A domestic appliance

Abstract

A domestic appliance includes a resistive load and a power converter configured to convert supplied electrical power from a mains power supply to a delivered electrical power for delivery to the resistive load. The power converter is an unregulated power converter.

Description

1 P005340-W001A DOMESTIC APPLIANCEBACKGROUND

[0001] Haircare appliances are typically used to style and / or dry a user’ s hair. Some haircare appliances therefore comprise heaters for heating a user’s hair, whether through direct contact of the user’s hair with a surface heated by the heater, or through a heated airflow that is delivered to the user’s hair. Other domestic appliances may also utilise heaters, for example to heat an airflow for delivery to a user.SUMMARY

[0002] A first aspect provides a domestic appliance comprising: a resistive load; and a power converter configured to convert supplied electrical power from a mains power supply to a delivered electrical power for delivery to the resistive load; wherein the power converter is an unregulated power converter.

[0003] Some domestic appliances, such as haircare appliances, cooking appliances, or heating appliances, may require a high current, low voltage, power supply in order to operate. These appliances may also need to be safe for the user to touch. It may be desirable for such domestic appliances to operate with low losses, especially because of the increase in the electrical current necessary to comply with a low voltage regime. For input power levels above 75 watts, conventional power converters may utilise multi-stage power supply architectures that are actively controlled to regulate the output voltage of the converter to overcome the effect of varying line and loading conditions.

[0004] It has been found that, where the domestic appliance comprises a resistive load supplied with electrical power by a power converter, the power converter may be unregulated. This may improve the efficiency of the system, since the unregulated power converter can be further optimised for high energy efficiency and power factors. This may also reduce at least one of a cost of the domestic appliance, a size of at least part of the domestic appliance, and a weight of at least part of the domestic appliance. For example, as the energy storage requirements of the system decrease, the domestic appliance can be designed to be more compact and lightweight.

[0005] An unregulated power converter may be a converter that, for a predetermined set of operating conditions, does not adjust an output voltage or an output current to be at a fixed2 P005340-W001target value. The predetermined set of operating condition may comprise, for example, a range of input voltages of the power converter and a range of equivalent load impedances of the power converter.

[0006] The power converter may be configured to operate at a fixed switching frequency and at a fixed duty cycle.

[0007] The power converter may be configured to operate in a fixed mode of operation irrespective of at least one of: a variation of magnitude of power supply voltage; and a variation of the magnitude of the resistive load.

[0008] The domestic appliance may comprise a load controller and a switching arrangement for disconnecting the resistive load from the power converter. The load controller may be configured to control the switching arrangement to control the delivered electrical power to the resistive load.

[0009] The load controller may be configured to control the switching arrangement to control the delivered electrical power to the resistive load based on at least one of a variation of magnitude of a power supply voltage and a variation of a magnitude of the resistive load.

[0010] The load controller may be configured to control the switching arrangement based on at least one of: a load controller output value exceeding a load controller target value; a target time for the load controller to control the load controller output value to reach the load controller target value; an output voltage of the power converter; a temperature of the resistive load; and the delivered electrical power to the resistive load.

[0011] The load controller may be configured to measure and process electrical parameters of the domestic appliance at a load controller update rate. The load controller may be configured to control the load controller update rate based on a mode of operation of the domestic appliance.

[0012] The load controller may be configured to control the delivered electrical power to the resistive load based on a target delivered electrical power. The load controller may be configured to control the load controller update rate to reduce a difference between the target delivered electrical power to the resistive load and the delivered electrical power to the resistive load. For example, when the magnitude of the resistive load changes over a predetermined time window, the load controller update rate may be a first load controller update rate. When the magnitude of the resistive load does not change over the predetermined time window, the load controller update rate may be a second load controller3 P005340-W001update rate. The first load controller update rate may be different from the second load controller update rate.

[0013] The load controller may be configured to: determine a difference between the temperature of the resistive load and a target temperature value of the resistive load; determine a transition time for the temperature of the resistive load to reach the target temperature value; and control the load controller update rate based on the transition time.

[0014] The load controller may be configured to control the switching arrangement based on zero-crossing data indicative of a zero-crossing of the output voltage of the power converter.

[0015] The output voltage of the power converter and the zero-crossing data may be defined as feedforward signals of the power converter in the context described herein. A temperature value of the temperature of the resistive load, and a value of the delivered electrical power to the resistive load may be defined as a feedback signals in the context described herein.

[0016] The load controller may be configured to control the switching arrangement based on the feedforward signals of the power converter and the feedback signals of the resistive load.

[0017] The switching arrangement may comprise one or more metal oxide semiconductor field effect transistors (MOSFETs).

[0018] The load controller may control a transition between the first load controller update rate and the second load controller update rate based on a difference between the load controller output and the load controller target value. The load controller may control the transition between the first load controller update rate and the second load controller update rate using a hysteresis band.

[0019] The load controller may control the transition between the first load controller update rate and the second load controller update rate based on at least one of a difference between a maximum delivered electrical power to the resistive load and a minimum delivered electrical power to the resistive load.

[0020] The load controller may be configured to estimate a time for the load controller output to transition to the load controller target value, and control the transition between the first load controller update rate and the second load controller update rate based on this estimation.4 P005340-W001

[0021] The load controller may be configured to obtain zero-crossing data indicative of a zero-crossing of an output voltage of the power converter. The load controller may obtain zero-crossing data indicative of the zero-crossing of the output voltage of the power converter, for example, via a zero-crossing detection circuit.

[0022] The domestic appliance may comprise an output voltage sensor for sensing an output voltage of the power converter, and the voltage sensor may be configured to communicate the output voltage of the power converter to the load controller. The voltage sensor may comprise, for example, at least one of a sense coil, and a potential divider.

[0023] The domestic appliance may comprise a temperature sensor. The temperature sensor may be configured to generate a temperature sensor signal representative of a temperature of the resistive load, and the temperature sensor may be configured to communicate the temperature sensor signal to the load controller. The temperature sensor may comprise, for example, at least one of a thermistor, a thermomechanical sensor, and an infrared sensor.

