Electrical system

Abstract

The invention relates to an electrical system (1) comprising a high-voltage battery (2) consisting of at least n battery cells (BZ1-BZn) connected in series, at least one circuit for cell balancing of the n battery cells (BZ1-BZn), and at least one DC / DC converter (4), wherein a low-voltage electrical system (5) is connected to the DC / DC converter (4), wherein the at least one circuit for cell balancing consists of n or n / 2 resonant converters (3), wherein the resonant converters (3) are arranged with their primary side in parallel to one or two battery cells (BZ1-BZn) each, and the resonant converters (3) are connected in parallel on the output side of the secondary side, wherein the parallel-connected outputs on the secondary side of the resonant converters (3) are connected to the DC / DC converter (4), wherein a control unit (11) of the resonant converters (3) is configured such that the resonant converters (3) operate at a fixed frequency and a fixed sampling ratio. to head for,wherein the resonant transducers (3) are magnetically decoupled.

Description

[0001] The invention relates to an electrical system comprising a high-voltage battery consisting of at least n battery cells connected in series, at least one circuit for cell balancing of the n battery cells and at least one DC / DC converter, wherein a low-voltage electrical system is connected to the DC / DC converter.

[0002] Such a system is found, for example, in electric vehicles. Cell balancing occurs during the charging of the high-voltage battery. Various circuits are known for this purpose. For instance, fully charged battery cells are bridged by a transistor connected in series with a resistor, allowing the charging process to continue for the less-charged cells. Inductive balancing circuits are also known, where energy is inductively transferred from the battery cells and then fed back into the system. In these circuits, all inductive transmitters are magnetically coupled. One such balancing circuit is disclosed, for example, in US Patent 20220045628 A1.

[0003] The invention is based on the technical problem of creating an electrical system with improved cell balancing.

[0004] The solution to the technical problem is achieved by means of an electrical system with the features of claim 1. Further advantageous embodiments of the invention are set forth in the dependent claims.

[0005] The electrical system comprises a high-voltage battery consisting of at least n battery cells connected in series. Additional battery cells can be connected in parallel to the series-connected cells. Furthermore, the electrical system includes at least one circuit for cell balancing of the n battery cells and at least one DC / DC converter, to which a low-voltage electrical system is connected. The at least one cell balancing circuit consists of n or n / 2 resonant converters, with the primary side of each resonant converter arranged in parallel to one or two battery cells, respectively, and the outputs of the resonant converters connected in parallel on the secondary side. In the embodiment where one resonant converter is connected in parallel to two battery cells, n is an even number. The parallel outputs on the secondary side of the resonant converters are connected to the DC / DC converter.The resonant converters are controlled by a system designed to drive them at a fixed frequency and sampling ratio, with the converters being magnetically decoupled. Because the converters are driven at a fixed frequency, the resonant frequency, and the sampling ratio is constant (e.g., the PWM signal is always 0.5), the control is very simple, and the converters can operate at very high frequencies. Another advantage is that current flows even without a load when the converters are at resonance. The output voltage at the parallel connection of the outputs is determined by the battery cell with the lowest voltage, while the resonant converters of the battery cells with the higher voltage feed current into the DC / DC converter, thus reducing their state of charge. This results in cell balancing.This cell balancing can occur not only while the battery cells are charging, but also continuously during operation, as long as the DC / DC converter is switched on and can transfer energy to the low-voltage electrical system. The voltage at the output of the resonant converter depends on the turns ratio of the primary windings to the secondary windings.

[0006] In one embodiment, the inverter on the secondary side of the resonant converters is designed as a passive inverter, meaning it only has passive elements such as diodes, capacitors, and inductors, but no transistors. This further simplifies the control, although in this case the resonant converters only operate unidirectionally.

[0007] In another embodiment, the winding ratio of primary windings to secondary windings is 1:8 or 1:16, with the DC / DC converter configured as a buck converter. Assuming a battery cell voltage of 3 V, the output voltage of the resonant converter is then 48 V or 24 V, which can then be reduced to 12 V by the buck converter.

[0008] However, a different winding ratio can also be chosen (e.g. 1 to 1), in which case the DC / DC converter would be operated as a boost converter to provide the 12 V at the output of the DC / DC converter.

[0009] In another embodiment, the control of the resonant transducers is located on the low-voltage side and incorporates an inductive transformer. In this case, the inductive transmission is less critical because the frequency and sampling ratio are constant.

[0010] In another embodiment, in which a resonant converter is connected in parallel to two battery cells, an additional inductance is arranged between the center tap of the battery cells and a center tap of the resonant converter, through which compensating currents can flow.

[0011] In another embodiment, the control system of the DC / DC converter is designed to switch on the DC / DC converter during one of the charging processes for the battery cells. This allows cell balancing to be performed even while the battery cells are being charged.

