Determining a negative control voltage

Abstract

The present invention relates to a method for determining a negative control voltage for application to a control terminal of a passive semiconductor switch (18) in a half-bridge circuit (20) in a traction inverter (14) of a vehicle (10), comprising the steps: (a) setting (S10) an initialization value for the negative control voltage; (b) increasing (S12) the negative control voltage by an increment value; (c) performing (S14) an emission measurement to determine an emission parameter representing the strength of an electromagnetic emission during operation of the traction inverter, based on the increased negative control voltage; (d) checking (S16) whether the emission parameter falls below a limit value, and repeating steps (b) to (d) until the emission parameter falls below the limit value. The present invention further relates to a traction inverter (14) with a half-bridge circuit (20).

Description

[0001] The present invention relates to a method for determining a negative control voltage for application to a control terminal of a passive semiconductor switch in a half-bridge circuit in a vehicle traction inverter. The present invention further relates to a traction inverter with a half-bridge circuit.

[0002] The power electronics of electric and hybrid vehicles transfer traction energy from the battery to the electric motor, converting direct current (DC) into alternating current (AC). This is accomplished using an AC converter, also known as an inverter or traction converter. Typically, several transistors, such as MOSFETs (metal-oxide-semiconductor field-effect transistors), IGBTs (insulated-gate bipolar transistors), and JFETs (junction field-effect transistors), are used as switches (semiconductor switches). Several of these semiconductor switches are connected in a half-bridge circuit, with one switch conducting the positive or negative battery voltage (active switch) while the other blocks it (passive switch). High-frequency switching operations generate an AC voltage waveform that can then be converted into traction energy in the electric motor.To increase the current-carrying capacity, several power semiconductors are usually connected in parallel.

[0003] In the prior art, a positive (VCC) and negative control voltage (VEE) are used to switch power semiconductors. The positive control voltage is applied to the gate (control terminal) for the on state, and the negative control voltage is applied to the gate for the off state. When the active switch is turned on, the gate voltage at the passive switch (negative control voltage applied) increases due to the parasitic effect of Miller cycle feedback. An excessive increase can lead to so-called parasitic turn-on (PTO) of the passive switch, which in turn can cause high switching losses and potentially unstable states of the semiconductor. To avoid this, the current state of the art selects the negative control voltage such that PTO is avoided at all operating points.

[0004] Prior art, EP 4 383 570 A1 discloses that a negative gate voltage at the switched-off semiconductor can prevent parasitic turn-on. DE 699 04 811 T2 proposes reducing high-frequency oscillations during the switching on and off of a single transistor by using a smooth switching process.

[0005] The high-frequency switching processes lead to the generation of electromagnetic emissions (EME). These EME (sometimes also called electromagnetic interference, EMI) pose a challenge because they can disrupt the functionality of electronic components. Furthermore, they complicate compliance with standards or other requirements for electromagnetic compatibility (EMC), which are particularly important for ensuring operational reliability in vehicles. The EME in the relevant frequency ranges is significantly influenced by the switching behavior of the power semiconductors.

[0006] In this context, the present invention addresses the problem of reducing electromagnetic emissions (EME). On the one hand, switching losses should be minimized. On the other hand, unstable states of the semiconductors should also be avoided.

[0007] To solve this problem, the present invention relates in a first aspect to a method for determining a negative control voltage for application to a control terminal of a passive semiconductor switch in a half-bridge circuit in a traction converter of a vehicle, comprising the steps: (a) Setting an initialization value for the negative control voltage; (b) Increase the negative control voltage by a certain amount; (c) Performing an emission measurement to determine an emission parameter that represents the strength of electromagnetic emission during operation of the traction converter, based on the increased negative control voltage; (d) Check if the emission parameter falls below a limit value and repeat steps (b) to (d) until the emission parameter falls below the limit value.

[0008] In another aspect, the present invention relates to a traction converter with a half-bridge circuit with a negative control voltage determined according to a method according to one of the preceding claims.

