GB2513943A

GB2513943A - Method and system for cooling a device

Info

Publication number: GB2513943A
Application number: GB1401204.1A
Authority: GB
Inventors: John Paul Kurpiewski; Simon David Hart
Original assignee: Nidec Control Techniques Ltd
Current assignee: Nidec Control Techniques Ltd
Priority date: 2013-05-03
Filing date: 2013-05-03
Publication date: 2014-11-12
Anticipated expiration: 2033-05-03
Also published as: US20140326442A1; GB201401204D0; GB2513650B; GB201308014D0; IN2014MU01105A; CN104133502A; GB2513943B; GB2513650A; CN104133502B

Abstract

A method / system of cooling a device 16 generating heat comprises monitoring temperature 18 of the device, automatically operating a cooling means 14 at a first rate if the monitored temperature rises above a first temperature threshold, and automatically operating the cooling means at a second increased rate if the monitored temperature rises above a second temperature threshold. Current of the device is monitored 11 and the cooling means is automatically operated at the second rate if the monitored current rises above a threshold. The device may be a motor and the cooling means may comprise a fan or pump arranged to push or suck a coolant through a jacket. Cooling rate may comprise speed of the fan or a pumping rate at which the liquid is pumped. Cooling rate may be automatically decreased if the monitored temperature drops below the second threshold, which decrease may be to the first rate. Cooling rate may be automatically decreased if the monitored temperature drops below the first threshold, which decrease may be to zero. The first, second rate may be constant, variable. The second threshold may be higher than the first threshold. The second rate may be a maximum rate.

Description

METHOD AND SYSTEM FOR COOLING A DEVICE

Field of the Invention

The present invention relates to a method of cooling a heat-generating device, and in particular to a method of cooling a heat-generating device through controlled use of cooling means such as a fan. The invention also relates to a system arranged to cool a heat-generating device.

Background to the Invention

Motor drives or simply drives are used to control the flow of power delivered to electric motors for their operation. During high-intensity bursts of output current, for example when the motor is being operated at its rated threshold, the heat generated by the motor drive can become quite high, even for a burst or pulse of relatively short duration (such as of the order of ten seconds or so). Increased heat generation can cause a motor or its drive to operate above its safety threshold, which if sustained can cause damage to the motor and/or its surroundings.

A typical method of extracting heat generated in a motor is to use a fan to cool the drive. Fan cooling, whilst relatively efficient, generates a substantial amount of noise. In certain applications, the noise generated by a fan can be especially undesirable.

For example, in theatre applications, noise levels must be kept to a minimum to avoid interfering with the filming, lighting or stage movements, even when a motor is in use. In another example application, motors used to operate lifts or elevators are often located at the top of multi-storey buildings, where property is typically more expensive. Because of the premium charged for such properties, the need to keep noise levels to a minimum is therefore particularly desirable in such locations. Thus, given the proximity of such properties to the cooling system or fan, it is desirable to reduce the noise level of the fan to a minimum or at least acceptable level without also compromising the cooling of the motor.

The present invention seeks to address this and other deficiencies encountered

in the prior art.

Summary of the Invention

In accordance with a first aspect of the invention, there is provided a method of cooling a device generating heat. The method comprises monitoring a temperature associated with the device. The method also comprises automatically operating a cooling means at a first rate if the monitored temperature rises above a first temperature threshold. The method also comprises automatically operating the cooling means at a second increased rate if the monitored temperature rises above a second temperature threshold.

The device may be any device capable of generating heat. For example, the device may be an electric motor drive. In particular, if left unchecked the sustained heat generation may be such that damage is caused to the device. The monitored temperature may be monitored substantially continuously or periodically. The temperature may be an ambient air temperature in close proximity to the device. In other embodiments, the measured or monitored temperature may be a measured/monitored temperature of a particular component of the device, such as a heat sink, and may be designated an operating temperature of the device. Various types of measuring equipment may be used to monitor the temperature, such as a thermistor, a thermometer, etc. In some embodiments, the point at which the temperature climbs above the first threshold may be measured using a first temperature measuring means, whilst the point at which the temperature climbs above the second threshold may be measured using a second temperature measuring means. Alternatively, they may be measured using common means.

