Method for controlling a circuit arrangement for power semiconductors

Abstract

A method is proposed for controlling a circuit arrangement for power semiconductors of an inverter with at least one phase, comprising a high-side switch and a low-side switch, each of which has at least two power semiconductors connected in parallel, wherein the power semiconductors are formed from different semiconductor types and in a switching operation one acts as an active power semiconductor and the other as an inactive power semiconductor, and wherein in a preliminary step a limit value for a predetermined load current is determined for each of the power semiconductors from a value of a current gradient at the onset of a reverse recovery process of the freewheeling diode of the active power semiconductor, and wherein in operation, in the event of an exceedance or a fall below the limit value, depending on which power semiconductor is currently active,This limit value is reached during the switch-on process of the active first power semiconductor, and a switch to the inactive power semiconductor occurs in the next switching process.

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 electronic 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.

[0003] Inverters (DC / AC inverters), also called power converters, require a power electronics module or a semiconductor package to convert the direct current from a battery or accumulator into alternating current. The power electronics module has topological switches with power transistors that are used to control the currents and generate the alternating current. Different designs of power transistors are known. Among other things, the use of so-called MOSFETs (metal oxide semiconductor field-effect transistors) or IGBTs (insulated gate bipolar transistors) is known. The semiconductor material used can be silicon (Si), silicon carbide (SiC), gallium nitride (GaN), or any other semiconductor material. The use of different types of semiconductors in a topological semiconductor switch is also already known, for example a combination of the power semiconductors SiC MOSFET and Si IGBT.

[0004] The decision as to which of the parallel-connected power semiconductors is controlled must be made based on suitable criteria. A promising approach is to select the semiconductor types used based on the current electrical load. One approach is therefore to implement a switching threshold between the parallel-connected power semiconductors based on the phase current. The problem with this is that the phase current is not measured by the gate driver unit itself, and a long delay in the switching command can arise due to the detour via the higher-level controller. This delay can lead to the power semiconductor designed for the lower load (current) experiencing excessive load (excessive current) and potentially being damaged.

[0005] The invention is therefore based on the object of ensuring rapid detection of the current load of the active power semiconductor, which can be quickly detected by the executing element, the gate driver unit.

[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 a circuit arrangement for power semiconductors of an inverter with at least one phase, each comprising a high-side switch and a low-side switch, each of which has at least two power semiconductors connected in parallel, wherein the power semiconductors are formed from different types of semiconductors and in a switching process one acts as an active power semiconductor and the other as a non-active power semiconductor, and wherein in a preliminary step for each of the power semiconductors a limit value for a predetermined load current is determined from a value of a current gradient upon the onset of a reverse recovery process of the freewheeling diode of the active power semiconductor, and wherein during operation in the event of an exceedance or undershoot, depending on which power semiconductor is currently active,this limit value in the switch-on process of the active first power semiconductor, a switchover to the inactive power semiconductor occurs in the next switching process.

[0008] In one embodiment, the limit value is a minimum or a maximum of the current gradient associated with the specified load current.

[0009] In one embodiment, a prioritized decision signal from a higher-level control system is additionally implemented, which can prevent switching.

[0010] Furthermore, a computer program is provided with software for performing all steps of the method when executed on a computer.

[0011] Furthermore, a circuit arrangement is provided which is part of an inverter of an electronic module for controlling the electric drive of a vehicle equipped with an electric drive, comprising a high-side switch and a low-side switch, each of which has at least two power semiconductors connected in parallel to one another, wherein the power semiconductors are formed from different types of semiconductors, as well as at least one comparator and a gate driver unit formed as a control unit, and wherein the circuit arrangement is controlled by the method.

[0012] In one embodiment, one of the power semiconductors is formed as a SiC MOSFET and the other power semiconductor as a Si IGBT.

[0013] Furthermore, an electric drive of a motor vehicle is provided, comprising an electronic module for controlling the electric drive, which has an inverter with the circuit arrangement.

[0014] Furthermore, a motor vehicle is provided, comprising the electric drive.

[0015] 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.

[0016] Preferred embodiments of the invention are explained in more detail below with reference to the accompanying drawings. Fig. 1 shows a basic structure of a topological semiconductor switch with power semiconductors of different semiconductor types, according to an embodiment of the present invention. Fig. 2 shows three diagrams with time signals when switching on the active power semiconductor from the perspective of the active power semiconductor, according to an embodiment of the present invention. Fig. 3 shows a flow of the decision logic of the switching according to an embodiment of the present invention. Fig. 4 shows parameters of the current gradient evaluated per switching operation as a function of the switching current according to an embodiment of the present invention. Fig. 5 shows a motor vehicle with an inverter and a control device according to an embodiment of the present invention.

