Commissioning a system for charging electric vehicles

Abstract

The commissioning of a system for charging electric vehicles involves connecting a first charging unit to a second charging unit via a first conductor and a second conductor, such that a first recharg

Description

The present invention relates to a method of commissioning a system for charging electric vehicles, of the type comprising the steps of: connecting a first charging unit to a second charging unit via a first conductor and a second conductor, such that a first rechargeable battery in said first charging unit may be electrically connected in parallel with a second rechargeable battery in said second charging unit. The present invention also relates to an apparatus for charging electric vehicles, of a type comprising a first charging unit having a first rechargeable battery with a first positive terminal and a first negative terminal; a second charging unit having a second rechargeable battery with a second positive terminal and a second negative terminal; a first conductor for connecting said first positive terminal to said second positive terminal; and a second conductor for connecting said first negative terminal to said second negative terminal, thereby electrically connecting said first rechargeable battery in parallel with said second rechargeable battery. It is known to charge electric vehicles from a set of charging units, as disclosed in GB 2552769, assigned to the present applicant. A battery storage system is shown, that allows electric vehicles to be charged at a rate that is higher than that available from a standard grid supply. Ideally, all of the charging units should be used for substantially similar operational periods, to optimise the ability to receive electrical power at a relatively modest rate and then recharge vehicles at a much higher rate. However, in practice, it is likely for some charging stations will become more popular than others, usually due to their geographical positioning, therefore optimal power transfer does not take place due to missed charging opportunities. Furthermore, the maximum rate at which charging can take place is limited by the capabilities of the local charging unit itself, which in turn may eliminate possibilities for providing very high rates of charge to high performance vehicles. According to a first aspect of the present invention, there is provided a method as set out in claim 1. Thus, it is possible for the rechargeable batteries to be combined in such a way that they operate as a unified battery such that, for example, a popular charging unit may receive current from a less popular charging unit in order to maintain operational performance, irrespective of the actual charging unit selected by a user. In an embodiment, one or more additional charging units are connected, each having a respective additional rechargeable battery. Thus, the charge on each rechargeable battery is assessed and the rechargeable battery with the highest level of charge is identified. The remaining batteries are then charged to a level substantially as high as the highest level. Thus, this may continue such that in an embodiment, the method further comprises the step of electrically connecting a next rechargeable battery and a next charging unit via a next current limiting resistance; measuring current flow into said next rechargeable battery from the previous rechargeable battery; and bypassing said next current limiting resistance when the current flow falls below a predetermined value, thereby sequentially connecting rechargeable batteries in parallel such that, in operation, all of said rechargeable batteries function as a unified source of charge. In an embodiment, a final charging unit is connected to the first charging unit, thereby creating a ring. It is possible for current to flow in either direction around the ring and operation may continue following a single point of failure. In an embodiment, the assessing step comprises assessing the charge on rechargeable batteries that have received a transportation charge prior to respective charging units being received at an installation site. Thus, at an installation site, it is known for batteries to be received in a charged state. However, for safety reasons, this is typically at thirty percent of full charge. After being commissioned, the batteries are recharged and then become fully operational. In an embodiment, the charging step comprises a step of receiving charging current from a local grid supply. Alternatively, or in addition, current may be received from renewable sources. In an embodiment, each charging unit is connected to a grid supply, thereby optimising the amount of electricity available for charging purposes. However, it has been appreciated that in some situations it may be appropriate to provide a charging unit at a location where it is not possible for connection to occur to a grid supply. Under the circumstances, during normal operation, current is received from the other charging units connected to the ring. During the commissioning of the system, following the method detailed above, the charging step comprises a step of receiving charging current from an adjacent rechargeable battery. This may include the step of receiving the charging current via a charge balancing procedure that includes current-limited DC to DC conversion. In an embodiment, the charge balancing procedure provides hysteresis in anticipation of voltage changes occurring upon disconnection. When charged, it is then possible to continue with the commissioning procedure. According to a second aspect of the present invention, there is provided an apparatus as set out in claim 11. Embodiments of the invention will be described, by way of example only, with reference to the accompanying drawings. The detailed embodiments show the best mode known to the inventor and provide support for the invention as claimed. However, they are only exemplary and should not be used to interpret or limit the scope of the claims. Their purpose is to provide a teaching to those skilled in the art. Components and processes distinguished by ordinal phrases such as “first” and “second” do not necessarily define an order or ranking of any sort. In the drawings: Figure 1 shows a national distribution of geographical sites where charging facilities have been provided; Figure 2 details the positioning of charging facilities at the second site identified in Figure 1; Figure 3 details the third parking location identified in Figure 2; Figure 4 details the first parking location identified in Figure 2; Figure 5 details the second parking location identified in Figure 2; Figure 6 shows a schematic representation of the charging unit identified in Figure 5; Figure 7 details the charging head identified in Figure 5; Figure 8 shows a graphical image displayed on the visual display unit identified in Figure 5; Figure 9 shows an alternative graphical image; Figure 10 shows an alternative graphical image; Figure 11 shows an alternative graphical image; Figure 12 details the battery charging base identified in Figure 5; Figure 13 shows the rechargeable battery module identified in Figure 12; Figure 14 details the DC switching module identified in Figure 12; Figure 15 shows the connection of two charging units; Figure 16 shows a further embodiment with a third charging unit connected; Figure 17 shows a further embodiment with a fourth charging unit connected; Figure 18 shows ring connected units; Figure 19 shows a flowchart illustrating procedures performed for installing electric vehicle charging units at a selected site; Figure 20 details the procedures for ring commissioning identified in Figure 16; Figure 21 details procedures for balancing the states of charge identified in Figure 20; Figure 22 shows procedures performed by a site coordination processor to achieve sequential connection, as identified in Figure 15; Figure 23 shows an example of a data presentation processor; Figure 24 shows a further embodiment in which 12 charging units have been connected in a ring; Figure 25 shows a charge balancer that includes a controller; and Figure 26 details the controller identified in Figure 25. Figure 1 The charging of electric vehicles can be relatively straightforward if it is possible to gain access to a national power grid at a position that is capable of providing high levels of power, far above that of a standard supply. This approach can be adopted, for example, when establishing a new motorway service station, in which the infrastructure for feeding appropriate levels of electrical energy to the service station is similar to that for providing trunk connections to a small town or village. As demand for charging facilities increases, these are required at existing locations where it would not be