Operation of a linear compressor of a domestic appliance

Abstract

The invention relates to a method (10-17) for operating a linear compressor (1, 1') of a domestic appliance (H), in which method a setpoint current profile (i~ ref) of an electrical current (i) to be applied to a drive coil (9A) of the linear compressor (1, 1') is calculated from a setpoint reversal position of a front reversal point (x+,max ref) of a piston (3) of the linear compressor (1, 1') and a front actual reversal position (x+,max) of the piston, a current (i) to be applied to the drive coil (9A) is regulated by means of the setpoint current profile (i- ref) and an actual current profile (i~), and the front actual reversal position (x+,max) is observed or measured. The invention also relates to a linear compressor (1, 1') of a domestic appliance (H) which is configured to carry out the method (10 - 17). The invention also relates to a household appliance (H) comprising a linear compressor (1, 1'), wherein the household appliance (H) is configured to carry out the method (10 - 17). The invention can in particular be advantageously applied to refrigeration appliances such as refrigerators, freezers or combinations thereof.

Description

[0001] Operating a linear compressor of a household appliance

[0002] The invention relates to a method for operating a linear compressor of a household appliance. The invention also relates to a correspondingly configured linear compressor. The invention further relates to a household appliance having such a linear compressor. The invention is particularly advantageously applicable to cooling appliances such as refrigerators, freezers, or combinations thereof.

[0003] Cooling devices are known whose refrigeration circuit uses a linear compressor as a drive. The linear compressor has a piston driven in a linear motion, the front face of which forms the face of a working volume filled with working fluid. On the opposite face of the working volume, there is an inlet and an outlet for the working fluid. When the piston moves towards the opposite face ("forward"), the working volume is compressed, so that the working fluid is pushed out of the outlet but does not flow through the inlet. A gap remains between the front face of the piston and the opposite face (also referred to as the "valve plate") to prevent mechanical contact between them. When the piston is deflected to its maximum forward position, which corresponds to the smallest distance to the opposite face, a so-called"Dead volume" exists. When the piston moves in the opposite direction away from the opposite end face ("backward"), the working volume expands, so that the working fluid is drawn in from the inlet but does not flow through the outlet. By moving the piston back and forth, the working fluid can be moved through a working fluid circuit connected to the inlet and outlet. To move the piston, a corresponding alternating voltage signal is applied to an electromagnet driving the piston.

[0004] The object of the present invention is to at least partially overcome the disadvantages of the prior art and, in particular, to provide a particularly efficient way of operating a linear compressor of a household appliance. This object is achieved according to the features of the independent claims. Preferred embodiments can be found in particular in the dependent claims.

[0005] The object is achieved by a method for operating a linear compressor of a household appliance, in which

[0006] - a target current (value) curve of an electric current to be impressed into a drive coil of the linear compressor is calculated at least from a target reversal position of a front or upper reversal point of a piston or cylinder (2) as the lifting body of the linear compressor (also referred to as "front target reversal position") and a front actual reversal position of the lifting body,

[0007] - a current or current curve to be impressed into the drive coil is controlled by means of the desired current curve and an actual current curve, in particular a comparison thereof, and

[0008] - at least the actual front reversing position is estimated or measured by an observer.

[0009] This method has the advantage that the movement of the lifting body can be regulated to its front target reversal position and thus, firstly, this target reversal position can be reached particularly precisely, which enables high efficiency, even with changing boundary conditions such as temperatures of the working medium, at the inlet and / or at the outlet, etc. and, secondly, it can be particularly reliably prevented that the lifting body hits the valve plate.

[0010] The linear compressor drives a working fluid circulating in a circuit. The circuit can be a refrigeration circuit or a heat pump circuit. In addition to the linear compressor, the circuit can comprise at least one evaporator, at least one expansion fluid, and at least one condenser in a generally known manner.

[0011] To achieve high efficiency of the linear compressor, the dead volume is kept as low as possible and, consequently, the maximum forward deflection position of the piston (also referred to as the "front reversal point") is kept as low as possible while avoiding contact. It is advantageous to select a suitable initial or rest position of the piston relative to the valve plate. The rest position has a significant influence on the compressor's refrigeration capacity. The rest position is chosen in particular so that a specified maximum refrigeration capacity or "limit capacity" can be achieved with symmetrical current supply or control. However, this limit capacity is rarely reached in practice.For a lower cooling capacity, which is more frequently required in practice, the level of the alternating voltage signal can be reduced, whereby the piston no longer comes as close to the valve plate at the front reversal point and consequently the efficiency decreases due to the increased dead volume.

