MANAGING THE VOLTAGE OF A POLYPHASE SUPPLY

Background

[0001] Aspects of the invention relate to a method and apparatus for managing the voltage of a polyphase supply.

[0002] In many parts of the world, electrical distribution companies deliver power to end users at the upper end of a permitted range of voltage. For example, in the UK and certain other parts of the world, the supply voltage must be between 216.2V and 253V. The permitted statutory European voltage range is 207V-253V. In the UK, a typical average supply voltage may be around 245 volts. Most currently manufactured electrical appliances for use in Europe are designed to operate at a nominal voltage of 230V. Running these appliances at a higher voltage will reduce their expected operating life.

[0003] To reduce the supplied voltage to between 220V and 230V would have no negative impact upon the consumer, and in fact there are many benefits to be gained by maintaining the supply in this range. Such benefits include a reduction in the energy consumed, and consequently in the cost to the bill-payer, an increased life expectancy of electrical appliances, and a reduction in excessive CO2 emissions resultant from supplying electricity at an unduly high voltage level. It has been shown that a 10% reduction in voltage will yield an average 6-12% reduction in energy consumption.

[0004] Polyphase systems are often deployed in power distribution, and a three-phase supply is common for higher power commercial and industrial applications. For example, high power loads such as air conditioning or large electric motors often require a three- phase supply. However, in the case of polyphase supplies, issues may arise due to a lack of balance between the phase voltages. Voltage imbalance may be introduced to the system where, for example, the substation transformers are loaded unevenly (i.e. where the load on one phase is significantly higher than another). Having unbalanced phase voltages on the transformer and three-phase loads causes inefficiency, erratic performance and a shortened operational life.

[0005] It is an object of embodiments of the invention to at least mitigate one or more of the problems of the prior art. Summary of Invention

[0006] According to the invention, there is provided a method for managing the voltage of a polyphase supply, comprising: measuring a load voltage on each phase of the polyphase supply; deriving an adjustment component from each phase of the supply, wherein: the adjustment component is adapted to adjust the load voltage of that phase to a predefined set point, wherein the set point is the same value for all phases of the polyphase supply; and combining each adjustment component with its respective phase of the supply so as to maintain the load voltage on each phase at the set point.

[0007] Optionally, the adjustment component is a waveform in phase with its respective phase of the supply, or the adjustment component may be a waveform in antiphase with its respective phase of the supply.

[0008] Optionally, deriving the adjustment component comprises deriving each adjustment component from its respective phase of the supply using a pulse width modulation signal.

[0009] The set point may be between 200 volts and 250 volts, is typically between 210V and 230V, and in one embodiment, is 220 volts.

[0010] The method may comprise a method of thermal management comprising measuring a temperature of a component and if the temperature reaches a critical temperature, adjusting the set point to the supply voltage and temporarily ceasing managing the voltage of the polyphase supply.

[0011] Optionally, the set-point may be adjusted toward the supply voltage, if the temperature reaches a predefined sub-critical temperature.

[0012] According to the invention, there is provided an apparatus for managing the voltage of each phase of a polyphase supply, adapted to be connected in series with the supply, the apparatus comprising a microcontroller and, for each phase: a voltmeter for measuring a load voltage on a phase of the polyphase supply and outputting load voltage information to the microcontroller; the microcontroller adapted to: receive the load voltage information from the voltmeter; and calculate a desired magnitude of an adjustment component based on the received load voltage information, wherein the adjustment component is adapted to adjust the load voltage of that phase to a predefined set point, and wherein the set point is the same value for all phases of the polyphase supply; and an AC/AC converter and a transformer for deriving the adjustment component, wherein the transformer is arranged to combine the adjustment component with its respective phase of the supply so as to maintain the load voltage on the phase at the set point.

[0013] The transformer may be wound in antiphase. Optionally, the transformer primary is driven with a chopped and smoothed supply. [0014] In an embodiment, the desired magnitude of the adjustment component calculated by the microcontroller is output to the AC/AC converter via a pulse width modulation signal.

[0015] Optionally, the apparatus may comprise a thermal management system. The thermal management system may comprise: at least one of an AC/AC converter temperature sensor for measuring a temperature of the AC/AC converter and outputting AC/AC converter temperature information to the microcontroller, and a transformer temperature sensor for measuring a temperature of the transformer and outputting transformer temperature information to the microcontroller; a first relay switch that shuts off power to a power stage of the AC/AC converter when opened; a second relay switch across the primary winding of the transformer; a third relay switch across the secondary winding of the transformer, which bypasses the system when closed; and wherein the microcontroller is further adapted to: receive the AC/AC converter temperature information and transformer temperature information from the temperature sensors; determine if at least one of the AC/AC converter or the transformer has reached a critical temperature; and, if it has, enter the apparatus into a bypass mode, wherein the load voltages on each phase are gradually increased to the supplied levels and the first relay switch is opened in order to shut off power to the power stage, the second relay switch is closed across the primary winding of the transformer and the third relay switch is closed across the secondary winding of the transformer.

