Method and circuit for protecting an on-board charging device

Abstract

1. A method for protecting an on-board charging device, comprising: detecting phase and neutral voltages from a grid; detecting a current signal representative of a compensation current generated by a compensation circuit; combining the phase voltages to obtain a homopolar voltage signal; squaring the current signal and the homopolar voltage signal to obtain a first rectangular current wave and a second rectangular voltage wave; combining the first and second square waves to generate an output signal having a first logic level when the first and second square waves are in phase and a second logic level when the first and second square waves are not in phase; generating a voltage that increases in proportion to a duration of each section of the output signal having a first value; comparing a value of the voltage with a limit value; and generating an alarm signal if the value of the voltage exceeds the limit value.

Description

[Technical field]

[0001] The present invention relates to a method and circuit for protecting an on-board charging device.

[0002] The invention therefore finds primary application in the automotive field, in particular in the design and construction of charging systems for on-board batteries. [Background technology]

[0003] In fact, in the field of electric vehicles, the charging modes of the battery pack are divided into two different respective macro categories: on-board chargers and ground chargers.

[0004] An "on-board charger," as the name suggests, is built into the vehicle and contains all the power and control electronics needed to convert the alternating current from the grid into the direct current needed to recharge the battery pack.

[0005] "Ground" chargers, on the other hand, are ordinary "columns" or wall boxes that provide the conversion directly by supplying direct current to the vehicle.

[0006] Therefore, on-board battery chargers present a significant problem from the point of view of user safety and would have to be equipped with appropriate protection systems, since they must manage the AC provided by the grid and convert it to DC in order to recharge the high voltage battery.

[0007] This is extremely important in building a non-isolated on-board charging system, where the battery charger has a direct electrical connection to the AC hardwired outlet, thus defining a true mesh that can close the circuit to earth.

[0008] These types of battery chargers present the problem of compensating for leakage currents caused by the continuous switching of electronic components in the converter block, which actually changes the voltage on the battery capacitor, resulting in current leakage to ground.

[0009] In three-phase systems, these currents exceed 100mA RMS and often reach amplitude levels approaching 150mARMS, which must be compensated for to avoid circuit breaker or differential switch intervention.

[0010] For this reason, a compensation circuit is inserted into the charging device, which is configured to generate a current equal to and opposite to the current flowing through the battery capacitor to ground.

[0011] Unfortunately, this created a significant safety hazard associated with the possibility that the compensation circuit could also intervene if there was an insulation loss between the battery charger and the vehicle chassis, and potentially even "fool" the differential switch, preventing it from operating.

[0012] To overcome this drawback, software systems have been developed that are managed by a microcontroller and that are able to distinguish between cases where the current flowing through the system is capacitive, and therefore flows through a capacitor and should therefore be compensated, and cases where the current is resistive, and therefore dangerous (i.e., current flowing through the human body or another resistor).

[0013] However, because these are such critical safety systems in electric vehicles, the applicant has realised that having purely software level safety at such critical points in the system may not be sufficient. Summary of the Invention

[0014] Therefore, an object of the present invention is to provide a method and circuit for protecting an on-board charging device, which can overcome the above-mentioned shortcomings of the prior art.

[0015] In particular, it is an object of the present invention to provide a method and circuit for protecting an on-board charging device that is both reliable and simple to implement or manufacture.

[0016] Said object is achieved by a method and a circuit for protecting an on-board charging device in a vehicle, comprising one or more of the features of the following claims.

[0017] In particular, the method includes detecting phase and neutral voltages derived from the grid and detecting a current signal representative of the compensation current generated by the compensation circuit.

[0018] Preferably, the phase voltages are therefore combined to obtain a homopolar voltage signal.

[0019] Preferably, the current signal and the homopolar voltage signal are squared to obtain a first square current wave and a second square voltage wave.

[0020] Preferably, the first square wave and the second square wave are coupled to generate an output signal having a first logic level when the first square wave and the second square wave are in phase and a second logic level when the first square wave and the second square wave are not in phase.

[0021] Thus, preferably a first voltage is generated which increases proportionally to the duration of each section of the output signal having said first value.

[0022] The value of the first voltage is compared to a limit value and an alarm signal is generated if the value of the first voltage exceeds the limit value.

[0023] It is a further object of the present invention to provide a circuit that protects a charging device.

[0024] The circuit comprises a summing network configured to receive as inputs signals representative of the phase and neutral voltages of the grid and return as an output a homopolar voltage signal.

[0025] Preferably, an element is provided for detecting a current signal representative of the compensation current.

