Cooling device and method for operating a cooling device

Abstract

The invention relates to a cooling device (11) with a refrigeration circuit operated by means of a linear compressor (1) and with a control unit (10) which is configured to set an operating frequency (f w ) of a piston (3) of the linear compressor (1) driven by means of at least one drive magnet (9) equipped with at least one drive coil (9A) in such a way as to ensure a minimum power consumption (P min ) of the linear compressor (1). The invention also relates to methods for operating a cooling device (11) equipped with a refrigeration circuit operated by means of a linear compressor (1), in which an operating frequency (f w ) of a piston (3) of the linear compressor (1) is regulated such that minimal energy consumption (P) is achieved. min ) 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 refrigeration circuit operated by a linear compressor and with a control or regulation system configured to regulate the operating frequency of a piston of the linear compressor. The invention also relates to a method for operating a refrigeration device equipped with a refrigeration circuit operated by a linear compressor, in which the operating frequency of a piston of the linear compressor is regulated. The invention is particularly advantageously applicable to household refrigeration devices.

[0002] Cooling devices are known whose refrigeration circuit uses a linear compressor as the drive. To achieve low energy consumption, the operating frequency of the piston is adjusted so that a predetermined resonance frequency of the oscillating system is matched as accurately as possible. The linear compressor is thus operated at a constant, predetermined operating frequency. Implementing this method in production requires that every linear compressor of the same type exhibit the predetermined resonance frequency as accurately as possible, which poses a major challenge for production and assembly because tolerances must be maintained within strict limits. Furthermore, the resonance frequency can change depending on load and temperature.Consequently, it often happens that the actual resonance frequency deviates from the predetermined resonance frequency, resulting in increased energy losses during operation of the linear compressor.

[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 a simple, reliable and energy-saving way of operating a linear compressor of a refrigeration 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 problem is solved by a cooling device with a refrigeration circuit operated by means of a linear compressor and with a control system which is designed to adjust or control an oscillation or operating frequency of a piston of the linear compressor in such a way that a power consumption of the linear compressor results in a range of minimum power consumption.

[0006] This provides the advantage that the operating frequency is automatically adjusted to minimize the linear compressor's power consumption. This avoids the aforementioned problems of the state-of-the-art compressors during operation.

[0007] 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.

[0008] The piston is mounted in particular in a cylindrical piston housing of the linear compressor so that it can be moved longitudinally and is hinged by at least one elastic spring element. The piston, which is 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") operated with an alternating electrical voltage, and is thereby set into oscillation. Depending on the direction of movement, a working volume delimited by the piston housing and an end face of the piston is increased or reduced. 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 operating 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 operating frequency. The basic operation of a linear compressor in a refrigeration circuit of a refrigeration appliance is well known and will therefore not be discussed further here. The linear compressor can also be considered a linear motor, with the piston acting as the rotor or "mover."

[0009] The piston stroke can be understood in particular as the displacement of the piston from its rest position, especially "forward," whereby the working volume is then compressed. This can also be understood as the direction of movement in the direction of inlet and outlet. The piston stroke can be understood specifically as the displacement of the piston up to its forward reversal point, i.e., the position at which the piston is maximally deflected forward.

[0010] The fact that the control is designed to regulate the oscillation or working frequency of the piston in such a way that a power consumption of the linear compressor results in a range of minimum power consumption is based on the fact that the working frequency is not set constantly, but is automatically adjusted using at least one feedback variable in such a way that a minimum power consumption of the linear compressor results.

[0011] The minimum power consumption can be an absolute minimum or a local minimum, particularly in a frequency band of the operating frequency between 10 Hz and 200 Hz. The minimum power consumption can occur, in particular, at an operating frequency that corresponds to the resonant frequency or lies within a frequency range around the resonant frequency, for example, within + / - 8 Hz of the resonant frequency. The operating frequency is adjusted, in particular, while maintaining or keeping constant one or more adjustable target variables, such as the piston stroke, the amplitude of an electrical excitation signal such as an excitation current, etc.

[0012] In addition to or as an alternative to power consumption, energy consumption can be used to control the linear compressor. Power consumption and energy consumption are interchangeable for defined periods of time and can therefore be used interchangeably unless otherwise stated. Power consumption can also be referred to as power input, and energy consumption can also be referred to as energy input.

[0013] One embodiment is that the control system is configured to regulate or adjust the operating frequency in such a way that minimal power consumption of the linear compressor is achieved. This is advantageously particularly energy-saving. The minimum power consumption corresponds, in particular, to the minimum that can be achieved as precisely as possible by the control system.

