Method and system for power distribution

Abstract

A method for distributing power from a set power rate power source to a plurality of loads 16a, 16b, 16c comprising determining, for each of the loads, an individual energy requirement over a first up

Description

BACKGROUND A power supply (or power source) is a device configured to supply electric power to a load. Power supplies are designed to convert an input voltage and / or current to a particular voltage and / or current required by the load. For example, an AC-to-DC power supply takes an AC input voltage and converts it to a DC output voltage, whilst a DC-to-DC power supply takes a DC input voltage and provides a DC output voltage. An AC-to-DC power supply generally includes a rectifier stage for converting from an AC voltage to a DC voltage, and can include a further stage for stepping the voltage up or down as required. A set rate power source, which may also be referred to as a constant-power source, is a power source that is configured to deliver a constant power to a load, independently of changes in load resistance. A power output of such a constant-power source may be controllable, to provide a desired constant output power level. SUMMARY According to a first aspect of the invention, there is provided a method for distributing power from a set power rate power source to a plurality of loads, the method comprising: determining, for each of the plurality of the loads, an individual energy requirement over a first upcoming time period; determining a set power delivery rate of the set power rate power source; and controlling a power distribution module, configured to be connected between the power source and the plurality of loads, to: simultaneously deliver power from the power source to each of the plurality of loads having a non-zero individual energy requirement at a respective first power rate, over a first portion of the first upcoming time period, wherein the respective first power rate is based on the set power delivery rate; and deliver power from the power source to each of a first subset of the plurality of loads having a non-zero individual energy requirement at a respective second power rate, over a second portion of the first upcoming time period, wherein the respective second power rate is based on the set power delivery rate and is different to the respective first power rate. The method of the invention contributes to reducing losses associated with distributing power from the set power rate power source to the plurality of loads. For example, by simultaneously delivering power from the power source to each of the plurality of loads having a non-zero individual energy requirement over a first portion of the first upcoming time period, a number of switching events required for providing power to the plurality of loads may be reduced. Generally, a switching event (e.g. connecting or disconnecting a load from the power source) has an associated switching loss, e.g. where energy is dissipated as heat in the switching element. Accordingly, the method enables improved efficiency of power distribution to the plurality of loads. Moreover, when power from the power source is simultaneously delivered to multiple loads, power from the power source may be split between the multiple loads such that each load experiences a power level that is less than the total power output of the power source. This may contribute to reducing a wear on the load elements. The method of the invention may be implemented in hardware and / or software. The method may be performed by a controller. The controller may include any suitable processing or computing device, which is configured to perform the method steps described herein. The individual energy requirement for each load may correspond to an amount of energy to be provided to that load over the first upcoming time period. The individual energy requirement may in some cases be predetermined. Alternatively, the individual energy requirement may be determined as part of the method, e.g. based on a measurement (detection) of a parameter associated with the load. For instance, the individual energy requirement may be determined based on (as a function of) a difference between a current (actual) value of a parameter associated with the load and a target value associated with the load. A suitable sensor may be provided for detecting the current value of the parameter associated with the load. In some examples, power is delivered to a load of the plurality of loads having a non-zero individual energy requirement at the same rate as power is delivered to each other load of the plurality of loads having a non-zero individual energy requirement. For example, for each portion of an (upcoming) time period in which more than one load of the plurality of loads has a non-zero individual energy requirement, power is delivered to a load of the plurality of loads having a non-zero individual energy requirement at the same rate as power is delivered to each other load of the plurality of loads having a non-zero individual energy requirement. By way of example, where the load is a heater, the individual energy requirement may be determined on a difference between a current (actual) temperature and a target temperature for the load. As another example, where the load is a battery, the individual energy requirement may be determined on a difference between a current (actual) charge level of the battery and a target charge level of the battery. The set power rate power source corresponds to a power source configured to output a set power delivery rate. In other words, the set power rate power source may be a constantpower source, that is configured to output of constant power level, e.g. where the output power (power level) is independent of any changes in resistance of the plurality of loads. The first upcoming time period may correspond to a (first) time period of a control cycle for the power distribution module, e.g. a control cycle implemented by the controller mentioned above. For example, the method may involve a periodic control process for controlling distribution of power from the power source to the plurality of loads, the periodic control process comprising a sequence of time periods. The steps of the method may then be implemented for a next (upcoming) time period in the periodic control process. Accordingly, herein a time period may refer to a time period of a periodic control process. The power source may be controllable to set the power delivery rate (power output) of the power source. The set power delivery rate (i.e. power output) of the power source may be constant over the first upcoming time period. The power delivery rate may be maintained to deliver a constant average power to the plurality of loads over the time period. Thus, there may be some variation (e.g. ripple) over time in the delivered power, with the average power being controlled to provide a constant average power delivery rate over the time period. The set power delivery rate (power output) of the power source may be determined in any suitable manner. For instance, the set power delivery rate may be obtained from a memory, determined based on a setting of the power source, calculated, and / or measured (detected). The power distribution module is electrically connected between the power source and the plurality of loads, to distribute power from the power source to the plurality of loads. The power distribution module may be configured to selectively deliver power from the power source to each of the plurality of loads. The power distribution module may comprise any suitable arrangement of components for selective distribution of power from the power source to the plurality of loads. One or more of the plurality of loads may have a non-zero (i.e. greater than zero) individual energy requirement for the first upcoming time period. The power distribution module is controlled to fulfil the individual energy requirement