Electric vehicle charging

Abstract

This invention provides an electric vehicle charging apparatus comprising a primary circuit arrangement and a secondary circuit arrangement for charging a traction battery of an electric vehicle. The primary circuit arrangement has a primary transformer winding configured to electrically couple to an alternating current supply. The secondary circuit arrangement has a secondary transformer winding configured to electrically couple to the traction battery of the electric vehicle to define a secondary winding circuit. The secondary circuit arrangement also has a power converter system configured to receive an alternating current from the secondary transformer winding and to provide a direct current to the traction battery of the electric vehicle. The secondary transformer winding has fewer turns primary transformer winding. The apparatus also comprises a tap changing mechanism arranged to vary the operative number of turns in either the primary transformer winding or the secondary transformer winding.

Description

[0001] S P3206

[0002] ELECTRIC VEHICLE CHARGING

[0003] Field of the Invention

[0004] This invention relates to an apparatus for charging an electric vehicle .

[0005] Background of the invention

[0006] As electric vehicle ( EV) technology develops , there is a growing need for improved charging infra structure which can meet the charging needs of different battery systems in electric pas senger cars , trucks and ves sels . Existing electric vehicle charging stations typically employ a multi- stage convers ion system to convert alternating current (AC ) from the grid into the direct current ( DC ) required for charging . Such systems generally involve a central transformer for stepping down the AC supplied to each charging station , a three-phase power converter for converting AC to DC , a galvanically isolated DC to DC converter for adj usting to the required charging voltage , and optionally a matrix converter for catering to various charging needs .

[0007] For safety reasons , the se systems require two layers of galvanic isolation : one between the grid and the charging station via the transformer , and another between the each connected vehicle via the isolated DC to DC converter . The double isolation and power electronic components are costly and susceptible to los ses which result in ineff icient and unreliable charging performance .

[0008] It is an aim of the pre sent invention to overcome at least some of the disadvantages of known EV charging apparatus and systems .

[0009] Summary of the Invention

[0010] According to an aspect of the invention , there is an electric vehicle charging apparatus provided . The apparatus comprises a primary circuit arrangement and a secondary circuit arrangement . The primary circuit arrangement comprises a primary transformer winding configured to electrically couple to an alternating current supply . The secondary circuit arrangement i s for charging a traction battery of a first electric vehicle , and compri ses a first secondary transformer winding configured to electrically couple to the traction battery of the first electric vehicle to define a first secondary winding circuit . The secondary circuit arrangement further comprises a f irst power converter system configured to receive an alternating current from the first secondary trans former winding and to provide a direct current to the traction battery of the f irst electric vehicle . The primary transformer winding comprises a number of primary winding turns and the secondary circuit arrangement comprises a number of first secondary winding turns that is les s than the number of primary winding turns . In other words , the f irst secondary winding has fewer turns than the primary winding .

[0011] The apparatus further comprises a first tap changing mechani sm arranged to vary the operative number of primary winding turns or the operative number of first secondary winding turns . The f irst tap changing mechanism may be arranged along the first secondary transformer winding .

[0012] The apparatus of the invention advantageously provide s a wide range of AC output voltage for various electric vehicle type s using simplified power electronics . The combination of a tap changing mechani sm followed by a power converter system eliminates the need for complex multi-stage power conversion systems which are currently required by known apparatus . The apparatus optionally comprises a further ( or another ) secondary circuit arrangement for charging a traction battery of another ( i . e . a second) electric vehicle . Like the first secondary circuit arrangement , the optional further secondary circuit arrangement comprises a secondary transformer winding and a power converter system . The secondary transformer winding of the optional further secondary circuit arrangement i s configured to electrically couple to the traction battery of the second electric vehicle to define an a ssociated secondary winding circuit , and comprises a number of secondary winding turns that is les s than the number of primary winding turns . The power converter system of the optional further secondary winding circuit is configured to receive an alternating current f rom the as sociated secondary trans former winding and to provide a direct current to the traction battery of the second electric vehicle .

[0013] Examples of the apparatus comprising a further secondary circuit arrangement may optionally include a second tap changing mechanism arranged along the further secondary trans former winding to vary the operative number of turns in the further secondary transformer winding .

