Technical Field

The present disclosure relates to a refrigeration apparatus and a method of operating a refrigeration apparatus.

Background

There are many devices and apparatus that are susceptible to freezing or frosting, that is, devices and apparatus that are susceptible or prone to a build up of ice on some part of the device or apparatus. Some examples include refrigeration apparatus, including specifically freezers and refrigerators and the like, air conditioning units, etc.

So-called frost-free refrigeration apparatus, such as freezers and refrigerators and the like, employ various methods for preventing a build-up of ice. One example of such a method is periodically heating the freezer or refrigerator to melt any ice that may have formed inside. For example, a part of the freezer or refrigerator that is susceptible to ice build-up may be heated for 5 or 10 minutes or so every 8 or 10 hours or so. This process can be wasteful and inefficient as it has no regard to whether ice has actually formed.

In addition, many types of refrigeration apparatus have an electric motor which is used to drive a component. For example, freezers and refrigerators and the like use a compressor as part of the drive for the refrigeration cycle, and the compressor is typically driven by an electric motor. It is desirable to maximise the working life of such electric motors.

Summary

According to a first aspect disclosed herein, there is provided a refrigeration apparatus, the refrigeration apparatus comprising: a chamber in which items to be cooled can be located; a compressor for compressing vaporised refrigerant; an electric motor for driving operation of the compressor; an ambient temperature sensor for measuring ambient temperature in the neighbourhood of the refrigeration apparatus; at least one inner temperature sensor for measuring a temperature of the interior of the refrigeration apparatus; and a controller constructed and arranged to receive outputs from the ambient temperature sensor and the inner temperature sensor; the controller being constructed and arranged to obtain measures of a motor current of the electric motor at time intervals which are based on the ambient temperature and the inner temperature; the controller being constructed and arranged, based on the measures of the motor current of the electric motor at the time intervals, to at least one of (ii) control operation of the electric motor and (ii) initiate a defrost procedure for the refrigeration apparatus.

This allows a dynamic control of the operation of the electric motor and/or initiation of the defrost procedure for the refrigeration apparatus, in a manner that is related directly to the environmental and operating conditions. Examples described herein make use of components, such as ambient and inner temperatures sensors, motor controllers, etc., that are typically already provided in a refrigeration apparatus and therefore the cost of implementing this in practice is low.

In an example, the controller is arranged such that the time intervals at which the measures of the motor current of the electric motor are obtained are based on the difference between the ambient temperature and the temperature of the interior of the refrigeration apparatus.

In an example, the controller is arranged such that the time intervals in units of time are proportional to the magnitude of the difference between the ambient temperature and the temperature of the interior of the refrigeration apparatus.

By way of one example only, the time intervals in units of minutes may be equal or proportional to the difference between the ambient temperature and the temperature of the interior of the refrigeration apparatus in units of degree Kelvin (or, equivalently, Celsius).

In an example, the controller is arranged to at least one of (ii) control operation of the electric motor and (ii) initiate a defrost procedure for the refrigeration apparatus based on comparing the values of the motor current as measured at adjacent time intervals.

In an example, the values of the motor current as measured at adjacent time intervals are compared by, for each adjacent pair of time intervals, taking a difference of the motor currents as measured in the adjacent time intervals, and comparing the number of said difference of the motor currents that are less than a predetermined percentage threshold with the number of said difference of the motor currents that are more than the percentage threshold.

Broadly speaking and in general, in an example, if the difference of the motor currents at an adjacent pair of time intervals is more than a predetermined percentage threshold, this is taken to mean that the change in current is because of a (deliberate) change in operation of the compressor. That is, the compressor is being correctly driven to cool the refrigeration apparatus, with associated large changes in the compressor motor drive current. On the other hand, if the difference of the motor currents at an adjacent pair of time intervals is less than a predetermined percentage threshold, this means that the change in current is small. This is taken to mean that there has been no commanded change in the compressor motor drive current and the change in current is therefore due to icing in the refrigeration apparatus.

