EP4222015A1

EP4222015A1 - A transformer with split winding circuitry for an electric vehicle

Info

Publication number: EP4222015A1
Application number: EP21786434.7A
Authority: EP
Inventors: Vishnu KURUP; Hui Zhu; Manoj Choudhary; Chinmaya JOSHI; Tobias BURGSTALLER; John Stamford
Original assignee: Jaguar Land Rover Ltd
Current assignee: Jaguar Land Rover Ltd
Priority date: 2020-09-30
Filing date: 2021-09-30
Publication date: 2023-08-09
Also published as: GB202015449D0; GB2599386A; WO2022069666A1

Abstract

A transformer circuit (100) for an electric vehicle comprises an input (104); an output (106); and a transformer (108) located between the input (104) and the output (106). The transformer (108) comprises a primary winding (110) connected to the input (104); and a secondary winding (102) connected to the output (106). At least one of the primary winding (110) and the secondary winding (102) comprises a first split winding (112) and a second split winding (114). The circuit (100) comprises switching means (116) configured to selectively connect the first (112) and second (114) split windings in series or in parallel in the circuit. Where the primary winding comprises the first split winding and the second split winding, the windings are connected to the input. Where the secondary winding (102) comprises the first split winding (112) and the second split winding (114), the windings (112, 114) are connected to the output (156).

Description

A TRANSFORMER WITH SPLIT WINDING CIRCUITRY FOR AN ELECTRIC VEHICLE

TECHNICAL FIELD

The present disclosure relates to circuitry for an electrical vehicle. Aspects relate to a transformer circuit, to a control system, to a system, to a vehicle, to a method, and to computer software.

BACKGROUND

Electric vehicles and hybrid electric vehicles comprise traction motors, and traction batteries for supplying electrical energy to the traction motors. Some traction batteries can be recharged with electrical energy from outside the vehicle, such as electrical energy from an electrical grid. DC-DC and OBC (on-board charger) circuitry in electric vehicles are generally of fixed voltage output. However, in electric car designs, there may be multiple voltage outputs depending on the systems inside the car. Examples include: drive inverters which operate at 400V, advanced driver assistance systems (ADAS) at 12V / 48V and a HV battery may charge at 800V. So, for every new system design, if the voltages change from what has been used in a previous design, a new design/type of voltage converter is required per different voltage. This may be achieved by using multiple DC-DC converters inside the vehicle, which undesirably contribute to an increasing complexity, and cost, of the electrical architecture of the vehicle. It is an aim of examples disclosed herein to address one or more of the disadvantages associated with the prior art.

SUMMARY OF THE INVENTION

A possible solution to the above-mentioned problems may be one system that can dynamically adjust its voltage outputs depending on which electrical system it is serving. This may provide a flexible and re-configurable electrical system, which may be initially designed and delivered, but can then be used in different applications and in various configurations of the vehicle. Improving the flexibility of the electrical circuitry to provide different output voltages may be desirable, in particular in the automotive industry, where it is desirable to use common designs for electrical circuitry. This may allow for lower manufacturing and design costs and labour, and still provide a flexibility in electrical configuration for application for different vehicles, i.e. for different customers and markets. Such a system may, for example, supporting both 800V and 400V traction systems. Such a system may, for example, support both LV (low voltage) and HV (high voltage) systems simultaneously.

Aspects disclosed herein provide a transformer circuit, a control system, a system, a vehicle, a method, and computer software, as claimed in the appended claims.

In an aspect there is provided a transformer circuit for an electric vehicle, the circuit comprising: an input for receiving electrical energy; an output for providing electrical energy to an electrical bus; a transformer located between the input and the output, the transformer comprising: a primary winding connected to the input; and a secondary winding connected to the output, wherein at least one of the primary winding and the secondary winding comprises a first split winding and a second split winding; and switching means configured to: where the primary winding comprises the first split winding and the second split winding, selectively connect the first split winding and the second split winding to the input in series to accept a first input voltage, and connect the first split winding and the second split winding to the input in parallel to accept a second input voltage; and where the secondary winding comprises the first split winding and the second split winding, selectively connect the first split winding and the second split winding to the output in series to provide a first output voltage, and connect the first split winding and the second split winding to the output in parallel to provide a second output voltage.

Where the primary winding comprises the first split winding and the second split winding, the second input voltage may be substantially half of the first input voltage. Where the secondary winding comprises the first split winding and the second split winding, the second output voltage may be substantially half of the first output voltage.

The first and second split windings may each be configured to carry substantially the same current.

The transformer circuit may comprise an input selection switch connected to the switching means, wherein the input selection switch may be configured to: where the primary winding comprises the first split winding and the second split winding, connect the first split winding and the second split winding to the input in series to accept the first input voltage, and connect the first split winding and the second split winding to the input in parallel to accept the second input voltage; and where the secondary winding comprises the first split winding and the second split winding, connect the first split winding and the second split winding to the output in series to provide the first output voltage, and connect the first split winding and the second split winding to the output in parallel to provide the second output voltage.

The first split winding may be formed of first wire/cable, the second split winding may be formed of second wire, and the first wire may be substantially a same thickness (e.g. diameter) as the second wire.

The first split winding may have substantially a same number of turns as the second split winding.

The transformer circuit may be configured to operate at one or more of: a high voltage at the input; and a high voltage at both the input and the output; wherein the high voltage is between 60 V and 1500 V DC.

Between 60 V and 1500 V DC may be considered equivalent to between 30 V and 1000 V AC root mean square (rms).

The switching means may comprise three switches configured to: where the primary winding comprises the first split winding and the second split winding, connect the first split winding and the second split winding to the input in series based on receipt of a high logic signal by the switching means and connect the first split winding and the second split winding to the input in parallel based on receipt of a low logic signal by the switching means; and where the secondary winding comprises the first split winding and the second split winding, connect the first split winding and the second split winding to the output in series based on receipt of a high logic signal by the switching means and connect the first split winding and the second split winding to the output in parallel based on receipt of a low logic signal by the switching means.

In examples in which the primary winding comprises the first split winding and the second split winding, the first input voltage may comprise a nominal voltage in the range 600V to 1000V when the first split winding and the second split winding are connected to the input in series, and the second input voltage may comprise a nominal voltage in the range 300V to 500V when the first split winding and the second split winding are connected to the input in parallel.