[0016] Optionally, the microcontroller is adapted to adjust the set point toward the supply voltage if either temperature sensor indicates that the temperature has reached a defined sub-critical temperature.

[0017] In an embodiment, the apparatus comprises a plurality of microcontrollers, at least one associated with each phase. Each microcontroller may be in communication with at least one other microcontroller.

Brief Description of the Drawings

[0018] Embodiments of the invention will now be described by way of example only, with reference to the accompanying figures, in which:

Figure 1 is a block diagram of an apparatus according to an embodiment of the invention;

Figure 2 is a circuit diagram of an apparatus according to an embodiment of the invention; Figure 3 is a block diagram of a portion of an apparatus according to an embodiment of the invention;

Figure 4 is a flow chart illustrating a method according to an embodiment of the invention;

Figure 5 is a circuit diagram of an apparatus according to an alternative embodiment of the invention;

Figure 6 is a flow chart illustrating a method of thermal management according to an embodiment of the invention;

Figure 7(a) is a circuit diagram of an apparatus according to an embodiment of the invention; and

Figure 7(b) is a plot of input and output waveforms according to an embodiment of the invention.

Detailed Description

[0019] Throughout the description, like reference numerals are used to refer to like parts.

[0020] Referring initially to Figure 1 , there is shown a block diagram of an apparatus for managing the voltage of each phase of a polyphase supply according to an embodiment of the invention, the apparatus indicated generally by reference numeral 100. The apparatus 100 is adapted to be connected in series with a three-phase supply, and comprises three portions, A, B and C. Each phase of the supply is connected to one portion A, B, C of the apparatus 100. All portions A, B, C are shown to be controlled by a single microcontroller 110. The microcontroller 110 independently controls the load voltage on each portion A, B, C, and therefore controls the voltage of each phase of the supply. The use of a single microcontroller is cost effective and provides for convenient synchronisation between phases. In an alternative embodiment, multiple microcontrollers could be deployed, each to control one phase, with appropriate signals being exchanged between the microcontrollers to ensure synchronisation of the polyphase system.

[0021] For each portion A, B, C thereof, the apparatus 100 comprises a voltmeter 120, an AC/AC converter 130, a transformer 140, a mains input 150, and an output 160 to supply a premises. Each portion A, B, C is controlled by the microcontroller 110. Each phase of the mains supply is input to a mains input 150A, 150B, 150C, combined with an adjustment component (which is output by each transformer 140A, 140B, 140C), and output, via the output 160A, 160B, 160C, to a respective load circuit in order to supply the premises. In this way, the supply to the respective load circuit may be considered a modified supply. Each voltmeter 120A, 120B, 120C measures a load voltage on its respective portion A, B, C of the apparatus 100. The microcontroller 110 is adapted to store a set point for the load voltage of each portion A, B, C and calculate the desired rms value of each adjustment component to be combined with its respective phase of the supply to the premises. Each adjustment component is derived (from the component 135A, 135B, 135C of the mains input) by the AC/AC converter 130A, 130B, 130C and the transformer 140A, 140B, 140C in conjunction. Each transformer 140A, 140B, 140C combines the adjustment component with its respective mains input 150A, 150B, 150C so as to maintain the load voltage on the portion A, B, C at the set point, and as such, the voltage of each phase of the supply to the premises is maintained at the set point.

[0022] Each voltmeter 120A, 120B, 120C, measuring the voltage at an output 160A, 160B, 160C to supply a premises, measures the load voltage of the portion A, B, C, and outputs a signal 125A, 125B, 125C indicative of the measured load voltage to the microcontroller 110. The voltmeters 120A, 120B, 120C measure the load voltage on each portion A, B, C, and output the signals 125A, 125B, 125C to the microcontroller 1 10. The voltmeters 120A, 120B, 120C measure the rms value of the load voltage. The load voltage may be sampled at between 1 and 10 Hz, and in a preferred arrangement the load voltage is sampled at 2 Hz, although it will be appreciated that other sampling frequencies may be used. The load voltage may be sampled more often or less often, for example in the range 0.1-100Hz or higher. However, the range of 1-10Hz provides a balance between under sampling, which would result in the load voltage varying more from the set point, and over sampling, which would require more processing power. Increasing the sampling rate to several MHz would see no improvement in performance. The signals 125A, 125B, 125C are output to the microcontroller 1 10 at the same rate as the sample rate.