The cooling means may take various different forms and in a preferred embodiment is a cooling fan or other airflow generating means design to blow, suck or otherwise draw air over the device. In another embodiment, the cooling means may be a pump arranged to push or suck a cooling liquid such as cool water or some other coolant through a jacket. The jacket may be adjacent the device (or in particular may surround the device) and thereby may be arranged to extract heat from the device as the device is being run. The rate of the cooling means may therefore be a speed at which a fan is operated, or a pumping rate at which a liquid is pumped through a jacket. Other types of cooling means are contemplated, such as any cooling means capable of being operated at different rates.

The first rate may be qualified as a relatively low rate, and for example may be from about 10% to about 25% of a maximum rate of the cooling means. In one embodiment, the first rate is from about 10% to about 85% of a maximum rate of the cooling means. The second rate may be qualified as a relative high rate and for example may be from about 50% to about 100% of the maximum rate. In one embodiment, the second rate is from about 85% to about 100% of a maximum rate of the cooling means. These rates may depend on various factors, such as the operating characteristics of the cooling means. In one embodiment, the second rate may be the maximum rate of the cooling means. For example, the maximum rate may be a maximum operating or maximum safe' rate of the cooling means. The rate of the cooling means may be automatically increased to a maximum rate if the monitored temperature rises above the second temperature threshold. The rate of the cooling means may also be automatically increased from the first rate to the second increased rate if the monitored temperature rises above the second temperature threshold.

According to the above method, the point at which the monitored temperature reaches the second threshold may be delayed by operating the cooling means at a first rate prior to operating the cooling means at an increased second rate. In applications in which short periods of relatively high heat generation are experienced, this can be advantageous as it may delay the point at which the cooling means needs to be operated at a high level, reducing the overall noise generation of the cooling means. Furthermore, by operating the cooling means at a first rate before it is actually thermally necessary to activate the cooling means, the duration of time over which the cooling means is operated at a second, higher rate (which may be a maximum rate) is reduced. This for example may help to conserve power if operating the cooling means on maximum power is particularly resource intensive. It may also entirely avoid the need to operate the cooling means at the second, increased rate if the second temperature threshold is not reached, thereby reducing the likelihood of the device malfunctioning due to excessive heat generation.

The method may further comprise automatically decreasing the rate of the cooling means if the monitored temperature drops below the second temperature threshold. In particular, the rate of the cooling means may be automatically decreased to the first rate if the monitored temperature drops below the second temperature threshold. Advantageously, the noise output from the cooling means may be minimised by reducing the rate of the cooling means when the temperature drops below the second threshold. Furthermore, cooling of the heat-generating device may be maintained at a relatively low rate so as to minimise noise generation of the cooling means without compromising on the cooling of the device.

The method may further comprise automatically decreasing the rate of the cooling means if the monitored temperature drops below the first temperature threshold. Thus, if the temperature drops below the first, warning' threshold, the system may be configured such that the cooling rate may be reduced further and in fact the cooling means may be switched off entirely, to conserve power. Thus, the rate of the cooling means may be automatically decreased to zero if the monitored temperature drops below the first temperature threshold. The rate of the cooling means may be automatically increased from zero to the first rate if the monitored temperature rises above the first temperature threshold. Below the first temperature, there may be no thermal requirement to operate the cooling means, thereby saving on power.

In the embodiments described herein, increasing or decreasing the cooling rate may be a substantially instantaneous change or else may be effected over a certain timespan. Varying the cooling rate over a non-trivial time period, according to the measured temperature, would prevent the system rapidly switching the cooling means from one rate to another, and would provide a more gradual rate of change in the cooling rate, as well as more efficient noise management.

The first and second rates may be pre-set by the controller, or else may be dynamically configured. The first and second rates may represent optimum cooling rates existing between the first and second thresholds, and above the second threshold. For example, the first rate may be selected such that the noise generated by the cooling means is at an acceptable level (e.g. below a certain noise threshold) whilst providing sufficient cooling to the device to at least appreciably delay the onset of the second temperature threshold given a constant power output. The second cooling rate may be selected such that maximum cooling power is delivered to the device, to minimise the time spent above the second temperature threshold. This may be the case for example if the slope of the temperature increase is relatively high, and if continued temperature increase at this rate may present a danger to the device.

Alternatively, noise considerations may also be taken into account when the temperature is above the second threshold, such that a compromise is arrived at between the noise output and the cooling efficiency. For example, it may be determined by the system that the rate of change of the temperature as it passes the second threshold is relatively low. Therefore, the system may only moderately further increase the cooling rate to avoid operating the cooling means at a substantially increased or maximum rate. More particularly, the system may operate the cooling means at a rate selected such that the slope of the temperature, given constant power output, will reverse itself.

