Cooling device and method for operating a cooling device

Abstract

The invention relates to a cooling device (11) with a linear compressor (1) provided as a drive for a refrigeration circuit, which can be controlled by means of a control unit (10) so that it can be selectively operated at a first operating frequency (f w1 ) at the resonance frequency (f res ) of the linear compressor (1) can be operated or with a second operating frequency (f w2 ) below and disjoint from the resonance frequency (f res ) of the linear compressor (1). The invention also relates to a method for operating a cooling device (11) with a linear compressor (1) provided as a drive for a refrigeration circuit, in which the linear compressor (1) can be selectively operated at a first operating frequency (f w1 ) at its resonant frequency (f res ) is operated or with a second operating frequency (f w2 ) below and disjoint from the resonance frequency (f res) of the linear compressor (1). The invention is particularly advantageously applicable to household refrigerators.

Description

[0001] The invention relates to a refrigeration device with a linear compressor provided as a drive for a refrigeration circuit. The invention also relates to a method for operating a refrigeration device with a linear compressor provided as a drive for a refrigeration circuit. The invention is particularly advantageously applicable to household refrigeration devices.

[0002] It is well known that a linear compressor in a refrigeration device is designed for an operating frequency of its piston, or "mover," that corresponds to or is close to the resonant frequency of the linear compressor's oscillating system. If maximum (cooling) performance is required, the operating frequency must be set to the resonant frequency. On the other hand, if better efficiency is desired, it is better to set the operating frequency to a value other than the resonant frequency.

[0003] It is the object of the present invention to at least partially overcome the disadvantages of the prior art and in particular to provide an improved possibility of operating a cooling device of a linear compressor or a linear compressor of a cooling device.

[0004] 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 task is solved by a cooling device with a linear compressor provided as a drive of a refrigeration circuit, which can be selectively controlled by means of a control system so that it - can be operated with a first operating frequency at the resonance frequency of the linear compressor or - can be operated with a second operating frequency below and disjoint from the resonance frequency of the linear compressor.

[0006] This cooling device has the advantage that the linear compressor can be set to at least two significantly different operating frequencies or operating frequency bands (also referred to as "stages") during operation of the cooling device, each of which serves a different purpose. The first operating frequency is specifically intended for operating the linear compressor at maximum power, while the second operating frequency is specifically intended for efficient operation of the linear compressor. It is also possible to set or switch the linear compressor to three or more disjoint operating frequencies or operating frequency bands.

[0007] In one embodiment, the cooling device is a refrigerator, a freezer, or a combination thereof. The cooling device is, in particular, a household cooling device.

[0008] For example, in addition to the linear compressor, the refrigeration circuit may comprise at least one evaporator, at least one expansion medium and at least one condenser in a basically known manner.

[0009] The basic principle of operation of a linear compressor in a refrigeration circuit of a refrigeration appliance is well known. Typically, a piston is mounted for longitudinal displacement in a hollow cylindrical piston housing of the linear compressor and is pivoted by at least one elastic spring element. The piston, equipped with at least one permanent magnet, is driven by a magnetic field of at least one electromagnet (also known as a "drive magnet") powered by at least one alternating electrical voltage, thereby causing it to oscillate. Depending on the direction of movement, a working volume defined by the piston housing and an end face of the piston is increased or decreased. If the working volume is increased, refrigerant or working fluid is sucked into the working volume at an inlet from a refrigeration circuit connected to the working volume.If the working volume is then reduced again, the working fluid is forced into the refrigeration circuit at an outlet. The amplitude of the alternating voltage determines the piston stroke, which in turn determines the mass flow of the working fluid in the refrigeration circuit. In the steady state, the working or oscillation frequency of the piston is determined by the voltage frequency of the alternating voltage signal. The efficiency of the linear compressor depends on the voltage frequency and thus the working frequency. The linear compressor can also be viewed as a linear motor, with the piston corresponding to the rotor or "mover."

[0010] The control system is configured to adjust the oscillation or operating frequency of the piston, in particular selectively to the first operating frequency or the second operating frequency (generally also to other disjoint operating frequencies). The control system can, in particular, be implemented as a closed-loop control. The fact that a closed-loop control is implemented can be based on the fact that the operating frequency is then not simply adjusted, but can be adjusted using at least one feedback variable.

