Method for controlling topological switches of a half-bridge in a power module of an inverter

Abstract

Method for controlling two mutually complementary topological switches of a half-bridge in a power module of an inverter, wherein - in a first step (S1) a bridge short circuit is detected at one of the topological switches, and - in a second step (S2) first the topological switch complementary to the topological switch at which the bridge short circuit was detected is de-energized, and - in a third, subsequent step (S3), the short-circuit current in the topological switch where the bridge short circuit was detected is switched off.

Description

[0001] The present invention relates to the field of electromobility, in particular to electronic modules for an electric drive.

[0002] The use of electronic modules, such as power electronics modules, in motor vehicles has increased significantly in recent decades. This is due, on the one hand, to the need to improve fuel economy and vehicle performance, and, on the other hand, to advances in semiconductor technology. The main component of such an electronic module is a DC / AC inverter, which is used to supply electrical machines such as electric motors or generators with a multi-phase alternating current (AC). In this process, a direct current generated by a DC energy source, such as a battery or accumulator, is converted into a multi-phase alternating current. For this purpose, the inverters comprise a variety of electronic components with which bridge circuits (e.g. half-bridges) are implemented, for example semiconductor power switches, which are also known as power semiconductors.

[0003] In addition to normal operation, various faults can occur under certain circumstances that are therefore outside of normal operation. Nevertheless, these areas must be controlled to the extent that they do not result in total failure or total destruction. One of these potential faults is a bridge short circuit. When a bridge short circuit occurs, a very high short-circuit current is generated, which must be detected in a timely manner and switched off as quickly as possible. The challenges here are that if the bridge short circuit is not detected in a timely manner at a topological switch, the energy value increases very quickly, which can lead to thermal destruction of the topological switch.In addition, after a bridge short circuit is detected in a topological switch, the bridge short-circuit current should be switched off as quickly as possible to protect the topological switch from overheating due to the rising energy value. However, rapid switch-off generates a very high overvoltage across the topological switch. This voltage can exceed the maximum voltage tolerance of the semiconductor, which can also lead to the destruction of the semiconductor. Therefore, developing a safe short-circuit capability for a power electronic system and ensuring it under all circumstances is very difficult and often involves compromises.

[0004] Both DE 10 2010 062 377 A1 and the scientific publication “GHOSH, K et al.: Design of a Parasitic Inductance Based Shoot-Through Protection Scheme for SiC MOSFET Gate Driver. In: 2022 IEEE International Industrial Electronics Society Annual On-Line Conference (ONCON), 2022, pp. 1 ~ 6. doi: 10.1109 / ONCON56984.2022,10127089” deal with the detection of short circuits in inverters.

[0005] The invention is therefore based on the object of providing a method for controlling topological switches of a half-bridge in a power module of an inverter, which method provides improved short-circuit strength.

[0006] This problem is solved by the features of the independent claims. Advantageous embodiments are the subject of the dependent claims.

[0007] A method is proposed for controlling two mutually complementary topological switches of a half-bridge in a power module of an inverter, wherein in a first step a bridge short circuit is detected at one of the topological switches, and in a second step the topological switch complementary to the topological switch at which the bridge short circuit was detected is first switched off, and in a third, chronologically subsequent step the short-circuit current in the topological switch at which the bridge short circuit was detected is switched off.

[0008] By switching off the complementary topological switch shortly before the short-circuit current in the topological switch where the short circuit was detected is switched off, the overvoltage is distributed across both topological switches. This reduces both the maximum overvoltage at the moment of switch-off and the maximum energy to be dissipated during the short circuit.

[0009] In one embodiment, the detection of a bridge short circuit is carried out in the first step by detecting a desaturation of a power semiconductor of the topological switch at which the bridge short circuit was detected.

[0010] In one embodiment, the complementary topological switch is de-energized immediately after the bridge short circuit is detected.

[0011] In one embodiment, the method is implemented in an integrated component of the power module.

[0012] In one embodiment, one of the topological switches is a high-side switch and the other is a low-side switch, each comprising at least one power semiconductor.

[0013] Furthermore, a circuit arrangement is provided which is part of a power module of an inverter of an electronic module for controlling the electric drive of a vehicle equipped with an electric drive, and has at least one half-bridge with two mutually complementary topological switches which are controlled by the described method.

[0014] Furthermore, an integrated module is provided in which the described method is implemented as a software product, wherein the integrated module is part of a power module of an inverter of an electronic module for controlling the electric drive of a vehicle equipped with an electric drive.

[0015] Furthermore, an inverter with an integrated component is provided. Furthermore, an electric drive of a vehicle is provided, comprising an electronic module for controlling the electric drive, which has an inverter with a described circuit arrangement or a described integrated component or a described inverter. Furthermore, a vehicle is provided, comprising a described electric drive.

[0016] Further features and advantages of the invention will become apparent from the following description of exemplary embodiments of the invention, with reference to the figures of the drawing, which illustrate details of the invention, and from the claims. The individual features can be implemented individually or in combination in a variant of the invention.

