Method and device for controlling a synchronous machine separately excited by means of an excitation winding

Abstract

Method for controlling a synchronous machine externally excited by means of an excitation winding, wherein the excitation winding is supplied with a unipolar current to which an additional signal is superimposed, the synchronous machine is powered by an inverter whose switches are controlled by pulse width modulation, where the frequency of the additional signal is synchronized with the modulation frequency, wherein the additional signal inductively coupled from the excitation winding to the stator winding is separated from the actual controlled variables by suitable selection of the sampling times, whereby sampling synchronous to the modulation frequency is applied, wherein the additional signal is generated by an electronic circuit supplied by a rectifier arranged on the rotor, which is fed by a secondary winding inductively coupled to a stationary primary winding, - wherein the additional signal is synchronous with the current component which is supplied by the feed unit of the primary winding to supply the excitation winding, - where the frequency of the additional signal is an integer multiple of the frequency of the current component supplied by the primary winding's feed unit to supply the excitation winding, an electronic circuit detects the additional signal coupled to the stator winding and determines the angular position of the rotor from this.

Description

[0001] The invention relates to a method and a device for controlling a synchronous machine excited by means of an excitation winding.

[0002] In synchronous machines, the rotor position can be determined at high speeds by measuring the voltage induced by the permanent magnets or, in separately excited synchronous machines, by the field coils on the stator winding. At low speeds, however, the induced voltage signal is very weak and therefore difficult to detect.

[0003] WO 2005 / 0 83 877 A1 discloses a position determination method for a synchronous motor as the closest prior art.

[0004] A winding field synchronous machine control device is known from DE 10 2005 010 332 A1.

[0005] A magnetic pole position determination is known from JP 2006- 136 123 A.

[0006] A field winding synchronous machine is known from DE 10 2006 029 459 A1.

[0007] The invention is therefore based on the object of improving the control of a synchronous machine.

[0008] According to the invention, the object is achieved by the method according to the features specified in claim 1 and by the device according to the features specified in claim 5.

[0009] Important features of the invention in the method for controlling a synchronous machine excited by means of an excitation winding are that the excitation winding is supplied with a unipolar current to which an additional signal is superimposed.

[0010] The advantage here is that the additional signal contains at least an AC voltage component, so that even at low speeds or even when the rotor of the machine is at a standstill, a clearly recognizable signal of the induced voltage can be introduced, i.e., a signal that clearly stands out from the noise. At low speeds or when the machine is at a standstill, only a small induced voltage would be detectable at the stator winding from an excitation field winding supplied only with direct current. However, the additional signal can be implemented at a high frequency, thus ensuring good detectability.

[0011] In an advantageous embodiment, the additional signal has at least one alternating voltage component, in particular one whose frequency is higher, in particular more than approximately twice higher, than the electrical frequency, i.e., the frequency of the induced voltage, at the maximum permissible speed of the rotor of the synchronous machine. The advantage here is that a very good signal-to-noise ratio can be achieved when detecting the additional signal.

[0012] According to the invention, the frequency of the additional signal is synchronized with the pulse width modulation frequency of the power semiconductors used to power the stator winding. The advantage here is that the additional signal, which is inductively coupled from the excitation winding to the stator winding, can be separated from the actual controlled variables by appropriately selecting the sampling times. Sampling synchronous to the modulation frequency is applicable in this case.

[0013] In an advantageous embodiment, the additional signal is transmitted contactlessly to an electronic circuit located on the rotor that feeds the excitation winding. This is advantageous because no additional electronics are required on the rotor, thus achieving a low imbalance and a low moment of inertia, thus enabling greater dynamic performance with the same overall volume.

[0014] In an alternative advantageous embodiment, the additional signal is generated by an electronic circuit powered by a rectifier, in particular a rectifier arranged on the rotor, which is fed by a secondary winding inductively coupled to a stationary primary winding. The advantage here is that a simple electronic circuit is sufficient, and damping of the mechanical vibrations can be achieved through a higher moment of inertia.

[0015] According to the invention, an electronic circuit detects the additional signal coupled to the stator winding and uses it to determine the angular position of the rotor. This is advantageous in that the stator current measurement signal can be fed to the electronic circuit, thus allowing the additional signal coupled to the stator winding to be separated. In particular, the electronic circuit can be designed such that it particularly accurately detects, and in particular filters out, a specific property of the additional signal, for example, frequency and / or edge rise rate. This enables a particularly accurate, i.e., reliable, error-free determination of the angular position of the rotor.

[0016] According to the invention, the electronic circuit determines a current stator current space vector and sets a stator voltage space vector such that the determined stator current space vector is regulated to a setpoint assigned to it. The advantage here is that no significant additional effort is required to detect the additional signal coupled to the stator winding. Furthermore, in a synchronous machine, a rotating field can be easily generated, so that the space vectors are rotating vectors. In contrast, the additional signal can be implemented such that it corresponds to a pulsating space vector and is thus easily distinguishable and recognizable.

