Switching device, household system and method for operating a heating apparatus

Abstract

The invention relates to a switching device (10) for operating an external heating apparatus (20) for heating a medium (F) by means of a plurality of heating elements (21-i) of the heating apparatus (20). The invention also relates to a household system (100), and various methods for heating a medium (F). The switching device (10) can, when heating elements (21-i) of the heating apparatus (20) are connected to one another at a common star point (22) and can be connected to the switching device (10) independently of one another, is designed to be supplied by at least one current phase (L) and can comprise a control apparatus (11) which is designed to switch the heating elements (21-i), independently of one another, in each case via at least one associated switch (Ki, Kia, KN) of the switching device (10) for the graduated setting of a heating power generated in total by the heating apparatus (20) according to a respective heating stage, wherein the control apparatus is implemented by a computing unit.

Description

[0001]Title Switching device, domestic system, and method for operating a heating device Field of the invention The invention relates to a switching device and a method for operating or controlling a heating device for heating a medium, as well as to a domestic system with such a switching device and such a heating device. The medium can in particular be a fluid, i.e. a gas or a liquid, e.g. water. The heating device can thus in particular have a plurality of heating elements in order to heat water in a water tank. For example, the switching device can operate a 3-phase heating rod for a water tank of a domestic system. Technical background The best possible use of available electrical power is also becoming increasingly important with the increasing spread of renewable energy sources. Energy storage in particular is an important component in this regard.It is known that many media, particularly fluids such as water or molten salt, can be used to store energy in the form of heat. Particularly in households, where hot water is repeatedly needed, water can be heated in advance in a water tank whenever there is a surplus of electrical power. For this purpose, it is advantageous if the heating output used to heat the medium can be adjusted as precisely as possible in a cost-effective manner so that the available surplus power can be used optimally. Existing domestic systems are usually already equipped with a water tank with a heating device, frequently a 1-phase or 3-phase heating element. However, power electronics to operate such heating devices with precisely adjustable electrical power are not usually available, and retrofitting would be relatively expensive.Summary of the Invention In view of all the foregoing, it is therefore an object of the present invention to provide a switching device with which even an existing heating device can be switched cost-effectively to provide different heating levels and thus desired heating outputs. A further object is to provide a method for operating an existing heating device in the manner mentioned, as well as an improved domestic system for better utilization of available electrical power, in particular from renewable energy sources. These objects are achieved by the subject matter of the independent patent claims.Accordingly, according to a first aspect of the invention, a switching device is provided for operating an external heating device for heating a medium by means of a plurality of heating elements of the heating device, which are interconnected at a common star point (in a star shape) and can be connected (or are connected) to the switching device independently of one another, wherein the switching device is designed to be supplied by at least one current phase and comprises a control device which is designed to switch the heating elements independently of one another via at least one associated switch of the switching device for the stepwise adjustment of a heating power generated overall by the heating device according to a respective heating stage, wherein the control device is implemented by a computing unit. It can be provided that a desired heating power value (iea total heating output setpoint) is communicated, and the control device then selects a heating level which optimally realizes the communicated total heating output setpoint. Alternatively, it can also be provided that the control device is only communicated with a heating level (for example by a higher-level energy management system). The information as to which heating level corresponds to which total heating output can accordingly be available at the energy management system and / or at the switching device, in particular the control device. The boundaries can also be fluid, since the energy management system can be integrated into the switching device or vice versa. The same can apply to the selection of a specific switching combination to realize a desired heating level, i.e. it can be specified by a higher-level instance (e.g. the energy management system) or selected by the control device itself.For improved compatibility of the switching device with existing energy management systems, it can be advantageous if the energy management system simply communicates the desired total heating output (i.e., total heating output setpoint) to the switching device, and the switching device then selects and sets the heating level and a suitable switching combination for its implementation. This enables ideal utilization of the available electrical energy, particularly the energy available from renewable energy sources. This does not necessarily mean complete utilization orUse, since other parameters and boundary conditions may play a role, for example a desired upper threshold for a water temperature, the priority to charge a battery connected to the house system (e.g. a vehicle battery of an electric car due to an upcoming trip), and the like. According to some variants, the battery can be considered as a renewable energy source, according to other variants it can be considered separately. The present solution is also cost-effective to implement, as it has low hardware requirements and can also be advantageously combined with existing heating devices. Advantageously, the controllable switches of the switching device have relays or (preferably) semiconductor switches, or each consist of a relay or (preferably) a semiconductor switch.According to some preferred embodiments, variants, or refinements of embodiments, the switching device is configured to switch between at least five heating levels, particularly preferably at least seven heating levels, of different heating output. In this way, many control and regulation programs can be implemented with comparatively high precision. Switching devices with nine, eleven, twelve, thirteen, or even more realizable heating levels are also advantageously provided. According to some preferred embodiments, variants, or refinements of embodiments, a diode is connected in parallel to at least one switch, optionally exclusively this diode, or preferably a series connection comprising the diode and another switch. A half-wave of electrical alternating voltage can be filtered out via the parallel-connected diode in order to implement additional heating levels.This diode can also be selectively switched on or off by the additional switch in order to realize additional heating levels. According to some preferred embodiments, variants or refinements of embodiments, the switching device has an output for each heating element to be connected, wherein the switch associated with the corresponding heating element is connected in series with the output. Each switch can advantageously be controlled individually by the control device. However, other variants are also conceivable according to which some outputs are wired differently, for example by means of a toggle switch that can switch back and forth between a current phase and the neutral conductor. In this way, additional heating levels can be realized even with existing hardware of the heating device. The outputs of the switching device can be implemented mechanically in a common socket or in separate sockets.According to some preferred embodiments, variants or refinements of embodiments, the control device is also configured to switch periodically or cyclically one after the other between implementations of the same heating output by means of different switching combinations (i.e. combinations of switch positions of the switches). As will be explained below, there are often heating levels that can be implemented using multiple switching combinations. The periodic switching can ensure that the individual heating elements of the heating device and switches of the switching device are worn evenly in order to maximize the service life of the heating device. Additionally or alternatively, it can also be provided that with each new setting of a heating level with multiple implementation options, the various switching combinations are cycled one after the other.In this way, particularly even wear of the heating elements, switches, etc. can also be achieved. According to some preferred embodiments, variants, or refinements of embodiments, the switching device, in particular the control device, is configured to receive a current power value of a renewable energy source (in particular a PV system) and to adapt a current heating level at least based on the received current power value. This makes it possible to achieve optimal utilization of the power currently provided by the renewable energy source. This can include adjusting an overall heating power setpoint by the switching device. According to some preferred embodiments, variants, or refinements of embodiments, the control device is configured to further adapt the current heating level based on an overall heating power setpoint.In this way, the switching device according to the invention can advantageously be used within the framework of an energy management system or a managed home system according to a control or regulation method. The instructions (or control commands) for adjusting the current heating level can therefore be generated, for example, by the energy management system. According to some preferred embodiments, variants, or refinements of embodiments, the control device is configured to set the current heating level such that a difference between the total heating output generated by the heating device and the total heating output setpoint is minimized. The switching device can also be used in a control or regulation system in this way.According to some preferred embodiments, variants or refinements of embodiments, the control device is designed to carry out a measuring method to determine