GB2501480A

GB2501480A - Electrical vehicle supply equipment (EVSE)

Info

Publication number: GB2501480A
Application number: GB1207129.6A
Authority: GB
Inventors: Martin Banks
Original assignee: Nissan Motor Manufacturing UK Ltd
Current assignee: Nissan Motor Manufacturing UK Ltd
Priority date: 2012-04-24
Filing date: 2012-04-24
Publication date: 2013-10-30
Anticipated expiration: 2032-04-24
Also published as: GB2501480B; WO2013160748A1; GB201207129D0

Abstract

An electrical supply unit includes a supply unit controller 76 that controls the supply of electricity through a supply line for a battery charger and a control pilot line 24 that carries a PWM control pilot signal between the supply unit and the battery charger controller. Control unit 76 drives a control pilot signal generator to generate the PWM pilot signal and includes a switched bridge circuit 73. The bridge can comprises switches SW1,SW2 to connect pilot 24 and earth 42 lines alternately to a zero volt reference line 84, and resistors R1,R1 connecting the lines to supply 82 giving a Â±12V voltage relative to earth on the control pilot line. The supply unit can include a resistor divider network 75 having measuring node 78 whose voltage is proportional to the voltage on the pilot line and is connected to a measuring device such as analogue to digital converter (ADC) 80 in controller 76. Electrical supply unit may be an EVSE for an electric vehicle including a mains electricity switch, controlled by controller 76, to control the supply of power through the supply line.

Description

Electrical Supply Equipment The present invention relates to electrical supply equipment; and in particular, but not exclusively, to electric vehicle supply equipment for supplying electrical energy to recharge the battery of an electric vehicle. The electrical supply equipment may however also be used for other purposes, such as for recharging other types of electrical equipment.

Most electric vehicles are supplied as standard with a built-in battery charger; and with a portable electric vehicle supply equipment (EVSE) unit that can be used with the battery charger to recharge the vehicle battery as required from a mains electricity supply. In theory, an electric vehicle could simply be plugged into any mains socket for charging; but use of an EVSE unit improves safety and economy during vehicle battery charging operations, and may discourage theft of electricity from a publicly accessible mains socket.

As an optional extra, it may be possible to purchase a fixed EVSE unit that is permanently connected to a mains electricity supply. Fixed EVSE units are generally able to provide larger charging currents than portable EVSE units; and can therefore charge the vehicle battery more quickly.

In both cases, the EVSE unit includes a cable that can be plugged into a vehicle inlet to deliver a mains electricity supply to the vehicle; and a control unit that controls operation of the EVSE unit. The electric vehicle includes a charger unit that rectifies the mains electricity supply received from the BYSE, and delivers a charging current to the vehicle battery. It also includes a charger controller that controls the delivery of the charging current to the battery.

The EVSE and the vehicle charger controller communicate with one another through a control line known as a "control pilot". The control pilot is the primary control conductor, and performs some or all of the following functions: * it verifies that a vehicle is present and connected to the EVSE; * it controls energisation and de-energisation of the electrical supply; * it transmits information to the vehicle regarding the current rating of the supply equipment; * it monitors the presence of an earth (also known as ground) connection, and * it establishes whether the vehicle has any specific ventilation requirements and, if so, checks that those requirements are met during charging.

Conventionally, control information is transmitted through the control pilot line in the form of a +12V (24V peak-to-peak) pulse width modulated (PWM) signal, having a frequency of 1kHz. Control information is carried by the amplitude and duty cycle of this signal.

The EVSE includes a voltage measuring circuit that measures the amplitude of its output control signal to establish whether the vehicle is connected and ready to receive a charging current. The vehicle charger controller senses the duty cycle of the PWM signal, to establish the maximum continuous current capacity of the supply, and to detect certain crror statcs.

The main problem with conventional EVSE units is that they are complex, requiring a dual rail power supply for the +12V PWM signal; as well as operational amplifiers, and printed circuit boards to support those components. This makes conventional EVSE units large and expensive.

As a result, many owners of electric vehicles usc the portable EVSE unit that is supplied as standard equipment with the vehicle for all charging purposes. However, the current that can be supplied by a portable EVSE is usually limited to a maximum of about 10 amps, which means that the time required to achieve a full charge can be very long, typically about 12 hours. This can limit the availability and uscifilness of the vehicle.