[0017] In the following descriptions of the figures, the same elements or functions are provided with the same reference symbols.

[0018] The parallel operation of topological semiconductor switches 100 with parallel-connected power semiconductors 10, 20 of different semiconductor types, e.g. a silicon carbide (SiC) MOSFET 10 and a silicon (Si) IGBT 20, as in Fig. 1, is possible by several control methods, which are carried out by a corresponding gate driver unit T. The gate driver unit T serves as a control unit 200 or is part of a control unit 200 and is connected to the respective gates G MOSFET , G IGBT1 the power semiconductors 10, 20 connected

[0019] One goal of designing circuits for power semiconductors 10, 20 of an inverter in the automotive sector is to generate as few switching losses as possible. This can be achieved to a certain extent through intelligent circuit design and the selection of circuit components. However, there is further optimization potential by optimizing the control of the circuit arrangement.

[0020] The following description assumes a circuit arrangement for power semiconductors 10, 20 of an inverter 400 with at least one phase, each of which has a high-side switch (HS switch for short) and a low-side switch (LS switch for short). In the described embodiment, each of the HS or LS switches has at least two power semiconductors 10, 20 connected in parallel, as shown in Fig. 1. A first power semiconductor 10 is formed as a unipolar semiconductor component, here a SiC MOSFET. The second power semiconductor 20 is advantageously a bipolar semiconductor component, e.g., a Si IGBT. This means that the power semiconductors 10, 20 are formed from different semiconductor types, thus they can comprise different component types and / or materials.

[0021] In this embodiment, the first power semiconductor 10 is formed as a SiC MOSFET, but can also be formed as another semiconductor component suitable for the application, e.g., a Si MOSFET, JFET, or cascode. Likewise, another suitable bipolar component can be used instead of the IGBT (power semiconductor 20).

[0022] The aim of the invention is to enable the fastest possible detection of a load that is too high for the active (switched-on) power semiconductor 10 (too high a load current I_high), in order to then carry out a switchover to the other power semiconductor 20 in the next switching operation. For this purpose, a limit value G of the current gradient di / dt is specified for each power semiconductor (here 10) as a switchover criterion, and if this limit value is exceeded, the switchover to the other power semiconductor 20 takes place. In addition, a new switchover is provided when the load drops below a limit value G specified for the other power semiconductor (here 20). The method is described below with reference to Fig. 2, Fig. 3 and Fig. 4. Switching when a predetermined limit value G is exceeded occurs to the power semiconductor 20 with the larger semiconductor surface or higher current carrying capacity, usually a Si component such as an IGBT. The limit value G is preferably determined in advance in a series of tests, as described in Fig. 2 using characteristic curves for a MOSFET. For this purpose, a switching threshold S is selected, which corresponds to a given load current I Last corresponds. In the Fig. 2, the switching threshold S is the load current I Last2 selected, which is, for example, 200A. The switching threshold S can also be set at other load currents. It must be specified by a specialist.

[0023] It is advantageous to choose the switching threshold S somewhat lower than the actually determined value.

[0024] The proposed method is based on the evaluation of a signal in the switching process of the active power semiconductor 10, 20 (hereinafter also referred to as switch), which depends on the electrical load. Fig. 2 shows three diagrams showing time signals when switching on the active power semiconductor (in this embodiment, the power semiconductor 10, which is formed as a MOSFET) from the perspective of the active power semiconductor 10. Several characteristic curves for different drain-source voltages U are shown. DS (top diagram) and load currents I Last (I Last1 to I Last3 ) and drain currents I D , I D1 to I D3 , (middle diagram). The load current I Last1 to I Last3 is to be considered constant in the time domain of the switching process and is therefore shown as a constant, continuous line in the middle diagram. The drain current I D1 to I D3is transient in the time domain and is shown as a dashed or dotted line in the middle diagram. The bottom diagram shows the time profile of the current gradient di / dt (in A / ns) of the power semiconductor 10 for different switched load currents I Last (the currents I Last1 to I Last3 from the middle diagram) under otherwise identical conditions.

[0025] In the middle diagram it can be seen that the drain current I D1 to I D3 in the active power semiconductor 10 during the switch-on process transiently over the load current I to be switched Last1 to I Last3 increases, which is due to capacitive charge transfer current and reverse recovery charging of the free-running (inactive) power semiconductor. The subsequent progression until the quasi-static reaching of the load current I Last1 to I Last3 In the SiC MOSFET (shown here), the drain current ID1 to I D3 The oscillation and the gradient of the drain current I D1 to I D3 , which follows the reaching of the maximum, depends on the parameters of the switching process.

