ELECTRICAL CONTROL SYSTEM

Abstract: A control system for an electricity distribution circuit which is connected or adapted to be connected to an electrical supply of limited amperage and which, in use, is arranged to distribute electricity from the supply to a number of appliances which are connected permanently to the circuit and/or plugged into sockets in the circuit and which are required to be brought into operation from time to time, the control system comprising means operable, in use, continuously to sense the total current consumption of the circuit and adapted if any one or more appliances is or are brought into operation and as a result causes the total current consumption to exceed a predetermined maximum value, automatically to render at least one appliance inoperative so that the current consumption of the circuit does not remain above said maximum value, and means adapted when at least one appliance has been rendered inoperative by the control system automatically to render such appliance inoperable, such means being operable only by a user to render the said appliance operable.

Description: ELECTRICAL CONTROL SYSTEM This invention relates to control systems for electricity distribution circuits of small dwellings and other accommodation such as chalets and mobile homes sited on holiday parks and mobile offices, and caravans. In particular, the invention is concerned with a control system for an electricity distribution circuit of the kind, hereinafter referred to as "the kind specified", which is connected to an electrical supply of limited amperage and is arranged to distribute electricity from the supply to a number of appliances which are connected permanently to the circuit and/or plugged into sockets in the circuit and which are required to be brought into operation from time to time. A problem which frequently arises with electricity distribution circuits of this kind is that being of limited amperage they can become overloaded if too many appliances are switched on at the same time. The higher the wattage of an appliance the greater is the risk of the circuit becoming overloaded when it is brought into operation with other appliances already in use. To prevent this it is common practice to provide such circuits with overload cut-out devices adapted to operate when the current consumption of the circuit exceeds a set maximum amperage. Such devices, however, have the disadvantage that they cut off the electricity supply to the whole circuit so that the occupants of, for example, a mobile home are deprived of all facilities such as lighting, heating and cooking until the device has been reset, which may require the attendance of a holiday park warden. The use of electricity in mobile homes is increasing as gas appliances are replaced by their electrical equivalents for energy-saving and safety reasons. There is therefore a growing demand for a more convenient way of preventing overloading of the electricity distribution circuits used in mobile homes (and other forms of accommodation including caravans). According to the invention there is provided a control system for an electricity distribution circuit of the kind specified, the system comprising means operable, in use, continuously to sense the total current consumption of the circuit and adapted if any one or more appliances is or are brought into operation and as a result causes the total current consumption to exceed a predetermined maximum value, automatically to render at least one appliance inoperative so that the current consumption of the circuit does not remain above said maximum value. Preferably, the control system includes means adapted when at least one appliance has been rendered inoperative by the control system automatically to render such appliance inoperable, such means being operable only by a user to render the said appliance operable. This feature is particularly advantageous if the said appliance is an appliance which, if left switched on when it has been rendered inoperative by the control system, could create a dangerous situation if it were to become operative again as a result of the control system restoring the electricity supply to it without the user being aware of it. Examples of such an appliance are an electric toaster, hairdryer and cooker, all of which might cause a fire if they are rendered operative without the user being aware of it. Such a condition is prevented by the appliance being rendered inoperable by the control system until the user operates the said means to render the appliance operable again. These means may include a manually operable reset button. The circuit may be adapted when operated in response to an increase in the total current consumption above such predetermined value to switch off at least one appliance which is already in operation, or/and to prevent at least one appliance being brought into operation. If the circuit is provided with an overload cut-out device, the control system accordingly prevents such device being operated and cutting off the electricity supply to the circuit. Preferably the control system is adapted to select the appliance or appliances which is or are rendered inoperative in a potential overload condition on the basis of predetermined operational priorities of the appliances connected to the circuit. Thus, the system is arranged to operate on the principle that it may be preferable or desirable to switch off one appliance rather than another for any one of a number of reasons. For example, the circuit may include an appliance such as an immersion water heater which can be switched off for a short period, while another appliance such as a kettle requiring only a short period of use is brought into operation and the system in this case is adapted to give priority to the second appliance. On the other hand the system is adapted to give the utmost priority over all other appliances to any appliance which for safety reasons ought not to be switched off, for example, fixed lighting. Priority may even be given to appliances whose operation the user may not wish to be interrupted simply for personal convenience, for example a television. In a preferred form of control system according to the invention the appliances are arranged to be rendered inoperative in groups each comprising two or more appliances having similar priorities or only one