Method for operating an inverter, inverter, and domestic appliance

Abstract

The invention relates to a method for operating an inverter (41) electrically connected to a stator winding of an electric AC voltage machine (36) which drives a component (21) that rotates at least temporarily about a rotational axis in an intended operation of a domestic appliance (1). The inverter (41) supplies an electric AC voltage to the stator winding, said AC voltage being provided by means of at least one series circuit of the inverter (41) with two switching elements. The series circuit is supplied with an intermediate circuit DC voltage, and switch signals are provided for the switching elements. A control unit (8) ascertains the switch signals according to a pulse-width modulation principle on the basis of a clock rate according to an operating signal for the component (21), wherein a component (21) operating rotational speed to be set is first determined on the basis of the operating signal, the operating rotational speed is assigned an operating clock rate, the switch signals are determined on the basis of the operating clock rate, the operating rotational speed of the component (21) is set, and the switching elements are then supplied with the switch signals based on the operating clock rate.

Description

[0001] Method for operating an inverter, inverter and household appliance

[0002] The invention relates to a method for operating an inverter to which a stator winding of an electrical AC machine is electrically connected, which drives a component which rotates at least partially about a rotational axis during normal operation of a household appliance, wherein the inverter applies an electrical AC voltage to the stator winding, which is provided by means of at least one series circuit of the inverter having two switching elements, wherein the series circuit is supplied with an intermediate circuit DC voltage, wherein switching signals for the switching elements are provided by means of a control unit of the inverter, wherein the control unit determines the switching signals according to a pulse width modulation principle based on a clock rate as a function of an operating signal for the component, wherein the clock rate is greater than a frequency corresponding to the rotational speed of the component.The invention further relates to an inverter for applying an electrical alternating voltage to a stator winding of an electrical alternating voltage machine, which is electrically connected to the inverter and which drives a component which rotates at least partially about a rotational axis during normal operation of a household appliance, wherein the inverter has at least one series circuit having two switching elements for providing the alternating voltage and a control unit for providing switching signals for the switching elements, wherein the series circuit can be supplied with an intermediate circuit direct voltage, wherein the control unit is designed to determine the switching signals according to a pulse width modulation principle based on a clock rate as a function of an operating signal for the component, wherein the clock rate is greater than a frequency corresponding to a rotational speed of the component.Finally, the invention also relates to a household appliance with a component which, during normal operation of the household appliance, rotates at least temporarily about a rotational axis, an electrical AC machine which is rotationally coupled to the component for rotatably driving the component, the AC machine having a stator winding, and an inverter which is electrically connected to the stator winding for supplying the.

[0003] Stator winding with an alternating electrical voltage.

[0004] Household appliances that have a component that rotates about a rotational axis during normal operation of the household appliance, inverters, and methods for operating them are fundamentally well known in the prior art. Such household appliances include, for example, washing machines, tumble dryers, refrigerators or refrigeration appliances, dishwashers, or the like. For their normal operation, these household appliances require rotatable devices that have at least one rotating component, for example, in a household refrigeration appliance, a drive shaft of a rotary-driven compressor, in particular without a transmission, in a washing machine, a drive pin of a rotary-driven washing drum, in particular in a washing machine with a transmission by coupling the drive to the washing drum by means of a belt coupling, or the like.The rotating component can be, for example, a drive shaft, a rotatably mounted journal, a belt pulley, or the like. In the case of a compressor of a household refrigeration appliance, the rotating component can be a drive shaft. Typically, such household appliances are designed for the rotating component to be rotatably driven by a rotor of an AC electrical machine during normal operation.

[0005] The AC electrical machine is usually designed as a rotating or rotatable electrical machine and is also extensively known in the prior art, so that, as with household appliances, no separate written proof is required in this regard. A rotating electrical machine is a device which, in motor mode, converts electrical energy into mechanical energy, in particular rotational energy, and / or in generator mode, converts mechanical energy into electrical energy. The movement is usually a rotary movement carried out by a rotor of the rotating electrical machine which is arranged so as to be rotatable relative to a stator of the rotating electrical machine. In contrast to the rotor, the stator is usually arranged in a rotationally fixed manner, i.e. a rotary movement is a rotary movement of the rotor relative to the stator.The rotor is mounted so that it can rotate relative to the stator, with an air gap usually being formed between the rotor and the stator.

[0006] During normal operation, the stator and rotor are linked by a magnetic flux, which provides the force or torque during motor operation, which drives the rotor to rotate relative to the stator. In generator operation, the mechanical energy supplied to the rotor in the form of rotation combined with a torque is converted into electrical energy. For this purpose, at least the stator has an electrical winding through which an electric current flows, also called a stator winding. The rotor can also have an electrical winding as a rotor winding and / or one or more permanent magnets.

[0007] For proper operation, the stator winding is supplied with alternating voltage. Depending on the design of the electrical machine, particularly its stator winding, a single-phase or multi-phase stator winding can be provided, which is accordingly supplied with a single-phase or multi-phase electrical alternating voltage. A multi-phase alternating voltage generally has phase alternating voltages corresponding to the number of phases, which generally have approximately the same frequency and approximately the same amplitude, but are shifted in phase with one another. A very common multi-phase alternating voltage, for example, is a three-phase alternating voltage in which the phase voltages are each shifted in phase by 120°. This type of alternating voltage is also used, for example, in the public power grid.

[0008] To operate the AC motor in such a way that the component can be rotated as desired, the AC motor, in particular its stator winding, is connected to an inverter. An inverter is a type of energy converter or energy transformer by which electrical energy of a first form, for example, a direct current, can be converted or transformed into electrical energy of a second form, namely an alternating current. Nowadays, inverters are generally used in the form of so-called static energy converters or energy transformers. This means that, unlike dynamic energy converters or energy transformers, they do not have any mechanically movable, particularly rotatable, parts.Inverters of this type are static energy converters or energy converters, usually designed as clocked electronic energy converters or energy converters, and for this purpose generally have at least one series circuit consisting of two switching elements connected in series. The series circuit is connected to a DC intermediate circuit and is accordingly supplied with an intermediate DC voltage. The stator winding of the AC motor is connected to a center tap of the series circuit.

[0009] The switching elements are supplied with switching signals provided by a control unit of the inverter or household appliance. The control unit determines the switching signals using a pulse-width modulation (PWM) principle based on a clock rate dependent on an operating signal for the component. The operating signal can be provided by a higher-level control unit of the household appliance and, for example, indicate data or signal values ​​regarding a component's speed, torque, and / or the like. The operating signal for the component is usually an electronic signal, which can be in the form of an analog and / or digital signal.The operating signal is provided, for example, by the higher-level control device which belongs to the household appliance and which may comprise an operating device by means of which the household appliance or its functions can be controlled or adjusted by a user.

