Operating a linear compressor in a household appliance

Abstract

The invention relates to a method (10-17) for operating a linear compressor (1) of a household appliance (H), in which a target reversal position of a front reversal point (x) is used. +,max ref ) of a piston (3) of the linear compressor (1) and a front actual reversal position (x +,max ) of the piston a target flow profile (i ~ ref ) of an electric current (i) to be impressed into a drive coil (9A) of the linear compressor (1) is calculated, a current (i) to be impressed into the drive coil (9A) is calculated using the target current profile (i ~ ref ) and an actual current waveform (i ~ ) is regulated and the front actual reversal position (x +,maxThe invention also relates to a linear compressor (1) of a household appliance (H) configured to perform the method (10-17). The invention further relates to a household appliance (H) with a linear compressor (1), wherein the household appliance (H) is configured to perform the method (10-17). The invention is particularly advantageously applicable to cooling appliances such as refrigerators, freezers, or combinations thereof.

Description

[0001] 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. Furthermore, the invention relates to a household appliance with such a linear compressor. The invention is particularly advantageously applicable to cooling appliances such as refrigerators, freezers, or combinations thereof.

[0002] Refrigeration devices are known that use a linear compressor as the drive for their refrigeration circuit. The linear compressor has a linearly driven piston whose front face forms an end face of a working volume filled with working fluid. An inlet and an outlet for the working fluid are located on the opposite end face of the working volume. When the piston moves towards the opposite end face ("forward"), the working volume is compressed so that the working fluid is forced out of the outlet but does not flow through the inlet. A gap remains between the front face of the piston and the opposite end face (also referred to as the "valve plate") to prevent mechanical contact between them. At the piston's maximum forward deflection, which corresponds to the smallest distance to the opposite end face, a so-called...A "dead volume" exists. When the piston moves in the opposite direction, away from the opposite end face ("backwards"), the working volume expands, so that the working fluid is drawn in through the inlet but does not flow through the outlet. Therefore, by moving the piston back and forth, the working fluid can be moved through a working fluid circuit connected to the inlet and outlet. A corresponding alternating voltage signal is applied to an electromagnet that drives the piston to initiate its movement.

[0003] To achieve high efficiency in the linear compressor, the dead volume is kept as low as possible, and consequently, the maximum forward deflection of the piston (also known as the "forward reversal point") is minimized while avoiding contact. Selecting a suitable initial or rest position of the piston relative to the valve plate is crucial. The rest position significantly influences the compressor's achievable cooling capacity. Specifically, the rest position is chosen to achieve a predetermined maximum cooling capacity, or "limit capacity," under symmetrical power supply or control, at which the dead volume is minimal. However, this limit capacity is rarely reached in practice.For lower cooling capacities, which are more frequently required in practice, the level of the AC voltage signal can be reduced, which means that the piston at the front reversal point no longer comes as close to the valve plate and consequently reduces efficiency due to the increased dead volume.

[0004] The object of the present invention is to overcome at least some of the disadvantages of the prior art and, in particular, to provide a particularly efficient way of operating a linear compressor of a household appliance.

[0005] This problem is solved according to the features of the independent claims. Preferred embodiments can be found in particular in the dependent claims.

[0006] The problem is solved by a method for operating a linear compressor of a household appliance, in which - at least from a target reversal position of a front or upper reversal point of a piston of the linear compressor (also denoted as "front target reversal position") and a front actual reversal position of the piston, a target current (value) profile of an electric current to be impressed into a drive coil of the linear compressor is calculated, - a current or current profile to be impressed into the drive coil is controlled by means of the target current profile and an actual current profile, in particular a comparison thereof and - at least the forward actual reversal position is estimated or measured by an observer.

[0007] This method offers the advantage that the movement of the piston can be controlled to its forward target reversal position, thus firstly making this target reversal position particularly easy to achieve, which enables high efficiency even under changing boundary conditions such as temperatures of the working fluid, at the inlet and / or at the outlet, etc., and secondly preventing the piston from striking the valve plate with particular reliability.