practical to provide new trunk cabling for supplying high levels of charging current. Thus, for example, when establishing parking and charging facilities on existing streets, the only electrical energy available may be that originally installed for supplying power to street lamps. Thus, from an existing street supply, only four hundred watts may be available, although more may become available when sodium lights are replaced with more efficient light-emitting diode-based lighting. Thus, on many sites where electric vehicle charging facilities are required, the availability of electrical power is limited. An average vehicle does nine thousand miles per year which works out at twenty-five miles per day and most electric vehicles are capable of travelling three miles per kilowatt hour. Thus, when directly connected to a standard power source, charging times become quite significant, requiring many hours, and are therefore of little use if, say, a two-hour period is available during a shopping trip. The present applicant has developed charging units that themselves contain a rechargeable battery. In this way, it is possible to continually charge this battery at a relatively low rate, such that it is then possible to transfer this electrical energy to an electric vehicle at a relatively high rate. Thus, a vehicle could receive a substantial charge, of say eighty per cent of capacity, during a charging period, of say, thirty minutes. The provision of systems of this type allow electric vehicle charging units to be located at many sites that would not otherwise be available. In addition, as shown in Figure 1, it is possible for the operation of these sites to be monitored by a national data collection centre 101. Thus, an embodiment provides for the national data collection centre 101 to receive charging related data from a first site 111, a second site 112, a third site 113 and a fourth site 114. The national data collection centre includes data presentation processors, an example of which will be described with reference to Figure 20. Figure 2 Second site 112 is detailed in Figure 2. The site includes a first row of shops 201, a second row of shops 202 and an office block 203. Parking, with charging facilities, is provided ata first location 211, a second location 212 and a third location 213. First and second locations represent street parking, whereas the third location is in a dedicated carpark. At some sites, charging facilities could be provided in multi-storey carparks. A site coordination office 214 includes a site coordination processor 215. In an embodiment of the present invention, individual charging units (at the first parking location 211, the second parking location 212 and the third parking location 213) are mutually connected in a ring and for each ring, a ring supervising processor is included, as described with reference to Figure 15. Each ring supervising processor collects data relating to the operation of each charging unit within its ring and transfers this data to the site coordination processor 215. The site coordination processor 215 is then in a position to convey this usage data to the national data collection centre 101. Figure 3 The third parking location 213 is illustrated in Figure 3. This example shows a first charging unit 301, a second charging unit 302 and a third charging unit 303. In this example, a total of twelve charging units are provided at the third parking location, arranged in three banks of four. Figure 4 The first parking location 211 is illustrated in Figure 4. For this on street parking, a thirteenth charging unit 413 is shown, along with a fourteenth charging unit 414 and a fifteenth charging unit 415. Charging units 413 to 415 are located substantially close to a respective street lamp and make use of the electrical supply to the respective street lamp for receiving electricity continually from the grid. Figure 5 A sixteenth charging unit 516 is shown in Figure 5, positioned at the second parking location 212. In this embodiment, a vehicle charging head 517 has been separated from a battery charging base 518, with appropriate connecting cables being installed beneath a pavement 519 between the head and the base. Although a single charging unit is illustrated, in the embodiment, a total of four charging units are ring connected at the second parking location 212. In the embodiment shown in Figure 5, the vehicle charging head 517 includes a vehicle connecting cable 520 and a visual display unit 521. Figure 6 A schematic representation of the sixteenth charging unit 516 is illustrated in Figure 6. A data cable 601 provides data communication between the vehicle charging head 517 and the battery charging base 518. A power transmission cable 602 transfers charging current from the battery charging base to the charging head and then on to a connected vehicle 603 via a second power transmission cable 604. An alternating current supply 605 from the national grid is supplied to the battery charging base 518, either as a single-phase supply or, if available, as a three-phase supply. As described with reference to Figure 12, this AC supply is rectified to direct current for charging the rechargeable battery. The vehicle charging head 517 also receives user input, identified generally at 606. In an embodiment, the visual display unit 521 is implemented as a touchscreen and as such, user input is received via this touchscreen. The vehicle charging head is also responsive to contactless card payments and, in an embodiment, is provided with optical number plate recognition. The present embodiment provides for the rechargeable battery contained within the battery charging base 518 to be connected in parallel with similar batteries contained within similar charging bases connected together in a ring. Thus, a West power port 607 connects to an East power port of the adjacent charging unit in the ring, in an anticlockwise direction. This in turn connects to the next charging unit in the ring, as described with reference to Figure 15, until a West power port of an adjacent unit is connected to an East power port 608 of the battery contained within base 518, thereby closing the ring. In addition, a data ring is provided with a similar topology, such that a West data port 609 connects with an East data port of an adjacent vehicle charging head and so on until a connection is made from a West data port of an adjacent unit to an East data port 610 of charging head 517. An embodiment therefore shows an apparatus for charging an electric vehicle, comprising a rechargeable battery with a positive terminal and a negative terminal. A power transfer controller is arranged to configure direct current switching means to selectively supply charge to the battery from a rectified grid supply, supply charge from the battery for the recharging of an electric vehicle and control the parallel connection of a second battery. Thus, advantages are gained from connecting plural batteries in a ring, such that their terminals are effectively connected in parallel. However, to achieve this, specific operations are required to control the parallel connection of a second battery and all subsequent batteries until the ring has been completely installed. An example of a power transfer controller will be described with reference to Figure 12 and details of its operation, in order to control the parallel connection of a second battery, will be detailed with reference to Figure 14. Figure 7 An example of a vehicle charging head 517 is detailed in Figure 7. The battery charging base 518 communicates with a unit data processor 701. In an embodiment, the unit data processor 701 is responsible for controlling the parallel connection of a second battery by issuing commands to a power transfer controller over the first data cable 601. Within the vehicle charging head 517, the unit data processor 701 also communicates with a communications controller 702. The communications controller 702 facilitates communication with a contactless card payment device 703 and a number plate recognition device 704. To facilitate human input, the communications controller 702 also interfaces with a touchscreen controller 705 and the visual display unit 521. Figure 8 An embodiment of the invention supports the charging of electric vehicles in accordance with the CCS protocol. Alternative embodiments support the CHAdeMO protocol and in some embodiments, it is possible for both protocols to be supported. Further embodiments may also support AC charging up to three kilowatts, to be compatible with domestic supplies. An example of a graphical display shown on the display unit 521 is illustrated in Figure 8. A first graphical representation 801 is shown having a shape consistent with a CCS charging interface. In addition, a second graphical display 802 