EP4653702A1

EP4653702A1 - Controlling compressor operation

Info

Publication number: EP4653702A1
Application number: EP24177427.2A
Authority: EP
Inventors: Daniel Youssef; Miroslav Zatko; Jaroslav Pekar; Adam VONDRAK
Original assignee: Garrett Transportation I Inc
Current assignee: Garrett Transportation I Inc
Priority date: 2024-05-22
Filing date: 2024-05-22
Publication date: 2025-11-26
Also published as: WO2025245304A1

Abstract

Disclosed is processing circuitry for controlling the operation of a fluid compressor device configured to compress refrigerant vapour as part of a vapour-compression cycle to achieve a target temperature of a region to be heated or cooled. The processing circuitry is configured to obtain target temperature data indicating the target temperature to be achieved in the region to be heated or cooled, obtain temperature data indicating a temperature of the region to be heated or cooled; and obtain compressor data indicating a compressor parameter associated with the operation of the fluid compressor device. The processing circuitry is configured to determine, based on the compressor data, whether the fluid compressor device is approaching a surge state. If it is determined that the fluid compressor device is approaching the surge state, the processing circuitry is configured to cause the fluid compressor device to operate in a capacity modulation mode according to which the compressor speed is modulated between two speeds such that, in the capacity modulation mode, the temperature of the region to be heated or cooled is maintained to within a predetermined range of the target temperature.

Description

The present disclosure relates to controlling the operation of a fluid compressor device, for example to ensure that it operates as part of a vapour-compression cycle to achieve a target temperature without surging.

BACKGROUND

In general, a fluid (e.g. gas) compressor device may be used as part of a vapour-compression cycle to accept, at an inlet thereof, refrigerant fluid and to compress the refrigerant fluid, increasing the temperature and pressure thereof. The compressed refrigerant fluid, at an increased temperature and pressure, is output from an outlet of the fluid compressor device. The refrigerant fluid may be in a vapour form. The vapour-compression cycle may be used as part of a thermal management system as part of a heating or refrigeration cycle to increase or decrease the temperature of a region to be heated or cooled.

SUMMARY OF THE INVENTION

The mass flow rate of a fluid (e.g. gas) compression device (hereafter described as a "compressor") may be considered as the amount of fluid flowing through the compressor over a given time. If the mass flow rate is low, meaning that an insufficient amount of fluid is being compressed for it to be functioning properly, this can cause a condition known as compressor surge in which the compressor can oscillate violently which can lead to hardware damage as well as degraded performance. Since the mass flow rate through a compressor is proportional to the heating or cooling rate of a vapour-compression cycle using the compressor, the demand on the compressor (in the form of a target heating or cooling power to be achieved by the vapour-compression cycle) can risk operating the compressor in, or close to, surge conditions.
According to this disclosure there is provided processing circuitry for controlling the operation of a fluid compressor device (e.g. a gas compression device or a vapour compression device), which may also be referred to as a "compressor" that is configured to compress refrigerant vapour as part of a vapour-compression cycle to achieve a target temperature of a region to be heated or cooled, the processing circuitry is configured to: obtain target temperature data indicating the target temperature to be achieved in the region to be heated or cooled; obtain temperature data indicating a temperature of the region to be heated or cooled; obtain compressor data indicating a compressor parameter associated with the operation of the fluid compressor device; determine, based on the compressor data, whether the fluid compressor device is approaching a surge state; and, if it is determined that the fluid compressor device is approaching the surge state, the processing circuitry is configured to: cause the fluid compressor device to operate in a capacity modulation mode according to which the compressor speed is modulated between two speeds such that, in the capacity modulation mode, the temperature of the region to be heated or cooled is maintained to within a predetermined range of the target temperature. The capacity modulation mode may be considered to be a second mode of operation of the compressor. The region to be cooled may be any suitable region of space or of a component to be heated/cooled, e.g. a region in a vehicle cabin or of a battery component.
The processing circuitry, in the capacity modulation mode, may be configured to cause the fluid compressor device to operate at a first compressor speed until the temperature data indicates that the temperature of the region to be heated or cooled is at the upper bound of the predetermined range at which point the processing circuitry is configured to cause the fluid compressor device to operate at a second compressor speed, greater than the first compressor speed, until the temperature data indicates that the temperature of the region to be heated or cooled is at the lower bound of the predetermined range at which point the processing circuitry is configured to cause the fluid compressor device to return to operating at the first compressor speed.
In the capacity modulation mode, the fluid compressor device may be caused to operate between an idle mode in which the first compressor speed is substantially at a minimum and a high-speed mode. In the high-speed mode the second compressor speed may be greater than, or greater than or equal to, the surge speed. For example, the second compressor speed may be the minimum, stable, compressor speed at which the compressor operates outside of its surge state, this speed may correspond to a boundary of the normal operation region on the compressor map, and/or may be a point on or just before the surge line. The second compressor speed may alternatively or additionally cause the compressor to operate at a maximum coefficient of performance.
The fluid compressor device may comprise an air foil bearing, and wherein the first compressor speed is substantially equal to a minimum lift-off speed of the air foil bearing.
In the capacity modulation mode, the temperature of the region to be heated or cooled may be maintained to within one degree Celsius of the target temperature.
The predetermined range may be adjustable. The predetermined range may be symmetric about the target temperature.
To determine whether the fluid compressor device is approaching the surge state, the processing circuitry may be configured to determine a mass flow rate of the fluid compressor device based on the compressor data, locate the mass flow rate on a compressor performance map, and determine a distance between the mass flow rate and a surge line on the compressor performance map, the processing circuitry being configured to determine that the fluid compressor device is approaching the surge state if the distance between the mass flow rate and the surge line is less than a predetermined threshold distance.
The processing circuitry may be configured to determine a corrected mass flow rate and wherein the distance is between the corrected mass flow rate and the surge line.
The predetermined threshold distance may be adjustable.
The processing circuitry may be configured to determine, based on the compressor data (e.g. based on measured compressor inlet and/or outlet conditions and/or a stored compressor map), whether the fluid compressor device is operating remote from the surge state and, if it is determined that the fluid compressor device is operating remote from the surge state while operating in the capacity modulating mode, the processing circuitry is configured to cause the fluid compressor device to cease operating in the capacity modulation mode.
If, at any time while operating in the capacity modulation mode, the compressor is required to operate to achieve a cooling or heating power that corresponds to a point on the compressor performance map that is in the nominal region (e.g. not proximate the surge state), then it may exit capacity modulation mode. Put another way, a demand on the compressor that, to be fulfilled, no longer requires the compressor to be proximate the surge state while operating in its nominal mode, is an exit condition for the capacity modulation mode, and in response to the detection of an exit condition the compressor may be caused to cease operating in the capacity modulation mode and return to its nominal mode. Such a "new" power demand on the compressor may correspond to, for example, a change in road gradient or a user braking the vehicle in such a way to cause the battery plate to heat up requiring a higher demand on the compressor to cool it. In these examples, whilst the target temperature to be achieved remains constant, the work required to cool the region to that target temperature has changed resulting in different operating conditions for the compressor if the vapour-compression cycle is to achieve the target temperature.
In other words, when the fluid compressor device is operating in the capacity modulation mode, the processing circuitry may be configured to determine whether the fluid compressor device would operate proximate the surge state to achieve the target temperature in the region to be heated or cooled, and, if it is determined that the fluid compressor device can operate so that the target temperature can be achieved in the region to be heated or cooled without operating proximate the surge state then the processing circuitry may be configured to cause the fluid compressor device to cease operating in the capacity modulation mode.
The target temperature of the region to be heated or cooled may be related to a preferred cabin temperature of an electric vehicle or to a preferred temperature of a battery of an electric vehicle.
The processing circuitry may be configured to control the first compressor speed of an expansion valve of the vapour-compression cycle when the fluid compressor device is operating in the capacity modulation mode.
According to another example of the disclosure there is provided a drive system for an electric vehicle. The drive system comprises a source of AC current configured to supply the AC current to a fluid compressor device configured to compress refrigerant vapour as part of a vapour-compression cycle based on target temperature data indicating a target temperature to be achieved in a region to be heated or cooled, and a controller for the source of AC current, wherein the controller comprises the processing circuitry as described above, the controller being configured to vary the current supplied to the fluid compressor device to cause the fluid compressor device to operate in the capacity modulation mode. The drive system may be part of an e-powertrain system. The drive system may comprise other components, for example other components of an e-powertrain system such as an electric motor, battery etc. In one example the source of AC current is an inverter configured to convert DC current to AC current and which may receive DC current from a motor (e.g. an electric motor).