[0010] The clock rate is usually significantly higher than a frequency corresponding to the component's rotational speed. The stator winding is typically supplied with an alternating voltage, which is essentially a rectangular alternating voltage corresponding to pulse-width modulation. According to the pulse-width modulation, an electric current is established in the stator winding, allowing the function of the AC motor and, consequently, the drive function of the rotating component to be adjusted. For this purpose, the control unit evaluates the operating signal for the component and determines, for example, the rotational speed, torque, and / or the like. The switching signals for the switching elements are then determined based on this.

[0011] The pulse-width modulation principle is fundamentally known in the prior art, for example, from "Control Methods for Self-Commutated Power Converters" by Felix Jenni and Dieter Wüest, University Press at ETH Zurich, Stuttgart, Teubner, 1995, ISBN 3-519-06176-7, which is why detailed explanations of the pulse-width modulation principle will be omitted here. In this context, WO 2008 / 141407 A1 also discloses a method and system for reducing electromagnetic interference in a cooling system.

[0012] Even though the state of the art technology has proven itself, disadvantages still exist. Firstly, using the inverter at a high clock rate limits overall efficiency due to switching losses, among other things. At the same time, acoustic and electromagnetic compatibility issues can arise, which can be perceived as disruptive by users during normal operation.

[0013] The invention is based on the object of improving the efficiency, electromagnetic compatibility and / or acoustics.

[0014] As a solution, the invention proposes a method, an inverter and a household appliance according to the independent claims.

[0015] Advantageous further training results from features of the dependent claims.

[0016] With regard to a generic method, the invention proposes in particular that an operating speed of the component to be set is determined as a function of the operating signal, an operating clock rate is assigned to the operating speed, the switching signals are determined based on the operating clock rate, the operating speed of the component is set, and the switching elements are subjected to the switching signals based on the operating clock rate either before or only after the operating speed is set.With regard to a generic inverter, the invention proposes in particular that the control unit is designed to determine an operating speed of the component to be set depending on the operating signal, to assign an operating clock rate to the operating speed, to determine the switching signals based on the operating clock rate, to set the operating speed of the component and to apply the switching signals based on the operating clock rate to the switching elements either before or only after the operating speed has been set.

[0017] With regard to a generic household appliance, the invention proposes that the inverter is designed according to the invention.

[0018] The invention is based, among other things, on the idea that by appropriately selecting the clock rate, at least the efficiency, the electromagnetic compatibility, in particular with regard to conducted interference, or the acoustics can be improved. For example, it is possible to reduce the clock rate, especially at a comparatively low speed of the AC motor, so that switching losses of the inverter can be reduced overall. This allows efficiency to be improved. Furthermore, when disturbing acoustically perceptible noises occur, which can be detected, for example, by means of a suitable acoustic sensor, the clock rate can be changed in such a way that a reduction in the disturbing acoustic noises can be achieved depending on this. Likewise, an improvement in electromagnetic compatibility can also be achieved alternatively or additionally.At a high operating speed, however, the maximum operating clock rate does not need to be selected, but can be selected to be correspondingly lower. The invention therefore creates a possibility of improving efficiency and / or improving acoustics. Of course, a combination can also be provided, for example by reducing a clock rate to improve efficiency, particularly in a partial load range where the speed of the AC motor or component is low, while at the same time the reduction in the clock rate can be selected such that the acoustics are at least not impaired. This can also have a positive effect on the service life of the household appliance as a whole, as well as on electromagnetic compatibility, for example with regard to conducted interference, as defined in the EN 61000 standard.The variation or change of the operating clock rate is therefore preferably carried out essentially outside of dynamic processes related to the rotational speed of the component, such as acceleration, braking and / or the like. In addition, with regard to determining the assigned operating clock rate, other parameters can also be taken into account, such as a temperature of the inverter, in particular its switching elements, a current value of the intermediate circuit DC voltage to which the inverter is electrically coupled, and / or the like. Thus, it can be provided that the operating clock rate is lower at a high temperature than at a low temperature. Furthermore, it can be provided that the operating clock rate is lower at a high intermediate circuit DC voltage than at a low intermediate circuit DC voltage.

[0019] The set operating speed is a target speed of the rotor of the AC machine or component. The operating cycle rate is preferably not changed or varied while the set operating speed is being adopted. This means that the operating cycle rate is preferably assigned either before the operating speed is set, in particular before the process of setting the operating speed is started, or only when the set operating speed is reached.

[0020] According to the invention, for example, an operating speed to be set for the component is therefore first determined depending on the operating signal. For this purpose, the control unit can evaluate the operating signal accordingly and determine the operating speed to be set. Once the operating speed has been determined, an operating cycle rate can be assigned to it, for example by assigning an operating cycle rate to the operating speed using a table. Of course, functional relationships can also be used to calculate the operating cycle rate, for example based on the operating speed. For this purpose, the control unit can, for example, have a program-controlled computer unit which, using a computer program, calculates the operating cycle rate depending on the operating speed as part of the assignment.Once the operating clock rate has been assigned by the control unit, the switching signals can be determined based on this using the pulse-width modulation principle. The operating speed of the component is then set using the control unit. For this purpose, the inverter, specifically its switching elements, are controlled accordingly so that the component reaches the operating speed. The switching signals determined based on the operating clock rate do not need to be applied during the period determined by this. Only then are the switching elements supplied with the switching signals based on the operating clock rate.

[0021] This has the advantage, among other things, that the method according to the invention enables high stability during intended operation, thus increasing not only reliability but also service life. This proves to be particularly advantageous compared to WO 2008 / 141407 A1, which provides for a continuous change in the clock rate. As already explained, however, the problem here is particularly related to stability during intended operation, which is why the teaching of WO 2008 / 141407 A1 is particularly unsuitable for household appliances, which require high reliability and safety.

[0022] The invention is particularly suitable, among other things, for use in refrigerators for domestic use. However, it is not limited to this application and can, of course, also be used in almost any other household appliance that has rotatable components that are to be driven by an AC motor. The invention is also particularly suitable when the component to be driven does not provide a substantially uniform, in particular constant, torque. The invention makes it possible to take into account torque fluctuations, such as those that can occur, for example, in a reciprocating compressor of a refrigeration appliance, for proper operation, as will be explained in more detail below.

[0023] An AC machine is an electrical machine, in particular a rotating electrical machine, which is supplied with alternating voltage during its intended operation. This alternating voltage is provided by the inverter, with the alternating voltage being provided as a function of the operating signal for the component, so that the component can be operated in a desired operating state using the operating signal. For this purpose, the inverter is connected to a DC intermediate circuit or comprises such a DC intermediate circuit, to which the at least one series circuit comprising the two switching elements is preferably also connected. The DC intermediate circuit provides an intermediate DC voltage, which is converted or transformed into the AC voltage by the inverter.The inverter thus establishes an electrical coupling between the DC link and the stator winding of the AC electrical machine.

[0024] In order to be able to realize the desired energy conversion or energy transformation by means of the inverter, the switching elements of the at least one series circuit are operated in a predetermined switching mode.