which heating levels are available and / or which total heating power is realized with each of the available heating levels. For this purpose, a test voltage can be applied to each switch of the switching device, each possible switching combination can be switched through, and a power consumed by the heating device for each switching combination can be determined. In this way, it is possible to determine which switching combinations belong to the same heating level, i.e., realize the same total heating power, and what this total heating power is numerically in each case. The measuring method can be carried out automatically, e.g., each time the switching device is initialized, or at the request of a user.Within the scope of the measuring method, it can also be determined whether the heating device has a 1-phase or 3-phase connection to the switching device. The switching device is therefore particularly versatile and easy to install, as it can obtain the necessary information itself. According to a second aspect, the present invention provides a domestic system which has a switching device according to an embodiment of the first aspect of the present invention and a heating device which is connected (or wired) to the switching device and for which the switching device is configured to operate. The domestic system can also comprise a medium to be heated, e.g. a heat-radiating material of an infrared heating panel, and / or a fluid tank for storing a fluid, wherein the fluid in the fluid tank can be heated by means of the heating device. In particular, the fluid can be water.According to some preferred embodiments, variants, or refinements of embodiments, the heating elements are arranged in an infrared heating panel or a continuous-flow heater or in a fluid tank. In the case of the fluid tank, the heating elements can, for example, be arranged in a wall opening of the fluid tank, in particular, screwed therein. According to some preferred embodiments, variants, or refinements of embodiments, the domestic system also comprises a user interface by means of which one or more target parameters of the heating device, the medium, and / or a fluid tank for the medium can be set. The parameter can be, for example, a target temperature of the medium, an upper threshold value for the temperature of the medium, a total heating output target value, a heating energy target value, and / or the like.Using the user interface, further parameters of the building system can also be set, for example a charge level threshold for the charge level of a battery in the building system or the like. The user interface can be integrated into the switching device or into an energy management system of the building system, or it can be designed separately. The user interface can comprise a graphical user interface which is implemented – e.g. as part of an application – by a smartphone, a tablet, a desktop PC or the like. According to some preferred embodiments, variants or refinements of embodiments, if several heating elements, e.g. at least two, more than 50% of the heating elements or all heating elements of the heating device have the same electrical heating resistance value. If all heating elements have the same heating resistance value, this can also be referred to as a symmetrical variant S.This is often the case with existing heating devices, e.g. 3-phase heating elements, so that high synergy effects arise here with the numerous switching combinations and correspondingly realizable heating levels of the switching device according to the invention. Alternatively, some or all of the heating elements can have different electrical heating resistances. This makes additional heating levels possible. If all heating elements have a different heating resistance value, this can also be referred to as asymmetric variant A. According to some preferred embodiments, variants or refinements of embodiments, the house system also comprises a battery and an energy management system which is configured to monitor a charge level of the battery and to allow or prevent energy from being drawn from the battery to operate the heating device based on the charge level.This allows optimal interaction between the two energy sinks or energy storage devices, namely the medium on the one hand and the battery on the other, to be achieved. The energy management system can be configured to control the switching device to set a heating level higher than the current one. To this end, or independently of this, the energy management system can, for example, provide, in accordance with a user-configurable or preset prioritization, that additional power is provided from a renewable energy source of the building system and / or from a battery of the building system and / or that additional power is drawn from the public power grid and / or that the power consumption of at least one local consumer of the building system is reduced. In particular, the power consumption of local consumers connected to the (multi-pole) power grid of the building system (“building power grid”) can be reduced.Such a local consumer could be, for example, a heat pump or a well or pool pump. The energy management system can also be configured to control the switching device to set a lower heating level than the current one. To do this, the above-mentioned measures can be carried out or terminated in reverse. The energy management system can also be configured to monitor the charge level of a battery in the building's system and only allow additional power to be drawn from the battery if the battery charge level is above a user-adjustable or preset charge level threshold. The building's system can be configured so that the switching device switches to a lower heating level than the current one if there is insufficient power (from renewable energy sources in the building's system).To this end, the energy management system can either instruct the control device of the switching device to reduce the heating level if sufficient power is not available. Alternatively, the energy management system can communicate information about the available power to the control device, which in turn can be configured to change the heating level accordingly, i.e., to increase or decrease it.According to a third aspect, the present invention provides a switching device for operating an external heating device for heating a medium by means of at least one heating element of the heating device, wherein the switching device is configured to be supplied by at least one current phase and comprises a control device configured to switch the heating element via at least one associated switch of the switching device for (stepwise) adjustment of a total heating power generated by the heating device as a whole according to a respective heating stage, wherein a diode is connected in parallel to the switch. In this way, by selectively bridging or not bridging the diode by means of the switch, at least one additional heating stage can be realized, since the diode filters out one of the half-waves of electrical alternating voltage.According to a fourth aspect, the invention provides a method for operating a heating device (or: for heating a medium by means of a heating device) having a plurality of heating elements which are interconnected (in a star configuration) at a common star point and can be connected (or are connected) independently of one another to an energy source. The method comprises at least the steps of: detecting a desired total heating output, i.e. a total heating output setpoint; determining a heating level which corresponds as closely as possible (or exactly), i.e. in particular, comes as close as possible to the desired heating output (i.e. the total heating output setpoint); and switching the heating elements independently of one another, each via at least one associated switch, for (step-by-step) adjustment of the determined heating level.According to a fifth aspect, the invention provides a method for operating a heating device with at least one heating element (or: for heating a medium by means of at least one heating element of a heating device). The method comprises at least the steps of: detecting a desired total heating output, i.e., a total heating output setpoint; determining a heating level that best corresponds to the desired total heating output (i.e., the total heating output setpoint); and switching at least one switch, which is arranged between a current phase and the at least one heating element of the heating device, and which is connected in parallel with a diode (optionally with a series circuit comprising the diode and a further switch), for (step-by-step) adjustment of the determined heating level.According to a sixth aspect, the invention provides a computer program product comprising executable program code which, when executed (e.g., by means of a computing device), is configured to carry out the method according to an embodiment of the fourth or fifth aspect of the present invention. According to a seventh aspect, the invention provides a non-volatile computer-readable data storage medium comprising executable program code which, when executed (e.g., by means of a computing device), is configured to carry out the method according to an embodiment of the fourth or fifth aspect of the present invention. The non-volatile computer-readable data storage medium can, for example, be designed as or comprise a semiconductor memory, e.g., an SSD memory chip.The data storage medium can also have or comprise a CD, DVD, Blu-ray or a magnetic storage device. According to an eighth aspect, the invention provides a data stream which comprises executable program code or is designed to generate program code which, when executed (e.g. by means of a computing device), is designed to carry out the method according to an embodiment of the fourth or fifth aspect of the present invention. The computing device can be any device which is designed and configured for digital computing, in particular for executing software, an application or an algorithm. The computing device can, for example, comprise at least one processor unit (e.g. at least one CPU), at least one graphics processor unit (e.g.: at least one GPU), at least one field-programmable gate array, FPGA and / or at least one application-specific integrated circuit, ASIC, and / or any combination of the aforementioned elements. The computing device can also have a main memory and / or a non-volatile data memory, which are operatively linked to one another and / or to some or all of the aforementioned elements. The computing device can be implemented partially or completely in a local unit (for example a personal computer, PC, a laptop, a notebook or the like) and / or partially or completely in a distributed system, e.g. a cloud computing platform or a spatially separated server. Brief