WO2024194785A1

WO2024194785A1 - Control of a functional component of a haircare appliance

Info

Publication number: WO2024194785A1
Application number: PCT/IB2024/052606
Authority: WO
Inventors: Li NIU; Kaijie LIN; Xinyi Li
Original assignee: Dyson Operations PTE. LTD.
Priority date: 2023-03-23
Filing date: 2024-03-18
Publication date: 2024-09-26
Also published as: GB2628400A; GB202304234D0

Abstract

Controlling a functional component (102) of a haircare appliance (100) is described. A haircare appliance (100) comprises a functional component (102), and a controller (106) adapted to control power from an AC power source to the functional component (102) according to a switching pattern. The switching pattern is indicative of the switching on of power supplied from the power source to the functional component. The switching pattern has a pattern index length determined by the following expression: if a selected total number of half cycles is divisible by k: pattern index length = i_X (selected total number of half cycles), and if the selected total number of half cycles is indivisible by k: pattern index length = i_X (k half cycles_X n), where n is selected such that (k half cycles_X n) is closest to selected total number of half cycles and i and k are positive natural numbers. A method for controlling of a haircare appliance, use of the control method to control a haircare appliance, computer program product and a computer-readable storage medium are also described.

Description

CONTROL OF A FUNCTIONAL COMPONENT OF A HAIRCARE APPLIANCE

BACKGROUND

Modern household appliances, e.g., haircare appliances like hairdryers or hair straighteners, regularly use a high-powered functional component, like e.g., one or more heating elements, for the operation. Operating such a functional component may thus be seen as significant energy consumers that impact the power circuit a household appliance are connected to by consuming available power. When power is drawn from the power circuit, such regularly results in a small but measurable voltage drop of the line voltage. Other consumers that are connected to the same power circuit thus experience said voltage drop themselves. In other words, the actual voltage of a power circuit is impacted, i.e. , reduced, when a power consuming appliance is drawing power from the power circuit. Depending on the power consuming appliance, and in particular the manner in which power is drawn from the power circuit and fed to the functional component, other power consuming appliances on the same circuit experience a fluctuating instantaneous voltage. Put another way, depending on the grid impedance, drawing power from the power circuit results in a voltage drop that other devices on the same power grid experience. Such a fluctuating instantaneous voltage may cause a variety of different reactions and effects on these further power consuming devices.

SUMMARY

While a slow, low-frequency change in the instantaneous voltage of a power circuit normally has minimal effect like reducing the total available power, a fast, high-frequency change may result in a variety of adverse effects on power consuming devices. One such adverse effect related to a high-frequency change may be the generation of flicker in other power consuming devices. Flicker is the term used to describe electrical voltage fluctuations in power systems that result in a visually perceptible variation in the luminance of unregulated electrical light sources such as fluorescent and incandescent lamps. Flicker is one of several criteria used to assess the quality of voltage in power systems and to evaluate system feedback from loads on such systems. The occurrence of flicker is related to the frequency and magnitude of voltage fluctuations in a power circuit. Modern household appliances are often powered not by regulating the input voltage to a defined voltage and feeding said reduced voltage to the functional component but rather using pulse width modulation (PWM), where a constant voltage, i.e., the power circuit voltage, is applied to the functional component only for the fraction of a PWM cycle. Using PWM, the average value of a voltage can be reduced continuously proportional to the duty cycle of the PWM. For pulse width modulation control, switching elements or power switches are used that are able to connect and disconnect the input voltage to the functional component with high frequency. The setting of the reduced voltage is possible with relatively low power losses, since the power switches are only operated in two states, fully on or fully off, or in other words being either in a conductive state or a non-conductive state. In the fully on state, supplied power is substantially consumed by the functional component to provide its function, e.g., heating in the case of a heating element, whereas in the fully off state, no voltage is applied to the functional component and thus no power is used.

Said high frequency switching of the supply power to the functional component however impacts the power circuit resulting in a slight reduction of the voltage level when the power switches are in the fully on state. Depending on the frequency of the switching, such high frequency switching may impart a modulation on the voltage level of the power circuit, and any other electric devices connected to the same power circuit in turn are exposed to the same voltage modulation. Depending on the type of electric device, such a modulation of the line voltage may have a more or less recognizable effect For example, in the case of unregulated electrical light sources such as fluorescent and incandescent lamps, such a modulation may result in a visually recognizable change in luminance, which may be more or less perceptible depending on the modulation.

Two different types of control schemes are regularly used, namely phase angle control, and burst control or zero crossing control. Phase angle control varies an average Root Mean Square (RMS) voltage by connecting the load to the mains for only a fraction of each half cycle, starting at an adjustable point in each half cycle and ending at the next current zero crossing. Burst control varies the average RMS voltage (over time) by connecting the load for an integer number of full half cycles in a burst and then disconnecting it for another integer number of full half cycles. Burst control mode has higher low frequency ripple than phase control, but produces less high frequency and harmonic noise as all switch-on points are very close to zero voltage points in the mains voltage waveform and all the switch-off points are at zero current points in the load current waveform. Phase angle control may therefore be more suitable for ripple sensitive loads such as motors, while burst control mode is more suitable for heating elements with long thermal time constants. Regardless, phase angle control may be used to control heating elements and may in particular used in low voltage (LV) territory to improve flicker performance, at the cost of higher harmonics, in case flicker is too high when using the burst control.

One way of controlling power applied to a functional component, e.g., a heating element, is to modulate switching elements e.g., TRIAC. A pulse width modulated signal is applied to the TRIAC gate electrode, thereby controlling the switching on of the TRIAC, which regularly remains on until the end of a particular half cycle of the AC supply voltage. Using such a control scheme allows to quickly reach a target temperature of a heating element, while complying with EMC (Electro- Magnetic-Compatibility) requirements like flicker and harmonics. For a haircare appliance running in high voltage (HV) territory, one important element in compliance testing may be the assessment on the reading of short-term flicker severity P_st. This term generally describes the human’s sensitivity to visible light fluctuations of an incandescent light. For HV applications - e.g., in a 230V, 50Hz power system, performance of a quantified flicker is evaluated based on the published standard IEC61000-3-3. This standard specifies, if performance lies under P_st =1 , it is then believed to be allowable and create less disturbance to the supply network. This strongly correlates to the way of designing the modulation signal output to load, i.e., by which control scheme and how the switching elements are controlled/switched on. Thus, beneficially, a specific set of modulation signal enables to suppress or reduce a current flickering value and improve the haircare appliances EMC performance in HV territory.