[0012] With symmetrical current supply, a balanced gas pressure results in a nearly symmetrical oscillation around a mechanical zero position (rest position) determined by mechanical springs. When the load conditions change, especially when the gas pressure is unbalanced, the position oscillation around a mechanical zero position (rest position) becomes asymmetrical even with symmetrical current supply. This asymmetry is referred to here as load asymmetry. This results in a shift of the mechanical zero position to a virtual zero position determined by mechanical springs and the gas pressure acting as a gas spring.

[0013] With this symmetrical current supply, a maximum cooling performance of the symmetrical current supply is achieved, which is associated with a maximum deflection of the oscillating body.

[0014] According to the invention, an additional asymmetric flow is applied to the symmetrical flow, which increases the load asymmetry. By increasing the intake path Ax at the lower reversal point, the maximum cooling capacity can be increased. This additional intake path Ax is calculated by an upstream algorithm by specifying the target cooling capacity, taking into account boundary conditions such as frequency / temperature at the inlet and outlet of the displacement.

[0015] The generation of the additional asymmetric flow from the specified additional intake path Ax is described below.

[0016] The household appliance can be a refrigeration appliance. The cooling appliance can be, for example, a refrigerator, a freezer, or a combination of these. The household appliance can be a laundry appliance equipped with a heat pump, e.g., a washing machine, a tumble dryer, or a combination of these, or even a dishwasher.

[0017] The invention relates both to a linear motor in which the piston is driven as a lifting body and moves relative to the cylinder as a stationary component, and to a linear motor in which the cylinder is driven as a lifting body and moves relative to the piston as a stationary component.

[0018] The piston of the linear compressor is arranged in a cylinder within a housing of the linear compressor. The piston and cylinder are mounted so that they can be moved longitudinally relative to each other, with one of the piston and cylinder being immobile in the housing and thus also relative to a coil of the motor, while the other is movable as a reciprocating body. The reciprocating body is connected to the immobile component or the housing by at least one elastic spring element. The reciprocating body, equipped with at least one permanent magnet, is typically driven by the magnetic field of at least one electromagnet, which is equipped with at least one coil ("drive coil") powered by an alternating electrical voltage, thereby causing it to oscillate. Depending on the direction of movement, a working volume defined by the cylinder and an end face of the piston is increased or decreased.The linear compressor can also be considered a linear motor, with the moving body corresponding to the rotor or "mover." The basic operation of a linear compressor in a refrigeration circuit or heat pump circuit of a refrigeration appliance is well known and will therefore not be discussed further here.

[0019] Regarding the terms alternating voltage and sinusoidal voltage in this description: Alternating voltage refers to a periodic voltage of any signal shape. To control the motor, a symmetrical alternating voltage is used here, which can otherwise have any signal shape. A sine wave is the preferred signal shape due to its simplicity, so a sinusoidal voltage and a sine generator are also mentioned in examples. For a symmetrical target current, a symmetrical alternating voltage, for example a sinusoidal voltage, is generated to supply the motor with current. From this alternating voltage, PWM signals are generated for the individual windings. From these PWM signals, voltage patterns are created that are then applied to the motor. This creates a current in the motor that is then measured.

[0020] The nonlinear load is a gas spring, which depends on the current pressure conditions on the suction and discharge sides. This results in an asymmetric movement of the lifting body, even with symmetrical flow.

[0021] As usual, the symmetrical target current is adjusted to the current load conditions and changes over time, sometimes even temporarily. The symmetrical target current is determined based on refrigeration requirements and aims to optimize the current requirements and load conditions, e.g., maximum energy efficiency at a specific cooling capacity. Regardless of the refrigeration requirements, a protective control can be used to prevent the lifting body from mechanically striking the fixed component. Such a protective control does not change the symmetry of the symmetrical target current.

[0022] There is a maximum cooling capacity that can be achieved with symmetrical current flow. The present invention aims to impose an asymmetrical current component on the symmetrical current flow in order to achieve a cooling capacity that is greater than the maximum cooling capacity that can be achieved with symmetrical current flow.

[0023] The desired cooling capacity can be specified, and the symmetrical flow is then applied to the maximum cooling capacity achievable with symmetrical flow. This symmetrical flow corresponds to a specific stroke with a specific bottom dead center of the lifting body. The remaining difference to the desired cooling capacity is calculated by extending the stroke of the lifting body beyond the specific bottom dead center as an additional intake path.

[0024] The asymmetrical flow extends the stroke of the reciprocating body beyond the specified bottom dead center, thus creating an additional intake path without actively changing the top dead center. This results in an increase in the displacement and thus in the flow rate and ultimately in the cooling capacity.