[0024] The domestic appliance may comprise a power sensor for sensing the delivered electrical power to the resistive load, and the power sensor may be configured to communicate the delivered electrical power to the load controller. The power sensor may comprise, for example, at least one of a sense resistor, and a Hall sensor.

[0025] The load controller may be configured to control the switching arrangement to control the delivered electrical power to the resistive load using burst fire control. The burst fire control may be multicycle symmetric burst fire control.

[0026] The load controller may be configured to control the switching arrangement to control the delivered electrical power to the resistive load based on control parameters stored in a look-up table (LUT).

[0027] The resistive load may comprise a first resistive element and a second resistive element and the load controller may be configured to: monitor a resistive element power delivered to one of the first resistive element or the second resistive element; and control the resistive element power by controlling the switching arrangement to disconnect the other one of the first resistive element or the second resistive element from the power converter using one of phase angle control or high-frequency pulse width modulation. This may increase the resistive element peak power as opposed to not controlling the switching arrangement to disconnect the other one of the first resistive element or the second resistive element using phase angle control or high-frequency pulse width modulation. This may be5 P005340-W001used, for example, to increase a maximum deliverable resistive element power when an output voltage from the power supply is close to a maximum value. The maximum value may be a value associated with a high voltage region (176 volts to 264 volts RMS) or a low voltage region (85 volts to 140 volts RMS) respectively. The first resistive element may be, for example, a first heater, and the second resistive element may be, for example, a second heater.

[0028] The load controller may be configured to control the switching arrangement based on predetermined power maps and a predetermined control pattern such that a maximum variation of temperature of the resistive load is within a predetermined temperature variation range. The predetermined control pattern may be selected based on the predetermined power maps and a target reduction of temperature variation of the resistive load. Controlling the switching arrangement to maintain the temperature variation of the heaters within the predetermined temperature variation range may mitigate the effects of temperature ripple in heaters in general, and especially low thermal mass heaters.

[0029] The resistive load may be located in a first appliance housing and the power converter may be located in a second appliance housing different from the first appliance housing. The first appliance housing and the second appliance housing may be spaced from each other and may be connected via a cable. There may be no communication between the first appliance housing and the second appliance housing, for example, no communications cable extending between the first appliance housing and the second appliance housing, which may reduce the cost and size of the domestic appliance. The first appliance housing may be a housing of a main unit of the domestic appliance. The first appliance housing may define a handle of the domestic appliance.

[0030] The load controller may be configured to control the switching arrangement to control the delivered electrical power to the resistive load based on a set of electrical parameters that are measured within the first appliance housing. The set of electrical parameters may comprise a subset of electrical parameters indicative of electrical signals associated with the power converter.

[0031] The resistive load may be galvanically isolated from the mains power supply when the domestic appliance is connected to the mains power supply.

[0032] The domestic appliance may comprise at least one of an inductive load, and a capacitive load.6 P005340-W001

[0033] Where the domestic appliance comprises a resistive load, the resistive load may be a heater. The heater may be configured to operate at a power greater than 75 W.

[0034] The domestic appliance may comprise an electric motor, for example, an electric motor configured to cause rotation of an impeller to generate an airflow through the domestic appliance. The electric motor may be configured to operate at a power in the region of SOWSOW.

[0035] The power converter may be a resonant power converter.

[0036] The power converter may comprise a power converter controller configured to obtain mains voltage data indicative of at least one of a zero-crossing of a voltage of the mains power supply to which the domestic appliance is connected and a root mean square (RMS) voltage of the mains power supply to which the domestic appliance is connected, and to control the power converter based on the mains voltage data. In some examples, the power converter controller may control a peak output voltage of the power converter based on the RMS value of the voltage of the mains power supply to which the domestic appliance is connected.

[0037] The power converter and the load controller may be synchronised based on the zerocrossing of the voltage of the mains power supply to which the domestic appliance is connected. This may be used by the load controller to control the delivered electrical power to the resistive load based on one of symmetric multicycle burst fire control, phase angle control, or high-frequency pulse width modulation.

[0038] The load controller may be configured to control the switching arrangement to control the delivered electrical power to the resistive load using one of phase angle control or high-frequency pulse width modulation. For example, this may reduce peaks in the delivered electrical power to the resistive load when the voltage of the mains power supply to which the domestic appliance is connected exceeds an input voltage threshold. The load controller may be configured to use phase angle control or high-frequency pulse width modulation based on zero-crossing of a voltage of the mains power supply to which the domestic appliance is connected. For example, the load controller may be configured to use phase angle control or high-frequency pulse width modulation based on one of a first zerocrossing data time point, a second zero-crossing data time point, or a combination of the first and second zero-crossing data time points; the first and second zero crossing data time points different from each other.7 P005340-W001

[0039] The power converter may comprise a rectifier and the power converter controller may be configured to: obtain at least one of rectifier input voltage data and rectifier output current data; and control the power converter based on the at least one of rectifier input voltage data and rectifier output current data.

[0040] The power converter controller may be configured to: sense the peak output voltage of the power converter; determine that the peak output voltage of the power converter exceeds a threshold voltage; and control, based on the peak output voltage of the power converter exceeding the threshold voltage, the power converter such that the peak output voltage decreases to a level below the threshold voltage.

[0041] The threshold voltage may be a voltage between and including 35V and 42V.

[0042] The power converter may comprise a primary side, a secondary side, and an actively controlled power converter stage located on the primary side. The actively controlled power converter stage may be the only actively controlled power converter stage located on the primary side.

[0043] The power converter may comprise a galvanic isolator, and the primary side and the secondary side may be opposite sides of the galvanic isolator. The galvanic isolator may be a transformer. The transformer may be a high-frequency transformer.

[0044] “Actively controlled” means that the actively controlled power converter stage, and in particular one or more switches of the actively controlled power converter stage, is actively controlled by the power converter controller. This is in contrast to, for example, a passive stage of the power converter such as a diode bridge rectifier or the like.

[0045] There may be no boost converter on the primary side of the power converter.

[0046] The power converter controller may control one or more power converter switches such that the one or more power converter switches are configured in a closed position when a switch voltage associated with the one or more power converter switches is approximately zero. The power converter may, for example, control at least one of a switching frequency and a duty cycle of the power converter switches. This may reduce switching losses of the power converter.

