WO2003007657A2

WO2003007657A2 - Power supply for electrical resistance operated installations and appliances

Info

Publication number: WO2003007657A2
Application number: PCT/IB2002/002577
Authority: WO
Inventors: Rosemary Ann Ainslie
Original assignee: Rosemary Ann Ainslie
Priority date: 2001-07-09
Filing date: 2002-07-03
Publication date: 2003-01-23
Also published as: WO2003007657A3; AU2002314444A1

Abstract

A power supply is provided for an electrial installation or appliance presenting a resistive load (1, 8, 12, 19, 40). The power supply has electrical input means for connection to a supply of electrical energy and output means for connection to a suitable resistive load and is characterized in that electronic switching means (3, 9, 13, 25, 26) is provided for switching the electrical power supply to the output means on and off at a switching frequency of at least about 100 Hz is embodied therein. The power supply thus creates a series of cycles each having an 'on' and an 'off' component with a duty cycle of from about 3 percent to about 90 percent. The power supply optionally includes one or more inductors (4, 10, 11, 18, 23, 24, 37,38, 39), as may be necessary, to provide, together with the resistive load, a circuit inductance. The circuit includes means, typically diode means that may be inherently present in the switching means, for ensuring that any back emf or transient energy generated across the inductance is dissipated across the resistive load or is fed back to the power supply source, or both, during the 'off' component of the duty cycle. The switching frequency, duty cycle, and inductance in the power supply are chosen so as to cooperate with the resistive load to provide a required operation of the resistive load and generally an enhanced efficiency when compared to the efficiency thereof in the absence of the said power supply.

Description

POWER SUPPLY FOR ELECTRICAL RESISTANCE OPERATED INSTALLATIONS AND APPLIANCES

FIELD OF THE INVENTION

This invention relates to a power supply for electrical resistance operated installations and appliances and to installations and appliances embodying same. The invention thus also relates to a method of energizing electrical heat generating resistances.

More particularly, the invention relates to electrical installations and appliances in which electrical resistance elements become heated in order to achieve their objective and thus the invention extends to installations employing incandescent electric light bulbs as well as to appliances such as electric stoves, water heaters (commonly termed geysers in some countries), space heaters (which could be of the radiant type, the oil filled type, or any other type utilizing electrical resistance heating), as well as to smaller appliances such as kettles, electric frying pans, toasters and the like. The invention also, of course, extends to larger scale applications, particularly industrial applications, such as the production and processing of metals.

BACKGROUND TO THE INVENTION

Electrical installations and heating appliances of the general type indicated above are all typically operated either on a standard alternating current of either 110-120 volts or 220-240 volts and a frequency of 50 or 60 cycles per second or on the direct current output of a battery of some sort or another. Of course, larger installations and appliances are also operated on a three phase supply which in each case results in a phase voltage of about 220 volts and 380 volts respectively. In the alternative, and in a system that is common in small electrical installations such as in rural areas in which the electrical installation comprises a limited number of light bulbs and other facilities, the power supply may be a battery or other electrical storage facility that may be energized by an alternative energy supply source such as solar energy or wind or water power.

In either case it has now been found that by operating such installations and appliances with a different type of power supply arrangement certain benefits can be achieved and, most importantly, greater efficiency can be achieved than would be the case in directly utilizing a standard power supply.

OBJECT OF THE INVENTION

It is, accordingly, an object of this invention to provide a power supply for electrical resistance operated installations and appliances as well as appliances and installations embodying the principles of the power supply that exhibit improved efficiency of electricity utilization.

SUMMARY OF THE INVENTION

In accordance with one aspect of this invention there is provided a power supply for an electrical installation or appliance presenting a resistive load, the power supply having electrical input means for connection to a supply of electrical energy and output means for connection to a suitable resistive load; the power supply being characterized in that electronic switching means for switching the electrical power supply to the output means on and off at a switching frequency of at least about 100 Hz is included to thereby create a series of cycles each having an "on" and an "off component with a duty cycle of from about 3 percent to about 90 percent; the power supply optionally including one or more inductors, as may be necessary, to provide, together with the resistive load, a circuit inductance; and wherein the switching frequency, duty cycle, and any inductors in the power supply are chosen so as to cooperate with the resistive load to provide a required operation of the resistive load and wherein the circuit includes means for ensuring that any back emf or transient energy generated across the inductance is dissipated across the resistive load or fed back to the power supply source, or both.