In an example, in the case that, over a time period, the number of said difference of the motor currents that are less than the predetermined percentage threshold is substantially the same as the number of said difference of the motor currents that are more than the percentage threshold, then the controller is arranged to command the electric motor to run at a lower speed and to initiate a defrost procedure for the refrigeration apparatus. This reflects the fact that some, but not major, icing of the refrigeration apparatus has occurred. A defrost procedure should be carried out, but the compressor can still operate, though at a lower speed to preserve the working life of the motor.

In an example, in the case that, over a time period, the number of said difference of the motor currents that are less than the predetermined percentage threshold is more than around twice the number of said difference of the motor currents that are more than the percentage threshold, then the controller is arranged to command the electric motor to stop and to initiate a defrost procedure for the refrigeration apparatus.

This reflects the fact that major icing of the refrigeration apparatus has occurred. A defrost procedure should be carried out, and the compressor motor should be stopped as the icing is so severe.

In an example, the refrigeration apparatus comprises: an evaporator in which refrigerant vaporises in use to absorb heat from the chamber; pipes for respectively carrying refrigerant from the evaporator to the compressor and for carrying refrigerant from the compressor to the evaporator; one or more fans for circulating air within the refrigeration apparatus; and one or more air channels through which cold air passes in use to circulate cold air within the refrigeration apparatus.

According to a second aspect disclosed herein, there is provided a method of operating a refrigeration apparatus, the refrigeration apparatus comprising: a chamber in which items to be cooled can be located; a compressor for compressing vaporised refrigerant; an electric motor for driving operation of the compressor; an ambient temperature sensor for measuring ambient temperature in the neighbourhood of the refrigeration apparatus; and at least one inner temperature sensor for measuring a temperature of the interior of the refrigeration apparatus; the method comprising: a controller receiving outputs from the ambient temperature sensor and the inner temperature sensor; the controller obtaining measures of a motor current of the electric motor at time intervals which are based on the ambient temperature and the inner temperature; and based on the measures of the motor current of the electric motor at the time intervals, the controller at least one of (ii) controlling operation of the electric motor and (ii) initiating a defrost procedure for the refrigeration apparatus.

In an example, the time intervals at which the measures of the motor current of the electric motor are obtained are based on the difference between the ambient temperature and the temperature of the interior of the refrigeration apparatus.

In an example, the time intervals in units of time are proportional to the magnitude of the difference between the ambient temperature and the temperature of the interior of the refrigeration apparatus.

In an example, the controller at least one of (ii) controls operation of the electric motor and (ii) initiates a defrost procedure for the refrigeration apparatus based on comparing the values of the motor current as measured at adjacent time intervals.

In an example, the values of the motor current as measured at adjacent time intervals are compared by, for each adjacent pair of time intervals, taking a difference of the motor currents as measured in the adjacent time intervals, and comparing the number of said difference of the motor currents that are less than a predetermined percentage threshold with the number of said difference of the motor currents that are more than the percentage threshold.

In an example, in the case that, over a time period, the number of said difference of the motor currents that are less than the predetermined percentage threshold is substantially the same as the number of said difference of the motor currents that are more than the percentage threshold, then the controller commands the electric motor to run at a lower speed and initiates a defrost procedure for the refrigeration apparatus.

In an example, in the case that, over a time period, the number of said difference of the motor currents that are less than the predetermined percentage threshold is more than around twice the number of said difference of the motor currents that are more than the percentage threshold, then the controller commands the electric motor to stop and initiates a defrost procedure for the refrigeration apparatus.

Brief Description of the Drawings

To assist understanding of the present disclosure and to show how embodiments may be put into effect, reference is made by way of example to the accompanying drawings in which:

Figure 1 shows schematically an example of a refrigeration apparatus according to an embodiment of the present disclosure; and

Figure 2 shows schematically a flow of operations in an example of a method of operating refrigeration apparatus according to an embodiment of the present disclosure.

Detailed Description

The term “refrigeration apparatus” will be used herein specifically to include freezers and refrigerators and the like. The term “refrigeration apparatus” as used herein may also include air conditioning units and other devices or apparatus that are susceptible to frosting, including in particular devices or apparatus that rely on the flow of a refrigerant, unless the context requires otherwise.