appliance. The control system may be provided with means for varying the said predetermined maximum value of current consumption. The control system may incorporate the facility of preventing an appliance in any one group being brought into operation until one or more appliances in the same or another group which are already in operation, is or are switched off manually. The system may include an audible or/and visual indicator which is arranged to warn a user when switching on an appliance if such action has caused an overload condition and that the said appliance will not become operative until the user has switched off at least one other appliance of an appropriate wattage in the same group. The system may include an indicator for displaying the maximum current available and the actual current consumption of the circuit at all times so that a user can take pre-emptive action before the system automatically switches off any appliance. The invention will now be described, by way of example, with reference to the accompanying drawings in which:- FIGURE 1 is a schematic drawing of one form of control system according to the invention, FIGURE 2 shows the control and information panel of the control system, FIGURE 3 shows the functional blocks of the software incorporated in the control system, and FIGURE 4 is a schematic drawing of an electricity distribution circuit incorporating another form of control system according to the invention. Referring to FIGURE 1 of the drawings, this shows a preferred form of control system according to the invention connected to an electricity distribution circuit in which the mains electricity supply 1 is typically limited in current by an external thermo-magnetic circuit breaker. The electrical loads 2,3,4,5,6 comprise all of the electrical loads of the circuit, including lighting, cooking, heating and electrical appliances. The load comprising lights and essential services 2 is classified as uninterruptible. The loads for cooking and mains sockets 3,4 are classified as interruptible with manual restoration. The loads 5,6 for space and water heating are classified as interruptible with automatic restoration. To measure the current taken by the loads, current sensors 7,8,9,10,11 are employed. Each current sensor comprises a 5mΩ resistive current shunt carrying the return current from its respective load, and a differential signal amplifier. This outputs an analogue voltage in proportion to the mains current drawn. The control system 12 includes a microcontroller (single chip microprocessor) with analogue to digital converters. This allows the conversion of the current sensor readings 7,8,9,10,11 to digital values, which are then stored and processed by the microcontroller. The processor is programmed to sample the instantaneous current for each sensor at 2mS intervals, giving ten samples of the current waveform for each mains cycle at 50Hz. These ten readings are then arithmetically processed to give an approximation of the root mean squared current for each sensor. Detection of a 60Hz mains waveform results in the sampling interval being decreased to 1.677mS, ensuring that ten samples are stored and processed for each mains cycle. The microcontroller in the control system 12 provides digital outputs to control the power interrupters 13,14,15,16,17. The interrupters comprise electro-mechanical relays or solid state triacs with the ability to remove power from the load under the control of the microcontroller. The control systems is also connected to a user control and information panel 18, as shown in FIGURE 2. This comprises a liquid crystal display 20, function buttons 21, an alarm buzzer 22 and a reset button 23. The control panel allows the setting of the maximum current available by means of the function buttons. In the case of the invention being applied to touring caravans and similar, this limit is variable and adjustable by the end user, to suit the mains electricity supply. In fixed installations, the current limit is set by the installer and not adjustable by the end user. The control panel display indicates to the user the current usage and current limit. In the event of shedding either of the manually resettable loads 3,4, the display indicates that an overload has occurred and an audible alarm is sounded by the buzzer 22. Operation of the reset button causes the microcontroller to restore power to the manually restored loads 3,4 by operation of the interrupter relays 13, 14. The control panel 18 and interrupter relays 15,16, together with the room temperature sensor 19 also provide the function of a thermostatic space heating control. This allows the room temperature to be compared to the desired setting, and the required level of heating to be switched by the interrupter relays. The space heater 5 comprises two elements of nominally one kilowatt and two kilowatts which when operated together give three kilowatts space heating. The control chooses the power level subject to the thermostat demand and available current. In a similar manner, the control panel allows the water heater 6 to be switched on and off by the user, by enabling or disabling the interrupter relay 17. In some installations, a load such as the space heater 5 may be of fixed wattage and without user switches or thermostats. In such a case, and assuming constant supply voltage, the current may be calculated from the state of the relays 15,16 and the specification of the space heater 5. The respective current sensor 10 is therefore redundant and not used. FIGURE 3 represents the functional blocks of the software embedded within the control system 20 required to perform the load shedding and restoration functions. On applying power to the control system, the initialisation of registers is performed, and the processor tests to see whether 50Hz or 60Hz mains is in use (24). The main loop 25,26,27,28,29,30,31 is performed once per mains cycle. Ten samples of each current waveform are captured and stored by a timer interrupt driven routine running in the background. When a set of ten samples are available, the root mean squared (RMS) value for each current sensor is evaluated (25). To avoid spurious tripping by loads with large inrush currents (e.g. vacuum cleaners) the software digitally filters each current value by averaging. The averaging is designed to give a response faster than the