Electrical systems particularly for motor vehicles

Abstract

The invention relates to an electrical system (10), in particular for a motor vehicle, comprising: a first electronic circuit (12), which has a first ground (GND1) and is powered by a first voltage (V1) at a first power supply terminal (B1); a second electronic circuit (14), which has a second ground (GND2) separated from the first ground (GND1) and is powered by a second voltage (V2) different from the first voltage (V1) at a second power supply terminal (B2); and a capacitive element (20), which connects a first potential point (A) of the first electronic circuit (12) to a second potential point (B) of the second electronic circuit (14).

Description

Technical Field

[0001] The invention relates to an electrical system, in particular for a motor vehicle. Background Art

[0002] The invention relates in particular to rotating electrical machines equipped with an integrated electrical system. In particular, in particular in motor vehicles, there are more and more so-called high voltage (e.g. 48V) electronic devices. This type of high voltage device is usually connected to one or more sensors powered by a low voltage (usually 12V).

[0003] Therefore, in the electronic equipment of motor vehicles, there is increasingly coexistence between low-voltage parts and high-voltage parts, wherein the low-voltage parts are generally connected to circuits supplied with 12 volts from the vehicle, and the high-voltage parts are generally connected to circuits supplied with 48V or higher voltage from the vehicle.

[0004] In this case, the so-called "LV148" standard specifies that the voltage of 70 volts be maintained so that the leakage current between the two grounds of the low voltage circuit (usually 12 V) and the high voltage circuit is less than 1 μA.

[0005] In order to meet this requirement, it is known to use galvanic isolation for analog and digital signals.

[0006] However, this type of isolation is expensive. Summary of the invention

[0007] The present invention therefore proposes to provide an electrical system for correcting this problem.

[0008] To this end, an object of the invention is an electrical system, in particular for a motor vehicle, comprising:

[0009] - a first electronic circuit having a first ground and being supplied with a first voltage at a first supply terminal,

[0010] a second electronic circuit having a second ground separate from the first ground and being supplied at a second power supply terminal with a second voltage different from the first voltage,

[0011] - a capacitive element connecting a first potential point of the first electronic circuit to a second potential point of the second electronic circuit.

[0012] In other words, the capacitive element is arranged between two points whose potentials, ie, voltages, are different.

[0013] Advantageously, such an electrical system makes it possible to dispense with the galvanic isolation usually used and to replace it with a capacitive isolation, thereby reducing production costs, in particular in the case of temperature measurement in electrical systems.

[0014] The electrical system according to the invention may also include one or more of the following features, which may be considered individually or in any technically feasible combination:

[0015] When a voltage substantially equal to or equal to 70V is applied between a first ground connected to the first power terminal of the first circuit 12 and a second ground connected to the second power terminal of the second circuit 14, a leakage current measured between the first circuit and the second circuit is less than 1 μA; and / or

[0016] The second voltage is greater than or equal to the first voltage; and / or

[0017] The first voltage is between 3V and 40V, and the second voltage is between 20V and 70V; and / or

[0018] The capacitance of the capacitive element is between 1 and 4.7 μF; and / or

[0019] The RNS electrical system further comprises a variable resistor having a resistance that varies with temperature, the variable resistor being arranged in series between the capacitive element and the second ground; and / or

[0020] The electrical system further comprises a temperature measuring device comprising: a voltage generator, an acquisition device, a calculation unit and a first resistor, a first electrical terminal of the first resistor being connected to a terminal of the voltage generator and a second electrical terminal of the first resistor being connected to a first potential point of the first electronic circuit, wherein:

[0021] o a voltage generator configured to emit a periodic signal at a first terminal of a first resistor,

[0022] o the acquisition means are configured to periodically sample the potential present at an input terminal connected to a first potential point of the first electronic circuit, and

[0023] o the computing unit is configured to estimate the temperature from the samples collected by the collection device;

[0024] and / or

[0025] The periodic signal emitted at the first terminal of the first resistor is a periodic voltage; and / or

[0026] The potential at the input terminals of the acquisition device is a voltage; and / or