description of the figures The invention is explained in more detail below with reference to exemplary embodiments in the figures of the drawings. In the figures: Fig.1 shows a schematic block diagram of a switching device and of a building installation according to embodiments of the present invention; FIGS. 2 to 15 show various possible interconnections which can be implemented using switching devices according to the invention; FIG. 16 shows a schematic flow diagram for explaining a method according to one embodiment of the present invention; FIG. 17 shows a schematic flow diagram for explaining a method according to a further embodiment of the present invention; FIG. 18 shows a schematic block diagram of a computer program product according to yet another embodiment of the present invention; FIG. 19 shows a schematic block diagram of a data storage medium according to yet another embodiment of the present invention; and FIG. 20 shows a schematic flow diagram for explaining a method according to yet another embodiment of the present invention. In all figures, identical orFunctionally equivalent elements and devices - unless stated otherwise - have been provided with the same reference numerals. The designation and numbering of the method steps does not necessarily imply a sequence, but serves to better distinguish them, although in some variants the sequence can also correspond to the sequence of the numbering. Detailed description of the figures Fig. 1 shows a schematic block diagram of a switching device 10 and a building system 100 according to embodiments of the present invention. The switching device 10 can also be used or provided independently of the building system 100. The various components of the building system 100 are optional and can be provided or not depending on the planned use or already existing infrastructure. In addition, additional components not shown can of course be added.The switching device 10 is designed to operate an external heating device 20 (relative to the switching device 10), which is designed to heat a medium. In the present case, a fluid F in a fluid tank 50 (here, in particular, water in a water tank) is used as an example of such a medium. The heating device 20 can, for example, be arranged, in particular screwed, in a wall opening of the fluid tank 50. However, it is understood that a wide variety of other media can also be heated, for example, heat radiators of an infrared panel or the like. As will be explained in more detail below, the switching device 10 is designed such that it can set the heating device 20 to one of a plurality of possible heating levels, wherein each heating level advantageously is associated with a different heating output of the heating device 20.It is particularly advantageous that the switching device 10 is also compatible with existing, relatively simply designed heating devices 20. The switching device 10 comprises a control device 11, which can be implemented by any desired computing unit, for example a microcontroller, an application-specific integrated circuit (ASIC), a programmable logic controller (PLC), and / or the like. The control device 11 can, in particular, be implemented partly in hardware and partly in software. The switching device 10 is also configured to be supplied via at least one electrical line 34 by at least one current phase L, which can be a single current phase (L1, L2, L3) of a 3-phase alternating current, or two, or all of these current phases.The switching device 10 can also be coupled to a neutral conductor N and / or a protective conductor PE via the at least one electrical line. The switching device 10 also has a plurality of switches K1, K2, K3, which are sometimes referred to jointly below (or if it is irrelevant which switch is meant). The control device 11 is configured to switch the switches Ki, i.e. in particular to either open or close each switch Ki independently of the others (or: switch it on or off). Each of the switches Ki is designed to be connected to an individual heating element 21-1, 21-2, 21-3 of a heating device 20, in particular such that the corresponding heating element 21-i heats when the corresponding switch Ki is closed and does not heat when the corresponding switch Ki is open.For this purpose, each switch Ki can be electrically connected to a (in particular: exactly one) corresponding terminal 16-i on a housing of the switching device 10, so that each heating element 21-i only needs to be electrically connected to one of the corresponding terminals 16-i. At an output of the heating elements 21-1, 21-2, 21-2 facing away from the switches K1, K2, K3, the heating elements 21-i are connected to a common star point 22, i.e., they are star-coupled. A neutral conductor N can be connected via a terminal 17 of the switching device 10, which neutral conductor can optionally be switched by the control device 11 via a switch KN of the switching device 10. Which switches Ki, KN can be switched in each case can differ from installation location to installation location depending on the applicable rules, standards, or laws and can be adjustable in the control device 11.The switches K1, K2, K3 can be designed as relays or semiconductor switches or comprise a relay or a semiconductor switch. Here, the invention is described by way of example with three (preferably semiconductor) switches K1, K2, K3 for operating exactly three heating elements 21-i. However, it is understood that fewer (for example, two switches K1) or more switches K1 can be present. This applies to each of the embodiments described herein. It is advantageous if the number of switches K1 is equal to, or at least greater than, the number of heating elements 21-i. Each heating element 21-i controls its own heating power P. i to heat the fluid F, with a maximum total heating power P max = P1+P2+P3 is provided when all switches Ki are closed. Advantageously, the control device 11 has information about which of the switches Ki or which of the terminals 16-i is used to determine which heating power Pi can be made available. This information (which individual heating output P i can be provided in each case) can be programmed, for example, by means of a user interface 12 of the switching device or selected from a table. It is also conceivable that the control device 11 contains a database with common models of the heating device 20, from which the corresponding model with the corresponding individual heating outputs P ican then be selected by a user. The user interface 12 can, instead of and / or in addition to the switching device 10, also be provided on an energy management system 40 of the building system 100, which is coupled to the switching device 10 for data communication. The energy management system 40 of the building system 100 can also be integrated into the switching device 10, or vice versa. For models of heating devices 20 which have different heating outputs P i of their heating elements 21-i, the user may additionally be asked to specify, when installing the switching device 10, at which terminal 16-i which heating power P i(or: which heating resistor) is present. However, the control device 11 is particularly preferably designed to carry out a measuring process (e.g. for current, voltage, and / or frequency) in order to determine which heating resistors are present, which heating levels are available, and / or which total heating power P is realized with each of the available heating levels. For this purpose, the control device 11 can apply a test voltage to each switch K1, K2, K3 of the switching device 10, switch through each possible switching combination, and determine the power consumed by the heating device 20 for each switching combination. In this way, it is possible to determine which switching combinations belong to the same heating level, ie, realize the same total heating power P, and which total heating power P this is numerically (or quantitatively). The measuring process can be automatic, e.g.during each initialization of the switching device 10, or at the request of a user via the user interface 12. Within the scope of the measuring method, it can also be determined whether a 3-phase or a 1-phase connection of the heating device 20 to the switching device 10 is present. If the control device 11 has the information as to which heating level corresponds to which total heating output, the control device 11 can advantageously only be informed of a total heating output setpoint (for example by the energy management system 40), whereupon the control device 11 independently determines which heating level best corresponds to this total heating output setpoint, selects a corresponding switching combination, and then sets this.Accordingly, the following will primarily refer to the desired heating level, although it is understood that this can be determined in each case for the best possible realization of a total heating output setpoint. The total heating output setpoint can be determined, for example, depending on how much electrical power is currently generated by renewable energy sources, how much electrical power remains after deducting the total consumption of consumers 32, the current electricity price, and / or the like. The following primarily describes the case where all heating elements 21-i have the same heating output P. i (“symmetrical variant”, S), since this is a common design of heating devices 20. However, it is understood that everything said can also be applied analogously to heating devices 20 which have different heating elements 21-i with different heating outputs P iThe heating elements 21-i can each have (at least) one heating resistor or consist of one. The total number of all resistors of a heating element 21-i used for heating represents the heating power P iof the corresponding heating element 21-i. The precise interconnection of the heating elements 21-i with one another and with current phases of a power supply is shown only schematically in Fig. 1. Actual possible circuits that can be implemented using the switching device 10 will be explained in more detail below. However, it is already apparent that the control device 11 is configured to switch the heating elements 21-i independently of one another, each via at least one associated switch Ki of the switching device 10, for the stepwise adjustment of a total heating power P to be generated (or generated) by the heating device 20 as a whole, according to a respective heating stage. The domestic system 100 according to the invention comprises at least the switching device 10 and the heating device 20. The switching device 10 is supplied with electrical power via a power grid 30 (for example, a multi-pole domestic power grid of a household).The power grid 30 can have a grid connection point 31 for connection to the public power grid 35 and at least one consumer 