BRIEF DESCRIPTION OF THE DRAWINGS

Examples of the present disclosure will be described in detail with reference to the accompanying drawings, which should not be considered limiting, in which:

Figure 1 shows a schematic diagram of a thermal cycle;
Figure 2 shows an example compressor performance map;
Figure 3 shows a flowchart of a process for operating a compressor;
Figure 4 shows a chart indicating the operation of a compressor;
Figure 5 shows a chart indicating a process for detecting whether a compressor is operating proximate a surge state;
Figures 6 and 7 show example compressor performance maps;
Figures 8-16 show graphs that illustrate the performance of components of a system, including a compressor configured as part of a vapour-compression cycle to cool a region, during a simulation.

DETAILED DESCRIPTION

These drawings should not be considered limiting, rather they are used for explaining and understanding the present disclosure.
Figure 1 shows a schematic diagram of a thermal cycle 1. Mostly, the thermal cycle 1 will be described herein with reference to cooling and so hereafter will often be referred to as a refrigeration cycle. However the skilled person will understand how the present disclosure, when describing a cooling operation, would be adapted to refer to a heating operation. The refrigeration cycle is to lower the temperature of a region to be cooled, indicated at 10, and comprises a fluid compression device (hereafter, "compressor") 20, a fluid condensing device (hereafter, "condenser") 22, an expansion device (depicted as an expansion valve) 24, and a fluid evaporation device (hereafter, "evaporator") 26. A refrigerant, which may be considered a fluid capable of absorbing and releasing heat, and capable of undergoing a phase transition between liquid and gas states, flows around the refrigeration cycle clockwise, entering the compressor 20 at an inlet thereof as low-pressure low-temperature refrigerant vapour. The compressor 20 is configured to increase the pressure of the refrigerant fluid therein by reducing its volume, thereby increasing its density. High-pressure high-temperature (relative to the inlet) refrigerant gas (superheated gas) exits the compressor 20 at an outlet thereof and enters the condenser 22 in which the gas releases heat and condenses into a low temperature liquid. The low-temperature high-pressure liquid flows through an expansion valve 24 which reduces the pressure, and the refrigerant exits the expansion valve 24 as very low-temperature, low-pressure liquid. When this liquid passes through the evaporator 26 it accepts heat from a region to be cooled 10, arrow 28 schematically indicating the flow of cold air, and the liquid exits the evaporator as low-temperature low-pressure vapour to enter the compressor 20 and the cycle repeats. The refrigerant may be considered a to be a working fluid. It may be considered a cooling fluid, or coolant.
Due to the operation of the compressor 20 on the refrigerant therethrough, the thermal cycle 1 may also be considered a vapour-compression cycle.
Schematically indicated at 30 is a controller for the compressor 20. The controller 30 is to control the operation of the compressor 20. The controller 30 is to control at least one operating parameter of the compressor 20, for example it's speed (referred to herein as compressor speed). To do so, the controller 30 may be configured to control (or vary) the current supplied to the compressor 20. Accordingly, the controller 30 may comprise a motor and/or an inverter and/or a rectifier depending on the type of compressor 20 and type of current it requires. This will be explained in further detail later.
Figure 2 shows a graph 200 that may be referred to as a compressor performance graph (or map) or a compressor efficiency graph (or map). The horizontal axis is the mass flow rate through the compressor 20 which may be defined as the volume of fluid flowing through the compressor 20 per unit of time. The vertical axis is the pressure ratio of the compressor 20 which may be defined as the ratio of the pressure of the fluid exiting the compressor 20 at the outlet thereof to the pressure of the fluid entering the compressor 20 at the inlet thereof. Each point on the graph 200 therefore represents the compressor 20 operating at a particular mass flow rate and a particular pressure ratio and may therefore be considered to represent an operating condition of the compressor 20. The mass flow rate and pressure ratio may be determined by obtaining compressor data indicating a parameter of the compressor 20 associated with the operation of the compressor 20, e.g. the current through the compressor 20, the compressor speed etc.
Line 201 represents the operational speed limit of the compressor 20, meaning the maximal flow rate and pressure ratio that the design of the compressor 20 allows. As stated above, low mass flow rates through the compressor can lead to violent flow oscillations due to the amount of fluid being compressed being insufficiently low for the compressor to work properly. This unstable state is known as compressor "surge" and region 215 of the compressor map represents an operating state of the compressor 20 in a surge condition, or in a surge state, e.g. those combinations of mass flow rate and pressure ratio that would cause the compressor to surge. Region 210 indicates a normal, or nominal, operation of the compressor 20 and the line 202 is the "surge line" of the compressor map 200, representing the boundary between the compressor 20 operating normally and operating in a surge state. "ETAC" as used in the figure indicates compressor aero dynamic efficiency. The shaded region represents different areas of compressor efficiency.
The mass flow rate of refrigerant flowing through the compressor 20 is directly proportional to the heating or cooling power, or rate, of the thermal cycle 1. Therefore, when a low-power operation of the compressor 20 is required, for instance arising from requests that require a relatively low heat or cooling rates, this demand on the compressor 20 can place it at risk of being operating in a surge state. Two examples of such a low-demand on the compressor may be a low cooling rate required to cool a battery (when the thermal cycle 1 is a refrigeration cycle being used to cool a battery, such as that of an electric vehicle), and a user requiring a low temperature decrease or increase than the current temperature (when the thermal cycle 1 is a refrigeration cycle used as part of an air conditioning or heating system).
As will now be described one aspect of the present disclosure is a process for controlling, or operating, the compressor 20 to provide such low heating/cooling rates while ensuring that the compressor 20 is not operating in a surge state.
Figure 3 illustrates the flowchart of such a process 300. The process 300 may be a process for controlling the operation of a compressor 20 and may be implemented as a software algorithm to be executed be a controller 30 for the compressor 20.
Block 302 of the process 300 represents the compressor 20 being operated , or being caused to operate (e.g. by the controller 30), in a "nominal mode," meaning that the compressor is caused to operate at a substantially constant speed (and therefore mass flow rate) so that the vapour-compression cycle can achieve a target temperature and pressure of compressed refrigerant being output from the compressor 20, so that the vapour-compression cycle can achieve a target temperature of a region (e.g. of space or on/in a component). In the Figure 3 illustrative example, the region 10 is a region to be cooled 10 and so the vapour-compression cycle is part of a refrigeration cycle. The compressor 20 while being operated in the nominal mode may be operated such that a compressor parameter is maintained, such as a constant speed, a constant inlet and/or outlet vapour pressure and/or temperature, a constant mass flow rate, and/or a constant pressure ratio. The compressor 20 being operated in the nominal mode also corresponds to the compressor 20 being operated in the region 210 of the compressor performance map 200 (e.g. operated at parameters that lead to a mass flow rate and pressure ratio that is within the region 210 of the compressor performance map 200).
