 in which the control signal injecting means is adapted to inject the control signal into the signal to be broadcast as an audio signal, the control signal being inaudible and broadcast on an audio frequency outside of the normal humanly audible frequency range.

15. A control system for a controllable electrical load according to any one of claims 11 to 14 in which the publicly broadcast signal is constituted by the radio frequency (RF) signal publicly broadcast by a public FM radio station and which includes the specific steps of inserting the switch actuation codes as in-band audio signals into the normal audio broadcast of the radio station.

16. A control system for a controllable electrical load according to any one of claims 11 to 14 in which the publicly broadcast signal is constituted bythe publicly broadcast television signal publicly broadcast by a public television station and which includes the specific steps of inserting the switch actuation codes as an in-band audio signal into the audio portion ofthe normal broadcast of the television station.

17. A control system for a controllable electrical load according to any one of claims 4 to 16 in which the audio control signal is injected bymeans of either or both phase shift keying (PSK) or frequency shift keying (FSK) of a reference signal constituted by the audio signal stream to be broadcast, to either or both the sub- or super-audio band.

18. A control system for a controllable electrical load according to claim 17 in which, in the sub-audio band, the audio control signal frequency is any one or more frequencies between 10 Hz and 20 Hz and, in the super-audio band, the audio control signal frequency is an one or more frequencies between 13 kHz and 18 kHz.

19. A control system for a controllable electrical load according to any one of claims 11 to 18 in which the control signal is adapted to be injected without the intervention of the broadcaster, the code injection means being constituted by a coding unit connected in circuit between the broadcaster audio equipment and the broadcaster RF transmission equipment and the the coding unit being adapted to operate under the control of a person other than the broadcaster, by means of suitable communication means.

20. A control system for a controllable electrical load according to any one of claims 2 to 19 in which the load controller receiver interface programmable logic means is programmed with a unique communications address to render the receiver interface specifically addressable by means of a broadcast control signal including the programmed address and the load controller control circuit switch interface is programmed, on receipt of a publicly broadcast control signal including the programmed address of the receiver interface, to actuate the control circuit to actuate the switch, in use to switch the load OFF or ON, the control system including means, at the broadcaster, to inject the control signal into the audio signal to be broadcast together with a code representing the address of the load controller receiver interface address.

21 . A control system for a controllable electrical load according to anyone of claims 12 to 20 in which the code injection means includes means to encrypt the control signals broadcast by the broadcaster and the load controller programmable logic means includes means to decrypt the encrypted control signals broadcast by the broadcaster.

22. A control system for a controllable electrical load according to claim 21 in which the load controller programmable logic means includes memory means adapted to to store one or more actuation codes in load controller control circuit, the control circuit being programmed to compare an incoming authorisation code to at least one stored code before actuating the switch interface.

23. A control system for a controllable electrical load according to any one of claims 11 to 22 in which the load controller programmable logic means is provided with means to switch ON different loads in a predetermined geographical area in a predetermined sequence.