Integrated multi-phase battery tap

Abstract

Circuit arrangement for a motor vehicle, with • a battery string (BS) for providing energy, which has a series connection of individual battery cells (z1 to 26) between two terminals, • a multi-phase conductor device with at least two lines (11, 12, 13), each line (11, 12, 13) being assigned to a separate electrical phase (u1, u2, u3), • a number of coupling devices (k1 to k6) correlated with the number of battery cells (z1 to 26), each of which is designed to couple or disconnect a node (p1 to p6) between two of the battery cells (z1 to 26) to one of the lines (11, 12, 13), and • a control device which is designed to control the coupling devices (k1 to k6) in such a way that an alternating current is formed in each of the lines (11, 12, 13), wherein a predetermined phase difference exists between each two of the alternating currents, wherein the multi-phase conductor device comprises three lines (11, 12, 13), and the circuit arrangement is designed to generate a three-phase alternating current characterized in that wherein each coupling device (k0' to k6') has only a single switching element (s) which, along the battery string (BS), alternately connects the respective node point (p1 to p6) to a first of the three lines (11, 12, 13), a different second of the three lines or a different third of the three lines in the closed state.

Description

The present invention relates to a circuit arrangement for a motor vehicle for obtaining polyphase current from a battery. The present invention furthermore relates to a method for operating such a circuit arrangement.Motor vehicles, in particular electric vehicles or hybrid vehicles, have a battery which can comprise a series circuit of many individual battery cells, that is to say a battery string. For example, each battery cell has a voltage of 3.5 V and approximately 100 battery cells are combined to form the battery string.The voltage provided by the series circuit is not equally suitable for all consumers. Therefore, a voltage converter can be interposed between the battery and the load in order to adapt the voltage to the respective load. In the broadest sense, this voltage converter can also comprise an inverter.From the document U.S. Pat. No. 5,986,909 A, a polyphase voltage supply with a multiplicity of cells per phase is known. Failed cells in one phase are bypassed to provide a current path in the respective phase. All non-failed cells are used for generating the respective output voltage. The cells are switching cells.Furthermore, a voltage converter is known from the publication US 2011 / 0044082 A1. This voltage converter also has switching cells and converts the direct voltage provided into an alternating voltage.Furthermore, the document US 2012 / 0091963 A1 discloses a bypass circuit for a battery system which disconnects parallel-connected cells or modules from a battery circuit. The disconnection occurs when a cell has failed or is likely to fail. The circuit can also be used for current control.From the generic DE 10 2011 006 762 A1, a battery direct converter in ring configuration is known in order to obtain a polyphase alternating current or a polyphase alternating voltage from a battery string.The object of the present invention is to provide a polyphase voltage with improved voltage utilization of a battery.According to the invention, this object is achieved by a circuit arrangement according to claim 1. Furthermore, according to the invention, a method according to claim 6 is provided.A circuit arrangement according to the invention for a motor vehicle has a battery string for providing energy, which has a series circuit of individual battery cells between two connections, a polyphase conductor device having at least two lines, each line being assigned to a separate electrical phase in each case, a number of coupling devices correlated with the number of battery cells, each of which is designed to couple or separate a junction point between two of the battery cells to one of the lines, and a control device which is designed to actuate the coupling devices in such a way that an alternating current is formed in each of the lines, an alternating current existing between in each case two of the alternating currents.Advantageously, a polyphase alternating current or a polyphase alternating voltage is therefore obtained from a battery string which has a series circuit of individual battery cells. Coupling devices are used to control taps on the battery string in such a way that the respective alternating voltages with the associated phase difference are present on the lines of the system.The polyphase conductor device has three lines and the circuit arrangement is designed to generate a three-phase alternating current. A three-phase alternating current is typically used for drive motors of electric or hybrid vehicles.According to the invention, each coupling device has only a single switching element which alternately connects the respective node point along the battery string to a first of the three lines, a second of the three lines different therefrom or a third of the three lines different therefrom in the closed state. The junction point between two battery cells is thus connected to a single one of the three lines only via the respective coupling device. This significantly reduces the circuit complexity in comparison with a variant where each coupling device has three switching elements.A single coupling device may be arranged between each pair of adjacent battery cells of the battery string. It is thus possible to use practically each individual battery cell individually for voltage formation.Specifically, each of the switching elements may include an IGBT, a combination of two MOSFETs, or a bipolar transistor. Such switching elements can be reliably used as power switches.It is particularly advantageous that the control device can be designed to select and control a pair of the coupling devices at a predefined point in time such that a voltage is established between two of the lines depending on the point in time. The control device is thus able to set a voltage between two of the lines. This means that the voltages in the lines are adjusted relative to each other. It is therefore less relevant at what absolute level the voltages in the lines are situated, for example, with respect to a motor vehicle ground. Rather, as in typical three-phase systems, it is important to establish the respective voltages between the phases or lines at any point in time. Thus, among other things, a neutral conductor for a reference potential can be dispensed