[0027] in the electrical system, when the electrical system is in operation, a first ground of the first electronic circuit is electrically connected to a second ground of the second electronic circuit, preferably only via a cable; and / or

[0028] The voltage generator is configured to emit a square wave signal; and / or

[0029] The voltage generator is configured to generate a signal having a duty cycle greater than or equal to 40% and less than or equal to 60%; and / or

[0030] The temperature measurement device further comprises a filtering device, which is arranged and configured to filter the potential before the acquisition device samples the potential present at the first potential point of the first electronic circuit, and the filtering device comprises:

[0031] o a second resistor connected between the first potential point of the first electronic circuit and the input terminal of the acquisition device,

[0032] o a first filter capacitor and a first switch connected in series, the series combination of the first filter capacitor and the first switch being arranged in parallel between an input terminal of the acquisition device and a first ground,

[0033] o a second filter capacitor and a second switch connected in series, the series combination of the second filter capacitor and the second switch being arranged in parallel between an input terminal of the acquisition device and a first ground,

[0034] o The on or off state of the first and second switches is controlled by a square wave signal emitted by a voltage generator; when the second switch is on, the first switch is off, and vice versa. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Other characteristics and advantages of the invention will become apparent on reading the detailed description of an embodiment given by way of non-limiting example and illustrated in conjunction with the following drawings.

[0036] - Figure 1 A circuit diagram according to a first embodiment of the present invention is shown;

[0037] - Figure 2 Shows an example Figure 1 Timing diagram of the operation of the electrical system in;

[0038] - Figure 3 shows a circuit diagram according to a second embodiment of the present invention;

[0039] - Figure 4 A timing diagram is shown which illustrates the presence of noise between the first ground and the second ground and the effect of the noise Figure 1 the impact on the operation of the electrical system in the

[0040] - Figure 5 shows a timing diagram which shows Figure 3 The operation of filtering devices in electrical systems.

[0041] In the accompanying drawings, similar elements are represented by the same reference numerals. In addition, in order to provide an easy-to-understand view of the present invention, various elements are not necessarily shown to scale. DETAILED DESCRIPTION

[0042] Figure 1 and Figure 2 A first embodiment of an electrical system according to the invention is shown, in particular for a motor vehicle.

[0043] The electrical system 10 comprises a first electronic circuit 12 having a first ground GND1 and being supplied by a first voltage V1 at a first power supply terminal B1 .

[0044] The electrical system 10 further comprises a second electronic circuit 14 having a second ground GND2 and being supplied by a second voltage V2 at a second power supply terminal B2 .

[0045] The first ground GND1 of the first electronic circuit 12 is separated from the second ground GND2 of the second electronic circuit 14 .

[0046] In addition, the second voltage is different from the first voltage. For example, the second voltage V2 is greater than or equal to the first voltage V1.

[0047] Preferably, the first voltage V1 is between 3V and 40V, and the second voltage V2 is between 20V and 70V. In the example shown in the drawings, the first voltage V1 is about 12V, and the second voltage V2 is about 48V.

[0048] According to the invention, the electrical system advantageously comprises a capacitive element 20 connecting a first potential point (referenced A) of the first electronic circuit 12 with a second potential point (referenced B) of the second electronic circuit 14 .

[0049] The capacitive element 20 preferably has a capacitance between 1 and 4.7 μF and preferably between 1 and 2.2 μF. This particular size of the capacitive element 20 makes it possible to ensure that, when a voltage substantially equal to 70 V is applied between a first ground connected to the first terminal of the first electronic circuit 12 and a second ground connected to the second terminal of the second electronic circuit 14, the leakage current measured between the first ground of the first circuit 12 and the second ground of the second circuit 14 is less than 1 μA. The electrical system 10 thus complies with the E48-20 test of the LV148 standard.

