DC meters for electric vehicle charging stations

Abstract

A DC meter (1) for an electric vehicle charging station has a pair of DC power lines (27a, 27b) extending from a charging station controller (40) to an electric vehicle connector (28), the DC meter comprising a meter unit (2) and a sensor unit (3). The meter unit comprises a user interface (9), a sensor interface (11) for connecting to the sensor unit (3), a metering interface (30) for connecting to the charging station controller, and a microprocessor (10), which is configured to receive and process signals received from the sensor unit (3), exchange data with the charging station controller, and receive commands from the user interface and output information to the user interface. The sensor unit is separate and connected at a point away from the meter unit via an interconnection cable (25) for transmitting measurement signals, the sensor unit is coupled to one of the pair of DC power lines (27a, 27b), and is configured to measure the current flowing through the power line, and the sensor unit also comprises a voltage sensor (6) for coupling to each of the pair of power lines to measure the voltage difference between the pair of power lines.

Description

[0001] The present invention relates to a direct current (DC) meter for an electric vehicle charging station.

[0002] Currently implemented charging stations for electric vehicles generally allow charging at a flat rate based on connection time or per charge. However, given the increase in the use of electric vehicles, it is necessary to measure the actual power consumption during charging in order to bill the user for the amount of energy consumed.

[0003] Given the need to bill users for the amount of energy consumed, the measurement of consumed energy must be accurate, reliable and protected from tampering.

[0004] In view of the foregoing, an object of the present invention is to provide a DC meter for an electric vehicle charging station that is accurate, reliable, and easy to implement.

[0005] An object of the present invention is to provide a DC meter that is easy to install and economical to manufacture and operate in electric vehicle charging stations, where mechanical, thermal and system integration represent the main constraints.

[0006] The object of the present invention is achieved by providing a DC meter according to claim 1 .

[0007] A DC meter for an electric vehicle charging station is disclosed herein, having a pair of DC power lines extending from a charging station controller to an electric vehicle connector. The DC meter includes a meter unit and a sensor unit. The meter unit includes a user interface, a sensor interface for connecting to the sensor unit, a metering interface for connecting to the charging station controller, and a microprocessor configured to receive and process signals received from the sensor unit, exchange data with the charging station controller, and receive commands from the user interface and output information to the user interface.

[0008] The sensor unit is separate and connected at a point remote from the meter unit via an interconnection cable for transmitting measurement signals, the sensor unit is coupled to one of a pair of DC power lines and is configured to measure the current flowing through the power line, the sensor unit also includes a voltage sensor for coupling to each of the pair of power lines to measure the voltage difference between the pair of power lines. The sensor unit also includes a microprocessor having an analog-to-digital converter (ADC) to convert received analog voltage measurement and current measurement signals into digital signals, and the sensor unit also includes a communication interface configured to transmit encrypted data to the meter unit via the interconnection cable.

[0009] In an embodiment, the microprocessor of the sensor unit comprises a module for calculating the power consumed by the electric vehicle using the voltage measurement and the current measurement signals, the power measurement values ​​being transmitted to the meter unit.

[0010] In an embodiment, the power measurement calculation is calculated from the current measurement signal and / or the voltage measurement signal sampled every 1 to 0.01 seconds, preferably between 0.5 and 0.05 seconds.

[0011] In an embodiment, the voltage sensor comprises a connector coupled to a voltage cable having a connection end remote from the sensor unit for connection to the DC power line at or near the electric vehicle connector.

[0012] In an embodiment, the sensor unit and the meter unit include unique identification numbers stored in respective memories, and once the sensor unit and the meter unit have been paired with their unique identification numbers, they are able to communicate.

[0013] In an embodiment, the sensor unit and the meter unit include an encryption module for data encryption communication between the sensor unit and the meter unit.

[0014] In an embodiment, the current sensor is a current measuring shunt and one of the DC supply lines is split and comprises connection ends for connection to respective connection terminals of the sensor unit.

[0015] In an embodiment, the sensor unit comprises a housing having at least a base and a cap, the primary conductor connection terminals being arranged to extend out of the base and covered by the cap, the sensor unit further comprising a connector for a voltage sensor cable and a connector for connecting to a communication interface of an interconnect cable, the cover being removably positionable over the terminals and the connector and comprising means for securing to the base for anti-tampering.

[0016] In an embodiment, in addition to the power measurement signal transmitted from the sensor unit to the meter unit, also voltage and current measurement data are transmitted.

[0017] In an embodiment, the sensor unit communication interface transmits data to the instrument unit via the interconnect cable at a voltage less than 50 volts, preferably equal to or less than 24 volts, such as 5 or 12 volts.

