Control circuit for a separately excited electric machine with a SiC power electronics module for the stator winding and a GaN excitation module for the rotor winding

Abstract

In various embodiments, a control circuit for a separately excited electric machine (E) is provided, comprising: a power electronics module (10) with an inverter (W), which is configured to convert a direct voltage into at least one alternating voltage; an excitation module (20), which is configured to provide a current flow for at least one rotor winding (L); wherein the power electronics module (10) has power switches (S1-S6) based on a SiC semiconductor; and wherein the excitation module (20) has power switches (T1-T8) based on a GaN semiconductor. Furthermore, an separately excited electric machine comprising the control circuit is provided.

Description

The present invention relates to a drive circuit for a separately excited E-machine having an SiC power electronics module for the stator winding and a GaN exciter module for the rotor winding. The invention further relates to a separately excited electric machine having the drive circuit.In the selection of semiconductors for power electronics, efficiency and costs are of particular importance nowadays. In the field of electromobility, where large currents are switched, wide bandgap semiconductors are increasingly being used, i.e. compound semiconductors with a large band gap compared to pure silicon. Two representatives of wide-bandgap semiconductors are silicon carbide (SiC) and gallium nitride (GaN). Switching elements based on these two semiconductors can be operated at higher switching frequencies than comparable silicon-based switching elements, among other things, and have smaller dimensions.Although SiC and GaN semiconductors have a similarly large band gap that is about a factor of 3 compared to silicon, there are still differences between these two materials. Although both result in efficient switching elements, SiC semiconductors are very efficient, but expensive. GaN semiconductors, on the other hand, are favorable, but in comparison are less efficient for this purpose. Switching elements based on these two semiconductors are used in particular in electric drives.For example, document DE 10 2019 128 721 A1 discloses a power electronics device for a separately excited electric machine, wherein the power electronics device has a converter unit and an exciter unit for the rotor winding, wherein wide bandgap semiconductors are used in the converter unit and in the exciter unit.The object of the present invention can be seen in the provision of a drive circuit for a separately excited electric machine which enables a high electrical power with simultaneously high electrical efficiency of the overall system.This object is achieved by means of the subject matter of the independent claims. Further preferred embodiments are found in the dependent claims.The present invention is based on the basic idea in the drive circuit or operating circuit of a separately excited synchronous machine to use a combination of a power part for the stator winding based on SiC semiconductors and an exciter module for the rotor winding based on GaN semiconductors. The drive circuit thus has a high electrical power with simultaneously high electrical efficiency. The higher switching frequency in the exciter module compared to an approach based on Si semiconductors results in a lower current ripple and, associated therewith, better controllability. At the same time, the costs are lower compared to the use of SiC semiconductors in the exciter module. Such a design of the drive circuit provides an optimal combination of cost and efficiency.According to the invention, a drive circuit for a separately excited electric machine is provided, having a power electronics module with an inverter which is configured to convert a DC voltage into at least one AC voltage, and an exciter module which is configured to provide a current flow for at least one rotor winding. The power electronics module has power switches based on a SiC semiconductor and the exciter module has power switches based on a GaN semiconductor.The power electronics module can have a structure known from the prior art and can have an intermediate circuit capacitor and a converter, for example a pulse inverter. The exciter module is configured to provide a current flow through the rotor winding when connected to at least one rotor winding, as a result of which the rotor field is generated. For the basic implementation of the exciter module for energizing the at least one rotor winding, there are numerous possibilities known from the prior art. The drive circuit can be designed, for example, as a symmetrical H-bridge or with free-wheeling diodes.Circuit breakers are understood to mean electronic components whose current-conducting behavior can be varied by means of a drive signal which can be supplied, in particular transistors.According to further embodiments of the drive circuit, the exciter module can be embodied in a 2-level topology.According to further embodiments of the drive circuit, the exciter module can be embodied in a 3-level topology.According to the invention, a separately excited electric machine is also provided, which has an electric motor with at least one stator winding and at least one rotor winding and the above-described drive circuit. In this case, the power electronics module of the drive circuit is coupled to the at least one stator winding and the exciter module is coupled to the at least one rotor winding.According to further embodiments of the externally excited electric machine, the latter can furthermore have an inverter, wherein the drive circuit is integrated into the inverter. Alternatively, in the case of the foregoing basic embodiment of the externally excited electric machine, the drive circuit may be incorporated in the electric motor.It is understood that the features mentioned above and those still to be explained below can be used not only in the respectively specified combination, but also in other combinations or alone, without departing from the scope of the present invention.Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings. FIG. 1 shows an exemplary power electronics module of a drive circuit according to the invention. FIG. 2 shows an exemplary embodiment of an exciter module of a drive circuit according to the invention. FIG. 3 shows a further exemplary embodiment of an exciter module of a drive circuit according to the invention. FIG. 4 shows a further exemplary embodiment of an exciter module of a drive circuit according to the invention.FIG. 1 shows an exemplary topology of a power electronics module 10 of a drive circuit according to the invention. Since the structure is sufficiently known from the prior art, it will not be described in detail.The power electronics module 10 has an intermediate circuit capacitor 2, to which a voltage, for example the voltage of a supply battery (e.g. of a traction battery in an electric vehicle), can be applied via the two connections 11, 12. The power electronics module 10 has an inverter W, which in the example shown is designed for the operation of a three-phase electric motor E, which is coupled to the drive circuit 10 and is represented by the three stator windings W 1, W 2 and W 3. The inverter W has three half bridges H1, H2 and H3, each of which has two power switches S1-S6. A free-wheeling diode D 1-D 6 is provided on each of the power switches S 1-S 6.According to the invention, the power switches S 1-S 6 are embodied on the basis of SiC semiconductors.The stator winding of the electric motor E is here exemplarily embodied in 3-phase. However, polyphase winding systems, for example 6-phase or 2.times.3-phase winding systems, are also possible.FIG. 2 shows an exemplary embodiment of an exciter module 20 of a drive circuit according to the invention, which is embodied in a 2-level topology.The exciter module 20 has an intermediate circuit capacitor C, to which a DC voltage can be applied via the two connections 21, 22, for example from a high-voltage battery, in particular a traction battery of an electric vehicle. The intermediate circuit capacitor C is coupled to an H-bridge B. In each of the two bridge branches, a power switch T 1, T 2 and a diode D 1, D 2 are arranged in a series circuit. The rotor winding L is arranged in the cross connection.According to the invention, the two power switches T 1, T 2 are embodied as GaN-semiconductor-based transistors. The two diodes D 1, D 2 can be embodied on the basis of any desired semiconductors (e.g. silicon (Si), silicon carbide (SiC) or gallium arsenide (GaN)).The exciter module 20 illustrated in FIG. 2 can preferably be used at high voltages (HV DC) of up to approximately 500 V or, when using GaN semiconductors with ≥1200 V voltage stability at high voltages up to approximately 1000 V.In a modified embodiment, in the circuit in FIG. 1, the two diodes D 1, D 2 can be used by two GaN-semiconductor-based transistors, so that a symmetrical H-bridge is produced. This would have the advantage that the current can flow through the rotor winding L in both directions, in contrast to the exemplary embodiment shown with the two diodes D 1, D 2, in which the current can flow only in one direction.FIG. 3 shows an exemplary embodiment of an exciter module 20 of a drive circuit according to the invention, which is embodied in a 3-level topology. While the 2-level topology can provide only two voltage levels-the full positive and the full negative intermediate circuit voltage-half the positive and half the negative intermediate circuit voltage can additionally be provided by means of the 3-level topology.In the 3-level topology, the exemplary exciter module 20 has two intermediate circuit capacitors C 1, C 2 in a series circuit. The series connection of the two intermediate circuit capacitors C 1, C 2 is coupled to a symmetrical H-bridge B. In each of the two bridge branches, two transistors T 1, T 2 / T 5, T 6 are arranged in the upper part and two transistors T 3, T 4 / T 7, T 8 are arranged in the lower part. At each of the transistors T 2, T 3, T 6, T 7 coupled to the cross connection, a diode D 1, D 2, D 3, D 4 is provided. One terminal each of the diodes D 1, D 2, D 3, D 4 is coupled to a node point between the two intermediate circuit capacitors C 1, C 2. The rotor winding L is arranged in the cross connection of the H-bridge B. Since the H-bridge B is designed as a symmetrical H-bridge, the current can flow bidirectionally through the rotor winding L.According to the invention, the power switches T 1-T 8 are embodied as GaN semiconductor-based transistors. The four diodes D 1-D 4 may be implemented on the basis of any desired semiconductors (e.g. silicon, silicon carbide or gallium arsenide).The exciter module 20 illustrated in FIG. 3 can preferably be used at high voltages (HV DC) of about 500 V to about 1000 V, so that inexpensive GaN semiconductors with ≥700 V voltage stability can be used for the construction of the exciter module 20.A modified embodiment of the exciter module 20 in 3-level topology shown in FIG. 3 is shown in FIG. 4, in which the transistors (transistors T 3, T 4 and T 5, T 6 in FIG. 3 ) have been replaced by diodes D 5, D 6 in two of the four sub-branches of the H bridge B (including omission of the corresponding diodes D 2 and D 3 in FIG. 3 ). The embodiment shown in FIG. 4 may have the advantage that it requires fewer components, whereby costs can be saved. As in the embodiment shown in FIG. 2, the current can flow through the rotor winding L in only one direction.According to the invention, the power switches T 1-T 4 are embodied as GaN semiconductor-based transistors. The four diodes D 1, D 2, D 5, D 6 can be embodied on the basis of any desired semiconductors (e.g. silicon, silicon carbide or gallium arsenide).The 3-level topologies of the exciter modules shown in FIGS. 3 and 4 are to be understood only as examples. Further circuit variants are also possible for their realization, e.g. "T-type".In principle, the bridge circuits B outlined in the figures are to be understood as exemplary and not as restricting the scope of application of the invention.Rather, further embodiments are possible and are therefore known from the prior art. The essence of the invention is that in the drive circuit generally the combination of GaN-based semiconductors in the exciter module 20 and SiC-based semiconductors in the power electronics module 10 are used.References included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Patent Literature citedDE 10 2019 128 721 A1

[0004]

Claims

Drive circuit for a separately excited electric machine (E), comprising: a power electronics module (10) with an inverter (W) which is configured to convert a DC voltage into at least one AC voltage; an exciter module (20) which is configured to provide a current flow for at least one rotor winding (L); wherein the power electronics module (10) has power switches (S1-S6) which are based on a SiC semiconductor; and wherein the exciter module (20) has power switches (T1-T8) which are based on a GaN semiconductor.The drive circuit according to claim 1, wherein the exciter module (20) is implemented in a 2-level topology.The drive circuit according to claim 1, wherein the exciter module (20) is implemented in a 3-level topology.Externally excited electric machine, comprising: an electric motor (E) which has at least one stator winding (W1, W, W3) and at least one rotor winding (L); a drive circuit according to one of Claims 1 to 3, wherein the power electronics module (10) of the drive circuit is coupled to the at least one stator winding (W1, W2, W3) and the exciter module (20) is coupled to the at least one rotor winding (L).The externally excited electric machine of claim 4, further comprising: an inverter; wherein the drive circuit is integrated into the inverter.

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