In contrast, there is no strong flicker restriction in the low voltage (LV) territory. However, since severe flickering phenomenon may be captured by human’s eyes easily and result in discomfort, particular consideration may be warranted also for LV applications.

One method used in current haircare appliances is to switch on the power supplied to the functional component using a set of defined control instructions. Said instructions may specify when to provide supply power to a functional component and when not to, to provide a mean power value to the functional component to obtain a certain effective output thereof. For a heater application, the output may be related to the temperature of the heating element, or a defined downstream temperature, e.g., an air exit temperature in the case of a hair dryer. The control instructions may be in the form of a switching pattern that has a defined length and specifies for which half-cycle of an AC power supply, the half cycle is actually applied to the functional component (switched on) and for which half-cycle of an AC power supply, the half cycle is not applied to the functional component (not switched on). As such, the control information or the switching pattern may be indicative of when to switch on a switching element that in turn applies the AC power supply voltage to the functional component. The pattern index length of the control information or the switching pattern may e.g., be 100, consisting of 100 half cycle switching instructions, resulting an effective duration of one pattern of 1 second in a 50Hz power system. In other words, it is determined once every second, after 100 half-cycles, which power value is to be applied to the functional component over the next 100 half-cycles, and then the suitable switching sequence of the control information or the switching pattern is chosen that corresponds to said power level. Using such a control scheme, setting a defined power level every second/every 100 half-cycles results in meeting flickering requirement in HV applications. Although the resulting flicker is still within standard requirements in HV applications, the same switching pattern applied in LV applications may result in a reduced flicker performance. Further, when using such a control scheme, its dynamic temperature response may be slow when the heater duty is updated only every second, possibly resulting in overheat and nuisance trips of the haircare appliance.

Thus, a new control scheme for switching AC power to a functional component may provide good flickering performance for both LV and HV territory. In particular, it may be beneficial to have a control scheme with a reduction in flicker, EMC harmonics issues and a fast dynamic performance of the controlled property of the functional component. Accordingly, this disclosure provides a haircare appliance, a method for controlling of a haircare appliance, use of the method for controlling a haircare appliance and a computer program product or a computer-readable storage medium according to the independent claims.

According to a first aspect of the present disclosure, there is provided a haircare appliance comprising a functional component, and a controller adapted to control power from an AC power source to the functional component according to a switching pattern, wherein the switching pattern is indicative of the switching on of power supplied from the power source to the functional component, wherein the switching pattern has a pattern index length determined by the following expression: if a selected total number of half cycles is divisible by k: pattern index length = i x (selected total number of half cycles), and if the selected total number of half cycles is indivisible by k: pattern index length = i x (k half cyclesx n), where n is selected such that (k half cycles x n) is closest to selected total number of half cycles and i and k are positive natural numbers.

According to a second aspect of the present disclosure, there is provided a method for controlling of a haircare appliance comprising a functional component and a controller comprising the step of control power from an AC power source to the functional component according to a switching pattern, wherein the switching pattern is indicative of the switching on of power supplied from the power source to the functional component, wherein the switching pattern has a pattern index length determined by the following expression: if a selected total number of half cycles is divisible by k: pattern index length = i x (selected total number of half cycles), and if the selected total number of half cycles is indivisible by k: pattern index length = i x (k half cyclesx n), where n is selected such that (k half cycles x n) is closest to selected total number of half cycles and i and k are positive natural numbers.

According to a third aspect of the present disclosure, there is provided the use of the method according to the present disclosure for controlling a haircare appliance according to the present disclosure.

According to a fourth aspect of the present disclosure, there is provided a computer program product or a computer-readable storage medium comprising instructions which, when the program is executed by a processing element, cause the processing element to carry out the steps of the method according to the present disclosure.

According to a fifth aspect of the present disclosure, there is provided a haircare appliance, comprising a processing element, a memory element, a functional component or a heating element, wherein the processing element is adapted to control the switching on of power supplied from a power source to the at least one heating element, wherein the switching on of power supplied is performed at a zero-voltage crossing of a particular half cycle of the power source, wherein the memory element comprises control information for the switching on of power supplied over a control cycle, wherein the control cycle comprises a positive integer plurality of half cycles, wherein the control information comprises switching information for the switching on of power supplied for each half cycle in the control cycle, wherein the control information further comprises power level information on a plurality of power levels of power supplied to the functional component or the heating element where each power level is a defined switching sequence of switching on of power supplied over the control cycle, wherein the processing element is adapted to determine a power demand of the at least one heating element and to determine a corresponding next power level of the control information, wherein the processing element is adapted to control the switching on of power supplied based on the defined switching sequence of the determined next power level, wherein the processing element is adapted to perform the determining of the power demand, and/or the determining of the corresponding next power level, and the controlling of the switching on of power based on the defined switching sequence of the determined next power level multiple times in a single control cycle.

According to a sixth aspect of the present disclosure, there is provided a method for controlling heating of a haircare appliance comprising a processing element, a memory element and functional component or a heating element, wherein the processing element is adapted to control the switching on of power supplied from a power source to the at least one heating element, wherein the switching on of power supplied is performed at a zero-voltage crossing of a particular half cycle of the power source, wherein the memory element comprises control information for the switching on of power supplied over a control cycle, wherein the control cycle comprises a positive integer plurality of half cycles, wherein the control information comprises switching information for the switching on of power supplied for each half cycle in the control cycle, wherein the control information further comprises power level information on a plurality of power levels of power supplied to the functional component or the heating element where each power level is a defined switching sequence of switching on of power supplied over the control cycle, the method comprising the steps of determining a power demand of the heating element and a corresponding next power level of the control information, controlling the switching of power supplied based on the defined switching sequence of the determined next power level, and performing the determining of the power demand and/or the corresponding next power level, and the controlling of power supplied based on the defined switching sequence of the determined next power level multiple times in a single control cycle.

This disclosure proposes a new control scheme to further reduce flicker and EMC harmonics issues and improve the dynamic performance of the controlled property of the functional component.

The new proposed method comprises revaluating the required power level set by the switching on of the power supplied to the functional component not only after conclusion of a full pattern index length of the control information or the switching pattern, but to re-evaluate and select a next power level already during the progression through the control information or the switching pattern. E.g., the method comprises switching on of power supplied to the functional component for a half cycle in an allocated slot based on a computed power ratio with a certain size of patternindex length given while the update rate of pattern is every k, e.g., 6, AC half cycles. Each allocated slot of the control information or the switching pattern is the place that holds, i.e., switches on one half cycle. The control information or the switching pattern comprises an arrangement of the slots, and which half-cycles power supplied to the functional component is switched on greatly impacts on the flickering performance since it is strongly related to the change of current or power drawn. A computed power ratio is the relation of desired power Pdesired against power capacity P capactiy-

Pdesired: Desired output power computed by system controller to set a desired output property of the functional component.

