A device for operating an externally excited synchronous motor and motor arrangement

Abstract

The present disclosure relates to a device for operating an externally excited synchronous motor (EESM). The device comprises one or more exciters each being configured to provide a direct current and direct voltage of a first polarity and a direct current and direct voltage of a second polarity to a respective field winding of a rotor of the EESM. Each of the one or more exciters is configured to control the direction of magnetic flux generated by the respective field winding by providing the direct current and direct voltage of the first polarity or the direct current and direct voltage of the second polarity to the respective field winding. Further a motor arrangement is disclosed, the motor arrangement comprising such a device and an EESM.

Description

[0001] A DEVICE FOR OPERATING AN EXTERNALLY EXCITED SYNCHRONOUS MOTOR AND MOTOR ARRANGEMENT

[0002] TECHNICAL FIELD

[0003] The present disclosure relates to a device for operating an externally excited synchronous motor (EESM), and to a motor arrangement comprising such a device and an EESM.

[0004] BACKGROUND

[0005] Externally excited synchronous motors (EESMs) are electrical motors which comprise a winding, so-called field winding, to produce the magnetic flux in the airgap of the EESM. The field winding plays the role of the permanent magnets in permanent magnets synchronous motors (PMSMs).

[0006] SUMMARY

[0007] In PMSMs and conventional EESMs, the number of poles at the rotor is fixed by the field winding configuration and the arrangement of the magnets. Thus, a pole-phase reconfiguration is not possible at least in a simple manner. The phase represents the number of independent coils for a fixed stator of a motor. For example, a three-phase motor is a motor comprising three independent coils at an interval of 120 degrees.

[0008] A pole-phase reconfiguration allows improving an EESM in terms of at least one of the following: efficiency, power density, flexibility, operation, reliability, and robustness.

[0009] In view of the above, this disclosure aims to provide a device for operating an EESM; that allows providing an EESM, which is improved in terms of at least one of efficiency, power density, flexibility, operation, reliability, and robustness. An objective of this disclosure is to provide a device for operating an EESM that allows a pole-phase reconfiguration at the EESM. This disclosure aims to provide a motor arrangement comprising an EESM that is improved in terms of at least one of efficiency, power density, flexibility, operation, reliability, and robustness. An objective of this disclosure is to provide a motor arrangement comprising an EESM, wherein a pole-phase reconfiguration of the EESM is possible. These and other objectives are achieved by the solution of this disclosure as described in the independent claims. Advantageous implementations are further defined in the dependent claims.

[0010] A first aspect of this disclosure provides a device for operating an externally excited synchronous motor (EESM). The device comprises one or more exciters each being configured to provide a direct current and direct voltage of a first polarity and a direct current and direct voltage of a second polarity to a respective field winding of a rotor of the EESM. Each of the one or more exciters is configured to control the direction of magnetic flux generated by the respective field winding by providing the direct current and direct voltage of the first polarity or the direct current and direct voltage of the second polarity to the respective field winding.

[0011] In other words, the one or more exciters are configured to operate in at least two quadrants by being configured to provide a direct current and direct voltage of a first polarity and a direct current and direct voltage of a second polarity to a respective field winding of a rotor of the EESM. The direct current and direct voltage of the first polarity may be for example a positive current and positive voltage, respectively. Accordingly, the direct current and direct voltage of the second polarity may be a negative current and negative voltage, respectively. This may be vice versa.

[0012] Thus, each exciter of the one or more exciters may be configured to provide to a different field winding of the rotor of the EESM the direct current and direct voltage of the first polarity and the direct current and direct voltage of the second polarity. When an exciter of the one or more exciters provides a direct current and direct voltage (of the first polarity or the second polarity) to the respective field winding of the rotor of the EESM, a magnetic flux is generated by the respective field winding. The direction of the generated magnetic flux depends on the polarity of the direct current and direct voltage provided to the respective field winding. Therefore, the exciter may control the direction of magnetic flux generated by the respective field winding by providing the direct current and direct voltage of the first polarity or the direct current and direct voltage of the second polarity to the respective field winding. Thus, each exciter of the one or more exciters may be configured to change the direction of magnetic flux generated by the respective field winding by changing the polarity of the of the direct current and direct voltage provided by the exciter to the respective field winding. Controlling the direction magnetic flux generated by the respective field winding of the rotor of the EESM allows controlling, e.g. changing, one or more poles (negative pole or positive pole) at the rotor and, thus, controlling the number of pair of poles at the rotor. A pole at the rotor represents either the positive or negative direction of the magnetic field at the rotor. A pair of poles may be also referred to as pole pair.

[0013] Therefore, the device according to the first aspect allows a pole-phase reconfiguration at the EESM. Thus, the device according to the first aspect allows providing an EESM that is improved in terms of at least one of efficiency, power density, flexibility, operation, reliability, and robustness.

[0014] In an implementation form of the first aspect, each of the one or more exciters is configured to provide the direct current and direct voltage of the first polarity and the direct current and direct voltage of the second polarity to the respective field winding via one or more non-isolated conductive means. The one or more non-isolated conductive means may be for example one or more slip rings.

[0015] In an implementation form of the first aspect, each of the one or more exciters comprises a first series connection of two unidirectional switching elements, and a second series connection of two unidirectional switching elements. The first series connection and second series connection may be electrically connected in parallel to each other.

[0016] Herein, the term “electrically connect” may be abbreviated by the term “connect”. A unidirectional switching element is configured to control current flow only in one direction. Each unidirectional switching element of the first series connection and second series connection of two unidirectional switching elements may comprise or be a controlled semiconductor switch, such as a transistor. The term “controlled semiconductor switch” may refer to a semiconductor switch comprising a control terminal, such as a transistor. Each unidirectional switching element of the first series connection and second series connection of two unidirectional switching elements may comprise or be a transistor. Herein, a transistor may be an insulated-gate bipolar transistor (IGBT), a field-effect transistor (FET), a metal-oxide-semiconductor field-effect transistor (MOSFET), a bipolar junction transistor (BJTs), a junction gate field-effect transistor (JFETs), a high-electron-mobility transistor (HEMT) etc. An example of a HEMT is a gallium nitride HEMT (GaN HEMT). For example, each unidirectional switching element of the first series connection and second series connection of two unidirectional switching elements may comprise or be a MOSFET optionally with a diode connected in parallel, an IGBT optionally with a diode connected in parallel, or a gallium nitride transistor (GaN transistor) such as a GaN HEMT. The GaN transistor may optionally be a GaN MOSFET. Optionally, at least one of the unidirectional switching elements of the first series connection and second series connection of two unidirectional switching elements may be different to the other unidirectional switching element(s).

[0017] In an implementation form of the first aspect, each of the one or more exciters comprises two terminals for providing the direct current and direct voltage of the first polarity or direct current and direct voltage of the second polarity depending on the switching states of the unidirectional switching elements. A first terminal of the two terminals may be electrically connected to a node between the two unidirectional switching elements of the first series connection of two unidirectional switching elements. A second terminal of the two terminals may be electrically connected to a node between the two unidirectional switching elements of the second series connection of two unidirectional switching elements.

[0018] In an implementation form of the first aspect, at least one exciter of the one or more exciters comprises a circuit comprising an inductor and / or a capacitor. The first terminal of the two terminals of the at least one exciter may be electrically connected via the circuit to the node between the two unidirectional switching elements of the first series connection of two unidirectional switching elements of the at least one exciter. The second terminal of the two terminals of the at least one exciter may be electrically connected via the circuit to the node between the two unidirectional switching elements of the second series connection of two unidirectional switching elements of the at least one exciter.

[0019] That is, the first terminal of the two terminals may be directly connected or connected via the aforementioned circuit to the node between the two unidirectional switching elements of the first series connection of two unidirectional switching elements. The second terminal of the two terminals may be directly connected or connected via the aforementioned circuit to the node between the two unidirectional switching elements of the second series connection of two unidirectional switching elements. Optionally, each of the one or more exciters comprises a circuit comprising an inductor and / or a capacitor. The first terminal of the two terminals is electrically connected via the circuit to the node between the two unidirectional switching elements of the first series connection of two unidirectional switching elements. The second terminal of the two terminals is electrically connected via the circuit to the node between the two unidirectional switching elements of the second series connection of two unidirectional switching elements.

[0020] For example, the circuit may comprise an inductor and a capacitor. The inductor and capacitor may be configured to aid operation of the exciter. The inductor and capacitor may be configured to serve as a filter. Optionally, the circuit may comprise an inductor and a capacitor, wherein the inductor may be connected between the first terminal of the two terminals of a respective exciter and the node between the two unidirectional switching elements of the first series connection of two unidirectional switching elements of the respective exciter, and the capacitor may be electrically connected between the node between the two unidirectional switching elements of the first series connection of two unidirectional switching elements of the respective exciter and the node between the two unidirectional switching elements of the second series connection of two unidirectional switching elements of the respective exciter. This may result in a buck-converter configuration of the respective exciter.

[0021] In an implementation form of the first aspect, each of the one or more exciters comprises a galvanic isolated barrier and is configured to provide the direct current and direct voltage of the first polarity and the direct current and direct voltage of the second polarity via the galvanic isolated barrier to the respective field winding of the rotor.

[0022] In an implementation form of the first aspect, the galvanic isolated barrier of each exciter of the one or more exciters divides the respective exciter in a primary side and a secondary side that is galvanically isolated from the primary side. The secondary side of the respective exciter of the one or more exciters may be configured to be arranged on the rotor of the EESM.

[0023] In an implementation form of the first aspect, the first series connection of two unidirectional switching elements and the second series connection of two unidirectional switching elements of the respective exciter of the one or more exciters are arranged on the primary side of the respective exciter of the one or more exciters. In an implementation form of the first aspect, each of the one or more exciters comprises a wireless power coupler with a primary winding and a secondary winding, a first series connection of two bidirectional switching elements, a second series connection of two bidirectional switching elements, and two terminals for providing the direct current and direct voltage of the first polarity or direct current and direct voltage of the second polarity depending on the switching states of the bidirectional switching elements. The first series connection of two bidirectional switching elements and second series connection of two bidirectional switching elements may be electrically connected in parallel to each other. The primary winding of the wireless power coupler may be electrically connected between a node between the two unidirectional switching elements of the first series connection of two unidirectional switching elements and a node between the two unidirectional switching elements of the second series connection of two unidirectional switching elements. The secondary winding of the wireless power coupler may be electrically connected between a node between the two bidirectional switching elements of the first series connection of two bidirectional switching elements and a node between the two bidirectional switching elements of the second series connection of two bidirectional switching elements. A first terminal of the two terminals may be electrically connected to a first end of the first and second series connection of two bidirectional switching elements. A second terminal of the two terminals may be electrically connected to a second end of the first and second series connection of two bidirectional switching elements.

[0024] The wireless power coupler may be for example a transformer, such as a rotational transformer.

[0025] A bidirectional switching element is configured to control current flow in two directions. A bidirectional switching element may be formed by a bidirectional switch or by two unidirectional switching elements electrically connected in series. A bidirectional switch may be a bidirectional transistor, such as a monolithically-integrated bidirectional GaN transistor. Each bidirectional switching element of the first series connection and second series connection of two bidirectional switching elements may comprise or be one or more controlled semiconductor switches, such as one or more transistors. Each bidirectional switching element of the first series connection and second series connection of two bidirectional switching elements may comprise or be one or more transistors. For example, each bidirectional switching element of the first series connection and second series connection of two bidirectional switching elements may comprise or be a bidirectional transistor, such as a monolithically-integrated bidirectional GaN transistor. For example, each bidirectional switching element of the first series connection and second series connection of two bidirectional switching elements may comprise or be a series connection of two MOSFETs optionally with a diode connected in parallel to each MOSFET, a series connection of two IGBTs optionally with a diode connected in parallel to each IGBT, or a series connection of two GaN transistors such as two GaN HEMTs. The series connection of two GaN transistors may optionally be a series connection of two GaN MOSFETs. Optionally, at least one of the bidirectional switching elements of the first series connection and second series connection of two bidirectional switching elements may be different to the other bidirectional switching element(s).

[0026] In an implementation form of the first aspect, at least one exciter of the one or more exciters comprises an inductor and / or a capacitor. The primary winding of the wireless power coupler of the at least one exciter may be electrically connected via the inductor and / or capacitor to the node between the two unidirectional switching elements of the first or second series connection of two unidirectional switching elements of the at least one exciter.

[0027] That is, the primary winding of the wireless power coupler of the at least one exciter may be directly connected or connected via the inductor and / or capacitor to the node between the two unidirectional switching elements of the first or second series connection of two unidirectional switching elements of the at least one exciter.

[0028] Optionally, each of the one or more exciters comprises an inductor and / or a capacitor, and the primary winding of the wireless power coupler is electrically connected via the inductor and / or capacitor to the node between the two unidirectional switching elements of the first or second series connection of two unidirectional switching elements.

[0029] For example, the respective exciter may comprise the inductor without the capacitor. This may result in a DAB-based exciter. DAB-based exciter stands for “dual active bridge based exciter”. Optionally, the respective exciter may comprise a series connection of the inductor and capacitor, wherein the primary winding of the wireless power coupler of the respective exciter is electrically connected via the series connection of the inductor and capacitor to the node between the two unidirectional switching elements of the first or second series connection of two unidirectional switching elements of the respective exciter. This may result in a resonant converter configuration of the respective exciter. In an implementation form of the first aspect, at least one exciter of the one or more exciters comprises an inductor and / or a capacitor. The secondary winding of the wireless power coupler of the at least one exciter may be electrically connected via the inductor and / or capacitor to the node between the two bidirectional switching elements of the first or second series connection of two bidirectional switching elements of the at least one exciter.