[0014] The apparatus of the invention advantageously provide s a single point of galvanic isolation between the grid and one or more electric vehicles , and between multiple electric vehicle charging ports . The streamlined architecture saves space , improves reliability, and improve s electrical efficiency without compromi sing on electrical safety .

[0015] The or each power converter system may be nonisolated ( i . e . not galvanically isolated) , meaning that current can flow through the power converter system . In other words , there is a direct conduction path from an input side of the power converter system to an output side of the power converter system. Optionally, the or each power converter system may comprise a power converter which may be one of a bidirectional active front end converter or a unidirectional full bridge rectifier. Optionally, the or each power converter system may further comprise a voltage regulator arranged to be electrically connected in the respective secondary winding circuit between the respective power converter and the traction battery of the corresponding electric vehicle.

[0016] Examples of the apparatus comprising multiple secondary circuit arrangements (e.g. a first and a second secondary circuit arrangement) may optionally also comprise a multipurpose converter electrically coupled to each of the secondary circuit arrangements. When a secondary winding circuit is defined (i.e. when a traction battery of an electric vehicle is connected to one of the secondary circuit arrangements) , that traction battery defines a power load or electrical load. The multipurpose converter may be configured to permit the connected traction battery to draw at least a portion of the power load (i.e. at least a portion of the power required to service the electrical load) from the other or another secondary circuit arrangement.

[0017] When another secondary winding circuit is defined (i.e. when traction batteries of two electric vehicles are connected at the same time) , the second traction battery defines another (or second) power load. The multipurpose converter may be further configured to distribute the two power loads across the two secondary winding circuits.

[0018] The multipurpose converter advantageously allows for power sharing between charging ports. Galvanic isolation is maintained with minimal hardware complexity. This approach advantageous ly replaces the need for complex and ineff icient mechanical or solid state relays .

[0019] Optionally, the multipurpose converter may be electrically connected to one of the secondary circuit arrangements between the respective power converter system and the traction battery of the corresponding electric vehicle to define a direct current link between the multipurpose converter and the respective secondary circuit arrangement .

[0020] Additionally or alternatively, the multipurpose converter may be electrically connected to one of the secondary circuit arrangements between the re spective secondary trans former winding and the corresponding power converter arrangement to def ine an alternating current link between the multipurpose converter and the respective secondary circuit arrangement .

[0021] Optionally, the multipurpose converter comprise s a bypas s switch arranged so that the alternating current link and the direct current link are defined between the bypas s switch and the respective secondary circuit arrangement .

[0022] Optionally, at least one of the secondary circuit arrangements may comprise an energy storage device arranged to be electrically connected in the re spective secondary winding circuit between the respective power converter arrangement and the respective voltage regulator . Optionally, if present , the multipurpose converter may be electrically connected to the or each energy storage device . Brief Description of the Drawings

[0023] Figure 1 shows a schematic view of an apparatus according to an embodiment of the invention ;

[0024] Figure 2 shows a schematic view of another apparatus according to an embodiment of the invention ; Figure 3 shows a schematic view of a secondary circuit arrangement of an apparatus according to an embodiment of the invention;

[0025] Figures 4, 5 and 6 show schematic views of apparatus comprising a multipurpose converter according to embodiments of the invention.

[0026] Figures 7a to 7c show circuit diagrams of components suitable for use in the multipurpose converter of Figures 4 , 5 and 6.

[0027] These drawings depict one or more implementations in accordance with the present teachings, by way of example only, not by way of limitation. In the figures, like reference numerals refer to the same or similar elements. Detailed Description of the Drawings

[0028] In general terms, the examples described below provide an electric vehicle charging apparatus which includes a variable voltage transformer (WT) coupled with power electronics. The WT serves to dynamically transform the input voltage from the grid to a lower working voltage that is appropriate for consumer use. The WT is 'variable' , meaning that the turns ratio across the transformer can be varied, through means of a mechanical or electronic tap based system. This allows the step change in voltage at the WT to be incrementally adjusted depending on the charging needs of a connected vehicle. The power electronics serves to convert the AC voltage output from the WT into the DC voltage required to charge the connected vehicle. Utilising a WT eliminates the need for multiple power electronics conversion stages and therefore allows the power electronics to be simplified. In turn, this leads to reduced electrical losses.