Pcapacti_y: maximum output power of the power delivery system used to supply power to the functional component.

With the power ratio computed, the amount of power needed for a particular electrical load/a particular functional component is determined. The total power for one switching period or control cycle is fixed. Although the switching period, which is represented by the pattern-index length of the control information or the switching pattern, may differ, the power is evenly distributed among the half cycles within the pattern-index length. In other word, with longer pattern-index length, the distributed power in each half cycle is less than in one half-cycle with shorter pattern-index length. Because of this lesser power distributed to each half cycle, finer power level changes may be realized during the closed-loop control adjustment. This results in a reduced impact on the power supply loading followed by the flickering phenomenon. The pattern-index length influences the time required from the first half cycle to the last half cycle of a control cycle. A larger length then takes a longer time to complete for one full control cycle. Regardless of this size of length, the update rate within the pattern is every k, e.g., 6, AC half cycles, which enables a faster response for the control system to adjust the change of output power in real time. Such a faster adjustment promotes the dynamic performance.

One example of a control method according to the present disclosure has a pattern-index length of e.g., 96, as a selected total number s of half cycles, with an update of the switching sequence of power supplied to the functional component every 6 AC half cycles. Full (100%) power is then divided into the number of 96 segments. The extension of a pattern index length of the control information or the switching pattern from 96 to a larger number, for example, 3 times 96 = 288, helps to move the occurring flicker frequency away from sensitive range of the human eye.

If the pattern index length is further extended to a larger number, flicker P_st may be reduced even further. Although there is no strict flicker requirement for LV territory, the quantified LV flicker is helpful for comparison and to understand the severity of impact generated by the designed switching pattern. Result shows the measured flicker is inversely proportional to the increment of the pattern-index length. E.g., there is a 0.76 drop between a pattern index length of 96 vs. a pattern index length of 960, i.e., 10 times of 96.

Table 1 : Quantified LV Flicker dependent on pattern index length

A larger pattern-index length required a longer time to complete a one full control cycle. If longer time is taken, response to the change of target temperature is slower and a slightly larger temperature variation during transition may appear. However, since a fast update of every k, e.g., 6, AC half cycles is designed in the algorithm, a control system may make adjustments quicker during dynamic operation regardless of the actual size of the switching pattern. For example, a pattern index length of 288 is normally completed in approx. 3 seconds. The update rate when using in-pattern-switching of power levels is even faster than a device having a pattern index length of e.g., 96 but that implements no in-pattern-switching, and thus selects a new desired power level only every 1 second. The increment of pattern-index length therefore does not impede but promote dynamic operation.

The foregoing explanation uses intervals of 6 half cycles of the AC power supply as one unit. A different number of half cycles per unit is conceivable and may be chosen depending on a specific implementation. Since a pattern index length corresponds to the same number of half cycles, a certain pattern index length defines a particular duration that is required to run through the switching pattern.

In a first example, a switching pattern having a pattern index length of 96 or 102 corresponds to 96 or 102 half cycles, which corresponds to approximately one second in a 50 Hz power system. The pattern index length is one unit, i.e., 6 half cycles times n. N is chosen so that the total length of switching pattern is an integer multiple of one unit, i.e., 6 half cycles. In the case of a duration of the switching pattern of approximately one second, n would be calculated to be 16 or 17, corresponding to a pattern index length of 96 or 102. Since 100 is not divisible by 6, a pattern index length of approximating 100 is required.

In a second example, a duration of the switching pattern of two seconds is assumed. This corresponds to 200 half cycles in a 50 Hz power system. Since the pattern index length of 200 again is not divisible by 6, a pattern index length approximating 200 is required. The closest numbers of 200 divisible by 6 are 198 or 204, thus resulting in an n value of 33 or 34. In a third example, a duration of the switching pattern of three seconds is assumed, which would correspond to 300 half cycles in a 50 Hz power system. Pattern index length of 300 in turn is divisible by 6, resulting in an n value of 50.

Stable power ratio in a steady state operation may result in a stable burst pattern and flicker shall be at the designed minimum. A fixed pattern for switching on power supplied for a half-cycle to the functional component results in the scenario where not much current change is introduced to the power supply loading and the likelihood of obvious flickering occurring is low. Therefore, a method of suppression on variations of the set power ratio is provided in the following. Particularly, a filter for smoothing the output property of the functional component or a downstream property, here exemplarily the air output temperature of a hair dryer, is provided to reduce variations in change of power ratio.

Equation 1 : AET Filter for Stabilising Power Ratio

Here, the output property, e.g., the air exit temperature, is related to the power ratio set by a particular power level of the switching pattern or control information. Depending on said output property, e.g., a new, desired output property, a new power ratio is chosen every k AC half cycles as described previously. To smooth and thus reduce variations in the change of the power ratio, the proposed filter calculates the new desired output property based on current and past values of the output property depending on a weighing factor Ki, here exemplarily 0.9. From tests, results show that LV flickering through an incandescent light bulb has a higher chance to be more related to the length itself instead of a completely fixed power ratio at steady state. Meanwhile, since the control of the desired output power is closed loop and dynamic, it is preferrable to adjust the power ratio set by a desired power level of the switching pattern based on a determined real-time AET change followed by the current change to power supply loading.

One advantage of the described control method is the method of driving switching components, e.g., TRIACs. It is preferable to adjust the status of driving, i.e. , switching on of, TRIACs every half AC cycle while ensuring the symmetry within k, e.g., 6 .half cycles instead of full AC cycles, namely, 2 half cycles in one time. The pattern index length is designed to be a larger and flexible in number, for example, having a pattern index length of 288 instead of approximately 100 (e.g., 96 or 102). The extension of the pattern index length in a design control algorithm helps the power supply in reducing its sensitivity to the current change generated from the pattern driving the load. With the lower sensitivity, the quantified flickering result is therefore lower. The described control method provides flicker improvement in both LV and HV territory. Burst fire control switches on whole half cycles, i.e., turn-on at zero-crossing instead of switching on at a non-zero AC phase angle (like in phase angle control) to drive the load instead of switching on at a specific phase angle. Thereby, the control method is unified while processor memory space is reduced. The proposed method may be seen as having a faster update rate at every k, e.g., 6, AC half cycles than a method updating at every 1 second. The fast update rate is independent from a specific pattern index length and provides quick response to not only the target temperature change, but also the heater loading change (feedback temperature change) during the dynamic operation. A filter may be added for stabilisation to feedback a property of the functional component of a downstream property, like, e.g., an air exit temperature. In this example, the process with the addition of the filter delivers a desired target temperature and ensures thermal performance. Further, the filter helps in the suppression of large power ratio fluctuations at steady state. The lesser fluctuations results in the smaller current change to the power supply loading followed by a potentially improved flicker.