with.In particular, the control device can be designed to provide current and / or historical state data and to use these for selecting the pair of coupling devices. In this way, it is possible to use battery cells or groups of battery cells that are different from one another to form a predefined or predefinable voltage. Thus, for example, if thirty battery cells need to be used to form a predetermined voltage, then these thirty battery cells may be used from the beginning of the battery string, which includes, e.g., a hundred battery cells, from the end of the battery string, or from the center of the battery string. If, for example, the battery cells have already aged from the beginning of the battery string or have been or have been more heavily loaded, then battery cells from another point of the battery string, for example from the end or from the center, should be used better to form the respectively desired voltage.According to the invention, a method for operating a circuit arrangement as described above is furthermore provided. This method includes the steps of presetting the phase difference and driving the coupling devices so that an alternating current is formed in each of the lines, wherein the preset phase difference exists between every two of the alternating currents. A polyphase system is thus formed by the specific actuation of the coupling devices by the voltages of the battery cells, the phase differences being formed via the temporal actuation of the coupling devices.The method according to the invention can also be further developed with the features mentioned in connection with the circuit arrangement. In particular, at a predeterminable point in time, a pair of the coupling devices can be selected and controlled in such a way that a voltage is established between two of the lines, which voltage is dependent on the point in time. As explained above in connection with the circuit arrangement, the battery cells are thus coupled to the respective lines in such a way that the desired voltage is established at the respective point in time. A relative voltage is thus generated between the lines with the aid of the battery cells. The selection of the pair of coupling devices or the selection of the battery cells to be used can be effected again using current and / or historical state data.The present invention will now be explained in more detail with reference to the accompanying drawings, in which: FIG. 1 shows a circuit diagram of a circuit arrangement according to the invention in a first switching state; FIG. 2 shows the idealised voltage curve of a three-phase system; FIG. 3 shows a circuit diagram of the circuit arrangement of FIG. 1 in a second switching state; and FIG. 4 is a circuit diagram of an alternative circuit arrangement according to the present invention.The exemplary embodiments described in more detail below represent preferred embodiments of the present invention.FIG. 1 shows a battery string BS, as it is installed, for example, in a motor vehicle for driving it. The battery string BS comprises a plurality of battery cells z 1 to 26, which are connected in series one behind the other. Typically, in an electric vehicle or hybrid vehicle, approximately one hundred such battery cells are connected in series, wherein each battery cell supplies a voltage of 3.5 V, for example. The battery cell z 1 illustrated in FIG. 1 does not have to be the first battery cell at the beginning of the battery string BS. Rather, it can be located at any point within the strand.Between each two adjacent battery cells there is a junction point p 1 to p 6. Node p 1 is thus located between battery cells z 1 and z 2, node p 2 is located between battery cells z 2 and z 3, etc. Node p 6 is located between battery cell 26 and a further battery cell that is connected thereto and is no longer drawn in FIG. 1. As a rule, the number of coupling devices will be correlated with the number of battery cells in such a way that the number of coupling devices is greater by one than the number of battery cells.Furthermore, three lines 11, 12 and 13 of a polyphase conductor device are drawn in in FIG. 1, in which the respective phases of a three-phase system are routed. In general, this is a polyphase system, so that a corresponding number of lines must be provided. Thus, alternatively, it can be a two-phase system, four-phase system, etc.A coupling device k1 is connected to the node p1, which connects the node p1 to the three lines 11, 12 and 13. The coupling device k 1 here comprises three switching elements s, via which the connection between the node p 1 and the respective line 11, 12 and 13 can be realized. In the first switching state, which is illustrated in FIG. 1, the two switching elements s, which connect the node p 1 to the lines 12 and 13, are open. The further switching element, which connects the node p 1 to the line 11, is closed. This means that the line 11 is at the potential of the node p 1 between the battery cells z 1 and z 2.The switching elements s of the coupling devices k 2 and k 3 are open. Consequently, nodes p2 and p3 are not connected to either of lines 11, 12 and 13. In contrast, one of the switching elements s of the coupling device k 4 is closed, so that the node p 4 is connected to the line 12. The two other switching elements s of the coupling device k 4 are open. Consequently, the line 12 is at the potential of the node p 4 between the battery cells z 4 and z 5.The switching elements s of the coupling device k 5 are open. In the coupling device k 6, on the other hand, that switching element s which connects the node p 6 to the line 13 is closed. The two other shift elements are open. The line 13 is thus at the potential of the node p6.Overall, this means that the voltage between the lines 11 and 12 is determined by the three battery cells z 2, z 3 and z 4; if one battery cell supplies the voltage U, for example, the voltage 3U exists between the lines 11 and 12. Accordingly, a voltage 2U would be produced between the lines 12 and 13, which voltage would be produced by the two battery cells z 5 and z 6.FIG. 2 shows the voltage profile of a three-phase system in an idealized manner. The voltages in each phase have exactly sinusoidal curves. However, when the voltages are generated by the circuit arrangement of FIG. 1 in reality, they are step-shaped. The granularity of the stages is refined as the number of battery cells increases. The smallest voltage level corresponds to the voltage of a single cell.The switching elements s of the coupling devices k 1 to k 6, etc., are preferably formed by IGBTs or combinations of two MOSFETs