Method and system for insulation measurement on battery modules of a modular battery

Abstract

The present invention relates to a method for insulation measurement on battery modules of a modular battery (110), wherein the modular battery (110) comprises a central controller and a plurality of battery modules (103) connected to each other in at least one string, wherein a two-wire connection (111) to a double star point (101, 102) is formed from each string at a first end and a respective phase connection (105, 106, 107) to a traction machine (120) is formed at the second end, wherein the insulation measurement is carried out by assigning a bypass switching state to all battery modules (103) and interrupting the electrical connection to its terminal (117) connected to the phase connection only in the battery module (103) arranged last in the respective string towards the second end.A test voltage is applied to the two-wire input terminal (111) of the battery module (103) arranged first in the respective string towards the first end, a test current is measured, and thus an insulation fault is detected. Furthermore, an insulation measuring system (100) with which the procedure is carried out is presented.

Description

[0001] The present invention relates to a method for measuring insulation on battery modules of a modular battery. Furthermore, an insulation measurement system with which the method is carried out is presented.

[0002] A modular battery is used in electric vehicles to supply power to a traction system. Each battery module has an energy storage device or a DC voltage source, whereby one or more phases for supplying AC power to a traction motor are generated by continuously alternating interconnection of the battery modules. Such a modular battery can be implemented using a modular multilevel converter system, for example, as described in "Goetz, SM; Peterchev, AV; Weyh, T., "Modular Multilevel Converter With Series and Parallel Module Connectivity: Topology and Control," Power Electronics, IEEE Transactions on, vol. 30, no. 1, pp. 203-215, 2015. doi: 10.1109 / TPEL.2014.2310225."

[0003] The energy storage device in the individual battery module is connected to the respective input and output terminals via half-bridges of semiconductor switches, e.g., MOSFETs. Depending on the design, the battery module can assume various switching states, such as "serial," "parallel," or "bypass," which each indicates the connection of the respective energy storage device in a respective (phase) string with battery modules. Each switching state then corresponds to a configuration of switching positions of the semiconductor switches in the half-bridges.

[0004] At each switching cycle, the central controller sends a switching command to each battery module, specifying the respective switching state. This command is transmitted in coded form to the respective battery module via a high-speed bus. The respective battery module calculates the switching positions to be assumed by its semiconductor switches from the respective switching command.

[0005] In a symmetrical topology, a battery module is formed, for example, by at least one energy storage device and, for example, four half-bridges connected in parallel. A two-wire input connection is formed by the respective center taps on two first half-bridges, and a two-wire output connection is formed by the respective center taps on two second half-bridges. In the symmetrical topology, two adjacent battery modules each control a connection or interconnection between the two battery modules—that is, those half-bridges or semiconductor switches arranged within them that connect the two battery modules to each other via center taps. Therefore, during switching, both battery modules must exhibit a high degree of synchronicity in their respective module control.

[0006] At the start of operation, known as "boot-up," it is advantageous to place the modular battery in an "Idie" operating state with a "parallel" switching state, in which all energy storage devices are connected in parallel so that charge equalization can occur. This allows all energy storage devices to have a balanced charge state for a transition to an "engine operation" operating state. However, if, for example, two battery modules exhibit at least one insulation fault, a short circuit with high currents and thermal degradation of components of the modular battery can occur when the parallel connection is initiated.

[0007] A device for ruling out insulation faults, a so-called insulation monitor, is therefore essential for the safe operation of the modular battery. State-of-the-art implementations involve measuring a test current emitted by the insulation monitor; if the measurement result is below a specified threshold (measurement uncertainty), this excludes the presence of an insulation fault. For battery modules with the symmetrical topology described above, so-called safe switching states are possible. In these states, the battery modules remain in the "passive" switching state with open semiconductor switches after a system shutdown, e.g., due to a fault occurring during charging at a charging station.An insulation measurement would be incorrect here, since a battery module with MOSFET semiconductor switches has a high resistance (e.g. 680 kOhm) between a negative pole of the battery module and outputs of a power board of the battery module, which is intended to prevent a floating potential of the outputs when the semiconductor switches are open and would falsify measurement results of the test current.

[0008] The publication DE 10 2019 103 757 B3 describes an insulation monitoring system for a modular battery whose battery modules, arranged in phase strings, are connected to a double star point. The insulation measurement is performed at the double star point.