The first rate of the cooling means may be substantially constant if the monitored temperature is between the first and second temperatures thresholds. This may be a default setting of the device, or else may be dynamically configured by the controller. Similarly, the second rate of the cooling means may be substantially constant if the monitored temperature is above the second temperature threshold.

Alternatively, there may be a quantisation in the cooling rate increase, such that the cooling rate at which the cooling means is operated may be staged as a function of time and/or measured temperature of the device. For example, the rate of the cooling means may be ramped so as to further reduce overall noise output. For example, once the first temperature threshold has been reached, the rate of the cooling means may be gradually increased or ramped up to the first rate. The same may be true for the second rate once the second temperature threshold has been reached. The ramping may be based on the rate of change of the temperature, or other factors such as an output current of the device.

In addition to monitoring a temperature associated with the device, a current associated with the device may also be monitored. The cooling means may be operated at the second increased rate if the monitored current rises above a current threshold. In one embodiment, the current threshold may be from about 70% to about 90% of a maximum operating current of the device. Preferably the current threshold may be about 75% of a maximum operating current of the device.

This feature therefore provides a safety mechanism for the system. For example, irrespective of the monitored temperature, if the monitored current rises above a pre-set threshold, then the cooling means may need to be operated at an increased or a maximum rate to protect the device. The current may be measured using typical means known in the art, for example an ammeter. Other current-measuring devices may be used.

In addition to its temperature, other parameters associated with the device may be monitored. This may include for example radiation flux, fuel flow, fluid flow such as hot air flow, latent heat of such a flow, etc. Measuring such additional parameters may allow the system to more accurately determine the rate of change of the temperature and may therefore allow the system to adjust the rate of change of the cooling means accordingly, with greater accuracy. The measurement of such additional parameters may also serve as further safety mechanisms. For example, if it is determined that hot airflow has reached a critical level then the cooling means may be operated at a maximum rate.

The first rate and/or the second rate may be a function of a duration and/or an intensity of a peak power output of the device. Thus, the system may adjust the cooling rate based on how long or at what the level it is known the peak power output will be experienced. The system may also adjust the rate at which the desired cooling rate will be reached. For example, if the peak power output will be experienced for a relatively long period of time, the system may be configured such that the cooling means is operated at the first and second cooling rates as soon as the first and second temperature thresholds, respectively, are reached. Alternatively, if the peak power output is anticipated as lasting for a relatively short duration, and/or if the peak output current is relatively low, then the rate of the cooling means may be increased only incrementally as and when the first and second temperature thresholds are reached. Furthermore, the first and/or second temperature thresholds may be a function of a duration and/or an intensity of a peak power output of the device. The first temperature threshold may be independent of the device. Thus, the first temperature threshold may be set by the programmer and may be a function of the noise generated by the cooling means when under operation. The second temperature threshold may be device-dependent, and may be a function of the operating characteristics of the device. For example, in the case of a motor, the second temperature threshold may depend on the motor's rated threshold.

In any of the above described embodiments, there may be a delay incorporated into the algorithm or method such that the cooling rate is not varied until the temperature reaches a predetermined point above/below either temperature threshold. Thus, hysteresis may be incorporated into the method so as to avoid the cooling means being rapidly operated at two different rates as the temperature fluctuates above and below a temperature threshold. The hysteresis may be of the order of 1% of the threshold.

In a second aspect of the invention, there is provided a machine-readable medium having instructions stored thereon. When read by a machine, the instructions are configured to execute the steps of any of the above methods. Thus, the instructions may be stored for example on a CD-ROM or other readable disc, a flash disk, a portable disk drive, or any other medium capable of being read by a computer or other machine. The instructions may be stored in firmware embedded in the device itself. The instructions may be loaded onto a computer configured to control and operate the cooling means at various rates.

In a third aspect of the invention, there is provided a system for cooling a device generating heat. The system includes means for monitoring a temperature associated with the device. The system also includes cooling means. The system also includes a controller for operating the cooling means at various rates. The controller is arranged to automatically operate the cooling means at a first rate if the temperature rises above a first temperature threshold. The controller is further arranged to automatically operate the cooling means at a second increased rate if the temperature rises above a second temperature threshold. In one particular embodiment, the device is a motor drive, and/or the temperature monitoring means is a thermistor, and/or the cooling means is a fan.