[0050] Furthermore, the leakage current of such an electrical system can be easily measured by a measurement method in which the leakage current is measured between the first electronic circuit 12 and the second electronic circuit 14 after applying a voltage substantially equal to 70 V between a first ground connected to a first terminal of the first circuit 12 and a second ground connected to a second terminal of the second circuit 14. The electrical system also advantageously includes a variable resistor 30 whose resistance varies with temperature. The variable resistor 30 is electrically connected to a second potential point of the second electronic circuit 14 via one terminal thereof, and is electrically connected to a second ground GND2 of the second circuit 14 via the other terminal thereof. In other words, the variable resistor 30 is connected between the capacitive element 20 and the second ground GND2 of the second circuit 14.

[0051] In the example described here, the variable resistor 30 is an NTC (negative temperature coefficient) thermistor, whose resistance R30 decreases as the temperature increases, and vice versa.

[0052] As a variant, the variable resistor 30 may be a PTC (Positive Temperature Coefficient) thermistor, the resistance of which increases as the temperature rises, and vice versa.

[0053] Advantageously, the electrical system 10 according to the invention also comprises a temperature measurement device 40. The temperature measurement device 40 comprises a voltage generator 42, an acquisition device 44 and a resistor 46 having a value R46. The resistor 46 has a first electrical terminal C connected to a terminal of the voltage generator 42 and a second electrical terminal D connected to the first potential point A of the first electronic circuit 12.

[0054] The voltage generator 42 is preferably configured to emit a periodic signal at a first terminal C of the resistor 46 .

[0055] In the example described here, the periodic signal emitted at the first terminal C of the resistor 46 is a periodic voltage.

[0056] like Figure 2 As shown, the voltage generator 42 is preferably configured to emit a square wave signal with a period T0, so that the shape of the signal to be processed can be simplified.

[0057] Preferably, the acquisition device 44 is configured to sample an analog signal at the second terminal D of the resistor 46 connected to the first potential point A of the first electronic circuit 12. For example, the analog signal at the second terminal D corresponds to the potential present at this point D, ie, the voltage.

[0058] Preferably, the acquisition device 44 is configured to: when the signal emitted by the voltage generator 42 is a periodic signal, sample the analog signal at the second terminal D of the resistor 46 at a sampling frequency T1 that is half of the period T0 of the signal.

[0059] Preferably, the voltage generator 42 is formed by arranging in series a general purpose input / output GPIO port of the microcontroller μC and a buffer stage amplifier 48, the GPIO port being configured as an output port on which a binary digital signal amplified by the buffer stage amplifier 48 is emitted. In other words, the voltage present at the output of the buffer stage amplifier 48 comprises a square wave periodic signal development with a period T0. The buffer stage amplifier 48 also makes it possible to avoid any load fluctuations at the first electrical terminal C from interfering with the frequency of the signal emitted by the GPIO port of the microcontroller μC.

[0060] Preferably, the acquisition means 44 is formed by an analog-to-digital converter. In the example described here, the analog-to-digital converter is already integrated into the microprocessor μC and is accessible via a so-called A / D or ADC (Analog-to-Digital Converter) input.

[0061] In the example depicted in the figure, but not limited thereto, the digital binary signal emitted by the GPIO port has a high level amplitude of 3.3V, and a low level amplitude of 0V, while the square wave periodic signal at the output of the buffer stage amplifier 48 has an amplitude varying between 0 and 5V.

[0062] When the electrical system 10 is in operation, the first ground of the first electronic circuit 12 is electrically connected to the second ground of the second electronic circuit 14 , preferably only through a cable.

[0063] When the voltage generator 42 emits a periodic signal at the first terminal C of the resistor 46 , the connection impedance Z between the first and second grounds is preferably negligible relative to the impedance R30 of the variable resistor 30 and relative to the impedance R46 of the resistor 46 .

[0064] Therefore, when the electrical system 10 is running, compared with using a transformer, the advantage of the present invention is that only one wire is used to form an electrical connection between the variable resistor 30 and the acquisition device 44, and a ground loop is formed through the first ground of the first electronic circuit 12 and the second ground of the second electronic circuit 14.

[0065] Advantageously, the voltage generator 42 is configured to emit a signal with a duty cycle greater than or equal to 40% and less than or equal to 60%, preferably substantially equal to 50%. Thus, the temperature measurement can be obtained from the analog signal (ie, the reference Figure 2 The measurement is obtained by the acquisition device 44 between the high state and the low state of the potential or voltage at the point D.