[0025] The target current waveform is an alternating current waveform, in particular a sinusoidal current (value) waveform, which can be defined by its amplitude and frequency (which corresponds to the "operating frequency" of the lifting body). The actual current waveform or actual motor current can be measured, for example, using a current measuring device. The voltage applied to the drive coil corresponds, in particular, to a manipulated variable for a current control. This current control is then nested or interlinked, in particular, with the ("amplitude") control for controlling the actual front reversing position of the lifting body. Controlling the current or current waveform to be impressed into the drive coil using the target current waveform and an actual current waveform can involve applying the control directly to the current waveforms.Alternatively or additionally, the current or current waveform to be impressed into the drive coil can be controlled indirectly using the corresponding manipulated variable, namely the voltage applied to the drive coil. Control via this voltage can generally be used below, even if this is not explicitly stated.

[0026] Estimating the actual front reversing position by an observer can involve reconstructing or estimating it from known input variables (e.g., measurable disturbance variables) and output variables (e.g., manipulated variables and / or measured variables) of an observed reference system. For this purpose, the observed reference system can, for example, be modeled and use a controller to track the measurable, and therefore comparable, state variables. Possible input variables to the observer can include, for example, at least the measured actual current and / or an output voltage or excitation voltage applied to the drive coil and / or an excitation or operating frequency.

[0027] Measuring the actual front reversing position may involve measuring it directly or deriving it from other measurements.

[0028] The fact that the target current (value) curve is calculated "at least" from the front target reversing position and the front actual reversing position can, for example, include the possibility of additionally calculating the target current curve based on other target and / or actual positions. Analogously, the corresponding actual position can then be additionally estimated or measured by an observer.

[0029] One embodiment includes an additional "rear" actual reversal position corresponding to the rear or lower reversal point of the lifting body being estimated or measured by an observer. The rear actual reversal position can then be used, for example, to calculate the total lifting body stroke between the two reversal points and, from this, to estimate the internal pressure difference.

[0030] It is a further development that at least one reference position lying between the two reversal positions is additionally estimated or measured by an observer.

[0031] In one embodiment, a movement or position profile of the lifting body is estimated or measured by an observer, and from this, at least the front actual reversal position, possibly also the rear actual reversal position and / or at least one reference position of the lifting body is determined. For example, the front actual reversal position can be determined or extracted from a local maximum of the profile, the rear actual reversal position from a local minimum of the profile, etc. In particular, the position of the lifting body can be estimated or measured with a constant measuring or sampling rate. In one development, the profile can be a curve fitted to the estimated or measured positions.

[0032] In one embodiment, an amplitude ("target current value amplitude") is calculated at least from the front desired reversing position and the front actual reversing position, and the desired current curve is calculated from the target current value amplitude and a desired desired operating frequency of the lifting body. This is advantageously particularly easy to implement and results in robust control. The desired operating frequency can in principle be set arbitrarily. For example, it can correspond to the resonance frequency, i.e. the operating frequency at which the lifting body can be deflected the furthest from its non-driven rest position (with the same current value amplitude). However, it can also correspond to a frequency that is, for example, higher or lower than the resonance frequency. This embodiment can be implemented, for example, by means of or in the manner of a sine generator, which generates the, for example, sinusoidal desired current value orThe target current curve is calculated or generated from the specified values ​​of target current value amplitude and target operating frequency.

[0033] It is a further development that the calculation of the target current value amplitude is also carried out based on the rear target reversing position and the rear actual reversing position, which has the advantage that the internal pressure difference and thus the cooling capacity can be determined particularly precisely.

[0034] In one embodiment, the current or current waveform to be impressed into the drive coil is formed by a pulsed voltage. For this purpose, in one embodiment, a (general) sinusoidal current waveform to be impressed, output by the sine generator as a manipulated variable, can be converted into a corresponding pulsed voltage waveform to be impressed by means of a PWM element serving as an actuator. This can mean that the first and second current half-waves - even between different periods - can be of different lengths, while the period duration is identical and, in particular, corresponds to the operating frequency. In other words, with pulse width modulation, the duty cycle or pulse duration can differ for different periods, while the period duration remains the same.

[0035] Alternatively, or additionally, the current profile can be generated from any harmonics of the fundamental frequency. This has the advantage of minimizing pressure pulses due to the discontinuous movement of the inlet and exhaust valves, which can also lead to increased efficiency.

