Transformer circuit to provide a charging current for a battery

Abstract

Title: Transformer circuit for providing a battery charging current. Transformer circuit (1) comprising a control unit (10) configured to operate the DC / DC converters (61, 62) in a series circuit on the input side, such that a partial input current (Idc1, Idc2) flows through them, resulting in a difference current (Icomp) at the intermediate node (Z), equal to the difference between the partial input currents (Idc1, Idc2), which at least partially compensates for the capacitor currents between the intermediate circuit capacitors (51, 52) and the intermediate node (Z). Figure for the abstract: Fig. 1

Description

Title of the invention: Transformer circuit for providing a battery charging current. Technical field

[0001] The invention relates to transformer circuits for converting an alternating current supply voltage into a charging current for charging a battery, in particular a high-voltage traction battery of a vehicle. Technical background

[0002] A charging circuit installed in a motor vehicle for charging a vehicle battery (traction battery) via an AC power supply typically includes an AC / DC transformer in the form of a PFC, for example, of the Vienna or TNPC type. This AC / DC transformer provides an intermediate circuit voltage, which has a voltage ripple. This means that the intermediate circuit voltage is not a constant DC voltage, but is superimposed on an AC voltage with an amplitude that, based on the input voltage ripple of the AC voltage from the AC power supply, is determined by the input AC voltage.The intermediate circuit potentials, i.e., the intermediate circuit potentials, are applied via capacitors (intermediate circuit capacitances) through an intermediate node to a neutral conductor, into which the voltage ripple enters, so that a ripple current can pass through the neutral conductor.

[0003] The voltage ripple or alternating voltage amplitude, particularly in single-phase operation of the AC / DC transformer, is so large that it results in a significant charge on the capacitors of the intermediate circuit. This is due to the fact that the half-waves of the AC supply pass almost completely through the capacitors.

[0004] To reduce the load on the capacitors, a condensing current can be applied at the intermediate nodes to compensate for the ripple current. This opposes the ripple in the intermediate circuit voltage. However, applying the compensation current at the intermediate nodes usually requires an additional half-bridge, which generates the appropriate compensation current from the intermediate circuit voltage. This increases the circuit load, which requires more space and compromises safety in the event of a failure.

[0005] A transformer circuit intended to provide battery charging currents has, downstream of the AC / DC transformer, a DC / DC converter, which includes current regulation, in order to transform the intermediate circuit voltage produced on the AC / DC transformer side into a battery voltage (or charging voltage) and a battery current (or charging current). This DC / DC converter may be provided, for example, in the form of an LLC, PSFB, DAB, or a comparable galvanically isolated circuit. Depending on the power requirement, several DC / DC converters may also be operated in parallel.

[0006] The present invention relates to a transformer circuit for obtaining battery voltage and battery current from an AC power supply, in which the capacitor charge is minimized and, in particular, the ripple current in the intermediate circuit capacitors is reduced or compensated. The invention further aims to achieve this solution with a small circuit cost. Description of the invention

[0007] This is achieved according to the invention by the following steps:

[0008] Item 1 Transformer circuit, in particular for an on-board vehicle battery charging device, for obtaining a controlled output voltage and current from a single-phase or polyphase alternating voltage from an alternating voltage supply network comprising:

[0009] On the input side, an AC / DC converter to have an intermediate circuit voltage in an intermediate circuit, the intermediate circuit potentials of which are applied to a neutral conductor respectively by an intermediate circuit capacitor;

[0010] On the output side, a DC / DC converter system comprising at least two DC-DC converters, which are connected on the input side to the intermediate circuit and which, with respect to the intermediate circuit voltage, are connected in series or may be connected in series, wherein the two DC-DC converters are connected together on the input side in a series arrangement via an intermediate node, wherein the DC-DC converters are connected in parallel on the output side to give respectively the output voltage and the output current as the sum of the partial output current of each of the DC / DC converters;

[0011] In which the intermediate node is connected or electrically linked to the neutral conductor;

[0012] A control unit which is constituted to operate the DC / DC converters following a series circuit on the input side so as to pass through it respectively a partial input current, so that at the intermediate node there follows a difference current of a difference between the partial input currents, which compensates at least in part the capacitor currents between the intermediate circuit capacitances and the intermediate node.