Although more powerful fixed EVSE units that can provide a charging current of 16A can charge a vehicle fully in as little as 8 hours, the take-up of these optional units has been poor, owing to their high cost.

It is an object of the present invention to provide an electrical supply apparatus that mitigates at least some of the aforesaid problems.

According to the present invention, there is provided an electrical supply unit for supplying electricity to a battery charger, the electrical supply unit including a supply line through which electricity is supplied to the battery charger, a supply unit controller that controls the supply of electricity through the supply line, and a control pilot line that carries a PWM control pilot signal between the electrical supply unit and the battery charger, wherein the supply unit includes a control pilot signal generator that generates the PWM control pilot signal, and said control pilot signal generator includes a switched bridge circuit.

The control pilot signal generator may be included in the supply unit controller.

The electrical supply unit is able to generate a ±12V PWM control pilot signal from a single rail power supply using only the switched bridge network. It does not thereibre require a dual rail power supply or the use of operational amplifiers, and as a result is considerably less expensive than conventional EVSE units. This will encourage the take-up of fixed EVSE units, or may allow both fixed and portable EVSE units to be supplied as standard equipment with electric vehicles. The EVSE unit may also be smaller than a conventional unit, as it does not require the large printed circuit boards that support the additional components required in a prior art EVSE unit.

Advantageously, the control pilot signal generator includes pilot and earth lines and first and second switch elcments configured to connect the pilot and carth lines alternately to a OV supply line. The switch elements may be either physical switches, for example relays; or solid state switching devices, lbr example transistors used as low side drivers.

The electrical supply unit preferably includes first and second supply resistors, each connected in series between a respective one of the first and second switch elements and a +12V supply line. For example, lkS resistors may be used.

Advantageously, an earth connection is connected between the first supply resistor and the fIrst switch element, and the control pilot line is connected between the second supply resistor and the second switch element.

The electrical supply unit may include a switch control device configured to control the switching of said first and second switch elements, so as to control the duty cycle of the control pilot signal.

The electrical supply unit preferably includes a divider network that is connected between pilot and earth lines and includes a measuring node, and a voltage measuring device connected to measure the voltage at the measuring node, the divider network being configured such that the voltage at the measuring node is positive and proportional in magnitude to the voltage on the control pilot line.

Advantageously, the divider network comprises a T-network of resistors and the measuring node is located at the central junction of the T-network. The T-network preferably consists of relatively high resistance resistors, for example having a resistance of at least 10th and mere preferably at least 100th.

The control pilot signal generator preferably generates a ±12V PWM control pilot signaL According to another aspect of the invention, there is provided an EVSE unit including an electrical supply unit according to any one of the preceding statements of invention.

The supply line is preferably configured to supply mains electricity to a vehicle battery charger.

Mvantageously, the EVSE unit includes a mains electricity switching device!br controlling the supply of mains electricity through the supply line, said mains electricity switching device being controlled by the supply unit controller.

An embodiment of the present invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a block diagram of a typical conventional electric vehicle charging system; Figure 2 is a block diagram illustrating the main components of a conventional electric vehicle supply equipment (EVSE) unit; Figurc 3 illustrates a typical conventional control pilot circuit; Figurc 4 is a circuit diagram of a control pilot circuit of an EVSE unit according to an embodiment of the invention; and FigureS illustrates a control pilot circuit of an EVSE unit according to an embodiment of the invention.

The architecture and operation of a conventional EVSE unit will now be described with rcfcrence to Figures 1-3.

As shown in Figure 1, the EVSE unit 2 is connected by a mains supply cable 4 to an electrical mains outlet 6. The EVSE unit 2 is also connected by a mails supply lead S and a supply plug 10 to the vehicle inlet 12. Within the vehicle, the electrical supply is delivered via lead 14 to thc onboard chargcr 16, which supplics a rcctificd charging currcnt to the vehicle battery 18 via supply lead 20. The EVSE unit 2 is connected to the vehicle battery charger controller 22 via control pilot line 24.