[0008] The linear compressor drives a working fluid circulating in a closed loop. This loop can be a refrigeration cycle or a heat pump cycle. In addition to the linear compressor, the loop can include at least one evaporator, at least one expansion fluid, and at least one condenser, all in a generally known manner.

[0009] The household appliance can be a refrigeration appliance. For example, a refrigerator, a freezer, or a combination of both. The household appliance can also be a laundry treatment appliance equipped with a heat pump, such as a washing machine, a tumble dryer, a combination of both, or a dishwasher.

[0010] The piston of the linear compressor is mounted for longitudinal displacement within a cylindrical piston housing and connected to the housing by at least one elastic spring element. The piston, equipped with at least one permanent magnet, is typically driven and set into oscillation by the magnetic field of at least one electromagnet equipped with at least one coil ("drive coil") powered by an alternating electrical voltage. Depending on the direction of movement, a working volume limited by the piston housing and an end face of the piston is increased or decreased. The linear compressor can also be considered a linear motor, whose piston corresponds to the rotor or "mover." The basic operating principle of a linear compressor in a refrigeration circuit or heat pump circuit of a refrigeration unit is well-known and therefore will not be described further here.

[0011] The target current waveform is, in particular, a sinusoidal current waveform, defined by its amplitude and frequency (which corresponds to the piston's operating frequency). 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 control variable for current regulation. This current regulation is then, in particular, interlocked or linked with the (amplitude) control for regulating the piston's forward reversal position. The fact that the current or current waveform applied to the drive coil is regulated by means of the target current waveform and an actual current waveform can include the direct application of the control to the current waveforms.Alternatively or additionally, the current or current waveform to be applied to the drive coil can be indirectly controlled by means of the corresponding manipulated variable, namely the voltage applied to the drive coil. Control via this voltage can be generally used in the following, even if this is not explicitly stated.

[0012] The estimation of the forward current reversal position by an observer can involve reconstructing or estimating it from known input variables (e.g., measurable disturbances) and output variables (e.g., manipulated variables and / or measured variables) of an observed reference system. For this purpose, the observed reference system may, for example, have been modeled and a controller may be used to adjust the measurable state variables, which are therefore comparable to the reference system. Possible input variables to the observer can include, for example, at least the measured current and / or an output voltage or excitation voltage applied to the drive coil and / or an excitation or operating frequency.

[0013] Measuring the front actual reversal position can involve measuring it directly or deriving it from other measured quantities.

[0014] The fact that the target current (value) profile is calculated "at least" from the target forward reversal position and the actual forward reversal position can, for example, include the possibility of calculating the target current profile additionally based on further target and / or actual positions. Similarly, the corresponding actual position can then also be estimated or measured by an observer.

[0015] One configuration involves an additional "rear" actual reversal position, corresponding to the rear or lower reversal point of the piston, which is estimated or measured by an observer. This rear actual reversal position can then be used, for example, to calculate the total piston stroke between the two reversal points and, from this, the internal pressure difference, etc.

[0016] It is a further development that, in addition, at least one reference position lying between the two reversal positions is estimated or measured by an observer.

[0017] This configuration involves an observer estimating or measuring the movement or position profile of the piston and determining at least the front actual reversal position, and optionally also the rear actual reversal position and / or at least one reference position of the piston. 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, and so on. In particular, the piston's position can be estimated or measured at a constant measurement or sampling rate. In a further development, the profile can be a curve fitted to the estimated or measured positions.

[0018] This configuration calculates an amplitude ("target current amplitude") from at least the forward target reversal position and the forward actual reversal position, and then calculates the target current profile from this target current amplitude and a desired target operating frequency of the piston. This is advantageously very easy to implement and results in robust control. The target operating frequency can, in principle, be set arbitrarily. It can, for example, correspond to the resonant frequency, i.e., the operating frequency at which the piston (with the same current amplitude) can be deflected furthest from its unpowered rest position. However, it can also correspond to a frequency that is, for example, higher or lower than the resonant frequency. This configuration can be implemented, for example, using a sine wave generator, which generates the target current value, for example, in a sinusoidal waveform.The target current profile is calculated or generated from the specified parameters target current value amplitude and target operating frequency.