[0047] The power converter may be a resonant LLC power converter. The LLC power converter may have different configurations of a rectifier arrangement in its secondary winding. The power converter may be a full bridge LLC resonant power converter. The8 P005340-W001power converter may be a split capacitor LLC resonant power converter. The power converter may be a single stage resonant LLC power converter.

[0048] The actively controlled power converter stage may be an LLC resonant power converter stage. This may reduce switching losses of the LLC resonant power converter stage for a predetermined variation in a magnitude of the resistive load and voltage of the mains power supply to which the domestic appliance is connected.

[0049] The LLC resonant power converter stage may be configured such that a voltage gain of the LLC resonant power converter stage is approximately one for at least one of: a predetermined load range of the LLC resonant power converter; and a predetermined input voltage range of the LLC resonant power converter. The LLC resonant power converter stage may be configured such that a ratio between a total primary inductance and a resonant inductance is above an inductance ratio threshold. The inductance ratio threshold may be, for example, between 3 and 12, or above 12. This may reduce power losses of the resonant power converter stage.

[0050] The power converter may be configured such that a peak output voltage of the power converter is no greater than 42V.

[0051] The power converter may comprise an energy storage capacity of less than lOOnF. This may characterise the power converter as a low energy storage (LES) power converter.

[0052] The power converter controller may be configured to obtain current data indicative of current flowing through the power converter, and to control the power converter to be in an off state based on the current data. This may reduce power losses of the power converter.

[0053] The power converter may be configured to provide a rectified output voltage, for example, a rectified output voltage having an approximately sin2form.

[0054] The power converter may be configured to operate with an output power of at least 75W. The power converter may be configured to operate with an output power of at least 100W, at least 200W, at least 300W, at least 400W, or at least 500W or at least 1000W or at least 1500W.

[0055] The domestic appliance may comprise a haircare appliance. The domestic appliance may comprise a cooking appliance or a heating appliance.BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure l is a schematic illustration of a domestic appliance;9 P005340-W001

[0057] Figure 2 is a schematic illustration of a power converter of the domestic appliance of Figure 1;

[0058] Figure 3 is a schematic illustration of an LLC converter stage of the power converter of Figure 2;

[0059] Figure 4 is a schematic illustration of heater and motor control circuitry of the domestic appliance of Figure 1;

[0060] Figure 5 is a schematic illustration of an output voltage waveform of the power converter of Figure 2; and

[0061] Figure 6 is a schematic example of a circuit configuration for controlling a heater of the domestic appliance of Figure 1.DETAILED DESCRIPTION

[0062] A domestic appliance 10 is illustrated schematically in Figure 1, and has a power supply unit 12 and a main unit 14. The domestic appliance 10 is a haircare appliance 10.

[0063] The power supply unit 12 has a first housing 16, which may also be referred to as an appliance housing in the context described herein, electrical contacts 18 for connecting to a mains power supply, and a power converter 20 located within the first housing 16.

[0064] The power converter 20 is shown in isolation in Figure 2. The power converter 20 is a resonant LLC converter.

[0065] The power converter 20 has a first potential divider 22, a second potential divider 23, an EMC filter 24, a third potential divider 26, a rectifier 28, a first inductor LI, a first capacitor Cl, a sense resistor Rl, an LLC converter stage 30, a first zero-cross detection circuit 32, a power converter controller 34, a gate drive circuit 36, an auxiliary power supply unit 38 and an analogue to digital converter 40.

[0066] The first potential divider 22 is formed by a pair of resistors R2 and R3, and the second potential divider 23 is formed by a pair of resistors R4 and R5. The first 22 and second 23 potential dividers are connected to opposite sides of the mains power supply, and between the mains power supply and the EMC filter 24. The first 22 and second 23 potential dividers provide a scaled down version of the voltage associated with the mains power supply to the first zero-cross detection circuit 32. The EMC filter 24 is connected between the mains power supply and the rectifier 28. The exact form of the EMC filter 24 may vary, and will not be described here for sake of brevity. The third potential divider 26 is formed10 P005340-W001by a pair of resistors R6 and R7, and is connected between the EMC filter 24 and the rectifier 28. The third potential divider 26 provides a VIN SENSE signal, indicative of a scaled down version of the rectifier input voltage, to the power converter controller 34. The rectifier 28 is a diode bridge rectifier. In other aspects, the rectifier 28 is implemented as a synchronous rectifier, or any other suitable rectifier topology for mains voltage rectification.

[0067] The first inductor LI is connected between the rectifier 28 and the LLC converter stage 30. The first capacitor Cl is connected between a high side input voltage terminal and a low side input voltage terminal of the LLC converter stage 30. The sense resistor R1 is connected between the low side input voltage terminal of the LLC converter stage 30, and the low side output voltage terminal of the rectifier 28. The analogue to digital converter 40 is configured to sense a sense resistor voltage across the sense resistor Rl, and transmit the sense resistor voltage to the power converter controller 34.

[0068] The auxiliary power supply unit 38 is connected between the output voltage terminals of the rectifier 28, and is configured to produce a supply voltage for the first zero-cross detection circuit 32, the power converter controller 34, and the gate drive circuit 36. The auxiliary power supply unit 38 can comprise a single output voltage rail, or multiple output voltage rails, and in some examples the output voltage rails associated with the gate drive circuit 36 comprise additional filtering to limit the effect of switching noise to the power converter controller 34 and the zero-cross detection circuit 32.

[0069] The first zero-cross detection circuit 32 is configured to process voltages from the first potential divider 22 and the second potential divider 23, and determine when the mains power supply voltage has a value that is close to zero volts.

[0070] The LLC converter stage 30 is shown in Figure 3. The LLC converter stage 30 has a first switch SW1, a second switch SW2, a second capacitor C2, a second inductor L2, a third inductor L3, a transformer 42, a first synchronous rectification switch SRI, a second synchronous rectification switch SR2, a fourth inductor L4, a third capacitor C3, a peak detection circuit 41, a tank current sense circuit 43, an auxiliary inductor L aux and an auxiliary peak detection circuit 45.