[0023] The microcontroller 110, connected with each portion A, B, C of the apparatus 100 and receiving the output of each voltmeter 120A, 120B, 120C, is adapted to store the set point - a load voltage to which each portion A, B, C is managed. The microcontroller 1 10 may include a memory (not shown) in which the set point is stored, however the apparatus 100 may comprise separate memory for storing the set point. The set point may be a predefined set point. The set point may be defined by the user. Typically, the set point will be the same value for all portions A, B, C of the apparatus 100, and thus for all phases of the three-phase supply to the premises. In this way, the apparatus can improve the voltage balance between the phases. Phase voltage imbalance may be said to exist where the phase voltages are different. In the UK, utility supplies are required to be unbalanced by no more than 4%, however other territories may vary. Phase imbalance causes problems for polyphase loads such as motors, leading to inefficient and erratic performance and a shortened operational life. If the set point of each phase is the same value for all phases of the supply to the premises, the proposed system reduces and may eliminate voltage imbalance, matching voltages on all phases at the defined set point. It will be understood that the system may use different set points for each portion A, B, C and therefore different for each phase, if the user so chose.

[0024] The set point may be between 200 Volts and 250 Volts, and in a preferred arrangement the set point is 220 Volts. The set point may take other values dependent on the legislated voltage range of the mains supply, which may vary from country to country. Advantageously, the set point may be at the lower end of a legislated range of the mains supply, thereby reducing the power demand of the connected appliances. Research indicates that from a reduction in load voltage from the UK average of 245V to a set point of 220V (approx. 10% reduction), savings of 6-12% are typical. Where phase voltage is reduced, many appliances operate more efficiently; if supply voltage should fall below the set point, the voltage is increased to the set point, preventing brownout conditions. Commercial premises may see a range of 3-15% savings for a 10% reduction in load voltage, due to the wider variety of loads.

[0025] The microcontroller 1 10 receives the signal 125A, 125B, 125C indicative of the measured load voltage from the voltmeter 120A, 120B, 120C, and compares the measured load voltage to the defined set point. For each phase, the microcontroller 110 calculates the required rms value of the adjustment component based on the measured voltage and the set point. The microcontroller calculates the difference between the two values and calculates the adjustment component from the difference i.e. such that the magnitude of the adjustment component is equal to the difference between the two values. The adjustment components are chosen to adjust the load voltage on each portion A, B, C to the defined set point when combined with the mains input 150A, 150B, 150C via the transformer 140A, 140B, 140C, and thus to adjust the voltage of each phase of the supply to the premises to the set point. The microcontroller 110 recalculates the adjustment component based on the signal 125A, 125B, 125C indicative of the measured load voltage. The microcontroller 110 therefore may recalculate the adjustment component at the same rate as or at a similar rate to the sample rate. The recalculation ensures that the adjustment component is always adapted to manage the measured load voltage to the defined set point.

[0026] Given the AC mains supply, the microcontroller 1 10 calculates an adjustment component for each portion A, B, C of the apparatus 100 which will have an appropriate amplitude to produce the desired load voltage when summed with the mains input 150A, 150B, 150C. The adjustment component may be in phase or in anti-phase with its respective phase of the mains supply in order to increase or decrease the load voltage.

[0027] The microcontroller 1 10 includes switching logic (not shown) adapted to generate and send a control signal 1 15A, 115B, 1 15C indicative of the value of the desired adjustment component to the AC/AC Converter 130. The control signal 115A, 1 15B, 1 15C indicative of the desired adjustment component may be a Pulse Width Modulation signal, a phase angle control signal, or another suitable kind of signal.

[0028] The AC/AC converter 130A, 130B, 130C receives the component 135A, 135B, 135C of the mains input and processes it according to the control signal 1 15A, 115B, 1 15C to create an AC signal indicative of the desired adjustment component. The AC/AC converter 130A, 130B, 130C chops and filters the component 135A, 135B, 135C. The output 145A, 145B, 145C of the AC/AC converter 130A, 130B, 130C, referred to herein as the chopped and filtered mains signal 145A, 145B, 145C is input to the primary winding of the transformer 140A, 140B, 140C. The AC/AC converter 130A, 130B, 130C configures the chopped and filtered mains signal 145A, 145B, 145C to induce the adjustment component in a secondary winding of the transformer 140A, 140B, 140C when passed through the primary winding of the transformer 140A, 140B, HOC.

[0029] The chopped and filtered mains signal 145A, 145B, 145C is passed to the portion’s transformer 140A, 140B, HOC, which causes the adjustment component to be added to the mains input 150A, 150B, 150C. The adjustment component is added to the mains input 150A, 150B, 150C in order to manage the load voltages of each portion A, B, C to the set point. The managed voltage of each portion is then sent via output 160A, 160B, 160C to supply the location or premises at which the apparatus is installed.