[0013] Item 2 Transformer circuit according to Item 1, in which the capacitor currents between the intermediate circuit capacitors and the intermediate node are determined, in particular as a function of determined phase currents of the AC supply voltage of the AC supply network, as a function of capacitor current determined by the intermediate circuit capacitors as a function of a determined intermediate circuit voltage or as a function of a determined voltage at at least one of the intermediate circuit capacitors, in order to determine a setpoint compensation current as a phase current inverse to the capacitor currents between the intermediate circuit capacitors and the intermediate node, in which the control unit is constituted to regulate the partial input currents so that the resulting difference current corresponds to the determined opposite phase current.

[0014] Item 3 Transformer circuit according to item 1 or 2, in which a voltage sensor is provided respectively to determine a proportion of DC voltage of the respective voltages at the intermediate circuit capacitances and to determine, as a function of their difference, a potential offset of the midpoint, in which the control unit is constituted to regulate the partial input currents so as to minimize the determined potential offset.

[0015] Item 4 Transformer circuit according to one of items 1 to 3, in which a switching device is provided for switching the assembly on the input side of the DC / DC converters between a series and a parallel assembly.

[0016] Item 5 Transformer circuit according to item 4, in which the control unit is constituted to control the switching device so as to establish a series connection, if single-phase operation of the AC / DC converter is observed, and to establish a parallel connection, if polyphase operation of the AC / DC converter is observed.

[0017] Item 6 Transformer circuit according to item 4 or 5, in which the control unit commands the switching device to establish a series connection if the capacitor currents between the intermediate circuit capacitors and the intermediate node exceed a predetermined capacitor current threshold value, and to establish a parallel connection if the capacitor currents between the intermediate circuit capacitances and the intermediate node fall below a compensator current threshold value given in advance.

[0018] The invention also relates to a method for operating a transformer circuit according to the invention, in which DC / DC converters are operated on the input side in a series arrangement such that they respectively give a partial input current and there follows at the intermediate node a difference current of a difference between the partial input currents, which compensates at least in part for the capacitor currents between the intermediate circuit capacitances and the intermediate node.

[0019] A transformer circuit designed to provide an output voltage (battery voltage, charging voltage, DC voltage) and an output current (battery current, charging current, DC current), particularly for charging a vehicle battery, especially a traction battery, from an AC power supply, typically includes an AC / DC converter, which provides an intermediate circuit voltage. This intermediate circuit voltage or potential is applied to a neutral conductor via capacitors or intermediate circuit capacitors.

[0020] The AC / DC converter can operate in single-phase or polyphase mode. In single-phase operation, a particularly large voltage ripple is generated in the intermediate circuit, essentially encompassing the entire half-wavelength of the AC voltage applied to the input side. This voltage ripple is applied by the capacitors to the neutral conductor, thereby charging them.

[0021] A known proposition in itself for reducing capacitor charge consists of applying to the intermediate nodes a compensating current, which is opposite in phase to the current ripple.

[0022] To obtain the appropriate output voltage (battery voltage) and output current (battery current), particularly for operation under load, a DC / DC converter is usually provided, which brings the intermediate circuit voltage to the required output voltage level (battery voltage) and which serves to provide the required output current (battery current).

[0023] The transformer circuit above proposes to provide for this purpose a two-part DC / DC converter system having two separate DC / DC converters, in which each of the two DC / DC converters operates or is adjusted separately. The DC / DC converters are operated by a suitable control unit so that the Two DC / DC converters provide the necessary output voltage. For this purpose, the DC / DC converters are connected in parallel on the output side. Each DC / DC converter thus provides a proportion of the output current as a partial output current. However, on the input side, the DC / DC converters can be connected in series or parallel. Preferably, the transformer circuit comprises a DC / DC converter system having at least two DC-DC converters, which are connected on the input side to the intermediate circuit and which can be switched with respect to the intermediate circuit voltage between a parallel and a series configuration, and which are connected to each other by an intermediate node.This preferably means that the DC / DC converters can be connected in series or in parallel.

[0024] The DC / DC converters are controlled by the common control unit so that the DC / DC converters can have different current draws as partial input currents at the same output voltages. It follows that a different current difference of OA is obtained at the intermediate node for unequal partial input currents. The intermediate node is connected to the neutral conductor. Preferably, a difference current is generated from the current difference, which is injected into the intermediate node.

[0025] By appropriately regulating the various DC / DC converters, the differential current at the intermediate node can be adjusted so that the differential current is in opposite phase to the capacitor currents. The differential current thus acts as a compensating current, which is injected into the intermediate node and thereby reduces or compensates for the capacitor currents. This reduces the capacitor charge.

[0026] It is thus obtained that, without a separate compensation circuit, only by using two DC / DC converters which are mounted in series on the input side, a compensation current can be produced, which reduces the charge of the capacitors.