[0030] That is, the secondary winding of the wireless power coupler of the at least one exciter may be directly connected or connected via the inductor and / or capacitor to the node between the two bidirectional switching elements of the first or second series connection of two bidirectional switching elements of the at least one exciter.

[0031] Optionally, each of the one or more exciters comprises an inductor and / or a capacitor, and the secondary winding of the wireless power coupler is electrically connected via the inductor and / or capacitor to the node between the two bidirectional switching elements of the first or second series connection of two bidirectional switching elements.

[0032] For example, the respective exciter may comprise the inductor without the capacitor. This may result in a DAB-based exciter. Optionally, the respective exciter may comprise a series connection of the inductor and capacitor, wherein the secondary winding of the wireless power coupler of the respective exciter is electrically connected via the series connection of the inductor and capacitor to the node between the two bidirectional switching elements of the first or second series connection of two bidirectional switching elements of the respective exciter. This may result in a resonant converter configuration of the respective exciter.

[0033] In an implementation form of the first aspect, the secondary winding of the wireless power coupler, the first series connection of two bidirectional switching elements, the second series connection of two bidirectional switching elements, and the two terminals of each exciter of the one or more exciters are configured to be arranged on the rotor of the EESM.

[0034] In an implementation form of the first aspect, the device comprises a further exciter that is configured to provide a direct current and direct voltage of the first polarity to a respective field winding of the rotor of the EESM. In other words, the further exciter is configured to operate in one quadrant by being configured to provide a direct current and direct voltage of the first polarity to a respective field winding of the rotor of the EESM. The term “second type exciter” may be used for referring to the further exciter. The term “first type exciter” may be used for referring to the one or more exciters each being configured to provide a direct current and direct voltage of the first polarity and a direct current and direct voltage of the second polarity to a respective field winding of a rotor of the EESM.

[0035] In an implementation form of the first aspect, the further exciter is configured to provide the direct current and direct voltage of the first polarity to the respective field winding via one or more non-isolated conductive means. The one or more non-isolated conductive means may be for example one or more slip rings.

[0036] In an implementation form of the first aspect, the further exciter comprises a series connection of two unidirectional switching elements.

[0037] In an implementation form of the first aspect, the further exciter comprises two terminals for providing the direct current and direct voltage of the first polarity depending on the switching states of the unidirectional switching elements. A first terminal of the two terminals may be electrically connected to a node between the two unidirectional switching elements of the series connection of two unidirectional switching elements. A second terminal of the two terminals may be electrically connected to an end of the series connection of two unidirectional switching elements.

[0038] Each unidirectional switching element of the series connection of two unidirectional switching elements may comprise or be a controlled semiconductor switch, such as a transistor. Each unidirectional switching element of the series connection of two unidirectional switching elements may comprise or be a transistor. For example, each unidirectional switching element of the series connection of two unidirectional switching elements may comprise or be a MOSFET optionally with a diode connected in parallel, an IGBT optionally with a diode connected in parallel, or a GaN transistor such as a GaN HEMT. The GaN transistor may optionally be a GaN MOSFET. Optionally, the unidirectional switching element connected to the first terminal and second terminal may comprise or be an uncontrolled semiconductor switch, such as a diode. Herein, a unidirectional switching element may comprise or be a diode (may be referred to as p-n semiconductor diode), a pin diode, a Schottky diode, an intrinsic body diode of a respective device / transistor etc. For example, the unidirectional switching element connected to the first terminal and second terminal may comprise or be a diode. The cathode of the diode may be connected to the first terminal and the anode of the diode may be connected to the second terminal. The other unidirectional switching element of the series connection of two unidirectional switching elements may comprise or be a transistor, for example a MOSFET optionally with a diode connected in parallel, or an IGBT optionally with a diode connected in parallel.

[0039] In an implementation form of the first aspect, the further exciter comprises a circuit comprising an inductor and / or a capacitor. The first terminal of the two terminals may be electrically connected via the circuit to the node between the two unidirectional switching elements of the series connection of two unidirectional switching elements. The second terminal of the two terminals may be electrically connected via the circuit to the end of the series connection of two unidirectional switching elements.

[0040] That is, the first terminal of the two terminals may be directly connected or connected via the aforementioned circuit to the node between the two unidirectional switching elements of the series connection of two unidirectional switching elements. The second terminal of the two terminals may be directly connected or connected via the aforementioned circuit to the end of the series connection of two unidirectional switching elements.

[0041] For example, the circuit may comprise an inductor and a capacitor. The inductor and capacitor may be configured to aid operation of the further exciter. The inductor and capacitor may be configured to serve as a filter. Optionally, the circuit may comprise an inductor and a capacitor, wherein the inductor may be connected between the first terminal of the two terminals and the node between the two unidirectional switching elements of the series connection of two unidirectional switching elements, and the capacitor may be electrically connected between the node between the two unidirectional switching elements of the series connection of two unidirectional switching elements and the end of the series connection of two unidirectional switching elements. This may result in a buck-converter configuration of the further exciter.

[0042] In an implementation form of the first aspect, the further exciter comprises a galvanic isolated barrier and is configured to provide the direct current and direct voltage of the first polarity via the galvanic isolated barrier to the respective field winding of the rotor. In an implementation form of the first aspect, the galvanic isolated barrier of the further exciter divides the further exciter in a primary side and a secondary side that is galvanically isolated from the primary side, and the secondary side of the further exciter is configured to be arranged on the rotor of the EESM.

[0043] In an implementation form of the first aspect, the series connection of two unidirectional switching elements is arranged on the primary side of the further exciter.

[0044] In an implementation form of the first aspect, the further exciter comprises a wireless power coupler with a primary winding and a secondary winding, a second series connection of two unidirectional switching elements, a third series connection of two unidirectional switching elements, a fourth series connection of two unidirectional switching elements, and two terminals for providing the direct current and direct voltage of the first polarity depending on the switching states of the unidirectional switching elements. The series connection of two unidirectional switching elements and the second series connection of two unidirectional switching elements may be electrically connected in parallel to each other. The third series connection of two unidirectional switching elements and fourth series connection of two unidirectional switching elements may be electrically connected in parallel to each other. The primary winding of the wireless power coupler may be electrically connected between a node between the two unidirectional switching elements of the series connection of two unidirectional switching elements and a node between the two unidirectional switching elements of the second series connection of two unidirectional switching elements. The secondary winding of the wireless power coupler may be electrically connected between a node between the two unidirectional switching elements of the third series connection of two unidirectional switching elements and a node between the two unidirectional switching elements of the fourth series connection of two unidirectional switching elements. A first terminal of the two terminals may be electrically connected to a first end of the third and fourth series connection of two unidirectional switching elements. A second terminal of the two terminals may be electrically connected to a second end of the third and fourth series connection of two unidirectional switching elements.

[0045] The wireless power coupler may be for example a transformer, such as a rotational transformer. The series connection of two unidirectional switching elements may be referred to as “first series connection of two unidirectional switching elements”. Each unidirectional switching element of the series connection and second series connection of two unidirectional switching elements may comprise or be a controlled semiconductor switch, such as a transistor. Each unidirectional switching element of the series connection and second series connection of two unidirectional switching elements may comprise or be a transistor. For example, each unidirectional switching element of the series connection and second series connection of two unidirectional switching elements may comprise or be a MOSFET optionally with a diode connected in parallel, an IGBT optionally with a diode connected in parallel, or a GaN transistor such as a GaN HEMT. The GaN transistor may optionally be a GaN MOSFET. Optionally, at least one of the unidirectional switching elements of the series connection and second series connection of two unidirectional switching elements may be different to the other unidirectional switching element(s).

[0046] Each unidirectional switching element of the third series connection and fourth series connection of two unidirectional switching elements may comprise or be a controlled semiconductor switch, such as a transistor, or a uncontrolled semiconductor switch, such as a diode. Optionally, each unidirectional switching element of the third series connection and fourth series connection of two unidirectional switching elements may comprise or be a transistor. For example, each unidirectional switching element of the third series connection and fourth series connection of two unidirectional switching elements may comprise or be a MOSFET optionally with a diode connected in parallel, an IGBT optionally with a diode connected in parallel, or a GaN transistor such as a GaN HEMT. The GaN transistor may optionally be a GaN MOSFET. Optionally, each unidirectional switching element of the third series connection and fourth series connection of two unidirectional switching elements may comprise or be a diode. Optionally, at least one of the unidirectional switching elements of the third series connection and fourth series connection of two unidirectional switching elements may be different to the other unidirectional switching element(s).

[0047] In an implementation form of the first aspect, the further exciter comprises an inductor and / or a capacitor. The primary winding of the wireless power coupler may be electrically connected via the inductor and / or capacitor to the node between the two unidirectional switching elements of the series connection of two unidirectional switching elements or of the second series connection of two unidirectional switching elements. That is, the primary winding of the wireless power coupler may be directly connected or connected via the inductor and / or capacitor to the node between the two unidirectional switching elements of the series connection of two unidirectional switching elements or of the second series connection of two unidirectional switching elements.

[0048] For example, the further exciter may comprise the inductor without the capacitor. This may result in a DAB-based exciter. Optionally, the further exciter may comprise a series connection of the inductor and capacitor, wherein the primary winding of the wireless power coupler is electrically connected via the series connection of the inductor and capacitor to the node between the two unidirectional switching elements of the series connection of two unidirectional switching elements or of the second series connection of two unidirectional switching elements. This may result in a resonant converter configuration of the further exciter.

[0049] In an implementation form of the first aspect, the further exciter comprises an inductor and / or a capacitor. The secondary winding of the wireless power coupler may be electrically connected via the inductor and / or capacitor to the node between the two unidirectional switching elements of the third or fourth series connection of two unidirectional switching elements.

[0050] That is, the secondary winding of the wireless power coupler may be directly connected or connected via the inductor and / or capacitor to the node between the two unidirectional switching elements of the third or fourth series connection of two unidirectional switching elements.

[0051] For example, the further exciter may comprise the inductor without the capacitor. This may result in a DAB-based exciter. Optionally, the further exciter may comprise a series connection of the inductor and capacitor, wherein the secondary winding of the wireless power coupler is electrically connected via the series connection of the inductor and capacitor to the node between the two unidirectional switching elements of the third or fourth series connection of two unidirectional switching elements. This may result in a resonant converter configuration of the further exciter.

[0052] In an implementation form of the first aspect, the secondary winding of the wireless power coupler, the third series connection of two unidirectional switching elements, the fourth series connection of two unidirectional switching elements, and the two terminals of the further exciter are configured to be arranged on the rotor of the EESM. In an implementation form of the first aspect, the device comprises one exciter and the further exciter. The device may be configured to operate the EESM having a rotor with two field windings arranged on four physical poles, eight physical poles or twelve physical poles of the rotor such that: each of the exciter and the further exciter provides a direct current and direct voltage of the first polarity to a respective field winding of the two field windings to generate two pairs of poles, four pairs of poles or six pairs of poles, respectively, at the rotor; and the further exciter provides a direct current and direct voltage of the first polarity to a respective field winding of the two field windings and the exciter provides a direct current and direct voltage of the second polarity to a respective field winding of the two field windings to generate one pair of poles, two pairs of poles or three pairs of poles, respectively, at the rotor.

[0053] Thus, the device allows to change the number of pairs of poles by controlling the exciter to provide a direct current and direct voltage of the first polarity or a direct current and direct voltage of the second polarity. For example, in case of the rotor with two field windings having four physical poles, the device may control the rotor to have two pairs of poles by controlling the exciter to provide a direct current and direct voltage of the first polarity. That is, the exciter and the further exciter provide a direct current and direct voltage of the same polarity. In the aforementioned case, the device may control the rotor to have one pair of poles by controlling the exciter to provide a direct current and direct voltage of the second polarity. That is, the exciter and the further exciter provide a direct current and direct voltage of different polarity.

[0054] In case the rotor has two field windings and eight physical poles, the device may control the rotor to have four pairs of poles (by controlling the exciter to provide a direct current and direct voltage of the first polarity) or two pairs of poles (by controlling the exciter to provide a direct current and direct voltage of the second polarity). In case the rotor has two field windings and twelve physical poles, the device may control the rotor to have six pairs of poles (by controlling the exciter to provide a direct current and direct voltage of the first polarity) or three pairs of poles (by controlling the exciter to provide a direct current and direct voltage of the second polarity). The exciter of the device allows control of the direction of magnetic flux generated by the respective field winding. This control of the respective field winding permits the number of poles at the rotor to be reconfigured.

[0055] Therefore, the device allows a pole-phase reconfiguration at the EESM. Thus, the device allows providing an EESM that is improved in terms of at least one of efficiency, power density, flexibility, operation, reliability, and robustness.