[0071] Each of the first switch SW1 and the second switch SW2 is a metal oxide semiconductor field effect transistor (MOSFET) that is controlled by the gate drive circuit 36 in response to signals from the power converter controller 34. In other examples, the first switch SW1 and the second switch SW2 may each be a bi-directional Gallium Nitride11 P005340-W001(BiGaN switch). Where BiGaN switches are used the diode bridge rectifier 28 is omitted. The first SW 1 and second SW2 switches are arranged in a half-bridge configuration. The second capacitor C2, the second inductor L2, and the third inductor L3 define a resonant tank. Collectively, the first switch SW1, the second switch SW2, the second capacitor C2, the second inductor L2, and the third inductor L3, define an actively controlled power converter stage 44.

[0072] The transformer 42 has a primary winding 46 and a secondary winding 48. Thus, the power converter 20 can generally be considered to have a primary side 50 and a secondary side 52. The actively controlled power converter stage 44 is located on the primary side 50 of the power converter 20, and as will be appreciated from Figures 2 and 3, the actively controlled power converter stage 44 is the only actively controlled power converter stage located on the primary side 50 of the power converter 20. The transformer 42 acts to galvanically isolate and provide user safety to the main unit 14 from the mains power supply. The transformer 42 is a high-frequency transformer.

[0073] The first synchronous rectification switch SRI, the second synchronous rectification switch SR2, the inductor L4 and the third capacitor C3 are located on the secondary side 52 of the power converter 20. The first synchronous rectification switch SRI is connected between a high side terminal of the secondary winding 48, and the fourth inductor L4. The fourth inductor L4 is connected between the first synchronous rectification switch SRI and a high side output voltage terminal VOUT LLC+ of the LLC converter stage 30. The third capacitor C3 is connected between the high side output voltage terminal VOUT LLC+ and a low side output voltage terminal VOUT LLC- of the LLC converter stage 30. The second synchronous rectification switch SR2 is connected between a low side terminal of the secondary winding 48 and the fourth inductor L4. The first and second synchronous rectification switches SRI and SR2 are actively controlled metal oxide semiconductor field effect transistors (MOSFETs). In other examples GaN devices may be utilised. Controllers of the first synchronous rectification switch SRI and the second synchronous rectification switch SR2 are not shown here for the sake of clarity. The secondary winding 48 is a centretapped winding, and the centre-tapped terminal of the secondary winding 48 is connected to the low side output voltage terminal VOUT LLC-.

[0074] The peak detection circuit 41 is connected between the first and second switches SW1 and SW1 and is configured to sense a peak voltage of the resonant tank, and transmit12 P005340-W001a signal Vpeak_p indicative of the peak voltage of the resonant tank to the power converter controller 34.

[0075] The tank current sense circuit 43 is connected on a return path of the resonant tank, and is configured to sense a current flowing through the resonant tank, and transmit a signal Isense indicative of the current flowing through the resonant tank to the power converter controller 34. In some examples, the tank current sense circuit 43 comprises a capacitive divider to obtain a scaled down version of an AC component of the current flowing through the resonant tank.

[0076] The auxiliary inductor L aux is coupled to the primary winding 46 and is connected to the auxiliary peak detection circuit 45. The auxiliary peak detection circuit 45 is configured to measure a voltage induced on the auxiliary inductor L aux by the primary winding 46, and transmit a signal Vsec, indicative of a scaled down version of a peak voltage across the secondary winding 48, to the power converter controller 34.

[0077] The power converter controller 34 is configured to generate instructions for the gate drive circuit 36, such that the gate drive circuit 36 generates a switching signal for the first and second switches SW 1 and SW2. The power converter controller 34 receives a zero-cross detection signal from the first zero-cross detection circuit 32, the VIN SENSE signal from the third potential divider 26, and the sense resistor voltage, indicative of a return current from the LLC converter stage 30. The power converter controller 34 processes this data and transmits instructions to the gate drive circuit 36.

[0078] The main unit 14 has a second housing 56, which may also be referred to as an appliance housing in the context described herein, a heater 58, an electric motor 60, and heater and motor control circuitry 62. Although not illustrated in Figure 1 due to the schematic nature of Figure 1, it will be appreciated that the second housing 56 may have an air inlet and an air outlet to enable an airflow to be generated by the electric motor 60 in use.

[0079] The heater 58 has first 64 and second 66 heating elements, and presents a resistive load to the power converter 20, as will be discussed in further detail hereinafter. The heater 58 is configured to operate at a power of several kW. The electric motor 60 is any electric motor suitable for generating an airflow. An example electric motor is the Dyson V9 Motor produced by Dyson Technology Limited. The motor is configured to operate at a power of around 30W to 50W.13 P005340-W001

[0080] The heater and motor control circuitry 62 is shown schematically in Figure 4, with the first 64 and second 66 heating elements and the electric motor 60 in place. The heater and motor control circuitry 62 has a fourth potential divider 68, third SW3 and fourth SW4 switches, an inverter 70, and a load controller 74. The load controller comprises a second zero-cross detection circuit 72. The fourth potential divider 68 is formed of a pair of resistors R8, R9. The fourth potential divider 68 is located on a high side of the heater and motor control circuitry 62, and provides a scaled down version of the output voltage of the LLC converter stage 30 to the load controller 74. The scaled down version of the output voltage of the LLC converter stage 30 is indicative of zero-cross detection points and proportional to the rms value of the output voltage of the LLC converter stage 30. A Schottky diode DI is used for the isolation of the heater output voltage to the electric input of the inverter 70.

[0081] A capacitor may be connected across the inverter input to store the energy and to supply electrical power input to the inverter 70 for driving the electric motor 60. The size of the capacitor may be rated depending on the acceptable ripple output voltage. The inverter 70 is connected in parallel with a capacitor C4 and the first 64 and second 66 heating elements. The inverter 70 is an appropriate inverter for use with the electric motor 60, and may be a single phase or three phase inverter, as appropriate.