[0036] One embodiment involves adding a specific additional amplitude value ("additional current value") to the target current amplitude, and reducing the target current curve by the same additional current value. This transforms the previously symmetrical target current curve or symmetrical current supply into a target current curve or asymmetrical current supply that is asymmetrical with respect to the zero value. The asymmetrical target current curve remains sinusoidal or similar with the set operating frequency. However, compared to the symmetrical current supply, the absolute value of the positive or negative amplitudes of the target current curve with respect to the equilibrium position has been increased by the additional current value, while the mean or equilibrium value of the target current curve has been reduced by this additional current value. This advantageously ensures that the positive amplitude of the target current curve for moving the lifting body forward remains the same.This is due to the pre-calculated controlled current curve; in addition, the control of the upper amplitude remains active. Thus, the distance between the lifting body and the valve plate at the front reversing position of the lifting body also remains the same. However, the negative amplitude of the target current curve for the rearward deflection is noticeably increased. Consequently, the intake path of the lifting body is noticeably increased, thereby increasing the transported volume flow of the working fluid and, in turn, increasing the cooling capacity. While this may be less energy-efficient than operation with symmetrical current supply, it does enable an increase in cooling capacity, which can be used particularly for comparatively short cooling phases where increased cooling capacity is required, for example, after switching on a cooling device, when activating a "super cooling" mode, etc.This, in turn, helps to dimension the unit in such a way that the influence of the dead volume ("clearance volume") and the associated losses are minimized for the specified cooling capacity, which is normally required continuously. Thus, for a refrigeration unit, the advantage is that the cooling capacity can be temporarily increased through asymmetric operation of a linear compressor.

[0037] If, for example, with symmetrical current supply the positive amplitude A+ of the target current curve is at a value A > 0 and the negative amplitude A. is at a value -A, the equilibrium position of the current curve i~ is at (A+ + A.) / 2 = (A + (-A)) / 2 = 0. If with asymmetrical current supply the additional current value AA > 0 is added, the amplitudes A+ = A + AA and A. = - (A + AA). By lowering the equilibrium position by AA the amplitudes are then at A+ = A and A. = - (A + 2 AA) and the equilibrium position is at (A - A - 2 AA) / 2 = -AA. The positive forward amplitude A+ remains the same with asymmetrical current supply, while the negative backward amplitude A. increases by twice the additional current value and the lifting body is therefore deflected backwards accordingly more.

[0038] In one embodiment, for a desired additional deflection of the lifting body to the rear (i.e., away from the valve plate), a necessary mechanical force on the lifting body is calculated, and from this mechanical force, the additional flow value required to achieve the desired additional deflection of the lifting body is calculated. This provides the advantage that the additional cooling capacity can be adjusted quickly and precisely with little effort. The additional deflection to the rear can also be referred to as an additional intake path. The mechanical force F f can be calculated from the spring constant k f the elastic spring hinged to the lifting body according to F f = k f ■ Ax. with Ax. the additional intake path to the rear. The mechanical force F f can the force F mwhich the drive magnet must exert on the lifting body in order to deflect it by an additional amount of Ax. From F m = k m • Ai with k m the motor constant and Ai > 0 the additional DC component, Ai can be calculated according to Ai = (kf / k m ) ■ Calculate Ax. The additional current value AA can be calculated from this as AA = Ai / 2.

[0039] In one embodiment, the additional current value is applied with a gradient limit, i.e. not abruptly or suddenly at full value. This advantageously ensures that the lifting body oscillation adapts more evenly to the additional current value. The gradient limitation can, for example, comprise an increase in the additional current value with a limited, in particular constant, gradient. In another embodiment, the additional current value is applied with a gradient limit, by increasing it in steps, in particular by means of inclined steps of a certain gradient. In another embodiment, the additional current value is reduced with a gradient limit, i.e. not suddenly at full value. This can be done in a similar way to gradient-limited application. In another embodiment, the additional current value is applied continuously, i.e. without noticeable jumps.

[0040] One embodiment includes estimating the actual front reversing position of the lifting body using an observer, in particular a Luenberger observer. Alternatively, the actual front reversing position of the lifting body can be estimated using a flow estimator, a so-called "sliding-mode" observer, or a Kalman filter, etc. Another possibility for increasing accuracy is a data-based method for improving the accuracy of an observer, in particular using artificial intelligence. These alternatives can each be combined with nonlinear characteristic maps of the machine variables in a further development. One embodiment includes measuring at least the actual front reversing position of the lifting body using laser radiation. Alternatively, the actual front reversing position can be measured using a position reference sensor. Other actual positions of the lifting body can also be measured accordingly.

[0041] In one embodiment, the linear compressor is operated in one operating mode without an additional current value and in at least one other operating mode with an additional current value. This advantageously allows for simple, low-wear, and quick switching between a particularly effective operating mode without use of the additional current value and an operating mode with use of the additional current value for increased cooling capacity. In a further development, the linear compressor can be operated in several operating modes with an additional current value, which differ in terms of different additional current values ​​and thus different additional cooling capacities. In general, the additional cooling capacity can be set as desired within possible operating conditions, e.g., continuously or quasi-continuously.

[0042] The object is also achieved by a linear compressor of a household appliance, wherein the linear compressor is configured to carry out the method as described above. The linear compressor can be designed analogously to the method, and vice versa, and has the same advantages.

[0043] The linear compressor can comprise, as a component, a control or regulation system that is configured, e.g., programmed, to implement the method described above. The linear compressor as such and the control or regulation system can also be considered together as a compressor module. The control or regulation system can be data-linked to a control device of the household appliance, which control device can, for example, output a signal for switching between different operating modes.