[0011] In a further development, the fact that the first operating frequency is at the resonant frequency means that the first operating frequency corresponds to or practically corresponds to the resonant frequency. The fact that the first operating frequency is at the resonant frequency can also mean that the first operating frequency corresponds to an operating frequency that is very close to the resonant frequency, e.g., within a band of ± 2 Hz or, even better, ± 1 Hz around the resonant frequency.

[0012] In one embodiment, the cooling device is designed to monitor a phase shift between an electrical voltage applied to the linear compressor and a current consumed by the linear compressor and to set the operating frequency to the first operating frequency by varying the operating frequency step by step until the target phase shift corresponding to the resonant frequency is reached. This advantageously enables a particularly simple implementation of setting the first operating frequency to the resonant frequency or at least approximating it as closely as possible. Furthermore, the particular advantage is achieved that this is also the case if the actual resonant frequency shifts with respect to a theoretical, pre-calculated value, e.g. due to environmental influences.

[0013] One embodiment assumes or is equal to 45° in magnitude for the target phase shift Δcp. This takes advantage of the fact that a phase angle between voltage and lagging current in the resonance case is typically -45° or 45° in magnitude, respectively, and in particular corresponds to a point of highest gradient with respect to a curve of Δφ in relation to the operating frequency. The phase shift Δφ can be calculated directly or derived from a curve of the phase shift Δφ, e.g., as at least a local curve extremum.

[0014] The fact that the second operating frequency lies below the resonance frequency means that it is lower than the resonance frequency. The fact that the second operating frequency is disjoint from the resonance frequency of the linear compressor means in particular that the second operating frequency has no overlap with the first operating frequency, i.e. the largest possible adjustable value of the second operating frequency is always smaller than the smallest possible adjustable value of the first operating frequency. At the second operating frequency, a lower cooling capacity is typically achieved than at the first operating frequency, but less power is also consumed. Thus, the linear compressor can potentially be operated more efficiently at the second operating frequency than at the first operating frequency.

[0015] In one embodiment, the second operating frequency lies in the range of a minimum power consumption of the linear compressor. This advantageously allows for particularly efficient operation of the linear compressor. The fact that the second operating frequency lies "in the range" of a minimum power consumption of the linear compressor can include that the second operating frequency corresponds to an operating frequency at which the power consumption of the linear compressor is minimal or practically minimal. The fact that the second operating frequency lies "in the range" of a minimum power consumption of the linear compressor can, however, also include that the second operating frequency corresponds to an operating frequency at which the power consumption of the linear compressor is not minimal, but close to the minimum power consumption P min lies, e.g. in an area P min ± 10%, especially P min ± 5%.

[0016] A further development is that the second operating frequency is deliberately shifted in frequency from the operating frequency with the lowest power consumption. This advantageously reliably ensures that the piston stroke reaches a value high enough to generate a sufficiently high mass flow of the working medium. This takes into account that at the operating frequency with the lowest power consumption, the piston stroke can also be particularly small.

[0017] In one embodiment, the second operating frequency lies between the resonant frequency and a (calculated or actual) anti-resonant frequency. The anti-resonant frequency corresponds in particular to a minimum of a transfer function between a constant applied voltage and the current consumed by the linear compressor for different operating frequencies and lies lower than the resonant frequency. Thus, within the framework of the transfer function—especially under the boundary condition of a constant voltage level or maximum voltage level—the anti-resonant frequency also corresponds to the operating frequency with the lowest power consumed. The more accurately the transfer function maps the linear compressor, the more accurately the anti-resonant frequency determined from the transfer function corresponds to the real anti-resonant frequency or the operating frequency with the lowest actual power consumed.The position of the second operating frequency between the resonant frequency and the anti-resonant frequency provides the advantage that the second operating frequency is always higher than the anti-resonant frequency. The second operating frequency can be increased, for example, to specifically compensate for calculation inaccuracies in a model-based calculated anti-resonant frequency (described below) and / or to specifically increase the piston stroke (described above).

[0018] A further development is that the second operating frequency is set at the anti-resonance frequency. This allows a transfer function that closely reflects reality to achieve the advantage that the linear compressor can be operated with particularly low power consumption simply by adjusting the second operating frequency.