[0029] According to some examples, the WT defines one primary circuit on the grid side and multiple secondary circuits on the charging side. Each secondary circuit is configured to couple to a vehicle to be charged , meaning that the apparatus is configured to couple to and charge multiple vehicles at once . The WT provides galvanic isolation between the higher voltage circuitry connected to the grid and the lower voltage circuitry which supplies the variable voltages to the connected vehicles . Meanwhile , each secondary circuit i s inherently galvanically isolated from the others , thus ensuring that connected vehicles are galvanically isolated from each other . Providing galvanic i solation in this way eliminates the need for isolated converters within the power electronics , therefore allowing the circuit topology of the power electronics to be simplified . As above , this further enhance s reliability and improves overall efficiency .

[0030] Figure 1 schematically illustrates a single pha se view of the circuit architecture of an apparatus 100 for charging a traction battery 102 of an electric vehicle . The apparatus 100 comprises a variable step-down trans former 104 and a power converter system 106 . The step-down transformer 104 comprises a primary trans former winding 108 ( shown on the left side of Figure 1 ) and a secondary transformer winding 110 ( shown on the right s ide of Figure 1 ) . The primary transformer winding 108 i s configured to receive a input primary voltage , while the secondary transformer winding i s conf igured to provide an output secondary voltage .

[0031] The primary transformer winding 108 is configured to electrically couple to an AC power supply ( not shown ) , such as the National Grid in the UK . More specifically, the AC power supply i s a medium voltage power supply which provide s an input primary voltage of between ll kV and 33 kV. Together , the primary transformer winding 108 and the

[0032] AC power supply form at least part of a primary circuit arrangement, and a primary winding circuit is defined when they are connected.

[0033] The secondary transformer winding 110 is configured to electrically couple to a traction battery 102 of an electric vehicle via a battery connector, or charging port 114. The secondary transformer winding 110 forms at least part of a secondary circuit arrangement 116, and a secondary winding circuit is defined when the battery 102 is connected. It will be appreciated that, when connected, the traction battery 102 defines a load on the secondary winding circuit. In other words, the traction battery 102 will draw a certain amount of power through the circuit depending on its charging needs at a given time. The defined load may, therefore, be referred to as a power load.

[0034] As shown, the primary transformer winding 110 comprises a number of turns 118 that is less than the number of turns 120 of the secondary transformer winding 108. Thus, as will be understood, the transformer 104 is configured to transform the voltage across the primary transformer winding 108 (i.e. the input primary voltage) to a lower voltage across the secondary transformer winding 110 (i.e. the output secondary voltage) . As will be appreciated, both the input primary voltage and the output secondary voltage are alternating, or AC.

[0035] The apparatus 100 further includes a tap changing mechanism 122 (or tap changer) which is generally arranged to selectively vary the operative number of turns in one of the windings 110, 108. In other words, the tap changing mechanism 122 is arranged to selectively vary the turns ratio in distinct steps so as to output different voltages from the transformer 104 depending on the charging requirements of the traction battery 102. More generally, the tap changing mechanism 122 is configured to dynamically adj ust the output secondary voltage . In this example , the tap changing mechanism 122 i s arranged on the secondary trans former winding 110 . As such , the tap changing mechanism 122 is configured to alter the turns ratio of the transformer 104 by altering the number of operative turns in the secondary winding 110 . The tap changing mechanism 122 may be implemented mechanically or electronically . A tap changing mechanism may alternatively or additionally be arranged on the primary trans former winding 108 . It should be noted that , although the number of operative turns is variable , the operative number of turns 118 on the secondary winding 110 i s always lower than that of the primary winding 108 so that the output secondary voltage is lower than the input primary voltage , and the step-down function of the trans former 104 is maintained

[0036] The power converter system 106 is arranged within the secondary circuit arrangement 116 and is configured to convert the stepped-down AC power received from the variable voltage transformer 104 into DC power suitable for charging the traction battery 102 . In other words , the power converter system 106 is configured to receive an alternating current f rom the secondary transformer winding 110 and to provide a direct current to a traction battery 102 of an electric vehicle that is connected to define the secondary circuit . Accordingly, the power converter system 106 comprises an input side 124 which is electrically coupled to the secondary winding 110 , and an output side 126 which is electrically couplable to the traction battery 102 , i . e . the power converter system 106 is arranged electrically between the secondary winding 110 and the battery connector 114 .