In examples in which the secondary winding comprises the first split winding and the second split winding, the first output voltage may comprise a nominal voltage in the range 600V to 1000V when the first split winding and the second split winding are connected to the output in series, and the second output voltage may comprise a nominal voltage in the range 300V to 500V when the first split winding and the second split winding are connected to the output in parallel.

The transformer circuit may be configured to provide a low voltage output. A low voltage may be defined as a working voltage of 50 V DC or lower.

In examples in which the secondary winding comprises the first split winding and the second split winding, the first output voltage may comprise a nominal first low voltage in the range 30V to 50V (e.g. 36V or 48V) when the first split winding and the second split winding are connected in series to the output, and the second output voltage may comprise a nominal second low voltage in the range 5V to 28V (e.g. 12V or 24V) when the first split winding and the second split winding are connected in parallel to the output. The nominal second low voltage may be lower than the nominal first low voltage.

In examples in which the primary winding comprises a further first split winding and a further second split winding, the first input voltage may comprise a nominal voltage in the range 600V to 1000V when the first further split winding and the second further split winding are connected in series to the input, and the second input voltage may comprise a nominal voltage in the range 300V to 500V when the first further split winding and the second further split winding are connected in parallel to the input.

The secondary winding may be a split secondary winding comprising the first split winding, the second split winding, a third split winding and a fourth split winding. The switching means may be configured to selectively connect the first, second, third and fourth split windings to the output to provide first, second, third, and fourth voltages. The first, second, third and fourth secondary windings may each be configured to carry the same current. The transformer circuit may comprise an output selection switch connected to the switching means, wherein the output selection switch is configured to provide a logic signal to each of the split windings to selectively connect the first, second, third and fourth split windings to the output to provide first, second, third, and fourth voltages.

The primary winding may comprise a further first split winding and a further second split winding. The input voltage may comprise a nominal voltage in the range 600V to 1000V when the first further split winding and the second further split winding are connected in series to the output, and the input voltage may comprise a nominal voltage in the range 300V to 500V when the first further split winding and the second further split winding are connected in parallel to the output. In a further aspect there is provided a transformer circuit comprising a combination of circuits as disclosed herein, wherein the output of the first is connected to the input of the further circuit. An example is a circuit comprising a first circuit accepting a high voltage (e.g. 400V or 800V) connected to a second circuit providing a low voltage. In other words, there may be provided a transformer circuit for an electric vehicle, the circuit comprising: a first input for receiving electrical energy; a first transformer comprising: a first primary winding connected to the input; and a first split secondary winding comprising a first secondary winding and a second secondary winding; a first output for providing electrical energy to a second input of a second transformer; first switching means configured to selectively connect the first split secondary winding and the second split secondary winding to the first output in series to provide a first output voltage, and connect the first split secondary winding and the second split secondary winding to the first output in parallel to provide a second output voltage; the second input connected to the first output; the second transformer comprising: a split primary winding comprising a first split primary winding and a second split primary winding, wherein the first switching means is configured to selectively connect the first split primary winding and the second split primary winding to the second input in series to receive a first output voltage when the first secondary winding and the second secondary winding of the first split secondary winding are connected to the first output in series, or connect the first split primary winding and the second split primary winding of the split primary winding in parallel to the second input when the first secondary winding and the second secondary winding of the first split secondary winding is connected in parallel to the first output; and a second split secondary winding comprising at least a first secondary winding and a second secondary winding; a second output for providing electrical energy to an electrical bus; and second switching means configured to selectively connect the first secondary winding and the second secondary winding of the second split secondary winding to the second output in series to the second output, or connect the first secondary winding and the second secondary winding of the second split secondary winding to the second output in parallel to the second output.

One or more of the switching means and the input switching means may comprise a metal-oxide-semiconductor field-effect transistor (MOSFET), or other power device, such as an insulated-gate bipolar transistor (IGBT) or a bipolar junction transistor (BJT).

In a further aspect there is provided a control system for controlling a transformer circuit for an electric vehicle, the control system comprising one or more controllers, and the transformer circuit comprising: an input for receiving electrical energy; an output for providing electrical energy to an electrical bus; a transformer located between the input and the output, the transformer comprising a primary winding connected to the input and a secondary winding connected to the output, wherein at least one of the primary winding and the secondary winding comprises a first split winding and a second split winding; and switching means configured to: where the primary winding comprises the first split winding and the second split winding, selectively connect the first split winding and the second split winding to the input in series to accept a first input voltage, and connect the first split winding and the second split winding to the input in parallel to accept a second input voltage; and where the secondary winding comprises the first split winding and the second split winding, selectively connect the first split winding and the second split winding to the output in series to provide a first output voltage, and connect the first split winding and the second split winding to the output in parallel to provide a second output voltage wherein the control system is configured to control switching means of the circuit to: where the primary winding comprises the first split winding and the second split winding, selectively connect the first split winding and the second split winding to the input in series to accept a first input voltage, and connect the first split winding and the second split winding to the input in parallel to accept a second input voltage; and where the secondary winding comprises the first split winding and the second split winding, selectively connect the first split winding and the second split winding to the output in series to provide a first output voltage, and connect the first split winding and the second split winding to the output in parallel to provide a second output voltage.

The one or more controllers may collectively comprise at least one electronic processor having an electrical input for receiving information from one or more sensors and/or one or more external controllers; and at least one electronic memory device connected to the at least one electronic processor and having instructions stored therein; and wherein the at least one electronic processor is configured to access the at least one memory device and execute the instructions thereon so as to cause the control system to control the switching means in dependence on the information.

The control system may be configured to: where the primary winding of a transformer comprises the first split winding and the second split winding: receive information indicative of a requirement to connect the first split winding and the second split winding into the circuit in series, or connect the first split winding and the second split winding into the circuit in parallel; and connect, in dependence on the received information, the first split winding and the second split winding to the input; and where the secondary winding of a transformer comprises the first split winding and the second split winding: receive information indicative of a requirement to connect the first split winding and the second split winding into the circuit in series, or connect the first split winding and the second split winding into the circuit in parallel; and connect, in dependence on the received information, the first split winding and the second split winding to the output.

The switching means may comprise a plurality of switches, and the control system may be configured to control the plurality of switches to: connect the first split winding and the second split winding to the output in series based on receipt of a high logic signal by the switching means; and connect the first split winding and the second split winding to the output in parallel based on receipt of a low logic signal by the switching means.