thermal response of the external supply circuit breaker. The room temperature is measured by reading an analogue to digital converter connected to the room temperature sensor. The status of the user control panel is received via a serial communications link. The software receives this information, and evaluates the desired space heating power and water heater status (26). The information sent from the user control panel also contains the maximum current setting, which is stored. Information to be displayed to the user is transmitted by the serial communications link, back to the user control panel. The status of the reset button is transmitted from the user control, and if pressed, flags are reset to enable restoration of power to the manually restored loads (27). The result of this process is a byte value which represents, in binary format, the desired loads, before power limitations are accounted for. The algorithm for power shedding consists of calculating all possible combinations of outputs. With five controlled loads this gives thirty two combinations from binary 00000 representing all loads disabled to binary 11 1 11 representing all loads enabled (28). Each of the thirty two combinations is logically anded to mask loads which have been disabled, and tested to find the best valid combination. For each combination of loads, the total current is calculated by adding up the currents of each load in that combination. To facilitate a priority of load shedding, the system has allocated a weighted score to each load. For each combination of load, the system calculates the total score for the loads in that combination. If the total current does not exceed the current limit, and the weighted score for that combination is greater than the previous best found score then that combination becomes the best found score. After iterating through all the possible combinations, the resulting best combination represents, in binary, those loads which should be enabled and disabled. The system will then immediately turn off digital outputs controlling load relays not enabled in the best combination (29). As a result the corresponding appliances are rendered inoperative. To prevent erratic operation, automatically restored loads are not immediately restored. A software timer (30) is reset when the best combination has changed. If the value of the best combination is stable for more than one second, the timer switches on the digital outputs connected to the load relays, as enabled in the best combination. Manually restored loads are not subject to this timer, and are restored immediately. Where a manually restored load has been shed, the software stores this status (31) to ensure that the load remains disabled until the reset button is pressed (27). Thus, the loads for cooking and mains sockets which may have appliances such as a toaster or hair dryer connected to them, will not be restored, which could be dangerous, until the user has pressed the reset button and rendered them operable again. FIGURE 4 of the drawings shows an electricity distribution circuit installed in, for example, a mobile home and comprising four separate ring circuits R1,R2,R3 and R4. These ring circuits have a range of electrical appliances connected to them either permanently or through sockets into which the appliances are plugged, and the appliances are arranged in groups of different operational priorities as follows :- Ring Circuit RI (High Priority) Overhead lights Refrigerator Television Personal Computer Ring Circuit R2 (Priority 2) Microwave Oven Grill Cooker Hob Ring 1 Cooker Hob Ring 2 Ring Circuit R3 (Priority 3) Toaster Socket Kettle Socket Lounge Socket 1 Lounge Socket 2 Ring Circuit R4 (Low Priority) Space Heater (lKw) Space Heater (2Kw) Air Conditioner Water Immersion Heater Bedroom 1 Socket Bedroom 2 Socket The ring circuit RI is for a group of electrical appliances which when brought into operation should preferably remain in operation for as long as required, for example for safety reasons as in the case of lighting, or simply for personal convenience as in the case of a television. Ring circuit R2 is for appliances of a lower operational priority in that it is desirable that their operation should not be interrupted, that is to say in the case of cooking appliances interrupting the cooking of food is likely to spoil the food which in the case of a microwave may lead to food poisoning. Ring circuit R3 is for appliances where it is not quite so desirable to maintain their operation, for example the use of a kettle or toaster can be delayed or interrupted at little inconvenience. Appliances having a low operational priority are connected to ring circuit R4. Thus, in the case of space or water heaters or air conditioners their operation can be interrupted for short periods and resumed subsequently without affecting the overall heating or air conditioning effect. In accordance with the invention the ring circuits are all connected to a mains supply LN through an electronic control system 32 which is also connected to a display panel 33. The control system 32 is constructed and arranged to control the supply of electrical current to the groups of appliances and sockets in accordance with the operational priorities set out above. The control system includes a current sensor and electronic micro- controller and is arranged to sense the current consumption of the circuit at all times. The system is adapted in the event that any appliance is switched on and as a result the current consumption exceeds the maximum amperage of the mains supply, either to switch off the group containing that appliance or to switch off another group of appliances according to the established priorities. The display panel provides a visual indication of the maximum current available from the mains supply and an audible or/and visual warning when a potential overload condition arises so that the user can chose to switch off an appliance manually or refrain from switching on an appliance or in order to prevent the control system operating automatically. Also, the control system is adapted, in the event that the cooker or one of the sockets is rendered inoperative whilst it is in use as a result of an overload condition being detected, to maintain the cooker or socket inoperable until such time a manually operable reset button is operated by the user.