[0019] One embodiment provides that the resonant frequency and the (calculated or real) anti-resonant frequency are at least 10 Hz apart, in particular at least 15 Hz apart. This has the advantage that the second operating frequency can be set particularly reliably and robustly. This takes into account the fact that linear compressors have not yet been designed to be set to an operating frequency that is noticeably lower than the resonant frequency. Therefore, the frequency difference between the resonant frequency and the anti-resonant frequency in conventional linear compressors is typically between 3 Hz and 6 Hz. Precisely setting the second operating frequency with such a small frequency difference is comparatively difficult, especially if an iterative method is used.In this embodiment, the linear compressor is designed such that the frequency separation reaches at least 10 Hz to facilitate adjustment to the second operating frequency. It has been found that a large frequency separation can be achieved, in particular, by appropriately dimensioning a coil connected upstream of the at least one drive magnet. The coil can, in particular, be a component of a serial RL element that is fed from a voltage source with, in particular, a constant voltage.

[0020] In one embodiment, the second operating frequency is 1 Hz to 6 Hz higher than the (calculated or real) anti-resonance frequency. It has been found to be particularly advantageous if the second operating frequency is 2 Hz to 5 Hz higher than the anti-resonance frequency, in particular 3 Hz to 5 Hz. In particular, the distance between the second operating frequency and the calculated anti-resonance frequency can be set smaller the better the model used to calculate the anti-resonance frequency reflects reality, e.g. whether it takes frictional forces into account or not. This embodiment advantageously takes into account that the calculated anti-resonance frequency tends to be lower than the real anti-resonance frequency. Therefore, if an anti-resonance frequency has been calculated, a frequency premium or offset can be added to the calculated anti-resonance frequency to compensate for this deviation.The frequency penalty can, for example, be estimated, determined from experiments, or calculated from simulations. Even if the actual anti-resonance frequency or operating frequency with the lowest actual power consumption is not exactly achieved, it will still be close. However, the frequency penalty can be applied additionally or alternatively to increase a piston stroke.

[0021] In one embodiment, at least the position of the anti-resonance frequency (and possibly also the resonance frequency) has been determined from a transfer function of a model, in particular an electro-magneto-mechanical model, of the linear compressor. This is advantageous for determining the transfer function with the desired accuracy and for easily implementing variations of the linear compressor. Thus, a simpler or more complex model can be set up as needed to calculate the transfer function, from which the anti-resonance frequency can be calculated.

[0022] One embodiment of the model is a simplified model in which frictional forces and / or loads in particular have not been taken into account. This simplifies the setup of the model while still maintaining sufficient accuracy to achieve an operating frequency with low power consumption or high efficiency by adding a frequency to the calculated anti-resonance frequency. The load can in particular comprise a force exerted on the moving piston by the working fluid present in the working volume. In very simplified terms, this force can be viewed as the force of a "gas spring", but in reality it is far more complex. In these cases, it may be more advantageous to ignore the load entirely in the model than to use a gas spring.

[0023] In one embodiment, the cooling device is designed to monitor the electrical power consumed by the linear compressor and to set the operating frequency to the second operating frequency by varying the operating frequency step by step until a target power corresponding to the second operating frequency is reached. This has the advantage that the target power of the linear compressor can be easily set step by step and can be maintained at this value even if the environmental influences on the linear compressor change. This iterative approximation method does not require knowledge of an anti-resonance frequency for its implementation, but can advantageously be combined with it, as explained in more detail below. In a further development, the target power of the linear compressor corresponds to the minimum power or a power slightly higher than the minimum power.The approximation method according to this embodiment can be repeated continuously or event-driven to achieve the target performance of the linear compressor even under changing boundary conditions. When repeated, the target value of the previous iteration can be used as the starting or initial value. Possible events that trigger a repetition can include, for example, a percentage or absolute deviation of the power consumption from the target performance.

[0024] One embodiment involves varying the operating frequency starting from an initial operating frequency corresponding to the calculated anti-resonance frequency, optionally plus a predefined frequency offset. This corresponds to a starting point for the iteration at least close to the assumed target power and enables a particularly rapid iterative approach to the actual target power.