[0018] Other objects and advantageous features of the present invention will be apparent from the claims, detailed description and accompanying drawings, in which:

[0019] Figure 1 is a schematic diagram of a DC meter according to an embodiment of the present invention implemented in an electric vehicle charging system;

[0020] Figure 2 is a schematic diagram of a DC meter according to an embodiment of the present invention;

[0021] Figure 3a is a perspective view of a sensor unit of a DC meter according to an embodiment of the present invention, with a cover in an open position;

[0022] Figure 3b yes Figure 3a A perspective view of the sensor unit with the cover and cables removed.

[0023] Figure 3c yes Figure 3a A detailed view of a portion of a sensor unit;

[0024] Figure 3d yes Figure 3a A detailed view of a portion of a sensor unit;

[0025] Figure 4 is a schematic diagram of multiple sensor units connected to a single common meter unit of a DC meter according to an embodiment of the present invention.

[0026] Figure 5a and Figure 5b A sensor unit of a DC meter installed on different wires of a power line pair according to an embodiment of the present invention is described;

[0027] Figure 6 is a schematic circuit diagram of a voltage sensor of a sensor unit of a DC meter according to an embodiment of the present invention.

[0028] Referring to the drawings, a DC meter 1 according to an embodiment of the present invention is connected to an electric vehicle charging station controller 40, which is connected to a DC power link via a power converter 41 and connected at the other end to an electric vehicle (EV) connector 28, which is standardized and configured for coupling to an electric vehicle.

[0029] The DC meter 1 comprises a meter unit 2 and a sensor unit 3 interconnected by an interconnection cable 25. The meter unit 2 is connected to the sensor unit 3 via said interconnection cable 25 on the one hand and to a controller 41 of a charging station controller supplying DC current to the electric vehicle on the other hand. The interconnection to the charging station controller comprises a data connection, which is preferably a cable connection, such as a cable using an Ethernet protocol. In a variant, the data connection may also be a wireless data communication connection, for example using Wi-Fi and / or a mobile phone cellular communication network.

[0030] The interconnection cable 25 may include electrical and / or optical cables for data communication between the sensor unit 3 and the meter unit 2, and may optionally further include a power cable for supplying power from the meter unit to the sensor unit. The data and power cables may use, for example, a standard protocol according to a CAN bus network. Other data communication standards may be employed.

[0031] The meter unit 2 includes a user interface 9 which may include a screen (e.g., a liquid crystal display), buttons for inputting user commands, and status lights for indicating errors or other operating states. The meter unit also includes a microprocessor 10 for managing incoming sensor signals and outgoing signals to the metering interface with the charging station controller and various input and output functions. The meter unit includes a tamper sensor in the housing of the DC meter which detects the integrity of the DC meter and can signal and record any intrusion or opening of the DC unit housing or cutting of cables. Events in the DC meter unit such as authorized access for maintenance or other purposes can also be recorded by the tamper sensor connected to the memory 36 of the processor.

[0032] Using a standard CAN network for the interconnection between the sensor unit 3 and the instrument unit 2 is advantageous because it is robust to electromagnetic interference and allows for secure data communication.

[0033] The separation of the current sensor unit 2 from the meter unit 3 is particularly advantageous in that the meter unit can be located in a convenient location for operator and user access, while the sensor unit can be in a protected environment that may not be easily accessible. The functions of the meter unit include connection to the charging station controller and processing and transmission of measurement signals, while the sensor unit can be located along the charging DC cable not too far from the electric vehicle charging post in order to accurately measure the voltage and current near the actual charging connector 28.

[0034] The sensor unit is adapted to be coupled to the primary conductor 27a to measure the current flowing through the primary conductor. In the illustrated embodiment, the sensor unit comprises a current sensor 5 having a primary conductor connection terminal 18, thereby allowing the end of the primary conductive cable to be bolted, clamped, welded or otherwise connected thereto. In this embodiment, the current sensor takes the form of a current measuring shunt, which shunt sensor itself is well known in the art of current measurement and will not be described in detail herein.

[0035] In an embodiment, the sensor unit 3 comprises at least one temperature sensor, mounted in such a way that the temperature of the shunt can be sensed directly or indirectly. The measured temperature is used to compensate for temperature drifts of the measurements in the sensor unit 3. In practice, the operating temperature of the measuring electronics may be, for example, from -40°C to +130°C.

[0036] When two temperature sensors are used, they are placed in a way that the temperature on both sides of the shunt can be accurately sensed. This symmetrical temperature measurement allows the temperature on both sides of the shunt to be estimated. Due to this estimation, the thermal EMF generated by the two metal junctions is mitigated. The calculation of the thermal EMF can be done in a microprocessor.