Claims: CLAIMS 1. A control system for an electricity distribution circuit which is connected or adapted to be connected to an electrical supply of limited amperage and which, in use, is arranged to distribute electricity from the supply to a number of appliances which are connected permanently to the circuit and/or plugged into sockets in the circuit and which are required to be brought into operation from time to time, the control system comprising means operable, in use, continuously to sense the total current consumption of the circuit and adapted if any one or more appliances is or are brought into operation and as a result causes the total current consumption to exceed a predetermined maximum value, automatically to render at least one appliance inoperative so that the current consumption of the circuit does not remain above said maximum value. 2. A control system as claimed in Claim 1 which includes means adapted when at least one appliance has been rendered inoperative by the control system automatically to render such appliance inoperable, such means being operable only by a user to render the said appliance operable. 3. A control system as claimed in Claim 1 or 2 which is adapted when operated in response to an increase in the total current consumption above the said predetermined value, to switch off at least one appliance which is already in operation, or/and to prevent at least one appliance being brought into operation. 4. A control system as claimed in Claim 1, 2 or 3 which is connected or adapted to be connected to an electrical circuit provided with an overload cut- out device, wherein the control system is adapted, when operated in response to an increase in the total current consumption above the said predetermined value, to render at least one appliance inoperative before the overload cut-out device is operated and cuts off the electricity supply to the circuit. 5. A control system as claimed in Claim 1, 2, 3 or 4 wherein the control system is adapted to select the appliance or appliances which is or are rendered inoperative in a potential overload condition on the basis of predetermined operational priorities of the appliances connected to the circuit. 6. A control system as claimed in Claim 5 which is connected or adapted to be connected to an electrical circuit arranged, in use, to distribute electricity to an appliance (for example an immersion water heater) which can be switched off for a short period without causing undue inconvenience, and an appliance (for example a kettle) requiring only a short period of use, the control system being adapted to give priority to the second appliance. 7. A control system as claimed in Claim 5 or 6 which is adapted to give priority to appliances whose operation the user may not wish to be interrupted simply for personal convenience (for example a television). 8. A control system as claimed in Claim 5, 6 or 7 which is adapted to give the utmost priority over all the other appliances to any appliance which for safety reasons ought not to be switched off, for example fixed lighting. 9. A control system as claimed in any one of the preceding claims which is adapted to render the appliances inoperative in groups each comprising two or more appliances having similar priorities. 10. A control system as claimed in any one of the preceding claims which is provided with means for varying the said predetermined maximum value of current consumption. 11. A control system as claimed in any one of the preceding claims which includes an audible or/and visual indicator arranged to warn a user when switching on an appliance if such action has caused an overload condition and that the said appliance will not become operative until the user has switched off at least one other appliance of an appropriate wattage. 12. A control system as claimed in any one of the preceding claims which includes an indicator for displaying the maximum current available and the actual current consumption of the circuit at all times so that a user can take pre- emptive action before the system automatically switches off any appliance. 13. A control system as claimed in any one of the preceding claims which further includes manual override means operable to render the control system inoperative to enable a user to select the appliance or appliances which are to be brought into operation. 14. A method of controlling the operation of an electricity distribution circuit to maintain the total current consumption of the circuit below a predetermined value, which comprises continuously sensing the total current consumption of the circuit and in the event that any one or more appliances is or are brought into operation and as a result causes the total current consumption to exceed a predetermined maximum value, automatically rendering at least one appliance inoperative so that the current consumption of the circuit does not remain above the said maximum value. 15. A method as claimed in Claim 14 which includes rendering at least one appliance inoperable in the event that the appliance is rendered inoperative by the system and maintaining the appliance inoperable until the user operates means adapted to render the appliance operable. 16. A control system substantially as herein described with reference to FIGURES 1 to 3 of the accompanying drawings. 17. A control system substantially as herein described with reference to FIGURE 4 of the accompanying drawings.

Inventors: BRYER KEITH NIGEL, WRIGHT ALAN THOMAS, BRYER, KEITH, NIGEL, WRIGHT, ALAN, THOMAS
Applicants: BRYER KEITH NIGEL, CARVER PLC, WRIGHT ALAN THOMAS, BRYER, KEITH, NIGEL, WRIGHT, ALAN, THOMAS
Application year: 2000
Main classification: H02J3
IPC codes: H02J3