The proposed method thus may have at least one of the following features: Switching on of power supplied each half cycle to update status of driving a switching component, like, e.g., TRIACs, while taking care of the symmetry within every k, e.g., 6, half cycles. The updating after k half cycles may be seen as only a small portion of one switching period or control cycle, the size of which is known as pattern-index length. An extension of the pattern-index length has a positive impact on flicker. The optional features of filtering and disabling control at steady state in the proportional integral (PI) controller stabilizes the power ratio when the system is about to reach its steady state where it observes temperature error of target and feedback. When the temperature is stable, the power ratio value may be considered to remain constant at a certain level. Since power drawn is related to power ratio, its stabilisation may be seen improving flicker behaviour. Since the power ratio relates to the switching on pattern, stabilisation of the power ratio benefits flicker performance. With a minor change of the pattern and its usage, the impact on the power supply loading change is reduced. Implementation of burst fire control in LV territory may be particularly beneficial in light of US harmonics requirements. Since phase angle control may have the potential issue of low margin of EMC-CE performance, burst fire control may be preferred. Lowering flicker through extension of pattern-index length also improves EMC harmonics. With the extension of the pattern-index length, the implementation of an intra pattern update rate at k, e.g., 6, AC half cycles improves system response so as to avoid the risk of overheating of a functional component implemented as a heating element and nuisance tripping. Further, a faster update rate enables to tolerate the increment of pattern-index length to a large value. An update rate at e.g., 6 AC half cycles is also quicker than in products with a pattern-index length of approx. 100 and no intra pattern update.

According to an embodiment of the present disclosure, k may be 6.

According to a further embodiment of the present disclosure, the power demand and the corresponding next power level of the control information may be determined every k half cycles, half cycle, every two half cycles, every three half cycles, every four half cycles, every five half cycles, every six half cycles, every seven cycles, every eight half cycles, every nine half cycles or every ten half cycles.

Re-evaluating the power demand and thus determining of an updated power demand and/or the next corresponding next power level every k, e.g., 6, half cycles may allow a very quick reaction to a change in the demand situation of a haircare appliance. Such a quick reaction promotes more closely following a desired property of the functional component and thus a more precise setting of said desired property. In the context of a heating element, re-evaluating the power demand based on a feedback value every 6 half cycles may avoid overheating and nuisance trips of a haircare appliance.

According to a further embodiment of the present disclosure, the controller may be configured to evenly distribute the power among the half cycles within the pattern-index length.

According to a further embodiment of the present disclosure, the power among the half cycles within the pattern-index length or the control cycle may be evenly distributed by the following expression,

where

Power Demand or Next Power Level of the Control Cycle

Power Ratio = - — — - - - - - - -

Power Capacity of the at least one heating element and FloorQ relates to a function to round a number down to the nearest integer.

Evenly distributing the power among the half cycles within the full pattern index length allows an improved power distribution in case of an increasing pattern index length. In other words, in case the pattern index length is increasing significantly, it may be beneficial to distribute the power over the total number of half cycles in the switching pattern, corresponding to a switching on of power supplied to the functional component for a single half cycle, rather than setting the power at the beginning of a switching pattern having a certain pattern index length. Otherwise, it may occur that a comparably small number of switch on instructions are present at the beginning of the switching pattern while the majority of the switching pattern remains in the off state. Such a switching pattern would unnaturally cycle through an initial power supplied to the functional component with a following extended period of time where no power is supplied to the functional component.

According to a further embodiment of the present disclosure, the functional component may be one or more heating elements, and the switching pattern may be indicative of the individual switching on of power supplied from the power source to each of the one or more heating elements. Exemplarily, the haircare appliance may comprise two heating elements and the switching pattern may be indicative of power supplied to each of the heating elements. E.g., a switching pattern may comprise a value of “0” that may symbolize that no power is provided to either of the heating elements, while a value of “1” may symbolize that power is provided to one heating element by switching on power supplied for a particular half cycle to that heating element, whereas a value of “2” may symbolize that power is provided to both heating elements by switching on power supplied or a particular half cycle to both heating elements.

According to a further embodiment of the present disclosure, i may be an integer value between 2 and 10.

The parameter i may indicate an extension of a usual pattern index length or a selected total number of half cycles by a particular factor. E.g., a usual pattern index length may be in the range of 96 to 100 half cycles, so that i times said number of half cycles corresponds to a longer switching pattern, which is still divisible by the same integer number of half cycles, e.g., k half cycles, like 6 half cycles. Here, an extension of 96 half cycles by 2 to 10 thus results in a pattern index length of 192, 288, 384, 480, 576, 672, 768, 864a and 960 respectively.

According to a further embodiment of the present disclosure, the control information may consist of switching information having s switching instructions and power level information having t power levels, s and t may be positive integer values, and the s switching instructions may constitute a single control cycle.

According to a further embodiment of the present disclosure, s may equal t, and/or s may be a positive integer value of 96, 98, 99, 100, 102, 104, or 105 or a positive integer multiple of 96, 98, 99, 100, 102, 104, or 105 below or equal to 1050.

5 may in particular be i times an initial or usual pattern index length or selected total number of half cycles. The initial pattern index length may be an integer multiple of k as the number of half cycles after which a re-evaluating of the power demand and thus determining of an updated power demand and/or the next corresponding next power level is performed. E.g., 96 may be 16 times

6 half cycles, while 100 may be 20 times 5 half cycles. Having an even number of half cycles provides the benefit of a symmetrical switching with regard to the positive and negative half cycles of the AC waveform. The greater s and thus the longer the control cycle is, the finer the total power can be distributed for a single control cycle.

According to a further embodiment of the present disclosure, the power demand and/or the next power level may be determined based on error computation of a target temperature of air exiting the haircare appliance and a feedback temperature TAET-

According to a further embodiment of the present disclosure, a smoothing function may be applied to the feedback temperature TAET -

According to a further embodiment of the present disclosure, the smoothing function may be defined as AET_filter(n) = K x AET_filter n - 1) + (1 - K x AET(r) where

Ki may be a weighing factor between 0 and 1 ;

AET may be an air exit temperature of air exiting the haircare appliance;

AETfiiter may be a filtered temperature for determining the power demand and/or the next power level; and n may be a positive integer index value.