of each of the plurality of loads over the first upcoming time period, i.e. such that each of the plurality of loads receives (over the course of the time period) an amount of energy from the power source corresponding to its individual energy requirement. In the first portion of the first upcoming time period, the power distribution module is controlled to simultaneously deliver power from the power source to each of the plurality of loads having a non-zero individual energy requirement. Thus, the power output by the power source may be split between the plurality of loads having a non-zero individual energy requirement over the first portion of the time period. The respective first power rate for each load having a non-zero individual energy requirement corresponds to a power rate (i.e. amount of power, power level) received by the load from the power source for the first portion of the time period. As the power from the power source is split between the loads, the respective power rates are based on (i.e. depend on, are a function of) the set power delivery rate (i.e. power output) of the power source. For instance, each respective first set power rate may correspond to a respective portion of the set power delivery rate from the power source that is allocated to a corresponding load for the first portion of the time period. The respective first set power rate may, for example, be determined as a function of the set power delivery rate of the power source, a number of loads to which power is delivered, and a resistance of the load. Thus, the set power delivery rate from the power source may be distributed (split) between the plurality of loads having a non-zero individual energy requirement as a function of the resistances of the loads. In the second portion of the first upcoming time period, the power distribution module is controlled to deliver power from the power source to each of the first subset of the plurality of loads having a non-zero individual energy requirement. The first portion and the second portion of the first upcoming time period may be successive portions of the time period. The first subset may be a smaller group (i.e. comprise fewer loads) than the plurality of loads having a non-zero individual energy requirement to which power is delivered in the first portion of the time period. The first subset may correspond to loads having a non-zero individual energy requirement, whose individual energy requirement is not fulfilled in the first portion of the time period. Loads having a non-zero individual energy requirement that is fulfilled in the first portion of the time period may not receive power from the power source in the second portion of the time period, i.e. only the first subset of loads may receive power in the second portion of the time period. Thus, loads in the first subset may each have a higher individual energy requirement compared to loads not in the first subset. The respective second power rate for each load in the subset is different to its respective first power rate. Thus, a load in the first subset will receive a different power rate in the first portion and the second portion of the time period. For example, as there may be fewer loads in the first subset compared to the loads that receive power in the first portion of the time period, the respective second power rate may be greater than the respective first power rate, e.g. because power from the power source may be split between fewer loads in the second portion of the time period. Each respective second set power rate may correspond to a respective portion of the set power delivery rate from the power source that is allocated to a corresponding load in the first subset for the second portion of the time period. The respective second set power rate may, for example, be determined as a function of the set power rate of the power source, a number of loads to which power is delivered, and a resistance of the load. Power may be delivered simultaneously to each of the loads in the first subset during the second portion of the time period. When power is delivered simultaneously to each of the plurality of loads having a non-zero energy requirement, each of the plurality of loads having a non-zero individual energy requirement may be connected in parallel with the power source. This may facilitate distributing (splitting) power from the power source between the plurality of loads having a non-zero energy requirement. Accordingly, power from the power source may be split between the plurality of loads having a non-zero energy requirement in accordance with (based on) their resistances. Similarly, where power is delivered simultaneously to each of the loads in the first subset during the second portion of the time period, the first subset of loads may be connected in parallel with the power source. The power distribution module may comprise a switching module configured to selectively control the power delivered to each of the plurality of loads. This may facilitate selective connection of each load to the power source, so as to control distribution of power between the plurality of loads over the course of the time period. The switching module may comprise any suitable arrangement of switches between the power source and the plurality of loads. In some cases, the switching module may comprise a respective switch associated with each of the plurality of loads. Each respective switch may be connected between the power source and the associated load. Any suitable type of switch may be used in the switching module, such as a field-effect transistor (FET). The switching module may be controlled to minimise a number of switching events of the switching module over the first upcoming time period. This reduces energy losses associated with switching events, thus improving efficiency of power distribution to the plurality of loads. Here, a switching event may refer to switching on or off a switch in the switching module. Thus, a number of times each load is connected or disconnected to the power source over the first upcoming time period may be minimised. This may, for instance, be achieved by maximising an amount of time in which power from the power source is simultaneously delivered to multiple ones of the plurality of loads. The switching module may be controlled to minimise a number of switching events of the switching module over the first upcoming time period by increasing and / or decreasing the power delivered to each of the plurality of loads no more than once during the first upcoming time period. In other words, the number of switching events may be minimised by connecting and / or disconnecting each of the plurality of loads to the power source no more than once during the upcoming time period. The power distribution module may be controlled to minimise a number of switching events of the switching module between chronologically adjacent upcoming time periods by one of increasing and decreasing power delivered to each of the plurality of loads no more than once during the first upcoming time period and another of increasing and decreasing power delivered to each of the plurality of loads no more than once during a chronologically adjacent upcoming time period. In some examples, the chronologically adjacent upcoming time period may be chronologically adjacent to the first upcoming time period. Similarly to the above, such an arrangement contributes to reducing switching losses associated with switching events, resulting in more efficient power distribution from the power source to the plurality of loads. The method may further comprise: determining a combined energy requirement for the plurality of loads over the time period; and transmitting a signal to the power source to cause the power source to provide the combined energy requirement over the time period. In this manner, the set power delivery rate (i.e. power output) of the power source can be set to ensure that the individual energy