Method for monitoring the continuity of a protective conductor of a charging system for electric vehicles and charging system

Abstract

The invention relates to a method for monitoring the continuity of a protective conductor (PE) of a conductive charging system (2) for electric vehicles (4) designed in accordance with the IEC 61851-1 standard, wherein the charging system (2) comprises a charging station (6) with a CP generator (8) for generating a CP control signal (10) and a charging cable (12) which has the protective conductor (PE), active conductors (N, L1, L2, L3), a CP signal conductor (CP) and a PP signal contact (PP). The method according to the invention comprises the method steps of detecting and evaluating a differential current (14) flowing in the active conductors N, L1, L2, L3 by means of an all-current sensitive differential current monitoring module (RCM) in combination with a measuring current transformer (16), wherein an interruption (18) of the protective conductor (PE) is detected in the differential current (14) by detecting and evaluating the CP control signal (10) generated by the CP generator (8). Furthermore, the invention relates to a conductive charging system for electric vehicles according to the invention, which is based on the standard IEC 61851-1 and implements the method according to the invention.

Description

[0001] The invention relates to a method for monitoring the continuity of a protective conductor of a conductive charging system for electric vehicles designed according to the IEC 61851-1 standard, wherein the charging system comprises a charging station with a CP generator (Control Pilot) for generating a CP control signal and a charging cable which has the protective conductor (PE - Protective Earth), active conductors, a CP signal line and a PP signal contact (Proximity Pilot).

[0002] Furthermore, the invention relates to a conductive charging system for electric vehicles designed in accordance with the IEC 61851-1 standard, which is designed to carry out the method according to the invention for monitoring the continuity of a protective conductor.

[0003] The IEC 61851-1 standard applies to wired charging systems for electric vehicles and describes, among other things, the characteristics and operating conditions of the power supply equipment and the connection to the electric vehicle. In particular, continuous monitoring of the continuity of the protective conductor to the electric vehicle is also required.

[0004] This system standard defines different charging modes. In conjunction with a permanently installed charging station, charging mode 3 is primarily used for single-phase and three-phase charging with alternating current. The control of the charging process, as well as the safety functionality and communication between the charging station and the electric vehicle, are integrated into the charging station and are implemented there as functional units, preferably by a charge controller. According to the standard, the charging cable and the associated Type 2 plug have four current-carrying (active) conductors / contacts – three outer conductors L1, L2, L3 and the neutral conductor N – as well as the protective conductor, the CP signal line, and the PP signal contact.

[0005] Communication between the charging station and the electric vehicle takes place via the CP signal line. When the electric vehicle is connected, the CP generator in the charging station generates the CP control signal in the form of a square wave with a 1 kHz base frequency and applies it to the CP signal line. Pulse-width modulation (PWM signaling / coding) of the square wave informs the electric vehicle of the maximum charging current available from the charging station.

[0006] The CP control signal sent from the charging station to the electric vehicle via the CP signal conductor is returned via the protective conductor of the charging cable when the electric vehicle is connected. The charge controller in the charging station can thus detect that an electric vehicle is connected to the charging station by measuring the voltage on the CP signal conductor against earth (protective conductor). This is because, when the electric vehicle is connected, a circuit is formed in which a current flows. The magnitude of this current is determined by the connection of various resistances on the vehicle side. Since the protective conductor serves as the return conductor for the CP control signal, the continuity of the protective conductor can also be monitored.

[0007] The CP control signal and thus the measured voltages determined on the charging station side between the CP signal conductor and the protective conductor have different signal waveforms with different amplitudes (constant or PWM-modulated signal waveforms), with each waveform being assigned a state of charge (basic status) A to F. For example, a measured, constant open-circuit voltage indicates that no electric vehicle is connected to the charging station (state of charge A). If an electric vehicle is connected, the CP generator transitions to state of charge B with a PWM-modulated square-wave signal and reduced amplitude as the CP control signal. When the electric vehicle is ready to charge, state of charge C follows with a further reduced amplitude of the PWM-modulated square-wave signal. The other states of charge D to F describe specific operating or error states. If the status changes to state of charge A or state of charge B, the electric vehicle is disconnected from the charging station within 100 ms.