[0025] A switching element or an electronic switching element, in particular a semiconductor switch, within the meaning of this disclosure is a preferably controllable electronic switching element, for example a transistor, a thyristor, combination circuits thereof, in particular with parallel-connected freewheeling diodes, for example a metal oxide semiconductor field-effect transistor (MOSFET), an insulated-gate bipolar transistor (IGBT), preferably with integrated freewheeling diodes, or the like. The switching element is operated in switching mode.

[0026] The switching operation of the semiconductor switch in the form of a transistor means that, in the switched-on state, a very low electrical resistance is provided between the terminals of the transistor forming the switching path, allowing a high current flow with a very low residual voltage. In the switched-off state, the switching path of the transistor is high-ohmic, meaning it provides a high electrical resistance, so that even with a high voltage applied to the switching path, there is essentially no current flow or only a very small, particularly negligible, current flow. Linear operation of transistors differs from this.

[0027] The DC link can be electrically coupled to a DC voltage source to provide an electrical power supply. However, it is often also provided that the DC link is connected to an AC voltage network, such as a public power grid or the like, via another energy converter or transformer. The required energy converter or transformer can convert an AC voltage into a DC voltage for this purpose, as can be achieved, for example, using a rectifier unit or the like.

[0028] If the stator winding is designed for multi-phase operation, the inverter is generally designed accordingly and can, for example, have at least one series circuit comprising two switching elements to provide a respective phase alternating voltage. Depending on the circuit topology, however, it can also be provided that for each phase alternating voltage, at least two corresponding series circuits are connected in parallel to the DC intermediate circuit. The switching elements can be operated complementarily, with the stator winding or the corresponding phase of the stator winding being connected between the two series circuits, specifically their respective center taps. Of course, other combinations can also be provided. Preferably, all series circuits are connected in parallel and electrically coupled to the DC intermediate circuit.

[0029] The clock rate on the basis of which the switching signals are provided according to the pulse-width modulation principle is preferably at least twice the frequency corresponding to the component's rotational speed. However, the clock rate is often at least five to ten times, for example, 40 times, the frequency corresponding to the component's rotational speed. In the prior art, which generally does not provide for any significant change in the clock rate during normal operation, the clock rate is therefore selected in relation to the frequency corresponding to the component's maximum rotational speed.

[0030] Changing the clock rate according to the invention preferably takes place in two stages, namely in a first stage, the operating speed of the component to be set is determined depending on the operating signal, the operating clock rate is assigned to the operating speed, the switching signals are determined based on the operating clock rate, and the operating speed of the component is set. Thereafter, in a second stage, particularly when the component has reached the operating speed, the switching elements can be supplied with the switching signals based on the operating clock rate. Alternatively, it can also be provided that the second stage is carried out before the operating speed is set. The invention therefore avoids having to make changes to the operating clock rate at the same time, particularly when the operating state of the component changes, such as a change in the operating speed.As a result, the invention allows for a high degree of stability and reliability in the process control. At the same time, the invention makes it possible to detect acoustic effects and, if necessary, intervene with a modified first section to improve the acoustics. The operating cycle rate can be changed over a predetermined period of time consisting of several operating cycles. However, it can also be provided that the operating cycle rate is switched at a predetermined time determined by the control unit.

[0031] The operating speed is a speed of the component that is to be set for a desired operating state of the component. This operating state can be specified by the operating signal via the control device of the household appliance. Depending on the operating signal or the operating speed that is to be set, the control unit determines the operating cycle rate and assigns this to the operating speed that is to be set. This can be done, for example, by calculating the appropriate operating cycle rate as part of the assignment based on an operating speed value for the component and the functional relationship. This can be a single value that can be individually assigned to the respective operating speed.However, it can also be provided that one is selected from a plurality of possible operating clock rates that can be assigned to this operating speed. Depending on the consideration of further circumstances, it can be provided that the operating clock rate is reassigned, for example if acoustic interference or the like occurs. It can further be provided that the operating clock rate is determined using an assignment table. Based on this, the control unit determines the switching signals according to the pulse width modulation principle. As soon as the operating speed of the component is set to the operating speed to be set, the control unit can apply the switching signals based on this operating clock rate to the switching elements of the inverter. This changes the operating clock rate.

[0032] The control unit is preferably designed as an electronic hardware circuit and can include a program-controlled computer unit to implement the desired functionality. Of course, the control unit can also be formed solely by the computer unit or can include a combination of a hardware circuit and the computer unit. In principle, however, it is also possible for the control unit to comprise solely a hardware circuit. The control unit can also be at least partially included in the higher-level control device of the household appliance. However, it can also be provided as a separate component in the household appliance. In particular, it is provided at least partially as a component of the inverter.

[0033] According to an advantageous development, it is proposed that during an acceleration process of the component, a maximum operating clock rate or an operating clock rate dependent on the operating speed to be set is set. This has the advantage that the acceleration process of the component can be carried out with high reliability and essentially without disruption. The maximum operating clock rate can ensure that a maximum operating speed of the component can also be reached reliably and without disruption. Of course, it may be sufficient to select the operating clock rate depending on the operating speed to be set. In this case, the maximum operating clock rate does not need to be selected, which can result in further advantages, particularly with regard to the switching losses of the inverter.The maximum operating cycle rate or the operating cycle rate dependent on the operating speed to be set is preferably set at least briefly for the start or at the start of the acceleration process.

[0034] A further development proposes maintaining the operating cycle rate set prior to the braking process during a component braking operation. This can also significantly improve the stability and reliability of the process control during normal operation. However, the maximum operating cycle rate does not need to be set during the braking process, especially since it can be assumed that the operating speed will decrease over time during a braking process. The operating cycle rate set immediately prior to the braking process is therefore generally sufficient to reliably implement even a reduced operating speed of the component.

[0035] Furthermore, it is proposed that after the acceleration or braking process has ended, the operating cycle rate be adjusted depending on the current operating speed. This development makes it possible to further improve the method according to the invention by adjusting the operating cycle rate, adapted to the current operating speed reached after the acceleration or braking process, to the then existing operating speed. For this purpose, the previously explained method according to the invention can again be implemented, preferably according to the two sections described above.

[0036] According to a further development, it is proposed that the operating cycle rate be determined linearly as a function of the operating speed. This embodiment provides for the operating cycle rate to be determined using a constant factor proportional to the operating speed. This allows for a particularly simple determination of the operating cycle rate depending on the operating speed to be set.

[0037] Furthermore, it is proposed that an integer ratio be selected between the operating clock rate and the operating speed. This can further simplify or improve the determination of the operating clock rate. This design can also be implemented particularly easily retrofitted to existing control units. Furthermore, advantageous effects with regard to electromagnetic compatibility can be achieved.

