Half-bridge circuit, method for operating the half-bridge circuit, device for controlling an electric machine, and electric drive system

Abstract

The invention relates to a half-bridge circuit (100) having two semiconductor switch arrangements (110, 120) connected in series, wherein each of the two semiconductor switch arrangements (110, 120) has a series connection of a normally-on semiconductor switch (111, 121) and a normally-off semiconductor switch (112, 122). The normally-on semiconductor switch (111, 121) has a higher dielectric strength than the normally-off semiconductor switch (112, 122), and the normally-off semiconductor switch (112, 122) is equipped with a measuring functionality (113, 123; 114, 124) for measuring the intensity of a current flowing through the normally-off semiconductor switch (112, 122) and / or a temperature.

Description

[0001] Description

[0002] title

[0003] Half-bridge circuit, method for operating the half-bridge circuit, device for controlling an electrical machine and electrical drive

[0004] The present invention relates to a half-bridge circuit, a method for operating the half-bridge circuit, a device for controlling an electrical machine and an electrical drive system.

[0005] Background of the invention

[0006] In semiconductor switches, such as MOSFETs or IGBTs, as used in power converters to operate electrical machines, the current flowing through the semiconductor switch can be measured, for example, using a current sensor or a Rogowski coil. The temperature of a semiconductor layer can be measured using appropriate diodes or a temperature sensor. In so-called sense FETs or sense IGBTs, part of the semiconductor surface is used for current measurement. However, this leads to increased costs due to the high chip area consumption, particularly with current SiC semiconductors with high dielectric strength for so-called high-voltage applications (several 100 V, e.g., in electric vehicles).

[0007] Disclosure of the invention

[0008] According to the invention, a half-bridge circuit, a method for operating the half-bridge circuit, a device for controlling an electric machine, and an electric drive system with the features of the independent patent claims are proposed. Advantageous embodiments are the subject of the dependent claims and the following description.

[0009] The invention presents a solution that can reduce the overall cost and complexity of power converter circuits. The invention enables the safe use of cost-effective and robust power semiconductors and simplifies the required measuring devices for phase current. Furthermore, short-circuit resistance and detection can be improved without complex detection circuits.

[0010] The invention makes use of the measure of using a normally-off and a normally-on semiconductor switch in series in each of the semiconductor switch arrangements in a half-bridge circuit comprising two series-connected semiconductor switch arrangements, wherein the normally-off semiconductor switch is equipped with a measuring functionality of a current intensity of a current flowing through the normally-off semiconductor switch and / or a temperature, and wherein the normally-on semiconductor switch has a higher dielectric strength than the normally-off semiconductor switch, for example by a factor of 2 or more.

[0011] By using a normally-on semiconductor switch with high dielectric strength, particularly a junction field-effect transistor (SFET, JFET, or non-insulated-gate FET, NIGFET), the costs of the semiconductor switch providing the switching functionality of the half-bridge circuit can be kept low. Such semiconductor switches advantageously exhibit lower ros.on and more robust short-circuit behavior than comparable SiC MOSFETs and, in particular, are cheaper and faster to manufacture than SiC MOSFET semiconductor switches. Since a junction field-effect transistor has no gate oxide, it cannot age, which increases reliability.

[0012] At the same time, the use of a normally-off semiconductor switch with low dielectric strength, e.g., a MOSFET, IGBT, or bipolar transistor, especially a so-called LV (low voltage) version, which provides current or temperature measurement functionality, also keeps the costs of the measurement functionality low. The self-locking feature can ensure the necessary operational reliability, even though the normally-off semiconductor switch is typically only operated in the conductive state (since it may not even have the dielectric strength required for blocking operation; however, it is not required, since the normally-on semiconductor switch provides the switching functionality).

[0013] The self-locking semiconductor switch serves, on the one hand, to safeguard the self-conducting behavior against applied voltages, in a vehicle, for example, the battery and the start-up of the intermediate circuit, and, on the other hand, to provide the measuring functionality at low cost due to the low chip area costs of such a low-voltage semiconductor.