[0027] A switching device may also be provided to switch the assembly on the input side of the DC / DC converter between a series assembly and a parallel assembly.

[0028] It is thus possible, using the switching circuit, to switch the DC / DC converters from a series configuration to a parallel configuration, provided that the voltage ripple in the intermediate circuit or the capacitor currents are sufficiently small. This is the case, for example, during three-phase or, more generally, polyphase operation of the current converter. alternating current / direct current. It is therefore possible to perform a switching operation on a parallel circuit on the input side of the direct current / direct current converters, if a polyphase operation is observed or depending on the level of currents determined in the capacitors.

[0029] Overall, the above transformer circuit allows for a fairly compact transformer circuit structure, which does not require additional components to minimize or compensate for the currents flowing through the capacitors. This results in a lower load on the intermediate capacitors and on the voltage load of the semiconductor switch of the AC / DC converter.

[0030] It may also be provided respectively a voltage sensor to determine respectively a proportion of DC voltage of the respective voltages at the intermediate circuit capacitances and to determine, as a function of their difference, a potential offset of the midpoint, the control unit being constituted to regulate the partial input currents so as to minimize the determined potential offset.

[0031] In reverse operation, or preferably in source operation, of the transformer circuit, an asymmetrical load on the intermediate circuit capacitors may occur. In this case, the series-connected DC / DC converters can be adjusted to minimize the currents flowing through the capacitors and thus stabilize the voltage at the intermediate node at the midpoint of the intermediate circuit voltage. This minimizes an asymmetrical load on the intermediate circuit capacitors, particularly for an asymmetrical load in a V2L or V2G (vehicle-to-load, vehicle-to-grid) function.

[0032] Preferably a voltage sensor is provided in order to measure the proportion of direct current in the voltage of the capacitors and to detect a shift in the midpoint, preferably by an asymmetric load on one phase.

[0033] In a still preferred manner, the control unit is used, by regulating the various DC / DC converters by means of the resulting difference current in the intermediate circuit node, to regulate the DC voltage of the intermediate circuit capacitors, in particular with a view to maintaining the intermediate node in the middle of the intermediate circuit voltage.

[0034] In a suitable manner, the control unit is preferably constituted to regulate, both in forward and reverse operation, the transformer circuit, the DC / DC converters mounted in series, so as to minimize a load on the capacitors.

[0035] According to another aspect, the invention relates to a method for operating a transformer circuit according to one of the points 1 to 6, in which are operated DC / DC converters on the input side in a series arrangement so that they give a partial input current and it follows at the intermediate node a difference current of a difference between the partial input currents, which at least partially compensates for the capacitor currents between the intermediate circuit capacitors and the intermediate node.

[0036] Brief description of the drawings

[0037] Further embodiments are explained below with reference to the accompanying drawings, in which:

[0038] Fig. 1 is a schematic representation of a transformer circuit according to one embodiment of the invention;

[0039] Figure 2 is another embodiment of the transformer circuit having a switchable configuration of DC / DC converters;

[0040] Figure 3 is another embodiment of the transformer circuit having an additional DC / AC converter for V2L operation;

[0041] Description of embodiments

[0042] Figure 1 is a schematic representation of a transformer circuit 1 for use, for example, as an on-board charging device for a vehicle. The transformer circuit 1 rectifies a single-phase or polyphase alternating voltage from an AC power supply network Uvers and provides an output voltage Ubat and an output current Ibat for charging or discharging a vehicle battery L.

[0043] The transformer circuit 1 includes an AC / DC converter 2, which may be constructed, for example, as a PFC, for example of the Vienna type or TNPC type. The AC / DC converter 2 may operate in single-phase or polyphase (in particular in three-phase) and provides an intermediate circuit voltage Uz at the potentials Vzh, Vzi of an intermediate circuit of the transformer circuit 1.

[0044] The intermediate circuit voltage Uz is applied between the intermediate circuit potentials Vzh, Vzi. The intermediate circuit potentials Vzh, Vzi are applied to a neutral conductor 4 via intermediate circuit capacitances 51, 52 (capacitors).

[0045] When the AC / DC converter operates, a voltage ripple is generated at the intermediate circuit potentials Vzh, Vzi, which takes on different values ​​depending on the operating state. Preferably during single-phase operation, the voltage ripple is particularly large. The voltage ripple is controlled by the circuit capacitors 51, 52 Intermediate current injected into the neutral conductor 4 in the form of partial ripple currents IR1, IR2. The partial ripple currents Irb Ir2 cause a large charge on the intermediate circuit capacitors 51, 52.