[0008] However, the charging station cannot reliably detect the current status or a status change if a conductive connection other than the protective conductor serves as the return conductor for the CP control signal. In particular, if the protective conductor is interrupted, it is not available as the return conductor for the CP control signal.

[0009] From the prior art, published patent application DE 10 2017 110 955 A1 discloses a method and system for detecting a protective conductor failure in a charging cable when a shield of another conductor is connected to both ends. The shield is actively electrically supplied to at least one potential connection, and a protective conductor failure is detected if an electrical value occurring during the active supply exceeds at least a threshold value.

[0010] Furthermore, the disclosure US 2021 / 0048485 A1 shows a method for detecting a protective conductor interruption during a charging process of an electric vehicle by evaluating the signal curve on the PP signal contact line.

[0011] The present invention is therefore based on the object of designing a further method for monitoring the continuity of the protective conductor and a charging system implementing this method, with which an interruption of the protective conductor can be detected.

[0012] This object is achieved in conjunction with the features of the preamble in claim 1 in that an interruption of the protective conductor is detected by detecting and evaluating the CP control signal generated by the CP generator in the differential current.

[0013] The fundamental idea of ​​the method according to the invention is therefore based on the fact that, if the CP control signal cannot be fed back via the protective conductor due to a defect in the protective conductor, a current driven by the CP generator can normally only flow back from the electric vehicle to the charging station via the active conductors. The residual current detected by the universal current-sensitive residual current monitoring module in combination with a measuring current transformer enclosing the active conductors is then evaluated to determine whether it contains a CP control signal generated by the CP generator as a residual current component. If a CP control signal is detected in the residual current, an interruption in the protective conductor is deemed to have been detected. If the protective conductor connection is continuous (intact), no CP control signal will be detectable in the residual current detected via the active conductors.

[0014] In a further advantageous embodiment, the transmission of the PWM-modulated square wave signal generated in the CP generator is signaled to the differential current monitoring module via a transmission status signal line.

[0015] The application of the 1 kHz square wave signal, defined in the IEC 61851-1 standard as a CP control signal, to the CP signal conductor is communicated to the residual current monitoring module via a transmit status signal line. This synchronization allows the residual current monitoring module to know the period of time (in the case of a defective protective conductor) within which a CP control signal can be expected, so that an undesirably superimposed 1 kHz interference signal generated by external influences does not lead to malfunction.

[0016] In addition to the transmission status (send / do not send CP control signal) of the CP generator, the duty cycle of the PWM-modulated 1 kHz square wave signal is also communicated to the residual current monitoring module via the transmission status signal line in order to enable reliable detection of the CP control signal in the residual current monitoring module through appropriate parameter settings.

[0017] Preferably, the detection and evaluation of the CP control signal generated by the CP generator in the detected differential current is carried out by means of a software-based extension of the differential current monitoring module.

[0018] The detection and evaluation of the CP control signal as part of the measured residual current is preferably carried out in the existing residual current monitoring module. For this purpose, this module is expanded using software, using digital filter architectures whose parameters are configured using the transmitted PWM duty cycle.

[0019] Advantageously, an interruption of the protective conductor detected by the differential current monitoring module is reported to a charge controller of the charging station by means of a PE status signal on a PE status line.

[0020] If the residual current monitoring module detects a CP control signal in the form of a 1 kHz square wave signal in the detected residual current and thus detects an interruption of the protective conductor, this interruption of the protective conductor is reported to the charging controller of the charging station by means of a PE status signal on a PE status line.

[0021] The PE status signal is evaluated in the charge controller to control the charging process.

[0022] If an interruption of the protective conductor is detected and signalled by the PE status signal, the charge controller can activate a contactor to disconnect the electric vehicle and, if necessary, initiate further process steps.

[0023] Furthermore, the object underlying the invention is achieved by a conductive charging system for electric vehicles designed according to the standard IEC 61851-1, which implements the method according to the invention.

