Drive system and method for operating a drive system

Abstract

Drive system comprising an electric motor (M), at least one energy storage device and at least two inverters (1, 2), wherein the electric motor (M) has first and at least second stator windings (L), wherein the first stator windings (L) can be supplied from a first inverter (1) which is arranged to be supplied from an energy storage device, characterized in that the second stator windings (L) can be supplied from a second inverter (2) which can be supplied from a unipolar voltage of a DC link, wherein the second inverter (2) can be supplied from the energy storage device via two switches (S1, S2) when these switches (S1, S2) are closed, wherein a respective first stator winding (L) is inductively coupled to a respective second stator winding (L) so that energy flow from the unipolar voltage to the energy storage device can be transferred inductively, i.e., without potential difference, when the switches (S1, S2) are open.

Description

[0001] The invention relates to a drive system and a method for operating a drive system.

[0002] It is known to use a DC-powered inverter, a three-phase winding of an electric motor to create a To provide a rotary clamping system.

[0003] The invention is therefore based on the objective of further developing an energy-buffered drive system.

[0004] According to the invention, the problem is solved in the drive system according to the features specified in claim 1 and in the method for operating a drive system according to the features specified in claim 11.

[0005] Important features of the invention in the drive system are that the drive system comprises an electric motor, at least one energy storage device and at least two inverters, wherein the electric motor has first and at least second stator windings, wherein the first stator windings can be supplied from a first inverter which is arranged to be supplied from an energy storage device, wherein the second stator windings can be supplied from a second inverter which can be supplied from a unipolar voltage, in particular DC link, where the first and second stator windings are inductively coupled.

[0006] An advantage of this is that the unipolar voltage can deviate from the DC voltage and yet synchronous operation of the inverters to drive the motor is still possible. Furthermore, charging the energy storage device is possible with a unipolar voltage that can be selected over a wide range.

[0007] In an advantageous embodiment, the first stator windings are configured as three-phase windings, and the second stator windings are configured as co-acting three-phase windings, particularly in that the motor is configured as an asynchronous motor, a synchronous motor, or a reluctance motor. It is advantageous that the stator of the electric motor is composed of two stator windings, i.e., essentially two stators. Thus, the rotor can be driven by both the first and second stator windings. Although the first and second stator windings are galvanically isolated, energy can be transferred between them due to inductive coupling. In this way, the inductive coupling can be used as a transformer.

[0008] In an advantageous embodiment, the first and / or second stator windings are connected in a star point connection or the first and / or second stator windings are connected in a delta connection. An advantage of this is that a simple connection is possible; in particular, in the star point connection, a star point is provided whose potential can be compared with the potential of the neutral conductor, thus enabling fault monitoring.

[0009] In an advantageous embodiment, each first stator winding is assigned a second stator winding, in particular wherein the respective assigned windings are wound around the same coil former and / or tooth of a laminated core. An advantage of this is that very good inductive coupling can be achieved, and thus a high efficiency can be attained in the transformer-based transmission.

[0010] In an advantageous embodiment, three first and three second stator windings are provided, or an integer multiple thereof. An advantage of this is that simple winding schemes and thus cost-effective and simple manufacturing processes can be applied.

[0011] In an advantageous embodiment, each inverter comprises half-bridges of semiconductor switches, in particular wherein each semiconductor switch is associated with a freewheeling diode, especially such that the freewheeling diodes can be operated as rectifiers. An advantage of this is that a bidirectional energy flow can be realized without additional effort.

[0012] In an advantageous embodiment, the energy storage device can be connected to the unipolar voltage by means of a switch, in particular a contactor. An advantage of this is that a smoothing effect can be achieved, since the energy storage device can be implemented as a capacitor or as a battery. Thus, a smoothing capacitor on the unipolar voltage side can be omitted or at least dimensioned smaller.

[0013] In an advantageous embodiment, the first and subsequent inverters can each be controlled by a control circuit in such a way that the inverters can be operated synchronously. It is advantageous that the power output of the individual inverters is additive, meaning that a high output power of the entire inverter can be achieved even with low power output from the individual inverters.

[0014] In an advantageous embodiment, the motor has an electromagnetically actuated brake, in particular a holding brake. This is advantageous because in that a very good undisturbed inductive coupling is achievable, in particular the entire power is transferred from the second to the first stator windings and thus the efficiency is optimized.

[0015] In an advantageous embodiment, pulse-width modulated control signals for the semiconductor switches can be generated by means of the inverter's control circuits, in particular with such a high pulse-width modulation frequency that the rotor is unable to follow this frequency. An advantage of this is that no brake is necessary.