The components making up a conventional EVSE init 2 are shown in more detail in Figure 2. The EVSE unit 2 is connected to the mains supply line 6 by a mains plug 26 and socket 28. Although the mains supply is shown in this Figure as 240V, 50 Hz single phase, this is only an example; EVSE units are tuned to run from the supply voltage and frequency used in the markets in which the EVSE units are sold, and can also operate from a three-phase supply.

The EVSE unit 2 includes a supply unit controller 30, a current and leakage detector (or sensor) 32 and a pair of relays 34 in the live and neutral supply lines of the mains supply lead 8. The supply unit controller 30 includes a microcontroller 36 that controls switching of the relays 34 via a relay driver 38, and a pulse width modulator 40 that generates the PWM signal in the control pilot line 24. Modulator 40 in turn comprises an oscillator 140 (Fig. 3) which generates an AC signal by switching alternately between the +2V and - 12V rails of a dual rail power supply. The microcontroller 36 is also connected to thc current and leakage detector 32 to receive signals indicating any leakage in the current supply.

The supply unit controllcr 30 also includes a user interface 41, which indicates thc opcrational status of thc EVSE unit 2, for cxamplc by LED indicators showing rcady, charge, and fault operatiollal statuses.

A conventional pilot control circuit is shown in Figure 3. The EVSE unit 2 is connected via the control pilot line 24 and an earth line 42 to a vehicle interface 44, through the plug and thc vchiclc inlet 12. The pulse width modulator 40 incorporated in the supply unit controller 30 in the EVSE unit 2 includes a 12V power supply and an electronically controlled switch Si for switching the control pilot line 24 between the 12V power supply and the outlet of the PWM oscillator MO, under the control of the control unit 30. A lkQ supply resistor RI is provided in the control pilot line 24 and a voltage measurement line 48 is connected to the control pilot line 24 at the outlet side of the supply resistor RI to measure the voltage at that point.

Within the vehicle interface 44, the charger controller 22 is connected to the control pilot line 24 via a diode 52 and a buffer 54 that measures the duty cycle of the PWM control signal. First and second load resistors R2, R3 are connected bctwecn the control pilot 24 and the earth line 42. The first load resistor R2 comprises a 1.3kQ resistor, which can be connected to or disconnected from the earth line 42 via a switch S2, which is controlled by the charger controller 22. The second load resistor R3 comprises a 2.74kQ resistor, which is permanently connected between the control pilot 24 and the earth line 42. The diode 52 allows the EVSE to differentiate between a valid charging request that affects only the positive side of the waveform; and leakage from pilot to earth, which is an error condition and affects both sidcs of the waveform.

Whcn thc EVSE unit 2 is activatcd, the control pilot line 24 is initially connectcd by thc switch Si to the 12V D.C. supply. If the plug 10 is unconnected, there will be no voltage drop across the supply resistor Ri; and the voltage measured on the outlet side of the lkI2 supply resistor Ri will therefore be 12V.

When the plug 10 is inserted into the vehicle inlet 12, a current will flow through the lkQ supply resistor Ri and the 2.74k11 load resistor R3 into the earth line 42. This causes the measured voltage to drop to approximately 9V. This voltage drop is sensed by the control unit 30, and recognised as an indication that the EVSE unit is connected to a vehicle.

Upon sensing connection to a vehicle, the switch SI is activated, connecting the control pilot line 24 to the ±12V PWM signal generated by the oscillator 140.

The PWM signal is detected by the charger controller 22, which determines the maximum available charging current from the duty cycle of the PWM signal. At the same time, the charger controller 22 closes switch S2; allowing current to flow from the control pilot line 24 to the earth line 42 through the 1.3k12 load resistor R2, as well as through the 2.74k12 load resistor R3. This causes the voltage measured at the outlet side of the lkfl supply resistor RI to drop to approximately 6V, which indicates to the EVSE control unit 30 that the vehicle is ready to charge. The EVSE unit then closes relays 34 (Fig. 2). The charger controller 22 then instructs the charger 16 (Fig. 1) to commence charging of the vehicle battery 18. When charging has been completed, the charger controller 22 causes the switch S2 to open. The resulting increase in the measured voltage to 9V indicates to the EVSE control unit 30 that charging has been completed. The EVSE unit opens relays 34 in response to this signal.