[0009] The publication WO 2022 / 040 036 A1 discusses a current test of battery cells of a battery with a plurality of battery cells.

[0010] The document EP 3 780 376 A1 discloses a battery with a plurality of battery cells connected in series, wherein each battery cell is repeatedly actively inserted into a converter branch or switched to a bypass state at regular or irregular time intervals.

[0011] Against this background, it is an object of the present invention to provide a method for measuring insulation in a modular battery. As long as no result of the insulation measurement is available, the operation of the modular battery is interrupted. Furthermore, a system for implementing the method is to be presented.

[0012] To achieve the above-mentioned object, a method for insulation measurement on battery modules of a modular battery is proposed, wherein the modular battery comprises a central controller and a plurality of battery modules. The respective battery module has at least one energy storage device and four half-bridges connected in parallel. A two-wire input connection is formed by a respective center tap on two first half-bridges, and a two-wire output connection is formed by a respective center tap on two second half-bridges. The battery modules are arranged in at least one string connected to one another. From the respective string, a two-wire connection to a double star point is formed at a first end, and a respective phase connection for an AC power supply of a traction machine is formed at the second end. The insulation measurement is carried out by • the central controller transfers the modular battery to an “insulation measurement” state, in which all switching operations on the modular battery are stopped, • under specified bypass switching states, by means of which an electrical line between the input terminal and the output terminal in the respective battery module is only connected to a single pole of the at least one energy storage device, a test switching state is assigned, • all battery modules are controlled by the central controller with the test switching state and only in the last battery module in the respective string arranged towards the second end is the electrical line to its connection connected to the phase connection interrupted, • a test voltage is applied to the two-wire input terminal of the battery module arranged first in the respective string towards the first end, • a test current is measured and a measurement result is evaluated, • In the event that there is no insulation fault, the state controller transfers the battery modules to an operating state “Idie”, from which the modular battery continues to operate, • In the event of an insulation fault, the status controller transfers the battery modules to an “Error” operating state and stops the operation of the modular battery.

[0013] In one embodiment of the method according to the invention, the predetermined bypass switching state is selected from the following list: bypass minus, bypass plus, semi-bypass minus, semi-bypass plus. The bypass switching state is formed via both half-bridges at the input terminal and both half-bridges at the output terminal. The semi-bypass switching state is formed via only one half-bridge at a time. If an electrical line formed by the bypass, through which the at least one energy storage device is bypassed, is in contact with a negative pole of the at least one energy storage device, this is referred to as "minus"; if it is in contact with the positive pole, this is referred to as "plus".

[0014] In a further embodiment of the method according to the invention, test voltage is applied to the double star point. This embodiment is particularly advantageous because a test function typically performed by an insulation monitor thus finds a single contact point.

[0015] In yet another embodiment of the method according to the invention, with open contactors at the respective phase connection, the central controller activates all battery modules with the test switching state, and only the battery module arranged first in the respective string, toward the first end, interrupts the electrical line to its terminal connected to the double star point. A test voltage is applied to the two-wire output terminal of the battery module arranged last in the respective string, toward the second end.

[0016] In a further embodiment of the method according to the invention, the battery modules, coming from the “insulation measurement” state, assume a parallel switching state in the “idle” operating state, in which all energy storage devices of the battery modules are connected in parallel with one another.

[0017] Furthermore, an insulation measuring system for a modular battery is claimed, wherein the insulation measuring system comprises the modular battery, which has a central controller and a plurality of battery modules, and an insulation monitor. The respective battery module has at least one energy storage device and four half-bridges connected in parallel. A two-wire input connection is formed by a respective center tap on two first half-bridges, and a two-wire output connection is formed by a respective center tap on two second half-bridges. The battery modules are arranged in at least one string connected to one another. At a first end of the respective string, a two-wire connection to a double star point is formed, and at the second end, a respective phase connection for an AC power supply of a traction machine is formed.The insulation monitor is designed to apply a test voltage to the two-wire input terminal of the battery module located first in the respective string, measure a test current, and evaluate the measurement result. The insulation measuring system is designed to perform an insulation measurement by • the central controller transfers the modular battery to an “insulation measurement” state, in which all switching operations on the modular battery are stopped, • under specified bypass switching states, by means of which an electrical line between the input terminal and the output terminal in the respective battery module is connected to only a single pole of the at least one energy storage device, a test switching state is assigned, • all battery modules are controlled by the central controller with the test switching state and only in the last battery module in the respective string arranged towards the second end is the electrical line to its connection connected to the phase connection interrupted, • the measurement result of the insulation monitor indicates the presence of an insulation fault, • In the event that there is no insulation fault, the state controller transfers the battery modules to an operating state “Idie”, from which the modular battery continues to operate, • In the event of an insulation fault, the status controller switches the battery modules to an “Error” operating state and stops the operation of the modular battery.