Further features of the invention provide for the required operation of the resistive load to have an enhanced efficiency when compared to the efficiency thereof in the absence of the said power supply; for the circuit to include diode means for ensuring that any back emf or transient energy generated across the inductance is dissipated across the resistive load or fed back to the power supply source, or both; for the resistance, inductance, duty cycle and frequency to be chosen to ensure operation of the circuit in a state of resonance or a state of oscillation; for the electronic switching means to be adapted to effect switching at a frequency of between about 800 Hz and 200,000Hz; for the duty cycle to be from about 5% to 75%, more particularly between about 10 and 50% and, preferably, about 15 to 40 percent and typically about 25%; for the electronic switching means to comprise an electronic switch operating in combination with a signal generator, the electronic switch optionally being a mos-fet which embodies diode means which serve as said diode means defined above, a fet, an IGBT transisitor, thyhstor or other electronic switching device; and for the circuit inductance to be chosen to provide a large back emf.

Still further features of the invention provide for the power supply circuit to optionally include electrical energy storage means for receiving electrical energy associated with any back emf or transient energy generated and for returning it to the circuit; and for the electrical storage means to be either a battery, conveniently the same battery as forms the power supply in the case of a battery supply, or for the electrical storage means to be a capacitor in the case of an alternating current power supply.

In some cases the inherent inductance of the resistive load may be adequate 5 and in such a case it will not be necessary to add any further inductance to either the electrical power supply or the resistive load of the circuit. On the other hand, it may be desirable to adjust the inductance in any event in order to adjust the overall effectiveness of the inductance as may be desirable for any particular resistive load type and with the objective of creating a large l o back emf or packet of transient energy.

It is to be noted that the exact interrelationship between the resistance of the load, the frequency of switching, the duty cycle and the inductance is not yet fully understood and it is therefore necessary that the various values for any

15 particular application be determined empirically and with suitable experimentation. It is envisaged, in this regard that special resistive elements may need to be designed and produced in order to best employ the features of the present invention and, in particular, resistive elements inherently having a particularly advantageous inductance, may be desirable. It is also

20 to be noted that components, in particular switching devices suitable to conduct an elevated power output level will apparently have to be developed in order to most effectively exploit the advantages provided by this invention.

The resistive load may be that of any appliance, such as an electric stove, an 25 electric space heater which could be fan assisted or not, a water heater (geyser), or on the smaller side, a toaster, a kettle, an electric frying or deep fryer, or any other appliance. The resistive load may, however, also be a simple incandescent light bulb circuit such as may be found in rural areas and which may be based on a battery which is charged using solar and/or 30 wind energy. The power supply of this invention may be built into such appliance or it may be a separate unit. The invention also therefore provides, as an article of commerce, a power supply unit comprising an electric circuit having an input and an output for connection between an existing supply of electrical energy and a resistive load circuit and wherein the power supply unit embodies electronic circuitry adapted to provide an output having the characteristics defined above.

In the latter case the power supply unit can simply be connected between the existing power supply and, for example, an appliance in order to achieve the advantages provided by this invention.

Still further, the invention provides, as an article of commerce, an appliance embodying a power supply as defined above.

Of course, the invention can also be applied to industrial scale heat generating resistances such as those that are commonplace in the metals processing industry and in the generation of steam for use in numerous different applications.

In addition, the invention also provides a method of operating a heat generating resistive load comprising applying, across the resistive load, the output of a power supply as defined above.

It should also be noted that operation of the power supply of this invention is not limited to any particular type of input supply of electrical energy although the circuit design of the power supply will in all likelihood vary according to the nature of the input power supply. Thus, it is envisaged that any voltage input could be used, typically a voltage appropriate to the relevant source that, in the case of an alternating current supply, is typically 110-120 volts; 220-250 volts; or 380 volts, as case may be. In the case of a direct current power supply, the voltage could be that typically inherent in any battery that is being used as a power supply source or, for that matter, any other source of electrical energy such as solar photo panels, wind or water driven generators.