[0014] In one embodiment, the control is set up to regulate the working frequency such that it has a specific frequency difference from the working frequency with minimal power consumption. This has the advantage that the linear compressor can still be operated with a low power consumption close to the minimum, but a noticeably higher piston stroke can be achieved due to the frequency difference. In one development, the working frequency is higher by a specific frequency difference than the working frequency with minimum power consumption. In one development, the frequency difference is not more than 6 Hz, in particular in a range between 1 Hz and 6 Hz, in particular in a range between 2 Hz and 5 Hz.

[0015] In one embodiment, the control system is configured to calculate a target AC voltage for the at least one drive coil of the at least one drive magnet from the currently set operating frequency and a target piston stroke of the piston. This is advantageously particularly easy to implement and enables simple implementation of a variation of the piston's operating frequency. The characteristic variables of the target AC voltage can include, for example, a voltage frequency and the voltage amplitude. The target AC voltage can be applied as a sinusoidal voltage signal or as a pulsed, e.g., pulse-width-modulated, voltage signal.

[0016] In one embodiment, the control system is designed to calculate the power consumption of the linear compressor for a set operating frequency from a target voltage signal for the at least one drive coil and a measured actual current consumption of the at least one drive coil. This offers the advantage of simple implementation with precise determination of the electrical power currently consumed by the linear compressor at the set operating frequency. This takes advantage of the fact that the target voltage signal can be implemented very precisely, i.e. there is only a slight to practically no difference between the target value and the actual value. Therefore, a voltmeter for the linear compressor, in particular for its drive coil(s), can be dispensed with, and only an ammeter for the current flowing through the linear compressor, in particular its drive coil(s), is required.

[0017] Alternatively, the voltage signal applied to the linear compressor or the at least one drive coil can be measured, which advantageously allows its more precise determination.

[0018] A further development involves calculating the electrical power by averaging the alternating voltage or voltage signal and the measured current over a specific period of time. This advantageously enables a particularly robust and reliable power determination.

[0019] It is a further development that the averaging is a quadratic averaging, whereby the consumed electrical power P is then calculated from the effective values ​​of the voltage signal and the measured current.

[0020] The period used for averaging can include one or more periods of the voltage signal.

[0021] In one embodiment, the control system is configured to vary the operating frequency by means of an iteration method, in particular an approximation method, towards minimum energy consumption, and to set the operating frequency to the consumption-optimal operating frequency found by means of the iteration method (i.e., the operating frequency at which minimum power consumption results). The consumption-optimal operating frequency can correspond to the resonant frequency, but this is not necessary. The minimum power consumption can occur, in particular, at an operating frequency that corresponds to the resonant frequency or lies within a frequency range around the resonant frequency, for example, within + / - 8 Hz of the resonant frequency.

[0022] If a specific frequency offset is to be added, this can be done in addition to the consumption-optimal operating frequency found using the iteration method.

[0023] In one embodiment, the control system is configured to vary the target operating frequency and to regulate it to a value (the "consumption-optimal" frequency or operating frequency) at which a minimum energy consumption of the linear compressor, determined from the variation, results. By using a variation method, the consumption-optimal frequency can advantageously be determined reliably and with comparatively little effort under virtually all boundary conditions and manufacturing tolerances. To carry out the variation method, in particular, all suitable iteration algorithms for determining the minimum value can be used, especially approximation or approximation algorithms that approximately solve the optimization problem at hand. If a specific frequency difference is to be added, this can be done additively to the consumption-optimal operating frequency found using the iteration method.

[0024] One embodiment is that the control system is configured to vary the set operating frequency (previously considered optimal for consumption) again after a specified period of time. This offers the advantage that the previously determined and set optimal operating frequency can be regularly adjusted to possible changes in the boundary conditions. The period can range, for example, from 15 minutes to several hours, but is not limited to this.

[0025] In one embodiment, the control system is configured to vary the set operating frequency again if the electrical power consumed reaches or exceeds a predetermined threshold, in particular with respect to the previously determined power or the previously determined power consumption. The electrical power consumed is advantageously a particularly good indicator that the operating conditions of the linear compressor have changed noticeably. In a further development, this embodiment can also be expressed in such a way that the control system is configured to vary the set operating frequency again if the electrical power consumed reaches or exceeds an upper threshold or reaches or falls below a lower threshold, in particular deviates significantly from the previously determined power.In a further development, this can also be expressed by the controller being configured to vary the set operating frequency again if the calculated power falls or falls outside a specific band or range around the previously determined minimum power. In a further development, the previously determined consumed power corresponds to the previously determined minimum power consumption or the power consumption at the operating frequency that, in contrast, has the specified frequency difference.

[0026] In one embodiment, the control system is configured to vary the set operating frequency again if the specified target piston stroke has been changed. The target piston stroke may, for example, have been changed to increase cooling capacity, for example, if a target cooling chamber temperature of the refrigeration device is lowered. The target piston stroke can be set, for example, by means of a control system for the linear compressor, in particular its drive magnet or its drive coil(s). The control system may also include the control of the operating frequency.