[0019] It is a further development that the calculation of the target current value amplitude is also based on the rear target reversal position and the rear actual reversal position, which has the advantage that the internal pressure difference and thus the cooling capacity can be determined particularly accurately.

[0020] It is a further development that the current or current waveform to be applied to the drive coil is generated by a pulsed voltage. In this further development, a (general) sinusoidal current waveform output by the sine wave generator can be converted into a corresponding pulsed voltage waveform by means of a PWM element acting as the actuator. This can include the possibility that the first and second half-cycles of the current can be of different lengths – even between different periods – while the period remains 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 remains the same.

[0021] Alternatively or additionally, the current profile can be generated from any harmonics of the fundamental frequency. This has the advantage that the pressure pulses due to the discontinuous movement of the inlet and outlet valves can be minimized, which can also lead to higher efficiency.

[0022] One configuration 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 flow into an asymmetrical target current curve or asymmetrical current flow with respect to zero. The asymmetrical target current curve remains sinusoidal or similar, corresponding to the set operating frequency. However, compared to the symmetrical current flow, the absolute value of the positive and negative amplitudes of the target current curve relative to the equilibrium position is increased by the additional current value, while the average or equilibrium value of the target current curve is decreased by this additional current value. This advantageously ensures that the positive amplitude of the target current curve remains constant for the forward movement of the piston.This is due to the pre-calculated, controlled flow pattern; additionally, the upper amplitude control remains active. Thus, the distance between the piston and the valve plate remains constant at the piston's forward reversal position. However, the negative amplitude of the target flow pattern for the rearward deflection is significantly increased. Consequently, the piston's intake path is considerably extended, thereby increasing the volume flow of the working fluid and, in turn, the cooling capacity. While this may be less energy-efficient than operation with symmetrical flow, it allows for an increase in cooling capacity, which is particularly useful for relatively short cooling phases requiring increased cooling capacity, for example, after switching on a cooling unit, activating a "supercool" mode, etc.This, in turn, helps to dimension the unit so that the influence of the dead volume ("clearance volume") and the associated losses are kept to a minimum for the specified, normally continuously required cooling capacity. Therefore, a particular advantage for a refrigeration unit is that the cooling capacity can be temporarily increased by operating a linear compressor asymmetrically.

[0023] For example, in the case of symmetrical current flow, the positive amplitude A + of the target current profile at a value A > 0 and the negative amplitude A - At a value of -A, the equilibrium position of the current flow is i. ~ at (A + + A - ) / 2 = (A + (-A)) / 2 = 0. If the additional current value ΔA > 0 is added during asymmetrical current supply, the amplitudes A are + = A + ΔA and A -= - (A + ΔA). By lowering the equilibrium position by ΔA, the amplitudes then lie at A. + = A and A - = - (A + 2·ΔA) and the equilibrium position is at (A - A - 2·ΔA) / 2 = -ΔA. The positive forward amplitude A + With asymmetrical current flow, it therefore remains the same, while the negative backward amplitude A changes. - The additional current value is increased by twice, and the piston is therefore deflected correspondingly further backwards.

[0024] This design involves calculating the necessary mechanical force on the piston for a desired additional rearward deflection (i.e., away from the valve plate). From this mechanical force, the additional flow rate required to achieve the desired piston deflection is calculated. This offers the advantage of quick and precise adjustment of the additional cooling capacity with minimal effort. The additional rearward deflection can also be described as an additional intake path. The mechanical force F f For example, the spring constant k can be used to determine the spring constant k f the elastic spring articulated to the piston according to F f = k f · Δx - with Δx - The additional intake path to the rear is calculated. The mechanical force F f can the force F m equated to the force that the drive magnet must exert on the piston to move it by Δx -to deflect additionally. From F m = k m · Δi with k m The motor constant and Δi > 0, the additional DC component, Δi can be calculated according to Δi = (k f / k m ) · Δx - Calculate. The additional current value ΔA can then be calculated as ΔA = Δi / 2.

