EP2904336A2

EP2904336A2 - Method for controlling a compressor of a refrigeration system, and refrigeration system

Info

Publication number: EP2904336A2
Application number: EP13745660.4A
Authority: EP
Inventors: Xiaoming Peng; Ulf KRETSCHMER; Christian Ellwein
Original assignee: Kriwan Industrie Elektronik GmbH
Current assignee: Kriwan Industrie Elektronik GmbH
Priority date: 2012-08-06
Filing date: 2013-08-05
Publication date: 2015-08-12
Also published as: WO2014023694A2; CN104520658A; US20150198361A1; WO2014023694A3; US9746227B2; CN104520658B

Abstract

The invention relates to a method for controlling a compressor of a refrigeration system, said compressor having a motor, wherein the temperature of the cooling point is controlled by means of switch-on and switch-off operation of the motor if the temperature in the compressor exceeds an upper temperature threshold and the temperature of the cooling point is controlled by means of continuously switched-on operation of the motor as soon as the motor has cooled down to a lower temperature threshold, wherein the control system converts a manipulated variable corresponding to the cooling demand of the cooling point into a switching signal for a valve, which switching signal causes clocked opening and closing of the valve, or a frequency converter controls the refrigerant flow through the compressor by controlling the voltage and the frequency of the motor, in that the frequency converter converts a manipulated variable corresponding to the cooling demand of a cooling point into a voltage and a frequency for the motor.

Description

Method for controlling a compressor of a refrigeration system and a refrigeration system

The invention relates to a method for controlling a compressor having a motor of a refrigeration system and a refrigeration system.

In conventional refrigeration systems, a controller for determining the current refrigeration demand of a refrigeration point is provided next to the compressor. If the controller determines an increased cooling demand, the compressor is controlled by the controller in the sense of an increase in output. In a refrigeration system equipped with a frequency converter on the compressor, a frequency converter is provided in addition to the compressor and a controller for determining the current refrigeration demand of a refrigeration point, which can change the speed of the compressor motor between a lower and an upper speed. If the controller determines an increased cooling demand, the compressor is controlled by the controller in the sense of an increase in output by adjusting its speed and thus the conveyed refrigerant flow.

Furthermore, it is known to equip the refrigeration system with a motor protection circuit to monitor at least one parameter characterizing the operation of the compressor, for example, the winding temperature of the motor, wherein overshooting or falling below a predetermined temperature threshold leads to switching off of the compressor. Such a motor protection circuit is known for example from DE 10 2005 052 042 AI. However, the tripping of the motor protection means an inevitable interruption of the cooling circuit and can therefore have considerable consequences. In addition, a restart (automatic or manual) is associated with the uncertainty about the cause of the trip. Some manufacturers of compressors only allow further operation of the compressor in such a case when the cause has been clarified or eliminated. Such a shutdown is particularly annoying if there is no actual component defect or malfunction in the system and the shutdown is done only by an increased demand of the cooling point. In DE 10 2005 052 042 AI has therefore been proposed that in a power control of the compressor, the current operating state of the compressor is taken into account. This can be prevented that a further increase in performance is initiated, although the compressor is operated shortly before the switch-off.

From DE 10 2004 048 940 AI a method for controlling the performance of a refrigeration compressor is also known, where the compressor has a pneumatic or hydraulic servo device for intermittent interruption of the supply of refrigerant to a suction chamber. Furthermore, the compressor has a regulator, by which a pulse-width-modulated switching signal for the pneumatic or hydraulic servo device can be generated for controlling the intermittent interruption of the refrigerant supply. The duty cycle ratio for controlling the pneumatic or hydraulic servo device can be adapted to the needs of the cooling point.

From DE 699 28 055 T2 and US 2009/0205349 AI compressors are known which regulate the flow of coolant via a pulse width modulated switching signal. In US Pat. No. 6,925,823 B2, it is proposed to drive the compressor with reduced load when it has reached a first system state and to switch it off only when a second system state is reached, in order to delay the switch-off time. DE 100 64 218 A1 describes a method for controlling a cooling device with at least one compressor and at least two separate cooling chambers for different temperatures.

EP 1 710 435 B1 describes a controller for controlling the valves on the input side of the compressor, which generates an opening interval or a closing interval. Together, the two intervals form the switching interval, wherein the switching interval is to be less than the shortest period of time within which the temperature at the evaporator in the refrigeration system increases by 10% when the inlet flow is interrupted. However, the clocked opening and closing of the valve also has the disadvantage that the refrigerant flow, which usually flows through the engine and cools this is reduced accordingly. As a result, the cooling of the engine in the compressor is deteriorated, which makes the risk of engine shutdown by the motor protection circuit more likely.