32, for example, a heat pump. The combination of the switch positions of the switches Ki and the interconnection of the terminals 16-i by the switching device 10 results in a hierarchy of heating levels, with the lowest heating level (all switches Ki open) corresponding to a heating output of 0 watts, and the highest heating level (all switches Ki closed) corresponding to a maximum total heating output of P. max. In the following, a series of possible connections will first be described with reference to Figs. 2 to 15 in order to demonstrate the diverse possibilities of the present invention. The corresponding hierarchy of heating levels provided will also be explained in each case. Subsequently, it will be explained how the heating levels can be used for an efficient use of available energy, in particular from renewable energy sources. However, it is already apparent that by providing a large number of heating levels, the current total heating output P of the heating device 20 can be set particularly appropriately and flexibly. As a result, a difference between the total heating output generated by the heating device 20 and the total heating output setpoint is kept to a minimum. Fig. 2 shows a possible connection using the switching device 10 according to one embodiment. In this case, the switching device 10 (in Fig.2 not fully shown), each of the three terminals 16-1, 16-2, 16-3 is connected to a corresponding current phase L1, L2, L3 of a 3-phase alternating current, while the star point 22 is connected to a neutral conductor N or directly to the output 17 of the switching device 10. The heating elements 21-i each have a heating resistor R1, R2, R2. In this variant, no switch KN is required on the neutral conductor N and can therefore also be omitted from the switching device 10, i.e., the neutral conductor N can remain switchless. This is advantageous in areas where switching the neutral conductor N is prohibited. In a first variant S ("symmetrical"), which corresponds to the operation of a conventional 3-phase heating element, R1=R2=R3=R (not shown). This connection enables four different heating levels, each corresponding to a different total heating output P.In the following Table 1, the first three columns list the individual setting options for the switches (0 corresponds to "switch open", 1 corresponds to "switch closed"). The correspondingly set (or selected) total heating outputs P are shown in the fourth column as a fraction of the maximum total heating output P. max Thus, the four different realizable heating levels correspond to the total heating outputs 0, 1 / 3 P max , 2 / 3 P max and P max The fifth column gives examples of corresponding wattage values ​​for a heating resistance R=26.45 Ω, a voltage of 230 V (N to Li, ie from neutral conductor to phase) and a maximum total heating power of P max =6kW. Connection according to Fig.2, variant S: 4 heating stages K1 K2 K3 P R1=R2=R3=26.45 Ω 0 0 0 0 Pmax 0 0 0 1 1 / 3 P max 2000W 0 1 0 1 / 3 Pmax 2000W 0 1 1 2 / 3 Pmax 4000W 1 0 0 1 / 3 Pmax 2000W 1 0 1 2 / 3P max4000 W 1 1 0 2 / 3 Pmax 4000 W 1 1 1 Pmax 6000 W Table 1: Available heating levels of variant S from Fig. 2 The two middle heating levels, corresponding to the total heating power 1 / 3 P max and 2 / 3 P max, can be achieved in combination by three different switching combinations of the switches Ki. Thus, the control device 11 can be configured, when one of these two heating levels is set, to periodically and / or with each new setting of one of these heating levels, cyclically select a different switching combination of the switches Ki in order to evenly load or wear the corresponding heating elements 21-i and the switches 16-i. This also applies to each of the embodiments discussed below, provided they have at least one heating level that can be implemented by more than one switching combination. Thus, switching between the switching combinations can take place periodically and / or cyclically. In a second variant A ("asymmetric"), R1, R2, and R3 are all different, as shown in Fig. 2. This wiring enables seven different heating levels, each with a different total heating output P.According to the following Table 2, the seven different realizable heating levels correspond to the total heating outputs 0.1 / 6 P. max , 1 / 3 P max , 1 / 2 P max , 2 / 3 P max, 5 / 6 P max , and P max , when R2=R1 / 3 and R3=R1 / 2. The fifth column gives examples of corresponding wattage values ​​for heating resistors of R1=52.9 Ω, R2=17.63 Ω, and R3=26.45 Ω, and a voltage of 230 V (LN). Connection according to Fig. 2, variant A: 7 heating stages K1 K2 K3 P R1 = 52.9 Ω / R2 = 17.63 Ω / R3 = 26.45 Ω 0 0 0 0 Pmax 0 0 0 1 1 / 2 P max 3000W 0 1 0 1 / 3 Pmax 2000W 0 1 1 5 / 6 Pmax 5000W 1 0 0 1 / 6 Pmax 1000W 1 0 1 2 / 3P max4000 W 1 1 0 1 / 2 Pmax 3000 W 1 1 1 Pmax 6000 W Table 2: Available heating levels of variant A from Fig. 2 Here and in the following, the case is described where, in the asymmetrical variants, R1 has the greatest ohmic resistance. However, it goes without saying that other permutations are also possible. The resistor designated R1 can also be connected to terminal 16-2 or 16-3, and so on in any permutation. Fig. 3 shows a connection using the switching device 10 according to a further embodiment. Here, the heating device 20 to be operated is a 3-phase heating element which, however - in contrast to the variants in Fig. 2 - is to be operated with a 1-phase power supply. Accordingly, all three terminals 16-i can be connected to the L1 power phase by the switching device 10. The heating levels that can be achieved in this way for the symmetrical variant S with R=R1=R2=R3 oran asymmetrical variant again correspond to those in Table 1 and Table 2. Fig. 4 shows a connection through the switching device 10 according to a further embodiment. This embodiment differs from that according to Fig. 2 in that the switching device 10 here has the switch KN on the neutral conductor N. Accordingly, a total of 5 heating levels according to the following Table 3 are available for the symmetrical variant with R1=R2=R3=R (shown in Fig. 4): Connection according to Fig. 4, variant S: 5 heating levels K1 K2 K3 KN PR = 26.45 Ω 0 0 0 0 0 0 0 0 0 1 0 0 0 0 1 0 0 0 0 1 1 1 / 3 Pmax 2000 W 0 1 0 0 0 0 0 1 0 1 1 / 3 P. max 2000W 0 1 1 0 1 / 2Pmax 3000W 0 1 1 1 2 / 3P max 4000W 1 0 0 0 0 0 1 0 0 1 1 / 3 P max 2000W 1 0 1 0 1 / 2Pmax 3000W 1 0 1 1 2 / 3P max 4000W 1 1 0 0 1 / 2Pmax 3000W 1 1 0 1 2 / 3P max4000 W 1 1 1 0 Pmax 6000 W 1 1 1 1 Pmax 6000 W Table 3: Available heating levels of variant S from Fig. 4 The five heating levels correspond to the total heating outputs P of 0 (5 switching combinations), 1 / 3 P max (3 switching combinations), 1 / 2 P max (3 switching combinations), 2 / 3 P max (4 switching combinations), and P max(2 switching combinations). An asymmetrical variant would result in a correspondingly higher number of heating levels. Even with the wiring according to Fig. 4, the operation of a single-phase heating element is possible by substituting L1 for L2 and L3 in Fig. 4 (not shown). Fig. 5 shows a wiring using the switching device 10 according to a further embodiment. This embodiment differs from that according to Fig. 2 or 4 in that the switching device 10 here has the switch KN on the neutral conductor N, and that the output 16-2 can be switched between a connection to L2 or a connection to the neutral conductor N via the switch K2 (toggle switch). Accordingly, a total of 7 heating levels are available according to Table 4 below for the symmetrical variant S with R1=R2=R3=R (not shown) and 12 heating levels are available according to Table 5 for the asymmetrical variant A (shown): Wiring according to Fig.5, variant S: 7 heating levels K1 K2 K3 KN P R1=R2=R3=R= 26.45 Ω 0 N 0 0 0 0 0 N 0 1 0 0 0 N 1 0 1 / 6 Pmax 1000 W 0 N 1 1 1 / 3 Pmax 2000 W 0 L2 0 0 0 0 0 L2 0 1 1 / 3 p. ampf 2000W 0 L2 1 0 1 / 2 Pmax 3000 W 0 L2 1 1 2 / 3 P max 4000W 1N 0 0 1 / 6Pmax 1000W 1N 0 1 1 / 3P max 2000W 1N 1 0 5 / 9Pmax 3333W 1N 1 1 2 / 3P max 4000W 1 L2 0 0 1 / 2 Pmax 3000 W 1 L2 0 1 2 / 3 P max 4000W 1 L2 1 0 Pmax 6000 W 1 L2 1 1 P max 6000 W Table 4: Available heating levels of variant S from Fig. 5 The seven heating levels each correspond to the total heating power P of 0.1 / 6 P max , 1 / 3 P max , 1 / 2 P max , 2 / 3 P max , and P max. This variant thus illustrates the general case in which the switching device 10 can have a switch (here: K2) which can be switched between one of the current phases L1, L2, L3, i.e. a current conductor on the one hand and the neutral conductor N on the other. This means that the corresponding heating element 21-2 with its heating resistor R2 is alternatively coupled to the corresponding current phase L1, L2, L3 or the neutral conductor N. Connection according to Fig. 5, variant A: 12 heating stages K1 K2 K3 KN P R1 = 52.9 Ω / R2 = 26.45 Ω / R3 = 17.63 Ω 0 N 0 0 0 0 0 N 0 1 0 0 0 N 1 0 1 / 5 P max 1200W 0 N 1 1 1 / 2 Pmax 3000 W 0 L2 0 0 0 0 0 L2 0 1 1 / 3 Pmax 2000 W 0 L2 1 0 3 / 5 P max 3600W 0 L2 1 1 5 / 6 Pmax 5000 W 1 N 0 0 1 / 9 P max 666 W 1 N 0 1 1 / 6 Pmax 1000 W 1 N 1 0 10 / 31 P max 1935 W 1 N 1 1 2 / 3 Pmax 4000 W 1 L2 0 0 1 / 3 P max 2000W 1 L2 0 1 1 / 2 Pmax 3000 W 1 L2 1 0 11 / 12 P max5500 W 1 L2 1 1 Pmax 6000 W Table 5: Available heating levels of variant A from Fig. 5 The twelve heating levels that can be realized here with R1=2R2=3R3 correspond to the total heating power P of 0.1 / 9 P max , 1 / 6 P max , 1 / 5 P max , 10 / 31 P max , 1 / 3 P max , 1 / 2 P max , 3 / 5 P max , 2 / 3 P max , 5 / 6 P max , 11 / 12 P max , and P maxFig. 