A control pilot circuit 70 for an EVSE unit 2 according to an embodiment of the invention is shown in Figures 4 and 5. The control pilot circuit 70 includes a PWM oscillator circuit 72, first and second IkQ supply resistors RI', RI" and a 12V D.C. single rail power supply 74. The control pilot circuit 70 is connected to the control pilot line 24 and to the earth line 42. The control pilot circuit 70 replaces the oscillator 140 of the conventional EVSE unit 2 shown in Fig. 3. In other respects, the EVSE unit of the present invention is substantially similar to the conventional EVSE unit 2 described above.

The PWM oscillator 72 includes a switched bridge arrangement 73 consisting of first and second control pilot switches SW1, SW2; and a switching control unit 76 that includes drivers for controlling operation of the control pilot switches. The control pilot switches SWI, SW2 may be either mechanical switches such as relays; or electronic switches, such as transistors used as low side drivers.

The PWM oscillator 72 also includes a sensing or divider network 75 comprising three identical sensing resistors Psi, Rs2 and Rs3, having a central node 78 that is connected to the input of an analogue-to-digital converter (ADC) 80 comprising part of the switching control unit 76. The sensing resistors RsI, Rs2 and Rs3 each have a resistance that is much higher than the resistance of the supply resistors Ri, Ri', so that they do not significantly affect the voltage drop on the supply resistors Ri', RI". For example, they may each have a resistance of lOOk&»=.

In use, the switching control unit 76 drives the control pilot switches SWI, SW2 so that they open and close alternately (SWI opens as SW2 closes, then SW2 opens as SWI closes). This connects the 12V outlet line 82 and the OV outlet line 84 of the power supply 74 alternately to the earth line 42.

When switch SW1 is closed and switch SW2 is open, the OV outlet line 84 is directly connected to the earth line 42; and the control pilot line 24 is connected via supply resistor RI" to the 12V outlet of the power supply 74, thus providing a voltage of+12V relative to earth on the control pilot line 24.

When switch SW2 is closed and switch SWI is open, the 12V outlet line 82 is connected to the earth line 42 via supply resistor RI!; and the control pilot line 24 is connected to the OV outlet line 84. Because the 12V outlet line 82 is connected to earth, the voltage on the control pilot line 24 is then -12V relative to earth.

Furthermore, because power supply 74 is isolated, the OV and 12V supply lines arc allowed to float relative to the earth line. The earth connection only has a positive voltage relative to the pilot line, and not relative to any other pan of the vehicle, nor to the mains electric socket.

Therefore, as the switches SWI and SW2 open and close, a +1 2V signal relative to earth is provided on the control pilot line 24. The switching control unit 76 controls the timing of the switches SW1, SW2 to generate the required PWM control pilot signal, which sends information relating to the supply current capacity to the vehicle charging controller 22.

When a conventional EVSE unit 2 is plugged into the charging inlet 12 of a vehicle as shown in Fig. 3, the control pilot line 24 is connected to earth through either one or both load resistors R2, R3 depending on whether the switch 52 is open or closed. This causes the voltage at the measurement point 46 between the supply resistor Ri and the load resistors R2, R3 to drop. The voltage at the measurement point 46 is sensed by the supply unit controller 30 through mcasuremcnt line 48 to establish whether a vchicle is eonncctcd, and when charging is taking place.

In the EVSE unit of the prcscnt invention, the single supply resistor Ri of the conventional EVSE unit is replaced by a pair of identical supply resistors RI', Ri" as shown in Fig. 4.

These supply resistors RI', RI" are switched alternately into the control pilot circuit 70 as the control pilot switches SWI, 5W2 open and close. Instead of measuring the voltage directly at the output side of the supply resistors Ri', Ri", the voltage on the control pilot line 24 is instead measured indirectly via the network of sensing resistors Rid, Rs2, 1W, which fbrm a voltage divider 75. Specifically, the ADC 80 is connected to sense the voltage at the node 78 between the three sensing resistors Rsl, Rs2, Rs3. The voltage at this point will always be positive with respect to the OV outlet of the power supply 74 and, because the sensing resistors Rsl, Rs2, 1W are identical, the voltage at the node 78 will be approximately one third the voltage at the outlet side of the respective supply resistor RI', RI".

