EP2873925A1

EP2873925A1 - Arrangement to supply a resistive load of a household appliance and method for feeding a resistive load of a household appliance

Info

Publication number: EP2873925A1
Application number: EP20130192996
Authority: EP
Inventors: Sorin Tcaciuc
Original assignee: Electrolux Appliances AB
Current assignee: Electrolux Appliances AB
Priority date: 2013-11-15
Filing date: 2013-11-15
Publication date: 2015-05-20
Anticipated expiration: 2033-11-15
Also published as: EP2873925B1

Abstract

The present invention describes a circuit arrangement (2000) for controlling the power of a resistive load of a household appliance such as a top heater (4150), a bottom heater (4200) and a grill (4100). The power is supplied asymmetrically to the respective resistive loads by using a diode (2120) that is e.g. serially connected to one of the resistive loads. In this manner, a simple configuration is provided that can be used in household appliances. According to measurements it saves power and is pricewise and technically competitive in comparison to electromechanical thermostats.

Description

In modern household appliance technology, such as kitchen ovens, there is always a need to provide reliable and technically simple solutions. Robust products can be manufactured with lesser manufacturing steps and usually have a higher reliability in use.
Usually, household power supplies referring to a single-phase electric power, commonly have three wired contacts at each outlet, and are generally used within the kitchen environment.
The life wire or the phase carries alternating current between the power supply and the appliance and it can have positive or even negative values over time. The neutral wire or the null wire completes the electrical circuit by carrying alternating voltage between the power supply and the appliance in the same known manner and has symmetrically negative respectively positive values in the same given period. The neutral wire is connected to the ground in order to have the same electrical potential as the earth.
Normally, the neutral wire prevents the power circuit of the appliance from rising beyond the earth voltage reference. The ground wire or the earth ground connects the housing of the appliance with the lowest voltage value. It is theoretically and generally considered to have a voltage value equal to zero as being the reference voltage value for the protection against an electric shock. Because the neutral wire of the electrical supply system is often connected to the earth, the ground and the neutral wires have a close meaning of understanding.
Under certain applications of wiring arrangements, the wire used to connect to a system, the neutral voltage is also used for the grounding of an appliance. In fact, the alternating current carried on the ground wire can result in dangerous voltages appearing on the housing of the metallic parts that are exposed to the external parts of a household appliance so that the installations of such wiring arrangements are very carefully selected and defined in all the regulations in force as main scope to protect the user when the appliance is in use.
In such cases where a neutral conductor is used also to connect the metal parts to the earth, care must be taken that the neutral conductor never rises to a high voltage with respect to local ground, but generally such situations are strived to be avoided, and especially in electrically powered appliances which are designed for cooking purposes as well as ovens, free standing cookers, microwave ovens, hobs and so on.
Considering poly-phase systems, three wires are carrying the alternating current. The neutral wire is intended to have the same voltage to each of the other circuit wires that are considered as line wires, as well as it was aforementioned. With respect to the referenced voltage, the voltage value which is zero corresponds to the earth potential of the neutral wire and is widely adopted as reference in calibration and measurement of instantaneous, effective or continuous voltages that carry the alternating currents in the electric circuit. Practically, such a power supply represents a means for voltage transfer that provides the needed energy to run any household appliance in safe conditions. Under any circumstances and regarding the same considerations as specified above, the actual electric power system is able to provide a unique voltage level that is defined by a maximum voltage, be it positive or negative, and the reference, in order that the electrical components of the electric appliance are to comply to a range of such voltage levels in order to be operated safely and according to the manufacturer's specifications.
The document US 4,196,330 discloses a combination oven fully utilizing the current-supplying capability of a power source. The circuit disclosed there requires the presence of a zero crossing device to trigger both triacs that are used in the circuit arrangement to drive a microwave oven and corresponding electrical resistance heating means.
No further related prior art is known.
The invention is based on the problem to provide a simple arrangement to supply a resistive load of a household appliance.
This problem is solved by an arrangement for supplying a resistive load of a household appliance according to claim 1 and a method for feeding a resistive load of a household appliance according to claim 15.
Further developments of the invention are given in the dependent claims.
Advantageously, the arrangement according to the present invention provides a very simple configuration to drive two different resistive loads with main power by providing circuitry that unsymmetrically feeds at least one resistive load with a maximum of every second half-wave of the alternating current. In this manner, no additional power-conditioning circuitry is required, in particular circuitry to change the frequency of the alternating current provided by the mains power.
Beneficially, according to a further development of an embodiment of the arrangement according to the present invention, a circuit comprises a diode. In this manner, a simple electrical circuit can be provided that fulfills the purpose of reliably providing power in a quantified manner to at least one of two resistive loads.
Beneficially, according to a further development of an embodiment of the arrangement according to the present invention, the diode is arranged parallel to a resistive load. In this manner, flexible circuitry can be provided.
Beneficially, according to a further development of an embodiment of the arrangement according to the present invention, the diode is mounted serially to the resistive load. In this manner, a flexible minimum configuration for only supplying one half-wave of an alternating current depending on the prefix of the current and the direction of the mounting of the diode is facilitated.
Beneficially, according to a further development of an embodiment of the arrangement according to the present invention, the electric loads are mounted in parallel. In this manner, a flexible electrical circuit arrangement for supplying both resistive loads can be provided.
Favorably, according to a further development of an embodiment of the arrangement according to the present invention, a further electric load is accommodated in the arrangement. In this manner, an even improved temperature and power control in a household appliance can be achieved by utilizing three different resistive heating elements.
Advantageously, according to a further development of an embodiment of the arrangement according to the present invention, two e.g. different diodes are provided in the circuit. In this manner, a more flexible power control in the presence of three resistive loads in an electric household appliance can be provided.
Beneficially, according to a further development of an embodiment of the arrangement according to the present invention, only a single diode may be provided in the presence of three resistive loads in order to further simplify the circuit arrangement according to the present invention, while at the same time providing flexibility in power control of the resistive loads.
Advantageously, according to a further development of an embodiment of the arrangement according to the present invention, the diodes are arranged in reverse order regarding their polarity and the respective resistive load they are connected to. In this manner, in an easy fashion, voltage of a different polarity can be switched through to a respective resistive load.
Beneficially, according to a further development of an embodiment of the arrangement according to the present invention, one resistive load is a grill because usually a grill of a household appliance possesses a high thermal output and can thus be used to efficiently control the heat in an oven.
Advantageously, according to a further development of an embodiment of the arrangement according to the present invention, a resistive load is implemented as a top heater of an oven. In this manner, efficient power control of a top heater of an oven of a kitchen appliance can be realized.
Advantageously, according to a further development of an embodiment of the arrangement according to the present invention, one of the resistive loads is a bottom heater of an oven of a kitchen appliance. In this manner, a circuit arrangement can be flexibly applied to all possible arrangements of heaters of a kitchen oven.
Beneficially, according to a further development of an embodiment of the arrangement according to the present invention, a diode is arranged switchable in order to be able to provide further flexibility in the presence of one or more diodes in the arrangement according to the present invention.
Advantageously, according to the method of the present invention, an alternating current fed to a kitchen arrangement can be controlled to supply at least two different resistive loads in a very efficient manner.
Subsequently, embodiments of the invention will be explained on the basis of examples given in drawings, wherein

