Method of controlling an electrical appliance

Abstract

An electrical appliance comprises an electric motor, a sensor to detect whether the electrical appliance is in free fall, and a controller to receive fall data from the sensor. In the event that the e

Description

BACKGROUND Some electrical appliances, such as vacuum cleaners and haircare appliances, utilise electric motors to generate an airflow that is used by a user of the electrical appliance to perform a particular function. SUMMARY A first aspect provides a method of controlling an electrical appliance comprising an electric motor, the method comprising: receiving fall data indicative of whether the electrical appliance is in free fall; and braking the electric motor, based on the fall data, in the event that the electrical appliance is in free fall. During rotation of a rotor assembly of an electric motor, particularly at relatively high speeds, rotating components of the electric motor can deviate from their at rest position. For example, an impeller of an electric motor can deform radially outwardly when rotating at relatively high speeds, and / or the rotor assembly of the electric motor can orbit its rotational axis in a non-circular manner due to unbalanced forces experienced during rotation. Such deformation and uneven orbiting may increase with a speed of rotation of the rotor assembly. When a user is using an electrical appliance, conditions may occur in which the user drops the electrical appliance, whether accidentally or on purpose. Impacts caused by such dropping of the electrical appliance can cause damage to the electric motor. For example, where rotating components of the electric motor have deviated from their rest position, they may be closer to static and / or other rotating components of the electric motor than they would be at the rest position, and impacts to the electric motor may result in undesirable contact between the rotating components and the static and / or other rotating components. This can result in damage to components of the electric motor, including frictional wear caused by relative rotation between the components. Furthermore, such damage and / or frictional wear can result in small debris particles contaminating the electric motor, leading to reduced lifespan and / or failure of the electric motor. By receiving the fall data indicative of whether the electrical appliance is in free fall, and braking the electric motor, based on the fall data, in the event that the electrical appliance is in free fall, the method of the first aspect may mitigate for the above mentioned effects. For example, by braking the electric motor when free fall is detected, the electric motor may be operating at a reduced speed when contact is made with a surface and / or object than if no braking were applied. This may result in an increased distance between components of the electric motor, which may reduce a likelihood of and / or avoid contact between components of the electric motor when the electrical appliance experiences an impact, and / or may result in reduced damage if contact between components of the electric motor occurs. The electrical appliance may comprise a controller, and the method may comprise receiving, at the controller, the fall data. The method may comprise determining, for example determining at the controller, that the electrical appliance is in free fall. The method may comprise the controller braking of the electric motor, for example by issuing an instruction to at least one further component of the electrical appliance. The fall data may be indicative of acceleration of the electrical appliance, and may, for example, comprise at least one of acceleration data, velocity data, time data, image data, direction data, and / or processed data based on at least one of the acceleration data, the velocity data, the time data, the image data, and the direction data. The method may comprise receiving, from at least one sensor, the fall data. The method may comprise sensing, at the at least one sensor, at least one of the fall data, the acceleration data, and the velocity data. The method may comprise transmitting, from the sensor to the controller, the fall data. The electrical appliance may comprise the at least one sensor. The at least one sensor may comprise at least one of an accelerometer, an inertial measurement unit (IMU), a magnetometer, a gyroscope, and a camera. The method may comprise determining whether the fall data is above a pre-determined fall threshold, and causing, when the fall data is above the pre-determined fall threshold, the braking of the electric motor. The method may comprise determining whether the fall data is above a pre-determined fall threshold for longer than a pre-determined time period, and causing, when the fall data is above the pre-determined fall threshold for longer than the pre-determined time period, the braking of the electric motor. The pre-determined fall threshold may comprise an acceleration threshold. The electrical appliance may comprise an inverter for controlling a voltage provided to the electric motor, and braking the electric motor may comprise controlling the inverter. Controlling the inverter to brake the electric motor may provide for a simpler arrangement than, for example, application of a mechanical brake to the electric motor. Braking the electric motor may comprise controlling the inverter to interrupt a voltage supply to the electric motor. The inverter may comprise a plurality of switches, and braking the electric motor may comprise