[0044] The object is further achieved by a household appliance with a linear compressor, in particular as described above, wherein the household appliance is configured to carry out the method as described above. The household appliance can be designed analogously to the method and / or the linear compressor, and vice versa, and has the same advantages. For example, one embodiment provides that the household appliance is a cooling appliance, for example a refrigerator, freezer or a combination thereof. The working medium can then also be referred to as a cooling medium or coolant. However, the household appliance is not limited to this and can use the linear compressor, for example, to drive a heat pump. In this case, the description of the invention can be applied analogously with regard to a cooling appliance or cooling circuit, for example in a dishwasher or a laundry treatment appliance.

[0045] The above-described properties, features and advantages of this invention, as well as the manner in which they are achieved, will become clearer and more clearly understood in connection with the following schematic description of an embodiment, which is explained in more detail in connection with the drawings.

[0046] Fig.1 shows a sectional side view of a sketch of a possible linear compressor with driven piston;

[0047] Fig.2A shows a schematic plot of a desired current impressed into a drive coil of the linear compressor against time with sinusoidal symmetrical current supply;

[0048] Fig.2B shows a schematic plot of a deflection of the stroke body of the linear compressor against time for the sinusoidal symmetrical current supply according to Fig.2A;

[0049] Fig.3 shows a possible block diagram for a symmetrical current supply of the linear compressor;

[0050] Fig.4A shows a schematic plot of a desired current impressed into a drive coil of the linear compressor against time with sinusoidal asymmetric current supply;

[0051] Fig.4B shows a schematic plot of a deflection of the stroke body of the linear compressor against time with sinusoidal asymmetric current supply according to Fig.4A;

[0052] Fig.5 shows a possible block diagram for an asymmetrical current supply of the linear compressor; and

[0053] Fig. 6 shows a sectional side view of a possible linear compressor with a driven cylinder. Fig. 1 describes a linear motor in which the piston, acting as a reciprocating body, is driven and moves relative to the cylinder as a stationary component. Fig. 6 describes a linear motor in which the cylinder, acting as a reciprocating body, is driven and moves relative to the piston as a stationary component. Identical components are designated by the same reference numerals; corresponding components are given primed reference numerals.

[0054] Fig. 1 shows a sectional side view of a sketch of a possible linear compressor 1. The linear compressor 1 has a cylinder 2 rigidly connected to the housing 20 within a housing 20 of the linear compressor 1, and a piston 3 which can be moved linearly in the cylinder 2, as indicated by the double arrow. A rear side of the piston 3 is hinged to the housing 20 via a spring element 4 and the front side of the piston delimits a working volume 5. The piston 3 is provided with permanent magnets 3A. During operation, the piston 3 moves as a lifting body 23 relative to the cylinder 2 as a stationary component. A unidirectional inlet 6 opens into the working volume 5, through which the working medium 7 can flow into the working volume 5, and a unidirectional outlet 8 opens into the working volume 5, through which the working medium 7 can flow out of the working volume 5. The linear compressor 1 also has an electromagnet or solenoid arranged outside the cylinder 2.Drive magnet 9. The drive magnet 9 has a drive coil 9A, which is typically operated on the basis of a possibly pulsed alternating voltage U~, and a stator 9B made of magnetic material, e.g., sheet steel segments. The operated drive magnet 9 exerts a magnetic force on the permanent magnets 3A of the piston 3, whereby the lifting body 23 is excited to a linear oscillating linear movement in the cylinder 2. With a constant alternating voltage U~, a back-and-forth movement of the lifting body 23 occurs at a specific oscillation or operating frequency f. w which at least approximately corresponds to the voltage frequency of the alternating voltage U~. In particular, the operating frequency f w a resonance frequency f resof an oscillation system comprising at least the lifting body 23 and the spring element 4. The oscillating lifting body 23 elastically expands the spring element 4 when moving forward or in the direction against the spring element 4 and reduces the working volume 5, so that the working medium 7 is pressurized and flows out through the outlet 8 against a final pressure. An outflow through the inlet 6 is prevented, e.g. by a one-way valve. In the opposite direction, backward or in the direction of the spring element 4, the lifting body 23 elastically compresses the spring element 4 and increases the working volume 5, so that a negative pressure is created there. The negative pressure, in turn, causes the working medium 7 to flow in through the inlet 6 against an intake pressure. An inflow through the outlet 8 is prevented, e.g. by a one-way valve. The inlet 6 and the outlet 8 can, for example, both be arranged on a valve plate 2A on the front side of the cylinder 2.