[0038] It is further proposed that the operating cycle rate be changed depending on the mechanical rotor position of a rotor of the AC electric machine. This makes it possible to take into account mechanical properties, in particular with regard to the torque provision of the AC machine, a torque load on the AC machine by the driven component, and / or the like. For this purpose, it can be provided that the control unit has suitable sensors, for example, rotational position sensors or the like, or is connected to such sensors and / or determines a corresponding rotor position from electrical parameters of the stator winding.

[0039] Furthermore, it is proposed that the component comprise a reciprocating piston compressor, and that a change in the operating cycle rate occurs outside of a compression stroke. This refinement has the advantage of improving stability when changing the operating cycle rate. Furthermore, during a compression stroke, greater power can be provided by the inverter or greater torque by the AC motor, which can lead to unfavorable dynamic processes in the inverter due to the change in the operating cycle rate. By changing the operating cycle rate outside of the compression stroke, the disadvantages and problems that would otherwise occur can be avoided.

[0040] According to an advantageous development, it is proposed that the operating clock rate be swept. Sweeping refers to the provision of oscillations, particularly harmonic oscillations such as sinusoidal oscillations, whereby the frequency of these oscillations is cyclically varied between two predeterminable end values ​​of the frequency. This can reduce acoustic interference. Furthermore, this development makes it possible to improve electromagnetic compatibility, particularly with regard to conducted interference, as explained above. Interference energy can be distributed across a broader frequency spectrum, which can improve overall compliance with interference limits and reduce interference suppression effort. The acoustics can also be improved in this way.

[0041] It is preferably provided that the sweep covers a frequency range in which a maximum frequency value is at least approximately 10%, preferably approximately 20%, particularly preferably approximately 30%, greater than the assigned operating clock rate and / or a minimum frequency value is at least approximately 10%, preferably approximately 20%, particularly preferably approximately 30%, lower than the assigned operating clock rate. It has been shown that sweeping in this range proves particularly advantageous for improving acoustics and / or electromagnetic compatibility, particularly with regard to conducted interference. The sweeping can be achieved by means of the control unit in that it varies the operating clock rate accordingly. For the sweeping, it can be provided that the variation between the maximum frequency value and the minimum frequency value occurs according to a predetermined characteristic and / or within a predetermined sweep period.For example, the sweep can be determined based on a functional relationship, as will be explained in more detail below. For example, the sweep can be performed at a sweep frequency that is lower than the operating clock rate. Accordingly, the sweep period is longer than one period of the operating clock rate to be swept.

[0042] According to a further development, it is proposed that the component has a reciprocating compressor and that the wobbling is synchronized with a compression process of the reciprocating compressor. This allows power fluctuations that occur during the intended operation of the reciprocating compressor to be taken into account, particularly during wobbling, and thus to improve not only the acoustics but also, if necessary, the electromagnetic compatibility. For example, it can be provided that the wobbling is essentially only carried out during a compression process in which a greater power supply from the inverter is required. However, the invention is not limited to this. Other processes that can be synchronized with the wobbling can also be provided.For example, it can also be provided that a wobble amplitude of the wobble, that is to say a frequency difference between the maximum frequency value or the minimum frequency value and the average operating cycle rate, is changed, in particular depending on properties of the component, as in the case of the reciprocating piston compressor.

[0043] It is further proposed that the wobbling occur as a function of a rotational position of the reciprocating compressor. In addition to the amplitude of the wobbling, the dependency can also take into account the rotational position of the reciprocating compressor in such a way that the wobbling is activated at the start of a compression process or the wobbling amplitude is increased and the compression process is ended or reduced in terms of amplitude. Other embodiments are also feasible from a person skilled in the art. With regard to the inverter according to the invention, it is particularly proposed that the stator winding be designed as a multi-phase stator winding and the inverter be designed to operate the multi-phase stator winding. As already explained above, the particularly advantageous properties that can be achieved in particular with a three-phase stator winding can thereby also be utilized for the invention.

[0044] The advantages and effects stated for the method according to the invention also apply equally to the inverter according to the invention and the household appliance equipped with the inverter according to the invention, and vice versa. In particular, method features can therefore also be formulated as device features, and vice versa.

[0045] Further features of the invention emerge from the claims, the figures and the description of the figures. The features and combinations of features mentioned above in the description, as well as the features and combinations of features mentioned below in the description of the figures and / or shown alone in the figures can be used not only in the respective combination specified, but also in other combinations without departing from the scope of the invention. Thus, embodiments are to be regarded as encompassed and disclosed by the invention that are not explicitly shown and explained in the figures, but which emerge and can be produced by separate combinations of features from the explained embodiments. Embodiments and combinations of features are also to be regarded as disclosed that therefore do not have all the features of an originally formulated independent claim.Furthermore, embodiments and combinations of features are to be regarded as disclosed, in particular by the embodiments set out above, which go beyond or deviate from the combinations of features set out in the reliances of the claims.

[0046] They show:

[0047] Fig. 1 shows a household refrigeration appliance in a schematic perspective view, Fig. 2 shows a schematic view of the refrigerant circuit of the household refrigeration appliance having a reciprocating compressor,

[0048] Fig. 3 shows a schematic view of the reciprocating compressor driven by a three-phase AC machine connected to an inverter,

[0049] Fig. 4 shows a schematic circuit diagram of an electrical power supply for the inverter, which is designed as a three-phase inverter, with three phase windings of a stator winding of the AC machine being connected to the inverter,

[0050] Fig. 5 shows a schematic block diagram of a section of a control device of the household appliance, in particular for the inverter,

[0051] Fig. 6 is a schematic diagram showing a differential efficiency-power diagram for an effect of the operation of the inverter when using a variable clock rate depending on an input power,

[0052] Fig. 7 is a schematic diagram showing a differential power figure performance diagram to illustrate an improved effect of the operation of the household appliance when using a variable clock rate depending on an input power,

[0053] Fig. 8 shows a schematic diagram of the generation of phase control signals for determining switching signals for switching elements of the inverter,

[0054] Fig. 9 shows in a schematic diagram the phase control signals determined based on Fig. 8, and

[0055] Fig. 10 shows a schematic diagram illustrating line-based power supply disturbances under different operating conditions. Fig. 1 shows a schematic perspective view of a household refrigeration appliance 1 comprising a thermally insulated body 10 with an inner container 2 defining a coolable interior 3. The coolable interior 3 is intended for storing foodstuffs (not shown in detail).

[0056] In the present exemplary embodiment, the household refrigeration appliance 1 has a pivoting door 4 for closing the coolable interior 3. The door 4 is pivotally mounted with respect to a vertical axis. When the door 4 is open, as shown in Fig. 1, the coolable interior 3 is accessible from the outside. On the side of the door 4 facing the coolable interior 3, several door racks 5 for storing food are arranged. In the coolable interior 3, several shelves 6 for storing food are arranged, and in the lower area of ​​the coolable interior 3, a drawer 7 is arranged, in which food can also be stored.