is also provided representing a gauge showing the extent to which the vehicle has been charged. When a vehicle has been plugged in, a local indication is provided to show that a connection has been made and messages are sent back up the data network to indicate that a transaction is about to commence. Thus, in the present embodiment, a message is sent from the unit data processor 701 to a ring supervising processor which may then pass data up to the site coordination processor 215. Thus, in an embodiment, real-time communications occur within the environment of each site, as illustrated in Figure 2, with aggregated data being transmitted up to the national data collection centre, described with reference to Figure 1. Having made a physical connection, a user is invited to authenticate the transaction using an appropriate card identified by the contactless card payment device 703. Initially, the first graphical image 801 is presented in black and the second graphical image 802 confirms that no charging is actually taking place. Figure 9 After authenticating the transaction, the first graphical image, initially displayed in black, changes to amber. The second graphical image now shows that no charging has taken place but given that a communication has taken place with a vehicle, an estimate has been made as to how long the charging process will take. In this example, the display shows that the charging process will take one hour and twenty-three minutes, as identified in a timing region 901. Figure 10 Having displayed the first graphical image in amber, showing that a connection has been made, the colour of the image changes to blue, as shown in Figure 10, when charging is actually taking place. After two minutes, as illustrated in Figure 10, the second graphical image 802 shows that the state of charge is now at three percent and that charging will continue, as shown by the timing region 901, for a further one hour and twenty-one minutes. In an embodiment, it is possible to select alternative displays, possibly showing the level of the charging current and similar technical information. However, in this embodiment, by default, large graphical images are presented showing the extent to which charge has taken place, while estimating the amount of time required for the charging period to be complete. This information is useful to the owner of the vehicle under charge but experiments have shown that this information is also appreciated greatly by other potential users who are given an indication as to when a charging location may become available. Figure 11 The charging of an electric vehicle either from a direct supply or from a stored supply, as illustrated by the present embodiment, is controlled by the battery management system contained within the vehicle itself. Thus, this battery management system will inform the unit data processor 701 as to its state of charge, via a vehicle communication cable 611. When the vehicle has received a sufficient charge, this situation is identified to the unit data processor 701 and the charging session will end. The first graphical image 801 changes colour to a green, the second graphical image shows that a one hundred percent charge has been performed and the timing region 901 shows that no more charging time is required. Figure 12 An example of a battery charging base 518 is detailed in Figure 12. The unit data processor 701 communicates with a power transfer controller 1201 over the first data cable 601. The AC supply 605 is received by an AC to DC power module 1202 and power is supplied to the second power transmission cable 604 from a DC to DC power module 1203. A DC switching module 1204 selectively connects the AC to DC power module 1202 to a rechargeable battery module 1205 when the battery is being recharged. During discharge, which is to say during the recharging of a vehicle, the DC switching module 1204 connects the rechargeable battery module 1205 to the DC to DC power module 1203. In some applications, when the rechargeable battery module is being discharged, it is necessary to disconnect the AC source. Alternatively, when recharging an electric vehicle, is may be possible to combine the output from the AC to DC power module 1202 with the output from the rechargeable battery module 1205. This latter approach is more energy efficient but may be restricted by local regulation. A transient voltage suppressor 1206 is included to prevent high voltage transients reaching the rechargeable battery module 1205. Suppressors of this type are required given that the conduction ring, established by the West power port 607 and the East power port 608, will have an inductance when connected in the ring formation described with reference to Figure 15. Thus, should the ring experience damage during operation, its inherent inductance could create a relatively high back emf. Local sensors 1207 include temperature sensors, smoke detectors and proximity sensors, the latter being to detect human presence during operational and non-operational periods. In an embodiment, the DC to DC power module is constructed from smaller power converters, with a similar power converter being used to provide the AC to DC power module function 1202. In an embodiment, the DC to DC power module 1203 includes four individual converters, each capable of supplying up to fifteen kilowatts to give a total output power of sixty kilowatts. In an embodiment, this is then de-rated to fifty kilowatts to provide a level of thermal headroom. Operation of module 1202 and module 1203 is controlled by the power transfer controller 1201, possibly using RS485. The DC to DC power module 1203 works predominantly in a constant current mode but then reverts to a constant voltage mode towards the end of a charging period. Figure 13 The rechargeable battery module 1205 is illustrated in Figure 13. Many suitable battery technologies are available, including lithium ion and lithium titanite; along with more conventional implementations such as lead acid. The present embodiment uses lithium ferro-phosphate cells, with each cell providing three-point-two volts and one-hundred amp-hours. In this embodiment, one-hundred-and-ninety-two cells 1301 are connected in series, to provide a total output of six hundred and fourteen volts. The battery is sized at fifty kilowatt hours, therefore discharging at a maximum rate of fifty kilowatts is well below a maximum permitted discharge rate, thereby substantially reducing the risk of generating excessive heat. The rechargeable battery module 1205 includes a manually operable master circuit breaker 1302 which is opened at the end of the production process and not closed again until the system commissioning process. A battery management system 1303 includes a battery management processor 1304 that communicates with the power transfer controller 1201. The battery management processor 1304 controls the operation of a multiplexer 1305 and a switching network 1306. Lithium based technologies are highly attractive in terms of giving a high charge density with a low physical density. Thus, for a similar energy capacity, lithium-based batteries are substantially lighter than a similar lead acid battery. A known problem with lithium-based technologies is that the batteries can degrade rapidly at very high levels of charge or a very low levels of charge. Thus, a purpose of the battery management system 1303 is to protect the battery from operating outside of its safe and preferred operating region. In addition to the battery as a whole being maintained within a preferred operating region, it is also necessary for each individual cell to be monitored in this way, if optimum performance is to be maintained. To achieve this, the battery management processor 1304 controls the multiplexer 1305 to present the voltage of each individual cell across the switching network 1306. A first switch 1307 is closed to allow current to pass through an internal resistor 1308, which in turn allows current to be monitored. The flow of current is integrated over a period of time by a process identified as coulomb counting. In addition, other measures may be taken to identify the state of charge for the cell, representing its level of charge relative to its total capacity. Similar measures are invoked to identify the state of charge for the battery 1301 as a whole and this information may be conveyed from the battery management processor 1304 to the power transfer controller 1201 and then on to the unit data processor 701. Thus, it is possible for the state of charge of the battery as a whole to be known by the unit data processor 701 and for this information to be compared with similar batteries within an operational ring, as described with reference to Figure 15. In a passive battery management system, if an individual cell