Method and circuit for an active short circuit across module strings of a modular battery

Abstract

The present invention relates to a method and a circuit for an active short circuit of a traction system, wherein the traction system (20) comprises an electric traction machine (13) and a modular battery (11) connected thereto, the modular battery (11) comprising a central controller and a plurality of battery modules (15) arranged in at least one string, each of which has a plurality of semiconductor switches and a plurality of switching states. The traction machine (13) is connected to short-circuit contactors (12), thereby forming a first short-circuit circuit in the millisecond range.The connections of the modular battery (11) to the traction machine (13) are connected within a microsecond range to form a second short-circuit circuit (17) by sending a signal from the central controller to all battery modules (15) to assume a conducting switching state (16, 26), whereby immediately afterwards all battery modules (15) switch to the conducting switching state (16, 26), thereby preventing overcharging of the traction system and overvoltages.

Description

[0001] The present invention relates to a method and a circuit for an active short circuit across module strings of a modular battery.

[0002] If a fault occurs in the traction system, a traction machine must be actively short-circuited as quickly as possible in order to prevent overloading of the system due to recuperation currents and to short-circuit the voltages induced in the stator by the rotor, which may rotate at high speed during driving, and to prevent overvoltage.

[0003] The document DE 10 2012 110 236 A1 discloses a disconnecting device for a power supply unit in order to electrically disconnect it from an electric drive.

[0004] The publication DE 10 2020 210 554 A1 discusses an inverter with a protective circuit. The protective circuit disconnects a DC link connection to the inverter from the power section as soon as a maximum load is exceeded.

[0005] The publication DE 10 2020 129 130 B3 deals with the switching states of an AC battery or a modular multilevel converter. Generally, a bypass switching state is proposed as the safety switching position for all modules of the AC battery. However, at no point is this associated with a rotor stop of a traction motor.

[0006] Against this background, it is an object of the present invention to provide a method for an active short circuit in an electrical machine that can be implemented on a microsecond scale to avoid the induction of large voltages. Especially in power electronics, contactors operating on a millisecond scale, for example, are too slow to prevent such overvoltages and charging currents that could damage the traction system.

[0007] To achieve the aforementioned object, a method for actively short-circuiting a traction system is proposed, wherein the traction system comprises an electric traction motor and a modular battery connected thereto. The modular battery comprises a central controller and a plurality of battery modules arranged in at least one string, each of which has a plurality of semiconductor switches and a plurality of switching states. The traction motor is connected to short-circuit contactors, thereby forming a first short-circuit circuit in the millisecond range.Connections of the modular battery to the traction machine are connected together within a microsecond range to form a second short-circuit circuit by sending a signal from the central controller to all battery modules to assume a conducting switching state, whereby all battery modules are immediately switched to the conducting switching state, thereby preventing overloading of the traction system by energy stored in coils of the electric traction machine and overvoltages at higher speeds of a rotor of the electric traction machine.

[0008] In the event of a short circuit in the electric traction motor, e.g., a three-phase machine, the circuit is formed via the module strings of the modular battery assigned to the respective phases. One such modular battery is, for example, a modular multilevel converter, 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." The semiconductor switches of the battery modules, e.g., MOSFETs, form a suitable switching state in which a current flowing through a respective battery module does not affect any other electrical components and, in particular, energy storage devices are removed from a current path.Since the semiconductor switches have switching times of less than one microsecond, the short-circuit circuit can be formed sufficiently quickly via the modular battery, thus avoiding overloading of the traction system.

[0009] In one embodiment of the method according to the invention, the respective battery module is formed by at least a first half-bridge, a second half-bridge, a third half-bridge, a fourth half-bridge, and an energy storage device, wherein the four half-bridges are connected in parallel with the energy storage device. In the respective battery module, a two-wire input terminal is formed by a respective center tap on the first half-bridge and the second half-bridge, and a two-wire output terminal is formed by a respective center tap on the third half-bridge and the fourth half-bridge.

[0010] In a further embodiment of the method according to the invention, the conducting switching state is selected from a group of the following switching states: low-side bypass, high-side bypass, low-side semi-bypass, high-side semi-bypass.

[0011] In a modular multilevel converter with serial and parallel connectivity, a short circuit in an energy storage device can occur if a first battery module is switched to a bypass using all half-bridges and the neighboring battery module is either in a parallel switching state with the first battery module or in an impermissible switching state. According to the invention, a "semi-bypass" switching state is therefore introduced, which uses only a single wire of the two-wire input connection or a single wire of the two-wire output connection for each connection to a neighboring module. This eliminates the possibility of a short circuit, regardless of the switching state of the respective neighboring battery module.In addition, the semi-bypass can be implemented by two different current paths in the battery module, which supply differently closed semiconductor switches, so that a faulty semiconductor switch in one of the two paths can be advantageously bypassed and the entire system can continue to operate. Furthermore, in the event that a first MOSFET of a half-bridge is conductive and the second MOSFET of the half-bridge is turned on, an active short circuit of this half-bridge can be advantageously prevented by implementing a semi-bypass via the irreparably conductive first MOSFET.