[0025] One embodiment involves applying the additional current value with a limited gradient, i.e., not abruptly or suddenly at its full value. This advantageously results in the piston oscillation adapting more smoothly to the additional current value. The gradient limitation can, for example, involve increasing the additional current value with a limited, particularly constant, gradient. A further development involves applying the additional current value with a limited gradient by increasing it in stages, particularly by means of inclined steps with a specific gradient. Another development involves reducing the additional current value with a limited gradient, i.e., not suddenly at its full value. This can be done analogously to the gradient-limited application. A further development involves applying the additional current value continuously, i.e., without noticeable jumps.

[0026] One implementation involves estimating the piston's forward actual reversal position using a Luenberger observer. Alternatively, the piston's forward actual reversal position can be estimated using a flux estimator, a so-called "sliding-mode" observer, a Kalman filter, etc. These alternatives can each be combined with nonlinear characteristic maps of the machine parameters in a further development.

[0027] One configuration involves measuring at least the front actual reversal position of the piston using laser radiation. Alternatively, the front actual reversal position can be measured using a position reference sensor. Other actual positions of the piston can also be measured accordingly.

[0028] One configuration involves operating the linear compressor in one mode without an additional current value and in at least one other mode with an additional current value. This advantageously allows for simple, low-wear, and rapid switching between a particularly efficient operating mode without utilizing the additional current value and an operating mode utilizing the additional current value for increased cooling capacity. A further development enables the linear compressor to operate in multiple modes with an additional current value, each distinguished by different additional current values ​​and thus different additional cooling capacities. Generally, the additional cooling capacity can be set as desired within possible operating parameters, e.g., continuously or quasi-continuously.

[0029] The task can also be accomplished using a linear compressor from a household appliance, where the linear compressor is configured to perform the procedure as described above. The linear compressor can be designed analogously to the procedure, and vice versa, and offers the same advantages.

[0030] The linear compressor can include a control unit as a component, which is configured, for example, programmed to implement the procedure described above. The linear compressor itself and the control unit can also be considered together as a compressor module. The control unit can be digitally linked to a control device of the household appliance, which, for example, can output a signal to switch between different operating modes.

[0031] The problem is further solved 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.

[0032] One embodiment of the invention involves the household appliance being a cooling appliance, such as a refrigerator, freezer, or a combination thereof. The working medium can then also be referred to as a cooling medium or refrigerant. However, the household appliance is not limited to this and can, for example, use the linear compressor to drive a heat pump. In this case, the description of the invention can be applied analogously to a cooling appliance or cooling circuit.

[0033] The properties, features and advantages of this invention described above, as well as the manner in which they are achieved, will become clearer and more easily understood in connection with the following schematic description of an exemplary embodiment, which will be explained in more detail in conjunction with the drawings. Fig. Figure 1 shows a sketch of a possible linear compressor in a sectional view in side view; Fig. Figure 2A shows a schematic plot of a target current impressed into a drive coil of the linear compressor against time with sinusoidal symmetrical current flow; Fig. Figure 2B shows a schematic plot of the displacement of the piston of the linear compressor against time under sinusoidal symmetrical current flow according to Fig. 2A; Fig. Figure 3 shows a possible block diagram for a symmetrical power supply to the linear compressor; Fig. Figure 4A shows a schematic plot of a target current impressed into a drive coil of the linear compressor against time under sinusoidal asymmetric current; Fig. Figure 4B shows a schematic plot of the displacement of the piston of the linear compressor against time under sinusoidal asymmetric current flow according to Fig. 4A; and Fig. Figure 5 shows a possible block diagram for an asymmetrical current supply to the linear compressor.