[0037] In this example , the power converter system 106 comprises a power converter 128 on the input side 124 and a voltage regulator 130 on the output side 12 6 . The power converter 128 i s conf igured to convert AC to pulsating DC , and the voltage regulator 130 is configured to perform further regulation and filtering to provide the precise power output required to charge the traction battery 102 . The power converter 128 may be a rectifier in the form of a diode rectifier bridge ( or full bridge rectif ier ) which allows charging in the direction of grid-to-vehicle only . In other words , the power converter 128 may be configured to be unidirectional . Alternatively, the power converter 128 may be conf igured to be bidirectional to additionally allow for vehicle-to-grid power transfer . In such example s , the power converter 128 may take the form of a three-phase active front-end (AFE ) converter which allows bidirectional power f low . The voltage regulator 130 is a non-i solated DC to DC converter with buck and / or boost functionality . The voltage regulator 130 is optional and therefore not e s sential in embodiments compri sing an AFE converter .

[0038] In view of the above , it shall be appreciated that electrical couplings between the secondary transformer winding 110 and the power converter system 106 carry AC power , while the electrical couplings between the power converter system 106 and the traction battery 102 carry DC power . In examples such as that shown in Figure 1 , the electrical couplings between the power converter 128 and the voltage regulator 130 carry DC power . Couplings which carry AC power may be referred to a s AC links 132 . Couplings which carry DC power may be referred to as DC links 134 .

[0039] As is generally known , transformers also compri se a magnetic core which pas ses through the windings . The variable transformer 104 of the invention may be implemented as a liquid-immersed transformer , meaning that the magnetic core ( not shown ) and the windings 108 , 110 are immersed in a liquid, such as mineral oil . The tap changing mechanism 122 and power converter system 106 may also be immersed in the same or a s imilar liquid . Oil immersion provides improved voltage insulation and cooling . Oil immersed temperature , voltage and / or current sensing equipment may also be used for monitoring and controlling the apparatus .

[0040] Although described above in the context of a single phase view of the circuit architecture of the apparatus 100 , it will be understood that the circuit architecture of the apparatus 100 may be implemented with a three phase variable voltage transformer . In the des cription above , and in the description that follows , a single phase view of the circuit architectures are shown and de scribed for the sake of simplicity . It will be understood that each circuit architecture described herein may be implemented with a three phase transformer .

[0041] Figure 2 schematically illustrates the circuit architecture of another electric vehicle charging apparatus 200 . This apparatus comprises four charging ports 114 , thus allowing for four separate electric vehicle s to be connected to the apparatus 200 at once .

[0042] As shown , the apparatus 200 compri ses multiple secondary windings 110 , each being configured to connect to separate traction batteries 102 to thereby define multiple secondary winding circuits . In other words , the apparatus 200 comprises multiple secondary circuit arrangements 116 . The example shown comprise s four secondary circuit arrangements , but other examples may have more or fewer secondary circuit arrangements . The separate secondary circuit arrangements 116 and their components may be referred to by the terms ' f irst ' , ' second' , 'third' , and ' fourth' . In this example , each of the secondary circuit arrangements 116 are the same, but in other examples they may be different to accommodate different types of traction batteries.

[0043] In more detail, each secondary circuit arrangement 116 is as described above and comprises a secondary transformer winding 110 and a power converter system 106. For example, each secondary circuit arrangement is configured for charging a traction battery 102 of an electric vehicle. Each secondary transformer winding 110 is as previously described and comprises a number of secondary winding turns that is less than the number of primary winding turns . Accordingly, a step-down transformer is defined between each secondary winding 110 and the primary winding 108. A tap changing mechanism 122 is arranged along each secondary transformer winding 110 to vary the operative number of secondary winding turns in that winding 110. As above, a tap changing mechanism may alternatively or additionally be arranged on the primary transformer winding 108.

[0044] Each power converter system 106 is also as described above, and is generally configured to convert the AC power received from the respective secondary transformer winding 110 to the DC power required to charge the respective traction battery 102. Each power converter system 106 is non-isolated, meaning that there is a direct electrical connection between the respective input and output sides 124, 126. In other words, the input and output sides 124, 126 are not galvanically isolated from each other. Nonetheless, each secondary circuit arrangement 116 is galvanically isolated from the others because each independently receives power from the AC supply via its own distinct secondary transformer winding 110.