[0027] In one embodiment, the control system is configured to vary the operating frequency again if a change in temperature and / or load reaches or exceeds a predetermined threshold. This advantageously enables an adjustment of the consumption-optimized operating frequency if certain boundary conditions change significantly. The temperature can include a temperature of the working fluid, a temperature of the linear compressor or in the vicinity of the linear compressor, and / or a cooling chamber temperature. The load depends in particular on the intake pressure at the inlet to the working volume and on the discharge pressure at the outlet.

[0028] One embodiment is that the control system is configured to specify a precalculated resonant frequency of the piston as the initial value of the iteration process when the operating frequency begins or is varied again. This prevents an unwanted drift of the initial value over a longer period of time. A further development is that when the cooling device is switched on, the iteration process is started with the precalculated resonant frequency, and subsequent iteration processes begin with the last determined consumption-optimal operating frequency as the initial value.

[0029] One embodiment of the control system is designed to continuously perform the iteration process. This achieves the advantage that the energy or power consumption of the linear compressor remains virtually constant at a minimum. In particular, after the operating frequency with optimal consumption has been found, the operating frequency is immediately varied again using this as a starting value.

[0030] 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.

[0031] The problem is also solved by a method for operating a refrigeration device equipped with a refrigeration circuit operated by a linear compressor, in which the operating frequency of a piston of the linear compressor is controlled such that the energy consumption of the (operated or working) linear compressor is in the range of minimum energy consumption. The method can be designed analogously to the refrigeration device, and vice versa, and has the same advantages.

[0032] 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. Figure 2 shows a plot of the power consumption of a motor of a linear compressor installed in a refrigerator against the set operating frequency; and Fig. 3 shows a control for regulating the operating frequency.

[0033] Fig. Figure 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 is linearly displaceable in a housing 2, as indicated by the double arrow. The piston 3 is hinged to the housing 2 via a spring element 4 and the front side of which defines 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 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 ~operated, and a stator 9B made of magnetic material, e.g., 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. The oscillating piston 3 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 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. An inflow through the outlet 8 is prevented, e.g.,through a one-way valve. The inlet 6 and the outlet 8 can, for example, both be arranged on a front-end valve plate 2a.

[0034] The vibration system comprising at least the piston 3 and the spring element 4 has a certain resonance frequency f res At constant alternating voltage U ~ a uniform back and forth movement of the piston 3 occurs with a certain piston stroke A and a certain vibration 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 ~ set so that the operating frequency f w the precalculated resonance frequency f res meets.

[0035] Fig. 2 shows a plot of a power consumption P of a linear compressor 1 installed in a refrigerator against the set operating frequency f w . It is currently assumed that in a certain frequency range around the resonance frequency f res around a curve K of the power consumption P against the operating frequency f w the frequency as shown schematically at f res a minimum P min and, based on this, with a larger frequency spacing to f res steadily increasing. However, it has been shown that the consumption-optimal operating frequency f opt , at which the electrical energy or power consumption of the linear compressor 1 is minimal, does not necessarily correspond to the exact resonance frequency f res of the oscillation system, but the relationship f opt = f res only applies to certain operating conditions. In addition, the resonance frequency f reschange due to changes in external influences.

[0036] Fig. 3 shows a control 10 for controlling the working frequency f w of the linear compressor 1, which, like the linear compressor 1, can be a component of a cooling device 11, e.g. a household refrigerator.

[0037] The control 10 is supplied with a desired piston stroke A, for example via a control device of the cooling device 11. ref for piston 3. The target piston stroke A ref is used together with a specific or 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 coil 9A. 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 ~,ref corresponding current pulses are generated to energize the drive coil 9A.

[0038] The target AC voltage U specified for the PWM module 13 ~,ref and the current I measured by a current sensor 14 meas The current pulses output to the drive coil 9A are fed to a third module (“power calculation module”) 15, 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 determined, for example, by averaging the desired AC voltage U ~,ref and the measured current I meas over 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 include.

[0039] The consumed electrical power P is fed to a fourth module (“frequency control algorithm”) 16, which uses the knowledge of the consumed electrical power P to determine the operating frequency f w to adjust until the minimum power consumption P (t) = P min is reached.