[0024] The functional units of the conductive charging system according to the invention, described with the claimed structural features, carry out the corresponding method steps of the method according to the invention. Thus, the technical effects achieved with the method and the resulting advantages also apply equally to the charging system.

[0025] In particular, the charging system comprises an all-current sensitive residual current monitoring module which is designed to detect and evaluate the CP control signal generated by the CP generator in the detected residual current in order to detect an interruption of the protective conductor.

[0026] The residual current monitoring module, implemented using a software-based extension, is thus able to detect the CP control signal in the form of the 1 kHz square wave signal on the active conductors.

[0027] In accordance with the task, this provides a further, particularly component-efficient option for monitoring the continuity of the protective conductor.

[0028] Further advantageous design features emerge from the following description and the drawings, which explain a preferred embodiment of the invention using examples.

[0029] They show: Fig. 1 a conductive charging system according to the invention with intact protective conductor and Fig. 2 a conductive charging system according to the invention when the protective conductor is interrupted.

[0030] Fig. 1 shows a conductive charging system 2 for electric vehicles 4 according to the invention, designed according to the standard IEC 61851-1, with an intact protective conductor PE.

[0031] The charging system 2 comprises a charging station 6 and a charging cable 12 with active conductors L1, L2, L3, N and the protective conductor PE to be monitored as well as with a CP signal conductor CP and a PP signal contact as a plug contact of a standard Type 2 plug.

[0032] The charging station 6 has a CP generator 8 that generates a CP control signal 10. The CP control signal 10 is applied to the CP signal conductor CP, with the protective conductor PE serving as the return conductor. When the electric vehicle 4 is connected, a circuit 30 is thus formed that runs via the CP signal conductor CP, a diode-resistor branch in the electric vehicle 4, and the protective conductor PE.

[0033] In the illustrated embodiment, the CP generator 8 and a residual current monitoring module RCM are functional units of a charge controller 7. The residual current monitoring module RCM is connected to a measuring current transformer 16 which encloses the active conductors L1, L2, L3, N and detects a residual current 14.

[0034] Based on a voltage measurement on the charging station side (measurement voltage U m) between the CP signal conductor CP and the protective conductor PE, the charging station 6 determines whether an electric vehicle 4 is connected. If no electric vehicle 4 is connected (charge state A), the measuring voltage U m a DC voltage (open circuit voltage) applied by the CP generator 8 is measured.

[0035] If the electric vehicle 4 is connected, the circuit 30 is formed due to a resistor connected on the vehicle side, whereby a drop in the measuring voltage U m at the CP signal conductor CP against the protective conductor PE is detected by the charging station 6 (charging state B) and the CP generator then switches a PWM-modulated 1 kHz square wave signal as CP control signal 10 to the CP signal conductor CP.

[0036] If the electric vehicle 4 is ready for charging, it connects another (parallel) resistor between the CP signal conductor CP and the protective conductor PE, so that a corresponding voltage drop in the measuring voltage U m is detected by charging station 6 and the charging current is enabled. The currently available charging current is communicated to the electric vehicle 4 by pulse-width modulation of the 1 kHz square-wave signal from charging station 6.

[0037] A continuous, intact protective conductor connection (PE protective conductor) is therefore essential not only for ensuring electrical safety but also for controlling the charging process and for communication between charging station 2 and electric vehicle 4.

[0038] Fig. 2 shows a conductive charging system 2 according to the invention for electric vehicles 4, designed according to the standard IEC 61851-1, in the event of an interruption 18 of the protective conductor PE.

[0039] In this case, the current caused by the CP control signal 10 cannot be returned via the protective conductor PE. Typically, the circuit 30 is then closed via the active conductors L1, L2, L3, and N.

[0040] According to the invention, the differential current monitoring module RCM is designed such that a differential current curve in the differential current 14 corresponding to the CP control signal 10 can be detected and evaluated.

[0041] For this purpose, the residual current monitoring module RCM includes a software-based extension 22, which detects the 1 kHz square wave signal using digital signal processing (filtering) methods.