[0026] In the proposed method, for a given load current I Last1 to I Last3 (Switching threshold S, in the version shown I Last2 ) a limit value G of the corresponding current gradient di / dt (curve in the bottom diagram) is set, from which point on the next switching operation is switched to the power semiconductor 10, 20 of the other semiconductor type (in this case, this would be power semiconductor 20, which is formed as an IGBT). This limit value G is either a minimum di / dt min or a maximum di / dt max, which is shown in the di / dt curve for the load current I Last2 by a corresponding comparator or component for detecting extreme values, e.g. provided in the driver.

[0027] In Fig. 2, the curves are shown as an example for a (SiC) MOSFET as the active power semiconductor 10. For example, if the maximum permissible current of the semiconductor 10 is approximately I Last = 200A (as switching threshold S at I Last2 in Fig. 2, Fig. 3 and Fig. 4), the limit value G for di / dt can be read from the bottom diagram. In the illustrated embodiment, the limit value G corresponds to the value of the minimum current gradient di / dt min that occurs when the active power semiconductor 10 is switched on.

[0028] In Fig. 3 is in a much larger time interval compared to Fig. 2 a view of a possible current waveform of the drain current I D and represents the switching threshold S. If, for example, the comparator has detected (via the di / dti criterion) that the drain current I Dexceeds the switching threshold S, the next switching operation E involves switching to the other power semiconductor (in this case from the MOSFET to the IGBT). The decision to switch to the other power semiconductor (here 20) is made during the switching operation E, as in Fig. 3 shown schematically.

[0029] In Fig. 4 are di / dt values ​​(in A / ns) for different load currents I Last where this is divided by the current density in A / mm 2 (which depends on the semiconductor area). In this diagram, for the considered load current (here load current I Last2 ) the switching threshold S (here I Last2 = 200A) is plotted on the X-axis and the corresponding di / dt is read off the Y-axis as the limit value G. The switching threshold S is in Fig. 4 at a current density of 2 A / mm 2where the load current can be calculated based on the current density and the knowledge of the available semiconductor area and, for example, at 2 A / mm 2 200A. The Fig. The diagram shown in Figure 4 is another representation and possibility to determine the limit value G.

[0030] It should be noted that for each power semiconductor 10 and 20, a separate limit value G must be determined, above which switching to the other power semiconductor 10 and 20 must occur. Since the principle is the same for both power semiconductors 10 and 20, only the switching when the limit value G for the MOSFET is exceeded is described here.

[0031] If the limit value G is exceeded during operation (in the case of the SiC component), the next switching operation involves switching to the other power semiconductor 20. In the embodiment shown, the limit value G is approximately -10 A / ns at a switching threshold S of approximately 200 A, as can be seen from Fig. 4 is recognizable.

[0032] In the illustrated embodiment, the term "exceeding" with respect to the current gradient means that the absolute current gradient Abs (di / dt) increases, i.e., in this case, it is more than +10 A / ns. Conversely, if the limit value G is again undershot (based on the diagrams valid for the then active power semiconductor 20), switching occurs again to the other power semiconductor 10. In the illustrated embodiment, the term "undershooting" means that the absolute current gradient Abs (di / dt) decreases.

[0033] Due to the specified limit value G, no complex temporal resolution of the signal is required, since the detection of exceedance or undershoot of the specified limit value G can be performed by an analog comparator. When the comparator is triggered by the drain current I present in the active power semiconductor 10 D1 to I D3 or its gradient di / dt, the switching E to the other power semiconductor 10, 20 takes place in the next switching operation, as in Fig. 3 is indicated schematically.

[0034] The method can utilize the effect that both the value of the negative and the positive current gradient di / dt depend monotonically on the current intensity, as in Fig. 4. This shows the current gradient di / dt parameters evaluated for each switching operation as a function of the switching current. It can be seen that both the maximum and minimum current gradients di / dt min and di / dt max increase monotonically with increasing switching current. If the minimum current gradient di / dt is compared against the selected limit value G during the switching operation, the result serves as the decision logic for the comparator to determine which semiconductor type (power semiconductor 10 or 20) should be used in the subsequent switching operation.

[0035] In principle, both values ​​are therefore suitable for evaluation. Since the power semiconductors 10, 20 of both semiconductor types access the same freewheeling path, it is to be expected that the di / dt limit does not differ systematically. However, due to different turn-on speeds (di / dt entering the zero crossing), the commutation process of the diodes of the power semiconductors 10, 20 can differ. Therefore, it is useful to implement two threshold values ​​as limit values ​​G. The first threshold value applies to the semiconductor type designed for low current (wide bandgap, small chip area), in this case the SiC MOSFET 10, and the second to the semiconductor type designed for high current (Si, large chip area), in this case the Si IGBT 20.