closing at least one of the plurality of switches. By closing at least one of the plurality of switches to brake the electric motor, a pathway may be provided for current to flow through the electric motor. This may result in resistive conduction losses occurring in the electric motor, for example in a winding of the electric motor, and may result in quicker deceleration of the electric motor when compared to arrangements in which all switches are opened, and the electric motor is slowed by mechanical and / or eddy current and / or resistive losses alone. Braking the electric motor may comprise freewheeling the inverter. Freewheeling the inverter may result in lower peak currents than, for example, continually allowing current to flow through the electric motor and back to a DC link of the electric motor. The inverter may comprise a high side and a low side. Freewheeling the inverter may comprise closing at least one switch on the high side and opening all switches on the low side, and / or may comprise closing at least one switch on the low side and opening all switches on the high side. The method may comprise the controller causing operation of at least one of the plurality of switches of the inverter to freewheel the inverter. Braking the electric motor may comprise controlling the inverter to provide a generating current path from the electric motor to a power supply supplying power to the electrical appliance. By providing the generating current path, a reduced deceleration time to zero may be achieved when compared with freewheeling and / or arrangements in which all switches are opened. Furthermore, by providing a generating current path, current may be actively induced and stored in one or more DC link capacitors of the inverter, making such stored current available for future use. The method may comprise the controller causing operation of at least one of the plurality of switches of the inverter to provide the generating current path. The inverter may comprise a first leg and a second leg. Providing the generating current path may comprise closing one switch on the high side of the first leg, opening one switch on the low side of the first leg, opening one switch on the high side of the second leg, and closing one switch on the low side of the second leg. Providing the generating current path may comprise opening one switch on the high side of the first leg, closing one switch on the low side of the first leg, closing one switch on the high side of the second leg, and opening one switch on the low side of the second leg. Opening and closing of switches to provide the generating current path may depend on a polarity of current intended to flow through the electric motor. Braking the electric motor may comprise sequentially controlling the inverter to provide the generating current path, and freewheeling the inverter. Provision of the generating current path may provide for relatively quick deceleration of the electric motor. However, solely providing the generating current path may result in excessive peak current magnitudes occurring. By sequentially controlling the inverter to provide the generating current path and freewheeling the inverter, relatively quick deceleration of the electric motor may be achieved, whilst also reducing peak current magnitudes that may occur. The method may comprise freewheeling the inverter for a fixed time period following providing the generating current path. The method may comprise receiving current data indicative of a phase current flowing through the electric motor, and transitioning, based on the current data, from controlling the inverter to provide the generating current path to freewheeling the inverter. Transitioning based on the current data may enable transitioning to freewheeling when, or in advance of, the current reaches a level above which undesirable effects would occur. The method may comprise receiving, at the controller, the current data, for example from a current sensor of the electrical appliance. The method may comprise transitioning, when the current data is indicative of the phase current being greater than, or within less than 10% of, a phase current threshold, from controlling the inverter to provide the generating current path to freewheeling the inverter. The method may comprise the controller determining whether the phase current is greater than, or within less than 10% of, the phase current threshold. The inverter may comprise a plurality of switches, and braking the electric motor may comprise opening each of the plurality of switches simultaneously. This may provide a relatively simple mechanism for braking the electric motor, for example not requiring analysis of current flowing through the electric motor and / or not requiring relatively complex switching patterns. The method may be performed whilst electrical power is supplied to the inverter from a power source. For example, the method may be performed whilst the inverter is electrically connected to a battery of the electrical appliance and / or whilst the inverter is electrically connected to a mains power supply to which the electrical appliance is electrically connected. A second aspect provides an electrical appliance comprising: an electric motor; a sensor configured to sense whether the electrical appliance is in free fall; and a controller configured to: receive fall data from the sensor; and brake the electric motor, based on the fall data, in the event that the electrical appliance is in free fall. The electrical appliance may comprise a plurality