Fig. 1: explains a known heating arrangement;
Fig. 2: gives an example of an arrangement according to an embodiment of the present invention;
Fig. 3: gives an example of voltage and power diagrams according to the embodiment shown in Fig. 2;
Fig. 4: gives a further example of an embodiment of the arrangement according to the present invention; and
Fig. 5: gives another example of an embodiment of the arrangement according to the present invention having two diodes.

As Fig. 1 shows, a heater has two heating elements 300 and 400 which can be considered as a resistive load of an arrangement according to the present invention.
In this case, voltage diagram 100 shows two different voltage curves 110 and 120 with a positive prefix and two other 130 and 140 with a negative prefix. Accordingly, the alternating currents 110 and 140 can be supplied, for instance, to the heating element 300, and the alternating currents 120 and 130 can be provided to the heating element 400.
In a second diagram 200, the power is shown. Here it can be seen that the power 210 associated to the currents 110 and 120 with a positive prefix is the same as the power associated to the current with the negative prefix 130 and 140. Thus, the power distributed to a single or more heating elements, in this case heating elements 300 and 400, is in balance, because it has the same value for the voltage with the positive prefix and the voltage with the negative prefix.
The power provided by the mains can be considered to be the imaginary sum of two voltages delivered by the same two imaginary power lines in which these power lines are connected in different electric configurations, so that these are able to run effectively an alternating current through at least a resistive load in which the first one S+ can deliver pulses to an electric load, pulses that alternate in time under the same frequency as well as S- that have the same maximum positive values of voltage and have a sinusoidal shape, a sinus form. The second one S- can deliver negative pulses to an electric resistive load, pulses that alternate in the same frequency as S+ that have the same maximum negative values of voltages, current and have a sinusoidal shape.
The sinusoidal voltage pulses of both power lines are matching to the 50% on, 60% off-rule, in the same manner as well as a square-wave signal generator can be put in such an operating mode. Permanently, when the power line S+ is on, the power line S- is off and vice versa. Thus, they operate with a phase shift of a half-cycle to each other. Both power lines S+ respectively S- that have a common reference that isn't used directly in order to distribute the power to a dissipation resistive load, such a power delivers a power at 100% level.
Both power lines S+ respectively S- with respect to each other are permanently in a parallel configuration, and each of these operates in a serial configuration with respect to a respective resistive load so that these have a common reference that is used directly in order to distribute the power to a resistive load. Such an electrical configuration delivers 50% of the electric power to the same resistive load.
In any wiring system of an electrically power appliance that includes at least an electrical resistor named R and according to an embodiment of the present invention, the electric power lines S+ and S- may exist independently under the constraint to be installed only in a serial circuit to such a resistive load which has e.g. a notation CR.
According to embodiments of the present invention, a technical procedure is revealed that is applicable on a range of household appliances designed for cooking purposes and is not limited in the uses on the electric appliance that only have resistive heaters. Especially the concept of the present invention offers a different approach in using an electric appliance, especially containing an electrically heated oven.
Beneficially, an arrangement according to the embodiments of the present invention ensures the usage of heating elements that have a high power to be run at a predefined lower power level without requiring complex devices such as electric, electromechanic or electronic means or modules or without a functional mode that involves a control unit that is defined by an operating algorithm. It represents a very efficient technical solution that is easy to implement, technically simple and low-cost. Comparable to an electric oven which operates with electromechanical thermostats, it also provides consistent energy savings.
Fig. 2 shows an arrangement according to an embodiment of the present invention. The arrangement 2000 shows an alternating power source 2100 with 230 V at 50 Hz. Further, a first resistive load 2130 is shown that may be a grill of an electric oven, and a second resistive load 2110 is shown that may be a top heater of an electric oven. The applicant has realized that power control of heating elements can be improved and simplified by supplying power provided by an alternating current source unsymmetrically to respective heating elements