6 shows a circuit through the switching device 10 according to a further embodiment, which represents a variant of the circuit of Fig. 5. In Fig. 6, the heating device 20 to be operated is again a 3-phase heating rod, which, however, is to be operated with a 1-phase power network. Accordingly, all three connections 16-i are connected to the L1 current phase by the switching device 10. This allows six heating stages to be implemented, which are listed in Table 6 below. Although a symmetrical variant S is shown in Fig. 6, it is understood that an asymmetrical variant with partially or completely different heating resistors R1, R2, R2 can also be provided. Circuit according to Fig. 6, variant S: 6 heating stages K1 K2 K3 KN P R1=R2=R3=R= 26.45 Ω 0 N 0 0 0 0 0 N 0 1 1 / 3 P max 2000 W 0 N 1 0 0 0 0 N 1 1 2 / 3 Pmax 4000 W 0 L2 0 0 0 0 0 L2 0 1 0 0 0 L2 1 0 1 / 6 Pmax 1000 W 0 L2 1 1 1 / 3 P max2000W 1N 0 0 0 0 1N 0 1 2 / 3P max 4000 W 1 N 1 0 0 0 1 N 1 1 P max 6000W 1 L2 0 0 1 / 6 Pmax 1000W 1 L2 0 1 1 / 3 P max 2000 W 1 L2 1 0 2 / 9 Pmax 1333 W 1 L2 1 1 2 / 3 Pmax 4000 W Table 6: Available heating levels of variant S from Fig. 6 The six heating levels each correspond to the total heating power P of 0.1 / 6 P max , 1 / 3 P max , 2 / 3 P max , 2 / 9 P max , and P max. In the following, embodiments are shown and explained, each of which has at least one diode connected in parallel with a respective switch. The diodes make it possible to implement additional heating stages by blocking half-waves. Fig. 7 shows a circuit through the switching device 10 according to a further embodiment. In this simple variant, a 1-phase heating device 20 is operated, which comprises a single heating element 21-i with a heating resistor R (or a sum of heating resistors, which can be represented with R as an equivalent resistor). The switching device 10 can be designed for such 1-phase heating devices 20 with only two connections 16-1, 17 for the L1 current conductor and the neutral conductor, or can be programmed to supply current only to these connections. At the connection for the L1 current conductor orThe switching device 10 has a terminal 16-1 provided for the L1 current phase, a switch K1 controllable by the control device 11, and a diode 14 connected in parallel with this switch K1. In this way, three heating stages can be realized, as listed in Table 7 below: 0, 1 / 2 P. max, and P max . Connection according to Fig.7: 3 heating stages K1 KN PR=26.45 Ω 0 0 0 0 0 1 1 / 2 P max1000 W 1 0 0 0 1 1 Pmax 2000 W Table 7: Available heating levels of the variant from Fig. 7 Fig. 8 shows a connection through the switching device 10 according to a further embodiment, which can be referred to as a variant of the embodiment according to Fig. 7. In this variant, the switching device 10 has a series circuit connected in parallel with the switch K1 and comprising a further switch K1a, which can be controlled by the control device 11, and the diode 14. The switch K1a forms a series circuit with the diode 14. In this way, three heating levels can also be realized, as listed in Table 8 below: 0, 1 / 2 P max, and P max . Connection according to Fig.8: 3 heating stages K1 K1a PR=26.45 Ω 0 0 0 0 0 1 1 / 2 P max1000 W 1 0 Pmax 2000 W 1 1 Pmax 2000 W Table 8: Available heating levels of the variant from Fig. 8 The diode 14 (either alone in parallel connection to a switch K1, K2, K3 as in Fig. 7, or in series connection with a further switch K1a, this series connection being connected in parallel to a switch K1, K2, K3, as in Fig. 8) can advantageously also be combined with other variants, in particular with 3-phase heating devices 20. Fig. 9 shows a variant of the circuit from Fig. 2, which differs from this in that there is a diode 14 connected in parallel with the switch K1 and the missing connection of the star point 22 to the neutral conductor N. Accordingly, the switching device 10 can also be designed without the connection 17 and thus, for example, have only exactly one connection 16-1, 16-2, 16-3 per current phase L1, L2, L3.In a symmetrical variant S with R1=R2=R3=R (not shown), 5 heating stages can be realized in this way, as listed in Table 9: Connection according to Fig.9, variant S: 5 heating stages K1 K2 K3 P R1=R2=R3=R= 26.45 Ω 0 0 0 0 0 0 0 0 1 / 4 Pmax 1500 W 0 0 1 1 / 4 Pmax 1500 W 0 0 1 3 / 4 P. max 4500 W 0 1 0 0 0 0 1 0 1 / 2 P max 3000 W 0 1 1 1 / 2 P max 3000 W 1 1 1 Pmax 6000 W Table 9: Available heating levels of variant S from Fig. 9 The five heating levels that can be realized in this way are: 0, 1 / 4 P max, 1 / 2 P max, 3 / 4 P max, and P max . In an asymmetrical variant A (shown) with three different resistors R1, R2, R3, 7 heating stages can be realized, as listed in Table 10: Connection according to Fig.9, variant A: 7 heating stages K1 K2 K3 P R1 = 52.9 Ω / R2 = 26.45 Ω / R3 = 17.63 Ω 0 0 0 0 0 0 0 56 / 275 Pmax 1120 W 0 0 1 2 / 11 P max1000 W 0 0 1 91 / 110 Pmax 4550 W 0 1 0 0 0 0 1 0 9 / 22 Pmax 2250 W 0 1 1 4 / 11 P max 2000 W 0 1 1 Pmax 5500 W Table 10: Available heating levels of variant A from Fig. 9 The seven heating levels that can be realized in this way with R1 = 2R2 = 3R3 are therefore: 0, 2 / 11 Pmax, 56 / 275 Pmax, 4 / 11 Pmax, 9 / 22 Pmax, 91 / 110 Pmax, and Pmax. Fig. 10 shows a single-phase operated (or: single-phase coupled) variant of the circuit from Fig. 9. The neutral conductor N can be connected to the switch K2 and connection 16-2 (shown) or to the switch K3 and connection 16-3 (not shown). In a symmetrical variant S with R1=R2=R3=R (not shown), 5 heating stages can be realized in this way, as listed in Table 11: Connection according to Fig.10, variant S: 5 heating stages K1 K2 K3 P R1=R2=R3=R= 26.45 Ω 0 0 0 0 0 0 0 0 0 0 0 0 1 3 / 8 Pmax 500 W 0 0 1 22 / 25 Pmax 1175 W 0 1 0 0 0 0 1 0 0 0 1 1 3 / 4 Pmax 1000 W 0 1 1 Pmax 1333 W Table 11: Available heating levels of variant S from Fig. 10 The five heating levels that can be realized in this way are: 0, 3 / 8 P max, 3 / 4 P max, 22 / 25 P max, and P max . In an asymmetrical variant A (shown in Fig. 10) with three different resistors R1, R2, R3, five heating stages can also be realized, as listed in Table 12: Connection according to Fig.10, variant A: 5 heating stages K1 K2 K3 P R1 = 52.9 Ω / R2 = 17.63 Ω / R3 = 26.45 Ω 0 0 0 0 0 0 0 0 1 / 4 Pmax 375 W 0 0 1 0 0 0 0 1 9 / 10 Pmax 1350 W 0 1 0 0 0 0 1 0 1 / 2 Pmax 750 W 0 1 1 0 0 1 1 1 P max 1500 W Table 12: Available heating levels of variant A from Fig. 10 The five heating levels that can be realized in this way with R1=3R2=2R3 are therefore: 0, 1 / 4 P max, 1 / 2 P max, 9 / 10 P max , P maxFig. 11 shows a variant of the circuit from Fig. 9, wherein the circuit or switching device 10 from Fig. 11, in contrast to the circuit or switching device 10 from Fig. 9, has a neutral conductor N connected to the terminal 17 of the switching device 10, which can be switched by a switch KN ("neutral conductor switch") of the switching device 10. In a symmetrical variant S with R1=R2=R3=R (not shown), 9 heating stages can be realized in this way, as listed in Table 13: Circuit according to Fig. 11, variant S: 9 heating stages K1 K2 K3 KN P R1=R2=R3=R= 26.45 Ω 0 0 0 0 0 0 0 0 1 1 / 6 P max 1000 0 0 1 0 1 / 4 Pmax 1500 0 0 1 1 1 / 2 Pmax 3000 0 1 0 0 1 / 4 Pmax 1500 0 1 0 1 1 / 2 P max 3000 0 1 1 0 3 / 4 Pmax 4500 0 1 1 1 5 / 6 P max 5000 1 0 0 0 0 0 1 0 0 1 1 / 3 p max 2000 1 0 1 0 1 / 2 Pmax 3000 1 0 1 1 2 / 3 P max 4000 1 1 0 0 1 / 2 Pmax 3000 1 1 0 1 2 / 3 P max4000 1 1 1 0 Pmax 6000 1 1 1 1 Pmax 6000 Table 13: Available heating levels of variant S from Fig. 11 The nine heating levels that can be realized in this way are therefore: 0, 1 / 6 P max, 1 / 4 P max, 1 / 3 P max, 1 / 2 P max, 2 / 3 P max, 3 / 4 P max, 5 / 6 P max and P max . In an asymmetrical variant A (shown) with three different resistors R1, R2, R3, 13 heating stages can be realized, as listed in Table 14: Connection according to Fig.11, variant A: 13 heating stages K1 K2 K3 KN P R1 = 52.9 Ω / R2 = 26.45 Ω / R3 = 17.63 Ω 0 0 0 0 0 0 0 0 1 1 / 12 P max 500 0 0 1 0 3 / 16 Pmax 1125 0 0 1 1 7 / 12 Pmax 3500 0 1 0 0 1 / 6 Pmax 1000 0 1 0 1 5 / 12 P max 2500 0 1 1 0 91 / 120 Pmax 4550 0 1 1 1 11 / 12 P max 5500 1 0 0 0 0 0 1 0 0 1 1 / 6 p max 1000 1 0 1 0 3 / 8 Pmax 2250 1 0 1 1 2 / 3 P max 4000 1 1 0 0 1 / 3 Pmax 2000 1 1 0 1 1 / 2 P max3000 1 1 1 0 11 / 12 Pmax 5500 1 1 1 1 Pmax 6000 Table 14: Available heating levels of variant A from Fig. 11 The thirteen heating levels that can be realized in this way with R1=2R2=3R3 are therefore: 0, 1 / 12 P max, 1 / 6 P max, 3 / 16 P max, 1 / 3 P max, 3 / 8 P max, 5 / 12 P max, 1 / 2 P max, 7 / 12 P max, 2 / 3 P max, 91 / 120 P max, 11 / 12 P max, and P max . Fig. 12 shows a single-phase variant of the circuit from Fig. 11. In a symmetrical variant S with R1=R2=R3=R (not shown), 7 heating stages can be realized in this way, as listed in Table 15: Circuit according to Fig. 12, variant S: 7 heating stages K1 K2 K3 KN P R1=R2=R3=R= 26.45 Ω 0 0 0 0 0 0 0 0 0 1 1 / 6 Pmax 1000 0 0 1 0 0 0 0 0 1 1 1 / 2 Pmax 3000 0 1 0 0 0 0 0 1 0 1 1 / 2 Pmax 3000 0 1 1 0 0 0 0 1 1 1 5 / 6 Pmax 5000 1 0 0 0 0 0 1 0 0 1 1 / 3 P max 2000 1 0 1 0 0 0 1 0 1 1 2 / 3 p max4000 1 1 0 0 0 0 1 1 0 1 2 / 3 Pmax 4000 1 1 1 0 0 0 1 1 1 1 P max 6000 Table 15: Available heating levels of variant S from Fig. 12 The seven heating levels that can be realized in this way are: 0, 1 / 6 P max, 1 / 3 P max, 1 / 2 P max, 2 / 3 P max, 5 / 6 P max, and P max. In an asymmetrical variant A (shown) with three different resistors R1, R2, R3, 9 heating stages can be realized, as listed in Table 16: Connection according to Fig.12, variant A: 9 heating stages K1 K2 K3 KN P R1 = 52.9 Ω / R2 = 26.45 Ω / R3 = 17.63 Ω 0 0 0 0 0 0 0 0 0 1 1 / 12 Pmax 500 0 0 1 0 0 0 0 0 1 1 7 / 12 Pmax 3500 0 1 0 0 0 0 0 1 0 1 5 / 12 Pmax 2500 0 1 1 0 0 0 0 1 1 11 / 12 Pmax 5500 1 0 0 0 0 0 1 0 0 1 1 / 6 Pmax 1000 1 0 1 0 0 0 1 0 1 1 2 / 3 Pmax 4000 1 1 0 0 0 0 1 1 0 1 1 / 2 Pmax 3000 1 1 1 0 0 0 1 1 1 1 Pmax 6000 Table 16: Available heating levels of variant A from Fig. 12 The nine heating levels that can be realized in this way with R1=2R2=3R3 are therefore: 0, 1 / 12 P max, 1 / 6 P max, 5 / 12 P max, 1 / 2 P max, 7 / 12 P max, 2 / 3 P max, 11 / 12 P max, and P maxFig. 13 shows a variant of the circuit shown in Fig. 11, which differs from the latter in that diode 14 can be switched instead of switch KN in the neutral conductor N; Furthermore, the symmetrical variant S is shown. This means that another switch K1a is connected in series with diode 14, by means of which diode 14 (and preferably only diode 14) can be switched in parallel with switch K1 when switch K1a is closed. When switch K1a is open, the diode plays no role in the circuit. In a symmetrical variant S with R1=R2=R3=R (shown), 7 heating stages can be realized in this way, as listed in Table 17: Connection according to Fig.13, variant S: 7 heating stages K1 K2 K3 K1a P R1=R2=R3=R= 26.45 Ω 0 0 0 0 0 0 0 0 1 1 / 6 P max 1000 0 0 1 0 1 / 3 Pmax 2000 0 0 1 1 1 / 2 Pmax 3000 0 1 0 0 1 / 3 Pmax 2000 0 1 0 1 1 / 2 P max 3000 0 1 1 0 2 / 3 Pmax 4000 0 1 1 1 5 / 6 P max5000 1 0 0 0 1 / 3 Pmax 2000 1 0 0 1 1 / 3 P max 2000 1 0 1 0 2 / 3 Pmax 4000 1 0 1 1 2 / 3 P max 4000 1 1 0 0 2 / 3 Pmax 4000 1 1 0 1 2 / 3 P max 4000 1 1 1 0 Pmax 6000 1 1 1 1 Pmax 6000 Table 17: Available heating levels of variant S from Fig. 13 The seven heating levels that can be realized in this way are therefore: 0, 1 / 6 P max, 1 / 3 P max, 1 / 2 P max, 2 / 3 P max, 5 / 6 P max, and Also with the symmetrical variant S with R1=R2=R3=R (shown in Fig. 13), but with a 1-phase connection (ie, L1=L2=L3, not shown), 7 heating stages can be realized, as listed in Table 18: Connection according to Fig.13, variant S, 1-phase: 7 heating stages K1 K2 K3 K1a P R1=R2=R3=R= 26.45 Ω 0 0 0 0 0 0 0 0 1 1 / 6 P max 1000 0 0 1 0 1 / 3 Pmax 2000 0 0 1 1 1 / 2 Pmax 3000 0 1 0 0 1 / 3 Pmax 2000 0 1 0 1 1 / 2 P max 3000 0 1 1 0 2 / 3 Pmax 4000 0 1 1 1 5 / 6 P max 5000 1 0 0 0 1 / 3 Pmax 2000 1 0 0 1 1 / 3 Pmax 2000 1 0 1 0 2 / 3 Pmax 4000 1 0 1 1 2 / 3 P max 4000 1 1 0 0 2 / 3 Pmax 4000 1 1 0 1 2 / 3 P max 4000 1 1 1 0 Pmax 6000 1 1 1 1 Pmax 6000 Table 18: Available heating levels of variant S from Fig. 13 with 1-phase connection The seven heating levels that can be realized in this way are therefore: 0, 1 / 6 P max, 1 / 3 P max, 1 / 2 P max, 2 / 3 P max, 5 / 6 P max, and P max . Fig. 14 shows a variant of the circuit from Fig. 13, with the two differences that it is a 1-phase circuit and an asymmetrical variant A. In this asymmetrical variant A with, for example, R1=2R2=3R3, 11 heating stages can be realized, as shown in the following Table 19: Circuit according to Fig. 14, variant A, 1-phase: 11 heating stages K1 K2 K3 K1a P R1 = 52.9 Ω / R2 = 26.45 Ω / R3 = 17.63 Ω 0 0 0 0 0 0 0 0 1 1 / 12 P max500 0 0 1 0 1 / 2 Pmax 3000 0 0 1 1 7 / 12 Pmax 3500 0 1 0 0 1 / 3 Pmax 2000 0 1 0 1 5 / 12 P max 2500 0 1 1 0 5 / 6 Pmax 5000 0 1 1 1 11 / 12 P max 5500 1 0 0 0 1 / 6 Pmax 1000 1 0 0 1 1 / 6 P max 1000 1 0 1 0 2 / 3 Pmax 4000 1 0 1 1 2 / 3 P max 4000 1 1 0 0 1 / 2 Pmax 3000 1 1 0 1 1 / 2 P max 3000 1 1 1 0 Pmax 6000 1 1 1 1 Pmax 6000 Table 19: Available heating levels of variant A from Fig. 14 with 1-phase connection The eleven heating levels that can be realized in this way are therefore: 0, 1 / 12 P max , 1 / 6 P max , 1 / 3 P max , 5 / 12 P max , 1 / 2 P max , 7 / 12 P max , 2 / 3 P max , 5 / 6 P max , 11 / 12 P max , and P max. With a 3-phase connection (not shown) of the asymmetric variant, the same heating levels could be realized. Fig. 15 shows a variant of the connection from Fig. 13, with the difference that a series connection consisting of diode 14 and additional switches K1a, K2a, K3a is arranged on all current phases L1, L2, L3 in parallel with the respective switch K1, K2, K3 (and not just with switch K1 as in Fig. 13). The heating levels that can be realized in this way are the same as those described with reference to Fig. 13 as well as Table 17 (symmetrical variant S, 3-phase) and Table 18 (symmetrical variant S, 1-phase). However, each heating level in the variant from Fig. 15 can be realized with more different switching combinations. The variant from Fig. 15 also clearly enables phase-accurate switching, so that phase-accurate consumption of the heating device 20 can also be set accordingly.If an unbalanced load occurs at the grid connection point 31 and / or in the (in-house) power grid 30, i.e., if one or more current phases L1, L2, L3 have a significantly different load than one or more of the other current phases L1, L2, L3, then the switching device 10 can be controlled (e.g. by an energy management system 40) in such a way (or control itself in such a way) that the unbalanced load is counteracted by selecting a suitable heating level and / or a suitable switching combination of the switches K1, K1a, K2, K2a, K3, K3a. The unbalanced load can be detected by the energy management system 40, which then either controls the switching device 10 directly accordingly, or transmits the necessary information to the switching device 10 so that the switching device 10 can carry out the necessary control itself. The variant from Fig.15 is also useful in the event of an emergency power supply, for example, if the public power grid 35 fails or is switched off. In this case, the inverter often establishes an emergency power supply in the local power grid 30 at a frequency of, for example, 53 Hz, and detects this via a frequency measurement by the control unit 11, while in normal operation, the 50 Hz of the public power grid 35 is present, for example. In this situation, often only a few consumers are operated, and it can be important to be able to precisely select which power phase (L1, L2, L3) and how much power is drawn from. The variant from Fig.15 allows a user, via a user interface 12 (of the switching device 10, the energy management system 40, or the like), to manually activate a single (or multiple) of the power phases L1, L2, L3 of the heating device 20, for example, at the lowest heating level with a heating output greater than zero, in order not to overload the emergency power supply. If an overload or failure of the emergency power supply nevertheless occurs, the user can again select a different power phase L1, L2, L3 for a second or third attempt. Similar options are also available to the user for the other wiring variants described above.In the domestic system 200 according to the invention, in asymmetrical wiring variants in which a diode 14 is connected to at least one terminal 16-i (be it in parallel with the corresponding switch Ki and / or in series with the further switch Kia), it is preferred that this terminal 16-i is connected to a heating element 21-i which has the lowest heating power or the highest heating resistance (in the examples usually R1). In this way, it is ensured that by using the diode 14 (and corresponding switching) a further heating stage is or can be provided. Fig. 16 shows a schematic flow diagram for explaining a method according to an embodiment of the present invention, namely a method for operating a heating device 20 orfor heating a medium, in particular a fluid F, by means of a heating device 20 with a plurality of heating elements 21-i, which are connected to one another in a star shape at a common star point 22 and can be connected independently of one another to an energy source. The method can be carried out by means of the switching device 10 and / or the building installation 100 according to an embodiment (in particular according to one of Figures 1-6 and 9-15) of the present invention, but also independently thereof. Accordingly, the method is adaptable in accordance with all embodiments, variants, options and further developments described with reference to the switching device according to the invention or the building installation according to the invention, and vice versa. An energy management system 40 which carries out this method can, for example, also be integrated into a switching device 10 according to the invention. In a step S100, a desired total heating power P of the heating device 20, i.e.h is detected, for example, by a user interface 12, by an energy management system 40 or the like. Detecting the total heating output setpoint can comprise determining the total heating output setpoint, in particular calculating it. In a step S200, a heating level is determined (for example by the energy management system 40 or the control device 11 of the switching device 10) which corresponds as best as possible to the detected total heating output setpoint, i.e., comes as close as possible. As a result, a difference between the total heating output generated by the heating device 20 and the total heating output setpoint can advantageously be kept to a minimum. Alternatively, it can also be provided that (according to one option) the lower heating level closest to the total heating output setpoint is selected, or (according to another option) the next higher heating level to the total heating output setpoint is selected.In a step S300, heating elements 21-i of the heating device 20 are switched independently of one another, each via at least one associated switch Ki; K1a, for (step-by-step) adjustment of the specific heating level. Examples of such and further switching actions as method steps can be found in the description of Figures 1-6 and 9-15 and are derived in particular from the tables listed there. Fig. 17 shows a schematic flow diagram for explaining a method according to an embodiment of the present invention, namely a method for operating a heating device 20 or for heating a medium F by means of at least one heating element 21-i of a heating device 20. The method can be carried out by means of the switching device 10 and / or the building system 100 according to an embodiment of the present invention, but also independently thereof.Accordingly, the method is adaptable according to all embodiments, variants, options, and further developments described with reference to the switching device according to the invention or the domestic system according to the invention, and vice versa. In a step S400, a desired total heating output P of the heating device 20, i.e., a total heating output setpoint, is detected, for example, by a user interface 12, by an energy management system 40, by a thermostat, or the like. In a step S500, a heating level is determined which corresponds as best as possible (or exactly), i.e., in particular, comes as close as possible to the detected total heating output setpoint.In a step S600, at least one first switch K1 connected in series with at least one heating element 21-i and connected in parallel with a diode 14 is switched for the (stepwise) setting of the specific heating level. The switch is arranged between a current phase L1 and the at least one heating element 21-i. In an optional additional step S700, a further switch K1a connected in series with the diode 14 and, together with the diode 14, connected in parallel with the first switch K1 is switched for the (stepwise) setting of the specific heating level. This parallel connection is thus also arranged between a current phase L1 and the at least one heating element 21-i. Examples of these and other switching actions as in method steps S600 and S700 can be found in the description of Figures 7-15 and are evident in particular from the tables listed there. Fig.18 shows a schematic block diagram of a computer program product 200 according to an embodiment of the present invention. The computer program product 200 comprises executable program code 250 which, when executed, is configured to carry out the method according to an embodiment of the present invention, for example, according to FIG. 16 or FIG. 17. FIG. 19 shows a schematic block diagram of a non-volatile computer-readable data storage medium 300 according to an embodiment of the present invention. The data storage medium 300 comprises executable program code 350 which, when executed, is configured to carry out the method according to an embodiment of the present invention, for example, according to FIG. 16 or FIG. 17. The non-volatile computer-readable data storage medium 300 can, for example, be designed as a semiconductor memory, e.g., an SSD memory chip, or comprise such a memory.The data storage medium 300 can also comprise or include a CD, DVD, Blu-ray, or a magnetic storage device. Referring again to Fig. 1, it will now be explained how the switching device 10 according to the invention can advantageously be integrated into a home system 100 according to the invention and operated there. Accordingly, the methods according to Fig. 16 or Fig. 17, in all their variants and embodiments, can also be adapted accordingly to control the home system 100, and / or specifically the switching device 10.The home system 100 can have an energy management system 40, which can, in particular, control electrical energy flows via the power grid 30, in particular between power sources and / or