[0025] So there are at least three ways to set the working frequency to the second working frequency: - the operating frequency is set to a previously determined second operating frequency, e.g. to the second operating frequency calculated using the anti-resonance frequency; - The operating frequency is set purely iteratively to the second operating frequency, where the second operating frequency corresponds to an operating frequency with a specific target power. In particular, the operating frequency with the lowest power consumption can be iteratively searched for and then a frequency premium applied to it; - the working frequency is determined iteratively starting from the anti-resonance frequency, if necessary with a frequency supplement, as a starting point.

[0026] In one embodiment, the cooling device is configured to evaluate a target voltage applied to the linear compressor and a current consumed by the linear compressor for monitoring purposes. This offers the advantage of simple and cost-effective implementation of monitoring both the electrical power and the power consumed. It takes advantage of the fact that the target voltage signal can be implemented very precisely, meaning that the target value and actual value differ only slightly or practically not at all. Therefore, a voltmeter for the linear compressor, in particular for its drive magnet(s), is not required, and only an ammeter for the current flowing through the ("drive") coil(s) of the drive magnet is required. Alternatively, the voltage signal applied to the linear compressor or the drive coil(s) can be measured, which advantageously allows its more precise determination.

[0027] In one embodiment, the cooling device is configured to operate the linear compressor at the second operating frequency for continuous operation and at the first operating frequency for temporary operation with higher cooling capacity. This offers the advantage that the cooling device can be cooled particularly efficiently for most of the time, but can switch to increased cooling capacity quickly and precisely when required (e.g. after switching on the cooling device, activating a "super cooling" mode, lowering a cooling temperature, etc.). During continuous operation with an operating frequency reduced compared to the resonant frequency, the mechanical stress on the linear compressor can also be advantageously kept low, thereby increasing its service life.

[0028] The problem is also solved by a method for operating a refrigeration device with a linear compressor provided as the drive for a refrigeration circuit, in which the linear compressor is optionally operated at a first operating frequency at its resonant frequency or at a second operating frequency below and disjoint from the resonant frequency of the linear compressor. The method can be designed analogously to the refrigeration device, and vice versa, and has the same advantages.

[0029] 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. Fig. 1 shows a sectional side view of a sketch of a possible linear compressor; Fig. 2 shows a possible electro-magneto-mechanical replacement model of a linear compressor; Fig. Figure 3A shows a transfer function between an applied constant voltage and a displacement of the piston of a linear compressor of the type Fig. 2 for different operating frequencies; Fig. Figure 3B shows a transfer function between a constant voltage applied to a drive coil of a drive magnet and a current flowing through the drive coil of the linear compressor from Fig. 3A for different operating frequencies; Fig. Figure 4A shows a transfer function between an applied constant voltage and a displacement of the piston of an optimized linear compressor according to the Fig. 2 for different operating frequencies; Fig. Figure 4B shows a transfer function between a constant voltage applied to a drive coil and a current flowing through the drive coil of the linear compressor from Fig. 4A for different operating frequencies; and Fig. 5 shows a circuit diagram of a possible control of a linear compressor.

[0030] Fig. 1 shows a sectional side view of a sketch of a possible linear compressor 1. The linear compressor 1 has a piston 3 which is provided with permanent magnets 3A and which can be moved linearly in a housing 2, as indicated by the double arrow. The rear side of the piston 3 is hinged to the housing 2 via a spring element 4 and the front side of the piston 3 delimits a working volume 5. 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 drive magnet 9 arranged outside the housing 2. The drive magnet 9 has a drive coil 9A, which is typically operated on the basis of an alternating voltage U-, and a stator 9B made of magnetic material, e.g. made of sheet steel segments.and then exert a magnetic force on the permanent magnets 3A, whereby the piston 3 is excited to oscillate linearly in the housing 2. As the oscillating piston 3 moves forward or towards the spring element 4, the spring element 4 elastically expands and reduces the working volume 5, so that the working medium 7 is pressurised 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, towards the rear or towards the spring element 4, the piston 3 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 front-side valve plate 2a.