[0057] The household refrigeration appliance 1 comprises a refrigerant circuit 20 shown in Fig. 2 for cooling the coolable interior 3. In the present embodiment, the refrigerant circuit 20 comprises a refrigerant not shown in detail, a reciprocating compressor

[0058] 21 , a condenser arranged downstream of the reciprocating compressor 21

[0059] 22, a throttle device 23 fluidically connected downstream of the condenser 22, which in this case is designed as a throttle or capillary tube, and an evaporator 24 arranged between the throttle device 23 and the reciprocating compressor 21. The reciprocating compressor 21 is arranged within a machine compartment (not shown) of the household refrigeration appliance 1, which is located behind the drawer 7. The reciprocating compressor 21 is shown in more detail in Fig. 3.

[0060] Fig. 3 shows a schematic representation of the reciprocating piston compressor 21. The reciprocating piston compressor 21 comprises a compressor chamber 31 with an inlet 32 ​​and an outlet 33 for the refrigerant, and a piston 34 displaceably mounted within the compressor chamber 31. The inlet 32 ​​and the outlet 33 are each provided with corresponding valves, as is known in principle to the person skilled in the art.

[0061] The reciprocating compressor 21 further comprises a connecting rod 35, which is connected at one end to the piston 34 and at the opposite end to an eccentric disc arranged on a rotor 38 as a rotating component. The rotor 38 is part of an AC motor 36 of the household refrigeration appliance 1. The AC motor 36 is designed here as a three-phase, permanently excited synchronous motor.

[0062] The AC motor 36 has a stator 37 and a rotor 38 mounted rotatably relative to the stator 37. The connecting rod 35 is coupled to the rotor 38 via the eccentric disc, so that during normal operation of the household refrigeration appliance 1, when cooling power is to be provided, the piston 34, by means of the AC motor 36, can cyclically change a volume 39 enclosed by the compression chamber 31 and the piston 34 to compress the refrigerant.

[0063] The household refrigeration appliance 1 further comprises an electronic control device 8 (Fig. 1) configured to operate the refrigerant circuit 20 such that the coolable interior 3 at least approximately reaches a predetermined or predeterminable target temperature. The electronic control device 8 is configured to detect a current temperature of the interior 3 using a temperature sensor (not shown), compare it with the predetermined or predeterminable target temperature, and output at least one control signal depending on the comparison.

[0064] In order to operate the refrigerant circuit 20, the household refrigeration appliance 1 in the present embodiment has an electrical power supply 40 (Fig. 4) which, in addition to a DC intermediate circuit 17, has the electrical inverter 41, which has three series circuits each consisting of two switching elements 11, 12, 13, 14, 15, 16, which are connected in parallel to the DC intermediate circuit 17. Furthermore, a capacitor C is provided on the inverter side, which is connected in parallel to the series circuits.

[0065] The switching elements 11, 12, 13, 14, 15, 16 in this case are MOSFETs operated in switching mode. Alternatively, other transistors such as IGBTs or the like can of course also be used instead of the MOSFET. For this purpose, gate terminals of the MOSFETs are connected to the electronic control device 8 as control terminals of the switching elements 11, 12, 13, 14, 15, 16 and are supplied with respective switching signals as control signals by the electronic control device 8. Respective phase windings 42 of a stator winding of the stator 37 of the AC machine 36 are connected to respective center terminals of the series circuits, so that a star connection is provided in the present case. The DC voltage intermediate circuit 17 is supplied with electrical energy from a public power grid 19 via a bridge rectifier 18 (Fig. 5).

[0066] Fig. 5 shows a schematic block diagram of a section of the control device 8, which in this case is a component of the inverter 41. In principle, however, the control device 8 can also be designed separately from the inverter 41 and at least partially form the control device of the household appliance 1. Fig. 5 schematically shows the part of the control device 8 that serves to provide the switching signals for the switching elements 11, 12, 13, 14, 15, 16 so that the inverter 41 can provide a three-phase alternating voltage for the phase windings 42 of the alternating voltage machine 36.

[0067] From Fig. 5, it can also be seen that the inverter 41 is connected on the DC side to the DC intermediate circuit 17 of the power supply 40. The DC intermediate circuit 17 provides an intermediate DC voltage Ude, with which the inverter 41, in particular its series circuits comprising the switching elements 11 to 16, is supplied with electrical energy. The DC intermediate circuit 17 is further connected to the bridge rectifier 18, which in turn is connected on the AC side to the public power grid 19, which in this case provides a single-phase electrical AC voltage with an effective value of approximately 230 V at a frequency of approximately 50 Hz.

[0068] In this embodiment, the control device 8 is based on a vector control, but the invention is not limited to this. Vector control is generally known to those skilled in the art, so detailed explanations thereof will be omitted here. The control device 8 is further connected to current sensors 43, 44, 45, with which the respective phase currents of the phase windings 42 of the stator winding can be detected. Furthermore, the control device 8 is connected to the switching elements 11 to 16, so that the control device 8 can apply the respectively assigned switching signal to them. Finally, the intermediate DC voltage Ude of the DC voltage intermediate circuit 17 is detected by means of a voltage sensor 46. The voltage sensor 46 is also connected to the control device 8.

[0069] The electrical phase currents of the respective phase windings 42, detected by current sensors 43 to 45, are fed to a first transformation block 52 of control device 8, which calculates transformation values ​​Ia, Iß as transformed current quantities from the measured current values ​​of current sensors 43 to 45 using a Clarke transformation. In this case, multiphase quantities, such as the measured current values ​​of current sensors 43 to 45 in this case, are converted into a simpler two-axis coordinate system with the axes a, ß, so that the transformation values ​​Ia, Iß can be determined. In this way, transformation block 52 provides the transformation values ​​Ia and Iß.

[0070] The transformation values ​​1a, 1ß are then fed to blocks 51 and 53. Block 51 implements a monitoring function and provides a speed signal w as well as a signal for the current rotational position 0 of the rotor of the AC motor 36. For this purpose, block 51 receives additional signals Va and Vß, which are explained below. The rotational position 0 determined in block 51 is then fed, together with the transformation values ​​1a and 1ß, to transformation block 53, which performs a d / q transformation, also known as a Park transformation, and from this determines transformation values ​​Iq and Id.

[0071] Block 50 denotes a reference generator that provides a target speed for the AC machine 36, specifically its rotor 38. Block 50 is part of a higher-level control system that, among other things, specifies a target speed for the rotor 38. A comparator 55 determines a difference between the target speed of block 50 and the speed w determined by block 51. This difference is fed to a reference unit 56, as are the intermediate circuit DC voltage Ude determined by the voltage sensor 46 and a vector Vs. From this, the reference unit 56 determines transformation target values ​​for Id and Iq. These transformation target values ​​are compared with the transformation values ​​Iq and Id determined by block 53 using further comparators 57, 58, and the differences determined are fed to a current unit according to block 59.The current unit according to block 59 determines vectors Vd and Vq, which are fed to an inverse Park transformation in a block 60, which determines vectors Va and Vß taking into account the rotational position 0 determined by block 51. The vectors Va and Vß are fed to an SVPWM block 49. The SVPWM block 49 receives the switching signals for the switching elements 11 to 16, taking into account the intermediate circuit DC voltage Ude determined by the voltage sensor 46 and a clock rate signal explained below, and makes them available for proper operation.