requirements of all the loads is fulfilled over the time period. Thus, for each upcoming time period in the periodic control process, the total energy requirement for the plurality of loads can be determined and the set power delivery rate can be set accordingly. The power distribution module is then controlled to ensure that the power from the power source is distributed so as to fulfil the individual energy requirement of each load. The combined energy requirement may be determined by summing the individual energy requirements of the plurality of loads. The power delivery rate of the power source may be set based on (as a function of) the combined energy requirement. As noted above, the set power delivery rate (i.e. power output) of the power source may be constant over the first upcoming time period. However, the set power delivery rate may be changed for subsequent time periods, e.g. as a function of the combined energy requirement for each subsequent time period. In other words, the set power delivery rate may be changed between successive time periods. The signal may be transmitted to the power source by the controller mentioned above. The power source may be configured to set its power delivery rate based on the received signal. The method may comprise determining that a first load has a higher individual energy requirement than a second load, and controlling the power distribution module to deliver power from the power source to the first load and the second load over the first portion of the upcoming time period, and to the first load and not the second load in the second portion of the upcoming time period. In this manner, the first load with the higher individual energy requirement may receive power for both the first and second portions of the time period, whilst the second load with the lower individual energy requirement may only receive power for the first portion of the time period. This enables the individual energy requirements of both the first and second loads to be fulfilled over the time period. As the first load receives power for both the first and second portions of the time period, this reduces a number of switching events associated with the first load, as the first load can be continuously connected to the power source for the first and second portions of the time period. Controlling the power distribution module may comprise determining a schedule for distributing power from the power source across the plurality of loads over one or more upcoming time periods, wherein the schedule comprises, for each of the plurality of loads, an indication of a portion of the one or more upcoming time periods in which the power distribution module is arranged to deliver power to the load. In this manner, the power distribution module can be automatically controlled during the one or more upcoming time periods, in accordance with the determined schedule. Thus, the schedule may be determined in advance of the one or more upcoming time periods, which may reduce an amount of processing required during the one or more upcoming time periods. The schedule may be determined to ensure that the individual energy requirement of each load is fulfilled for each of the one or more upcoming time periods. The schedule may be determined in accordance with the principles discussed above, e.g. to reduce a number of switching events and / or to increase a proportion of time in which multiple loads receive power simultaneously. As an example, where the power distribution module comprises the switching module mentioned above, the schedule may comprise, for each switch in the switching module, an indication of when the switch is turned on or off. The power distribution module may be controlled to deliver power from the power source to one or more of the plurality of loads over the whole upcoming time period or over a whole sequence of upcoming time periods. In this manner, the one or more of the plurality of loads may continuously receive power from the power source over the whole upcoming time period or over the whole sequence of upcoming time periods. Thus, there may be no need to connect or disconnect the one or more loads to the power source during the upcoming time period or sequence of time periods. This may avoid or reduce switching events associated with the one or more loads, resulting in improved efficiency of energy delivery to the loads. The schedule mentioned above may comprise an indication of upcoming time period and / or the sequence of upcoming time periods over which the power distribution module is controlled to continuously provide power to the one or more loads. The one or more of the plurality of loads to which power is delivered over the whole upcoming time period or over a whole sequence of upcoming time periods corresponds to one or more of the plurality of loads having a highest individual energy requirement over the whole upcoming time period or over the whole sequence of upcoming time periods. In this manner, the one or more of the plurality of loads having a highest individual energy requirement for the upcoming time period or sequence of upcoming time periods, may continuously receive power from the power source for the whole upcoming time period or the whole sequence of upcoming time periods. This facilitates fulfilling the individual energy requirement for the one or more loads with the highest individual energy requirement, whilst avoiding or reducing switching events associated with the one or more loads. In a first control pattern, the power distribution module may be controlled to, for each remaining load having a non-zero individual energy requirement, deliver power from the power source to the load from a respective start time to an end of the time period to fulfil the individual energy requirement of that load, wherein the respective start time is after a beginning of the first upcoming time period. In this manner, after its respective start time, each remaining load having a non-zero individual energy requirement will continuously receive power for the rest of the time period. This contributes to reducing a number of times the load is connected or disconnected to the power source during the time period, thus reducing a number of switching events associated with the load for the time period. The respective start time for each remaining load may be determined based on (as a function of) its individual energy requirement, to ensure that its individual energy requirement is fulfilled. For instance, the larger the individual energy requirement of a load, the earlier its respective start time may be. In a second control pattern, the power distribution module may be controlled to, for each remaining load having a non-zero individual energy requirement: deliver power from the power source to the load from a start of the time period, and stop, at a respective stop time before an end of the time period, delivery of power from the power source to the load when the individual energy requirement for the load is fulfilled. In this manner, each remaining load may continuously receive power from the power source from a beginning of the time period to its respective stop time. This contributes to reducing a number of times the load is connected or disconnected to the power source during the time period, thus reducing a number of switching events associated with the load for the time period. The respective stop time for each remaining load may be determined based on (as a function of) its individual energy requirement, to ensure that its individual energy requirement is fulfilled. For instance, the larger the individual energy requirement of a load, the later its respective stop time may be. The method may comprise controlling the power distribution module in accordance with a control pattern, for the plurality of loads, that alternates between the first control pattern and the second control pattern over successive time periods. Alternating between the first control