In a further aspect there is provided a system comprising a control system as described herein and a transformer circuit as described herein.

In a further aspect there is provided a vehicle comprising any transformer circuit described herein, a control system as described herein, or a system as described herein.

In a further aspect there is provided a method of controlling a transformer circuit for an electric vehicle, the transformer circuit comprising: an input for receiving electrical energy; an output for providing electrical energy to an electrical bus; a transformer located between the input and the output, the transformer comprising a primary winding connected to the input and a secondary winding connected to the output, wherein at least one of the primary winding and the secondary winding comprises a first split winding and a second split winding; and switching means configured to: where the primary winding comprises the first split winding and the second split winding, selectively connect the first split winding and the second split winding to the input in series to accept a first input voltage, and connect the first split winding and the second split winding to the input in parallel to accept a second input voltage; and where the secondary winding comprises the first split winding and the second split winding, selectively connect the first split winding and the second split winding to the output in series to provide a first output voltage, and connect the first split winding and the second split winding to the output in parallel to provide a second output voltage the method comprising one or more of: where the primary winding comprises the first split winding and the second split winding, selectively connect the first split winding and the second split winding to the input in series to accept a first input voltage, and connect the first split winding and the second split winding to the input in parallel to accept a second input voltage; and where the secondary winding comprises the first split winding and the second split winding, selectively connect the first split winding and the second split winding to the output in series to provide a first output voltage, and connect the first split winding and the second split winding to the output in parallel to provide a second output voltage.

In a further aspect there is provided computer software that, when executed, is arranged to perform any method described herein. The computer software may be stored in a micro-controller, firmware, and/or on a computer readable medium. The computer software may be tangibly stored on a computer readable medium.

Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and/or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and/or features of any embodiment can be combined in any way and/or combination, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and/or incorporate any feature of any other claim although not originally claimed in that manner.

BRIEF DESCRIPTION OF THE DRAWINGS

One or more examples will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 a shows a portion of a transformer circuit having a split secondary winding according to examples disclosed herein;

Figure 1 b shows a portion of a transformer circuit having a split primary winding according to examples disclosed herein;

Figure 1c shows a portion of a transformer circuit having a split primary winding and a split secondary winding according to examples disclosed herein; Figure 2 shows a portion of a transformer circuit having a split secondary winding with schematic switching means according to examples disclosed herein;

Figure 3 shows a portion of a transformer circuit having a split primary winding with schematic switching means according to examples disclosed herein;

Figure 4 shows a portion of a transformer circuit having a first transformer with a split secondary winding, coupled to a second transformer having split primary and secondary windings according to examples disclosed herein;

Figure 5 shows a control system according to examples disclosed herein;

Figure 6 shows a system according to examples disclosed herein;

Figure 7 shows a vehicle according to examples disclosed herein;

Figures 8a-8b show methods of controlling a transformer circuit according to examples disclosed herein;

Figure 9 illustrates a circuit diagram of a transformer circuit having a split secondary winding according to examples disclosed herein;

Figure 10 illustrates a circuit diagram of a transformer circuit having a split primary winding according to examples disclosed herein; and

Figure 11 illustrates a circuit diagram of a transformer circuit having a split primary winding according to examples disclosed herein.

DETAILED DESCRIPTION

Examples disclosed herein may provide a flexible voltage output for use in an electrical vehicle. Certain examples may support both 800V and 400V traction systems. Having the capability to generate 400V or 800V at the On- Board Charger (OBC) output allows the vehicle (i.e. the vehicle's electrical systems) to be compatible with both 800V and 400V charging. This may be desirable so the battery of the vehicle may be charged at either a 400V supply or an 800V supply, and provide a 400V voltage to the vehicle circuitry. Allowing three phase input and single phase input depending on the available input also improves the flexibility of the electrical architecture of the vehicle. Allowing for bi-directional operation (i.e. allowing the battery of the vehicle to be charged, and allowing the charged stored in the vehicle battery to be used to power the vehicle) is desirable. It may also desirable to provide electrical circuity which does not require the use of electromechanical relays, although in some examples relays may be used.

Certain examples may support both LV (low voltage) and HV (high voltage) systems simultaneously. Having the capability to accept substantially 800V (e.g. a voltage between 650V to 850V) or substantially 400V (e.g. a voltage between 270V to 470V) at the same input allows for a flexible system capable of operating with different voltage requirements.

Examples discussed herein provide electrical topologies suitable for use with OBC and DCDC converters in the automotive industry, which may be advantageous so that existing systems can be altered rather than entirely new and different electrical topologies being required. Figure 1 a shows a portion of a transformer circuit 100 for an electric vehicle, in which the transformer circuit 100 has a split secondary winding 102. The circuit 100 comprises an input 104 for receiving electrical energy and an output 106 for providing electrical energy to an electrical bus. A transformer 108 is located between the input 104 and the output 106. The transformer 108 comprises a primary winding 110 connected to the input 104, and a secondary winding 102 connected to the output 106. In this example the secondary winding 102 comprises a first split winding 112 and a second split winding 114.

The circuit 100 also comprises switching means 116 configured to (in this example in which the secondary winding 102 comprises the first split winding 112 and the second split winding 114) selectively connect the first split winding 112 and the second split winding 114 to the output 106 in series to provide a first output voltage, and connect the first split winding 112 and the second split winding 114 to the output 106 in parallel to provide a second output voltage. In examples in which the secondary winding 102 comprises the first split winding 112 and the second split winding 114, the second output voltage may be substantially half of the first output voltage.

Figure 1b shows a portion of a transformer circuit 150 for an electric vehicle, the transformer 150 having a split primary winding 152. The circuit 150, as in Figure 1 a, comprises an input 154 for receiving electrical energy and an output 156 for providing electrical energy to an electrical bus. A transformer 158 is located between the input 154 and the output 156. The transformer 158 comprises a primary winding 152 connected to the input 154, and a secondary winding 160 connected to the output 156. 1 n this example the primary winding 152 comprises a first split winding 162 and a second split winding 164.

The circuit 150 also comprises switching means 166 configured to (in this example in which the primary winding 152 comprises the first split winding 162 and the second split winding 164) selectively connect the first split winding 162 to the input 154 in series to provide a first output voltage, and connect the first split winding 162 and the second split winding 164 to the output 106 in parallel to provide a second output voltage.