[0030] Referring now to Figure 2 there is shown a circuit diagram of an apparatus according to an embodiment of the invention connected to a three-phase supply, indicated generally by reference numeral 200. The apparatus 200 comprises three different portions, labelled A, B, and C each connected in series to a phase of a three- phase mains supply. Each portion has an associated transformer 140A, 140B, 140C, and an associated AC/AC converter 130A, 130B, 130C. Each portion A, B, C has an input 150A, 150B, 150C and an output 160A, 160B, 160C. Each input 150A, 150B, 150C is connected to a phase of the mains supply. Each output 160A, 160B, 160C is connected to the respective load circuit in order to supply the premises.

[0031] As can be seen in Figure 2, the inputs 150A, 150B, 150C of each of the portions A, B, C split to allow the component 135A, 135B, 135C of the mains input to be delivered to the AC/AC converter 130A, 130B, 130C. As described in relation to Figure 1 , the AC/AC converter 130A, 130B, 130C receives the component 135A, 135B, 135C of the mains input and processes it according to the control signal 115A, 115B, 1 15C to create an AC signal indicative of the desired adjustment component. The chopped and filtered mains signal 145A, 145B, 145C of the desired magnitude is used to induce the adjustment component in the secondary winding of the transformer 140A, 140B, 140C when passed through the primary winding of the transformer 140A, 140B, 140C.

[0032] The transformer 140A, 140B, 140C is arranged so that the output of the AC/AC converter 130A, 130B, 130C is connected across the primary winding, and the secondary winding is connected in series with the mains input 150A, 150B, 150C. The transformer may be a step-down transformer in order to induce the relatively low voltage adjustment component in the secondary winding from the chopped and filtered mains signal 145A, 145B, 145C input into the primary winding. For a mains supply with a voltage range as per the UK or EU legislation, a suitable turns ratio of the transformer 140A, 140B, 140C may be 8: 1. The turns ratio selected for the transformer is dependent on the mains supply and the desired set point. For example, because in the UK a typical average supply voltage may be around 245 volts, and the desired set point may be 220 Volts, a desired maximum adjustment that can be made to the supply by the adjustment component would be around 25 Volts. The turns ratio defines the maximum adjustment: for an 8:1 ratio, a 245V supply produces a maximum adjustment of ~30V. In practice, this value is closer to 28V because of transformer losses. In Argentina, for example, the mains supply averages 220V, and a set point of 202 Volts has been suggested. For an 8: 1 ratio, a 220V supply produces a maximum adjustment of 27.5V, and thus a set point of 202V is reasonable for a supply of 220V.

[0033] The chopped and filtered mains signal 145A, 145B, 145C is passed through the primary winding of the transformer 140A, 140B, 140C, causing the adjustment component to be induced in the secondary winding of the transformer 140A, 140B, 140C, and thus combined with the mains input 150A, 150B, 150C. In this way, the adjustment component manages the load voltage of the portion A, B, C to the set point, resulting in a modified supply. The modified supply is output to the respective load circuit in order to supply the premises via the output 160A, 160B, 160C and thus the adjustment component is added to the respective phase of the supply to the premises. The transformer 140A, 140B, 140C may be an autotransformer, with primary and secondary circuits instead of primary and secondary windings.

[0034] The primary winding may be wound in anti-phase or in phase, in order to allow the adjustment component to destructively or constructively combine with the mains input 150A, 150B, 150C and thus with the supply to the premises, regardless of the sign of the voltage. The primary winding being wound in anti-phase means that a positive voltage on the primary winding results in a negative voltage on the secondary winding. The primary winding may be driven by a chopped, smoothed and filtered supply.

[0035] The transformers 140A, 140B, 140C may be rated for a continuous load of approximately 100 amps in a 75 kVA system. It will be understood that other suitable amperages and volt-amperages may be envisioned. The 100A specification has been selected to correspond with the fuse rating in many premises. At 250V supply, this means a 100 x 250 = 25kVA system. Where the fuse is a higher rating, this system will not be suitable. Similarly, the 75kVA system is 100A per phase on 3 phases. Single- and 3-phase systems with a higher current rating e.g. 200A, 400A etc. may be possible.

[0036] The transformers 140A, 140B, 140C may be toroidal. The transformers 140A, 140B, 140C may each weigh around 18kg for a 75kVA system. It will be understood that electrical devices operating at too high current may be subject to overheating. To prevent this, embodiments of the invention may include a thermal management system, as will be described in relation to Figures 5 and 6. However, it is possible to avoid the use of the thermal management with the choice of a suitable transformer. The transformers 140A, 140B, 140C in this embodiment do not necessarily need to be thermally managed by the later described thermal management system, as they may operate at full load without overheating.

[0037] Polyphase domestic supplies are typically fused at 32A per phase. The three- phase solution may be designed appropriately for the load profile of the premises, from as low as 20A continuous to 400A continuous and beyond. [0038] Referring now to Figure 3, there is shown a block diagram of a portion of the apparatus 100. The portion of the apparatus comprises the microcontroller 1 10 and the AC/AC converter 130. The AC/AC converter comprises an input filter 310, a Complex Programmable Logic Device (CPLD) 320, a power stage 330, and an output filter 340. The power stage 330 may be made up of switching elements, such as MOSFETs, IGBTs or the like. As in Figure 1 , while a single microcontroller is shown, the apparatus may comprise a plurality of microcontrollers, at least one associated witheach phase. A microcontroller associated with a phase may control that one phase. The microcontrollers associated with a phase may exchange appropriate signals to ensure synchronisation of the polyphase system.