[0056] The EESM may comprise a stator with n coils (e.g. n terminals). The term “n” is an integer greater than or equal to two. The device may comprise an inverter with n legs, wherein each leg of the n legs may provide an alternating current and alternating voltage with a phase angle of 360° / n or 27t / n to a respective coil of the stator of the EESM. The term “multi-leg inverter” may be used for referring to the inverter. The EESM may comprise m phases. That is, the stator of the EESM may comprise m independent coils. The term “m” is an integer greater than or equal to two. Optionally, the number n of coils of the stator may equal the number m of independent coils of the stator. That is, each coil of the stator of the EESM may be an independent coil. In this case the EESM comprises m = n phases. Optionally, the number m of independent coils of the stator of the EESM may be smaller than the number n of coils of the stator of the EESM. This case may be due to the operation of the EESM by the device, e.g. by the inverter of the device. For example, the stator of the EESM may be assumed to have six coils (e.g. n = 6). In case the inverter provides an alternating current and voltage with a phase angle of 60° (360° / 6) to each coil of the six coils of the stator, the six coils are six independent coils and, thus, the EESM comprises six phases. That is, the EESM may be configured as a six-phase-motor due to the operation of the EESM by the device. In case the inverter provides an alternating current and voltage with a phase angle of 120° (360° / 3) to each of a first pair of coils, a second pair of coils and a third pair of coils of the six coils of the stator, the six coils merely represent three independent coils. Namely, a respective pair of coils of the six coils represents the independent coils. That is, the EESM may be configured as a three-phase-motor due to the operation of the EESM by the device.

[0057] For example, when the rotor of the EESM has two field windings and the device comprises one exciter and the further exciter, then the device may comprise an inverter with six legs (e.g. n = 6), the stator of the EESM may comprise six coils, and the EESM may comprise at maximum six phases (e.g. m = n = 6). For example, the device may be configured to operate the EESM such that the inverter provides an alternating current and voltage to a first pair of coils, a second pair of coils and a third pair of coils of the six coils of the stator, wherein the alternating current and voltage between the first pair, second pair and third pair of coils has a phase angle of 120° (e.g. 360° / 3), when each of the exciter and the further exciter provides a direct current and direct voltage of the first polarity to a respective field winding of the two field windings of the rotor of the EESM. In this case, the EESM is operated by the device as a three-phase-motor. The device may be configured to operate the EESM such that the inverter provides an alternating current and voltage to each coil of the six coils of the stator, wherein the alternating current and voltage between the six coils has a phase angle of 60° (e.g. 360° / 6), when the exciter provides a direct current and direct voltage of the second polarity to a respective field winding of the two field windings of the rotor of the EESM. In this case, the EESM is operated by the device as a six-phase-motor.

[0058] In an implementation form of the first aspect, the device comprises three exciters and the further exciter. The device may be configured to operate the EESM having a rotor with four field windings arranged on eight physical poles or twelve physical poles of the rotor such that: each of the three exciters and the further exciter provides a direct current and direct voltage of the first polarity to a respective field winding of the four field windings to generate four pairs of poles or six pairs of poles, respectively, at the rotor; and the more of the three exciters provide a direct current and direct voltage of the second polarity to a respective field winding of the four field windings the less pairs of poles are generated at the rotor.

[0059] For example, when the rotor of the EESM has four field windings arranged on eight physical poles and the device comprises three exciters and the further exciter, then the device may comprise an inverter with twelve legs (e.g. n = 12), the stator of the EESM may comprise twelve coils and the EESM may comprise at maximum twelve phases (e.g. m = n = 12). In the aforementioned case, the device may be configured to operate the EESM such that the inverter provides an alternating current and voltage to a first group of four coils, a second group of four coils and a third group of four coils of the stator, wherein the alternating current and voltage between the first group, second group and third group of coils has a phase angle of 120° (e.g. 360° / 3), when each of the three exciters and the further exciter provides a direct current and direct voltage of the first polarity to a respective field winding of the four field windings of the rotor of the EESM. In the aforementioned case, the EESM is operated by the device as a three- phase-motor. The device may be configured to operate the EESM such that the more of the three exciters provide a direct current and direct voltage of the second polarity to a respective field winding of the four field windings, the smaller the phase angle of an alternating current and voltage between respective independent coils of the stator provided by the inverter and the greater the number of phases of the EESM.

[0060] For example, when the rotor of the EESM has four field windings arranged on twelve physical poles and the device comprises three exciters and the further exciter, then the device may comprise an inverter with nine legs (e.g. n = 9), the EESM may comprise nine coils and the EESM may comprise at maximum nine phases (e.g. m = n = 9). In the aforementioned case, the device may be configured to operate the EESM such that the inverter provides an alternating current and voltage to a first group of three coils, a second group of three coils and a third group of three coils of the stator, wherein the alternating current and voltage between the first group, second group and third group of coils has a phase angle of 120° (e.g. 360° / 3), when each of the three exciters and the further exciter provides a direct current and direct voltage of the first polarity to a respective field winding of the four field windings of the rotor of the EESM. In this case, the EESM is operated by the device as a three-phase-motor The device may be configured to operate the EESM such that the more of the three exciters provide a direct current and direct voltage of the second polarity to a respective field winding of the four field windings, the smaller the phase angle of an alternating current and voltage between respective independent coils of the stator provided by the inverter and the greater the number of phases of the EESM.

[0061] In an implementation form of the first aspect, the device comprises five exciters and the further exciter. The device may be configured to operate the EESM having a rotor with six field windings arranged on twelve physical poles of the rotor such that: each of the five exciters and the further exciter provides a direct current and direct voltage of the first polarity to a respective field winding of the six field windings to generate six pairs of poles at the rotor; each of three exciters of the five exciters and the further exciter provides a direct current and direct voltage of the first polarity to a respective field winding of the six field windings and each of two exciters of the five exciters provides a direct current and direct voltage of the second polarity to a respective field winding of the six field windings to generate three or two pairs of poles at the rotor; and each of two exciters of the five exciters and the further exciter provides a direct current and direct voltage of the first polarity to a respective field winding of the six field windings and each of three exciters of the five exciters provides a direct current and direct voltage of the second polarity to a respective field winding of the six field windings to generate one pair of poles at the rotor.

[0062] For example, when the rotor of the EESM has six field windings and the device comprises five exciters and the further exciter, then the device may comprise an inverter with eighteen legs (e.g. n = 18), the stator of the EESM may comprise eighteen coils and the EESM may comprise at maximum eighteen phases (e.g. m = 18).

[0063] The device may be configured to operate the EESM such that the inverter provides an alternating current and voltage to a first group of six coils, a second group of six coils and a third group of six coils of the eighteen coils of the stator, wherein the alternating current and voltage between the first group, second group and third group of coils has a phase angle of 120° (e.g. 360° / 3), when each of the five exciters and the further exciter provides a direct current and direct voltage of the first polarity to a respective field winding of the six field windings of the rotor of the EESM. This operation allows generating six pairs of poles at the rotor. In this case, the EESM is operated by the device as a three-phase-motor.

[0064] The device may be configured to operate the EESM such that the inverter provides an alternating current and voltage to a first group of three coils, a second group of three coils, a third group of three coils, a fourth group of three coils, a fifth group of three coils, and a sixth group of three coils of the eighteen coils of the stator, wherein the alternating current and voltage between the first group, second group, third group, fourth group, fifth group and sixth group of coils has a phase angle of 60° (e.g. 36076), when each of three exciters of the five exciters and the further exciter provides a direct current and direct voltage of the first polarity and each of two exciters of the five exciters provides a direct current and direct voltage of the second polarity. This operation allows generating three pairs of poles at the rotor. In this case, the EESM is operated by the device as a six-phase-motor.

[0065] The device may be configured to operate the EESM such that the inverter provides an alternating current and voltage to a first group of two coils, a second group of two coils, a third group of two coils, a fourth group of two coils, a fifth group of two coils, a sixth group of two coils, a seventh group of two coils, a eighth group of two coils, and a ninth group of two coils of the eighteen coils of the stator, wherein the alternating current and voltage between the first group, second group, third group, fourth group, fifth group, sixth group, seventh group, eighth group, and ninth group of coils has a phase angle of 40° (e.g. 360° / 9), when each of three exciters of the five exciters and the further exciter provides a direct current and direct voltage of the first polarity and each of two exciters of the five exciters provides a direct current and direct voltage of the second polarity. This operation allows generating two pairs of poles at the rotor. In this case, the EESM is operated by the device as a nine-phase-motor.

[0066] The device may be configured to operate the EESM such that the inverter provides an alternating current and voltage to each coil of the eighteen coils of the stator, wherein the alternating current and voltage between the eighteen coils has a phase angle of 20° (e.g. 360° / 18), when each of two exciters of the five exciters and the further exciter provides a direct current and direct voltage of the first polarity and each of three exciters of the five exciters provides a direct current and direct voltage of the second polarity. This operation allows generating one pair of poles at the rotor. In this case, the EESM is operated by the device as an eighteen-phase-motor.

[0067] In an implementation form of the first aspect, each of the one or more exciters is configured to provide the direct current and direct voltage of the first polarity and the direct current and direct voltage of the second polarity to a respective field winding of a rotor of one or more further EESMs. Each of the one or more exciters may be configured to control the direction of magnetic flux generated by the respective field winding of the rotor of the one or more further EESMs by providing the direct current and direct voltage of the first polarity or the direct current and direct voltage of the second polarity to the respective field winding of the rotor of the one or more further EESMs.

[0068] In other words, the device may be configured to operate two or more EESMs. That is, two or more EESMs may be operated using the device and, thus, the same one or more exciters and optionally the same further exciter. Each EESMs of the two or more EESMs has its own filed windings on its rotor. The excitation circuit may be the same for feeding the field windings of the two or more EESMs.

[0069] The further exciter of the device may be configured to provide a direct current and direct voltage of the first polarity to a respective field winding of the rotor of the one or more further EESMs. The device may comprise a control unit and / or may be configured to be electrically connected to a control unit, wherein the control unit is configured to control operation of the device, e.g. control the one or more exciters and the optional further exciter of the device.

[0070] The control unit may comprise or be at least one of a controller, microcontroller, processor, microprocessor, application specific integrated circuit (ASIC) and field programmable gate array (FPGA). In addition or alternatively, the control unit may comprise or be any other known control means.

[0071] For example, the device may be used in an electrical vehicle, e.g. in the framework of a traction powertrain for electrical vehicles. That is, the device may be used in electric drives systems such as the one used in automotive powertrains.

[0072] In order to achieve the device according to the first aspect of the disclosure, some or all of the implementation forms and optional features of the first aspect, as described above, may be combined with each other.

[0073] A second aspect of this disclosure provides a motor arrangement. The motor arrangement comprises the device according the first aspect, and an externally excited synchronous motor (EESM). The EESM comprises a rotor with two or more field windings. The device is configured to operate the EESM by providing a direct current and direct voltage of the first polarity or a direct current and direct voltage of the second polarity to at least one of the two or more field windings of the rotor.

[0074] The EESM may comprise a stator. The stator may comprise m independent coils. The term “m” is an integer greater than or equal to two.

[0075] In an implementation form of the second aspect, the rotor of the EESM comprises four, eight or twelve physical poles. The rotor of the EESM may comprise any number of physical poles. That is, the EESM is not limited to a specific number of physical poles.

[0076] The above description of the device according to the first aspect is correspondingly valid for the motor arrangement of the second aspect. That is, the description with regard to the device of the first aspect is correspondingly valid for the device and the EESM of the motor arrangement. The description of the motor arrangement of the second aspect is correspondingly valid for the device of the first aspect.

[0077] For example, the motor arrangement may be used in an electrical vehicle, e.g. in the framework of a traction powertrain for electrical vehicles. That is, the motor arrangement may be used in electric drives systems such as the one used in automotive powertrains.

[0078] The motor arrangement of the second aspect and its implementation forms and optional features achieve the same advantages as the device of the first aspect and its respective implementation forms and respective optional features.

[0079] In order to achieve the motor arrangement according to the second aspect of the disclosure, some or all of the implementation forms and optional features of the second aspect, as described above, may be combined with each other.

[0080] It has to be noted that all devices, elements, units and means described in the present application could be implemented in software or hardware elements or any kind of combination thereof. All steps which are performed by the various entities described in the present application as well as the functionalities described to be performed by the various entities are intended to mean that the respective entity is adapted to or configured to perform the respective steps and functionalities. Even if, in the following description of specific embodiments, a specific functionality or step to be performed by external entities is not reflected in the description of a specific detailed element of that entity which performs that specific step or functionality, it should be clear for a skilled person that these methods and functionalities can be implemented in respective software or hardware elements, or any kind of combination thereof.

[0081] BRIEF DESCRIPTION OF DRAWINGS

[0082] The above described aspects and implementation forms will be explained in the following description of specific embodiments in relation to the enclosed drawings, in which:

[0083] Fig. 1 shows an example of a device according to an embodiment of this disclosure for operating an externally excited synchronous motor (EESM). FIG. 2 shows an example of a motor arrangement according to an embodiment of this disclosure.

[0084] FIG. 3 shows an example of an implementation form of an exciter of a device according to an embodiment of this disclosure for operating an externally excited synchronous motor (EESM).

[0085] FIG. 4 shows an example of an implementation form of an exciter of a device according to an embodiment of this disclosure for operating an externally excited synchronous motor (EESM).

[0086] FIG. 5 shows an example of an implementation form of an exciter of a device according to an embodiment of this disclosure for operating an externally excited synchronous motor (EESM).

[0087] FIG. 6 shows an example of an implementation form of an exciter of a device according to an embodiment of this disclosure for operating an externally excited synchronous motor (EESM).

[0088] FIG. 7 shows an example of an implementation form of a device according to an embodiment of this disclosure for operating an externally excited synchronous motor (EESM).

[0089] FIG. 8 shows an example of an implementation form of a device according to an embodiment of this disclosure for operating an externally excited synchronous motor (EESM).

[0090] FIG. 9 shows an example of an implementation form of a device according to an embodiment of this disclosure for operating an externally excited synchronous motor (EESM).