[0018] In one embodiment of the insulation measuring system according to the invention, the predetermined bypass switching state is selected from the following list: bypass minus, bypass plus, semi-bypass minus, semi-bypass plus.

[0019] In a further embodiment of the insulation measuring system according to the invention, the insulation monitor is connected to the double star point for supplying the test voltage.

[0020] In yet another embodiment of the insulation measurement system according to the invention, the central controller is designed to activate all battery modules with the test switching state when the contactors at the respective phase connection are open, and to interrupt the electrical line to the terminal connected to the double star point only in the battery module arranged first in the respective string toward the first end. The insulation monitor is designed to apply a test voltage to the two-wire output terminal of the battery module arranged last in the respective string toward the second end.

[0021] In a further further embodiment of the insulation measuring system according to the invention, the battery modules have a parallel switching state after the “insulation measurement” state in the “Idie” operating state, in which all energy storage devices of the battery modules are connected in parallel with one another.

[0022] Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings.

[0023] It is understood that the features mentioned above and those to be explained below can be used not only in the combination specified in each case, but also in other combinations or on their own, without departing from the scope of the present invention.

[0024] Fig. 1 schematically shows an embodiment of the insulation measuring system according to the invention.

[0025] In Fig.1 schematically shows an embodiment of the insulation measurement system 100 according to the invention. A modular battery 110 has three strings of battery modules (illustrated by reference numeral 103) forming a U-phase connection 105, a V-phase connection 106, and a W-phase connection 107, wherein each battery module 103 is formed in a symmetrical topology with four half-bridges and an energy storage device 104. At their first end, the strings are connected 111 to form a double star point 101, 102. The modular battery 110 can be electrically disconnected from a traction motor 120 by contactors 108. In general, the modular battery 110 is connected to the remaining vehicle electronics, e.g., the auxiliary power supply, via external connections 119.An insulation monitor 109 is arranged at the double star point 101, 102 to inject a test voltage to perform the insulation measurement, measure a corresponding test current, and evaluate the resulting measurement result. An insulation fault is present depending on whether a threshold value is exceeded or not reached. To perform the insulation measurement, all battery modules 103 are placed in a switching state that bypasses the energy storage device 104, shown here as a semi-bypass minus. In this case, for connections or interconnections 112, 113, 114, 115, 116 between adjacent battery modules, only one connecting wire of the two-wire connections is energized. A respective output connection 117 of the battery module arranged toward the phase connection is not connected. List of reference symbols 100 Schematic circuit for insulation measurement 101 Positive star point connection 102 Negative star point connection 103 Battery module 104 energy storage 105 Phase U 106 Phase V 107 Phase W 108 shooters 109 insulation monitors 110 Modular Battery 111 Input connection first battery module 112 Interconnection 113 Interconnection 114 Interconnection 115 Interconnection 116 Interconnection 117 Output connection last battery module 119 External connections 120 traction machine