The invention is based on the object to improve the method for controlling the compressor of a refrigeration system or a refrigeration system with a compressor to the effect that the response of the motor protection circuit is further delayed or prevented.

According to the invention, this object is solved by the features of claims 1, 12, 13 and 19.

In the method according to the invention according to a first embodiment of the refrigerant flow is controlled by the compressor via at least one valve and thereby regulated the temperature of the cooling point, wherein also at least one temperature in the compressor is measured and evaluated and a control of the temperature of the cooling point by a switch on and off of the engine is reached when the temperature in the compressor exceeds an upper temperature threshold and a control of the temperature of the cooling point by a continuously powered operation of the engine, as soon as the engine has cooled to a lower temperature threshold, the controller doing a cooling demand of the Cold spot corresponding manipulated variable converts into a switching signal for the valve, which causes a clocked opening and closing of the valve.

The refrigeration system according to the invention according to the first embodiment consists essentially of at least a compressor for compressing the refrigerant, which is driven by a motor (la),

a valve that regulates the flow of refrigerant through the compressor, a controller, the one manipulated variable depending on the refrigeration demand of a

Cooling point generated, and

a controller, which communicates with the controller and the valve and controls the valve to control the temperature of the cooling point, wherein, further provided a temperature measuring device for detecting at least one temperature in the compressor, which is provided in or on the engine, and is in communication with the controller and the controller is in communication with the engine and configured such that a control of the temperature of the cooling point by an on and off operation of the engine is achieved when the temperature in the compressor exceeds an upper temperature threshold and a Control of the temperature of the cooling point by a continuously activated operation of the engine is carried out as soon as the engine has cooled to a lower temperature threshold, the controller thereby implementing the cooling demand of the cooling point corresponding control variable in a switching signal for the valve, the clocked opening and Close the Valve causes.

According to the switching signal for the valve is not only adjusted depending on the refrigeration demand of the cooling point, but it is also considered at least one temperature in the compressor to prevent premature shutdown of the compressor by starting the motor protection circuit. In DE 10 2005 052 042 AI also a temperature in the compressor was measured, wherein the usual control algorithm was overridden from a certain temperature threshold. Furthermore, it has been proposed that the power of the compressor can be reduced independently of the demand, when the compressor is in the predetermined critical operating condition, in order to prevent the premature response of the compressor protection device.

The improvement of the invention consists in the fact that upon reaching an upper temperature threshold, a targeted on-off operation of the engine of the compressor is used by the engine off for a predetermined or adjustable first time period of, for example, 12 minutes and then for a predetermined or adjustable second time period is turned on, for example, 5 min, this shutdown is maintained until a lower temperature threshold is reached. The switch-on or switch-off time depends on the setpoint specification and the permissible operating parameters (minimum run time, permissible number of starts per hour, etc.) of the refrigerant compressor. By this measure, a certain refrigerant flow can continue to be maintained during the switch-on. A caused by an increased refrigeration demand of the cooling point shutdown of the compressor by a motor protection circuit can be reliably avoided in most cases. Once the compressor has cooled down to a lower temperature threshold, then the continuous operation with a continuously switched-on motor by clocked opening and closing of the valve can again take place.

By the above measures, the response of the motor protection circuit can be reliably avoided in most applications, which are caused by an increased refrigeration demand.

Further embodiments of the invention are the subject of the dependent claims.

According to a preferred embodiment of the invention, the switching signal of the valve is a pulse-width-modulated signal. In addition, the engine is switched on and off in the on or off periodically. The switching signal preferably has an adjustable duty cycle ratio, wherein the controller adjusts the ratio as a function of the manipulated variable and the measured temperature in the compressor. Furthermore, it can be provided that the duty cycle ratio of the switching signal is continuously shifted during the change from the continuous operation of the engine to the on-off operation of the engine and vice versa in a predetermined switching period.