[0091] FIG. 10 shows four different operating states of a rotor with twelve physical poles of an externally excited synchronous motor (EESM), when the EESM is operated by an implementation form of a device according to an embodiment of this disclosure for operating an EESM.

[0092] FIG. 11 shows three different operating states of a rotor with eight physical poles of an externally excited synchronous motor (EESM), when the EESM is operated by an implementation form of a device according to an embodiment of this disclosure for operating an EESM.

[0093] FIG. 12 shows the relationship between torque and speed of a rotor with eight physical poles of an externally excited synchronous motor (EESM) for three different operating states of the rotor when the EESM is operated by an implementation form of a device according to an embodiment of this disclosure for operating an EESM.

[0094] FIG. 13 shows the relationship between torque and speed of a rotor with eight physical poles of an externally excited synchronous motor (EESM) for three different operating states of the rotor when the EESM is operated by an implementation form of a device according to an embodiment of this disclosure for operating an EESM.

[0095] FIG. 14 shows an example of an implementation form of a device according to an embodiment of this disclosure for operating an externally excited synchronous motor (EESM), and two different operating states of a rotor with four, eight and twelve physical poles of an externally excited synchronous motor (EESM) when the EESM is operated by the device.

[0096] Same elements shown in the figures (FIGs.) are labeled with the same reference sign, and may be implemented likewise.

[0097] DETAILED DESCRIPTION OF EMBODIMENTS

[0098] Fig. 1 shows an example of a device according to an embodiment of this disclosure for operating an externally excited synchronous motor (EESM). The device 1 of FIG. 1 is an example of the device according to the first aspect of this disclosure. Thus, the description of the device according the first aspect is correspondingly valid for the device 1 of FIG. 1.

[0099] The device 1 of FIG. 1 comprises one or more exciters 3 each being configured to provide a direct current and direct voltage of a first polarity (e.g. +1, +U) and a direct current and direct voltage of a second polarity (e.g. -I, -U) to a respective field winding 22a of a rotor 22 of the EESM 2. The number of exciters 3 and respective field windings 22a shown in FIG. 1 is only by way of example and may be different. One exciter 3 and the respective field winding 22a of the EESM 2 are shown in dashed lines in order to indicate that there may be only one exciter 3 or more than one exciter 3. As shown in FIG. 1, there is a corresponding field winding 22a (which is called respective field winding) of the rotor 22 of the EESM 2 for each exciter 3 of the device 1. Each of the one or more exciters 3 is configured to control the direction of magnetic flux generated by the respective field winding 22a by providing the direct current and direct voltage of the first polarity or the direct current and direct voltage of the second polarity to the respective field winding 22a.

[0100] The device 1 may comprise a further exciter that is configured to provide a direct current and direct voltage of the first polarity to a respective field winding 22a of the rotor 22 of the EESM 2 (not shown in FIG. 1). The rotor 22 of the EESM may comprise a respective field winding 22a for each of the one or more exciters 3 and the optional further exciter (not shown in FIG. 1).

[0101] For further information on the device 1, such as information on optional implementation forms and / or optional features of the device 1, reference is made to the description of the device according to the first aspect and to FIGs. 3 to 14. Examples of implementation forms of the one or more exciters 3 of the device 1 are described with regard to FIGs. 3 and 4. Examples of implementation forms of the aforementioned optional further exciter are described with regard to FIGs. 5 and 6.

[0102] FIG. 2 shows an example of a motor arrangement according to an embodiment of this disclosure. The motor arrangement 100 of FIG. 2 is an example of the motor arrangement according to the second aspect of this disclosure. Thus, the description of the motor arrangement according to the second aspect is correspondingly valid for the motor arrangement of FIG. 2. The motor arrangement 100 of FIG. 2 comprises a device 1 for operating an externally excited synchronous motor (EESM), and an EESM 2. The EESM 2 comprises a rotor 22 with two or more field windings 22a. The device 1 is configured to operate the EESM 2 by providing a direct current and direct voltage of a first polarity or a direct current and direct voltage of a second polarity to at least one of the two or more field windings 22a of the rotor 22.

[0103] The device 1 may comprises a further exciter that is configured to provide a direct current and direct voltage of the first polarity to a respective field winding of the two or more field windings 22a of the rotor 22 (not shown in FIG. 2).

[0104] The device 1 of the motor arrangement 100 of FIG. 2 is the device 1 of FIG. 1. Thus, the description of the device 1 of FIG. 1 is valid for the device 1 of the motor arrangement 100 of FIG. 2.

[0105] FIG. 3 shows an example of an implementation form of an exciter of a device according to an embodiment of this disclosure for operating an externally excited synchronous motor (EESM). The exciter 3 of FIG. 3 is an example of an implementation form of the one or more exciters 3 of the device 1 of FIG. 1. Therefore, the description of the device 1 of FIG. 1 is valid for the exciter 3 of FIG. 3.

[0106] As shown in FIG. 3, the exciter 3 may comprise a first series connection of two unidirectional switching elements Si l and S12, and a second series connection of two unidirectional switching elements S21 and S22. The first series connection and second series connection may be electrically connected in parallel to each other. According to the example of FIG. 3, each of the unidirectional switching elements SI 1, S12, S21 and S22 of the exciter 3 may be a MOSFET (optionally with a diode connected in parallel to the MOSFET). This is only by way of example and, thus, the unidirectional switching elements may be differently implemented, e.g. the unidirectional switching element may comprise or be any other known transistor type. For example, as indicated in FIG. 3, each of the unidirectional switching elements SI 1, S12, S21 and S22 of the exciter 3 may be an IGBT (optionally with a diode connected in parallel to the IGBT) or a GaN transistor such as a GaN MOSFET. Optionally, a capacitor Cl may be connected in parallel to the first and second series connection of two unidirectional switching elements. The capacitor Cl may be a DC-link capacitor. The capacitor Cl may provide an electrical energy supply, e.g. in the form of the direct current and direct voltage of the first polarity (e.g. +1, +U) or direct current and direct voltage of the second polarity (e.g. -I, -U).

[0107] The exciter 3 may comprise two terminals T1 and T2 for providing the direct current and direct voltage of the first polarity (e.g. +1, +U) or direct current and direct voltage of the second polarity (e.g. -I, -U) depending on the switching states of the unidirectional switching elements SI 1, S12, S21 and S22. This is indicated in FIG. 3 with the voltage current graph, wherein the quadrant, in which the direct current and direct voltage have the first polarity (e.g. +1, +U), and the quadrant, in which the direct current and direct voltage have the second polarity (e.g. -I, -U), are highlighted.

[0108] Optionally, the exciter 3 comprises a circuit 5 comprising an inductor L5 and / or a capacitor C5. The first terminal T1 of the two terminals T1 and T2 may be electrically connected via the circuit 5 to a node N1 between the two unidirectional switching elements Si l and S12 of the first series connection of two unidirectional switching elements. The second terminal T2 of the two terminals T1 and T2 may be electrically connected via the circuit 5 to a node N2 between the two unidirectional switching elements S21 and S22of the second series connection of two unidirectional switching elements. For example, as shown in FIG. 3, the circuit 5 may comprise an inductor L5 and a capacitor C5, wherein the inductor L5 may be connected between the first terminal T1 and the node N1 between the two unidirectional switching elements SI 1, S12 of the first series connection of two unidirectional switching elements, and the capacitor C5 may be electrically connected between the node N1 between the two unidirectional switching elements SI 1 and S12 of the first series connection of two unidirectional switching elements and the node N2 between the two unidirectional switching elements S21 and S22 of the second series connection of two unidirectional switching elements. This result in a buck-converter configuration of the exciter 3. This is only by way of example and, the circuit 5 may be differently implemented. The circuit 5 may be configured to aid operation of the exciter 3. The circuit 5 may be configured to serve as a filter.

[0109] The circuit 5 is merely optionally and, thus, may be omitted. In this case, the first terminal T1 of the two terminals T1 and T2 is connected to the node N1 between the two unidirectional switching elements Si l and S12 of the first series connection of two unidirectional switching elements, and the second terminal T2 of the two terminals T1 and T2 is connected to the node N2 between the two unidirectional switching elements S21 and S22 of the second series connection of two unidirectional switching elements.

[0110] As shown in FIG. 3, the exciter 3 may be configured to provide the direct current and direct voltage of the first polarity (e.g. +1, +U) and the direct current and direct voltage of the second polarity (e.g. -I, -U) to the respective field winding 22a of the rotor 22 of the EESM 2 via one or more non-isolated conductive means 4. For this the first terminal T1 of the exciter 3 may be connected via a non-isolated conductive means 4 to an end of the respective field winding 22a of the rotor 22 of the EESM 2 and the second terminal T2 of the exciter 3 may be connected via a non-isolated conductive means 4 to another end of the respective field winding 22a of the rotor 22 of the EESM 2. The one or more non-isolated conductive means 4 may be for example one or more slip rings. Thus, FIG. 3 shows an example of an exciter 3 for providing the direct current and direct voltage of the first polarity (e.g. +1, +U) and the direct current and direct voltage of the second polarity (e.g. -I, -U) to the respective field winding 22a of the rotor 22 of the EESM 2 without a galvanic isolated barrier.

[0111] Alternatively, the exciter 3 may comprise a galvanic isolated barrier and is configured to provide the direct current and direct voltage of the first polarity (e.g. +1, +U) and the direct current and direct voltage of the second polarity (e.g. -I, -U) via the galvanic isolated barrier to the respective field winding of the rotor. An example of such an implementation form is shown in FIG. 4.

[0112] For further details on the exciter 3 of FIG. 3 reference is made to the corresponding description of the device according to the first aspect.

[0113] FIG. 4 shows an example of an implementation form of an exciter of a device according to an embodiment of this disclosure for operating an externally excited synchronous motor (EESM). The exciter 3 of FIG. 4 is an example of an implementation form of the one or more exciters 3 of the device 1 of FIG. 1. Therefore, the description of the device 1 of FIG. 1 is valid for the exciter 3 of FIG. 4.

[0114] As shown in FIG. 4, the exciter 3 may comprise a first series connection of two unidirectional switching elements Si l and S12, and a second series connection of two unidirectional switching elements S21 and S22. The first series connection and second series connection may be electrically connected in parallel to each other. According to the example of FIG. 4, each of the unidirectional switching elements SI 1, SI 2, S21 and S22 of the first series connection and second series connection of two unidirectional switching elements may be a MOSFET (optionally with a diode connected in parallel to the MOSFET). This is only by way of example and, thus, the unidirectional switching elements may be differently implemented, e.g. the unidirectional switching element may comprise or be any other known transistor type. For example, as indicated in FIG. 4, each of the unidirectional switching elements SI 1, SI 2, S21 and S22 of the first series connection and second series connection of two unidirectional switching elements may be an IGBT (optionally with a diode connected in parallel to the IGBT) or a GaN transistor such as a GaN MOSFET. Optionally, a capacitor Cl may be connected in parallel to the first and second series connection of two unidirectional switching elements. The capacitor Cl may be a DC-link capacitor. The capacitor Cl may provide an electrical energy supply, e.g. in the form of the direct current and direct voltage of the first polarity (e.g. +1, +U) or direct current and direct voltage of the second polarity (e.g. -I, -U).

[0115] As shown in FIG. 4, the exciter 3 may comprise a wireless power coupler 6 with a primary winding PW and a secondary winding SW. This wireless power coupler provides a galvanic isolated barrier. That is, the exciter 3 comprises a galvanic isolated barrier by comprising the wireless power coupler 6. As shown in FIG. 4, the wireless power coupler 6 may be for example a transformer, such as a rotational transformer. This is only by way of example and, thus, the wireless power coupler may be differently implemented for providing a galvanic isolated barrier. The galvanic isolated barrier, e.g. the wireless power coupler 6, of the exciter 3 divides the exciter 3 in a primary side and a secondary side that is galvanically isolated from the primary side. The primary winding PW of the wireless power coupler 6 is arranged on the primary side of the exciter 3 and the secondary winding SW of the wireless power coupler 6 is arranged on the secondary side of the exciter 3. The secondary side of the 3 may be configured to be arranged on the rotor 22 of the EESM 2. As shown in FIG. 4, the first series connection of two unidirectional switching elements SI 1 and S12 and the second series connection of two unidirectional switching elements S21 and S22 are arranged on the primary side of the exciter 3.

[0116] As shown in FIG. 4, the exciter 3 may comprise a first series connection of two bidirectional switching elements SI lb and S12b, a second series connection of two bidirectional switching elements S21b and S22b, and two terminals T1 and T2 for providing the direct current and direct voltage of the first polarity (e.g. +1, +U) or direct current and direct voltage of the second polarity (e.g. -I, -U) depending on the switching states of the bidirectional switching elements SI lb, S12b, S21b and S22b. The first series connection of two bidirectional switching elements SI lb and S12b and second series connection of two bidirectional switching elements S21b and S22b may be electrically connected in parallel to each other. According to the example of FIG. 4, each of the bidirectional switching elements SI lb, S12b, S21b and S22b of the exciter 3 may be a series connection of two MOSFETs (optionally with a diode connected in parallel to each MOSFET). The two MOSFETs may be connected to each other such that the drain terminal of one MOSFET is connected to the drain terminal of the other MOSFET. A diode may be connected in parallel to each MOSFET such that the anode of the diode is connected to the source terminal of the MOSFET and the cathode of the diode is connected to the drain terminal of the MOSFET. This is only by way of example and, thus, the bidirectional switching elements may be differently implemented, e.g. the bidirectional switching element may comprise or be one or more transistors of any other known type. For example, as indicated in FIG. 4, each of the bidirectional switching elements SI lb, S12b, S21b and S22b of the exciter 3 may be a mono- lithically-integrated bidirectional GaN transistor, a series connection of two IGBTs (optionally with a diode connected in parallel to each IGBT) or two GaN transistors in antiseries connection. The two IGBTs may be connected to each other such that the collector terminal of one IGBT is connected to the collector terminal of the other IGBT. A diode may be connected in parallel to each IGBT such that the anode of the diode is connected to the emitter terminal of the IGBT and the cathode of the diode is connected to the collector terminal of the IGBT). Optionally, a capacitor C2 may be connected in parallel to the first series connection of two bidirectional switching elements SI lb and S12b and second series connection of two bidirectional switching elements S21b and S22b.

