GB2597735A

GB2597735A - Power supply apparatus

Info

Publication number: GB2597735A
Application number: GB2011969.9A
Authority: GB
Inventors: Harrison Lee
Original assignee: Energy Research Lab Ltd
Current assignee: Energy Research Lab Ltd
Priority date: 2020-07-31
Filing date: 2020-07-31
Publication date: 2022-02-09
Also published as: GB202011969D0

Abstract

A high frequency AC power supply 1 comprises a power circuit 2 inductively coupled to a load circuit 3, and a controller 4. The load circuit comprises a load circuit detector 7 which detects an electrical signal of the load circuit. The power circuit comprises a power factor correction circuit (PFCC), a DC to AC converter, and an LC resonant bridge circuit. The converter is controlled in response to the detected signal on the load circuit. The converter may comprise a half bridge (figure 6a) and controlling the converter may comprise adjusting a clock frequency of the half bridge. The voltage, current, frequency and/or power of the load circuit may be monitored. The total harmonic distortion of the output waveform on the load circuit may be monitored. The load circuit may comprise a pair of side by side wires. One or more peripheral devices, such as LEDs, may be inductively coupled to the load circuit. By detecting harmonic distortion/noise, elements of the power circuit can be adjusted to reduce or eliminate standing waves in the load circuit and avoid excess power delivery.

Description

Intellectual Property Office Application No G1320119699 RTM Date January 2021 The following terms are registered trade marks and should be read as such wherever they occur in this document: Alen Bluetooth Google Home Li-Fi Wi-H Intellectual Property Office is an operating name of the Patent Office www.gov.uk/ipo Power Supply Apparatus The invention relates to a power distribution system for distributing variable high frequency alternating current (HFAC), in particular a power distribution system whereby the HFAC output supply is automatically or manually controlled.

The HFAC power system inductively powers loads coupled to the power bus.

Conventional electrical mains distribution systems and the grid as we know it usually supply electricity at 90-264V AC and the frequency 47-63 Hz, depending on the jurisdiction. Electrical products are either hard wired with connectors or junction boxes using a variety of mains power connection plugs and sockets or other permanently fixed connection systems. Standard mains voltage is known to be potentially hazardous to work on due to the frequency of 47-63Hz and all connections to an installation with the exception of plugging in appliances with traditional mains plugs require the expertise of qualified and agency approved electricians.

Furthermore, AC power presents a danger of electrocution, which is exacerbated in wet conditions or where there is exposed or damaged cabling.

When providing power in outside environments, for example, communal play areas, gardens, swimming pools, around ponds, parks and elsewhere, additional safety procedures must be legally followed, for example, IP6x water proof junction boxes, the use of armoured cables and resin filled connector blocks. Not only can this be notoriously difficult and time consuming but it has to be professionally installed by qualified electricians and carries a potential electrical shock risk to people and other life and fire risk to property in the event of a fault or damage.

Increasing the frequency of the AC supply above 10kHz provides a safe alternative to traditional, dangerous AC power distribution, providing a system whereby appliances may be connected inductively, taking the improved safety aspect one step further as the power/load circuit is inductively coupled to a HFAC power supply. High frequencies, typically in excess of 10kHz are used so that efficient inductive power transfer can take place. -1 -

As electrical devices and components are inductively powered installation is quicker and simpler and furthermore does not carry the same risks of electrocution in any condition, especially wet environments.

Inductively coupled loads and power supplies using high frequency AC are known and have been in use for some time. For example, NASA trialled HFAC in the 1980s during experiments for the space station. As a further example, US4264827 describes a power cable that uses a twisted wire pair which is short circuited at both ends. To couple to the bus transformer core elements are connected to the twisted wire pair so that the wires form a single turn transformer winding about each of two legs of the core elements. An output winding suitably placed on the core element of the cable driver will be inductively coupled to the twisted wire pair and can be used to draw power for a load. The core elements which connect through the twisted wire are formed by two pads which can be formed as a U-I shape, an E-I shape, U-U shape or E-E shape with the 'legs' of the U or E being inserted between twists of the twisted wire pair cable. The device of US4264827 was designed for aviation use as a way of providing power to various locations of an aircraft without galvanic connections. In other contexts there are various disadvantages, including the use of a relatively high voltage as the power supply.

Known HFAC systems use a constant current mode of operation which can cause the output voltage, which is proportional to load, to be high as the load increases. This can compromise the safety as high voltage HFAC can cause burns. It is not uncommon to generate over 400V AC output voltage in these typical HFAC systems. More importantly, these systems too may become dangerous in wet and especially fault conditions, due to the constant current mode of operation. During fault conditions they are able to supply the current directly into the faulty circuit, causing thermal failure modes where temperatures have been witnessed to be high enough to melt cables, plastic enclosures and ceiling tiles, setting off smoke detectors, tripping circuit breakers and putting buildings into darkness Due to the nature of these -2 -traditional constant current systems, in the event of a faulty load the main HFAC power supply will continue to drive the faulty load at high current until the inevitable thermal runaway that follows causes complete failure. These previous HFAC systems are traditionally controlled by hard wired control systems, have limited if any user interface to control the power supplies and have been used in the main for small scale lighting applications.

WO 2010/106375 provides another example of a power distribution system for high frequency AC, which again uses a constant current HFAC as the main power supply. In this case the power distribution system is designed for use with mains electricity as the input power and for supplying power to a lighting system, in particular to a lighting system using LEDs. An output cable in the form of a twisted wire pair is used in a fashion similar to US4264827, with inductively coupled loads being attached to the twisted wire pair via a transformer type arrangement, which is again similar to that disclosed in 1JS4264827. This system effectively adopts the same basic principles as US4264827 to provide power for domestic installations and similar lighting systems, but systems with a potential for very high AC voltages at 50kHz with peak currents approaching 3A as described in WO 201 0/1 06375 can be potentially dangerous, especially in fault conditions.