[0026] Further, preferably, a conversion stage is provided configured to receive as input said homopolar voltage signal and said current signal and to generate a first square wave representative of said homopolar voltage signal and a second square wave representative of said current signal.

[0027] The combining stage is located downstream of the conversion stage and is configured to combine the first and second square waves together to generate an output signal having a first logic level when the first and second square waves are in phase and a second logic level when the first and second square waves are not in phase.

[0028] A charging module (or charger) is also preferably provided and operably arranged downstream of the combining stage and configured to generate a first voltage that increases in proportion to the duration of each section of the output signal having the first value.

[0029] A comparator element is preferably associated with the charging module and configured to compare a value of the first voltage with a limit value and to generate an alarm signal if the value of the first voltage exceeds the limit value.

[0030] The dependent claims, which are incorporated herein by reference, correspond to different embodiments of the invention. [Brief description of the drawings]

[0031] Further features and advantages of the present invention will become more apparent from the illustrative, and therefore non-limiting, description of preferred but non-exclusive embodiments of a method and circuit for protecting an on-board charging device, as illustrated in the accompanying drawings. [Figure 1] 1 shows a schematic structure of an on-board charging device. [Diagram 2] 2 shows a schematic structure of a circuit for protecting an on-board charging device according to the present invention; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0032] With reference to the accompanying drawings, reference numeral 1 generally indicates a circuit for protecting an on-board charging device 100 according to the present invention.

[0033] The term on-board charging device 100 in this specification is intended to generally define any charging system for a traction battery pack 6 that can be connected to an AC grid and converted to DC before powering the battery.

[0034] Preferably, the grid is of the three-phase type.

[0035] To this end, the charging device 100 comprises at least one casing C associated with a connection socket 101 for connection to a grid G ​​(connected to earth), the casing C housing a converter assembly 104 configured to convert alternating current provided by the grid G ​​into direct current usable for recharging the battery pack 105.

[0036] The connection socket 101 is therefore configured to receive both the three phases L1, L2, L3 and the neutral conductor N.

[0037] Preferably, the charging device 100 further comprises at least one electromagnetic disturbance filter element arranged along the current input line, i.e. between the connection socket 101 and the converter assembly 104 .

[0038] More preferably, there are two electromagnetic disturbance filter elements, a first filter element 102 along the (AC) current input line and a second filter element 103 along the (DC) current output line, i.e. between the converter assembly 104 and the battery pack 105.

[0039] In a preferred embodiment, charging device 100 is non-isolated, ie, provides a physical (ie, non-inductive) connection between the battery and the power distribution system.

[0040] Preferably, in this type of device 100, the converter assembly 104 comprises at least one step-up module and at least one step-down module.

[0041] In a preferred embodiment, the converter assembly 104 comprises: a first conversion stage (or AC-DC converter) configured to convert an alternating current provided by the grid G ​​into a direct current, a charging stage, preferably defined by a capacitor bank, operatively arranged downstream of the first conversion stage and adapted to be charged by receiving its output; - A second conversion stage (or DC-DC converter) configured to modulate the level of direct current sent to the battery pack 105.

[0042] In a preferred embodiment, as previously mentioned, the charging device 100 is non-isolated so that the second conversion stage is connected directly to the battery pack (ie, no conversion / induction stage).

[0043] Additionally, the charging device 100 preferably includes a compensation circuit 106 configured to generate a compensation current equal to and opposite to the leakage current flowing towards ground PE.

[0044] In order to avoid the safety problems described at the beginning, the charging device 100 may comprise a microcontroller equipped with a protection module 107 configured to generate an alarm signal if a relevant resistive component is detected in the leakage current.

[0045] Alternatively, or in conjunction with, the charging device is associated with a protection circuit 1 according to the invention.

[0046] The protection circuit 1 is therefore preferably arranged to receive as inputs signals representative of the phase and neutral voltages of the grid G ​​and a current signal representative of the compensation current and is configured to generate as output an alarm signal if an associated resistive component is detected in the leakage current.

[0047] More specifically, the protection circuit 1 comprises a summing network 2 configured to receive as inputs signals representative of the phase and neutral voltages of the grid G ​​and to return as an output a homopolar voltage signal.

[0048] The term "homopolar voltage" in this specification is intended to mean the voltage of the actual star point of a three-phase system relative to the voltage of the ideal star point that coincides with the centroid of the line voltage triangle.

[0049] Also provided is a device for sensing a current signal Icomp representative of the compensation current.

[0050] These signals, ie the current signal and the homopolar voltage signal, are then injected into the conversion stage X.