[0031] The vibration system comprising at least the piston 3 and the spring element 4, possibly also the housing 2, has a certain resonance frequency f res At a constant alternating voltage U-, a uniform back and forth movement of the piston 3 occurs with a specific piston stroke A and a specific oscillation or working frequency f w So far, the resonance frequency f res for a specific linear compressor 1 type-related in advance (e.g. by solving a system of equations or a simulation program) and the alternating voltage U- is set directly so that the working frequency f w the type-related precalculated resonance frequency f res meets.

[0032] Fig. 2 shows a possible electro-magneto-mechanical replacement model of a linear compressor, described as an example using the linear compressor 1 from Fig. 1. The drive coil 9A is supplied with the alternating voltage U~ via a series RL circuit with a resistor Rc and an inductance or coil Lc, for example with a pulse-width modulated alternating voltage U~ with voltage pulses of constant voltage level ui. As a result, the drive magnet 9 exerts a magnetic force Fm proportional to the flowing electric current i in the direction of movement of the piston 3 ("mover") with a force constant km. The piston 3 with mass mp is thereby deflected from its rest position along its direction of movement by the piston stroke xp. The movement of the piston 3 is counteracted by a frictional force Fr and a load FI caused by compression or expansion of the working volume 5. In addition, the housing 2 with mass ms, which is elastically hinged to the cooling device 11 and has the drive magnet 9, moves by a distance xs.The movement of the piston 3 relative to the housing 2 can be described by the spring constant kp and the damping constant cp, the movement of the housing 2 relative to the cooling device 11 can be described by the spring constant ks and the damping constant cs.

[0033] The analytical formulas for a possible simplified model neglecting the friction force Fr and the load FI include, for example, for piston 3: Fm = mp · ẍp + kp · (xp - xs) + cp · (ẋp - ẋs) for housing 2: -Fm = ms - ẍs + ks · xs + cs · ẋs - kp · (xp - xs) - cp · (ẋp - ẋs) and for the magnetic force: Fm = km ̇· i and ui = Rc · i + Lc · (i) + km · (ẋp - ẋs)

[0034] From this, the Fig. 3A to Fig. 4B described in more detail.

[0035] Fig. Figure 3A shows a plot of a transfer function H xp | ui (f w) between a pulsed alternating voltage with a constant voltage level ui applied to the drive coil 9 and a maximum deflection xp of the piston 2 (corresponding to the piston stroke A) of a linear compressor 1 according to the simplified model according to Fig. 2 for different operating frequencies f w . The considered operating frequencies f w at 10 Hz, so that a resonance caused by the movement of the housing 2 is not reproduced.

[0036] This transfer function H xp | ui (f w ) indicates, due to the constant voltage ui, in particular how high the maximum deflection xp of the piston 3 is for a certain operating frequency f w It points at the resonance frequency f res a maximum, ie at the resonance frequency f res the highest maximum deflection xp of piston 2 and thus also the highest cooling performance.

[0037] Taking into account the friction force Fr and the load FI, transfer functions result in which the maximum deflection xp of the piston 3 is typically below the values ​​plotted in the simplified model used here.

[0038] Fig. 3B shows a simplified model according to Fig. 2 based transfer function H i | ui (f w ) between a pulsed alternating voltage with a constant voltage level ui applied to the drive coil 9 and a current i flowing through the drive coil 9 of the linear compressor 1 from Fig. 3A for different operating frequencies f w . This transfer function H i | ui (f w ) gives, due to the constant voltage level ui, the consumed electrical power P = ui · i depending on the operating frequency f w again. At the resonance frequency f res the maximum power is also consumed. In addition, the transfer function Hi | ui (f w ) at an “antiresonance” frequency f anti a minimum current consumption i and thus, under the stated boundary conditions, also a minimum power P. The resonance frequency f res and the antiresonance frequency f anti are approximately 6 Hz apart (at a scale spacing of 5 Hz, for example). If the operating frequency f w to set a given power P in a range between the resonance frequency f res and the antiresonance frequency f anti This is comparatively difficult to implement, since even small inaccuracies in f w a noticeable deviation of the set power P from the desired power.