pattern and the second control pattern in this manner may avoid or reduce switching events at a transition between successive time periods. In particular, this enables loads having a non-zero individual energy requirements for two successive time periods to remain connected to the power source at the transition between the two successive time periods. The plurality of loads may comprise a plurality of heaters. In this manner, the method can be used to control delivery of power to the plurality of heaters, e.g. to control a temperature of each of the plurality of heaters. By way of example, the plurality of heaters may be in a haircare device (or appliance), such as a hair dryer, a hairbrush, a hair styler, and / or an attachment for a haircare appliance. The plurality of loads may comprise a plurality of batteries. In this manner, the method can be used to control delivery of power to the plurality of batteries, e.g. to control a charge level of each of the plurality of batteries. Each battery may comprise one or more battery cells. The individual energy requirement for each of the plurality of loads may be determined based on a comparison between a detected value of a parameter associated with that load and a target value for the parameter. In this manner, power delivery to each of the plurality of loads can be controlled to achieve the target value for each load. The individual energy requirement may be determined in order to bring the value of the parameter closer to the target value, e.g. using a predetermined relationship between energy delivery and the parameter. Various suitable algorithms may be used for determining the individual energy requirement based on the comparison. For instance, a proportional-integral-derivative (PID) algorithm may be used for determining the individual energy requirement for each of the plurality of loads, taking as input for each load the detected value of the parameter and target value for the parameter. The parameter may correspond to any suitable parameter of the load, which may change with delivery of power to the load. For example, where the load is a heater, the parameter may comprise a temperature and / or resistance of the heater. Then, individual energy requirement for the heater can be determined based on a comparison between a detected temperature (or resistance) of the heater and a target temperature for the heater. As another example, where the load is a battery, the parameter may comprise a charge level and / or voltage of the heater. Then, individual energy requirement for the load can be determined based on a comparison between a detected charge level (or voltage) of the battery and a target charge level for the battery. The method may comprise controlling the power distribution module to deliver power from the power source to each load of a second subset of the plurality of loads having a non-zero energy requirement at a respective third power rate, over a third portion of the upcoming time period, wherein the second subset is a subset of the first subset, and wherein the third power rate is based on the set power rate and is different to the first power rate and the second power rate. Thus, in the third portion of the first upcoming time period, the second subset of loads is arranged to receive power from the power source. The second subset may correspond to loads from the first subset, whose individual energy requirement is not fulfilled in the first and second portions of the time period. Loads having a non-zero individual energy requirement that is fulfilled in the first and second portions of the time period may not receive power from the power source in the third portion of the time period, i.e. only the second subset of loads may receive power in the third portion of the time period. Thus, loads in the second subset may each have a higher individual energy requirement compared to loads not in the second subset. The respective third power rate for each load in the second subset is different to its respective first power and second power rate. Thus, a load in the second subset will receive a different power rate in each of the first, second and third portions of the time period. For example, as there may be fewer loads in the second subset compared to the loads that receive power in the first portion and the second portion of the time period, the respective third power rate may be greater than the respective first power rate and second power rate, e.g. because power from the power source may be split between fewer loads in the third portion of the time period. Each respective third set power rate may correspond to a respective portion of the set power delivery rate from the power source that is allocated to a corresponding load in the second subset for the third portion of the time period. The respective third set power rate may, for example, be determined as a function of the set power delivery rate of the power source, a number of loads to which power is delivered in the third portion of the time period, and a resistance of the load. Power may be delivered simultaneously to each of the loads in the second subset during the third portion of the time period. The second subset may be a smaller group (i.e. comprise fewer loads) than the first subset of loads having a non-zero individual energy requirement. The set power delivery rate of the power source may be constant over one or more upcoming time periods. Thus, as noted above, the set power delivery rate of the power source may be kept constant over the course of the first upcoming time period. Additionally, in some cases, the set power delivery rate may be kept constant over multiple successive time periods. The method may comprise controlling the power distribution module to start or stop delivery of power to each of the plurality of loads having a non-zero individual energy requirement at a chronologically distinct time. In other words, the power distribution module may be controlled to start or stop delivery of power to each of the plurality of loads having a non-zero individual energy requirement one load at a time. This contributes to reducing a magnitude in step changes of current drawn from the power source, compared to situations where multiple loads are simultaneously connected or disconnected from the power source. This in turn contributes to reducing an amount of associated EMC emissions and losses which arise due to changes in the amount of current drawn from the power source. This may be achieved, for example, by staggering times at which power delivery to each load is started or stopped. According to a second aspect of the invention, there is provided a power delivery system for supplying power to a plurality of loads, the power delivery system comprising: a power distribution module connectable between a power source and the plurality of loads, the power distribution module being configured to distribute power from the power source across the plurality of loads; and a controller configured to perform a method according to the first aspect of the invention. Any of the features described in relation to the first aspect of the invention may be shared with the second aspect of the invention (and vice versa). For instance, features of the power distribution module and / or the controller discussed in relation to the first aspect are equally applicable to the second aspect. The controller can include any suitable processing device or system for controlling the power distribution module. The controller can include a processor and a memory storing computer instructions, such that execution by the processor of the computer instructions causes the processor to perform the method of the first aspect of the invention. The power delivery system may comprise the power source. The power source may comprise a single-ended primary inductor converter (SEPIC). A SEPIC is a power converter which enables a voltage at its output terminals to be greater than, less than, or equal to a voltage at its input terminals. The SEPIC may be connected between a power supply and the plurality of loads. The SEPIC may act as an isolation barrier between the power supply and the plurality of loads. According to a third aspect of the invention, there is provided a computer-readable storage medium comprising instructions which when executed by a processor, cause the processor to perform the method according to the first aspect of the invention. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shows a schematic diagram of a power delivery system; Figure 2 shows a flow diagram of a method for distributing power; Figure 3 shows an example schedule for power delivery that may be used with the method of Figure 2; Figure 4 shows an example schedule for power delivery that may be used with the method of Figure 2; and Figure 5 shows an example schedule for power delivery that may be used with the method of Figure 2. DETAILED DESCRIPTION Fig. 1 shows a schematic diagram of a power delivery system 10. The power delivery system 10 comprises a power distribution module 12 which is connected between a power source 14 and a plurality of loads 16a, 16b, 16c. The power delivery system 10 further comprises a controller 18, which is configured to control the power distribution module 12, to distribute power from the power source 14 to the plurality of loads 16a, 16b, 16c. The loads 16a, 16b, 16c are connected in parallel between output terminals of the power source 14. The power source 14 comprises an AC power supply 20 (which may for instance be mains power), and an AC-DC converter 22 for converting AC power from the power supply 18 to a DC output power. The power source 14 is configured as a set power rate power source, i.e. it is configured to provide a constant output power, regardless of changes in resistance of loads connected to the power source 14. The controller 18 may be configured to control the power supply 20 and / or the converter 22, to control the set power delivery rate (i.e. the output power level) of the power source 14. The converter 22 may comprise a single-ended primary inductor converter (SEPIC), or any other suitable AC-DC converter. The converter 22 acts to provide an isolation barrier between the AC power supply 20 and the plurality of loads 16a, 16b, 16c. Other configurations and types of constant-power sources may be used instead of the power source 14. A SEPIC converter may allow for efficient delivery of energy at desired power levels (e.g. 100s of Watts). The SEPIC may be controllable to control an amount of current drawn from the AC power supply 18, to thereby control the power delivery rate of the power source 14. As another example, the converter 22 may comprise a power factor correction (PFC) converter, such as a PFC flyback converter. The power distribution module 12 is implemented as a switching module having a plurality of switches SW1, SW2, SW3, each of which is associated with a respective one of the plurality of loads 16a, 16b, 16c. In the example shown, there are three loads 16a, 16b, 16c and three associated switches SW1, SW2, SW3; however, other numbers of loads may be used, with the number of switches being adapted accordingly. Each load is connected in series with its associated switch between the output terminals of the power source 14. Thus, each of the three loads 16a, 16b, 16c with its associated switch SW1, SW2, SW3 is connected in parallel to the output terminals of the power source 14. Each switch may be implemented, for example, using a suitable field-effect transistor (FET). Accordingly, each switch SW1, SW2, SW3 can be controlled to control delivery of power from the power source 14 to its associated load. Each switch SW1, SW2, SW3 is connected to the controller 18, so that the controller can control operation (e.g. opening and closing) of each switch individually. For example, the controller 18 may be configured to provide a respective control signal to each switch (e.g. gate-source voltage) for controlling a state (e.g. open or closed) of the switch. In this manner, the controller 18 can control how power from the power source 18 is distributed amongst the plurality of loads 16a, 16b, 16c. Different types of load may be used, depending on an application of the power delivery system 10. For example, the loads 16a, 16b, 16c may be in the form of heaters (resistive heaters). The power distribution module 12 can then be controlled to control heating of each of the loads 16a, 16b, 16c. As another example, the loads 16a, 16b, 16c may be in the form of batteries (e.g. each having one or more battery cells). The power distribution module 12 can then be controlled to control charging of each of the loads 16a, 16b, 16c. A method 30 for distributing power from a set power rate power source to a plurality of loads is shown in Fig. 2. For illustration purposes, the method 30 is described in the context of the power delivery system 10. The controller 18 is configured to implement the method 30, to distribute power from the power source 14 to the plurality of loads 16a, 16b, 16c. At step 32, the method 30 comprises determining an individual energy requirement for each of the plurality of loads 16a, 16b, 16c for an upcoming time period. This provides an indication of an amount of energy to be received from the power source 14 by each load, over the course of the upcoming time period. For example, the controller 18 may store a predetermined individual energy requirement for each of the plurality of loads 16a, 16b, 16c. The upcoming time period may correspond to a period of a periodic control process performed by the controller 18. Alternatively, the controller 18 may determine the individual energy requirement for each load based on a measurement of a parameter associated with each load. For example, as shown in Fig. 1, a respective sensor 24a, 24b, 24c may be associated with each of the loads 16a, 16b, 16c, and arranged to detect a parameter of the associated load. Each sensor 24a, 24b, 24c is connected to the controller 18, such that the controller 18 receives an output signal from each sensor indicative of the detected parameter. The controller 18 may then, for each load 16a, 16b, 16c, compare the detected value of the parameter (as obtained from the output signal of the associated sensor) to a predetermined target value of the parameter for that load. Then, using the comparison (e.g. difference) between the detected value and the target value, the controller 18 can determine an amount of energy to be provided to the load to reach the target value, or get closer to the target value, over the upcoming time period. For instance, an algorithm such as a PID algorithm or similar may be used for determining the individual energy requirement as a function of the detected and target values of the parameter. Where the loads 16a, 16b, 16c are heaters, the sensors 24a, 24b, 24c may be temperature sensors (e.g. thermocouples). The controller 18 can then determine the individual energy requirement for each load based on a difference between a detected temperature of the load and a predetermined target temperature for the load. In some cases, the power delivery system 10 may be implemented in a haircare device, such as a hair dryer or a hair styler. The plurality of loads 16a, 16b, 16c may then correspond to heaters in the haircare device. The haircare device may have multiple selectable temperature settings, with the controller 18 being configured to control the temperature of each load based on a selected temperature setting. For instance, for each temperature setting, the controller 18 may store a predetermined target temperature for each of the plurality of loads. Where the loads 16a, 16b, 16c are batteries, the sensors 24a, 24b, 24c may be voltage sensors for detecting a voltage (or charge level) of the batteries. The controller 18 can then determine the individual energy requirement for each load based on a difference between a detected voltage of