[0034] Fig. Figure 1 shows a sketch of a possible linear compressor 1 in a sectional side view. The linear compressor 1 has a piston 3, equipped with permanent magnets 3A, which is linearly displaceable within a housing 2, as indicated by the double arrow. The rear of the piston is articulated to the housing 2 via a spring element 4, and the front of the piston defines a working volume 5. A unidirectional inlet 6, through which 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, open into the working volume 5. The linear compressor 1 also has an electromagnet or drive magnet 9 arranged outside the housing 2. The drive magnet 9 has a drive coil 9A, which is typically driven by an alternating voltage U, which may be pulsed. ~The drive magnet 9 is operated by a stator 9B made of magnetic material, e.g., sheet steel segments. The driven drive magnet 9 exerts a magnetic force on the permanent magnets 3A of the piston 2, thereby exciting the piston 3 to a linear oscillating motion within the housing 2. With a constant alternating voltage U ~ This results in a back-and-forth movement of the piston 3 at a specific oscillation or operating frequency f. w one that corresponds to the voltage frequency of the alternating voltage U ~ at least approximately corresponds. In particular, the operating frequency f w a resonant frequency f res a vibration system comprising at least the piston 3 and the spring element 4.

[0035] The oscillating piston 3 elastically expands the spring element 4 when moving forward, i.e., towards the spring element 4, and reduces the working volume 5. This pressurizes the working medium 7, causing it to flow out through the outlet 8 against a final pressure. Flow through the inlet 6 is prevented, for example, by a one-way valve. In the opposite direction, moving backward, i.e., towards the spring element 4, the piston 3 elastically compresses the spring element 4 and increases the working volume 5, creating a vacuum. This vacuum, in turn, causes the working medium 7 to flow in through the inlet 6 against a suction pressure. Flow through the outlet 8 is prevented, for example, by a one-way valve. The inlet 6 and the outlet 8 can both be arranged, for example, on a front-mounted valve plate 2A.

[0036] At a fixed or predetermined operating frequency f wThis results in an upper or front reversal point x for piston 3. +,max as well as a lower or rear reversal point x -,max , which is determined by the amplitude of the current i impressed into the drive magnet 9 or into the drive coil 9A or current waveform i ~ depend. The larger the current amplitude, the further the piston 3 tends to be deflected from its unloaded rest position x0. The effect occurs that even with symmetrical excitation, as e.g. in Fig. Figure 2A shows the forward deflection of piston 2 at the forward reversal point x. +,max is smaller than at the rear turning point x -,max , also in absolute values ​​|x -,max - x0| > |x +,max- x0| applies. This effect of an asymmetrical displacement, even with symmetrical excitation, is caused by the working medium 7 located in the working volume 5, which exerts a force on piston 3 that opposes the movement of piston 2. At the front reversal point x +,max Of the working volume 5, a dead volume 5A remains. 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. Furthermore, in a further development, valve plate 2A can even be touched, as it has been shown that touching valve plate 2A does not lead to a defect in the overall system.

[0037] Fig. Figure 2B shows this effect by plotting a piston displacement x from its rest position x0 over time with symmetrical excitation according to Fig. 2A. Fig. 2A shows that the impressed sinusoidal current i or current waveform i ~ a positive current amplitude A + exhibits a value that has the same absolute value as the negative current amplitude A - , namely approximately 0.6 A each. The in Fig. The deflection x of piston 2 shown in 2B is nevertheless asymmetrical, namely such that piston 3 moves forward from the rest position x0 to the forward reversal point x +,max is deflected by approximately 1.9 mm and backwards to the rear reversal point x -,max It is deflected by approximately 4.1 mm in absolute terms, which is roughly or even more than twice the forward deflection. The dynamic mean or equilibrium position x g,s The diameter of piston 2 is then approximately [1.9 mm + (- 4.1 mm)] / 2 = approximately - 1.1 mm.