[0082] The first heating element 64 is connected in series with the third switch SW3, to form a first controllable heating element branch 71, and the first controllable heating element branch 71 is connected between the low side output voltage terminal VOUT LLC- of the LLC converter stage 30 and the high side output voltage terminal VOUT LLC+ of the LLC converter stage 30. The second heating element 66 is connected in series with the fourth switch SW4, to form a second controllable heating element branch 73, and the second controllable heating element branch 73 is connected between the low side output voltage terminal VOUT LLC- of the LLC converter stage 30 and the high side output voltage terminal VOUT LLC+ of the LLC converter stage 30. The first 71 and second 73 controllable heating element branch are connected in parallel with each other.

[0083] First 65 and second 67 temperature feedbacks are connected to temperature sensors of the first 64 and second 66 heating elements respectively, and they provide temperature signals associated with the first 64 and second 66 heating elements to the load controller 74. The temperature sensors of the first 64 and second 66 heating elements can be implemented as any form of temperature sensor that is suitable for monitoring the temperature of a heating14 P005340-W001element. For example, thermistors, thermomechanical sensors, and infrared sensors are envisioned for this application. In some examples the temperature sensors of the first 64 and second 66 heating elements are supplemented with or replaced by power sensors. In some examples the power sensors are implemented as current sense resistors. In some other examples the power sensors are Hall sensors.

[0084] The second zero-cross detection circuit 72 is configured to receive a voltage from the fourth potential divider 68 and determine when the output voltage of the LLC converter stage 30 has a value that is close to zero volts.

[0085] The load controller 74 is configured to receive signals from the first 65 and second 67 temperature feedbacks, and the fourth potential divider 68. The load controller 74 is configured to, based on the received signals, control switching of SW3 and SW4, and operation of the inverter 70, to obtain a target power or target temperature for the first 64 and second 66 heating elements, and a motor target power for the electric motor 60.

[0086] In use, the domestic appliance 10 draws power from the mains power supply. The first 22 and second 23 potential dividers provide scaled down versions of the mains power supply voltage to the first zero-cross detection circuit 32. The first zero-cross detection circuit 32 determines when the voltage of the mains power supply has a value that is close to zero volts, and transmits this information to the power converter controller 34. The third potential divider 26 provides a scaled down version of the input voltage of the rectifier 28, VIN SENSE, to the power converter controller 34. The data from the first zero-cross detection circuit 32 and the third potential divider 26 is used by the power converter controller 34 to send instructions to the gate drive circuit 36, so that the gate drive circuit 36 can generate the switching signals for SW1 and SW2. VIN_SENSE and the first zero-cross detection circuit signal may be referred to as feed-forward signals. VIN_SENSE is processed by the power converter controller 34 to produce a signal that is indicative of the root mean square (RMS) voltage of the mains power supply to which the domestic appliance 10 is connected.

[0087] The LLC converter stage 30 has a voltage gain of approximately one for some predetermined operating conditions of the LLC converter stage 30. The operating conditions for which the voltage gain is one comprise, for example, a predetermined range of LLC converter load impedance magnitudes and load impedance angles, and a predetermined input voltage range of the LLC converter stage 30.15 P005340-W001

[0088] The power converter 20 is an unregulated power converter, and the power converter controller 34 does not adjust the instructions sent to the gate drive circuit 36 according to the output voltage or output current of the LLC converter stage 30 such that the value of the output voltage is controlled to be a target output voltage value. The power converter 20 also generates an output voltage that is below the safety extra low voltage (SELV) limit of 42 volts for the domestic appliance 10.

[0089] The switching frequency of the signals generated by the power converter controller 34 to drive SW1 and SW2 is the same as the resonant frequency of the resonant tank. The switches SW1 and SW2 are driven with a signal that is fixed in switching frequency and duty cycle.

[0090] For a predetermined range of LLC converter load impedance magnitudes and load impedance angles, the output voltage of the LLC converter stage 30 remains within the SELV limit. This is achieved by selecting a combination of passive components (turns ratio of the transformer 42, EMC filer 24, L2, L3, Cl and C2) and switching frequency and duty cycle of SW 1 and SW2, such that for a predetermined variation in input voltage to the LLC converter stage 30, and for a predetermined variation of load impedance of the LLC converter stage 30, the output voltage of the LLC converter stage 30 does not exceed a predetermined output voltage threshold of 35 volts to 42 volts. It will be appreciated that it is possible to utilize different values for the predetermined output voltage threshold.

[0091] The LLC converter stage 30 generates a flow of alternating current through the primary winding 46, which in turn generates an induced voltage across the secondary winding 48. The first SRI and second SR2 synchronous rectification switches rectify the voltage across the secondary winding 48. The fourth inductor L4 along with the third capacitor C3 forms a low pass filter and acts to minimise the high-frequency ripple from the output voltage, and an example output voltage waveform of the power converter 20 is shown in Figure 5. As can be seen, the output voltage has a rectified, generally sin2, form.

[0092] In the context described herein, ‘Q’ is the quality factor of the circuit and ‘m’ is the ratio of the total primary inductance to the resonant inductance.

[0093] Since the power converter 20 is an unregulated power converter, ‘m’ is selected to be a large value to reduce power losses of the power converter 20 compared to a power converter with a small ‘m’. The LLC converter stage 30 has a value of ‘m’ between 3 and16 P005340-W00112. In other examples ‘m’ is a value above 12. High values of ‘m’ and operation of the LLC converter stage 30 at resonance may reduce switching losses of the LLC converter stage 30.

[0094] The output of the power converter 20 is passed to the heater and motor control circuitry 62 via an electrical cable 54. The fourth potential divider 68 provides a voltage signal to the second zero-cross detection circuit 72, and the second zero-cross detection circuit 72 determines zero-crossing points in the rectified output voltage of the power converter 20. The second zero-cross detection circuit 72 provides a signal indicative of the zero-crossing points to the load controller 74. Using the signal indicative of the zerocrossing points, the load controller 74 controls the third SW3 and fourth SW4 switches to control the supply of electrical power to the first 64 and second 66 heating elements. The power converter 20 and the load controller 74 are synchronised based on the zero-crossing of the voltage of the mains power supply to which the domestic appliance 10 is connected. This may reduce the need of providing additional cables associated with a communication protocol between the power supply unit 12 and the main unit 14.