Should the output cable become disconnected, dangerous voltages at high frequency introduce a burn risk as well as an electric voltage shock risk, causing connected loads to be damaged.

Conventional HFAC products operate at a fixed current, fixed frequency and, beginning at cable lengths as short as 10m, standing wave problems have been identified by the inventors. As the cable length increases, the HFAC output waveform is progressively degraded. The issue is exacerbated by progressively higher loads. This causes poor current regulation and overdriving of inductively connected devices as the peak currents in the HFAC cable increase in line with the rise in standing wave elements. Noise from the standing waves causes power supplies to deliver higher power than is safe to do so. Some prior art systems designed to operate at a fixed constant current have been seen to lose control of their current regulation when the loads are varied or increased, for example, as lighting is taken from a low dimmed state to full brightness. Dangerous system conditions can result in which increases in current, to more than 75% of their intended designed operating condition, have been seen.

The loss of current regulation worsens significantly as output cables reach 100M due to the standing wave issues and as the subsequent noise on the HFAC power bus increases. The current regulation may degrade to a point whereby the sine wave output waveform is heavily distorted and only vaguely resembles a sine wave. Additionally, individual devices connected inductively are designed to run at a safe rating. For example, a LED may be designed to run at 700mA and may be configured to do so (via a transformer) while being powered by a power bus operating at a typical 1.5A in prior art examples. However, when the control of the current of the operating bus is lost and the current increases to circa 3A, the LED will operate at approximately 1200mA. Powering any device above its maximum rating will reduce the life of the device considerably. Driving LEDs above their maximum rating will shorten the life of the LED considerably, whilst at the same time shortening the life of the HFAC driver and the HFAC converter as both will be operating almost 67% above their designed operating points. In the case of lighting systems, every light fitted to the HFAC bus will be overdriven, eventually leading to premature system failures. In the past these have caused thermal system failures with catastrophic end results in which devices connected to the HFAC bus slowly overheat causing them to melt undetected in ceiling spaces before they eventually fail, causing noxious odours and potential for smoke damage to buildings.

Prior art examples of HFAC operate at a constant frequency and a constant current over their complete load curve, which contribute to the problems described above. Furthermore, known HFAC systems are relatively simple in their operation, allowing minimal user control with little or no indication of status, fault conditions, power level etc. and no connection to building management systems, fire systems, security systems or the internet for safety control. More importantly, the inventors have found that some of the prior art examples may fail in an unsafe manner, causing burn risks in addition to electric shock risk. Prior art systems consist of -4 -various elements, but fundamentally, single outputs with twisted pair cables for carrying the HFAC power.

It is therefore an object of the invention to provide a power distribution 5 system which overcomes these problems.

According to the invention there is provided a high frequency AC power supply comprising: a power circuit, a load circuit and a controller, the power circuit and the load circuit being inductively coupled, the load circuit comprising a load circuit detector configured to detect the electrical signal of the load circuit and the power circuit comprising a power factor correction circuit (PFC), a DC to AC driver, and a driver circuit comprising a LC resonant bridge circuit and a primary inductor inductively coupled to the load circuit, the driver circuit having a variable capacitance, wherein the controller is configured to control the variable capacitance in response to the detected electrical signal on the load circuit. By controlling the capacitance of the resonant tank the current level on the load circuit can be maintained at a desired level to remain in specification. The LC circuit preferably comprises an LLC circuit.

The variable capacitance may be controlled to keep the load circuit at a particular current. This may be specific value or a user may be able to set a particular value according to the conditions of the system and desired output.

The controller may be configured to control variable capacitance in parallel with the primary inductor in response to a detected electrical signal. Adjusting this capacitance gives a coarse adjustment to the current on the load circuit and so it may be adjusted in response to a change in the load on the load circuit detected by the electrical signal.

The controller may be configured to control variable capacitance arranged within the LC circuit and this may give a finer adjustment to the output current. For example, the controller may be configured to control the variable capacitance -5 -within the LC circuit in response to detected total harmonic distortion in the detected electrical signal.

According to the invention there is provided a high frequency AC power supply comprising a power circuit, a load circuit and a controller, the power circuit and the load circuit being inductively coupled, and the power circuit comprising a power factor correction circuit, a DC to AC driver, and a driver circuit comprising a LC resonant bridge circuit and a primary inductor inductively coupled to the load circuit, the driver circuit having a variable capacitance and comprising a resonant circuit detector configured to indicate the LC resonant bridge circuit voltage, wherein the controller is configured to control the variable capacitance in response to the resonant bridge circuit voltage.

There may be variable capacitance in parallel with the primary inductor and/or within the LC resonant bridge circuit arranged in parallel with the inductor in the LC circuit.

According to the invention there is provided a high frequency AC power supply comprising a power circuit, a load circuit and a controller, the power circuit and the load circuit being inductively coupled, the load circuit comprising a load circuit detector configured to detect the electrical signal of the load circuit and the power circuit comprising a power factor correction circuit, a DC to AC converter, a LC resonant bridge circuit and wherein the controller is configured to control the power factor correction circuit in response to the detected electrical signal on the load circuit. The power factor correction circuit is to be controlled to change the output voltage of the power factor correction circuit and this changes the output current on the load circuit. Thus adjusting the power factor correction circuit can control the current on the output circuit.

Controlling the power factor correction circuit in response to the electrical signal on the load circuit may comprise adjusting the output voltage to a different voltage by increasing the current through switching elements in the PFC. The power factor correction circuit may comprise a plurality of phases and additional -6 -phases may be interleaved in the power factor correction circuit when additional load is detected on the load circuit from the detected electrical signal. The use of a plurality of phases results in a more efficient PFC. The power factor correction circuit may be configured to adjust the output voltage between 300 and 450V.