[0046] The intermediate circuit and its intermediate circuit potentials Vzh, Vzi are further electrically connected to a two-converter assembly 61, 62 of a DC / DC converter system 6. The inputs of the two DC / DC converters 61, 62 are connected in series with the intermediate circuit and in parallel on the output side to provide a common output voltage Ubat. The series connection on the input side of the DC / DC converters 61, 62 results in a current flow through both DC / DC converters 61, 62, thus providing the output current Ibat on the side of the DC / DC converter assembly 61, 62.

[0047] In a series connection on the input side, one connection terminal of the DC / DC converters 61, 62 is connected on the input side to one of the intermediate circuit potentials Vzh, Vzi, while the other connection terminals on the input side are connected together to a common connection terminal, the intermediate node Z. The intermediate node Z is connected to the neutral conductor 4. During proper operation of the DC / DC converters 61, 62, a compensating current ICOmP can be injected into the intermediate node via the intermediate node Z.

[0048] The DC / DC converters 61, 62 can perform current and voltage transformation. For example, an input power of 10 kW (400 V, 25 A) can be transformed into an output power of 10 kW (800 V, 12.5 A). The input and output currents of the DC / DC converters 61, 62 can therefore be different.

[0049] A control unit 10 is provided for this purpose, which controls the operation of the DC / DC converters 61, 62. Voltage and current regulation are carried out separately for each of the DC / DC converters 61, 62, such that an identical required output voltage Ubat is made available on the output side of both DC / DC converters 61, 62.

[0050] The output current Ibat and a setpoint compensation current LomP_soii are set, a difference current Icomp corresponding to the sum of the partial input currents Idcb Idc2 given by the two DC / DC converters 61,62.

[0051] The currents are adjusted so that the difference in partial input currents results in the instantaneous value of the setpoint compensation current Icomp_son and so that the sum of the output currents corresponds to the output current Ibat.

[0052] By separately controlling the two DC / DC converters 61, 62 and thus obtaining a determined partial input current Idci, Idc2, a differential current Icomp can be set, which is preferably injected as a compensation current into the intermediate node. This differential current Icomp serves to minimize the capacitor currents flowing through capacitors 51, 52.

[0053] For determining the setpoint compensation current Icomp_sou, a measurement can preferably be taken in the neutral conductor 4 or in the phase currents, or the injected ripple current IR can be determined using the intermediate circuit voltage. The ripple current preferably refers to capacitor currents between the intermediate circuit capacitors 51, 52 and the neutral conductor 4. The capacitor currents between the intermediate circuit capacitors 51, 52 and the neutral conductor 4 are determined in particular as a function of specific phase currents of the AC voltage from the AC power supply network, as a function of specific capacitor currents flowing through the intermediate circuit capacitors 51, 52, as a function of a specific intermediate circuit voltage Uz, or as a function of a specific voltage across at least one of the intermediate circuit capacitors 51, 52.

[0054] In the embodiment of [Fig. 2], a switching device 11 is provided, which can switch between a series connection on the input side of the DC / DC converters 61, 62, as shown in the embodiment of [Fig. 1], and a parallel connection of the DC / DC converters 62, 62. This is carried out under the control of the control unit 10. In the parallel connection, there is no injection into the intermediate node, since there is no independent connection of the intermediate node to the DC / DC converters.

[0055] Connecting the input side of the DC / DC converters 61, 62 in parallel with the DC / DC converter system 6 results in greater converter circuit efficiency and can therefore be used when the ripple IR current is small, i.e., below a predetermined ripple current threshold value, or if the capacitor currents between the intermediate circuit capacitors 51, 52 do not exceed a predetermined capacitor control threshold value. Switching to series connection with injection of the compensation current can be performed accordingly. Using the number of phases in the AC power supply, i.e., if the AC power supply is single-phase, we can assume that a larger ripple current will occur and must be compensated by injecting the compensation current. If the AC / DC converter's power supply is polyphase, the ripple current (IR) is smaller, and normal operation with the DC / DC converters in parallel is possible. Alternatively, switching can also be performed based on a measured ripple current between the capacitors, thus switching in series. This occurs as soon as the ripple current exceeds a predetermined ripple current threshold value.