[0095] The fourth potential divider 68 also provides the voltage signal to the load controller 74. The load controller 74 processes the voltage signal from the fourth potential divider 68 to obtain information regarding the RMS value of the output voltage of the LLC converter stage 30.

[0096] The load controller 74 controls the third SW3 and fourth SW4 switches (or a switching arrangement) to control the delivered electrical power to each of the first 64 and the second 66 heating elements (or resistive load) based on a set of electrical parameters that are measured within the main unit 14. As explained above, the set of electrical parameters comprises a subset of electrical parameters indicative of electrical signals associated with the power converter 20, such as, for example, zero-crossing data.

[0097] The load controller 74 controls the third SW3 and fourth SW4 switches using multicycle burst fire control of the rectified mains. In some examples the load controller 74 controls the third SW3 and fourth SW4 switches using one of symmetric multicycle burst fire control, phase angle control, or high-frequency pulse width modulation. In some examples, the load controller 74 uses symmetric multicycle burst fire control, phase angle control, or pulse width modulation based on a first zero-crossing data time point, a second zero-crossing data time point, or a combination of the first and second zero-crossing data time points. For example, the phase angle control or high-frequency pulse width modulation17 P005340-W001can be done on the leading edge or a combination of the leading edge and trailing edge of the zero-crossing data.

[0098] The temperature signals from the first 65 and second 67 temperature feedbacks are also used by the load controller 74 to control the third SW3 and fourth SW4 switches. The load controller 74 measures and processes electrical parameters of the domestic appliance 10 at a load controller update rate.

[0099] In some examples, the load controller 74 uses multicycle burst fire control of the rectified mains based on parameters stored in a first look-up table (LUT).

[0100] The load controller 74 controls the operation of the third SW3 and fourth SW4 switches such that the temperature of one of the first 64 or the second 66 heating elements, or the delivered electrical power to one of the first 64 or the second 66 heating elements reach a target value within a target time. The load controller 74 also controls the load controller update rate such that the target value is reached within the target time.

[0101] The load controller 74 also controls the load controller update rate to reduce a difference between the target delivered electrical power to the resistive load and the delivered electrical power to the first 64 or the second 66 heating elements. This may occur, for example, when the response of the load controller 74 presents an overshoot, an undershoot or steady-state error. The load controller 74 may, for example, select a slower update rate to reduce an overshoot.

[0102] The load controller 74 also controls the load controller update rate based on a mode of operation of the domestic appliance 10. This may be desirable when the domestic appliance 10 comprises operating modes that require different heating profiles for the first 64 and second 66 heating elements: a small target time may be required when the first 64 or second 66 heating elements need to achieve a large temperature variation in a short amount of time.

[0103] For example, the load controller 74 operates using a first load controller update rate suitable for when the magnitude of the resistive load changes over a predetermined time window. The load controller 74 switches to a second load controller update rate when the magnitude of the resistive load does not change over the predetermined time window. The first load controller update rate is different from the second load controller update rate. In some examples, the first load controller update rate and the second load controller update rate are obtained by the load controller 74 using a second LUT. In some other examples, the18 P005340-W001load controller 74 performs a mathematical operation to map the combination of an operating condition of the domestic appliance 10, and a plurality of parameters monitored by the load controller 74 (temperature for the first 64 and second 66 heating elements, power for the first 64 and second 66 heating elements, output voltage of the LLC converter stage 30, zerocrossing data) to a required update rate.

[0104] The load controller 74 controls a transition between the first load controller update rate and the second load controller update rate based on a difference between the load controller output and the load controller target value. In some examples, the load controller 74 performs this update based on a hysteresis band. In some examples, the load controller 74 controls the transition between the first load controller update rate and the second load controller update rate based on a difference between a maximum delivered electrical power to the resistive load and a minimum delivered electrical power to the resistive load. It is typically advantageous to mitigate this phenomenon, usually defined as ‘flicker’, in order to obtain a stable and consistent temperature of the first 64 or the second 66 heating elements. In some examples, the load controller 74 controls the load controller update rate based on an estimated time to reach the load controller target value. The load controller target value may be associated with minimum delivered electrical power to the heater 58 or the temperature of the heater 58.

[0105] A control circuit configuration 80 suitable to be implemented as part of the load controller 74 is illustrated schematically in Figure 6. For the sake of simplicity, the control circuit configuration 80 illustrated in Figure 6 only controls the first controllable heating element branch 71. It will be appreciated that the same circuit configuration is also suitable for controlling the second controllable heating element branch 73. The control circuit configuration 80 comprises a feedforward controller 82, a proportional integral (PI) controller 84, a table index controller 86, and a lookup table (LUT) 88.

[0106] The control circuit configuration 80 receives the temperature signal associated with the first controllable heating element branch 71 via the first temperature feedback 65, and the output of the fourth potential divider 68, indicative of the output voltage of the LLC converter stage 30.

[0107] The PI controller 84 determines and processes a difference between the temperature signal from the first temperature feedback 65 and a target temperature of the first heating element 64 to produce a PI controller output signal.19 P005340-W001

[0108] The feedforward controller 82 obtains and processes the output of the fourth potential divider 68 together with the target temperature of the first heating element 64 to produce a feedforward control signal. In some examples the feedforward controller 82 comprises the second zero-cross detection circuit 72.

[0109] The table index controller 86 receives the PI controller output signal and the feedforward control signal to generate a table index. The table index controller 86 sends the table index to the LUT 88. Based on the table index, the LUT 88 generates a control pattern to be used for selectively switching the first 71 controllable heating element branch.

[0110] The load controller 74 selects the control pattern based on a predetermined relationship between power maps and the control pattern to reduce a variation in the temperature of the heater 58 during steady state operation (e.g., the load and input voltage have been maintained approximately constant for an extended period of time). In some examples, the load controller 74 selects a control pattern that reduces ‘flicker points’ (e.g., a maximum variation of the delivered electrical power to the heater 58 during a predetermined time window), and maintains the temperature variation of the heater 58 below a temperature variation threshold.[OHl] The output of the LLC converter stage 30 is also passed to the inverter 70, with the load controller 74 controlling operation of the inverter 70 to control operation of the electric motor 60 to generate an airflow through the main unit 14 of the domestic appliance 10.