The temperature in the compressor can be determined in particular by measuring the winding temperature of the motor or by measuring the temperature of a compressed hot gas in the compressor. In particular, a

Sensor circuit with at least one, preferably a plurality of PTC sensors with at least two different response temperatures or a linear temperature sensor whose output signal is divided into several sections, are used. The engine is also preferably operated with a motor protection circuit which shuts off the motor when an upper limit temperature of the engine is reached, the upper temperature threshold at which the engine changes to on-off operation is below the upper limit temperature. Depending on the position of the valve this is either fully opened or closed in the on-off operation of the engine. Is the valve on the suction side of the

Compressor, it will be in the on-off operation of the engine in the fully open state. On the other hand, if the valve is provided in a bypass of the compressor, it will be closed during the on-off operation of the engine. The controller may further comprise a filter which depends on the

Change rate of the manipulated variable automatically changed to suppress oscillation tendencies.

In the inventive method for controlling a compressor having a motor of a refrigeration system according to a second embodiment of the invention Refrigerant refrigerant flow through the compressor is controlled by a speed change of the motor through a frequency converter, where the frequency converter converts a frequency and voltage corresponding to the refrigeration demand of a refrigeration unit to the motor of the compressor. In addition, at least one temperature in the compressor is measured and evaluated, the regulation of the temperature of the cooling point by switching the motor on and off, preferably at the rated frequency of the motor (typically the mains frequency of 50Hz or 60Hz), is reached when the temperature in the compressor exceeds an upper temperature threshold and more accurate control of the refrigeration point temperature with continuously on motor by changing the speed of the motor by controlling the frequency and voltage through the frequency converter is reached when the engine has cooled to a lower temperature threshold.

The refrigeration system according to the second embodiment of the invention consists essentially of

a. a compressor driven by a motor for compressing the refrigerant,

b. a frequency converter for regulating the speed of the motor to regulate the refrigerant flow through the compressor,

c. a controller for generating a manipulated variable as a function of the refrigeration demand of a refrigeration unit,

d. Furthermore, a temperature measuring device provided in or on the motor and connected to the frequency converter for determining at least one temperature in the compressor is provided and the frequency converter is designed such that the motor is operated in the on and off mode, preferably at the rated frequency of the motor, if the determined temperature in the compressor exceeds an upper temperature threshold and the motor is operated continuously at a regulated frequency as soon as the motor has cooled down to a lower temperature threshold in the on and off mode. According to the frequency of the motor current (and thus the engine speed) is not only adjusted depending on the refrigeration demand of the cooling point, but it is also considered at least one temperature in the compressor to prevent premature shutdown of the compressor by starting the motor protection circuit. In DE 10 2005 052 042 AI a temperature in the compressor was also measured, the usual control algorithm was set above a certain temperature threshold. Furthermore, it has been proposed that the power of the compressor can be reduced independently of the demand, when the compressor is in the predetermined critical operating condition, in order to prevent the premature response of the compressor protection device.

In Bouchareb, M. et al: Speed regulation of refrigeration compressors with intelligent frequency converters; AI Air Conditioning and Air Conditioning 1/2003; P. 25 - 30, it is described that when using a frequency converter for controlling a motor, the winding temperature has an approximately parabolic shape over the frequency. The result is a minimum of the winding temperature at the rated frequency of the motor (typically the mains frequency of 50Hz or 60Hz) and a significant increase in the winding temperature when the frequency of the motor current is controlled lower (eg 20Hz or 30Hz) or higher (eg 70Hz). The improvement of the invention consists in the fact that upon reaching an upper temperature threshold, a targeted on-off operation of the motor of the compressor, preferably in the vicinity of the rated frequency of the motor is used until a lower temperature threshold is reached. The switch-on or switch-off time depends on the setpoint specification and the permissible operating parameters (minimum run time, permissible number of starts per hour, etc.) of the refrigerant compressor. By this measure, a certain refrigerant flow can continue to be maintained during the switch-on. A caused by an increased refrigeration demand of the cooling point shutdown of the compressor by a motor protection circuit can be reliably avoided in most cases. Once the compressor has cooled down to a lower temperature threshold, then the continuous operation with a continuously switched on motor and changing the frequency of the motor current.

Further embodiments of the invention are the subject of the dependent claims.

The temperature in the compressor can be determined in particular by measuring the winding temperature of the motor or by measuring the temperature of a compressed hot gas in the compressor. In particular, a sensor circuit having at least one, preferably a plurality of PTC sensors with at least two different response temperatures or else a linear temperature sensor whose output signal is subdivided into a plurality of sections can be used.

The engine is also preferably operated with a motor protection circuit which shuts off the motor when an upper limit temperature of the engine is reached, wherein the upper temperature threshold at which the engine switches to the on-off operation is below the upper limit temperature.