Referring now to the drawings, Figure 1 shows schematically an example of a refrigeration apparatus 10 according to an embodiment of the present disclosure. The refrigeration apparatus 10 may be for example a refrigerator or a freezer. In this example, the refrigeration apparatus 10 is specifically a “fridge-freezer”. In some examples, the refrigeration apparatus may be an air conditioning unit or some other apparatus that is susceptible to freezing or has parts that are susceptible to freezing.

The refrigeration apparatus 10 implements a vapour-compression refrigeration cycle to cool one or more spaces (indicated generally at 12) within the refrigeration apparatus 10. In an example, the vapour-compression refrigeration cycle (described in more detail below) is implemented to cool a freezer portion 12’ of the space 12 to below 0°C. Other portions of the space 12, such as a cool chamber 12”, will also be cooled (to a low temperature above 0°C) depending on the temperature of the freezer portion 12’ and the layout of the refrigeration apparatus 10. In any event, the freezer portion 12’ represents a subsection of the space 12 in which substances, such as foodstuffs 14, etc., may be placed to freeze them and the cool chamber 12” represents a subsection of the space 12 in which substances, such as foodstuffs 14, etc., may be placed to cool them. More generally, the vapour-compression refrigeration cycle may be used to cool a space 12 of a refrigeration apparatus 10 even if the refrigeration apparatus 10 does not have a freezer portion as such.

The refrigeration apparatus 10 comprises a closed circuit of pipe or tubing 16 containing a selected refrigerant for cooling the space 12. The tubing 16 connects an evaporator 18 and a compressor 20 to pass refrigerant therebetween. The refrigerant is selected having a temperature of vaporisation such that it will vaporise in the evaporator 18 as it absorbs heat from the space 12 (in this example, specifically from the freezer portion 12’ of the space 12).

The compressor 20 is provided to compress the vaporised refrigerant and so raise its temperature significantly. The high pressure, high temperature refrigerant vapour passes from the compressor 20 through a first portion of the tubing 16. This first portion of the tubing 16 acts as a condenser in the refrigeration cycle, transferring heat to the environment (e.g. the room in which the refrigeration apparatus 10 is located). The transfer of heat causes at least some of the refrigerant vapour in the first portion of the tubing 16 to condense back to a liquid form. The high pressure refrigerant, now cooled and at least partially in liquid form, passes to an expansion valve (not shown) which reduces the pressure of the refrigerant, causing it to expand and cool. The low pressure low temperature refrigerant then passes through the evaporator 18, where the refrigerant absorbs heat from the space 12 (particularly from the freezer portion 12’ in this example). As a result, the cool refrigerant liquid passing through the evaporator 18 vaporises before passing through a second portion of the tubing 16 back to the compressor 20 to complete the refrigeration cycle.

The compressor 20 is driven by a motor 22. The motor 22 is provided with electrical power from a power supply (such as a mains electricity power supply) via a power board 24 of the refrigeration apparatus 10. The motor 22 may be a direct current electric motor. In a particular example, the motor 22 is a BLDC motor, that is, a brushless direct current electric motor. As another example, the motor 22 may be a permanent magnet synchronous motor (PMSM) or some other type of synchronous motor. The power board 24 may include an inverter which causes appropriate motor phase currents to be produced and output to control the rotational speed of the motor 22 in a manner known per se.

One or more fans 26 may be provided in the refrigeration apparatus 10 to blow air around in order to improve the transfer of heat out of the freezer portion 12’ and the cool chamber 12” to the refrigerant liquid.

The various parts of the refrigeration apparatus 10 described above are contained within a housing 28, as conventional, which typically has a first door 30 to allow access to the freezer portion 12’ and a second door 32 to allow access to the cool chamber 12”.

The refrigeration apparatus 10 further has an ambient temperature sensor 34 for measuring the ambient temperature, that is, the temperature in the surrounding environment of the refrigeration apparatus 10 (e.g. the room in which the refrigeration apparatus 10 is located). The refrigeration apparatus 10 also has at least one temperature sensor for measuring the internal temperature of the refrigeration apparatus 10. In this example, the refrigeration apparatus 10 has a freezer compartment temperature sensor 36 for measuring the temperature within the freezer portion 12’ and a cool compartment temperature sensor 38 for measuring the temperature within the cool chamber 12”. In other examples, there may be a single temperature sensor for measuring the temperature in one or other of the freezer portion 12’ and the cool chamber 12”. Outputs from the temperature sensors 34, 36, 38 are passed to a main board 40, which operates as a controller to monitor and control the operation of the refrigeration apparatus 10 generally. The main board 40 is in serial communication with the power board 24 of the motor 22. The main board 40 may have one or more processors, memory and the like.