[0051] Conversion stage 3 is preferably configured to receive as input said homopolar voltage signal and said current signal and to generate a first square wave representative of said homopolar voltage signal and a second square wave representative of said current signal.

[0052] Preferably, the conversion stage 3 comprises a first conversion module 4 (or transformer) and a second conversion module 5 (or transformer) configured to generate a first square wave and a second square wave, respectively.

[0053] In a preferred embodiment, the first transformation module 4 and the second transformation module 5 are each defined by a comparator.

[0054] The comparator is configured to receive as an input a homopolar voltage or current signal and generate a square wave representative of the sign of the signal.

[0055] In other words, the comparator is configured to compare an input signal with a null reference and to output a signal with a value of 1 if the input signal has a positive sign and a signal with a value of 0 if the input signal has a negative sign (or to output a signal with a value of 0 if the input signal has a positive sign and a signal with a value of 1 if the input signal has a negative sign).

[0056] The electronic protection circuit 1 further comprises a combining stage 6 configured to combine the first square wave and the second square wave together to generate an output signal having a first logic level when the first square wave and the second square wave are in phase and a second logic level when the first square wave and the second square wave are not in phase.

[0057] In other words, the combination stage 6 is configured to generate a signal representative of the phase shift between the first and second square waves and to return a first logic level in time intervals when the two waves are in phase (i.e. when the current signal and the homopolar voltage signal have the same sign) and to return a second logic level in time intervals when the two waves are not in phase (i.e. when the current signal and the homopolar voltage signal have different signs).

[0058] In a preferred embodiment, the combining stage 6 is defined at least in part by a multiplier which returns the value 1 only if the two square waves overlap.

[0059] A charging module 7 operatively disposed downstream of the docking stage 6 is also provided.

[0060] This charging module 7 is configured to generate a first voltage that increases proportionally to the duration of each section of the output signal having said first value.

[0061] In other words, the first voltage generated by the charging module 7 is proportional to the duration of the overlap between the first and second square waves, and thus defines an accurate indication of the phase shift between the homopolar voltage and current signals.

[0062] Preferably, the charging module is defined by an RC circuit comprising a resistor 8 and a capacitor 9 in series with each other.

[0063] The protection circuit 1 then comprises a comparator element 10 configured to compare the value of said first voltage with a limit value and to generate an alarm signal if the voltage level on said capacitor exceeds said limit value.

[0064] The value of the first voltage is proportional to the time constant of the RC circuit and the allowable phase level between the two input signals.

[0065] In a preferred embodiment, the time constant is equal to 2.2 ms and the first voltage limit is reached in approximately 9 ms.

[0066] In a preferred embodiment, the protection circuit 1 is placed in parallel (ie redundant) with the protection module 107 of the microcontroller.

[0067] Advantageously, in this way it is possible to have two safety levels which are independent of each other and thus increase the reliability of the system.

[0068] Preferably, in this regard, the charging device 100 includes at least one enable node (108) connected to the module 107 and the protection circuit 1 and configured to generate an enable signal to the compensation circuit 106 only in the absence of an alarm signal generated by the module 107 and the protection circuit 1.

[0069] A further object of the invention is a method for protecting an on-board charging device 100, preferably, but not necessarily, implemented by the inventive protection circuit 1 described above.

[0070] The method will therefore be described in more detail below, with the emphasis being that all features mentioned and described in relation to circuit 1 should be considered as applicable mutatis mutandis to the following description of the method of the invention, unless expressly indicated or incompatible.

[0071] The method includes detecting phase and neutral voltages provided from the grid G, and detecting a current signal representative of the compensation current generated by the compensation circuit.

[0072] Thus, the phase voltages are combined together to obtain a homopolar voltage signal.

[0073] Thus, the current signal and the homopolar voltage signal are squared to obtain a first rectangular current wave and a second rectangular voltage wave.

[0074] More specifically, the square wave actually defines the sign of the input signal.

[0075] Thus, the first square wave and the second square wave are combined to generate an output signal having a first logic level when the first square wave and the second square wave are in phase and a second logic level when the first square wave and the second square wave are not in phase.

[0076] Preferably, the first square wave and the second square wave are multiplied together. When the two square waves overlap, the multiplication results in a value of 1, so that the first logic level is equal to 1 and the second logic level is equal to 0.

[0077] Advantageously, in this way it is possible to obtain an easily interpretable signal that provides precise information regarding the phase shift between the current signal and the homopolar voltage signal.

[0078] In fact, the degree of phase shift is proportional to the duration of the overlap interval and therefore to the duration of the output signal section having the first logic value.