The controller may further include a filter that automatically changes depending on the rate of change of the manipulated variable to suppress vibrational tendencies.

Further advantages and embodiments of the invention will be explained in more detail below with reference to the following description and the drawing.

In the drawing show

Fig. 1 is a schematic diagram of a refrigeration system according to the first

Embodiment with a valve arranged in the bypass, 2 is a schematic diagram of a refrigeration system according to the first embodiment with a valve arranged on the suction side,

Fig. 3 is a schematic block diagram of the refrigeration system according to the first

Exemplary embodiment with control and regulator,

Fig. 4 characteristic of the duty cycle ratio of the pulse width modulated

Signal depending on the manipulated variable,

5 shows different characteristics of the first embodiment during the continuous operation and the on-off operation of the engine,

Fig. 6 is a schematic diagram of a refrigeration system according to the second

Embodiment with a frequency converter for controlling the frequency and the voltage of the motor,

Fig. 7 is a schematic block diagram of the refrigeration system according to the second

Embodiment with frequency converter and regulator and

8 shows different characteristics of the second embodiment during the continuous operation and the on-off operation of the engine,

In the following, the first embodiment of the invention will be described with reference to Figures 1 to 5. The refrigeration plant shown schematically in Fig. 1 consists essentially of a compressor 1, a condenser 2, a collector 3, an expansion valve 4 and an evaporator 5. In the compressor 1, which is for example designed as a reciprocating compressor, vapor refrigerant is sucked and compressed. In the following condenser, the refrigerant is condensed and passes through the collector 3 to the expansion valve 4, where it is relaxed. During expansion, the refrigerant pressure decreases, causing the refrigerant to cool and partially evaporate. In the evaporator 5, which is arranged in the region of a cooling point 6, the refrigerant absorbs the heat from the cooling point by evaporation. The compressor 1 sucks the evaporated refrigerant again, so that the refrigerant circuit is closed. The refrigerant flow is using a valve 7 arranged on or in the compressor is controlled as a function of the cooling requirement of the cooling point 6.

In the embodiment shown in FIG. 1, the valve 7 is arranged in a bypass lb, so that the refrigerant flow in the refrigerant circuit can be increased by closing the valve 7 and reduced by opening the valve 7.

Instead of the arrangement of the valve 7 in a bypass line to the compressor, the valve can also be integrated directly into the refrigerant circuit. A corresponding embodiment is shown in Fig. 2, where the valve 7 'on the suction side of the compressor 1, d. H. between evaporator 5 and compressor 1, is arranged. Also in this embodiment, the valve 7 'is for regulating the flow of refrigerant through the compressor 1. However, since this valve is directly incorporated in the refrigerant circuit, opening the valve will increase the refrigerant flow and closing will reduce the refrigerant flow.

The representations of FIGS. 1 and 2 are schematic representations. As a rule, the valves are integrated directly in the compressor, as this offers energy advantages. The valves 7 and 7 'often do not affect the complete refrigerant flow through the compressor but only partial flows e.g. through individual cylinders or cylinder banks.

The control of the refrigerant flow through the compressor as a function of the refrigeration demand of the cooling point 6 is explained in more detail below with reference to the block diagram of FIG. 3. For this purpose, a controller 8 is provided for generating a manipulated variable 9 as a function of the refrigeration demand of the cooling point 6. By way of an unspecified measuring device, for example, the actual temperature of the cooling point 6 is compared with a desired temperature. A possible deviation 10 is fed to the controller 8, which generates a manipulated variable 9 according to a predetermined algorithm, which is forwarded to a controller 11, where the cooling demand of the cooling point 6 corresponding manipulated variable 9 in one or more switching signal (s) 12 for / the valve (s) 7, 7 ', 17, 17' ... is implemented. The compressor 1, which is designed for example as a reciprocating compressor, has at least one motor la, which heats up according to the work to be done. According to an advantageous embodiment of the invention, the compressor 1 is constructed so that the refrigerant flowing through the compressor is also used for cooling the engine at the same time. Nevertheless, the temperature in the compressor can

Achieve values that no longer allow a further increase in power and trigger a motor protection circuit, which causes a shutdown of the engine with a further increase in temperature. It is therefore necessary that a temperature in the compressor determined by a suitable sensor circuit 13 and a corresponding temperature signal 14 is passed to the controller 11. In the

Sensor circuit 13 may be, for example, a sensor for measuring the winding temperature of motor 1. For this purpose, the sensor circuit can be formed, for example, by at least one, preferably a plurality of PTC sensors with at least two different response temperatures or else by a linear temperature sensor whose output signal is subdivided into a plurality of sections. A sensor circuit suitable for this purpose can be found, for example, in EP 2 187 494 A1.