[0055] The control of the linear compressor shown in Fig. 1 and the linear compressor shown in Fig. 6 is explained with reference to Fig. 2A - 5. The positions x, xo and reversal points x + ,max, x-,max of the stroke body refer to the front of the movable piston 3 with respect to the linear compressor 1 according to Fig.1, and to the cylinder bottom 21 of the movable cylinder 2' with respect to the linear compressor T according to Fig.6.

[0056] At a fixed or predetermined operating frequency f w an upper or front reversal point x+ results for the lifting body 23, max and a lower or rear reversal point x-,max, which depend on the amplitude of the current i or current curve i~ impressed into the drive magnet 9 or the drive coil 9A, respectively. The greater the current amplitude, the further the lifting body 23 tends to be deflected from its unloaded rest position xo. This results in the effect that even with symmetrical excitation, as shown, for example, in Fig. 2A, the deflection of the lifting body 23 forward at the front reversal point x+ max is smaller than backward at the rear reversal point x. m ax, i.e. in absolute values ​​|x.,max - Xo| > |x + , m ax - Xo| applies. This effect of asymmetric deflection, even with symmetrical excitation, is caused by the working medium 7 located in the working volume 5, which exerts a force on the lifting body 23 that is opposite to the movement of the lifting body 23. At the front reversal point x+, mAt ax, a dead volume 5A remains from the working volume 5. The dead volume 5A also includes residual volume around inlet 6 and outlet 8. It is not mandatory that there be a distance between the front reversal point x+, max and the stop or valve plate 2A. Rather, in a further development, the valve plate 2A can even be touched, since it has been shown that touching the valve plate 2A does not lead to a defect in the entire system.

[0057] Fig. 2B shows this effect by plotting a displacement x of the lifting body from its rest position x0 over time under symmetrical excitation according to Fig. 2A. Fig. 2A shows that the impressed sinusoidal current i or current curve i~ has a positive current amplitude A+, which has the same absolute value as the negative current amplitude A_, namely approximately 0.6 A. The displacement x of the lifting body 2 shown in Fig. 2B is nevertheless asymmetric, namely such that the lifting body 23 moves from the rest position x0 forward to the front reversal point x+, ma x is deflected by approximately 1.9 mm and backwards to the rear reversal point x., ma x is deflected by approximately 4.1 mm, i.e., by approximately or even more than twice the forward deflection. The dynamic center or equilibrium position x g , s of the lifting body 23 is then approx. [1.9 mm + (- 4.1 mm)] / 2 = approx. - 1.1 mm.

[0058] Specifically, the current i impressed into the drive magnet 9 or the drive coil 9A can be adjusted by appropriately designing the alternating voltage U~ so that the front reversal point x+, ma x a certain setpoint x+, ma x ref . A possible block diagram for such a current supply or control of the linear compressor 1 is shown in Fig.3:

[0059] For example, a control device (not shown) of a household appliance H having the linear compressor 1 determines a front target reversing position x+, ma x ref specified, e.g. based on a certain operating frequency f w and a desired cooling capacity. The front target reversing position x+, ma x ref is used together with a measured or observed actual reversal position x+, max is input into an "amplitude controller" 10, which can be configured, for example, as a PI or PID controller. The amplitude controller 10 outputs the target current amplitude A, which should be required to reach the target reversal position x+, ma x ref to reach.

[0060] The target current value amplitude A is determined together with the desired operating frequency f w fed into a sine generator 11, which generates a sinusoidal current setpoint curve i~ ref with A+ = A, A. = -A and the frequency f w and outputs it to a current controller 12. The current controller 12 compares the current setpoint curve i~ re f with a measured (actual) curve i~ of the impressed current i and outputs a corresponding voltage signal as a manipulated variable for feeding into the drive coil 9, if necessary via a PWM module (not shown). The current controller 12 can be designed, for example, as a PI or PID controller.

[0061] By means of a feedback device 13 (e.g. in the form of an observer or a measuring device), the reconstructed or measured actual reversal position x+, ma x is fed back to the amplitude controller 10.

[0062] Fig. 4A shows an asymmetric current flow or an imprinting of a current i with amplitude values ​​A+ and A- asymmetric with respect to the zero point. Specifically, A. > A+ with A+ at approximately 0.5 A and A. at approximately -0.9 A. The positive amplitude value A+ therefore corresponds approximately to the positive amplitude value A+ with symmetric current flow and is only slightly lower because the effect has been taken into account that with asymmetric current flow the amplitude value A+ can drop slightly, since more energy is transferred into the spring 4 towards the rear reversal point x. ma x is introduced. The equilibrium position x g , aThe current curve is now no longer zero, but approximately -1.9 to -0.2 A.