[0039] The microcontroller 1 10 is configured to calculate the desired rms value of each adjustment component as previously. The microcontroller 110 includes a switching logic module (not shown) adapted to generate and send a control signal 115 indicative of the required adjustment component to the CPLD 320. The CPLD 320 is adapted to implement a switching sequence based on the control signal 115. The control signal 115 may be a pulse width modulation signal, a phase angle control signal or another suitable kind of signal. The switching sequence is adapted to switch the switching elements in the power stage 330 based on the control signal 1 15 in order to cause the power stage 330 to chop the signal filtered by the input filter 310 and output the chopped signal to the output filter 340.

[0040] Figure 7(a) shows a circuit diagram of the power stage 330, consisting of two banks of switching elements, for example, MOSFETs, IGBTs, or the like, that are used to switch the primary winding 730 in and out of circuit. Each bank of switching elements is arranged to function as an ideal AC switch in the configuration shown in Figure 7(a). This configuration consists of a first switch 710 in series with the AC input from the input filter, a second switch 720 in parallel with the first switch 710 and the AC input, and the output filter 340 and primary winding 730 in series with each other and in parallel with the second switch 720.

[0041] The power stage 330 uses a switching strategy to control the amplitude of the voltage across the load. When the first switch 710 is closed the second switch 720 must be open, and power is delivered to the load i.e. the primary winding 730 of the transformer. When the second switch 720 is closed the first switch 710 will be open and the primary winding is shorted to neutral. Adding in the output filter 340 removes the switching frequency and leaves a sinusoidal waveform which is then applied to the primary winding 730. Increasing the duty cycle will have the effect of increasing the amplitude of the voltage applied to the primary 730, and similarly reducing the duty cycle will reduce the amplitude of the voltage across the primary 730. These input and output waveforms 740, 750 are shown in Figure 7(b).

[0042] The component 135 of the mains input is fed into the input filter 310, which processes the component 135 of the mains input in order to filter out any unwanted frequency components. The filter also prevents switching frequencies from conducting back to the supply. The filtered component of the mains input is output to the power stage 330. The CPLD 320 causes the power stage 330 to produce a chopped signal from the filtered component of the mains input by providing the switching sequence to the power stage 330 via gate drive signals. The gate drive signals are produced by the switching sequence generated by the CPLD 320. The power stage 330 outputs the chopped signal to be passed through the output filter 340, which filters out any unwanted frequency components producing a smooth sine wave. The output filter 340 then filters the chopped signal to form the chopped and filtered mains signal 145.

[0043] Referring now to Figure 4, there is shown a flow chart illustrating a method of voltage management for each phase of a polyphase supply, according to an embodiment of the invention, indicated generally by reference numeral 400. The method 400 may be performed by the apparatus 100 illustrated in Figure 1 , and as such the same reference numerals are used.

[0044] The method comprises measuring a load voltage on each portion A, B, C; deriving an adjustment component from a component 135A, 135B, 135C of the mains input, wherein the adjustment component is adapted to adjust the load voltage of that phase to a predefined set point, and wherein the set point is the same value for all phases of the polyphase supply; and combining each adjustment component with its respective phase to maintain the load voltage on each phase at the set point. The method may include the step of defining the set point for the load voltage of each portion A, B, C of the apparatus 100.

[0045] In step 410, the set point or set points, to which the load voltages are managed, are defined. The set point may be programmed during manufacture or at installation, may be altered during operation and may be the same or different for each phase of the supply to the premises. The set point or set points may be stored in the memory of the microcontroller 110 or in memory external to the microcontroller 110. The apparatus may include communications such as Wi-Fi, Ethernet or GSM by which means the desired set point value may be received. Typically, the set point is the same for each portion and is programmed at manufacture or installation.

[0046] The set point may be controlled via an analogue input pin on the microcontroller. The voltage on the pin is altered by connecting different resistances in series and parallel across the DC supply to the microcontroller. The microcontroller 110 defines the set point value based on the measured input voltage on the analogue pin, for example, 2.8V might dictate a set point of 210V, 2.3V could mean 215V. The set point or set points may be stored in the memory of the microcontroller 110. The memory for storing the set point may be outside the microcontroller 110.

[0047] By regulating each portion A, B, C (and thus each phase of the supply to the premises) to the same set point, phase imbalance is reduced and may be eliminated, and the efficiency and lifetime of three-phase appliances such as motors is increased. The set point may be between 200V and 250V. The set point may be between 210V and 230V. Typically, it may be 220V for an installation with UK or EU voltages; or it may be any other suitable voltage indicated by the voltage of the mains supply in the jurisdiction, for example it may be 202V for an Argentinian installation.