[0117] As shown in FIG. 4, a first terminal T1 of the two terminals T1 and T2 may be electrically connected to a first end of the first and second series connection of two bidirectional switching elements. A second terminal T2 of the two terminals T1 and T2 may be electrically connected to a second end of the first and second series connection of two bidirectional switching elements. The first terminal T1 of the exciter 3 may be connected to an end of the respective field winding 22a of the rotor 22 of the EESM 2 and the second terminal T2 of the exciter 3 may be connected to another end of the respective field winding 22a of the rotor 22 of the EESM 2.

[0118] As shown in FIG. 4, the primary winding PW of the wireless power coupler 6 may be electrically connected between a node N1 between the two unidirectional switching elements SI 1 and S12 of the first series connection of two unidirectional switching elements and a node N2 between the two unidirectional switching elements S21 and S22 of the second series connection of two unidirectional switching elements, wherein the primary winding PW of the wireless power coupler 6 may optionally be connected via an inductor L3 and / or capacitor C3 to the node N1 between the two unidirectional switching elements Si l and S12 of the first series connection of two unidirectional switching elements. Alternatively, the primary winding PW of the wireless power coupler 6 may optionally be connected via an inductor L3 and / or capacitor C3 to the node N2 between the two unidirectional switching elements S21 and S22 of the second series connection of two unidirectional switching elements (not shown in FIG. 4). The inductor L3 and capacitor C3 on the primary side of the exciter 3 are only optional and may be omitted.

[0119] As shown in FIG. 4, the secondary winding SW of the wireless power coupler 6 may be electrically connected between a node Nib between the two bidirectional switching elements SI lb and S12 b of the first series connection of two bidirectional switching elements and a node N2b between the two bidirectional switching elements S21b and S22b of the second series connection of two bidirectional switching elements, wherein the secondary winding SW of the wireless power coupler 6 may optionally be connected via an inductor L3 and / or capacitor C3 to the node N2b between the two bidirectional switching elements S21b and S22b of the second series connection of two bidirectional switching elements. Alternatively, the secondary winding SW of the wireless power coupler 6 may optionally be connected via an inductor L3 and / or capacitor C3 to the node Nib between the two bidirectional switching elements SI lb and S12b of the first series connection of two bidirectional switching elements (not shown in FIG. 4). The inductor L3 and capacitor C3 on the secondary side of the exciter 3 are only optional and may be omitted.

[0120] The following is true for the primary side and secondary side of the exciter 3: For example, the exciter 3 may comprise the inductor L3 without the capacitor C4. This may result in a DAB- based exciter. Optionally, the exciter 3 may comprise a series connection of the inductor L3 and capacitor C3, wherein the primary winding PW of the wireless power coupler 6 is electrically connected via the series connection of the inductor L3 and capacitor C3 to the node N1 between the two unidirectional switching elements Si l and S12 of the first series connection of two unidirectional switching elements or to the node N2 between the two unidirectional switching elements S21 and S22 of the second series connection of two unidirectional switching elements. This may result in a resonant converter configuration of the exciter 3. Optionally, the exciter 3 may comprise a series connection of the inductor L3 and capacitor C3, wherein the secondary winding SW of the wireless power coupler 6 is electrically connected via the series connection of the inductor L3 and capacitor C3 to the node Nib between the two bidirectional switching elements SI lb and S12b of the first series connection of two bidirectional switching elements or to the node N2b between the two bidirectional switching elements S21b and S22b of the second series connection of two bidirectional switching elements. This may result in a resonant converter configuration of the exciter 3.

[0121] For further details on the exciter 3 of FIG. 4 reference is made to the corresponding description of the device according to the first aspect.

[0122] FIG. 5 shows an example of an implementation form of an exciter of a device according to an embodiment of this disclosure for operating an externally excited synchronous motor (EESM). The exciter 30 of FIG. 5 is an example of an implementation form of the optional further exciter of the device 1 of FIG. 1 (not shown in FIG. 1). Therefore, the description of the device 1 of FIG. 1 is valid for the exciter 30 of FIG. 5.

[0123] The exciter 30 of FIG. 5 is configured to provide a direct current and direct voltage of the first polarity (e.g. +1, +U) to a respective field winding 22a of the rotor 22 of the EESM 2. As shown in FIG. 5, the exciter 30 comprises a series connection of two unidirectional switching elements SI 1 and S12 and two terminals T1 and T2 for providing the direct current and direct voltage of the first polarity depending on the switching states of the unidirectional switching elements SI 1 and S12. According to the example of FIG. 5, each of the unidirectional switching elements SI 1 and S12 of the exciter 30 may be a MOSFET (optionally with a diode connected in parallel to the MOSFET). This is only by way of example and, thus, the unidirectional switching elements may be differently implemented, e.g. the unidirectional switching element may comprise or be any other known transistor type. For example, as indicated in FIG. 3, each of the unidirectional switching elements SI 1 and S12 of the exciter 30 may be an IGBT (optionally with a diode connected in parallel to the IGBT) or a GaN transistor such as a GaN MOSFET. Optionally, the unidirectional switching element S12 connected to the first terminal T1 and second terminal T2 may be a diode. This is only by way of example and, thus, the unidirectional switching element S12 connected to the first terminal T1 and second terminal T2 may be any other type of uncontrolled semiconductor switch. Optionally, a capacitor Cl may be connected in parallel to the series connection of two unidirectional switching elements. The capacitor Cl may be a DC-link capacitor. The capacitor Cl may provide an electrical energy supply.

[0124] The exciter 30 may comprise the two terminals T1 and T2 for providing the direct current and direct voltage of the first polarity (e.g. +1, +U) depending on the switching states of the unidirectional switching elements Si l and S12. This is indicated in FIG. 5 with the voltage current graph, wherein the quadrant, in which the direct current and direct voltage have the first polarity (e.g. +1, +U) is highlighted.

[0125] Optionally, the exciter 30 comprises a circuit 5 comprising an inductor L5 and / or a capacitor C5. The first terminal T1 of the two terminals T1 and T2 may be electrically connected via the circuit 5 to the node N1 between the two unidirectional switching elements SI 1 and S12 of the series connection of two unidirectional switching elements. The second terminal T2 of the two terminals may be electrically connected via the circuit 5 to an end of the series connection of two unidirectional switching elements. For example, as shown in FIG. 5, the circuit 5 may comprise an inductor L5 and a capacitor C5, wherein the inductor L3 may be connected between the first terminal T1 and the node N1 between the two unidirectional switching elements Si l and S12 of the series connection of two unidirectional switching elements, and the capacitor C4 may be electrically connected between the node N 1 between the two unidirectional switching elements Si l and S12 of the series connection of two unidirectional switching elements and the end of the series connection of two unidirectional switching elements. This results in a buckconverter configuration of the exciter 30. This is only by way of example and, the circuit 5 may be differently implemented. The circuit 5 may be configured to aid operation of the exciter 30. The circuit 5 may be configured to serve as a filter.

[0126] The circuit 5 is merely optionally and, thus, may be omitted. In this case, the first terminal T1 of the two terminals T1 and T2 is electrically connected to the node N1 between the two unidirectional switching elements SI 1 and S12 of the series connection of two unidirectional switching elements, and the second terminal T2 of the two terminals T1 and T2 is electrically connected to the end of the series connection of two unidirectional switching elements.

[0127] As shown in FIG. 5, the exciter 30 may be configured to provide the direct current and direct voltage of the first polarity to the respective field winding 22a of the rotor 22 of the EESM 2 via one or more non-isolated conductive means 4. For this the first terminal T1 of the exciter 30 may be connected via a non-isolated conductive means 4 to an end of the respective field winding 22a of the rotor 22 of the EESM 2 and the second terminal T2 of the exciter 30 may be connected via a non-isolated conductive means 4 to another end of the respective field winding 22a of the rotor 22 of the EESM 2. The one or more non-isolated conductive means 4 may be for example one or more slip rings. Thus, FIG. 5 shows an example of an exciter 30 for providing the direct current and direct voltage of the first polarity to the respective field winding 22a of the rotor 22 of the EESM 2 without a galvanic isolated barrier.

[0128] Alternatively, the exciter 30 may comprise a galvanic isolated barrier and is configured to provide the direct current and direct voltage of the first polarity via the galvanic isolated barrier to the respective field winding 22a of the rotor 22. An example of such an implementation form is shown in FIG. 6.

[0129] For further details on the exciter 30 of FIG. 5 reference is made to the corresponding description of the device according to the first aspect.

[0130] FIG. 6 shows an example of an implementation form of an exciter of a device according to an embodiment of this disclosure for operating an externally excited synchronous motor (EESM). The exciter 30 of FIG. 6 is an example of an implementation form of the optional further exciter of the device 1 of FIG. 1 (not shown in FIG. 1). Therefore, the description of the device 1 of FIG. 1 is valid for the exciter 30 of FIG. 6.

[0131] As shown in FIG. 6, the exciter 30 may comprise a series connection of two unidirectional switching elements Si l and S12, and a second series connection of two unidirectional switching elements S21 and S22. The series connection and second series connection may be electrically connected in parallel to each other. According to the example of FIG. 6, each of the unidirectional switching elements SI 1, S12, S21 and S22 of the series connection and second series connection of two unidirectional switching elements may be a MOSFET (optionally with a diode connected in parallel to the MOSFET). This is only by way of example and, thus, the unidirectional switching elements Sil, S12, S21 and S22 may be differently implemented, e.g. the unidirectional switching element may comprise or be any other known transistor type. For example, as indicated in FIG. 6, each of the unidirectional switching elements SI 1, S12, S21 and S22 of the series connection and second series connection of two unidirectional switching elements may be an IGBT (optionally with a diode connected in parallel to the IGBT) or a GaN transistor such as a GaN MOSFET. Optionally, a capacitor Cl may be connected in parallel to the series connection of two unidirectional switching elements and the second series connection of two unidirectional switching elements. The capal may be a DC-link capacitor. The capacitor Cl may provide an electrical energy supply.

[0132] As shown in FIG. 6, the exciter 30 may comprise a wireless power coupler 6 with a primary winding PW and a secondary winding SW. This wireless power coupler 6 provides a galvanic isolated barrier. That is, the exciter 30 comprises a galvanic isolated barrier by comprising the wireless power coupler 6. As shown in FIG. 6, the wireless power coupler 6 may be for example a transformer, such as a rotational transformer. This is only by way of example and, thus, the wireless power coupler 6 may be differently implemented for providing a galvanic isolated barrier. The galvanic isolated barrier, e.g. the wireless power coupler 6, of the exciter 30 divides the exciter 30 in a primary side and a secondary side that is galvanically isolated from the primary side. The primary winding PW of the wireless power coupler 6 is arranged on the primary side of the exciter 30 and the secondary winding SW of the wireless power coupler 6 is arranged on the secondary side of the exciter 30. The secondary side of the 30 may be configured to be arranged on the rotor 22 of the EESM 2. As shown in FIG. 6, the series connection of two unidirectional switching elements SI 1 and S12 and the second series connection of two unidirectional switching elements S21 and S22 are arranged on the primary side of the exciter 30.

[0133] As shown in FIG. 6, the exciter 3 may comprise a third series connection of two unidirectional switching elements S31 and S32, a fourth series connection of two unidirectional switching elements S41 and S42, and two terminals T1 and T2 for providing the direct current and direct voltage of the first polarity depending on the switching states of the unidirectional switching elements SI 1, S12, S21, S22, S31, S32, S41 and S42. The third series connection of two unidirectional switching elements and fourth series connection of two unidirectional switching elements may be electrically connected in parallel to each other. According to the example of FIG. 6, each of the unidirectional switching elements S31, S32, S41 and S42 of the third series connection and fourth series connection of two unidirectional switching elements may be a diode. This is only by way of example and, thus, each of the unidirectional switching elements S31, S32, S41 and S42 of the third series connection and fourth series connection of two unidirectional switching elements may be any other type of uncontrolled semiconductor switch. Alternatively, each of the unidirectional switching elements S31, S32, S41 and S42 of the third series connection and fourth series connection of two unidirectional switching elements may be a controlled semiconductor switch such as a transistor. For example, as indicated in FIG. 6, each of the unidirectional switching elements S31, S32, S41 and S42 of the third series connection and fourth series connection of two unidirectional switching elements may be an IGBT (optionally with a diode connected in parallel to the IGBT) or a GaN transistor such as a GaN MOSFET. This is only by way of example and, thus, the unidirectional switching elements may be differently implemented, e.g. the unidirectional switching element S31, S32, S41 and S42 may comprise or be any other known transistor type. Optionally, a capacitor C2 may be connected in parallel to the third series connection of two unidirectional switching elements S31 and S32 and fourth series connection of two unidirectional switching elements S41 and S42.