[0112] In use of the domestic appliance 10, there may be periods of time in which the power required to be delivered to the first 64 and second 66 heating elements varies. For example, there may be periods of time in which the third SW3 and fourth SW4 switches are turned off such that the first 64 and second 66 heating elements are disconnected from the power converter 20. In such scenarios, the power converter 20 sees no load, and there is a risk of gain distortion occurring for the power converter 20. Such gain distortion may be caused by parasitic components such as resonant inductances and stray capacitances distributed to the high-frequency transformer and synchronous rectifier. The gain distortion can lead to an increase in gain, which may in turn lead to an increase in peak voltage and a decrease in energy efficiency of the power converter 20. If the power converter 20 continues to be operated as normal, then there is a risk that the peak output voltage of the LLC converter stage 30 may exceed the SELV limit for the domestic appliance 10.20 P005340-W001

[0113] To mitigate for this risk, the power converter controller 34 receives a current measurement from the shunt resistor R1 via the analogue to digital converter 40, and calculates a mean current for a given time period in the mains cycle. In some examples the given time period is 100ps-500ps. When the mean current is less than or equal to a threshold value based on the output power of the power converter 20 and the above-mentioned time period, the power converter controller 34 determines that the third SW3 and fourth SW4 switches are turned off, and hence that there is no load connected to the power converter 20. In such circumstances, the power converter controller 34 controls the first SW1 and second SW2 switches of the LLC converter stage 30 to be open, such that the power converter 20 is turned off. This inhibits the peak output voltage of the LLC converter stage 30 from exceeding the SELV limit and improves the energy efficiency of the LLC converter stage 30. In some variations, the power converter controller 34 receives a current measurement from the tank current sense circuit 43, determines that the third SW3 and fourth SW4 switches are turned off, and controls the first SW1 and second SW2 switches of the LLC converter stage 30 to be open, such that the power converter 20 is turned off.

[0114] As the power converter controller 34 controls the power converter 20 to be in an off state when the first 64 and second 66 heating elements are disconnected from the power converter 20, the above-mentioned increase in peak voltage and decrease in energy efficiency may be mitigated for and / or avoided. As the determination made by the power converter controller 34 is based on the current value measured by the shunt resistor Rl, there is no need for a communications cable to be present between the power supply unit 12 and the main unit 14, which may reduce cost and / or complexity compared to a similar arrangement where a communications cable is present.

[0115] When the mean current is greater than the threshold value the power converter controller 34 controls the first SW 1 and second SW2 switches in the manner described above to deliver the regulated output voltage to the main unit 14.

[0116] In the examples described above, the power converter 20 has a single actively controlled power converter stage on the primary side 50 of the power converter 20, in the form of the LLC converter stage 30, and the power converter controller 34 is able to determine, without active communication from the main unit 14, when the power converter 20 sees no load, and to subsequently turn the power converter 20 off. It will be appreciated that examples in which only one of those features is present are also envisaged. For example,21 P005340-W001examples with a single actively controlled power converter stage on the primary side 50 of the power converter 20, but without the power converter turn off capability discussed above, are envisaged. Similarly, examples with the power converter turn off capability discussed above and more than one actively controlled power converter stage on the primary side 50 of the power converter 20 are also envisaged.

[0117] Other variations to the domestic appliance 10 described above are also envisaged. For example, the LLC converter stage 30 is illustrated as a half bridge resonant LLC converter stage, it will be appreciated that full bridge resonant LLC converter stages and split capacitor resonant LLC converter stages are also envisaged.

[0118] In some variations the power converter controller 34 adjusts the switching signals provided to switches SW1 and SW2 to reduce power losses of the LLC converter stage 30. In some examples this is achieved by sensing a switching waveform of the LLC converter stage 30, determining a voltage of the switching waveforms during the switching events of either SW1 or SW2, and controlling the gate drive circuit 36 such that the voltage of the switching waveform during the switching event reduces. In some examples this is implemented by changing at least one of the switching frequency and duty cycle of the switching signals for switches SW1 and SW2.

[0119] In some variations the power converter controller 34 controls the gate drive circuit 36, such that the LLC converter stage 30 adjusts its output voltage, an intermediate voltage (such as, for example, Vpeak_p and / or Vsec) and / or an output current (such as, for example, Isense) such that they decrease below a predetermined threshold. This may be advantageous when at least one of the output voltage of the power converter 20, the output current of the power converter 20, and an intermediate voltage of the power converter 20, exceed predetermined thresholds, indicative that the domestic appliance may be operating outside of a SELV regime. The predetermined thresholds may be different for the output voltage of the power converter 20, the output current of the power converter 20, and the intermediate voltage of the power converter 20. In some examples this is implemented by changing at least one of the switching frequency and duty cycle of the switching signals for switches SW1 and SW2. In some other examples this is implemented by powering off at least part of the power converter 20. It will be appreciated that the power converter 20 qualifies as an unregulated power converter even during these operating conditions, since the power22 P005340-W001converter controller 34 does not switch SW1 and SW2 such that the value of the output voltage is controlled to be a target output voltage value.

[0120] In some variations, the output of at least one of the peak detection circuit 41, the tank current sense circuit 43, and the auxiliary peak detection circuit 45 is used by the power converter controller 34 to control the switches SW1 and SW2 such that at least one of Vpeak_p, Vsec and Isense decrease.

[0121] In some variations the load controller 74 uses a combination of burst fire control and one of phase angle control and high-frequency pulse width modulation to increase the maximum deliverable power to one of the first 64 and the second 66 heating elements. For example, if it is necessary to increase the delivered power to the first heating element 64, the load controller 74 controls SW3 using burst fire control, and to control SW4 such that the second resistive element 66 draws intermittent spikes of current such that the overall power delivered to the first heating element 64 also increases. This may be useful when it is difficult for the load controller 74 to achieve a target temperature or target power of the first 64 and the second 66 heating elements by using burst fire control alone. This may be, for example, because the domestic appliance 10 is operated in a high voltage region, where the input voltage supplied by the mains power supply is between 176 volts and 264 volts RMS, or in a low voltage region, where the input voltage supplied by the mains power supply is between 85 volts and 140 volts RMS.