Using parameters such as a target temperature of air exiting a haircare appliance and a feedback temperature, e.g., a measured temperature fed back to the controller, may allow a determination of a power demand and/or a corresponding next power level. The controller may then choose from the control information, i.e. , the switching pattern, a suitable next set of k half cycles, e.g., the next 6 half cycles, at a current position within the switching pattern of the control cycle, corresponding to said target temperature. In other words, dependent on the parameter, the controller may choose the next k half cycles best suited to obtain the desired output property of the functional component. To avoid a fluctuation of the output property, in a worst-case, an oscillation of the output property, a smoothing function may be implemented that uses not only a current determined property value of the functional component to set the next power level but also previous determined property values of the functional component so that a change in the output property is more gradual. The smoothing function may use a single previous property, e.g., the determined property directly before the current determined property, in particular using a weighing factor. Alternatively or additionally, a plurality of previously determined property values may be used, with or without weighing factors.

According to a further embodiment of the present disclosure, the control information or the switching pattern may be a table as provided in one of the tables as depicted in one of Figs. 6a, 6b and 7a-1 to 3, 7b-1 to 3.

BRIEF DESCRIPTION OF THE DRAWINGS

Figs 1a,b show exemplary haircare appliances according to the present disclosure.

Fig. 2 shows exemplary embodiments of switching periods according to the present disclosure.

Fig. 3 shows an exemplary embodiment of a controller and a controlled plant of a haircare appliance according to the present disclosure.

Fig. 4 shows exemplary embodiment of a conversion of power ratio to a switching sequence according to the present disclosure.

Figs. 5a to 5c show exemplary flicker behaviour of haircare appliances depending on the length of a switching pattern according to the present disclosure. Figs. 6a, b show an exemplary embodiment of switching patterns having a pattern index length of 96.

Figs. 7a-1 , 7a-2, 7a-3, 7b-1 , 7b-2, 7b-3 show an exemplary embodiment of switching patterns having a pattern index length of 288.

DETAILED DESCRIPTION OF THE DRAWINGS

Now referring to Figs 1a, b, which show exemplary haircare appliances according to the present disclosure.

Figure 1 a depicts a haircare appliance 100 embodied as a hair dryer. The haircare appliance 100 has an opening 104, which allows heated air to exit the haircare appliance 100. The heated air may be directed towards hair to be dried or styled. A functional component 102 is arranged in the interior of the haircare appliance 100 of figure 1a, which however is not visible. In the haircare appliance of figure 1a, the functional component is a heating element used to heat air that is sucked into the haircare appliance by a blower, which is also not further depicted in figure 1a. A controller, not depicted in figure 1A, is arranged within the haircare appliance 100 for controlling the temperature of the heating element 102. An appropriate sensor arrangement may determine that the air exit temperature of air exiting opening 104. The air exit temperature may be used as an input parameter to a smoothing function for determining a next power level or new power demand of the haircare appliance.

Figure 1 b depicts a haircare appliance 100 embodied as a hair straightener. The haircare appliance 100 has a scissor type mechanism, to open and close and to hold hair to be treated in between two opposing sides. A functional component 102 is provided at the far end of each of the opposing sides. In the haircare appliance 100 of figure 1b, the functional component is a heating surface used to heat hair arranged between the two heating surfaces to remove curls in the hair. A controller, not depicted in figure 1b, is arranged within the haircare appliance 100 for controlling the temperature of the heating surfaces 102. An appropriate sensor arrangement may determine the surface temperature of the heating surfaces 102 and may use said surface temperature, comparable to the air exit temperature of the haircare appliance of figure 1a. Much like the air exit temperature, the surface temperature of the heating surfaces 102 of the haircare appliance 100 figure 1b may be used as an input parameter to the smoothing function for determining a next power level or new power demand.

In an alternative embodiment, the haircare appliance 100 may be a combination of hair dryer and straightener. For example, instead of heating hair arranged between the two heating surfaces to remove curls in the hair, the hair straightener shown in figure 1b may have openings provided on opposing surfaces and/or edge of the opposing clamps such that heated air exit the haircare appliance 100 to dry and straighten the hair. In this alternative embodiment, the functional component 102 is arranged in the interior of the haircare appliance 100 of figure 1 b, which however is not visible. In this alternative embodiment, the functional component is a heating element used to heat air that is sucked into the haircare appliance by a blower, which is also not depicted in figure 1b. A controller, not depicted in figure 1 b, is arranged within the haircare appliance 100 for controlling the temperature of the heating element 102. An appropriate sensor arrangement may determine that the air exit temperature of air exiting openings. The air exit temperature of the openings provided on the opposing surfaces and/or edge of the opposing clamps may be used as an input parameter to a smoothing function for determining a next power level or new power demand of the haircare appliance.

The haircare appliances 100 of figures 1a, b and the alternative embodiment may be operated in accordance with the present disclosure and as further depicted with regard to figure 3 by using a switching pattern for switching on of power supplied to the functional component 102.

Now referring to Fig. 2, which shows exemplary embodiments of switching periods according to the present disclosure.

In figure 2, a switching pattern having a pattern index length of 480 and a switching pattern having a pattern index length of 96 are depicted schematically. Each entry of a switching pattern corresponds to information whether to switch on or not switch on a switching element which in turn is used to supply voltage from an AC voltage source to the functional component. Each entry of the switching pattern corresponds to a single half cycle of the AC power source. As such, a switching pattern having a pattern index length of 96 half cycles, in a 50 Hz power system comprises control information for approximately one second of operation. A switching pattern having a pattern index length of 480 half cycles, in a 50 Hz power system, comprises control information for approximately five seconds of operation. The pattern index length is chosen as a multiple of six in the embodiment of figure 2. Thereby, it is possible to divide the switching pattern by an integer number of intervals of 6 half cycles each. It is thus possible to re-evaluate a power demand of the functional component, depending on a desired output property, every 6 half cycles. Each entry of both the 480-length switching pattern and the 96-length switching pattern corresponds to a single half cycle, with the 480-length switching pattern being five times the length of the 96-length switching pattern.

In figure 2, exemplarily all entries are depicted as “1”, which would symbolize that for every half cycle, power is supplied to the functional component. A “0” could symbolize that for a particular half cycle, no power is supplied to the functional component. Further, in case more than one functional component is present in the haircare appliance, a ”1” may symbolize that power is supplied to only a single functional component while e.g., a “2” may symbolize that power is supplied to two functional components essentially simultaneously.