[0017] In an advantageous embodiment, the control is a field-oriented control, comprising a flux model that is based on the separated additional signal, in particular on the signal for the angular position of the rotor determined from the separated additional signal. This is advantageous in that no additional angle sensor is required to detect the angular position of the rotor, and a high dynamic response of the speed control loop of the field-oriented control can be achieved, in particular by always taking a flux model into account, i.e., by regularly determining the flux. The physical quantities are represented in a coordinate system whose abscissa is in the direction of the determined flux and whose ordinate is perpendicular to it. Thus, field-oriented control is feasible.

[0018] According to the invention, the additional signal is synchronous with the current component supplied by the supply unit to the primary winding to power the excitation winding. This is advantageous in that further improved detection is achieved.

[0019] In an advantageous embodiment, the frequency of the additional signal is an integer multiple of the frequency of the current component supplied by the supply unit to the primary winding to power the excitation winding. Advantageously, the current sampling can be synchronized in such a way that fluctuations caused by the additional signal can be filtered out by moving averaging.

[0020] Important features of the device are that the excitation field winding is supplied via an inductive transformer whose primary winding is connected to a feed unit and whose secondary winding supplies a rectifier that feeds the excitation winding.

[0021] The advantage here is that a contactless supply of the excitation field winding is possible. Furthermore, an electronic circuit is provided on the rotor, which also enables additional functionalities.

[0022] In an advantageous embodiment, the additional signal is generated by the feed unit connected to the primary winding, in particular, the feed unit comprises corresponding means for generating the additional signal. This is advantageous because the additional signal coupled to the stator winding can be easily synchronized with other signals. In particular, a portion of the additional signal can be fed to comparison means that detect the additional signal. This enables even better and less error-prone detection.

[0023] In an alternative advantageous embodiment, the additional signal is generated by an electronic circuit powered by the rectifier, in particular, the supply unit comprises appropriate means for generating the additional signal. This is advantageous in that low-loss generation of the additional signal is achievable, since no transmission of the additional signal is required via the inductive coupling between the primary and secondary windings.

[0024] In an advantageous embodiment, the stator winding of the synchronous machine is fed by an inverter output stage, with pulse-width-modulated control signals from an electronic circuit being supplied to the electronic switches of the inverter output stage. The circuit has means for detecting the motor current and a means for detecting the additional signal coupled to the stator winding. This advantageously enables control of the electric machine by a control unit that operates according to field-oriented control and adjusts the stator voltage space vector such that the detected stator current space vector is controlled to its setpoint.

[0025] In an advantageous embodiment, the means for detecting the additional signal coupled to the stator winding is connected to a means for determining the angular position of the rotor. This is advantageous because the angular position of the rotor can be determined, in particular directly, from the additional signal coupled to the stator winding.

[0026] In an advantageous embodiment, means are provided for data exchange between the supply unit and the electronic circuit provided on the rotor. This is advantageous in that synchronous operation is possible and / or a change in the frequency of the additional signal can be adapted to the operating parameters, such as the speed or torque of the machine.

[0027] Further advantages arise from the subclaims.

[0028] The invention will now be explained in more detail: The electric machine is designed as a separately excited synchronous machine. An excitation winding comprising at least one field coil winding is provided on the rotor of the electric machine. Preferably, the rotor has a rotor core with limbs around which a respective field coil winding is arranged.

[0029] The field coil windings are supplied with unipolar current, particularly direct current, generated by a rectifier arrangement arranged on the rotor. The rectifier is supplied by a secondary winding, also arranged on the rotor, which is inductively coupled to a primary winding connected to the machine housing. This enables contactless supply of the secondary winding. The secondary winding is preferably arranged axially outside the rotor core.

[0030] The stator winding of the electric machine is preferably designed as a multi-phase three-phase winding, in particular as a three-phase three-phase winding, and is fed by an inverter supplied with a unipolar voltage. This is generated, for example, by a battery voltage or a rectified mains voltage. The control signals for the inverter switches are generated by signal electronics, which include a control unit to which current measurements are fed to determine the stator current space vector. The control unit adjusts the stator voltage space vector so that the stator current space vector is controlled to a setpoint.

[0031] Within the control electronics, a computer determines a flux space vector based on a flux model and determines physical quantities in a coordinate system aligned with it. In this way, field-oriented control of the electric machine can also be implemented by the computer.

[0032] During normal operation, the excitation winding is supplied with a direct current or at least with a unipolar current, so that the excitation winding acts similarly to a permanent magnet arrangement.