[0037] The sensor unit comprises a housing having a base 14 and a cap 16, a microprocessor 7 mounted within the housing, a communication interface 8 mounted in the housing and presenting a connector 12 (e.g. a pluggable connector to an interconnect cable 25), and a voltage sensor 6 for measuring a voltage difference between a pair of DC power lines 27a, 27b.

[0038] The current measuring shunt measures the DC current flowing through one of the DC supply lines 27 a across the connection terminals 29 a , 29 b and the current measurement signal is fed to the analog front end and then to the microprocessor 7 .

[0039] The current measurement analog front end integrates an amplifier whose gain is controlled by a microprocessor. This technique, known per se, allows the measurement of very low-amplitude signals from current shunts.

[0040] The microprocessor may advantageously comprise an analogue-to-digital converter (ADC) 24a for converting the analogue current measurement signal into a digital signal. The ADC may advantageously take the form of a known sigma-delta converter, for example.

[0041] The sensor unit advantageously comprises a tamper sensor which detects the integrity of the housing and any violation of opening the housing in order to detect any tampering, in particular of the analog signal.

[0042] The sensor unit also includes a voltage sensor 20, which is suitable for measuring the voltage between a pair of DC power lines 27a, 27b, the voltage measurement signal is fed into the microprocessor 7 and converted from an analog signal to a digital signal via an analog to digital converter 24b, which can be of a type similar to or different from the ADC of the current sensing measurement.

[0043] Voltage and current measurements can be used to calculate power measurements.

[0044] The power measurement signal and optionally the voltage and current measurement signals and other data fed into the interconnection cable 25 to the meter unit 2 can advantageously be encrypted by an encryption module in the microprocessor 7 of the sensor unit. Data communication between the sensor unit and the meter unit, which is also provided with an encryption and decryption module, is thus secure. Furthermore, the meter unit 2 and the sensor unit 3 are each provided with a unique identifier and matched from time to time during an authentication process before first use or, for example, during maintenance operations, so that the sensor unit 3 and the meter unit 2 can only be used together if they are authenticated and matched. This will also allow, depending on the application, multiple sensor units from different charging posts to be connected to a single meter unit, such as e.g. Figure 4 Schematically illustrated in .

[0045] Advantageously, the power measurement can be performed within the sensor unit and transmitted to the meter unit. This improves reliability and safety and reduces the number of measurement signals to be transmitted between the sensor unit and the meter unit. However, the voltage and / or current measurements of the sensor unit 3 can be sent to the charging station controller 41 via the meter unit 2. The transmitted voltage and / or current measurements can be used to add redundancy to the control of the power converter 42 of the charging station.

[0046] In an advantageous embodiment, the voltage sensor 6 comprises a voltage cable 22 connected to the DC power lines 27a, 27b at a connection point remote from the sensor unit, in particular at a connection point 37 in or near the EV connector, so that an accurate voltage measurement is measured at the connection point. Preferably, the voltage cable is connected to a connection terminal in the EV connector to ensure that any resistance in the portion of the cable between the sensor unit and the EV connector causing a voltage drop does not affect the power measurement. This arrangement also allows the sensor unit 3 to be positioned on the charging cable 27a at a distance (e.g. 2 to 50 meters) from the connector 28, so that the sensor unit can be positioned in a charging post in a safety enclosure, while the cables 27a, 27b with the EV connector 28 can be provided with a certain length to allow connection to a vehicle at a distance from the charging post.

[0047] In a variant, voltage measurements may be made at the sensor unit 3, one taken from one of the connection terminals 29a on the first power line 27a, the other taken through a cable or other conductor connected to the other DC power line 27b. In the latter variant, before first use and optionally from time to time, for example during maintenance intervals, the voltage drop between the EV connector 28 and the voltage cable connection point 37 may be measured and taken into account in the calibration function during the calculation of the power measurement output signal.

[0048] like Figure 6As best described, the voltage sensor 6 may advantageously include a voltage input 43, wherein the two inputs may be at different potentials relative to ground potential, thereby providing safety in the event that one of the two series-connected resistors in the upper branch of the illustrated voltage divider is short-circuited. The input 43 is connected to an amplifier circuit 44 that allows for a single-ended ADC input. In the illustrated circuit, the lower input is grounded, so that the two illustrated "ADC" blocks actually form a single ADC 24b. The input 43 is further connected to a comparator circuit 45 to detect the higher absolute value of the input voltage relative to ground potential, and the output of the comparator circuit is fed to a logic circuit 46 that determines which of two possible gains is used to interpret the output value of the ADC: The two voltage dividers on the left may have slightly different attenuation levels because they are made of different components with specific tolerances. In a typical use case, only one voltage is high relative to ground (hundreds of volts), while the other voltage is quite small (millivolts to volts). Therefore, when different gains are used depending on the output of the comparator, the overall measurement error can be minimized.