[0079] At this point, a first voltage is generated that increases proportionally to the duration of each section of the output signal having said first value.

[0080] The step of generating a first voltage is preferably performed by charging a capacitor arranged in an RC circuit similar to that described above.

[0081] Thus, the value of the first voltage is compared to a limit value and an alarm signal is generated if the level of the first voltage on the capacitor exceeds the limit value.

[0082] Therefore, following generation of the alarm signal, a step is provided of disabling the compensation circuit 106.

[0083] The present invention achieves its intended objectives and offers important advantages.

[0084] In fact, it is possible to increase the reliability of a protection system by using completely physical / hardware protection methods and circuits.

Claims

1. A method for protecting an on-board charging device (100), comprising: The charging device (100) comprises a socket for connection to a grid (G), a converter assembly (104) configured to convert alternating current provided by the grid (G) into direct current usable for charging a battery pack (105), and a compensation circuit (106) configured to generate a compensation current (Icomp) equal to and opposite to one or more leakage currents flowing towards earth, and the method comprises: - detecting the phase and neutral voltages from the grid (G); - detecting a current signal representative of said compensation current (Icomp) generated by said compensation circuit (106); - combining said phase voltages to obtain a homopolar voltage signal; - squaring said current signal and said homopolar voltage signal to obtain a first rectangular current wave and a second rectangular voltage wave; - combining the first and second square waves to generate an output signal having a first logic level when the first and second square waves are in phase and a second logic level when the first and second square waves are not in phase; - generating a first voltage that increases proportionally to the duration of each section of said output signal having said first logic level; - comparing the value of said first voltage with a limit value; generating an alarm signal if said value of said first voltage exceeds said limit value.

2. 2. The method of claim 1, wherein the step of combining the first square wave and the second square wave comprises multiplying the first square wave and the second square wave together.

3. 3. The method according to claim 1 or 2, wherein the step of generating the first voltage is performed by charging a capacitor (9).

4. 4. The method of claim 1, further comprising disabling the compensation circuit (106) following generation of the alarm signal.

5. A circuit for protecting an in-vehicle charging device (100), The charging device (100) comprises a socket for connection to a grid (G), a converter assembly (104) configured to convert alternating current provided by the grid (G) into direct current usable for charging a battery pack (105), and a compensation circuit (106) configured to generate a compensation current (Icomp) equal and opposite to one or more leakage currents flowing towards earth, the device comprising: a summing network (2) configured to receive as input signals representative of the phase voltages (L1, L2, L3) and neutral voltage (N) of said grid (G) and to produce as output a homopolar voltage signal; an element for detecting a current signal (Icomp) representative of said compensation current; a conversion stage (3) configured to receive as input said homopolar voltage signal and said current signal and to generate a first square wave representative of said homopolar voltage signal and a second square wave representative of said current signal; a combining stage (6) configured to combine said first and second square waves to generate an output signal having a first logic level when said first and second square waves are in phase and a second logic level when said first and second square waves are not in phase; a charging module (7) operatively arranged downstream of said combining stage (6) and configured to generate a first voltage that increases in proportion to the duration of each section of said output signal having said first logic level; a comparator element (10) configured to compare the value of said first voltage with a limit value and to generate an alarm signal if said value of said first voltage exceeds said limit value.

6. 6. The circuit of claim 5, wherein the conversion stage (3) comprises a first conversion module (4) and a second conversion module (5) configured to generate the first and second square waves, respectively.

7. 7. The circuit of claim 6, wherein the first and second conversion modules (4, 5) are each defined by a comparator configured to receive as input the corresponding homopolar voltage or current signal and to generate a square wave representative of the sign of the signal.

8. 8. The circuit of claim 5, wherein the combining stage (6) is at least partly defined by a multiplier.

9. 9. The circuit according to any one of claims 5 to 8, wherein the charging module (7) is defined by a circuit having a resistor (8) and a capacitor (9) in series with each other.

10. An in-vehicle charging device (100), - a socket (101) for connection to the grid (G); a converter assembly (104) configured to convert the alternating current provided by said grid (G) into direct current usable to recharge the battery packs (105); a compensation circuit (106) configured to generate a compensation current equal and opposite to the leakage current flowing towards earth (PE); a microcontroller comprising a protection module (107) configured to generate an alarm signal if an associated resistive component is detected in said leakage current; - a protection circuit (1) according to any one of claims 5 to 9 arranged in parallel with said protection module (107); - at least one enable node (108) connected to the module (107) and the protection circuit (1) and configured to generate an enable signal for the compensation circuit (106) only when there is no alarm signal generated by the module (107) and the protection circuit (1).

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