Other features of the invention are set out below. Any of the below features may be combined with the above embodiments by making the appropriate changes.

A general aim of the invention is to postpone the need for a product cooling fan to be turned on to full speed when the product is used for example in typical theatre applications where fan noise must be minimised. As part of the thermal management of the product, the invention may increase the time taken for a temperature of a heat sink to reach a threshold at which a fan must be turned on to full speed. This may be achieved by turning the cooling fan on at a low speed once the heat-sink temperature has increased to above a lower threshold. This may be done in order to increase the cooling of the product, and thus reduce the rate at which the heat sink temperature rises given constant power dissipation, which in turn delays the point at which the cooling fan needs to be turned on to full speed. In many theatre applications, this delay would prevent the cooling fan from ever being turned on to full speed as the product generally provides output power for short intervals between which the product will cool down. The invention may increase the rate of cooling when the product has stopped providing output power, as the fan may be operating at a reduced but non-zero rate until the heat-sink temperature has dropped below the lower threshold. Thus, the heat-sink may be already cooler when the product is next required to provide output power.

In a particular embodiment, the thermal management system has two inputs: a heat-sink temperature measured using a thermistor; and a device for measuring the peak output current from the drive. The thermal management system may use two temperature thresholds: a low temperature threshold' used to trigger the action of the fan turning at low speed; and a product dependent threshold' used to trigger the action of the fan turning at full speed. The low temperature threshold may provide the theatre/quiet mode' function trigger. It may be possible for the low temperature threshold' to be user selectable. The product dependent threshold may be determined for each product based on the need to provide thermal protection.

The increase in cooling rate may increase the time between the heat-sink temperature rising from the low temperature threshold to the product dependent threshold. The fan speed may be increased to its maximum speed when the temperature is above the product dependent threshold to provide thermal protection for the product. The fan at full speed is too loud for certain applications such as those within theatres. Although the invention may not prevent the temperature rising to above the product dependent threshold, it will delay this point. The delay is intended to prevent the fan having to be set to full given a specific operating duty often experienced in theatre applications. Thus, by decoupling the principle of device thermal safety from that of noise reduction, the present invention is able to satisfy both in an improved manner.

Brief Description of the Drawings

Preferred embodiments of the invention will now be described in connection with the accompanying drawings, of which: Figure 1 is a block diagram of a system in accordance with a first embodiment of the invention; Figure 2 is a flowchart showing the steps taken by a method in accordance with a first preferred embodiment of the invention Figure 3 is a flowchart showing the steps taken by a method in accordance with a second preferred embodiment of the invention; Figure 4 is a graph showing temperature management of a device in

accordance with a method of the prior art;

Figure 5 is a first graph showing temperature management of a device in accordance with a preferred embodiment of the invention; and Figure 6 is a second graph showing temperature management of a device in accordance with a preferred embodiment of the invention.

Detailed Description of Preferred Embodiments

The present invention seeks to provide an improved algorithm/method for operating a cooling means to cool a device generating heat. Whilst various embodiments of the invention are described below, the invention is not limited to these embodiments, and variations of these embodiments may well fall within the scope of the invention which is to be limited only by the appended claims.

Figure 1 is a block diagram of a system 10 according to a preferred embodiment of the invention. System 10 comprises a controller 12, a cooling means 14, a heat-generating device 16, a temperature measuring device 18 and a current sensing device 11. In the present embodiment, cooling means 14 is a fan or other similar airflow generating means arranged to direct airflow towards heat-generating device 16. Other types of cooling means are envisaged. For example, cooling means 14 may comprise a jacket or other insulation surrounding device 16 and through which a coolant may be pumped. Heat-generating device 16 may be an electric motor drive, and temperature measuring means may be a thermistor arranged in proximity to heat-generating device 16 so as to monitor or measure a temperature associated with heat-generating device 16. For example, thermistor 18 may be arranged to measure a temperature of a heat sink of heat-generating device 16, or else an operating temperature of device 16 generated when device 16 is in operation.

Controller 12 is arranged to control a cooling rate of cooling means or fan 14.

For example, controller 12 may be arranged to control a speed at which fan 14 operates. If cooling means 14 comprises a jacket or other insulation surrounding device 16, then controller 12 may be arranged to control a flow rate of a fluid such as a coolant within the jacket.