[0134] As shown in FIG. 6, a first terminal T1 of the two terminals T1 and T2 may be electrically connected to a first end of the third and fourth series connection of two unidirectional switching elements. A second terminal T2 of the two terminals T1 and T2 may be electrically connected to a second end of the third and fourth series connection of two unidirectional switching elements. The first terminal T1 of the exciter 30 may be connected to an end of the respective field winding 22a of the rotor 22 of the EESM 2 and the second terminal T2 of the exciter 30 may be connected to another end of the respective field winding 22a of the rotor 22 of the EESM 2.

[0135] As shown in FIG. 6, the primary winding PW of the wireless power coupler 6 may be electrically connected between a node N1 between the two unidirectional switching elements SI 1 and S12 of the series connection of two unidirectional switching elements and a node N2 between the two unidirectional switching elements S21 and S22 of the second series connection of two unidirectional switching elements, wherein the primary winding PW of the wireless power coupler 6 may optionally be connected via an inductor L3 and / or capacitor C3 to the node N1 between the two unidirectional switching elements SI 1 and S12 of the series connection of two unidirectional switching elements. Alternatively, the primary winding PW of the wireless power coupler 6 may optionally be connected via an inductor L3 and / or capacitor C3 to the node N2 between the two unidirectional switching elements S21 and S22 of the second series connection of two unidirectional switching elements (not shown in FIG. 6). The inductor L3 and capacitor C3 on the primary side of the exciter 30 are only optional and may be omitted.

[0136] As shown in FIG. 6, the secondary winding SW of the wireless power coupler 6 may be electrically connected between a node N3 between the two unidirectional switching elements S31 and S32 of the third series connection of two unidirectional switching elements and a node N4 between the two unidirectional switching elements S41 and S42 of the fourth series connection of two unidirectional switching elements, wherein the secondary winding SW of the wireless power coupler 6 may optionally be connected via an inductor L3 and / or capacitor C3 to the node N4 between the two unidirectional switching elements S41 and S42 of the fourth series connection of two unidirectional switching elements. Alternatively, the secondary winding SW of the wireless power coupler 6 may optionally be connected via an inductor L3 and / or capacitor C3 to the node N3 between the two unidirectional switching elements S31 and S32 of the third series connection of two unidirectional switching elements (not shown in FIG. 6). The inductor L3 and capacitor C3 on the secondary side of the exciter 3 are only optional and may be omitted.

[0137] The following is true for the primary side and secondary side of the exciter 30: For example, the exciter 30 may comprise the inductor L3 without the capacitor C4. This may result in a DAB-based exciter. Optionally, the exciter 30 may comprise a series connection of the inductor L3 and capacitor C3, wherein the primary winding PW of the wireless power coupler 6 is electrically connected via the series connection of the inductor L3 and capacitor C3 to the node N1 between the two unidirectional switching elements SI 1 and S12 of the series connection of two unidirectional switching elements or to the node N2 between the two unidirectional switching elements S21 and S22 of the second series connection of two unidirectional switching elements. This may result in a resonant converter configuration of the exciter 30. Optionally, the exciter 30 may comprise a series connection of the inductor L3 and capacitor C3, wherein the secondary winding SW of the wireless power coupler 6 is electrically connected via the series connection of the inductor L3 and capacitor C3 to the node N3 between the two unidirectional switching elements S31 and S32 of the third series connection of two unidirectional switching elements or to the node N4 between the two unidirectional switching elements S41 and S42 of the fourth series connection of two unidirectional switching elements. This may result in a resonant converter configuration of the exciter 30.

[0138] For further details on the exciter 30 of FIG. 6 reference is made to the corresponding description of the device according to the first aspect.

[0139] FIG. 7 shows an example of an implementation form of a device according to an embodiment of this disclosure for operating an externally excited synchronous motor (EESM). The device 1 of FIG. 7 is an example of an implementation form of the device 1 of FIG. 1. Therefore, the description of the device 1 of FIG. 1 is valid for the device 1 of FIG. 7.

[0140] The device 1 of FIG. 7 is configured to operate an EESM 2 comprising a rotor 22 with four field windings 22a. For example, the rotor 22 of the EESM 2 may comprise eight or twelve physical poles. That is, the four field windings 22a may be arranged on eight or twelve physical poles. The device 1 comprises three exciters 3 each being configured to provide a direct current and direct voltage of a first polarity (e.g. +1, +U) and a direct current and direct voltage of a second polarity (e.g. -I, -U) to a respective field winding 22a of the four field windings 22a of the rotor 22 of the EESM 2. The device 1 comprises a further exciter 30 that is configured to provide a direct current and direct voltage of the first polarity (e.g. +1, +U) to a respective field winding 22a of the four field windings 22a of the rotor 22 of the EESM 2. Thus, the device 1 comprises the three exciters 3 and the further exciter 30 for providing a direct current and direct voltage to the four field windings 22a of the rotor 22 of the EESM 2.

[0141] The EESM 2 may comprise a stator 23 with n coils 23a (e.g. n terminals). The term “n” is an integer greater than or equal to two. The device 1 may comprise an inverter 12 with n legs, wherein each leg of the n legs may provide an alternating current and alternating voltage with a phase angle of 360° / n or 27t / n to a respective coil 23 a of the stator 23 of the EESM 2. The EESM 2 may comprise m phases. That is, the stator 23 of the EESM 2 may comprise m independent coils. The term “m” is an integer greater than or equal to two. Optionally, the number n of coils 23a of the stator 23 may equal the number m of independent coils of the stator 23. That is, each coil 23a of the stator 23 of the EESM 2 may be an independent coil. In this case the EESM 2 comprises m = n phases. Optionally, the number m of independent coils of the stator 23 of the EESM 2 may be smaller than the number n of coils 23a of the stator 23 of the EESM 2. This case may be due to the operation of the EESM 2 by the device 1, e.g. by the inverter 12 of the device 1. According to the example, of FIG. 7, the stator 23 of the EESM 2 may comprise twelve coils 23a, e.g. n = 12, which optionally may be twelve independent coils. Alternatively, the stator 23 of the EESM 2 may comprise nine coils 23a, e.g. n = 9, which optionally may be nine independent coils (not shown in FIG. 7).

[0142] In the example of FIG. 7, with the assumed number of four field windings 22a of the rotor 22 and an assumed number of twelve coils 23a of the stator 23, the device 1 may operate the EESM 2 such that the EESM 2 has four pairs of poles, two pairs of poles or one pair of poles at the rotor 22, when assuming that the rotor 22 has eight physical poles. In the example of FIG. 7, with the assumed number of four field windings 22a of the rotor 22 and an assumed number of nine coils 23a of the stator 23, the device 1 may operate the EESM 2 such that the EESM 2 has six pairs of poles, three pairs of poles or two pairs of poles at the rotor 22, when assuming that the rotor 22 has twelve physical poles.

[0143] As shown in FIG. 7, the device 1 may comprise a capacitor Cl 1 connected to the three exciters 3, the further exciter 30 and the inverter 12 for providing an electrical supply to the respective circuit. The capacitor Cl 1 may be a DC-link capacitor. The device 1 may comprise a control unit 11 for controlling operation of the device 1, e.g. for controlling the three exciters 3, the further exciter 30 and the inverter 12. As indicated in FIG. 7, the control unit 11 may obtain measurements of the direct currents and voltages provided by the three exciters 3 and the further exciter 30 and the alternating currents and voltages provided by inverter 12.

[0144] The sum of the one further exciter 30 and the number of one or more exciters 3 of the device 1 may equal to the number of field windings 22a of the rotor 22 of the EESM 2 to be operated by the device 1. The number of field windings 22a of the rotor 22, the number n of the coils 23a of the stator 23 and the number of exciters 3 shown in FIG. 7 or described with regard to the example of FIG. 7 is only by way of example and may be different. The description of FIG. 7 is correspondingly valid in such case.

[0145] According to the example of FIG. 7, the device 1 is configured to excite the field windings 22a of the rotor 22 of the EESM 2 without a galvanic isolation barrier. That is, the device 1 is configured to excite the field windings 22a of the rotor 22 of the EESM 2 via one or more nonisolated conductive means 4, such as one or more slip rings. That is, each of the three exciters 3 is configured to provide the direct current and direct voltage of the first polarity and the direct current and direct voltage of the second polarity to the respective field winding 22a of the four field windings 22a of the rotor 22 via one or more non-isolated conductive means 4, and the further exciter 30 is configured to provide the direct current and direct voltage of the first polarity to the respective field winding 22a of the four field windings 22a of the rotor 22 via one or more non-isolated conductive means. As shown in FIG. 7 by the area labelled with the reference sign “A”, a part of the one or more non-isolated conductive means 4, e.g. one or more slip rings 4, and the field windings 22a may be arranged on the rotor 22 and, thus, on the rotating part of the EESM 2. Each of the exciters 3 may be implemented as described with regard to FIG. 3, and the further exciter 30 may be implemented as described with regard to FIG. 5. At least one of the exciters 3 may be differently implemented to the other exciter(s) 3 of the device 1. The device 1 and the EESM 2 may form a motor arrangement.

[0146] Alternatively to the example of FIG. 7, the device 1 may comprise a galvanic isolated barrier for exiting the field windings 22a of the rotor 22 of the EESM 2 via the galvanic isolated barrier. An example of such an implementation form is shown in FIG. 8.

[0147] FIG. 8 shows an example of an implementation form of a device according to an embodiment of this disclosure for operating an externally excited synchronous motor (EESM). The device 1 of FIG. 8 is an example of an implementation form of the device 1 of FIG. 1. Therefore, the description of the device 1 of FIG. 1 is valid for the device 1 of FIG. 8.

[0148] The device 1 and EESM 2 of FIG. 8 corresponds to the device 1 and EESM 2 of FIG. 7 with the difference that the device 1 of FIG. 8 comprise a galvanic isolation barrier for exciting the field windings 22a of the rotor 22 of the EESM 2, whereas the device 1 of FIG. 7 does not comprise such a galvanic isolation barrier. Therefore, for describing the device 1 and EESM 2 of FIG. 8 reference is made to the description of FIG. 7 and in the following mainly the difference of the device 1 and EESM 2 of FIG. 8 with regard to the device 1 and EESM 2 of FIG. 7 is described.

[0149] Since the device 1 of FIG. 8 comprises a galvanic isolation barrier for exciting the field windings 22a of the rotor 22 of the EESM 2, each of the exciters 3 comprises a galvanic isolated barrier and is configured to provide the direct current and direct voltage of the first polarity and the direct current and direct voltage of the second polarity via the galvanic isolated barrier to the respective field winding 22a of the rotor 22; and the further exciter 30 comprises a galvanic isolated barrier and is configured to provide the direct current and direct voltage of the first polarity via the galvanic isolated barrier to the respective field winding 22a of the rotor 22. The respective galvanic isolation barrier divides each of the three exciters 3 and the further exciter 30 in a primary side and a secondary side. As indicated in FIG. 8 by the area labeled with the reference sign “A”, the secondary side of each of the exciters 3 and the further exciter 30 may be arranged on the rotor 22 and, thus, on the rotating part of the EESM 2. For achieving the galvanic isolation barrier each of the exciters 3 and the further exciter 30 may comprise a wireless power coupler with a primary winding and a secondary winding. The wireless power coupler may be for example a transformer, such as a rotational transformer.

[0150] Each of the exciters 3 may be implemented as described with regard to FIG. 4, and the further exciter 30 may be implemented as described with regard to FIG. 6. At least one of the exciters 3 may be differently implemented to the other exciter(s) 3 of the device 1. The device 1 and the EESM 2 may form a motor arrangement.

[0151] FIG. 9 shows an example of an implementation form of a device according to an embodiment of this disclosure for operating an externally excited synchronous motor (EESM). The device 1 of FIG. 9 is an example of an implementation form of the device 1 of FIG. 1. Therefore, the description of the device 1 of FIG. 1 is valid for the device 1 of FIG. 9.

[0152] The device 1 of FIG. 9 corresponds to the device of FIG. 8, wherein the device 1 is used for operating two or more EESM 2. For describing the device 1 and the two or more EESM 2 of FIG. 9 reference is made to the description of FIGs. 7 and 8 and in the following mainly the difference of the device 1 of FIG. 9 with regard to the device 1 of FIG. 8 is described. The device 1 of FIG. 9 comprises two or more inverters 12, wherein each inverter provides alternating current and voltage to a respective EESM 2 of the two or more EESMs 2. The number of inverters 12 may equal to the number of EESMs 2 to be operated by the device 1. The exciters 3 and the further exciter 30 may provide a direct current and direct voltage to a respective field winding 22a of the rotor 22 of each of the two or more EESM 2. Thus, the same excitement circuit, e.g. the exciters 3 and the further exciter 30, of the device 1 may be used for exciting the field windings 22a of the rotor 22 of two or more EESMs 2. The galvanic isolation barrier in the form of a wireless power coupler of each of the exciters 3 and the further exciter 30 comprises for the rotor 22 of each EESM 2 of the two or more ESSMs 2 a respective secondary wiring that is coupled to the primary winding of the wireless power coupler. The device 1 may alternatively comprise no galvanic isolation barrier. The above description is correspondingly valid, wherein the connection of the three exciters 3 and the further exciter 30 to the respective field winding 22a of the rotor 22 of each EESM 2 of the two or more EESMs 2 may be implemented as outlined with regard to the connection of the three exciters 3 and the further exciter 30 of the device 1 of FIG. 7 to the respective field winding 22a of the rotor 22 of the single EESM 2. The two or more inverters may be differently implemented depending on the implementation of the two or more EESM 2. The two or more EESM 2 may be differently implemented, e.g. comprising a different number of coils 23a of the stator 23.