[0045] Turning now to Figure 3, an example of a secondary circuit arrangement 116 is shown. Any or all of the secondary circuit arrangements 116 shown in Figure 2 may alternatively be as shown in Figure 3 . The power converter system 106 of the secondary circuit arrangement 116 in Figure 3 comprises a power converter 128 and a voltage regulator 130 as des cribed above with reference to Figure 1 . However , this secondary circuit arrangement 116 further comprises an energy storage device 136 ( such as a battery or supercapacitor ) coupled to the DC links 134 between the power converter 128 and the voltage regulator 130 . In other words , the energy storage device 136 is arranged in parallel with the power converter 128 and the voltage regulator 130 . Figure 3 shows the energy storage device 136 as being a separate module from the power converter system 106 but in other example s it may be provided a s an integrated part of the power converter system 106 .

[0046] The energy storage device 136 is arranged to be charged by the AC power supply when the available power is surplus to the requirements of the load at the charging port 114 . For example , the energy storage device 136 may be charged when there is no traction battery 102 connected to the charging port 114 , or when a connected traction battery 102 is fully charged . Then , when a traction battery 102 requiring charging is subsequently connected, it can draw power from the energy storage device 136 instead of , or as well as , f rom the secondary winding 110 . In other words , the power output from the secondary winding arrangement 116 to the traction battery 102 may comprise a portion from the secondary winding 110 and / or a portion from the energy storage device 136 . Accordingly, the maximum power output may be temporarily increased beyond the rating of the secondary winding 110 until the energy storage device 136 is depleted . Alternatively, the demand on the AC power supply may be temporarily reduced while the energy storage device 136 supplies power to the load at the charging port 114.

[0047] Figures 4 and 5 show examples of apparatus 300, 400 comprising two secondary circuit arrangements (a first 116 and a second 116' ) and a multipurpose converter (MPC) 138 arranged between the two. Each of the secondary circuit arrangements 166, 116' comprises an energy storage device 136, 136' as described above with reference to Figure 3, but the MPC 138 can be implemented without these being present. It should also be noted that secondary circuit arrangements 116, 116' without an energy storage device 136, 136' may be implemented without a voltage regulators 130, 130' if the power converter 128, 128' is implemented as a bidirectional power converter (i.e. an AFE) .

[0048] Although the examples shown include only two secondary circuit arrangements 116, 116' , other examples may include more secondary circuit arrangements with a single MPC 138 connected to each.

[0049] Generally, the MPC 138 is configured to selectively transfer power between the secondary circuit arrangements 116, 116' . Accordingly, the MPC 138 allows the charging port 114 of the first secondary circuit arrangement 116 to be at least partially supplied with power from the second secondary circuit arrangement 116' . In other words, the MPC 138 is configured to permit a traction battery 102 coupled to the first secondary circuit arrangement 102 to draw power from the second secondary circuit arrangement 116' . Similarly, the MPC 138 allows the charging port 114' of the second secondary circuit arrangement 116' to be at least partially supplied with power from the first secondary circuit arrangement 116. As a result, the maximum power output from each charging port 114, 114' may be temporarily increased by supplying power from the secondary winding 110, 110' and / or energy storage device 136, 136' of the other secondary circuit arrangement 116, 116' .

[0050] In an example scenario, a first traction battery 102 is coupled to the first secondary circuit arrangement 116 and a second traction battery 102' is coupled to the second secondary circuit arrangement 116' . The first traction battery 102 defines a first power load and the second traction battery 102' defines a second power load. The first power load exceeds the combined power available from the first secondary winding 110 and the first energy storage device 136, while the second power load is lower than the combined power available from the second secondary winding 110' and the second energy storage device 136' . Therefore, the MPC 138 transfers a portion of the combined power available in the second secondary circuit arrangement 116' to the first secondary circuit arrangement 116 in order to make up the shortfall (or at least a portion of the shortfall) . In other words, the MPC 138 is configured to distribute the total power available across the first and second secondary circuit arrangements 116, 116' in order to meet the varying charging needs at each charging port 114, 114' . Enabling power distribution in this way advantageously means that the secondary windings 110, 110' can be configured with lower power ratings without causing the maximum power output from each charging port 114, 114' to be reduced.