[0063] Fig.4B shows the effect of the asymmetric excitation or current supply according to Fig.4A by plotting a displacement x of the lifting body from its rest position xo over time. While the front reversal point x+, ma x remains at approximately 1.9 mm, the rear reversal point x., ma x is now approximately -6 mm. The dynamic center or equilibrium position Xg, a of the lifting body 23 is now approximately -2 mm. The dead volume 5A thus remains at least approximately the same, while the intake path is noticeably increased by an additional intake path Ax. of approximately 1.9 mm.

[0064] A possible block diagram for such a power supply or control of the linear compressor 1 is shown in Fig. 5. It is based on the control shown in Fig. 3 with the blocks or functional sections 10 to 14, but additionally has blocks 15 to 18.

[0065] If additional cooling capacity is required, a desired additional intake path Ax is entered into block 15. For example, in Fig. 4B, this distance is approximately 1.9 to 2 mm. Block 15 calculates the required (additional) force F based on the spring constant kf of spring 4 and passes this value on to block 16.

[0066] In block 16, the required additional force and the known motor constant k m of the linear compressor 1, the required additional direct current component Ai is determined and halved in block 16 to obtain the additional current value AA = Ai / 2.

[0067] The additional current value AA can optionally be subjected to a gradient limitation in block 17.

[0068] The additional current value AA is then added to the target current value amplitude A output by block 10, so that a more symmetrical current curve i~ ref with amplitudes A+ and A increased by AA.

[0069] The additional current value AA is also subtracted from the current setpoint curve i~ ref output by block 11 as a DC component, so that the equilibrium position drops by AA compared to the symmetrical current supply. Overall, this results in a positive amplitude A+ that is the same as with the symmetrical current supply and a negative amplitude A that is increased by 2 AA. As a result, the front reversal point x+ max remains the same, while the intake path to the rear reversal point x. ma x increases noticeably, and with it the conveyed mass flow of the working fluid 7.

[0070] The blocks do not need to be understood as hardware or software units, but can be implemented in any functionally analogous manner, e.g., as a computer program product. The blocks can be understood as process steps or process sections.

[0071] Of course, the present invention is not limited to the embodiment shown.

[0072] In general, "a", "an", etc., can be understood as a singular or a plural, in particular in the sense of "at least one" or "one or more", etc., as long as this is not explicitly excluded, e.g. by the expression "exactly one", etc. A numerical specification can also include exactly the specified number as well as a usual tolerance range, as long as this is not explicitly excluded.

[0073] Fig. 6 shows a sectional side view of a sketch of an alternative possible linear compressor T. The linear compressor T has a cylinder 2' within a housing 20' of the linear compressor T, which cylinder, as indicated by the double arrow, is linearly displaceable relative to the piston 3', which is rigidly connected to the housing 20'. A side wall of the cylinder 2' and a cylinder base 21 act as movable walls, together with a front side of the piston 3' as an immovable wall, delimiting a working volume 5. The cylinder 2' is provided with permanent magnets 3A which are arranged on a cylinder frame 22. The cylinder frame 22 extends the cylinder 2' beyond the cylinder base 21 relative to the working volume. The cylinder 2' is hinged to the housing 20' by means of the cylinder frame 22 via a spring element 4. During operation, the cylinder 2' moves as a lifting body 23 relative to the piston 3' as a stationary component.A unidirectional inlet 6 opens into the working volume 5, through which a working medium 7 can flow into the working volume 5, and a unidirectional outlet 8, through which the working medium 7 can flow out of the working volume 5. The linear compressor 1 also has an electromagnet or drive magnet 9 arranged outside the housing 20'. The drive magnet 9 has a drive coil 9A, which is typically operated on the basis of a possibly pulsed alternating voltage U~, and a stator 9B made of magnetic material, e.g., sheet steel segments. The operated drive magnet 9 exerts a magnetic force on the permanent magnets 3A' of the cylinder 2', whereby the lifting body 23 is excited to a linear oscillating movement relative to the rigid piston 3'. With a constant alternating voltage U~, a back and forth movement of the lifting body 23 occurs at a specific oscillation or operating frequency f. wwhich at least approximately corresponds to the voltage frequency of the alternating voltage U~. In particular, the operating frequency f w a resonance frequency f res of a vibration system comprising at least the lifting body 23 and the spring element 4.

[0074] The oscillating cylinder 2 elastically expands the spring element 4 as it moves forward or against the spring element 4 and reduces the working volume 5, so that the working medium 7 is pressurized and flows out through the outlet 8 against a final pressure. Outflow through the inlet 6 is prevented, e.g., by a one-way valve. In the opposite direction, backward or towards the spring element 4, the cylinder 2 elastically compresses the spring element 4 and increases the working volume 5, so that a negative pressure is created there. The negative pressure, in turn, causes the working medium 7 to flow in through the inlet 6 against an intake pressure. Inflow through the outlet 8 is prevented, e.g., by a one-way valve. The inlet 6 and the outlet 8 can, for example, both be arranged on a valve plate 2A on the front side of the piston 3'.