[0012] In a further embodiment of the method according to the invention, the respective battery module for the active short circuit of the traction machine is switched to the low-side semi-bypass switching state or the high-side semi-bypass switching state.

[0013] In a further embodiment of the method according to the invention, an inner low-side semi-bypass switching state or an outer low-side semi-bypass switching state is selected as the low-side semi-bypass switching state. An inner high-side semi-bypass switching state or an outer high-side semi-bypass switching state is selected as the high-side semi-bypass switching state. The switching state referred to as "inner" or "outer" semi-bypass refers to an arrangement in a circuit diagram of the respective battery module (see reference numeral 15 in the figures), wherein the first and fourth half-bridges shown on the outside in the battery module are considered "outer" half-bridges, and wherein the second and third half-bridges closest to the energy storage device in the battery module are considered inner half-bridges. The respective selected switching state is continued in all battery modules, so that a respective short-circuit circuit is formed.It is taken into account that the selected switching state is compatible with the parallel state and connects active half bridges.

[0014] Furthermore, a circuit for an active short circuit of a traction system is claimed, wherein the circuit comprises the traction system with an electric traction machine and a modular battery. The modular battery comprises a central controller and a plurality of battery modules arranged in at least one string, each of which has a plurality of semiconductor switches and a plurality of switching states. The traction machine is connected to short-circuit contactors, whereby a first short-circuit circuit can be formed in the millisecond range.Connections of the modular battery to the traction machine are interconnectable within a microsecond range to form a second short-circuit circuit, or can be interconnected. The circuit is designed to send a signal from the central controller to all battery modules to assume a conducting switching state, and immediately thereafter, to switch all battery modules to the conducting switching state. As a result, the torque of a rotor of an operating traction machine is reduced, and overloading of the traction system due to energy stored in the coils of the electric traction machine and overvoltages at higher speeds of a rotor of the electric traction machine are prevented.

[0015] In one embodiment of the circuit according to the invention, the respective battery module comprises a first half-bridge, a second half-bridge, a third half-bridge, a fourth half-bridge, and an energy storage device. The four half-bridges are connected in parallel with the energy storage device. In the respective battery module, a two-wire input connection is formed by a respective center tap on the first half-bridge and the second half-bridge, and a two-wire output connection is formed by a respective center tap on the third half-bridge and the fourth half-bridge.

[0016] In a further embodiment of the circuit according to the invention, the conducting switching state is selected from a group of the following switching states: low-side bypass, high-side bypass, low-side semi-bypass, high-side semi-bypass.

[0017] In a further embodiment of the circuit according to the invention, the respective battery module for the active short circuit of the traction machine is connected to the low-side semi-bypass or the high-side semi-bypass.

[0018] In a further embodiment of the circuit according to the invention, an internal low-side semi-bypass switching state or an external low-side semi-bypass switching state is selected as the low-side semi-bypass switching state. An internal high-side semi-bypass switching state or an external high-side semi-bypass switching state is selected as the high-side semi-bypass switching state.

[0019] Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings.

[0020] 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.

[0021] The figures are described coherently and comprehensively; the same components are assigned the same reference symbols. Fig. 1 shows schematically a traction system with a bypass circuit in an embodiment of the method according to the invention. Fig. 2 schematically shows a traction system with a possible implementation of a semi-bypass circuit in a further embodiment of the method according to the invention.

[0022] In Fig. 1 schematically shows a traction system 10 with a bypass circuit in one embodiment of the method according to the invention. A modular battery 11 is connected to a traction motor 13. Short-circuit contactors 12 can short-circuit the traction motor 13. Each battery module 15 comprises an energy storage device and four half-bridges, each half-bridge having two semiconductor switches, e.g., MOSFETs. Three strings with these battery modules 15 are interconnected at one end to form two star points with a secondary supply connection 14; at their other end, they form a respective phase for the traction motor 13. If a fault occurs in the modular battery 11 during operation, the traction motor 13 must be actively short-circuited in its three phases so that an induced voltage, which arises from a rotor of the traction motor 13 initially continuing to rotate, does not generate an overvoltage that would damage the system.In addition, overcharging of the system in the event of recuperation is prevented. However, since the short-circuit contactors 12, in comparison to the semiconductor switches of the battery modules 15, have a reaction time in the millisecond range, during which time damage can already occur, the method according to the invention advantageously forms a short-circuit path 17 through all battery modules 15 of the modular battery 11 in the microsecond range by a central controller of the modular battery 11 sending a corresponding signal to all battery modules 15. Such a short-circuit path 17 is provided, for example, by a bypass minus switching state 16, i.e. a current path is routed via a low side of the respective battery module 15. Equivalently, a bypass plus switching state would also be conceivable, i.e. the current path is routed via a high side of the respective battery module 15 (not shown).