of sensors configured to sense fall data indicative of whether the electrical appliance is in free fall, and configured to provide the fall data to the controller. The electrical appliance may comprise an inverter for controlling a voltage provided to the electric motor, and the controller may be configured to control the inverter to brake the electric motor. The electric motor may be a single phase motor. The inverter may be a single phase inverter. The controller may be configured to control the inverter to interrupt a voltage supply to the electric motor to brake the electric motor. The inverter may comprise a plurality of switches. The controller may be configured to close at least one of the plurality of switches to brake the electric motor. The controller may be configured to freewheel the inverter to brake the electric motor. The controller may be configured to operate at least one of the plurality of switches of the inverter to freewheel the inverter. The inverter may comprise a high side and a low side. The controller may be configured to close at least one switch on the high side and open all switches on the low side, and / or may be configured to close at least one switch on the low side and open all switches on the high side, to freewheel the electric motor. The controller may be configured to control the inverter to provide a generating current path from the electric motor to a power supply of the electrical appliance to brake the electric motor. The controller may be configured to operate at least one of the plurality of switches of the inverter to provide the generating current path. The inverter may comprise a first leg and a second leg. The controller may be configured to close one switch on the high side of the first leg, open one switch on the low side of the first leg, open one switch on the high side of the second leg, and close one switch on the low side of the second leg, to provide the generating current pathway. The controller may be configured to open one switch on the high side of the first leg, close one switch on the low side of the first leg, close one switch on the high side of the second leg, and open one switch on the low side of the second leg, to provide the generating current pathway. The electrical appliance may comprise a power supply. For example, the electrical appliance may comprise a battery. The electrical appliance may comprise a connector for connecting to an external power supply. The controller may be configured to sequentially control the inverter to provide the generating current path, and to freewheel the inverter, to brake the electric motor. The controller may be configured to control the inverter for a fixed time period following providing the generating current path. The electrical appliance may comprise a current sensor configured to sense phase current flowing through the electric motor, and the controller may be configured to receive current data from the current sensor, and to transition, based on the current data, from controlling the inverter to provide the generating current path to freewheeling the inverter. The controller may be configured to transition, when the current data is indicative of the phase current being greater than, or within less than 10% of, a phase current threshold, from controlling the inverter to provide the generating current path to freewheeling the inverter. The controller may be configured to determine whether the phase current is greater than, or within less than 10% of, the phase current threshold. The controller may be configured to open of the plurality of switches simultaneously to brake the electric motor. Each of the plurality of switches may comprise a metal oxide semiconductor field effect transistor (MOSFET), for example comprising an anti-parallel diode. The electrical appliance may comprise a power switch configured to switch the electrical appliance from a powered configuration in which electrical power is delivered from a power source to the electric motor, and an unpowered configuration in which electrical power is not delivered from the power source to the electric motor, and wherein the power switch is latched. In electrical appliances where the power switch is not latched, the lack of electrical power provided to the electric motor when the power switch is not actuated by a user may automatically result in braking of the electric motor. However, in electrical appliances where the power switch is latched, no such braking may occur. Accordingly, the controller being configured to receive the fall data and brake the electric motor based on the fall data may find particular utility in electrical appliances where the power switch is latched. The controller may be configured to receive the fall data and to brake the electric motor when the electrical appliance is in the powered configuration. The electric motor may comprise a rotor assembly rotatable within a frame, and the rotor assembly may comprise a bearing soft-mounted to the frame. Where the bearing is soft-mounted to the frame, there may be a greater risk of components of the rotor assembly clashing with the frame in the event that the electrical appliance is dropped with the electric motor operating at relatively high speeds, for example in comparison to arrangements in which the bearing is hard mounted to the frame. Accordingly, the controller being configured to receive the fall data and brake the electric motor based on the fall data may find particular utility in electrical appliances having electric motors where the bearing is