Fig. 2 further shows that a diode 2120 is connected in parallel to the resistive load 2110. For instance, the resistor 2110 may have the value of 49 Q, and the resistive load 2130 may be of the value 30 Q. Accordingly, a simple configuration is shown in Fig. 2 for supplying two resistive loads and running them at different power levels.
The details can be further understood from in Fig. 3. The upper three diagrams 3100, 3200 and 3300 show respectively the voltage, the power and the average power regarding the resistive load 2130 of Fig. 2. It can be easily recognized how the diode 2120 influences the negative half-wave of the sinusoidal alternating current. The maximum negative value of the voltage in diagram 3100 is much smaller than the peak of the voltage having a positive prefix. The same holds true once the power over time is observed as shown in the further diagram 3200. This also holds true for the average power in the next diagram 3300 which depicts that the negative half-wave of the alternating current provides lesser power to the resistive load 2130.
On the other hand, in the middle row of Fig. 3 diagrams 3400, 3500 and 3600 show the respective values for the resistive load 2110 in Fig. 2. It can be recognized that due to the function of the diode 2120, the resistive load 2110 does not receive any share of the positive voltage of the supply power and only receives parts of the negative voltage of the mains power by operation of the diode. It can also be seen once the negative peaks of the voltage in the diagram 3100 and 3400 are added that they add up to the value of the peak with the positive prefix. Diagrams 3500 and 3600 show respectively the power and average power associated to the resistive load 2110. The lower row shows the diagrams for the added voltage 3900, the added power 3800 and the average power 3700 of the resistive loads 2110 and 2130.
Fig. 4 explains another example of an arrangement according to an embodiment of the present invention. In this case, three resistive loads 4100, 4150 and 4200 are shown. Those loads can respectively be associated to a grill 4100 of an electric oven, e.g. having an electric resistance of 31 Q, and to a top heating element of an electric oven 4150 respectively having e.g. an electric resistance of 52 Q, as well as to a bottom heating element 4200 of an electric oven being associated to an electric resistance of 53 Ω. In this case, also one diode 2120 is shown that is serially connected to the resistive load 4100.
On the other hand, Fig. 4 shows that all the resistive loads 4100, 4150 and 4200 are elsewise connected in parallel regarding the supply voltage which is provided by a power supply 2100 e.g. presenting 230 V at 50 Hz. In a similar fashion, as explained in connection with Fig. 2, the diode influences the supply voltage of the resistive load 4100 and the resulting currents are calculated according to the law of Kirchhoff. The arrangement as shown in Fig. 4 can be used to efficiently control the power of all electrical heating elements of an oven of a household appliance and thus in order to save power and time when preparing food in an oven.
Fig. 5 depicts another example of an arrangement according to an embodiment of the present invention. In a similar manner, as shown in Fig. 4, three resistive loads are arranged in this circuit 5000. They are referenced by the same numerals and e.g. comprise the same electric resistances respectively.
In this case, however, two diodes are electrically connected respectively serially to a first resistive load 4100 and to the second resistive load 4150. The resistive load 4100 and diode 2120 are arranged serially, whereas the resistive load 4150 and the diode 5120 are also arranged serially. However, the diodes 2120 and 5120 are arranged in reverse order regarding their polarity. Thus, according to this circuit arrangement, the resistive load 4100 receives another half-wave of the alternating current supplied by power supply 2100, then the resistive load 4150. Again, the electric currents are calculated by the law of Kirchhoff.
In this case, three resistive loads can be controlled, and thus the power e.g. supplied to a grill 4100, to a top heater 4150 and to a bottom heater 4200 can individually be controlled by correspondingly arranging the diodes 2120 and 5120. Thus, an electric oven of a household appliance can be efficiently controlled by using a minimum number of circuits and thus providing a reliable configuration in a technically simple manner best suited for a household appliance and a consumer environment.