is identified as having a state of charge that is relatively high compared to other cells in the battery, a second shunting switch 1309 is closed, resulting in an internal discharge to balance the state of charge of that cell with respect to other cells within the battery. As is known in the art, alternative active systems allow this charge to be redistributed to other cells within the battery. Figure 14 The DC switching module 1204 is detailed in Figure 14. This includes an input contactor 1401 for isolating the DC charging current from the AC to DC power module 1202. A similar output contactor 1402 disconnects the DC to DC power module 1203. Consequently, and when required, it is possible to completely isolate the AC to DC power module 1202 from the DC to DC power module 1203. Alternatively, in a different configuration, it may be possible to combine power from the AC to DC power module 1202 with power from the rechargeable battery module 1204, to provide maximum power to the second power transmission cable 604. A battery contactor 1403 isolates the rechargeable battery module 1205. The DC switching module 1204 also includes a commissioning network 1404 which is deployed, in accordance with this embodiment, during the commissioning of a ring of charging units, as described with reference to Figure 15. A first commissioning contactor 1405 is controlled by the power transfer controller 1201 to place a current limiting resistor 1406 and a current sensor 1407 in series with a west port transmission line 1409 and an east port transmission line 1410. As described with reference to Figure 15, when this connection is made, current may flow between the west port transmission line 1409 and an east port transmission line of the next charging unit in the ring. In an embodiment, the current sensor 1407 is a Hall effect current sensor with an internal integrated circuit amplifier. Zero current output voltage is midway between the supply voltages that maintain a four to eight volt differential. Under the control of the unit data processor 701, or a similar networked processor, current detected by the current sensor 1407 is monitored and when below a predetermined level, a second commissioning contactor 1410 may be closed, thereby shunting the current limiting resistor 1406 and connecting the two adjacent batteries directly in parallel. Figure 15 An embodiment is shown in Figure 15 for charging electric vehicles. The embodiment has a first charging unit 1501 with a first rechargeable battery having a first positive terminal 1502 and a first negative terminal 1503. A second charging unit is provided having a second rechargeable battery with a second positive terminal 1512 and a second negative terminal 1513. A first conductor 1521 connects the first positive terminal 1502 to the second positive terminal 1512. In addition, a second conductor 1522 connects the first negative terminal to the second negative terminal, thereby electrically connecting the first rechargeable battery in parallel with the second rechargeable battery. Each charging unit (1501,1511) is substantially similar to that described with reference to Figure 12. Each is provided with a supply of recharging electricity 1531 and is capable of delivering DC charging current to a vehicle via an output cable 1532. Each has a state of charge detection device, as required during standard operation to thereby monitor the recharging of the battery module 1205 and the discharging of this battery module as it is used to recharge a vehicle. It can be appreciated that substantial currents are used during the recharging of a vehicle that must be sustained for a significant period of time. Consequently, the level of energy contained within the battery module is significant and great care must be taken when batteries are connected together in order to provide the enhanced functionality combination. Thus, in an embodiment of the present invention, each charging unit is also provided with a current measuring device 1407, possibly in the form of a Hall effect detector, and a current limiting device 1406 possibly in the form of a resistor. A processing device, possibly implemented as the power transfer controller 1201, is configured to assess the state of charge of the first rechargeable battery and the second rechargeable battery. If the batteries have recently arrived at a construction site, it is likely that the state of charge will be around thirty percent. However, it is likely that differences will be present, therefore it would not be possible to directly connect these batteries in parallel without experiencing significant current flow that could be dangerous and is likely to inflict damage upon the batteries. Having assessed the state of charge of each of the rechargeable batteries, the rechargeable battery assessed as having the lower state of charge is charged until it has a state of charge substantially similar to that of the battery assessed to have the higher state of charge. Thus, it is possible for charging unit 1501 to have the higher state of charge or for charging unit 1511 to have the higher state of charge. The unit having the lower state of charge, in this example, may be the second charging unit 1511. Charging unit 1511 receives electricity from a local grid supply 1532 and this is used, in an embodiment, to bring the state of charge at the second charging unit 1511 up to a level that is substantially similar to the charge present at the first charging unit 1501. The first rechargeable battery is now connected to the second rechargeable battery via the first conductor and the second conductor. At the second charging unit 1511, the electrical connection is completed via the current limiting device 1406. Thus, it is possible for current flow to occur between the batteries present at 1501 and 1512 but the level of current is limited to an extent that damage will not occur. Thus, having brought the levels of charge to substantially similar values, the process of balancing is completed by allowing current to flow through resistor 1406. However, to achieve operational functionality, with the batteries connected in parallel, resistor 1406 is bypassed by activation of the second commissioning switch 1410. Thus, after activation of switch 1405, current flow is monitored between the first rechargeable battery and the second rechargeable battery through the first conductor and the second conductor by means of the current measuring device 1407. As previously described, when the level of current flow reaches an acceptable level, the current limiting device is then bypassed and the first charging unit and the second charging unit are now considered commissioned and may be deployed for the recharging of electric vehicles. Figure 16 In the embodiment shown in Figure 16, a third charging unit 1601 includes a rechargeable battery that is to be connected in parallel with the rechargeable batteries present at the first charging unit 1501 and the second charging unit 1502. Thus, the third charging unit 1601 is also connected to the first conductor 1521 and the second conductor 1522. For the arrangement shown in Figure 16, the balancing procedure is first performed with respect to all three charging units. Thus, again, the rechargeable battery having the highest state of charge is identified and then the charge present on the remaining two batteries is brought up to a substantially similar level, using their respective connections 1531 to the mains supply. The commissioning procedure is then performed as previously described with the second charging unit 1502 being connected to the first charging unit 1501. Thereafter, it is possible for the third charging unit 1601 to be connected. At the third charging unit 1601, a first commissioning contactor 1405 is operated, thereby allowing current to flow through the current limiting resistor 1406. Current flow is again monitored by the respective current sensor 1407 and again, when the level of current flow reaches an acceptable level, the second commissioning contactor 1410 is operated, thereby bypassing the current limiting resistor 1406. Figure 17 An embodiment is shown in Figure 17 in which a fourth charging unit 1701 is connected to the third charging unit 1601. However, the embodiment of Figure 17 may be seen as a general case in that significantly more charging units may be connected in this way. Thus, the fourth charging unit 1701 may be identified as a final charging unit having a final rechargeable battery connected to the first conductor 1521 and the second conductor 1522. The final charging unit 1701 is connected to the previous charging unit which, in this embodiment, may be identified as a third charging unit 1601. However, in other embodiments, significantly more charging units may be connected in this way consisting