[0012] In another embodiment, the diodes of the passive inverter on the secondary side are designed as Schottky diodes, which have a lower forward voltage.

[0013] In a further embodiment, a sampling voltage measuring device is arranged on at least one capacitor of the inverter on the secondary side, wherein an evaluation unit of the voltage measuring device is designed to determine a current, more precisely an average current, from the resonant converter on the basis of the voltage signals.

[0014] In another embodiment, a further high-voltage component is arranged on the battery cells, wherein the high-voltage component has means for detecting or determining an input current. This allows the total current from the high-voltage battery to be determined very simply as the sum of the currents from the resonant converters and the high-voltage component, thus eliminating the need for a separate current sensor (e.g., a shunt resistor) in the battery unit.

[0015] In another embodiment, the additional high-voltage component is designed as a boost converter, which is then connected, for example, to an inverter, in particular a pulse inverter, which controls an electric machine.

[0016] The electrical system is preferably part of a traction network of an electric vehicle.

[0017] The invention is explained in more detail below with reference to preferred embodiments. The figures show: Fig. 1 a schematic circuit arrangement of an electrical system in a first embodiment, Fig. 2 a schematic circuit arrangement of an electrical system in an alternative embodiment and Fig. 3 an exemplary voltage curve across a capacitor of an inverter of a resonant converter.

[0018] In the Fig. Figure 1 shows an electrical system 1 comprising a high-voltage battery 2 consisting of n battery cells BZ1-BZn connected in series. n is, for example, greater than 40. The electrical system 1 also includes n resonant converters 3. Each resonant converter 3 is connected to a battery cell BZ1-BZn at its input and is connected in parallel at its output to a DC / DC converter 4. A low-voltage electrical system 5 with a low-voltage battery 6 is connected to the DC / DC converter 4. A voltage measuring device 7, which detects the voltage of the high-voltage battery 2, is also shown. The high-voltage battery 2 is further connected to another DC / DC converter 8, which is configured as a boost converter and is connected to an inverter for an electric motor. The resonant converters 3 are magnetically decoupled, meaning they are designed to largely avoid mutual interference.The resonant converters 3 each have an inverter 9 on the primary side and an inverter 10 on the secondary side, which are inductively coupled. The inverter 10 on the secondary side is a rectifier, and the resonant converters 3 are DC / DC converters. The resonant converters 3 are all driven at a fixed frequency and a fixed sampling ratio, with the voltage ratio between the input voltage (voltage of the respective battery cell BZ1-BZn) and the output voltage at the inverter 10 being determined by the winding ratio. The input voltage depends on the state of charge of battery cell BZ1-BZn. The output voltage is determined by the battery cell BZ1-BZn with the lowest voltage, while the other resonant converters 3 compensate for the voltage difference by current flow from battery cells BZ1-BZn with higher voltages.When the DC / DC converter 4 is active, it is primarily powered by the resonant converters 3, which are assigned to the battery cells BZ1-BZn with a higher voltage. As a result, their state of charge decreases and their voltage drops, thus cell balancing occurs. This takes place continuously during operation as long as the DC / DC converter 4 is active. This cell balancing can also occur when charging the high-voltage battery 2 from an external AC or DC voltage source, provided the DC / DC converter 4 is switched on and can draw power. The DC / DC converter 4 can, for example, be configured as a buck converter, which reduces the output voltage at the resonant converters 3 from 24 V or 48 V to a 12 V voltage for the low-voltage electrical system 5. In this case, additional loads can also be connected directly to the output of the resonant converters 3 (e.g., 48 V or 24 V components such as heating elements or fans).Alternatively, the winding ratio can also be chosen such that the output voltage is less than or equal to 12 V, so that the DC / DC converter 4 is operated as a boost converter.

[0019] In the Fig. Figure 2 shows an alternative embodiment of an electrical system 1. For clarity, the high-voltage battery 2 is shown with only four battery cells BZ1-BZ4. A resonant converter 3 is assigned to each pair of battery cells BZ1, BZ2 and BZ3, BZ4, respectively. The inverter 9 of the resonant converter 3 for battery cells BZ1, BZ2 consists of two transistors MB4, MB3 and two capacitors CB4, CB3 connected in series. An inductor LB1 is arranged between a center tap between transistors MB4, MB3. On the secondary side, the inverter 10 (or rectifier) ​​has two capacitors CR22, CR21 and two diodes D22, D21, which are designed as Schottky diodes. Furthermore, an inductor LR2 is connected between the center taps of capacitors CR22, CR21 and diodes D22, D21. A transformer is formed via the inductors L1 and L2.Accordingly, inverter 9 of the second resonant converter 3 is formed by transistors MB2 and MB1, capacitors CB2 and CB1, and inductors LB2, while inverter 10 is formed by capacitors CR12 and CR11, diodes D12 and D11, and inductors LR1. The transformer is formed via inductors L3 and L4. Also shown are the controllers 11 of the resonant converters 3. The controllers 11 feature a PWM control circuit located on a low-voltage side of the electrical system and generate a PWM signal with a fixed frequency and sampling rate. This signal is inductively transmitted to a secondary side. The output then provides the control signals for the transistors of inverter 9.