soft-mounted to the frame. The bearing may be mounted to the frame by a mounting member, and the mounting member may have a stiffness at least two orders of magnitude lower than a radial stiffness of the bearing. The rotor assembly may comprise a shaft, and an impeller mounted to the shaft. The frame may comprise a shroud at least partially surrounding the impeller, and the impeller may be spaced from the shroud to define an impeller tip clearance in the region of 0.1mm to 0.5mm. The rotor assembly may comprise first and second bearing assemblies, the first bearing located closer to the impeller than the second bearing, and at least the first bearing may be soft mounted to the frame. The electric motor may be configured such that the rotor assembly is rotatable at a speed of at least 200krpm. The electric motor may be any of a floorcare appliance, a haircare appliance, and an air distribution appliance. Optional features of aspects may be equally applied to other aspects, where appropriate. BRIEF DESCRIPTION OF THE DRAWINGS Figure lisa schematic perspective view of a vacuum cleaner; Figure 2 is a schematic view of a main unit of the vacuum cleaner of Figure 1; Figure 3 is a schematic illustration of an electric motor of the main unit of Figure 2; Figure 4 is a schematic illustration of an inverter of the main unit of Figure 2; Figure 5 is a schematic illustration of the inverter of Figure 4 in a first state; Figure 6 is a schematic illustration of the inverter of Figure 4 in a second state; Figure 7 is a schematic illustration of the inverter of Figure 4 in a third state; Figure 8 is a schematic illustration of the inverter of Figure 4 in a fourth state; and Figure 9 is a flow diagram illustrating a method according to an example. DETAILED DESCRIPTION A vacuum cleaner 10 is illustrated in Figure 1, and has a main unit 12, a wand 14, and a cleaner head 16. The vacuum cleaner 10 is typically referred to as a stick vacuum cleaner. The main unit 12 is removably attached to the wand 14 and the cleaner head 16, so that the main unit 12 may be used as a standalone handheld vacuum cleaner, as shown in Figure 2. The main unit 12 is illustrated in Figure 2 has a separation system 20, an electric motor 22, an inverter 24, a controller 26, a battery 28, a user interface 30, and an accelerometer 32. The separation system 20 is a cyclonic separation system, though other separation systems are also envisaged, and further details of the separation system 20 are not provided here for the sake of brevity. The electric motor 22 is illustrated schematically in Figure 3, and has a stator assembly 35, a rotor assembly 36, and a frame 37. The electric motor 22 is a single-phase electric motor, although three-phase electric motors are also envisaged. The stator assembly 35 has a stator core 38, and a winding 39 wound around the stator core 38. The rotor assembly 36 has a shaft 40, a first bearing 42, a first bearing mount 44, a permanent magnet 46, a second bearing 48, a second bearing mount 50, and an impeller 52. The shaft 40 is elongate in form, and has a first end 54 and a second end 56. The first bearing 42 is mounted towards the first end 54 of the shaft 40. The first bearing 42 is mounted to the frame 37 by the first bearing mount 44. The first bearing mount 44 has a stiffness of at least two orders of magnitude lower than a radial stiffness of the bearing itself, which is typically around 10,000 N / mm. In view of the stiffness of the first bearing mount 44, the first bearing 42 is considered to be soft-mounted to the frame 37 by the first bearing mount 44. The permanent magnet 46 is mounted to the shaft 40 between the first bearing 42 and the second bearing 48. The second bearing 48 is mounted to the frame 37 by the second bearing mount 50. Again, the second bearing mount 50 has a stiffness of at least two orders of magnitude lower than a radial stiffness of the bearing itself, which is typically around 10,000 N / mm. In view of the stiffness of the second bearing mount 50, the second bearing 48 is considered to be soft-mounted to the frame 37 by the second bearing mount 50. The impeller 52 is mounted at the second end 56 of the shaft 40. The frame 37 has a shroud portion 58 that overlies the impeller 52 such that an impeller tip clearance of around 0.22 mm is defined between the impeller 52 and the shroud portion 58. The inverter 24 is electrically connected to the stator winding 39 of the electric motor 22, and to the battery 28, and is controlled in use by the controller 26. The inverter 24 is illustrated schematically in Figure 4, and has four power switches Q1-Q4 and a current sensor RI. The power switches Q1-Q4 are MOSFETs, although other types of power switch are also envisaged. The power switches Q1-Q4 are arranged in a full H-bridge configuration with two legs, each leg having a high-side switch Q1,Q2 and a low side switch Q3,Q4. The current sensor RI comprises a shunt resistor located on the low side of the inverter 24. The controller 26 is configured to control operation of the electric motor 22 via the inverter 24. The controller 26 is connected to the inverter 24 via a gate driver (not shown), and is also connected to the battery 28, the user interface 30, and the accelerometer 32. The battery 28 is configured to selectively provide electrical power to the electric motor 22, via the inverter 24, and the controller 26. The user interface 30 has a latched switch configured to selectively provide electrical power from the battery 28 to other components of the vacuum cleaner 10. The accelerometer 