Instead of the sensor circuit 13 or in addition to this, a sensor circuit 15 may be provided, with which the temperature of the compressed hot gas in the compressor is determined. A corresponding temperature signal 16 is also the

Control 11 forwarded. The controller 11 may include a motor protection circuit lc that shuts off the motor la when an upper limit temperature T3 measured by at least one of the sensor circuits 13, 15 is reached. Further details of such a motor protection circuit can also be found in EP 2 187 494 A1. Reaching the limit temperature T3 and the consequent shutdown of the compressor causes the cooling point 6 is not further cooled until the cause of the shutdown found and the compressor is restarted.

The switching signal 12 is preferably formed by a pulse width modulated signal (PWM signal), wherein the duty cycle ratio (ED) so the ratio the phases in which the valve is opened or closed, is adjusted depending on the manipulated variable 9. It should be noted that the duty cycle ratio of course depends on the arrangement of the valve to be controlled (bypass or suction side).

4 shows a possible duty cycle ratio ED of the PWM signal as a function of the manipulated variable 9. A duty cycle ratio (ED) = 0 means that the valve 7 arranged in the bypass is completely closed or the suction side is arranged Valve 7 'is fully open. When the duty cycle ratio of 1, the valve 7 is fully open or the valve 7 'completely closed. If the duty cycle ratio is in a range between 0 and 1, the valve is open during a period of, for example, 20 seconds, one part of the period and the other part is closed. However, such a control can cause the temperature in the compressor to rise to the limit temperature T3 at which the motor protection circuit responds.

In order to avoid this situation, at least in most cases, the compressor is not operated exclusively in continuous operation, in which the engine is switched on continuously and a timed opening and closing of the valve takes place in accordance with the switching signal 12. Rather, it is provided that, when an upper temperature threshold T2, which is still below the limit temperature T3, an on-off operation of the engine is provided. In the on-off operation, the engine is periodically turned off for a predetermined period of, for example, 10 minutes and then turned on again for a predetermined second duration. The duty cycle of the valve is set during the switch-on phase so that a maximum flow of refrigerant flows through the compressor. This on-off operation of the engine is carried out until the engine has cooled to a lower temperature threshold TO. From then on, the continuous operation can again take place with the motor continuously on and clocked opening and closing of the valve. In Fig. 5, four characteristic of the method for controlling the motor la of the compressor 1 characteristic curves are plotted over time. From top to bottom are the manipulated variable 9, the operation of the engine, the duty cycle ratio of the valve 7 'of FIG. 2 and the temperature signal T14 or T16. The control value 9 of the uppermost characteristic shows in section A after switching on the cooling in the area of the cooling point 6 a maximum control value (100%), which requires a maximum power of the compressor. The motor according to the second characteristic is therefore turned on. The valve 7 'is driven with a duty cycle ratio of 0%, which means that the valve is fully open. The temperature in the compressor shown in the lowest characteristic curve therefore initially increases. In the further course of section A, the further cooling demand drops in the area of the cooling point 6, so that the manipulated variable 9 is correspondingly reduced. However, the engine of the compressor remains continuously on over the entire period. The smaller manipulated variable 9 causes a shift of the duty cycle ratio (ED) of the P WM signal corresponding to the third characteristic.

The temperature of the compressor initially decreases accordingly. Due to the reduced refrigerant flow, however, the situation may arise that, as shown here, the temperature increases in the compressor. In order to reduce the temperature rise, the duty cycle (ED) is shifted from reaching the temperature Tl so that an increased flow of coolant through the compressor flows, whereby the temperature increase is somewhat mitigated.

Nevertheless, at the end of section A, the upper temperature threshold T2 is reached. This has the consequence that the motor of the compressor in section B is now operated in the on and off operation. While the engine is switched off, the temperature increases in the area of the cooling point, which is reflected by a correspondingly higher control value. In Einschaltbetrieb the engine, the valve is suitably set to maximum refrigerant flow through the engine and at the same time by the refrigerant circuit. What also has a corresponding reduction in the manipulated variable result. This is followed by further off or switch-on phases. During the on-off operation, the engine will start from the upper temperature threshold T2 to a lower temperature threshold TO cool. As soon as the lower temperature threshold TO has been reached, the motor is again operated continuously and the more precise regulation of the temperature by clocked opening and closing of the valve is carried out again (section C). In this way, it can be prevented in most cases that the temperature in the compressor reaches the upper limit temperature T3 at which engages the motor protection circuit. The on-off operation in Section B is characterized by a periodic switching on and off of the engine, with the respective on or off duration on the external circumstances (design features of the compressor, cooling load, etc.) must be adjusted.