[0072] A clock rate determination block 54 also receives the speed signal w from block 50 in relation to the target speed value and uses this to determine an operating clock rate, as will be explained below. Block 54 then provides a clock rate signal to the SVPWM block 49, which determines the switching signals for the switching elements 11 to 16 based on the clock rate signal.

[0073] Block 54 serves to optimize the switching behavior of the inverter 41 and its switching elements 11 to 16. The control device 8 explained with reference to Fig. 5 allows the operating clock rate or operating clock frequency, also called the carrier frequency, to be varied in order to improve the efficiency of the inverter 41 and the household refrigeration appliance 1. Although the invention is explained below with reference to the household refrigeration appliance 1, it is not limited thereto and can equally be used in other household appliances, such as washing machines, tumble dryers, and the like.

[0074] The invention therefore deviates from the prior art, among other things, in that the operating cycle rate no longer needs to be constant during normal operation of the household refrigeration appliance. This allows the operating cycle rate to be selected, among other things, depending on the speed of the rotor 38 of the AC motor 36, so that not only switching losses of the switching elements 11 to 16 but also acoustic interference can be reduced.

[0075] Based on the target speed of block 50, the clock rate unit 54 determines the operating clock rate to be used for the target speed. The operating clock rate determined in this way is transmitted to the SVPWM block 49, which, based thereon, provides the switching signals for the switching elements 11 to 16.

[0076] Even if the switching elements 11 to 16 are formed by MOSFETs in the present case, other transistors can of course also be used in alternative embodiments, for example bipolar transistors or the like.

[0077] Block 50 specifies or determines an operating speed for the reciprocating compressor 21 as a target speed, depending on an operating signal (not shown). The operating speed is then assigned to the operating cycle rate. This can be implemented, for example, as follows:

[0078] At a constant clock rate / PWM, the following relationship results for the resolution of a rotor angle Acp of the rotor according to formula 1 : f Motor ' P

[0079] A(p = 2 TI — - - PWM

[0080] Here, / Motor corresponds to a frequency corresponding to the speed of the rotor.

[0081] This means that the resolution of the rotor angle and the number of cycles per revolution of the rotor 38 depend on the rotor frequency of the motor, the clock rate / PWM, and the number of pole pairs p of the AC motor 36. An increased resolution of the rotor angle leads to an increased resolution of the AC voltage provided by the inverter 36, which simultaneously also forms a manipulated variable for the control according to the control device 8. It follows that, with a constant clock rate, the resolution and also the control quality increase at low speeds of the rotor 38. In this context, the control quality can be evaluated, for example, with regard to a distortion current and a torque ripple.A degree of modulation with respect to the pulse width modulation can thus be adapted by the control device 8 to a currently existing operating state, for example with respect to a speed, a torque and an available intermediate circuit DC voltage and / or if necessary, further.

[0082] With the invention, it is now possible to achieve a substantially constant resolution of the rotor angle Acp. This can be achieved by adjusting the clock rate to the rotor frequency corresponding to the rotor speed, as follows from the following formula 2: f Motor ' P

[0083] This clock rate can be assigned a constant switching frequency r, as follows from the following formula 3:

[0084] / PWM r = - - f Motor ' P

[0085] If the switching frequency is an integer, this can also be called synchronous modulation.

[0086] The resolution of the rotor angle Acp can thus be selected depending on a maximum value of the rotor speed, the clock rate, an execution time for the control, a permissible distortion current or a permissible torque ripple, and / or the accuracy of the observer system according to block 51. By selecting a constant switching frequency, a reduction in the clock rate can be achieved, especially at low speeds of the rotor 38. The constant resolution of the rotor angle Acp also allows high efficiency or a high degree of effectiveness with respect to the AC machine 36 to be achieved. Not shown in the figures is that the control device 8 has a computer unit whose functionality is controlled by a computer program and which implements the functions described above. In detail, the functionality of the method control can preferably be implemented as follows:

[0087] 1. First, the clock rate is determined according to formula 2.

[0088] 2. An implementation strategy is defined, for example, by determining a suitable time for changing the cycle rate. This time is preferably selected when the rotor 38 has reached a predetermined speed. To achieve the highest possible stability, the cycle rate should preferably not be changed when starting a cooling process, stopping a cooling process, accelerating or decelerating, and / or during a compression process of the reciprocating compressor.

[0089] In the present embodiment, these processes are therefore preferably carried out at a suitable, essentially constant operating cycle rate. With regard to a starting process, this means that in the present embodiment, the changing of the operating cycle rate is only carried out after the target speed of the rotor 38 has been reached. If a dynamic process such as acceleration or braking is provided, these can preferably be differentiated. During an acceleration that also involves an increase in the speed of the rotor 38, the operating cycle rate is changed before the acceleration process to a maximum operating cycle rate or to an operating cycle rate that corresponds to the operating speed to be set.During a braking operation corresponding to a speed reduction of the rotor 38, however, it is preferably provided that the operating cycle rate is only changed once the target speed or the operating speed to be set has been reached. Furthermore, it can be considered that the operating cycle rate is only changed within a predetermined range of a mechanical rotor position. This makes it possible to avoid changing the operating cycle rate, for example, during a compression process of the reciprocating compressor 21. 3. The control parameters of the preferably vector-based control unit 8 are determined based on the operating cycle rate to be set.

[0090] 4. The operating clock rate is then activated in accordance with the previous point 1 at the time determined under point 2. It can also be considered that the change in the operating clock rate only occurs at the end of a current completed period of the current operating clock rate. In this context, it should be noted that changing the operating clock rate has no influence on a dead time with respect to the respective switching elements of a respective series circuit.

[0091] 5. At the same time, the relevant parameters, in particular those relating to the regulation, shall be adjusted or updated accordingly at the time described in point 4.

[0092] In this way, it is possible to change or adapt the operating cycle rate as required, so that the efficiency of the inverter 36 and thus also that of the household refrigeration appliance 1 can be improved.

[0093] At the same time, this can also lead to improved acoustics. It is possible to record corresponding acoustic signals using an acoustic sensor (not shown in the figures) and take them into account when determining the operating cycle rate. This can also simultaneously improve the acoustic properties of the household refrigeration appliance 1.