[0023] In Fig. 2 schematically shows a traction system 20 with a possible implementation of a semi-bypass circuit in a further embodiment of the method according to the invention. For the respective battery module 15, a semi-bypass minus 26 is selected as the switching state. In this case, the short-circuit path 17 in the respective battery module 15 is only routed via two of the four half-bridges. Should switching delays occur in the modular battery 11 when establishing the short-circuit path 17 (e.g. a first battery module already assumes the new semi-bypass minus switching state, while the immediately adjacent battery module, previously connected in parallel with the first battery module, still has this parallel switching state), the semi-bypass minus 26 switching state establishes an inherently secure connection to the respective adjacent battery module 15, since, in contrast to the bypass switching state (see Fig.1) the possibility of a short circuit is excluded in previously parallel-connected energy storage devices of adjacent battery modules 15. List of reference symbols 10 Traction system diagram 11 Modular Battery 12 short-circuit contactors 13 Traction machine 14 Auxiliary supply connection 15 Battery module 16 Bypass Minus 17 Short-circuit path 20 Traction system diagram with semi-bypass 26 Semi-Bypass Minus QUOTES CONTAINED IN THE DESCRIPTION

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

[0000] DE 10 2012 110 236 A1

[0003] DE 10 2020 210 554 A1

[0004] DE 10 2020 129 130 B3

[0005] Zitierte Nicht-Patentliteratur

[0000] Goetz, S.M.; Peterchev, A.V.; 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

[0008]

Claims

[1] A method for an active short circuit of a traction system, wherein the traction system (10, 20) comprises an electric traction machine (13) and a modular battery (11) connected thereto, wherein the modular battery (11) comprises a central controller and a plurality of battery modules (15) arranged in at least one string, each of which has a plurality of semiconductor switches and a plurality of switching states, wherein the traction machine (13) is connected to short-circuit contactors (12), whereby a first short-circuit circuit is formed in the millisecond range, wherein connections of the modular battery (11) to the traction machine (13) are interconnected within a microsecond range to form a second short-circuit circuit (17) by sending a signal from the central controller to all battery modules (15) to assume a conducting switching state (16, 26),wherein immediately following this, all battery modules (15) are switched to the conducting switching state (16, 26), thereby preventing overloading of the traction system and overvoltages, [2] Method according to claim 1, wherein the respective battery module (15) is formed by at least a first half-bridge, a second half-bridge, a third half-bridge, a fourth half-bridge and an energy storage device, wherein the four half-bridges are connected in parallel to the energy storage device, wherein in the respective battery module (15) a two-wire input connection is formed by a respective center tap on the first half-bridge and the second half-bridge and a two-wire output connection is formed by a respective center tap on the third half-bridge and the fourth half-bridge. [3] Method according to claim 2, wherein the conducting switching state (16, 26) is selected from a group of the following switching states: low-side bypass (16), high-side bypass, low-side semi-bypass (26), high-side semi-bypass. [4] Method according to claim 3, wherein the respective battery module (15) for the active short circuit of the traction machine (13) is switched into the low-side semi-bypass switching state (26) or the high-side semi-bypass switching state. [5] Method according to claim 3 or 4, wherein an inner low-side semi-bypass switching state or an outer low-side semi-bypass switching state is selected as the low-side semi-bypass switching state (26), and wherein an inner high-side semi-bypass switching state or an outer high-side semi-bypass switching state is selected as the high-side semi-bypass switching state. [6] Circuit for an active short circuit of a traction system, wherein the circuit comprises the traction system (10, 20) with an electric traction machine (13) and a modular battery (11), wherein the modular battery (11) comprises a central controller and a plurality of battery modules (15) arranged in at least one string, each of which has a plurality of semiconductor switches and a plurality of switching states, wherein the traction machine (13) is connected to short-circuit contactors (12), whereby a first short-circuit circuit can be formed in the millisecond range, wherein connections of the modular battery (11) to the traction machine (13) are or can be connected together to form a second short-circuit circuit (17) within a microsecond range, wherein the circuit is designed toto send a signal from the central controller to all battery modules (15) to assume a conducting switching state (16, 26), and immediately thereafter to switch all battery modules (15) to the conducting switching state (16, 26). [7] Circuit according to claim 6, wherein the respective battery module (15) has a first half-bridge, a second half-bridge, a third half-bridge, a fourth half-bridge and an energy storage device, wherein the four half-bridges are connected in parallel to the energy storage device, wherein in the respective battery module (15) a two-wire input connection is formed by a respective center tap on the first half-bridge and the second half-bridge and a two-wire output connection is formed by a respective center tap on the third half-bridge and the fourth half-bridge. [8] Circuit according to claim 7, wherein the conducting switching state (16, 26) is selected from a group of the following switching states: low-side bypass (16), high-side bypass, low-side semi-bypass (26), high-side semi-bypass. [9] Circuit according to claim 8, wherein the respective battery module (15) for the active short circuit of the traction machine (13) is connected to the low-side semi-bypass (26) or the high-side semi-bypass. [10] Circuit according to one of claims 6 to 9, wherein an inner low-side semi-bypass switching state or an outer low-side semi-bypass switching state is selected as the low-side semi-bypass switching state (26), and wherein an inner high-side semi-bypass switching state or an outer high-side semi-bypass switching state is selected as the high-side semi-bypass switching state.

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