of, say, twelve charging units, fifteen charging units or twenty charging units etc. For any number of charging units present within the configuration, the first stage involves assessing the charge present on each respective rechargeable battery. Again, the battery having the highest state of charge is identified and the remaining batteries are charged from local supplies 1531 to ensure that all of the batteries within the group have been charged to a substantially similar level. Commissioning is then performed, as previously described, on a stage-by-stage basis. Thus, the third charging unit 1601 is only commissioned after full connection has been achieved between the first charging unit 1501 and the second charging unit 1502. Eventually, the procedure will reach the final charging unit 1701, whereafter the configuration becomes fully commissioned. Figure 18 At the second parking location 212, four charging units of the type described with reference to Figure 6 are connected in a ring. This comprises a power balancing ring 1801 and a data transmission ring 1802. This creates a system for charging electric vehicles having a set of charging units with a first direct current transmission conductor and a second direct current transmission conductor. Each charging unit of the set includes a rechargeable battery with a positive terminal and a negative terminal. The first direct current transmission conductor directly connects the positive terminals of the rechargeable batteries and the second direct current transmission conductor directly connects the negative terminals of the rechargeable batteries in parallel. A processor is then configured to control the sequential connection of the batteries to form an electrical ring, with the power balancing ring 1801 being defined by a first transmission conductor 1811 (connected to positive terminals) and a second transmission conductor 1812 (connected to negative terminals). In an embodiment, the charging unit includes a unit data processor 701 which is configured to control respective user interface devices and communicate with a respective power transfer controller. Thus, at each charging unit, a vehicle charging head communicates with the battery charging base. This includes the vehicle charging head 517 and the battery charging base 518, along with a second vehicle charging head 1822, a third vehicle charging head 1823 and a fourth vehicle charging head 1824. Thus, these communicate with a respective second battery charging base 1832, a third battery charging base 1833 and a fourth battery charging base 1834 respectively. In an embodiment, one of the data processors (unit data processor 701) in combination with its respective power transfer controller 1201 are exclusively selected to control the sequential selection of the batteries to complete the electrical ring. Thus, in an embodiment, a first node 517 may be identified as a master, with the second node 1822 being a slave, along with the third node 1823 and the fourth node 1824. In an alternative embodiment, each node is configured with appropriate instructions to implement the master function. A selection is then made during installation and commissioning. Thus, in an embodiment, each node could carry a unique number and the lowest number within the ring could be selected. Alternatively, it would be possible to perform an election process where all nodes claim to assume the functionality after a random period, with the first to call becoming the master. Thus, under these scenarios, if the master is lost, it is possible for one of the other nodes to take over. In addition to the vehicle charging units connected to the data transmission ring 1802, a ring supervising processor 1825 is also connected to the data transmission ring 1802. The main purpose of the ring supervising processor is to collect operational data and transfer this to the site coordination processor 215. However, in addition, in an embodiment, the ring supervising processor 1825 could be configured as the master for ring commissioning purposes. Thus, in this embodiment, commissioning commands are generated by the ring supervising processor 1825 and transmitted, as addressed packets, to selected unit data processors 701, such that, internally, further communication can take place with the respective power transfer controller 1201 to control the respective commissioning circuit 1404. It is possible for a similar set of charging units to be provided at the first parking location 211 and at the third parking location 213. Each is provided with a respective ring supervising processor and these in turn communicate with the site coordination processor 215. Data communication over the data transmission ring 1802 takes place in accordance with the Ethernet ring protection switching protocol, such that routers are told that they have been configured in a ring. In accordance with this protocol, a first node is identified as the owner and an adjacent node is identified as the neighbour. If the owner receives a packet, it is possible for this packet to be transmitted to the next node via its west port. That is to say, the first node 517 can send a packet to the second node 1822 but not to the neighbour, that is, not to node 1825. Thus, a packet is dropped if an address suggests that it should be sent to the east port. If a packet cannot get to its destination, the connection between the owner and the neighbour will be re-established, to allow the packet to go the other way around; this being due to the presence of a fault on the data ring. When the data ring is re-established, this is detected due to the echoing of packets, such that the connection between the owner (517) and the neighbour (1825) is closed again. Figure 19 A flowchart illustrating the procedures performed for installing electric vehicle charging units at a selected site, such as that described with reference to Figure 2, is shown in Figure 16. At step 1901, the charging units are manufactured, each consisting of a vehicle charging head and a battery charging base of the type described with reference to Figure 5. Before being dispatched, the batteries are charged at step 1902 to facilitate commissioning. However, in accordance with regulations relating to transportation, the batteries are charged to a state of charge of only thirty percent. At step 1903, the charging units are transported to site; whereafter, at step 1904, the charging units are allocated to positions, thereby specifying where the ring sets will be located. Having allocated the rings at step 1904, a ring is selected at step 1905 and a unit within the ring is then selected at step 1906. The unit is installed at step 1907, whereafter the next unit is selected until the question asked at step 1908 is answered in the negative. This results in the creation of a complete ring, where physical connections will have been made of the type illustrated in Figure 15. However, for each battery, the master circuit breaker 1302 will be open and the output contactor 1402 will also be open. In this condition, it is not possible to derive charge from any of the batteries and the configuration is completely safe. At step 1909, the ring is commissioned, as detailed in accordance with an embodiment of the present invention. Thereafter, at step 1910, a question is asked as to whether another ring is present and when answered in the affirmative, the next ring is selected at step 1905. Eventually, all of the rings at the site will have been commissioned, resulting in the question asked at step 1910 being answered in the negative and the site being coordinated at step 1911. Thus, site coordination ensures that each ring set is communicating with the site coordination processor 215. Having established site coordination, the site coordination processor 215 reports to the national data collection centre 101 at step 1912. Figure 20 Although the batteries are at this stage only charged to thirty percent of their total capacity, this still represents a substantial amount of energy and great care must be taken when connecting these batteries into the ring configuration described with reference to Figure 15, to ensure that dangerous levels of current do not flow during the balancing exercise. Having physically connected the charging units into the topology described with reference to Figure 15, master circuit breakers 1302 may be opened and communication may be established with the rechargeable battery modules. To achieve this, it is necessary for a twelve-volt supply to be connected to each of the rechargeable battery modules, derived from their respective local grid supply 605. Thus, to initiate the commissioning process, in this embodiment, it is necessary for each of the charging units to be connected to an appropriate grid supply. Flow of current into the battery, for