[0009] Preferred embodiments of the invention are described in the dependent claims. It is understood that the features mentioned above and those to be explained below can be used not only in the combinations specified, but also in other combinations or individually, without departing from the scope of the present invention. In particular, the traction converter can comprise a half-bridge circuit in which a negative control voltage is used for the semiconductor switches, determined according to the approach described in the dependent claims.

[0010] According to the present invention, an initial value is first set as the output value for the negative control voltage. Starting from this initial value, the negative control voltage is iteratively increased to perform an emission measurement and determine or estimate the strength of any electromagnetic emission. Based on this measurement, it can then be checked whether a limit value is met or not reached, where this limit value describes a maximum value for electromagnetic emission. If the limit value is not met or not yet reached, the negative control voltage is further increased and another emission measurement is performed. As soon as the limit value for electromagnetic emission is met, the iterative process is terminated and the final determined value is recorded.The set negative control voltage is used as the result.

[0011] According to the invention, an approach for determining a negative control voltage is proposed that reduces electromagnetic emissions and / or interference. Within the scope of the invention, it was recognized that EME / EMI can be reduced by increasing the negative control voltage and, if necessary, accepting parasitic turn-on events. In particular, parasitic turn-on events are deliberately accepted due to Miller effect in order to prevent or reduce voltage oscillations and the associated emissions and interference. In an iterative process, the negative control voltage is gradually increased until, under certain circumstances, gentle parasitic turn-on events occur, thereby reducing voltage oscillations.

[0012] In contrast to previous approaches for setting the negative control voltage, the inventive approach deliberately accepts parasitic turn-on processes at the passive semiconductor switch. It has been recognized that these parasitic turn-on processes can have a damping effect on the drain-source voltage of the passive semiconductor switch. The proposed iterative process avoids an excessive increase in the negative control voltage. In this respect, switching losses or even potentially unstable states of the semiconductor switch are avoided. In prior art approaches, the negative control voltage is usually selected to avoid any parasitic turn-on processes, particularly to ensure that unstable states do not occur and that these are excluded at all operating points.The inventive approach of accepting parasitic switching processes enables an efficient reduction of electromagnetic emissions. In this respect, the proposed increase in the negative control voltage, as described in the invention, provides a cost-effective reduction in emissions.

[0013] In a preferred embodiment, the initialization value in step (a) is in the range of -5 volts to 0 volts. Preferably, the initialization value is in the range of -5 volts to -3 volts, and particularly preferably in the range of -5 volts to -4 volts. Additionally or alternatively, in step (a), the initialization value is selected based on a known value, depending on the type and / or design of the semiconductor switch. Furthermore, additionally or alternatively, in step (a), the initialization value is selected such that no parasitic activation of the passive semiconductor switch occurs when the active semiconductor switch is switched. Typically, the negative control voltage is in the range of -5 volts or slightly higher. With currently available semiconductor switches, this voltage ensures a sufficient safety margin to prevent unwanted switching in all cases.This value, or a value representing this commonly chosen negative control voltage, is preferably used as the initialization value in the inventive approach. Starting from this initialization value, an iterative increase is then performed. In particular, the initialization value can depend on the type and design of the semiconductor switch. Depending on which semiconductor switch is used, a different voltage, or a different negative control voltage, results, at which unwanted or parasitic switching-on processes can be excluded. This value can be used as the initialization value. This results in an efficient implementation of the method and an efficient achievement of a negative control voltage value with reduced electromagnetic emission.

[0014] In a preferred embodiment, a predefined increment value is used in step (b). Alternatively, an increment value is selected depending on the distance between the negative control voltage and a threshold voltage—preferably known beforehand—at which the passive semiconductor switch conducts and a potentially unstable state occurs. In particular, the increment value can be chosen to be smaller as the distance between the negative control voltage and the threshold decreases. In other words, depending on how close the current negative control voltage is to the increment value, a smaller increment value can be selected to avoid a potentially unstable state as much as possible. By selecting a predefined increment value, efficient initialization of the method according to the invention is achieved.By choosing an increase value depending on the distance between the negative control voltage and a threshold voltage, the safety when choosing the negative control voltage is improved and an efficient choice is made possible.