The duty cycle ratio (ED) shows in the characteristic curve an abrupt transition between the different states. In the context of the invention, however, it is possible that the change takes place with a continuous transition.

In the following, the second embodiment of the invention will be described with reference to Figures 6 to 8.

The refrigeration system shown schematically in FIG. 6, in turn, consists essentially of a compressor 1, a condenser 2, a collector 3, an expansion valve 4 and an evaporator 5. In the compressor 1, which is designed for example as a reciprocating compressor, vapor refrigerant is sucked and compressed , In the following condenser, the refrigerant is condensed and passes through the collector 3 to the expansion valve 4, where it is relaxed. During expansion, the refrigerant pressure decreases, causing the refrigerant to cool and partially evaporate. In the evaporator 5, which is arranged in the region of a cooling point 6, the refrigerant absorbs the heat from the cooling point by evaporation. The compressor 1 sucks the evaporated refrigerant again, so that the refrigerant circuit is closed. The refrigerant flow is controlled by means of a frequency converter 70 arranged on or in the compressor as a function of the refrigeration requirement of the refrigerating point 6. In the illustration of FIG. 6 is a schematic diagram. The control of the refrigerant flow through the compressor as a function of the refrigeration demand of the cooling point 6 is explained in more detail below with reference to the block diagram of FIG. 7. For this purpose, a controller 8 is provided for generating a manipulated variable 9 as a function of the refrigeration demand of the cooling point 6. For example, the actual temperature of the cooling point 6 is compared with a desired temperature via a measuring device, not shown. Any deviation 10 is fed to the controller 8, which generates a manipulated variable 9 according to a predetermined algorithm, which is forwarded to the frequency converter 70, where the cooling demand of the cooling point 6 corresponding manipulated variable 9 in frequency and voltage for the

Compressor 1 is implemented.

The compressor 1, which is designed for example as a reciprocating compressor, has at least one motor la, which heats up according to the work to be done. According to an advantageous embodiment of the invention, the compressor 1 is constructed so that the refrigerant flowing through the compressor is also used for cooling the engine at the same time. Nevertheless, the temperature in the compressor may reach levels which no longer allow for further increase in power and, if the temperature continues to rise, trigger a motor protection circuit which will cause the motor to stop. It is therefore necessary that a temperature in the compressor determined by a suitable sensor circuit 13 and a corresponding temperature signal 14 is passed to the frequency converter 70. The sensor circuit 13 may, for example, be a sensor for measuring the winding temperature of the motor 1. For this purpose, the sensor circuit can be formed, for example, by at least one, preferably a plurality of PTC sensors with at least two different response temperatures or else by a linear temperature sensor whose output signal is subdivided into a plurality of sections. A sensor circuit suitable for this purpose can be found, for example, in EP 2 187 494 A1.

Instead of the sensor circuit 13 or in addition to this, a sensor circuit 15 may be provided, with which the temperature of the compressed in the compressor Hot gas is determined. A corresponding temperature signal 16 is also supplied to the frequency converter 70. The frequency converter may include a motor protection circuit lc that shuts off the motor la when an upper limit temperature T3 measured by at least one of the sensor circuits 13, 15 is reached. Further details of such a motor protection circuit can also be found in EP 2 187 494 A1. Reaching the limit temperature T3 and the consequent shutdown of the compressor causes the cooling point 6 is not further cooled until the cause of the shutdown found and the compressor is restarted.

In order to avoid this situation, at least in most cases, the compressor is not operated exclusively in operation with regulated voltage and frequency at which the motor is continuously switched on. Rather, it is intended that upon reaching an upper temperature threshold Tl, which is still below the limit temperature T2, an on-off operation of the motor at the rated frequency of the motor (for example, 50Hz or 60Hz) is provided. In on-off operation, the motor is periodically switched off for a predetermined period of time, for example, 10 minutes and then turned on again for a predetermined second duration. This on-off operation of the engine is carried out until the engine has cooled to a lower temperature threshold TO. From then on, the continuous operation can again take place with the motor switched on continuously and with regulated voltage and frequency.