charging purposes, may be achieved by closing the input contactor 1401 and the battery contactor 403. All commissioning contactors 1405 / 1410 will be open. This represents the end of a manual stage of the commissioning process, with automated procedures now taking over, possibly under the control of the ring supervising processor 1525, as illustrated in Figure 17. At step 2001 the state of charge of the unconnected batteries is balanced. That is to say, before parallel connection is possible, it is necessary for all of the batteries in the parallel ring to be brought to substantially the same state of charge. Thereafter, at step 2002, connection is made in a strict sequential fashion. Thus, after balancing, the battery of the first node is connected anticlockwise to the battery of the second node at charging base 1532. Thus, base 518 and base 1532 become parallel connected. Then and only then is a similar connection made between the second base 1532 and the third base 1533. This results in the first three batteries being parallel connected, which must be achieved before the fourth battery is connected. Thus, having connected the first three, the sequence continues with a connection being made between the third base 1533 and the fourth base 1534. The ring is then completed by connecting the fourth base 1534 back to the first base 518. Thus, this final connection results in the completion of the ring at step 2003, followed by confirmation being provided back to the site coordinator 214 at step 2004. Figure 21 Procedures 1701 performed by the ring supervising processor 1525, for balancing the state of charge, are detailed in Figure 18. At step 2101 a variable representing the maximum charge present is set to zero percent. The first unit is selected at step 2102 and the state of charge of this battery is measured at step 2103. The state of charge should be around thirty percent. For the purposes of this illustration, it is assumed that the charging unit has been in storage for a period of time and the state of charge C has been reduced to twenty-five percent. At step 2104 a question is asked as to whether the current state of charge is larger than the maximum and when answered in the affirmative, C max is set to the value of C. Thus, on this first iteration, C max will be set to twenty-five percent. At step 2106, a question is asked as to whether another unit is present and when answered in the affirmative, the next unit is selected at step 2102. Again, the state of charge is measured at step 2103 and assuming that this charging unit was manufactured relatively recently, it may be assumed that the state of charge is still thirty percent. Thus, the question asked at step 2104 will again be answered in the affirmative and C max will now be set to thirty percent. Thus, this process continues until all of the charging units have been considered and the variable C max will represent the highest charge present. To complete the balancing procedure, the batteries are selected again with the first being selected at step 2107. The state of charge is measured again at step 2101 and a question is asked at step 2109 as to whether the state of charge is smaller than the variable C max. When answered in the affirmative, local charging of the battery occurs, to bring the state of charge up to level C max at step 2110. A question is then asked as to whether another battery is to be considered and when answered in the affirmative, the next battery is selected at step 2107. Often, this procedure will result in all of the batteries being recharged to a certain extent, except for the one that arrived on site with the maximum charge. Thus, in theory, all of the batteries should be brought up to a state of charge of thirty percent. Having completed the balancing procedures 1701, it is possible for the first battery at the first node to be activated within the system, followed by the second battery at the second node. Figure 22 Procedures performed by the ring supervising processor 1825 to achieve sequential connection are detailed in Figure 22. At step 2201, the first unit (517 / 518) is selected. The ring supervising processor 1825 issues commands to the unit data processor 701, which in turn communicates with the power transfer controller 1201 to control the DC switching module 1204. At step 1802 the first commissioning contactor 1405 is closed and the current sensor 1407 is monitored at step 2203. At step 2204, a question is asked as to whether the current flowing through current limiting resistor 1406 is greater than plus fifty amps or minus fifty amps. That is to say, is the modulus of the current greater than fifty amps? If the question asked at step 2204 is answered in the affirmative, the first commissioning contactor 1405 is opened and a first fault is reported at step 2204. Thus, this first fault condition would be identified by the ring supervising processor 1825 and transmitted to the site coordination processor 215. This indicates that a serious fault condition exists, possibly in the form of a short circuit within the power balancing ring 1801 itself. Thus, a major investigation will be required before it is possible for the commissioning process to be reinstigated. If the question asked at step 2204 is answered in the negative, to the effect that the modulus of the current is less than fifty amps, a question is asked at step 2206 as to whether the modulus of the current is less than two amps. When less than two amps, this is considered to be an acceptable current flow for the power balancing ring 1801 and as such the second commissioning contactor 1410 is closed at step 2210. This bypasses the current limiting resistor 1406 and establishes a direct parallel connection between the first battery and the second battery. If the question asked at step 2202 is answered in the negative, to the effect that the amount of current flowing is between two amps and fifty amps, the value is stored at step 1807 and the procedure waits for a predetermined period of time before sampling the current value again. Thus, a question is then asked at step 2208 as to whether the new current measurement I2 is 5 smaller than the previous current measurement 11. If answered in the negative, confirming that the level of current is being maintained and is not balancing, the first commissioning contactor 1405 is opened and a second fault type is reported at step 2209. Again, the existence of this fault is reported back to the site coordination processor 215 for appropriate action to be taken before the 10 commissioning procedure is resumed. If the question asked at step 2208 is answered in the negative, to the effect that the current is reducing, the question at step 2206 is again asked as to whether the modulus of the current is less than two amps. If higher than two amps, the question is answered in the negative, resulting in the value being 15 stored again at step 2207 and the comparison being made again at step 2208 to confirm that the current is decreasing. Again, if this decrease does not continue, a fault condition will be reported at step 2209. However, under normal circumstances, the level of current flow will continue to decrease until, eventually, the question asked at step 2206 is 20 answered in the affirmative, thereby allowing the second commissioning contactor 1410 to be closed and the next unit selected at step 2211. The embodiment therefore provides a method of connecting batteries in parallel, in which each battery is contained within a charging unit for charging an electric vehicle and receives charge from an external source. A set of 25 charging units are received that contain batteries for direct current ring connection. The state of charge of each battery is assessed to ensure that the states of charge are similar. Parallel connection of the first battery to an adjacent battery is performed via a current limiting resistance and the resulting current flow is measured. This current limiting resistance is then bypassed if 30 the current flow is below a predetermined threshold. A further part of this procedure involves the partial charging of each battery to a predetermined state of charge after manufacturing but before being received on site. This minimises the commissioning time, given that charge is already available that may in turn be balanced. To achieve balancing, internal battery management processors are interrogated to provide reliable information identifying a state of charge. External direct voltage measurement is avoided, given that this can provide unreliable results. An optimised coulomb counting process embedded within the battery management system of each battery module is relied upon to produce accurate state of charge information to within acceptable tolerance levels. In the embodiment, the method continues to