[0049] The housing 4 comprises a base 14 and a removable cap 16 which allows the connection ends 29a, 29b of one of the DC power supply lines 27a to be connected to the sensor unit 3 and is also used to connect the voltage sensor cable 22 to the connection terminals in the sensor housing. The cap is configured to cover the terminals and may further comprise a locking post on the housing which passes through an aperture in the cap, the locking post being provided with an aperture to allow the wires of the seal 38 to pass therethrough to ensure that the cover can only be removed if the seal is broken.

[0050] An integrity sensor (not shown) may also be provided to detect if the cover 16 is removed from the base 14, with integrity sensor data being stored in the memory 36 of the processor 7 and transmitted to the meter unit 2 to alert the sensor unit of cover tampering or opening.

[0051] A sealing ring may be provided between the base and the cover around its outer periphery to provide a watertight seal between the housing and the base.The electrical and electronic components within the housing are in a hermetically sealed environment which in a variant may be filled with an insulating potting material known per se in the art of current transducers.

[0052] The power of the sensor unit 3 may be supplied from the meter unit 2. In a variant, the power of the sensor unit may be obtained from the DC power supply lines 27a and 27b. Considering the negligible amount compared to the amount of power used to charge the vehicle, there will be no need to compensate for the obtained power.

[0053] Another advantage of separating the sensor 3 unit and the meter unit 2 is protection from high voltages of the DC housing power line, which may be of the order of 1 to 2 kilovolts. This separation is accomplished in the sensor unit 3, thereby placing the communication cable 25 and the meter unit 2 in a safe extra-low voltage area. Thus, the meter unit 2 and the communication cable 25 can be safely operated.

[0054] The power measurement signal calculated from the digital measurement signals output by the ADCs of the voltage measurement sensor and the current measurement sensor can be calculated at a relatively low frequency, for example, in the order of about 1 to 100 Hz (e.g., typically about 10 Hz). Considering that the changes in current and voltage during the charging operation have low-frequency fluctuations, measurements in this range reduce the computational requirements and memory, but allow accurate power measurements. Low-frequency measurement sampling also reduces the amount of data transmission between the sensor unit and the meter unit. However, the sampling of the ADCs 24a 24b can be performed at a high frequency, for example, about 500 kHz, which is a typical operating frequency of a sigma-delta ADC.

[0055] Another advantage of separating the sensor unit 3 and the meter unit 2 is that several sensor units may be connected to a single meter unit 2. An electric vehicle charging station may provide several independent DC power lines to charge several independent electric vehicles.

[0056] Another advantage of separating the sensor unit 3 from the meter unit 2 is that the sensor unit 3 can be installed in a high-side position or a low-side position. This flexibility enhances the integration possibilities in charging piles where space is limited.

[0057] Depending on the high-side or low-side installation of the sensor unit 3, the electrical configuration of the voltage measurement analog front end is different. The leg of the high-impedance voltage divider used depends directly on the installation configuration. The gain of the two legs of the high-impedance resistor divider is not the same. The gain difference causes inaccurate voltage measurements. To compensate for this effect and avoid the use of high-precision resistors, an intermediate circuit senses which leg is being used and indicates the result to the microprocessor. Therefore, the microprocessor uses two internal compensation registers to mitigate the gain errors of the two different legs.

[0058] The intermediate circuit senses which of the two internal signals is closest to the reference voltage. This indicates whether the high side or low side is attached to the microprocessor.

[0059] The voltage measurement analog front end may also include temperature sensors T1, T2 (such as Figure 2 The drift of the reference voltage can be compensated in the microprocessor by taking into account the measured temperature from the temperature sensor.