The power factor correction circuit may comprise a feedback loop configured to regulate the output of the power factor correction circuit. Thus the PFC is regulated to output the frequency specified by the controller in response to the detected electrical signal.

According to the invention there is provided a high frequency AC power supply comprising a power circuit, a load circuit and a controller, the power circuit and the load circuit being inductively coupled, the load circuit comprising a load circuit detector configured to detect the electrical signal on the load circuit and the power circuit comprising a power factor correction circuit, a DC to AC converter, a LC resonant bridge circuit, wherein the controller controls the DC to AC converter in response to the electrical signal. The frequency of the DC to AC converter, and thus the frequency of the load circuit can be controlled.

The DC to AC converter may comprise a half bridge and the controlling of the DC to AC converter comprises adjusting the clock frequency of the half bridge. The controller may generate a synchronization pulse which is output to the half bridge and used as the input for the clock frequency of the half bridge. The clock frequency of the half bridge may be adjusted in response to a load detected on the load circuit by the electrical signal.

A synchronization pulse from the controller may control the deadtime, or duty cycle of switching elements in the DC to AC converter.

Detecting the electrical signal of the load circuit may comprise detecting one or more of the voltage of the load circuit, the current of the load circuit, the frequency of the load circuit or the power of the load circuit. Each of these can be used to detect the load on the load circuit, and thus whether the load has changed. -7 -

Elements of the power system, such as the PFC, the variable capacitance and the DC to AC converter can be changed in response to a change in load to ensure that the current, voltage and frequency remain at desired levels.

Detecting the electrical signal of the load circuit may comprise detecting the total harmonic distortion and the output waveform on the load circuit and controlling the variable capacitance in response to the detected AC noise. Detecting total harmonic distortion of the output waveform on the load circuit detects the noise on the load circuit. However, other ways of detecting the noise may also be used. Elements of the power system can be varied to reduce and eliminate noise.

The controller may comprise a digital signal processor, a field-programmable gate array (FPGA) or a microcontroller. The controller receives inputs from, inter alia, the load detector and controls various elements of the system. When there are a plurality of load circuits, signals may be transmitted between different controllers for respective load circuits in order to synchronise signals.

The load circuit may comprise a pair of side by side wires. Furthermore, the power management of the system, as defined by the invention, reduces noise and standing waves such that side by side wires of 100m or more can be used.

The load circuit may have a variable frequency of 10kHz to 350kHz 25 whereas the input frequency of the power circuit may be between 10Hz and 500Hz. The load circuit may be controlled to within safety extra low voltage standards.

The controller may be controllable through radio frequency (RF), encrypted RF, Bluetooth or WiFi devices. This allows the user to control the system. For example, the user may specify the power level of the system. There may be two-way communication and the user may receive alerts from the controller. -8 -

There may be a plurality of peripheral devices inductively coupled to the load circuit and powered by the HFAC power supply. The peripheral devices may include lights, sensors, battery chargers, audio devices, cameras, irrigation devices, motors.

The power factor correction circuit may comprise a bridgeless power factor correction circuit. The AC to DC converter may comprise a half bridge or a full bridge. The LC circuit preferably comprises an LLC circuit.

There may be variable capacitance in parallel with the primary inductor.

There may also or additionally be variable capacitance within the LC resonant bridge circuit, which may be arranged in parallel with the inductor in the LC circuit.

The current on the load circuit may be set to be a value in the range 0.115 2.5A and the load on the load circuit may be up to 1KW.

The controller may be configured to control one or more of: the variable capacitance in response to the detected electrical signal on the load circuit or the resonant bridge circuit voltage; the power factor correction circuit in response to the detected electrical signal on the load circuit; the DC to AC converter in response to the detected electrical signal.

The LC resonant bridge circuit may form part of a driver circuit together with a primary inductor inductively coupled to the load circuit, the driver circuit having a variable capacitance and comprising a resonant circuit detector configured to indicate the LC resonant bridge circuit voltage and wherein the controller is configured to control the variable capacitance in response to the resonant bridge circuit voltage. Detecting the voltage in the resonant circuit provides an alternative, accurate way of detecting noise or other disturbances in the output signal. -9 -

The power supply may further comprise a plurality of load circuits each with a load detector configured to detect the electrical signal on the load circuit, a plurality of DC to AC drivers, a plurality of LC resonant bridge circuits and a plurality of primary inductors with each primary inductor being coupled to a separate load circuit, each driver circuit having a variable capacitance and the controller being configured to control one or more of: the variable capacitance of each of the driver circuits in response to the electrical signal on the respective load circuit or the resonant bridge circuit voltage on the respective resonant bridge circuit; the power factor correction circuit in response to the electrical signal on the respective load circuit; and the DC to AC converter is controlled in response to the electrical signal on the respective load circuit.

Thus a plurality of load circuits may be coupled to a single input power source.

There is provided a HFAC power supply comprising a power circuit, a load circuit and a controller. , the power circuit and the load circuit being inductively coupled, the load circuit comprising means for measuring the load and the power circuit comprising: a power factor correction circuit, a DC to AC driver and a driver circuit comprising an LC resonant bridge circuit and a primary inductor inductively coupled to the load circuit, wherein the load measured is the power on the load circuit and, in response to the detected load any one or more of: the capacitance of the resonant bridge circuit, the operating frequency of the DC to AC driver or the output voltage of the PFC is adjusted. These may be adjusted to reduce the power transmitted to the load circuit.