While operating in the nominal mode it is determined, at block 304, whether the compressor is operating in a state that is proximate to the surge state, or proximate to a surge condition. One example way of determining whether the compressor is operating in a state proximal to a surge condition will be discussed later with reference to Figure 5 but, in general, the process 300, at block 304, determines whether a precondition is met by the compressor, the precondition being met being synonymous with the compressor operating proximate to the surge state. The precondition may be based on a predetermined threshold in the sense that if compressor data is within a predetermined threshold of a precondition then it is determined that the compressor is being operated proximate a surge state. With reference to the map 200 the compressor being operated proximate a surge state may be considered synonymous with the compressor being operated at parameters that lead to a mass flow rate and pressure ratio coordinate on the map 200 that is proximate the surge line 202, for example, the coordinate on the map 200 may be within a predetermined threshold distance of the surge line 202. The precondition (e.g. the predetermined threshold or otherwise) may be programmable and/or adjustable and/or settable and/or controllable and/or customisable, for example by an OEM configuring the controller 30 for the compressor 20 so that the OEM has the freedom to determine the conditions which constitute a determination that the compressor 20 is operating proximate a surge state. Block 304 may be performed automatically and may be performed continuously or at regular intervals, e.g. after a predetermined time has elapsed.
If it is determined that the compressor 20 is operating proximate a surge state then, at block 306, the compressor 20 is caused to operate in a capacity modulation mode 306, which is distinct from the nominal operation mode 302.
In the capacity modulation mode 306 the compressor is firstly caused to operate in an idle mode 308 at which the compressor is driven 310 at a first speed until a first precondition is met, indicated at 312. If the precondition is not met at 312 then the compressor continues to be driven 310 at the first speed and therefore continues to be operated in the idle mode 308. If however the precondition is met then the compressor is caused to transition to a high-speed mode 314 at which the compressor is driven 316 at a second speed, higher than the first speed, until a second precondition is met, indicated at 318. If the second precondition is not met at 318 then the compressor continues to be driven 316 at the second speed and therefore continues to be operated in the high-speed mode 318. If however the precondition is met then the compressor is caused to transition to the idle mode 308 and the cycle continues until an exit condition 320 is detected, or present. In the capacity modulation mode 306 the compressor is therefore caused to modulate between two modes of operation (the idle mode 308 and the high-speed mode 314) and will continue to do so until an exit condition 320 is met (to be described later).
In the capacity modulation mode (hereafter, for brevity, this will be referred to the compressor being "in CMM") the compressor is therefore operating between two states, corresponding to two mass flow rates (compressor speed being directly proportional to the mass flow rate therethrough) and hence in this mode the "capacity" (which could be considered synonymous with mass flow rate) of the compressor is modulated. Using alternate terminology the nominal mode 302 may be considered a "first mode of operation" and the CMM 306 may be considered a "second mode of operation."
The operation of the compressor in CMM, between the two modes of operation, operating between the two speeds, is such that the target temperature to be achieved at the region to be cooled (see 10 in Fig. 1) is achieved, or maintained, to within a predetermined threshold of the target temperature. Put another way, in CMM the compressor is operated such that the target temperature is achieved, on average, in the region 10 to be heated/cooled.
In one example, first and second preconditions may be related to time so that the compressor is caused to operate in the idle mode 308 for a first period of time after which the compressor is caused to operate in the high-speed mode for a second period of time after which the compressor is caused to operate in the idle mode 308 for a third period of time (which may be equal to the first period of time) etc. and the compressor is caused to cycle between the modes in this way until an exit condition 320 is detected. The time periods may be the same so that the compressor is caused to operate in each mode for the same period of time before being caused to operate in the other etc., or the time periods may be all different, or some may be the same and some may be different etc. The time periods may be predetermined or may be determined on-the-fly.
However, in another example (which is the example shown in Figure 3) the first and second preconditions are related to temperature (and, as stated above, to illustrate the principles of the disclosure Figure 3 relates to a refrigeration cycle to cool a region). As indicated by 312 operation in the idle mode 308 continues until it is detected that the actual temperature of the region 10 to be heated/cooled is greater than an upper bound of a predetermined temperature range. If this occurs then the compressor is caused to operate in the high-speed mode 314. As indicated at 318 operation in the high-speed mode 314 continues until it is detected that the actual temperature of the region 10 to be heated/cooled is less than a lower bound of the predetermined temperature range. In this way, the compressor in CMM maintains the temperature of the region 10 to be within the predetermined temperature range which includes the target temperature. Put another way, the temperature of the region 10 is approximately the target temperature, such that the target temperature is achieved, on average, when the compressor operates in CMM. In this example the controller 30 implementing the process 300 may receive data from other sources. This may include receiving not only data indicating the target temperature to be achieved in the region to be cooled but also data indicating the temperature (e.g. the current temperature) that is actually achieved so that the controller 30 can determine whether the temperature-based preconditions are met at 312 and 318.
In the Figure 3 example, in the idle mode 308, the compressor is driven at a first speed which is a minimum speed and in the high-speed mode 314 the compressor is driven at a second speed which is a maximum speed. Herein, the minimum and maximum speeds may be determined, all or in part, by properties of the compressor or the wider system in which it is used. Driving the compressor at a minimum speed may be considered driving the compressor "as slow as possible" and driving the compressor at a maximum speed may be considered driving the compressor "as fast as possible." The first and/or second speeds may be programmable and/or adjustable and/or settable and/or controllable and/or customisable, for example by an OEM configuring the controller 30 for the compressor 20.
In one example, the compressor comprises a foil bearing. Such a bearing, via rotation due to its geometry, eliminates contact between rotor and stator components by allowing rotating fluid (e.g. vapour) to act as a lubricant. However, a minimum rotational speed is required for the foil to operate such that there is fluid film lubrication and no contact/low friction and this is known as the "lift-off" speed of the foil bearing. The minimum speed at which the compressor is driven at 310 in the idle mode 308 in this example may be substantially equal to the minimum lift-off speed of the compressor foil bearing. In another example the minimum speed at which the compressor is driven 310 in the idle mode 380 is within a range of the minimum lift-off speed, for example within range defined from the minimum lift-off speed to a value to that is the minimum lift-off speed + a percentage or proportion of the minimum lift-off speed, e.g. 10%. So if the minimum lift-off speed is V in the idle mode 380 the compressor may be driven at a speed that is within the range of (V, V+0.1*V). The speed at which the compressor is driven in the idle mode 380 may be predetermined and therefore stored. The speed at which the compressor may be driven (at 316) in the high-speed mode 314 may be considered a maximum (in the sense that the compressor speed in the idle mode is a minimum). The speed at which the compressor is driven in the high-speed mode 314 may be greater than, or equal to, the surge speed. This compressor speed may be the minimum, stable, compressor speed at which the compressor operates outside of its surge state. With reference to the compressor performance map 200, this speed may correspond to a boundary of the normal, nominal, operation region 210 on the compressor map, and/or may be a point on, or just before, the surge line 202. Alternatively or additionally this speed may correspond to a speed that causes the compressor to operate at a maximum coefficient of performance. Put another way, the compressor, in the high-speed mode, may be caused to operate at a maximum coefficient of performance.