In examples in which the primary winding 152 comprises the first split winding 162 and the second split winding 164, the second input voltage may be substantially half of the first input voltage.

In the above examples of Figures 1 a-1 b, the first split winding 112, 162 may each be configured to carry substantially the same current. In some examples the first split winding 112, 162 may be formed of first wire, the second split winding 114, 164 may be formed of second wire, and the first wire 112, 162 may be substantially a same thickness of the second wire 114, 164. In some examples the first split winding 112, 162 may have substantially a same number of turns as the second split winding 114, 164. Thus, the first split winding 112, 162 may be configured to carry substantially the same current of the second split winding 114, 164.

The transformer circuit 100, 150 may be configured to operate at a high voltage at the input 104, 154, or at both the input 104, 154 and the output 106, 156. A high voltage may be defined as between 60 V and 1500 V DC in some examples. Between 60 V and 1500 V DC may be considered equivalent to between 30 V and 1000 V AC root mean square (rms). For example, the secondary winding 102 may comprise the first split winding 112 and the second split winding 114 as in Figure 1 a. The output voltage may comprise a nominal voltage in a first higher range, e.g. 600V to 1000V, or e.g. 650V to 850V, when the first split winding 112 and the second split winding 114 are connected in series to the output 106, and the output voltage may comprise a nominal voltage in a second lower range of e.g. 300V to 500V, or e.g. 270V to 470V, when the first split winding 112 and the second split winding 114 are connected in parallel to the output 106.

For example, the primary winding 152 may comprise the first split winding 162 and the second split winding 164 as in Figure 1b. The input voltage may comprise a nominal voltage in the range e.g. 600V to 1000V (or e.g. in the range 650V to 850V) when the first split winding 162 and the second split winding 164 are connected in series to the input 154, and the input voltage may comprise a nominal voltage in the range e.g. 300V to 500V (or e.g. in the range 270V to 470V) when the first split winding 162 and the second split winding 164 are connected in parallel to the input 154.

The transformer circuit 100, 150 may be configured to provide a low voltage at the output 106,156. A low voltage may be defined as a working voltage of 50 V DC or lower in some examples.

For example, as in Figure 1 a, where the secondary winding 102 comprises the first split winding 112 and the second split winding 114, the output voltage may comprise a nominal first low voltage in the range 30V to 50V (e.g. substantially 36V or substantially 48V) when the first split winding 112 and the second split winding 114 are connected in series to the output 106, and the output voltage may comprise a nominal second low voltage in the range 5V to 28V (e.g. substantially 12V or substantially 24V) when the first split winding 112 and the second split winding 114 are connected in parallel to the output 106. The nominal second low voltage (range) is lower than the nominal first low voltage (range). Of course, in other examples, a low output voltage may be provided by a transformer circuit which also comprises a split primary winding and/or which may comprise more than one transformer.

In some examples in which the secondary winding 102 comprises a first split winding 112 and a second split winding 114 and the output voltage is a low voltage (e.g. below 50V), the primary winding 152 may also comprise a further first split winding 162 and a further second split winding 164. This is illustrated in the circuit 180 in Figure 1c. The first input voltage may comprise a nominal voltage in the range e.g. 600V to 1000V, or e.g. 650V to 850V when the first further split winding 162 and the second further split winding 164 are connected in series to the input 154, and the second input voltage may comprise a nominal voltage in the range 300V to 500V, or e.g. 270V to 470V, when the first further split winding 162 and the second further split winding 164 are connected in parallel to the input 154. Switching in the first and second split windings 112, 114 of the secondary winding 102 may be performed by secondary switching means 116. Similarly, switching in the first and second further split windings 162, 164 of the primary winding 102 may be performed by primary switching means 166.

A low voltage output may be desirable for powering auxiliary electrical loads of a vehicle. For example, an auxiliary load may comprise a heater, a chiller, an air conditioning compressor, a power-assisted steering system, an active roll control pump, a suspension compressor, an in-vehicle device charging point, and a heated windscreen. An auxiliary load may be any other auxiliary device that may be converted from operating at 12V to operating at 400V. This could include a power inverter for providing alternating current (AC) for supplying domestic appliances.

Figure 2 shows a portion of a transformer circuit 100 having a split secondary winding 112, 114 with schematic switching means 116. As in Figure 1 a, the transformer circuit 100 comprises a transformer 108 located between the input 104 and the output 106, wherein the transformer 108 has a primary winding 110 connected to the input 104 and a split secondary winding 102 connected to the output 106. The split secondary winding 102 comprises a first split winding 112 and a second split winding 114.

The transformer circuits 100, 150, 180 of Figures 1 a-1 c may, in some examples comprise an input selection switch (not shown in the figures) connected to the switching means (e.g. in examples with a split primary winding 152, to switch in the first and second split primary windings 162, 164, and/or in in examples with a split secondary winding 102, to switch in the first and second split secondary windings 112, 114). Such an input selection switch may be configured to, where the primary winding 152 comprises the first split winding 162 and the second split winding 164, connect the first split winding 162 and the second split winding 164 to the input 104 in series to accept the first input voltage, and connect the first split winding 162 and the second split winding 164 to the input 104 in parallel to accept the second input voltage. Such an input selection switch may be configured to, where the secondary winding 102 comprises the first split winding 112 and the second split winding 114, connect the first split winding 112 and the second split winding 114 to the output 106 in series to provide the first output voltage, and connect the first split winding 112 and the second split winding 114 to the output 106 in parallel to provide the second output voltage.

Figure 2 shows a portion of a transformer circuit 100 having a split secondary winding 102 with schematic switching means 116 according to examples disclosed herein. Elements of the transformer 108 are as in Figure 1 a. The switches 118, 120, 122 are shown as general electronic switches in Figure 2. In some examples, the switching means (e.g. one or more of the switches 118, 120, 122) may comprise one or more MOSFETs , IBGTs or BJTs.

The switching means 116 in this example comprises three switches 118, 120, 122. These switches 118, 120, 122 are configured to connect the first split winding 112 and the second split winding 114 to the output 106 in series based on receipt of a high logic signal by the switching means 116 and connect the first split winding 112 and the second split winding 114 to the output 106 in parallel based on receipt of a low logic signal by the switching means 116.