measure current if the current is below a predetermined level but above a predetermined threshold. A fault condition is raised if the measured current is not falling towards the predetermined level. When the measured current is above the predetermined level, an appropriate fault condition is identified. Figure 23 An example of a data presentation processor 2301, of the type resident at the national data collection centre 101, is illustrated in Figure 23. The data presentation processor is configured to receive usage data from the site coordination processors 215. In this way, it is possible for the data to be presented graphically in dashboard-from, including a graphical representation 2302 of the geographical position of the charging sites. In the example shown in Figure 2, a display dashboard identifies specific electricity suppliers in a first region 2311. Thus, a first supplier EC1 is shown, along with a second supplier EC2. Either may be selected, resulting in relevant information being displayed in a second region 2312, a third region 2313 and a fourth region 2314. The second region 2312 identifies four sites receiving power from the selected electricity supplier and displays the use of electrical energy over a predetermined period of time. If site two is selected, this being the site described with reference to Figure 2, the third region 2313 displays the three rings that are present of that site and again shows the amount of electrical usage for each ring. When the second ring is selected, the actual charging units present within that ring are shown in the fourth region 2314, again showing the actual usage made of each charging unit. This approach allows ring connected systems to be compared with non-ring selected systems and allows operatives to optimise decision making processes in terms of how charging unit allocation should be made or modified at particular sites. Figure 24 An embodiment is shown in Figure 24 in which twelve charging units have been connected in a ring, following a procedure substantially as described with reference to Figure 18. Most of the charging units have been provided with a local connection 1531 to the local grid supply. However, the third charging unit 2403 and the eighth charging unit 2408 have been located at positions where a grid supply is not available. If the local rechargeable battery at unit 2403 and at unit 2408 have been brought up to a state of charge that is substantially similar to that present at the other batteries within the ring, commissioning can be performed as previously described. However, a difficulty arises in that these charging units (2403 / 2408) do not have a local connection and therefore cannot be recharged independently. To complete the first stage of the procedure, it is necessary to charge batteries present at unit 2403 and 2408, unless one of these batteries has been identified as having the highest state of charge within the collection. For the purpose of this example, it will be assumed that the local rechargeable battery present within charging unit 2403 does require additional charge before the battery may be fully connected to the second charging unit 2402. To achieve the transfer of charge to the third charging unit 2403, in an embodiment, a DC to DC converter supplies charge from a previous rechargeable battery prior to connecting the rechargeable batteries via the first and second conductors 1521 / 1522. Figure 25 A charge balancer is illustrated in Figure 25 that includes an isolated DC to DC converter 2501, possibly implemented as a UR75020-AD device rated at 750V and 15kW with an output set to 865V at 21 Amps. However, in alternative embodiments, alternative devices may be selected and different settings may be deployed to satisfy the requirements of a local environment. After performing the first procedure, as previously described, the state of charge of each battery is known. Thus, the balancing requirements are known in terms of which battery is to be a source and which battery is to be a destination. In the example described with reference to Figure 24, it has been determined that, in order to commission the third charging unit 2403, it will be necessary to transfer charge from the second charging unit 2402. In the embodiment of Figure 25, the charge balancer is bi-directional and, as such, could be included as part of the overall design for each charging unit deployed. Alternatively, it may be a separate device that is connected when required. In the embodiment of Figure 25, the downstream charging unit 2402 is connected at 2502 and the upstream charging unit 2403 is connected at 2503. The DC to DC converter 2501 will transfer current in the direction of arrow 2504. To achieve transfer in the required direction, a first direction transfer switch 2511 is activated in combination with a second direction transfer switch 2512. In the configuration shown in Figure 25, transfer will occur from 2502 to 2503. In the alternative configuration for switches 2511 and 2512, transfer will occur in the opposite direction. Connection and disconnection may result in the creation of high transient voltages, therefore the charge balancer is provided with a voltage regulator 2513 and a capacitor 2514. To initiate the transfer of charge from the first battery, at charging unit 2402, to the second battery at the third charging unit 2403, an activation switch 2515 is operated in response to an activation signal from a controller 2516. Figure 26 Controller 2516 is detailed in Figure 26. The voltage from the first battery is presented at A and the voltage from the second battery is presented at B. The controller examines these voltages and whichever is identified as the source, is used to move energy to the other side of the balancer in a controlled way until the voltages become substantially equal. Voltages A and B are supplied to a comparator 2601 which, in an embodiment, is constructed around an operational amplifier circuit to produce an output to a latch 2602 when a difference is present. Upon detecting this difference, the controller 2516 activates switch 2515, such that the transfer of current is initiated at a level limited by the DC to DC converter 2501. If left in this way, the transfer of charge will continue until the source battery has been depleted and all of the charge has been transferred to the destination battery. To prevent this occurring, the latch 2602 detects when the output from the comparator 2601 changes, which will occur when the voltages A and B are substantially similar. An output from the latch 2602, indicating that the transfer is complete, is passed on to a delay and hysteresis circuit 2603. It is appreciated that changes to battery voltages will occur when the disconnection is made. Thus, when connected, substantially similar voltages will be present. However, upon disconnection, the voltage at the source battery will tend to increase and the voltage at the destination battery will tend to decrease. Consequently, further charge transfer is required beyond the point at which an equilibrium position has been detected. Thus, circuit 2603 introduces a delay before generating the activation signal for switch 2515. Furthermore, having been forced to operate in a particular way, hysteresis is present, such that a higher level of detection is required in order to deactivate the switching operation. This ensures that once a decision has been made to produce the activation signal, a further activation in the opposite direction is not introduced which in turn could lead to undesirable oscillations. Thus, in an embodiment, more charge is supplied to the destination battery before the charge balancer is disconnected. This ensures that the charge levels will be substantially similar after their post disconnection realignment has taken place, such that it is then possible to perform the next stage of the commissioning procedure as previously described. Having supplied charge to the battery present at the third charging unit 2403, a similar procedure may be performed for the eighth charging unit 2405 5 which, again, does not include a local supply. To achieve charge balancing, the rechargeable battery present at the eighth charging unit 2408 may receive charge from the seventh charging unit 2407 or from the ninth charging unit 2409. It should also be noted that local grid supplies are also relied upon 10 during an initial wakeup of the charging unit itself and, in particular, involving an activation of the rechargeable battery and its own battery maintenance system. Consequently, for the charging units (2403 / 2408) that are not connected to the grid supply, a secondary low capacity battery is provided which will power the local control system of the charging unit, thereby allowing 15 its local high voltage battery to be brought online.

