Apparatus for generating virtual neutral point

Abstract

An apparatus for generating a virtual neutral point comprises a first terminal (2), a second terminal and a third terminal connectable to a first phase (V1), a second phase (V2) and a ground node (PE), respectively, of a multi-phase electrical network. A control circuit (5) connected to the first terminal (2), the second terminal (3) and the third terminal (4) and configured to maintain a constant value of the potential of the third terminal (4) in response to an interference signal generated on the third terminal (4) by the low voltage load (L); the control circuit (5) is provided with a storage stage (6) and a control stage (9) operably interposed between the storage stage (6) and the third terminal (4) and configured for extracting energy from the first storage means (7a) when the potential of the third terminal (4) falls below a reference value and for extracting energy from the second storage means (7b) when the potential of the third terminal (4) rises above a reference value.

Description

Technical Field

[0001] The present invention relates to a device for generating a virtual neutral point.

[0002] The main and preferred application of the invention is in the automotive field, in particular in the design and manufacture of charging systems for batteries. Background Art

[0003] In fact, in the context of electric vehicles, the battery pack charging mode is divided into two different macro categories involving: on-board chargers and ground chargers.

[0004] The on-board charger, as the name implies, is integrated into the vehicle and includes all the power and control electronics required to convert the AC power from the grid into the DC power needed to charge the battery pack.

[0005] On the other hand, 'ground-based' chargers are commonly known as 'columns' or wall boxes and convert DC power directly by supplying it to the vehicle.

[0006] It is therefore clear that both types of battery chargers have to manage the AC power coming from the grid and have to convert it into DC power to charge the high voltage battery and are of considerable importance in terms of user safety as they have to be equipped with appropriate protection systems.

[0007] Such protection systems are usually associated with the need to verify the quality of the circuit's earth ground (PEM) and the need to compensate for leakage currents to avoid accidental failure of the protection circuit (I-COMP); in most cases, these systems involve injecting a preset measurement or control signal (usually at a low voltage) into the earth ground.

[0008] To do this, the circuit that generates this voltage must be between two nodes at different potentials, one of which is ground.

[0009] In charging systems connected to a grid with a neutral point, measurement or control signals are usually injected between the neutral point and ground, which are at very close, but different, potentials.

[0010] However, disadvantageously, this is not possible in topologies in which all charging sockets are not directly connected to the neutral point.

[0011] A solution to this problem has already been proposed by patent document DE102020119106, which shows a circuit for generating a virtual neutral point connected to a grid connection terminal (i.e. connected to the phases in the case of a grid without a neutral point) and configured to generate a preset voltage close to the ground voltage at a node of the circuit.

[0012] Such a circuit comprises an active voltage divider acting between two end nodes connected to the phase terminals and, under suitable control, makes it possible to compensate for fluctuations in the neutral point by maintaining its voltage constant (close to ground as previously mentioned).

[0013] However, this solution is disadvantageous only for network configurations that guarantee the presence of a neutral point or perfect balance between the two phase terminals; an example of such a configuration is a split-phase network (or single-phase three-wire network), in which the two phases are 180° out of phase and symmetrical with respect to the ground connection, thus making it possible to compensate for positive and negative imbalances of the virtual neutral point at any time by utilizing the phase voltage at a voltage opposite to the imbalance.

[0014] However, such topologies are not able to guarantee voltage balancing of the virtual neutral point in an unbalanced grid, such as a three-phase grid with phase connections and a grounded star point. Summary of the Invention

[0015] Therefore, an object of the present invention is to provide a device for generating a virtual neutral point which can overcome the above-mentioned disadvantages of the prior art.

[0016] In particular, it is an object of the present invention to provide a device for generating a virtual neutral point which is highly versatile and efficient in all currently existing major power grid configurations.

[0017] This object is achieved by a device for generating a virtual neutral point having the characteristics listed in one or more of the following claims.

[0018] Specifically, the object is achieved by a device for generating a virtual neutral point, which comprises a first terminal, a second terminal, a third terminal and a control circuit.

[0019] The first terminal is connectable to (or capable of receiving) a first phase of a multi-phase electrical network.

[0020] The second terminal is connectable to (or capable of receiving) a second phase or neutral branch of the multi-phase grid.