[0014] In embodiments, the normally-on semiconductor switch has a dielectric strength of at least 400 V or at least 800 V or at least 1000 V. Thus, the half-bridge arrangement can also be advantageously used in so-called high-voltage (HV) networks of electric or hybrid vehicles, which, for example, have DC voltages of 400 V or 800 V.

[0015] In some embodiments, the normally-off semiconductor switch has a dielectric strength of at most 100 V or at most 60 V. Semiconductor switches with such dielectric strengths are comparatively cost-effective.

[0016] In some embodiments, the normally-on semiconductor switch and the normally-off semiconductor switch can be controlled independently of each other. This allows for the full implementation of common control patterns, such as PWM control methods used for operating electrical machines.

[0017] In a method according to the invention for operating a half-bridge circuit according to the invention, the normally-on semiconductor switch of a first of the two series-connected semiconductor switch arrangements is controlled to be conductive in a first operating phase and to be off in a second operating phase, wherein the normally-off semiconductor switch of the first of the two series-connected semiconductor switch arrangements is controlled to be conductive in both the first and second operating phases. Thus, any desired switching pattern can be realized with the first semiconductor switch arrangement while retaining all of the aforementioned advantages.

[0018] In embodiments of the invention, the normally-on semiconductor switch of the second of the two series-connected semiconductor switch arrangements is controlled to be blocking in the first operating phase and to be conducting in the second operating phase, wherein the normally-off semiconductor switch of the second of the two series-connected semiconductor switch arrangements is controlled to be conducting in both the first and second operating phases. This allows any desired switching patterns to be represented with the entire half-bridge circuit while retaining all of the advantages mentioned above. In particular, switching patterns modulated in this way, e.g. PWM switching patterns or block clocking, can be provided for the motor operation or generator operation of a connected electrical machine.

[0019] In embodiments of the invention, a first current flowing through the normally-off semiconductor switch of the first of the two series-connected semiconductor switch assemblies is detected, a second current flowing through the normally-off semiconductor switch of the second of the two series-connected semiconductor switch assemblies is detected, and a total current is determined from the first and second currents. This allows the total current in the half-bridge circuit to be determined in a simple manner without requiring the provision of an external current sensor in the load current path.

[0020] In embodiments of the invention, a temperature of the normally-off semiconductor switch of the first and / or second of the two series-connected semiconductor switch arrangements is detected. This allows, in particular, a deduction to be made regarding a junction temperature of the normally-off semiconductor switch and / or of the normally-on semiconductor switch arranged spatially close to it, for example, using suitable thermal models.

[0021] A computing unit according to the invention, e.g. a control unit of an inverter, is configured, in particular in terms of programming and / or circuitry (e.g. as a discrete circuit), to carry out a method according to the invention.

[0022] The invention can be advantageously applied to a permanent magnet synchronous machine (PSM) or electrically excited synchronous machine (ESM) as an electrical machine, but also to other types of machines that require commutation of the stator current, such as asynchronous machines (ASM), etc.

[0023] The implementation of a method according to the invention in the form of a computer program or computer program product with program code for carrying out all method steps is also advantageous, as this entails particularly low costs, in particular if an executing control unit is also used for other tasks and is therefore already present. Finally, a machine-readable storage medium is provided with a computer program stored thereon, as described above. Suitable storage media or data carriers for providing the computer program are, in particular, magnetic, optical, and electrical memories, such as hard disks, flash memories, EEPROMs, DVDs, and others. Downloading a program via computer networks (Internet, intranet, etc.) is also possible. Such a download can be wired or cable-based or wireless (e.g., via a WLAN network, a 3G, 4G, 5G, or 6G connection, etc.).

[0024] Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings.

[0025] The invention is illustrated schematically in the drawings using exemplary embodiments and is described below with reference to the drawings. Brief description of the drawings

[0026] Figure 1 shows a schematic representation of a block diagram of an electric drive system according to an embodiment.

[0027] Figure 2 shows a schematic representation of a half-bridge circuit according to an embodiment.