Claims

1. A method of commissioning a system for operationally charging electric vehicles, comprising the steps of:connecting a first charging unit to a second charging unit via a first conductor and a second conductor, such that a first rechargeable battery in said first charging unit may be electrically connected in parallel with a second rechargeable battery in said second charging unit;assessing the charge of each said rechargeable battery;charging the rechargeable battery assessed as having the lower charge substantially to the level of the rechargeable battery assessed as having the higher charge;electrically connecting said rechargeable batteries within a charging unit via a current limiting resistance;measuring the current flowing between the rechargeable batteries; and bypassing the current limiting resistance when said current falls below a predetermined level.

2. The method of claim 1, further comprising the steps of:connecting one or more additional charging units, each having a respective additional rechargeable battery;assessing the charge on each said rechargeable battery;identifying the rechargeable battery with the highest level of charge; and charging the remaining batteries to a level substantially as high as said highest level.

3. The method of claim 2, further comprising the step of electrically connecting a next rechargeable battery of a next charging unit via a next current limiting resistance;measuring current flow into said next rechargeable battery; andbypassing said next current limiting resistance when said current flow falls below a predetermined value, thereby sequentially connectingrechargeable batteries in parallel such that, in operation, said rechargeable batteries function as a unified source of charge.

4. The method of claim 3, wherein a final charging unit is connected to the first charging unit, thereby creating a ring.

5. The method of any of claims 1 to 4, wherein said assessing step comprises assessing the charge on rechargeable batteries that have received a transportation charge prior to respective charging units being received at an installation site.

6. The method of any of claims 1 to 5, wherein said charging step comprises the step of receiving charging current from a local grid supply.

7. The method of any of claims 1 to 6, wherein said charging step comprises the step of receiving charging current from an adjacent rechargeable battery.

8. The method of claim 7, wherein said step of receiving charging current from an adjacent rechargeable battery includes the step of receiving said charging current via a charge balancing procedure that includes current limiting de to de conversion.

9. The method of claim 8, wherein said charge balancing procedure provides hysteresis in anticipation of voltage changes occurring upon disconnection.

10. The method of any of claims 1 to 9, wherein said current limiting resistance is a resistor and bypassing step comprises the step of operating a shunting switch connected in parallel with said resistor.

11. An apparatus for charging electric vehicles, comprising:a first charging unit having a first rechargeable battery with a first positive terminal and a first negative terminal;a second charging unit having a second rechargeable battery with a second positive terminal and a second negative terminal;a first conductor for connecting said first positive terminal to said second positive terminal;a second conductor for connecting said first negative terminal to said second negative terminal, thereby electrically connecting said first rechargeable battery in parallel with said second re-chargeable battery;a supply of re-charging electricity;a state of charge detection device;a current measuring device;a current limiting device; and further comprising a processing device configured to:assess the state of charge of said first re-chargeable battery and said second re-chargeable battery;charge the re-chargeable battery assessed as having the lower state of charge until it has a state of charge substantially similar to that of the battery assessed to have the higher state of charge;connecting said first rechargeable battery to said second rechargeable battery via said first conductor and said second conductor; and at said second charging unit:completing said connection via said current limiting device;monitoring current flow between said first rechargeable battery and said second rechargeable battery through said first conductor and said second conductor by means of said current measuring device; andbypassing said current limiting device when said monitored current flow falls below a predetermined value, thereby commissioning the apparatus for the recharging of electric vehicles.

12. The apparatus of claim 11, further comprising a third charging unit having a third rechargeable battery connected to said first conductor and said second conductor.5 13. The apparatus of claim 12, further comprising a final chargingunit having a final rechargeable battery connected to said first conductor and said second conductor, wherein said final charging unit.

14. The apparatus of any of claims 11 to 13, wherein said current 10 limiting device is a resistor and said resistor is bypassed by a current shunting switching device.

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