[0021] The third terminal is a virtual neutral terminal, located between the first terminal and the second terminal, connectable to a ground node and having a preset potential. More specifically, the third terminal is preferably connected / connectable to a low-voltage load, which in turn is connected to the ground.

[0022] The control circuit is connected to the first terminal, the second terminal, and the third terminal.

[0023] Preferably, the control circuit is configured to maintain (and thereby control) a constant value of the third terminal potential in response to a disturbance signal generated on the third terminal by a low voltage load (eg PEM or I-COMP) or by natural voltage variations of the grid.

[0024] Preferably, the control circuit is configured to maintain the voltage of the third terminal at approximately zero.

[0025] Preferably, the control circuit is provided with a storage stage connected to the first terminal and the second terminal.

[0026] The storage stage preferably includes a first storage device and a second storage device configured to store charge until a positive peak voltage and a negative peak voltage are obtained.

[0027] A positive peak voltage (or positive saturation voltage) is reached in the first storage device.

[0028] A negative peak voltage (or negative saturation voltage) is reached in the second storage device.

[0029] The control circuit is preferably provided with a control stage operatively interposed between the storage stage and the third terminal.

[0030] Preferably, the control stage is configured to draw power from the first storage means or the second storage means.

[0031] Preferably, the control stage is configured to:

[0032] - extracting energy (ie voltage) from the first storage device when the potential of the third terminal falls below a reference value, and / or

[0033] - When the potential of the third terminal rises above a reference value, energy (ie voltage) is extracted from the second storage device.

[0034] Preferably, the reference value is equal to the potential of the ground node (ie substantially zero).

[0035] Thus, in other words, the control stage is configured to extract energy (ie voltage) from the first storage device when the potential of the third terminal is positive, and to extract energy (ie voltage) from the second storage device when the potential of the third terminal is positive.

[0036] Advantageously, the presence of a storage stage equipped with means capable of storing voltages of opposite sign allows compensation of all types of disturbances on the virtual neutral, whatever the voltage level, phase shift and phase balance of the grid.

[0037] This therefore makes the device universal; it can be connected to any power grid currently installed around the world.

[0038] The dependent claims incorporated herein by reference correspond to different embodiments of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Further features and advantages of the invention will become more apparent from the indicative and non-limiting description of a preferred but non-exclusive embodiment of the device for generating a virtual neutral point, as shown in the accompanying drawings:

[0040] - Figure 1 Schematically shows a circuit structure of an apparatus for generating a virtual neutral point according to the present invention in a first embodiment;

[0041] - Figure 2 The circuit structure of the device for generating a virtual neutral point according to the present invention in the second embodiment is schematically shown. DETAILED DESCRIPTION

[0042] Referring to the drawings, an apparatus for generating a virtual neutral point is generally indicated by the reference numeral 1 and is preferably mounted inside an automotive battery charger apparatus (not shown).

[0043] The term "charging device" is used in this text to generally define any charging system for a traction battery pack that is capable of connecting to an AC grid and converting it to DC current before supplying power to the battery.

[0044] The device 1 is configured to be connected to a connection socket 9 of an electrical grid G.

[0045] The grid G can be of any kind, single-phase or multi-phase.

[0046] In case of a single-phase grid, the device 1 is configured to be connected to one phase of the grid and to the neutral point of the grid.

[0047] In case of a multi-phase grid, the device 1 is configured to be connected to at least two phases of the grid G with a predetermined phase shift.

[0048] The device 1 can also be connected to one or more low-voltage loads by means of the virtual neutral point it generates.

[0049] Examples of such loads may be a device for measuring the ground resistance PEM or a leakage current compensation circuit I-COMP, which typically has a current generator injecting a current signal between the neutral point and ground.

[0050] Thus, the device 1 comprises a first terminal 2 , a second terminal 3 and a third terminal 4 .

[0051] The first terminal 2 is connectable to a first phase V1 of a power grid G.

[0052] The second terminal 3 can be connected to the second phase V2 of the grid G or to a neutral branch.

[0053] The third terminal 4 (or virtual neutral terminal) is interposed between the first terminal 2 and the second terminal 3 and can be connected to the ground node PE in use.

[0054] The third terminal 4 preferably has a preset potential; more preferably, the preset potential is close to the potential of the ground node PE.