[0028] Figure 3 shows a schematic representation of a detection of currents in the half-bridge circuit according to one embodiment.

[0029] Embodiment(s) of the invention

[0030] Figure 1 shows a schematic representation of a block diagram of an electric drive system 1 with a device 10 for controlling an electric machine 30. The electric drive system 1 comprises an electric machine 30 with a stator, which can be fed by a power converter 11 (so-called inverter), and a rotor. For this purpose, the power converter 11 can be fed, for example, by a DC voltage source such as a battery 20 or the like. The example of a three-phase electric machine 30 shown here serves only to improve understanding and does not represent a limitation of the present invention. Furthermore, any electric machines 30 with a number of electrical phases other than three are of course also possible.For example, it may also be a five- or six-phase electrical machine 30 or an electrical machine 30 with any other number of phases or a connection to an electrical network or another electrical load.

[0031] To control the stator of the electric machine 30, the power converter 11 can convert the DC voltage provided by the battery 20 into a suitable AC voltage. In the case of a three-phase electric machine 30, the power converter 11 can, for example, convert the DC voltage into a three-phase AC voltage. In particular, the amplitude of the AC voltage and / or the value of the output current from the power converter 11 to the stator windings (phases) of the electric machine 30 can be adjusted based on a predetermined setpoint S.

[0032] For example, the power converter 11 can be a power converter with multiple half-bridge circuits 100, as shown in Figure 2. In particular, the power converter 11 can comprise at least one half-bridge circuit 100 with two semiconductor switch arrangements 110, 120 for each phase of the electric machine 30. For example, the power converter 11 for a three-phase electric machine 30 can have a B6 topology with six semiconductor switch arrangements. The switching elements of the power converter 11 can be controlled by the control device 12 using suitable control signals using the setpoint value S. In this case, the control device 12 can, for example, provide a control signal for each semiconductor switch arrangement 110, 120 of the power converter 11 in order to open or close the corresponding switching element.The control of an upper switching element of a half-bridge is complementary to the control of the corresponding lower switching element. Each semiconductor switch arrangement is constructed, in particular, as shown in Figure 2.

[0033] In Figure 2, a half-bridge circuit according to an embodiment of the invention is shown schematically and in circuit diagram form and designated by 100. The half-bridge circuit 100 has a high-side terminal 101, a low-side terminal 102 and a center tap 103, wherein the battery 20 in Fig.

[0034] 1 to the high-side terminal 101 and the low-side terminal 102, and the center tap 103 can be connected to an AC load, for example a winding or phase of the electrical machine 30.

[0035] The half-bridge circuit 100 has two series-connected semiconductor switch arrangements 110, 120, wherein each of the two semiconductor switch arrangements 110, 120 comprises a series circuit consisting of a normally-on semiconductor switch 111, 121 and a normally-off semiconductor switch 112, 122. The semiconductor switches 112, 122 together form a "switch." The normally-on semiconductor switch 111, 121 is embodied as a junction field-effect transistor (SFET, JFET), in particular as an n-channel JFET. The normally-off semiconductor switch 112, 122 is embodied as a MOSFET, in particular as an n-channel MOSFET (NMOSFET).

[0036] In each semiconductor switch arrangement 110, 120, the normally-on semiconductor switch 111 or 121 and the normally-off semiconductor switch 112 or 122 can be controlled independently of one another, ie the control terminals or gates do not have to be directly electrically connected.

[0037] The normally-on semiconductor switch 111, 121 serves to provide the switching functionality of the half-bridge circuit 100 and therefore has a dielectric strength that is sufficiently dimensioned for the DC voltage applied to the high-side terminal 101 and low-side terminal 102, e.g., at least 400 V or 800 V or more. The normally-off semiconductor switch 112, 122 serves, on the one hand, to provide self-off capability of the half-bridge circuit 100 and, on the other hand, to provide a measuring functionality 113, 123 for a current intensity flowing through the normally-off semiconductor switch 112, 122 and a measuring functionality 114, 124 for a temperature. Since the self-locking semiconductor switch 112, 122 is preferably operated in a permanently conductive state, it does not need to have a dielectric strength that is sufficiently dimensioned for the DC voltage applied to the high-side terminal 101 and low-side terminal 102.It can therefore be an LV MOSFET, e.g. with a dielectric strength of at most 100 V or at most 60 V. The normally-on semiconductor switch 111, 121 therefore has a (significantly) higher dielectric strength than the normally-off semiconductor switch 112, 122.