[0015] In a preferred embodiment of the method according to the invention, an emission measurement is carried out in a predefined frequency range in step (c). In particular, this predefined frequency range may result from a legal or other requirement or standard. Emission measurements are usually carried out in specific frequency ranges for electromagnetic emissions. Depending on whether emissions are present in this specific frequency range or not, it can then be ensured that the correspondingly defined limit value is complied with.

[0016] In a preferred embodiment, step (c) involves performing an emission measurement according to a standardized and / or prescribed measurement procedure. The measurement procedure may be legally prescribed or described in a relevant industry standard. Using such a standardized measurement procedure for the EME measurement ensures a meaningful measurement.

[0017] In a preferred embodiment, step (d) checks whether the passive semiconductor switch conducts and a potentially unstable state occurs. If so, steps (b) to (d) are not repeated. Thus, as an additional termination condition for the iterative increase of the negative control voltage, it is checked whether a potentially unstable state has already been reached. If this is the case, the process is terminated. In this case, a further increase may no longer be possible, so the already reached value for the negative control voltage must be considered the best possible value. This further improves safety.

[0018] In a preferred embodiment, step (d) involves a comparison with a predefined limit value. Specifically, the emission parameter can be compared with a predefined or known limit value. Such a limit value can be specified by the semiconductor switch manufacturer or derived from legal or industry standard requirements. In particular, a corresponding reference table for limit values, depending on the semiconductor technology used, etc., can be provided. This results in an efficient assessment of whether the electromagnetic emission is acceptable or not.

[0019] In a preferred embodiment of the method according to the invention, step (d) involves a comparison with a limit value according to an industry standard, a legal requirement, and / or a manufacturer's specification. In particular, step (d) can be used to verify compliance with a standard. This enables an efficient assessment of whether the relevant requirements are met or not.

[0020] In a preferred embodiment, the method according to the invention is designed to determine a negative control voltage of a SiC MOSFET semiconductor switch. This is particularly advantageous in the field of SiC MOSFET semiconductor switches. With these, parasitic turn-on processes can be accepted, if necessary, to reduce oscillations and electromagnetic emissions.

[0021] A semiconductor switch can be, in particular, a transistor. For example, MOSFETs, IGBTs, and JFETs can be used as semiconductor switches. It is possible to combine several identical or different semiconductor switches in a power semiconductor module or a half-bridge circuit, for example, by connecting them in parallel. A semiconductor switch has a gate terminal to which a positive or negative control voltage is applied to achieve either switching on or off. An initialization value, a negative control voltage, and a ramp-up value are voltage values ​​that can be negative relative to a (perhaps arbitrarily defined) zero point. The emission parameter can be a value specified on an absolute or relative scale. For example, a dimensionless value can also be used.

[0022] The invention is described and explained in more detail below with reference to some selected embodiments in conjunction with the accompanying drawings. These show: Fig. 1 a vehicle shown schematically in a side view with a battery, a traction inverter and an electric motor; Fig. 2 a schematic representation of a method according to the invention; Fig. 3 a schematic and simplified representation of a circuit diagram of a gate driver circuit; Fig. 4a and Fig. 4b a schematic representation of an equivalent circuit diagram to visualize the behavior of the gate driver circuit at different negative control voltages; Fig. 5 a schematic qualitative representation of the voltage over time at the passive switch when the active switch is turned on at different negative control voltages; and Fig. 6 A schematic qualitative representation of the drain-source voltage curve at the passive semiconductor switch when the active switch is turned on at different negative control voltages.

[0023] Fig. Figure 1 shows a simplified schematic representation of a vehicle 10 in a side view, comprising a battery 12, a traction inverter 14, and an electric motor 16. Two semiconductor switches 18 are arranged in a half-bridge circuit 20 within the traction inverter 14 to generate an alternating voltage for the electric motor 16. The method according to the invention enables the determination of a negative control voltage to reduce electromagnetic interference or emissions and, if applicable, to comply with existing EMC requirements.