[0039] Fig. 4A shows analogous to Fig. 3A based on the simplified model according to Fig. 2 based transfer function H xp | ui (fw) for an optimized linear compressor 1, in which at least one of the Fig. 2 has been adjusted so that the frequency difference between the resonance frequency f res and the antiresonance frequency f anti It has been shown that the size of the inductance Lc has the greatest influence on the frequency difference f res - f anti By adjusting the characteristic quantities, the resonance frequency f res as shown in the example, to higher values, here in comparison to Fig. 3A, for example, at about 20 Hz.

[0040] Fig. 4B shows analogous to Fig. 3B a simplified model according to Fig. 2 based transfer function H i | ui (f w ) for the according to Fig. 4A optimized linear compressor 1. By adjusting the characteristic parameters, the frequency spacing could be increased to approximately 18 Hz, i.e. compared to Fig. 3B will be approximately tripled.

[0041] Fig. Figure 5 shows a control system 10 for controlling the operating frequency fw of a linear compressor, which, like the linear compressor 1, can be a component of a cooling device 11, e.g., a household refrigerator. The control system 10 is configured to control the operating frequency f w between with a first operating frequency f w1 and a second operating frequency f w2 to switch, for example, upon instruction from a higher-level control device (not shown), in order to set different cooling modes such as continuous operation or super-cooling operation. The first operating frequency f w1 the resonance frequency f res , while the second operating frequency f w2 between the resonance frequency f res and the antiresonance frequency f anti , in particular closer to the antiresonance frequency f anti . The first operating frequency f w1can achieve a maximum piston stroke A and thus a maximum cooling capacity at maximum power P, e.g. for super-cooling operation or after switching on the cooling device 11. At the second operating frequency f w2 Linear compressor 1 operates with lower cooling capacity but higher efficiency.

[0042] In one variant, the control 10 can be designed, for example, in such a way that a desired piston stroke A ref for piston 3. The target piston stroke A ref is determined together with the desired operating frequency f w a first module (“amplitude control module”) 12, which then generates the corresponding or “correct” target AC voltage U ∼,ref for the drive coils 9. The nominal AC voltage U ∼,ref is fed to a second module (pulse width or “PWM module”) 13, which generates the desired AC voltage U ∼,refcorresponding current pulses are generated to energize the drive coils 9.

[0043] The target alternating voltage U ∼,ref and the current I measured by a current sensor 14 meas is fed to a third module (“phase shift calculation module”) 15, which calculates the current phase shift Δφ between voltage U ∼,ref and current I meas The phase shift Δφ is fed to a fourth module (“first frequency control algorithm”) 16, which determines a specific operating frequency f w to the amplitude control module 12 and checks on the basis of the returned phase shift Δφ whether this is at the specified target phase shift of 45° for f res or not. The first frequency control algorithm 16 can then determine the operating frequency f wmaintain or reset to the target phase shift of 45°, for example by means of an iterative approximation process with a stepwise variation of the first operating frequency f w1 . If the linear compressor 1 is to be operated at the first operating frequency f w1 than the desired operating frequency f w operated, the first operating frequency f w1 passed to the amplitude control module 12.

[0044] The target alternating voltage U ∼,ref and the current I meas are also fed to a fifth module (“power calculation module”) 17, which calculates the electrical power P (t) consumed by the linear compressor 1, or alternatively the electrical energy consumed over a specific period of time. The consumed electrical power P (t) can be calculated, for example, by averaging the desired AC voltage U ∼,ref and the measured current I measover a certain period of time, in particular by quadratic averaging. The consumed electrical power P (t) can thus be calculated in particular from the effective values ​​of U ∼,ref and I meas The period used for averaging can be one or more periods of the target AC voltage U ∼,ref The consumed electrical power P is fed to a sixth module (“second frequency control algorithm”) 18, which uses the knowledge of the consumed electrical power P to determine the operating frequency f w2 until the desired low power consumption is achieved. If the linear compressor 1 is to be operated at the second operating frequency f w2 than the desired operating frequency f w operated, the second operating frequency f w2 passed to the amplitude control module 12.

[0045] Of course, the present invention is not limited to the embodiment shown.

[0046] 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.