One or more air channels 42 are provided within the refrigeration apparatus 10 to allow air flow (shown by wavy arrows in Figure 1) generally through the refrigeration apparatus 10 so as to promote and facilitate cooling of the freezer portion 12’ and the cool chamber 12”. In particular, in this example air channels 42 are provided towards the rear of the refrigeration apparatus 10, generally vertically arranged behind the freezer portion 12’ and the cool chamber 12”, with the air channels passing into the freezer portion 12’ and the cool chamber 12” to allow air to flow into and out of the freezer portion 12’ and the cool chamber 12”. One or more of the fans 26 may be arranged in one or more of the air channels 42 to promote air flow thought the air channels 42.

Because of the low temperatures generated within the refrigeration apparatus 10, and particularly within the freezer portion 12’, humidity from the air may freeze to one or more parts of the refrigeration apparatus 10, causing ice to build up over time. For example, ice can particularly form on one or more of the evaporator 18, the tubing 16 and in or on bearings of one or more of the fans 26. Ice can also form within one or both of the freezer portion 12’ and the cool chamber 12”. In addition, as indicated schematically in Figure 1, ice 44 can also form in and partially block the air channels 42. This can particularly occur if the user has placed a foodstuff 14 or other material such that it blocks an air inlet/outlet to the freezer portion 12’ and/or the cool chamber 12” as that restricts the flow of air in and out of the freezer portion 12’ and/or the cool chamber 12”, as indicated schematically in Figure 1. Ice build-up (also called “frost”) in the freezer portion 12’ and/or the cool chamber 12” is undesirable because it occupies space within the freezer portion 12’ or the cool chamber 12”, which could otherwise be used for storage (e.g. of foodstuffs 14) and reduces the efficiency of the refrigeration apparatus 10. Ice build-up on the evaporator 18 and/or in other parts of the refrigeration apparatus 10, such as the air channels 42 and in or on bearings of one or more of the fans 26, is undesirable because it reduces the efficiency of the refrigeration apparatus 10. This in turn can cause the compressor motor 22 to drive the compressor 20 for longer periods of time and/or at a higher rate (e.g. in terms of the revolutions per minute of the compressor motor 22) which consumes energy and can also reduce the working life of the compressor motor 22 through wear.

A user of the refrigeration apparatus may manually “defrost” the refrigeration apparatus 10 periodically by allowing the freezer portion 12’ and/or other frozen parts of the refrigeration apparatus 10 to heat up to a point at which the ice melts, and then removing the resulting liquid water.

Some known refrigeration apparatus have an arrangement, such as a heating resistor or other heating element, for heating up the freezer portion 12’ and/or other frozen parts of the refrigeration apparatus 10 briefly in order to melt the ice layer and thereby defrost the freezer portion 12’ and/or other frozen parts of the refrigeration apparatus 10. In such known refrigeration apparatus, the defrost process may be performed automatically and periodically on a cycle (such as, by way of example only, for 5 or 10 minutes or so every 8 or 10 hours or so), irrespective of how much frost has actually built up. This process can be wasteful and inefficient as it has no regard to whether ice has actually formed.

Discussing further the compressor motor 22, as mentioned, this may be for example a BLDC motor, or for example a permanent magnet synchronous motor (PMSM) or some other type of synchronous motor. The power board 24 may include an inverter which causes appropriate motor phase currents to be produced and output to control the motor 22 in a manner generally known per se. In any case, the power board 24 controls the rotation speed of the motor 22 so as to drive the compressor 20 to operate in accordance with a control algorithm, to achieve the desired or set temperature for one or both of the freezer portion 12’ and the cool chamber 12”. Such arrangements are increasingly used in refrigeration apparatus as they are more efficient than the traditional on/off control type refrigerators which were operated using simple thermostats. In general, the cooling algorithms of BLDC or similar type refrigerators have different speed commands for different conditions. As a particular example, BLDC-type compressor producers generally offer three or five level speed operation from low speeds (300-500rpm) to high speeds (3000-5000rpm). This is intended to provide a long operation life for the motor 22.