[0153] FIG. 10 shows four different operating states of a rotor with twelve physical poles of an externally excited synchronous motor (EESM), when the EESM is operated by an implementation form of a device according to an embodiment of this disclosure for operating an EESM.

[0154] As shown in FIGs. 10 (a), 10 (b), 10 (c) and 10 (d) the EESM 2 with the rotor 22 having twelve physical poles may be operated by a device according to an embodiment of this disclosure for operating an EESM such that six pairs of poles, three pair of poles, two pair of poles or one pair of poles, respectively, are generated on the rotor 22. In the FIGs. 10 (a), 10 (b), 10 (c) and 10 (d), the two different pole types, e.g. positive pole and negative pole, are indicated by two opposite directed arrows, wherein at each physical pole of the rotor 22 the pole generated at the respective operation state is shown. For example, an arrow directed to the center of the rotor may indicate a positive pole and an arrow directed away from the center of the rotor may indicate negative poles or vice versa. In the FIGs. 10 (a), 10 (b) and 10 (c) a respective pair of poles is highlighted by a dashed circle.

[0155] The device 1 for operating the EESM 2 and thus achieving the different number of poles at the rotor 22 of the EESM 2 shown in FIGs. 10 (a), 10 (b), 10 (c) and 10 (d) may be as shown in FIGs. 7 and 8, wherein the number of exciters 3 and number of legs of the inverter 22 may be as outlined in the following table “Table 1” with columns Cl to C5 and rows R1 to R7, wherein p is the number of poles that may be generated at the rotor 22 with the respective configuration of the device 1, m is the number of independent coils of the stator 23 of the EESM 2 that should be achieved due to the hardware of the stator 23 or the operation by the device 1, e.g. the operation by the inverter 12 of the device 1, and 9 is the phase angle of an alternating current and voltage that may be provided to the independent coils of the stator 23 of the EESM by the device 1, e.g. by the inverter 12 of the device 1. The number of field windings 22a at the rotor 22 corresponds to the sum of the further exciter 30 and the number of one or more exciters 3 of the device 1. The number of pair of poles that may be generated at the rotor 22 equals to the number of poles that may be generated at the rotor 22 divided by two (e.g. p / 2).

[0156] Table 1

[0157] The symbol “#” in the Table 1 stands for “number of’. As shown in the Table 1 for generating at a rotor 22 with twelve physical poles six or three pairs of poles it is sufficient that the device comprises one exciter 3 and the further exciter 30 (cf. row R5 of Table 1). In this case the rotor 22 may comprise two field windings 22a. For generating at the rotor 22 with twelve physical poles six or three pairs of poles, the inverter 12 of the device 1 may comprise six legs (cf. row R5 of Table 1). Nevertheless, six or three pairs of poles may also be achieved when the device 1 comprises three exciters 3 and the further exciter 30 (cf. row R6 of Table 1) or when the device 1 comprises five exciters 3 and the further exciter 30 (cf. row R7 of Table 1). In the aforementioned first case the rotor 22 may comprise four field windings 22a, and in the aforementioned second case the rotor 22 may comprise six field windings 22a.

[0158] As shown in the Table 1 for generating at a rotor 22 with twelve physical poles six pairs of poles, three pairs of poles or two pairs of poles it is sufficient that the device comprises three exciters 3 and the further exciter 30 (cf. row R6 of Table 1). In this case the rotor 22 may comprise four field windings 22a and the inverter 12 of the device 1 may comprise nine legs (cf. row R6 of Table 1).

[0159] As shown in the Table 1 for generating at a rotor 22 with twelve physical poles six pairs of poles, three pairs of poles, two pairs of poles or one pair of poles it is sufficient that the device comprises five exciters 3 and the further exciter 30 (cf. row R7 of Table 1). In this case the rotor 22 may comprise six field windings 22a and the inverter 12 of the device 1 may comprise eighteen legs (cf. row R7 of Table 1).

[0160] FIG. 11 shows three different operating states of a rotor with eight physical poles of an externally excited synchronous motor (EESM) when the EESM is operated by an implementation form of a device according to an embodiment of this disclosure for operating an EESM.

[0161] As shown in FIGs. 11 (a), 11 (b) and 11 (c) the EESM with the rotor 22 having eight physical poles may be operated by a device according to an embodiment of this disclosure for operating an EESM such that four pairs of poles, two pair of poles, or one pair of poles, respectively, are generated on the rotor 22. In the FIGs. 11 (a), 11 (b), and 11 (c), the two different pole types, e.g. positive pole and negative pole, are indicated by two opposite directed arrows, wherein at each physical pole of the rotor 22 the pole generated at the respective operation state is shown. For example, an arrow directed to the center of the rotor may indicate a positive pole and an arrow directed away from the center of the rotor may indicate negative poles or vice versa In the FIGs. 11 (a) and 11 (b) a respective pair of poles is highlighted by a dashed circle.

[0162] The device 1 for operating the EESM and thus achieving the different number of poles at the rotor 22 of the EESM 2 shown in FIGs. 11 (a), 11 (b), and 11 (c) may be as shown in FIGs. 7 and 8, wherein the number of exciters 3 and number of legs of the inverter 22 may be as outlined in the following table “Table 2” with columns Cl to C4 and rows R1 to R6, wherein p is the number of poles that may be generated at the rotor 22 with the respective configuration of the device 1, m is the number of independent coils of the stator 23 of the EESM 2 that should be achieved due to the hardware of the stator 23 or the operation by the device 1, e.g. the operation by the inverter 12 of the device 1, and 9 is the phase angle of an alternating current and voltage that may be provided to the independent coils of the stator 23 of the EESM by the device 1, e.g. by the inverter 12 of the device 1. The number of field windings 22a at the rotor 22 corresponds to the sum of the further exciter 30 and the number of one or more exciters 3 of the device 1. The number of pairs of poles that may be generated at the rotor 22 equals to the number of poles that may be generated at the rotor 22 divided by two (e.g. p / 2).

[0163] Table 2 The symbol “#” in the Table 2 stands for “number of’. As shown in the Table 2 for generating at a rotor 22 with eight physical poles four or two pairs of poles it is sufficient that the device comprises one exciter 3 and the further exciter 30 (cf. row R5 of Table 2). In this case the rotor 22 may comprise two field windings 22a. For generating at the rotor 22 with eight physical poles four or two pairs of poles, the inverter 12 of the device 1 may comprise six legs (cf. row R5 of Table 2). Nevertheless, four or two pairs of poles may also be achieved when the device 1 comprises three exciters 3 and the further exciter 30 (cf. row R6 of Table 2). In the aforementioned case the rotor 22 may comprise four field windings 22a.

[0164] As shown in the Table 2 for generating at a rotor 22 with eight physical poles four pairs of poles, two pairs of poles or one pair of poles it is sufficient that the device 1 comprises three exciters 3 and the further exciter 30 (cf. row R6 of Table 2). In this case the rotor 22 may comprise four field windings 22a and the inverter 12 of the device 1 may comprise twelve legs (cf. row R6 of Table 2). FIG. 12 shows the relationship between torque and speed of a rotor with eight physical poles of an externally excited synchronous motor (EESM) for three different operating states of the rotor when the EESM is operated by an implementation form of a device according to an embodiment of this disclosure for operating an EESM.

[0165] In the graph of FIG. 12, the vertical axis is the torque of the EESM and the horizontal axis is the speed of the EESM. The curve 12a indicates the relationship between the torque and the speed of the EESM in case four pair of poles are generated at the rotor of the EESM. The curve 12b indicates the relationship between the torque and the speed of the EESM in case two pair of poles are generated at the rotor of the EESM. The curve 12c indicates the relationship between the torque and the speed of the EESM in case one pair of poles is generated at the rotor of the EESM. The area 120a indicates a high efficiency region in case four pairs of poles are generated at the rotor of the EESM. The area 120b indicates a high efficiency region in case two pairs of poles are generated at the rotor of the EESM. The area 120c indicates a high efficiency region in case one pair of poles is generated at the rotor of the EESM.

[0166] As may be derived from the graph of FIG. 12, the pole configuration of the rotor of the EESM has an impact on the torque-speed characteristics of the EESM. As shown in the graph of FIG. 12, increasing the number of poles translates in higher torques but lower nominal speeds (comer speeds / frequency). The region of high efficiency (see areas 120a, 120b and 120c) reshapes according to the torque-speed curve. The combination of these areas results in a larger overall high-speed area of the EESM. Even if the torque and speed of the EESM are limited, an improvement on the efficiency may still be ensured. This may be seen from the graph of FIG. 13 corresponding to the graph of FIG. 12, where the high efficiency torque-speed region has been normalized.

[0167] FIG. 13 shows the relationship between torque and speed of a rotor with eight physical poles of an externally excited synchronous motor (EESM) for three different operating states of the rotor when the EESM is operated by an implementation form of a device according to an embodiment of this disclosure for operating an EESM.

[0168] The graph of FIG. 13 corresponds to the graph of FIG. 12, where the high efficiency torquespeed region has been normalized. Thus, the description of FIG. 12 is valid for the graph of FIG. 13. The area 130a of the graph of FIG. 13 is the normalized area 120a of the graph of FIG. 12. The area 130b of the graph of FIG. 13 is the normalized area 120b of the graph of FIG. 12. The area 130c of the graph of FIG. 13 is the normalized area 120c of the graph of FIG. 12.

[0169] FIG. 14 an example of an implementation form of a device according to an embodiment of this disclosure for operating an externally excited synchronous motor (EESM), and two different operating states of a rotor with four, eight and twelve physical poles of an externally excited synchronous motor (EESM) when the EESM is operated by the device.

[0170] The device 1 of FIG.14 corresponds to the device 1 of FIG. 7 with the difference that the device

[0171] 1 merely comprise one exciter 3 instead of three exciters 3. Therefore, the rotor 22 of the EESM

[0172] 2 comprises two field windings 22a. The stator 23 of the EESM 2 comprises six coils 23a, which optionally may be six independent coils. The inverter 12 of the device 1 may comprise six legs. The description of the device 1 of FIG. 7 is correspondingly valid for the device 1 of FIG. 14. In the FIGs. 14 (a), 14 (b), 14 (c), 14 (d), 14 (e), and 14 (f), the two different pole types, e.g. positive pole and negative pole, are indicated by two opposite directed arrows, wherein at each physical pole of the rotor 22 the pole generated at the respective operation state is shown. For example, an arrow directed to the center of the rotor may indicate a positive pole and an arrow directed away from the center of the rotor may indicate negative poles or vice versa. In the FIGs. 14 (a), 14 (c), 14 (d), 14 (e), and 14 (f) a respective pair of poles is highlighted by a dashed circle.

[0173] FIGs. 14 (a) and 14 (b) each show a rotor 22 having four physical poles, wherein Fig. 14 (a) shows the case when two pair of poles are generated at the rotor 22 and Fig. 14 (b) shows the case when one pair of poles is generated at the rotor 22. FIGs. 14 (c) and 14 (d) each show a rotor 22 having eight physical poles, wherein Fig. 14 (c) shows the case when four pair of poles are generated at the rotor 22 and Fig. 14 (d) shows the case when two pair of poles are generated at the rotor 22. FIGs. 14 (e) and 14 (f) each show a rotor 22 having twelve physical poles, wherein Fig. 14 (e) shows the case when six pair of poles are generated at the rotor 22 and Fig. 14 (f) shows the case when three pair of poles are generated at the rotor 22.

[0174] For the operation state of FIGs. 14 (a), 14 (c) and 14 (e), the device 1 may be configured to operate the EESM 2 such that the inverter 12 provides an alternating current and voltage to a first pair of coils, a second pair of coils and a third pair of coils of the six coils 23a of the stator 23, wherein the alternating current and voltage between the first pair, second pair and third pair of coils has a phase angle of 120° (e.g. 360° / 3). In the aforementioned case, each pair of coils represents an independent coil. Thus, in the aforementioned case the EESM 2 has three phases. For the operation state of FIGs. 14 (b), 14 (d) and 14 (f), the device 1 may be configured to operate the EESM 2 such that the inverter 12 provides an alternating current and voltage to each coil of the six coils 23a of the stator 23, wherein the alternating current and voltage between the coils 23a has a phase angle of 60° (e.g. 36076). In the aforementioned case, each coil represents an independent coil. Thus, in the aforementioned case the EESM 2 has six phases.

[0175] In the light of the above, the device for operating an EESM and motor arrangement disclosed herein, such as the device according to the first aspect, the motor arrangement according to the second aspect and the device described with regard to any one of the FIGs. 1 to 14, allows providing an improved EESM. The device and motor arrangement of the present disclosure may lead to higher efficiencies of an EESM at light load. Moreover, the device according to the present disclosure allows a pole-phase configuration and, thus, selecting an optimal pole-phase configuration for each operating points of the EESM. This allows enhancing the overall driving cycle efficiencies (e.g. WLTC efficiency) of a vehicle comprising an EESM and the device. Additionally, a pole-phase-modulated EESM (PPM-EESM), that is an EESM operated by a device according to the present disclosure, allows reducing the size of a DC-link capacitor in an inverter of the device, which may be the largest component in the traction inverter. The use of multi-leg inverters (may be referred to as multi-phase inverters) may be beneficial with regard to EMI filters. Moreover, it can increase the reliability of the inverter-motor system by allowing limp-mode operation and providing redundancy. Thus, in the event of a failure, the motor system can retain operation with reduced capacity.