Figure 3 shows a portion of a transformer circuit having a split primary winding with schematic switching means according to examples disclosed herein. Elements of the transformer 158 are as in Figure 1 b. The switches 168, 170, 172 are shown as general electronic switches in Figure 3. In some examples, the switching means (e.g. one or more of the switches 168, 170, 172) may comprise one or more MOSFETs, IGBTs or BJTs. The switching means 166 in this example comprises three switches 168, 170, 172. These switches 168, 170, 172 are configured to connect the first split winding 162 and the second split winding 164 to the input 154 in series based on receipt of a high logic signal by the switching means 166 and connect the first split winding 162 and the second split winding 164 to the input 154 in parallel based on receipt of a low logic signal by the switching means 166.

Figure 4 shows a transformer circuit 200 comprising a combination of circuits as disclosed herein, wherein the output of the first circuit is connected to the input of the further circuit and the output voltage provided by the first circuit is matched to the input voltage provided to the input of the further circuit. An example is a circuit 200 comprising a first circuit accepting a high voltage (e.g. 400V or 800V) connected to a second circuit providing a low voltage (e.g. under 50V output).

The transformer circuit 200 thus comprises a first input 104 for receiving electrical energy; a first transformer 108 comprising a first primary winding 110 connected to the input 104, and a first split secondary winding 102 comprising a first secondary winding 112 and a second secondary winding 114; a first output for providing electrical energy to a second input of a second transformer 258; and first switching means 116, 166. The first switching means 116, 166 is configured to selectively connect the first split secondary winding 112 and the second split secondary winding 114 to the first output in series to provide a first output voltage, and connect the first split secondary winding 112 and the second split secondary winding 114 to the first output in parallel to provide a second output voltage. The second input of the second circuit is connected to the first output of the first circuit. Therefore, for example, a high voltage of 400V or 800V may be provided by the first transformer 108.

The second transformer 258 comprises a split primary winding 152 comprising a first split primary winding 162 and a second split primary winding 164, wherein the first switching means 116, 166 is configured to selectively connect the first split primary winding 162 and the second split primary winding 164 of the split primary winding 152 to the second input in series to receive a first output voltage when the first secondary winding 112 and the second secondary winding 114 of the first split secondary winding 102 are connected to the first output in series, or connect the first split primary winding 162 and the second split primary winding 164 of the split primary winding 152 in parallel to the second input when the first secondary winding 112 and the second secondary winding 114 of the first split secondary winding 102 is connected in parallel to the first output. Thus the second transformer circuit can accept 400V or 800V depending on the voltage provided by the first transformer circuit. The first switching means 116, 166 is illustrated as two modules for comparison with the earlier described circuits. In some examples the first switching means may be two separate modules as shown, which are electrically connected for mutual combined operation. In some examples, the first switching means may be a single switching module connected between the first and second transformer circuits, for example to aid in providing control signals to control the switching of split windings 112, 114, 162, 164, at the secondary side of the first circuit and the primary side of these second circuit, since the voltage provided by the first circuit should match the voltage provided to the second transformer circuit. A second split secondary winding 202 of the second transformer 258 comprises at least a first secondary winding 212 and a second secondary winding 214 (but in other examples may comprise more than two secondary winding). A second output 206 of the circuit 200 is for providing electrical energy to an electrical bus. Second switching means 216 are present at the secondary side of the second transformer 258 and are configured to selectively connect the first secondary winding 212 and the second secondary winding 214 of the second split secondary winding 202 to the second output 206 in series to the second output, or connect the first secondary winding 212 and the second secondary winding 214 of the second split secondary winding 202 to the second output in parallel to the second output. For example, after receiving a high voltage of either 400V or 800V, the second transformer 258 may convert this to a low voltage of e.g. 24V or 48V, dependent on the switching configuration of the second switching means 216.

Figure 5 shows a control system 500 for controlling a transformer circuit for an electric vehicle as described above. The control system 500 comprises one or more controllers 508. The control system 500 is configured to control the switching means of a circuit as described to, where the primary winding comprises the first split winding and the second split winding, selectively connect the first split winding and the second split winding in parallel to the input, or connect the first split winding and the second split winding in series to the input; and where the secondary winding comprises the first split winding and the second split winding, selectively connect the first split winding and the second split winding in parallel to the output, or connect the first split winding and the second split winding in series to the output.

The one or more controllers 508 may collectively comprise at least one electronic processor 512 having an electrical input 502 for receiving information from one or more sensors and/or one or more external controllers; and at least one electronic memory device 510 connected to the at least one electronic processor 512 and having instructions stored therein. The at least one electronic processor 512 may be configured to access the at least one memory device 510 and execute the instructions thereon so as to cause the control system 500 to control the switching means in dependence on the information.

The control system 500 may be configured to, where the primary winding 152 of a transformer 158 comprises the first split winding 162 and the second split winding 164 as in Figure 1 b, receive information indicative of a requirement to connect the first split winding 162 and the second split winding 164 into the circuit in series, or connect the first split winding 162 and the second split winding 164 into the circuit in parallel; and connect, in dependence on the received information, the first split winding 162 and the second split winding 164 to the input 104. The control system 500 may be configured to, where the secondary winding 102 of a transformer 108 comprises the first split winding 112 and the second split winding 114 as in Figure 1 a, receive information indicative of a requirement to connect the first split winding 112 and the second split winding 114 into the circuit in series, or connect the first split winding 112 and the second split winding 114 into the circuit in parallel; and connect, in dependence on the received information, the first split winding 112 and the second split winding 114 to the output 106. In examples where the switching means comprises a plurality of switches, the control system 500 may be configured to, for example where the primary winding 152 of a transformer 158 comprises the first split winding 162 and the second split winding 164 as in Figure 1 b, control the plurality of switches to connect the first split winding 162 and the second split winding 164 to the input 154 in series based on receipt of a high logic signal by the switching means, and connect the first split winding 162 and the second split winding 164 to the input 156 in parallel based on receipt of a low logic signal by the switching means. In other examples the control system 500 may be configured to, for example where the secondary winding 102 of a transformer 108 comprises the first split winding 112 and the second split winding 114 as in Figure 1a, control the plurality of switches to connect the first split winding 112 and the second split winding 114 to the output 106 in series based on receipt of a high logic signal by the switching means, and connect the first split winding 112 and the second split winding 114 to the output 106 in parallel based on receipt of a low logic signal by the switching means.