or, if appropriate, also by suitable bipolar transistors. Other switching elements may also be suitable for this purpose. The shift elements s are controlled, i.e. opened or closed, by a control device not shown for the sake of clarity.If a three-phase sinusoidal alternating voltage according to FIG. 2 is now to be generated with the circuit arrangement of FIG. 1, the respectively valid voltage differences between the phases or lines 11, 12 and 13 must be produced at any point in time. At a time a, the relative voltages between the individual phases u1, u2and u3are shown roughly in FIG. 2. Accordingly, at time a, a voltage of approximately 3U results between the first phase u 1 and the second phase u 2, and a voltage of 2U results between the second phase u 2 and the third phase u 3. In order to set these voltage differences between the individual phases at the time a, the circuit arrangement of FIG. 1 would have to assume the first switching state indicated there. It is immaterial which battery cells ensure exactly the respective voltage difference. The absolute voltages in the three lines 11, 12 and 13 are in fact unimportant. The same voltage differences, which are achieved here with short-circuiting of the lines 11, 12 and 13 to the nodes p 1, p 4 and p 6, can also be achieved, for example, by short-circuiting at nodes p 4, p 7 and p 9 or nodes p 11, p 14 and p 16, which result when the battery string BS of FIG. 1 is continued.At a time b, the phases (short for phase voltages) u2and u3in FIG. 2 are the same. There is therefore no voltage difference between the two phases, which is why at this time the control device should control the coupling devices in such a way that the two lines 12 and 13 are present at the same node, e.g. p 1 (cf. FIG. 3 ). For this purpose, the coupling device k 1 couples the junction point p 1 to the two lines 12 and 13 in the second switching position illustrated in FIG. 3.The voltage difference between one of the phases u2and u3and the phase u1at the time b is ideally 4.5 U. Since only integer voltage values having a multiple of U can be achieved with the circuit arrangement of FIG. 3, which corresponds to that of FIG. 1, the value 4.5U must be approximated by 4U or 5U. In the example of FIG. 3, the value 5U was selected, for which reason the line 11 of the phase u1 is short-circuited to the node p6 by means of the coupling device k6. The two other switching elements of the coupling device k 6 are open. Consequently, lines 12 and 13 are at the potential of node p1 and line 11 is at the potential of node p6. The difference between the nodes p 1 and p 6 is 5U here, i.e. the voltage which is generated here by five battery cells z 2 to z 6. Here too, only the relative voltages are important, which means that the same result is obtained even if, for example, the lines 12 and 13 were connected to a node p21 and the line 11 were connected to a node p26.The present invention is thus based on the idea that in a polyphase system it is irrelevant on which potential the various terminals are located as long as the voltage between them always has the desired amplitude and polarity. If, for example, in a combination of ten cells each having 3.5 V, a voltage of 3 x 3.5 V=10.5 V can be measured between the first tap and the second tap at a first tap between the first and the second battery cell and at a second tap between the fourth and the fifth battery cell. If the taps are interchanged so that the second tap is between the first and second cells and the first tap is between the fourth and fifth cells, the voltage between the second and first taps is negative and is at -10.5 V. It is therefore not necessary to define a fixed zero point and use this as a reference for a genuine negative voltage. Thus, in simple serial cell groups, a system with true polyphase voltage can be constructed by suitable selection of the taps.If-as in the example of FIG. 2-the polarity of all three phase voltages is to be changed between the times a and b, this can be achieved in the circuit arrangement by merely changing the position of the taps relative to one another. No circuit for establishing the polarity change is required.A further advantage is that in such a circuit the maximum voltage between two phases / contact poles is exactly equal to the maximum available battery voltage, formed from the cell voltage multiplied by the cell number:In contrast, in a three-phase interconnection based on SCT (single cell topology) according to US 2012 / 0091963 A1, the maximum voltage between two phases / contact poles would be only slightly more than half the sum of all installed cells, since the cells are distributed dedicated to three phases and only one of the phases is always at the maximum. With the concept according to the invention, a better voltage utilization can thus be achieved compared to the prior art.An improvement in circuit complexity results from a structure of the circuit arrangement according to FIG. 4. the battery string BS is constructed with its battery cells z 1 to z 6 etc. and the nodes p 1 to p 6 etc. lying therebetween in the same way as that in the examples of FIGS. 1 and 3. Only the coupling devices k0' to k6' are of different construction and each have only a single switching element s. Thus, there are no more taps arranged between the cells z1 to z6 etc. for each phase, but rather only a single tap each, which is connected fixedly but with alternating sequence to the different phases or lines 11 to 13.Such an arrangement reduces the number of switches to a reduced level without limiting the basic functionality. Only the granularity at which the voltages can be adjusted is somewhat degraded.Both systems proposed above are capable of more or less loading individual cells by suitable control and thus taking into account inhomogeneous capacity distributions or aging of the individual cells. For this purpose, the respective cell is activated less often than other cells during partial load operation (i.e. if the full number of cells is not required). For this purpose, the control device or, if appropriate, another unit monitors current and / or historical state data of the battery cells, such as, for example, the state of charge, cell voltage or temperature of the respective battery cell. In this way, a higher operational reliability is achieved. The availability of the energy store can thus be increased by redundant design.List of reference charactersBS battery string a time b time k1 to k6 coupling devices k0' to k6' coupling devices 11, 12, 13 lines p1 to p6 nodes s switching elements U voltage u1, u2, u3 phases z1 to 26 battery cells