In general, if the compressor 20 is working harder, for example to compress vaporised refrigerant at a higher rate, then a larger drive current is applied to the compressor motor 22 and the compressor motor 22 rotates at a higher speed. The compressor 20 works harder than necessary if for example ice has built up in the refrigeration apparatus 10 because of the reduced efficiency of the refrigeration cycle in the refrigeration apparatus 10. Constantly or frequently running the compressor motor 22 at a high speed can damage the compressor motor 22 or at least make it less efficient and reduce its useful working life before it has to be replaced.

According to an example of the present disclosure, an automated procedure is carried out to at least one of (ii) control operation of the electric motor 22 and (ii) initiate a defrost procedure for the refrigeration apparatus 10. This is based on measures of the motor current of the electric motor 22 at time intervals. The time intervals, at which the measures of the motor current of the electric motor 22 are taken, are based on the ambient temperature and an inner temperature of the refrigeration apparatus 10. Amongst other things, this means that the control of the operation of the electric motor 22 and/or initiation of the defrost procedure for the refrigeration apparatus 10 is dynamic in that it is related directly to the environmental and operating conditions (in particular, the ambient temperature and the inner temperature of the refrigeration apparatus 10 and the motor current of the electric motor 22). Such environmental and operating conditions can be analysed and used as an indication that icing of the refrigeration apparatus 10 has occurred. Such conditions can also be used to provide a measure of the severity of the icing of the refrigeration apparatus 10. Appropriate action can be automatically taken.

Discussing now a particular example in more detail and with reference to Figure 2, first it is noted that if the internal temperature of the refrigeration apparatus 10 is much lower than ambient temperature, then it can be assumed that the refrigeration apparatus 10 is operating well. On the other hand, if the internal temperature of the refrigeration apparatus 10 is close to ambient temperature, then it can be assumed that the refrigeration apparatus 10 is not operating well. The fact that the refrigeration apparatus 10 is not operating well is an indication that one or more parts of the refrigeration apparatus 10 have iced up. In a particular example, this is utilised to ensure that action is taken at the most appropriate times. For example, control of operation of the electric motor 22 and/or initiation of a defrost procedure for the refrigeration apparatus 10 is carried out dynamically, in response to changing temperature conditions. This differs from a number of know arrangements which always defrost at fixed time intervals, as noted above.

The internal temperature of the refrigeration apparatus 10 which is used for this may be the temperature of one or other of the freezer portion 12’ and the cool chamber 12”, as measured by the freezer compartment temperature sensor 36 and the cool compartment temperature sensor 38 respectively. As another example, the internal temperature of the refrigeration apparatus 10 which is used for this may be the average of the temperatures of the freezer portion 12’ and the cool chamber 12” as measured by the respective temperature sensors 36, 38. That is, in an example:

T inner = (T freezer + T_cooler)/2 Eq. 1

This internal temperature of the refrigeration apparatus 10 is then compared with the ambient temperature as measured by the ambient temperature sensor 34 in order to determine the time intervals at which the measures of the motor current of the electric motor 22 are taken. Simply put and in general, if there is a large difference between the internal temperature and the ambient temperature, then the motor current does not need to be measured so frequently, and so the measurement time interval may be large. On the other hand, if there is a small difference between the internal temperature and the ambient temperature, then the motor current needs to be measured more frequently, and so the measurement time interval may be small. Accordingly, in one example, the measurement time intervals are based on the difference between the internal temperature and the ambient temperature, such that larger differences in temperature result in larger (longer) measurement time intervals and smaller differences in temperature result in smaller (shorter) measurement time intervals. As one particular example, the time intervals in units of time are proportional to the magnitude of the difference between the ambient temperature and the temperature of the interior of the refrigeration apparatus 10. That is: t_measurement = A |(T_ambient - T_inner)| Eq. 2 where A is some constant of proportionality.