[0024] In Fig. Figure 2 schematically illustrates the inventive method for determining the negative control voltage for application to a control terminal of a passive semiconductor switch in a half-bridge circuit in a vehicle traction inverter. The method comprises a step of setting S10 an initialization value for the negative control voltage. The method comprises a step of increasing S12 the negative control voltage. The method comprises a step of performing S14 an emission measurement. Furthermore, the method comprises a step of checking S16 to ensure compliance with a limit value for electromagnetic emissions. Depending on whether the limit value is met or not, steps S12 to S16 are repeated iteratively. The method can, in particular, be a test procedure for the automated setting of a negative control voltage during testing or commissioning of traction inverters.

[0025] As part of the homologation process for vehicle components (e.g., inverters, traction converters, or other power electronics components), it must be demonstrated that certain (predefined) EMC limits are not exceeded or are met. Of particular relevance in this context are limits derived from legal standards, OEM requirements, or other specifications. This verification is typically carried out through various EMC measurements, which measure EME in different frequency ranges. Specifically, conducted and radiated emissions are quantified.

[0026] Meeting these EMC requirements in specific frequency ranges depends particularly on the switching behavior of the semiconductor switches. Specifically, when SiC MOSFETs are switched on, oscillations occur in the drain-source voltage and drain current of the active MOSFET, as well as in the reverse voltage of the passive / complementary SiC diode. The nature of these oscillations has a strong influence on the electromagnetic interference (EMI). In simplified terms, a higher amplitude and longer decay of the oscillations lead to higher EMI in the corresponding frequency range. Conversely, lower amplitudes and faster decay of the oscillations result in lower EMI in the relevant frequency range. In practice, a two-stage approach is often used.First, the switching behavior in the time domain is measured, and the optimization goal of reducing the oscillations in amplitude and duration is pursued. Subsequently, EMC measurements are performed to verify whether the EME in the considered frequency range can be sufficiently reduced to meet the limit value.

[0027] Referring to Fig. 3. In the prior art, gate driver circuits are used, for example, in drive inverters, where a positive (VCC) and a negative control voltage (VEE) are used to switch power semiconductors (especially SiC MOSFETs). The positive control voltage is applied to the gate (control terminal) for the on state and is, for example, approximately +15 volts. The negative control voltage is applied to the gate (control terminal) for the off state and is, for example, between -5 volts and 0 volts.

[0028] Referring to the Fig. 4a and Fig. 4b. When the active semiconductor switch is turned on, the gate voltage at the passive semiconductor switch (negative control voltage applied) can increase. This increase can be caused in particular by the parasitic effect of Miller feedback. If the gate voltage is below the corresponding threshold voltage U at this time... th of the canal remains (U GS < U th The passive semiconductor switch remains switched off. In this case, the equivalent circuit of the passive semiconductor switch (or the freewheeling diode) can be approximated as a capacitance over the relevant time interval. Fig. 4a). Is the threshold voltage U th exceeded (U GS > U th), so in the equivalent circuit, a resistor is connected in parallel to the capacitor. This resistor acts like a damper and reduces the oscillations ( Fig. 4b).

[0029] In Fig. Figure 5 shows the voltage waveform at the control terminal of the passive switch for two different applied control voltages (-2 V and -4 V). In simplified terms, the waveform can be shifted by applying a different negative control voltage. For a negative control voltage of -4 V, the gate voltage in the example shown never reaches the threshold voltage U shown in the dashed line. th of the component. However, with a negative control voltage of -2 V, the threshold voltage is exceeded, so the assumed equivalent circuit must be changed. This corresponds to a parasitic turn-on (PTO) of the semiconductor switch.

[0030] The effects of damping are in this context Fig. Figure 6 illustrates the drain-source voltage at the passive semiconductor switch. It is particularly evident that excessively increasing the negative control voltage can lead to high switching losses and, potentially, to unstable semiconductor states. To ensure a sufficient safety margin against these unstable states, the prior art typically selects the negative control voltage such that exceeding the threshold voltage or a PTO (phase-out) is avoided at all operating points.