[0016] Important features of the method are that it is designed to operate a drive system, comprising an electric motor having first and second stator windings, wherein during a first operating mode the second stator windings are supplied with a three-phase voltage system or with an alternating voltage such that an energy storage device is charged by rectifying the voltage induced on the first stator windings, wherein during a second operating mode the DC voltage applied to the energy storage device is converted to alternating voltage to supply the first stator windings and the unipolar voltage is converted to alternating voltage to supply the second stator windings.

[0017] An advantage is that it is possible to charge the energy storage device and / or to drive the motor.

[0018] In an advantageous embodiment, in the second operating mode, the inverter operation for the first and second stator windings is performed synchronously, in particular so that the torque that can be generated by the two stator windings is doubled. An advantage of this is that high power can be achieved simply and with cost-effective semiconductor switches.

[0019] In an advantageous embodiment, during the first operating mode the motor, in particular the rotor of the motor, is braked or held stationary. An advantage of this is that a high efficiency can be achieved when charging the energy storage device.

[0020] In an advantageous embodiment, during the first operating mode, the frequency of the alternating voltage or the three-phase voltage system is provided at the second stator windings at such a high frequency that the rotor of the motor is unable to follow, i.e., no significant torque is transmitted to it. An advantage of this is that a brake is unnecessary and yet a high efficiency can still be achieved.

[0021] In an advantageous embodiment, during the first operating mode the motor is set in rotational motion and the energy storage device is charged simultaneously. An advantage of this is that charging is possible during operation of the motor, thus saving time. The software of the control electronics can be implemented accordingly.

[0022] Further advantages arise from the dependent claims. Reference symbol list 1 Inverter between motor M and energy storage C 2 Inverter between motor M and DC link M Electric motor with stator windings L L Stator winding S1 Switch S2 Switch

[0023] The invention will now be explained in more detail with reference to illustrations:

[0024] In Fig. 1 a device according to the invention is schematically sketched.

[0025] An inverter 1 is provided between the motor M and the energy storage device C, which converts the voltage applied to the energy storage device C, i.e., for example a capacitor or a battery, into a three-phase voltage for the electric motor M. The first stator windings of the electric motor are connected in a star point connection.

[0026] The electric motor M consists of first stator windings L and second stator windings L, with each first stator winding being identical to the second stator winding. The first and second stator windings are oriented in the same way within the stator of the electric motor. The second stator windings L are connected in a star-point configuration in the same way and can be supplied with three-phase voltage from a second inverter using a unipolar voltage. The unipolar voltage is referred to here as a DC link and can be generated, for example, from a rectifier supplied by a generator. However, it can also be generated in another way.

[0027] The first and second stator windings are therefore designed as three-phase windings. The two three-phase windings are galvanically isolated but act in unison on the rotor of the electric motor. The motor is, for example, an asynchronous motor, a synchronous motor, or a reluctor motor. dance motor executed.

[0028] In the closed state, switches S1 and S2 allow the energy storage device and the DC link to be connected in parallel.

[0029] In this state, the first and second inverters can be operated synchronously, thus doubling the power output with two inverters. The energy storage system smooths the unipolar voltage. Each inverter consists of identically constructed half-bridge circuit breakers supplied with DC or unipolar voltage. Advantageously, a redundant inverter is available in case of failure of one inverter, thus increasing reliability. Furthermore, the two inverters can each be housed in smaller spaces compared to a single inverter of the same power output. Therefore, instead of a large, contiguous space, only two small, separate spaces are required. Moreover, economies of scale can be utilized, meaning systems with half or double the power output can be manufactured without new development.

[0030] When open, switches S1 and S2 enable a wide-range charging circuit for the energy storage device. In this circuit, the motor is either mechanically braked and prevented from rotating, or alternatively, the output frequency of the second inverter is rapidly set to very high values, so that the motor cannot follow this frequency. In this state, the stator windings act as inductive transformers, since the first and second stator windings are inductively coupled. Thus, the energy storage device can be charged, allowing a wide range of voltages at the DC link. The first inverter is operated in generator mode because there is an energy flow from the motor towards the energy storage device C. The diodes of the first inverter act as rectifiers in this process.The second inverter is motor-driven, as it generates a three-phase or alternating current system from the unipolar voltage of the DC link to the motor. Pulse-width modulated control of the semiconductor switches in the second inverter allows for control of the motor voltage applied to the second stator windings, thus converting the unipolar voltage, which is in the wide voltage range, into a three-phase or alternating current voltage of a predefined amplitude. The amplitude is selected such that the voltage required to charge the energy storage device can be generated by the diodes of the first inverter, which are operating as rectifiers.

[0031] Advantageously, when switches S1 and S2 are open, there is a potential separation between the energy storage device and the DC link. A further advantage is that only a small number of components are required.