[0047] A numerical value may also include the exact number stated as well as a usual tolerance range, as long as this is not explicitly excluded. List of reference symbols 1 linear compressor 2 housings 2a Valve plate 3 pistons 3A permanent magnet 4 spring element 5 Working volume 6 Entrance 7 Working medium 8 Outlet 9 Drive magnet 9A drive coil 9B Stator 10 Regulation 11 Cooling device 12 Amplitude control module 13 PWM module 14 Current sensor 15 Phase shift calculation module 16 First frequency control algorithm 17 Performance calculation module 18 Second frequency control algorithm cp Damping constant between piston and housing cs Damping constant between housing and cooling unit Fm Magnetic Force Frictional force FI load f anti Antiresonance frequency f res Resonance frequency f w Working frequency H transfer function Lc inductance i electricity I meas Measured current kp spring constant between piston and housing ks spring constant between housing and cooling unit km Magnetic force constant mp mass of the piston ms mass of the housing P Performance Rc resistance ui tension U~ AC voltage signal xp deflection of the piston xs deflection of the housing Δφ phase shift

Claims

[1] Cooling device (11) with a linear compressor (1) provided as a drive for a refrigeration circuit, which can be controlled by means of a control (10) in such a way that it can optionally - with a first operating frequency (f w1 ) at the resonance frequency (f res ) of the linear compressor (1) or - with a second operating frequency (f w2 ) below and disjoint from the resonance frequency (f res ) of the linear compressor (1). [2] Cooling device (11) according to claim 1, wherein the cooling device (11) is arranged to - a phase shift (Δφ) between an electrical voltage (U~, ui) applied to the linear compressor (1) and a current (I meas , i) monitor and - the operating frequency (f w ) thereby to the first working frequency (f w1 ) to set the working frequency (f w) is varied step by step until one of the resonance frequencies (f res ) corresponding target phase shift is achieved. [3] Cooling device (11) according to claim 2, wherein the target phase shift is assumed to be 45° in magnitude. [4] Cooling device (11) according to one of the preceding claims, wherein the second operating frequency (f w2 ) is in the range of a minimum power consumption of the linear compressor (1). [5] Cooling device (11) according to one of the preceding claims, wherein the second operating frequency (f w2 ) between the resonance frequency (f res ) and an anti-resonance frequency (f anti ) lies. [6] Cooling device (11) according to one of the preceding claims, wherein the resonance frequency (f res ) and the anti-resonance frequency (f anti ) are at least 20 Hz apart. [7] Cooling device (11) according to claim 6, wherein the second operating frequency (f w2) between 1 Hz and 6 Hz, especially between 3 Hz and 5 Hz, is greater than the anti-resonance frequency (f anti ). [8] Cooling device (11) according to one of the preceding claims, wherein the position of the calculated anti-resonance frequency (f anti ) has been determined from a transfer function (H) of a model of the linear compressor (1). [9] Cooling device (11) according to claim 6, wherein the model is a simplified model in which, in particular, frictional forces and / or loads have not been taken into account. [10] Cooling device (11) according to one of the preceding claims, wherein the cooling device (11) is designed to - to monitor the electrical power (P) consumed by the linear compressor (1) and - the operating frequency (f w ) thereby to the second operating frequency (f w2 ) to set the working frequency (f w) is varied gradually until a certain target performance is achieved. [11] Cooling device (11) according to claim 10, wherein the operating frequency (f w ) starting from an initial operating frequency (f w ) is varied, which of the calculated anti-resonance frequency (f anti ) plus a specified frequency premium, which is in particular between 1 Hz and 6 Hz, in particular between 3 Hz and 5 Hz. [12] Cooling device (11) according to one of claims 2 to 11, wherein the cooling device (11) is designed to evaluate a target voltage applied to the linear compressor (1) and a current consumed by the linear compressor for monitoring purposes. [13] Cooling device (11) according to one of the preceding claims, wherein the cooling device (11) is designed to set up the linear compressor (1) for continuous operation at the second operating frequency (f w2) and for a limited period of operation with higher cooling capacity at the first operating frequency (f w1 ) to operate. [14] Method for operating a cooling device (11) with a linear compressor (1) provided as a drive for a refrigeration circuit, in which the linear compressor (1) can optionally - with a first operating frequency (f w1 ) at its resonance frequency (f res ) or - with a second operating frequency (f w2 ) below and disjoint from the resonance frequency (f res ) of the linear compressor (1).

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