[0066] Preferably, the time constant of the RC circuit formed by the capacitive element 20, the variable resistor 30 and the resistor 46 (the product of the value of the capacitor 20 and the sum of the resistors 30 and 46) is much larger than the half period of the square wave signal emitted by the voltage generator 42 (i.e., in the example described, emitted at the output of the buffer stage amplifier 48).

[0067] Under these conditions, the RC circuit acts as an RC integrator circuit. In steady state, the capacitive element 20 has a constant voltage across its terminals that is equal to the average value V of the signal from the voltage generator 42. av .

[0068] For example, Figure 2 The RC circuit formed for the components having the following values ​​is shown. When the temperature measuring device 40 is as Figure 1 When the voltage generator 42 emits a square wave periodic signal with T0=0.2ms, the shape of the signal under consideration is:

[0069] At 25°C, R30 = 10kΩ,

[0070] R46 = 10 kΩ, and

[0071] C20 = 1 μF.

[0072] exist Figure 2 In the example shown, the amplitude of the square wave periodic signal at the output of the voltage generator 42 varies between 0 and 5V.

[0073] Figure 2 Also shown is the corresponding voltage present at the first potential point A of the first electronic circuit 12 .

[0074] The time constant of the RC circuit is t au is 0.02s, which is much longer than the 0.2ms period T0 of the signal that excites the RC circuit. In addition, the average value of the voltage at point C is V av =2.5V.

[0075] In steady state, resistors 30 and 46 form a voltage divider bridge.

[0076] In addition, Figure 2 In the example described in FIG. 4 , the acquisition device 44 is configured to sample the analog signal at point A with a sampling period T1 equal to half the period T0 of the signal emitted by the voltage generator 42. Therefore, the sample E sampled by the sampling device 44 is max and E min Have values ​​V max and V min .

[0077] Moreover, the potential difference V max-V min Depending on the value R30 of the variable resistor 30 , this value itself depends on the temperature surrounding the variable resistor 30 .

[0078] The potential difference Vmax-Vmin therefore depends on the temperature around the variable resistor 30, and this relationship can be described in a correspondence table comprising two columns. The first column lists V max -V min The second column lists the temperatures around the variable resistor 30, which are related to the V values ​​listed in the first column. max -V min The value corresponds to .

[0079] Thus, in this example, the microcontroller μC of the temperature measuring device 40 continuously receives samples E at its input A / D max and E min , calculate the difference between them, and calculate the temperature around the resistor 30 by using the correspondence table.

[0080] In the above example, the microcontroller μC uses the difference E max -E min to determine the temperature around the resistor 30. As a variant, the microcontroller μC may use only the sample E max Or just use sample E min To determine the temperature around the resistor 30 .

[0081] according to Figure 3 In the second embodiment shown, the electrical system 10 further comprises a filtering device 50 , which is arranged and configured to filter the analog signal present at point A before the acquisition device 44 samples the analog signal.

[0082] In the example described here, the analog signal present at point A is a potential, ie a voltage, relative to the first ground GND1.

[0083] Since the sampling time of the acquisition device 44 is usually about several microseconds, the measurement time of the square wave pattern has a great influence on the measurement accuracy in the presence of high-frequency noise. For example, the noise may be generated by the power switching operation of the electrical system.

[0084] like Figure 4 As shown in FIG. 1 , the noise is represented as a fluctuating voltage VF between the first ground GND1 and the second ground GND2, and can be modeled as a voltage source SB between the first ground GND1 and the second ground GND2. This noise adds a high amplitude peak to the square wave signal (see FIG. 1 ). Figure 4 b), sometimes occurs in synchronous cycles. Although the noise averages to zero, if the temporal pattern of the switching noise is similar to that of the sample Emax and / or E min If the acquisition time of the resistor 30 is not synchronized, the temperature around the resistor 30 determined by the temperature measuring device 40 will have a deviation.

[0085] In addition, since the temporal pattern of the noise is not symmetric, in sample E max and E min The resulting deviations will be different.