[0038] The current measuring functionality 113, 123 can, for example, comprise a current conduction that occurs via the silicon of the LV MOSFET and is then evaluated. The temperature measuring functionality 114, 124 can, for example, be implemented by evaluating a temperature-dependent conduction behavior of diodes on the chip. Figure 3 schematically illustrates an embodiment of a method according to the invention in which, for example, the normally-on semiconductor switch 111 of the upper (high-side) semiconductor switch arrangement 110 is controlled to be conductive in a first operating phase and controlled to be blocking in a second operating phase, wherein the normally-off semiconductor switch 112 of the upper semiconductor switch arrangement 110 is controlled to be conductive in the first and second operating phases.

[0039] Furthermore, for example, the normally-on semiconductor switch 121 of the lower (low-side) semiconductor switch arrangement 120 is controlled in the first operating phase such that it is blocking, and in the second operating phase such that it is conducting, wherein the normally-off semiconductor switch 122 of the lower semiconductor switch arrangement 110 is controlled in the first and second operating phases such that it is conducting.

[0040] By alternating operation in the first and second operating phases, the half-bridge circuit 100 can be operated in a modulated mode, e.g. PWM mode, in which the DC voltage applied between the high-side terminal 101 and low-side terminal 102 is inverted, or an AC voltage applied to the center tap 103 is rectified.

[0041] Furthermore, the method comprises detecting a first current intensity of a current flowing through the normally-off semiconductor switch 112 of the upper semiconductor switch arrangement 110, which current intensity is sketched in a diagram a) in Figure 3, in which a curve of the current intensity I is plotted against time t.

[0042] According to embodiments of the invention, overcurrent monitoring can also take place, in which, for example, an exceeding of an upper current threshold value Io is monitored, and upon detection of the exceeding, a measure is taken, for example a permanent blocking of the semiconductor switch 111. A simple comparator circuit can be used for the monitoring. This allows, for example, rapid short-circuit detection. Furthermore, the method comprises detecting a second current intensity of a current flowing through the normally-off semiconductor switch 122 of the lower semiconductor switch arrangement 120, which is sketched in a diagram b) in Figure 3, in which a curve of the current intensity I is plotted against time t.

[0043] According to embodiments of the invention, overcurrent monitoring can also take place, for example, monitoring for an exceedance of an upper current threshold Io. Upon detection of the exceedance, a measure is taken, such as permanently blocking semiconductor switch 121. A simple comparator circuit can be used for monitoring. This allows, for example, rapid short-circuit detection.

[0044] The method further includes determining a total current from the first and second currents, which is outlined in diagram c) in Figure 3, in which a curve of the current I is plotted against time t. This results in a reconstruction of the phase current in the electrical machine from the current signals of the high-side and low-side semiconductor switches 112, 122. The sum of both measurements corresponds to the load current of the phase. This allows a separate current sensor for the phase to be completely replaced!

[0045] Furthermore, the method may include determining a temperature. Particularly if the normally-off semiconductor switch 112, 122 is embodied as a standard Si component, this enables a more direct measurement and thus better utilization of the maximum temperature, which reduces the necessary safety margin in the chip area.

[0046] Overall, the use of generally normally-off and normally-on semiconductor switches or specifically of JFETS and LV-MOSFETs as semiconductor switch arrangements (topological switch units) and the integration of otherwise expensive functions into the cost-effective LV-MOSFET for use in an inverter can significantly reduce system costs, semiconductor costs and peripheral costs.