In Fig. 8, four characteristic of the method for controlling the motor la of the compressor 1 characteristic curves are plotted over time. From top to bottom are the control value 9, the mode of operation of the motor, the frequency with which the frequency converter drives the motor la and the temperature signal T14 or T16. The control value 9 of the uppermost characteristic shows in section A after switching on the cooling in the area of the cooling point 6 a maximum control value (100%), which requires a maximum power of the compressor. The motor according to the second characteristic curve is therefore switched on and operated at a frequency greater than the nominal frequency. The temperature in the compressor shown in the lowest curve therefore increases first. In the further course of section A, the further cooling demand drops in the area of the cooling point 6, so that the manipulated variable 9 is correspondingly reduced. However, the motor of the compressor remains continuously on over the entire period, but is operated at a lower frequency than the nominal frequency.

The temperature of the compressor initially decreases accordingly. Due to the reduced refrigerant flow, however, the situation may arise that, as shown here, the temperature increases in the compressor. At the end of section A, the upper temperature threshold Tl is reached. This has the consequence that the motor of the compressor in section B is now operated in the on and off operation. While the engine is switched off, the temperature increases in the area of the cooling point, which is reflected by a correspondingly higher control value. When the motor is switched on, the motor is operated at its rated frequency (eg 50Hz or 60Hz). This is followed by further off or switch-on phases. During the on-off operation, the motor will cool from the upper temperature threshold Tl to a lower temperature threshold TO because either more refrigerant flows through the motor during turn-on than at lower frequencies than the rated frequency or in off-mode the motor current is zero amps. As soon as the lower temperature threshold TO has been reached, the motor is again operated continuously and the more precise regulation of the temperature by regulation of the motor frequency is carried out again (section C). In this way, it can be prevented in most cases that the temperature in the compressor reaches the upper limit temperature T3 at which engages the motor protection circuit. The on-off operation in section B is characterized by a periodic switching on and off of the engine, with the respective on or off period on the external circumstances (design features of the compressor, cooling load, etc.) must be adjusted. The frequency of the motor current shows in the characteristic a sudden transition between the different states. In the context of the invention, however, it is possible that the change takes place with a continuous transition.

Claims

claims

1. A method for controlling a compressor (1) of a refrigeration system having a motor (la), wherein a controller (11) controls the flow of refrigerant through the compressor (1) via at least one valve (7, 7 ') and thereby the temperature the cooling point (6) is controlled, wherein also at least one temperature in the compressor (1) is measured and evaluated and a regulation of the temperature of the cooling point (6) by an on and off operation of the motor (la) is achieved when the temperature in Compressor (1) exceeds an upper temperature threshold (T2) and a control of the temperature of the cooling point (6) by a continuously switched operation of the motor (la) takes place as soon as the motor (la) has cooled to a lower temperature threshold (TO) , Wherein the controller (11) converts a control variable (9) corresponding to the refrigeration demand of the cooling point (6) into a switching signal (12) for the valve, which provides a timed opening and closing of the vent ls (7, 7 ') causes.

2. The method according to claim 1, characterized in that the motor (la) is switched on and off periodically in the on-off operation.

3. The method according to claim 1, characterized in that the switching signal (12) of the valve is formed by a pulse width modulated signal.

4. The method according to claim 1, characterized in that the switching signal (12) has an adjustable duty cycle ratio and the controller adjusts the ratio as a function of the measured temperature in the compressor (1).

5. The method according to claim 1, characterized in that the switching signal (12) has an adjustable duty cycle ratio and the controller (11) sets the ratio as a function of the manipulated variable (9).

6. The method according to claim 5, characterized in that the duty cycle ratio of the switching signal (12) when changing from the continuous operation of the motor (la) in the on-off operation of the motor (la) and vice versa continuously in a predetermined switching period becomes.

7. The method according to claim 1, characterized in that the temperature in the compressor (1) by measuring the winding temperature of the motor (la) or by measuring the temperature of the compressor (1) compressed hot gas is determined.

8. The method according to claim 1, characterized in that the temperature in the compressor (1) by means of a sensor circuit (15, 16) with at least one, preferably a plurality of PTC sensors having at least two different response temperatures or a linear temperature sensor whose output signal in several Sections is determined.

9. The method according to claim 1, characterized in that the motor (la) is operated with a motor protection circuit which shuts off the motor (la) when an upper limit temperature (T3) of the motor (la) is reached, the upper temperature threshold ( T2), at which the motor (la) switches to the on-off operation, is below the upper limit temperature (T3).