[0048] In step 420 the load voltage on each portion A, B, C of the apparatus 100 (and thus on each phase of the supply to the premises, as previously explained) is measured by the voltmeter 120A, 120B, 120C at the sample rate. This measurement allows the difference between the load voltage and the set point to be calculated at regular intervals by the microcontroller 110 or by the microcontrollers, in an example with a plurality of microcontrollers .

[0049] In step 430 the desired adjustment components to be combined with each phase of the supply to the premises are derived. The rms values of the required adjustment components are calculated by the microcontroller/s 110. Each adjustment component is calculated based on the measured load voltage and the defined set point for each portion A, B, C of the apparatus 100. The microcontroller/s 110 calculates a difference between the two values and calculates the adjustment component from the difference - i.e. such that the magnitude of the adjustment component is equal to the difference between the two values. The adjustment component is adapted to adjust the load voltage of its respective portion A, B, C to the set point.

[0050] A signal indicative of the required adjustment component is generated by the switching logic module of the microcontroller/s 110, and sent to the AC/AC converter 130A, 130B, 130C. The AC/AC converter 130A, 130B, 130C derives a chopped and filtered mains signal 145A, 145B, 145C from the component 135A, 135B, 135C of the mains input. The chopped and filtered mains signal 145A, 145B, 145C is output to the primary winding of the transformer 140A, 140B, 140C, causing the adjustment component to be generated in the secondary winding. Thus, the adjustment component is derived from the component 135A, 135B, 135C of the mains input by the AC/AC converter 130A, 130B, 130C and the transformer 140A, 140B, 140C in conjunction.

[0051] Given the AC mains supply, the adjustment component calculated by the microcontroller/s 1 10 for each portion A, B, C of the apparatus 100 must have an appropriate amplitude to produce the desired load voltage when summed with the mains input 150A, 150B, 150C. The adjustment may be in phase or in anti-phase with its respective phase of the mains supply.

[0052] In step 440 each adjustment component is combined, via the transformer 140A, 140B, 140C, with its respective phase of the supply to the premises in order to maintain or adjust the load voltage to the defined set point or set points. As mentioned, the chopped and filtered mains signal 145A, 145B, 145C is sent to the primary winding of the transformer 140A, 140B, 140C, which causes the adjustment component to be induced in the secondary winding. The secondary winding is connected in series with the mains input 150A, 150B, 150C and so the adjustment component is combined with the mains input 150A, 150B, 150C, and consequently with the phase of the supply to the premises via output 160A, 160B, 160C. By adding the adjustment component to the phase of the supply to the premises, the voltage of the phase is increased or decreased to the defined set point.

[0053] The adjustment component is a waveform in phase or in anti-phase with the waveform of the respective phase of the mains supply. Consequently, the adjustment component may constructively or destructively interfere with the waveform of the respective phase, and therefore may increase or decrease the load voltage on the phase to the set point.

[0054] Referring now to Figure 5 there is shown a circuit diagram of a portion of an apparatus according to an alternative embodiment of the invention including a thermal management system, the portion being indicated generally by reference numeral 500. The portion 500 is an extension of the portions of the apparatuses 100, 200, 300 shown in Figures 1 , 2 and 3, and like reference numerals are used to refer to like parts. The portion 500 comprises the transformer 140, the voltmeter 120, the AC/AC converter 130, and the thermal management system. The portion 500 is connected to the microcontroller 1 10. The microcontroller 110 may be shared between the three portions of apparatus for the polyphase system, or each portion may include its own microcontroller. The thermal management system comprises two temperature sensors - an AC/AC converter temperature sensor 510 for the AC/AC converter 130 and a transformer temperature sensor 530 for the transformer 140; a normally-closed first relay switch 520A that disconnects the AC/AC converter from the component 135 of the mains input when opened, such that power to the power stage 330 is shut off; a normally-open second relay switch 520B across the primary winding of the transformer 140; and a normally-open third relay switch 540 across the secondary winding of the transformer 140. The first relay switch 520A and the second relay switch 520B may be implemented as a two-pole switch, for simultaneous actuation thereof. Alternatively, the thermal management system may comprise only one temperature sensor, either the AC/AC converter temperature sensor 510 or the transformer temperature sensor 530.

[0055] When opened, the first relay switch 520A shuts off power to the AC/AC converter 140 (and thus the power stage 330) in order to protect the power stage 330. When closed, the second relay switch 520B shorts the primary winding of the transformer 140. When closed, the third relay switch 540 across the secondary winding of the transformer 140 shorts the transformer secondary winding, effectively connecting the live input to the live output and bypassing the transformer completely. In an embodiment of the invention, the system may operate at full load without the thermal management system with an appropriately rated transformer. The thermal management system may still be included to handle unexpected overheating due to, for example, high ambient temperature, a blocked heatsink or other reasons.