[0060] Reference numerals list

[0061] DC Meter 1

[0062] Meter unit 2

[0063] User Interface 9

[0064] LCD, buttons, status lights

[0065] Microprocessor 10

[0066] Sensor interface 11

[0067] Connector 12

[0068] electric

[0069] Optics

[0070] Metering interface (with charging station controller) 30

[0071] Power Supply 31

[0072] Tamper-proof sensor 35

[0073] Sensor unit 3

[0074] Housing 4

[0075] Base 14

[0076] Cap 16

[0077] Tamper-evident seal 38

[0078] Current sensor 5

[0079] Primary conductor connection terminals 18a, 18b

[0080] Voltage sensor 6

[0081] Voltage connector 20

[0082] Voltage cable 22

[0083] Remote connection point 37

[0084] Voltage input 43

[0085] Amplifier circuit 44

[0086] Comparator circuit 45

[0087] Logic circuit 46

[0088] Microprocessor 7

[0089] ADC 24a, 24b, 24c

[0090] Memory 36

[0091] Communication interface 8

[0092] Data connector 33

[0093] Interconnect Cable 25

[0094] DC power supply lines 27a, 27b

[0095] Connection terminals 29a, 29b

[0096] EV Connector 28

[0097] Charging Station

[0098] Charging station controller 40

[0099] Controller 41

[0100] Power converter 42

Claims

1. A DC meter for an electric vehicle charging station, the electric vehicle charging station having a pair of DC power lines (27a, 27b) extending from a charging station controller (40) to an electric vehicle connector (28), the DC meter comprising a meter unit (2) and a sensor unit (3), the meter unit comprising a user interface (9), a sensor interface for connecting to the sensor unit (3), a metering interface (30) for connecting to the charging station controller, and a microprocessor (10), the microprocessor (10) being configured to receive and process signals received from the sensor unit (3), exchange data with the charging station controller, and receive commands from the user interface and output information to the user interface, wherein: The sensor unit is separate and connected at a point remote from the meter unit via an interconnection cable (25) for transmitting a measurement signal, the sensor unit is coupled to one of the pair of DC power lines (27a, 27b) and is configured to measure a current flowing through the DC power line, the sensor unit further comprising a voltage sensor (6) for coupling to each of the pair of DC power lines to measure a voltage difference between the pair of DC power lines, the sensor unit further comprising a microprocessor having an analog-to-digital converter ADC (24a, 24b) for converting a received analog voltage measurement signal into a digital voltage. and current measurement signals into digital signals, the sensor unit further comprising a communication interface configured to transmit encrypted data to a meter unit via an interconnect cable (25), wherein the sensor unit communication interface (8) transmits data to the meter unit via the interconnect cable (25) at a voltage of less than 50 volts, wherein the voltage sensor comprises a connector (20) coupled to a voltage cable (22), the voltage cable (22) having a connection end (37) remote from the sensor unit for connection to a DC power line (27a, 27b) at or near an electric vehicle connector.

2. The DC meter according to claim 1, wherein: The microprocessor (7) of the sensor unit comprises a module for calculating the power consumed by the electric vehicle using the voltage measurement signal and the current measurement signal, the power measurement value being transmitted to the meter unit.

3. The DC meter according to claim 2, wherein: The power measurement calculation is based on the current measurement signal and / or the voltage measurement signal sampled every 0.01 seconds to 1 second.

4. The DC meter according to claim 2, wherein: The power measurement calculation is based on the current measurement signal and / or the voltage measurement signal sampled every 0.05 seconds to 0.5 seconds.

5. The DC meter according to claim 1, wherein: The sensor unit and the meter unit include unique identification numbers stored in respective memories, and once the sensor unit and the meter unit have been paired with their unique identification numbers, they are able to communicate.

6. The DC meter according to claim 1, wherein: The sensor unit and the meter unit include an encryption module for encrypted communication of data between the sensor unit and the meter unit.

7. The DC meter according to claim 1, wherein: The current sensor (5) is a current measuring shunt, and one of the DC power supply lines (27a) is split and includes connection ends (29a, 29b) to be connected to corresponding connection terminals (18a, 18b) of the sensor unit (3).

8. The DC meter according to claim 1, wherein: The sensor unit comprises a housing having at least a base (14) and a cap (16), the primary conductor connection terminals (18) being arranged to extend out of the base and covered by the cap, the sensor unit further comprising a connector (20) for a voltage cable (22) and a connector (33) for a communication interface (8) connected to an interconnection cable (25), the cap being removably positionable over the terminals and the connector and comprising means for securing to the base for tamper resistance.

9. The DC meter according to claim 1, wherein: In addition to the power measurement signal transmitted from the sensor unit to the meter unit, voltage and current measurement data are also transmitted.

10. The DC meter according to claim 1, wherein: The sensor unit communication interface (8) transmits data to the instrument unit via the interconnect cable (25) at a voltage less than 24 volts.

11. The DC meter according to claim 1, wherein: The sensor unit communication interface (8) transmits data to the instrument unit via the interconnect cable (25) at a voltage of less than 5 volts.

12. The DC meter according to claim 1, wherein: The sensor unit communication interface (8) transmits data to the instrument unit via the interconnect cable (25) at a voltage of less than 12 volts.

Images