Figure 2 shows two possible pattern index lengths of 96 and 480. That said, the pattern index length can be determined by the following expression: if a selected total number of half cycles is divisible by k: pattern index length = i x (selected total number of half cycles), or if the selected total number of half cycles is indivisible by k: pattern index length = i x (k half cyclesx n), where n is selected such that (k half cycles x n) is closest to selected total number of half cycles and i and k are positive natural numbers.

The foregoing explanation uses intervals of 6 half cycles (i.e. k=6) of the AC power supply as one unit. A different number of half cycles per unit, i.e. k, is conceivable and may be chosen depending on a specific implementation. Since a pattern index length corresponds to the same number of half cycles, a certain pattern index length defines a particular duration that is required to run through the switching pattern.

In a first example, a switching pattern having a pattern index length of 96 or 102 corresponds to 96 or 102 half cycles, which corresponds to approximately one second in a 50 Hz power system. The pattern index length is one unit, i.e., 6 half cycles times n. N is chosen so that the total length of the switching pattern is an integer multiple of one unit, i.e., 6 half cycles. In the case of a duration of the switching pattern of approximately one second, n would be calculated to be 16 or 17, corresponding to a pattern index length of 96 or 102. Since 100 is not divisible by 6, a pattern index length approximating 100 is required.

In a second example, a duration of the switching pattern of two seconds is assumed. Such would correspond to 200 half cycles in a 50 Hz power system. Since 200 is not divisible by 6, a pattern index length approximately 200 is required. The closest numbers of 200 divisible by 6 are 198 or 204, thus resulting in an n value of 33 or 34.

In a third example, a duration of the switching pattern of three seconds is assumed, which would correspond to 300 half cycles in a 50 Hz power system. 300 in turn is divisible by 6, resulting in an n value of 50.

One example of a control method according to the present disclosure has a pattern-index length of e.g., 96, as a selected total number s of half cycles, with an update of the switching sequence of power supplied to the functional component every 6 AC half cycles. Full (100%) power is then divided into the number of 96 segments. The extension of a pattern index length of the control information or the switching pattern from 96 to a larger number, for example, i=3 meaning 3 times 96 = 288, helps to move the occurring flicker frequency away from sensitive range of the human eye.

If the pattern index length is further extended to a larger number, flicker P_st may be reduced even further. Although there is no strict flicker requirement for LV territory, the quantified LV flicker is helpful for comparison and to understand the severity of impact generated by the designed switching pattern. Result shows the measured flicker is inversely proportional to the increment of the pattern-index length. E.g., there is a 0.76 drop between a pattern index length of 96 vs. a pattern index length of 960, i.e., i=10 meaning 10 times of 96. Reference is again made to table 1.

A larger pattern-index length required a longer time to complete a one full control cycle. If longer time is taken, response to the change of target temperature is slower and a slightly larger temperature variation during transition may appear. However, since a fast update of every k, e.g., 6, AC half cycles is designed in the algorithm, a control system may make adjustments quicker during dynamic operation regardless of the actual size or length of the switching pattern. For example, a pattern index length of 288 is normally completed in approx. 3 seconds. The update rate when using in-pattern-switching of power levels is even faster than a device having a pattern index length of e.g., 96 but that implements no in-pattern-switching, and thus selects a new desired power level only every 1 second. The increment of pattern-index length therefore does not impede but promote dynamic operation. Whilst the above table 1 only illustrates i up to 10, one skilled in the art will recognise that i may go beyond 10 without departing from the disclosure. The actual number for i is left to one skilled in the art which will need to consider, among other things, the response to the change of target temperature.

Now referring to Fig. 3, which shows an exemplary embodiment of a controller and a controlled plant of a haircare appliance according to the present disclosure.

In figure 3, a controller 106 is provided for controlling switching elements 108 which are in turn used to supply an AC supply voltage to functional components 102. The controller 106 employs a switching pattern 110 used to determine when to switch on the switching elements 108. In figure 3, exemplarily two switching elements 108 are depicted. Each switching element 108 in figure 3 is exemplarily embodied as a TRIAC. The switching elements 108 in turn are connected to functional components 102, which are exemplarily embodied as heating elements the haircare appliance which includes controller 106 exemplarily comprises two independent heating elements, which may be controlled, i.e., switched on by the switching elements 108 independently. When implementing the control method according to the present disclosure, the switching pattern 110 is employed defining for which half cycle a particular switching element 108 is switched on and thus provides AC supply power to the respective functional component 102 it is connected to. In other words, for each half cycle, the switching pattern defines whether no switching element, one switching element or both switching elements are switched on and thus provide power to the respective functional component 102.

Controller 106 of figure 3 exemplarily uses a burst fire control mode or a zero-crossing control mode. Such a control mode switches on a switching element essentially at the beginning of a particular half cycle when the waveform of the AC supply voltage crosses through 0V. Since a TRIAC remains on for the duration of the half cycle and switches off, i.e., becomes nonconductive, automatically at the next zero crossing, i.e., at the end of the same half cycle, it is not necessary to specifically switch off a switching element 108. As such, the control method of the present disclosure only defines a switching on of a switching element, e.g., the switching elements becoming conductive, to supply AC supply voltage to the functional component.

A particular measured property of the functional component may be used, e.g., fed back to the controller, to be used in a subsequent controlling of the switching on of the switching elements 108. Now referring to Fig. 4, which shows exemplary embodiment of a conversion of power ratio to a switching sequence according to the present disclosure.

The objective of the controller 106 is to adjust the power in a regular basis so that a target parameter value of the functional component, e.g., an air exit temperature TAET measured by a suitable sensor arrangement, e.g., thermistors as per the controller embodiment of figure 3, can be met. E.g., through error computation of a target temperature and a feedback temperature TAET > a system PI controller may determine the required delta of actual parameter and target parameter value and may compute the amount of desired power P_desired needed so that the functional component reaches the target parameter value.

Meanwhile, with the knowledge of the power capacity P_capacity>

the maximum output power that a system can reach, the controller 106 may compute a ratio of P_desired versus P_capacity by dividing the P_desired by the P_capacity’ obtaining a value between 0 and 1. This value is used to choose the desired power level, specifically, the next power level to be set by the switching components from the plurality of power levels of the switching pattern, in particular at a current position within the switching pattern. This next power lever at the current position in the switching pattern is then used to determine the switching sequence of the switching elements until the next evaluation of the target parameter value. The value of the power ratio between 0 and 1 is then used to calculate the appropriate pattern index, i.e., the power level within the switching pattern by the formula

Control Cycle Length Pattern Index — t = Floor(Power Ratio x ( - - - ) )x 2

The obtained switching information is then used to determine the switching sequence of the switching elements, i.e., for which half cycles the switching elements or TRI AC should be switched on.