[0056] An instance of the portion 500 is present for each phase of the polyphase mains supply. The portions for all instances may be controlled by the same microcontroller 110. Alternatively, each instance of the portion 500 may comprise its own microcontroller such that there is a plurality of microcontrollers, at least one associated with each phase. Each microcontroller may be in communication with at least one other microcontroller.

[0057] The AC/AC converter temperature sensor 510 measures a temperature of the AC/AC converter 130 and outputs a signal indicative of the temperature information to the microcontroller 110. The AC/AC converter temperature sensor 510 is situated proximal to the AC/AC converter 130 in order to accurately measure the temperature thereof. In order to accurately measure the temperature of the power stage 330, the AC/AC converter temperature sensor 510 may be located thereon. The AC/AC converter temperature sensor 510 may be a thermistor or another suitable temperature sensing device. There may be one or more temperature sensors present in the portion 500 in order to measure the temperature of each of the AC/AC converters 130.

[0058] The microcontroller 1 10 is adapted to receive the signal indicative of the temperature information from the AC/AC converter temperature sensor 510 and determine if the AC/AC converter 130 has reached a critical temperature. The critical temperature of the AC/AC converter 130 may be between 60°C and 100°C or any other suitable temperature greater than the normal operating temperature of the AC/AC converter 130, but within safe limits. The critical temperature of the AC/AC converter 130 may be adjusted dependent on the temperature limit of the power stage 330. The temperature limit of the power stage is the temperature at which the power stage 330 would overheat and fail. The critical temperature of the AC/AC converter 130 must be lower than the temperature limit. Thus, the higher the temperature limit of the power stage 330, the higher the critical temperature of the AC/AC converter 130 may be.

[0059] The transformer temperature sensor 530 measures a temperature of the transformer 140 and outputs a signal indicative of the temperature information to the microcontroller 1 10. The transformer temperature sensor 530 is situated proximal to the transformer 140 in order to accurately measure the temperature of the transformer 140. The transformer temperature sensor 530 may be situated in the windings of the transformer 140. The transformer temperature sensor 530 may be a thermistor or another suitable temperature sensing device. There may be one or more temperature sensors present in the portion 500 in order to measure the temperature of the transformer 140.

[0060] The microcontroller 1 10 is adapted to receive the signal indicative of the temperature information from the transformer temperature sensor 530 and determine if the transformer 140 has reached a critical temperature. The critical temperature of the transformer 140 may be between 60°C and 100°C or any other suitable temperature greater than the normal operating temperature of the transformer 140, but within safe limits. The critical temperature of the transformer 140 may be adjusted dependent on the temperature limit of the transformer. The temperature limit of the transformer 140 is the temperature at which the transformer 140 would fail due to overheating. The critical temperature must be lower than the temperature limit. Thus, the higher the temperature limit of the transformer 140, the higher the critical temperature of the transformer 140 may be. [0061] If either the transformer 140 or the AC/AC converter 130 has reached its respective critical temperature, the microcontroller 110 enters the portion 500 into a bypass mode, wherein the load voltage is gradually increased or decreased to the supplied level and the third relay switch 540 across the secondary winding of the transformer 140 is closed and the second relay switch 520B across the primary winding of the transformer 140 is closed. The first relay switch 520A is opened to remove power from the AC/AC converter. All phases (or instances of the portion 500) will be managed substantially synchronously to ensure that minimal voltage imbalance is introduced to the system by instances being in different modes. If the transformer 140 or AC/AC converter 130 for one instance overheats, then the whole system is entered into the bypass mode.

[0062] The microcontroller 110 signals the third relay switch 540 to close across the secondary winding of the transformer 140 to prevent further overheating. The microcontroller also signals the second relay switch 520B to close across the primary winding of the transformer 140 and the first relay switch 520A to open to protect the power stage 330. The first, second and third relay switches 520A, 520B, 540 may be any suitable type of bypassing switch.

[0063] Once the measured temperatures of both the AC/AC converter 130 and the transformer 140 have fallen to a defined value below the respective critical temperatures of the AC/AC converter 130 and the transformer 140, the microcontroller 1 10 will then return all portions 500 of the apparatus to a normal operating mode and return the load voltage on each phase to the set point. The microcontroller may also consider other operating conditions e.g. it could possibly not return the system to regulation if the current is above a threshold value or if either temperature has not fallen sufficiently below the critical temperature. The required value for the transformer 140 may be 10°C below the critical temperature, such that for a critical temperature of 60°C, the temperature of the transformer would need to fall to 50°C. Similarly, the required value for the power stage 330, and thus the AC/AC converter 130 may be 30°C, such that for a critical temperature of 80°C, the temperature of the power stage would need to fall to 50°C. These values implement hysteresis and so prevent continual switching from one operating mode to the other. When the microcontroller 1 10 switches back to the normal operating mode, the microcontroller 1 10 signals the third relay switch 540 to open and allow current to flow through the secondary winding of the transformer 140 across which the third relay switch 540 is located. It also signals the first relay switch 520A to close and the second relay switch 520B to open and allow the power stage 330 to drive the primary winding of the transformer 140. The voltage levels for each instance are gradually returned to the set point. Again, all instances will be managed synchronously to ensure that no voltage imbalance is introduced to the system by instances being in different modes.