[0055] Typically, the value of the neutral point is quantized at approximately 3 to 8 volts; however, the apparatus of the present invention is configured to generate a virtual neutral point having zero voltage relative to ground.

[0056] In this regard, according to one aspect of the invention, the device 1 comprises a control circuit 5 connected to the first terminal 2 , the second terminal 3 and the third terminal 4 .

[0057] The control circuit 5 is configured to maintain a constant value of the potential of the third terminal 4 in response to a disturbance signal generated on the third terminal 4 by the low-voltage load L or by natural grid variations.

[0058] It should be noted that the expression “maintain constant” in this context should be understood as the control circuit 5 intending to control the potential of the third terminal 4 so that the potential is kept at least near the previously mentioned preset value, more preferably near zero.

[0059] Preferably, the control circuit 5 comprises at least one storage stage 6 .

[0060] More preferably, the control circuit 5 further comprises a control stage 9 operatively interposed between the storage stage 6 and the third terminal 4 .

[0061] The storage stage 6 is connected to the first terminal 2 and the second terminal 3 and is provided with a first storage device 7 a and a second storage device 7 b .

[0062] The first storage device 7a and the second storage device 7b are configured to store electric charge until a positive peak voltage and a negative peak voltage are obtained in the first storage device 7a and the second storage device 7b, respectively.

[0063] Preferably, the peak voltage corresponds to the maximum voltage value of the first phase V1 and the second phase V2 of the grid to which the storage device is connected via the first terminal 2 and the second terminal 3 , respectively.

[0064] Preferably, the storage stage 6 comprises a bridge formed by two capacitors 7 a , 7 b arranged in parallel with a respective diode 8 .

[0065] The capacitors corresponding to the first storage device 7a and the second storage device 7b, respectively, are configured to store charges from the first terminal 2 and the second terminal 3 until a positive peak voltage and a negative peak voltage are obtained, respectively.

[0066] In a preferred embodiment, the storage stage 6 comprises a first parallel branch 6a in which the capacitors 7a, 7b are located and a second parallel branch 6b in which the diode 8 is located.

[0067] The first parallel branch 6 a has a first central node 11 between the two capacitors 7 a , 7 b and connected to the first terminal 2 .

[0068] The second parallel branch 6 b has a second central node 12 between the two diodes 8 and connected to the second terminal 3 .

[0069] The control stage 9 is configured to control the charging and discharging of the storage stage 6 depending on the interference signal on the third terminal 3 and the grid conditions (ie the phase voltage values).

[0070] Preferably, the control stage 9 is configured to control the storage stage 6 to extract power from the first storage device 7a when the potential of the third terminal 4 drops below zero (ground value), and to extract power from the second storage device 7b when the potential of the third terminal 4 rises above zero (ground value).

[0071] In other words, when natural grid variations or disturbances generated by the low-voltage loads L connected thereto modify the potential of the third terminal 4 by deviating its value from a reference value assumed to be equal to ground (ie substantially zero).

[0072] Preferably, the control stage 9 comprises a third control branch 9a which is arranged in parallel with the first branch 6a and the second branch 6b of the storage stage 6 and is provided with a triggering device 10 for triggering the discharge of the capacitors 7a, 7b.

[0073] Furthermore, preferably, the third branch 9 a includes a third central node 13 interposed between the two triggering devices 10 and connected to the third terminal 4 .

[0074] These trigger devices 10 can be selectively switched between a charging state and a discharging state according to the sign of the voltage on the third terminal 4. In the charging state, the trigger device allows one or both of the capacitors 7a, 7b to be charged, and in the discharging state, the trigger device allows one of the capacitors 7a, 7b (preferably, the capacitor having a peak voltage with an opposite sign to the interference signal) to be discharged.

[0075] Therefore, preferably, the device includes a control unit (not shown) configured to alternately and selectively control the trigger device 10 to continuously control the potential of the third terminal 4 so as to maintain it at a reference value.

[0076] According to a variation of the present invention, Figure 2 As shown, the control circuit 5 comprises a balancing stage 14 arranged operatively in parallel with the storage stage 6 .