[0086] These characteristics of noise mean that it is difficult to max and E min Simple continuous filtering is performed to obtain a zero mean value for the noise.

[0087] Figure 3 The filtering device 50 shown comprises:

[0088] A resistor R2 connected between the first potential point A of the first electronic circuit 12 and the input terminal A / D of the acquisition device 44 .

[0089] a first filter capacitor C21 and a first switch I1 connected in series, the series combination of the first filter capacitor C21 and the first switch I1 being arranged in parallel between an input terminal (referred to as A / D) of the acquisition device 44 and the first ground GND1,

[0090] - a second filter capacitor C22 and a second switch I2 are connected in series, the series combination of the second filter capacitor C22 and the second switch I2 being arranged in parallel between an input terminal (referred to as A / D) of the acquisition device 44 and the first ground GND1,

[0091] In addition, the on and off states of the first and second switches are controlled by the square wave signal from the voltage generator 42. When the second switch I2 is on, the first switch I1 is off, and vice versa.

[0092] The synchronization of the switching on and off of the switches I1 and I2 with respect to the square wave signal from the voltage generator 42 is realized by two logic gates for controlling the switches I1 and I2, respectively.

[0093] The first logic gate LO1 is an inverting logic gate that inverts the signal emitted by the voltage generator. The second logic gate LO2 is a logic gate with an input and an output, which copies the signal available on its input to its output. Thus, in the example described here, when the square wave signal emitted by the voltage generator 42 takes its maximum value, the first switch is open and the second switch is closed.

[0094] The switches I1 and I2 may be, for example, transistors, such as MOSFET transistors or bipolar transistors, which are controlled by signals from the voltage generator 42 via the logic gates LO1 and LO2 .

[0095] Under these conditions, the two RC circuits act as two so-called RC integrator circuits which alternately filter the potential present at point A before the acquisition device 44 samples the potential on the basis of the signal emitted by the voltage generator 42 .

[0096] Therefore, in steady state, capacitor C21 is charged to a voltage V min , while capacitor C22 is charged to voltage V max .

[0097] In other words, when the binary digital signal emitted from the GPIO output port of the microcontroller μC takes a high value, the switch I2 is turned on, while the switch I1 is turned off, and the acquisition device 44 samples the potential existing at both ends of the capacitor C22.

[0098] Likewise, when the binary digital signal emitted on the GPIO output port of the microcontroller μC takes a low value, the switch I2 is opened, while the switch I1 is closed, and the acquisition device 44 samples the potential present at both ends of the capacitor C21.

[0099] As an example, the following values ​​can be used to form Figure 3 The filtering device 50 shown:

[0100] C21 = C22 = 1 μF, and

[0101] R2=10kΩ.

[0102] The RC circuit formed by the capacitive element C21 and the resistor R2 has a time constant (the product of the value of the capacitor C21 and the value of the resistor R2) greater than or equal to 10 ms and a cutoff frequency less than or equal to 100 Hz.

[0103] Furthermore, the RC circuit formed by the filter element C22 and the resistor R2 has the same time constant and the same cutoff frequency as the RC circuit formed by the filter element C21 and the resistor R2.

[0104] Therefore, the filter arrangement 50 is configured to have a cut-off frequency well below the critical filter frequency, which is 10 kHz, and a very high time constant in order to obtain a satisfactory noise integration.

[0105] Thus, filtered values ​​may be obtained at very low frequencies corresponding to the high and low states of the signal acquired by the acquisition device 44, while having a very high level of noise attenuation.

[0106] Figure 5 The advantage of using the noise filtering device 50 is shown.

[0107] The curve CO1 shows the voltage present at the first potential point A of the first electronic circuit 12. This curve is very noisy due to the presence of noise between the first ground GND1 and the second ground GND2.

[0108] Curve CO2 shows the voltage seen by the acquisition device 44 .

[0109] These two curves show that in the face of the noise between the first ground GND1 and the second ground GND2, the suppression of the filtering device is low-frequency filtering, and the V max and V min are filtered independently.