List of reference numerals

300: first heater;
400: second heater;
100: mains voltage;
110, 120: positive voltages;
130, 140: negative voltages;
200: power diagram of period T;
210: power supplied by positive voltage;
220: power supplied by negative voltage;
250: main power;
2000, 4000, 5000: circuit arrangement;
2100: main supply voltage;
2120: diode;
2110: resistive load;
2130: resistive load;
3100: voltage at resistive load 2130;
3200: power at resistive load 2130;
3300: average power at resistive load 2130;
3400: voltage at resistive load 2110;
3500: power at resistive load 2110;
3600: average power at resistive load 2110;
3900: total voltage at resistive load 2110 and 2130;
3800: total power at resistive load 2110 and 2130;
3700: average power at resistive load 2110 and 2130;
4100, 4150, 4200: first, second and third resistive load;
5120: second diode.

Claims

Arrangement (2000) for supplying an electric load of a household appliance at least comprising:
- a first resistive load (2110);

- a second resistive load (2120);

- an alternating current source for feeding the electric load (2100);

- arranging a circuit (2120) to supply at least one of the electric loads (2110, 2130) only with maximally each second half-wave of the electric current.
Arrangement (2000, 4000, 5000) according to claim 1, wherein the circuit comprises a diode (2120, 5120).
Arrangement (2000, 4000, 5000) according to claim 2, wherein the diode is arranged parallel to the at least one resistive load (2110, 2130).
Arrangement (2000, 4000, 5000) according to claim 2, wherein the diode (2120, 5120) is arranged serially to the at least one electric load (2110, 2130).
Arrangement (2000, 4000, 5000) according to any one of the previous claims, wherein the resistive loads (2110, 2130) are arranged in parallel.
Arrangement (2000, 4000, 5000) according to any one of the previous claims comprising a third resistive load (4100, 4150, 4200).
Arrangement (2000, 4000, 5000) according to any of the claims 2 to 6, comprising two diodes (2120, 5120).
Arrangement (4000) according to any one of the claims 5 to 6 comprising one diode (2120).
Arrangement (5000) according to claim 7, wherein the diodes (5120 and 2120) are arranged in opposite polarity.
Arrangement (2000, 4000, 5000) according to any one of the previous claims, wherein the household appliance is an oven.
Arrangement (2000, 4000, 5000) according to any one of the previous claims, wherein at least one resistive load (4100) is a grill.
Arrangement (2000, 4000, 5000) according to any one of the previous claims, wherein at least one resistive load (2110) is a top heater.
Arrangement (2000, 4000, 5000) according to any one of the previous claims, wherein at least one resistive load (4200) is a bottom heater.
Arrangement (2000, 4000, 5000) comprising a switch for bypassing at least one diode (5120, 2120).
Method for supplying voltage to at least one resistive load (2110, 2130; 4100, 4150, 4200) of a household appliance comprising at least a first electric load (2120) and a second electric load (2130), wherein an alternating current (2100) is supplied in a manner that one of the electric loads (2110, 2120) receives only maximally each second half-wave of the alternating current (2100).