[0176] The present disclosure has been described in conjunction with various embodiments as examples as well as implementations. However, other variations can be understood and effected by those persons skilled in the art and practicing the claimed matter, from the studies of the drawings, this disclosure and the independent claims. In the claims as well as in the description the word “comprising” does not exclude other elements or steps and the indefinite article “a” or “an” does not exclude a plurality. A single element or other unit may fulfill the functions of several entities or items recited in the claims. The mere fact that certain measures are recited in the mutual different dependent claims does not indicate that a combination of these measures cannot be used in an advantageous implementation.

Claims

CLAIMS1. A device (1) for operating an externally excited synchronous motor (2), EESM, the device (1) comprising one or more exciters (3) each being configured to: provide a direct current and direct voltage of a first polarity and a direct current and direct voltage of a second polarity to a respective field winding (22a) of a rotor (22) of the EESM (2), and control the direction of magnetic flux generated by the respective field winding (22a) by providing the direct current and direct voltage of the first polarity or the direct current and direct voltage of the second polarity to the respective field winding (22a).

2. The device (1) according to claim 1, the one or more exciters (3) each being configured to provide the direct current and direct voltage of the first polarity and the direct current and direct voltage of the second polarity to the respective field winding (22a) via one or more non-isolated conductive means (4).

3. The device (1) according to claim 1 or 2, wherein each of the one or more exciters (3) comprises a first series connection of two unidirectional switching elements (Si l, S12), and a second series connection of two unidirectional switching elements (S21, S22), and the first series connection and second series connection are electrically connected in parallel to each other.

4. The device (1) according to claim 3, wherein each of the one or more exciters (3) comprises two terminals (Tl, T2) for providing the direct current and direct voltage of the first polarity or direct current and direct voltage of the second polarity depending on the switching states of the unidirectional switching elements (Si l, SI 2, S21, S22), a first terminal (Tl) of the two terminals (Tl, T2) is electrically connected to a node (Nl) between the two unidirectional switching elements (Si l, S12) of the first series connection of two unidirectional switching elements (SI 1, SI 2), anda second terminal (T2) of the two terminals (Tl, T2) is electrically connected to a node (N2) between the two unidirectional switching elements (S21, S22) of the second series connection of two unidirectional switching elements (S21, S22).

5. The device (1) according to claim 4, wherein at least one exciter of the one or more exciters (3) comprises a circuit (5) comprising an inductor (L5) and / or a capacitor (C5), and the first terminal (Tl) of the two terminals (Tl, T2) of the at least one exciter is electrically connected via the circuit (5) to the node (Nl) between the two unidirectional switching elements (Si l, S12) of the first series connection of two unidirectional switching elements (SI 1, SI 2) of the at least one exciter, and the second terminal (T2) of the two terminals (Tl, T2) of the at least one exciter is electrically connected via the circuit (5) to the node (N2) between the two unidirectional switching elements (S21, S22) of the second series connection of two unidirectional switching elements (S21, S22) of the at least one exciter.

6. The device (1) according to claim 1 or 3 when depending on claim 1, wherein each of the one or more exciters (3) comprises a galvanic isolated barrier (6) and is configured to provide the direct current and direct voltage of the first polarity and the direct current and direct voltage of the second polarity via the galvanic isolated barrier (6) to the respective field winding (22a) of the rotor (22).

7. The device (1) according to claim 3 when depending on claim 1 or claim 6 when depending on claim 3 that depends on claim 1, wherein each of the one or more exciters (3) comprises a wireless power coupler (6) with a primary winding (PW) and a secondary winding (SW), a first series connection of two bidirectional switching elements (SI lb, S12b), a second series connection of two bidirectional switching elements (S21b, S22b), and two terminals (Tl, T2) for providing the direct current and direct voltage of the first polarity or direct current and direct voltage of the second polarity depending on the switching states of the bidirectional switching elements (SI lb, S12b, S21b, S22b), the first series connection of two bidirectional switching elements (SI lb, S12b) and second series connection of two bidirectional switching elements (S21b, S22b) are electrically connected in parallel to each other,the primary winding (PW) of the wireless power coupler (6) is electrically connected between a node (Nl) between the two unidirectional switching elements (SI 1, S12) of the first series connection of two unidirectional switching elements (SI 1, S12) and a node (N2) between the two unidirectional switching elements (S21, S22) of the second series connection of two unidirectional switching elements (S21, S22), the secondary winding (SW) of the wireless power coupler (6) is electrically connected between a node (Nib) between the two bidirectional switching elements (SI lb, S12b) of the first series connection of two bidirectional switching elements (SI lb, S12b) and a node (N2b) between the two bidirectional switching elements (S21b, S22b) of the second series connection of two bidirectional switching elements (S21b, S22b), a first terminal (Tl) of the two terminals (Tl, T2) is electrically connected to a first end of the first and second series connection of two bidirectional switching elements (SI lb, S12b; S21b, S22), and a second terminal (T2) of the two terminals (T 1 , T2) is electrically connected to a second end of the first and second series connection of two bidirectional switching elements (SI lb, S12b; S21b, S22).

8. The device (1) according to claim 7, wherein at least one exciter of the one or more exciters (3) comprises an inductor (L3) and / or a capacitor (C3), and the primary winding (PW) of the wireless power coupler (6) of the at least one exciter is electrically connected via the inductor (L3) and / or capacitor (C3) to the node (Nl; N2) between the two unidirectional switching elements (SI 1, SI 2; S21, S22) of the first or second series connection of two unidirectional switching elements (Si l, S12; S21, S22) of the at least one exciter.

9. The device (1) according to claim 7 or 8, wherein at least one exciter of the one or more exciters (3) comprises an inductor (L3) and / or a capacitor (C3), and the secondary winding (SW) of the wireless power coupler (6) of the at least one exciter is electrically connected via the inductor L3 and / or capacitor C3 to the node (Nib; N2b) between the two bidirectional switching elements (SI lb, S12b; S21b, S22) of the first or second series connection of two bidirectional switching elements (SI lb, S12b; S21b,10. The device (1) according to any one of the previous claims, the device comprising: a further exciter (30) that is configured to provide a direct current and direct voltage of the first polarity to a respective field winding (22a) of the rotor (22) of the EESM (2).

11. The device (1) according to claim 10, wherein the further exciter (30) is configured to provide the direct current and direct voltage of the first polarity to the respective field winding (22a) via one or more non-isolated conductive means (4).

12. The device (1) according to claim 10 or 11, wherein the further exciter (30) comprises a series connection of two unidirectional switching elements (Si l, S12).

13. The device (1) according to claim 12, wherein the further exciter (30) comprises two terminals (Tl, T2) for providing the direct current and direct voltage of the first polarity depending on the switching states of the unidirectional switching elements (Si l, S12), a first terminal (Tl) of the two terminals (Tl, T2) is electrically connected to a node (Nl) between the two unidirectional switching elements (Si l, S12) of the series connection of two unidirectional switching elements (SI 1, SI 2), and a second terminal (T2) of the two terminals (Tl, T2) is electrically connected to an end of the series connection of two unidirectional switching elements (SI 1, S12).

14. The device (1) according to claim 13, wherein the further exciter (30) comprises a circuit (5) comprising an inductor (L5) and / or a capacitor (C5), and the first terminal (Tl) of the two terminals (Tl, T2) is electrically connected via the circuit (5) to the node (Nl) between the two unidirectional switching elements (Si l, SI 2) of the series connection of two unidirectional switching elements (SI 1, SI 2), and the second terminal (T2) of the two terminals (Tl, T2) is electrically connected via the circuit (5) to the end of the series connection of two unidirectional switching elements (Si l, S12).

15. The device (1) according to claim 10 or 12 when depending on claim 10, wherein the further exciter (30) comprises a galvanic isolated barrier (6) and is configured to provide the direct current and direct voltage of the first polarity via the galvanic isolated barrier (6) to the respective field winding (22a) of the rotor (2).

16. The device (1) according to claim 12 when depending on claim 10 or claim 15 when depending on claim 12 that depends on claim 10, wherein the further exciter (30) comprises a wireless power coupler (6) with a primary winding (PW) and a secondary winding (SW), a second series connection of two unidirectional switching elements (S21, S22), third series connection of two unidirectional switching elements (S31, S32), a fourth series connection of two unidirectional switching elements (S41, S42), and two terminals (Tl, T2) for providing the direct current and direct voltage of the first polarity depending on the switching states of the unidirectional switching elements (Si l, S12, S21, S22, S31, S32, S41, S42), the series connection of two unidirectional switching elements (SI 1, SI 2) and the second series connection of two unidirectional switching elements (S21, S22) are electrically connected in parallel to each other, the third series connection of two unidirectional switching elements (S31, S32) and fourth series connection of two unidirectional switching elements (S41, S42) are electrically connected in parallel to each other, the primary winding (PW) of the wireless power coupler (6) is electrically connected between a node (Nl) between the two unidirectional switching elements (SI 1, S12) of the series connection of two unidirectional switching elements (S21, S22) and a node (N2) between the two unidirectional switching elements (S21, S22) of the second series connection of two unidirectional switching elements (S21, S22), the secondary winding (SW) of the wireless power coupler (6) is electrically connected between a node (N3) between the two unidirectional switching elements (S31, S32) of the third series connection of two unidirectional switching elements (S31, S32) and a node (N4) between the two unidirectional switching elements (S41, S42) of the fourth series connection of two unidirectional switching elements (S41, S42), a first terminal (Tl) of the two terminals (Tl, T2) is electrically connected to a first end of the third and fourth series connection of two unidirectional switching elements (S31, S32; S41, S42), anda second terminal (T2) of the two terminals (T 1 , T2) is electrically connected to a second end of the third and fourth series connection of two unidirectional switching elements (S31, S32; S41, S42).

17. The device (1) according to claim 16, wherein the further exciter (30) comprises an inductor (L3) and / or a capacitor (C3), and the primary winding (PW) of the wireless power coupler (6) is electrically connected via the inductor (L3) and / or capacitor (C3) to the node (Nl; N2) between the two unidirectional switching elements (Si l, S12; S21, S22) of the series connection of two unidirectional switching elements (SI 1, SI 2) or of the second series connection of two unidirectional switching elements (S21, S22).

18. The device (1) according to claim 16 or 17, wherein the further exciter (30) comprises an inductor (L3) and / or a capacitor (C3), and the secondary winding (SW) of the wireless power coupler (6) is electrically connected via the inductor (L3) and / or capacitor (C3) to the node (N3; N4) between the two unidirectional switching elements (S31, S32; S41, S42) of the third or fourth series connection of two unidirectional switching elements (S31, S32; S41, S42).

19. The device (1) according to any one of claims 10 to 18, wherein the device (1) comprises one exciter (3) and the further exciter (30), and the device (1) is configured to operate the EESM (2) having a rotor (22) with two field windings (22a) arranged on four physical poles, eight physical poles or twelve physical poles of the rotor (22) such that: each of the exciter (3) and the further exciter (30) provides a direct current and direct voltage of the first polarity to a respective field winding of the two field windings (22a) to generate two pairs of poles, four pairs of poles or six pairs of poles, respectively, at the rotor (22); and the further exciter (30) provides a direct current and direct voltage of the first polarity to a respective field winding of the two field windings (22a) and the exciter (3) provides a direct current and direct voltage of the second polarity to a respective field winding of the two field windings (22a) to generate one pair of poles, two pairs of poles or three pairs of poles, respectively, at the rotor (22).

20. The device (1) according to any one of claims 10 to 18, wherein the device (1) comprises three exciters (3) and the further exciter (30), and the device (1) is configured to operate the EESM (2) having a rotor (22) with four field windings (22a) arranged on eight physical poles or twelve physical poles of the rotor (22) such that: each of the three exciters (3) and the further exciter (30) provides a direct current and direct voltage of the first polarity to a respective field winding of the four field windings (22a) to generate four pairs of poles or six pairs of poles, respectively, at the rotor (22); and the more of the three exciters (3) provide a direct current and direct voltage of the second polarity to a respective field winding of the four field windings (22a) the less pairs of poles are generated at the rotor (22).

21. The device (1) according to any one of claims 10 to 18, wherein the device (1) comprises five exciters (3) and the further exciter (30), and the device (1) is configured to operate the EESM (2) having a rotor (22) with six field windings (22a) arranged on twelve physical poles of the rotor (22) such that: each of the five exciters (3) and the further exciter (30) provides a direct current and direct voltage of the first polarity to a respective field winding of the six field windings (22a) to generate six pairs of poles at the rotor (22); each of three exciters of the five exciters (3) and the further exciter (30) provides a direct current and direct voltage of the first polarity to a respective field winding of the six field windings (22a) and each of two exciters of the five exciters (3) provides a direct current and direct voltage of the second polarity to a respective field winding of the six field windings (22a) to generate three or two pairs of poles at the rotor (22); and each of two exciters of the five exciters (3) and the further exciter (30) provides a direct current and direct voltage of the first polarity to a respective field winding of the six field windings (22a) and each of three exciters of the five exciters (3) provides a direct current and direct voltage of the second polarity to a respective field winding of the six field windings (22a) to generate one pair of poles at the rotor (22).

22. A motor arrangement (100) comprising: the device (1) according to any one of the previous claims, andan externally excited synchronous motor (2), EESM, comprising a rotor (22) with two or more field windings (22a), wherein the device (1) is configured to operate the EESM (2) by providing a direct current and direct voltage of the first polarity or a direct current and direct voltage of the second polarity to at least one of the two or more field windings (22a) of the rotor (22).

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