[0032] The device can be designed such that the wide voltage range at the DC link even includes voltages that are three times or even ten times higher than the intended DC voltage at the energy storage device. Power levels of more than 1 kW can be transmitted.

[0033] The invention is not limited to the voltage at the DC link being greater than the DC voltage at the energy storage device; rather, it is permitted for it to be lower. It is also possible for the first and second stator windings to each have a different number of turns, and thus, with inductive coupling, the transmitted voltage is higher than the voltage applied on the primary side, i.e., the voltage applied to the second stator windings.

[0034] Recharging the energy storage device is therefore possible even when the motor is stationary. When the motor is running, the inverters operate synchronously.

[0035] In another embodiment of the invention, the synchronous operation of the two inverters is used to start the electric motor. Thus, the motor generates a high torque during starting, as is necessary, for example, when driving a heavily loaded conveyor belt. During uniform operation, i.e., operation at constant speed, essentially only overcoming frictional forces is necessary, and therefore a correspondingly low torque is required. In this operating mode, it is therefore possible for only the second inverter to generate torque for the motor by means of the second stator windings. The energy storage device can be charged from the rectifier of the first inverter, which is supplied by the first stator windings. In this way, charging is possible while the motor is rotating.When a critical voltage is exceeded at the energy storage device, the first inverter is controlled accordingly, so that some energy is also returned to the motor to prevent the critical voltage values ​​from being exceeded.

Claims

[1] Drive system comprising an electric motor, at least one energy storage device and at least two inverters, wherein the electric motor has first and at least second stator windings, characterized by the fact that the first stator windings can be supplied from a first inverter which is arranged to be supplied from an energy storage device, wherein the second stator windings can be supplied from a second inverter which can be supplied from a unipolar voltage, in particular DC link, where the first and second stator windings are inductively coupled. [2] Drive system according to at least one of the preceding claims, characterized in that the first stator windings are designed as three-phase windings, wherein the second stator windings are designed as co-acting three-phase windings, in particular wherein the motor is designed as an asynchronous motor, synchronous motor or as a reluctance motor. [3] Drive system according to at least one of the preceding claims, characterized in that the first and / or second stator windings are connected in star point connection or the first and / or second stator windings are connected in delta connection. [4] Drive system according to at least one of the preceding claims, characterized in that each first stator winding is assigned a second stator winding, in particular wherein the respective assigned windings are wound around the same coil former and / or tooth of a laminated core. [5] Drive system according to at least one of the preceding claims, characterized in that three first and three second stator windings are provided or an integer multiple thereof. [6] Drive system according to at least one of the preceding claims, characterized in that each inverter comprises half-bridges of semiconductor switches, in particular wherein each semiconductor switch is assigned a freewheeling diode, in particular such that the freewheeling diodes can be operated as rectifiers. [7] Drive system according to at least one of the preceding claims, characterized in that the energy storage device can be connected to the unipolar voltage by means of a switch, in particular a contactor. [8] Drive system according to at least one of the preceding claims, characterized in that the first and further inverters can each be controlled by a control circuit in such a way that the inverters can be operated synchronously. [9] Drive system according to at least one of the preceding claims, characterized in that the motor has an electromagnetically actuated brake, in particular a holding brake. [10] Drive system according to at least one of the preceding claims, characterized in that pulse width modulated control signals for the semiconductor switches can be generated by means of the control circuits of the inverters, in particular with such a high pulse width modulation frequency that the rotor is unable to follow this frequency. [11] Method for operating a drive system, comprising an electric motor having first and second stator windings, characterized in that during a first operating mode the second stator windings are supplied with a three-phase voltage system or with an alternating voltage in such a way that an energy storage device is charged by rectifying the voltage induced on the first stator windings, wherein during a second operating mode the DC voltage applied to the energy storage device is converted to alternating voltage to supply the first stator windings and the unipolar voltage is converted to alternating voltage to supply the second stator windings. [12] Method according to at least one of the preceding claims, characterized in that in the second operating mode the inverter for the first and second stator windings is performed synchronously, in particular so that the torque that can be generated by the two stator windings is doubled. [13] Method according to at least one of the preceding claims, characterized in that during the first operating mode the motor, in particular the rotor of the motor, is braked or held. [14] Method according to at least one of the preceding claims, characterized in that during the first operating mode such a high frequency of the alternating voltage or the rotating voltage system is provided at the second stator windings that the rotor of the motor is unable to follow, i.e. no significant torque is transmitted to it. [15] Method according to at least one of the preceding claims, characterized in that during the first operating mode the motor is set into rotary motion and the energy storage device is charged simultaneously.

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