Claims

Claims 1. A half-bridge circuit (100) comprising two series-connected semiconductor switch arrangements (110, 120), wherein each of the two semiconductor switch arrangements (110, 120) comprises a series circuit comprising a normally-on semiconductor switch (111, 121) and a normally-off semiconductor switch (112, 122), wherein the normally-on semiconductor switch (111, 121) has a higher dielectric strength than the normally-off semiconductor switch (112, 122), wherein the normally-off semiconductor switch (112, 122) is equipped with a measuring functionality (113, 123; 114, 124) of a current intensity of a current flowing through the normally-off semiconductor switch (112, 122) and / or a temperature.

2. Half-bridge circuit (100) according to claim 1, wherein the normally-on semiconductor switch (111, 121) is a junction field-effect transistor.

3. Half-bridge circuit (100) according to claim 1 or 2, wherein the normally-off semiconductor switch (112, 122) is a MOSFET or IGBT or bipolar transistor.

4. Half-bridge circuit (100) according to one of the preceding claims, wherein the normally-on semiconductor switch (111, 121) has a dielectric strength of at least 400 V, and / or wherein the normally-off semiconductor switch (112, 122) has a dielectric strength of at most 100 V.

5. Half-bridge circuit (100) according to one of the preceding claims, wherein the normally-on semiconductor switch (111, 121) and the self-locking semiconductor switches (112, 122) can be controlled independently of one another.

6. A method for operating a half-bridge circuit (100) according to claim 5, comprising: Controlling the self-conducting semiconductor switch (111, 121) of a first of the two series-connected semiconductor switch arrangements (110, 120) in a first operating phase so that it is conductive, Controlling the self-conducting semiconductor switch (111, 121) of the first of the two series-connected semiconductor switch arrangements (110, 120) in a second operating phase so that it is blocking, Controlling the self-locking semiconductor switch (112, 122) of the first of the two series-connected semiconductor switch arrangements (110, 120) in the first and second operating phases so that it is conductive.

7. The method of claim 6, further comprising: Controlling the self-conducting semiconductor switch (111, 121) of the second of the two series-connected semiconductor switch arrangements (110, 120) in the first operating phase so that it is blocking, Controlling the self-conducting semiconductor switch (111, 121) of the second of the two series-connected semiconductor switch arrangements (110, 120) in the second operating phase so that it is conductive, Controlling the self-locking semiconductor switch (112, 122) of the second of the two series-connected semiconductor switch arrangements (110, 120) in the first and second operating phases so that it is conductive.

8. The method of claim 7, comprising: alternately operating the half-bridge circuit (100) in the first and second operating phases to achieve modulated operation.

9. The method according to claim 7 or 8, further comprising: Detecting a first current intensity of a current flowing through the normally-off semiconductor switch (112, 122) of the first of the two series-connected semiconductor switch arrangements (110, 120), Detecting a second current intensity of a current flowing through the normally-off semiconductor switch (112, 122) of the second of the two series-connected semiconductor switch arrangements (110, 120), Determining a total current from the first and second currents.

10. The method according to any one of claims 6 to 9, further comprising: detecting a temperature of the normally-off semiconductor switch (112, 122) of the first and / or the second of the two series-connected semiconductor switch arrangements (110, 120). 11 . Computing unit (12) which is configured to carry out all method steps of a method according to one of claims 6 to 10.

12. Device (10) for controlling an electrical machine (30), comprising: a power converter (11) which is designed to be coupled to an electrical machine (30) having a stator and a rotor and to provide an electrical voltage for controlling the stator of the electrical machine (30), wherein the power converter (11) has at least one half-bridge circuit (100) according to one of claims 1 to 5; and a computing unit (12) according to claim 11, which is electrically coupled to the power converter (11) and provides the control signals for the power converter (11).

13. An electric drive system (1), comprising: a device (10) for controlling an electric machine (30) according to claim 12, and an electric machine (30) having a stator and a rotor, which is electrically coupled to the power converter (11) of the device (10) for controlling the electric machine (30).

14. A computer program that causes a computing unit to perform all method steps of a method according to any one of claims 6 to 10 when executed on the computing unit.

15. A machine-readable storage medium having a computer program according to claim 14 stored thereon.

Images