Due to the automatically controlled method of operation in real time of variable current, variable resonance, variable frequency and variable power, the power bus in the load circuit can extend over much longer distances than current known or prior art systems, without incurring the previously discussed standing wave issues. -10-

According to the invention there is provided a method of controlling the current on a load circuit of an HFAC system, the HFAC system comprising a driver circuit having variable capacitance, a power factor correction circuit and a DC to AC converter, the method comprising one or more of: controlling the variable capacitance of the driver circuit in response to the electrical signal on the load circuit, controlling the power factor correction circuit in response to the detected electrical signal on the load circuit or controlling the DC to AC converter in response to the electrical signal on the load circuit.

According to the invention there is provided a method of controlling the current on a load circuit of an HFAC system, the HFAC system a driver circuit comprising an LC resonant bridge circuit and a primary inductor inductively coupled to the load circuit, the driver circuit having a variable capacitance and comprising a resonant circuit detector configured to indicate the LC resonant bridge circuit voltage, the method comprising controlling the variable capacitance in response to the resonant bridge circuit voltage.

There is also provided a computer program configured to instruct an HFAC system comprising a driver circuit having variable capacitance and a load circuit to 20 carry out the method as described above.

Figure 1 depicts a power distribution system according to an embodiment of the invention; Figure 2 depicts a device driver coupled to a power bus of a load circuit; Figure 3 depicts a schematic diagram of the power circuit according to an embodiment of the invention; Figure 4 depicts a resonant tank and primary inductor according to an embodiment of the invention; and Figure 5 depicts a power factor correction circuit according to an embodiment of the invention; and Figure 6a depicts a half bridge according to an embodiment of the invention; Figure 6b depicts a full bridge according to an embodiment of the invention; and Figure 7 depicts a power detector; and Figure 8 depicts a power distribution system with a plurality of load circuits.

Figure 1 of the accompanying drawings depicts a power distribution system 1 according to an embodiment of the invention. The power distribution system comprises a power circuit 2, a controller 4 and a load circuit 3. The input power is from an AC source such as mains electricity, a generator or renewable sources such as solar, wind or wave. The input power is supplied to the power circuit which then modifies the electrical waveform. The power circuit and the load circuit are inductively coupled by a transformer with the primary inductor 5 on the power circuit and the secondary conductor 6 on the load circuit. The load circuit comprises a power bus 8 which is formed by a loop of insulated wire. The wire of the loop may be arranged as side by side wires and does not need to be twisted. Along the power bus are a plurality of device drivers 10 for peripheral devices. The peripheral devices may be, for example, lights, sensors, battery chargers, audio devices, cameras, irrigation devices, motors. Arranged on the load circuit is also a load detector 7 which is used to detect characteristics of the electrical signal on the power bus. The load detected may detect one or more of the current, the voltage, the power, the frequency, noise and/or the waveform on the power bus. The load detector transmits details of the electrical signal to the controller 4 which then controls variables of the power circuit to ensure that the electrical signal on the load circuit remains stable and within acceptable boundaries ensuring optimal performance under all load and line conditions. The load detector may be connected to the controller either by a wire or wirelessly and may be built into the power supply. The controller may be a digital signal processor (DSP), a microcontroller or a FPGA.

In addition to being in communication with the load detector 7 the controller 4 may be controlled by a user wirelessly using RF, encrypted RF, Bluetooth or VViFi devices. The user may be able to specify operating conditions such as operating frequency and power levels. -12-

Figure 2 depicts a device driver 10 according to the invention inductively coupled to the power bus 8. The power bus provides the primary coupling and a coil of wire 12 provides the secondary coupling. To concentrate the magnetic flux an iron core 11 forms a loop around a portion of the power bus and through the centre of the coil of wire 12. The current induced in the wire coil 12 is used to power a peripheral device.

Figure 3 depicts a power circuit 2, or supply, according to an embodiment of the invention. In this example the power supply is fed by an alternating current, for example a mains power supply at 50Hz and 240V. The power is input into a power factor correction (PFC) circuit 40 which converts the alternating current to DC power at, for example, 400V. Coupled to the PFC circuit is a DC to AC converter 30 with variable clock frequency or sync pulse and variable deadtime control. The alternating current is fed to the resonant tank 20 and a primary inductor. The primary inductor 5 forms part of a transformer with a coil 6 on the load circuit and generates an alternating current at a high frequency on the load circuit 3. As described below the frequency of the HFAC circuit can be varied in the range 10kHz to 350kHz. The system can provide power of up to 1kW at 0.1- 3A and voltages from zero to 450V AC.

HFAC systems have an optimal operating current. However, when conditions vary, such as different loads, the current will vary resulting in suboptimal operating conditions. In this novel HFAC system elements of the power circuit can be varied such that the load circuit continues operating at the desired, optimal frequency. This also ensures that the alternating current is a pure sinusoidal wave. Three different elements of the power circuit can be varied to adjust the current on the load circuit: the resonance of the resonant tank; the PFC, in particular adjusting the output voltage of the PFC; and adjusting the frequency of the DC to AC converter. The current on the load circuit is detected by the load detector and this is used as an input to determine how the different elements of the power circuit are controlled. Although the current is often used, the voltage could alternatively be determined and used as an input to the controller. The -1..) -different elements of the power circuit (the resonance of the resonant tank, the PEG and the frequency and deadtime of the DC to AC converter) can also be adjusted to optimise the efficiency of the system.

Figure 4 depicts the resonant tank 20 and primary inductor 5. The resonant tank 20 is formed by an LLC circuit with a first inductor 21 and a second inductor 22 and some capacitance. In parallel with the primary inductor 5 is a first variable capacitance 23. In the present embodiment this is formed by a plurality of capacitors in parallel. Different capacitors can be connected or disconnected from the first capacitance by either a switch or a metal-oxide-semiconductor field-effect transistor (MOSFET) (not depicted). In addition to the first variable capacitance 23 there is also a second variable capacitance 24 which is in parallel with the first inductor 21 and the primary inductor 5. Again, different capacitors may be connected or disconnected from the arrangement to give different levels of capacitance.