Referring again to Figure 2, the operation of the compressor in CMM is schematically depicted at 220. Here, the compressor performance in CMM is shown, as the combination of compressor mass flow rate and pressure ratio are modulated between an idle mode (indicated at 221) and the high-speed mode (during which the CMM operates in the region 210). The arrows and lines indicate the back-and-forth nature of the compressor operation in CMM until an exit condition is detected.
Figure 4 shows a chart 400 indicating the operation of a compressor 20 in CMM. The parameters shown are heat transfer, time, and compressor speed. As the chart 400 shows, the compressor 20 being modulated between its idle mode (region 401) and its high-speed mode (region 403, termed "rated mode" in this figure) comprises operating the compressor 20 in a further mode which may be considered a transitory mode or "spin-up" mode in which the compressor speed is ramped-up (e.g. increased as fast as possible) to a maximum compressor speed until it reaches the second speed (that it is to maintain in the high-speed mode). Chart 400 shows this in three phases, phase 1 being the idle mode that begins the CMM in some examples, at which the compressor speed is a minimum. Once the first precondition is met the compressor is caused to operate in a spin-up mode, phase 2, in which the speed is ramped up to the second speed which, once reached, causes the compressor to operate in the high-speed mode, phase 3 ("rated mode"). The leftmost portion of the chart 400 indicates the transition between the high-speed mode (phase 3) and the idle mode (phase 1), e.g. when the second precondition is met. As shown by the chart 400 this is achieved by causing the compressor speed to decrease from its second speed (the speed in the high-speed mode, phase 3) as fast as possible by ramping-down the speed (e.g. switching off or causing the current supplied to the compressor 20 to be at a minimum).
The heating/cooling power of the thermal cycle when the compressor 20 operates in the idle mode may be close to zero when the first compressor speed is at a minimum. This is shown in region 401 of the chart 400. The spin-up time in region 402, the time between the compressor speed reaching approximately its second speed from its first speed will depend on factors such as the motor torque and overall inertia of the equipment or components of the system. The average cooling power of the thermal cycle will depend on the length of time the compressor spends in the idle mode and in the high-speed mode.
It will be appreciated that the compressor 20 is under the control of a controller 30 which executes the process 30 to control the compressor 20. The controller 30 may be a standalone controller or may be part of another entity such as the compressor 20 itself or indeed another entity. In one example the controller 30 may be associated with an inverter which is to supply AC current to the compressor to drive the compressor. The inverter may receive DC current from a motor, convert this to AC current, and supply the AC current to the compressor. The inverter may comprise the controller 30. The current may be supplied to the compressor at a certain frequency, e.g. according to a pulse-width-modulation algorithm. It will therefore be appreciated that to effect a change in speed of the compressor 20 the controller 30 may vary a property of the power (e.g. voltage or current) supplied to the compressor, for example the controller may control the current frequency (e.g. the duty cycle of the PWM signal) supplied to the compressor 20 to cause the compressor to operate in the modes described with reference to Figure 3. The controller 30 comprises processing circuitry configured to cause the compressor 30 to operate according to the process 300, or to perform the process. The processing circuitry may be implemented according to any suitable hardware and/or software combination sufficient to cause the process 300 to be executed. For instance the processing circuitry may be implemented on, or on any suitable combination of, a digital signal processor, field programmable gate array, and/or application specific integrated circuit (ASIC). The processing circuitry may be configured to execute instructions, such as processor control code, that, cause the compressor 20 to operate according to the process 300. Such instructions may be stored on a non-transitory machine-readable medium. Such instructions may be stored in a memory. Such instructions may be stored on any suitable memory medium, e.g. on a volatile or non-volatile medium, programmed memory (e.g. read-only memory such as firmware), or a data carrier. The processing circuitry may comprise such a memory storing the instructions. In examples where a compressor performance map is used to determine the compressor's proximity to the surge state, this may also be stored in the same memory as the operating instructions. In other words, a non-transitory machine-readable medium may store instructions that, when executed by processing circuitry, cause the process 300, with reference to the process 500, to be performed. The instructions may comprise code or microcode. The instructions, when executed, may be in any suitable programming language to allow the compressor 20 to be dynamically configured and/or reconfigured. As stated above, the processing circuitry may cause the current supplied to the compressor 20 to be varied to cause the compressor 20 to operate according to CMM and in the idle and high-speed modes thereof. As stated above, for this purpose a current supply device, such as a motor or inverter, may comprise the processing code depending on the type of compressor 20 and how it is controlled. The controller and/or processing circuitry may equally comprise, and may therefore be referred to as, a processor, microcontroller or microprocessor.
The predetermined temperature range may symmetrical about the target temperature or may be asymmetrical about the target temperature, depending on the implementation. The range may be programmable and/or adjustable and/or settable and/or controllable and/or customisable, for example by an OEM configuring the controller 30 for the compressor 20.
For the purposes of this disclosure "greater and less than" should be considered a disclosure of "greater or equal to and less than or equal to," depending on the example.
Figure 3 has been described with reference to a cooling operation. As such, the compressor 20 in CMM operates in the idle mode 308 until the temperature of the region 10 to be cooled is greater than (or greater than or equal to) an upper temperature bound. In the idle mode the mass flow rate through the compressor is as low as possible and therefore the heat rate of the compressor and refrigeration cycle will decrease and the temperature of the region 10 will increase. The upper temperature bound at 312 therefore represents the temperature of the region 10 hitting the maximum temperature allowed by the process 300. When this temperature is reached operation of the compressor 20 in the high-speed mode will cause a high heat rate of the compressor and refrigeration cycle causing the temperature of the region 10 to decrease. The heat rate of the compressor in the high-speed mode is higher than the heat rate of the compressor in the nominal mode and therefore it could be said that the heat rate provided in the high-speed mode is higher than that required to maintain the region 10 at the target temperature, since the purpose of the high compressor speed in the high-speed mode is to decrease the temperature at the region 10 from the upper temperature bound. The lower temperature bound at 318 therefore represents the temperature of the region 10 hitting the minimum temperature allowed by the process 300.
It will therefore be appreciated that selecting the upper and lower bounds to be closer to the target temperature (the predetermined range thereby being narrow) will lead to the actual temperature of the region 10 being maintained at a temperature that is closer to the target than if the upper and lower bounds were further away (and if the predetermined range was larger). In some practical implementations the predetermined range may be set as close as possible to the target so as to achieve the minimum difference between the actual temperature of the region 10 and the target temperature of the region 10. In one example, the predetermined range may be ±1°C of the target temperature (in Celsius).