10. The method according to claim 1, characterized in that the compressor (1) with a on the suction side of the compressor (1) arranged valve (7 ') is operated, which during the on-off operation of the motor (la) in the fully open State is.

11. The method according to claim 1, characterized in that the compressor (1) with a bypass (lb) is operated, wherein in the bypass (lb) arranged Valve (7) is in the closed state during the on-off operation of the engine (1a).

12. Refrigeration system with at least

a. a compressor (1) for compressing the refrigerant which is driven by a motor (1a)

b. a valve (7, 7 ') which regulates the flow of refrigerant through the compressor (1),

c. a controller (8) which generates a manipulated variable (9) as a function of the refrigeration demand of a refrigeration unit (6), and

d. a controller (11) communicating with the controller (8) and the valve (7, 7 ') and driving the valve (7, 7') to control the temperature of the refrigeration unit (6), wherein, e , Furthermore, a temperature measuring device for determining at least one temperature in the compressor (1) is provided, which is provided in or on the motor, and with the controller (11) is in communication and f. the control with the motor (la) is in communication and is designed such that a regulation of the temperature of the cooling point (6) by an on and off operation of the motor (la) is achieved when the temperature in the compressor (1) a upper temperature threshold (T2) and a control of the temperature of the cooling point (6) by a continuously switched operation of the motor (la) takes place as soon as the motor (la) has cooled down to a lower temperature threshold (TO), wherein the control ( 11) while the refrigeration needs the cooling point (6) corresponding control variable (9) converts into a switching signal (12) for the valve, which causes a clocked opening and closing of the valve (7, 7 ').

13. A method for controlling a compressor (1) of a refrigeration system having an engine (1a), wherein a frequency converter (70) controls the refrigerant flow through the compressor (1) by regulating the voltage and the frequency of the motor by the frequency converter (70) a control variable (9) corresponding to the refrigeration demand of a refrigeration point (6) is converted into a voltage and a frequency for the motor, characterized in that in addition at least one temperature in the

Compressor (1) is measured and evaluated, the control of the temperature of the cooling point (6) by switching on and off of the motor (la) is achieved when the temperature in the compressor (1) exceeds an upper temperature threshold (Tl) and a control the temperature of the cooling point with continuously switched on engine (la) by regulation of the

Voltage and the frequency of the motor is reached as soon as the motor (la) has cooled down to a lower temperature threshold (TO).

14. The method according to claim 13, characterized in that the motor (la) is switched on and off periodically in the on-off operation.

15. The method according to claim 13, characterized in that the motor (la) in

On-off operation is operated at its nominal frequency.

16. The method according to claim 13, characterized in that the temperature in the compressor (1) by measuring the winding temperature of the motor (la) or by measuring the temperature of the compressor (1) compressed hot gas is determined.

17. The method according to claim 13, characterized in that the temperature in the compressor (1) by means of a sensor circuit (15, 16) with at least one, Preferably, a plurality of PTC sensors having at least two different response temperatures or a linear temperature sensor whose output signal is divided into several sections, is determined.

18. The method according to claim 13, characterized in that the motor (la) is operated with a motor protection circuit which shuts off the motor (la) when an upper limit temperature (T2) of the motor (la) is reached, the upper temperature threshold ( Tl), at which the motor (la) changes to the on-off operation, is below the upper limit temperature (T2).

19. Refrigeration system with at least

a. a compressor (1) driven by a motor (1a) for compressing the refrigerant,

b. a controller (8) for generating a manipulated variable (9) as a function of the refrigeration demand of a cooling point (6) and

c. a frequency converter (70) in communication with the controller (8) and the motor (1a) for converting the control variable corresponding to the refrigeration demand of the refrigeration unit (6) into a voltage and a frequency for the motor (la) for controlling the refrigerant flow through the Compressor, characterized in that provided in or on the motor and with the frequency converter (70) in communication temperature measuring device for detecting at least one temperature in the compressor (1) is provided and the frequency converter with the motor (la) is so in communication and so is formed so that the engine (la) is in the on-off operation when the determined temperature in the compressor (1) exceeds an upper temperature threshold (Tl) and the motor (la) operated again continuously and the voltage and the frequency of the motor current in dependence the manipulated variable is controlled as soon as the motor (la) in the on and off operation up to a lower Temperatursch Has cooled (TO).