[0020] The current flowing through inverter 10 can be determined by means of a sampling voltage measurement across a capacitor of inverter 10. The voltage U is... Ca sinusoidal oscillation around a voltage value U, which is determined by the battery cell BZ1-BZ4 with the lowest voltage (see Fig. 3) The voltage U is now... C at the two peaks of the voltage U C measured. Then the following applies: UC(T2)−UC(T1)=1C⋅∫T1T2iC(t)⋅dt

[0021] This equation can now be multiplied by the factor 1=T2−T1T2−T1 multiplied so that: UC(T2)−UC(T1)=1C⋅(T2−T1)⋅∫T1T2iC(t)dtT2−T1=1C⋅(T2−T1)⋅lC¯, where lC¯ The average current through inverter 10 is thus calculated. lC¯ to: lC¯=UC(T2)−UC(T1)T2−T1⋅C Reference symbol list 1 electrical system 2 high-voltage batteries 3 resonant transducers 4 DC / DC converters 5 Low-voltage electrical system 6 low-voltage batteries 7 Voltage measuring device 8 DC / DC converters 9 inverters 10 inverters 11 Control 12 PWM control BZ1-BZ4 battery cells CB1-CB4 capacitors CR11, CR12 capacitors CR21, CR22 capacitors D11, D12 diodes D21, D22 diodes L1-L4 inductances LB1, LB2 inductors LR1, LR2 inductors MB1-MB4 transistors U C Tension QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] US 20220045628 A1

[0002]

Claims

[1] Electrical system (1) comprising a high-voltage battery (2) consisting of at least n battery cells (BZ1-BZn) connected in series, at least one circuit for cell balancing of the n battery cells (BZ1-BZn) and at least one DC / DC converter (4), wherein a low-voltage electrical system (5) is connected to the DC / DC converter (4), characterized by, that the at least one circuit for cell balancing consists of n or n / 2 resonant converters (3), wherein the resonant converters (3) are arranged with their primary side in parallel to one or two battery cells (BZ1-BZn) and the resonant converters (3) are connected in parallel on the output side of the secondary side, wherein the parallel-connected outputs on the secondary side of the resonant converters (3) are connected to the DC / DC converter (4), wherein a control (11) of the resonant converters (3) is configured to drive the resonant converters (3) with a fixed frequency and fixed sampling ratio, wherein the resonant converters (3) are magnetically decoupled. [2] Electrical system (1) according to claim 1, characterized by , that the inverter (10) on the secondary side of the resonant converter (3) is designed as a passive inverter (10). [3] Electrical system (1) according to claim 1 or 2, characterized by, that the winding ratio of primary windings to secondary windings is 1 to 8 or 1 to 16, wherein the DC / DC converter (4) is designed as a buck converter. [4] Electrical system (1) according to any one of the preceding claims, characterized by , that the control (11) of the resonant transducer (3) is located on the low-voltage side and has an inductive transformer. [5] Electrical system (1) according to any one of the preceding claims, characterized by , that a resonant converter (3) is connected in parallel to two battery cells (BZ1, BZ2; BZ3, BZ4), wherein an additional inductance (LB1, LB2) is arranged between a center tap of the battery cells (BZ1, BZ2; BZ3, BZ4) and a center tap of the resonant converter (3). [6] Electrical system (1) according to any one of the preceding claims, characterized by, that a control of the DC / DC converter (4) is designed to switch on the DC / DC converter (4) during a charging process of the battery cells (BZ1-BNn). [7] Electrical system (1) according to any one of claims 2 to 6, characterized by , that the diodes (D11-D22) of the passive inverter (10) on the secondary side are designed as Schottky diodes. [8] Electrical system (1) according to any one of the preceding claims, characterized by , that a sampling voltage measuring device is arranged on at least one capacitor of the inverter (10) on the secondary side, wherein an evaluation unit of the voltage measuring device is designed to determine a current from the resonant converter (3) on the basis of the voltage signals. [9] Electrical system (1) according to any one of the preceding claims, characterized by, that a further high-voltage component is arranged on the battery cells (BZ1-BZn), wherein the high-voltage component has means for detecting or determining an input current. [10] Electrical system (1) according to claim 9, characterized by that the additional high-voltage component is designed as a boost converter.

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