[0038] Specifically, the current i impressed into the drive magnet 9 or the drive coil 9A can be controlled by appropriately designing the alternating voltage U. ~so that the front reversal point x +,max a specific target value x +, max ref This corresponds to a possible block diagram for such an energizing or control of the linear compressor 1 is shown in Fig. 3 shown: For example, a front target reversal position x is set by a control unit (not shown) of a household appliance H having a linear compressor 1. +, max ref specified, e.g. based on a specific operating frequency f w and a desired cooling capacity. The front target reversal position x +, max ref is combined with a measured or observed actual reversal position x +, max The input is fed into an "amplitude controller" 10, which can be configured, for example, as a PL or PID controller. The amplitude controller 10 outputs the target current amplitude A as its output, which should be required to achieve the desired reversal position x. +, max ref to reach.

[0039] The target current amplitude A is determined together with the desired operating frequency f. w fed into a sine wave generator 11, which generates, for example, a sinusoidal current setpoint curve i. ~ ref with A + = A, A - = -A and the frequency f w The current is generated and output to a current controller 12. The current controller 12 compares the current setpoint curve i. ~ ref with a measured (actual) trend i ~ The current controller 12 measures the applied current i and outputs a corresponding voltage signal as a control variable for injection into the drive coil 9, optionally via a PWM module (not shown). The current controller 12 can, for example, be configured as a PL or PID controller.

[0040] 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 is determined. +, max fed back to the amplitude controller 10.

[0041] Fig. 4A shows an asymmetric current or an imprint of a current i with amplitude values ​​A that are asymmetric with respect to the zero point. + and A-. Specifically, the amount of A is... - > A + with A + at approximately 0.5 A and A - at approximately -0.9 A. The positive amplitude value A + This corresponds approximately to the positive amplitude value A. + with symmetrical current flow and is only slightly lower because the effect that the amplitude value A is lower with asymmetrical current flow has been taken into account. + It can sink slightly, as more energy is transferred to spring 4 in the direction of the rear reversal point x. -,max is introduced. The equilibrium position x g,a The current curve is no longer at zero, but at approximately -1.9 to -0.2 A.

[0042] Fig. Figure 4B shows, using a plot of a piston displacement x from its rest position x0 over time, the effect of the asymmetric excitation or current application according to Fig. 4A. While the front reversal point x +,max The rear reversal point x remains at approximately 1.9 mm. -,max now at approximately -6 mm. The dynamic mean or equilibrium position x g,a The displacement of piston 2 is now approximately -2 mm. The dead volume 5A therefore remains at least roughly the same, while the intake path is increased by an additional intake path Δx. - is noticeably increased by approximately 1.9 mm.

[0043] A possible block diagram for such an energizing or control system for the linear compressor 1 is shown in Fig. 5 shown. It builds on the one in Fig. The regulation shown in Figure 3 has blocks or functional sections 10 to 14, but also includes blocks 15 to 18.

[0044] In block 15, a desired additional intake path Δx is added if additional cooling capacity is required. - entered, regarding the Fig. 4B, for example, has a magnitude of approximately 1.9 to 2 mm. Block 15 calculates this using the spring constant k. f The spring 4 provides the required (additional) force F and passes this on to block 16.

[0045] In block 16, the required additional force and the known motor constant k are used to calculate m The required additional DC component Δi of the linear compressor 1 is determined and halved in block 16 to obtain the additional current value ΔA = Δi / 2.

[0046] The additional current value ΔA can optionally be subjected to a slope limitation in block 17.

[0047] The additional current value ΔA is then added to the target current value amplitude A output by block 10, resulting in a still symmetrical current waveform i. ~ refwith amplitudes increased in magnitude by ΔA A + and A - results.

[0048] The additional current value ΔA is also determined by the current setpoint curve i output by block 11. ~ ref The DC component is subtracted, causing the equilibrium position to drop by ΔA compared to symmetrical current. Overall, this results in the same positive amplitude A as with symmetrical current. + and a negative amplitude A increased in absolute value by 2·ΔA - This means the front turning point remains x +,max same, while the intake path to the rear reversal point x -,max noticeably increases, and with it also the mass flow of the working fluid 7.

[0049] The blocks need not be understood as hardware or software units, but can be implemented in any functionally analogous way, e.g., as a computer program product. The blocks can be understood as process steps or process sections.