[0110] Advantageously, the sample E can be collected at any time during the successive half-cycles T0 / 2 corresponding to the high state and the low state of the signal emitted by the voltage generator 42, respectively. max and / or E min .

[0111] The present invention is not limited to the above-described embodiments. In particular, it is obvious to those skilled in the art that modifications may be made thereto.

[0112] Furthermore, the terms used should not be understood as being limited to the elements of the above-described embodiments, but rather should be understood to cover all equivalent elements that can be derived by those skilled in the art from their common knowledge.

Claims

1. An electrical system (10) for a motor vehicle, the electrical system (10) comprising: a first electronic circuit (12) having a first ground (GND1) and being powered by a first voltage (V1) at a first power supply terminal (B1), a second electronic circuit (14) having a second ground (GND2) and being powered at a second power supply terminal (24) by a second voltage (V2) which is proportional to the first voltage (V1), a capacitive element (20) connecting a first potential point (A) of the first electronic circuit (12) to a second potential point (B) of the second electronic circuit (14), and - a variable resistor (30) whose resistance varies with temperature, the variable resistor (30) being arranged in series between the capacitive element (20) and the second ground (GND2).

2. The electrical system according to claim 1, wherein: The second voltage (V2) is greater than or equal to the first voltage (V1).

3. The electrical system according to claim 2, wherein: The first voltage (V1) is between 3V and 40V, and the second voltage (V2) is between 3V and 40V.

4. An electrical system according to any one of the preceding claims, wherein: The capacitive element (20) has a capacitance between 1 and 4.7 μF.

5. The electrical system according to claim 1, further comprising a temperature measuring device (40), wherein the temperature measuring device (40) comprises: A voltage generator (42), a collection device (44), a calculation unit (μC), and a first resistor (46), a first electrical terminal (C) of the first resistor (46) being connected to a terminal of the voltage generator (42) and a second electrical terminal (D) of the first resistor (46) being connected to the first potential point (A) of the first electronic circuit (12), wherein: - the voltage generator (42) is configured to emit a periodic signal at the first electrical terminal (C) of the first resistor (46), - the acquisition means (44) are configured to periodically sample the potential present at an input terminal (A / D) connected to the first potential point (A) of the first electronic circuit (12), and The calculation unit (μC) is configured to estimate the temperature from the samples acquired by the acquisition means (44).

6. The electrical system according to claim 5, wherein: When the electrical system (10) is in operation, the first ground (GND1) of the first electronic circuit (12) is electrically connected to the second ground (GND2) of the second electronic circuit (14).

7. The electrical system according to claim 6, wherein: When the electrical system (10) is in operation, the first ground (GND1) of the first electronic circuit (12) is electrically connected to the second ground (GND2) of the second electronic circuit (14) only through a cable.

8. The electrical system according to claim 5 or 6, wherein: The voltage generator (42) is configured to emit a square wave signal.

9. The electrical system according to one of claims 5 to 7, wherein: The voltage generator (42) is configured to generate a signal with a duty cycle greater than or equal to 40% and less than or equal to 60%.

10. The electrical system of claim 8, wherein: The temperature measuring device (40) further comprises a filtering device (50), wherein the filtering device (50) is arranged and configured to filter the potential before the acquisition device (44) samples the potential at the first potential point (A) of the first electronic circuit (12), wherein the filtering device (50) comprises: a second resistor (R2) connected between the first potential point (A) of the first electronic circuit (12) and an input terminal (A / D) of the acquisition device (44), - a first filter capacitor (C21) and a first switch (I1) connected in series, the series combination of the first filter capacitor (C21) and the first switch (I1) being arranged in parallel between the input terminal (A / D) of the acquisition device (44) and the first ground (GND1), - a second filter capacitor (C22) and a second switch (I2) connected in series, the series combination of the second filter capacitor (C22) and the second switch (I2) being arranged in parallel between the input terminal (A / D) of the acquisition device (44) and the first ground (GND1), - The on or off state of the first switch and the second switch is controlled by a square wave signal emitted by the voltage generator (42); when the second switch is on, the first switch is off, and vice versa.

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