the load and a predetermined target voltage for the load. The predetermined target voltage may correspond to a voltage of the battery when it is fully charged. At step 34, the method 30 comprises determining a set power delivery rate of the power source 14, i.e. the amount of power output by the power source. For example, the controller 18 may obtain the set power delivery rate from a memory (e.g. an internal memory of the controller 18), or the set power delivery rate may be determined based on a setting of the power source 14. The controller 18 may be configured to detect (measure) the set power delivery rate of the power source 14. In some cases, the controller 18 is configured to calculate the set power delivery rate. In more detail, using the individual energy requirements obtained in step 32, the controller determines a combined (e.g. total) energy requirement for the plurality of loads 16a, 16b, 16c over the upcoming time period, e.g. by summing the individual energy requirements for the plurality of loads. The controller 18 then calculates (determines) the power delivery rate of the power source 14, so that the power source 14 delivers the combined energy requirement over the upcoming time period. The power delivery rate of the power source 14 is kept constant over the time period, such that the power delivery rate can be determined based on the combined energy requirement and a duration of the time period. The controller 18 then sets the power delivery rate of the power source 14 to the determined (calculated) power delivery rate, so that the power source 14 delivers the combined energy requirement over the time period. To set the power delivery rate of the power source 14 for the time period, the controller 18 may transmit a control signal to the power source 14. The control signal is arranged to cause the power source 14 to set its power delivery rate to the rate determined by the controller 18. By way of example, the controller 18 may control (via the control signal) an input current drawn from the AC power supply 20 by the converter 22. For instance, where the converter 22 is a SEPIC, the controller 18 may define an amplitude of a reference signal (e.g. a reference sine wave) which determines an amount of current drawn from the AC power supply 20. At step 36, the method 30 comprises controlling the power distribution module 12, to deliver energy from the power source 14 to the plurality of loads 16a, 16b, 16c, in order to fulfil the individual energy requirement of each load for the upcoming time period. Figs. 3 to 5 illustrate examples of how the power distribution module 12 can be controlled. Fig. 3 shows a table 40 illustrating a first schedule for distributing power from the power source 14 across the plurality of loads 16a, 16b, 16c over a first upcoming time period 42. The right-hand column of the table 40 indicates the individual energy requirement (in Joules) determined for each of the loads 16a, 16b, 16c (e.g. in step 32 described above). In the example shown, the loads 16a, 16b, 16c have individual energy requirements of 0.1 J, 0.4 J and 0.5 J for the first upcoming time period 42. The first upcoming time 42 period may, for example, have a duration of 10 ms, and is split into ten 1 ms intervals numbered 1 to 10 in the bottom row of the table 40. Taking the individual energy requirements shown in the table 40, the combined energy requirement of the loads 16a, 16b, 16c is 1 J for the first upcoming time period 42. The power delivery rate for the first upcoming time period may then be determined as 1 J / 10 ms = 100 W. The controller 18 can therefore set the power delivery rate of the power source 14 to 100 W for the duration of the time period 42. For the sake of example, the loads 16a, 16b, 16c may all have a same resistance (although loads with different resistances may also be used). The rows in the table 40 indicate an amount of energy in Joules received by each load 16a, 16b, 16c for each 1 ms interval in the time period 42. Where an interval is shown as blacked-out for a load, this indicates that the load does not receive any energy during that interval. In the example shown, the load 16c has the highest individual energy requirement amongst the plurality of loads. The controller 18 controls the power distribution module 12 such that the load 16c receives power from the power source 14 for the whole period 42. In particular, the switch SW3 associated with the load 16c is controlled to be closed for the whole period 42, so that the load 16c receives power from the power source 14. At a start of the period 42, only the switch SW3 is closed, and the other switches SW1 and SW2 are open, such that only the load 16c receives power from the power source 14 in the first interval of the period 42. Thus, in interval 1 of table 40, all of the power from the power source 14 is delivered to the load 16c, such that the load 16c receive 0.1 J over interval 1. For each of the remaining loads 16a, 16b, the controller 18 determines a respective start time from which power is provided to the load from the power source 14, with the load remaining connected to the power source 14 for the rest of the interval 42. The start time for each load 16a, 16b is determined so that the individual energy requirement of the load is fulfilled by delivering power to the load between the start time and an end of the interval 42. For example, as shown, the load 16b, which has the second highest individual energy requirement, has a start time of 1 ms after a beginning of the time period 42. Thus, at 1 ms after the beginning of the time period 42, the switch SW2 is switched on and kept on for the rest of the time period 42. Thus, the load 16b receives power from the power source 14 in intervals numbered 2 to 10. The load 16a, which has the lowest individual energy requirement, has a start time of 7 ms after the beginning of the time period 42. Thus, at 7 ms after the beginning of the time period 42, the switch SW1 is switched on and kept on for the rest of the time period 42, such that the load 16a receives power in intervals numbered 8 to 10. Accordingly, as shown in Fig. 3, there is a first portion 44 of the time period 42 (corresponding to intervals 8 to 10) where all of loads 16a, 16b, 16c are arranged to simultaneously receive power from the power source 14. In other words, in the first portion 44, all of the loads having a non-zero individual energy requirement simultaneously receive power from the power source 14. In the first portion 44 of the time period 42, the switches SW1, SW2, SW3 are closed, such that the loads 16a, 16b, 16c are connected in parallel to the power source 14. Accordingly, the power delivery rate from the power source 14 is split between the loads 16a, 16b, 16c, in accordance with the resistances of the loads. Thus, in the first portion 44 of the time period 42, each load 16a, 16b, 16c receives a respective first power rate, corresponding to a respective portion of the power output from the power source 14. In a second portion 46 of the time period 42 (corresponding to intervals 2 to 7), the switches SW2 and SW3 are closed, such that the loads 16b and 16c are connected in parallel to the power source 14. Thus, power from the power source 14 is split between the loads 16b and 16c, in accordance with the resistances of the loads. In the second portion 46 of the time period 42, each load 16b, 16c receives a respective second power rate, corresponding to a respective portion of the power output from the power source 14. The respective second power rate for each load 16b, 16c is different to the respective first power rate for the loads 16b, 16c, as power from the power source 14 is split between different numbers of loads in the first and second portions 44, 46 of the time period 42. The loads 16b, 16c constitute a first subset of the loads having a non-zero individual energy requirement for the time period 42. In a third portion 48 of the time period 42 (corresponding