[0033] According to the invention, an additional signal is superimposed on the unipolar current, which is preferably implemented as a direct current, in the excitation winding, wherein the additional signal has a predetermined frequency, i.e. has a periodic course.

[0034] The additional signal is preferably sinusoidal. However, triangular or rectangular signal waveforms can also be used advantageously.

[0035] In a first embodiment of the invention, the additional signal is fed into the primary side and thus inductively transmitted to the secondary coil. From there, it is passed on via the rectifier to the excitation winding.

[0036] In another embodiment of the invention, the additional signal on the rotor is generated by an electronic circuit that is fed from the secondary coil via the rectifier and preferably also includes means for a data exchange connection, whereby data can be exchanged with an electronic device arranged on the primary side that feeds the primary winding. This even makes it possible for the additional signal to be generated synchronously with the primary current of the primary winding.

[0037] In another embodiment of the invention, the additional signal has an AC voltage component whose frequency corresponds to an AC voltage component fed into the primary winding. Therefore, preferably, no special smoothing means, such as a smoothing capacitor, is connected downstream of the rectifier fed by the secondary winding. Thus, the primary AC voltage can be used for power supply without additional effort and, moreover, also as an additional signal.

[0038] The electronic circuit comprising the control unit also has means for detecting the additional signal coupled to the stator winding, which are connected to means for determining the angular position of the rotor, in particular to means for determining information about the angular position of the rotor. Clear detection of the additional signal coupled to the stator winding is important. Only then can a reliable determination of the angular position be carried out.

[0039] The invention also encompasses embodiments in which the rotor and stator are interchanged, i.e., the excitation winding is provided on the stator and the three-phase winding, which can be supplied contactlessly, is provided on the rotor. In this case, the additional signal does not need to be transmitted to a rotating part but can be fed into the excitation winding from a stationary circuit.

Claims

[1] Method for controlling a synchronous machine excited by means of an excitation winding, the excitation winding is supplied with a unipolar current, to which an additional signal is superimposed, the synchronous machine is fed by an inverter whose switches are controlled by pulse width modulation, where the frequency of the additional signal is synchronized with the modulation frequency, wherein the additional signal inductively coupled from the excitation winding to the stator winding is separated from the actual controlled variables by a suitable choice of sampling times, whereby a sampling synchronous to the modulation frequency is used, wherein the additional signal is generated by an electronic circuit supplied by a rectifier arranged on the rotor, which is fed by a secondary winding which is inductively coupled to a stationary primary winding, - the additional signal being synchronous to the current component supplied by the supply unit to the primary winding to supply the excitation winding, - where the frequency of the additional signal is an integer multiple of the frequency of the current component supplied by the supply unit of the primary winding to supply the excitation winding, An electronic circuit detects the additional signal coupled to the stator winding and uses this to determine the angular position of the rotor. [2] Method according to claim 1, characterized by that the additional signal has at least one alternating voltage component, in particular the frequency of which is higher, in particular more than about twice higher, than the electrical stator frequency at the maximum permissible speed of the rotor of the synchronous machine. [3] Method according to at least one of the preceding claims, characterized bythat the electronic circuit sets a stator voltage space vector by means of the inverter in such a way that the detected stator current space vector is regulated to its setpoint. [4] Method according to at least one of the preceding claims, characterized by that the control is a field-oriented control, wherein this comprises a flux model which is based on the additional signal coupled to the stator winding, in particular on the signal for the angular position of the rotor determined from the additional signal coupled to the stator winding, in particular wherein physical quantities are represented in an orthogonal coordinate system, one axis of which is aligned in the direction of the determined flux. [5] Device for carrying out a method according to at least one of the preceding claims, characterized bythat the excitation field winding is supplied via an inductive transformer whose primary winding is connected to a supply unit and whose secondary winding supplies a rectifier which feeds the excitation winding. [6] Device according to claim 5, characterized by that the additional signal is generated by the feed unit connected to the primary winding, in particular the feed unit comprises corresponding means for generating the additional signal. [7] Device according to one of claims 5 to 6, characterized by that the additional signal is generated by an electronic circuit supplied from the rectifier, in particular the feed unit comprises corresponding means for generating the additional signal. [8] Device according to one of claims 5 to 7, characterized bythat the stator winding of the synchronous machine is fed by an inverter output stage, wherein the electronic switches of the inverter output stage are supplied with pulse-width modulated control signals from an electronic circuit which has means for detecting the motor current and a means for detecting the additional signal coupled to the stator winding. [9] Device according to one of claims 5 to 8, characterized by that the means for detecting the additional signal coupled to the stator winding is connected to a means for determining the angular position of the rotor. [10] Device according to one of claims 5 to 9, characterized by that means are provided for data exchange between the feed unit and the electronic circuit provided on the rotor.