In the present embodiment the controller 4 is formed by a digital signal processor (DSP) and the DSP controls the variable capacitance levels of both the first 23 and second 24 variable capacitances. The first variable capacitance 23 may have a range of 0-100nF, with a typical value in use of 33nF. The second capacitance 24 is greater, and has a range of 10-330nF with a typical value in use of 100nF. If the load detector 7 (on the load circuit 3) detects an increase in current due to, for example, peripheral devices being removed from the load circuit, or power demand reducing, the digital controller DSP (not depicted in Figure 4) will decrease the variable capacitance of the first variable capacitance 23. This changes the resonance of the resonant tank to decrease the current on the load circuit. There is therefore decreased power transmitted across the transformer and the current on the load circuit remains stable and within specification. Conversely, if the load detector 7 detects a decrease in current due to, for example, additional peripheral devices 10 being added to the load circuit, or power demand increasing, the DSP will increase the capacitance of the first variable capacitance 23 so that the resonance of the resonant tank is changed and the amount of power transmitted across the transformer is increased. The first -14-variable capacitance may be varied because the current changes such that it is out of specification as determined by the DSP. The first variable capacitance can then be varied and the current brought back into specification and remains stable.

A system will have a desired operating current, for example 1.5A and if the current varies from this because of an increase or decrease in load on the load circuit the system adjusts (by, inter alia, adjusting the resonance of the resonant tank) so that the current remains at the optimal current. Closely monitoring and controlling output current in this way ensures that output current remains within safe, specification levels. Thus the current is regulated and potentially dangerous power levels on the HFAC bus are avoided.

If the load detector 7 (on the load circuit) detects noise, or a small variation in current on the load circuit the DSP 4 will vary the capacitance of the second capacitance 24. For example, if there is a small increase in load current, resulting from noise then the second capacitance may be decreased. If there is a small decrease in load current resulting from noise then the second capacitance may be increased.

Thus the first capacitance 23 is used to control current in response to large changes in load on the load circuit or excessive noise being produced on the HFAC bus due to a load change and the second capacitance 24 is used to respond to smaller changes, or noise, on the load circuit. The power circuit is therefore controlled to respond to changes on the load circuit to ensure that the electrical signal remains stable and is always optimised.

To control the variable capacitance of the resonant tank the load detector typically detects the current and/or the noise on the load circuit. However, a similar result can be achieved by detecting the voltage across the load circuit.

As an alternative, or in addition to using the load (in particular the current) detected on the load circuit as an input to control the resonant frequency of the resonant tank, the current of the resonant tank can be detected. A capacitor is -15 -used as part of the resonant tank detector, and may have a value of 220pF. The current from the resonant tank is rectified 27 and filtered 28 to convert to DC voltage. This DC voltage reflects the current in the resonant tank and gives a very accurate representation of the resonant current. This feature provides a more accurate way of detecting whether the current is at the desired level. For example, a 50mV DC voltage may indicate a 1.5A resonant current and a 25mV DC voltage may indicate a 0.75A resonant current. The DC voltage can be output to the DSP which determines whether the capacitance of the resonant tank needs to be varied to ensure that the resonant current is at the desired level.

Figure 5 depicts a power factor correction circuit 40 according to an embodiment of the invention. In the present example a Bi-Directional continuous conduction mode (CCM) Totem Pole bridgeless PFC with interleaved phases is used, it using a PFC microcontroller and GaN switching devices. In this example, the PFC has three phases each of which is formed by two GaN power devices, or MOSFETS, and an inductor. When the load detector detects low currents (and therefore low loads) the controller controls the PFC, via a microcontroller 45 such that only phase 1, comprising two MOSFETS 411 421 and an inductor 431 is connected. To increase the output voltage of the PFC a greater current is transmitted through the switching devices 411 421. When a larger PFC output voltage is needed a larger current is run through these switching devices. When the load detector detects a medium level of current (and therefore medium loads) the microcontroller controls the PFC such that both phase 1 and phase 2 are connected. Phase 2 comprises two MOSFETS 412 422 and an inductor 432.

When the load detector detects a high level of current (and therefore high loads) the microcontroller controls the PFC such that all three phases are connected. The third phase comprises two MOSFETS 413 423 and an inductor 433. The use of a plurality of phases results in increased efficiency at high load and reducing phases as the load drops results in higher efficiency at light loads. As an alternative to GaN devices equivalent Silicon devices could also be used. -16-

The PFC voltage adjustment is a method of coarse HFAC output current control. 300V DC from the PFC may be configured to provide 0.5A on the power bus of the load circuit and 425V may provide 2.5A.

This allows for coarse adjustment of the output current on the load circuit.

Therefore the positive rail voltage of the PFC can be automatically adjusted between 300V and 450V. Although the arrangement depicts a phase shedding arrangement, for power distribution systems with smaller loads a simpler, non-phase shedding arrangement may be used.

When the load detector detects an increase in the current on the load circuit the DSP will control the PFC, via the PFC microprocessor 45, to adjust the PFC voltage as described above. The PFC voltage is regulated via a feedback loop 44 to ensure that it is at the right level (i.e. the level specified by the DSP). To regulate the voltage the PFC output voltage is monitored, averaged and filtered to eliminate the noise from the signal within software. The computed average is then compared to a reference voltage in the PFC microprocessor and the PFC output regulated by adjusting the current through the switching devices, as described above. This feedback loop ensures that the PFC voltage is at the desired output for the current required. The PFC voltage regulation loop is assumed to provide the power reference of the output of the PFC. The power reference is divided by the square of the line voltages root mean square (RMS) to provide the conductance, which is further multiplied by the line voltage giving the instantaneous current command.