to interval 1), the switch SW3 is closed, such that the load 16c is connected to the power source, i.e. only the load 16c receives power in the third portion 48. Thus, all of the power from the power source 14 is delivered to the load 16c in the third portion 48, such that the load 16c receives power at a third respective power rate, which is different from its first and second respective power rates. The load 16c constitutes a second subset of the loads having a non-zero individual energy requirement for the time period 42. The schedule for power delivery to the loads 16a, 16b, 16c represented in table 40 corresponds to a first control pattern, where the one or more loads having a highest individual energy requirement are arranged to receive power for the whole time period 42. For each remaining load having a non-zero individual energy requirement, the load receives power from its respective start time (after the beginning of the time period 42) to the end of the time period 42, to fulfil its individual energy requirement. The first control pattern can be repeated for successive time periods, each time adapting the start times for the loads based on the individual energy requirements for the loads for the next (upcoming) time period. In general, at least one of the loads (i.e. the load having the highest individual energy requirement) remain continuously connected to the power source 14 throughout the time period. This avoids a situation where all of the switches are open (off) when power is still being drawn from the power supply 20. Fig. 4 shows a table 50 illustrating a second schedule for distributing power from the power source 14 across the plurality of loads 16a, 16b, 16c over a second upcoming time period 52. The table 50 illustrates power delivery to the loads 16a, 16b, 16c over the course of the time period 52, in an analogous manner to the table 40 described above. The second schedule corresponds to a second control pattern that can be used for controlling the power distribution module 12. Whereas in the first control pattern only the load(s) with the highest individual energy requirement is arranged to receive power at the beginning of the time period, in the second control pattern all of the loads having a non-zero individual energy requirement are arranged to receive power at the beginning of the time period. Thus, as shown in table 50, a first portion 54 of the time period 52 (corresponding to intervals 1 to 3) where all of loads 16a, 16b, 16c are arranged to simultaneously receive power from the power source 14 is at a start of the time period 52. The first portion 54 of the time period 52 is analogous to the first portion 44 of the time period 42 discussed above, with all of the switches SW1, SW2, SW3 being closed in the first portion 54. Similarly to the first control pattern illustrated in table 40, the load 16c having the highest individual energy requirement remains connected to the power source for the duration of the period 52 in the second control pattern. For the remaining loads 16a, 16b having a nonzero individual energy requirement, the controller determines a respective stop time (after the beginning of the period 52), at which point energy delivery to the load is stopped. The respective stop time is determined such that the individual energy requirement of the load is fulfilled at its respective stop time. Thus, in the example of table 50, a stop time for the load 16a is determined to be 3 ms after the beginning of the time period 52, at which time the switch SW1 is switched off. A stop time for the load 16b is determined to be 9 ms after the beginning of the time period 52, at which time the switch SW2 is switched off. Accordingly, there is a second portion 56 of the time period 52 in which the loads 16b, 16c are arranged to simultaneously receive power from the power source 14, in an analogous manner to the second portion 46 of the time period 42 discussed above. Likewise, there is a third portion 58 of the time period 52 in which only the load 16c receives power from the power source 14, in an analogous manner to the third portion 48 of the time period 42 discussed above. It is to be noted that the schedules illustrated in tables 40 and 50, and the values used therein, are for illustrative purposes only. In practice, different schedules and values may be used or determined, depending on details of the application. A schedule for power delivery to the loads 16a, 16b, 16c may be determined by the controller 18 in advance of the upcoming (e.g. next) time period. The schedule may be determined in accordance with the first control pattern and / or the second control pattern described above, depending on a type of control to be performed by the controller 18. The controller 18 can then control the switches SW1, SW2, SW3 in accordance with the determined schedule over the course of the time period. For example, the schedule may be determined during a preceding time period, or during an interval between the preceding time period and the upcoming time period. In some cases, a schedule can be determined which encompasses multiple upcoming time periods, i.e. a sequence of multiple upcoming time periods. Fig. 5 shows a schematic diagram illustrating an example schedule 60 determined for a sequence of successive time periods 62, 64, 66. In an analogous manner to the tables 40 and 50 discussed above, each line in the schedule corresponds to a respective one of the loads 16a, 16b, 16c. Each time period 62, 64, 66 is divided into ten intervals, represented as boxes in the schedule 60. Where a box is shown as blank (white), this indicates that the load for that row is arranged to receive power from the power source 14 for that interval (i.e. its associated switch is on). Where a box is shown as blacked-out, this indicates that the load for that row does not receive power from the power source 14 for that interval (i.e. is associated switch is off). The schedule 60 alternates between the first control pattern (e.g. illustrated in table 40) and the second control pattern (e.g. illustrated in table 50) for successive time intervals. For example, in the time period 62, the power distribution module 12 is controlled in accordance with the first control pattern. Thus, at a beginning of the time period 62, only the load(s) with the highest individual energy requirement (load 16c in the example shown) for the time period 62 receives power from the power source 14. The remaining loads having a non-zero energy requirement (loads 16a and 16b in the example shown) are connected to receive power at later times, with all of the loads having non-zero requirements being connected to receive power at the end of the time period 62. Then for the next time period 64, the second control pattern is used. Thus, in line with the discussion above for the second control pattern, all of the loads having non-zero individual energy requirements for the period 64 are connected to receive power at the beginning of the time period 64. Accordingly, where all of the loads 16a, 16b, 16c have non-zero individual energy requirements for both time periods 62 and 64, all of the loads can remain connected to the power source at a transition between the time period 62 and 64, i.e. no switching events need take place at the transition between the two time periods. Following 5 the time period 64, the control pattern may return to the first control pattern for the next time period 66. The control pattern used by the controller 18 may in this manner alternate between the first and second control patterns for successive time periods. In the example shown, the load 16c has a highest individual energy requirement for each of the time periods 32, 64, 66. Accordingly, the load remains continuously connected to receive power 10 from the power source (i.e. the switch SW3 is continuously closed) over the course of the time periods 32, 64, 66, thus minimising a number of switching events associated with the load 16c.