power consumers, such as the grid connection point 31, at least one consumer 32, a battery 60 of the home system 100, a renewable energy source 70 (e.g., a PV system) of the home system 100, an inverter 80 of the home system 100, and / or the like. In principle, the capabilities and common programs of such energy management systems 40 are known.For example, for various reasons, it is generally desirable that the electrical energy generated by a renewable energy source 70 be consumed within the building's system 100 as much as possible, stored within the battery 60 if this is not possible, and fed into the public power grid via the grid connection points 31 from the building's system 100 if this is also no longer possible. However, other schemes are also conceivable, for example, schemes based on a current electricity price that attempt to generate financial profit through electricity trading. Fig. 19 shows a schematic flow diagram illustrating a possible method for selecting heating levels, wherein the selected heating levels can be implemented by the various embodiments of the present invention.Accordingly, the switching device 10 and / or the building system 100 can be configured to carry out such a method, or the methods according to Fig. 16 or Fig. 17 can be designed or modified to include such a method. The description begins with a start step S1; however, it is understood that the described method is usually carried out cyclically, i.e., it always starts again from the beginning, as shown by the arrows. In step S1, a target temperature for the medium, here (merely by way of example) a fluid F in a fluid tank 50, is first recorded. The target temperature can be specified directly by a user, for example via a user interface 12 in a smart home control application. Alternatively, the target temperature can also be specified by an algorithm, which can, for example, take into account the time of day, the time of year, and / or a user input.Detecting S1 can also consist of maintaining a predefined target temperature. In a step S2, a current actual temperature of the fluid F in the fluid tank 50 is detected, in particular measured. The actual temperature can be determined using a temperature sensor of the building system 100, which can be integrated, for example, into the fluid tank 50. In a step S3, it is checked whether an actual temperature of the fluid F in the fluid tank 50 is lower than a target temperature. Here and in the following, it is understood that whenever a comparison with a reference or threshold value (here: with the target temperature) is mentioned, a tolerance range can always be provided within which the method continues as if there were no difference. In this way, constant switching back and forth or other unstable control behavior can be prevented.The tolerance ranges can be arranged symmetrically or asymmetrically around the comparison or threshold value. The latter can be used, for example, to achieve a hysteresis effect, e.g., a greater deviation from the threshold value is required to revise a decision than was necessary to originally trigger the decision. In the following, corresponding tolerance ranges will not be mentioned explicitly each time in order to keep the explanations concise. If, according to the test in step S3 (as mentioned, optionally taking into account a tolerance range), the actual temperature is lower than the target temperature (plus sign, "+" in the drawing), a check is carried out in step S4 to determine whether there is excess power in the building system 100, initially from renewable energy sources 70, e.g., from a PV system. Preferably, only renewable energy sources 70 of the building system 100 are taken into account.For the test, a current power value of at least one renewable energy source 70 can be obtained in step S4. Optionally, further power values, for example, power consumed by consumers 32, etc., can also be received. From the received power values, it can be calculated in a known manner whether excess power from renewable energy sources 70 of the building system 100 is present. If excess electrical power is present (plus sign, "+" in the drawing), a check is carried out in step S5 to determine whether the state of charge of the battery 60 is above a state of charge threshold. This state of charge threshold can, for example, indicate a state of charge above which states of charge are generally undesirable, either to maintain the battery 60 or because such a high state of charge is considered unnecessary, or the like.If the charge level exceeds this first threshold (plus sign, "+" in the drawing), the energy management system 40 controls the home system 100 such that, in a step S6, an output power available at the battery 60 and released (e.g., by the customer) is added to the excess power. Regardless of whether this happens or not (in home systems 100 without a battery 60, steps S4 and S5 are omitted), a check is next performed in a step S7 to determine whether the now determined excess power is sufficient to switch the heating device 20 to a higher heating level.Accordingly, bidirectional communication can be established between the switching device 10 and the energy management system 40, so that, on the one hand, the energy management system 40 knows the currently set heating level and / or the total heating output setpoint, and, on the other hand, it can specify a heating level to be set and / or the total heating output setpoint to the switching device 10. A higher heating level is understood to be a heating level which, ceteris paribus, provides a greater heating output than a lower heating level. In the preceding examples, the lowest heating level was reached when all switches were opened (P=0), and the highest heating level was reached when all switches were closed (P=P). max). If a higher heating level is not possible (minus sign, "-" in the drawing), for example because the surplus power is insufficient, or because there is no higher heating level available, the method continues at step S1. If a higher heating level is possible (plus sign, "+" in the drawing), a higher heating level is set in step S8. For this purpose, the switching device 10 is instructed, for example, by the energy management system 40 (or it decides itself) to set a higher heating level, and then the switching device 10 sets the corresponding heating level by switching the switches Ki, KN, Kia accordingly. The method then continues again at step S1. If it is determined in step S4 that no surplus power is available from renewable energy sources 70 (minus sign, "-" in the drawing), a check is carried out in step S9 as to whether electricity from the supply grid is currently being consumed, i.e.flows into the building system 100 at the grid connection point 31. If this is not the case (minus sign, "-", in the drawing), the current heating level is maintained and the process continues at step S1. If this is the case (plus sign, "+", in the drawing at step S9), a check is carried out in step S10 to determine whether a lower heating level is available (i.e., whether the lowest heating level, i.e., with a power of zero, is not already set). If no lower heating level is available (minus sign, "-", in the drawing at step S10), this heating level remains, and the process continues at step S1. If a lower heating level is available (plus sign, "+", in the drawing), the heating level is reduced in step S11. For this purpose, for example,the switching device 10 is instructed by the energy management system 40 (or it decides itself) to set a lower heating level, and then the switching device 10 sets the corresponding heating level by switching the switches Ki, KN, Kia accordingly. The method then continues again at step S1. However, if it is determined in step S3 that the actual temperature is not lower than the target temperature (i.e., the actual temperature is equal to, higher than, or possibly within a tolerance range around the target temperature), represented by a minus sign, "-", to the left of step S3 in the drawing, a check is carried out in step S12 to determine whether the actual temperature is lower than a user-adjustable or predefined upper temperature threshold value, which is higher than the target temperature.If this is the case (plus sign, "+", in the drawing under step S12), a check is carried out again in step S13 to determine whether excess power is available, initially from renewable energy sources. If this is not the case (minus sign, "-", in the drawing), the process continues with step S9, as already explained. If excess power from renewable energy sources is available (plus sign, "+", in the drawing under step S13), the process continues with step S7, i.e., with a check to determine whether a higher heating level is possible. If the result of the check in step S12 is negative, i.e., the current temperature (actual temperature) is equal to or greater than the upper temperature threshold (symbol "-" in the figure at step S12), the lowest heating level of the heating device 20 is set in step S14, which will usually be the heating level with power P=0, i.e., the heating device 20 is switched off.The process then continues with step S1. The method according to Fig. 20 thus makes it possible to use the heating of the medium F (e.g., in the fluid tank 50) to store thermal energy. However, this should not be done with electricity from the public power grid 35, but only with electrical power from renewable energy sources 70 of the building system 100, and only if this does not cause the actual temperature to exceed the upper temperature threshold. In addition, a charge state of the battery 60 of the building system 100 above the threshold can be utilized (step S5). It is understood that a person skilled in the art can adapt the method according to Fig. 20f in a variety of ways to add to or omit individual steps in order to effect a desired regulation or control.In particular, depending on the building system 100 and the current situation, step S8 of increasing the heating level can alternatively be replaced or supplemented by a step of switching on at least one consumer 32, e.g., a heat pump. Likewise, depending on the building system 100 and the current situation, step S11 of decreasing the heating level can alternatively be replaced or supplemented by a step of switching off at least one consumer 32, e.g., a heat pump. Switching on and off can also be replaced by increasing and decreasing energy consumption, respectively. From the preceding description, it is clear how the stepwise adjustability of the heating output of the heating device 20 by the switching device 10 according to the invention enables complex control and regulation processes such as that in Fig. 20 to be carried out cost-effectively and without major hardware expenditure, even with simple, already installed heating devices 20.