Now referring to Figs. 5a to 5c, which show exemplary flicker behaviour of haircare appliances depending on the length of a switching pattern according to the present disclosure.

Figure 5a shows the flicker performance of an existing haircare appliance with the following simulation condition per table 2.

Table 2 As can be seen from figure 5a, the short-term flicker "perceptibility" value P_st is below 1 , which is the requirement for this test parameter over a standardized 10-minute observation interval, at all times and for all power ratios.

Figure 5b shows the flicker performance of a haircare appliance using a control method according to this disclosure with a pattern length of 96 (shown in solid line) and 288 (shown in dotted line)with the following simulation condition per table 3.

Table 3

As can be seen in figure 5b, the P_st value is improved by approximately 0.2 by using a pattern index length of 96. A further improvement is obtainable when extending the pattern length to 288, i.e. , times 3, where the P_st value is approximately 0.1 lower that the pattern index length of 96 across all power ratio points.

Figure 5c shows the flicker performance of an existing haircare appliance as shown in solid line and a pattern index length of 288 according to the present disclosure as shown in dotted line with the same simulation condition as figure 5b. As can be seen from figure 5c, the existing haircare appliance would exhibit a worst-case P_st value of approximately 1.5 for certain power ratios but would essentially stay above a P_st value of 1.2 for almost all power ratios with the same simulation condition as figure 5b. Compared hereto, the pattern index length of 288 exhibits a worst-case P_st value of approximately 0.7 and thus remains comfortably well below 1. The 288-switching pattern used in figure 5c corresponds to the 288-switching pattern used in figure 5b.

Now referring to Figs. 6a, b, which shows exemplary embodiments of switching patterns having a pattern index length of 96.

Fig. 6a depicts a switching pattern having a length of 96 AC half cycles, thus having a duration of approx. 1 second. The table uses values “0” and “1”, indicating a switching-on of zero, one switching element for providing power to one functional component, e.g., a heating element. In Fig. 6a, a white background in a cell represents value “0” while a grey background represents value “1”.

Fig. 6b depicts a switching pattern having a length of 96 AC half cycles, thus having a duration of approx. 1 second. The table uses values “0”, “1” or “2”, indicating a switching-on of zero, one or two switching elements for providing power to two functional components, e.g., two heating elements. In Fig. 6b, a white background in a cell represents value “0”, while a light grey background represents value “1” and a dark grey background represents value “2”.

The switching pattern in figure 6a is an exemplary embodiment for controlling one switching element to apply the AC supply voltage to one functional components and Fig. 6b is an exemplary embodiment for controlling two switching elements to apply the AC supply voltage to two functional components.

Horizontally, the individual indexes or steps through the switching pattern are depicted whereas vertically, the different power levels for driving the functional components are depicted. A “0” in a cell of the switching pattern symbolizes that no switching element is switched on, i.e. , that no AC supply voltage is applied to either one of the two functional components. A “1” in a cell of the switching pattern symbolizes that one switching element is switched on, i.e., that AC supply voltage is applied to one of the two functional components. A “2” in a cell of the switching pattern symbolizes that both switching elements are switched on, i.e., that AC supply voltage is applied to both of the functional components. Each cell in turn symbolizes that the AC supply voltage is switched on for one half cycle of the AC supply voltage. Thus, the switching pattern of figure 6b has a duration of approximately one second.

The switching patterns of figures 6a and 6b are based on a switching order with improved flicker performance which updates the status of the switching elements every half cycle while maintaining the AC current symmetry within 6 half cycles. This is realized by providing a set of half cycles at the beginning of each set of 6 half cycles with skipping an interval of one AC cycle, i.e., 2 half cycles. With filling up to the end, it starts again adding half cycles to the next column from the begin.

The switching pattern of figure 6b follows a certain rule where as stated fills from the beginning at row “2” with index [1 ,4,7,10] and there is a “0” interval of every 2 columns. The next row “4” follows same to fill index [1 ,4,7,10,13,16,19,22], This applies to the rest up to row “16”. From row “18” onwards, the adjacent slot is filled (index [2,5,8,11]). The same principle applies from row “3”4 to “48”. From row “48” onwards, when all the slots are filled with “1” the pattern restarts from index 1 again. The values (0,1 or 2) in each cell represents 0, 1 and 2 heater element(s) turn-on respectively. Both of the two heater elements may in particular be working in burst fire control mode. This is for an appliance where two independent temperatures may be regulated. In case there is only one heating element to be switched on, the switching pattern would only comprise values “0” and “1”, as depicted in Fig. 6a.

Now referring to Figs. 7a, b, which shows exemplary embodiments of switching patterns having a pattern index length of 288.

Fig. 7a, spread over three pages figs. 7a-1 to 7a-3, depicts a switching pattern having a length of 288 AC half cycles, which is 3 times of the pattern index length of 96 of figure 6a. Similar to figure 6a, the table uses values “0” and “1”, indicating a switching-on of zero or one switching elements for providing power to a single functional component. In Fig. 7a, a white background in a cell represents value “0” while a grey background represents value “1”.

Fig. 7b, spread over three pages figs. 7b-1 to 7b-3, depicts a switching pattern having a length of 288 AC half cycles, which is 3 times of the pattern index length of 96 of figure. Similar to figure 6b, the table uses values “0”, “1” or “2”, indicating a switching-on of zero, one or two switching elements for providing power to two functional components. In Fig. 7b, a white background in a cell represents value “0”, while a light grey background represents value “1” and a dark grey background represents value “2”.

The switching pattern of figures 7a, b follow the same principle of the switching parent of figures 6a, b, however is extended to a total duration of three seconds. Each cell again has a value of “0” or“1” in Fig. 7a, or“0”, “1” or “2” in Fig. 7b, symbolizing the switching on of no, one or two switching elements for a particular half cycle. Since the total power provided by switching on AC supply power to the functional component is now distributed over 288 half cycles, the switching pattern also comprises 144/288 individual power levels as depicted by the horizontal lines.