[0064] The use of a single microcontroller provides for convenient synchronisation between phases when changing mode of operation. However, multiple microcontrollers may be used without loss of convenience or efficiency

[0065] Referring now to Figure 6, there is shown a flow chart illustrating a method of thermal management of the voltage management system for each instance of the portion 500, according to an embodiment of the invention, indicated generally by reference numeral 600. The method 600 may be performed by the portion 500 illustrated in Figure 5, with each instance being connected to a respective phase of a polyphase mains supply.

[0066] In step 610, the temperature of the transformer 140 is measured by the transformer temperature sensor 530.

[0067] In step 620, it is determined whether the critical temperature of the transformer 140 has been reached. If it hasn’t been reached, the portion 500 continues to operate as normal - i.e. the method returns to step 610. If the critical temperature has been reached, then the method continues to step 630.

[0068] In step 630, the load voltages are gradually increased or decreased to supplied levels. The voltages are adjusted concurrently in order to prevent phase imbalance.

[0069] In step 640, once the load voltages reach the supplied levels, the third relay switch 540 is closed across the secondary winding of the transformer 140 in order to bypass the transformer 140. The transformer 140 will therefore be allowed to cool to normal operating temperature. Additionally, the first relay switch 520A is opened to remove power from the AC/AC converter 130 and the second relay switch 520B is closed to short the transformer primary.

[0070] The method 600 may be performed in relation to the thermal management system of the AC/AC converter 130 as well as the transformer 140. The third relay switch 540 and second relay switch 520B will be closed and relay switch 520A will be opened if either of the transformer 140 or the AC/AC converter 130 reach their respective critical temperature. The bypass mode will be entered dependent on either of the transformer 140 or the AC/AC converter 130 reaching their respective critical temperature.

[0071] The method 600 may include the optional step 650. In step 650, the load voltage is allowed to vary from the set point when measured temperatures are approaching their critical levels, in order to avoid entering bypass mode. The load voltage is allowed to rise above the set point where the supply voltage is higher than the set point or fall below the set point where the supply voltage is lower than the set point. For example, in a system where the set point is 220V and the supply is 245V, the method could allow the load voltage to rise to 230V to keep the system cooler than the critical temperature of either the AC/AC converter 130 or the transformer 140. In another example, the set point may be 230V and the supply voltage may be 210V, and the method could allow the load voltage to fall to 220V to keep the system cooler than the critical temperature of either the AC/AC converter 130 or the transformer 140. In this way, by adjusting the set-point toward the supply voltage if the temperature reaches a predefined sub-critical temperature, entering bypass mode may be avoided. The higher the load, the faster the temperature rise will be and so the set point may be increased according to the load level.

[0072] The method 600 may be performed for each instance of the portion 500, although the microcontroller/s 110 will perform the steps 610-640 for all instances of the portion 500.

[0073] Throughout the specification, the term “manage” in relation to voltage is understood to refer to maintaining control over or controlling. Thus, managing the voltage of a supply comprises maintaining the voltage at, or increasing or decreasing the voltage to, an appropriate level, the appropriate level being the set point or set points.

[0074] It will be appreciated that embodiments of the present invention can be realised in the form of hardware, software or a combination of hardware and software. Any such software may be stored in the form of volatile or non-volatile storage such as, for example, a storage device like a ROM, whether erasable or rewritable or not, or in the form of memory such as, for example, RAM, memory chips, device or integrated circuits or on an optically or magnetically readable medium such as, for example, a CD, DVD, magnetic disk or magnetic tape. It will be appreciated that the storage devices and storage media are embodiments of machine-readable storage that are suitable for storing a program or programs that, when executed, implement embodiments of the present invention. Accordingly, embodiments provide a program comprising code for implementing a system or method as claimed in any preceding claim and a machine- readable storage storing such a program. Still further, embodiments of the present invention may be conveyed electronically via any medium such as a communication signal carried over a wired or wireless connection and embodiments suitably encompass the same.

[0075] All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. [0076] Each feature disclosed in this specification (including any accompanying claims, abstract and drawings), may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features. [0077] The invention is not restricted to the details of any foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed. The claims should not be construed to cover merely the foregoing embodiments, but also any embodiments which fall within the scope of the claims.