Claims

[1] Method for an insulation measurement on battery modules of a modular battery (110), wherein the modular battery (110) comprises a central controller and a plurality of battery modules (103), in which the respective battery module (103) connected in parallel to one another has at least one energy storage device (104) and four half-bridges, wherein a two-wire input connection is formed by a respective center tap on two first half-bridges and a two-wire output connection is formed by a respective center tap on two second half-bridges, wherein the battery modules (103) are arranged connected to one another in at least one string and from the respective string at a first end a two-wire connection (111) to a double star point (101, 102) is formed and at the second end a respective phase connection (105, 106, 107) for an AC power supply of a traction machine (120), wherein the insulation measurement is carried out by • the central controller transfers the modular battery (110) to an “insulation measurement” state in which all switching operations on the modular battery (110) are stopped, • under predetermined bypass switching states, by means of which an electrical line between the input terminal and the output terminal in the respective battery module (103) is connected to only a single pole of the at least one energy storage device (104), a test switching state is assigned, • all battery modules (103) are controlled by the central controller with the test switching state and only in the last battery module (103) arranged in the respective string towards the second end is the electrical line to its terminal (117) connected to the phase terminal interrupted, • a test voltage is applied to the two-wire input terminal (111) of the battery module (103) arranged first in the respective string towards the first end, • a test current is measured and a measurement result is evaluated, • in the event that there is no insulation fault, the state controller transfers the battery modules (103) to an “idle” operating state, from which the modular battery (110) continues to operate, • in the event of an insulation fault, the state controller transfers the battery modules (103) to an “error” operating state and stops operation of the modular battery (110). [2] Method according to claim 1, wherein the predetermined bypass switching state is selected from the following list: bypass minus, bypass plus, semi-bypass minus, semi-bypass plus. [3] Method according to one of the preceding claims, in which the test voltage is applied to the double star point (101, 102). [4] Method according to one of claims 1 or 2, in which, when the contactors (108) at the respective phase connection (105, 106, 107) are open, all battery modules (103) are controlled by the central controller with the test switching state and only in the battery module (103) arranged first in the respective string towards the first end is the electrical line to its connection connected to the double star point (101, 102) interrupted, and in which a test voltage is applied to the two-wire output connection (117) of the battery module (103) arranged last in the respective string towards the second end. [5] Method according to one of the preceding claims, in which the battery modules (103) coming from the “insulation measurement” state assume a parallel switching state in the “Idie” operating state, in which all energy storage devices of the battery modules (103) are connected in parallel with one another. [6] Insulation measuring system for a modular battery (110), wherein the insulation measuring system (100) comprises the modular battery (110), which has a central controller and a plurality of battery modules (103), and an insulation monitor (109), wherein the respective battery module (103) has at least one energy storage device (104) and four half-bridges connected in parallel with one another, wherein a two-wire input connection is formed by a respective center tap on two first half-bridges and a two-wire output connection is formed by a respective center tap on two second half-bridges, wherein the battery modules (103) are arranged in at least one string connected to one another, and a two-wire connection to a double star point is formed from the respective string at a first end and a respective phase connection (105, 106, 107) for an AC power supply of a traction machine (120) is formed at the second end,wherein the insulation monitor (109) is designed to apply a test voltage to the two-wire input terminal (111) of the battery module (103) arranged first in the respective string towards the first end, to measure a test current and to evaluate a measurement result, wherein the insulation measuring system (100) is designed to carry out an insulation measurement by, • the central controller transfers the modular battery (110) to an “insulation measurement” state in which all switching operations on the modular battery (110) are stopped, • under predetermined bypass switching states, by means of which an electrical line between the input terminal and the output terminal in the respective battery module (103) is connected to only a single pole of the at least one energy storage device, a test switching state is assigned, • all battery modules (103) are controlled by the central controller with the test switching state and only in the last battery module (103) arranged in the respective string towards the second end is the electrical line to its terminal (117) connected to the phase terminal (105, 106, 107) interrupted, • the measurement result of the insulation monitor (109) indicates the presence of an insulation fault, • in the event that there is no insulation fault, the state controller transfers the battery modules (103) to an operating state “Idie”, from which the modular battery (110) continues to operate, • in the event of an insulation fault, the state controller transfers the battery modules (103) to an “Error” operating state and stops operation of the modular battery (110). [7] Insulation measuring system according to claim 6, wherein the predetermined bypass switching state is selected from the following list: bypass minus, bypass plus, semi-bypass minus, semi-bypass plus. [8] Insulation measuring system according to one of claims 6 or 7, wherein the insulation monitor (109) is connected to the double star point (101, 102) for supplying the test voltage. [9] Insulation measuring system according to one of claims 6 or 7, in which the central controller is designed to control all battery modules (103) with the test switching state when the contactors (108) at the respective phase connection (105, 106, 107) are open and to interrupt the electrical line to the connection (111) connected to the double star point only in the battery module (103) arranged first in the respective string towards the first end, and in which the insulation monitor (109) is designed to apply a test voltage to the two-wire output connection (117) of the battery module arranged last in the respective string towards the second end. [10] Insulation measuring system according to one of claims 6 to 9, wherein the battery modules (103) have a parallel switching state in the "idle" operating state after the "insulation measurement" state, in which all energy storage devices of the battery modules (103) are connected in parallel with one another.

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