[0051] In the example shown in Figure 4, the MPC 138 is configured to transfer DC power between the secondary circuit arrangements 116, 116' . In more detail, the MPC 138 is electrically coupled to each secondary circuit arrangement 116, 116' to define separate (or decentralised) DC links 140, 140' between the MPC 138 and each secondary circuit arrangement 116, 116' . In each case, the MPC 138 is coupled to the respective secondary circuit arrangement 116, 166' on the output side of the respective power converter 128, 128' ; i.e. between the power converter 128, 128' and the voltage regulator 130, 130' . The MPC 138 comprises an isolated DC to DC converter 142 which ensures galvanic isolation is maintained between the two secondary circuit arrangements 116, 116' . The isolated DC to DC converter 142 may be implemented as a dual active bridge, an example of which is shown in Figure 6a.

[0052] Although galvanic isolation is achieved using the isolated DC to DC converter 142, it should be appreciated that this isolated DC to DC converter 142 may be configured to a much lower power rating than those required by the state of the art. This is because the MPC 138 does not need to be configured to transfer up to the maximum power output in order to achieve effective power distribution among the secondary circuit arrangements 116, 116' .

[0053] As suggested above, examples of the apparatus may include multiple secondary circuit arrangements 116. Such examples may include an MPC 138 connected to each of the secondary circuit arrangements 116. In these cases, the MPC 138 may be implemented as a multi-active bridge (MAB) isolated DC to DC converter, an example of which is shown in Figure 6b.

[0054] Figure 5 shows an example of an arrangement 400 comprising multiple secondary circuit arrangements 116, 116' , specifically three secondary circuit arrangements. Referring to both Figures 5 and 6b, the MPC 138 comprises a primary side 150 and a secondary side 152 . As shown, one of the secondary circuit arrangements 116 is coupled to the primary side 150 of the MPC 138, while the other secondary circuit arrangements 116' are coupled to the secondary side 152 of the MPC 138. The MPC 138 is coupled to each secondary circuit arrangement 116, 116' on the DC side of the respective power converter 128, 128' , thereby defining a DC link 140, 140' with each of the secondary circuit arrangements 116, 116' .

[0055] The secondary circuit arrangement 116 coupled to the primary side 150 of the MPC 138 may be referred to as the 'master' secondary circuit arrangement, and the associated charging port 114 may be similarly referred to as the 'master' port. The secondary circuit arrangements 116' coupled to the secondary side 152 of the MPC 138 may be referred to as 'slave' secondary circuit arrangements, and the associated charging ports 114' may be referred to as 'slave' ports. Although this example shows only two slave secondary circuit arrangements 116' , it will be appreciated that other examples may include more than two slave secondary circuit arrangements 116' .

[0056] The master secondary circuit arrangement 116 is configured to have the highest power rating of all the secondary circuit arrangements 116, 116' , and more specifically, is configured for Megawatt Charging System (MCS) applications. Meanwhile, the slave secondary circuit arrangements 116' are configured for lower power charging, specifically Combined Charging System (CCS) applications. Accordingly, the multi-active bridge MPC 138 facilitates bidirectional transfer of DC power from the highest rated port (i.e. the master port 114) to the lower rated charging ports 114' .

[0057] In the example shown in Figure 6, the MPC 138 comprises an isolated DC to DC converter 142, a single- stage AC to DC converter 144, and an input bypass switch 146. The MPC 138 is also electrically coupled to the first secondary circuit arrangement 116 to define an AC link 148 between the MPC 138 and the first secondary circuit arrangement 116. That is to say, the MPC 138 is coupled to the AC side 124 of the f irst power converter system 106 . The input bypas s switch 146 may be implemented using mechanical and / or solid state switches and i s operable to control whether the first secondary circuit arrangement 116 supplies AC or DC power to the MPC 138 at a given time . Accordingly, the MPC 138 is configured for both AC to DC and DC to DC power transfer between the secondary circuit arrangement s 116 , 116 ' . For example , the MPC 138 is conf igured to transfer AC power from the f irst secondary winding 110 to the DC side of the power converter 128 ' of the second secondary winding 116 ' . The transferred power may be used to charge the second energy storage device 136 ' and / or to charge a traction battery 102 ' connected to the second charging port 114 ' . In other examples , the MPC 138 may be arranged to define separate AC links with each of the secondary circuit arrangements .