In order that the invention may be more fully understood various embodiment thereof will now be described with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

Figure 1 is a schematic circuit diagram of an electrical installation or appliance configured to operate according to the invention off an alternating current supply;

Figures 2 & 3 are schematic circuit diagrams of two variations of electrical installation or appliance configured to operate according to the invention off a direct current supply in the form of a battery;

Figures 4 to 7 are similar circuit diagrams of variations of electrical installations or appliances configured to operate according to the invention off an alternating current supply;

Figures 8 to 10 are schematic circuit diagrams of variations of a power supply unit adapted to be installed between an existing power supply and an existing appliance, for example; and,

Figure 11 is a circuit diagram of a still further test circuit. DETAILED DESCRIPTION WITH REFERENCE TO THE DRAWINGS

Referring firstly to Figure 1 of the drawings, there is illustrated a circuit adapted to be connected to an alternating current power supply, for example, a 230 volt 60 cycles per second power supply. The circuit includes a heating element (1) that is connected to the output of a rectifier circuit (2) in turn connected to the alternating current power supply. The power supply to the heating element is controlled by means of a mosfet (3) adapted, in use, to switch on and off at a required frequency and with a predetermined duty cycle. In this case an inductance (4) is connected in series with the heating element (1). The mosfet (3) is fired by a signal generator (5). In this embodiment of the invention the electrical storage means assumes the form of a capacitor (6) connected across the output from the rectifier.

The values of the various components described above will depend entirely on the circuit and the nature of the load resistor(s) in each individual application. In each case the nature of the relevant resistive load and its own inherent inductance will dictate the value of the added inductance, if any, which is to be added to the relevant circuit, and at least initially, it is envisaged that this may have to be determined empirically. The capacitor (6) should be capable of operating at maximum anticipated voltages and in the case of a 230 volt supply, it is anticipated that this may be up to about 440 volts. The actual capacitance required may also have to be determined empirically initially.

It is envisaged that a circuit of the type described above will operate with a significant improvement in efficiency of electrical energy utilization. It will be understood that, in its application the invention can be applied to any type of resistive load that generates heat and thus to any of the appliances indicated above as well as to electrical circuits that include incandescent light bulbs. Turning now to Figure 2 of the drawings, there is illustrated a circuit similar to that described with reference to Figure 1 except that the power supply is a direct current power supply of a battery (7) thereby rendering the rectifier unnecessary. In this case the load is illustrated as being a resistance (8) and this could typically be the resistance of an incandescent light bulb or of a plurality thereof. The output from the mosfet (9) is, in this case, very much the same as that indicated above although it is expected that the selection of frequency and duty cycle may well have to be optimized for each application.

In regard to use in conjunction with batteries, it is envisaged that the invention may be particularly advantageously employed in that it appears that drawing a current from at least certain types of battery may well take place in a manner enabling a battery to more efficiently give up its energy when a circuit according to this invention is employed when compared to that which it would give up if its electrical energy were extracted in a conventional manner.

It will be understood that the inclusion or otherwise of an inductance in any circuit in practice will also be a matter for optimization as the heating resistors may be chosen to exhibit their own inductance in which case the addition of an inductance may prove to be unnecessary. Alternatively, it may prove to be advantageous to choose heat generating resistors which exhibit no appreciable inductance and the inductance necessary to give effect to this invention would then of necessity be added to the circuit.

Still further, it is not as yet clear as to whether it is always better to place any added inductance in series with the load, as indicated by numeral (10) in Figure 2 or if it should be connected in parallel as indicated by numeral (11) in Figure 3.

The circuit of Figure 3 is otherwise the same as the circuit of Figure 2 and includes a load resistor (12); a mos-fet (13) and signal generator (14). The circuit of Figure 3 was used to develop the test results reported below and with that end in view it also included a series measurement resistor (15) connected to the negative of the battery; a voltmeter (16) connected across that measurement resistor; and a voltmeter (17) connected across the load resistor (12).