The skilled person will readily see how this discussion above in relating to a cooling cycle will be adapted to a heating cycle following the principles of this disclosure.
In the Figure 3 example the preconditions are both related to the temperature of the region 10 to be heated/cooled.
The compressor 20 is controlled to remain in CMM until an exit condition is detected, as indicated at 320.
One example exit condition is the determination that the compressor 20 is no longer operating proximate to a surge state. In these examples, whichever metric is used to determine that the compressor is operating proximate a surge state (e.g. a normalised distance to the surge line is less than a predetermined threshold), an exit condition may be that this metric is no longer true (e.g. the normalised distance to the surge line is no longer less than the predetermined threshold). Another example exit condition is a request (e.g. from a user of the system) that requires the compressor to be operated at a speed higher than the second speed in the high-speed mode. This may correspond to a request that the compressor be operated at a higher temperature than the target, or a higher temperature than the upper temperature bound of the predetermined temperature range. Each exit condition may be programmable and/or adjustable and/or settable and/or controllable and/or customisable, for example by an OEM configuring the controller 30 for the compressor 20.
On return to the operating in the nominal mode, the compressor 20 may be driven at a constant speed (and therefore a constant mass flow rate) so that the temperature of the region 10 to be heated or cooled is maintained at the target temperature. To transition from the CMM back to the nominal mode the current (e.g. the PWM duty cycle) may be varied to correspond to the constant speed and mass flow rate that will lead to the region 10 being heated/cooled to the target temperature.
Although in this example the compressor 20 in CMM is caused to operate in the idle mode 308 first, in other examples the compressor 20 in CMM is caused to operate in the high-speed mode 314 first. Whichever mode the compressor 20 is caused to operate in first in CMM therefore depends on the example and being programmable and/or adjustable and/or settable and/or controllable and/or customisable, for example by an OEM configuring the controller 30 for the compressor 20.
It will therefore be appreciated that a controller 30 performing the process 300 will obtain various forms of data. For example, the controller 30 may obtain target temperature data indicating a target temperature to be achieved at the region 10 to be heated or cooled. The controller 30 may obtain temperature (e.g. current temperature) data indicating the temperature of the region 10 to be heated or cooled. The controller 30 may obtain compressor data indicating a compressor parameter associated with the operation of the compressor. The controller 30 may use the temperature data and current temperature data to manage the compressor operation while in CMM, since the compressor 20 being modulated between the idle and high-speed modes in the Figure 3 example is based on whether a current temperature of the region 10 is greater/less than the upper/lower bounds of the predetermined temperature range, which itself depends on the target temperature. The controller 30 may use the compressor data to determine whether the compressor is being driven proximate a surge state (this will be discussed with reference to Figures 5 and 6). Hence, various forms of data may be considered as inputs to the process 300.
The compressor 30 may, in some examples, be in communication with at least one sensor, for example a compressor sensor to determine the compressor data and/or a temperature sensor to determine a temperature of the region 10 to be heated or cooled. Alternatively, the compressor 30 may not be in direct communication with sensors but may instead have access to the data by being in communication with a memory storing the data. Therefore, "obtaining" data as used herein may comprise receiving data (e.g. from a sensor), measuring data (e.g. by a sensor), determining or calculating or estimating data (e.g. from data received from a sensor), or retrieving data (e.g. from a memory storing data), depending on the example.
Figure 5 shows a process 500 for surge proximity detection. Process 500 comprises blocks 502-506 which may form part of block 304 in the Figure 3 process 300 in one example. The skilled person will appreciate that this depicts on example of determining whether the compressor 20 is operating close to a surge state, but that other examples could be used.
At block 502 the process 500 comprises obtaining compressor data indicating a compressor parameter associated with the operation of the compressor 20. The data may comprise speed data indicating a speed of the compressor (e.g. the rotational speed of an impeller of a centrifugal compressor, which may be expressed in rpm) or the compressor torque, or the data may comprise data relating to a motor or inverter driving the compressor 20, such as a voltage value or current value, a duty cycle of a PWM signal etc. The data may comprise temperature and/or pressure data, either of the compressor itself or of the vapour therein (e.g. at the inlet and/or outlet), e.g. its pressure and/or temperature.
In the Figure 500 example the compressor data 502 allows the operation, or operating state, of the compressor 20 to be plotted, or located, on the compressor performance map 200. Accordingly, at block 504 the process 500 comprises determining the position on the compressor performance map 200 of the operating state of the compressor 20 based on the data obtained at block 502. In one example, this may comprise determining the mass flow rate of the compressor and/or the pressure ratio of the compressor and locating these on the horizontal and/or vertical axes, respectively, of the map 200.
In some examples determining the mass flow rate may comprise determining a corrected mass flow rate and locating that on the horizontal axis of the map 200, the horizontal axis being corrected mass flow rate in these examples. For example, the compressor parameter obtained at block 502 may be the speed of the compressor and/or the inlet pressure and/or the outlet pressure and/or a temperature at the compressor inlet and/or outlet and any one or more of these parameters may be used to calculate the mass flow rate. The process may then calculate a corrected mass flow rate by multiplying the mass flow rate by a factor proportional to an operating condition of the compressor (e.g. an inlet condition of the compressor such as inlet pressure or temperature), for example proportional to the difference between these conditions (e.g. inlet conditions) and those (e.g. inlet conditions) according to the compressor performance map.. The compressor map 200 may be stored in a memory and may depict the operation of a compressor in certain conditions and the factor may take into account the difference in operating conditions between those used to create the map 200 and the actual operating conditions of the compressor 20 which can affect the mass flow of air (different ambient densities, altitudes, temperatures etc.). In this way the determined mass flow rate based on actual operating parameters can be scaled so that the operation of the compressor can be accurately located on the map 200.
At block 506 the process 500 comprises determining whether the position on the compressor performance map 200 is less than a predetermined threshold away from the surge line 202.