By way of example only, the time intervals in units of minutes may be equal or proportional to the difference between the ambient temperature and the temperature of the interior of the refrigeration apparatus 10 in units of degree Kelvin (or, equivalently, Celsius). For example, a small temperature difference of say only 3K (or 3 °C) may result in a measurement time interval of 3 minutes, whereas a large temperature difference of say 3 OK (or 30°C) may result in a measurement time interval of 30 minutes. Other formulae for relating the measurement time intervals to the difference between the ambient temperature and the temperature of the interior of the refrigeration apparatus 10 are possible.

This is illustrated in Figure 2 with a number of measurement time intervals ti, t2, t3, t4, ... tn being indicated.

As noted, the ambient temperature and the temperature of the interior of the refrigeration apparatus 10 are measured in order in turn to calculate the of measurement time intervals ti, t2, t3, t4, ... tn at which the measures of the motor current of the electric motor 22 are taken. The time intervals at which the ambient temperature and the temperature of the interior of the refrigeration apparatus 10 are measured may be regular time intervals. The time intervals at which the ambient temperature and the temperature of the interior of the refrigeration apparatus 10 are measured may depend on for example the specification of the refrigeration apparatus 10. For example, a small refrigeration apparatus 10 is likely to cool down more quickly and heat up more quickly than a large refrigeration apparatus 10. Therefore, in general and in an example, the time intervals at which the ambient temperature and the temperature of the interior of the refrigeration apparatus 10 are measured are smaller for a small refrigeration apparatus 10 and large for a large refrigeration apparatus 10. The time intervals at which the ambient temperature and the temperature of the interior of the refrigeration apparatus 10 are measured may also depend on how many compressors and/or how many fans are present in the refrigeration apparatus 10.

As some illustrative but non-limiting examples:

(a) for small size refrigerators with a capacity smaller than 250 litres, one compressor and one fan, the ambient temperature and the temperature of the interior of the refrigeration apparatus 10 may be measured every 30 seconds,

(b) for middle size refrigerators with a capacity of 250-450 litres, one compressor and two fans, the ambient temperature and the temperature of the interior of the refrigeration apparatus 10 may be measured every minute, and

(c) for large refrigerators with a capacity more than 450 litres, one or two compressors and more than two fans, the ambient temperature and the temperature of the interior of the refrigeration apparatus 10 may be measured every 2 minutes.

It is emphasised that these time intervals at which the ambient temperature and the temperature of the interior of the refrigeration apparatus 10 may be measured are different from the (calculated) time intervals at which the motor current of the electric motor 22 is measured.

Next, the motor current of the electric motor 22 is measured or noted at those measurement time intervals to give a series of corresponding motor currents ii, i2, is, 14, ... in.. The motor current that is used for this may be different for different types of electric motor. In the specific case of a BLDC motor, which is commonly used in refrigeration apparatus, the motor current that is used for this may be the iq current, that is the measured value of the q axis current. As is known per se, in this notation, for a three phase power supply, the “d” and “q” axes are the single-phase representations of the flux contributed by the three separate sinusoidal phase quantities at the same angular velocity. The d axis, also known as the direct axis, is the axis by which flux is produced by the field winding. The q axis, or the quadrature axis, is the axis on which torque is produced. By convention, the quadrature axis always leads the direct axis electrically by 90°. The d axis may be regarded as the main flux direction and the q axis may be regarded as the main torque-producing direction. The measured values of the q and d axis currents are obtained from the 3- phase motor phase currents, which are commonly given the notation i _a , ib, ic. In itself, this is already carried out with known BLDC motors that use field-oriented control (FOC) to control the speed of rotation of the motor in an efficient way.

Having obtained the motor currents ii, i2, 13, 14, ... in at the respective time intervals ti, t2, t3, t4, ... tn, the difference (i(n+i) - in) of the motor currents in adjacent time intervals is calculated for each adjacent pair of time intervals/measured currents. This gives a series of current differences which, following the notation above, may be indicated as follows:

[| i 1- 12|, 112- 13|, 113- 14|, . . . , |l(n-l) - ln|] Eq. 2

Broadly speaking and in general, if the difference of the motor currents at an adjacent pair of time intervals is more than a predetermined percentage threshold, this is taken to mean that the change in current is because of a (deliberate) change in operation of the compressor 20. That is, the compressor 20 is being correctly driven to cool the refrigeration apparatus 10, with associated large changes in the compressor motor drive current. On the other hand, if the difference of the motor currents at an adjacent pair of time intervals is less than a predetermined percentage threshold, this means that the change in current is small. This is taken to mean that there has been no commanded change in the compressor motor drive current and the change in current is therefore due to icing in the refrigeration apparatus 10, with associated small changes in the compressor motor drive current.