The variations of basic circuits shown in Figures 4 to 7 are all adapted for use in respect of alternating current supplies. Figure 4 shows a circuit similar to that of Figure 1 but in which the added inductance (18) is connected in parallel with the load resistor (19) and without a capacitor equivalent to that indicated by numeral (5) in Figure 1.

Figure 5 shows a circuit substantially the same as that of Figure 4 but with the inclusion of a capacitor (20) equivalent to that indicated by numeral (5) in Figure 1.

Figure 6 shows a circuit in which there is no rectifier but the two half cycles of an alternating current supply are employed in separate sub-circuits each of which has a load resistor (21,22); any required added inductance (23,24); and its own mosfet (25,26), the two mosfets being of opposite polarity. The circuit has, however, only one signal generator (27) connected to fire both of the mosfets simultaneously. A diode (28,29) in each of the "live" lines directs the half cycles to the appropriate mosfet. This circuit has no capacitors to act as temporary storage units whereas the circuit of Figure 7 does have a capacitor (30,31) across each sub-circuit. Apart from that the circuit of Figure 7 is identical to that of Figure 6.

It is within the scope of this invention that a power supply unit may be supplied as an article of commerce for inclusion between a conventional power supply and a conventional appliance in order to employ the advantages provided by this invention in an existing situation. There is thus illustrated in Figure 8, a power supply unit indicated by a dotted line (32) having input terminals (33) for connection to an alternating current power supply and output terminals (34) that can be connected to the input terminals (35) of an appliance generally indicated by numeral (36). Of course, any added inductance (37) in the power supply unit, which is shown as being in series with the output terminals (34) may be absent in the event that the inductance of the circuit in the appliance is adequate.

Figure 9 illustrates the relevant part of the same arrangement but one in which any added impedance (38) is connected in parallel with (ie across) the output terminals whilst Figure 10 illustrates the same part of such arrangement but wherein any added impedance (39) is connected in parallel with (ie across) the load resistor (40) in the appliance.

Reverting now to some of the actual tests that have been conducted, these tests were conducted on a circuit as shown in Figure 3 in which a Fluke 20 megahertz bandwidth storage scope meter (with a digital display device) served as the voltmeter (17) to measure the rms voltage drop across the load resistor (12) which in this case was a 10 ohm resistor. The insulated probes were placed across the load. The level of energy dissipated at the load was calculated in line with classical energy computations being the instantaneous product of volts across the load squared divided by the Ohms value of the resistor over time.

The waveform over the load was stored and down loaded to a spreadsheet for detailed analysis and confirmation of the voltmeter measurements. The values were found to conform to the digitally displayed values.

A carbon measurement resistor (15) of 0.75 Ohms was employed in series with the negative terminal of the battery. The applied voltage across the resistor was measured in the same way. The level of energy delivered by the battery was calculated in line with classical computations being the instantaneous product of the applied voltage over the resistive value of the measurement resistor and the battery voltage

This waveform was also stored and downloaded to a spreadsheet for detailed analysis and confirmation of the digitally displayed values which were found to conform.

The results of tests conducted in this way at various different switching frequencies and different duty cycles are shown in Table 1 below.

It will be noted that there are significant improvements in all but one case.

In order to check these measurements a platinum based temperature probe was fixed inside the core of the resistor that was hollow. The probe, in turn, was linked to a digital display device that recorded temperature rise in degrees centigrade. The digital display device recorded a temperature rise to 47 degrees centigrade after a period of 20 minutes. The frequency used was 1.325 KHz and the duty cycle was 10% on.

The test apparatus, being the resistor and the temperature probe inside the hollow core of the resistor was allowed to cool. It was then applied to a regulated power supply source to test the wattage required to realise an equivalent temperature rise. A temperature rise to 47 degrees centigrade over a period of 20 minutes was consistent with an applied wattage of 7.5 watts or 8.66 volts. A temperature rise to 39 degrees centigrade was consistent with an applied wattage of 4.5 watts or 6.7 volts.