As an alternative feedback loop an error amplifier or operational amplifier could be used by computing a reference voltage to a proportion of the PFC output voltage and maintaining a fixed value for the microprocessor to use to control the current through the PFC output stage.

The PFC 40 may have an input of between 85V and 275V at 47-450Hz. The present example has an input of 240V and 50Hz and it outputs a DC signal which may vary between 300V and 425V according to the load on the load circuit. -17-

In this way the power on the load circuit can be controlled and, due to the phase shedding, the efficiency is closely monitored and controlled.

The boost PFC depicted in Figure 5 is illustrative and other variants of a 5 PFC may be used. Although the PFC described here is a bridgeless boost PFC circuit, for smaller loads a buck PFC could also be used As an alternative to a bridgeless PFC a bridge rectifier may be used.

Figure 6a depicts a half bridge circuit which converts the DC voltage into an AC current. As can be seen, there are two switching elements 31,32 which are, in the present embodiment transistors. The timings for the transistors are controlled by a synchronisation pulse generated by the DSP 4. The synchronisation pulse switches the different transistors on and off to generate an alternating current through the output. If the synchronisation pulse increases the transistors will be switched at a greater frequency and the output frequency, and therefore also the frequency on the load circuit (the HFAC frequency), increased.

The DSP can therefore control the HFAC frequency. The frequency may be adjusted because the user has specified a particular operating frequency. This may be via an interface with the DSP, either wirelessly or on site. The frequency may also be adjusted to control the power transmitted. If an increased load is detected on the load circuit, by detecting a decrease in the current, the frequency is increased. If a decreased load is detected the frequency is decreased.

The synchronisation signal includes not just a clock signal but on and off times for each of the transistors. Therefore, in addition to controlling the output frequency, the DSP also controls the dead time (or pulse width modulation) of the half bridge circuit. This may be in response to the frequency changing but it may also be in response to a change in the current on the load circuit which has resulted in the DC voltage from the PFC changing. If the DC voltage increases (in response to the current on the load circuit changing) the dead time of the half bridge may be increased. This is a safety measure to prevent a short circuit. Conversely, if the DC voltage decreases the dead time of the half bridge may be -18-decreased to keep the circuit as efficient as possible. The load detector 7 detects the voltage, or load on the load circuit and the DSP adjusts the synchronisation signal to adjust the dead time of the half bridge accordingly.

The automatic clock frequency and deadtime control offer extremely high levels of efficiency and stability of the HFAC sine wave as the load increases or decreases under both short and long cable lengths.

The synchronisation can also be used to facilitate on-the-fly synchronisation across multiple power supplies. For this the synchronisation pulse would be used across multiple power supplies.

Figure 6b depicts a full bridge circuit which can be used as an alternative to the half bridge depicted in Figure 6a. The full bridge comprises four switching elements 31, 32, 33, 34. In an alternative embodiment both a full and half bridge can be present with the full bridge being used at high power (for example above 500W) and the half bridge being used at low power (for example up to 500W).

Although Figures 4, 5 and 6 each depict different elements of the power circuit which can be adjusted independently each element described in conjunction with figures 4, 5 and 6 can be adjusted in combination with one or more of the others. For example the variable capacitance of the resonant stage (described in conjunction with Figure 4) may be adjusted and controlled in combination with the power factor correction circuit (described in conjunction with Figure 5). This may also be done in combination with control of the frequency and dead time in the half bridge circuit. This arrangement gives the optimum control of the frequency and current in the load circuit.

The system may have an optimum operating current but the system may also have a range of operating currents, for example 0.1-2.5A. Different current values may be used in different scenarios. For example, the user may want a lower current value when lower power is required or a higher current value when a higher power is required. The system would then operate to keep the current at -19-this value such as by adjusting the capacitance, frequency or operation of the PFC as described above.

The load detector may detect a plurality of characteristics of the load circuit.

Although the current can be detected and used as an input for the DSP, the voltage or power of the load circuit could also be used as an alternative input for the DSP. The load detector 7 may also detect the the total harmonic distortion (THD) of the output waveform on the load circuit. The THD of the output waveform indicates the level of noise in the electrical signal. The total harmonic distortion may also be used as an input for the DSP to adjust the characteristics of the power circuit. Often the current is used for coarse adjustments to the power circuit: for example as an input to adjust the first capacitance, the operating frequency and large adjustments to the output voltage of the PFC. The THD may then be used as an input to make finer adjustments to the characteristics of the power circuit: for example as an input to adjust the second capacitance, finer adjustments to the operating frequency and finer adjustments to the output voltage of the PFC.

Through the detection of total harmonic distortion/noise, standing waves can be detected and the controller can adjust elements of the power circuit to reduce and eliminate undesirable standing waves.

It is through control of noise and standing waves that side by side wires, rather than twisted wires can be used. The use of side by side wires, rather than twisted wires facilitates a considerably simpler-to-use system.

The load detector 7 may be any detector capable of detecting one or more of the current, load, power and THD of the load circuit. An illustrative load detector is depicted in Figure 7.

To ensure that the temperature of the system remains within safe limits, there may also be one or more temperature sensors arranged on or around the system These can be connected to the DSP either wirelessly or via a wired -20 -connection, but in the preferred embodiment are built in to the power supply. The temperature sensors may include an internal ambient temperature sensor, an external ambient temperature sensor, a PFC power stage temperature sensor, a PFC inductor temperature sensor, an output stage temperature sensor, a transformer temperature sensor and/or resonant inductor temperature sensors. Each of these temperatures may be recorded over time and for each power load so can be used as a reference. As the operating conditions of different power systems will be different, the system may use the past data (for example using artificial intelligence) to set a normal operating temperature range for the system.