Figure 6 shows a schematic illustration of the process 500. Figure 6 shows a compressor performance map 600, like the one 200. The horizontal axis depicts a corrected mass flow rate. Point 601 indicates the operating point on the map 600 of a compressor 20 while operating in its nominal mode 302. Put another way, from the compressor data obtained at 502, a corrected mass flow rate can be determined and the pressure ratio of the compressor 20 may be determined, or known, leading to the point 601 being located on the map 600. The "path" traced by lines 603 and 604 lead to the shortest distance between the point 601 and the surge line 602. In other words, determining a point 601 on the compressor map 600 enables a measure of proximity to the surge line 602 to be determined. This may be known as the "surge margin." In one example, block 506 may comprise determining whether the surge margin is less than a predetermined percentage (or distance, e.g. a normalised distance) and, if so, then it is determined that the compressor is proximate its surge state (which triggers the compressor 20 being taken out of its nominal mode and begin operated in CMM). According to one example, the predetermined threshold for the surge margin may be 5%, meaning that if, at block 506, the operating point corresponds to a surge margin less than 5% then the compressor is considered operating proximate a surge state. This predetermined percentage threshold may be programmable and/or adjustable and/or settable and/or controllable and/or customisable, for example by an OEM configuring the controller 30 for the compressor 20. In one example block 506 may comprise determining a normalised distance between the operating point 601 on the compressor performance map 600 and the surge line 615 and determining whether that normalised distance is less than a predetermined threshold distance. This example may be similar to the surge threshold but the measure of closeness to the surge line can be expressed as a distance measurement rather than as a percentage. The distance from the operating point 601 to the surge line 615, either expressed as a distance or as a percentage, may be considered "vertically" (e.g. for a constant corrected mass flow) or "horizontally" (e.g. for a constant pressure ratio) and, when either less than a predetermined threshold, it may be determined that the compressor is operating proximate to a surge state. Of course, as depicted in Figure 6, the shortest distance to the surge line may comprise a distance in both directions.
The skilled person will appreciate that any suitable measure of proximity to a surge state may be used depending on the example, including a measure of proximity from an operating point 601 on the compressor map to the surge line.
In one example, the measure of proximity to the surge line may comprise determining the distance between the operating point of the compressor on the compressor performance map and the surge line on the horizontal/mass flow rate axis only. In other words, the measure of proximity to the surge line may comprise determine the distance between the compressor operating mass flow rate and the mass flow rate on the surge line (e.g. the mass flow rate that would cause the compressor to operate in a surge state) for the operating pressure ratio of the compressor. As above, the measure of proximity may be within a range, e.g. a %, of this mass flow rate (e.g. 5% as above). For example, if for given operating parameters of the compressor it is operating at a pressure ratio for which a mass flow rate of 0.1 would place it into surge (e.g. a mass flow rate of 0.1 is on the surge line) then if the compressor operates at a mass flow rate of +5%, e.g. less than, or less than or equal to, 0.105, the compressor may be caused to operate in CMM. A mass flow rate of 0.15 (being the mass flow rate on the surge line for a given pressure ratio +5%) is therefore the condition that places the compressor in CMM (and constitutes the measure of proximity to the surge line in this example). 5%, or 0.005, may therefore be the predetermined threshold distance (that if the mass flow rate is under the compressor is caused to operate in CMM) in this example.
As stated above, "obtaining" the compressor data may comprise receiving, measuring, determining, calculating, estimating, or retrieving the compressor data.
The region 10 to be heated or cooled may be any region. In some implementations of the present disclosure the thermal cycle 1 may be used as part of a thermal cycle in a vehicle. In these examples, the region 10 may be a region of a vehicle.
In one particular example the region 10 is a region of a cabin of a vehicle. In these examples, a signal indicating a user request for dehumidification or solo cabin heating/cooling may correspond to low mass flow rate through the compressor leading to the compressor 20 being operated in CMM, as per the process 300.
In another particular example the region 10 is a battery of an electric vehicle.
As stated above, many parameters of the process are programmable and/or adjustable and/or settable and/or controllable and/or customisable, for example by an OEM configuring the controller 30 for the compressor 20 allowing a user to set their desired parameters, e.g. for the predetermined temperature range and/or the predetermined threshold. This allows a user, e.g. an OEM, to calibrate the process to a particular implementation. It will be understood that these parameters may be calibrated by configuring the controller 30 which controls operation of the compressor 20 by implementing the process.
Figure 7 shows a compressor performance map 700 when the compressor 20 is used as part of a cooling cycle to cool a battery of an electric vehicle to illustrate some of the principles of this disclosure. The map 700 illustrates, by the depicted curves, certain combinations of compressor speed (rpm), corrected mass-flow rate, and pressure ratio of the compressor 20. The four points on the graph correspond to the heat emitted by the electric vehicle battery and hence, by how much the battery requires cooling. In this example, when the battery is emitting 10kW or 13kW the corresponding points on the compressor map 700 (meaning the positions on the map corresponding to the compressor operational parameters required to cool the battery when the battery is emitting 10kW and 13kW of heat) are within the nominal area of the compressor map (see area 210 of Figure 2). In contrast, if the battery is only emitting 3kW or 5kW of heat, this is "low enough" in this example to require a cooling rate corresponding to a compressor speed and mass flow rate that places the compressor operating in a surge condition. Put another way, the points on the map 700 corresponding to 3kW and 5kW correspond to low enough mass flow rates that, to achieve cooling at these temperatures while in a nominal mode, the compressor 20 would be operating in the surge region (see area 215 of Figure 2). As Figures 8-12 indicate, when the compressor 20 operates according to the process 300 this triggers its operation in CMM.
Figures 8-11 schematically depict the outcome of simulations of compressor performance, with reference to Figure 7, to illustrate some of the principles and advantages of the present disclosure. Figure 8 shows an entire refrigeration cycle from time t=0 to time t=1300 (approx.) with Figures 9-14 showing snapshots of the cycle across specific time windows. In all of Figures 8-12, the (a) figures show compressor speed, the (b) figures show the temperature of a plate of the battery, the (c) figures show the heat generated by the battery, the (d) figures show the superheat (e.g. the temperature difference of the refrigerant above saturation temperature at a given pressure) that the expansion valve 24 is to maintain across the cycle so that the refrigerant is evaporated in the evaporator (the dotted line represents the area of the expansion valve and how it reacts to changing demand on the refrigeration cycle)in the refrigeration cycle, the (e) figures show the proximity of the compressor operation/performance to the surge line (indicating the compressor proximity to a surge state or a surge condition), and the (f) figures show the pressure at the inlet of the compressor 20. In all of Figures 8-14 the horizontal axis is time, and in each figure the (a)-(f) graphs have the same horizontal axis scale so all graphs in a given figure depict the same portion of the refrigeration cycle. In this way, each figure provides a snapshot of multiple components of the system at the same time and the (a)-(f) graphs of each figure should be understood together. Whilst some areas of the graphs are singled out by means of a label not every same/similar region is labelled for brevity but the skilled person will understand where certain areas of the graph repeat.
Figure 8 shows an entire refrigeration cycle from time t=0 to t=1300. In this cycle, the compressor is operated in both the nominal mode and in CMM.