[0075] List of reference symbols

[0076] 1, T Linear compressor

[0077] 2, 2' cylinder

[0078] 2a Valve plate

[0079] 3, 3' pistons

[0080] 3A permanent magnet

[0081] 4 spring element

[0082] 5 Working volume

[0083] 5A dead volume

[0084] 6 Entrance

[0085] 7 Working medium

[0086] 8 Outlet

[0087] 9 Drive magnet

[0088] 9A drive coil

[0089] 9B Stator

[0090] 10 amplitude controls

[0091] 11 Sine generator

[0092] 12 current regulators

[0093] 13 Return facility

[0094] 14-17 Function or process blocks for asymmetric power supply

[0095] 20, 20' housing

[0096] 21 Cylinder base

[0097] 22 cylinder frames

[0098] 23 lifting bodies

[0099] A Target current value amplitude

[0100] A+ Positive current amplitude

[0101] A. Negative current amplitude

[0102] AA additional current value

[0103] F force f w Working frequency

[0104] H household appliance i electricity i g , s Equilibrium position of the current flow with symmetrical current supply i g ,a Equilibrium position of the current curve with asymmetric current supply i~ Current curve i~ ref Target current curve

[0105] Ai Additional DC component t Time

[0106] U~ alternating voltage x deflection of the lifting body

[0107] Xg, s Equilibrium position of the deflection with symmetrical current supply

[0108] Xg, a Equilibrium position during the deflection of asymmetric current supply x+,max Front reversal point of the lifting body x+,max ref Front target reversal point of the lifting body x.,max Rear reversal point of the lifting body xo Rest position of the lifting body

[0109] Ax. Additional intake path

Claims

Patent claims 1. Method for operating a linear compressor (1 , T) of a household appliance (H), in which - at least from a front target reversing position (x+, ma x ref) of a piston (3) or cylinder (2') as a lifting body (23) of the linear compressor (1 , T) and a front actual reversing position (x+, ma x) of the lifting body (23) a desired current curve (i~ re f) an electric current (i) to be impressed into a drive coil (9A) of the linear compressor (1 , T) is calculated, - a current (i) to be impressed into the drive coil (9A) is controlled by means of the desired current curve (i~ref) and an actual current curve (i~) and - at least the front actual reversing position (x+, ma x) is estimated by an observer or measured by a sensor.

2. Method according to claim 1, in which a movement of the lifting body (23) is estimated or measured by an observer and from this at least the front actual reversal position (x+, ma x) is determined.

3. Method according to one of the preceding claims, in which additionally a rear actual reversing position (x+, ma x) is estimated by an observer or measured by a sensor.

4. Method according to one of the preceding claims, in which - at least from the front target reversing position (x+, ma x ref) and the front actual reversal position (x+, ma x) a target current value amplitude (A) is calculated and - from the target current value amplitude (A) and a desired operating frequency (f w ) of the lifting body (23) the desired current curve (i~ re f) is calculated.

5. The method according to claim 3, wherein - an additional current value (AA) is added to the current target value amplitude (A) and - the target current curve (i~ re f) is reduced by the additional current value (AA).

6. The method according to claim 5, wherein - for a desired additional deflection (Ax.) of the lifting body (23) to the rear, a necessary mechanical force (F) on the lifting body (23) is calculated and - the additional current value (AA) required to achieve the desired additional deflection (Ax.) of the lifting body (23) is calculated from the mechanical force (F).

7. Method according to claim 6, wherein the additional current value (AA) is gradient-limited.

8. Method according to one of the preceding claims, in which the front actual reversing position (x+, ma x) of the lifting body (23) is estimated by means of a Luenberger observer.

9. Method according to one of claims 1 to 7, wherein the front actual reversal position (x+,max) of the lifting body (23) is measured by means of laser radiation.

10. Method according to one of claims 3 to 9, wherein the linear compressor (1, T) is operated in an operating mode without additional current value (AA) and is operated in at least one other operating mode with additional current value (AA).

11. Linear compressor (1, T) of a household appliance (H), wherein the linear compressor (1, T) is designed to carry out the method according to one of the preceding claims.

12. Linear compressor (1) according to claim 11, wherein a piston (3) as a lifting body (23) is movable and drivable relative to a cylinder (2) as a stationary component.

13. Linear compressor (T) according to claim 11, wherein a cylinder (2') as a lifting body is movable and drivable relative to a piston (3') as a stationary component.

14. Household appliance (H) with a linear compressor (1, T), wherein the household appliance (H) is designed to carry out the method according to one of claims 1 to 8.

15. Household appliance (H) according to claim 14, wherein the household appliance (H) is a refrigerator, a dishwasher or a laundry treatment appliance.

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