The controller(s) 500 may each comprise a control unit 508 or computational device having one or more electronic processors 512. A vehicle (see Figure 7) and/or a system thereof (see Figure 6) may comprise a single control unit 508 or electronic controller 500 or alternatively different functions of the control ler(s) 500 may be embodied in, or hosted in, different control units 508 or controllers 500. A set of instructions could be provided which, when executed, cause said control ler(s) 500 or control unit(s) 508 to implement the control techniques described herein (including the described method(s)). The set of instructions may be embedded in one or more electronic processors 512, or alternatively, the set of instructions could be provided as software to be executed by one or more electronic processor(s) 512. For example, a first controller 508 may be implemented in software run on one or more electronic processors 512, and one or more other controllers 508 may also be implemented in software run on one or more electronic processors 512, or, optionally, on the same one or more processors 512 as the first controller 508. It will be appreciated, however, that other arrangements are also useful, and therefore, the present disclosure is not intended to be limited to any particular arrangement. In any event, the set of instructions described above may be embedded in a computer-readable storage medium (e.g., a non-transitory computer-readable storage medium) that may comprise any mechanism for storing information in a form readable by a machine or electronic processors/computational device, including, without limitation: a magnetic storage medium (e.g., floppy diskette); optical storage medium (e.g., CD-ROM); magneto optical storage medium; read only memory (ROM); random access memory (RAM); erasable programmable memory (e.g., EPROM and EEPROM); flash memory; or electrical or other types of medium for storing such information/instructions.

Figure 6 illustrates a system 600 comprising an input 602, a control system 500, for example as illustrated in Figure 5, a transformer circuit 100 as disclosed herein and controlled by the control system 500, and an output 604. Energy input goes into the transformer circuit 100 and is converted to energy output at output 604. Control input is provided to the controller at input 602, and control output is provided to the transformer circuit 100 from the controller 500. The controller 500 is not in the energy path as the transformer circuit 100 is. Figure 7 shows a vehicle 700 comprising a transformer circuit 100, 200 as described above, a control system 500 as described above, or a system 600 as described above. The example vehicle 700 may be a passenger vehicle, also referred to as a passenger car or as an automobile, or in other examples, the vehicle 700 may be an industrial vehicle. The vehicle 700 may be an electric vehicle (EV) or a hybrid electric vehicle (HEV). If the vehicle 700 is an HEV, the vehicle 700 may be a plug-in HEV or a mild HEV. If the vehicle 700 is a plug-in HEV, the vehicle 700 may be a series HEV or a parallel HEV. In a parallel HEV, a traction motor and an internal combustion engine are operable in parallel to simultaneously provide tractive torque. In a series HEV, the internal combustion engine generates electricity and the traction motor exclusively provides tractive torque.

Figures 8a-8b show methods of controlling a transformer circuit. Figure 8a shows a method 800 of controlling a transformer circuit for an electric vehicle as described above. The method 800 relates to a transformer circuit where the primary winding comprises a first split winding and a second split winding 802, and comprises controlling the switching means of the circuit to selectively connect the first split winding and the second split winding to the input in series to accept a first input voltage 804, and connect the first split winding and the second split winding to the input in parallel to accept a second input voltage 806

Figure 8b shows a method 850 of controlling a transformer circuit for an electric vehicle as described above. The method 850 relates to a transformer circuit where the secondary winding comprises a first split winding and a second split winding 852, and comprises controlling the switching means of the circuit to selectively connect the first split winding and the second split winding to the output in series to provide a first output voltage 854, and connect the first split winding and the second split winding to the output in parallel to provide a second output voltage 856.

The blocks illustrated in the Figures 8a-8b may represent steps in a method and/or sections of code in a computer program configured to control a transformer circuit as described above to perform the method steps. The illustration of a particular order to the blocks does not necessarily imply that there is a required or preferred order for the blocks and the order and arrangement of the block may be varied. Furthermore, it may be possible for some steps to be omitted or added in other examples.

Figure 9 illustrates an example circuit diagram of a transformer circuit having a split secondary winding 102 according to examples disclosed herein. As in Figures 1 a and 2, the circuit 900 comprises an input 104 for receiving electrical energy and an output 106 for providing electrical energy to an electrical bus. The transformer 108 is located between the input 104 and the output 106. The transformer 108 comprises a primary winding 110 connected to the input 104, and a secondary winding 102 connected to the output 106. In this example the secondary winding 102 comprises a first split winding 112 and a second split winding 114. The circuit 900 also comprises switching means 116, in this example comprising three MOSFETs, configured to selectively connect the first split winding 112 and the second split winding 114 in series to the output 106, or connect the first split winding 112 and the second split winding 114 in parallel to the output 106. The arrangement of three MOSFET switches in this example allows the two split secondary windings 112, 114 to be connected in the circuit in series or in parallel. The MOSFETs shown as M1-M14, M27-M28 may have associated have anti-parallel diodes (not illustrated).

For example, such a circuit may be used as part of an On Board Charger (OBC) to accept 400V or 800V at the input 104 and provide a voltage at the output. On the output (i.e. OBC output), the transformer 108 can provide either 400V or 800V depending on the switching means switching in particular windings of the first and second split windings 112, 114. In this example the switching means comprises MOSFETs 118, 120 arranged as illustrated, to connect the two split windings 112, 114 at the output of the transformer 108 in series to generate 800V at the output, and connect the two split windings 112, 114 at the output of the transformer 108 in parallel to obtain 400V at the output.

In examples in which the thickness of the wire of the first and second split windings 112, 114 is substantially the same, and the number of turns of each of the first and second split windings 112, 114 is the same, the output power level can remain constant in either arrangement of having the split windings connected in series or in parallel the circuit. The output power may remain substantially constant when the transformer is working in a constant power mode. In this constant power mode, the power may be regulated to remain at a certain value. When the voltage is increased, the current is decreased to maintain a constant power. In other modes of operation, the transformer may be used in a constant current mode in which the current is not relative to the voltage.

Figure 10 illustrates a circuit diagram of a transformer circuit 1000 having a split primary winding 162, 164. The example is labelled as allowing 400V or 800V at the input, and providing a 12V output voltage. As in Figures 1 b and 3, the circuit 1000 comprises an input 154 for receiving electrical energy and an output 156 for providing electrical energy to an electrical bus. The transformer 158 is located between the input 154 and the output 156. The transformer 158 comprises a split primary winding 152 connected to the input 154, and a secondary winding 160 connected to the output 156. In this example the primary winding 152 comprises a first split winding 162 and a second split winding 164. The circuit 1000 also comprises switching means 166, in this example comprising three MOSFETs, configured to selectively connect the first split winding 162 and the second split winding 164 in series to the input 154, or connect the first split winding 162 and the second split winding 164 in parallel to the input 154.