This can provide an early warning to a user: for example, if the temperature is outside a predetermined range the user may be alerted. In addition to, or as an alternative to a user alert the system may also adjust the system to ensure that the temperature remains within safe limits. For example, if the system is overheating it may reduce the power transmitted to the load circuit. This may be achieved by reducing the operating frequency (by adjusting the synchronisation pulse as described in conjunction with Figure 6), by reducing the capacitance of the resonant tank (by either the first capacitance or the second capacitance) or by adjusting the output voltage of the PFC. Thus the system reduces the power to avoid the system overheating and breaking down and provides predictive failure alerts.

As described above, the load detector 7 may comprise a power sensor to measure the power on the load circuit. This can be used as a safety feature to prevent the system operating outside safe limits. A given system will have a given operating range, for example up to 400W. If the detected power is greater than this range the user may receive an alert. The user could then either reduce the number of peripheral devices on the system or the system could reduce the power transmitted to the load circuit (by the methods described above) such that, for example the lights are made dimmer. Alternatively or additionally to alerting the user, the DSP may automatically reduce the power transmitted to the load circuit.

The power sensor may also be used as a control for the system. As described above, a user may specify a particular power. For example, a user may -21 -wish that there is greater power during the day (for brighter lights) and less power at night, or vice versa. The system can adjust the power supplied by using any of the ways described above such that the power is at a specified value, or within a specified range, which can be measured by the power sensor.

The system provides a method of anticipating and predicting when failure may occur. The system may monitor the current, power, frequency or temperature For each of these variables there may be an operational range. Alternatively or additional, the system may record the values over time to be used as a reference. If one of these values is out of the operational range, or out of the usual range the controller may transmit an alert to a user. The user can therefore reduce the power of the system, switch it off or take any other necessary action. Alternatively or additionally to a user alert the controller may control features of the system to reduce the power and/or current to avoid catastrophic failure.

When not in active use (i.e. no peripheral devices) the system may be put into a sleep mode to conserve power. In a sleep mode the operating frequency would be increased to a value between 33kHz and 150kHz. The load detector may detect (either by detecting the current or the power) that there are no loads on the power bus and the controller 4 may then put the system into a sleep mode by a variety of power saving modes including disabling the half bridge circuit and disabling the PFC.

Due to the improved control of the current and power in the load circuit the system is much more efficient. Power is not lost when there is no load as the circuit can automatically adjust. The sleep mode enables further efficiency and power savings to be made.

Figure 8 depicts a power distribution system with a plurality of load circuits 301 302, 303. As can be seen, for each load circuit there is a separate DC to AC converter 30, resonant tank 20 and primary inductor 5. Each load circuit has a controller 4 and a load detector 6 to detect the load on the individual circuit. The variables of the PFC circuit and the different DC to AC converters and resonant -22 -tanks are controlled by the respective controller 4. As each load circuit may have different loads, the power transmitted to each load circuit can be individually controlled and each load circuit can operate at a different frequency. However, when there are a plurality of load circuits it is desirable to synchronise the frequencies across the different load circuits so a synchronisation signal can be transmitted between the controllers of the different load circuits. As an alternative to different controllers for different load circuits a single controller could be used.

Parameters In the load circuit various parameters are detected; input and output voltage, input and output power, input and output current, resonant tank voltage, temperature, power factor correction voltage and periodic and random deviation. Based upon these monitoring functions, the controller adjusts the HFAC power supplies output in real time, adjusting output frequency, resonant capacitance and frequency, and output current to maintain the highest possible efficiency at all load conditions and output waveform signal integrity. Thus the frequency, voltage, current and power limit of the AC current can be adjusted and hence also the frequency of the power bus can be adjusted and controlled by the controller.

The table below indicates some of the different variables which may be detected, together with the features which may be adjusted and the resulting effects.

Variable Ad ust Effect Load circuit current Capacitance of resonant tank Adjusts load circuit Monitor drift from current and voltage specified target value Intended load circuit PFC output voltage Adjusts load circuit current adjustment current Load circuit frequency Synchronisation pulse which adjusts half bridge HFAC output frequency clock or pulse width modulation PFC output Voltage PFC Feedback loop Load circuit current adjustment Temperature Any one or more of PFC, synchronisation pulse, or capacitance of resonant tank Reduce power to safe limits Resonant tank Capacitance of resonant tank Load circuit current and noise control Load circuit power Any one or more of PFC, synchronisation pulse, or capacitance of resonant tank Control of maximum power Furthermore, the software is able to detect standing wave problems should they arise for any reason and take appropriate action to eliminate them, by adjusting the frequency, variable capacitance of the resonant tank, PFC voltage, or a combination thereof.

In addition, within the preferred embodiment, the HFAC power supply may be configured by a user to conform to separated or safety extra-low voltage (SELV) requirements, whereby the HFAC power supply will modify its output current and power capabilities to maintain operation to SELV requirements on the HFAC output power bus. This innovative mode of operation and the low voltages produced may facilitate compliance with extra low voltage standards such as SELV, further facilitating safe and user-friendly installations, without the need for specialised installers or qualified electricians.

With the use of SELV then even in jurisdictions with legal restrictions on domestic power supplies a householder will be able to manage a DIY electrical -24 -installation. When coupled with inductively connected loads this provides a system that is spark and arc free even in fault conditions.

The present invention provides a waterproof power transmission system due to the inductive power transmission. Thus it can be used in and around pools, boats, waterways and the sea.