Current-sensing device 11 is also included and is used to measure a current associated with device 16. Both thermistor 18 and current-sensing device 11 are in communication with controller 12 such that readings and measurements taken with thermistor 18 and current sensing device 11 may be transmitted to controller 12 for controller 12 to process and act thereon.

Figure 2 is a flowchart illustrating the steps taken by a method 20 according to a preferred embodiment of the invention, for example using system 10. This method may be made active or inactive by a user of device 16; for example the method may be part of a mode of operation of device 16 that may be toggled on or off. At step 21, a temperature associated with device 16 is measured or otherwise monitored. At step 22, controller 12 determines whether the measured temperature is less than a first temperature threshold Ti. Ti may be independent of heat-generating device 16. At step 23, if the measured temperature is less than Ti, the fan speed of fan 14 is set to zero. This represents a state in which the heat generated by device 16 is not sufficient so as to warrant cooling. Thus, fan 14 may be switched off and noise levels kept to a minimum as a result.

If the measured temperature is greater than Ti then, at step 24, controller 12 determines whether the measured temperature is less than T2. T2 may represent a device-dependent temperature threshold. For example, T2 may be a product-dependent threshold above which the heat generated by device 16 is dangerous for device 16 if the temperature level is sustained. If Ti > T c T2, then at step 25 controller 12 sets the speed of fan 14 to a relatively low speed. A low speed may be a speed at which little or at least acceptable levels of noise are generated by fan 14 and at which a minimum of cooling power is provided by fan i4, to reduce the rate of increase of the temperature. This state represents a state in which cooling of device 16 is not actually required from a safety perspective, and yet a state in which the temperature is closer to the critical threshold 12. Activating fan 14 at step 25 delays the point in time at which T2 will be reached.

At step 26, controller 12 determines whether the temperature has risen above T2, and if so then the fan speed is set to a maximum (or relatively high) speed so as to reduce the risk of damage to device 16. In this state, whilst the noise levels of fan 14 are relatively high, the high speed of fan 14 helps ensure that the temperature will drop below T2 as rapidly as possible.

Ti and 12 may be set by engineers to protect the motor drive, and Ti may further be set or altered by the user.

Figure 3 is a flow diagram showing an alternative embodiment of the present invention. The method 30 according to Figure 3 is similar to that of Figure 2 except for the addition of current measuring steps. At step 31, if it is determined that T < Ti, controller 12 first checks that the operating current of device 16 is below a critical threshold Ic (step 32) before setting the fan speed to off (step 33). If the current is above critical threshold Ic, then the fan speed may be set a maximum power (step 34). This is useful if the temperature of device 16 is not increasing at a rapid rate but if device 16 is nonetheless providing a high output power, and thus serves as a safety mechanism. The same steps 35-38 may be taken when it is determined that Ti cT c T2. If T > T2, the fan speed may be set to a maximum speed as in method 20.

Current sensing device ii may be continuously active, such that even if controller 12 is not measuring the temperature of device 16 then the fan speed may nonetheless be controlled as a function of the operating current.

It should be noted that the flowcharts of Figures 2 and Figure 3 are merely representative of particular methods of operation of the cooling means. Other steps may be taken in-between the steps listed in Figures 2 and 3. For example, in Figures 2 and 3, when T is between Ti and 12, the fan speed may be maintained at a relatively constant level. Alternatively, controller 12 may measure the gradient of the temperature curve (by taking multiple readings) and may adjust the fan speed accordingly. For example, if controller 12 determines that the temperature is increasing relatively rapidly as it climbs above Ti, then the fan speed may be increased accordingly (perhaps to a medium or intermediate fan speed).

Additionally, the fan speed may be subjected to hysteresis (for example of the order of 1% of the threshold) such that if it is determined that the temperature rises above or drops below a temperature threshold such as Ii or T2, then the change in fan speed may incorporate a delay to prevent the rate of change of the fan speed varying too rapidly.

-ii -The table below describes the actions taken by controller 12 based on measured temperature and current, according to a particular, exemplary embodiment of the invention. An "X" denotes that the state is independent of the system conditions.