32 is configured to provide acceleration data to the controller 26. In use, a user can press the latched switch to enable electrical power to be supplied from the battery 28 to the inverter 24. The controller 26 controls the inverter 24 to supply electrical power to the electric motor 22. The supply of electrical power to the electric motor 22 causes the rotor assembly 36 to rotate. Rotation of the rotor assembly 36 generates an airflow through the main unit 12 owing to the impeller 52. Entrained dirt and debris are then separated from the airflow by the separation system 20. The aerodynamic performance of the electric motor 22 (i.e., the mass flow rate that is achieved for a given rotational speed), and therefore the effective suction power generated by the electric motor 22, is influenced by the clearance between the impeller 52 and the shroud portion 58. A smaller running clearance is desirable to reduce leakage. In the present example, the static clearance is around 0.22 mm. However, the running clearance (i.e., the clearance between the impeller 52 and the shroud portion 58 when the impeller 52 is rotating) is likely to be smaller than this. When a user is using the vacuum cleaner 10 or the main unit 12, conditions may occur in which the user drops the vacuum cleaner 10 or main unit 12, whether accidentally or on purpose. As noted, the user interface 30 has a latched switch for powering on and off the main unit 12. Accordingly, when the vacuum cleaner 10 or main unit 12 is dropped, the electric motor 22 continues to operate. Owing to the small running clearance between the impeller 52 and the frame 37, as well as the soft mounting of the rotor assembly 36 to frame 37 (which permits greater displacement of the rotor assembly 36 relative to the frame 37), the impact to the electric motor 22 resulting from the drop may damage the electric motor 22. In particular, the impeller 52 may contact the shroud portion 58 of the frame 37. With the impeller 52 operating at relatively high speeds, the contact may damage the impeller 52 and / or the shroud portion 58. For example, the impeller 52 may score the surface of the shroud portion 58, resulting in degraded aerodynamic performance. Alternatively, a small part of impeller 52 (e.g., the tip of a blade) may be broken off by the impact. Not only would this then degrade the aerodynamic performance of the impeller 52, but the change in mass of the impeller 52 may introduce significant imbalance in the rotor assembly 36, leading to increased vibration and / or load on the bearings 42,48. Moreover, relatively large debris generated by the impact of the impeller 52 with the shroud portion 58 may jam in one of the small gaps between the rotor assembly 36 and the stator assembly 35 or frame 37 (e.g., between the impeller 52 and the shroud portion 58 or between the magnet 46 and the stator core 38). Finer debris (e.g., generated by the rubbing of the impeller 52 against the frame 37) may contaminate the bearings, thereby reducing their lifespan. To mitigate for such effects, during use the accelerometer 32 provides acceleration data, which may be considered fall data in the context described herein, to the controller 26. The controller 26 monitors the acceleration data, and where acceleration data is around 0g for longer than a pre-determined time period, the controller 26 determines that the vacuum cleaner 10 is in free fall. In response to such a determination, the controller 26 controls the inverter 24 to brake the electric motor 22, the details of which are explained below. By braking the electric motor 22 in response to free fall, the speed of the rotor assembly 36 may be significantly reduced at the point of impact. By reducing the speed of the rotor assembly 36, a larger running clearance may be achieved between the impeller 52 and the shroud portion 58 at the point of impact. As a result, contact between the impeller 52 and the shroud portion 58 may be avoided or significantly reduced. Moreover, even if contact were still to occur between the impeller 52 and the shroud portion 58, damage is less likely at the lower speed. As the drop height increases, the resulting impact and therefore the likelihood for damage increases. However, as the height increases, the time available to brake the electric motor 22 increases, and therefore a lower rotational speed may be achieved at impact. Depending on the height from which the main unit 12 is dropped, the controller 26 may brake the electric motor 22 such that the rotor assembly 36 is stationary or near stationary upon impact. In order to brake the electric motor 22, the controller 26 places the inverter 24 into a state in which a current generating path is defined between the electric motor 22 and the battery 28, i.e., the electric motor 22 behaves as a generator and returns electrical power to the battery 28. As the rotor assembly 36 rotates, the magnet 46 induces a current in the stator winding 39. As the polarity of the rotating magnet 46 changes, so too does the polarity of the induced current. The controller 26 places the inverter 24 into a different state according to the polarity of the current in the winding 39. When the polarity of the current in the winding 39 is positive (defined as left-to-right in the Figures), the controller 26 places the inverter 24 in a first state, illustrated in Figure 5. In the first state, the first QI and fourth Q4 switches are open, and the second Q2 and third Q3 switches are closed. Current in the stator winding 39 is therefore returned to the battery 28. When the