From t=0 to about t=250 the controller 30 is operating the compressor 20 in the nominal mode driven at constant speed (see region 801 in Figure a) with a constant inlet pressure (see Figure 8f) and the evaporation valve is operated at constant speed (see Figure 8d) as the heat generated by the battery, 10-13kW, (see Figure 8c) is high enough to correspond to a mass flow rate that is high enough so that the compressor performance is not proximate a surge state. The temperature of the battery plate is also constant (see 810 in Figure 8b). Figure 8e shows the proximity of the compressor 20 to a surge condition. In Figure 8e line 831 depicts compressor actual performance and line 833 depicts the surge line on the compressor performance map. As described above with reference to Figure 3 the proximity to a surge state may be set in the form of a predetermined threshold (e.g. a predetermined surge margin or predetermined distance, e.g. a normalised distance) which, if the compressor parameter (e.g. a location on the performance map corresponding to compressor operating conditions) falls below or exceeds (depending on the example) the CMM of the compressor is triggered. It will be appreciated that such a predetermined threshold may also be dependent on a parameter, e.g. a compressor parameter such as compressor speed, temperature, inlet and/or outlet temperature, pressure, inlet and/or outlet pressure, mass flow rate and/or pressure ratio. The predetermined threshold may therefore change with time, and this is represented as line 832. In other words, line 832 represents the predetermined threshold where, if the compressor operating conditions (line 831) fall below, it is determined that the compressor is operating proximate a surge state (line 833). At t=250 approx. the heat generated by the battery falls to a value, 5kW, (see 821 on Figure 8c) that causes the compressor operating performance 831 to fall below the predetermined surge threshold 832, which may also be referred to as a predetermined surge limit (Figure 8e). This causes the controller 30 to operate the compressor 20 in CMM.
Firstly, the controller 30 causes the compressor speed to ramp down to the idle mode (point 805 on Figure 8a indicating the point at which CMM is activated). Point 802 on Figure 8a indicates the compressor being driven at minimum speed corresponding to the idle mode. This continues until (see Figure 8b) at approx. t=290 the temperature of the battery plate, which may be considered as the region 10 to be cooled in this example, exceeds the upper temperature limit (upper dotted line in Figure 8b) which triggers the controller 30 to cause the compressor speed to ramp up placing the compressor 20 in the high-speed mode, as indicated by 803 on Figure 8a. Operation in the high-speed mode continues until (see Figure 8b) at approx. t=310 the temperature of the battery plate falls below the lower temperature limit (lower dotted line in Figure 8b) which triggers the controller 30 to cause the compressor speed to ramp down to the idle mode again. The cycle continues and the compressor 20 operates in CMM, cycling between the idle and high-speed modes (811 of Figure 8b designating the CMM cycle) until approx. t=525 when an exit condition is detected - in this example the heat generated by the battery being high enough (10kW) so that the compressor operation is no longer proximate a surge state. Then, the controller 30 causes the compressor to return to operate in its nominal mode, with point 806 designating the decrease in compressor speed to the constant speed in the nominal mode.
In this example, at t=710 approx. the battery heat generated falls to a low enough value again, 5kW and then 3kW, (Figure 8c) that triggers the compressor operation to fall within the predetermined threshold of the surge state (Figure 8e) which causes the controller 30 to place the compressor in CMM again, where it cycles between the idle and high-speed modes until t=1090 approx. where the battery heat rate returns to 13kW causing the controller 30 to operate the compressor 20 in the nominal mode as discussed above.
Figure 8f shows the inlet pressure of the compressor. It can be seen from Figure 8f that the inlet pressure is substantially constant in the nominal mode and in the idle and high-speed modes respectively is high and low.
Figure 8d shows the speed of the expansion valve 24. Figure 8d shows that in the nominal mode the expansion valve 24 is operated (e.g. caused to operate by the controller 30 or some other component) such that the superheat value of the refrigerant is substantially constant, e.g. maintained at a target of 5 degrees in this example. In the idle and high-speed modes respectively, the superheat value of the refrigerant cycles from between a minimum and a maximum (e.g. low and high). By way of further detail, the expansion valve is operated such that substantially all refrigerant that enters the evaporator 26 is evaporated, and when the compressor is caused to operate in the idle and high-speed modes there is a change in the area of the expansion valve 24 required so that all refrigerant is evaporated in the evaporator 26, and this change in area is reflected in Figure 8d. In some examples this disclosure comprises a process (which may be part of the process 300 or may be an additional process) for controlling the operation of the expansion valve 24. By controlling or operating the expansion valve 24 it is meant controlling the area of the expansion valve (e.g. to achieve substantially all refrigerant evaporating in the evaporator 26).
Figure 9 shows the cycle from t=236 to t=270 seconds. The Figure 9 graphs therefore show the nominal operation of the components of the system before the point (t=250) which triggers the compressor 20 to be operated in CMM, and the initial operation of the compressor 20 in CMM (e.g. the idle mode).
Figure 10 shows the cycle from t=220 to t=380. The Figure 10 graphs therefore show the compressor being caused to operate in CMM and how the compressor cycles between the idle and high-speed modes.
Figure 11 shows the cycle from t=450 to t=670. The Figure 11 graphs therefore show the compressor 20 switching back to nominal mode from the CMM.
Figure 12 shows a prior art process of preventing compressor surge using a recirculation valve (RCV) which is operated as a bypass valve to increase flow through the compressor to prevent it operating in a surge state. The graphs a-f of Figure 12 show the operation of the same components as for the Figure 8-11 graphs and across the same time window, and with the same battery heat generated profile (Figure 12c) to enable a meaningful comparison.
Figure 13 shows, for comparative purposes, the refrigeration cycle in which the compressor is operated in according to a prior art process using a RCV as in Figure 12 and
Figure 14 shows the refrigeration cycle in which the compressor is operated according to the present disclosure as in Figures 8-11.
In both figures graph (a) is a time series plot of the pressure ratio of the compressor, graph (b) shows the battery heat generated (as for the (c) graphs in Figures 8-12), graph (c) shows the compressor coefficient of performance profile in time (the "COP profile in time" is the ratio of instant cooling power to instant compressor power, e.g. the former divided by the latter) graph (d) shows the mass flow through the compressor, graph (e) shows the compressor power and total cooling power, and graph (f) shows the total coefficient of performance (the "COP total" is the ratio between the cumulative cooling power (energy) to the cumulative compressor power (energy), e.g. the former divided by the latter).
Figures 15 and 16 respectively show the Figure 13 and 14 graphs from t=700 to t=1100 to which corresponds to the second time the compressor 20 enters CMM (see Figures 8-11).
What Figures 13-16 indicate is that there is a significant saving in the total energy consumed by the compressor when it is operated according to the process 300 when compared to being operated in a prior art process using an RCV. In particular, Figures 13e and 14e indicate that the total coefficient of performance of the compressor in the prior art process is 1.2178 and the total energy consumed by the compressor is approx. 8703kJ. In contrast, when the compressor is operated according to the process 300 the total coefficient of performance is 1.3263, and the total energy consumed is approx. 8279 kJ. In the snapshot of the cycle shown in Figures 15 and 16 when the compressor 20 is operated in CMM, the total coefficient of performance of the compressor in the prior art process is 1.1858 and the total energy consumed by the compressor is approx. 1430kJ. In contrast, when the compressor is operated according to the process 300 the total coefficient of performance is 1.366, and the total energy consumed is approx. 1020 kJ. Up to 29% of energy has therefore been saved, in this example, by using the present disclosure.
Thereby, the present disclosure demonstrates that when the compressor 20 is operated according to the present disclosure, significant savings in terms of energy consumed and significant improvements in the coefficient of performance may be achieved not only during the portion of the cycle when the compressor is operated in CMM (see figures 15 and 16) but over the cycle as a whole (see Figures 13 and 14).
The person skilled in the art realizes that the present disclosure by no means is limited to what is explicitly described above. On the contrary, many modifications and variations are possible within the scope of the appended claims. Additionally, variations can be understood and effected by the skilled person in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims.