[0017] Preferred embodiments of the invention are explained in more detail below with reference to the accompanying drawings. Fig. 1 shows simulation results of a non-optimized method according to the prior art and an optimized method according to an embodiment of the present invention in comparison. Fig. 2 shows a schematic flow diagram of the method according to an embodiment of the present invention.

[0018] In the following descriptions of the figures, the same elements or functions are provided with the same reference symbols.

[0019] As already mentioned at the beginning, one goal of the design of circuits for power semiconductors of an inverter in the automotive sector is to provide the highest and most reliable short-circuit strength possible.

[0020] Power modules are used in power electronics as the central switching element in electronic devices. The topological switches are implemented using power semiconductors made, for example, of silicon (Si), silicon carbide (SiC), or gallium nitride (GaN). Bipolar transistors such as IGBTs and unipolar field-effect transistors such as MOSFETs are installed. As already mentioned above, a possible fault is a bridge short circuit in one of the half-bridges in the power electronics. Normally, there is one half-bridge per phase. Since three phases are usually provided, three half-bridges are also normally provided, which is then referred to as a B6 bridge. Each half-bridge has two series-connected and complementary topological switches, which are referred to as high-side switches and low-side switches. Each of the topological switches is formed from at least one power semiconductor.A center tap for the electrical load, such as an electric motor (not shown in the figures), is provided between the topological switches. The topological switches are required to convert a direct current coming from a direct current source into an alternating current suitable for use by a motor, for example.

[0021] In the following, the invention is described using a single half-bridge, since the method can be applied analogously to a larger number of half-bridges.

[0022] During a bridge short circuit, both series-connected power semiconductors of the topological switches are conductive, thus short-circuiting the DC power source (vehicle battery). This condition must be managed in any power electronic topology where such a condition can occur.

[0023] As already mentioned, a very high short-circuit current is generated when a bridge short circuit occurs. This can be up to ten times the usual maximum load current and must be detected in a timely manner and switched off as quickly as possible. The challenges that arise are that if the bridge short circuit is not detected in a topological switch in a timely manner, the energy value (consisting of the applied voltage times the current flowing through it) increases very rapidly, which can lead to thermal destruction of the topological switch. Furthermore, after the bridge short circuit is detected in a topological switch, the bridge short-circuit current must be switched off as quickly as possible to protect the topological switch from overheating due to the increasing energy value. However, rapid switch-off generates a very high overvoltage at the topological switch.This voltage can exceed the maximum voltage tolerance of the semiconductor, which can also lead to semiconductor destruction. Therefore, it is very difficult and often involves compromises to develop a safe short-circuit withstand capability for a power electronic system and to guarantee it for (as many) circumstances as possible.

[0024] In order to provide improved short-circuit resistance, it is proposed to carry out the following process in a first step S1 after detecting a bridge short circuit in a topological switch (hereinafter referred to as short-circuited topological switch).

[0025] In a second step S2, before the short-circuit current in the short-circuited topological switch is switched off, the complementary topological switch, i.e. the one located opposite it in series, is de-energized. This occurs directly after the short circuit is detected, i.e. at the moment of detection and, if possible, without delay. This means that the complementary topological switch (not affected by the short circuit) can also absorb part of the total overvoltage occurring due to the short circuit and thus reduce the voltage at the short-circuited topological switch. Ideally, the overvoltage is distributed exactly equally between both topological switches, whereby it is essentially sufficient if the complementary topological switch absorbs enough voltage so that the energy to be absorbed at the short-circuited topological switch is significantly reduced and thus no further damage is caused by the overvoltage.

[0026] After the complementary topological switch has been de-energized in the second step S2, the short-circuited topological switch is opened (de-energized) in a third step S3, ie the short-circuit current present there is switched off. The procedure is described in Fig. 2 shown in abstract form.

[0027] This control method has the advantage that the applied (over)voltage across the topological switch, which was previously solely affected by the short-circuit current, is now distributed between both topological switches. This also significantly reduces the energy that the short-circuited topological switch must withstand. Furthermore, due to the lower voltage drop across both topological switches, the characteristic overvoltage pulse will be the same in terms of its delta, but will start from a significantly lower offset, thus not jeopardizing the maximum dielectric strength of the topological switch.

[0028] Topological switches of half-bridges according to the invention can be all types of common bipolar and / or unipolar transistors, e.g., IGBTs, MOSFETs, BJTs, HEMTs, JFETs, and thyristors. The transistor materials can be silicon (Si), silicon carbide (SiC), or gallium nitride (GaN). Neither is essential for the control method, as it is applicable to all types and materials.

[0029] To verify the proposed method, a simulation model was used in which a typical bridge short circuit was simulated using a current standard method and a method optimized according to the invention. The simulated values ​​are shown in Fig. 1 superimposed in a plot, where the units voltage U (Y-axis) and time t (X-axis) do not play a role here.