[0122] In some variations the electric motor 60 is omitted. In some variations the first 64 and second 66 resistive elements are a single resistive load.

[0123] In some variations there are further resistive elements, which are controlled similarly to the first 64 and second 66 resistive elements described above by the load controller 74.

[0124] In other variations, the transformer 42 is replaced by an air-core inductive link.

[0125] In some variations, the switching frequency of the signals generated by the power converter controller 34 to drive SW1 and SW2 is different from the resonant frequency of the resonant tank.

[0126] The examples described above are illustrative of the present disclosure, and further examples are envisaged. It is to be understood that any feature described in relation to any one example may be used alone or in combination with other features of the example, and may also be used in combination with one or more features of any other of the examples, or any combination of any other of the examples. Furthermore, equivalents and modifications23 P005340-W001not described above may also be employed without departing from the scope of the disclosure, which is defined in the accompanying claims.

Claims

24 P005340-W001CLAIMS1. A domestic appliance comprising:a resistive load; anda power converter configured to convert supplied electrical power from a mains power supply to a delivered electrical power for delivery to the resistive load, wherein the power converter is an unregulated power converter.

2. The domestic appliance of claim 1, comprising:a switching arrangement for disconnecting the resistive load from the power converter; anda load controller configured to control the switching arrangement to control the delivered electrical power to the resistive load.

3. The domestic appliance of claim 2, wherein the load controller is configured to control the switching arrangement based on at least one of:a load controller output value exceeding a load controller target value; a target time for the load controller to control the load controller output value to reach the load controller target value;an output voltage of the power converter;a temperature of the resistive load; andthe delivered electrical power to the resistive load.

4. The domestic appliance of claim 3, wherein the load controller is configured to measure and process electrical parameters of the domestic appliance at a load controller update rate; and wherein the load controller is configured to control the load controller update rate based on a mode of operation of the domestic appliance.

5. The domestic appliance of claim 4, wherein the load controller is configured to:determine a difference between the temperature of the resistive load and a target temperature value of the resistive load;25 P005340-W001determine a transition time for the temperature of the resistive load to reach the target temperature value; andcontrol the load controller update rate based on the transition time.

6. The domestic appliance of any one of claims 3 to 5, wherein the load controller is configured to control the switching arrangement based on zero-crossing data indicative of a zero-crossing of the output voltage of the power converter.

7. The domestic appliance of any one of claims 2 to 6, wherein the switching arrangement comprises one or more metal oxide semiconductor field effect transistors (MOSFETs).

8. The domestic appliance of any one of claims 2 to 7, wherein the load controller is configured to control the switching arrangement to control the delivered electrical power to the resistive load using burst fire control.

9. The domestic appliance of any one of claims 2 to 8, wherein the load controller is configured to control the switching arrangement to control the delivered electrical power to the resistive load based on control parameters stored in a look-up table (LUT).

10. The domestic appliance of any one of claims 2 to 9, wherein the resistive load comprises a first resistive element and a second resistive element, and wherein the load controller is configured to:monitor a resistive element power delivered to one of the first resistive element or the second resistive element; andcontrol the resistive element power by controlling the switching arrangement to disconnect the other one of the first resistive element or the second resistive element from the power converter using one of phase angle control or high-frequency pulse width modulation.

11. The domestic appliance of any one of claims 2 to 10, wherein the load controller is configured to control the switching arrangement based on predetermined power maps and a26 P005340-W001predetermined control pattern such that a maximum variation of temperature of the resistive load is within a predetermined temperature variation range.

12. The domestic appliance of any one of the preceding claims, wherein the resistive load is located in a first appliance housing, and the power converter is located in a second appliance housing different from the first appliance housing.

13. The domestic appliance of any one of the preceding claims, wherein the domestic appliance is configured such that the resistive load is galvanically isolated from the mains power supply when the domestic appliance is connected to the mains power supply.

14. The domestic appliance of any one of the preceding claims, comprising at least one of an inductive load and a capacitive load.

15. The domestic appliance of any one of the preceding claims, wherein the power converter is a resonant power converter.

16. The domestic appliance of any one of the preceding claims, wherein the power converter comprises a power converter controller configured to obtain mains voltage data indicative of at least one of a zero-crossing of a voltage of the mains power supply to which the domestic appliance is connected and a root mean square (RMS) voltage of the mains power supply to which the domestic appliance is connected, and to control the power converter based on the mains voltage data.

17. The domestic appliance of claim 16, wherein the power converter comprises a rectifier and the power converter controller is configured to:obtain at least one of rectifier input voltage data and rectifier output current data; and control the power converter based on the at least one of rectifier input voltage data and rectifier output current data.

18. The domestic appliance of claim 16 or claim 17 wherein the power converter controller is configured to:27 P005340-W001sense a peak output voltage of the power converter;determine that the peak output voltage of the power converter exceeds a threshold voltage; andcontrol, based on the peak output voltage of the power converter exceeding the threshold voltage, the power converter such that the peak output voltage decreases to a level below the threshold voltage.

19. The domestic appliance of claim 18, wherein the threshold voltage is a voltage between and including 35 volts and 42 volts.

20. The domestic appliance of any one of the preceding claims, wherein the power converter comprises a primary side, a secondary side, and an actively controlled power converter stage located on the primary side, and the actively controlled power converter stage is the only actively controlled power converter stage located on the primary side.

21. The domestic appliance of claim 20, wherein the actively controlled power converter stage is an LLC resonant power converter stage.

22. The domestic appliance of any one of the preceding claims, wherein the power converter is configured such that a peak output voltage of the power converter is no greater than 42 volts.

23. The domestic appliance of any one of the preceding claims, wherein the power converter comprises an energy storage capacity of less than lOOnF.

24. The domestic appliance of any one of the preceding claims, wherein the power converter controller is configured to obtain current data indicative of current flowing through the power converter, and to control the power converter to be in an off state based on the current data.

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