In an example, the number of small changes in motor current at the measurement time intervals is compared with the number of large changes in motor current at the measurement time intervals. A number of ways of making this comparison are possible. In one example, if the motor currents at an adjacent pair of time intervals changes by less than for example 10%, that is for example if (i(n+i) - in) / in < 10%, then this is taken as a small change. On the other hand, if the motor currents at an adjacent pair of time intervals changes by for example 10% or more, that is for example if (i(n+i) - in) / in > 10%, then this is taken as a large change. The number of small changes over a time period is compared to the number of large changes in the time period. The optimum time period for this may depend on for example the specification of the refrigeration apparatus 10 (e.g. capacity, number of compressors, number of fans, etc.), ambient temperature, the ambient humidity, etc. In general, for a small refrigerator, the time period for the comparison of the number of small changes with the number of large changes may be around 30 minutes or so, for a medium size refrigerator around 45 minutes or so, and for a large size refrigerator around 60 minutes or so.

A decision is then made at the controller on the main board 40 as to whether to change the operation of the motor 22 and whether to initiate a defrost procedure. This may be based on various criteria for comparing the number of small changes of current with the number of large changes of current.

In a specific example, given by way of illustration, a first case is if the number of small changes of current is less than half the number of large changes of current. A second case is if the number of small changes of current is at least approximately the same as the number of large changes of current. A third case is if the number of small changes of current is more than twice the number of large changes of current. (In this example, the second case may be regarded as those not falling in the first or third cases, that is, the number of small changes of current is at least approximately the same as the number of large changes of current if the numbers are within around 50% of being the same.)

In the first case, where the number of large changes of current is (much) greater than the number of small changes of current, this means that the motor current changes are those commanded by the power board 24 in accordance with a predefined cooling algorithm. That is, in an example, these large changes are created by different speed levels of the motor 22. So, in the first case, there is no extreme load in the refrigeration apparatus 10 and cooling is being provided properly, without any unwanted icing.

In the second case, where the number of large changes of current is at least approximately the same as the number of small changes of current, this means that the motor current is changing because of both the cooling algorithm commands and unwanted icing. This can be inferred because small drops in the currents are independent of the cooling algorithm commands and reference speeds of the motor (see below) and therefore must be related to unwanted icing. So, in this case, there is loading in the refrigeration apparatus 10 because of some unwanted icing.

In the third case, where the number of small changes of current is (much) greater than the number of large changes of current, this means that the motor current changes predominantly because of unwanted icing. So, in this case, there is extremeloading in the refrigeration apparatus 10 because of a large amount of unwanted icing.

This can be visualised as indicated in Figure 2. It is noted that the controller on the main board 40 may operate in line with this visualisation. A row matrix 50, i.e. a single row of cells, is formed in which the elements in the cells are the respective differences (i(n+i) - in) of the motor currents in adjacent time intervals. In the bottom left of Figure 2, a graph is shown which illustrates the respective differences (i(n+i) - in) of the motor currents for the time intervals. It may be noted that this demonstrates that the duration of the time intervals differs as these depend on the difference between the ambient temperature and the inner temperature of the refrigeration apparatus 10 as discussed above. For any cell where the difference of the motor currents at an adjacent pair of time intervals is less than a predetermined percentage threshold (e.g. ±10%), then a first value (e.g. zero) may be attributed to that cell. For each of the other cells (having a large difference in motor current), a second, different value (e.g. one) may be attributed to that cell. The number Nzeros of zeros is counted, and the number Nones of ones is obtained (here as the total number of cells Ntotai less the number Nzeros of zeros). Case 1 is where Nzeros < Nones/2, which is taken as no extreme load and no unwanted icing. Case 2 is where Nzeros ~ Nones/2, which is taken as some loading due to some unwanted icing. Finally, case 3 is where Nzeros > 2*Nones, which is taken as an extreme load with a large amount of unwanted icing.