For example, such a circuit may be used to accept 400V or 800V at the input 104 for provision of a low voltage (e.g. 12V) at the output 156. At the input 154, the transformer 108 can accept either 400V or 800V depending on the switching means 166 switching in the first and second split windings 162, 164 in series (for 800V) or in parallel (for 400V). In this example the switching means comprises MOSFETs arranged as illustrated, to connect the two split windings 162, 164, 114 at the input of the transformer 158 in series or in parallel. The MOSFETs shown as M19-M24 may have associated have anti-parallel diodes (not illustrated).

In similar examples to that of Figure 10 which shows a split primary winding with one secondary winding, other examples may provide a split primary winding with a plurality of split secondary windings configured to provide a plurality of low voltages, dependent on the switching of the plurality of split secondary windings in series or parallel. For example, a circuit with four split secondary windings may be controlled to connect the four split secondary windings into the circuit in different combinations of series and parallel to provide 12V, 24V, 36V and 48V output voltage. The first, second third and fourth split secondary windings of such a circuit may each be configured to carry the same current in some examples. The switching may be achieved with an arrangement of logic gates to switch the switching means as required, for example. In some examples the output voltages may be voltage ranges (e.g. between 10V-14V, between 22V and 26V, between 34V and 38V, and between 46V and 50V) which do not overlap. In other examples a plurality of voltage ranges may be achievable at the output which at least partially overlap (e.g. between 10V and 30V, and between 25V and 45V).

In some examples, the transformer circuit having a secondary winding split into a plurality of split secondary windings may comprise an output selection switch connected to the switching means, and the output selection switch may be configured to provide a logic signal to each of the split windings to selectively connect the first, second, third and fourth split windings to the output to provide first, second, third, and fourth voltages. In other examples, two, three, five, or more than five split secondary windings may be used, with appropriate switching means to achieve various combinations of series and parallel connection of the split secondary windings in the circuit, to provide different voltage outputs.

Similarly to Figure 10, the circuit of Figure 11 illustrates a circuit diagram of a transformer circuit 1100 having a split primary winding 162, 164. This circuit example may be used to accept two possible high voltages (e.g. 400V or 800V) at the input 104 for provision of the lower of the two high voltages (e.g. 400V) at the output 156. For example, certain vehicles may allow for battery charging at a higher voltage (e.g. 800V), but may require a lower high voltage (e.g. 400V) to power particular vehicle functions. Using such a transformer circuit as in Figure 11 , the battery may be charged at the higher voltage (e.g. 800V) while the vehicle functions, such as windscreen heaters or air chiller units, are powered at the lower voltage e.g. 400V). At the input 154, the transformer 108 can accept either 400V or 800V depending on the switching means 166 switching in the first and second split windings 162, 164 in series (for 800V) or in parallel (for 400V). In this example the switching means comprises MOSFETs arranged as illustrated, to connect the two split windings 162, 164, 114 at the input of the transformer 158 in series or in parallel. The MOSFETs shown as M29-M30, M32-M33, M36-M40 may have associated have anti-parallel diodes (not illustrated).

Examples disclosed herein allow for port voltages to be configured in multiple ways, which may be desirable for use in multiple vehicles I vehicle configurations. These different voltage requirements for different vehicles may be described as ‘cross-car requirements'. Further, the configuration of the circuits described herein may be adapted by the user ‘on the fly'. For example, the vehicle battery may be charged using 800V or 400V chargers without any requirement to update the hardware in the vehicle by use of the switching means allowing acceptable of 400V or 800V at the circuit input.. This cannot be done with the existing topology. It will be appreciated that various changes and modifications can be made to the examples disclosed herein without departing from the scope of the present application as defined by the appended claims.

As used here 'module' refers to a unit or apparatus that excludes certain parts/components that would be added by an end manufacturer or a user.

As used here, 'connected' means ‘electrically interconnected' either directly or indirectly. Electrical interconnection does not have to be galvanic. Where the control system is concerned, connected means operably coupled to the extent that messages are transmitted and received via the appropriate communication means.

The term 'current' means electrical current. The term 'voltage' means potential difference. The term ‘series' means electrical series. The term 'parallel' means electrical parallel. The term 'power' means electrical power. The term 'charging' means electrical recharging of the battery. The term "winding” is synonymous with "coil” in terms of the transformer windings and split windings.

Although examples have been described in the preceding paragraphs with reference to various examples, it should be appreciated that modifications to the examples given can be made without departing from the scope of the invention as set out in the appended claims. Features described in the preceding description may be used in combinations other than the combinations explicitly described. Although functions have been described with reference to certain features, those functions may be performable by other features whether described or not. Although features have been described with reference to certain embodiments, those features may also be present in other embodiments whether described or not.

Whilst endeavouring in the foregoing specification to draw attention to those features believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not particular emphasis has been placed thereon.

Claims

1 . A transformer circuit for an electric vehicle, the circuit comprising: an input for receiving electrical energy; an output for providing electrical energy to an electrical bus; a transformer located between the input and the output, the transformer comprising: a primary winding connected to the input; and a secondary winding connected to the output, wherein at least one of the primary winding and the secondary winding comprises a first split winding and a second split winding; and switching means configured to: where the primary winding comprises the first split winding and the second split winding, selectively connect the first split winding and the second split winding to the input in series to accept a first input voltage, and connect the first split winding and the second split winding to the input in parallel to accept a second input voltage; and where the secondary winding comprises the first split winding and the second split winding, selectively connect the first split winding and the second split winding to the output in series to provide a first output voltage, and connect the first split winding and the second split winding to the output in parallel to provide a second output voltage.

2. The transformer circuit of claim 1 , comprising an input selection switch connected to the switching means, wherein the input selection switch is configured to: where the primary winding comprises the first split winding and the second split winding, connect the first split winding and the second split winding to the input in series to accept the first input voltage, and connect the first split winding and the second split winding to the input in parallel to accept the second input voltage; and where the secondary winding comprises the first split winding and the second split winding, connect the first split winding and the second split winding to the output in series to provide the first output voltage, and connect the first split winding and the second split winding to the output in parallel to provide the second output voltage.