[0077] The balancing stage comprises two compensation branches 15 respectively connected to the first terminal 2 and the second terminal 3 and capable of being selectively triggered to extract a voltage from the terminal having an opposite voltage sign to that of the interfering signal.

[0078] In a preferred embodiment, each compensation branch 15 comprises a capacitor and a current generator which can be selectively triggered to extract from the corresponding phase (ie from the corresponding first terminal 2 or second terminal 3) the voltage required to compensate for the interference signal on the third terminal.

[0079] Depending on the boundary conditions of the system and the grid, the storage stage 6 and the balancing stage 14 may operate simultaneously or alternatively.

[0080] The invention achieves the intended objects and realizes important advantages.

[0081] In fact, the storage circuit connected to the third node enables the compensation operation to be maintained even in the absence of a balanced grid, making the device universal and suitable for any application in any geographical area.

Claims

1. A device for generating a virtual neutral point, comprising: - a first terminal (2) connectable to a first phase (V1) of a power grid (G); - a second terminal (3) connectable to a second phase (V2) or a neutral branch of said electrical network (G); a virtual neutral third terminal (4), between the first terminal (2) and the second terminal (3), connectable to a ground node (PE) and having a preset potential; The device is characterized in that the device comprises a control circuit (5), which is connected to the first terminal (2), the second terminal (3) and the third terminal (4) and is configured to maintain a constant value of the potential of the third terminal (4) in response to an interference signal generated by a low-voltage load (L) on the third terminal (4) or a change in the grid voltage; the control circuit (5) is provided with: a storage stage (6) connected to the first terminal (2) and the second terminal (3) and provided with a first storage device (7a) and a second storage device (7b), the first storage device and the second storage device being configured to store charge until a positive peak voltage and a negative peak voltage are obtained in the first storage device (7a) and the second storage device (7b), respectively; - a control stage (9) operatively interposed between the storage stage (6) and the third terminal (4) and configured to: - extracting energy from the first storage device (7a) when the potential of the third terminal (4) falls below a reference value; - when the potential of the third terminal (4) rises above a reference value, energy is extracted from the second storage means (7b).

2. The device for generating a virtual neutral point according to claim 1, wherein: The reference value is substantially equal to ground potential, generating a zero voltage between the third terminal (4) and the ground node (PE).

3. The device for generating a virtual neutral point according to claim 1 or 2, wherein: The storage stage (6) of the control circuit (5) comprises a bridge formed by two capacitors (7a, 7b) arranged in parallel with respective diodes (8) and configured to store charge from the first terminal (2) and the second terminal (3) until the positive peak voltage and the negative peak voltage are respectively obtained; the capacitors (7a, 7b) correspond to the first storage means (7a) and the second storage means (7b), respectively.

4. The device for generating a virtual neutral point according to claim 3, wherein: The storage stage (6) of the control circuit (5) comprises a first parallel branch (6a) and a second parallel branch (6b), the capacitors (7a, 7b) being located in the first parallel branch and the diode (8) being located in the second parallel branch; the first parallel branch (6a) having a first central node (11) which is located between the two capacitors (7a, 7b) and connected to the first terminal (2), and the second parallel branch (6b) having a second central node (12) which is located between the two diodes (8) and connected to the second terminal (3).

5. The device for generating a virtual neutral point according to claim 3 or 4, wherein: The control stage (9) of the control circuit (5) comprises a third control branch (9a), which is arranged in parallel with the first branch (6a) and the second branch (6b) of the storage stage (6) and is provided with a trigger device (10) for triggering the discharge of the capacitors (7a, 7b), the trigger device being able to selectively switch depending on the sign of the interference signal at the third terminal (4).

6. The device for generating a virtual neutral point according to claim 5, wherein: The third branch (9a) comprises a third central node (13) which is interposed between the two triggering devices (10) and is connected to the third terminal (4).

7. The device for generating a virtual neutral point according to any one of the preceding claims, wherein The control circuit (5) comprises a balancing stage (14) which is operatively arranged in parallel with the storage stage (6) and comprises two compensation branches (15) which are respectively associated with the first terminal (2) and the second terminal (3) and can be selectively activated to extract a voltage from the terminal having a voltage sign opposite to that of the interference signal.

8. An on-board battery charger comprising a device for generating a virtual neutral point according to any one of the preceding claims.

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