For case 1, where it is taken that there is no unwanted icing in the refrigeration apparatus 10, no special action needs to be taken. The refrigeration apparatus 10 can operate as normal, including in particular operating the motor 22 to drive the compressor 20 using a conventional mode of operation.

On the other hand, for case 2, where there is some but not a large amount of unwanted icing, in an example the main board 40 initiates a defrost operation (for example, causing local heaters to operated to melt ice, in a manner known per se). In addition, the main board 40 instructs the power board 24 to reduce the rotation speed of the motor 22 which is driving the compressor 20. This is to avoid the motor 22 being driven unnecessarily hard, given that ice is present and so the cooling efficiency of the refrigeration apparatus 10 is reduced. This prolongs the working life of the motor 22. Once the ice has defrosted, which will be detected in line with the method described above, and the refrigeration apparatus 10 moves to case 1, the motor speed can be changed as normal in accordance with the predefined cooling algorithm.

Finally, for case 3, where there is a large amount of unwanted icing, in an example the main board 40 initiates a defrost operation (for example, causing local heaters to operated to melt ice, in a manner known per se). In addition, the main board 40 instructs the power board 24 to stop the rotation of the motor 22 which is driving the compressor 20. This is in view of the fact that the icing in the refrigeration apparatus 10 is so severe that operation of the compressor 20 is pointless as no cooling can be effectively achieved. This again will prolong the working life of the motor 22. Once the ice has defrosted, which will be detected in line with the method described above, and the refrigeration apparatus 10 moves to case 1, the motor 22 can be operated as normal in accordance with the predefined cooling algorithm.

Examples described herein provide for a dynamic control of the operation of the electric motor 22 and/or initiation of the defrost procedure for the refrigeration apparatus 10. That is the electric motor 22 is operated and/or a defrost procedure is carried out in a manner that is related directly to the environmental and operating conditions (in particular, the ambient temperature and the inner temperature of the refrigeration apparatus 10 and the motor current of the electric motor 22). Examples described herein make use of components, such as ambient and inner temperatures sensors, motor controllers, etc., that are typically already provided in a refrigeration apparatus 10 and therefore the cost of implementing this in practice is low.

It will be understood that the processor or processing system or circuitry referred to herein may in practice be provided by a single chip or integrated circuit or plural chips or integrated circuits, optionally provided as a chipset, an applicationspecific integrated circuit (ASIC), field-programmable gate array (FPGA), digital signal processor (DSP), graphics processing units (GPUs), etc. The chip or chips may comprise circuitry (as well as possibly firmware) for embodying at least one or more of a data processor or processors, a digital signal processor or processors, baseband circuitry and radio frequency circuitry, which are configurable so as to operate in accordance with the exemplary embodiments. In this regard, the exemplary embodiments may be implemented at least in part by computer software stored in (non-transitory) memory and executable by the processor, or by hardware, or by a combination of tangibly stored software and hardware (and tangibly stored firmware).

Although at least some aspects of the embodiments described herein with reference to the drawings comprise computer processes performed in processing systems or processors, the invention also extends to computer programs, particularly computer programs on or in a carrier, adapted for putting the invention into practice. The program may be in the form of non-transitory source code, object code, a code intermediate source and object code such as in partially compiled form, or in any other non-transitory form suitable for use in the implementation of processes according to the invention. The carrier may be any entity or device capable of carrying the program. For example, the carrier may comprise a storage medium, such as a solid- state drive (SSD) or other semiconductor-based RAM; a ROM, for example a CD ROM or a semiconductor ROM; a magnetic recording medium, for example a floppy disk or hard disk; optical memory devices in general; etc. The examples described herein are to be understood as illustrative examples of embodiments of the invention. Further embodiments and examples are envisaged. Any feature described in relation to any one example or embodiment may be used alone or in combination with other features. In addition, any feature described in relation to any one example or embodiment may also be used in combination with one or more features of any other of the examples or embodiments, or any combination of any other of the examples or embodiments. Furthermore, equivalents and modifications not described herein may also be employed within the scope of the invention, which is defined in the claims.