Device temperature Output current Resulting action measurement measurement Below low Below 75% Fan is off temperature threshold maximum drive Ti output current Above low X Fan is at the low speed unless other state temperature threshold conditions are met Ti and below critical or product dependent threshold 12 Above critical or X Fan is full on for at least 20 seconds product dependent threshold 12 X Above 75% Fan is full on for at least 20 seconds maximum drive output current Figure 4 is a graph showing a temperature profile as a function of time, in accordance with a prior art method of cooling a device. When the device is not being used (or else drawing little power), the fan or other cooling means is off. During a period of high output current, the temperature of the device rises steadily to a critical temperature threshold T2. Above this threshold, the heat levels generated by the device may be detrimental to the device, and so the fan switched on to a maximum power to cool the device. Even though the period of high output current is relatively short, the rapid increase in temperature is sufficient to require the fan being turned on to a maximum level to avoid damage to the device. Such a maximum level generates substantial noise.

A temperature profile according to the inventive algorithm/method described herein is illustrated in Figures 5 and 6.

-i2 -In Figure 5, during a period of operational use, but before Ti, the fan is off.

Above Ti, the fan is set to a low speed which delays the point at which the temperature reaches T2. Thus, it can be seen that the fan is switched on before it being thermally necessary (e.g. before the temperature reaches a critical, device-dependent level identified by T2). However, this delay is sufficient to avoid the need to operate the fan at a maximum rate, thereby reducing the noise generated by the fan.

Figure 6 is similar to Figure 5 except that whilst the temperature does reach T2 and thus the fan is eventually set to maximum power, the duration of this maximum power is reduced due to the fan being set to a low speed before the temperature reaches Ti. Thus, the time period during which the fan speed generates excessive levels of noise is reduced when compared to the prior art.

It should be noted that these temperature profiles are merely exemplary profiles and are used to highlight in simple terms the effect and advantages of the present invention. The profiles may vary depending on many factors, such as the type of device being cooled, the settings of Ti and 12, the different speeds at which the fan is set when the temperature rises above I drops below the thresholds, etc. Any feature of the above-described embodiments may be combined with the features of another embodiment, by making the appropriate changes. Whilst the invention has been described in connection with preferred embodiments, it is to be understood that the invention is not limited to these embodiments, and that alterations, modifications, and variations of these embodiments may be carried out by the skilled person without departing from the scope of the invention. -13-

Claims

CLAIMS1. A method of cooling a device generating heat, comprising: monitoring a temperature associated with the device; automatically operating a cooling means at a first rate if the monitored temperature rises above a first temperature threshold; automatically operating the cooling means at a second increased rate if the monitored temperature rises above a second temperature threshold; monitoring a current associated with the device; and automatically operating the cooling means at the second increased rate if the monitored current rises above a current threshold.
2. The method of claim 1, further comprising: automatically decreasing the rate of the cooling means if the monitored temperature drops below the second temperature threshold.
3. The method of claim 2, wherein the rate of the cooling means is automatically decreased to the first rate if the monitored temperature drops below the second temperature threshold.
4. The method of any preceding claim, further comprising: automatically decreasing the rate of the cooling means if the monitored temperature drops below the first temperature threshold.
5. The method of claim 4, wherein the rate of the cooling means is automatically decreased to zero if the monitored temperature drops below the first temperature threshold.
6. The method of any preceding claim, wherein the rate of the cooling means is automatically increased from zero to the first rate if the monitored temperature rises above the first temperature threshold.