polarity of the current changes and is negative (defined as right-to-left in the Figures), the controller 26 switches the inverter 24 to a second state, illustrated in Figure 6. In the second state, the first QI and fourth Q4 switches are closed, and the second Q2 and third Q3 switches are open. Current in the stator winding 39 is therefore again returned to the battery 28. The controller 26 then cycles the inverter 26 between the first and second states according to the polarity of the current in the winding 39. By providing the current generation path, braking of the electric motor 22 occurs through resistive conduction losses in the stator windings 39 of the electric motor 22, resistive conduction losses in the H-bridge of the inverter, and mechanical and eddy current losses in the electric motor 22. Whilst controlling the inverter 24 to cycle between the first and second states, the controller 26 receives current data from the current sensor 60, and compares the current data to a threshold value. If the current data indicates that current flowing through the stator winding 39 is greater than a threshold current value, the controller 26 controls the inverter 24 to freewheel the inverter 24. An example freewheeling state of the inverter 24 is shown in Figure 7. In the example freewheeling state, the third Q3 and fourth Q4 switches of the inverter 24 are closed, and the first QI and second Q2 switches of the inverter 24 are open. It will be appreciated that other freewheeling states are also envisaged. For example, a freewheeling state in which the first QI and second Q2 switches of the inverter are closed and the third Q3 and fourth Q4 switches of the inverter 24 are open is envisaged, as are single switch freewheeling states. By freewheeling the inverter 24, braking of the electric motor 22 may still be achieved, whilst limiting peak current values to acceptable levels. The inverter 24 is freewheeled for a pre-determined time period, before the controller 26 switches back to controlling the inverter 24 to provide the current generating path. The controller 26 thereby sequentially controls the inverter 24 to provide the current generating path and freewheels the inverter 24. Although the controller 26 is described above as controlling the inverter 24 to both provide a current generation path and to freewheel the inverter 24, it will be appreciated that embodiments in which the controller 26 only controls the inverter 24 to provide the current generating path, or only freewheels the inverter 24, to brake the electric motor 22 are also envisaged. Furthermore, embodiments in which the controller 26 controls the inverter 24 to be in an off state are also envisaged. Such an off state is illustrated in Figure 8. In the off state, all power switches Q1-Q4 of the inverter 24 are open. In the off state, anti-parallel diodes of the switches Q1-Q4 provide a path for phase current to dissipate and return to DC link capacitor (not shown) of the inverter 24. In Figure 8, the polarity of the phase current is positive and therefore current in the winding 39 is returned to the DC link capacitor via the diodes of switches Q2 and Q3. When the peak of the back-EMF induced in the winding 39 is higher than the DC link voltage, it will intermittently induce a current pulse in the winding 39 that will again flow back to the DC link capacitor, increasing their stored charge and hence boosting the DC link voltage to the level of the peak of the back-EMF, at which point no more induced current will arise. The intermittent current regeneration normally only takes a few (e.g. <10) electrical cycles to charge the DC link to a level where regeneration no longer occurs because the peak of the back-EMF no longer exceeds the DC-link voltage. From this point on, there is no electrical energy flow from the electric motor 22 to the DC link capacitor, therefore the kinetic energy stored in the rotating assembly can only be dissipated via mechanical means, i.e. air compression losses in the compressor, windage, bearing friction, and via induced Eddy-current losses in the stator laminations. A method 100 in accordance with the above is illustrated in Figure 9. The method 100 includes receiving 102 fall data indicative of whether the vacuum cleaner 10 is in free fall, determining 103 based on the fall data whether the vacuum cleaner 10 is in free fall, and braking 104 the electric motor 22 in the event that the vacuum cleaner 10 is determined to be in free fall. Although described above as utilising the acceleration sensor 32, embodiments in which additional and / or alternative sensors are utilised to provide fall data to the controller 26 are also envisaged. For example, any of an inertial measurement unit, a magnetometer, a gyroscope, and a camera, may be used to provide fall data to the controller 26 to determine when the vacuum cleaner 10 or main unit 12 is in free fall. Furthermore, although the braking of the electric motor 22 has been described above in relation to the vacuum cleaner 10, it will be appreciated that braking an electric motor in response to detection of free fall can be applied more generally to electrical appliances that have electric motors. For example, the concepts discussed herein may be applied to electrical appliances such as haircare appliances, and air distribution appliances. More generally, whilst particular examples have been described, it should be understood that these are illustrative examples only and that various modifications may be made without departing from the scope of the claims.