[0031] According to the invention, the negative control voltage is selectively shifted into a range where a smooth PTO occurs or can occur. This ensures that a potentially unstable state, i.e., a state with high switching losses, is avoided. In particular, the invention proposes an iterative process for gradually increasing the negative control voltage until a smooth PTO occurs and thus a reduction in oscillations is achieved. EMC measurements can be performed using the negative control voltage value determined in the inventive method to verify whether the corresponding limit value is met. Depending on the result, the negative control voltage can then be further increased in an iterative process. The inventive approach...The method according to the invention terminates, in particular, when the relevant EMC limits in the relevant frequency range are undershot or when the semiconductor switch enters a potentially unstable state. In the latter case, the safety margin to the unstable state is too small and the negative control voltage must be reduced again.

[0032] In other words, the transitions between an operating range with minimal PTO, reduced oscillations, and also reduced EME, which are not generally known, are determined iteratively. PTO is accepted in order to reduce EME.

[0033] The invention has been comprehensively described and explained with reference to the drawings and the description. The description and explanation are to be understood as examples and not as limiting. The invention is not limited to the disclosed embodiments. Other embodiments or variations will become apparent to a person skilled in the art when using the present invention and upon a detailed analysis of the drawings, the disclosure, and the subsequent claims.

[0034] In the claims, the words "comprise" and "with" do not preclude the presence of further elements or steps. The undefined article "a" or "an" does not preclude the presence of multiple elements. A single element or unit can perform the functions of several of the units mentioned in the claims. The mere mention of some measures in several different dependent claims is not to be understood as precluding the advantageous use of a combination of these measures. Reference numerals in the claims are not to be understood as limiting. Reference sign 10 vehicles 12 batteries 14 traction converters 16 Electric motor 18 semiconductor switches 20 Half-bridge circuit

Claims

[1] Method for determining a negative control voltage for application to a control terminal of a passive semiconductor switch (18) in a half-bridge circuit (20) in a traction converter (14) of a vehicle (10), comprising the steps: (a) Setting (S10) an initialization value for the negative control voltage; (b) Increase (S12) the negative control voltage by an increase value; (c) Performing (S14) an emission measurement to determine an emission parameter that represents the strength of an electromagnetic emission during operation of the traction converter, based on the increased negative control voltage; (d) Check (S16) whether the emission parameter falls below a limit value, and repeat steps (b) to (d) until the emission parameter falls below the limit value. [2] Method according to claim 1, wherein in step (a) the initialization value in the range of -5 V to 0 V, preferably in the range of -5 V to -3 V, particularly preferably in the range of -5 V to -4 V; depending on the type and / or design of the semiconductor switch (18) based on a previously known value; and / or is chosen so that there is no parasitic switching on of the passive semiconductor switch (18) when the active semiconductor switch (18) is switched. [3] Method according to any one of the preceding claims, wherein in step (b) a predefined increase value is used; or An increase value is selected depending on the distance between the negative control voltage and a, preferably previously known, threshold voltage at which the passive semiconductor switch (18) switches on and a potentially unstable state occurs, wherein the increase value is chosen to be smaller as the distance of the negative control voltage from the threshold decreases. [4] Method according to one of the preceding claims, wherein in step (c) an emission measurement is carried out in a predefined frequency range. [5] Method according to one of the preceding claims, wherein in step (c) an emission measurement is carried out in accordance with a standardized and / or prescribed measurement method. [6] Method according to one of the preceding claims, wherein in step (d) it is checked whether the passive semiconductor switch (18) switches on and a potentially unstable state occurs, and if necessary steps (b) to (d) are not repeated. [7] Method according to one of the preceding claims, wherein in step (d) a comparison with a predefined limit value is carried out. [8] Method according to any of the preceding claims, wherein in step (d) a comparison is carried out with a limit value in accordance with an industry standard, a legal requirement and / or a manufacturer's specification. [9] Method according to one of the preceding claims, wherein the method is designed to determine a negative control voltage of a SiC MOSFET semiconductor switch (18). [10] Traction converter (14) with a half-bridge circuit (20) with a negative control voltage determined according to a method according to one of the preceding claims.

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