[0050] Of course, the present invention is not limited to the embodiment shown.

[0051] In general, “ein”, “eine”, etc. can be understood to mean singular or plural, especially in the sense of “at least one” or “one or more”, etc., unless this is explicitly excluded, e.g. by the expression “exactly one”, etc.

[0052] A numerical specification can also include exactly the specified number as well as a normal tolerance range, unless this is explicitly excluded. Reference symbol list 1 linear compressor 2 cases 2A Valve plate 3 pistons 3A Permanent Magnet 4 spring element 5 work volume 5A Dead volume 6 Admission 7 Working medium 8 Outlet 9 Drive magnet 9A drive coil 9B Stator 10 amplitude controllers 11 Sine wave generator 12 current regulators 13 Return device 14-17 Functional or sequence blocks for asymmetrical current supply A Target current value amplitude A + Positive current amplitude A - Negative current amplitude ΔA Additional current value F force f w Operating frequency H Household appliance i electricity i g,s Equilibrium position of the current flow under symmetrical current conditions i g,a Equilibrium position of the current flow under asymmetric current conditions i~ Current flow i ~ ref Target current profile Δi Additional DC component t time U ~ Alternating current x piston deflection x g,s Equilibrium position of the deflection under symmetrical current flow x g,a Equilibrium position during the deflection of asymmetric current x +,max Piston's forward reversal point x +,max ref Front target reversal point of the piston x -,max Rear reversal point of the piston x0 Piston rest position Δx - Additional intake path

Claims

[1] Method for operating a linear compressor (1) of a household appliance (H), in which - at least from a front target reversing position (x +,max ref ) of a piston (3) of the linear compressor (1) and a front actual reversing position (x +,max ) of the piston (3) a desired current curve (i ~ ref ) of an electric current (i) to be impressed into a drive coil (9A) of the linear compressor (1) is calculated, - a current (i) to be impressed into the drive coil (9A) by means of the desired current curve (i ~ ref ) and an actual current curve (i ~ ) and - at least the front actual reversing position (x +,max ) is estimated or measured by an observer. [2] Method according to claim 1, in which a movement of the piston (3) is estimated or measured by an observer and from this at least the front actual reversal position (x +,max ) is determined. [3] Method according to one of the preceding claims, in which additionally a rear actual reversing position (x +,max ) is estimated or measured by an observer. [4] Method according to one of the preceding claims, in which - at least from the front target reversing position (x +,max ref ) and the front actual reversing position (x +,max ) 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 piston (3) the desired current curve (i ~ ref ) is calculated. [5] Method according to claim 3, in which - an additional current value (ΔA) is added to the current target value amplitude (A) and - the target current curve (i ~ ref ) is reduced by the additional current value (ΔA). [6] Method according to claim 5, in which - for a desired additional deflection (Δx -) of the piston (3) backwards, a necessary mechanical force (F) on the piston (3) is calculated and - the additional current value (ΔA) is calculated from the mechanical force (F) which is required to achieve the desired additional deflection (Δx - ) of the piston (3). [7] Method according to claim 6, wherein the additional current value (ΔA) is gradient-limited. [8] Method according to one of the preceding claims, in which the front actual reversing position (x +,max ) of the piston (3) is estimated using a Luenberger observer. [9] Method according to one of claims 1 to 7, wherein the front actual reversing position (x +,max ) of the piston (3) is measured by means of laser radiation. [10] Method according to one of claims 3 to 9, wherein the linear compressor (1) is operated in an operating mode without additional current value (ΔA) and is operated in at least one other operating mode with additional current value (ΔA). [11] Linear compressor (1) of a household appliance (H), wherein the linear compressor (1) is designed to carry out the method according to one of the preceding claims. [12] Household appliance (H) with a linear compressor (1), wherein the household appliance (H) is designed to carry out the method according to one of claims 1 to 8. [13] Household appliance (H) according to claim 11, wherein the household appliance (H) is a refrigerator.

Images