[0058] The AC to DC functionality advantageously enables the second secondary circuit arrangement 116 ' to draw power f rom the first secondary circuit arrangement 116 , even when the f irst power converter 128 i s already operating at it s maximum power rating to supply a load at the f irst charging port 114 . An example MPC topology that is suitable for use in the apparatus 500 shown in Figure 5 is depicted in Figure 6c .

[0059] It will be appreciated that various change s and modif ications can be made to the present invention without departing from the scope of the pre sent application .

Claims

S P320619C L A I M S1 . An electric vehicle charging apparatus comprising : a primary circuit arrangement comprising : a primary trans former winding configured to electrically couple to an alternating current supply, wherein the primary transformer winding comprises a number of primary winding turns ; a secondary circuit arrangement for charging a traction battery of a first electric vehicle , the secondary circuit arrangement comprising : a first secondary transformer winding configured to electrically couple to the traction battery of the first electric vehicle to define a first secondary winding circuit , wherein the first secondary transformer winding comprises a number of first secondary winding turns that is les s than the number of primary winding turns ; and a first power converter system configured to receive an alternating current from the f irst secondary trans former winding and to provide a direct current to the traction battery of the first electric vehicle ; and a first tap changing mechanism arranged to vary the operative number of primary winding turns or the operative number of first secondary winding turns .2 . An apparatus according to claim 1 , wherein the first tap changing mechanism is arranged along the first secondary trans former winding .3 . An apparatus according to claim 1 or 2 , comprising a further secondary circuit arrangement for charging atraction battery of a second electric vehicle , the further secondary circuit arrangement comprising : a second secondary transformer winding configured to electrically couple to the traction battery of the second electric vehicle to define a second secondary winding circuit , and comprising a number of second secondary winding turns that is les s than the number of primary winding turns ; and a second power converter system configured to receive an alternating current from the second secondary trans former winding and to provide a direct current to the traction battery of the second electric vehicle .4 . An apparatus according to claim 3 , further compris ing a second tap changing mechanism arranged along the second secondary transformer winding to vary the operative number of second secondary winding turns .5 . An apparatus according to any preceding claim, wherein the or each power converter system is nonisolated .6 . An apparatus according to any of claims 3 to 5 , further compris ing a multipurpose converter electrically coupled to both secondary circuit arrangement s , wherein the traction battery of the f irst electric vehicle defines a first power load when the first secondary winding circuit is defined; and the multipurpose converter is conf igured to permit the traction battery of the first electric vehicle to draw at least a portion of the first power load from the further secondary circuit arrangement .7 . An apparatus according to claim 6 , wherein :the traction battery of the second electric vehicle defines a second power load when the second secondary winding circuit is defined; and the multipurpose converter is conf igured to distribute the first and second power loads acros s the first and second secondary winding circuits .8 . An apparatus according to any preceding claim, wherein the or each power converter system comprises a power converter , wherein each power converter i s one of a bidirectional active front end converter or a unidirectional full bridge rectifier .9 . An apparatus according to any of claims 6 to 8 , wherein the multipurpose converter is electrically connected to one of the secondary circuit arrangements between the respective power converter system and the traction battery of the corresponding electric vehicle to define a direct current link between the multipurpose converter and the respective secondary circuit arrangement .10 . An apparatus according to any of claims 6 to 9 , wherein the multipurpose converter is electrically connected to one of the secondary circuit arrangements between the respective secondary transformer winding and the corresponding power converter to define an alternating current link between the multipurpose converter and the respective secondary circuit arrangement .11 . An apparatus according to claims 9 and 10 , wherein the multipurpose converter comprise s a bypas s switch arranged so that the alternating current link and the22 direct current link are defined between the bypas s switch and the secondary circuit arrangement .12 . An apparatus according to any preceding claim, wherein the or each power converter system further comprises a voltage regulator arranged to be electrically connected in the respective secondary winding circuit between the respective power converter and the traction battery of the corresponding electric vehicle .13 . An apparatus according to claim 12 , wherein at least one of the secondary circuit arrangements comprises an energy storage device arranged to be electrically connected in the respective secondary winding circuit between the respective power converter and the respective voltage regulator .14 . An apparatus according to claim 13 when dependent on claim 9 , wherein the multipurpose converter i s electrically connected to the energy storage device .

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