[0056] In [Fig. 3], based on the embodiment of [Fig. 1], energy is extracted from the intermediate circuit by a suitable DC / AC converter 9. This enables the battery energy to be used in V2L (Vehicle-to-Load) operation. The control unit 10 can further be configured to cause, during asymmetric operation of the AC / DC converter 2, energy extraction by the DC / AC converter 9 and a resulting voltage shift from the potential to the neutral conductor 4, which is established by a compensating current Icomp corresponding to a predetermined reference voltage. This can be achieved by a corresponding load input or discharge using the compensating current Icomp.In this case as well, the difference current between the currents Idci, Idc2 can be adjusted by the two DC / DC converters 61, 62 to produce compensating loads.

[0057] Voltage regulation to the reference voltage given in advance on the neutral conductor 4 can be carried out in particular on the basis of a measurement of an actual voltage of the neutral conductor using a voltage sensor or similar.

[0058] .

Claims

1. Demands Circuit (1) transformer, in particular for an on-board vehicle battery charging device, for obtaining a controlled output voltage (Ubat) and current (Ibat) from a single-phase or polyphase alternating voltage from an alternating voltage supply network comprising: - on the input side, an AC / DC converter to have an intermediate circuit voltage (Uz) in an intermediate circuit, whose intermediate circuit potentials (Vhz, Vsi) are applied to a neutral conductor (4) respectively by an intermediate circuit capacitor (51, 51); - on the output side, a DC / DC converter system (6) comprising at least two DC-DC converters (61, 62), which are connected on the input side to the intermediate circuit and which, with respect to the intermediate circuit voltage (Uz), are connected in series or may be connected in series, wherein the two DC-DC converters (61, 62) are connected together on the input side in a series arrangement via an intermediate node (Z), wherein the DC-DC converters (61, 62) are connected in parallel on the output side to give respectively the output voltage (Ubat) and the output current (Ubat) as the sum of the partial output current of each of the DC / DC converters (61, 62); - in which the intermediate node (Z) is connected or electrically linked to the neutral conductor (4); - a control unit (10) which is constituted to operate the DC / DC converters (61, 62) in a series circuit on the input side so as to pass through them respectively a partial input current (Idci, lidci), so that at the intermediate node (Z) there follows a difference current (Icomp) of a difference between the partial input currents (Idci, Iidc2), which compensates at least in part for the capacitor currents between the intermediate circuit capacitances (51, 52) and the intermediate node (Z).

2. Transformer circuit (1) according to claim 1, wherein the capacitor currents between the intermediate circuit capacitors (51, 52) and the intermediate node (Z) are determined, in particular as a function of determined phase currents of the AC supply voltage, as a function of capacitor current determined by the intermediate circuit capacitors (51, 52) as a function of a determined intermediate circuit voltage (Uz) or as a function of a determined voltage at at least one of the intermediate circuit capacitors (51, 52), in order to determine a setpoint compensation current (icomp_son) as a phase current inverse to the capacitor currents between the intermediate circuit capacitors (51, 52) and the intermediate node (Z), in which the control unit (10) is constituted to regulate the partial input currents (Idci, IdC2) so that the resulting difference current corresponds to the determined opposite phase current.

3. Transformer circuit (1) according to claim 1 or 2, wherein a voltage sensor is respectively provided to determine a proportion of DC voltage of the respective voltages at the intermediate circuit capacitors (51, 52) and to determine, as a function of their difference, a midpoint potential offset, wherein the control unit (10) is constituted to regulate the partial input currents (Idci, Idc2) so as to minimize the determined potential offset.

4. Transformer circuit (1) according to any one of claims 1 to 3, wherein a switching device (11) is provided for switching the assembly on the input side of the DC / DC converters between a series and a parallel assembly. [Claim 5) Transformer circuit (1) according to claim 4, wherein the control unit (10) is constituted to control the switching device (11) so as to establish a series arrangement, if single-phase operation of the AC / DC converter is observed, and to establish a parallel arrangement, if polyphase operation of the AC / DC converter is observed.

6. Transformer circuit (1) according to claim 4 or 5, wherein the control unit (10) controls the switching device (11) to establish a series connection if the capacitor currents between the intermediate circuit capacitors (51, 52) and the intermediate node (Z) exceed a capacitor current threshold value given in advance and to establish a parallel circuit, if the capacitor currents between the intermediate circuit capacitances (51, 52) and the intermediate node (Z) fall below a compensator current threshold value given in advance.

7. A method for operating a transformer circuit (1) according to any one of claims 1 to 6, wherein input-side DC / DC converters (61, 62) are operated in a series arrangement such that they respectively give a partial input current (Idci, Idc2) and a resulting difference current (Icomp) of a difference between the partial input currents (Idci, Idc2) at the intermediate node (Z) which at least partially compensates the capacitor currents between the intermediate circuit capacitances (51, 52) and the intermediate node (Z).

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