Claims

1. A method of controlling an electrical appliance comprising an electric motor, the method comprising:receiving fall data indicative of whether the electrical appliance is in free fall; andbraking the electric motor, based on the fall data, in the event that the electrical appliance is in free fall.

2. The method as claimed in Claim 1, wherein the electrical appliance comprises an inverter for controlling a voltage provided to the electric motor, and braking the electric motor comprises controlling the inverter.

3. The method as claimed in Claim 2, wherein braking the electric motor comprises controlling the inverter to interrupt a voltage supply to the electric motor.

4. The method as claimed in Claim 2 or Claim 3, wherein the inverter comprises a plurality of switches, and braking the electric motor comprises closing at least one of the plurality of switches.

5. The method as claimed in any one of Claims 2 to 4, wherein braking the electric motor comprises freewheeling the inverter.

6. The method as claimed in any one of Claims 2 to 5, wherein braking the electric motor comprises controlling the inverter to provide a generating current path from the electric motor to a power supply supplying power to the electrical appliance.

7. The method as claimed in Claim 6, wherein braking the electric motor comprises sequentially controlling the inverter to provide the generating current path, and freewheeling the inverter.

8. The method as claimed in Claim 7, wherein the method comprises:receiving current data indicative of a phase current flowing through the electric motor; andtransitioning, based on the current data, from controlling the inverter to provide the generating current path to freewheeling the inverter.

9. The method as claimed in Claim 2 or Claim 3, wherein the inverter comprises a plurality of switches, and the braking the electric motor comprises opening each of the plurality of switches simultaneously.

10. The method as claimed in any one of the Claims 2 to 9, wherein the method is performed whilst electrical power is supplied to the inverter from a power source.

11. An electrical appliance comprising:an electric motor;a sensor configured to sense whether the electrical appliance is in free fall; anda controller configured to:receive fall data from the sensor; andbrake the electric motor, based on the fall data, in the event that the electrical appliance is in free fall.

12. The electrical appliance as claimed in Claim 11, wherein the electrical appliance comprises an inverter for controlling a voltage provided to the electric motor, and the controller is configured to control the inverter to brake the electric motor.

13. The electrical appliance as claimed in Claim 13, wherein the controller is configured to control the inverter to interrupt a voltage supply to the electric motor to brake the electric motor.

14. The electrical appliance as claimed in Claim 12 or Claim 13, wherein the inverter comprises a plurality of switches, and the controller is configured to close at least one of the plurality of switches to brake the electric motor.

15. The electrical appliance as claimed in any one of Claims 12 to 14, wherein the controller is configured to freewheel the inverter to brake the electric motor.

16. The electrical appliance as claimed in any one of Claims 12 to 15, wherein the controller is configured to control the inverter to provide a generating current path from the electric motor to a power supply of the electrical appliance to brake the electric motor.

17. The electrical appliance as claimed in any one of Claims 12 to 16, wherein the controller is configured to sequentially control the inverter to provide the generating current path, and to freewheel the inverter, to brake the electric motor.

18. The electrical appliance as claimed in Claim 17, wherein the electrical appliance comprises a current sensor configured to sense phase current flowing through the electric motor, and the controller is configured to:receive current data from the current sensor; andtransition, based on the current data, from controlling the inverter to provide the generating current path to freewheeling the inverter.

19. An electrical appliance as claimed in Claim 12 or Claim 13, wherein the inverter comprises a plurality of switches, and the controller is configured to open each of the plurality of switches simultaneously to brake the electric motor.

20. An electrical appliance as claimed in any one of Claims 11 to 19, wherein the electrical appliance comprises a power switch configured to switch the electrical appliance from a powered configuration in which electrical power is delivered from a power source to the electric motor, and an unpowered configuration in which electrical power is not delivered from the power source to the electric motor, and wherein the power switch is latched.

21. The electrical appliance as claimed in Claim 20, wherein the controller is configured to receive the fall data and to brake the electric motor when the electrical appliance is in the powered configuration.

22. The electrical appliance as claimed in any one of Claims 11 to 21, wherein the electric motor comprises a rotor assembly rotatable within a frame, and the rotor assembly comprises a bearing soft-mounted to the frame.5s

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