[0094] The effect of the invention is evident from the schematic diagrams in Figures 6 and 7. Figure 6 shows a schematic diagram in which an abscissa corresponds to the electrical power supplied to the inverter 41 in W. An ordinate is assigned to a difference in the efficiency of the inverter of a clock rate variation according to the invention compared to a constant operating clock rate in %. Graphs 81 to 85 are assigned to respective operating temperature conditions at the reciprocating compressor 21, as follows: Graph 81 corresponds to a temperature on a pressure side of 55 °C and a temperature of -10 °C on a suction side. Graph 82 differs from graph 81 in that the temperature on the suction side is -25 °C. Graph 83 differs from graph 81 in that the temperature on the suction side is -30 °C.In graph 84, the temperature on the pressure side is 35 °C, whereas the temperature on the suction side is -10 °C. In graph 85, the temperature on the pressure side is also 35 °C, whereas the temperature on the suction side is -25 °C. It can be seen that the process according to the invention has a positive effect on efficiency, particularly in the partial load range. With regard to graph 81, an improvement is already apparent at a power of approximately 100 W or less. With regard to graph 84, the improvement is apparent at a power of approximately 82 W or less. In graphs 82 to 85, the improvement is apparent at a power of approximately 70 W or less. The lower the power, the greater the advantage according to the invention becomes.

[0095] Fig. 7 shows a corresponding schematic diagram for the efficiency of the household refrigeration appliance 1, with the abscissa being chosen as in Fig. 6 and the ordinate here corresponding to a difference in a coefficient of performance (COP) of a cycle rate variation according to the invention compared to a constant operating cycle rate in %. The graphs correspond in terms of the boundary conditions to those already explained with reference to Fig. 6, which is why reference is made to the corresponding explanations. Here, too, it is evident that an improvement in efficiency can be achieved, particularly in the partial load range.

[0096] The control device 8 generates control signals for determining the switching signals for the switching elements 11 to 16, as explained in more detail below with reference to Figures 8 and 9. Fig. 8 shows a schematic diagram in which an abscissa represents the time in seconds and an ordinate corresponds to counter readings of the computer unit (not shown) of the control device 8. It can be seen that in a first period 64, which extends from time t=0 to time t=2.5 ■ 10' 4 s extends, first a counter reading of a counter unit of the control device 8 for a first triangular signal 69 is counted up starting at time t=0 from a counter value =0 up to a counter value of 14000. This value is at a time t= 1.25 ■ 10' 4 s is reached. As soon as this counter value is reached, the counter is counted down again until the counter value reaches zero, which is at time t=2.5 ■ 10' 4s is achieved. Graphs 66, 67, and 68 provide comparison values ​​for the respective generation of the control signals for the three phases. These were previously determined using the vector control described above. By comparing them with the values ​​assigned to the respective phases according to graphs 66 to 68, the corresponding control signals are then determined.

[0097] Fig. 9 shows a schematic diagram of the switching signals generated in this way by means of graphs 61, 62, 63. The graph 61 is assigned to the graph 66 in Fig. 8, the graph 62 is assigned to the graph 67 according to Fig. 8, and the graph 63 is assigned to the graph 68 according to Fig. 8. The abscissa of the diagram according to Fig. 9 corresponds to the abscissa of the diagram according to Fig. 8. The ordinate is assigned to a relative switching state of the control signals, i.e. only the values ​​0 and 1 are present, which are assumed by the control signals.

[0098] It can be seen that the control signal according to the graph 63 in a time range from a time t=0.25 ■ 10' 4 s until time t=2.25 ■ 10' 4 s has the value 1. Before and after this time, its value is zero. A second control signal according to the graph 62 is during a time period from a time t = 0.625 ■ 10' 4 s up to a time of t=1 ,875 ■ 10' 4 s is switched on. Before and after this time, its value is zero. A switching signal according to graph 61 is present from time t = 10' 4 s up to a time 1.5 ■ 10' 4 s is switched on. Before and after, its value is zero.

[0099] Based on the control signals of graphs 61 to 63 determined in this way, the corresponding switching signals for the switching elements 11 to 16 are then generated by the control device 8, so that corresponding voltage curves are provided to the phase windings 42 of the stator winding connected to the inverter 36 in accordance with the control signals 61 to 63. As can be seen from Figures 8 and 9, graph 69, i.e., the counter reading at which the counting direction is changed, determines the operating clock rate. With the specified values, a clock rate of approximately 4 kHz results. At time t=2.5 ■ 10' 4s, the operating clock rate is changed. The maximum counter value at which the counting direction is changed is now approximately 9000. At the same time, adjusted values ​​according to graphs 66 to 68 are determined by the control device 8 and used for comparison with graph 69. As the second time period or time segment, designated by reference numeral 65, shows, the period of the clock rate changes to 1.67 ■ 10' 4 s, which corresponds to an operating frequency or clock rate of approximately 6 kHz. Fig. 9 shows the control signals generated in this way in the corresponding area 65, with graphs 61 to 63. This clearly shows that the switching signals are correspondingly shorter in time.

[0100] In addition, a further functionality can be provided, namely by sweeping the operating clock rate, as explained below. The sweeping is implemented here as a discrete sweep. This can, among other things, reduce line-borne interference. This development is based on the idea that the frequency spectrum of the interference signals can contain frequency components of the operating clock rate or the operating frequency, including harmonics and interharmonics, with the fundamental oscillation based on the current operating speed, especially at a constant clock rate. The operating clock rate or operating frequency can be varied according to the following formula 4: PWM = / PWM..Base (1 + 0.2 ■ sin(2 ■ (p)

[0101] In addition, further optimization can be added, particularly with regard to a load or load profile. For example, a ratio between a maximum and a currently existing torque can be considered in order to reduce or limit the wobble control range under high loads. For example, maximum and minimum values ​​can be introduced according to the following equation 5:

[0102] M max e [1,3]

[0103] M Furthermore, particularly when using a reciprocating compressor 21, an electrical rotor angle can be synchronized with the respective compression processes. Thus, an angle q>K can result from an electrical rotor position and an offset. The offset can be selected such that a positive half-wave of a sinusoidal oscillation, which corresponds to a mechanical angle of 90° with respect to the number of pole pairs, lies essentially within a range of a compression cycle of the reciprocating compressor 21. The then higher operating cycle rate can result in further advantages with regard to control, in particular with respect to torque ripple, a sampling rate, and / or the like. For example, the wobbling can be implemented according to the following formula 6:

[0104] Mmax PWM = / pWM_basis ' (1 + 0.1 1 ■ sin(2 ■ (pK)

[0105] Fig. 10 shows the corresponding results in a further schematic diagram. An abscissa of the diagram in Fig. 10 is assigned to the frequency in Hz and an ordinate to a noise level in dßpV. In Fig. 10, a graph 70 shows the standard limit for quasi-peak noise according to the EN 55014 / 1 standard. A graph 71 shows the standard limit for an average value defined according to this standard. A graph 74 shows the conducted noise in relation to graph 70, specifically for a control method with a constant operating clock rate of the prior art. A corresponding average signal is shown with graph 78, in relation to graph 71. A graph 73 shows the conducted noise in the quasi-peak range for a control method when an operating sweep is also provided. Graph 77 shows the same for the mean value.It can be seen that the interference is more uniform than in the prior art, meaning that it does not exhibit excessive fluctuations. Graphs 72 and 76 show the corresponding ratios according to the invention based on a variable operating clock rate, with graph 72 representing the quasi-peak value and graph 76 the mean value. The achievable reduction in line-borne interference is clearly visible. 5 The description of the figures serves exclusively to explain the invention and is not intended to limit it.