Claims

1. Switching device (10) for operating an external heating device (20) for heating a medium (F) by means of a plurality of heating elements (21-i) of the heating device (20), which are interconnected at a common star point (22) and can be connected to the switching device (10) independently of one another, wherein the switching device (10) is configured to be supplied by at least one current phase (L) and comprises a control device (11) which is configured to switch the heating elements (21-i) independently of one another via at least one associated switch (Ki, Kia, KN) of the switching device (10) for the stepwise adjustment of a total heating power generated by the heating device (20) according to a respective heating stage, wherein the control device (11) is implemented by a computing unit.Switching device (10) according to claim 1, configured to switch between at least five heating levels, preferably at least seven heating levels, of different heating power.

3. Switching device (10) according to one of the preceding claims 1 or 2, wherein a diode (14) is connected in parallel to at least one switch (Ki, KN).

4. Switching device (10) according to one of claims 1 to 3, comprising an output (16-i) for each heating element (21-i) to be connected, wherein the switch (Ki) associated with the corresponding heating element (21-i) is connected in series with the output (16-i).

5. Switching device (10) according to one of claims 1 to 4, wherein the control device (11) is additionally configured to switch between implementations of the same heating power by means of. different switch combinations of the switches (Ki, KN) to switch periodically and / or cyclically.

6. The switching device (10) according to one of claims 1 to 5, wherein the control device (11) is configured to receive (S4, S13) a current power value of a renewable energy source (70) and to adapt (S8) a current heating level at least based on the received current power value.

7. The switching device (10) according to claim 6, wherein the control device (11) is configured to further adapt the current heating level based on a total heating power setpoint.

8. The switching device (10) according to claim 7, wherein the control device (11) is configured to set the current heating level such that a difference between the total heating power generated by the heating device (20) and the total heating power setpoint is minimized.Switching device (10) according to claim 7 or 8, wherein the control device (11) is designed to carry out a measuring method to determine which heating levels are available and / or which total heating output is realized with each of the available heating levels.

10. Domestic system (100), comprising a switching device (10) according to one of claims 1 to 9 and a heating device (20) connected to the switching device (10), for the operation of which heating device the switching device (10) is designed.

11. Domestic system (100) according to claim 10, comprising a user interface (12) by means of which a target parameter of the heating device (20), the medium (F) and / or a fluid tank (50) for the medium (F) can be set, for example a target temperature of the medium (F).

12. A domestic system (100) according to one of claims 10 or 11, comprising an electrical connection (31) to a power grid (35), wherein the star point (22) of the heating device (20) is connected to a neutral conductor (N) of the power grid (30) via an associated switch (KN) and / or is switchable via an associated switch (KN).Switching device (10) for operating an external heating device (20) for heating a medium (F) by means of at least one heating element (21-i) of the heating device (20), wherein the switching device (10) is configured to be supplied by at least one current phase (L) and comprises a control device (11) configured to switch the heating element (21-i) via at least one associated switch (Kia) of the switching device (10) for the stepwise adjustment of a total heating power generated by the heating device (20) according to a respective heating stage, wherein a diode (14) is connected in parallel to the at least one associated switch (Kia).Method for heating a medium (F) by means of a heating device (20) with a plurality of heating elements (21-i), which are interconnected by a respective first connection end at a common star point (22) and which are switchable independently of one another at a respective second connection end, comprising: detecting (S100) a total heating power setpoint; determining (S200) a heating level which best corresponds to the desired total heating power setpoint; and switching (S300) the heating elements (21-i) independently of one another via at least one associated switch (Ki, Kia, KN) to set the determined heating level.

15. Method for heating a medium (F) by means of at least one heating element (21-i) of a heating device (20), comprising: detecting (S400) a total heating power setpoint;. Determining (S500) a heating level that best corresponds to the desired total heating power setpoint; and switching (S600) at least one switch (Kia), which is arranged between a current phase (L1) and at least one heating element (21-i) of the heating device (20), and which is connected in parallel with a diode (14), optionally with a series circuit comprising the diode (14) and a further switch (K1a), to set the determined heating level.

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