The system is also compatible with, and can be controlled by, a smart home device such as Alexa or Google home. Thus a user can control the lighting by giving instructions to the smart home device.

The preferred embodiment is designed to be implemented for powering HFAC powered wireless power transmitters, facilitating the wireless charging of wearable and other low power devices, ear pods, watches, game controllers, fitness bands, health monitors etc up to 20 feet away from the power supply and installed loads. It is envisaged within the preferred invention, HFAC distribution also enables the use of HFAC powered Li-Fi enabled devices, particularly advantageous as the HFAC output cables can now extend greater than 400m cable length with no standing wave issues.

It is envisaged the preferred invention will over time power many common items, with everyday items being powered by HFAC as opposed to mains AC power. This will enable many everyday products to realise the safety HFAC provides. Due to the high Power Factor of the HFAC output everyday products such as televisions may use new power architecture, eliminating the traditional use of Power Factor Correction, further saving product build cost; as the efficiency is therefore inherently higher, further costs may be realised in the reduction of consumer utility bills and a reduction of the power generated further reducing greenhouse gasses.

Various further aspects and embodiments of the present invention will be apparent to those skilled in the art in view of the present disclosure.

-25 - "and/or" where used herein is to be taken as specific disclosure of each of the two specified features or components with or without the other. For example "A and/or B" is to be taken as specific disclosure of each of (i) A, (ii) B and (iii) A and B, just as if each is set out individually herein.

Unless context dictates otherwise, the descriptions and definitions of the features set out above are not limited to any particular aspect or embodiment of the invention and apply equally to all aspects and embodiments which are described.

It will further be appreciated by those skilled in the art that although the invention has been described by way of example with reference to several embodiments. It is not limited to the disclosed embodiments and that alternative embodiments could be constructed without departing from the scope of the invention as defined in the appended claims.

-26 -

Claims

CLAIMS: 1. A high frequency AC power supply comprising a power circuit, a load circuit and a controller, the power circuit and the load circuit being inductively coupled, the load circuit comprising a load circuit detector configured to detect the electrical signal on the load circuit and the power circuit comprising: a power factor correction circuit; a DC to AC converter; an LC resonant bridge circuit; wherein the controller controls the DC to AC converter in response to the electrical signal on the load circuit.
2. A power supply according to claim 1 wherein the DC to AC converter comprises a half bridge and controlling the DC to AC converter comprises adjusting the clock frequency of the half bridge.
3. A power supply according to any one of the preceding claims wherein the controller comprises a digital signal processor, microcontroller or FPGA.
4. A power supply according to claim 3 wherein the controller generates a synchronization pulse which is output to the half bridge and used as the input for the clock frequency of the half bridge.
5. A power supply according to any one of the preceding claims wherein a synchronization pulse from the controller controls the deadtime of switching elements in the DC to AC converter.
6. A power supply according to any one of the preceding claims wherein the load is measured by measuring one or more of the voltage of the load circuit, the current of the load circuit, the frequency of the load circuit or the power of the load circuit.
-27 - 7. A power supply according to any one of the preceding claims wherein the clock frequency of the half bridge is adjusted in response to a load detected on the load circuit detected by the detected electrical signal.
8. A power supply according to any one of the preceding claims wherein the load detector is configured to detect the total harmonic distortion the output waveform.
9. A power supply according to any one of the preceding claims wherein the load circuit comprises a pair of side by side wires.
10. A power supply according to any one of the preceding claims wherein load circuit has a variable frequency of 10kHz to 350kHz.
11. A power supply according to any one of the preceding claims wherein the input frequency of the power circuit is between 10Hz and 500Hz.
12 A power supply according to any one of the preceding claims wherein the load circuit is controlled to within safety extra low voltage standards.
13. A power supply according to any one of the preceding claims wherein the controller is controllable through RE, encrypted RE, Bluetooth or WiFi devices.
14. A power supply according to any one of the preceding claims further comprising one or more peripheral devices inductively coupled to the load circuit, and powered by the high frequency AC power supply.
15. A power supply according to any one of the preceding claims further comprising a plurality of load circuits each with a means for detecting the load on the load circuit, a plurality of DC to AC drivers, a plurality of LLC resonant bridge circuits with each load circuit being coupled to a separate LLC resonant circuit through a different transformer and wherein the DC to AC converter is controlled in response to the electrical signal on the respective load circuit.
-28 - 16. A power supply according to any one of the preceding claims wherein the power factor correction circuit comprises a bridgeless power factor correction circuit.
17. A power supply according to any one of the preceding claims wherein the current on the load circuit is 0.1-2.5A.
18. A power supply according to any one of the preceding claims wherein the load on the load circuit is up to 1KW.
19. A power supply according to any one of the preceding claims wherein the AC to DC converter comprises a half bridge or full bridge.
20. A power supply according to any one of the preceding claims wherein the controller is configured to control the variable capacitance in response to the detected electrical signal on the load circuit.
21. A power supply according to any one of the preceding claims wherein the LC resonant bridge circuit forms part of a driver circuit together with a primary inductor inductively coupled to the load circuit, the driver circuit having a variable capacitance and comprising a resonant circuit detector configured to indicate the LC resonant bridge circuit voltage, wherein the controller is configured to control the variable capacitance in response to the resonant bridge circuit voltage.
22. A power supply according to any one of the preceding claims wherein the controller is configured to control the power factor correction circuit in response to the detected electrical signal on the load circuit.
23. A method of controlling the current on a load circuit of an HFAC system, the HFAC system comprising DC to AC circuit, the method comprising controlling the DC to AC converter in response to the electrical signal on the load circuit.-29 -
24. A computer program configured to instruct an HFAC system comprising a having a DC to AC converter and a load circuit to carry out the method according to claim 23. -3 -