[0036] An advantage of this method is that the decision logic can also be carried out directly in the gate driver unit T, e.g. by using a comparator, and thus the decision loop can be realized very quickly.

[0037] Such an implementation implies that the decision is made individually for each topological switch 100 (high-voltage or low-voltage). However, a prioritized decision signal from the higher-level control system (PWM generation) can also be implemented.

[0038] As already explained, the current gradient di / dt of the reverse recovery of the free-wheeling diode is considered according to the invention when the active power semiconductor 10, 20 is switched on. The current gradient di / dt depends on parameters of the switching process. These include, among others, the temperature of the free-wheeling (inactive) power semiconductor 10, 20, the dead time set in the system, and, above all, the switched load current I Last(I Last1 , I Last2 , I Last3 ).

[0039] The method as described is preferably implemented as a computer program comprising software which performs all steps of the method when executed on a computer, such as a control unit of a motor vehicle.

[0040] A power electronics module (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 electric drive has a three-phase electric motor and a battery, with the power electronics module being connected to both to convert direct current from the battery into alternating current usable by the electric motor by means of the inverter, thereby driving the electric motor. 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 power 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 a DC voltage from an energy source, such as a battery / accumulator.

[0041] Inverters 400 for electric drives of motor vehicles 300, especially cars and commercial vehicles, as well as buses, are designed for the high-voltage range and are particularly suitable for a blocking voltage class of approximately 650 volts and above. The inverter is advantageously used in power electronics to operate a three-phase electric motor of a vehicle and is signal-connected to an electronic control unit 200, or ECU for short, which serves as the driver. The ECU serves to control and regulate the inverter and the electric motor.

[0042] The circuit arrangement described is used, for example, in inverters 400 which are installed in motor vehicles 300, as in Fig. 5. The control unit 200 can be part of the inverter 400 or can have a signal connection therewith. The motor vehicle 300 can, in particular, have an electrically driven axle. The motor vehicle 300 can, in principle, be designed as a purely internal combustion engine motor vehicle, as a hybrid motor vehicle, or as an electric vehicle. List of reference symbols 100 topological semiconductor switches 10, 20 power semiconductors G limit S Switching threshold 200 control unit T Gate driver unit 300 motor vehicles 400 inverters

Claims

[1] Method for controlling a circuit arrangement for power semiconductors (10, 20) of an inverter (400) with at least one phase, each comprising a high-side switch and a low-side switch, each of which has at least two power semiconductors (10, 20) connected in parallel to one another, wherein the power semiconductors (10, 20) are formed from different types of semiconductors and in a switching operation one acts as an active power semiconductor (10, 20) and the other as a non-active power semiconductor (10, 20), and where in a preliminary step, for each of the power semiconductors (10, 20) a limit value (G) for a predetermined load current (I Last ) is determined from a value of a current gradient (di / dt) upon the onset of a reverse recovery process of the freewheeling diode of the active power semiconductor (10, 20), and wherein, during operation, in the event of this limit value (G) being exceeded or undershot, depending on which power semiconductor (10, 20) is currently active, in the switching-on process of the active first power semiconductor (10, 20), a switchover to the inactive power semiconductor (10, 20) takes place in the next switching process. [2] Method according to claim 1, wherein the limit value (G) is a minimum (di / dt min) or a maximum (di / dt max) of the predetermined load current (I Last ) associated current gradient (di / dt). [3] Method according to one of the preceding claims, wherein a prioritized decision signal is additionally implemented by a higher-level control which can prevent the switching. [4] A computer program comprising software for performing all the steps of the method according to any one of the preceding claims when executed on a computer. [5] Circuit arrangement which is part of an inverter (400) of an electronic module for controlling the electric drive of a vehicle equipped with an electric drive, comprising a high-side switch and a low-side switch, each of which has at least two power semiconductors (10, 20) connected in parallel to one another, wherein the power semiconductors (10, 20) are formed from different types of semiconductors, as well as at least one comparator and a gate driver unit (T) formed as a control unit (200), and wherein the circuit arrangement is controlled by the method according to one of claims 1 to 3. [6] Circuit arrangement according to claim 5, wherein one of the power semiconductors (10) is formed as a SiC-MOSFET, and the other power semiconductor (20) is formed as a Si-IGBT. [7] Electric drive of a motor vehicle (300), comprising an electronic module for controlling the electric drive, which has an inverter (400) with a circuit arrangement according to claim 5 or 6. [8] Motor vehicle (300) comprising an electric drive according to claim 7.

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