[0106] List of reference symbols

[0107] 1 household refrigeration appliance

[0108] 2 inner containers

[0109] 3 Interior

[0110] 4 Door

[0111] 5 door racks

[0112] 6 shelves

[0113] 7 drawers

[0114] 8 Control device

[0115] 10 Corpus

[0116] 11 Switching element

[0117] 12 switching element

[0118] 13 Switching element

[0119] 14 Switching element

[0120] 15 Switching element

[0121] 16 Switching element

[0122] 17 DC link

[0123] 18 bridge rectifiers

[0124] 19 Energy supply network

[0125] 20 Refrigerant circuit

[0126] 21 reciprocating compressors

[0127] 22 Condenser

[0128] 23 Throttle device

[0129] 24 evaporators

[0130] 31 Compressor chamber

[0131] 32 Entrance

[0132] 33 Outlet

[0133] 34 pistons

[0134] 35 connecting rods

[0135] 36 AC machine

[0136] 37 stands

[0137] 38 Runners 39 Volume

[0138] 40 Energy supply

[0139] 41 inverters

[0140] 42 phase windings

[0141] 43 Current sensor

[0142] 44 Current sensor

[0143] 45 Current sensor

[0144] 46 Voltage sensor

[0145] 49 Block

[0146] 50 blocks

[0147] 51 Block

[0148] 52 Block

[0149] 53 Block

[0150] 54 Block

[0151] 55 comparators

[0152] 56 Reference unit

[0153] 57 comparators

[0154] 58 comparators

[0155] 59 Block

[0156] 60 blocks

[0157] 61 graphs

[0158] 62 graphs

[0159] 63 Graph

[0160] 64 Period

[0161] 65 period

[0162] 66 Graph

[0163] 67 Graph

[0164] 68 Graph

[0165] 69 Graph

[0166] 70 graphs

[0167] 71 Graph

[0168] 72 Graph

[0169] 73 Graph

[0170] 74 Graph 76 Graph

[0171] 77 Graph

[0172] 78 Graph

[0173] 81 Graph

[0174] 82 Graph 83 Graph

[0175] 84 Graph

[0176] 85 Graph

Claims

Patent claims 1. Method for operating an inverter (41) to which a stator winding (42) of an AC electric machine (36) is electrically connected, which drives a component (21) that rotates at least temporarily about a rotational axis during the intended operation of a household appliance (1), wherein the inverter (41) supplies the stator winding (42) with an AC voltage, which is provided by means of a series connection of the inverter (41) comprising at least two switching elements (11, 12, 13, 14, 15, 16), wherein the series connection is supplied with a DC link voltage (Ude), wherein switching signals for the switching elements (11, 12, 13, 14, 15, 16) are provided by means of a control unit (8) of the inverter (41), wherein the control unit (8) outputs the switching signals according to a pulse width modulation principle based on a clock rate dependent on an operating signal for the Component (21) determined,wherein the clock rate is greater than a frequency corresponding to a rotational speed of the component (21), characterized in that, depending on the operating signal, an operating speed of the component (21) to be set is determined, an operating clock rate is assigned to the operating speed, the switching signals are determined based on the operating clock rate, the operating speed of the component (21) is set, and the switching elements (11, 12, 13, 14, 15, 16) are supplied with the switching signals based on the operating clock rate either before or only after the operating speed has been set.

2. Method according to claim 1, characterized in that during an acceleration process of the component (21) a maximum operating clock rate or an operating clock rate dependent on the operating speed to be set is set.

3. Method according to one of the preceding claims, characterized in that during a braking process of the component (21) the operating cycle rate set before the braking process is maintained.

4. Method according to claim 2 or 3, characterized in that after the acceleration process or the braking process has ended, the operating cycle rate is adjusted depending on the current operating speed.

5. Method according to one of the preceding claims, characterized in that the operating cycle rate is determined linearly dependent on the operating speed.

6. Method according to claim 5, characterized in that an integer ratio is selected between the operating cycle rate and the operating speed.

7. Method according to one of the preceding claims, characterized in that a change in the operating clock rate is made depending on a mechanical rotor position of a rotor (38) of the electric AC machine (36).

8. Method according to one of the preceding claims, characterized in that the component (21) comprises a reciprocating compressor and a change in the operating cycle rate takes place outside of a compression stroke.

9. Method according to one of the preceding claims, characterized in that the operating clock rate is swept.

10. Method according to claim 9, characterized in that the sweep covers a frequency range in which a maximum frequency value is at least 10%, preferably 20%, particularly preferably 30%, greater than the associated operating clock rate and / or a minimum frequency value is at least 10%, preferably 20%, particularly preferably 30%, less than the associated operating clock rate.

11. Method according to claim 9 or 10, characterized in that the component (21) has a reciprocating compressor and the wobbling is synchronized with a compression process of the reciprocating compressor.

12. Method according to one of claims 9 to 11, characterized in that the wobbling is dependent on a rotational position of the reciprocating compressor.

13. Inverter (41) for supplying an alternating voltage to a stator winding (42) of an AC machine (36) electrically connected to the inverter (41), which drives a component (21) that rotates at least temporarily about an axis of rotation during the intended operation of a household appliance (1), wherein the inverter (41) has at least one series circuit comprising two switching elements (11, 12, 13, 14, 15, 16) for providing the alternating voltage and a control unit (8) for providing switching signals for the switching elements (11, 12, 13, 14, 15, 16) wherein the series circuit can be supplied with a DC link voltage (Ude), wherein the control unit (8) is configured to determine the switching signals according to a pulse width modulation principle based on a clock rate depending on an operating signal for the component (21), wherein the clock rate is greater than a frequency corresponding to a rotational speed of the component (21), characterized in that the control unit (8) is configured to determine an operating speed of the component (21) to be set depending on the operating signal, to assign an operating clock rate to the operating speed, to determine the switching signals based on the operating clock rate, to set the operating speed of the component (21) and to supply the switching elements (11, 12, 13, 14, 15, 16) with the switching signals based on the operating clock rate either before or only after the operating speed has been set.

14. Inverter according to claim 13, characterized in that the stator winding (42) is designed as a multi-phase stator winding and the inverter (36) is designed for operating the multi-phase stator winding (42).

15. Household appliance (1) comprising a component (21) which rotates at least temporarily about an axis of rotation during the intended operation of the household appliance (1), an AC electrical machine (36) rotationally coupled to the component (21) for rotatably driving the component (21), wherein the AC electrical machine (36) has a stator winding (42), and an inverter (41) electrically connected to the stator winding (42) for applying an AC electrical voltage to the stator winding (42), characterized in that the inverter (36) is designed according to one of claims 13 or 14.

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