3. The transformer circuit of any preceding claim, wherein the first split winding is formed of first wire, the second split winding is formed of second wire, and the first wire is substantially a same thickness as the second wire.

4. The transformer circuit of any preceding claim, wherein the first split winding has substantially a same number of turns as the second split winding.

5. The transformer circuit of any preceding claim, configured to operate at one or more of: a high voltage at the input; and a high voltage at both the input and the output; wherein the high voltage is between 60 V and 1500 V DC.

6. The transformer circuit of any preceding claim, wherein the switching means comprises three switches configured to: where the primary winding comprises the first split winding and the second split winding, connect the first split winding and the second split winding to the input in series based on receipt of a high logic signal by the switching means and connect the first split winding and the second split winding to the input in parallel based on receipt of a low logic signal by the switching means; and where the secondary winding comprises the first split winding and the second split winding, connect the first split winding and the second split winding to the output in series based on receipt of a high logic signal by the switching means and connect the first split winding and the second split winding to the output in parallel based on receipt of a low logic signal by the switching means.

7. The transformer circuit of any preceding claim, where the primary winding comprises the first split winding and the second split winding, and wherein the first input voltage comprises a nominal voltage in the range 600V to 1000V when the first split winding and the second split winding are connected to the input in series, and the second input voltage comprises a nominal voltage in the range 300V to 500Vwhen the first split winding and the second split winding are connected to the input in parallel.

8. The transformer circuit of any preceding claim, where the secondary winding comprises the first split winding and the second split winding, and wherein the first output voltage comprises a nominal voltage in the range 600V to 1000V when the first split winding and the second split winding are connected to the output in series, and the second output voltage comprises a nominal voltage in the range 300V to 500V when the first split winding and the second split winding are connected to the output in parallel.

9. The transformer circuit of any of claims 1 to 7, wherein the circuit is configured to provide a low voltage output, wherein a low voltage is defined as a working voltage of 50 V DC or lower.

10. The transformer circuit of claim 9, where the secondary winding comprises the first split winding and the second split winding, and wherein: the first output voltage comprises a nominal first low voltage in the range 30V to 50V when the first split winding and the second split winding are connected in series to the output, and the second output voltage comprises a nominal second low voltage in the range 5V to 28V when the first split winding and the second split winding are connected in parallel to the output; wherein the nominal second low voltage is lower than the nominal first low voltage; optionally, the primary winding comprises a further first split winding and a further second split winding, and wherein: the first input voltage comprises a nominal voltage in the range 600V to 1000V when the first further split winding and the second further split winding are connected in series to the input, and the second input voltage comprises a nominal voltage in the range 300V to 500V when the first further split winding and the second further split winding are connected in parallel to the input.

11 . The transformer circuit of claim 9, wherein the secondary winding is a split secondary winding comprising the first split winding, the second split winding, a third split winding and a fourth split winding; wherein the switching means is configured to selectively connect the first, second, third and fourth split windings to the output to provide first, second, third, and fourth voltages; optionally, the primary winding comprises a further first split winding and a further second split winding, and wherein: the input voltage comprises a nominal voltage in the range 600V to 1000V when the first further split winding and the second further split winding are connected in series to the output, and the input voltage comprises a nominal voltage in the range 300V to 500V when the first further split winding and the second further split winding are connected in parallel to the output.

12. The transformer circuit of any preceding claim, comprising the circuit of claim 8; and a further circuit of claim 10 or claim 11; wherein the output of the circuit of claim 8 is connected to the input of the further circuit of claim 10 or claim 11.

13. A control system for controlling a transformer circuit for an electric vehicle, the control system comprising one or more controllers, and the transformer circuit comprising: an input for receiving electrical energy; an output for providing electrical energy to an electrical bus; a transformer located between the input and the output, the transformer comprising a primary winding connected to the input and a secondary winding connected to the output, wherein at least one of the primary winding and the secondary winding comprises a first split winding and a second split winding; and switching means configured to: where the primary winding comprises the first split winding and the second split winding, selectively connect the first split winding and the second split winding to the input in series to accept a first input voltage, and connect the first split winding and the second split winding to the input in parallel to accept a second input voltage; and where the secondary winding comprises the first split winding and the second split winding, selectively connect the first split winding and the second split winding to the output in series to provide a first output voltage, and connect the first split winding and the second split winding to the output in parallel to provide a second output voltage wherein the control system is configured to control switching means of the circuit to: where the primary winding comprises the first split winding and the second split winding, selectively connect the first split winding and the second split winding to the input in series to accept a first input voltage, and connect the first split winding and the second split winding to the input in parallel to accept a second input voltage; and where the secondary winding comprises the first split winding and the second split winding, selectively connect the first split winding and the second split winding to the output in series to provide a first output voltage, and connect the first split winding and the second split winding to the output in parallel to provide a second output voltage.

14. A vehicle comprising the transformer circuit of any preceding claim.

15. A method of controlling a transformer circuit for an electric vehicle, the transformer circuit comprising: an input for receiving electrical energy; an output for providing electrical energy to an electrical bus; a transformer located between the input and the output, the transformer comprising a primary winding connected to the input and a secondary winding connected to the output, wherein at least one of the primary winding and the secondary winding comprises a first split winding and a second split winding; and switching means configured to: where the primary winding comprises the first split winding and the second split winding, selectively connect the first split winding and the second split winding to the input in series to accept a first input voltage, and connect the first split winding and the second split winding to the input in parallel to accept a second input voltage; and where the secondary winding comprises the first split winding and the second split winding, selectively connect the first split winding and the second split winding to the output in series to provide a first output voltage, and connect the first split winding and the second split winding to the output in parallel to provide a second output voltage the method comprising one or more of: where the primary winding comprises the first split winding and the second split winding, selectively connect the first split winding and the second split winding to the input in series to accept a first input voltage, and connect the first split winding and the second split winding to the input in parallel to accept a second input voltage; and where the secondary winding comprises the first split winding and the second split winding, selectively connect the first split winding and the second split winding to the output in series to provide a first output voltage, and connect the first split winding and the second split winding to the output in parallel to provide a second output voltage.

16. Computer software that, when executed, is arranged to perform a method according to claim 15; optionally the computer software is stored on a computer readable medium.

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