[0042] To inform the residual current monitoring module RCM when the CP control signal 10 is sent in the (signal) form of the 1 kHz square wave signal, and thus when it is to be expected on the active conductors L1, L2, L3, N when the protective conductor PE is interrupted, the residual current monitoring module RCM is synchronized with the CP generator 8 via a data interface with a transmission status signal line 20. At the same time, the duty cycle of the PWM-modulated 1 kHz square wave signal is transmitted via the transmission status signal line 20 for the appropriate setting of the software-based filter parameters.

[0043] An interruption 18 of the protective conductor PE detected by the residual current monitoring module RCM is signaled to the charge controller 7 of the charging station 6 by means of a PE status signal 24 via a data interface with a PE status line 26. The charge controller 7 is thus able to enable the charging current after evaluating the PE status signal 24 or, if necessary, to deny the enablement.

Claims

[1] Method for monitoring the continuity of a protective conductor (PE) of a conductive charging system (2) for electric vehicles (4) designed in accordance with the IEC 61851-1 standard, wherein the charging system (2) comprises a charging station (6) with a CP generator (8) for generating a CP control signal (10) and a charging cable (12) which has the protective conductor (PE), active conductors (N, L1, L2, L3), a CP signal conductor (CP) and a PP signal contact (PP), comprising the method steps: Detecting and evaluating a residual current (14) flowing in the active conductors N, L1, L2, L3 by means of an all-current sensitive residual current monitoring module (RCM) in combination with a measuring current transformer (16), characterized by , that by detecting and evaluating the CP control signal (10) generated by the CP generator (8) in the differential current (14), an interruption (18) of the protective conductor (PE) is detected. [2] Method according to claim 1, characterized by that the transmission of the PWM-modulated square wave signal generated in the CP generator (8) is signaled to the differential current monitoring module (RCM) via a transmission status signal line (20). [3] Method according to claim 1 or 2, characterized by that the detection and evaluation of the CP control signal (10) generated by the CP generator (8) in the detected differential current (14) takes place by means of a software-based extension (22) of the differential current monitoring module (RCM). [4] Method according to one of claims 1 to 3, characterized by that an interruption (18) of the protective conductor (PE) detected by the differential current monitoring module (RCM) is reported to a charging controller (7) of the charging station (6) by means of a PE status signal (24) on a PE status line (26). [5] Method according to claim 4, characterized by that the PE status signal (24) is evaluated in the charging controller (7) to control the charging process. [6] Conductive charging system (2) for electric vehicles (4) designed according to the IEC 61851-1 standard, which is designed to monitor the continuity of a protective conductor (PE), wherein the charging system (2) comprises a charging station (6) with a CP generator (8) for generating a CP control signal (10) and a charging cable (12) which has the protective conductor (PE), active conductors (N, L1, L2, L3), a CP signal conductor (CP) and a PP signal contact (PP), with an all-current sensitive residual current monitoring module (RCM), which in combination with a measuring current transformer (16) detects and evaluates a residual current (14) flowing in the active conductors (N, L1, L2, L3) in the charging system (2), characterized by that the residual current monitoring module (RCM) is designed to detect and evaluate the CP control signal (10) generated by the CP generator (8) in the detected residual current (14) in order to detect an interruption (18) of the protective conductor (PE). [7] Conductive charging system (2) for electric vehicles (4) according to claim 6, characterized by a transmission status signal line (20) via which the transmission of the PWM-modulated square wave signal generated in the CP generator (8) is signaled to the differential current monitoring module (RCM). [8] Conductive charging system (2) for electric vehicles (4) according to claim 6 or 7, characterized by that the residual current monitoring module (RCM) has a software-based extension (22) for detecting and evaluating the CP control signal (10) generated by the CP generator (8) in the detected residual current (14). [9] Conductive charging system (2) for electric vehicles (4) according to one of claims 6 to 8, characterized by a PE status line (26), via which an interruption (18) of the protective conductor (PE) detected by the differential current monitoring module (RCM) is reported to a charging controller (7) of the charging station (6) by means of a PE status signal (24). [10] Conductive charging system (2) for electric vehicles (4) according to claim 9, characterized by that the charging controller (7) is designed to evaluate the PE status signal (24) in order to control the charging process.

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