[0030] The characteristic curves U_nor1 and U_nor2 (each shown in dotted lines) represent a current shutdown procedure in which, in the event that a short-circuit current I_KS is detected, e.g., by detecting desaturation at a topological switch (step S1), the affected topological switch (here the one with the dotted line U_nor1) is switched off as quickly as possible, i.e., immediately after the short circuit is detected. The voltage curve of the complementary topological switch is shown with the dotted line U_nor2. The effect specifically on the shutdown overvoltage, which is shown in the transparent oval 10 in Fig. The problem shown in Figure 1 can be clearly seen in the non-optimized process (dotted line U_nor1). Here, a typical overshoot of the voltage U_nor1 of the switching topological circuit can be seen.

[0031] Also in Fig.1, the voltage curves of the two topological switches according to the method according to the invention are shown superimposed on those of the standard method described above. Here, an earlier shutdown, i.e., currentless switching, of the complementary topological switch is carried out before the actual shutdown of the standard short-circuit detection (i.e., shutdown of the short-circuited topological switch). The curves of the characteristic curves U_opt1, U_opt2 show the intended distribution of the voltage levels of the two series-connected topological switches. The curve shows that, as mentioned above, the overvoltage is distributed between the two topological switches. This means that both the risk of overvoltage at the short-circuited topological switch is reduced and the applied short-circuit energy is significantly minimized, i.e., the energy input into the short-circuited topological switch is significantly reduced.

[0032] According to the invention, the moment a short circuit is detected at one of the topological switches, the complementary topological switch opens, increasing the voltage applied to it and thus distributing it between both topological switches. This also distributes the energy that the topological switch affected by the short circuit must withstand, thus relieving its load. Furthermore, due to the now lower voltage drop across both topological switches, the characteristic overvoltage pulse will be the same in terms of its delta, but will start from a significantly lower offset, thus not jeopardizing the maximum dielectric strength of the topological switches.

[0033] The voltage at the topological switches will be physically adjusted according to the state of the series-connected output capacitances and depends on the application, e.g. the semiconductor types and materials used, etc.

[0034] As a practical application, this shutdown procedure could be integrated into an integrated component. Furthermore, the currently standard desaturation detection could be used to detect a short circuit.

[0035] The proposed control method for the circuit arrangement used in an inverter with at least one half-bridge makes it possible to achieve a highly efficient inverter, which is used, for example, as a drive inverter or traction inverter, with improved short-circuit strength. The circuit arrangement for which the control method is proposed can be used in an inverter of an electronic module for controlling the electric drive of a vehicle equipped with an electric drive. Electrified axles can also be driven by the electric drive.

[0036] An electronic module within the scope of this invention serves to operate an electric drive of a vehicle, in particular an electric vehicle and / or a hybrid vehicle, and / or electrified axles. The electronic module comprises a DC / AC inverter. It can also comprise or be a part of an AC / DC rectifier, a DC / DC converter, a transformer, and / or another electrical converter or a part of such a converter. In particular, the electronic module serves to supply current to an electric machine, for example an electric motor and / or a generator. A DC / AC inverter preferably serves to generate a multi-phase alternating current from a direct current generated by means of a DC voltage from an energy source, such as a battery. List of reference symbols 10 Oval U_nor1, U_nor2 voltage curve standard procedure U_opt1, U_opt2 voltage curve new method I_KS short-circuit current U voltage t time S1-S3 process steps

Claims

[1] Method for controlling two complementary topological switches of a half-bridge in a power module of an inverter, wherein - in a first step (S1) a bridge short circuit is detected at one of the topological switches, and - in a second step (S2), the topological switch complementary to the topological switch at which the bridge short circuit was detected is first de-energised, and - in a third, subsequent step (S3), the short-circuit current in the topological switch at which the bridge short circuit was detected is switched off. [2] Method according to claim 1, wherein the detection of a bridge short circuit in the first step (S1) is carried out by detecting a desaturation of a power semiconductor of the topological switch at which the bridge short circuit was detected. [3] Method according to claim 1 or 2, wherein the complementary topological switch is de-energized immediately after the bridge short circuit is detected. [4] Method according to one of the preceding claims, wherein the method is implemented in an integrated component of the power module. [5] Method according to one of the preceding claims, wherein one of the topological switches is a high-side switch and the other is a low-side switch, each comprising at least one power semiconductor. [6] Circuit arrangement which is part of a power module of an inverter of an electronic module for controlling the electric drive of a vehicle equipped with an electric drive, and has at least one half-bridge with two mutually complementary topological switches which are controlled by the method according to one of claims 1 to 5. [7] Integrated module in which the method according to one of claims 1 to 5 is implemented as a software product, wherein the integrated module is part of a power module of an inverter of an electronic module for controlling the electric drive of a vehicle equipped with an electric drive. [8] Inverter with an integrated component formed according to claim 7. [9] Electric drive of a vehicle, comprising an electronic module for controlling the electric drive, which has an inverter with a circuit arrangement according to claim 6 or an integrated component according to claim 7 or an inverter according to claim 8. [10] Vehicle comprising an electric drive according to claim 9.

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