-14 -
7. The method of any preceding claim, wherein the rate of the cooling means is automatically increased from the first rate to the second increased rate if the monitored temperature rises above the second temperature threshold.
8. The method of any preceding claim, wherein the rate of the cooling means is automatically increased to a maximum rate if the monitored temperature rises above the second temperature threshold.
9. The method of any preceding claim, wherein the first/second rate of the cooling means is substantially constant if the monitored temperature is between the first and second temperature thresholds, or above the second temperature threshold.
10. The method of any preceding claim, wherein first/second rate of the cooling means is varied if the monitored temperature is between the first and second temperature thresholds, or above the second temperature threshold.
11. The method of any preceding claim, wherein the second temperature threshold is higher than the first temperature threshold.
12. The method of any preceding claim, wherein the second rate of the cooling means is a maximum rate of the cooling means.
13. The method of claim 1, wherein the current threshold is from about 70% to about 90% of a maximum operating current of the device.
14. The method of any preceding claim, wherein the first rate is from about 10% to about 25% of the second rate.
15. The method of any preceding claim, wherein the first temperature threshold is from about 80% to about 90% of the second temperature threshold.
16. The method of any preceding claim, wherein the first rate and/or the second rate is a function of a duration and/or an intensity of a peak power output of the device.
17. The method of any preceding claim, wherein the first and/or the second temperature threshold is a function of a duration and/or an intensity of a peak power output of the device.
18. The method of any of claims 1 -16, wherein the first temperature threshold is independent of the device.
19. A method of cooling a device generating heat, substantially as described hereinbefore and with reference to Figure 2; Figure 3; Figure 5; or Figure 6.
20. A machine-readable medium having instructions stored thereon, wherein when read by a machine the instructions are configured to execute the steps of any of claims 1 -19.
21. A system for cooling a device generating heat, comprising: means for monitoring a temperature associated with the device; means for monitoring a current associated with the device; cooling means; and a controller for operating the cooling means at various rates, wherein the controller is arranged to automatically operate the cooling means at a first rate if the temperature rises above a first temperature threshold, wherein the controller is further arranged to automatically operate the cooling means at a second increased rate if the temperature rises above a second temperature threshold, and wherein the controller is further arranged to automatically operate the cooling means at the second increased rate if the monitored current rises above a current threshold.
22. The system of claim 21, wherein the device is a motor drive, and/or the temperature monitoring means is a thermistor, and/or the cooling means is a fan.
23. A system for cooling a device generating heat, substantially as described hereinbefore and with reference to Figure 1.-16 -Amendments to the claims have been filed as followsCLAIMS1. A method of cooling a device generating heat, comprising: monitoring a temperature associated with the device; automatically operating a cooling means at a first rate if the monitored temperature rises above a first temperature threshold; automatically operating the cooling means at a second increased rate if the monitored temperature rises above a second temperature threshold; monitoring a current associated with the device; and automatically operating the cooling means at the second increased rate if the monitored current rises above a current threshold.2. The method of claim 1, further comprising: automatically decreasing the rate of the cooling means if the monitored temperature drops below the second temperature threshold.3. The method of claim 2, wherein the rate of the cooling means is automatically o decreased to the first rate if the monitored temperature drops below the second temperature threshold. (44. The method of any preceding claim, further comprising: automatically decreasing the rate of the cooling means if the monitored temperature drops below the first temperature threshold.5. The method of claim 4, wherein the rate of the cooling means is automatically decreased to zero if the monitored temperature drops below the first temperature threshold.6. The method of any preceding claim, wherein the rate of the cooling means is automatically increased from zero to the first rate if the monitored temperature rises above the first temperature threshold.7. The method of any preceding claim] wherein the rate of the cooling means is automatically increased from the first rate to the second increased rate if the monitored temperature rises above the second temperature threshold.B. The method of any preceding claim, wherein the rate of the cooling means is automatically increased to a maximum rate if the monitored temperature rises above the second temperature threshold.9. The method of any preceding claim, wherein the first/second rate of the cooling means is substantially constant if the monitored temperature is between the first and second temperature thresholds, or above the second temperature threshold.10. The method of any preceding claim, wherein first/second rate of the cooling means is varied if the monitored temperature is between the first and second temperature thresholds or above the second temperature threshold.11. The method of any preceding claim, wherein the second temperature o threshold is higher than the first temperature threshold. a)(\,j 12. The method of any preceding claim, wherein the second rate of the cooling means is a maximum rate of the cooling means.13. The method of claim 1, wherein the current threshold is from 70% to 90% of a maximum operating current of the device.14. The method of any preceding claim, wherein the first rate is from 10% to 25% of the second rate.15. The method of any preceding claim, wherein the first temperature threshold is from 80% to 90% of the second temperature threshold.16. The method of any preceding claim, wherein the first rate and/or the second rate is a function of duration and/or an intensity of a peak power output of the device.17. The method of any of claims 1 -16, wherein the first temperature threshold is independent of the device.18. A machine-readable medium having instructions stored thereon, wherein when read by a machine the instructions are configured to execute the steps of any of claims 1 -17.19. A system for cooling a device generating heat, comprising: means for monitoring a temperature associated with the device; means for monitoring a current associated with the device; cooling means; and a controller for operating the cooling means at various rates, wherein the controller is arranged to automatically operate the cooling means at a first rate if the temperature rises above a first temperature threshold, wherein the controller is further arranged to automatically operate the cooling means at a second increased rate if the temperature rises above a second temperature threshold and wherein the controller is further arranged to automatically operate the cooling means at the o second received rate of the monitored current rises above a current threshold. a)(\,j 20. The system of claim 19, wherein the device is a motor drive, and/or the temperature monitoring means is a thermistor, and/or the cooling means is a fan.