Referring now to the circuit of Figure 11 (which is substantially similar to that of Figure 3), a higher frequency test was carried out. In this case the necessary voltage measurements were taken using a calibrated Fluke 199C 200 MHz dual channel scope meter whereof the two channels were connected to measure the voltage across a 24 volt battery (41) as indicated schematically as a voltmeter (42) and across the shunt (43) as indicated schematically as a voltmeter (44). The signal generator (45) was adjustable and was set at a duty cycle of 3.7% 'on' at a frequency of 2.4 kHz. By removing any resistance from the gate of the mos-fet (46) an oscillating frequency of between 143 kHz and 200 kHz with the duty cycle of approximately 1.3% was achieved.

Utilizing heat dissipation at a steady state temperature in the manner described above, that in this case was 52 degrees centigrade, it was determined that the wattage extracted utilizing the power supply of this invention amounted to 1.13 watts whilst without the power supply of this invention the wattage was 17.74 watts. It was concluded that a frequency of the order of 200 kHz appeared to be highly appropriate in the case of implementation of the invention in instances in which a battery is the source of power.

It will be understood that numerous variations may be made to the circuits described above without departing from the scope of this invention and adapted in the implementation of the invention empirical tests will have to be done in respect of each application.

Claims

CLAIMS:

1. A power supply for an electrical installation or appliance presenting a resistive load (1 , 8, 12, 19, 40), the power supply having electrical input means for connection to a supply of electrical energy and output means for connection to a suitable resistive load; the power supply being characterized in that electronic switching means (3, 9, 13, 25, 26) for switching the electrical power supply to the output means on and off at a switching frequency of at least about 100 Hz is included to thereby create a series of cycles each having an "on" and an "off' component with a duty cycle of from about 3 percent to about 90 percent; the power supply optionally including one or more inductors (4, 10, 1 1 , 18, 23, 24, 37, 38, 39), as may be necessary, to provide, together with the resistive load, a circuit inductance; and wherein the switching frequency, duty cycle, and any inductors in the power supply are chosen so as to cooperate with the resistive load to provide a required operation of the resistive load and wherein the circuit includes means for ensuring that any back emf or transient energy generated across the inductance is dissipated across the resistive load or is fed back to the power supply source, or both, during the "off' component of the duty cycle.

2. A power supply as claimed in claim 1 in which the resistive load has an enhanced efficiency when compared to the efficiency thereof in the absence of the said power supply.

3. A power supply as claimed in either one of claims 1 and 2 in which the circuit includes diode means (28, 29) for ensuring that any back emf or transient energy generated across the inductance is dissipated across the resistive load or fed back to the power supply source, or both.

4. A power supply as claimed in any one of the preceding claims in which the resistance, inductance, duty cycle and frequency is chosen to ensure operation of the circuit in a state of resonance or a state of oscillating frequency.

5. A power supply as claimed in any one of the preceding claims in which the electronic switching means is adapted to effect switching at a frequency of between about 800 Hz and 200,000 Hz.

6. A power supply as claimed in any one of the preceding claims in which the duty cycle is from about 5% to about 75%.

7. A power supply as claimed in claim 6 in which the duty cycle is between about 10 and 50%.

8. A power supply as claimed in claim 6 in which the duty cycle is between about 15 to 40 percent.

9. A power supply as claimed in claim 6 in which the duty cycle is about 25%.

10. A power supply as claimed in any one of the preceding claims in which the power supply circuit includes electrical energy storage means for receiving electrical energy associated with any back emf or transient energy generated and for returning it to the circuit.

11. A power supply as claimed in claim 10 in which the electrical storage means is either a battery (7) or a capacitor (6, 20, 30, 31) in the case of an alternating current power supply.

12. A power supply as claimed in any one of the preceding claims in which the resistive load is that of an appliance.

13. A power supply as claimed in claim 12 in which the power supply is built into such appliance.

14. A power supply as claimed in claim 12 in which the power supply is a separate unit comprising an electric circuit having an input and an output for connection between an existing supply of electrical energy and a resistive load circuit and wherein the power supply unit embodies electronic circuitry adapted to provide an output as defined in any one of claims 1 to 11.

15. An appliance embodying a power supply as defined in claim 12.

16. A method of operating a heat generating resistive load comprising applying, across the resistive load, the output of a power supply as claimed in any one of claims 1 to 11.