According to an embodiment of the present disclosure, the power demand and/or the next power level may be determined based on error computation of a target temperature of air exiting the haircare appliance and a feedback temperature TAET - A smoothing function may be applied to the feedback temperature TAET- The smoothing function may be defined as

where

Ki may be a weighing factor between 0 and 1 ;

AET may be an air exit temperature of air exiting the haircare appliance;

Using parameters such as a target temperature of air exiting a haircare appliance and a feedback temperature, e.g., a measured temperature fed back to the controller may allow a determination of a power demand and/or a corresponding next power level. The controller may then choose from the control information, i.e. , the switching pattern, a suitable next set of k half cycles, e.g., the next 6 half cycles, at a current position within the switching pattern of the control cycle, corresponding to said target temperature. In other words, dependent on the parameter, the controller may choose the next k half cycles best suited to obtain the desired output property of the functional component. To avoid a fluctuation of the output property, in a worst-case, an oscillation of the output property, a smoothing function may be implemented that uses not only a current determined property value of the functional component to set the next power level but also previous determined property values of the functional component so that a change in the output property is more gradual. The smoothing function may use a single previous property, e.g., the determined property directly before the current determined property, in particular using a weighing factor. Alternatively or additionally, a plurality of previously determined property values may be used, again with or without weighing factors.

Claims

1. A haircare appliance (100) comprising a functional component (102), and a controller (106) adapted to control power from an AC power source to the functional component (102) according to a switching pattern, wherein the switching pattern is indicative of the switching on of power supplied from the AC power source to the functional component (102), wherein the switching pattern has a pattern index length determined by the following expression: if a selected total number of half cycles is divisible by k: pattern index length = i x (selected total number of half cycles) if the selected total number of half cycles is indivisible by k: pattern index length = i x (k half cycles x ri) where n is selected such that (k half cycles x n) is closest to selected total number of half cycles and i and k are positive natural numbers.

2. Method for controlling of a haircare appliance (100) comprising a functional component (102) and a controller (106) comprising the step of control power from an AC power source to the functional component (102) according to a switching pattern, wherein the switching pattern is indicative of the switching on of power supplied from the power source to the functional component (102), wherein the switching pattern has a pattern index length determined by the following expression: if a selected total number of half cycles is divisible by k: pattern index length = i x (selected total number of half cycles) if the selected total number of half cycles is indivisible by k: pattern index length = i x (k half cycles x n) where n is selected such that (k half cycles x n) is closest to selected total number of half cycles and i and k are positive natural numbers.

3. The haircare appliance according to claim 1 or the method according to claim 2, wherein k is 6.

4. The haircare appliance or the method according to claim 3, wherein the controller (106) is configured to evenly distribute the power among the half cycles within the pattern-index length.

5. The haircare appliance or the method according to at least one of claims 1 to 4, wherein the functional component is one or more heating elements (102), and wherein the switching pattern is indicative of the individual switching on of power supplied from the power source to each of the one or more heating elements (102).

6. The haircare appliance or the method according to at least one of claims 1 to 5, wherein i is an integer value between 2 and 10.

7. The haircare appliance according to at least one of claims 1 to 6, wherein the controller (106) is adapted to control the switching on of the power supplied from the AC power source to the functional component, wherein the switching on of power supplied is performed at a zero-voltage crossing of a particular half cycle of the power source, wherein the switching pattern defines a control cycle comprising a positive integer plurality of half cycles, wherein the controller (106) comprises control information for the switching on of power supplied over the control cycle, wherein the control information comprises switching information for the switching on of power supplied for each half cycle in the control cycle, wherein the control information further comprises power level information on a plurality of power levels of power supplied to the functional component where each power level is a defined switching sequence of switching on of power supplied over the control cycle, wherein the controller (106) is adapted to determine a power demand of the functional component and to determine a corresponding next power level of the control information, wherein the controller (106) is adapted to control the switching on of power supplied based on the defined switching sequence of the determined next power level, and wherein the controller (106) is adapted to perform the determining of the power demand, and/or the determining of the corresponding next power level, and the controlling of the switching on of power based on the defined switching sequence of the determined next power level multiple times in a single control cycle.

8. The method according to at least one of claims 2 to 6, wherein controller (106) is adapted to control the switching on of power supplied from the AC power source to the functional component, wherein the switching on of power supplied is performed at a zero-voltage crossing of a particular half cycle of the power source, wherein the switching pattern defines a control cycle comprising a positive integer plurality of half cycles, wherein the controller (106) comprises control information for the switching on of power supplied over the control cycle, wherein the control information comprises switching information for the switching on of power supplied for each half cycle in the control cycle, wherein the control information further comprises power level information on a plurality of power levels of power supplied to functional component where each power level is a defined switching sequence of switching on of power supplied over the control cycle, the method comprising the steps of determining a power demand of the functional component and a corresponding next power level of the control information, controlling the switching of power supplied based on the defined switching sequence of the determined next power level, and performing the determining of the power demand and/or the corresponding next power level, and the controlling of power supplied based on the defined switching sequence of the determined next power level multiple times in a single control cycle.

9. The haircare appliance according to claim 7 or the method according to claim 8, wherein the control information consists of switching information having s switching instructions and power level information having t power levels, wherein s and t are positive integer values, and wherein the s switching instructions constitute a single control cycle.

10. The haircare appliance according to at least one of claims 7 or 9 or the method according to at least one of claims 8 or 9, wherein the power demand and/or the next power level is determined based on error computation of a target temperature of air exiting the haircare appliance and a feedback temperature TAET-

11. The haircare appliance or method according to claim 10, wherein a smoothing function is applied to the feedback temperature TAET-

12. The haircare appliance or method according to claim 11 , wherein the smoothing function is defined as AET_filter(n) = K x AET_filter n - 1) + (1 - K x AET(r) where

Ki is a weighing factor between 0 and 1 ;

AET is an air exit temperature of air exiting the haircare appliance;

AETfiiter is a filtered temperature for determining the power demand and/or the next power level; n is a positive integer index value.

13. The haircare appliance or method according to at least one of claims 4 to 12, wherein the power among the half cycles within the pattern-index length or the control cycle is evenly distributed by the following expression,

where

Power Demand or Next Power Level of the Control Cycle

Power Ratio = - — — - - - - - - -

Power Capacity of the at least one heating element

14. Use of the method according to at least one of claims 2 to 6 and 8 to 13 for controlling a haircare appliance according to at least one of claims 1 , 3 to 7 and 9 to 13.

15. A computer program product or a computer-readable storage medium comprising instructions which, when the instructions are executed by a processing element, cause the processing element to carry out the steps of the method according to at least one of claims 2 to 6 or 8 to 13.