[0040] This can be done, for example, by means of an iterative process in the form of an approximation method that exploits the fact that, starting from a minimum power consumption P min at f opt the consumed power P with greater frequency separation of the operating frequency f w to f opt The approximation method can, for example, be implemented in such a way that for a starting value f0 of the operating frequency f w the electrical power P0 (f0) consumed at this frequency is determined and this pair of values ​​(f0; P0) is stored. For a next step, f w= f1 = f0 + Δf with Δf > 0 in a suitable step size. If the corresponding consumed electrical power P1 (f1) > P0 (f0), then f w = f2 = f0 - Δf. If P2 (f2) > P0 (f0), either f0 can be used as the consumption-optimal operating frequency f opt or this iteration can be repeated for a smaller step size Δf' with Δf > Δf' > 0. However, if P1 < P0 applies for the power P1, then f w = f2 = f1 + Δf. This process is repeated until P i (f i ) > P i-1 (f i-1 ) holds. Then either f i-1 as the consumption-optimal operating frequency f opt or the iteration starting at f i-1 for a smaller step size Δf'. This approximation procedure can be repeated for both directions of f wbe performed equivalently. Furthermore, other iteration schemes can also be used, such as the Newton method or variants thereof.

[0041] In addition, it is possible to continue the iteration process, in particular the approximation method, after finding a consumption-optimal operating frequency f opt to be triggered again, for example after a specified period of time, event-triggered, e.g. with a change in the electrical power consumed, a temperature and / or load above a certain threshold, or immediately in order to achieve a practically continuous iteration.

[0042] Of course, the present invention is not limited to the embodiment shown.

[0043] 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.

[0044] 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 3 pistons 4 spring element 5 Working volume 6 Entrance 7 Working medium 8 Outlet 9 Drive coil 10 Regulation 11 Cooling device 12 Amplitude control module 13 PWM module 14 Current sensor 15 Performance calculation module 16 Frequency control algorithm A piston stroke A ref Target piston stroke f optConsumption-optimized working frequency f w Working frequency I meas Actual current K History P Power consumed P min Minimum performance U ~ alternating voltage

Claims

[1] Cooling device (11) with a refrigeration circuit operated by means of a linear compressor (1) and with a control (10) which is designed to set an operating frequency (f w ) of a piston (3) of the linear compressor (1) driven by at least one drive magnet (9) equipped with at least one drive coil (9A) in such a way that a power consumption (P) of the linear compressor (1) is in the range of a minimum power consumption (P min ) results. [2] Cooling device (11) according to claim 1, wherein the control (10) is arranged to control the operating frequency (f w ) in such a way that a minimum power consumption (P min ) of the linear compressor (1). [3] Cooling device (11) according to claim 1, wherein the control (10) is arranged to control the operating frequency (f w ) so that they have a certain frequency difference from the working frequency (f w ) with minimal power consumption (Pmin ), in particular is greater by a certain frequency spacing than the operating frequency (f w ) with minimal power consumption (P min ), in particular not more than 6 Hz greater. [4] Cooling device (11) according to one of the preceding claims, wherein the control (10) is designed to determine from the set operating frequency (f w ) and a target piston stroke (A ref ) a nominal alternating voltage (U ~ ) for the at least one drive coil (9A) of the linear compressor (1). [5] Cooling device (11) according to claim 4, wherein the control (10) is designed to operate at a set operating frequency (f w ) the power consumption (P) of the linear compressor (1) from a target voltage amplitude for the at least one drive coil (9A) and a measured actual current consumption (I meas ) of the at least one drive coil (9A). [6] Cooling device (11) according to claim 5, wherein the control (10) is arranged to control the operating frequency (f w ) using an iteration method, in particular an approximation method, to a minimum energy consumption (P min ) and the working frequency (f w ) to the consumption-optimal operating frequency (f opt ) to set. [7] Cooling device (11) according to claim 6, wherein the control (10) is designed to set the operating frequency (f w ) to vary again if the consumed electrical power (P) reaches or exceeds a predetermined threshold, in particular with respect to the previously detected minimum power (P min ). [8] Cooling device (11) according to one of claims 6 to 7, wherein the control (10) is arranged to control the operating frequency (f w ) again if the specified target piston stroke (A ref) has been changed. [9] Cooling device (11) according to one of claims 6 to 8, wherein the control (10) is arranged to control the operating frequency (f w ) to vary again if a change in temperature and / or load reaches or exceeds a predetermined threshold. [10] Cooling device (11) according to one of claims 6 to 9, wherein the control (10) is designed to, upon a beginning or renewed variation of the operating frequency (f w ) to specify a pre-calculated resonance frequency of the piston (3) as the initial value of the iteration process. [11] Cooling device (11) according to one of claims 6 to 10, wherein the control (10) is designed to carry out the iteration process continuously. [12] Cooling device (11) according to one of claims 6 to 10, wherein the control (10) is designed to adjust the set operating frequency (f w ) to vary again after a specified period of time. [13] Cooling device (11) according to one of the preceding claims, wherein the cooling device (11) is a refrigerator, a freezer or a combination thereof. [14] Method for operating a cooling device (11) equipped with a refrigeration circuit operated by means of a linear compressor (1), in which an operating frequency (f w ) of a piston (3) of the linear compressor (1) is controlled so that an energy consumption (P) of the linear compressor (1) is in the range of a minimum energy consumption (P min ) results.

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