Claims

1. A method for distributing power from a set power rate power source to a plurality of loads, the method comprising:5 determining, for each of the plurality of the loads, an individual energyrequirement over a first upcoming time period;determining a set power delivery rate of the set power rate power source; andcontrolling a power distribution module, configured to be connected10 between the power source and the plurality of loads, to:simultaneously deliver power from the power source to each of the plurality of loads having a non-zero individual energy requirement at a respective first power rate, over a first portion of the first upcoming time period, wherein the respective first power rate is based on the set power15 delivery rate; anddeliver power from the power source to each of a first subset of the plurality of loads having a non-zero individual energy requirement at a respective second power rate, over a second portion of the first upcoming time period, wherein the respective second power rate is based on the set20 power delivery rate and is different to the respective first power rate.

2. A method according to claim 1 wherein, when power is delivered simultaneously to each of the plurality of loads having a non-zero energy requirement, each of the plurality of loads having a non-zero individual energy requirement is connected in parallel with the25 power source.

3. A method according to claim 1 or 2, wherein the power distribution module comprises a switching module configured to selectively control the power delivered to each of the plurality of loads.

304. A method according to claim 3, wherein the switching module is controlled to minimise a number of switching events of the switching module over the first upcoming29 10 25time period by increasing and / or decreasing the power delivered to each of the plurality of loads no more than once during the first upcoming time period.

5. A method according to any preceding claim, wherein the power distribution module 5 is controlled to minimise a number of switching events of the switching module between chronologically adjacent upcoming time periods by one of increasing and decreasing power delivered to each of the plurality of loads no more than once during the first upcoming time period and another of increasing and decreasing power delivered to each of the plurality of loads no more than once during a chronologically adjacent upcoming time 10 period.

6. A method according to any preceding claim, the method comprising: determining a combined energy requirement for the plurality of loads over the time period; and15 transmitting a signal to the power source to cause the power source toprovide the combined energy requirement over the time period.

7. A method according to any preceding claim, the method comprising determining that a first load has a higher individual energy requirement than a second load, and 20 controlling the power distribution module to deliver power from the power source to the first load and the second load over the first portion of the upcoming time period, and to the first load and not the second load in the second portion of the upcoming time period.

8. A method according to any preceding claim, wherein controlling the power 25 distribution module comprises determining a schedule for distributing power from the power source across the plurality of loads over one or more upcoming time periods, wherein the schedule comprises, for each of the plurality of loads, an indication of a portion of the one or more upcoming time periods in which the power distribution module is arranged to deliver power to the load.

309. A method according to any preceding claim, wherein the power distribution module is controlled to deliver power from the power source to one or more of the plurality of29 10 25loads over the whole upcoming time period or over a whole sequence of upcoming time periods.

10. A method according to claim 8, wherein the one or more of the plurality of loads to 5 which power is delivered over the whole upcoming time period or over a whole sequence of upcoming time periods corresponds to one or more of the plurality of loads having a highest individual energy requirement over the whole upcoming time period or over the whole sequence of upcoming time periods.10 11. A method according to claim 9 or 10 wherein, in a first control pattern, the powerdistribution module is controlled to, for each remaining load having a non-zero individual energy requirement, deliver power from the power source to the load from a respective start time to an end of the time period to fulfil the individual energy requirement of that load, wherein the respective start time is after a beginning of the first upcoming time15 period.

12. A method according to any of claims 9 to 11 wherein, in a second control pattern, the power distribution module is controlled to, for each remaining load having a non-zero individual energy requirement:20 deliver power from the power source to the load from a start of the timeperiod, andstop, at a respective stop time before an end of the time period, delivery of power from the power source to the load when the individual energy requirement for the load is fulfilled.2513. A method according to claims 11 and 12, the method comprising controlling the power distribution module in accordance with a control pattern, for the plurality of loads, that alternates between the first control pattern and the second control pattern over successive time periods.3014. A method according to any preceding claim, wherein the plurality of loads comprises a plurality of heaters or a plurality of batteries.29 10 2515. A method according to any preceding claim, wherein the individual energy requirement for each of the plurality of loads is determined based on a comparison between a detected value of a parameter associated with that load and a target value for the parameter.

16. A method according to any preceding claim, the method comprising controlling the power distribution module to deliver power from the power source to each load of a second subset of the plurality of loads having a non-zero energy requirement at a respective third power rate, over a third portion of the upcoming time period, wherein the second subset is a subset of the first subset, and wherein the third power rate is based on the set power delivery rate and is different to the first power rate and the second power rate.

17. A method according to any preceding claim, wherein the set power delivery rate of the power source is constant over one or more upcoming time periods.

18. A method according to any preceding claim, the method comprising controlling the power distribution module to start or stop delivery of power to each of the plurality of loads having a non-zero individual energy requirement at a chronologically distinct time.

19. A power delivery system for supplying power to a plurality of loads, the power delivery system comprising:a power distribution module connectable between a power source and the plurality of loads, the power distribution module being configured to distribute power from the power source across the plurality of loads; anda controller configured to perform a method according to any preceding claim.

20. A power delivery system according to claim 19 comprising the power source, wherein the power source comprises a single-ended primary inductor converter, SEPIC.

21. A computer-readable storage medium comprising instructions which when executed by a processor, cause the processor to perform the method according to one of claims 1 to 18.29 10 25s

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