For example, when switch SWI is closed and switch SW2 is open, and the EVSE unit 2 is not connected to a vchiclc charging point, the control pilot line 24 will be at a voltage of +12V relative to the OV outlet. Current will thereibre flow through the second sensing resistor Rs2 to the node 78, then through the first and third sensing resistors Rsl, 1W which are connected in parallel to the OV terminal of the power supply. Thereibre, the voltage drop across Rs2 will be +8V, leaving the node 78 at a voltage of +4V relative to the OV outlet line 84.

Conversely, when switch SW2 is closed and switch SW1 is open, the control pilot line 24 will be connected directly to the OV outlet line 84 of the power supply 74 and will there%re be at a voltage of-l2V relative to earth. Current will flow from the +12V outlet line 82 of the power supply 74 through the first sensing resistor Rid to the node 78, and then through the parallel-connected second and third sensing resistors Rs2, Rs3 to the OV outlet line 84 of the power supply, again leaving the node 78 at a voltage of +4V relative to the OV outlet line 84.

It can thus be seen that the voltage sensed by the ADC is always positive with respect to the OV outlet line 84 of the power supply 74. The voltage at this point is also proportional to the voltage on the conirol pilot line 24, thus allowing the EVSE to sense whether or not a vehicle is connected and whether charging is taking place. As the sensed voltage does not exceed approximately 4V, this allows the control pilot voltage to be sensed by a standard microcontroller, without the use of operational amplifiers.

It will be noted that the switched bridge circuit 73 of Figs. 4 and 5 comprises two switches and two resistors; and is therefore a half bridge circuit. Alternatively, a fisH bridge circuit could be used with further switches in place of resistors Ri' and Ri", and a resistor in the control pilot line 24 for sensing purposes.

Claims

CLAIMS1. An electrical supply unit fbr supplying electricity to a battery charger, the electrical supply unit including a supply line through which electricity is supplied to the battery charger, a supply unit controller that controls the supply of electricity through the supply line, and a control pilot line that carries a PWM control pilot signal between the electrical supply unit and the battery charger, wherein the supply unit includes a control pilot signal generator that generates the PWM control pilot signal, and said control pilot signal generator includes a switched bridge circuit.
2. An electrical supply unit according to claim 1, wherein the control pilot signal generator is included in the supply unit controller.
3. An electrical supply unit according to claim 1 or claim 2, wherein the control pilot signal generator includes pilot and earth lines, and first and second switch elements configured to connect the pilot and earth lines alternately to a zero volt reference point.
4. An electrical supply unit according to claim 3, including first and second supply resistors, each connected in series with a respective one of said first and second switch elements between said pilot and earth lines and a reference vokage.
5. An electrical supply unit according to claim 4, wherein an earth connection is connected between said first supply resistor and said first switch element, and said control pilot line is connected between said second supply resistor and said second switch element.
6. An electrical supply unit according to any one of claims 3 to 5, including a switch control device configured to control the switching of said first and second switch elements.
7. An electrical supply unit according to claim 6, wherein the switching of said first and second switch elements controls the duty cycle of the control pilot signal.
8. An electrical supply unit according to any one of claims 3 to 7, including a divider network that is connected between the pilot and earth lines and includes a measuring node, and a voltage measuring device connected to measure the voltage at the measuring node, the divider network being configured such that the voltage at the measuring node is positive, and proportional in magnitude to the voltage on the control pilot line with respect to the earth line.
9. An electrical supply unit according to claim 8, wherein the divider network compriscs a T-network of rcsistors; and thc mcasuring nodc is locatcd at thc ccntral junction of the T-network.
10. An electrical supply unit according to any one of the preceding claims, wherein the control pilot signal generator generates a +1 2V PWM control pilot signal.
11. An EVSE unit including an electrical supply unit according to any one of the preceding claims.
12. An EVSE unit according to claim 11, wherein the supply line is configured to supply mains clcctricity to a vchiclc battery chargcr.
13. An EVSE unit according to claim 11 or claim 12, whcrcin thc EVSE unit includes a mains electricity switching device for controlling the supply of mains electricity through the supply line, said mains electricity switching device being controlled by the supply unit controller.
14. An EVSE unit substantially as dcscribcd hcrcin, with rcfcrcncc to and as illustratcd by Figures 4 and 5 of the accompanying Figures.