Claims

Processing circuitry for controlling the operation of a fluid compressor device configured to compress refrigerant vapour as part of a vapour-compression cycle to achieve a target temperature of a region to be heated or cooled, the processing circuitry being configured to:
obtain target temperature data indicating the target temperature to be achieved in the region to be heated or cooled;

obtain temperature data indicating a temperature of the region to be heated or cooled;

obtain compressor data indicating a compressor parameter associated with the operation of the fluid compressor device;

determine, based on the compressor data, whether the fluid compressor device is approaching a surge state; and, if it is determined that the fluid compressor device is approaching the surge state, the processing circuitry is configured to:
cause the fluid compressor device to operate in a capacity modulation mode according to which the compressor speed is modulated between two speeds such that, in the capacity modulation mode, the temperature of the region to be heated or cooled is maintained to within a predetermined range of the target temperature.
Processing circuitry of claim 1 wherein, in the capacity modulation mode, the processing circuitry is configured to cause the fluid compressor device to operate at a first compressor speed until the temperature data indicates that the temperature of the region to be heated or cooled is at the upper bound of the predetermined range at which point the processing circuitry is configured to cause the fluid compressor device to operate at a second compressor speed, greater than the first compressor speed, until the temperature data indicates that the temperature of the region to be heated or cooled is at the lower bound of the predetermined range at which point the processing circuitry is configured to cause the fluid compressor device to return to operating at the first compressor speed.
Processing circuitry of claim 1 or 2 wherein, in the capacity modulation mode, the fluid compressor device is caused to operate between an idle mode in which the first compressor speed is substantially at a minimum and a high-speed mode in which the second compressor speed is such that the compressor is caused to operate at a maximum coefficient of performance.
Processing circuitry of claim 2 or 3 wherein the fluid compressor device comprises an air foil bearing, and wherein the first compressor speed is substantially equal to a minimum lift-off speed of the air foil bearing.
Processing circuitry of any preceding claim wherein, in the capacity modulation mode, the temperature of the region to be heated or cooled is maintained to within one degree Celsius of the target temperature.
Processing circuitry of any preceding claim, wherein the predetermined range is adjustable.
Processing circuitry of any preceding claim wherein the predetermined range is symmetric about the target temperature.
Processing circuitry of any preceding claim wherein, to determine whether the fluid compressor device is approaching the surge state, the processing circuitry is configured to determine a mass flow rate of the fluid compressor device based on the compressor data, locate the mass flow rate on a compressor performance map, and determine a distance between the mass flow rate and a surge line on the compressor performance map, the processing circuitry being configured to determine that the fluid compressor device is approaching the surge state if the distance between the mass flow rate and the surge line is less than a predetermined threshold distance.
Processing circuitry of claim 8, wherein the processing circuitry is configured to determine a corrected mass flow rate and wherein the distance is between the corrected mass flow rate and the surge line.
Processing circuitry of claim 8 or 9 wherein the predetermined threshold distance is adjustable.
Processing circuitry of any preceding claim wherein the processing circuitry is configured to determine, based on the compressor data, whether the fluid compressor device is operating remote from the surge state and, if it is determined that the fluid compressor device is operating remote from the surge state while operating in the capacity modulating mode, the processing circuitry is configured to cause the fluid compressor device to cease operating in the capacity modulation mode.
Processing circuitry of any preceding claim wherein, when the fluid compressor device is operating in the capacity modulation mode, the processing circuitry is configured to determine whether the fluid compressor device would operate proximate the surge state so that the vapour-compression cycle can achieve the target temperature in the region to be heated or cooled, and, if it is determined that the fluid compressor device can operate so that the target temperature can be achieved in the region to be heated or cooled without operating proximate the surge state then the processing circuitry is configured to cause the fluid compressor device to cease operating in the capacity modulation mode.
Processing circuitry of any preceding claim wherein the target temperature of the region to be heated or cooled is related to a preferred cabin temperature of an electric vehicle or to a preferred temperature of a battery of an electric vehicle.
Processing circuitry of any preceding claim wherein the processing circuitry is configured to control the area of an expansion valve of the vapour-compression cycle when the fluid compressor device is operating in the capacity modulation mode.
A drive system for an electric vehicle, the system comprising:
a source of AC current configured to supply AC current to a fluid compressor device configured to compress refrigerant vapour as part of a vapour-compression cycle based on target temperature data indicating a target temperature to be achieved in a region to be heated or cooled; and

a controller for the source of AC current, wherein the controller comprises the processing circuitry of any preceding claim, the controller being configured to vary the current supplied to the fluid compressor device to cause the fluid compressor device to operate in the capacity modulation mode.