Claims

Circuit arrangement for a motor vehicle, having • a battery string (BS) for providing energy, which battery string has a series circuit of individual battery cells (z1 to 26) between two connections, • a polyphase conductor device having at least two lines (11, 12, 13), each line (11, 12, 13) being assigned in each case to a separate electrical phase (u1, u2, u3), • a number of coupling devices (k1 to k6), which is correlated with the number of battery cells (z1 to 26) and each of which is designed to couple or separate a junction point (p1 to p6) between two of the battery cells (z1 to 26) with one of the lines (11, 12, 13), and • a control device which is designed to actuate the coupling devices (k1 to k6) in such a way that an alternating current is formed in each of the lines (11, 12, 13), wherein a predetermined phase difference exists between each two of the alternating currents, wherein the polyphase conductor device has three lines (11, 12, 13), and the circuit arrangement is designed to generate a three-phase alternating current, characterized in that each coupling device (k0' to k6') has only one single switching element (s) which alternately connects the respective node (p1 to p6) along the battery string (BS) to a first of the three lines (11, 12, 13), a second of the three lines different therefrom or a third of the three lines different therefrom in the closed state.Circuit arrangement according to Claim 1, wherein a single coupling device (k1 to k6) is arranged between each pair of adjacent battery cells (z1 to 26) of the battery string (BS).Circuit arrangement according to Claim 1 or 2, wherein each of the switching elements (s) has an IGBT, a combination of two MOSFETs or a bipolar transistor.Circuit arrangement according to one of the preceding claims, wherein the control device is designed to select and control a pair of the coupling devices (k1 to k6) at a predeterminable point in time (a, b) in such a way that a voltage (u1, u2, u3) dependent on the point in time (a, b) is established between two of the lines (11, 12, 13).Circuit arrangement according to Claim 4, wherein the control device is designed to provide current and / or historical state data and to use these for selecting the pair of coupling devices (k1 to k6).Method for operating a circuit arrangement according to one of the preceding claims, having the steps: • assigning the phase difference and • driving the coupling devices (k1 to k6) in such a way that an alternating current is formed in each of the lines (11, 12, 13), wherein the predefined phase difference exists between in each case two of the alternating currents.Method according to Claim 6, wherein, at a predeterminable point in time (a, b), a pair of the coupling devices (k1 to k6) is selected and controlled in such a way that a voltage (u1, u2, u3) dependent on the point in time (a, b) is established between two of the lines (11, 12, 13).

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